Apparatus and system for zero current switching

Abstract

A discrete battery module configured for energy transfer in a power system together with a plurality of other battery modules. Each module one or more battery cells, and a primary structure The primary structure includes a primary flux guide component, and a primary winding associated with the primary flux guide component, a switching circuit coupled to the battery cell and the primary winding and configured to generate an alternating current output; and a primary controller configured to operate the switching circuit. The battery module is adapted to removably engage with a secondary module, in use, such that the engagement causes alignment with a secondary structure of the secondary module. The secondary structure has a plurality of secondary flux guide components, one secondary winding associated with the plurality of the secondary flux guide components; such that the alignment causes the primary and secondary flux guide components to be arranged in complementary sets with a predetermined geometrical alignment for magnetic coupling. Each set produces a current transformer with a defined coupling factor that supports the energy transfer operation characteristics of the system.

Description

[0001]APPARATUS AND SYSTEM FOR ZERO CURRENT SWITCHING Technical Field The invention generally relates to energy storage systems, and in particular to a system configured to allow for zero current switching of high current energy sources and related technology. Background Energy storage systems for applications such as full electric vehicles, hybrid electric vehicles, and stationary energy storage in grid connected or off grid applications, frequently include an arrangement of multiple energy storage cell units. An increasingly common energy storage unit is a low voltage but very large capacity battery cell. Due to the low voltage, taking advantage of the large capacity typically requires configuring a string of series connected cells to deliver large amounts of current. However, controlling current flow to a load requires a switching circuit, often implemented by one or more transistors, such as a MOSFET, disposed in a current path of the cell unit. The switching phase of a transistor is known to be electrically inefficient due to the tangible inductance L of the transistor and battery cell opposing a change of current flowing through the transistor. During the switching phase it is desirable for the current in the switching devices to be at or near zero such that there is negligible opposition to changing current when a switch transition occurs. For very high currents, the wasted energy due to series inductance can be significant such that circuit paths and switching components are damaged. Summary of the invention In one broad aspect the invention relates to a magnetic coupling apparatus configured for reactive energy transfer comprising: a plurality of primary structures, each structure comprising: a primary flux guide component, a primary winding associated with the primary flux guide component; a secondary structure comprising: a plurality of secondary flux guide components, a secondary winding associated with the plurality of the secondary flux guide components; wherein the primary and secondary flux guide components are arranged in complementary pairs with a predetermined geometrical alignment for magnetic coupling. In one embodiment, each secondary flux guide comprises a core having one or more limbs which extend from a base portion to thereby define one or more regions bounded by the one or more limbs and the base portion, and the secondary coil is configured to extend through the one or more regions. In one embodiment, one or more secondary flux guide components comprise a core made of magnetic material, the core comprising: a central limb, two outer limbs, and a base portion connecting said limbs, forming a magnetic path. In one embodiment, one or more secondary flux guide components, and primary flux guide components, comprise an E core.. In one embodiment, one or more secondary flux guide components comprises a core made of magnetic material, the core comprising at least two limbs extending from a base portion. In one embodiment, the secondary flux guide component comprises a C core.. In one embodiment, one or more primary flux guide components comprise limbs extending complementary to the secondary flux guide.. In one embodiment, each limb of the primary and secondary flux guide defines a pole face, and the magnetic coupling apparatus comprises primary flux guide components and secondary flux guide components arranged with substantially opposing pole faces. In one embodiment, the central and outer limbs of each complementary pair are configured in an opposing arrangement. In one embodiment, a central limb of the primary or secondary flux guide comprises an edge surface contoured to the shape of a winding arranged to wrap around the central limb. In one embodiment, the central limb of the primary and / or secondary flux guide comprises a D- shaped profile, and a winding arranged to wrap around the central limb is configured to reside within the confines of the base portion. In one embodiment, the primary flux guide comprises a winding former component adapted to at least partially support a winding within the limbs. In one embodiment, one or more of the primary windings and secondary winding comprises Litz wire. In one embodiment, the primary winding comprises Litz wire with a terminal connected to each end of the wire, the terminals configured for bolted connection to a switching circuit. In one embodiment, the predetermined geometrical alignment further comprises a coplanar arrangement of the complementary sets. In one embodiment, each complementary set of primary and secondary flux guide components are separated by an air gap of up to about 2 mm. In one embodiment, the magnetic coupling apparatus is characterised by a k factor of between 0.85 and 0.95. In one embodiment, the magnetic coupling apparatus is characterised by a k factor of between 0.86 and 0.94. In one embodiment, the magnetic coupling apparatus is characterised by a k factor of between 0.87 and 0.93. In one embodiment, the magnetic coupling apparatus is characterised by a k factor of between 0.88 and 0.92. In one embodiment, the magnetic coupling apparatus is characterised by a k factor of between 0.89 and 0.92. In one embodiment, the magnetic coupling apparatus is characterised by a k factor of 0.91. In one embodiment, each primary structure is contained within a discrete module. In one embodiment, each of the primary windings are electrically isolated. In one embodiment, the primary structure further comprises an arrangement of layers, the layers comprising: a primary winding, and an insulator substrate. In one embodiment, one or more primary flux guide components comprise a core having a limb portion extending from a base portion, and the primary winding is configured to partly encircle the limb portion. In one embodiment, the limb portion extending from a base portion comprises a central limb. In one embodiment, the limb portion extending from a base portion comprises an outer limb. In one embodiment, the primary structure further comprises a primary winding comprising a wire loop segment extending at least twice through the primary flux guide. In one embodiment, the primary structure further comprises an insulator substrate comprising a terminal block, and the wire loop segment is connected to the insulator substrate at the terminal block. In one embodiment, the primary structure further comprises an arrangement of layers, the layers comprising: a primary winding segment, an insulator substrate, and a second primary winding segment sharing a common coupling with the first primary winding segment, thereby defining a primary winding centre tap. In one embodiment, one or more primary flux guide components comprise a core having a limb portion extending from a base portion, wherein: the primary winding is arranged to at least partially encircle the limb portion in a first rotational direction, and the second primary winding is arranged to at least partially encircle the limb portion in a rotational direction opposed to the primary winding in at least a region of co-encirclement. In one embodiment, the first and second primary windings are substantially U-shaped and arranged to at least partially encircle the limb portion in opposing rotational directions. In one embodiment, the primary winding associated with each primary flux guide component is arranged to wrap, at least in part, around the central limb. In one embodiment, each primary winding segment is arranged to wrap, at least in part, around the central limb, in an opposing direction. In one embodiment, a bridge circuit comprises: a first current path configured for a first current direction, the first current path including a first primary winding segment, a second current path configured for an opposing current direction, the second current path including a second primary winding segment. In one embodiment, the pair of primary winding segments are layered about the primary flux guide component. In one embodiment, the secondary winding comprises one wire loop. In one embodiment, the secondary winding comprises two wire loops. In one embodiment, the secondary winding comprises three wire loops. In one embodiment, the secondary winding comprises four wire loops. In one embodiment, the secondary winding comprises up to four wire loops. In one embodiment, the secondary winding comprises two or more segments, the segments extending substantially parallel to each other. In one embodiment, the secondary flux guide components are substantially aligned along an axis, and the secondary winding comprises a conductor extending substantially parallel to the axis of the secondary flux guide components. In one embodiment, the secondary flux guide components are substantially aligned sequentially along an axis, and each secondary flux guide comprises a form whereby there is a region whereby the secondary may pass within the region and within an outer peripheral form of the flux guide such that the secondary winding passes through the each secondary flux guide along an axis parallel to the axis of alignment of the secondary flux guide components. In one embodiment, the secondary winding comprises: a first segment which extends through each secondary flux guide component, with less than a full turn of engagement with each secondary flux guide component; and a second segment which extends through each secondary flux guide component, with less than a full turn of engagement with each secondary flux guide component. In one embodiment, the secondary winding is configured to: extend on first axis between a first outer limb and the central limb on each of the plurality of secondary flux guide components, and extend on a second axis between a second outer limb and the central limb on each of the plurality of secondary flux guide components. In one embodiment, the plurality of secondary flux guide components are arranged in a geometric sequence, and the secondary winding is configured to extend through the first window in the sequence of each secondary flux guide component, then, extend through the second window in the sequence of each secondary flux guide component. In one embodiment, the plurality of secondary flux guide components are arranged in a geometric sequence, and the secondary winding is configured to extend through each secondary flux guide component in a first direction, then, extend through each secondary flux guide component in a second direction. In one embodiment, each of the first and second axis are aligned substantially parallel, and the secondary cores are aligned substantially parallel with the first and second axis. In one embodiment, the secondary winding comprises one or more sections forming a 180-degree bend, transitioning the wire from the first axis to a second axis, wherein the bent section has a curved or folded structure to achieve the directional change. In one embodiment, the secondary winding is configured to form, at least in part, a resonant tank configured for connection with a rectification device and a load output.. In one embodiment, the load output comprises a rectification circuit and a load connection terminal. In one embodiment, the primary flux guide and secondary flux guide are separated by one or more layers of an insulator material. In one embodiment, the apparatus further comprises a retention assembly configured to support at least the secondary flux guide and the secondary winding, the retention assembly comprising: a base member and at least one retention member having a contact surface configured to engage a portion of one or more secondary flux guides; and wherein a dimensional tolerance exists between the retention member and the secondary flux guide, such that the retention member allows for a predefined amount movement of the secondary flux guide relative to the base member, while securing the secondary flux guide in place. In one embodiment, the primary modules having different overall heights and coplanarity, and the secondary structure having dimensional tolerance for movement (set amount, 6DOF) to allow alignment with individual coplanarity and predefined flux gap. In one embodiment, the retention assembly is further configured to support the secondary winding. In one embodiment, the secondary flux guide is secured within the retention assembly with a limited freedom of movement due to the dimensional tolerance, permitting positional adjustments without detaching the secondary flux guide from the assembly. In one embodiment, the limbs comprise an insulator material and is of a thickness constraining the gap between primary and secondary flux guides. In one embodiment, the retention assembly comprises one or more guiding surfaces configured to engage with the primary structure and extend toward the secondary structure, the guiding surfaces comprising a narrowing structure configured to receive the secondary structure as the secondary structure is moved toward the primary structure. In one embodiment, the insulator substrate configured to support a circuit comprising: a pair of cell connection terminals adapted for connection to a battery cell; a switching circuit comprising: a DC input terminal configured to receive a DC input voltage from the battery cell; switching devices configured to alternately switch the polarity of the DC input voltage to generate an alternating current output; wherein the alternating current output is operably connected to the associated primary winding by the switching circuit. In one embodiment, ach of the pair of the connection terminals define a terminal coupling region, and the switching devices are integrated within the terminal coupling region so as to control a circuit path between the terminal coupling region and the primary winding. In another broad aspect there is a system configured for resonant energy transfer comprising: the magnetic coupling apparatus, wherein each of the plurality of primary structures further comprises a battery module, each battery module comprising: a battery cell; a switching circuit comprising: cell terminals configured to receive a DC input voltage from the battery cell; switching devices configured to alternate the connection of the cell terminals with the primary winding. In one embodiment, there is a resonant tank comprising at least the secondary winding and a capacitor. In one embodiment, there is a rectification circuit connected to the resonant tank. In one embodiment, there are one or more controller devices configured to: generate switching signals for controlling the operation of the switching devices of each switching circuit and thereby control the alternate connection of the current connected with a primary winding, determine the magnitude and phase angle of the alternating current, and output the switching signals based on the measured magnitude and phase angle of the alternating current corresponding with an alternating current minima. In one embodiment, the controller is configured to: measure an alternating current (AC) waveform from an electrical circuit to obtain a real-time current signal; determine a phase angle of the measured AC current relative to a reference voltage waveform; identify a minimum phase angle corresponding to a point where the current is at or near zero; and control at least one switch within the circuit based on the identified minimum phase angle. In another broad aspect the invention relates to a battery module comprising: a primary structure comprising: a primary flux guide component, and a primary winding associated with the primary flux guide component; a battery cell; a switching circuit comprising: cell terminals configured to receive a DC input voltage from the battery cell; switching devices configured to alternate the connection of the cell terminals with the primary winding. In one embodiment, the primary flux guide component is configured for the complementary pairing with one of a plurality of secondary flux guide components of a secondary structure a predetermined geometrical alignment for magnetic coupling, wherein the secondary structure comprising a secondary winding associated with each of the plurality of the secondary flux guide components. In one embodiment, the battery device further comprises a controller device configured to: generate switching signals for controlling the operation of the switching devices of each switching circuit and thereby control the alternate connection of the current connected with a primary winding, determine the magnitude and phase angle of the alternating current, and output the switching signals based on the measured magnitude and phase angle of the alternating current corresponding with an alternating current minima. In one embodiment, the controller is configured to: measure an alternating current (AC) waveform from an electrical circuit to obtain a real-time current signal; determine a phase angle of the measured AC current relative to a reference voltage waveform; identify a minimum phase angle corresponding to a point where the current is at or near zero; and control at least one switch within the circuit based on the identified minimum phase angle. In one embodiment, there is a hermetically sealed enclosure adapted to encapsulate one or more of the battery cell, the switching circuit, and the primary structure. In one embodiment, the enclosure comprises one or more surfaces adapted for engagement with the secondary structure and control, at least in part, a separation gap between the primary structure and secondary structures. In another broad aspect, the invention relates to a secondary magnetic structure comprising: a plurality of secondary flux guide components, and a secondary winding associated with the plurality of the secondary flux guide components; wherein each of secondary flux guide components are arranged for the complementary pairing and magnetic coupling with one or a plurality primary structures, each comprising a primary flux guide component, and a primary winding associated with the primary flux guide component. In one embodiment, the secondary winding comprises two or more segments, the segments extending substantially parallel to each other. In one embodiment, the secondary winding comprises a conductor having two or more substantially linear segments, the segments extending substantially parallel to each other. In one embodiment, the secondary winding comprises a pair of more segments, the segments extending substantially parallel and offset to each other. In one embodiment, there are two or more substantially linear segments comprising a wire loop, and the secondary winding comprises up to four wire loops. In one embodiment, the secondary flux guide components are substantially aligned along an axis, and the secondary winding comprises a conductor extending substantially parallel to the axis of the secondary flux guide components. In one embodiment, the secondary flux guide components are substantially aligned sequentially along an axis, and each secondary flux guide comprises a form whereby there is a region whereby the secondary may pass within the region and within the outer peripheral form of the flux guide such that the secondary winding passes through the each secondary flux guide along an axis parallel to the axis of alignment of the secondary flux guide components. In one embodiment, the secondary winding comprises: a first segment which extends through each secondary flux guide component, with less than a full turn of engagement with each secondary flux guide component; and a second segment which extends through each secondary flux guide component, with less than a full turn of engagement with each secondary flux guide component. In one embodiment, the secondary winding is configured to: extend on first axis between a first outer limb and the central limb on each of the plurality of secondary flux guide components, and extend on a second axis between a second outer limb and the central limb on each of the plurality of secondary flux guide components. In one embodiment, each of the first and second axis are aligned substantially parallel, and the secondary cores are aligned substantially parallel with the first and second axis. In one embodiment, the secondary winding comprises a wire arranged to pass through a first window in a geometrical arrangement of all secondary flux guides, then passes through a second window in the geometrical arrangement of all secondary flux guides. In one embodiment, the secondary winding comprises one or more sections forming a 180-degree bend, transitioning the wire from the first axis to a second axis, wherein the bent section has a curved or folded structure to achieve the directional change. In one embodiment, the secondary winding is configured to form, at least in part, a resonant tank configured for connection with a rectification device and a load output. In one embodiment, the load output comprises a rectification circuit and a load connection terminal. In another board aspect there is a magnetic coupling apparatus configured for wireless power transfer comprising: a plurality of primary structures, each structure comprising: a primary flux guide component, one or more primary windings associated with the primary flux guide component; a secondary structure comprising: a plurality of secondary flux guide components, one secondary winding associated with the plurality of the secondary flux guide components; wherein the primary and secondary flux guide components are arranged in complementary sets with a predetermined geometrical alignment for magnetic coupling, each set defining a current transformer; and wherein each current transformer is defined by a k factor being greater than 1 / turns ratio. In one embodiment, the turns ratio is defined by the number of effective secondary turns divided by the number of effective primary turns of the primary and secondary windings in each set. In one embodiment, the k factor is further defined by the by being greater than 1 / (turns ratio x Nc), where Nc is the number of current transformers of the apparatus. In one embodiment, the k factor is further defined by a real power target interacting with a complex impedance network in a target frequency range. In one embodiment, the k factor is further defined by a distortion power factor target interacting with a complex impedance network in a target frequency range. In one embodiment, the secondary winding comprises between 1 and 4 effective turns. In one embodiment, the secondary winding comprises up to 6 effective turns when Nc is less than six. In one embodiment, each of the one or more primary windings of each primary structure is connected to one or more battery cells by a bridge circuit, and the secondary winding is connected to a load by a secondary rectification or bridge circuit. In one embodiment, the complementary set comprises a primary flux guide and a secondary flux guide pair. In one embodiment, the magnetic coupling apparatus achieves at least some magnetic cancellation through a negative leakage inductance which provides a 180 degree phase shift of current in the primary winding. In one embodiment, the k factor is further defined to achieve system power that is greater than the minimum desired power of the system for a given switching frequency.. In one embodiment, the k factor is further defined to achieve a system RMS current lower than that which would produce the maximum allowable distortion power factor / total harmonic distortion for a given Switching Frequency. In one embodiment, the k factor is further defined based on one or more of: the gap between the primary flux guide and secondary flux guide, the alignment between the primary flux guide and secondary flux guide, the relative cross section area of the primary flux guide and secondary flux guide, a number of opposing limbs located on primary flux guide and the secondary flux guide, the frequency of oscillatory current in the primary winding and secondary winding. In one embodiment, a k factor is greater than 0.5. In one embodiment, a k factor is lower than 0.95. In one embodiment, the predetermined geometrical alignment further comprises a coplanar arrangement of the complementary sets. In one embodiment, each complementary set of primary and secondary flux guide components are separated by an air gap of up to about 2 mm. In one embodiment, the sets of primary flux guides and secondary flux guide comprises a pair. In one embodiment, each primary structure is contained within a discrete module. In one embodiment, the primary windings of each discrete module are electrically isolated from one another. In one embodiment, the primary structure further comprises an arrangement of layers, the layers comprising: a primary winding, and an insulator substrate. In one embodiment, one or more primary flux guide components comprise a core having a limb portion extending from a base portion, and the primary winding is configured to partly encircle the limb portion. In one embodiment, the limb portion extending from a base portion comprises a central limb. In one embodiment, there is a retention assembly configured to support at least the secondary flux guide and the secondary winding, the retention assembly comprising: a base member and at least one retention member having a contact surface configured to engage a portion of one or more secondary flux guides; and wherein a dimensional tolerance exists between the retention member and the secondary flux guide, such that the retention member allows for a predefined amount movement of the secondary flux guide relative to the base member, while securing the secondary flux guide in place. In one embodiment, there is a retention assembly configured to support at least the secondary flux guide and the secondary winding, the retention assembly comprising: a contact surface configured to engage a portion of the one or more secondary flux guides comprising a dimensional tolerance adapted to restrain movement of the one or more secondary flux guides within the dimensional tolerance. In one embodiment, there is a retention assembly configured to support one or more primary flux guide relative to the secondary structure, the retention assembly comprising: a contact surface configured to engage a portion of at least one primary flux guide comprising a dimensional tolerance adapted to restrain movement of the one or more primary flux guides within the dimensional tolerance relative to the secondary flux guide in its set. In one embodiment, there is a plurality of primary modules at least partly enclosed within a housing, each module adapted to contain at least one primary structure. In one embodiment, the primary modules having different overall heights and coplanarity, and the secondary structure having dimensional tolerance for movement within six degrees of freedom to allow alignment with individual coplanarity and predefined flux gap. In one embodiment, the secondary flux guide is secured within the retention assembly with a limited freedom of movement due to the dimensional tolerance, permitting positional adjustments without detaching the secondary flux guide from the assembly. In one embodiment, the retention assembly comprises one or more guiding surfaces configured to engage with the primary structure and extend toward the secondary structure, the guiding surfaces comprising a narrowing structure configured to receive the secondary structure as the secondary structure is moved toward the primary structure. In one embodiment, the primary and secondary structures comprise an insulator material having a combined thickness constraining the gap between primary and secondary flux guides. In another board aspect, the invention is based on definition of the coupling factor k and where the constraints of the coupled inductor system are determined by a combination of physical design choices, operational requirements, and fundamental mathematical relationships. In one embodiment, a non-optimised, functional k factor may be preferred in circumstances where mechanical tolerance is imprecise, allowing for loose tolerance rather than tight manufacturing requirements. Practical considerations like resistance and copper material cost limit the viable range of turns ratios and k values. The goal is a k value that maximises real power transfer while keeping apparent power low. Design decisions are made to allow for system scalability, such as operating a larger system by using multiple packs in parallel rather than increasing the cell count in a single pack, based on how the k requirement increases with the number of cells. In another broad aspect there is a modular power management system comprising: a plurality of primary modules, each module comprising: a primary bridge circuit under the control of a primary controller and configured to operatively couple one or more battery cells to a primary winding associated with a primary flux guide; wherein each primary flux guide is coupled by magnetic flux with a secondary flux guide from a group of secondary flux guides, the group of secondary flux guides associated with a shared secondary winding; the secondary winding connected with a capacitor to thereby facilitate an oscillatory current; wherein each primary winding of each primary module shares the oscillatory current with the secondary winding; and each primary controller is configured to: determine, from its primary winding, the voltage and current magnitude and phase, and control conduction of the primary bridge circuit based on the determined voltage and current magnitude and phase to manage the current of the one or more battery cells. In one embodiment, each primary controller is configured to control switch transitions of its primary bridge circuit at a phase angle based on the determined current magnitude being below a predetermined current threshold. In one embodiment, the predetermined current threshold is based on an effective zero current switching threshold that establishes soft switching. In one embodiment, the primary controller of each primary module is further configured to control the effective duty of its primary bridge circuit based on the determined voltage and current magnitude and phase to regulate the current of the one or more battery cells. In one embodiment, control of the effective duty of the primary bridge comprises a predetermined rate of change limit. In one embodiment, one or more of the plurality of primary modules are removable from the system to thereby decouple the flux between a primary and secondary flux guide. In one embodiment, the system comprises a secondary module comprising a central controller, the group of secondary flux guides the shared secondary winding, and the capacitor; and the central controller is configured to control a secondary bridge circuit to define the frequency of the oscillatory current. In one embodiment, the central controller is configured to determine, from its secondary winding, the voltage and current magnitude and phase, and control the effective secondary bridge duty and / or secondary bridge switching frequency of the secondary bridge circuit based on the determined voltage and current magnitude and phase to collectively regulate the current of the one or more battery cells of each primary module. In one embodiment, control of the secondary bridge effective duty comprises a predetermined rate of change limit. In one embodiment, the central controller is configured to control a switch transition of the secondary bridge at a phase angle based on the determined voltage magnitude being below a predetermined secondary voltage threshold or a predetermined secondary current threshold. In one embodiment, the predetermined secondary voltage threshold or predetermined secondary current threshold is based on one or more secondary parameters comprising: the temperature of the secondary bridge, the temperature of a circuit region, the temperature of a cell, the current through the secondary bridge circuit, and an operation phase of the system being a startup phase. In one embodiment, the central controller is configured to operate the secondary bridge circuit to control an oscillating current frequency based on a determination that the determined voltage or current magnitude at the switching instant is above a predetermined threshold. In one embodiment, the central controller is configured to control the secondary bridge circuit to a frequency based on a determined phase misalignment between the voltage and current phase angles. In one embodiment, the determined phase misalignment exceeds a threshold phase angle. In one embodiment, the central controller shares a communication channel with the plurality of primary modules, and communicates, to one or more primary controllers, one or more phase offset angle data based on a predetermined difference between the phase angle of the primary winding of at least one primary module, and the secondary winding; and wherein each primary controller is configured to operate its primary bridge circuit based on the received phase offset angle data. In one embodiment, each phase offset angle data is unique to at least two of primary controllers / modules. In one embodiment, the phase offset angle data is based on the number of effective secondary turns divided by the number of effective primary turns of the primary and secondary windings in the primary flux guide and its flux coupled secondary flux guide. In one embodiment, the phase offset angle is based on one or more of a cell terminal voltage, the primary module position in the system, and cell chemistry. In one embodiment, the primary module further comprises a phase lock loop configured to determine the phase angle of the oscillatory current in the primary winding; and wherein the primary controller is configured to operate its primary switching circuit based on an agreement between the phase lock loop determined phase angle and phase angle offset data received from the secondary controller. In one embodiment, the agreement is based on a predetermined phase angle range. In one embodiment, each primary controller is configured to revise its operational phase offset angle based on the determined voltage and current magnitude and phase, and based on the revised operational phase offset angle falling within a predetermined phase angle range. In one embodiment, each primary controller is configured to revise its operational phase offset angle within the boundaries of a predetermined rate of change limit. In one embodiment, the frequency of the oscillatory current is based on a dynamic system impedance determined by the number of the primary modules coupled to the system. In one embodiment, each primary controller is configured to: control discharging of the one or more battery cells in its module by connection of the cell polarity substantially in phase with the determined voltage and current magnitude of the primary winding; and control charging of the one or more battery cells in its module by connection of the cell polarity substantially out of phase with the determined voltage and current magnitude of the primary winding. In one embodiment, each primary controller is configured to control its primary bridge circuit to effectively short circuit its primary winding when its one or more battery cells are not charging or discharging. In one embodiment, wherein the primary module further comprises a phase lock loop configured to determine the phase angle of the oscillatory voltage in the primary winding, and wherein one or more primary controllers are configured to: control its primary bridge circuit to effectively open circuit its primary winding, measure the oscillatory voltage of the primary winding in the open circuit, and operate its primary bridge circuit based on the determined oscillatory voltage.. In one embodiment, the secondary controller is configured to determine the number of primary windings flux coupled to the secondary winding based on an impedance determination, and one or more of: defining a new frequency of the oscillatory current based on a determined change in the impedance, operate the secondary bridge to control the collective regulated current. In one embodiment, the impedance substantially matches a predetermined change in impedance. In one embodiment, wherein at least one of the plurality of primary modules comprises a battery cell and a pressure-application mechanism configured to apply a compressive force to the body of the battery cell, and wherein a controller of the system is configured to output a control signal to the pressure-application mechanism to vary the compressive force applied to the battery cell. In one embodiment, the pressure-application mechanism comprises at least one of a motorised clamping assembly driven by an electromotive actuator, and a spring-loaded clamping assembly configured to engage or release in response to a control signal responsive to a release signal received from a controller of the system. In one embodiment, the system further comprises a communication interface between each primary module and the secondary module, the interface configured to establish a non-contact communication scheme whereby a data signal is superimposed on a power transfer waveform coupled between the primary winding and the secondary winding. In one embodiment, the non-contact communication scheme is configured to transmit operational parameters via a wireless channel, said operational parameters including one or more of cell voltage, cell current, State of Charge (SOC), State of Health (SOH), cell temperature, and primary module identification data. In one embodiment, wherein the non-contact communication scheme employs a modulated carrier signal within the same magnetic coupler used for power flow, the modulation selected from the group includes frequency, phase, or amplitude modulation. In one embodiment, the central controller is further configured to: receive cell data pertaining to the one or more battery cells from one or more primary modules, the cell data comprising one or more of: cell terminal voltage, cell current, SOH, SOC, and cell temperature; transmitting an operation target to the primary controller of the primary module pertaining to the determined cell data; and wherein each primary controller is configured to: change a conduction parameter of the primary bridge, being one or more of an effective duty cycle and a conduction phase angle based on the received operation target from the central controller. In one embodiment, wherein the central controller is configured to transmit the operation target is based on the cell data one or more battery cells exceeds a predetermined operating range. In one embodiment, each primary controller is configured to control a primary startup phase, comprising: controlling its primary bridge circuit to effectively short circuit the primary winding; determining, based on a voltage and current measurement from the primary winding, there is no oscillatory current operating in the system; then, either: controlling its primary bridge circuit to provide a startup oscillatory current at a startup frequency, to its primary winding, and thereby, other primary windings and the secondary winding; and the secondary controller is configured to: derive power from the oscillatory current in the secondary winding, and bootstrap a secondary startup phase based on the derived power, the procedure comprising operating the secondary bridge circuit at the startup frequency; or: controlling its primary bridge circuit to provide a startup oscillatory current at a startup frequency, to its primary winding, and thereby, other primary windings and the secondary winding; wherein the secondary module comprises a secondary power storage device operable to derive power from the oscillatory current in the secondary winding; and wherein the central controller is configured to control a secondary startup phase deriving power from the secondary power storage device. In one embodiment, the central controller is configured to signal the primary modules to end the primary startup phase based on the derived power. In one embodiment, the central controller is configured to transition the startup frequency to an operating frequency at the end of the primary startup phase. In one embodiment, the central controller is configured to signal the primary modules to end the primary startup phase based on the derived power. In one embodiment, the central controller is configured to operate the secondary bridge circuit at an operation frequency at the end of the primary startup phase. In one embodiment, the central controller is configured to control a startup phase, comprising: connecting the secondary bridge to a power source based on one of: a supply connected to the system output, a secondary power storage device, controlling the secondary bridge to generate an oscillatory current in the secondary winding proximate to a resonant frequency; and wherein each primary module controller is configured to: control its primary bridge circuit to effectively short its primary winding during the startup phase; and synchronise its primary bridge operation to the oscillatory current detected in its shorted primary winding. In one embodiment, each primary controller is further configured to operate its primary bridge based on one or more operational targets communicated by the central controller. In another broad aspect the invention relates to a discrete battery module configured for energy transfer in a power system together with a plurality of other battery modules, each module comprising: one or more battery cells; a primary structure, the primary structure including: a primary flux guide component, and a primary winding associated with the primary flux guide component; a switching circuit coupled to the battery cell and the primary winding and operable to be configured to generate an alternating current output; and a primary controller configured to operate the switching circuit; wherein the battery module is adapted to removably engage with a secondary module, in use, such that the engagement causes alignment with a secondary structure of the secondary module, the secondary structure comprising: a plurality of secondary flux guide components, one secondary winding associated with the plurality of the secondary flux guide components; such that the alignment causes the primary and secondary flux guide components to be arranged in complementary sets with a predetermined geometrical alignment for magnetic coupling, each set defining a current transformer with a defined coupling factor k. In one embodiment, each current transformer is defined by a k factor being greater than 1 / turns ratio. In one embodiment, the turns ratio of the engaged is defined by the number of effective secondary turns divided by the number of effective primary turns of the primary and secondary windings in each set. In one embodiment, the complementary set comprises a primary flux guide and a secondary flux guide pair. In one embodiment, the primary module further comprises an enclosure adapted to support at least the primary structure. In one embodiment, the enclosure incorporates a plastic support structure that simultaneously secures the winding and flux guide while forming part of the exterior wall. In one embodiment, the enclosure comprises an interfacing surface adapted to control a separation between the primary flux guide component and the secondary flux guide component of its complementary set, thereby controlling, at least in part, the coupling factor (K) of the module. In one embodiment, the interfacing surface comprises an exterior wall of a thickness or form which at least partly defines at least one of a gap and alignment with respect to the secondary flux guide of the secondary structure. In one embodiment, the complementary flux guide pairs have a gap of up to about 2 mm, and the gap is occupied by one or more of a polymer, air, and liquid media. In one embodiment, the enclosure includes one or more guiding surfaces adapted complementary to one or more surfaces of the secondary module such that engagement between the surfaces causes at least one of a predetermined gap and alignment with respect to the secondary structure to occur, and subsequently, define the predetermined coupling factor. In one embodiment, the enclosure comprises one or more guiding surfaces designed complementary to surfaces on the secondary structure such that when the module is engaged with the secondary module, these guiding surfaces automatically establish both alignment and gap spacing, thereby fixing the coupling factor k. In one embodiment, the enclosure includes one or more guide ribs which define a mechanical guide for the engagement between removable primary modules and the secondary module. In one embodiment, the enclosure comprises one or more guiding surfaces designed complementary to surfaces on the secondary structure such that when the module is engaged with the secondary module, these guiding surfaces gap spacings are imprecise and / or differ between at least two sets as the system is configured to allow for X / Y / Z tolerances. In one embodiment, there is a retention assembly configured to support at least the secondary flux guide and the secondary winding, the retention assembly comprising: a base member and at least one retention member having a contact surface configured to engage a portion of one or more secondary flux guides; and wherein a dimensional tolerance exists between the retention member and the secondary flux guide, such that the retention member allows for a predefined amount of movement of the secondary flux guide relative to the base member, while securing the secondary flux guide in place. In one embodiment, there is a retention assembly configured to support at least the secondary flux guide and the secondary winding, the retention assembly comprising: a contact surface configured to engage a portion of the one or more secondary flux guides comprising a dimensional tolerance adapted to restrain movement of the one or more secondary flux guides within the dimensional tolerance. In one embodiment, there is a retention assembly configured to support one or more primary flux guide relative to the secondary structure, the retention assembly comprising: a contact surface configured to engage a portion of at least one primary flux guide comprising a dimensional tolerance adapted to restrain movement of the one or more primary flux guides within the dimensional tolerance relative to the secondary flux guide in its set. In one embodiment, there is a plurality of primary modules at least partly enclosed within a housing, each module adapted to contain at least one primary structure In one embodiment, the primary modules have different overall heights and noncoplanarity, and the secondary structure having dimensional tolerance for movement within six degrees of freedom to allow alignment with individual coplanarity and predefined flux gap. In one embodiment, the secondary flux guide is secured within the retention assembly with a limited freedom of movement due to the dimensional tolerance, permitting positional adjustments without detaching the secondary flux guide from the assembly. In one embodiment, the retention assembly comprises one or more guiding surfaces configured to engage with the primary structure and extend toward the secondary structure, the guiding surfaces comprising a narrowing structure configured to receive the secondary structure as the secondary structure is moved toward the primary structure. In one embodiment, the primary and secondary structures comprise an insulator material having a combined thickness constraining the gap between primary and secondary flux guides. In one embodiment, the enclosure locates and supports an antenna in the form of a wireless data receiver / transmitter configured to support wireless communication with an external control system. In one embodiment, the enclosure locates and supports an electrical connector configured for the wired coupling of a communication channel. In one embodiment, the primary module comprises a hermetically sealed enclosure, wherein the enclosure is encapsulated in an insulating material. In one embodiment, the primary controller is configured to determine the primary structure is magnetically engaged with the secondary structure via a detection of a signal received by the primary winding. In one embodiment, the primary structure further comprises a communications winding configured to receive flux from the magnetic coupling apparatus, the communications winding configured to detect a communications signal modulated on the power transmission waveform. In one embodiment, there is a primary module container configured to support a wireless communication antenna adapted to facilitate non-contact data exchange between a primary cell controller and a secondary controller In one embodiment, the primary modules having different overall heights and noncoplanarity, and the secondary structure having dimensional tolerance for movement within six degrees of freedom to allow alignment with individual coplanarity and predefined flux gap. In one embodiment, the primary controller of each primary module is configured to: sense an oscillatory current induced in a primary winding of the primary module from the continuously operating system; determine if the magnitude of the induced oscillatory current is sufficient for synchronisation; synchronise local bridge switching operations with the oscillatory current to establish an operational frequency and zero-crossing references; control the primary bridge conduction based on the operational frequency and zero-crossing references. In one embodiment, the primary controller of each primary module is further configured to receive a target power contribution value or a target primary conduction angle from a central controller of a secondary module when engaged with the secondary module. In one embodiment, each primary controller is configured to control switch transitions of its primary bridge circuit at a phase angle based on the sensed oscillatory current having a magnitude being below a predetermined current threshold. In one embodiment, the predetermined current threshold is based on an effective zero current switching threshold that establishes soft switching. In one embodiment, the primary controller of each primary module is further configured to: sense the phase of the oscillatory current in its primary winding, and control the effective duty of its primary bridge circuit based on the sensed phase to regulate the current of the one or more battery cells. In one embodiment, the primary module further comprises a phase lock loop configured to determine the phase angle of the oscillatory current in the primary winding; and wherein the primary controller is configured to operate its primary switching circuit based on an agreement between the phase lock loop determined phase angle and received phase angle offset data. In one embodiment, each primary controller is configured to revise its operational phase offset angle based on the determined voltage and current magnitude and phase, and based on the revised operational phase offset angle falling within a predetermined range. In one embodiment, each primary controller is configured to revise its operational phase offset angle within the boundaries of a predetermined rate of change limit. In one embodiment, each primary controller is configured to: control discharging of the one or more battery cells in its module by connection of the cell polarity substantially in phase with the determined voltage and current magnitude of the primary winding; and control charging of the one or more battery cells in its module by connection of the cell polarity substantially out of phase with the determined voltage and current magnitude of the primary winding. In one embodiment, each primary controller is configured to control its primary bridge circuit to effectively short circuit its primary winding when its one or more battery cells are not charging or discharging. In one embodiment, each primary controller is configured to control a primary startup phase, comprising: controlling its primary bridge circuit to effectively short circuit the primary winding; determining, based on a voltage and current measurement from the primary winding, there is no oscillatory current operating in the system; controlling its primary bridge circuit to provide a startup oscillatory current at a startup frequency, to its primary winding, and thereby, other primary windings and the secondary winding. In one embodiment, the primary startup phase is of a first time period. In one embodiment, the primary startup phase is repeated after a second time period. In one embodiment, the primary module container locates and supports an antenna in the form of a wireless data / energy receiver / transmitter. In one embodiment, the wireless communication antenna is configured to support communication utilising a short-range wireless protocol, such as Near Field Communication (NFC). In one embodiment, the geometric structure of the primary structures, and the arrangement of the plurality of primary structures are configured to collectively define at least one coolant flow channel between adjacent primary structures, the flow channel adapted to pass a cooling fluid over heat- generating components during operation. In another broad aspect the invention relates to a power system configured for magnetic energy transfer from a plurality of discrete battery modules, the power system comprising: secondary structure comprising: a plurality of secondary flux guide components, a secondary winding associated with the plurality of the secondary flux guide components; a capacitor coupled to the secondary winding to form a resonant circuit; a secondary bridge circuit coupled between the resonant circuit and an output for a load; a central controller operatively coupled to the secondary bridge circuit, the central controller configured to manage the operating state and timing of the secondary bridge circuit; and an assembly adapted to support a plurality of the discrete battery modules relative to the plurality of secondary flux guides, wherein the battery modules each comprise a primary flux guide component that, when assembled, are arranged in complementary sets with a predetermined geometrical alignment for magnetic coupling, each set defining a current transformer. In one embodiment, each current transformer is defined by a k factor being greater than 1 / turns ratio. In one embodiment, the assembly includes a rack-like housing forming part of the secondary structure, whereby the containers of the primary modules provide a cartridge configured to engage with the rack. In one embodiment, the rack includes a track structure whereby the primary modules are able to slide on the track from one end to another. In one embodiment, the assembly comprises an interfacing surface adapted to control a separation between the primary flux guide component and the secondary flux guide component of its complementary set, thereby controlling, at least in part, the coupling factor (K) of the module In one embodiment, the interfacing surface comprises an exterior wall of a thickness or form which at least partly defines at least one of a gap and alignment with respect to the secondary flux guide of the secondary structure. In one embodiment, the assembly includes one or more guiding surfaces adapted complementary to one or more surfaces of the primary module such that engagement between the surfaces causes at least one of a predetermined gap and alignment, and subsequently, define the predetermined coupling factor. In one embodiment, each primary module includes a unique ID, and the track structure includes an ID reader operably connected to the central controller for position based determinations of the primary modules. In one embodiment, the central controller is configured to assign a position-based ID to each module slot. In one embodiment, the central controller is configured to: receive unique module ID code from each primary module; receive a positional code from each primary module; and transmit, to one or more primary modules supported by the assembly, control data based on the ID code and positional code. In one embodiment, the central controller is configured to: detect insertion or removal of modules by monitoring received ID codes; maintain a mapping of module unique IDs to rack slot positions; update module control parameters based on position-dependent requirements such as coupling factor, heat dissipation, or service order; and control one or more specific primary cell modules for discharging or charging based on their mapped ID and position. In one embodiment, the central controller is configured to control a switch transition of the secondary bridge at a phase angle based on the determined voltage magnitude being below a secondary voltage predetermined threshold. In one embodiment, the central controller is configured to control a switch transition of the secondary bridge at a phase angle based on the determined current magnitude being below a predetermined secondary current threshold. In one embodiment, the predetermined secondary current threshold is based on one or more secondary parameters comprising the temperature of the secondary bridge, the temperature of a circuit region, the temperature of a cell, the current through the secondary bridge circuit, and an operation phase of the system being a startup phase. In one embodiment, the central controller is configured to operate the secondary bridge circuit to control an oscillating current frequency based on a determination that the determined voltage or current magnitude at the switching instant is above a predetermined threshold. In one embodiment, the central controller is configured to control the secondary bridge circuit to a frequency based on a determined phase misalignment between the voltage and current phase angles. In one embodiment, the determined phase misalignment exceeds a threshold phase angle. In one embodiment, the central controller shares a communication channel with the plurality of primary modules, and communicates, to one or more primary controllers, one or more phase offset angle data based on a predetermined difference between the phase angle of the primary winding of at least one primary module, and the secondary winding; and wherein each primary controller is configured to operate its primary bridge circuit based on the received phase offset angle data. In one embodiment, each phase offset angle data is unique to at least two of primary controllers / modules. In one embodiment, phase offset angle data is based on the number of effective secondary turns divided by the number of effective primary turns of the primary and secondary windings in the primary flux guide and its flux coupled secondary flux guide. In one embodiment, the phase offset angle is based on cell chemistry. In one embodiment, the phase offset angle is based on the primary module position in the system. In one embodiment, the system further comprises a communication interface between each primary module and the secondary module, the interface configured to establish a non-contact communication scheme whereby a data signal is superimposed on a power transfer waveform coupled between the primary winding and the secondary winding. In one embodiment, the non-contact communication scheme is configured to transmit operational parameters from each primary module to the central controller via a wireless channel, said operational parameters including one or more of cell voltage, cell current, State of Charge (SOC), State of Health (SOH), cell temperature, and primary module identification data. In one embodiment, the non-contact communication scheme employs a modulated carrier signal within the same magnetic coupler used for power flow, the modulation selected from the group consisting of frequency, phase, or amplitude modulation. In one embodiment, the central controller is configured to control a startup phase, comprising: connecting the secondary bridge to a power source based on one of: a supply connected to the system output, a secondary power storage device, controlling the secondary bridge to generate an oscillatory current in the secondary winding proximate to a resonant frequency; and wherein each primary module controller is configured to: control its primary bridge circuit to effectively short its primary winding during the startup phase; and synchronise its primary bridge operation to the oscillatory current detected in its shorted primary winding. In one embodiment, each primary controller is further configured to operate its primary bridge based on one or more operational targets communicated by the central controller. In one embodiment, the enclosure locates and supports an antenna in the form of a wireless data receiver / transmitter configured to support wireless communication with an external control system. In one embodiment, the enclosure locates and supports an electrical connector configured for the wired coupling of a communication channel. In one embodiment, the enclosure is hermetically sealed by an insulating material. In one embodiment, comprising a retention assembly configured to support at least the secondary flux guide and the secondary winding, the retention assembly comprising: a base member and at least one retention member having a contact surface configured to engage a portion of one or more secondary flux guides; and wherein a dimensional tolerance exists between the retention member and the secondary flux guide, such that the retention member allows for a predefined amount of movement of the secondary flux guide relative to the base member, while securing the secondary flux guide in place. In one embodiment, there is a retention assembly configured to support at least the secondary flux guide and the secondary winding, the retention assembly comprising: a contact surface configured to engage a portion of the one or more secondary flux guides comprising a dimensional tolerance adapted to restrain movement of the one or more secondary flux guides within the dimensional tolerance. In one embodiment, the secondary flux guide is secured within the retention assembly with a limited freedom of movement due to the dimensional tolerance, permitting positional adjustments without detaching the secondary flux guide from the assembly. In one embodiment, the retention assembly comprises one or more guiding surfaces configured to engage with the primary structure and extend toward the secondary structure, the guiding surfaces comprising a narrowing structure configured to receive the secondary structure as the secondary structure is moved toward the primary structure. In one embodiment, the retention assembly is configured to support one or more primary flux guide relative to the secondary structure, the retention assembly comprising: a contact surface configured to engage a portion of at least one primary flux guide comprising a dimensional tolerance adapted to restrain movement of the one or more primary flux guides within the dimensional tolerance relative to the secondary flux guide in its set. In one embodiment, a plurality of primary modules at least partly enclosed within a housing, each module adapted to contain at least one primary structure, wherein the primary modules having different overall heights and noncoplanarity, and the secondary structure having dimensional tolerance for movement within six degrees of freedom to allow alignment with individual planarity and predefined flux gap. In one embodiment, the primary and secondary structures comprise an insulator material interspersed between them, the material having a combined thickness constraining the gap between primary and secondary flux guides. In one embodiment, the primary controller is configured to determine the primary structure is magnetically engaged with the secondary structure via a detection of a signal received by the primary winding. In one embodiment, the primary structure further comprises a communications winding configured to receive flux from the magnetic coupling apparatus, the communications winding configured to detect a communications signal modulated on the power transmission waveform. In one embodiment, there is a primary module container configured to support a wireless communication antenna adapted to facilitate non-contact data exchange between a primary cell controller and a secondary controller In one embodiment, the primary controller of each primary module is configured to: sense an oscillatory current induced in a primary winding of the primary module from the continuously operating system; determine if the magnitude of the induced oscillatory current is sufficient for synchronisation; synchronise local bridge switching operations with the oscillatory current to establish an operational frequency and zero-crossing references; control the primary bridge conduction based on the operational frequency and zero-crossing references. In one embodiment, the primary controller of each primary module is further configured to receive a target power contribution value or a target primary conduction angle from a central controller of a secondary module when engaged with the secondary module. In one embodiment, each primary controller is configured to control switch transitions of its primary bridge circuit at a phase angle based on the sensed oscillatory current having a magnitude being below a predetermined current threshold. In one embodiment, the predetermined current threshold is based on an effective zero current switching threshold that establishes soft switching. In one embodiment, the primary controller of each primary module is further configured to: sense the phase of the oscillatory current in its primary winding, and control the effective duty of its primary bridge circuit based on the sensed phase to regulate the current of the one or more battery cells. In one embodiment, the primary module further comprises a phase lock loop configured to determine the phase angle of the oscillatory current in the primary winding; and wherein the primary controller is configured to operate its primary switching circuit based on an agreement between the phase lock loop determined phase angle and received phase angle offset data. In one embodiment, each primary controller is configured to revise its operational phase offset angle based on the determined voltage and current magnitude and phase, and based on the revised operational phase offset angle falling within a predetermined range. In one embodiment, each primary controller is configured to revise its operational phase offset angle within the boundaries of a predetermined rate of change limit. In one embodiment, each primary controller is configured to: control discharging of the one or more battery cells in its module by connection of the cell polarity substantially in phase with the determined voltage and current magnitude of the primary winding; and control charging of the one or more battery cells in its module by connection of the cell polarity substantially out of phase with the determined voltage and current magnitude of the primary winding. In one embodiment, each primary controller is configured to control its primary bridge circuit to effectively short circuit its primary winding when its one or more battery cells are not charging or discharging. In one embodiment, each primary controller is configured to control a primary startup phase, comprising: controlling its primary bridge circuit to effectively short circuit the primary winding; determining, based on a voltage and current measurement from the primary winding, there is no oscillatory current operating in the system; controlling its primary bridge circuit to provide a startup oscillatory current at a startup frequency, to its primary winding, and thereby, other primary windings and the secondary winding. In one embodiment, the primary startup phase is of a first time period. In one embodiment, the primary startup phase is repeated after a second time period. In another broad aspect, the invention relates to a power system configured for magnetic energy transfer from a plurality of discrete battery modules, the power system comprising: a secondary structure comprising: a plurality of secondary flux guide components, a secondary winding associated with the plurality of the secondary flux guide components; a capacitor coupled to the secondary winding to form a resonant circuit; a secondary bridge circuit coupled between the resonant circuit and an output for a load; a central controller operatively coupled to the secondary bridge circuit, the central controller configured to manage the operating state and timing of the secondary bridge circuit; and an assembly adapted to support a plurality of the discrete battery modules relative to the plurality of secondary flux guides, wherein the battery modules each comprise a primary flux guide component that, when assembled, are arranged in complementary sets with a predetermined geometrical alignment for magnetic coupling, each set defining a current transformer. In one embodiment, each current transformer is defined by a k factor being greater than 1 / turns ratio. In one embodiment, the assembly comprises an interfacing surface adapted to control a separation between the primary flux guide component and the secondary flux guide component of its complementary set, thereby controlling, at least in part, the coupling factor (K) of the module In one embodiment, the interfacing surface comprises an exterior wall of a thickness or form which at least partly defines at least one of a gap and alignment with respect to the secondary flux guide of the secondary structure. In one embodiment, the assembly includes one or more guiding surfaces adapted complementary to one or more surfaces of the primary module such that engagement between the surfaces causes at least one of a predetermined gap and alignment, and subsequently, define the predetermined coupling factor. In one embodiment, the assembly includes a rack-like housing forming part of the secondary structure, whereby the primary modules comprise a cartridge configured to engage with the rack. In one embodiment, the rack includes a track structure whereby the primary modules are able to slide on the track from one end to another. In one embodiment, each primary module includes a unique ID, and the track structure includes an ID reader operably connected to the central controller for position based determinations of the primary modules. In one embodiment, the central controller is configured to assign a position-based ID to each module position. In one embodiment, the central controller is configured to: receive unique module ID code from each primary module; receive a positional code from each primary module; and transmit, to one or more primary modules supported by the assembly, control data based on the ID code and positional code. In one embodiment, the central controller configured to: detect insertion or removal of modules by monitoring received ID codes; maintain a mapping of module unique IDs to rack slot positions; update module control parameters based on position-dependent requirements such as coupling factor, heat dissipation, or service order; and control one or more specific primary cell modules for discharging or charging based on their mapped ID and position. In one embodiment, the central controller is configured to control a switch transition of the secondary bridge at a phase angle based on the determined voltage magnitude being below a secondary voltage predetermined threshold. In one embodiment, the central controller is configured to control a switch transition of the secondary bridge at a phase angle based on the determined current magnitude being below a predetermined secondary current threshold. In one embodiment, the predetermined secondary current threshold is based on one or more secondary parameters which comprise the temperature of the secondary bridge, the temperature of a circuit region, the temperature of a cell, the current through the secondary bridge circuit, and an operation phase of the system being a startup phase. In one embodiment, the central controller is configured to operate the secondary bridge circuit to control an oscillating current frequency based on a determination that the determined voltage or current magnitude at the switching instant is above a predetermined threshold. In one embodiment, the central controller is configured to control the secondary bridge circuit to a frequency based on a determined phase misalignment between the voltage and current phase angles. In one embodiment, the determined phase misalignment exceeds a threshold phase angle. In one embodiment, the central controller shares a communication channel with the plurality of primary modules, and communicates, to one or more primary controllers, one or more phase offset angle data based on a predetermined difference between the phase angle of the primary winding of at least one primary module, and the secondary winding; and wherein each primary controller is configured to operate its primary bridge circuit based on the received phase offset angle data. In one embodiment, each phase offset angle data is unique to at least two of primary controllers / modules. In one embodiment, the phase offset angle data is based on the number of effective secondary turns divided by the number of effective primary turns of the primary and secondary windings in the primary flux guide and its flux coupled secondary flux guide. In one embodiment, the phase offset angle is based on the primary module position in the system. In one embodiment, the system further comprises a communication interface between each primary module and the secondary module, the interface configured to establish a non-contact communication scheme whereby a data signal is superimposed on a power transfer waveform coupled between the primary winding and the secondary winding. In one embodiment, the non-contact communication scheme is configured to transmit operational parameters from each primary module to the central controller via a wireless channel, said operational parameters including one or more of cell voltage, cell current, State of Charge (SOC), State of Health (SOH), cell temperature, and primary module identification data. In one embodiment, the non-contact communication scheme employs a modulated carrier signal within the same magnetic coupler used for power flow, the modulation selected from the group consisting of frequency, phase, or amplitude modulation. In one embodiment, the central controller is configured to control a startup phase, comprising: connecting the secondary bridge to a power source based on one of: a supply connected to the system output, a secondary power storage device; controlling the secondary bridge to generate an oscillatory current in the secondary winding proximate to a resonant frequency; and wherein each primary module controller is configured to: control its primary bridge circuit to effectively short its primary winding during the startup phase; and synchronise its primary bridge operation to the oscillatory current detected in its shorted primary winding. In one embodiment, each primary controller is further configured to operate its primary bridge based on one or more operational targets communicated by the central controller. In one embodiment, the central controller is configured to: detect a change in system operational parameters, including an alteration to the switching frequency of the system required to meet soft switching criteria, resulting from the physical removal of the primary module; coordinating the continued operation of the remaining primary modules based on one or more load requirements. In another broad aspect there is a method executed by a primary cell module controller for maintaining operation within a resonant energy transfer system following the physical removal of a separate primary module during continuous operation (hot swap removal), the method comprising the steps of: detecting a change in system operational parameters, including an alteration to the resonant frequency of the system, resulting from the removal of the separate primary module; receiving an updated operational frequency from a central controller, the updated frequency being adapted to re- establish optimal soft switching for the entire system; maintaining phase-locked operation with the adjusted system waveform and the updated operational frequency; and adjusting the local primary conduction angle and local phase angle to rebalance the system current distribution and maintain soft-switching conditions despite the altered resonant conditions. In one embodiment, the primary cell module controller monitors system phase conditions by performing zero-crossing detection of local coil current and voltage waveforms. In one embodiment, the system continues normal operation with uninterrupted power delivery using remaining primary modules, albeit with a potentially increased power demand applied to the remaining cells. In one embodiment, the primary cell module controller utilizes an optimization algorithm to fine-tune its effective duty and effective phase offset parameters for optimal zero current crossing. In one embodiment, the primary cell module controller is configured to reduce its current contribution by adjusting its effective duty if monitored parameters, such as cell temperature or state of health (SOH), exceed a threshold, thereby overriding a target set by the central controller. In one embodiment, there is a permanent magnet provided within the structure to provide an initial alignment force to the mating primary parts before windings are energised. In another broad aspect there is a method executed by a central controller to integrate a new primary module while the system is operating continuously in a steady-state soft-switched condition, the method comprising the steps of: monitoring phase conditions between a resonant current and a secondary bridge voltage; detecting a change in the phase conditions, indicative of an alteration in the effective transfer function and resonant frequency of the system, upon the physical addition of the new primary module; adapting a switching frequency of the secondary bridge toward a new value that re-establishes soft-switching conditions across the entire system; and coordinating the system's ongoing operation such that the newly added module is integrated to contribute or absorb power in a soft-switched manner alongside existing modules. In one embodiment, the detection of the change in phase conditions is performed via zero-crossing detection of the resonant current and the secondary bridge voltage. In one embodiment, receiving communication from the newly added primary module indicates its presence and readiness for synchronisation. In one embodiment, there is a controller configured to calculate a target primary conduction angle or power contribution value for the newly added module and transmitting this target to a local primary cell module controller within the new primary module. In one embodiment, the frequency is adapted using a Proportional-Integral (PI) controller in a feedback loop to refine the control toward the new resonant frequency. In another broad aspect there is a method executed by a controller following the physical removal of a primary module during continuous operation, the method comprising the steps of: detecting a change in system operational parameters, including an alteration to the resonant frequency of the system, resulting from the physical removal of the primary module; monitoring system phase conditions via zero-crossing detection of resonant current and secondary bridge voltage; adapting the switching frequency of the secondary bridge toward a new value that re-establishes optimal soft-switching for the remaining modules; and coordinating the continued operation of the remaining primary modules such that bidirectional energy transfer continues in a stable and efficient manner despite the altered resonant conditions. In one embodiment, the adaptation of the switching frequency ensures that power provided to an output circuit is uninterrupted, albeit with a potentially increased power demand applied to the remaining cells. In one embodiment, the central controller utilises a closed-loop controller (PI controller) to regulate the switching frequency toward the new resonant frequency. In one embodiment, the central controller is configured to communicate updated target values of current, voltage, or power to the remaining cell module controllers to rebalance system current distribution following the reduction in the total number of active modules. In one embodiment, the adaptation step includes enforcing rate-of-change limits on the switching frequency to allow local controllers to adapt without disruption to stable soft-switched operation. In another broad aspect there is a method executed by a controller for maintaining operation within a resonant energy transfer system following the physical removal of a separate primary module during continuous operation (hot swap removal), the method comprising the steps of: detecting a change in system operational parameters, including an alteration to the resonant frequency of the system, resulting from the removal of the separate primary module; receiving an updated operational frequency from a central stack controller, the updated being adapted to re-establish optimal soft switching for the entire system; maintaining phase-locked operation with the adjusted system waveform and the updated operational frequency; and adjusting the local primary conduction angle and local phase angle to rebalance the system current distribution and maintain soft-switching conditions despite the altered resonant conditions. In one embodiment, each primary cell module controller monitors system phase conditions by performing zero-crossing detection of local coil current and voltage waveforms. In one embodiment, the system continues normal operation with uninterrupted power delivery using remaining primary modules, albeit with a potentially increased power demand applied to the remaining cells. In one embodiment, the primary cell module controller utilises an optimisation algorithm to fine-tune its conduction duty and phase offset parameters for optimal zero current crossing. In one embodiment, the primary cell module controller is configured to reduce its current contribution by reducing its bridge conduction duty if monitored parameters, such as cell temperature or state of health (SOH), exceed a threshold, thereby overriding a target set by the central controller In another broad aspect there is a method executed by a method executed by a central controller to integrate a new primary module while the system is operating continuously in a steady-state soft- switched condition, the method comprising the steps of: monitoring phase conditions between a resonant current and a secondary bridge voltage; detecting a change in the phase conditions, indicative of an alteration in the effective transfer function and resonant frequency of the system, upon the physical addition of the new primary module; adapting a switching frequency of the secondary bridge toward a new value that re-establishes soft-switching conditions across the entire system; and coordinating the systems ongoing operation such that the newly added module is integrated to contribute or absorb power in a soft-switched manner alongside existing modules. In one embodiment, the detection of the change in phase conditions is performed via zero-crossing detection of the resonant current and the secondary bridge voltage. In one embodiment, the method further comprises receiving communication from the newly added primary module indicating its presence and readiness for synchronisation. In one embodiment, the method further comprises calculating a target primary conduction angle or power contribution value for the newly added module and transmitting this target to a local primary cell module controller within the new primary module. In one embodiment, the frequency is adapted using a Proportional-Integral (PI) controller in a feedback loop to refine the control toward the new resonant frequency. In another broad aspect there is a method executed by a controller following the physical removal of a primary module during continuous operation, the method comprising the steps of: detecting a change in system operational parameters, including an alteration to the resonant frequency of the system, resulting from the physical removal of the primary module; monitoring system phase conditions via zero-crossing detection of resonant current and secondary bridge voltage; adapting the switching frequency of the secondary bridge toward a new value that re-establishes optimal soft-switching for the remaining modules; and coordinating the continued operation of the remaining primary modules such that bidirectional energy transfer continues in a stable and efficient manner despite the altered resonant conditions. In one embodiment, the adaptation of the switching frequency ensures that power provided to an output circuit is uninterrupted, albeit with a potentially increased power demand applied to the remaining cells. In one embodiment, the central controller utilizes a closed-loop controller (PI controller) to regulate the switching frequency toward the new resonant frequency. In one embodiment, the central controller is configured to communicate updated target values of current, voltage, or power to the remaining cell module controllers to rebalance system current distribution following the reduction in the total number of active modules. In one embodiment, wherein the adaptation step includes enforcing rate-of-change limits on the switching frequency to allow local controllers to adapt without disruption to stable soft-switched operation. In some embodiments, the invention relates to any one or more of the above statements in combination with any one or more of any of the other statements. Other aspects of the invention may become apparent from the following description which is given by way of example only and with reference to the accompanying drawings. The entire disclosures of all applications, patents and publications, cited above and below, if any, are hereby incorporated by reference. This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth. To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. The term “and / or” referred to in the specification and claim means “and” or “or”, or both. The term “comprising” as used in this specification and claims means “consisting at least in part of”. When interpreting statements in this specification and claims which include that term, the features, prefaced by that term in each statement all need to be present but other features can also be present. Related terms such as “comprise” and “comprised” are to be interpreted in the same manner. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms “includes,” “comprises,” “including,” and / or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. It is an object of the invention to alleviate or improve upon the aforementioned disadvantages of the prior art, or at least provide the public with a useful choice. Other objects will be apparent to those skilled in the art. Brief description of the drawings The invention can be better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale relative to each other, emphasis instead being placed upon clearly illustrating the principles of the invention. Furthermore, like reference numerals designate corresponding parts throughout the several views. Figure 1 shows a diagram of conduction through a MOSFET in response to an activation signal, and in particular the rising and falling conductivity as the MOSFET transitions from between conductive and nonconductive states. Figure 2 shows a diagram of current (top) flow when modified by a current modulation interference signal (middle), and the resultant modulated current flow (bottom) which includes a zero crossing in the current flow. Figure 3 shows a diagram of system components. Figure 4 shows another diagram of system components. Figure 5 shows examples of primary switching circuits. Figure 6 shows a schematic of the secondary side system. Figure 7 depicts the detailed switching arrangement of the secondary-side H-bridge circuit. Figure 8 shows a simplified view of the modular system from the perspective of the magnetic coupling components of the system. Figure 9 shows a more detailed view of the exemplary system embodiment comprising n primary-side modules . Figure 10 shows a relationship between coupling factor and the separation gap between primary and secondary flux guides. Figure 11 shows a diagram of the equivalent circuit for the effective current transformers, which form the coupled inductor of the resonant circuit. Figure 12 shows an equivalent circuit of the system including an exemplary magnetic coupling apparatus with three primary modules, Figure 13 illustrates the graphical relationship between k and the turns ratio. Figure 14 shows a graphical representation of the coupling factor k versus the product of NR x NC. Figure 15 shows a diagram of exemplary circuit design parameters according to a table. Figure 16 shows another example based on exemplary circuit design parameters according to a table. Figure 17 shows a cross section of such an exemplary flux guide cores and flux paths of a complementary pair flux guides. Figure 18 shows exemplary secondary windings with one, two, three and four turns. Figure 19 shows an exemplary circular arrangement of flux guide pairs, where the secondary winding is also configured in a complementary circular arrangement Figure 20 shows an exemplary configuration of the secondary module where the secondary winding passes outside of the flux guides. Figure 21 shows a further exemplary configuration where the secondary winding has a different number of secondary winding loops for each core. Figure 22 shows a flux guide which has four limbs, thereby defining 3 window regions between adjacent limbs. Figure 23 shows a top perspective view of a magnetic coupling apparatus. Figure 24 shows a bottom perspective view of the magnetic coupling apparatus of Figure 6. Figure 25 shows a battery system assembly including the magnetic coupling apparatus. Figure 26 shows a top view of the battery system assembly of Figure 25. Figure 27 shows a cross section AA of the battery system assembly. Figure 28 shows a cross section BB of the battery system assembly. Figure 29 shows an exploded view of a primary structure of the magnetic coupling apparatus and battery system assembly. Figure 30 shows a top view of the primary structure. Figure 31 shows cross section AA of the primary structure. Figure 32 shows cross section BB of the primary structure. Figure 33 shows an exploded view of the secondary structure of the magnetic coupling apparatus. Figure 34 shows an exemplary primary or secondary flux guide. Figure 35 shows an exemplary primary flux guide. Figure 36 shows a primary module including a battery and primary circuit and primary structure. Figure 37 shows an example of a secondary flux guide. Figure 38 shows simulated waveforms of switch timing and resulting current operating an exemplary circuit. Figure 39 shows a graph of current vs time and representations of current over time for a transient oscillation. Figure 40 illustrates operation of the primary and secondary bridges based on the exemplary three level modulation control parameters. Figure 41 shows a graph showing power control by bridge conduction duty. Figure 42 shows a graph of switching frequency against the system power output. Figure 43 illustrates exemplary control system components configured for regulating current in a magnetically coupled winding in the primary module. Figure 44 illustrates exemplary control system components configured for regulating current in a magnetically coupled winding in the secondary module. Figure 45 shows an example of a cell voltage in a primary module. Figure 46 shows a graph of the cell voltage phase aligned with the primary winding current. Figure 47 shows a graph whereby the cell voltage is about 180 degrees out of phase with the primary winding current. Figure 48 shows a graph of the bridge voltage and the bridge current which are phase aligned at the zero crossing point. Figure 49 shows a steady state operation where the voltage and current at the secondary bridge. Figure 50 shows a misalignment of the voltage and current phase. Figure 51 shows restored phase alignment between the voltage and current. Detailed description Embodiments of the present disclosure are now described. Exemplary methods, devices, assemblies and systems are described herein. It should be understood that the word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or feature described herein as “exemplary” or “illustrative” is not necessarily to be construed as preferred or advantageous over other embodiments or features. More generally, the embodiments described herein are not meant to be limiting. It will be readily understood that certain aspects of the disclosed systems and methods can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein. In this specification, the terms “cell”, “energy storage module”, "battery cell unit", "cell unit" are generally intended to refer to a module which can store an electrical charge and can refer to an individual battery cell or a block of cells connected in parallel, or a multitude of individual battery cells or blocks of parallel cells or a mix of cells connected in series and / or parallel. Where the terms battery cell, cell or cell unit is used, equally applicable are battery module, module, cell module or module unit, where a module may contain one or more cells in series and / or in parallel. In this specification, the term “energy storage module” may also refer to a block of cells connected in parallel and / or series and which further includes circuit components such as fuses, resistors, passively controlled diodes, capacitors or inductors are connected in series and / or parallel with individual cells. The term “energy storage unit”, “storage unit”, “battery cell unit” or “cell unit” may also refer to non-battery energy storage elements such as fuel cells and supercapacitors. In some embodiments, the energy storage modules may be designed to include one or more energy storage units enabling a charge capacity of at least 10Ah, 20Ah 40Ah, 60Ah, 100Ah, 200Ah, or 400Ah ampere hours. In some embodiments, the plurality of energy storage units may comprise a first and a second energy storage unit, with the first energy storage unit having a charge capacity that is substantially larger than the charge capacity of the second energy storage unit. A cell module may contain any number of cells in series, or parallel, or a combination of series and parallel. In this specification, the term “winding” is intended to refer to an electrical conductor of electrical current which has a meaningful interaction with the magnetic flux contained within its associated flux guide. In the context of the present invention, a meaningful interaction is considered to be true when the objective of the invention is achieved. One objective is to provide a magnetic coupling apparatus and system for use of that apparatus which facilitates soft switching of current used to generate magnetic flux when operated under predetermined oscillatory conditions. A turn of a winding is defined as a conductor path that fully encircles the principal magnetic flux path of one or more flux guides. The number of effective turns of a winding is the number of flux linkages established. For example, if a wire passes through one or more aligned flux guides, that may count as one turn relative to each of the one or more flux guides. The term geometric turns refers to the literal looping of the conductor around the core. The term controller as used in this specification will most commonly be used to describe the functions of one or more processing devices such as microprocessors. A controller may be a single processor, or a combination of multiple processing devices as may be practical. Separate and distinct processing devices are referred to with a preceding title, for example, “central controller”, or “primary cell module controller”. A controller will typically feature output pins which are operably connected to switching devices to control the state of that switching device. For example, the pin of a microprocessor may be connected to operate the gate of a MOSFET switching device. Some embodiments of the invention relate to the structure of a magnetic coupling apparatus configured for reactive energy transfer within a resonant system. A particular advantage of the disclosed magnetic coupling apparatus is its facilitation of zero-current or low-current switching. In such embodiments, semiconductor switching devices are controlled in coordination with the resonant behaviour of the magnetic coupling device to regulate current flow and reduce switching losses. The term “zero current switching” as used within the context of this specification refers to an alignment of voltage and current phase angles and the phase angle at which an alternating voltage and current pass through zero. The term “zero” as used in this specification refers to determination of zero which may fall within the measurement resolution of an analog to digital converter (ADC), and includes a threshold voltage or current within which the voltage or current can be considered to be negligibly different from zero. In some embodiments, there is a controller configured to compare a predetermined threshold to the measured voltage or current and treat that measurement as zero, for the purpose of control, when that threshold is not exceeded. Figure 1 illustrates an example of current through a MOSFET switching device in response to activation (MOSFET on-state) and deactivation (MOSFET off-state) control signals, highlighting the rise and fall of device conductivity during transitions between conductive and non-conductive states. When the switching device transitions from the on-state to the off-state, heat is generated due to the finite drain-to-source resistance while current is still flowing. During turn-off, the inductance of the circuit maintains current flow for a period of time determined by the initial current magnitude and the voltage developed across the inductance. According to the well- known relationship V=L⋅dt / di, the current decreases approximately linearly from its initial value, with slope −V / L, until it reaches zero (e.g., i(t)=i(0)−V / L⋅t). This process is commonly referred to as hard switching, because the MOSFET must sustain the drain-to-source voltage (along with any supply or cell voltage present in the circuit) in order to force the current in the inductance to decay. In systems carrying substantial current, the power dissipation during these transition periods can be considerable, leading to heating of the switching device, surrounding circuitry, and in some cases device failure or accelerated degradation. Beyond reducing efficiency, excessive heat may also induce thermal runaway in the electronic system. Some embodiments relate to the use of the resonant system to modulate the current from a power source, such as a battery, through at least a semiconductor switching device. Figure 2 shows a diagram of current (top) flow when modified by a current modulation interference signal (middle), and the resultant modulated current flow (bottom) which includes a zero crossing in the current flow. Control of the transition of switching devices may be timed to coincide with the zero crossing event so as to avoid heat generation. In this way, current can be sourced from a battery cell and current modulated to create the zero crossing. The modulation frequency is typically very high - tens to hundreds of kilohertz. Hence the modulated current is easily filtered to smooth the current delivery. Zero current switching uses a circuit of a resonant system to bring the switch current to zero, thereby creating an ideal situation for transitioning the state of a switching device. The main compromise being that the turn off time is predetermined by the frequency of the resonant circuit and is not a free choice. This compromise is not an issue of significance, as the current can be restarted at the next available opportunity, and the density of the switch timing intervals becomes a control variable as opposed to the more familiar duty cycle in a PWM based switching scheme. Embodiments of the invention are described with reference to exemplary system 10 of Figure 3, which illustrates system components including a magnetic coupling apparatus 50. Figure 3 further illustrates the system, showing a central controller 20 in communication with multiple primary cell module controllers via a communication bus 25. In alternative embodiments, system control may be fully centralised in a single controller operably coupled to all functional elements. The magnetic coupling apparatus 50, in combination with a capacitor 60, forms a resonant device 30. The capacitor 60 is located on the secondary side, such that the secondary winding and capacitor together form a tuned resonant circuit. This provides a single, centralised resonance point for the system. The magnetic coupling apparatus 50 is coupled to a plurality of cell units 78, each comprising one or more battery cells and a corresponding bridge circuit 48. Each bridge circuit is operable to connect or disconnect its associated battery cells to the primary winding of the magnetic coupling apparatus under the control of the central controller 20 or a local primary cell module controller. The magnetic coupling apparatus 50 includes multiple discrete primary windings, such as three or more, each of which couples inductively to a shared secondary winding. The apparatus 50 is physically constructed as an assembly of multiple primary structures and a secondary structure. Each primary structure is housed within a cell unit 40 and includes a primary flux guide component, such as a core segment or magnetic limb, and a primary winding wound on or around the flux guide component. The primary winding is electrically connected to the local bridge circuit and battery cells, allowing the current drawn or delivered by each cell unit to be modulated. The secondary structure comprises a plurality of secondary flux guide components, which may be arranged to align or overlap with the primary flux guide components, and a shared secondary winding, which extends across the multiple secondary flux guide components. The flux guide components of the primary and secondary structures are arranged in complementary pairs, each defining an effective current transformer (CT). In operation, the system therefore behaves as a distributed set of current transformers with a shared resonant secondary winding. This architecture enables a single resonant current to circulate in the secondary, while being proportionally shared and delivered into each primary winding. The system further includes an output circuit 77, which receives resonant current from the magnetic coupling apparatus 50 and converts it into a usable form for connection to an external circuit 76. The external circuit may include one or more of: a load, a filter circuit, or an inverter. In one embodiment, the output circuit 77 is a passive rectifier, such as a diode bridge, which provides a unidirectional current to the load. In another embodiment, the output circuit 77 is an active switching bridge circuit. In this case, the central controller 20 is operably coupled to the switches and configured to operate them in synchronisation with the resonant current. This allows precise rectification, current regulation, and bidirectional power flow. In some embodiments, the central controller 20 governs a hierarchical control structure. Commands are transmitted via communication bus 25 to individual primary cell module controllers, which directly manage their respective bridge circuits. Each primary cell module controller is configured to execute the central controller’s instructions, subject to local conditions such as overvoltage, undervoltage, or thermal constraints that may override or adjust operation for protection. The communication bus 25 facilitates coordination between the central controller and primary cell module controllers. Particular functions include where the central controller dictates system-level behaviour. Primary cell module controllers meanwhile are configured to perform status reporting functions such as the reporting of state-of-charge, voltage, temperature, and fault conditions. In some embodiments, primary cell module controllers are configured for peer-to-peer messaging between primary cell module controllers and this function may be preferable for some functions that do not involve central intervention. Figure 4 shows a diagram of the components of a primary cell module 40 which represents one unit of a modular battery energy transfer system 10. Each primary cell module 40 is responsible for managing one or more battery cells, regulating energy transfer via a bridge circuit, and interfacing with the magnetic coupling structure and control network. A cell module controller 41 is the central control unit of the module and is configured to coordinate all operations within the module, such as managing the charging and discharging of the associated battery cells, operating the bridge circuit 48 to regulate current flow between the cells 42 and the primary magnetic structure 44, receiving measurement data from the voltage / current detection circuit 45 and an optional current sensor 47 coupled in series with the battery cell 42. The primary cell module controller 41 may execute both local decision-making (e.g., fault protection) and distributed commands received from a central system controller. A communications interface is configured for communicating with the central controller 20 and optionally other primary cell module controllers. The communication interface may be a wired or wireless interface as is practical for the module construction. The communications interface 46 enables data exchange between the cell module controller 41 and external systems. This may include receiving operational commands from the central controller 20, reporting state-of-charge (SoC), voltage, current, and temperature data; exchanging synchronisation signals to coordinate resonant energy transfer across multiple modules. The interface may employ standard wired or long / short range wireless protocols, such as CAN bus, RS485, Ethernet, or NFC depending on system design. In some embodiments, the primary and secondary winding facilitate a wireless communication channel, whereby a data signal is superimposed on top of the power transfer waveform which is coupled between the primary and secondary windings. In such embodiments, primary modules may require an ID such that individual primary cell modules can be addressed on a shared communications bus for module specific control signals. The cell module 42 represents one or more rechargeable battery cells which provide or absorb electrical energy depending on the operational mode which defines the magnitude and direction of current flowing to or from the cell. Where there are two or more cells, the cells may be connected in series or parallel, and may also include a switching circuit which selectively connects one or more of the cells to the primary bridge circuit 48. The bridge circuit 48 is a controllable switching circuit which is configured to selectively connect the cells 42 to the primary winding to generate an alternating current to thereby contribute flux to the magnetic coupling apparatus, or receive flux and rectify induced current and connect to the cells 42. The primary module includes a voltage or current detection circuit 45 which is configured to provide real-time electrical measurements to the cell module controller. In some embodiments, the detection circuit is configured to measure the instantaneous voltage across the primary winding, measuring the instantaneous current through the primary winding, determining the phase relationship between voltage and current, provide synchronisation signals to the controller for soft-switching operation (e.g., ZCS / ZVS control). In some embodiments, the detection circuit 45 is a phase-locked loop (PLL) or equivalent phase- detection technique to track the operating frequency of the system. The PLL locks onto the fundamental resonant component of the current, enabling the controller to adjust bridge circuit timing so that switching events occur under optimal low-loss conditions. The detection circuit 45 may be implemented using high-speed ADCs with DSP algorithms in the controller, or dedicated analog front-end circuits including comparators, mixers, or PLL ICs. This phase information, combined with magnitude measurements, allows the system to operate the bridge circuit 48 in alignment with the resonant current waveform. The primary magnetic structure 44 comprises the modules magnetic coupling element and includes a primary winding and a flux guide component which couple magnetically to a shared secondary structure elsewhere in the system. This allows reactive energy transfer between the resonant device and the bridge circuit 48. In effect, the primary magnetic structure operates as one leg of a distributed current transformer, enabling energy to flow to or from the module cells 42 in synchrony with the system resonance. The bridge circuit 48 is a controllable switching network (e.g., a full-bridge or half-bridge of MOSFETs or IGBTs) that is connected between the cells 42 and the primary winding of the primary magnetic structure 44. The bridge circuit 48 is configured to modulate current flow from the cells into the primary winding, and to rectify resonant current from the primary winding into a controlled charge / discharge current for the cells. The bridge circuit is further configured to support bidirectional energy transfer, enabling both cell charging and discharging. The bridge circuit comprises a switching circuit that is commanded by the cell module controller 41, which adjusts switching patterns to achieve zero-current or zero-voltage switching where possible, thereby reducing losses. Further, the primary cell module controller 41 is configured to operate the bridge circuit 48 based on the phase of current in the primary winding to control the charge or discharge current experienced by the cell. In some embodiments, the primary cell module 40 includes a current sensing element 47 to measure the instantaneous current flowing between the bridge circuit 48 and the primary magnetic structure 44. This measurement provides feedback on the actual current experienced by the cell which the cell module controller 41 may use for regulating switching operations. Further, this sensor supports protective functions, such as detecting overcurrent or fault conditions. Current sensing may be implemented using a shunt resistor, Hall-effect sensor, or current transformer. In some embodiments, the current sensing element comprises the detection circuit 45. However, it can be useful to measure current directly from a battery cell separately from current in the winding. Figure 5 shows various circuit diagrams of examples of the primary magnetic structure, including configurations of the primary winding, the associated switching circuit which functions as bridge circuit to supply alternating current to the windings, and the associated primary flux guide. In some embodiments, there is a primary winding associated with the primary flux guide. In other embodiments, there are multiple primary windings associated with a single primary flux guide. The number of energised primary windings at any point in time establishes the number of effective turns engaged with the primary flux guide. For example, one active primary winding is considered to be one turn, two active primary windings would be considered as two turns, and so on. The timing of the switching devices of the bridge circuits allow for selective modulation of the winding current by pulse-width modulation, phase-shift control, or resonant switching techniques. In particular embodiments, the circuits are operated in a manner that supports soft-switching conditions, such as zero-voltage switching (ZVS) or zero-current switching (ZCS). In Figure 5(A), the primary winding and flux guide component of the primary magnetic structure 44 is implemented as a centre-tapped primary winding having a first section 51 and second section 51’. The centre tap is connected to one terminal of the battery cell 42, while each half of the winding is selectively energised through controllable switching devices P1, P2, P3, and P4. The switching devices are arranged such that each half of the winding can be independently driven, permitting alternating current to be generated across the full winding. When P1 and P3 are activated, current flows through one half of the winding in a first direction. Conversely, when P2 and P4 are activated, current flows through the opposite half of the winding in the reverse direction. An optional switch element SW1 is connected between the centre tap of the primary winding and the battery cell 42 which may be useful for isolating the battery cell from the primary winding. Isolation of the cell, in this circuit configuration, may be useful for impedance loading of the secondary winding and magnetic system when the cell is not being charged or discharged. As will be appreciated by the configuration of the bridge circuit and winding configuration, only one winding is energised at one time. In Figure 5(B), the primary winding 51 and flux guide component of the primary magnetic structure 44 is driven by a full bridge circuit. The full bridge circuit comprises four controllable switching devices, denoted P1, P2, P3, and P4, arranged in an H-bridge configuration to drive alternating current through the winding. The switching devices may be MOSFETs, IGBTs, or other semiconductor switches capable of high-speed and efficient switching. The full bridge circuit is connected between the one or more battery cells, and the winding of the primary magnetic structure. The full bridge configuration provides a high degree of control over the energisation of the primary winding. This includes the capability for forward energy transfer, reverse energy recovery, and the facilitation of resonant or quasi-resonant operation. The full bridge topology also supports selective isolation or shorting of the winding when not in use, which may be desirable depending on the present system operation. Effective isolation of the battery cell and shorting of the winding may require different MOSFET configurations, depending on the type of switching devices in use, such as silicon or GaN based MOSFETS and consideration of body diode locations as will be apparent to those skilled in the art. For example, SW1 would not be needed when GaN based FETs are implemented for the H-bridge. In Figure 5(C), there are two independent full bridge circuits connected to a common energy source. A first bridge circuit, comprising switching devices P1′, P2′, P3′, and P4′, drives a first primary winding of a first magnetic coupling apparatus. A second bridge circuit, comprising switching devices P1, P2, P3, and P4, drives a second primary winding of a second magnetic coupling apparatus. Both windings are thereby magnetically coupled within separate magnetic structures, yet operated from a common battery. The dual bridge configuration allows greater flexibility in distributing and balancing energy transfer from a cell source. The two bridges may be operated in phase, in anti-phase, or with controlled phase-shift relative to one another which enables a more constant load applied to the battery cell over time - preferable for cell health and longevity. This dual bridge circuit arrangement may also permit more complex current modulation strategies which shape the harmonic content within the system. In preferred implementations of this circuit, the dual primary bridges are phase-shifted by 90 degrees for magnetic balancing. Three or more bridges with an equal phase separation angle could also be useful, such as three bridges for the provision of a three-phase system. In Figure 5(D), there is an H-bridge switching circuit where the primary winding has a centre-tap which is connected via an optional switching device SW1 to a junction between two series cells. Each primary winding section shares a common primary flux guide 520 and is energised based on the wires being connected in series. Here, the optional switch SW1, when selectively opened, allows the load applied to each battery cell to be adjusted by facilitating control over the duty cycle of a half-wave of the alternating current. The primary winding sections 51, 51’ are considered to be both associated with the single primary flux guide, and constitute two windings due to having two flux encirclements of the flux guide. Figure 5(E) is a variation of the circuit shown in Figure 5(D) and further includes a first connection point 220 which is coupled to the positive output terminal of the series connected cells, and a second connection point 221 which is coupled to the negative output terminal of the series connected cells. The connection points 220, 221 facilitate the series connection of further primary cell modules 40 which thereby becomes a building block for a larger arrangement of battery cells and switching circuits. Each primary module includes a primary flux guide which can be coupled into a single or separate magnetic coupling apparatus. Such circuits may be most useful to provide a system which is configured to extract significant energy from high capacity cells. Figure 5(F) is a further variation of the circuit of Figure 5(E) where there are two primary windings 51a, 51b which are configured in series, and each primary winding is associated with a separate flux guide component 520a, 520b. The association of each winding with a separate primary flux guide is considered to be two windings and two flux guides, thereby each having one turn of engagement. Figure 5(G) is a variation of the circuit shown in Figure 5(F) and further includes a first connection point 220 which is coupled to the positive output terminal of the series connected cells, and a second connection point 221 which is coupled to the negative output terminal of the series connected cells. The connection points 220, 221 facilitate the series connection of further primary cell modules 40 which thereby becomes a building block for a larger arrangement of battery cells and switching circuits. Further, the provision of separate flux guides 520a and 520b allow for multiple magnetic coupling apparatus to be engaged with, or multiple primary flux guides of the same magnetic coupling apparatus. For each of the exemplary circuits of Figure 5, where there are multiple windings associated with a single flux guide, then each winding is considered a turn (assuming the winding is 1T). For example, two 1T windings would be considered as a 2T winding. In some embodiments, there each primary flux guide is predominantly flux coupled to a single secondary flux guide, thereby forming a pair of complementary flux guides. In other embodiments, two or more primary flux guides are predominantly coupled to a single secondary flux guide, thereby forming a set of complementary flux guides. The circuits of Figure 5 where two primary winding segments are operated in phase generally support the notion that the two windings may each have a dedicated primary flux guide and which share a common secondary flux guide. Figure 6 shows the secondary side 70 of system 10 in further detail. A secondary magnetic structure 510 includes the secondary winding 524 which is magnetically coupled to the primary magnetic structure within the magnetic coupling apparatus 50. The induced current in the secondary winding is processed by a bridge based output circuit 77. The output circuit converts the alternating current induced in the secondary winding into a controlled direct current or other desired output waveform suitable for the connected load. While some embodiments of the system operate based on a discrete passive rectifier circuit, which requires no active switching devices or associated controller, and where the primary modules set an operating frequency, the preferred secondary circuit is one with an actively controlled secondary bride due to the many additional advantages that can be achieved. The central controller 20 is electrically connected to the bridge based output circuit 77 and manages its operating state, including synchronous rectification timing, output regulation, and load coordination. In some embodiments, the central controller 20 also receives measurement data from a sensor module 75, which may include voltage, current, and phase parameters, enabling closed-loop control of the secondary system. A secondary side communications interface 76 of the central controller provides bidirectional data exchange between the secondary system and cell modules as earlier described. Figure 7 depicts the detailed switching arrangement of the secondary-side H-bridge circuit. The secondary winding of the magnetic structure is connected to a full bridge comprising four controllable switching devices S1, S2, S3, S4 arranged to rectify current from the secondary winding 524. Controllable switching devices are preferable for implementation of the bridge as duty cycle control and control over the switching frequency is provided directly by the switch timing. Figure 8 shows a simplified view of the modular system from the perspective of the magnetic coupling components of the system. In particular, there are a number of individual and discrete primary modules 40a … 40n, each including a primary structure which comprises a primary winding and a primary flux guide component 520. A single secondary module 70 is shown which includes a plurality of secondary flux guide components which share a single secondary winding component. Primary and secondary flux guide components are arranged in complementary pairs 515a for the exchange of magnetic flux between the windings. In some embodiments, the system has separable parts. A first part includes the secondary structure of the magnetic coupling apparatus, a resonant capacitor, and output circuitry. A second part includes multiple combinations of the battery cell, related electronics of the switching circuit, and primary structure associated with each battery cell. The battery cells do not require an electrical connection (e.g. electrodes or terminals) to the rectifier to deliver power to the load since they are magnetically coupled through the magnetic coupling apparatus. A battery cell may therefore advantageously be embedded within multiple primary-side subsystems including a battery cell (such as a cell pouch), primary structure, switching circuits (FETs, gate drivers) and control circuits (parameter measurement, data storage, communication). These subsystems are magnetically coupled, sharing no hard connections for the purpose of significant current transfer. Exchange of one or more of the primary side subsystems without interfering with other primary side subsystems, or the secondary side subsystem is possible. In some embodiments, one primary side subsystem is removable while other primary side subsystems are providing current to the system. This can be useful for maintenance in applications where a battery swap is desired, such as some mobile applications. This means that one or more primary modules may be physically removed from the system while one or more other primary modules remain. Further, the system may remain operational while one or more primary modules are removed. Further advantages may be derived from the system, such as immersion cooling of the cells becomes easier because there is no need to make electrical connections inside a cooling fluid chamber, or to pass electrical wires through a fluid bulkhead. Further, the multiple primary side modules could also be configured to form a modular high or low power system simply by having more or less primary modules, or upgrading a low power system to a higher power system by adding more subsystems. Figure 9 shows a more detailed view of the exemplary system embodiment comprising n primary-side modules 40a, 40b … 40n, each operably coupled to a common secondary structure 50 which includes a secondary winding associated with many secondary flux guides. Each primary module 40a … 40n includes at least one battery cell 42, represented with an associated series inductance 43 to model intrinsic parasitic inductance. In addition, each module comprises a switching circuit, a primary flux guide, and a primary winding magnetically coupled to the secondary structure. The secondary structure 50 comprises a plurality of secondary magnetic flux guides 510a … 510n, each arranged to form a complementary magnetic pair or set 515 with the corresponding primary flux guide of a given module. A continuous secondary winding spans across all of the secondary flux guides, providing a common magnetic coupling path for all modules. A single parallel capacitor 60 is connected across the secondary winding to form a resonant tank circuit. The output of the resonator device 30 is connected to an output circuit 70. In one embodiment, the output circuit includes a rectifier stage, which may be realised using diodes or synchronously controlled semiconductor switches under the command of the stack controller. The rectifier is followed by an output filter capacitor 71 that smooths the rectified waveform. Series inductive elements 73, typically implemented as wound inductors, are included to regulate rectifier current and prevent high- frequency resonant current components from propagating into the downstream circuitry. An inverter 75 is connected to the filtered DC output and is configured to convert the rectified energy into an AC output suitable for delivery to an external load. In various embodiments, the load may comprise a utility grid connection, a local distribution bus, or another form of current sink. The inverter may also incorporate additional control functions, including active power factor correction, voltage regulation, and fault handling. The resonant system includes a capacitor connected to a magnetic coupling apparatus. The term ‘magnetic coupling apparatus’ of described embodiments is characterised by a particular coupling factor (k) for optimum functionality and which differs from what may be considered a typical voltage transformer. The coupling coefficient, or coupling factor, k of a transformer is a measure of how effectively the magnetic flux induced by one or more primary windings links to one or more secondary windings, and represents the ratio of the magnetic flux linking the secondary winding(s) to the total flux produced by the primary winding(s). The coupling factor k varies from 0 to 1, where k = 1 means perfect coupling (all of the primary flux is linked to the secondary winding) and k = 0 means no coupling (the windings have no shared flux). A lower coupling factor results in increased leakage inductance. In ideal transformers, the coupling factor is assumed to be 1, but real transformers always have some degree of imperfect coupling due to practical limitations in construction and materials. Typical transformer design is therefore intended to be as high as possible. For most practical voltage transformers, k is greater than 0.98. The coupling factor is controlled primarily through the geometry of primary and secondary flux guides, and is affected by the gap, alignment, and relative cross sectional area of primary and secondary flux guides. Figure 10 shows a relationship between coupling factor and the separation gap between primary and secondary flux guides. Particularly observable is the relationship between the k factor and the gap between flux cores where a greater separation gap lowers the coupling factor. However, effective separation is also achieved through geometry, alignment and relative cross sectional areas of flux transmission paths. Embodiments of the magnetic coupling apparatus described herein have a k factor typically between around 0.80 to around 0.95, but ultimately the required k factor is deduced based on a relationship with the winding turns ratio of the magnetic coupling apparatus, the number of discrete interactive windings in the system, and, in some instances, the target power requirements of the system including real power and apparent power considerations. Embodiments of the invention employ a magnetic coupling apparatus which incorporates primary and secondary windings within a combination of distributed primary structures and a partly shared secondary structure where multiple primary windings are employed for a single secondary winding which is physically shared by each secondary flux guide. Unlike prior art, which often employ capacitors electrically connected to both primary and secondary windings achieved by localised capacitors at each coupler, preferred embodiments utilise a single central capacitor located on the secondary side to form a resonator. The preferred resonator includes a secondary winding in parallel with a capacitor, establishing a single resonant current path. The system of the invention functions primarily as a Current Transformer (CT) rather than a Voltage Transformer (VT). A single resonant current flows in the secondary winding and is distributed to each of the primary-side battery bridges via individual CT couplings. While each primary structure generates its own flux associated with a respective battery cell, the secondary winding provides a common resonant current shared across all primaries. The inductance of the single resonator is distributed across the magnetic system, contributing to an effective global resonance with the single secondary capacitor. While primary-side capacitors can be placed within the primary side circuit, they are not required, and serve to increase the component cost and power loss of the system without real benefit. Each primary module and primary winding interact with the secondary module and secondary winding to form coupled inductors which are effectively combined. Figure 11 shows a diagram of the equivalent circuit for the effective current transformers, which form the coupled inductor of the resonant circuit. The coupled inductor can be modelled as a T-model network, as shown, where current transformer coils L1 and L2 (and so on) are modelled as L1L, Lm, and L2L. The primary leakage inductance L1L = 1 - (k x NR), where NR is the turns ratio is the number of primary turns divided by the number of secondary turns at each instance of a current transformer. In order to resonate, the resonator requires some imaginary +j impedance and some -j impedance from the combination of L and C. Resonance occurs when the absolute value of imaginary impedances are equal. When k is greater than 1 / NR, then L1L is negative and provides some -j impedance cancellation. A negative inductor is not a real component, but it can be treated as a positive inductance with a 180 degree phase shift which in turn provides a cancellation in the Magnetomotive Force (MMF). This minimises core losses and ensures the core operates away from the saturation point. For effective operation as a CT with magnetic cancellation, the condition k > 1 / NRmust be satisfied, as deduced from the equivalent circuit model. Under this condition, the magnetic system exhibits negative inductance on the primary side which produces an effective –j reactance term in the primary-side impedance, cancelling inductive reactance and enabling resonance without requiring localised primary-side capacitors. The resulting frequency-independent magnetic cancellation produces a resonance which is not tied to frequency-dependent capacitive cancellation. The magnetic coupling apparatus achieves cancellation through magnetic coupling with a broad Q bandwidth through the single parallel secondary capacitor, making the system less sensitive to system variations. Further, robust soft switching is facilitated with transient soft switching achievable at k > 0.91 and steady-state soft switching achievable down to k ≈ 0.70. The central resonator formed by the capacitor connected to the combined inductance therefore enables soft switching within the primary modules without the need for individual local primary-side resonating capacitors. The omission of capacitors is one particular benefit of the system and this becomes a significant benefit where large resonant currents are desired. The resonator is set to resonate at a frequency in the order of 20kHz - 200kHz. Further, a low series resistance promotes high Q factor of the resonator. The capacitor should be rated for the current and voltage of the system, with low ESR. In some embodiments, other series and or parallel L and C elements which serve to adjust the reactance of the resonator may be used as desired to alter the resonant characteristics and any such adjustments would be application based. Therefore, some embodiments include further series tuning components in the secondary side resonator. The tuning components may include series inductors and / or capacitors, or parallel inductors and / or capacitors. Figure 12 shows an equivalent circuit of the system including an exemplary magnetic coupling apparatus with three primary modules, and therefore three current transformers, based on the equivalent circuit of Figure 11. M represents the mutual inductance where M1 = k1 x sqrt(L1 x L2) (and so on). K1 represents the coupling factor of the first module, and the resulting system k being the combination of the individual module coupling factors. Notable is the condition that k is greater than 1 / NR applies to individual current transformers and the coupling factor of the combined magnetic system. For a battery system, the nominal operating power is an operational objective and is therefore a design criteria. The present system is a resonant circuit and therefore the winding current is mostly sinusoidal at the fundamental frequency with some smaller higher-order harmonics. The average current will be approximately 0.9 x RMS current. This means that the real power of the system, the k factor (the minimum required k) and turns ratio can be determined based on regular modelling of the components of the equivalent circuit and an operational frequency set by the switching frequency of the bridge circuits. For example, a real power target or limit can be expressed by the time series product of the current and voltage to be drawn from the battery of each primary module. A real power limit can also be simplified as the average current and average voltage desired from the battery. The current seen from the battery of each primary module is determined by the circuit impedances and the magnitude / phase spectrum of each voltage source. The circuit impedances are formed by the elementary components (L, R, C) and the k factor of each current transformer. Since a battery will typically have a desired operational current, or current limit, this current can be used together with the elementary components to deduce the relevant k factor which can also be interpreted in terms of a real power limit or a target. The real power limit (or minimum cell average current) sets a lower operational boundary for the coupling factor of the magnetic system. The real power limit indicates the minimum coupling and turns ratio required to achieve the desired real power output from the system. This target may be treated as a design input, and adjusting the target will shift this operational boundary. An apparent power limit is another design criteria as an operational objective as operating beyond this limit leads to increased losses, heat generation, and stress on components, even if the real power target is met. This limit ensures that the system operates efficiently and within acceptable thermal and electrical stress parameters. The apparent power limit, or maximum RMS current, related to power factor or total harmonic distortion - THD) establishes an upper boundary for the k factor of the system. Generally, the nominal operating power and the apparent power limitations present design objectives where the real power is to be maximised and the apparent power minimised. A distortion power factor (PF) is another design criteria as an operational objective and is expressed as PF = Powerreal / Powerapparent or, with cancellation of voltage terms, it is the reciprocal of the current form factor (RMS current to average current). RMS current is the component that generates losses, while average current delivers useful real power. A lower distortion power factor (or higher form factor) indicates that the system is more lossy due to high RMS current for the same average power. High RMS current (which generates losses) relative to the average current (which does useful work) indicates a poor form factor and a lossy system. The PF is used to place a limit on the maximum current stress the components or cells can handle. The PF therefore establishes an operational ceiling based on the maximum allowable RMS current for a given average power, or a chosen acceptable power factor (for example, 0.5 to 0.9). To avoid exceeding a desired distortion power factor, the coupling factor k must fall below the limit derived from the PF. Operating above the PF limit can lead to diminishing performance, increased noise, EMI and higher heat related losses from excessive apparent power. Figure 13 illustrates the graphical relationship between k and the turns ratio of the magnetic coupling apparatus where the mathematical relationship defines that k must be greater than 1 / NR for magnetic cancellation to occur. In the graph, line 118 identifies the threshold, above which the resonant system is achieved. The turns ratio NR is generally defined by the number of turns of the primary winding of each primary magnetic structure divided by the number of turns of the winding of the secondary magnetic structure. This relationship between the coupling factor and the turns ratio is crucial because it leads to the creation of inductance of Z=−jωL which behaves like a negative inductor in an AC circuit and within the equivalent circuit model of the primary side. This negative inductance effectively cancels inductive impedance without requiring additional capacitors on the primary side. The resulting impedance cancellation is frequency-independent, offering a substantial advantage over frequency-dependent capacitor-based cancellation found in other technologies. This cancellation also helps minimise magnetic losses and ensures the magnetic core operates within its linear range, thereby preventing saturation. The number of secondary effective turns is typically between 1 and 4. A single secondary turn is atypical, but may be required in circuits where the primary winding has more than one turn. Further, more than 4 effective turns of the secondary winding is atypical as the conductor resistance begins to impact on the efficiency and cost without improving system performance. For these reasons, the circuit design is better steered toward a combination of system parameters which reduce the number of secondary turns. However, in systems with a low number of primary modules, such as up to six modules, the number of secondary effective turns may be as high as 6 turns. Therefore, the number of effective secondary turns may fall between any one of the following ranges: 1 and 2, 1 and 3, 1 and 4, 1 and 5, 1 and 6, 2 and 3, 2 and 4, 2 and 5, 2 and 6, 3 and 4, 3 and 5, 3 and 6, 4 and 5, 4 and 6, and 5 and 6. The turns ratio NR belongs to each CT set 515 and is not impacted by the other CTs in the system. The difference in the turns ratio for each CT will lead to the battery modules generating different amounts of current. For example, the primary module that connects to the secondary with a CT that has a higher turns ratio of 1:3 will deliver more current than a primary module that connects to the secondary with a CT that has a lower turns ratio of 2:3. The coupling factor parameter k represents each of the complementary sets of flux guides which form the magnetically coupled inductor in the magnetic coupling apparatus. The k factor of individual current transformers may also differ, as long as the magnetic cancellation condition of k > 1 / NR, is adhered to. The k factor of individual current transformers can therefore be designed based on the target k factor to support the operational design parameters of the system. The turns ratio belongs to each current transformer, being the windings of one primary flux guide and the windings of the secondary flux guide in the set, and it is not impacted by the other current transformers in the system. Therefore, a battery that connects to the secondary winding with a current transformer that has a higher turns ratio of 1:3 will deliver more current compared to the battery that connects to the secondary with a current transformer that has a lower turns ratio of 2:3. Individual k factors may therefore be specified within a system based on individualised current demands. While the above relationship between k and the turns ratio has been described, in any system there must be multiple primary magnetic structures to form a system. As each primary magnetic structure includes a primary winding, the k factor can also be expressed in terms of the turns ratio NR and the number of coupled inductors NC, that is, the number of CTs, thereby allowing the coupling factor to be based on a relationship with the product of NR x NC. The parameter NR x NC represents a compound factor that significantly influences the system's overall impedance network and operational characteristics. The product of NR x NC may therefore be used to define operational limits of the system, and provides for a graphical representation that defines the position and shape of various system performance boundaries based on the k factor. The interplay of the number of active CTs and the chosen turns ratio is a key design consideration for achieving desired performance and efficiency from the battery system. Figure 14 shows a graphical representation of the coupling factor k versus the product of NR x NC. As this relationship includes the number of primary windings coupled in the system, it follows that the battery cell(s) coupled to each primary winding, and the real and apparent power targets of the system can also be considered. In particular, real power and apparent power limitations can also be graphically represented as a consideration of specific system performance requirements based on the turns ratio, the number of primary modules, the operating voltage and switching frequency, and therefore together indicate a coupling factor which will allow operation which meets the desired power requirements. Figure 14 shows a line 120 representing the product of 1 / (NR x NC), and a line 121 identifying an exemplary location of the real power target or limit. It should be noted that where this line represents a limit, that it is a design consideration representing a system operational boundary that a designer would not intend to exceed during regular operation. True system operation may operate beyond the limit, during regular or momentary operation, noting the reduced system performance. Line 122 represents the power factor limit or current form factor constraint based on the ratio of RMS current to average current. Graphically, the line 120 representing the product of NR x NC, the line 121 representing the real power limit and the line 122 representing the apparent power limit together define the magnetic requirements and operational performance targets of the system, depicted as the hatched area 123 defined between lines 120, 121 and 122. Area 123 therefore represents a design space and operational capabilities of the magnetic coupling apparatus wherein the system is enabled to achieve soft switching across a wide operating range, thereby significantly reducing energy waste and enhancing overall system efficiency. The ability to precisely manage these parameters allows for individual tailoring of battery and cell current and effective energy transfer within a multi-cell energy storage system. The k factor must be chosen to place the real power and the apparent power inside the hatched region 123. Individual CTs are required to have a k factor which is within area 123, while their turns ratios may differ. Figure 15 shows a diagram of exemplary circuit design parameters according to the following table: Parameters Values fsw 50 kHz N 36 , AL is the Inductance factor that quantifies the inductance achieved by a primary structure with a single turn winding, fswis the switching frequency of the bridge, Preal is the real power target, Vr is the secondary voltage source of the rectifier bridge, and Vcell is the voltage applied to the primary winding. The minimum distortion power factor is selected at approximately 0.5, which represents a common choice for power electronics system design. Where the turns ratio of the magnetically coupled inductor is 2 and therefore the product of NC x NR is 72, the coupling factor k ranges from 0.825 (defined by line 121) to 0.875 (defined by line 122). Where the turns ratio is 3 and therefore the product of NC x NR is 108, the coupling factor k ranges from 0.875 (defined by line 121) to 0.925 (defined by line 122). The target k factor therefore determines how the flux guides defining the magnetically coupled inductors shall be sized, gapped and aligned. Alternatively, if the magnetic system has been designed based on a known factor, for example, k = 0.85, then the turns ratio can be determined by the k factor and the following graph. In this case, the turns ratio of the magnetically coupled inductor must be 2, 3 or 4 because the real power target of the system cannot be fulfilled with a higher turns ratio. Similarly, if the k factor was 0.7, then the turns ratio must be 1 since high turns ratios produce a k factor below the real limit 122. Further, if the k factor was 0.95, then the turns ratio must be 4 as the only option that falls within area 123. Figure 16 shows another example based on exemplary circuit design parameters according to the following table: Parameters Values . , , approximately at 0.5, and the maximum k is 0.625. If the turns ratio is 3, the working range for the coupling factor k ranges from 0.6 to 0.725. The process for evaluating and determining power limits and subsequently designing the system can be summarised in the following steps: The process of designing the battery system involves selecting system parameters that present a coupling factor that resides within the optimal working area. Initial Selection: The designer may begin by establishing the required power output and the number of battery modules available. Turns Ratio Selection: A low value turns ratio NR is chosen, such as between 1 and 4, based on cost and practical design constraints. For battery cells operating at high current, minimising resistance typically indicates use of a single turn on the primary side. Practical constraints limit the secondary turns to a small integer number, often suggested between one and four, as higher turns increase the cost of the conductor without significantly improving performance. The product (Nc * NR) plays a pivotal role in determining the maximum power or average current that a battery module with a given k can deliver. K-Range Determination: Using the selected parameters (power, NC, NR, the switching frequency, and the battery module voltage, the designer calculates the boundaries (lines 120, 121, 122) to define the specific range of the coupling factor required for a workable solution. In general, a very high coupling factor (e.g.0.99) is undesirable because the form factor of current becomes extremely poor, making the system inefficient and lossy, though technically functional. The goal is typically to achieve a coupling factor value that maximizes real power transfer while maintaining low apparent power and acceptable losses. For instance, an alpha sample tested had a turns ratio multiplied by cell number of 18, and a coupling factor around 0.9 which placed the k factor range above the distortion power limit. This required deliberately changing the frequency from 50 kHz to 42 kHz to shift the distortion power limit upward, allowing the system to work efficiently. Magnetic Design: The physical magnetic coupling apparatus is then engineered to achieve a coupling factor value that fits within the defined range. Physically, the coupling factor is determined by factors like the cross-sectional area of the magnetic coupled surface, the magnetic length, and the air gap between the complementary primary and secondary flux guides. For example, if the required coupling factor is lower than initially achieved in design, the designer may increase the air gap or introduce a lateral offset between the primary and secondary magnetics to deliberately reduce the coupling factor. The magnetic coupled inductance generally requires a higher k for a larger number of cell systems, or can be designed to have a lower k to benefit other design requirements such as larger air gap or imprecise geometric alignment. In practice, the X / Y / Z placement of primary modules relative to the secondary module only needs to be approximate. For example, within a range of + / -1mm in X / Y directions and about + / -0.5mm in Z dimension which sets the air gap. The resulting coupling factor therefore quantifies the magnetic coupling, defined by flux linkage, material properties, and the distance between components. The coupling factor can be measured through open and short circuit coil tests or determined through simulation or analytical calculation. The system utilises the relationship between the coupling factor and the turns ratio to create an equivalent negative inductance which helps cancel system impedance, reducing losses and keeping the core away from saturation. Unlike systems using capacitors for cancellation (which are frequency sensitive), this approach relies on the magnetic relationship, providing a wider operating range. A viable magnetic design must keep the coupling factor greater than 1 / NR to ensure good magnetic cancellation and system stability. If a calculation for the power terms (like minimum power) drops below k > 1 / NR, then the design of the power terms parameters should change to ensure operation. The angular frequency of the oscillatory current is defined by the switching frequency of the bridges. This is a key design consideration, typically chosen between 40 kHz and 60 kHz (with a nominal 50 kHz). Higher frequencies increase losses due to skin effect and proximity effect, while lower frequencies require larger core sizes. An optimal switching frequency can be calculated as a function of the number of primary modules Nc and the inductance factor AL. The value of the resonant capacitor is directly influenced by the choice of the K factor and switching frequency. The secondary magnetic structure 510 has a plurality of secondary flux guide components and a secondary winding associated with the plurality of the secondary flux guide components. The secondary winding is configured in such a way that it passes through the plurality of secondary flux guide components which are arranged in a geometrically predetermined alignment with one another. This is different from a traditional transformer where a secondary winding is typically associated with a single flux guide component. One exemplary alignment is where the complementary pairs of primary and secondary flux guide components have a coplanar arrangement where the pairs of flux guide components are arranged along an axis or plane. In some embodiments, each of the primary and secondary flux guides have a core formed from one or more limbs which extend from a base portion of the core, where each limb defines a pole face at the outer extent thereof. The limbs and base portion define one or more regions bounded by the one or more limbs and the base portion and which may be visualised as a window through the core. In some embodiments, the secondary winding is configured to extend through the one or more regions or windows of the secondary flux guide along an axis, passing through each secondary structure. In some exemplary embodiments of a flux guide, the primary winding is configured to pass through two windows of the primary flux guide of a single primary structure. The number of limbs of each core, the area of opposing pole faces, the alignment of pole faces, and the gap between pole faces provide design parameters which provide a designed coupling factor. The shape and arrangement of the flux guides therefore allow for the coupling factor of the system to be designed based on a determined target value. One exemplary embodiment of a secondary flux guide component has a flux guide made of magnetic material including a central limb, two outer limbs, and a base portion connecting said limbs, forming a magnetic path. The central outer limbs may therefore comprise an E shaped flux guide or similar, where the windows where the secondary winding passes is defined as the two regions between the central limb and each outer limb. Figure 17 shows a cross section of such an exemplary flux guide cores and flux paths of a complementary pair flux guides. In this example, an E-shaped primary flux guide 520 faces an E- shaped secondary flux guide 510 in a complementary and opposing arrangement. Each E-shaped flux guide 510, 520 has three limbs 171 and secondary flux guides and separation gap 174 relative to the primary and the secondary structures. Each primary winding 51 resides in the windows 172 between adjacent limbs 171 of the primary flux guide 520. Similarly, the secondary winding 524 resides in the windows 172 between each limb of the secondary flux guide 510. In some embodiments, the opposing pole faces of each complementary pair of flux guide components are separated by a distance of at least 0.25 mm, about 1 mm, or up to 2 mm. The separation distance may be maintained by a material which sits between the pole faces. Separation materials may include any one or more of solid polymers, liquids and air. In some embodiments, the opposing pole faces are separated by the abovementioned separation distance on only one face, or a selection of the total number of pole faces. In some embodiments, the magnetic coupling apparatus is characterised by a coupling factor which may be adjusted based on the separation distance between pole faces of the primary and secondary flux guides. In some circumstances, an operational but non-optimised coupling factor is desirable, for example, in circumstances where mechanical tolerance is imprecise leading to a variability in the physical relationship between primary and secondary components. In such circumstances, instead of requiring tight tolerance, which may not be desirable in some instances, a loose tolerance is preferred and a resulting nonoptimal, but functional k factor is realised. In some embodiments, the gap between the primary and secondary flux guide in a complementary pair differs compared to one or more other complementary pairs in the arrangement. The gap can be controlled to affect the magnitude of the current delivery ability of the battery cell of that primary module. In some embodiments, a separation member is customised to fit between opposing pole faces and thereby control the gap. In some embodiments, the primary module is contained in a housing, and the housing comprises a layer with a thickness defined by the magnitude of desired current from that primary module. In some embodiments, the housing provides for an offset of the primary flux guide when aligned with the secondary flux guide, whereby the offset is defined by the magnitude of desired current from that primary module. In some embodiments, the primary flux guide comprises one or more pole face areas which are defined by the pole face area of the secondary flux guide and the magnitude of desired current from that primary module. Such controls may be desirable in a system where different cell current is required, such as a system which includes cells with different c ratings, different cell chemistries, and different sources. Such controls may also be desirable to allow swapping of primary modules into engagement with a secondary module and using these physical features as a means to effect current delivery ability. In other exemplary embodiments, the secondary flux guide comprises a C-shaped flux guide where there are two limbs extending from a base portion. Other forms are possible to allow interaction of the secondary winding and primary flux guide while the coupling factor requirement is met. In some embodiments, there is a mixture of core forms, such as E cores and C cores. In one example, the primary and secondary cores are arranged adjacent and to span along a plane where the end cores are of a different form from those cores between the outer cores. In some embodiments, the secondary winding has two segments, such as a first segment which extends in a first direction, such as along the axis of the alignment of flux guides, through each secondary flux guide component, and a second segment which extends in a second direction through each secondary flux guide component. The first segment extends through each secondary flux guide component with less than a full turn of engagement with each secondary flux guide component. Further, the second segment extends through each secondary flux guide component with less than a full turn of engagement with each secondary flux guide component. In some embodiments, the plurality of secondary flux guide components are arranged in a geometric sequence, and the secondary winding is configured to extend through a first window in the sequence of each secondary flux guide component, then extend through a second window in the sequence of each secondary flux guide component. In other embodiments, the plurality of secondary flux guide components are arranged in a geometric sequence, and the secondary winding is configured to extend through each secondary flux guide component in a first direction, then extend through each secondary flux guide component in a second direction. In each embodiment, the secondary winding is a substantially straight wire, and it extends linearly through each flux guide. However, in other embodiments, the secondary winding wraps, at least partially, around some part of the flux guide before extending to the next flux guide in the sequence. For example, wrapping at least partially around the flux guide may include wrapping the secondary winding around the base portion or one or more limbs of the flux guide before it extends to the next flux guide. In each case, the secondary winding has segments where each segment extends from one end of the geometrically aligned sequence of flux guides, then turns around, and extends back to the other end in substantially the opposite direction. The secondary winding may further comprise two or more conductors which extend in each direction, essentially forming several loops which extend through each secondary flux guide twice in each loop. Other geometric arrangements of the flux guides are possible, such as a circular arrangement of flux guide pairs where the secondary winding is also circular and arranged complementary to the layout of the flux guides. Figure 18(A)-(D) shows exemplary secondary windings 524 with one, two, three and four turns. In each secondary winding 524, each wire passing through the secondary flux guides 510 is aligned substantially planar to the other wires. At the outer region of the flux guide structure, the wire will turn around at least once and the turn may be made in planar alignment as shown, or the wires may overlap vertically. Vertical overlap may be preferable in some environments to limit the physical space needed for the wires or to keep wire lengths shorter. Figure 19 shows an exemplary circular arrangement of flux guide pairs, where the secondary winding is also configured in a complementary circular arrangement. Figure 20 shows an exemplary configuration of the secondary module where the secondary winding passes from the first to the last of the secondary cores via a first path, then loops back to the first secondary core via a second path which is outside of the core windows. Figure 21 shows a further exemplary configuration where the secondary winding has a different number of secondary winding loops for each core. As described above, the turns ratio of complementary flux guide pairs can be individually determined to facilitate a different amount of current. In the shown example, the upper flux guide has a turns ratio of 2, and the lower flux guide has a turns ratio of 1. It should be noted that only two modules are depicted for exemplary purposes, whereas the system would typically include many more. Figure 22 shows a flux guide which has four limbs, thereby defining 3 window regions between adjacent limbs. The secondary winding extends through an outer window of each flux guide, through the centre window, through the opposite outer window, then back to the centre window and first outer window to complete the loop. It should also be noted that only three modules are depicted for exemplary purposes, whereas the system would typically include many more. Many other configurations of flux guides and winding arrangements are possible based on the principle of the secondary winding being associated with all of the flux guides of the secondary modules in the system. Each winding may be constructed from copper or aluminium materials, or materials with similar magnetic performance. The primary and secondary flux guides are constructed from a ferrite material such as TDK N87 ferrite, or similar high resistivity material having a relative material permeability >> 1. In some embodiments, the magnetic coupling device includes emissions control features that prevent or control stray coupling e.g. shielding either / or electrostatic shielding (controlling the electric field with faraday cage or part of a faraday cage) magnetic shielding (either an auxiliary flux guide with some high permeability material (e.g. ferrite or iron or some special alloy) or by use of eddy currents induced into a low resistance material such as aluminium or copper to provide cancellation of stray magnetic fields with a substantially equal and opposite eddy current in close proximity and approximately 180° out of phase. The primary structure includes the primary winding which may be implemented by a variety of different conductors. In some embodiments, the primary winding is fabricated from a printed circuit board track. This may be advantageous due to the requirement of switching devices, such as MOSFETs, to control the connection of the battery cell with the winding. In some embodiments the primary winding is formed from multiple layers of a PCB track. For example, a two sided printed circuit board may have a winging section located on each side of an insulating layer to facilitate a centre tapped winding from a segment located on each side of the insulating layer, or two winding segments joined end to end. In other embodiments, the primary winding is formed of a wire, such as Litz wire. In some embodiments the primary structure includes an arrangement of vertically aligned layers being a primary winding, and an insulator substrate. In one exemplary embodiment, the first and second primary windings are substantially U-shaped and arranged to at least partially encircle the limb portion in opposing rotational directions relative to the direction of current flow through each winding. This arrangement can help with the placement of switching devices, since the end of each U-shaped conductor is located in different locations for each segment, allowing the switching device associated with each segment to be distanced from those of other segments so that generated heat is not contained or isolated to one location of the circuit. In some embodiments, the insulator substrate is configured to support a circuit with a pair of cell connection terminals adapted for connection to a battery cell and a switching circuit. The switching circuit includes a DC input terminal configured to receive a DC input voltage from the battery cell, and switching devices configured to alternately switch the polarity of the DC input voltage to generate an alternating current output. The alternating current output is operably connected to the associated primary winding by the switching circuit. In some embodiments, the cell connection terminals each define a terminal coupling region, and the switching devices are integrated within the terminal coupling region so as to control a circuit path between the terminal coupling region and the primary winding. This allows for the switching devices, which generate heat, to be efficiently thermally coupled to the terminal coupling regions, which typically could have a large thermal mass or thermally conductive surface area for thermal dissipation of heat away from the switching devices, or thermally coupled to the battery cell terminals themselves. In some embodiments, the terminal coupling regions are also configured to provide heat sinks, and may have fins extending from the surface of the substrate for thermal conduction. In some embodiments, the primary winding is arranged about the primary flux guide component. In one exemplary embodiment, there are one or more primary flux guide components that have a core having a limb portion extending from a base portion, and the primary winding is configured to wrap at least part way around the limb portion. In some embodiments, segments of the primary winding are each configured to each wrap at least part way around a limb of the primary flux guide component. Each primary winding may at least partly encircle a central limb of the flux guide component, or may at least partly encircle one or more outer limbs. Further, one primary winding segment may encircle one limb, and another primary winding segment may encircle another limb. In one exemplary embodiment, the primary structure includes a first primary winding segment located on the first side of an insulating layer, and a second winging segment located on a second side of the insulating layer. Each of the first and second segments are configured, together with the switching circuit, to direct current in opposite directions about a limb of the primary flux guide. Accordingly, the switching circuit is operated to connect battery current to a first winding segment to thereby create a first magnetic field, then connect to the second winding segment to thereby create a magnetic field in the opposing direction. An alternating magnetic field to drive the magnetic coupling apparatus at resonance can thereby be controlled by directing current alternatively into each winding segment at the resonant frequency. Multiple winding segments may be advantageous in some circumstances to optimise the location and number of switching device components. For example, two winding segments on opposite sides of the insulating layer may be connected at a common location by vias, and switching devices located at the opposite ends. Therefore, in some embodiments, the primary structure includes an arrangement of vertically aligned layers, the layers being a primary winding segment, an insulator substrate, and a second primary winding segment sharing a common coupling with the first primary winding segment, thereby defining a primary winding centre tap. In some further embodiments, the one or more primary flux guide components comprise a core having a limb portion extending from a base portion, and the primary winding is arranged to at least partially encircle the limb portion in a first rotational direction, and the second primary winding is arranged to at least partially encircle the limb portion in a rotational direction opposed to the primary winding in at least a region of co-encirclement. In some embodiments, the primary winding associated with each primary flux guide component is arranged to wrap, at least in part, around the central limb. In some embodiments, each primary winding segment is arranged to wrap, at least in part, around the central limb, in an opposing direction. To appropriately control current flow into primary windings of the primary structures, each switching circuit has a first current path configured for a first current direction, the first current path including a first primary winding segment. Then, the switching circuit also includes a second current path configured for an opposing current direction, the second current path including a second primary winding segment. The pair of primary winding segments are vertically layered about or within the primary flux guide component. In some embodiments, the switching circuit of the primary module is a bridge circuit. In some embodiments, the magnetic coupling device includes a support assembly which is arranged to support the relative location of components. The supply assembly may at least partly encapsulate and provide positional support for any or all of the components contributing to the generation of magnetic flux including the primary flux guide, secondary flux guide, primary winding or secondary winding. In some embodiments, the assembly has multiple parts which join together and such parts may be held by fasteners, interference fit, or clip formations. In some embodiments, the gap between pole faces of the primary flux guide and secondary flux guide are separated by one or more layers of the support assembly. Often, battery cells and battery cell terminals have imprecise alignment. When battery cells are arranged alongside each other as may be electrically efficient to do, an additive misalignment may cause substantial misalignment in parts in the aligned sequence of battery cells. In some embodiments, primary flux guide components are rigidly associated with each battery cell. For example, the battery cell may be connected by way of fasteners to a circuit substrate supporting the switching circuit and primary winding. In such embodiments, the circuit substrate, such as a circuit board, has terminal coupling regions comprising conductive material configured for attachment to a battery cell terminal or connecting structure associated with a battery cell. Therefore, there is some need to allow an alignment tolerance with the secondary flux guides of the magnetic coupling apparatus such that the pole faces of primary and secondary flux guides can be substantially aligned despite the misalignment of battery cells to which they are otherwise fastened to. In some embodiments, the support assembly has a retention assembly configured to support at least the secondary flux guide and the secondary winding. The retention assembly of the support assembly has a base member and at least one retention member having a contact surface configured to engage a portion of one or more secondary flux guides. Further, a dimensional tolerance exists between the retention member and the secondary flux guide, such that the retention member allows for a predefined amount movement of the secondary flux guide relative to the base member, while securing the secondary flux guide in place. Relative movement of the secondary flux guide is possible. Further, magnetic forces caused by operation of the circuit will go some way toward pulling the pole faces into alignment. To further supplement the alignment of the magnetic structures, one or more magnets may be provided on one or both of the primary or secondary assemblies to provide an alignment force to the mating parts, this may be preferable to ensure alignment before current is provided through the magnetic coupling apparatus to ensure the coupling factor is uncompromised. In this way, the pole faces of the primary and secondary flux guides are self-aligning. The secondary flux guide is therefore secured within the retention assembly with a limited freedom of movement due to the dimensional tolerance, permitting positional adjustments without detaching the secondary flux guide from the assembly. Mechanical tolerance in the position of the secondary flux guide therefore allows for differences in cell terminal placement and possible misalignment between the pole faces of complementary pairs of primary and secondary flux guides. In some embodiments, the support assembly has apertures through which the pole faces of the secondary flux guide can extend. The apertures may be formed from a cutout in the material of the support assembly. Further, the cutouts may be oversized to provide for the mechanical tolerance in the position of the secondary flux guide. In some embodiments, a layer of material within the support assembly is provided to maintain a desired gap between primary and secondary pole faces. The layer of material may be required to mechanically restrict the pole faces of complementary pairs of primary and secondary flux guides from being pulled together by magnetic force. However, the layer of material may also serve to seal the primary flux guide or secondary flux guide, or both, from the environment. It follows that the material of the support assembly may encapsulate the primary structure, or secondary structure, or both. In some embodiments, one or more secondary flux guides are removable from the support assembly. In some embodiments, one or more of the plurality of primary structures are removable from the support assembly. For example, a primary structure may include a connected primary flux guide, primary winding, and electronics connected with the primary winding. It is advantageous in some circumstances to consider such a primary structure as modular. A modular primary structure allows for a battery cell and associated primary structure components to be removed from the magnetic coupling apparatus. For example, to replace a failed battery cell or associated electronics. To facilitate removal and replacement of a primary structure or secondary structure, the support assembly may contain a guiding surface to capture free-moving flux guides. In some embodiments, the retention assembly comprises one or more guiding surfaces configured to engage with the primary structure and extend toward the secondary structure, the guiding surfaces comprising a narrowing structure configured to receive the secondary structure as the secondary structure is moved toward the primary structure. The guiding surfaces act to intercept the free movement of the primary structure relative to a secondary structure, so that as magnetic attraction occurs, pulling the structures together, the guiding surface shifts one or both structures into a relative alignment. In some embodiments, the one or both of the primary or secondary structure includes a magnet such that an aligning magnetic attraction occurs before windings are energised. In some embodiments, the support assembly is further configured to support the secondary winding. For example, where the secondary winding is configured to extend through multiple secondary flux guides, the support assembly includes a wire guide which may be in the form of a tray, support surface, or wire clamp as required and based on the number of wires and wire gauge or shape of the conductive material of the winding. Figure 23 shows a top perspective view of a magnetic coupling apparatus 500 and Figure 24 shows a bottom perspective view of the magnetic coupling apparatus 500 of Figure 23. Shown are complementary pairs of primary flux guides 520 and secondary flux guides 510 linearly arranged along an axis. Each of the flux guides 510, 520 are shown as E cores whereby the pole faces of each pair of cores are oriented with opposing pole faces separated by a gap. In Figure 23, the secondary winding 524 is clearly visible and noted to include any one or more of the following features: A length of wire which linearly extends, in a first region, through a first part of multiple secondary flux guides along an axis of alignment of the flux guides, then, extends in a second region, through a second part of the multiple secondary flux guides along an axis of alignment of the flux guides. The secondary winding has preferably three, and up to four wire loops, where each loop includes the pass-through of the secondary winding through all secondary flux guides. The secondary winding includes up to four wire loops, where each loop is magnetically coupled to each secondary flux guide. The secondary winding comprises two segments, a first segment which extends along a first axis thereby associating with adjacently arranged secondary flux guides, a second segment which extends along a second axis, substantially parallel to the first axis, thereby associating with adjacently arranged secondary flux guides, and whereby the first and second segments are connected by a doubling back of the wire. The secondary winding is formed from a singular and continuous conductor. The secondary winding comprises at least one, and up to four, wire loops, which may be made of a single wire that loops up to four times or up to four separate wires each forming a loop or loop segment, and where each loop passes twice through each secondary flux guide. The secondary winding passes through a number of flux guides aligned along a longitudinal axis of the battery system, each flux guide is positioned transverse to the longitudinal axis of alignment of secondary flux guides, but linearly aligned with one another along the longitudinal axis. When the secondary flux guide is an E core, the core has two sections or windows separated by and alongside its central limb. The secondary winding runs along the longitudinal axis in one direction through the first sections or windows of the E cores, and passes through all the E cores, before returning in the opposite direction along the longitudinal axis through the second sections or windows of the E cores, and thereby completing the one or more loops. And thus the secondary winding loops around all the central limbs of the plurality of flux guides. In Figure 24, the primary structure is shown where a primary winding segment 51b is shown on an insulating layer 530, the combination implemented by a printed circuit board. Another second primary winding segment 51a is located on the opposing side of the insulating layer 530 and visible in Figure 23. Numerous semiconductor components 530 are shown on the substrate to represent switches of the switching circuit. The switches are coupled between the primary winding segments 51a, 51b and battery terminal coupling regions of the circuit board. The terminal connectors 522 are devices which are configured to attach to a battery cell on a lower side and to the circuit board on an upper side. The upper side of the terminal connectors 522 have two branches which form separate circuit paths between a cell terminal and sets of switching devices. Figure 25 shows a partly exploded assembly of a battery system 501 including the magnetic coupling apparatus 500. An arrangement of battery cell modules 40a-40f are shown aligned along a geometrical plane. Each battery cell module includes a battery cell 40 with an attached primary structure including a primary flux guide 520, circuit board 530, and primary winding segments 51a, 51b. A secondary structure is shown above the primary structures of the multiple battery cell modules. The secondary structure includes the secondary flux guide 510 and the secondary winding 524 encapsulated within a support assembly. The support assembly includes regions 526 which reside between secondary flux guides, and end regions 525 which encapsulate the ends of the secondary winding where the winding loops out of an end flux guide and back into that same flux guide in an opposing direction. Figure 25 thereby depicts the components of a system configured for resonant energy transfer which includes the magnetic coupling apparatus as described, where each of the plurality of primary structures further comprises a battery module, and each battery module has a battery cell and a switching circuit with cell terminals configured to receive a DC input voltage from the battery cell, and switching devices configured to alternate the connection of the cell terminals with the primary winding. Optionally included on the circuit board of the primary structure is one or more controller devices configured to generate switching signals for controlling the operation of the switching devices of each switching circuit and thereby control the alternate connection of the current connected with a primary winding, determine the magnitude and phase angle of the alternating current, and output the switching signals based on the measured magnitude and phase angle of the alternating current corresponding with an alternating current minima. In some embodiments, the circuit board comprises a controller winding configured to receive flux from the magnetic coupling apparatus and source energy from the system. The controller winding offers two functions. First, controller winding may be a source of power for the controller to operate and control the switches of the switching circuit. However, power for the controller may also be sourced from the battery cell or the primary winding. Further, the controller may determine the magnitude and phase of the current in the main circuit by sampling the voltage or current in the controller winding. In some embodiments, the controller winding encircles a limb of the primary flux guide. In some embodiments, there is a removable battery module which has a primary structure with a primary flux guide component, and a primary winding associated with the primary flux guide component; a battery cell; a switching circuit with cell terminals configured to receive a DC input voltage from the battery cell and switching devices configured to alternate the connection of the cell terminals with the primary winding. In such embodiments the battery module is physically separable from other system components such as the secondary magnetic structure and output circuit. In this way, the battery module is able to be removed from a system, and replaced. This may be advantageous in circumstances where a failure in a battery cell or component has occurred. As each of the battery modules in the above-described system are effectively configured in parallel by the magnetic structure, it follows that one battery module may be removed from the system while other battery modules remain operable such that any power provided to the output circuit is uninterrupted, albeit with a potentially increased power demand applied to the remaining cells. In some embodiments, the removable battery module may be encapsulated in an insulating material such as plastic such that the module is environmentally sealed. Sealing of the removable battery module may be advantageous for safety when handling, or allow for the battery module to be operated in an environment where exposure to liquids may occur. Some environments may include cooling liquids such as immersion cooling systems for battery cell operation. Accordingly, in some embodiments the system has a hermetically sealed housing containing at least a primary structure, one or more battery cells, a switching circuit and controller configured to operate the switching circuit. The controller can also be configured to determine whether the primary structure is magnetically engaged with a secondary structure. This can be achieved, for example, by the detection of a signal received by the primary winding. The signal could be in the form of data induced into the primary winding, which may be superimposed with the primary alternating waveform for power transmission, or simply the presence of an alternating waveform which is induced in the primary winding. In some embodiments, the primary structure further includes a second primary winding which is configured for electromagnetic data signals. In some embodiments, the hermetically sealed enclosure has a material with a thickness on at least one interfacing surface which has dimensions to control a separation gap, and thereby the coupling factor, when engaged with a secondary structure. Figure 26 shows a top view of the battery system assembly of Figure 25 and in particular the terminal coupling regions 540 of the circuit board 530. Figure 27 shows a cross section AA of the battery system assembly and Figure 28 shows a cross section BB of the battery system assembly. In Figure 27, the secondary winding based on an arrangement of wires is clearly shown within the window regions of the secondary flux guide. The secondary winding shown has three turns of wire 524a, 524b passing through each of the two windows as shown, whereby each wire comprises segments which each extend linearly through a first window of all secondary flux guides before looping back and extending linearly through a second window of all the secondary flux guides. Battery terminals 42 are shown in cross section and are connected with the terminal coupling region 540 of the circuit board 530 by connectors as previously described. In Figure 28, the structure of the support assembly 525, 526 is shown and in particular is shown to extend between the pole faces of the primary and secondary flux guides so as to maintain a desired separation distance and therefore the coupling factor. In some embodiments, the secondary winding is one turn of wire, two turns of wire, three turns of wire, or up to four turns of wire which pass through the secondary flux guide. In preferred embodiments, the primary and / or secondary windings are constructed substantially of Litz wire. Figure 29 shows an exploded view of a primary structure of the magnetic coupling apparatus and battery system assembly and in particular the relative form of the primary winding segments 51a, 51b. Each primary winding segment is arranged to partly encircle the central limb of the primary flux guide. Further, the direction of current to be directed through each winding segment, by the switching circuit, is in the opposite direction. Further, the direction of partial encirclement of the central limb is in the opposite direction. The insulating layer 530 includes a number of cutouts aligned with the location of the pole faces of the primary flux guide so as to allow the pole faces and limb of the flux guide to pass through, and the primary winding segments of to reside close to the base portion of the flux guide. Figure 30 shows a top view of the primary structure. Figure 31 shows cross section AA of the primary structure and Figure 32 shows cross section BB of the primary structure. In particular, each of the three limbs, the central limb 5201, and the outer limbs 5202, 5203 are shown protruding through the cutouts 5301 of the insulating layer, which in turn resides proximate the base portion 5204 of the of the flux guide. One exemplary solution to connect with the free wire ends can be from the use of crimped terminals applied to wire ends, and PCB mount terminal blocks to the crimped terminals to bolt to. Crimped terminals may be especially useful when used in conjunction with Litz wire which may be used to implement the primary or secondary windings. In some embodiments, the primary and / or secondary flux guide have a central limb which is shaped to follow the contour of the winding which wraps from one channel within the flux guide to the other. On the primary side, this is likely for each primary flux guide depending on the form of the winding implemented. On the secondary side, this is likely to be the secondary flux guides located on the ends of an adjacent arrangement of secondary flux guides such as 510a and 510f. The shaped central limb is most practical for use with a Litz wire winding material, where the winding is provided by a segment of a wire loop having two substantially parallel sections which are joined by a curved wire section. Figure 34 shows an exemplary primary or secondary flux guide 510 / 520 where the central limb 5101 / 5201 has a central limb which is curved complementary to the curved path of the winding as indicated by the broken line 210. When in a plan view, the curved end region of the central limb of the flux guide therefore has a D-shape. The outer extent of the D-shaped limb remains inside the extent of the outer limbs and base section, and this allows the wire of the winding to also reside within the outer form of the flux guide. In some circumstances, improved control of the flux and coupling factor may be realised by having the winding reside within the flux guide. Figure 35 shows an exemplary primary flux guide 520 whereby the central limb 5201 has one end with a curved shape, and with the extent of the limb inset from that of the outer limbs 5202, 5203 and the base section. Residing between the limbs is a former component 200 which acts to support a Litz wire based primary winding within the confines of flux guide. The former 200 has a recess 201 for locating and supporting the winding through the two parallel sections which extend between the central limb and each outer limb, and the curved section which is directed around the end of the central limb. The recess may be semicircular such that it is substantially complementary to the profile of the winding conductor. In some embodiments, the former has one or more clips 203 which extend partially over the winding to help retain it within the recess 201 of the former. Figure 36 shows a primary module including a battery and primary circuit and primary structure whereby each primary winding is a wire loop segment 527. In this example, a wire loop segment 527 passes twice through a primary flux guide 520. Each free end of the loop segment has attached a ring terminal, and the PCB 530 has a press in terminal block 531 with a threaded fastener extending from the terminal block 531 for a secure mechanical and electrical connection with the primary winding. In some embodiments, the primary winding loop segment 527 is substantially mechanically supported by the terminal block 531. Figure 36 also shows two primary windings located on a PCB fixed to a single battery cell. In some embodiments, it may be advantageous to configure two primary side structures, including two separate switching circuits, two separate windings, and two separate primary flux guides, to the single cell. The two primary structures may be operated with a phase offset between them which can help to smooth the current draw experienced by the battery cell. Figure 37 shows an example of secondary flux guide 510 whereby the central limb 5101 also has a central limb which is curved complementary to a curved wire section of the secondary winding 524 which wraps around the end-located guide in an arrangement of multiple secondary flux guides. The secondary flux guide 510 with the curved central limb 5101 is ideally located on the end of an arrangement of secondary flux guides where the secondary winding wraps around. However, the same secondary flux guide with the curved central limb may also be used as middle located secondary flux guides as depicted. In some embodiments, the secondary flux guide contains a former component to locate and support the secondary winding. Figure 33 shows an exploded view of the exemplary secondary structure and support assembly 525, 526 of the magnetic coupling apparatus. In particular, the support assembly includes a lower part or layer 560 and an upper part or layer 561. In some embodiments, the lower layer is of a thickness intended to maintain a desired separation between pole faces of the flux guides. The upper layer 561 includes a number of features to promote support of the secondary flux guides 510a-510f. First, a number of cutouts 565 are provided in the central region of the upper layer and are adapted to receive the central limb of the secondary flux guide. Complementary recess 567 is provided in the lower layer 560 to also receive the central limb. A number of edge located recesses are arranged to receive the outer limbs of the secondary flux guide. Each recess is shown to have a sidewall 563, a rear wall 564, and a lower surface 562. In some embodiments, the lower surface has a thickness intended to maintain the desired separation of the flux guides. The lower layer 560 further includes a cutout 566 adapted to receive the lower surface 562. In some embodiments, the upper side of the lower surface 562 engages with the secondary flux guide, and the lower side engages with the primary flux guide. To facilitate relative movement of each secondary flux guide 510a-510f, the cutouts 565 and recess 564 may be oversized so as to provide some tolerance to the fitment of the secondary flux guide. In some embodiments, the primary module 40 is encapsulated within a container. Within the container may reside components of a battery cell, a cell module controller, a primary magnetic structure including a primary winding and primary flux guide component, primary bridge circuit, detection circuit and a communications interface. This container lends to a suitability for harsh environments, where sealing against dust, moisture or liquid is required. In some embodiments, the container includes one or more components adapted to support at least the primary winding and the primary magnetic structure. One exemplary support is a plastic structure which forms a support for said components and the exterior wall of the container. In some embodiments, the exterior wall located between the primary flux guide is of a thickness or form which at least partly defines at least one of the gap and alignment with respect to the secondary flux guide of the secondary structure. In some embodiments, the container includes one or more guiding surfaces adapted complementary to one or more surfaces of the secondary structure such that engagement between the surfaces causes at least one of a predetermined gap and alignment with respect to the secondary flux guide of the secondary structure to occur, and subsequently, define a predetermined magnetic coupling factor. In some embodiments, the container locates and supports an antenna in the form of a wireless data receiver / transmitter configured to support wireless communication between the primary cell controller and the secondary controller. In some embodiments, the container locates and supports an electrical connector configured for the wired coupling of a communication channel. In some embodiments, the primary module 40 is encapsulated within a container that provides both physical protection and functional alignment for the contained electronics and magnetic structure. The container is more than a passive shell; it plays a direct role in determining magnetic coupling, thermal behaviour, electrical safety, and long-term system durability. Within the container, the following components may be housed and supported: ● A battery cell, being one or more electrochemical cells configured as the local energy source. ● The cell module controller 41, a distributed intelligence element that locally governs switching, measurement, and communication, and cooperates with the central controller. In some embodiments, the cell controller sources power from the battery cell and further, there may be a regulation circuit configured to stabilise the voltage source of the controller. In other embodiments, there is a regulation circuit configured to rectify and regulate that power induced into the primary winding and supply that power to the controller 41. ● The primary magnetic structure – including: a primary flux guide component (520), often comprising a base portion and a limb portion, sometimes with a contoured cross-section to maximise winding fill and flux density; and a primary winding (527), typically comprising one or more turns of Litz wire, optionally supported by a winding former (200) integrated into the container. ● The primary bridge circuit being the switching circuit. ● Sensing electronics, including voltage and current sensing circuits. ● The communication interface (wired or wireless) for data exchange with the central controller. ● One or more insulator substrates adapted to mount at least the controller, the sensing electronics, the switching circuit and optionally, communication hardware. In some embodiments, the insulator substrate incorporates a terminal block with a threaded fastener, providing secure bolted electrical connection to the winding leads. The substrate may support multiple winding layers to improve packing density and thermal conduction. The container not only holds the internal components but actively influences the magnetic and mechanical engagement with the secondary structure. ● Support of Winding and Flux Guide: In one embodiment, the container incorporates a plastic support structure that simultaneously secures the winding and flux guide while forming part of the exterior wall. This integration reduces mechanical tolerance stack-up and ensures consistent positioning of the magnetic structure relative to the exterior alignment surfaces. ● Wall Thickness and Magnetic Gap: The container wall between the primary flux guide and the external environment may be deliberately dimensioned to establish part of the predetermined separation gap with the secondary flux guide. In some cases, the wall thickness is reduced or locally shaped to control magnetic reluctance. ● Guided Engagement: The container may feature one or more guiding surfaces designed complementary to surfaces on the secondary structure. When the module is inserted or mated, these guiding surfaces automatically establish both alignment and gap spacing, thereby fixing the coupling factor k to a predictable value. For example, opposing pole faces of complementary flux guide pairs may be separated by a distance of at least 0.25 mm, typically about 1 mm, or up to about 2 mm. The gap may be occupied by solid polymer, air, or liquid media, each contributing to the effective coupling factor. In some embodiments, the container house one or more interfaces, including: ● A wireless communication antenna: An antenna or wireless energy receiver may be embedded within or upon the container, enabling short-range wireless communication with the secondary controller. Placement is coordinated to minimise electromagnetic interference with the primary winding and to exploit available clearances. ● A wired communication port: In other embodiments, a sealed electrical connector is integrated into the container to provide wired communication with external systems. This port may also double as a service or diagnostic interface. The coupling factor k between the primary and secondary is ultimately defined by both the magnetic geometry and the containers role in alignment by one or more of the following: ● Air Gap Control: The air gap, dominated by container wall thickness and surface conformity, is the strongest determinant of k. Small variations in gap size directly alter resonant frequency and efficiency. ● Flux Guide Geometry and Placement: Container-supported positioning ensures the primary flux guide faces the secondary flux guide with repeatable orientation. By locking geometry, the container ensures predictable flux linkage. ● System Boundaries: Because the primary modules are discrete, physically separable units, the container effectively sets the module’s electromagnetic boundary conditions. When one cell is idle, the reflected impedance to the secondary shifts slightly, leading to a small frequency detuning. This is practically tolerable when only a few cells are idle but complicates startup when many are idle simultaneously. In some embodiments, the container includes one or more guide ribs which define a mechanical guide for the engagement between removable primary modules and the secondary module. When the module is pressed into a mating slot of the secondary structure, the ribs ride against complementary grooves, forcing the module into a predetermined lateral alignment. In one embodiment, the container is moulded from a high-performance polymer. The container incorporates internal ribs that act as a winding former for the primary winding, holding the Litz wire in position relative to the flux guide. The external surfaces of the container feature snap-fit protrusions and guide ribs. The wall thickness between the flux guide and exterior surface is precisely controlled so that, when snapped in place, or held gravitationally, the air gap between flux guide faces is fixed to a predefined gap, such as ~1 mm. This arrangement provides repeatable coupling factor k, while also allowing quick assembly or removal of modules for service where no manual setting of the alignment or gap is required to ensure the desired coupling factor is achieved. In some embodiments, the system includes a rack whereby the containers of the primary modules provide a cartridge configured to engage with the rack. In some embodiments, the container is shaped as a cartridge that can be inserted into a rack-like housing forming part of the secondary structure. In such embodiments, each container has alignment bosses on its exterior. When engaged with complementary sockets in the secondary structure, the bosses lock in both angular orientation and axial spacing. The coupling factor k is defined not only by the flux guide geometry but also by the precise standoff distance enforced by the bosses, which may be moulded to a precise tolerance. In this embodiment scalable stacking of modules is achieved which facilitates easy addition or replacement. In some embodiments, the container walls at each flux guide location are shaped with angled chamfers, ensuring that when the module is slid into place, the chamfers engage complementary surfaces on the secondary structure and self-align the gap. In some embodiments, the rack includes a track structure whereby the primary modules are able to slide on the track from one to another. In this way, the primary modules may be loaded from one end of the track, and positioned to engage with a secondary coupler at any one of a number of discrete positions which may be configured by detent or by stacking against some mechanical limit. In such embodiments, the track may facilitate loading of primary modules from one end, and removal of primary modules from another end. This first-in first-out arrangement can be useful where primary modules are designed to be swapped regularly and ensures that the primary module that has been in the system the longest, and therefore discharged the most, is also the first removed from the system. A replacement primary module may then be loaded to the far end of the track, and all of the remaining modules will slide along the track by one position, where each position is defined by the placement of a secondary flux guide. In some embodiments, the battery module housing may provide a preload force or pressure to the battery cell. This could be achieved through the choice of housing material by way of having sufficient stiffness and / or through the use of domed or convex surface to apply pressure to at least one surface of a battery cell. Sloped or wedged surfaces are also applicable. In some embodiments, the battery module housing may transmit an externally applied force through the walls of the housing to provide a compressive force or pressure to one or more battery cells. In some embodiments, the container includes a compressive force interior to the container which transfers compressive force to the battery cells. In some embodiments, the container is compliant such that an external compressive force can be applied which transfers through the housing walls to the battery cells. In some embodiments, the container provides a thermal isolation to reduce the propagation of excessive temperature from a container to other parts of the system. In some embodiments, the container includes a dedicated antenna pocket. The antenna supports wireless communication between the primary cell controller and the stack controller. The antenna is housed in a non-magnetic recess offset laterally from the flux guide, to reduce electromagnetic interference from the AC magnetic field. The recess wall thickness is thinned to improve RF transparency, while the rest of the container remains thicker for mechanical robustness. In this embodiment, the wireless channel substitutes for a wired connector, allowing the module to remain fully encapsulated or sealed. In some embodiments, the container is filled with liquid to facilitate convective cooling of battery cells. In some embodiments, the geometric structure of the magnetic coupling apparatus is configured to define a flow channel (e.g., a gap between cells) to facilitate the flow of the cooling fluid (e.g., immersion oil) past components or around the primary module. In such embodiments, the geometric structure has a gap between cells which creates a flow channel, and the assembly has a fluid connection with that gap to create a flow path past the components. The geometric structure of the primary structures, and the arrangement of the plurality of primary structures are configured to collectively define at least one coolant flow channel between adjacent primary structures, the flow channel adapted to pass a cooling fluid over heat-generating components during operation. In some embodiments, the container supports two or more flux guides. Each flux guide is located at opposite ends of the container, separated by internal partitions. In some embodiments, the container supports two or more battery cells. In some embodiments, the container’s outer surface provides a heat sink and is thermally coupled to one or more of the battery cells and switching circuit. For example, the switching circuit or battery cell is mounted directly to an internal thermal spreader plate that transfers heat through the container wall. The exterior surface of the container makes direct contact with a secondary housing heat sink, with thermal pads or grease applied to improve conduction. The engagement surface for thermal transfer is located adjacent to, but distinct from, the magnetic alignment surface, ensuring thermal and magnetic interfaces remain decoupled. In some embodiments, the system includes provisions for associating an electronic identification code (ID) with each removable primary module. The ID code enables the central controller to determine both the absolute position of a module within the rack and the unique identity of that module when required. Such functionality is useful in modular battery systems where modules may be repositioned, replaced, or swapped during normal operation or service so that module specific commands can be relayed from the central controller to the primary cell module controllers. In one embodiment, each primary cell module includes a unique, factory-programmed identifier stored within the memory of the cell module controller. When inserted into a position of the rack, the module communicates its unique code to the central controller via either a wireless communication link or a wired connector. The stack controller maintains an internal mapping table that records the position of each unique ID. If a module is later moved to a different slot, the central controller updates the mapping by detecting a change in the positional arrangement. In another embodiment, the rack or secondary structure is configured to assign a position-based ID to each module slot. This may be achieved in several ways: Electrical Contact Encoding based on each slot having a small array of conductive pads arranged in a unique binary pattern. When a module is inserted, spring-loaded contacts on the module read the pattern and communicate the positional code to the cell controller. The controller relays this slot- based ID to the stack controller alongside its operational data. In some embodiments, the container includes magnetic or optical markers. For example, the rack may include permanent magnets, RFID tags, or optical markers at predefined slot locations. Each module includes a magnetic sensor, RFID reader, or optical detector embedded within its container wall. Upon insertion, the sensor reads the local marker, thereby identifying its physical position. In some embodiments, the system includes a track-based positional indexing where modules slide along a track structure, each detent position along the track may correspond to a discrete slot index. For example, a module includes a positional encoder (mechanical, magnetic, or optical) that detects when it has reached one of these indexed detents. This index is then stored as the module’s current position code. In some embodiments, the system employs both unique module codes and slot-assigned codes. The unique code ensures that a given physical module can always be recognized, even if moved. The slot-assigned code ensures that the central controller can easily correlate the modules electrical behavior, including flux coupling or thermal distribution, with its physical position. The central controller resolves any conflicts, such as duplicate slot reporting, and maintains a synchronised mapping of module ID vs. rack position. In some embodiments, the container supports wireless communication through a dedicated antenna pocket offset laterally from the flux guide. The wireless channel is configured to transmit both operational parameters (SOC, SOH, cell temperature) and ID-related data (unique ID, slot code, or both). In other embodiments, wired communication is achieved via an electrical connector integrated into the cartridge-style container. The connector engages automatically with the secondary rack when the module is fully seated, providing both power and data communication. In some embodiments, the central controller 20 is configured to undertake any one or more of: detecting insertion or removal of a module, based on a new ID appearing or an old ID no longer responding; assign position mapping dynamically, associating unique IDs with physical slot codes; maintain operational control of modules based on their position, for example, ensuring uniform heating or cooling distribution, targeting discharge of a particular module at a specific slot location for scheduled removal; controlling coupling factors based on positional symmetry or loading strategy. In some embodiments, positional ID assignment also supports thermal and service management. For example, modules located at central positions within the rack may experience higher temperatures. The central controller, aware of their IDs and positions, can derate their target current or prioritise them for early discharge. In a first-in-first-out track arrangement, the central controller may tag the oldest module by its ID and track position, then schedule its discharge and removal. For service personnel, a display may indicate the module for removal, ensuring both the physical position and the exact module are identified. Accordingly, in some embodiments there is a cell module controller is configured to: store and communicate a unique module identification code; detect a positional code (from slot contacts, optical markers, or track detents) and communicate this code to the central controller; combine positional and unique codes into transmitted status messages; Accordingly, in some embodiments there is a central controller configured to: detect insertion or removal of modules by monitoring received ID codes; maintain a mapping of module unique IDs to rack slot positions; dynamically update module control parameters based on position-dependent requirements such as coupling factor, heat dissipation, or service order. control one or more specific primary cell modules for discharge or bypass based on their mapped ID and position. In an embodiment the secondary system is a discrete subsystem in itself, the subsystem having a plurality of primary modules containing a plurality of primary windings and associated flux guides, a secondary rail comprising a loop of wire (with a number of turns) and plurality of flux guides, and a resonant capacitor. Subsystems can be concatenated by directly coupling one or more secondary rails together using an additional magnetic circuit with high coupling (k>0.95) to form a chain of systems. Suitable magnetic circuits could be constructed with an ungapped pair of E-cores or C- cores. In this case, there could be one single rectifier electrically coupled to one chosen capacitor, or multiple rectifiers, each with their own power input / output. Generally, separate subsystems would be tuned to similar frequencies, such that when concatenated the operating frequency is substantially similar to that of the separate systems. However, it is possible to concatenate systems of different tuned frequencies, and in so doing the resulting resonant frequency and impedance would be a result of the combined transfer function. In one embodiment there is at least one subsystem containing a capacitor and one or more concatenated subsystems could have no capacitor and instead have a secondary rail consisting of a short circuit loop of wire (with a number of turns). A central controller would administer the power delivery from each of the primary modules in the concatenated systems with each primary module having a unique ID for unambiguous exchange of data and commands. Severing the concatenation by removal or modification of the additional magnetic circuit could result in separating the systems to operate independently. This could occur during operation (hot-swap) and power delivery from at least one system could be maintained as in redundant operation. In the above described system, the controller 20 and primary cell module controllers 41 are configured to generate switching signals for controlling the operation of the switching devices of each switching circuit. Control of the switching devices in the primary module is to the alternate connection of a current source connected with a primary winding of the primary structure. Exemplary control logic includes the alternate and opposing control of switches controlling the direction of current flow within a winding. In some embodiments, the controller is configured to determine the magnitude and phase angle of the alternating current, and control switch timing events to synchronise with times of low or no current flow through the switch. The controller is therefore configured to output switching signals based on the measured magnitude and phase angle of the alternating current. Switch timing events are then operated based on the identified phase angle. For example, when the current crosses zero, or is below a threshold current, the controller is configured to change the state of the switch. To generate AC from the DC of a battery cell, the switching circuit operates to periodically connect the cell to the winding, or alternate the connection of the cell with the winding, or both. Other circuit forms are possible, for example, where two cells are each connected with a winding, or winding segment, and selectively connected to the winding to control magnetic field generation. The resonator device 30 provides real-time synchronisation between all of the cells in use. The opportunities to switch on and switch off are in common across all cells. Primary modules can be operated as subsystems to participate in the supply of power and operation can be synchronised by orchestration by the central controller over a low bandwidth communication link, but the actual time critical switching sequence is dictated by the resonator. The state phase angle of the resonators oscillation is observable as current or voltage via the magnetics. In preferred embodiments, there is a battery cell which has a current path that is physically and electrically isolated, while still being magnetically linked to the shared secondary. Figure 38 shows simulated waveforms of switch timing and resulting current operating an exemplary circuit of Figure 5(B). In particular, the voltages of Gate group A made up of switches P1 and P4, and Gate group B made up of switches P2 and P3, are indicative of the switch control signals transmitted by a controller and operable to connect the battery cell with the primary winding. In particular, Gate group A is the switch signal operable to connect the battery cell to the primary winding segment with a first polarity and Gate group B is the switch signal operable to connect the battery cell to the primary winding with a second opposing polarity. The resulting current, modulated by the resonator, is shown relative to the timing of the switch connections. Current is in phase with the switch timing. However, the phase angle of the current determines whether power is going out of a cell or into a cell, where 0deg is out, 180 is into the cell. Angles in between are a mixture of real and reactive power in the cell. Use of resonance is demonstrated to bring about the possibility of zero current switching. In some embodiments, the primary winding is a single conductor (without a centre-tap) where an alternating field is generated by a bridge circuit connected between the battery cell and the primary winding. In such configurations, the switch timing indicates timing of the bridge circuit. In some embodiments, the magnetic coupling apparatus is characterised by a k factor of between 0.86 and 0.94. In some embodiments, the magnetic coupling apparatus is characterised by a k factor of between 0.87 and 0.93. In some embodiments, the magnetic coupling apparatus is characterised by a k factor of between 0.88 and 0.92. In some embodiments, the magnetic coupling apparatus is characterised by a k factor of between 0.89 and 0.92. In some embodiments, the magnetic coupling apparatus is characterised by a k factor of 0.91. In some embodiments, wherein the magnetic coupling apparatus is characterised by a k factor of between 0.85 and 0.98. In some embodiments, the magnetic coupling apparatus is characterised by a k factor of between 0.86 and 0.97. In some embodiments, the magnetic coupling apparatus is characterised by a k factor of between 0.87 and 0.96. In some embodiments, the magnetic coupling apparatus is characterised by a k factor of between 0.88 and 0.95. In some embodiments, the magnetic coupling apparatus is characterised by a k factor of between 0.89 and 0.94. In some embodiments, the magnetic coupling apparatus is characterised by a k factor of between 0.89 and 0.93. In some embodiments, the magnetic coupling apparatus is characterised by a k factor of between 0.89 and 0.92. In some embodiments, the magnetic coupling apparatus is characterised by a k factor of between 0.89 and 0.91. The above ranges may be most applicable for transient state operation of the circuit to ensure a zero crossing (and therefore soft switching) is generated from an initial condition of zero current. This means, to reach zero current switching, a k factor of greater than 0.91 can reach soft switching immediately, even from the first switching cycle. If a temporary excursion into hard switching is permissible (such as during a start-up phase), it can be possible to reach a steady state operation of the circuit with zero current switching when the k factor is lower than 0.91. For example, a k factor of 0.7 has been confirmed as operational, while the operation may not represent an ideal circuit operation. In some embodiments, the magnetic coupling apparatus is characterised by a k factor of between 0.70 and 0.95. Therefore, there are two types of operation based on the k factor. A first so-called "Instant Soft Switching" type which requires a higher k factor (above 0.91) for immediate ZCS. And a second so- called "Steady-State Soft Switching" type where lower k factors (down to 0.70) provide an operable range, however these may involve an initial period of hard switching before ZCS is achieved. In steady-state operation, the resonant circuit is driven to resonate. This minimises core losses and is ideal for multi-cell battery systems where high efficiency is critical. In some embodiments, the operation type is determined by software / firmware and not the fixed mechanical structure (which defines the physical k factor). A single hardware design could therefore switch between transient and steady state modes via control of the circuit, and particularly by control of the timing of switching events. Figure 39 shows a graph of current vs time and representations of current over time for a transient oscillation. The line 391 represents current in a battery cell building over time due to inductance in the cell, magnetic coupler primary windings and switching circuit, the slope of which is V / L Amperes per second. The curve 393 represents a resonant current component coupled from the secondary side of the magnetic coupler to the primary side of the magnetic coupler by the coupling factor k. The curve 392 represents the superposition of the approximately linear battery cell current 391 with the resonant current component coupled from the secondary side of the magnetic coupler to the primary side of the magnetic coupler 393 in order to strike an optimal zero crossing 394 as the minimum of the curve 392 is tangent to the time axis. The zero current achieved by this combination of 391 and 393 provides an opportunity for the switching circuit to transition from the on state to the off state without incurring energy loss due to the inductive opposition. Without the superposition of 393, curve 392 would not have an opportunity to stop the increasing battery cell current without incurring significant energy loss due to the inductive opposition. The primary goal of the system is to achieve soft switching, which minimises switching losses. This is managed through the coordinated control of three key parameters including the switching frequency (omega) of the bridges, the conduction angle (theta) of the bridges, and phase angle (ϕ) of the bridge conduction relative to the phase of the current. While absolute zero-current switching isn't always strictly necessary, the system aims for low power losses and optimal current zero crossings. Each primary module 40 and complementary pair 515 of primary and secondary flux guides will have individual fluxes, and share a current in the secondary winding of the secondary module 70. The shared secondary current will have a magnitude and phase which is measured by the central controller 20 and controlled by operation of the secondary bridge circuit 77. Further, each primary winding of each primary module 40 will experience a current having a magnitude and phase. Due to the influences of parasitic inductance and capacitance inherent in any system, the phase of the current in each primary winding will differ somewhat compared to the primary windings of other modules. The detection circuit 45 of each primary module is configured to identify at least the phase of current in the primary winding in each primary module 40. Each local primary cell module controller 41 may then operate its local bridge circuit 48 based on the detected current phase angle and other factors which regulate current flowing into or out of the local cells 42, and thereby charging or discharging of those local cells. Similarly, the central controller 20 operates the secondary bridge circuit 77 based on either detected current phase in the secondary winding, or to set the current phase angle in the secondary winding. Operation of the switches in the primary bridges 48 and the secondary bridge 77 may be based on many control processes which align switch timing with the current phase angle. For the purposes of illustrating the control methods of various embodiments, the following control process is based on a three-level modulation technique. This technique bases bridge operation around three key parameters, being an operation frequency parameter which sets a timing period, a duty cycle parameter, and a phase offset parameter. The three levels represent a first winding connection polarity, off, and a second winding connection polarity. Figure 40 illustrates operation of the primary and secondary bridges based on the exemplary three level modulation control parameters. In the embodiments described, a base frequency ω is typically in the 10-200kHz region. The base switching frequency may be chosen based on the natural resonant frequency of the resonant circuit 30. However, the natural frequency is not necessarily the desired operation frequency which is a frequency selected or determined based on optimisation of a wider range of system parameters. Theta θ represents a duty cycle of the bridge conduction and is a parameter that can be controlled to regulate the current through the bridge, and align switch timing with current zero crossings or other desired switching points. Phi ϕ represents a separation angle or offset between the conduction timing of the primary bridges and secondary bridge. Based on these three parameters, the relative switching timing of the primary and secondary bridges can be controlled and the current flowing in the system regulated. The phase offset is controlled by ϕ which separates the switch timing of the primary bridges from the secondary bridge. The switch timing is, in preferred embodiments, in alignment with current and in particular when the current crosses zero, or is at least below a predetermined threshold. The phase offset phi may be a parameter received from the central controller, or it may be detected by the detection circuit of each primary module. Figure 41 shows a graph of the theta angle against power, illustrating how the theta angle and therefore the conduction duty cycle of the bridge can regulate the power through the bridge. Figure 42 shows a graph of omega against the system power output, indicating that the operation frequency can be used to regulate power from the system. In some embodiments, the operational frequency of the resonant system is set by the operation of the secondary bridge, such that no standalone phase-locked loop (PLL) circuit is required for frequency definition. Instead, a central controller is configured to time the transition of switching devices of the secondary bridge to directly control the system operating frequency. To refine this control, the central controller may employ a proportional–integral (PI) controller in a feedback loop that receives a measured indication of operational frequency and adjusts switch timing incrementally toward a target frequency. In certain embodiments, changes to the operational frequency are rate-limited, thereby allowing other controllers in the system—such as local PLLs in primary cell module controllers or additional PI controllers regulating current—to adapt to the small, incremental changes without disruption to stable soft-switched operation. In other embodiments, or in combination, the control system comprises a detection circuit, a PLL, a PI controller, a derivative function, and a pulse width modulation (PWM) generator configured to regulate current in magnetically coupled windings by means of the primary and secondary bridge circuits. The detection circuit is configured to sense the phase of current flowing in the coupled winding, and its output is provided to the PLL. The PLL establishes the instantaneous frequency (ω) of the resonant current and may further generate synchronisation pulses used by the cell module controllers to align switching events of the primary-side bridge circuits to the detected frequency. The PLL output may also be processed by a derivative function to determine the rate of change of frequency (dω / dt), providing a feed-forward adjustment that improves dynamic response under rapidly varying load or coupling conditions. Figure 43 illustrates an exemplary control system components configured for regulating current in a magnetically coupled winding by means of the primary and secondary bridge circuits operated with a three-level pulse width modulation (PWM) scheme. The control system comprises a detection circuit, a phase-locked loop (PLL), a proportional–integral (PI) controller, a derivative function, and a PWM generator configured to drive a bridge circuit. In operation, a detection circuit 45 is configured to sense the phase of current flowing in the magnetically coupled winding. The output of the detection circuit is provided to the PLL, which establishes the frequency (ω) of the current. In some embodiments, the PLL further generates a timing or synchronisation pulse, which is provided to a cell module controller 41 and used to align switching events of the bridge circuit to the detected frequency. The frequency output of the PLL may also be processed by a derivative function to determine the rate of change of frequency (dω / dt). This derivative term provides an additional feed-forward adjustment, improving dynamic response of the control system when operating under rapidly varying load or coupling conditions. Referring to the primary side system of Figures 43 and the secondary side system of Figure 44, a PI controller receives a reference signal, such as a desired current or power value (Iref / Pref), and compares the reference to a measured output signal (Iout / Pout). The PI controller generates a control output θp (for the primary), θs (for the secondary), which represents an adjustment to the phase or duty cycle of the PWM drive signals. By applying this corrective term, current delivered through the primary bridge, and therefore from the associated battery cell, is regulated toward the reference value. The outputs of the derivative function and the PI controller are combined and provided to a three-level modulation PWM generator. The PWM generator includes multiple timing comparators (Timer A, Timer B) configured to generate complementary switching signals displaced by the commanded phase angles θp, θs. These signals are used to operate the bridge switching devices, including Bridge A made up of switches P1, P2 (or S1, S2) and Bridge B made up of switches P3, P4 (or S3, S4). Control of the conduction intervals of the bridge legs regulates the magnitude and phase of current injected into the magnetically coupled winding, thereby compensating for both steady-state offsets and dynamic variations in operating frequency. The combined use of current phase detection, PLL-based frequency tracking, derivative-based dynamic compensation, and PI-based error correction provides stable regulation of winding current and improved robustness under varying load, coupling, and environmental conditions. The PI controller plays a central role in ensuring both soft switching and accurate target current delivery. Soft switching is achieved when the phase of the current and voltage are aligned at approximately zero degrees. On the primary side, this condition is established by aligning the bridge switch timing with the voltage and current which regulates voltage differences across the switching devices. In some embodiments, the cell module controller 41 may further monitor parameters of the associated battery cell, including temperature, voltage, or state of health. The regulation of current through the bridge can be modified based on these parameters. For example, if the cell temperature exceeds a threshold, the controller may reduce the current reference value, thereby reducing the duty cycle of the bridge and limiting stress on the battery cell. In other embodiments, a central controller 20 is configured to monitor environmental parameters or to determine imbalances across multiple cells in the system. In response, the central controller communicates updated θp commands or other reference values to individual cell module controllers 41 via communication interfaces 46, 76 and associated links. Each primary cell module controller then adjusts operation of its local bridge circuit accordingly. Due to the inherent reactance of the magnetic coupling apparatus, a phase offset may arise between current in the secondary winding and current in each primary winding. Likewise, currents in primary windings of different modules may differ in phase. The detection circuit 45 is therefore configured to determine the specific phase relationship for each module, enabling synchronised and precise control of current contributions from multiple cells in the system. The combined use of frequency detection, PLL-based tracking, derivative-based dynamic compensation, and PI-based error correction enables robust and stable regulation of the winding current. The PI controller plays a central role in ensuring both accurate target current delivery and soft switching. Soft switching is achieved by aligning the bridge switching instants such that voltage and current waveforms cross near zero, thereby reducing switching losses and improving efficiency under both steady-state and transient operating conditions. Figure 45 shows an example of a cell voltage 451 in a primary module compared to the secondary bridge voltage 452, and in particular the phase offset phi which is apparent between them. The central controller can estimate, based on circuit characterisation data, or have stored measured values of the phase offset to act as a reference for the operation of each cell controller. The central controller transmits this phase offset phi to each cell controller, and each cell controller uses this reference as either a starting phase offset angle for the synchronisation of the primary bridge, or for referencing the phase data provided by the PLL circuit to ensure it falls within an expected range. In some embodiments, the target current is transmitted by the central controller 20, which manages relative loads of battery cells in the system, to each primary cell module controller. Cell balancing functions can be achieved by the central controller by communication of different Θp commands to individual primary cell modules based on their state of charge. Both the primary and secondary circuits incorporate PI controllers with complementary roles. The secondary PI controller determines ω, typically operating at or near the natural resonant frequency of the magnetic circuit, and adjusts θ in response to instantaneous power requests. The primary PI controller, in contrast, adjusts the conduction angle to regulate local battery current while supporting synchronization. Together, the controllers cooperate to balance power delivery and to maintain resonance for soft switching. During operation, the secondary side is capable of faster power modulation because its control signals are applied directly to switching elements of the bridge to control conduction angle. By comparison, primary side adjustments are slower as they rely on communication from the central controller over the communication channel. For this reason, the secondary controller is ideally responsible for immediate adjustments to power flow, while the primary provides slower, supervisory regulation of current from each battery cell. Energy transfer between a cell and the current in the magnetic coupling apparatus depends on the relative phase angle of switching. When the primary phase angle is positive, energy is discharged from the cell into the magnetic coupling apparatus for use by other cell modules and the secondary circuit. Conversely, when the angle is negative, the current reverses direction and the cell is charged. Figure 46 shows a graph of the cell voltage 454 phase aligned with the primary winding current 453, thereby causing discharge of the cell. Further, the current and voltage intersect at the zero crossing, exhibiting phase alignment and facilitating soft switching. In charging operation, phase lock can be established using the natural voltage across the primary cell, with diodes in the bridge providing the necessary conduction paths during current reversal. Figure 47 shows a graph whereby the cell voltage 454 is about 180 degrees out of phase with the primary winding current 453, thereby causing charging of the cell. This phase control demonstrates that the system can charge a cell while other cells are simultaneously delivering energy to the output circuit. The cell being charged may lose absolute soft-switching, but still has a very low loss. Figure 48 shows a graph of the bridge voltage 452 and the bridge current 455 which are phase aligned at the zero crossing point thereby demonstrating that soft switching is achieved. The system also accommodates dynamic reconfiguration, such as adding or removing battery cells. When a cell is physically removed or bypassed, the effective transfer function of the system changes. The PI controllers respond by adjusting ω until a new soft switching point is identified, which may involve incrementally raising or lowering the switching frequency. Limits on ω are enforced by the controller, typically constrained to a band (e.g., 40–60 kHz) to ensure stable operation. The PLL of the primary modules tracks the change in ω to stay synchronised with the secondary bridge and operational current in the magnetic system. The PI in the primary modules regulate θ and ϕ to maintain operational current targets and phase alignment. Absolute zero-current switching is not always required. In some conditions, the system tolerates minor deviations from ideal soft switching if losses remain within acceptable bounds. By continuously adjusting ω and θ, the controller minimises switching losses while maintaining effective energy transfer. Thus, omega control serves primarily as a mechanism for soft switching, while energy transfer is governed by θ angles of the primary, rectifier, and secondary controllers. Large current draws on the secondary inverter may cause the DC bus voltage to increase, which in turn raises the voltage across tuning capacitors. This effect elevates the primary current, potentially leading to overcurrent conditions. To correct for this, the controller reduces current either by modifying the duty cycle angle of the secondary bridge or by adjusting ω. By increasing or decreasing ω, the reactance of the resonant network is modified, thereby regulating current flow back toward the desired level. Additionally, the central controller may transmit a theta command to each primary module to cause a change in duty cycle from each primary bridge circuit. Different parameters exhibit different update rates in the system. Fast parameters, such as ω and secondary θS, may be updated instantaneously by local controllers, allowing immediate response to load or coupling changes. Slower parameters, such as primary θp and Φ, are updated via the communication interface and thus respond over longer time scales. In some embodiments, the system parameters are categorised as fast or slow response parameters, thereby requiring different control bandwidth based on either rapid transient response or slower balancing requirements. In some embodiments, the central controller 20 operates as the supervisory entity, arbitrating among multiple primary cell module controllers 41 and designating roles such as the starting cell for ω control in a grid-forming scenario. Arbitration may be arbitrary or based on predetermined criteria such as the highest state of charge. The central controller also issues directives for power absorption or delivery at defined angles, while the individual cell module controllers implement local optimisation. Importantly, the system does not require perfect soft switching under all conditions. At light load, some degree of hard switching may be tolerated in exchange for reduced overall loss. The central controller 20 will control the switching frequency of the system ω to ensure the secondary bridge 77 is soft switched, and each primary controller 41 will control its local φ angle to ensure the primary bridge is also soft switched. If a cell is physically added or removed from the system (which is different from bypassing the cell by shorting the bridge) this changes the ωr of the system and causes the rectifier current and voltage to have a phase difference, thus not soft switching. The change in resonant frequency is due to the change in impedance of the magnetic coupling apparatus based on the decoupling of a primary structure. Many other system factors may also cause changes in the ωr of the system, including temperature changes, battery cell loads. The zero crossing detection in the secondary closed-loop controller will change the ω to (or proximate to) a new ωr to reinstate soft switching. The change in resonant frequencies is also indicative of the change in impedance. In some embodiments, the circuit is characterised such that impedance is determined from operational parameters and directly estimated in real time. Therefore, a controller may store data referencing known impedance to a particular number of modules. Figure 49 to Figure 51 show a temporal sequence of an impedance change occurring and being responded to. In Figure 49, the system is in a steady state operation where the voltage and current at the secondary bridge are phase aligned at the zero crossing, indicated by the circled regions. In this example, there are 36 primary modules in the system with a switching frequency of 50kHz. In Figure 50, a change system impedance has caused misalignment of the voltage and current phase, indicated by the circled regions. In this example, two primary modules are removed from the system while the switching frequency of 50kHz remains. In response, the central controller adjusts the switch timing of the secondary bridge circuit to alter the switching frequency of the system, track to a new resonant frequency and restore soft switching. In Figure 51, phase alignment between the voltage and current is restored with a new switching frequency of 54.45kHz. The following table indicates default parameters for the bridges for a basic discussion of exemplary modes, including an idle mode, an uninstalled mode where a primary module is removed from the system, a running mode, and a fault mode. Mode ω θp θS Φ , , s from the idle status where no current is flowing in the system, where the parameters are set according to the table above. The central controller 20 operates the secondary bridge 77 to start to switch at the resonant frequency ωr defined by the passive resonant circuit, and θs is 180 degrees while θp is 0 degrees. This means the current will flow in the coupled inductor of the primary winding of each primary module by either the first leg P1,P2 or the second leg P3,P4 of the primary bridge is shorted such that the inductor is coupled to the circuit, but that no current will flow in the cell. The primary voltage / current detection circuit 45 measures the voltage / current in the primary winding 44 and determines the ω and zero crossing point (reference of φ). The primary controller 41 then switches the primary bridge 48 with the measurement ω and at the φ angle that can achieve the soft switching. In the circuit illustrated in Figure 5(A), the bridge configuration is arranged such that the primary winding cannot be short-circuited by the switching devices of the bridge. As a result, no current is able to circulate in the primary winding when the bridge is in an idle state, and the winding is unable to directly interact with the magnetic structure. When implemented with silicon MOSFET technology, switching devices must comprise a pair of back- to-back MOSFETs in order to block reverse current flow through the intrinsic body diodes. An equivalent alternative arrangement may instead employ single MOSFETs, and introduce additional devices positioned in opposing polarity at the central junction of the two windings at the branch point from the battery connection. In either arrangement, it is not possible to intentionally short the winding as doing so would cause the battery to be directly short-circuited through the windings. Accordingly, the idle state of this embodiment is defined by all switching devices being in an open state, ensuring that no current circulates in the primary winding when a given cell module is inactive. The start-up process with this circuit in this embodiment differs from that of a full-bridge circuit. In the absence of a short-circuitable winding current path, a current-sensing PLL cannot be used. Instead, synchronisation requires sensing of the voltage across one or both windings, enabling the PLL to establish a phase reference and generate the appropriate switching signals for resonance tracking. However, when one or more cell modules are in an idle state, the effective impedance reflected to the secondary side of the system is altered as the primary winding is not interacting with the magnetic system. This produces a corresponding shift in the resonant frequency of the coupled system. The following observations are relevant: ● Where only a single cell is idle, while the majority of other primary modules remain magnetically coupled, the resulting frequency shift is minimal and the system remains within stable operational limits. ● However, during system start-up, when most cell modules are idle, the aggregate impedance change introduces a more significant shift in resonant frequency. This requires additional control adaptation during synchronisation but remains practically feasible with appropriately configured control algorithms. One advantage of the half-bridge style circuit of Figure 5(A) is the potential compatibility with wide- bandgap switching devices. Specifically, GaN MOSFETs do not include a parasitic body diode, and therefore avoid the conduction pathways that necessitate back-to-back pairing in silicon MOSFETs. This characteristic makes GaN devices ideally suited for use as the switching devices, simplifying the topology and reducing conduction losses. The system stops when the secondary controller operates the bridge with θs = 0 degrees, no energy will be transferred between cells and the voltage source. Similarly, the primary module controller 41 controls the primary bridge 48 at θp = 0 degrees. The system controller, comprising the central controller 20 and the primary cell module controller 41 in most embodiments, are configured to coordinate control steps to facilitate operation of various more complex operation strategies. These strategies include operating the system according to a mode, or with a particular set of operation parameters or system targets for a phase, these including: system startup, grid forming, grid following, steady state running, system shutdown, adding a primary module to the system, removing a primary module from the system, balancing of cell voltages across the primary modules in the system, and soft switching control. For a system startup mode, the primary side and secondary side controllers are configured to execute a method of coordinated control. The method is configured to establish resonant current and maintain a soft-switching operating state in the system to enable the advantages of reduced switching losses and improved efficiency during charge or discharge events. With no current flowing in the system, the system is considered to be in an idle state where all switching devices of the bridges on both the primary and secondary sides are rendered non- conductive. During an initial phase of the startup procedure, a resonant current must be established in the magnetic coupling apparatus. In this mode, this resonant current is sourced from at least one battery cell of a primary module. The selected primary module injects current into the primary winding by controlled switching of its local H-bridge, thereby initiating oscillation in the coupled magnetic structure. In other modes, resonant current is sourced from a supply connected to the secondary bridge. The system is configured to determine which primary cell module will provide the startup current. In some embodiments, the primary modules execute an arbitration process whereby cell data is communicated between modules to establish a master primary module. The master module may be selected based on state of charge, position within the magnetic structure, or other operational factors. In some embodiments, a primary primary cell module controller 41 has a high-power mode and a low- power mode. In the low-power mode, the controller processor is operated in a sleep state, configured to periodically and momentarily switch to the high-power mode to check for a startup current request. A startup current request may originate from the secondary controller and be communicated to one or more primary modules such that the next primary module to wake from low-power mode responds to the request by providing startup current. In other embodiments, the central controller 20 may initially be unpowered. In such cases, the primary module controller 41 operates its bridge circuit to inject cell current into the magnetic structure, from which the secondary side includes a rectification and regulation circuit to provide bootstrap power to the central controller 20. Thus, the secondary side derives its initial operating power only from current injected by a primary cell. In the idle state, either the upper switch pair (P3, P4) or the lower switch pair (P1, P2) of each primary bridge is shorted to create a current path through the primary winding. All control variables, including angular frequency (ω), primary conduction angle (θP), secondary conduction angle (θS), and relative phase angle (ϕ), are initialized to zero. Once the resonant current is established by the selected primary module, the secondary controller begins its coordination role. The secondary bridge 77 is switched at a frequency near the resonant frequency (ωr) to provide a synchronisation reference. The conduction angle of the secondary bridge (θS) is gradually increased from 0° toward 180° to shape the voltage waveform and assist in phase alignment. The secondary controller continuously regulates switching frequency ω so as to favour zero-current or near-zero-current commutation. Importantly, the secondary side does not act as a current source, but instead coordinates and conditions the system once primary current is present. Each primary controller monitors the primary winding current induced by the resonant oscillation. When the current exceeds a threshold, synchronisation begins. A phase-locked loop (PLL) or equivalent signal recovery technique is employed to identify zero-crossing instants. In some embodiments, high-speed comparators or high-resolution analog-to-digital conversion are used to generate a synchronisation signal. Once lock is achieved, a reference for the relative phase angle (ϕ) is established, aligning primary switching instants with the secondary waveform. Upon synchronisation, the primary controllers commence active switching of their respective bridges: ● For discharging: The primary conduction angle (θP) is gradually increased from 0° toward a target angle, typically up to 180°, thereby governing the rate of power delivery from the cell to the inductive path. ● For charging: The conduction angle is reduced from approximately –180° toward 0°. In certain embodiments, the MOSFETs are initially held open, allowing coil current to flow through body diodes, with active switching later applied to emulate the diode current waveform while reducing conduction losses. In steady-state operation, both the secondary and primary controllers continuously adapt their control parameters. Adjustments are made to maintain soft-switching by promoting zero-current commutation conditions, even in the presence of differing discharge rates among cells. Control strategies may include: trading conduction angle between cells to equalise switching conditions, introducing harmonic modulation to enforce clean zero crossings, or reverting to controlled hard-switching when current falls below a defined threshold for a limited interval. Accordingly, in some embodiments there is a central controller 20 is configured to execute one or more of: ● coordinate the collective operation of primary modules; ● in the idle state, render all switching devices of the secondary bridges non-conductive, ● in the idle state, render either the upper switch pair (P3, P4) or lower switch pair (P1, P2) of each primary bridge shorted to create a current path through the winding while bypassing the battery cell of the primary module; ● initialize all control variables, including angular frequency (ω), primary conduction angle (θP), secondary conduction angle (θS), and relative phase angle (ϕ), to zero; ● upon initiation by a primary module, begin switching the secondary bridge at a frequency near a resonant frequency (ωr) to provide a synchronisation reference; ● gradually increase a conduction angle (θS) of the secondary bridge from 0° toward 180° to shape the voltage waveform and assist in phase alignment; and ● continuously regulate switching frequency ω to favour zero-current or near-zero-current commutation, while not acting as a source of resonant current. Accordingly, in some embodiments there is a cell module controller 40 associated with each cell, configured to execute one or more of: ● provide resonant current during system startup by controlled switching of a local H-bridge, thereby injecting current from its associated battery cell into a primary winding to initiate oscillation in the coupled magnetic structure; ● participate in an arbitration process with other primary module controllers to establish a master module for startup, the master module being selected based on state of charge, position within the magnetic structure, or other operational factors; ● operate in a high-power mode or a low-power mode, wherein in the low-power mode the controller processor periodically wakes from a sleep state to check for a startup current request; ● respond to a startup current request communicated by the secondary controller by switching into high-power mode and injecting current into the magnetic structure; ● bootstrap operation of an initially unpowered secondary controller by providing injected current, wherein the secondary side includes rectification and regulation circuitry configured to derive operating power from the injected current; ● monitor induced current in the primary winding, and upon detecting that the current exceeds a threshold, begin synchronisation; ● employ a phase-locked loop (PLL), high-speed comparator, or high-resolution analog-to- digital conversion to detect zero-crossing instants and generate a synchronisation signal; ● establish a reference for relative phase angle (ϕ) and align local switching instants with the secondary waveform; ● upon synchronisation, commence active switching of its bridge, including: ○ for discharging: gradually increasing θP from 0° toward a target angle up to 180°, thereby governing the rate of power delivery; ○ for charging: reducing θP from approximately –180° toward 0°, initially holding MOSFETs open to permit diode conduction, then applying synchronised switching to emulate the diode current waveform while reducing conduction losses; and ● ensure that current flow always originates from or is absorbed into the primary cells, with bidirectional power transfer executed under controlled conditions. Startup Sequence - Secondary sourced power In some embodiments, the resonant current is sourced from a supply connected to the secondary solar MPPT input, or another external power source. bridge, which is operated to inject current into the secondary winding. The injected current produces oscillatory current in the coupled primary windings, thereby initiating resonance in the system. The central controller coordinates this process by commanding the secondary bridge to begin switching at a frequency determined to be at or predicted to be close to the resonant frequency (ωr). The conduction angle of the secondary bridge (θS) is gradually increased from 0° toward 180°, shaping the injected current and generating a progressively increasing voltage waveform across the secondary winding. This action results in oscillatory current being established in the coupled primary windings without requiring any primary cell to initially contribute energy. The primary bridge circuit is configured to short circuit the primary winding of each primary module such that a current flows in the winding while bypassing the battery. Each primary controller monitors its associated winding for induced current. When the induced current reaches a measurable threshold, synchronisation begins. A phase-locked loop (PLL) or equivalent signal recovery technique is employed to detect zero-crossing instants of the primary winding current. In some embodiments, high-speed comparators or high-resolution analog-to-digital conversion are used to generate a synchronisation signal. Once the PLL achieves lock, a reference for the relative phase offset angle (ϕ) is established, thereby aligning the primary switching instants with the secondary waveform. Upon synchronisation, the primary controllers commence active switching of their respective bridges. The specific conduction angle trajectory depends on the operational mode of the associated battery cell: ● For discharging: The primary conduction angle (θP) is gradually increased from 0° toward a target angle, typically up to 180°, thereby governing the rate of power delivery from the cell to the inductive path. ● For charging: The conduction angle is reduced from approximately –180° toward 0°. In certain embodiments, the primary MOSFETs are initially held open, permitting coil current to flow through their body diodes. Thereafter, active switching is applied in synchronism with the diode current to reduce conduction losses. In either case, once primary cells begin participating, current flow is bidirectional between the primary modules and the inductive path, with the secondary source having served only as the initial resonant current provider. In steady-state operation, both the secondary and primary controllers continuously adapt their control parameters. Adjustments are made to maintain soft-switching by promoting zero-current commutation conditions, even in the presence of differing discharge rates among cells. Control strategies may include trading conduction angle between cells to equalise switching conditions, introducing harmonic modulation to enforce clean zero crossings, or reverting to controlled hard-switching when current falls below a defined threshold for a limited interval. Accordingly, in some embodiments there is a central controller 20 is configured to execute one or more of: ● initiate resonance by commanding the secondary bridge to switch at a frequency proximate to a resonant frequency (ωr); ● gradually increase a conduction angle (θS) of the secondary bridge from 0° toward 180°, thereby shaping the injected current and generating a progressively increasing voltage waveform across a secondary winding; ● establish oscillatory current in coupled primary windings without requiring any primary cell to initially contribute energy; and ● continuously adapt control parameters during steady-state to maintain soft-switching across the system. ● operate the secondary bridge to couple the auxiliary supply to the secondary winding; ● operate the secondary bridge to inject current at the commanded frequency and conduction angle (θS); and ● operate the secondary bridge to generate oscillatory current in the coupled primary windings for resonance initiation. Accordingly, in some embodiments there is a cell module controller 40 associated with each cell is configured to execute one or more of: ● initially short its associated primary winding via its bridge circuit to provide a current path; ● monitor the associated winding for induced current; ● upon detecting that the induced current exceeds a measurable threshold, employ a phase- locked loop (PLL), a high-speed comparator, or high-resolution analog-to-digital conversion to detect zero-crossing instants of the induced current; ● establish a reference for a relative phase angle (ϕ), thereby aligning primary switching instants with the secondary waveform; ● commence active switching upon synchronisation, with conduction angle trajectories determined by cell operating mode, including: ○ for discharging: gradually increasing the primary conduction angle (θP) from 0° toward a target angle up to 180° to govern power delivery from the cell; ○ for charging: reducing the conduction angle (θP) from approximately –180° toward 0°, initially permitting coil current to flow through MOSFET body diodes and thereafter applying synchronised active switching to reduce conduction losses; ● enable bidirectional power transfer once primary cells begin participating, with the secondary source serving only as the initial resonant current provider; and ● continuously adapt local control parameters in steady-state to maintain soft-switching, including by: ○ trading conduction angle between cells to equalise switching conditions, ○ introducing harmonic modulation to enforce zero-crossing conditions, or ○ reverting to controlled hard-switching when current falls below a defined threshold for a limited interval. During normal operation, the system operates in a steady-state, soft-switched condition. The central controller oversees the collective operation of multiple cell-side modules, while individual primary cell module controllers regulate local parameters. The central controller continuously monitors the current and voltage at the secondary bridge and receives slow-updated status information from each cell module controller over a communication bus. This information may include state of charge (SOC), state of health (SOH), and temperature data. Using these aggregated parameters, the central controller calculates a per-cell current, voltage, or power target for balancing and overall energy management. Each primary cell module controller also performs its own local monitoring of SOC, SOH, and temperature. Where a primary cell module controller detects that its power delivery is below the target, it can flag this condition to the stack controller. Alternatively, the stack controller may detect under-delivery by comparing the actual measured secondary current against the expected aggregate of cell contributions. To compensate, the central controller can adjust its own local switching frequency (ω) and / or relative conduction timing (θ) to influence the aggregate output current profile. The central controller may also compute a system-wide current error term to refine the per-cell targets. Once a new target DC current (I_cell(dc)), voltage, or power value is determined for a given cell, the stack controller communicates this updated target to the corresponding primary cell module controller. The primary cell module controller continuously compares its received target against real-time measurements of its local coil current and voltage. If the measured values are consistent with the target and within safe operating limits, the cell maintains its present conduction parameters. If not, the primary cell module controller adjusts its conduction angle (θP) according to the ratio of the target to the measured current or voltage, thereby scaling its output contribution. At the same time, the primary cell module controller adjusts its local phase angle (ϕ) to ensure that zero-crossing conditions are maintained, allowing continued soft-switching operation. Through this iterative closed-loop process, each cell dynamically adapts its output contribution in coordination with the stack controller. The result is a balanced distribution of current among cells, maintained under soft-switching conditions, with continuous self-regulation in response to real-time operating conditions. The cell module information is communicated over a communication interface, which may be implemented by a wired connection, a dedicated wireless link, or a shared wireless link. In some embodiments, the shared wireless link includes the magnetic coupling between the primary and secondary windings, where frequency, phase, or amplitude modulation of a carrier signal contains the module information. Accordingly, in some embodiments there is a central controller 20 configured to execute one or more of: ● oversee the collective operation of multiple cell-side modules; ● continuously monitor current and voltage at a secondary bridge; ● receive status information from each cell module controller over a communication bus, the status information including at least state of charge (SOC), state of health (SOH), and temperature; ● calculate, based on the aggregated parameters, a per-cell target value of current, voltage, or power for balancing and energy management; ● detect under-delivery of current, either by receiving a flag from a primary cell module controller or by comparing measured secondary current against the expected aggregate of cell contributions; ● adjust a switching frequency (ω) and / or relative conduction timing (θs) to influence the aggregate output current profile; ● compute a system-wide current error term and refine the per-cell targets; and ● communicate an updated target direct current (I_cell(dc)), voltage, or power value to the respective cell module controllers. Accordingly, in some embodiments there is a cell module controller 40 associated with each cell configured to execute one or more of: ● perform local monitoring of SOC, SOH, and temperature; ● receive a per-cell target from the central controller; ● continuously measure a local coil current and / or coil voltage; ● compare the measured values against the received target; ● maintain present conduction parameters when the target is met and safe conditions are satisfied; ● adjust a conduction angle (θp) according to the ratio of the received target to the measured coil current or voltage when the target is not satisfied; ● adjust a local phase angle (ϕ) to align with zero-crossing conditions for continued soft- switching operation; and ● dynamically adapt its output contribution in closed-loop coordination with the central controller, thereby balancing current distribution among cells while maintaining soft-switching. The communication between the central controller and the cell module controllers is provided over a communication interface. The communication interface may be implemented as: ● a wired connection; ● a dedicated wireless link; or ● a shared wireless link, wherein the shared link comprises the magnetic coupling between primary and secondary windings, with frequency, phase, or amplitude modulation of a carrier signal conveying module information. In some embodiments, the system is configured with a coordinated shutdown sequence to ensure that all energy transfer between the primary side modules and the secondary side is safely and predictably terminated. The process is initiated by receipt of a shutdown command, which may originate from the central controller, a supervisory controller, an external management system, or based on a fault being detected. When the shutdown command is received, the system enters a controlled sequence rather than immediately deactivating switching elements. This prevents uncontrolled current collapse, avoids transient over-voltages, and ensures that resonant energy in the coupled magnetic structure is safely dissipated. The shutdown sequence first engages the secondary controller 20 which is configured to progressively reduce its commanded conduction angle (θS) toward 0°. Rate-of-change limits are applied to the θS reduction in order to avoid discontinuities in resonant current or phase alignment variables (ϕ). Once θS reaches 0°, all active modulation of the secondary bridge ceases where no further energy transfer occurs between the coupled magnetic apparatus and the secondary side voltage source (e.g., grid, backup battery, or load). Following secondary-side cessation, the primary module controllers are commanded to execute a similar procedure. Each primary controller progressively reduces the conduction angle (θP) of its associated bridge toward 0°. This ensures that all switching events are phased out under controlled conditions, with rate-of-change limits applied to θP to preserve soft-switching conditions until current naturally decays. The outcome is that no further reactive energy or net transfer of charge occurs between the primary cells. Once all conduction angles have been reduced to 0°, all primary and secondary bridge devices on both the primary and secondary sides may be controlled to a non-conductive state to ensure that residual current draw within the primary module is minimised. However, in some embodiments, the bridge of at least each primary side module is controlled to short the primary winding to ensure there are no stray magnetic fields in the system which can induce unwanted current in the circuits of the primary module. At this point, the system is in the idle state, with zero current flowing in the coupled magnetic structure. The system remains in this idle state until a new startup command is received. Further, primary modules may be removed from or added to the system without disrupting system operation. This controlled shutdown procedure enables predictable termination of energy transfer while avoiding resonant overshoot, uncontrolled reactive exchange, or device stress. Accordingly, in some embodiments there are one or more controllers configured to: ● Receive a shutdown command originating from a supervisory system or external interface. ● Control a secondary bridge by reducing the conduction angle (θS) of its bridge toward 0° with an applied rate-of-change limit, thereby ceasing energy transfer to the secondary source. ● Command one or more primary controllers to reduce the conduction angle (θP) of associated cell bridges toward 0° with an applied rate-of-change limit, thereby eliminating reactive energy exchange between primary cells. ● Enforce parameter constraints during shutdown, including limiting the rate of change of θS, θP, and relative phase angle (ϕ), so as to preserve soft-switching until the resonant current decays. ● Place the system into an idle state in which all bridge devices are non-conductive and no current flows in the magnetic coupling apparatus. In some embodiments, the system is configured to support “hot swap” removal of primary-side cell modules during normal operation. This capability allows defective, depleted, or unneeded modules to be physically removed without necessitating a full system shutdown, thereby enabling serviceability, fault tolerance, and dynamic reconfiguration of available capacity. The process begins when a primary-side cell module is physically disconnected from the system during continuous operation. Removal of the module alters the electrical parameters of the coupled resonant network, specifically reducing the number of primary inductive elements and associated cell sources. The change in resonant structure shifts the composite resonant frequency (ωr) of the system. The secondary closed-loop controller, which continuously monitors system phase alignment via zero- crossing detection of the resonant current and bridge voltage, detects a change in the phase angle. This shift reflects the new impedance characteristics caused by the absence of the removed module. Upon detection of this deviation, the secondary controller adjusts the commanded switching frequency (fsw) of the secondary bridge. The adaptation steers fsw toward the new resonant frequency ωr, or toward an operating point that restores soft-switching conditions and optimises system objectives such as reduced switching losses, balanced module loading, or efficiency targets. Once the frequency adjustment is complete, the system resumes steady-state operation with fewer primary cell modules. All remaining modules continue to operate in synchrony, maintaining bidirectional resonant energy transfer under soft-switching conditions. The system continues in normal operation, dynamically adjusted to reflect the new module population. Removal of additional modules may be accommodated through repeated execution of the same adaptive process. Accordingly, in some embodiments, the central controller is configured to execute one or more of the following steps: ● Detect removal of a primary-side cell module during normal operation of the resonant energy transfer system based on a change in phase conditions between resonant current and secondary bridge voltage. ● Monitor system phase conditions via zero-crossing detection of resonant current and bridge voltage. ● Adapt the switching frequency (fsw) of the secondary bridge toward a new value that re- establishes soft-switching following removal of the module. ● Coordinate ongoing operation of the remaining cell modules such that bidirectional energy transfer continues in a stable and efficient manner. Accordingly, in some embodiments, a primary cell module controller is configured to execute one or more of the following steps: ● Detect the absence of synchronisation signals or induced current associated with a removed module and adapt local participation accordingly. ● Maintain phase-locked operation with the system waveform after module removal, ensuring continued alignment of conduction angle (θP) with secondary bridge switching. ● Adjust local conduction angle and phase (θP, ϕ) to rebalance system current distribution following the reduction in total active modules. ● Coordinate steady-state operation such that the remaining modules contribute or absorb power in a balanced, soft-switched manner despite the altered system resonant conditions. In some embodiments, one or more of the battery cells housed within the primary modules derive operational benefit from the application of a compressive force to their body or casing. Such pressure may, for example, reduce internal impedance, improve charge or discharge uniformity, extend cycle life, or stabilise dimensional changes during operation. Accordingly, in some embodiments, the system includes a pressure-application mechanism configured to exert a controlled mechanical force upon at least one surface of the battery cell or module container. In some embodiments, the battery module housing may provide a preload force or pressure to the battery cell. This could be achieved through the choice of housing material by way of having sufficient stiffness and / or through the use of domed or convex surface to apply pressure to at least one surface of a battery cell. Sloped or wedged surfaces are also applicable. In some embodiments, the battery module housing may transmit an externally applied force through the walls of the housing to provide a compressive force or pressure to one or more battery cells. In some embodiments, the pressure-application mechanism comprises a clamping system actuated by an electromotive element. For example, the clamping system may include one or more linear actuators, motor-driven screw assemblies, or electromagnetic presses adapted to translate rotational or electromagnetic energy into linear compression upon the cell. In one embodiment, the clamping system comprises a motorised clamp in which an electric stepper motor drives a threaded rod coupled to a pressure plate, thereby allowing precise modulation of the applied force. In another embodiment, the mechanism includes a flexural spring element that is preloaded by an electrically actuated wedge or cam arrangement, such that releasing the actuator allows the spring to return to a relaxed position and remove pressure from the cell body. In some embodiments, a pressure sensor, strain gauge, or displacement transducer is coupled to the mechanism to provide real-time feedback of the applied force. Such feedback may be communicated to the central controller, which in turn regulates the motor current or actuator drive to maintain a target pressure profile. In certain embodiments, the applied pressure is varied dynamically based on operating conditions of the cell, such as state of charge, temperature, or current throughput, as determined by measurements of the primary module controller. In some embodiments, the system further includes a control function whereby the central controller identifies a primary module to be removed from the system. In response to this determination, the controller generates a release command signal to the clamping mechanism. Receipt of the release command causes the mechanism to disengage or retract, thereby removing compressive force from the module or cell and permitting safe extraction from the housing or rack. In some embodiments, the release action is coordinated with other system events, such as the disconnection of electrical terminals, decoupling of magnetic flux guides, or reduction of bus voltage, ensuring that the removal of the module is executed in a controlled and safe sequence. In some embodiments, the clamping mechanism is integrated into the rack structure of the secondary housing, such that each slot is equipped with a corresponding pressure-application assembly. When a module is inserted, the assembly automatically engages to apply pressure across the container wall in a direction substantially perpendicular to the longitudinal axis of the cell. In another embodiment, a common clamping bar spans across multiple modules, with individually addressable actuators allowing selective release of one module while maintaining pressure on the others. In some embodiments, the release mechanism is mechanically failsafe. For example, in the event of power loss to the actuator, the mechanism is biased by a spring to move into a released state, thereby ensuring that the module can be safely removed without active drive. Conversely, in some embodiments, the mechanism is biased toward the clamped state, such that pressure is maintained in the absence of power, and release occurs only upon deliberate electrical actuation. In some embodiments, the system is configured to support “hot swap” addition of new primary-side cell modules during normal operation, without requiring a complete shutdown or restart of the system. This capability enables improved serviceability, modularity, and dynamic scaling of available capacity. Referring to Figure 8, this could entail the introduction of primary cell module 40b, not previously present, while other cell modules 40a to 40n are present in the operating system. As the power is transferred via the current transformers, there is also a safety benefit from having no potentially hazardous conductors exposed. The process begins when a new primary cell module is introduced to the magnetic coupling structure and communication bus of the system while energy transfer is ongoing. The addition of the new module changes the electrical boundary conditions of the resonant network. The total number of primary cell modules and therefore coupled inductors in the magnetic system is altered by the added primary module, which in turn changes the composite resonant frequency (ωr). The central controller, which maintains closed-loop synchronisation via zero-crossing detection of current and voltage waveforms, detects a change in phase angle. Specifically, the phase relationship between the secondary bridge voltage and the resonant current shifts as the equivalent impedance of the network is modified. Upon detection of this phase deviation, the central controller adjusts its commanded switching frequency (fsw). This frequency is adapted toward a value that more closely aligns with the new resonant frequency of the expanded system. Although the selected fsw may not exactly equal the true ωr for the aforementioned current regulation requirements, it is chosen to re-establish soft-switching conditions and stabilise resonant current flow across all active modules. The controller of the newly added primary cell module enters a passive observation state upon connection. In this state, its primary bridge is held in a state that connects each end of the primary winding together, such as by closing switches P1,P2 while switches P3,P4 are held open (or vice versa), while the module senses the oscillatory current induced in its local primary coil from the already operating system. When the induced current reaches a sufficient magnitude, the new module measures the oscillation frequency and establishes phase synchronisation by locking onto the global resonant waveform. Once synchronisation is achieved, the new module transitions into an active mode. Its controller begins modulating its bridge switching, gradually ramping the conduction angle (θP) from zero toward a target value specified by the stack-level supervisory controller. The ramp-up is performed gradually to prevent current surges, transients, or disruption of established soft-switching conditions. The phase alignment of the conduction angle is based on whether charging or discharging of the local cell is intended. At the completion of this ramping process, the newly added module is integrated into the system. It is able to contribute to or absorb power in coordination with the other primary modules. Following integration, the system resumes continuous normal operation, now with an expanded population of active primary modules. The process may be repeated for additional hot-swapped modules without requiring a system-wide shutdown. Accordingly, in some embodiments, the central controller is configured to execute one or more of the following steps: ● Detect a new cell module connection during normal operation of the resonant energy transfer system based on determination of a phase shift in the oscillating current, a communication being received from the newly added module. ● Monitor system phase conditions via zero-crossing detection of resonant current and secondary bridge voltage. ● Adapt the switching frequency (fsw) of the secondary bridge toward a value that re- establishes soft-switching after the addition of the new module. Accordingly, in some embodiments, there is a primary cell module controller configured to execute one or more of the following steps: ● Operate in an observation mode, wherein the induced current in the primary coil is measured and used to determine system oscillation frequency and phase. Synchronise the bridge switch timing by phase-locking its local control loop to the system waveform once induced current is sufficient. ● Initiate gradual integration of the new module by ramping its bridge conduction angle (θP) from 0° toward a predetermined target angle or that determined by the central controller. ● Coordinate steady-state operation such that the new module contributes or absorbs power in a balanced, soft-switched manner with all other modules. Cell target state control sequence In some embodiments, the system is configured to control cell parameters toward a target state. based on any one or more cell parameters, including a state of conditions such as the temperature of the cell, switching circuit, or primary module. During normal operation of the resonant energy transfer system, the central controller 20 supervises the collective operation of all primary cell modules 40. One objective of the central controller is to direct each cell toward a desired target state. These target states may include equalisation of state of charge (SOC) across modules; adjustment of charge or discharge rates to maintain a desired load on the cell based on cell voltage, cell current, temperature of the cell, temperature of the circuit, SOH, or other constraints; deliberate discharge of one or more cells ahead of the rest of the system to prepare the associated primary module for removal and replacement; and bypass operation of selected cells when necessary. In steady-state, the system operates in a soft-switched resonant mode established by the secondary bridge, with individual primary cell modules participating according to their conduction angle (θP) and phase angle (ϕ). The central controller 20 continuously acquires data from each primary cell module controller. The data includes one or more of a state of charge, state of health (SOH), and temperature values. The central controller 20 evaluates the reported cell states against operational requirements. If all cells are operating within acceptable limits defined by a target cell state, then no specific target action is required and normal operation continues unchanged. If one or more cells must be steered toward a new state based on a determination one or more limits are exceeded, the central controller 20 determines the appropriate adjustment in terms of target DC power or current, and may additionally communicate initial θP and ϕ references to the primary cell module controller of the appropriate primary module. Each affected primary cell module controller receives the new target and implements local regulation. This involves measuring the reflected resonant current or voltage (Icoil / Vcoil) and adjusting its switching parameters. Specifically: θP is set according to the ratio of the commanded cell power or current, and ϕ is adjusted to maintain soft-switching conditions at zero current crossing. There are at least three options for determining θP and ϕ, including: A central reference from the central controller with local refinement from the primary cell module controller; where θP and ϕ are supplied by the central controller but modified by the primary cell module controller; A fully local determination: θP and ϕ are established solely by the primary cell module controller via zero-crossing detection; and A hybrid mode, where there is a combination of centralised reference and local zero-crossing detection. The result is that each cell can be selectively directed toward its desired state: charging, discharging, bypassing, or holding steady, while the overall system maintains resonant or quasi-resonant soft- switched conditions. Accordingly, in some embodiments, the central controller 20 is configured to execute one or more of the following steps: ● Continuously receive voltage, current SOC, SOH, and temperature data reported by each primary cell module controller via wired, wireless, or modulated communication links. ● Compare reported values against operational thresholds and system requirements. ● Determine whether one or more cells should be targeted for a new operational state, including: Equalisation with other cells, ○ Limiting or enhancing charge / discharge for safety, ○ Pre-discharge of a cell to enable its removal or replacement, ○ Bypass or idle state operation. ● Calculate new Icell or Pcell DC targets (and optionally θP / ϕ starting values) for affected cells. ● Communicate the new targets over the system communication channel to the appropriate primary cell module controllers. Accordingly, in some embodiments, there is a primary cell module controller 21 configured to execute one or more of the following steps: ● Receive Icell or Pcell targets from the central controller 20. ● Receive θP / ϕ references from the central controller 20. ● Measure coil current or voltage to determine local frequency and waveform phase. ● Establish conduction angle θP based on the ratio of the commanded Icell(dc) to the measured Icoil / Vcoil. ● Adjust the local phase angle ϕ to maintain zero-crossing soft-switching. ● Implement one of three control embodiments: ○ Modify centrally supplied θPand ϕ values. ○ Independently determine θP and ϕ by zero-crossing detection. ○ Combine central reference with local zero-crossing detection. ● Operate the cell according to the commanded state: ○ Positive θP for discharging into the resonant path, ○ Negative θPfor charging from the resonant path, ○ Zero θP for bypass / idle operation. ● Apply rate-limited changes to θP and ϕ to avoid disruption of resonant conditions. The system maintains soft switching through the coordinated control of three parameters: angular frequency (ω), conduction angle (θ), and phase angle (ϕ). These parameters are dynamically regulated by a hierarchy of controllers that interact across the secondary and primary levels of the energy transfer system. The soft switching may be defined by zero-current switching (ZCS), or by switching based on current being less than a threshold current. In some embodiments, the switching threshold current is dynamic and based on one or more other system variables which might include measurements such as current through the primary or secondary bridge circuit, the temperature of a particular circuit area or components such as the switching devices, the temperature of the cell, or a momentary control procedure which may require hard switching for one time, or short time event. A short time event may be based on the amount of heat generated in that amount of time considered. In steady-state operation, the resonant energy transfer system functions under soft-switching conditions. The central controller supervises the collective operation of the system and the secondary bridge controller establishes frequency and zero-crossing references for the operation of the secondary bridge. Each primary module controller regulates its own conduction parameters and establishes zero-crossing references for the operation of its local primary bridge circuit. The central controller is configured to continuously monitor secondary bridge current and voltage to supervise system operation. Each primary cell module controller is configured to measure its local primary winding current and voltage in real time. The central controller is configured to set and adjust the overall system switching frequency (ω) and continuously detect at least the zero-crossing points of secondary winding current and voltage. If the secondary current and voltage are substantially in phase, this indicates the system is at or near resonance ωr, and the operating frequency ω can be maintained. If they are not in phase, such as when tolerance drift or a change in the number of participating primary cell modules alters conditions, the central controller adjusts the operating frequency to a new ω until resonance or near zero-current soft-switching is re-established. In such embodiments, a predetermined current threshold establishes when the current is low enough to activate a switch transition. In some embodiments, the central controller is configured to dynamically adjust the current threshold based on one or more other system parameters. The design of the modular resonant power management system prioritises soft switching to minimise losses. However, the control strategy explicitly includes provisions for and leverages hard switching excursions when required for startup, optimisation, or managing specific low-load scenarios. The key objective is to achieve low power losses or an optimal result rather than strictly absolute ZCS. In some embodiments, the dynamic adjustment of the current threshold is based on the temperature of the secondary bridge or other circuit areas being below a temperature threshold. In some embodiments, the dynamic adjustment of the current threshold is based on an optimisation target where an optimal switching result is selected by trading off ZCS for lower overall system losses. The system is designed to achieve a result that is optimal, rather than exclusively soft switching. In some embodiments, the dynamic adjustment of the current threshold is based on a light loading condition indicated by the current through the secondary bridge: One example where hard switching may be preferred is at very light loading conditions. In this scenario, some hard switching might be tolerated to minimise flux in the core. The acceptable current deviation from zero during a switch event is discussed in terms of measurable amperage. The startup sequence uses hard switching which could itself be a novel startup sequence. The startup sequence is meticulously designed, despite these transient hard switching events, to achieve the ultimate goal of establishing stable, low-loss soft switching (Zero Current Switching, ZCS) in the steady state while minimising initial losses and potential damage. This method is a method of starting the system using a control frequency which transitions to the natural resonant frequency of the system, designed to minimise initial losses. Each primary module controller receives the system frequency ω and zero-crossing reference phase angle (phi) from the secondary controller which serves as a reference. In some embodiments, there is a controller configured to align its switching based on the provided zero-crossing references. One reason is that harmonics in the voltage or current may cause an alignment with a false zero - a zero crossing or minima that is not the intended or optimal zero crossing. This can cause issues with phase alignment of the primary bridge with the oscillatory current and therefore disrupt the charge or discharge efficiency of a primary cell module or the system. Based on desired power transfer direction and magnitude, each primary controller determines its own local phase angle (ϕ) relative to the secondary bridge. In some embodiments, there is a controller configured to determine a local phase angle relative to the provided secondary reference angle. In some embodiments, there is a phase angle threshold which defines a range within which the primary controller is above to make a determination of its true local phase offset. The range defines the likely phase angle where the true zero crossing would occur and allows for variations which cause further changes in the true phase angle from the reference phase angle. The range also minimises the likelihood of the PLL locking onto the aforementioned false zero. The primary controller then times its switching signals of the primary bridge to achieve this calculated phase difference, thereby regulating real and reactive power flow. This permits functions such as charging, discharging, and cell-to-cell energy transfer. In some embodiments, there is a controller configured to time its switching signals to regulate real and reactive power flow. In some embodiments, the primary cell module controller is configured to receive DC current targets which are unique for the module, and may differ from the current targets of other modules. To facilitate the unique target of the primary module, the communications may include an ID parameter which is unique for each primary module. In some embodiments, the ID parameter is based on the location in the magnetic coupling apparatus relative to other primary modules. The primary controller is configured to continuously compare its local coil current and voltage against the target. It then adjusts its conduction angle (θP) to achieve the commanded DC current target. As θP is adjusted, switching is constrained to occur precisely at the zero-crossing points of the local current waveform to maintain ZCS. In some embodiments, there is a controller configured to adjust conduction angle while maintaining zero-crossing soft switching. The foregoing description has reference to elements or integers having known equivalents, then such equivalents are included as if they were individually set forth. Although the invention has been described by way of example and with reference to particular examples, it is to be understood that modifications and / or improvements may be made without departing from the scope or spirit of the invention.

Claims

Claims 1. A discrete battery module configured for energy transfer in a power system together with a plurality of other battery modules, each module comprising: one or more battery cells; a primary structure, the primary structure including: a primary flux guide component, and a primary winding associated with the primary flux guide component; a switching circuit coupled to the battery cell and the primary winding and configured to generate an alternating current output; and a primary controller configured to operate the switching circuit; wherein the battery module is adapted to removably engage with a secondary module, in use, such that the engagement causes alignment with a secondary structure of the secondary module, the secondary structure comprising: a plurality of secondary flux guide components, one secondary winding associated with the plurality of the secondary flux guide components; such that the alignment causes the primary and secondary flux guide components to be arranged in complementary sets with a predetermined geometrical alignment for magnetic coupling, each set defining a current transformer with a defined coupling factor k.

2. A battery module as claimed in claim 1, wherein each current transformer is defined by a k factor being greater than 1 / turns ratio.

3. A battery module as claimed in claim 1 or claim 2, wherein the turns ratio of the engaged is defined by the number of effective secondary turns divided by the number of effective primary turns of the primary and secondary windings in each set.

4. A battery module as claimed in any one of claims 1 to 3, wherein the complementary set comprises a primary flux guide and a secondary flux guide pair.

5. A battery module as claimed in any one of claims 1 to 8, wherein complementary flux guides have a gap of up to about 2 mm, and the gap is occupied by one or more of a polymer, air, and liquid media.

6. A battery module as claimed in any one of claims 1 to 4, wherein the primary module further comprises an enclosure adapted to support at least the primary structure.

7. A battery module as claimed in claim 6, wherein the enclosure incorporates a plastic support structure that simultaneously secures the winding and flux guide while forming part of the exterior wall.

8. A battery module as claimed in claim 6 or claim 7, wherein the enclosure comprises an interfacing surface adapted to control a separation between the primary flux guide component and the secondary flux guide component of its complementary set, thereby controlling, at least in part, the coupling factor (K) of the module.

9. A battery module as claimed in claim 8, wherein the interfacing surface comprises an exterior wall of a thickness or form which at least partly defines at least one of a gap and alignment with respect to the secondary flux guide of the secondary structure.

10. A battery module as claimed in any one of claims 6 to 9, wherein the enclosure includes one or more guiding surfaces adapted complementary to one or more surfaces of the secondary module such that engagement between the surfaces causes at least one of a predetermined gap and alignment with respect to the secondary structure to occur, and subsequently, define the predetermined coupling factor.

11. A battery module as claimed in any one of claims 6 to 10, wherein the enclosure comprises one or more guiding surfaces designed complementary to surfaces on the secondary structure such that when the module is engaged with the secondary module, these guiding surfaces automatically establish both alignment and gap spacing, thereby fixing the coupling factor k.

12. A battery module as claimed in any one of claims 6 to 11, wherein the enclosure includes one or more guide ribs which define a mechanical guide for the engagement between removable primary modules and the secondary module.

13. A battery module as claimed in any one of claims 6 to 12, wherein the enclosure locates and supports an antenna in the form of a wireless data receiver / transmitter configured to support wireless communication with an external control system.

14. A battery module as claimed in any one of claims 6 to 12, wherein the enclosure locates and supports an electrical connector configured for the wired coupling of a communication channel.

15. A battery module as claimed in any one of claims 6 to 12, wherein the enclosure is hermetically sealed by an insulating material.

16. A battery module as claimed in any one of claims 1 to 15, further comprising a retention assembly configured to support at least the secondary flux guide and the secondary winding, the retention assembly comprising: a base member and at least one retention member having a contact surface configured to engage a portion of one or more secondary flux guides; and wherein a dimensional tolerance exists between the retention member and the secondary flux guide, such that the retention member allows for a predefined amount of movement of the secondary flux guide relative to the base member, while securing the secondary flux guide in place.

17. A battery module as claimed in any one of claims 1 to 15, further comprising a retention assembly configured to support at least the secondary flux guide and the secondary winding, the retention assembly comprising: a contact surface configured to engage a portion of the one or more secondary flux guides comprising a dimensional tolerance adapted to restrain movement of the one or more secondary flux guides within the dimensional tolerance.

18. The apparatus of any one of claims 16 or 17, wherein the secondary flux guide is secured within the retention assembly with a limited freedom of movement due to the dimensional tolerance, permitting positional adjustments without detaching the secondary flux guide from the assembly.

19. The apparatus as claimed in any one of claims 16 to 18, wherein the retention assembly comprises one or more guiding surfaces configured to engage with the primary structure and extend toward the secondary structure, the guiding surfaces comprising a narrowing structureconfigured to receive the secondary structure as the secondary structure is moved toward the primary structure.

20. A battery module as claimed in any one of claims 16 to 19, further comprising a retention assembly configured to support one or more primary flux guide relative to the secondary structure, the retention assembly comprising: a contact surface configured to engage a portion of at least one primary flux guide comprising a dimensional tolerance adapted to restrain movement of the one or more primary flux guides within the dimensional tolerance relative to the secondary flux guide in its set.

21. A battery module as claimed in any one of claims 1 to 20, wherein the apparatus further comprises a plurality of primary modules at least partly enclosed within a housing, each module adapted to contain at least one primary structure, wherein the primary modules having different overall heights and noncoplanarity, and the secondary structure having dimensional tolerance for movement within six degrees of freedom to allow alignment with individual planarity and predefined flux gap.

22. A battery module as claimed in any one of claims 1 to 21, wherein the primary and secondary structures comprise an insulator material interspersed between them, the material having a combined thickness constraining the gap between primary and secondary flux guides.

23. A battery module as claimed in any one of claims 1 to 22, wherein the primary controller is configured to determine the primary structure is magnetically engaged with the secondary structure via a detection of a signal received by the primary winding. wherein the primary structure further comprises a communications winding configured to receive flux from the magnetic coupling apparatus, the communications winding configured to detect a communications signal modulated on the power transmission waveform.

24. A battery module as claimed in any one of claims 1 to 23, wherein there is a primary module container configured to support a wireless communication antenna adapted to facilitate non- contact data exchange between a primary cell controller and a secondary controller 25. A battery module as claimed in any one of claims 1 to 24, wherein the primary controller of each primary module is configured to: sense an oscillatory current induced in a primary winding of the primary module from the continuously operating system; determine if the magnitude of the induced oscillatory current is sufficient for synchronisation; synchronise local bridge switching operations with the oscillatory current to establish an operational frequency and zero-crossing references; control the primary bridge conduction based on the operational frequency and zero- crossing references.

26. A battery module as claimed in any one of claims 1 to 25, wherein the primary controller of each primary module is further configured to receive a target power contribution value or a target primary conduction angle from a central controller of a secondary module when engaged with the secondary module.

27. A battery module as claimed in any one of claims 1 to 26, wherein each primary controller is configured to control switch transitions of its primary bridge circuit at a phase angle based on the sensed oscillatory current having a magnitude being below a predetermined current threshold.

28. A battery module as claimed in claim 27, wherein the predetermined current threshold is based on an effective current switching threshold that establishes soft switching.

29. A battery module as claimed in any one of claims 1 to 28, wherein the primary controller of each primary module is further configured to: sense the phase of the oscillatory current in its primary winding, and control the effective duty of its primary bridge circuit based on the sensed phase to regulate the current of the one or more battery cells.

30. A battery module as claimed in any one of claims 1 to 29, wherein the primary module further comprises a phase lock loop configured to determine the phase angle of the oscillatory current in the primary winding; and wherein the primary controller is configured to operate its primary switching circuit based on an agreement between the phase lock loop determined phase angle and received phase angle offset data.

31. A battery module as claimed in claim 30, wherein each primary controller is configured to revise its operational phase offset angle based on the determined voltage and current magnitude and phase, and based on the revised operational phase offset angle falling within a predetermined range.

32. A battery module as claimed in claim 30 or claim 31, wherein each primary controller is configured to revise its operational phase offset angle within the boundaries of a predetermined rate of change limit.

33. A battery module as claimed in any one of claims 1 to 32, wherein each primary controller is configured to: control discharging of the one or more battery cells in its module by connection of the cell polarity substantially in phase with the determined voltage and current magnitude of the primary winding; and control charging of the one or more battery cells in its module by connection of the cell polarity substantially out of phase with the determined voltage and current magnitude of the primary winding.

34. A battery module as claimed in any one of claims 1 to 33, wherein each primary controller is configured to control its primary bridge circuit to effectively short circuit its primary winding when its one or more battery cells are not charging or discharging.

35. A battery module as claimed in any one of claims 1 to 34, wherein each primary controller is configured to control a primary startup phase, comprising: controlling its primary bridge circuit to effectively short circuit the primary winding; determining, based on a voltage and current measurement from the primary winding, there is no oscillatory current operating in the system; controlling its primary bridge circuit to provide a startup oscillatory current at a startup frequency, to its primary winding, and thereby, other primary windings and the secondary winding.

36. A battery module as claimed in claim 35, wherein the primary startup phase is of a first time period.

37. A battery module as claimed in claim 35 or claim 36, wherein the primary startup phase is repeated after a second time period.

38. A power system configured for magnetic energy transfer from a plurality of discrete battery modules, the power system comprising: a secondary structure comprising: a plurality of secondary flux guide components, a secondary winding associated with the plurality of the secondary flux guide components; a capacitor coupled to the secondary winding to form a resonant circuit; a secondary bridge circuit coupled between the resonant circuit and an output for a load; a central controller operatively coupled to the secondary bridge circuit, the central controller configured to manage the operating state and timing of the secondary bridge circuit; and an assembly adapted to support a plurality of the discrete battery modules relative to the plurality of secondary flux guides, wherein the battery modules each comprise a primary flux guide component that, when assembled, are arranged in complementary sets with a predetermined geometrical alignment for magnetic coupling, each set defining a current transformer.

39. A power system as claimed in claim 38, wherein each current transformer is defined by a k factor being greater than 1 / turns ratio.

40. A power system as claimed in claim 38 or claim 39, wherein the assembly comprises an interfacing surface adapted to control a separation between the primary flux guide component and the secondary flux guide component of its complementary set, thereby controlling, at least in part, the coupling factor (K) of the module 41. A power system as claimed in claim 40, wherein the interfacing surface comprises an exterior wall of a thickness or form which at least partly defines at least one of a gap and alignment with respect to the secondary flux guide of the secondary structure.

42. A power system as claimed in any one of claims 38 to 41, wherein the assembly includes one or more guiding surfaces adapted complementary to one or more surfaces of the primary module such that engagement between the surfaces causes at least one of a predetermined gap and alignment, and subsequently, define the predetermined coupling factor.

43. A power system as claimed in any one of claims 38 to 42, wherein the assembly includes a rack-like housing forming part of the secondary structure, whereby the primary modules comprise a cartridge configured to engage with the rack.

44. A power system as claimed in claim 43, wherein the rack includes a track structure whereby the primary modules are able to slide on the track from one end to another.

45. A power system as claimed in any one of claims 38 to 44, wherein each primary module includes a unique ID, and the track structure includes an ID reader operably connected to the central controller for position based determinations of the primary modules.

46. A power system as claimed in any one of claims 38 to 45, wherein the central controller is configured to assign a position-based ID to each module position.

47. A power system as claimed in any one of claims 38 to 46, wherein the central controller is configured to: receive unique module ID code from each primary module; receive a positional code from each primary module; and transmit, to one or more primary modules supported by the assembly, control data based on the ID code and positional code.

48. A power system as claimed in claim 47, wherein the central controller configured to: detect insertion or removal of modules by monitoring received ID codes; maintain a mapping of module unique IDs to rack slot positions; update module control parameters based on position-dependent requirements such as coupling factor, heat dissipation, or service order; and control one or more specific primary cell modules for discharging or charging based on their mapped ID and position.

49. A power system as claimed in any one of claims 38 to 48, wherein the central controller is configured to control a switch transition of the secondary bridge at a phase angle based on the determined voltage magnitude being below a secondary voltage predetermined threshold.

50. A power system as claimed in any one of claims 38 to 49, wherein the central controller is configured to control a switch transition of the secondary bridge at a phase angle based on the determined current magnitude being below a predetermined secondary current threshold.

51. A power system as claimed in claim 50, wherein the predetermined secondary current threshold is based on one or more secondary parameters comprising: the temperature of the secondary bridge, the temperature of a circuit region, the temperature of a cell, the current through the secondary bridge circuit, and an operation phase of the system being a startup phase.

52. A power system as claimed in any one of claims 38 to 51, wherein the central controller is configured to operate the secondary bridge circuit to control an oscillating current frequency based on a determination that the determined voltage or current magnitude at the switching instant is above a predetermined threshold.

53. A power system as claimed in any one of claims 38 to 52, wherein the central controller is configured to control the secondary bridge circuit to a frequency based on a determined phase misalignment between the voltage and current phase angles.

54. A power system as claimed in claim 53, wherein the determined phase misalignment i is based on exceeding a threshold phase angle.

55. A power system as claimed in any one of claims 38 to 54, wherein the central controller shares a communication channel with the plurality of primary modules, and communicates, to one or more primary controllers, one or more phase offset angle data based on a predetermined difference between the phase angle of the primary winding of at least one primary module, and the secondary winding; and wherein each primary controller is configured to operate its primary bridge circuit based on the received phase offset angle data.

56. A power system as claimed in claim 55, wherein each phase offset angle data is unique to at least two of primary controllers / modules.

57. A power system as claimed in claim 55 or claim 56, wherein the phase offset angle data is based on the number of effective secondary turns divided by the number of effective primary turns of the primary and secondary windings in the primary flux guide and its flux coupled secondary flux guide.

58. A power system as claimed in any one of claims 55 to 57, wherein the phase offset angle is based on the primary module position in the system.

59. A power system as claimed in any one of claims 38 to 58, wherein the system further comprises a communication interface between each primary module and the secondary module, the interface configured to establish a non-contact communication scheme whereby a data signal is superimposed on a power transfer waveform coupled between the primary winding and the secondary winding.

60. A power system as claimed in claim 59, wherein the non-contact communication scheme is configured to transmit operational parameters from each primary module to the central controller via a wireless channel, said operational parameters including one or more of cell voltage, cell current, State of Charge (SOC), State of Health (SOH), cell temperature, and primary module identification data.

61. A power system as claimed in any claim 59 or claim 60, wherein the non-contact communication scheme employs a modulated carrier signal within the same magnetic coupler used for power flow, the modulation selected from the group consisting of frequency, phase, or amplitude modulation.

62. A power system as claimed in any one of claims 38 to 61, wherein the central controller is configured to control a startup phase, comprising: connecting the secondary bridge to a power source based on one of: a supply connected to the system output, a secondary power storage device; controlling the secondary bridge to generate an oscillatory current in the secondary winding proximate to a resonant frequency; and wherein each primary module controller is configured to: control its primary bridge circuit to effectively short its primary winding during the startup phase; and synchronise its primary bridge operation to the oscillatory current detected in its shorted primary winding.

63. A power system as claimed in any one of claims 38 to 62, wherein the secondary controller is configured to communicate one or more operational targets to each primary controller of each primary module, the operational targets operable to control one or more timing operations of the primary bridge.

64. A power system as claimed in any one of claims 38 to 63, wherein the central controller is configured to: operate the secondary bridge circuit based on soft switching criteria; detect a change in system operational parameters, including an alteration to the switching frequency of the secondary bridge required to meet soft switching criteria, resulting from the physical removal of the primary module; coordinate the continued operation of the remaining primary modules based on one or more load requirements.

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