Battery management using a reactive load

Abstract

A battery system configured to manage reactive energy transfer between battery cells, which includes a switching circuit configured to selectively connect any one or more the battery cell modules with the reactive circuit and configure the relative polarity of each battery cell module connected with the reactive circuit. A controller is configured to operate the switching circuit in a first mode and a second mode, where in the first mode, the controller is configured to connect one or more of the battery cell modules through the reactive circuit to an output for an external load, and in the second mode, the controller is configured to disconnect the battery cell modules from the output and drive a reactive current in the reactive circuit by alternately connecting selected one or more battery cell modules with the reactive circuit in a polarity that influences the reactive alternating cunent phase.

Description

[0001] Battery management using a reactive load

[0002] Technical Field

[0003] The invention generally relates to battery storage systems, and in particular to a battery system for managing cell balance using reactive current.

[0004] Background

[0005] 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 battery cells.

[0006] In multiple battery cell systems, battery cells and components within a cell management system may experience changes in state of health, such as cell degradation, environmentally influenced performance issues, and part failures. There are a few known ways to measure the state of health of cells or components within a system, but such ways require the connection of external testing equipment.

[0007] It would therefore be advantageous to have the system able to self-test for performance issues or part failures without a requirement for external equipment. It is an object of the invention to go at least some way toward providing such an advantage, or at least provide the public with a useful choice. Other objects will be apparent to those skilled in the art.

[0008] Summary of the invention

[0009] In one aspect the invention broadly relates to a battery system configured to manage reactive energy transfer between battery cells, the system comprising: a plurality of battery cell modules; a reactive circuit; a switching circuit configured to: selectively connect any one or more the battery cell modules with the reactive circuit, and configure the relative polarity of each battery cell module connected with the reactive circuit; and a controller configured to operate the switching circuit in a first mode and a second mode, wherein: in the first mode, the controller is configured to connect one or more of the battery cell modules through the reactive circuit to an output for an external load, and in the second mode, the controller is configured to: disconnect the battery cell modules from the output, and drive a reactive current in the reactive circuit by alternately connecting selected one or more battery cell modules with the reactive circuit in a polarity that influences the reactive alternating current phase, thereby enabling interaction between the reactive current and selected one or more battery cell modules.

[0010] In some embodiments, the controller is further configured, in the second mode, for one or more of: determining a state of health of the selected battery cell modules, measuring electrical characteristics of the selected battery cell modules, generating heat within the selected battery cell modules, and a condition or health of one or more switches in the switching circuit.

[0011] In some embodiments, the controller is configured to: determine a phase angle of the reactive current; connect a target battery cell module to the reactive current with an opposite polarity based on the determined phase angle; measure a voltage drop across the target battery cell module for a period upon connection; and determine a state of health of the target battery cell module based on the measured voltage drop.

[0012] In some embodiments, the controller is configured to: alternate the polarity of the connection of at least a target battery cell module at a plurality of test frequencies; for each frequency, determine a dataset comprising: amplitude of the voltage, amplitude of the reactive current, and phase angle between the voltage and current; and determine a measure of the state of health of the target battery cell module based on the dataset.

[0013] In some embodiments, the controller is configured to: identify one or more battery cell modules to be heated based on a temperature criterion, and control the rate of cell heating by adjusting one or more of: the number of cell modules connected in series, the alternation frequency of the polarity change, the phase angle of the connection relative to the current phase angle, and the phase duration of the connection.

[0014] In some embodiments, the controller is configured to: control the switching circuit to create a select circuit path including a switch and one or more battery cell modules; determine one or more of a voltage or reactive current within the select circuit; and determine a fault or degradation condition of the switch or the battery cell module based on the determined characteristic.

[0015] In some embodiments, the controller is configured to determine a target reactive current, and control the target reactive current by one or more of:

[0016] • determining a number of cell modules based on one or more of: o the target reactive current, and o a state of charge criteria of at least some cell modules,

[0017] • determining an alternation frequency based on the target reactive current, and

[0018] • controlling the switching circuit and the connection of cell modules at the determined alternation frequency.

[0019] In another aspect the invention broadly relates to a battery system configured to manage reactive energy transfer between battery cells, the system comprising: a plurality of battery cell modules; a reactive circuit; a switching circuit configured to: selectively configure any battery cell modules in a series connection with the reactive circuit, and configure the relative polarity of each battery cell module connected in the series connection; and a controller is configured to operate the switching circuit in a first mode and a second mode, wherein: in the first mode, the controller is configured to: connect one or more battery cell modules to an output for an external load through the reactive circuit, and in the second mode, the controller is configured to: disconnect the battery cell modules from the output for the external load; alternate a connection of select one or more battery cell modules with the reactive filter to thereby drive a reactive current in at least part of the reactive circuit; determine the phase angle and of the reactive current; connect a target cell module with the reactive current with an opposite polarity to the reactive current based on the determined phase angle; measure the voltage drop of the target cell module for a period at the time of connection; and determine a measure of the target cell state of health based on the measured voltage drop.

[0020] In one embodiment, the voltage drop is measured over a time period of up to 10 ms.

[0021] In one embodiment, the measure of the target cell state of health is based on a determination of a cell impedance according to Vceii(drop) I Iceii.

[0022] In one embodiment, the phase angle includes the phase and polarity of the reactive current, and the target cell is connected with an opposing polarity to the reactive current.

[0023] In one embodiment, the controller is further configured to control the voltage drop based on one or more of:

[0024] • the number of cells to configured to drive the reactive current in the reactive circuit,

[0025] • a connection interval of cell modules connected drive the reactive current in the reactive circuit, • a connection interval and phase angle of the one or more cell modules meeting at least a temperature criteria, and

[0026] • the alternation frequency.

[0027] In another aspect invention broadly relates to a battery system configured to manage reactive energy transfer between battery cells, the system comprising: a plurality of battery cell modules; a reactive circuit; a switching circuit configured to: selectively configure any battery cell modules in a series connection with the reactive circuit, and configure the relative polarity of each battery cell module connected in the series connection; and a controller is configured to operate the switching circuit in a first mode and a second mode, wherein: in the first mode, the controller is configured to: connect one or more battery cell modules to an output for an external load through the reactive circuit, and in the second mode, the controller is configured to: disconnect the battery cell modules from the output for the external load, alternate, for a selection of frequencies, the polarity of a connection of at least a target battery cell module with the reactive filter to thereby drive a reactive current in the reactive circuit, for each of the selection of frequencies, determine a dataset comprising: the amplitude of the voltage the amplitude reactive current, the phase angle between the determined voltage and current; and determine a measure of the target cell state of health from the determined amplitudes and phase angle.

[0028] In one embodiment, the controller is configured to determine the cell impedance based on FFT analysis of the magnitude and phase of the impedance in the frequency domain.

[0029] In one embodiment, the controller is configured to apply a phase analyser to the determined dataset to thereby deduce the real and imaginary impedance of the target cell module, wherein the cell impedance is based on the real impedance when the imaginary impedance is zero.

[0030] In one embodiment, the controller is configured to determine an equivalent circuit including the target cell impedance, the circuit comprising a R, L and C curve fit.

[0031] In one embodiment, in the first mode, the controller is configured to control the connection of the target cell module with the external load based on the state of health measurement.

[0032] In one embodiment, in the first mode, the controller is configured to control the cell contribution of a voltage output based on the state of health measurement.

[0033] In another aspect invention broadly relates to a battery system configured to manage reactive energy transfer between battery cells, the system comprising: a plurality of battery cell modules; a reactive circuit; a switching circuit configured to: selectively configure any cell modules in a series connection with the reactive circuit, and configure the relative polarity of each cell module connected in the series connection; and a controller is configured to operate the switching circuit in a first mode and a second mode, wherein: in the first mode the controller is configured to: connect one or more cell modules to an output for an external load through the reactive circuit, and in the second mode the controller is configured to: disconnect the cell modules from the output for the external load, identify one or more cell modules to be heated based on meeting at least a temperature criteria, alternate, at a frequency, the polarity of a connection of the identified one or more cell modules with the reactive filter to thereby drive a reactive current in the reactive circuit, wherein the controller is configured to control the rate of cell heating by one or more of: the number of cell modules connected in series, the alternation frequency, the phase angle of the connection of the one or more cells relative to the current phase angle, and the phase duration of the connection of the one or more cells relative to the current phase angle.

[0034] In one embodiment, the temperature criteria comprises one or more of: a temperature of one or more battery cells is below a predetermined temperature threshold, and a rate of change of temperature is below a predetermined temperature threshold.

[0035] In one embodiment, the controller is further configured to remove one or more cells from the connection of any one or more cell modules when a cell temperature reaches one or more of:

[0036] • the predetermined temperature threshold,

[0037] • the predetermined rate of temperature increase, and

[0038] • a voltage threshold.

[0039] In one embodiment, the controller is further configured to identify one or more cell modules to be heated based on meeting a state of charge criteria.

[0040] In another aspect invention broadly relates to a battery system configured to manage reactive energy transfer between battery cells, the system comprising: a plurality of battery cell modules; a reactive circuit; a switching circuit comprising switches configured to: selectively configure any cell modules in a series connection with the reactive circuit, and configure the relative polarity of each cell module connected in the series connection; and a controller is configured to operate the switching circuit in a first mode and a second mode, wherein: in the first mode the controller is configured to: connect one or more cell modules to an output for an external load through the reactive circuit, and in the second mode the controller is configured to: disconnect the cell modules from the output for the external load,

[0041] • control the switching circuit to drive a reactive current in a select circuit configuration comprising a combination of one or more cell modules and a plurality of switches of the switching circuit;

[0042] • determine one or more of a voltage and reactive current operating in the select circuit based on the control of the switching circuit, and

[0043] • determine the health status of at least one of a switch and a battery cell module in the select circuit based on the determined voltage or reactive current.

[0044] In one embodiment, the controller is configured to determine an operational health status of at least one cell module of the or at least one switch of the switching circuit, wherein, in the second mode, the controller is configured to:

[0045] • configure a series connection of a first group of components, the first group comprising a one or more cells and a plurality of switches.

[0046] • configure a series connection of a second group of components, the first group comprising one or more cells and a plurality of switches, where the first and second group share a component;

[0047] • connect the determined at least one cell in antiseries, with one or more other battery cells and the resonance circuit and rapidly alternating the polarity of the cells, to thereby control the transfer of reactive current in the battery pack.

[0048] • compare the reactive current to a predetermined reactive current, and

[0049] • determine the health status of the component shared by the first and second group based on the comparison.

[0050] In one embodiment, the controller is configured to, in the first mode, connect the one or more cell modules to an output for an external load by configuration of the switching circuit based on the determined health status of the at least one of a switch and a battery cell module.

[0051] In one embodiment, the select circuit comprises one or more of the following components:

[0052] • a cell module;

[0053] • a switch;

[0054] • a switch driver circuit;

[0055] • body diodes; • a voltage sensor;

[0056] • a current sensor; and

[0057] • wire connections between the controller and a component; and the controller is configured to determine the health status of any one or more of the components.

[0058] In one embodiment, the switching circuit comprises one or more switching circuits, each configured to:

[0059] • selectively connect zero, one or more cell modules in the series connection with the reactive filter,

[0060] • selectively bypass cell modules from the series connection, and

[0061] • selectively control the forward or reverse polarity of one or more cell modules in the series connection.

[0062] In one embodiment, the output connection is configured to selectively connect and disconnect the plurality of battery cells to a load.

[0063] In one embodiment, the reactive circuit is a low pass filter configured to receive the output of the one or more switching circuits.

[0064] In one embodiment, the reactive circuit is configured to filter an output from the plurality of battery cells when the output connection is connected to the load.

[0065] In one embodiment, in the second mode, the reactive circuit comprises a series connected inductive and capacitive component (an LC filter).

[0066] In one embodiment, in the first mode, the reactive circuit comprises an LCL filter.

[0067] In one embodiment, the controller is further configured to modulate the connection of one or more cell modules in the series connection based on one or more modulation parameters.

[0068] In one embodiment, the controller is configured to:

[0069] • determine a measured reactive current,

[0070] • compare the measured reactive current to a target reactive current, and,

[0071] • based on the comparison, change at least one of: o the alternation frequency, and o the number of series connected cell modules.

[0072] In one embodiment, the controller is configured to determine a target reactive current, and control the target reactive current by one or more of:

[0073] • determining a number of cell modules based on one or more of: o the target reactive current, and o a state of charge criteria of at least some cell modules,

[0074] • determining an alternation frequency based on the target reactive current, and

[0075] • controlling the switching circuit to create the series connection of cell modules at the determined alternation frequency.

[0076] In one embodiment, the controller is configured to:

[0077] • determine a measured reactive current, and

[0078] • change at least the alternation frequency based on a comparison between the target current and the measured reactive current.

[0079] In one embodiment, a modulation parameter comprises alternating the polarity of series connected cell modules at a frequency below the resonant frequency of the reactive filter, and increasing the reactive current comprises increasing the alternation frequency.

[0080] In one embodiment, the controller is configured to maximise the reactive current by alternating the polarity of series connected cell modules at a frequency substantially at the resonant frequency of the reactive filter. In one embodiment, a modulation parameter comprises alternating the polarity of the series connected cell modules at a frequency above the resonant frequency of the reactive filter, and increasing the reactive current comprises decreasing the alternation frequency.

[0081] In one embodiment, a modulation parameter comprises a number of series connected cell modules, and the controller is configured to control the number of series connected cells.

[0082] In one embodiment, the controller is configured to determine a measured reactive current, and change the number of series connected cell modules based on the one or more criteria comprising a comparison between a target current and the measured reactive current.

[0083] In one embodiment, the controller is configured to determine a state of charge of one or more cell modules, and based on the determined state of charge: change the number of series connected cells, or substitute one or more cell modules with one or more other cell modules.

[0084] In one embodiment, the controller is configured to modulate the connection of one or more cell modules, the modulation comprising a connection duty cycle within a connection interval, and the controller is configured to control the connection duty cycle of the one or more cell modules.

[0085] In one embodiment, the duty cycle within the connection time comprises one or more of a PWM and PDM based connection modulation during a time interval.

[0086] In one embodiment, the connection interval is based on the reactive current phase angle.

[0087] In one embodiment, the controller is configured to:

[0088] • determine a measured reactive current between the first and second cell groups, and

[0089] • change the duty cycle applied to at least one cell of one or more of the first or second cell groups based on a comparison between a target current and the measured reactive current.

[0090] In one embodiment, the one or more modulation parameters are based on one or more of:

[0091] • a determined voltage of the one or more cell modules;

[0092] • a target reactive charge current;

[0093] • a determined connection time;

[0094] • the phase angle of the reactive current;

[0095] • the connection phase of the second cell group; and

[0096] • the connection interval of the second cell group.

[0097] In one embodiment, the target reactive charge current is based on one or more of:

[0098] • a threshold reactive charge current;

[0099] • a reactive charge current limit;

[0100] • a target discharge current of the one or more battery cell modules; and

[0101] • the alternation frequency.

[0102] In another aspect invention broadly relates to a battery system configured to manage reactive energy transfer between battery cell modules, the system comprising: a plurality of battery cell modules; a switching circuit configured to: selectively configure any two or more of the battery cell modules in a series connection, configure either polarity of each battery cell module connected in the series connection; and a controller is configured to operate the switching circuit to: in a first mode: connect a series connection of one or more battery cell modules to an external load, and in a second mode: disconnect from the external load, determine the health status of a target component in a subcircuit by the steps of: controlling the switching circuit to alternatingly connect one or more battery cells in series with an internal reactive circuit, thereby creating a reactive current, determining a subcircuit to which the target component is a part of, configuring the switching circuit so that the reactive current is directed to the subcircuit determining an sequence of switching combinations and an expected voltage profile from the sequence comparing a measured voltage profile with the expected voltage profile to identify any dysfunction of the target component

[0103] In one embodiment, the internal reactive circuit is part of the battery system and is one of:

[0104] An LCL circuit

[0105] An LC circuit

[0106] In one embodiment, the one or more battery cells used to create the reactive current belongs to the target subcircuit

[0107] In one embodiment, the one or more battery cells used to create the reactive current does not belong to the target subcircuit

[0108] In one embodiment, the target component is:

[0109] A Cell

[0110] A switch (MOSFET, IGBT etc.) and its driven circuit (Gate driver etc..)

[0111] Body diodes.

[0112] A voltage sensor

[0113] A current sensor

[0114] Firmware and / or software for the switching mechanism, communication between circuits

[0115] Wire connections.

[0116] In another aspect invention broadly relates to battery system configured to manage reactive energy transfer between battery cell modules, the system comprising: a plurality of battery cell modules; a switching circuit configured to: selectively configure any two or more of the battery cell modules in a series connection, configure either polarity of each battery cell module connected in the series connection; and a controller is configured to operate the switching circuit to: in a first mode: connect a series connection of one or more battery cell modules to an external load, and in a second mode: disconnect from the external load, determine the impedance of a target cell by the steps of: controlling the switching circuit to alternatingly connect one or more battery cells in series with an internal reactive circuit, thereby creating a reactive current,

[0117] Determining a target cell to be measured for its impedance

[0118] Configure the switching circuit to include the target cell in the series connection, or

[0119] Configure the switching circuit to exclude the target cell from the series connection;

[0120] Measure the voltage drop profile in a time interval after the target cell is included or excluded from the series connection;

[0121] Determine RO impedance value based on the equation Ro = Vcell(Step) I Icell.

[0122] In one embodiment, the internal reactive circuit is part of the battery system and is one of:

[0123] An LCL circuit

[0124] An LC circuit

[0125] In one embodiment, the controller is further configured to include another cell in the reverse polarity to the target cell to cancel a DC voltage of the battery system

[0126] In one embodiment, the target cell is part of the one or more cells used to create the reactive current

[0127] In one embodiment, the target cell is not the same as the one or more cells used to create the reactive current.

[0128] In one embodiment, the controller is further configured to:

[0129] • Measure the reactive current

[0130] • determine a target reactive current value based on a desired Signal to Noise ratio.

[0131] • compare the measured reactive against the target reactive current. • change one or more of: o a number of cell modules connected in series to generate the alternating reactive current o alternation frequency of the connection based on a comparison between the target current and the measured reactive current.

[0132] In one embodiment, the alternation frequency is chosen to be near the resonant frequency the reactive circuit

[0133] In one embodiment, the time interval is at least 0.1s, 1s, or 10s

[0134] In one embodiment, the current change overtime before the inclusion I exclusion of the target cell is negligible over the time required to measure the voltage, and thus is treated as constant.

[0135] In one embodiment, the controller is configured to further perform a phasor analysis to determine the real and imaginary part of the impedance, and to determine the impedance RO when the imaginary part is zero.

[0136] In one embodiment, the controller is configured to further estimate the SOH based on the determined impedance RO.

[0137] In one embodiment, the controller is further configured to deduce an equivalent circuit of the cell impedance consisting of lumped passive components R L and C by curve fitting

[0138] In one embodiment, the controller is configured to perform FFT analysis to determine a magnitude and phase of the impedance in the frequency domain.

[0139] In another aspect invention broadly relates to battery system configured to manage reactive energy transfer between battery cell modules, the system comprising: a plurality of battery cell modules; a switching circuit configured to: selectively configure any two or more of the battery cell modules in a series connection, configure either polarity of each battery cell module connected in the series connection; and a controller is configured to operate the switching circuit to: in a first mode: connect a series connection of one or more battery cell modules to an external load, and in a second mode: disconnect from the external load, determine a parameter of first one or more battery cell modules, determine that the parameter of the first one or more battery cells is below a predetermined threshold, connect a second one or more cell modules with an internal reactive circuit to thereby generate an alternating reactive current to be conducted through the first one or more battery cell modules.

[0140] In one embodiment, the internal reactive circuit is part of the battery system and is one of: An LCL circuit An LC circuit

[0141] In one embodiment, at least one cell module of the first one or more battery cell modules is the same as a cell module of the second one or more battery cell modules

[0142] In one embodiment, the first one or more battery cell modules is not the same as the second one or more battery cell modules

[0143] In one embodiment, the controller is further configured to measure the parameter.

[0144] In one embodiment, the cell module parameter includes: a temperature a rate of temperature

[0145] In one embodiment, the predetermined threshold is one of: a minimum temperature a minimum rate of temperature In one embodiment, the controller is further configured to: determine a target value for the parameter based on one or more criteria:

[0146] The location of the cell module

[0147] The SOC of the cell module

[0148] The SoH of the cell module

[0149] The ideal operational temperature of the cell module

[0150] The ideal operational rate of temperature of the cell module

[0151] In one embodiment, the controller is configured to:

[0152] • compare the measured parameter against the target parameter

[0153] • determine a measured reactive current value

[0154] • determine a target reactive current value based on the comparison between the measured parameter and the target parameter

[0155] • change one or more of: o a number of cell modules connected in series to generate the alternating reactive current o alternation frequency of the connection based on a comparison between the target current and the measured reactive current.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] Brief description of the drawings

[0162] 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.

[0163] Figure 1 shows an exemplary battery cell structure with cell modules and a circuit module. Figure 2 shows an exemplary diagram of components within an exemplary battery system. Figure 3 shows an exemplary output of a reconfigurable battery system. Figure 4 shows a filtered output of the reconfigurable battery system of Figure 3.

[0164] Figure 5 shows an exemplary resonant circuit.

[0165] Figure 6 shows another example of a reconfigurable battery system including the resonant circuit. Figure 7 shows an example of a reconfigurable battery system including battery cells and a switching circuit.

[0166] Figure 8 shows another example of a reconfigurable battery system including battery cells and a switching circuit.

[0167] Figure 9 is a waveform indicating that cells see an inductive load as they are switched at a frequency greater than the resonant frequency.

[0168] Figure 10 is the waveform indicating that the battery system sees a capacitive load as it switches at a frequency lower than the resonant frequency.

[0169] Figure 11 shows a graph of voltage and the number of cells connected in series.

[0170] Figure 12 shows a graph of the relationship between reactive current and frequency based on components in a resonant filter circuit.

[0171] Figure 13 shows an exemplary closed loop control strategy for reactive current control.

[0172] Figure 14 shows another exemplary closed loop control strategy for reactive current control.

[0173] Figure 15 shows a simplified system diagram including cells and resonant filter components for the purpose of illustrating current control in the preceding diagrams.

[0174] Figure 16 shows a diagram of passive components of a simplified model of a battery cell where the state of health of a cell correlates to RO.

[0175] Figure 17 is a simulation circuit to demonstrate how RO, RC and C_terminal of Load 11 is representative of what the battery cell will see when it is included in the test circuit.

[0176] Figure 18 shows the cell voltage (terminal + to terminal -) step response when a cell under test is included or excluded from the test circuit, where three different RO cell resistance values are shown. Figure 19(A) shows a circuit arrangement whereby a selection of cell 271 is alternated in polarity to generate alternating voltage 272 and an thereby alternating reactive current.

[0177] Figure 19(B) shows an exemplary circuit configuration whereby a target cell under test 274 is connected in series with the circuit.

[0178] Figure 20(A) shows an exemplary voltage (solid line) of the selection of battery cells, and an exemplary current (broken line) showing the phase difference of the reactive current.

[0179] Figure 20(B) shows a time alignment between the test cell connection and the current of Figure 20(A).

[0180] Figure 21 shows a diagram of the circuit configuration with the test cell module 275 opposing the current direction and polarity of a balancing cell module 276.

[0181] Figure 22 shows a graph of exemplary reactive current and target cell voltage data for three phase cycles.

[0182] Figure 23 shows an example of a typical Nyquist plot of the internal resistance of a Lithium-ion battery.

[0183] Figure 24 can be measured from reactive current flow through the reactive filter.

[0184] Figure 25 shows an exemplary voltage (solid line) and reactive current (broken line) for ten different select circuit configurations.

[0185] Figures 26(A)-26(J) each show a particular configuration of a circuit based on a circuit module from the battery system of Figure 7.

[0186] Detailed Description

[0187] Embodiments of the invention discussed herein relate to reconfigurable battery system technology. In a reconfigurable battery system, there are cells which require balancing, and some embodiments relate to a cell balancing system which minimises or substantially eliminates energy waste, and also makes use of components already present in the system which are primarily implemented for other tasks, or have a secondary function within the system. The cell balancing system utilises a reactive filter circuit primarily used to filter the output of a switched series arrangement of battery cells. In embodiments of the system, control based on reactive filter characteristics manages energy transfer from one or more battery cells with high energy to one or more battery cells with low energy. A controller manages reactive current through the reactive filterto provide energy exchange between battery cells within the battery system, and controls the magnitude of reactive current based on control of switch modulation parameters, and the particular battery cells selected for energy exchange through the flow of the reactive current.

[0188] In this specification, the terms “energy storage module”, "battery cell unit", "cell unit" or “cell module” 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 series or parallel, or a multitude of individual battery cells, or blocks of parallel cells, or a combination 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.

[0189] Figure 1 shows an exemplary battery cell structure 10 with battery cell modules 30 and a circuit module 20. In the exemplary structure, the battery cell modules contain one or more battery cells and are attached to the circuit modules by cell terminals. The cell module, or combination of modules, may contain any number of cells in series, or parallel, or a combination of series and parallel.

[0190] The circuit module 20 includes a circuit board which supports a circuit path and electronic components which form part of and modify the circuit path. Electronic components include switching devices such as transistors, a controller for operating the transistors, and optional sensing devices. The circuit paths and electronic components together form a switching circuit configured to reconfigure the connections between battery cells in the system.

[0191] In one embodiment, the switching circuit controls the at least the series connection of any one of those cells to the cell terminals, and the polarity of any one or more cells in the series connection. For example, in a reconfigurable battery system it is common for the switching circuit to control the connection of those cells to terminals of the circuit module 20 or for the terminals to be connected such that the cells are bypassed. Polarity control of a cell or group of cells may be provided by, for example, H-Bridge or 2n+2 inverted H-Bridge circuit topologies.

[0192] Circuits for supporting cells and the arrangement of switches for controlling connected or bypassed states of cells can have many configurations. In some embodiments, the cells and associated switching circuit have a fixed number of switches, such as two, for each cell. However, in other embodiments, the switching circuit may have combinations of two or more switches which are configured to operate to connect or bypass a cell.

[0193] In preferred embodiments, a controller is provided and configured to control the switching of one or more cell modules in and out of a series configuration to target a system output voltage, and control the polarity of at least some cells in the series configuration, and further, to control the connection timing of all cell modules based on the phase of current flowing in the system. 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. 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 a switching device. In some embodiments, the controller is configured to control functionality of the system such as the determination of a target voltage, and control output signals required to operate the switching circuit of one or multiple cell modules to generate the target output voltage.

[0194] The term switching devices as used in this specification refers to a component which is capable of making and breaking an electrical connection to allow or prevent current flow, such as a relay or transistor. Various Figures in this specification show a SPST (Single Pole Single Throw) switch as an example of the switches provided. However, the present invention is not limited thereto, and it may be implemented with another switch element, for example, a power switch of MOSFET (Metal Oxide Field Effect Transistor), BJT (Bipolar Junction Transistor), IGBT (Insulated Gate Bipolar Transistor) and the like.

[0195] MOSFET based transistors are particularly advantageous for use in battery storage systems due to their speed of operation, cost and form factor. The presence of body diodes in most MOSFET devices means that two devices configured in antiseries and with common gates are typically used for the switching of bidirectional current as may be found in the system of the embodiments discussed herein. Figure 2 shows an exemplary diagram of components within an exemplary battery system 10 including battery cell modules and associated switching circuit, together forming a reconfigurable battery circuit 40. A reactive filter 50 configured to connect with the output of the reconfigurable battery circuit and in turn output a filtered response to an output connection. The output connection 60 is configured to connect the filter 50 with an output 80 which is connected or configured to connect with a load that ultimately receives energy from the battery modules.

[0196] A controller 70 is connected to at least the reconfigurable battery circuit 40 and the output connection 60. The controller is configured to operate functions of the switching circuit and in particular is configured to control the series connection of one or more battery cell modules with the reactive filter. Further, in some embodiments, the controller is also configured to control the polarity of at least some cell modules in the reconfigurable battery circuit.

[0197] The output voltage of the reconfigurable battery system is determined by the controller 70 operating to control specific switches which need to be connected and disconnected in order to connect a number of cell modules in series to achieve a target voltage. The target voltage will typically be predetermined on the basis of the output voltage requirement for the system. For example, in some embodiments, the system is configured to generate a mains output voltage which may be a sinusoidal 110 to 240V signal at 50 to 60Hz. Other examples include DC voltage applications such as would be found in an electric vehicle (EV), EV charging device, or other more general DC applications. As such, the target output voltage may be time varying or time static. A reconfigurable battery system is most often found with lithium-based cells and as such the voltage of individual cells is typically operated between 2.5 and 4.2V per cell.

[0198] In some embodiments, there are multiple controllers configured to control groups of switching devices which are arranged to control the series connection, bypass, and polarity of one or more cells. These controllers are referred to as cell controllers. In such embodiments, cell controllers are each connected to one or more switches and figured to control the switches in order to bypass or include any specific one or more cells in order to meet the target output voltage. In some embodiments, each cell controller operates under the control of a master controller which, for example, is configured to send a target output voltage requirement to the cell controllers which in turn interpret that requirement and determine whether to include or bypass cells under its control. The master cell controller is often referred to as a central stack controller. In other embodiments, the cell controllers operate together based on an algorithm which controls or determines the connection of cells. Various other control techniques are possible which operate cell controllers, connect or bypass cells and achieve a target output voltage. The collective operation of such controllers is referred to in this specification as operation of the controller 70.

[0199] Figure 3 shows an exemplary output of a reconfigurable battery system including a stepped voltage waveform which represents a battery cell being added or removed from a series connection of cells. Figure 4 shows a filtered output of the reconfigurable battery system of Figure 3 after a filter has smoothed the stepped voltage waveform. A stepped voltage output such as shown by Figure 3 may contain unwanted noise in the form of high frequency harmonics. Further, the shape of the output waveform may be desired to substantially match the smoother nature of a regular mains AC voltage waveform. Hence, filtration of the waveform is desirable in most reconfigurable battery systems. In some embodiments, the stepped output voltage comprises a positive and negative going voltage waveform which is created by control of the polarity of one or more cells connected to the system output. For example, voltage point 32 may represent a zero crossing, where upper waveform part 31 represents a positive going voltage, and lower waveform part 33 includes a negative voltage.

[0200] In some embodiments, the battery cell modules are configured to output a positive going voltage only, and a bridge circuit is configured to change the relative polarity of a cell or cells in relation to another cell or cells. In other embodiments, the polarity of each individual cell is controllable. In each configuration, all cells may be utilised for positive and negative going waveforms through polarity control of the cells during phase parts of the output waveform.

[0201] Accordingly, the controller is configured to generate DC current, or AC current based on polarity control of cells in the series configuration. The frequency of the AC current is controlled by the frequency at which the polarity of cells in the series configuration is changed, relative to the output.

[0202] Reactive filter A reconfigurable battery system has a filter configured to receive the switched output voltage from the battery cells and remove high frequency content. A reactive filter is a typical example of a filter best suited to this task, having the benefits of adequately performing the intended function and being constructed from reasonably low cost components.

[0203] In some embodiments, the reactive filter is an inductive-capacitive (LC) low-pass filter. In some embodiments, the reactive filter is a LCL filter. In some embodiments, the reactive filter is configured as an LC filter and the output filter is configured as an LCL filter, whereby LC components are shared. The sharing of components and configuration of components in the filter at any time can be provided by switching devices configured to connect L or C components in and out of the current path.

[0204] An LCL filter, also called line filter, is specially designed to suppress the switching frequency components caused by the rectifiers’ semiconductors (IGBTs). It consists of a parallel-series combination of reactors and capacitors adapted to reduce the THD(i) of rectifiers and switching circuits.

[0205] Figure 5 shows an exemplary reactive filter circuit 50 which includes a first inductor 51 and a first capacitor 52. Figure 7 also shows an output connection circuit which includes a second inductor 53 and output switches 61 , 62 configured to disconnect the filter from a load which may be connected to output terminals 80.

[0206] Observable is that the reactive filter is an LC filter which includes an inductor 51 and capacitor 52 when operating a reactive filter for the purposes of transmitting reactive current within the reconfigurable battery system when the output switches 61 , 62 are open. Further the reactive filter includes inductor 53 during operation to supply current to a load connected with the output terminals 80 to thereby form an LCL filter when the output switches 61 , 62 are closed.

[0207] In some embodiments, the reactive filter 50 further comprises a series resistor. The value of the resistance may be adjusted to change the reactive characteristics of the filter. Inclusion of a resistor may be beneficial in circumstances where alteration of the reactive characteristics is desirable, such as the resonant frequency, and may lack benefit if the value of the resistance is too high such that non-negl igible power is dissipated in the resistor, thereby impacting system efficiency.

[0208] Figure 6 shows another example of a reconfigurable battery system 40 including the reactive circuit 50. In particular, the battery system 40 depicts series configuration where there is a first one or more battery cells 41 configured with a first polarity. An AC current is generated by rapidly alternating the polarity of each cell in the series configuration of at least the battery cells 41 configured with the first polarity.

[0209] When output switches 61 , 62 are closed, the reactive filter includes the second inductor 53 and the battery system supplies current to the load, shown here as the mains grid with nominal series resistance. When the output switches 61 , 62 are open, the reactive filter 50 includes LC components, current is not supplied to the second inductor 53, nor to the output load, and instead reactive charge current flows between battery cells within the battery system.

[0210] The battery system also depicts a second one or more battery cells 42 which are configured with a second, opposite polarity. The second one or more battery cells are connected in the circuit based on parameters determined by the controller 70, including the phase angle of any reactive current and the state of the output switches. The second one or more battery cells 42 can be considered a cell under test, in some embodiments, and are configured to receive reactive current built up in the system by the first one or more battery cells 41 to thereby achieve some functions.

[0211] In some embodiments, the system 10 includes a current measurement device 44 and the controller 70 is configured to receive a signal from the device 44 indicative of series current flowing in the circuit. When the output switches 61 , 62 are closed, the current is indicative of current supplied to the load on the output. When the output switches 61 , 62 are open, the current is indicative of the reactive current in the cell modules and reactive filter.

[0212] The controller 70 is configured to execute control of the switching circuit parameters based on the current measurement to change the characteristics of current flow. Circuit parameters include the number of battery cells connected in series, bypassed from the series connection, the polarity of any one or more cells in the series connection, and the frequency of alternating current generated by the cells by control of effective alternating polarity state of cell modules in the series configuration, and the phase timing of the connection and disconnection events of cell modules.

[0213] Example reconfigurable battery cell circuits

[0214] The battery system of various embodiments includes a circuit module comprising a pair of output terminals configured to provide a target output voltage. The module comprises a string of cell modules, each cell module comprises a first terminal and a second terminal, at least one cell, and a switching circuit configured to operate in at least the following states: a state to connect the first terminal to the second terminal thereby bypassing the at least one cell, or a state to connect the at least one cell between the first terminal and the second terminal.

[0215] The controller is configured to control the switching circuit of each cell module to provide the target output voltage. The controller is configured to control of the switching circuit of one or more cell modules to meet the target circuit module output voltage by a combination of: series connection of one or more cell modules with the output terminals, and modulation of the switching state of at least one cell module such that the target voltage is substantially provided at the circuit module output terminals. For example, the controller will determine a set of cell modules for series connection to meet a target output voltage within a predefined time increment, then control the switching circuit of one or more cell modules comprising a combination of series connection of one or more cell modules with the output terminals, and optionally modulation, within the predefined time increment, of the switching state of at least one cell module such that the output voltage is substantially provided at the circuit module output terminals.

[0216] Figure 7 shows an example of a reconfigurable battery system 40 including battery cells and a switching circuit which supports the series connection of each cell, the bypassing of each cell from the series connection, and the polarity of each cell in the series connection. In this circuit, there are 2n+2 switches for n battery cells.

[0217] A 2n+2 battery circuit has a sequence of cell modules, each with positive and negative terminals. Each terminal is connected to an adjacent opposing polarity terminals of another cell module via a switch. Each cell module can therefore be connected to an ‘upstream’ cell terminal by the upstream switches, and connected to a downstream cell terminal by the downstream switches. The end of the sequence has a further two switches for completing the circuit.

[0218] In Figure 7, there are four cells shown, but it will be appreciated that there may be any number of cells configured in the circuit. In one example, each cell may be two or more cells placed in parallel such that they act like a single, larger capacity cell. In another example, each cell may be two or more cells configured in series such that they act like a single cell with a higher voltage. Other combinations of series and / or parallel cells may be used in place of those shown.

[0219] In this example, the switching circuit is configured such that each cell is connected with four switches. For example, cell 423 is connected to four switches 412, 413, 416 and 417. The four switches are configured such that two switches are directly connected to a first terminal of the cell, and two switches are directly connected to a second terminal of the cell. One of the two switches connected with opposite cell terminals is shared by an upstream adjacent cell. The other of the two switches connected with opposite cell terminals is shared by a downstream adjacent cell. Cells are also arranged such that the cell terminals have opposing polarity compared to adjacent cells.

[0220] The arrangement of the switching circuit is such that any one or more cells may be configured with an opposing polarity to any one or more other cells. This means that any cell may redistribute energy to any other cell. Various cell configurations are possible for connection to the reactive filter 50. Examples are as follows:

[0221] In one exemplary configuration, cells 420, 421 , 422 and 423 can be placed in series with a first polarity by closing switches 410, 415, 412 and 417. A second opposing polarity of these cells can be achieved by closing switches 414, 411 , 416 and 413.

[0222] In another exemplary configuration, cells 420 and 421 can be configured with a first polarity and in series with cell 423 which are in a second, opposing polarity. In this example, switches 414, 411 , 412 and 417 are closed. Or alternatively, switches 410, 415, 416 and 413 are closed to achieve the opposite polarity. In practice, to achieve alternating current, these two sets of closed switches are alternated between at a frequency operated by the controller to achieve an alternating current which flows through the reactive filter 50.

[0223] Alternating current is achieved by rapid switching between the two cell polarity arrangements in the series configuration.

[0224] Figure 8 shows another example of a reconfigurable battery system 40 including battery cells and a switching circuit. In this example, there are two sets 71 , 73 of battery cells configured where any cell may be connected in series with any other cell, or bypasses any cell from the series configuration of the set. Each set of battery cells is connected with a full bridge circuit 72, 74 such that the resulting polarity output from each string of cells is able to be alternated. In this way, the first string of cells 71 is able to be connected in series with the second string of cells 73. The polarity of each set of cells in the series connection may also be set by the configuration of each bridge such that the sets may be connected with like polarity, or opposing polarity. In such embodiments, the controller 70 is connected to the full bridge circuits and configured to control the output polarity from each bridge.

[0225] Other similar circuit configurations are possible while achieving the requirement of cells being controlled to have the same or opposing polarity with other cells. For example, the circuit of Figure 8 may be altered such that only one bridge circuit is present on the output of one cell string.

[0226] Operation of the controller 70

[0227] The controller 70 is configured to execute a number of control strategies in order to effect the creation and control of reactive current energy, and direction of that reactive current for one or more functions. In one embodiment, the controller is configured to control the magnitude of current flow from one or more cells configured with a first polarity to one or more cells configured with a second polarity. Accordingly, in some embodiments the controller is configured to operate in at least two modes. In the first mode, the output switches 61 , 62 are closed such that the battery cells are connected to the load output through the reactive filter, and the controller is configured to operate the switching circuit of the reconfigurable battery cells in order to produce a target output voltage and connect the cells to the output applicable forthat load. The target output voltage may be DC or AC or a time varying DC target such as that observable in Figure 3.

[0228] In the second mode, the output switches 61 , 62 are open such that cell modules are disconnected from the output 80. In the second mode, the controller is configured to build a reactive current to a target level and is configured to do so by one or more control strategies. The reactive current is generated by switching a group of cells in and out of series with the reactive filter to create a variable voltage overtime. When building the reactive current, the controller is said to be driving the reactive current by the control of the number of cells in the first group, polarity of the cells in the first cell group, and the timing of the connection of cells in the first cell group, to the effect of generating an AC reactive current through the reactive filter.

[0229] In some embodiments, a second cell group is connected based on the phase angle of that reactive current. However, the first and second cell groups may contain the same cell modules such that in one polarity, one or more cell modules drive the reactive current, and in another polarity, the one or more cell modules are configured to receive the reactive current. The controller is configured to control the connection time and polarity of one or more cells relative to the phase angle of the current to thereby control the cells ability to drive or receive current. Therefore there is a circuit configuration where a cell module will supply reactive current, and another circuit configuration where the controller is configured to receive the reactive current.

[0230] In some embodiments, the timing of the connection of cells from each cell group will depend on the frequency of operation relative to the resonant frequency of the filter, and whether the cells supplying energy see a primarily capacitive or inductive load, and therefore whether reactive current will lead or lag the voltage. Accordingly, the controller is configured to connect cells to receive reactive current based on a phase angle determination and the frequency of operation. The phase angle of connection of cells in the series configuration depends on the cyclic and alternating connection of the cells, and therefore the frequency of alternating reactive current generated in the system. Figure 9 and Figure 10 demonstrate the phase difference between the current and voltage in the circuit, depending on the AC current frequency relative to the resonant frequency of the filter. Figure 9 is a waveform indicating that cells see an inductive load as they are switched at a frequency greater than the resonant frequency. The combined cell voltage (Vstack) and combined cell current (l(B8)) of the cells which supply current have a 90-degree phase shift in which the voltage leads the current. However, the voltage of the cells to receive (Vcellincharge)) have a 0-degree phase shift to the current. It should be noted that regardless of whether the cells supplying current see an inductive or capacitive load, the cells that receive current always see a resistive load (0 degrees phase shift). Figure 10 is the waveform indicating that the battery system sees a capacitive load as it switches at a frequency lower than the resonant frequency. The Stack voltage (Vstack) and stack current (l(B8)) have a 90-degree phase shift, in which the current leads the voltage. However, the voltage of the cells to be charged (Vcellincharge) still has a 0-degree phase shift to the current.

[0231] The phase angle of the current, relative to the voltage, is shown in Figures 9 and 10 as being about 90 degrees apart. However, as the AC current frequency tends toward the resonant frequency of the filter, the phase difference will tend toward zero. At the resonant frequency, the phase angle will be zero such that the reactive current is in phase with the voltage. Embodiments of the invention include connection of cell modules based on the phase angle of the reactive current relative, which is in turn based on the AC frequency and resonant frequency of the filter.

[0232] It should also be noted that the voltage of the cells supplying energy (first group of cells), and those receiving energy (second group of cells) are each shown as positive voltages for the purpose of illustrating the voltage of the combined cells. However, the polarity of the cell receiving energy is connected opposite to that of the current and hence the relative voltages of cells connected in the circuit are the opposite at any one time. The connection timing between the first and second cell groups may overlap such that each cell is connected in the series configuration at the same time, or they may not overlap such that the first group of cells is disconnected from the series configuration at the time when the second group is connected. The connection timing depends on the phase of the current, with the second group of cells connected based on the phase of the current, the connection interval, and the desired function to be achieved by the energy transfer.

[0233] Controller - modulation parameters

[0234] The controller is configured to make use of the reactive filter as an impedance control device to thereby control the magnitude of reactive current flowing in the circuit. Although some power is stored in the LC circuit during resonance, it is reactive power only and negligible. The reactive filter used as an impedance control device produces a very high current capability and ability to operate with arbitrarily high current (limited only by the Q of the resonant filter).

[0235] In some embodiments, the controller is configured to determine data from each cell module, the cell data indicating criteria which may be used to select cells for a group of cells, comprising one or more of: voltage, state of charge, temperature, age, measured service life, predicted service life, rate of temperature change, internal resistance, position in a series arrangement, state of health, charge current ability, discharge current ability. The controller may be configured to determine a rank for each cell module based on the determined cell data, the rank also being a selection criteria. In some embodiments, the controller is configured to determine a rank for one or more cells based on a weighted combination of two or more determined cell data parameters.

[0236] The controller is configured to control one or more modulation parameters within the system. The parameters are those which have an effect on the magnitude of the current which flows from cell modules in the first group (cells to be discharged, or source cells) and cell modules in the second group (cells be charged, or sink cells). Parameters include the switching frequency which builds the AC reactive current, the number of cell modules in the first group and therefore the voltage and potential current, the connection interval of the first and / or second cell module groups, and the connection timing relative to the current phase of the second cell group and therefore the power factor and current transfer efficiency. Any of the above parameters may be combined as desired to control current transfer between the first and second cell module groups. The following exemplary strategies provide an overview of how each parameter may be controlled. In a first exemplary reactive current control strategy, the controller is configured to control the number of cells connected in series with a first polarity and a number of cells connected in series with a second opposing polarity. The voltage of the reactive energy is a contributing factor in the potential reactive current magnitude. Figure 11 shows a graph of reactive current for a number of cells connected in series at an arbitrary polarity switching frequency of 3 kHz. It is observable that the reactive current will ‘step’ between levels based on the number of cells connected in series. The magnitude of any given step will be determined by the voltage of the cell being connected in the series configuration. Accordingly, in some embodiments, the controller is configured to determine a target reactive current, and configure a series connection of cells which closely matches that target. In some embodiments, the controller is configured to measure the voltage of cells available for discharge and for connection in the series configuration, and connect those cells which best matches the reactive current target. For example, cells to be discharged are selected based on a combined voltage output.

[0237] In a second exemplary reactive current control strategy, the controller is configured to control the polarity alternation switching frequency of cells connected in series when driving the reactive current. The reactive current magnitude is dependent on the alternation frequency (AC current frequency) and the resonant frequency of the reactive filter. Figure 12 shows a graph of the relationship between reactive current and frequency based on arbitrary components in an LC reactive filter circuit. It is observable that the resonant frequency of the reactive filter provides the largest possible reactive current magnitude.

[0238] In some embodiments, a range of frequencies (f min to f max) would be such that they provide an equivalent change in the fine control of current (when applied to the LC circuit) compared to adding or subtracting one cell from the coarse control of the first exemplary reactive current control strategy. In some embodiments, the f min and f max would be extended to include a range of current adjustment which exceeds that of the first exemplary reactive current control strategy amount to ensure that component variations in the LC circuit are tolerated. In some embodiments, the controller is configured to commence frequency based control from f min. In some embodiments, the controller is configured to commence frequency based control from a frequency approximately midway between f min and f max.

[0239] In a third exemplary reactive current control strategy, the controller is configured to control a modulated connection of one or more cells in the series connection. For example, the modulated connection is PWM based modulation, where the duty cycle of the connection provides for a connection time variable from 0-100% of any cell relative to the connection time of another cell. Accordingly, PWM connection control is operable to provide a variable contribution to RMS current based on the PWM connection duty cycle.

[0240] In some embodiments, the controller is configured to commence PWM control with duty cycle = 0 which indicates the effective rms stack voltage is 0V. The rms voltage of the combined series cells is then increased so that a target current can be achieved. In some embodiments, the controller is configured to determine the difference between a target voltage and a measured voltage, then based on that difference, change the duty cycle to modulate the output voltage to get a higher voltage from the combined series cell combination.

[0241] The controller is configured to control the AC current frequency either below, at, or above the resonant frequency. Below the resonant frequency, the switching frequency is slower which may be beneficial based on the available processing speed of the controller. However, switching devices such as MOSFETS are required to be ‘hard switched’ which may lead to switching induced energy inefficiencies. Above the resonant frequency, the cell switching devices in the switching circuit see an inductive load. The switching devices can be at a zero crossing of the AC output voltage, or current, to reduce switching related energy inefficiency. However, transient voltages may be generated meaning voltage clamping is needed to protect the switching devices. For optimised energy efficiency, operating above the resonant frequency is desirable. Operating at the resonant frequency offers the largest amount of reactive current transfer. This may be desirable where high current or time critical current transfer tasks are desired.

[0242] In a fourth exemplary reactive current control strategy, the controller is configured to control the phase timing and interval of connection of one or more cells in the series connection with the reactive filter based on a power factor determination. While this control strategy is similar to that of the PWM based example above, here, the timing of connection is based on connecting one or more cells relative to the phase timing of the current and voltage, and therefore the power factor. The power factor is defined as the cosine of the phase angle between voltage and current and represents the instantaneous power and its direction. A lagging power factor is one in which the current is lagging behind the voltage and is characteristic of an inductive load. A leading power factor is one in which the current is leading the voltage and is characteristic of a capacitive load. Therefore the controller is configured to determine a connection time of the one or more cells relative to the phase angles of the voltage and current, which are determined by the frequency of the AC current relative to the resonant frequency of the filter. Figure 9 shows the current leading the driving voltage (upper graph) by about 90 degrees, and the connection interval of the cells (lower graph) centred around the current peak where the power factor is highest. Other connection intervals and timing of connections are possible based on a desired power factor. For example, the connection timing and interval is aligned according to a desired power factor which is a method of controlling the rate of charge transfer.

[0243] In a fifth exemplary reactive current control strategy, the controller is configured to control the connection of a resistive device in series with the LC components of the reactive filter. As mentioned above, the resonant characteristics may be alternated by the addition of series resistance in the reactive filter, and in particular to reduce the sensitivity of the resonant peak.

[0244] In some embodiments, the controller is configured to change the number of series connected cells based on a reactive current measurement, such as from the current measurement device 44. In some embodiments, the controller is configured to change the resonant frequency based on a reactive current measurement, such as from the current measurement device 44. In some embodiments, the controller is configured to connect a resistive device in series with the LC components of the filter based on a reactive current measurement, such as from the current measurement device 44.

[0245] In some embodiments, the controller is configured to combine any two or more of the above reactive control strategies. For example, the controller is configured to control the connection of a number of cells in series, then based on a reactive current measurement, change one or more of the resonant frequency and / or number of cells in series. In this specification, the ability of the controllerto change a configuration or operational characteristic of the reactive current is known as a modulation parameter. Therefore, in some embodiments, the controller is configured to operate in a closed loop based on a reactive current feedback signal and adjusts on or more modulation parameters based on that signal. In one exemplary embodiment, the controller is configured to configure a predetermined number of cells in series in accordance with the first exemplary reactive current control strategy. The number of cells is determined by a table which correlates between a current target and number of cells required to substantially effect that current target. The number of cells can be changed or the implementation of any one or more other exemplary reactive current control strategies based on a feedback signal indicative of the current in the circuit.

[0246] In some cases, the resonant frequency is predetermined. In some cases, the frequency is changed to be higher, and if current trends away from the target current, the frequency is changed to be lower. In some cases, the frequency is changed to be lower, and if current trends away from the target current, the frequency is changed to be higher. Predetermination of the resonant frequency would not be required in this instance.

[0247] In some embodiments, the state of charge (SOC) of one or more cells to be charged acts to interrupt a balancing charge control routine. For example, if a cell that has lower SOC (charging) reaches the target SOC, the controller will stop the battery system from generating current. In another example, if one or more cells that have a higher SOC (discharging) reaches a SOC limit, the controller is configured to select a new cell to be discharged to provide energy to the cell that needs to be charged. Accordingly, in some embodiments, the controller is configured to operate the switching circuit to configure cells into and out of the series configuration based on the SOC of any cell.

[0248] Cell ranking

[0249] Various embodiments discussed in this specification may use a cell ranking process as the determination for which cells should be prioritised to be charged, discharged, or both. A voltage target is defined by time varying amplitude and phase, and the controller is configured to control, at predetermined time intervals, the series connection of one or more cell modules and the modulation of the switching state over time based on the time varying amplitude and phase.

[0250] The controller is further configured to determine the target circuit module output voltage; and control the modulation duty cycle of the switching state of at least one cell, or cell module to meet the target circuit module output voltage. To do so, the controller is configured to determine the target circuit module output voltage and control the modulation duty cycle of the switching state of one or more cell modules based on the determined rank to meet the target circuit module output voltage. The determined rank of each cell module can be used to prioritise a higher modulation duty cycle of the switching state to those cell modules with a higher rank and / or a lower modulation duty cycle of the switching state to those cell modules with a lower rank. Modulation of the stitching state includes pulse width modulation (PWM), pulse density modulation (PDM), and any other form of modulation where connection time can be varied across a known interval.

[0251] In some embodiments, the controller is configured to determine a weighting factor attributing a modulation duty cycle priority to each cell module based on the determined rank, and control the modulation duty cycle of the switching state of each ranked cell module based on the weighting factor. The weighting factor may define an even distribution across the ranked cell modules. However, the weighting factor may also be used to define a nonlinear distribution across the ranked cell modules. Therefore, the controller is configured to control the energy distribution across multiple cells by executing a process with the following steps:

[0252] • determine a weighting factor assigning a cell contribution to one or more cells;

[0253] • determine a number of cells for connection to meet the target output voltage;

[0254] • control the switching circuit each cell module comprising a combination of: o series connection of one or more cell modules with the output terminals, and o modulation of the switching state of at least one cell module based on the weighting factor such that the output voltage is substantially provided at the circuit module output terminals;

[0255] • determine a new weighting factor based on cell data and / or cell rank; and

[0256] • determine a new number of cells for connection to meet the target output voltage;

[0257] • control the switching circuit of each cell module such that the output voltage is substantially provided at the circuit module output terminals based on the new number of cells.

[0258] In some embodiments, the controller is configured to control modulation applied to any one or more cells based on the weighting factor. For example, the controller can determine the target circuit module output voltage, determine the output voltage, determine the difference between the output voltage and the target voltage, then, based on the difference: adjust the weighting factor attributing the modulation duty cycle priority to each cell module based on the determined rank, and control the modulation duty cycle of the switching state of each ranked cell module based on the weighting factor. The weighting factor can be directly attributed to the modulation duty cycle applied to the connection of any cell in the series configuration. Accordingly, the controller is configured to map the weighting factor to the modulation duty cycle priority to each cell module based on the determined rank, and control the modulation duty cycle of the switching state of each ranked cell module based on the weighting factor. A feedback signal, such as one or more of reactive current flow in the series configuration and the voltage of any one or more cells can be used to adjust the modulation duty application to any one or more cells. Therefore, in some embodiments, the controller is further configured to measure a feedback signal from the system, and adjust the modulation duty cycle applied to any one or more cell modules based on the feedback signal. Other cell ranking based functions are possible for implementation, such as those described in Australian patent application number 2023902371.

[0259] Closed control loop

[0260] In some embodiments, the controller is configured to adjust one or more modulation parameters based on a feedback signal. The following diagrams outline possible closed loop control strategies operable by the controller to target a desired AC current flow.

[0261] Figure 13 shows an example diagram of a closed loop controller process where a proportionalintegral (PI) control loop is implemented as part of the feedback control to prevent or minimise fluctuations and target a setpoint. In particular, the controller is configured to receive or determine a target requirement for reactive current distribution between two or more cells in the system (Istack_req). The controller is configured to implement one or more reactive current control strategies as discussed above. The reactive current measurement is determined from a current sensor signal and combined with the target requirement. The PI control loop is configured to filter the reactive current control strategy based on its tuning parameters.

[0262] Figure 14 shows another exemplary closed loop control strategy diagram for reactive current control. A PI control loop is implemented as part of the feedback control to prevent or minimise fluctuations and target a setpoint. The Ki / s term is the integral overtime of an error term with a constant gain. This helps the PI controller to converge the error over time to zero, that is when the measured current is equal to the desired target current. The gain is selected to bring convergence in sufficient time without unstable or oscillatory side effects.

[0263] Figure 15 shows another exemplary closed loop control strategy for reactive current control. A PIR control loop is implemented as part of the feedback control to prevent or minimise fluctuations and target a setpoint. The PIR control loop includes a feed forward term, where a Kf term provides an estimate of the compensation required, leaving only a small error forthe Kp and Ki / s functions to address. This control loop is optimised to compensate for a high Q of an LC filter and may be advantageous when operating a wide range of the frequency that is close to the resonant frequency. The speed of current change of frequency becomes large around the resonant peak of the reactive filter, and the gain of the controller may not be not enough to follow the shape of the current.

[0264] Therefore, a high gain around the resonant frequency of the reactive filter is advantageous to compensate for a lack of response speed.

[0265] Controller - phase angle and control of switch timing

[0266] The controller is configured to operate the switching circuit to control the connection of series and anti-series aligned cells over the phase of an AC cycle. As discussed elsewhere in this specification, the phase angle of the AC reactive current will lead or lag the voltage depending on the switching frequency relative to the resonant frequency of the reactive filter. In most circumstances, operating the reactive filter predominantly in the inductive regime is mostly more advantageous, meaning the polarity switching or alternation frequency and resulting AC reactive current frequency is above the resonant frequency of the filter. The phase angle and connection interval of cells is controllable to achieve many advantageous functions. The controller can measure the reactive current and thereby determine the phase angle of the current by use of a current sensor configured in series with the cell modules. In some embodiments, the controller is configured to calculate a predicted phase angle of the current based on known or predetermined, or determined component values in the circuit.

[0267] In some embodiments, one function of the controller is to target a desired power transfer of energy. In some embodiments, the target power transfer is zero, in others, it is a maximum.

[0268] Antiseries cells are those configured with a polarity opposite to that of the current polarity, i.e., are orientated negatively for a positively going current and vice versa. This means that some cells are configured with a first polarity, and some cells are configured with a second, opposing polarity. Depending on the phase timing of cell connections, the same cell may be connected in both polarities over the waveform, switched based on the phase angle. The configuration and timing of connection in the series configuration of cell groups depends on the phase angle of the current.

[0269] Figures 9 and 10 show examples where the connection phase angle of cells (lower graphs) are connected for an interval substantially centred about the maxima of the AC current as that is where the power factor is the highest at that reactive current frequency. The rate of current transfer between cells can be controlled by the connection timing including the phase angle of the connection and the interval across the AC current waveform as detailed above as one of several modulation techniques. In Figure 10, the antiseries cells are shown to be connected for an interval where the series cells are not connected. However, the connection interval of the antiseries cells, and series cells, and operation frequency determines whether there overlap in the connection timing occurs. At or near the resonant frequency of the reactive filter, where current transfer is highest, will require the series cells and antiseries cells to be connected at the same time.

[0270] Controller method - cell impedance measurement

[0271] Cell impedance measurement can be an important factor in determining the state of health of a cell since it is understood by those skilled in the art that cell impedance, and change of impedance over time, is related to cell health. In some embodiments, the controller is configured to determine the impedance of a cell module based on control of reactive current in the circuit. Figure 16 shows a diagram of passive components of a simplified model of a battery cell where the state of health of a cell correlates to RO. Figure 17 is a simulation circuit to demonstrate how RO, RC and C_terminal of Figure 24 can be measured from reactive current flow through the reactive filter. Load 11 is representative of what the battery cell will see when it is included in the test circuit. In practice, a reactive current is built by a first cell group, and that current is then directed to a cell under test when it is switched into the series configuration of the circuit. A measurable voltage response is used to derive cell impedance.

[0272] Figure 18 shows the cell voltage (terminal + to terminal -) step response when a cell under test is included or excluded from the test circuit, where three different RO cell resistance values are shown.

[0273] The following table represents a relationship between an observable voltage dip of the terminal voltage and different cell resistances RO. The current and voltage data may also be used to deduce the equivalent circuit including the lumped passive components R, L and C in Figure 24 by curve fitting, if desired.

[0274] The controller is configured to determine the cell impedance measurement by implementing the following process steps.

[0275] At a first control step, the controller is configured to build a reactive current in the battery system at a desired frequency. Higher current produces more voltage dip than lower currents for any given resistance, therefore the controller is configured to build sufficient current by including more cells in the series configuration, and / or by alternating the polarity of cells at or near the resonant frequency of the filter, as may be required. Accordingly, the controller configures a selection of cell modules 271 connected in series, and alternates the polarity of the selection 271 at a desired frequency to thereby generate an alternating voltage 272 in the circuit. It should be noted that the controller is operating in the second mode whereby the load is disconnected. Accordingly, the circuit output switches 61 , 62 are open.

[0276] Figure 19(A) shows a circuit arrangement whereby a selection of cell 271 is alternated in polarity to generate alternating voltage 272 and an thereby alternating reactive current. A current sensor 273 may be connected in the circuit for current measurement the controller may use for determination of the current phase angle offset from the voltage. Figure 20(A) shows an exemplary voltage (solid line) of the selection of battery cells, and an exemplary current (broken line) showing the phase difference of the reactive current.

[0277] At a second control step, the controller is configured to connect a target cell for conducting a state of health measurement. The controller is configured to connect the target cell in series with and in the opposite polarity of the reactive current. At the time of connection, the cell voltage will drop by an amount which correlates with the cell impedance and therefore a state of health metric for the cell. The timing of the connection is based on the phase angle of the current. The most desirable connection time is shortly before or at where the peak current occurs in the current waveform as this will ensure a sufficient current is applied to the cell which has been found to improve the signal to noise ratio of the measurement. However, the particular phase timing will depend on desired current to be connected with the target cell, and other circuit factors such as how much current is available for testing. Accordingly, in some embodiments the controller is configured to ensure a minimum current is reached, and may do so by a method including operating at an alternation frequency which meets or is close to the resonant frequency, and / or configuring enough cells in series to generate enough voltage and / or other current control techniques. Figure 19(B) shows an exemplary circuit configuration whereby a target cell under test 274 is connected in series with the circuit.

[0278] Figure 20(B) shows a time alignment between the test cell connection and the current of Figure 20(A). Figure 20(B) also shows the resulting voltage across the test cell 274 (solid line) and the current delivered to the cell (broken line) during the connection interval.

[0279] Figure 20(C) shows the voltage drop over the instant the target cell is connected to the reactive current flow. Figure 20(D) shows the near instant current gain at the time of the voltage drop. The controller is configured to measure the voltage drop and current over this time period to thereby determine a correlation with cell impedance. In some embodiments, the controller is configured to deduce the equivalent circuit consisting of lumped passive components R L and C by curve fitting. The majority parameter that impacts the SOH is R0, where R0 is defined as Veen (drop) I Iceii.

[0280] The controller is configured to determine the R0 data to thereby determine a measure of the SOH of the cell. The current data is indicative of a linear relationship where the relationship of SOH vs R0 required minimal data to be sufficiently mapped and therefore allow the predetermination of a range of values based on measurement of a select few values. The predetermined range may be stored by the controller as a look-up table directly translating voltage drop to impedance or another SOH metric.

[0281] Data recorded during testing indicates a linear relationship between SOH and R0 such that a R0 measurement directly correlates to a SOH measurement. Accordingly, the controller can determine a SOH indication directly from R0 determinations. Within a battery system having many cells, each cell may be ranked based on R0 measurements. The measured voltage and current of the target cell can be used to determine real values of R0 based on one or more further processes, discussed as follows.

[0282] Figure 19(A) shows the resulting circuit diagram where one or more cell modules 271 are connected to the reactive filter and alternated in polarity by the switching circuit to thereby generate the alternating voltage and reactive current. Figure 20(A) shows the exemplary alternating voltage (solid line) and alternating current (broken line) measured by the current measurement device 273 where there is a phase offset between the waveforms.

[0283] When the alternating current has reached a desired level, the controller is configured to disconnect the cell modules from the circuit. At the same time, a target cell and one other cell for balancing the DC voltage is connected to the circuit and therefore the alternating reactive current. Further, the target cell is connected to the circuit with the opposite polarity to the alternating current, and the balancing cell is connected with the like polarity to the alternating current, therefore configuring the cell modules with opposing polarity. Figure 21 shows a diagram of the circuit configuration with the test cell module 275 opposing the current direction and polarity of a balancing cell module 276.

[0284] The controller is configured to measure the reactive voltage, the reactive current, and the voltage of the target cell for several current phase cycles. Figure 22 shows a graph of exemplary reactive current and target cell voltage data for three phase cycles.

[0285] The cell impedance can be determined from a variety of controller implemented methods, outlined as follows. In the first cell measurement method, the controller is configured to operate the battery system to conduct the following steps:

[0286] • Building the reactive current by alternating the first group of cell modules at a desired frequency, such as less than 100Hz.

[0287] • Selecting the cell for the impedance measurement and configuring that cell as the cell in the second cell group.

[0288] • Operating the switching circuit to configure the second cell group in phase with the peak of the reactive current. In some embodiments, the first group of cells connected in the circuit is configured to include cells with a combined voltage which cancels the DC voltage of the second group. High current provides for the best signal to noise ratio.

[0289] • Measuring the target cell voltage and reactive current with a sensing circuit operably connected with the controller.

[0290] • Performing phasor analysis to determine the real and imaginary part of the impedance. • Determining the RO based on the complex impedance, where RO is the impedance when the imaginary part is zero.

[0291] The controller is then configured to determine the measure of cell SOH based on the RO determination.

[0292] The target voltage cell measurement need only take place for as long as required to measure the voltage drop after the cell is connected. In practice, this period is about 10 microseconds since the current cannot rapidly change in a short period of time as it is limited by the inductance of the filter (di / dt). The voltage drop data then determines the SOH of the cell.

[0293] The above measurement is determinative of cell resistance, but may incorporate some influence from inductive resistive qualities. As the voltage drop occurs over a short transient, capacitive resistive effects are immeasurable.

[0294] In some embodiments, the controller is configured to execute a second process for determining cell impedance while also determining other cell properties including the C_terminal and L_terminal impedance as shown in Figure 16 and described above. This method may be considered a more accurate determination of cell state of health from the modelling of the capacitive property. In this second method, the controller implements a phaser analyser in which voltage across the cell and current flow through the cell are data points that are taken to model the RC network of the cell. The voltage across the LC filter can be taken if the reactive filter also needs to be modelled. The phase analyser determines the phase angle between the voltage and current. Using the magnitude of the impedance and the phase angle, it separates the resistance and reactance components. Finally, it calculates the resistance RO from the impedance magnitude and phase angle.

[0295] The impedance of the LC circuit at a given frequency can be determined from the voltage and current measurements using Ohm's law. The impedance of a series RLC circuit is a complex number consisting of a real part (resistance) and an imaginary part (reactance). The phase analyser calculates the phase angle between the voltage and current related to the impedance components.

[0296] To determine the resistance, the phase analyser uses the magnitude of the impedance and the phase angle. The phase analyser measures the alternating voltage across the circuit and the alternating current flowing through it. These measurements are taken at a specific frequency.

[0297] Therefore, in the second cell measurement method, the controller is configured to execute the following steps:

[0298] • A connection of a select group of one or more cells is alternated at a number of select frequencies to thereby generate an alternating voltage and reactive current at each select frequency. The select frequencies are ideally spaced apart and with enough data points for characterisation of the reactive components. For example, steps of lOOHz from 100Hz to 1 kHz would provide useful data.

[0299] • Measure the voltage of the generated alternating voltage at each step. It should be noted that the RMS voltage can be measured where the voltage is a square wave or other non-sinusoidal wave.

[0300] • Measure the reactive current at each step.

[0301] • Measure the phase shift or difference between the voltage and current at each step.

[0302] At each frequency step, the amplitude of the current will change, and further, the phase shift will also change.

[0303] • Apply the phase analyser to deduce RO (resistance) from analysis and determination of circuit model components of Figure 16 based on the modelling of the components which match with the measured phase shift.

[0304] The controller can then determine a measure of the cell state of health based on the determined value of RO. Optionally, values for L and C can be also deduced from analysis and determination of circuit model components.

[0305] In some embodiments, the controller is further configured to perform the above RO determination based on frequency analysis from the measured voltage and reactive current.

[0306] A Fast Fourier Transform (FFT) may also be used in the process of determining resistance from a measured alternating voltage and current in the circuit by analysing the frequency components of the signals. FFT is applied to both the voltage and current time-domain signals to transform them into the frequency domain and identify their constituent sinusoidal components. The FFT analysis can identify the fundamental frequency component which corresponds to the frequency of the alternating source signal - this is usually the frequency with the highest amplitude in the FFT spectrum. The amplitude and phase information of the voltage and current signals at the fundamental frequency can then be extracted. Using the amplitude and phase information from the FFT, the complex impedance at the fundamental frequency can be determined. The impedance can be expressed in terms of its real and imaginary parts. The real part is the cell resistance RO.

[0307] A Nyquist plot can be used to represent analysis of impedance characteristics of a lumping model of a battery cell, and thereby extract the resistance and reactance components. Based on the above measurements of the time-domain alternating voltage and reactive current signals. Data points can be plotted for a range of frequencies around the fundamental frequency to get a more comprehensive picture of the impedance behaviour of the LC circuit. At resonance, the inductive reactance and capacitive reactance cancel each other out, and the impedance is purely resistive. This will appear as a point on the x-axis of the Nyquist plot. Away from resonance, the plot will show the change in reactance with frequency, indicating whether the circuit is more inductive or capacitive. The presence of resistance flattens the semicircle, shifting it along the real axis (x-axis).

[0308] Figure 23 shows an example of a typical Nyquist plot of the internal resistance of a Lithium-ion battery. As mentioned above, the main parameter that impacts the SOH is RO, which is resistance at the self-resonant frequency of the lumped model where the reactance = 0. In some embodiments, the select frequencies are from 1 Hz to 1 kHz to gain a detailed view of the cell resistance in a Nyquist plot.

[0309] In the above methods, RO data is used to calculate the SOH of the cell, where there has been found to be a linear relationship. (The relationship of SOH vs RO required sufficient data to be mapped).

[0310] In some embodiments, the controller is configured to measure RO at two or more states of charge of the cell module, where the state of health of the cell module is based on a combination of the measurements. The combination is based on a statistical measure including an average, or best fit with the data.

[0311] Controller method - cell heating

[0312] A known limitation of many cell technologies is that performance degrades at low cell temperatures. For example, most lithium based cells can store energy and operate well in the standard temperature range of 20-60 °C, but performance significantly degrades when the temperature drops below zero. Performance includes current delivery ability, and can also include capacity. In some instances, it is advantageous to heat cells to ensure adequate performance should their resting temperature be low enough to affect performance for an intended application.

[0313] The controller is configured to determine a target cell or cells for heating based on a temperature measurement. The temperature measurement may be made by a temperature sensor placed proximate to one or more cells. In an electric vehicle having a cooling system connected to a bank of cells, the temperature measurement may be of a cooling system heat transfer medium. For example, the temperature of fluid coolant or metallic busbars may be indicative of cell temperature. In some embodiments, the controller is configured to determine cell temperature based on an ambient temperature measurement, and at a time the cells are dormant, or have not been subject to any substantial charge or discharge energy. The time may be indicative of the cells substantially matching the ambient temperature.

[0314] In some embodiments, the controller is configured to execute a cell heating method where one or more cells discharge stored energy which is converted to heat in that one or more cells due to the series resistance of each cell. The magnitude of heating is based on the internal resistance of the cell and the magnitude of current flowing through the cell, and in particular, the heat generated in a cell is proportional to the resistive power RO + Rc as noted by the model of Figure 16. The current is generated by the cells and controlled in the circuit as reactive current. The magnitude of reactive current is controlled by the controller largely based on the alternation frequency relative to the resonant frequency and also the number of cells used to generate the alternating current as described above with reference to Figure 11 and Figure 12.

[0315] The reactive current can be generated by just one cell and as such, a self-heating function is possible based on the energy stored in that cell. However, an increased rate of heating is achieved by higher current and therefore voltage and operation about the resonant frequency. The power factor of the alternating current is almost zero, and would be zero if the components were ideal. The nonzero component of the power factor contributes to the cell conducting resistive current. In some embodiments, the controller is configured to connect the one or more target cells based on the phase angle, including at least those phase angles where resistive current will flow. However, due to the power factor being about zero during the remaining phase cycle, cells may be connected for the full phase cycle of the alternating current. The internal resistance of the cell will determine the heating energy based on the I2R relationship.

[0316] The one or more target cells may be referred to as a target cell group. The temperature parameter may be temperature, or based on a temporal temperature determination, such as the rate of change of temperature or an absolute change in temperature. In some embodiments, the controller is configured to include one or more cells based on the temperature parameter overtime such that cells which heat quicker, or heat to a desired threshold, are removed from the group of target cells while others may remain. Similarly, new cells may be included in the target group at any time also based on the temperature parameter.

[0317] In some embodiments, the controller is configured to select cells for the target cell group based on a combination of two or more temperature parameters. For example, a cell may exhibit a rate of change significantly higher than others while being below a temperature threshold, indicating a possible cell fault. The controller may remove that cell from the target cell group based on the rate exceeding a predetermined limit.

[0318] In some instances, some cells may become relatively SOC imbalanced or fall below a desired SOC. In these instances, the controller is configured to remove these cells from the target group.

[0319] Other parameters are measurable and useful for determinations of the controller regarding cells to be heated or to supply energy for heating. For example, a cell minimum temperature and maximum temperature are determinative of a cell module ability to supply energy for heating, whereby the controller is configured to apply a threshold to temperature or rate of change of temperature. When the thresholds are exceeded, the controller is configured to disengage the cell from sourcing energy.

[0320] In some embodiments, the controller is configured to target a predetermined rate of temperature change for any one or more cells. Based on the measured rate of change, the controller is configured to increase or decrease the current. For example, if the rate of change was too high, the controller is configured to decrease current by a number of methods including reducing the power factor through a contribution controlled phase connection duty cycle, or by reducing the number of cells in series contributing to the alternating voltage and therefore current, or by adjusting the alternation frequency to move away from the resonant frequency of the reactive filter. Conversely, if the controller determines the rate of change of temperature is too low, the alternation frequency can be adjusted closer to the resonant frequency, the voltage could be increased by increasing the power factor or number of series cells, and the cell contribution duty cycle could be increased. The contribution would be controlled by connection of the cell based on the phase angle of the current, where the maximum heating would occur when connecting the cell in phase with the peak of the current.

[0321] The controller is configured to deactivate the alternating current once the cell temperature is determined to reach a threshold temperature. Due to heat soaking in a multi battery cell structure, heating a single cell higher than a desired operation temperature may be desirable such that excess heat in one cell is transferred to adjacent cells over time.

[0322] Figure 19(A) shows the configuration of a circuit where one or more cell modules are configured to generate alternating current in the reactive filter as the output switches are open to disconnect the load. Figure 20(A) shows an example of the reactive and resistive voltage and current where the current has a phase angle offset from the voltage. The voltage is shown as a sinusoid, however, the shape of the voltage waveform will be dependent on the number of cells, the timing of cell connections and the voltage levels of the cells. One single cell could be used and the voltage would exhibit a stepped form, however this would not affect the cell heating process. Multiple cells enable a voltage waveform closer to that of a sine wave to be generated. However, any number of cells is effective for heat generation. Figure 24 shows an illustrative graph indicative of the alternating reactive and resistive current, the reducing voltage of a cell and the increasing temperature of the cell.

[0323] The controller will cease cell heating based on a heating criteria being met. For example, the controller is configured to disconnect the selected at least one cell from the series connection when a cell temperature reaches one or more of: the predetermined temperature threshold, the predetermined rate of temperature increase, a voltage.

[0324] The above steps transfer energy from a cell into self-heating, or from some cells to others. In one example, half of a battery pack is configured as a first cell group, and the other half of the battery pack is configured as the second cell group. Charge may be continuously transferred back and forth between the first and second group of cells such that the balancing of cells is unaffected, all cells undertaking energy transfer undergo net discharging. In another example, one cell is operated to selfheat by connection and disconnection of the cell based on the phase angle and polarity of the current.

[0325] Accordingly, in one embodiment the controller is configured to heat cells in a reconfigurable battery system by executing a method including the steps of: disconnecting the cell modules from the output for the external load, determining one or more cell modules meeting at least a temperature criteria; alternating a connection of any one or more cell modules with the reactive filter to thereby drive a reactive current in the reactive circuit; and connecting the determined one or more cell modules meeting at least a temperature criteria with the reactive current based on an opposing polarity and a phase angle including resistive current.

[0326] In the above described method, the output connection to a load is disconnected such that the reactive current flows only in the battery system and reactive filter.

[0327] Controller method - system component health status check

[0328] The above described system potentially includes many battery cells and switches, any of which represents a possible failure point. It would therefore be advantageous to have a process operable to determine the operational status of any cell in the battery system, and any switch in the switching circuit. Accordingly, in some embodiments, the controller is configured to arrange the series configuration of cells and switches, and by changing the combination of cells and switches is able to determine that any particular cell or switch is operating as expected, or whether there may be a fault. For example, any one cell may be configured to discharge into one or more other cells. By measuring the current drawn from the discharging cell, the controller can determine whether the current is as expected, such as comparing the current to predetermined current profiles, which may be based on the SOC of the cell. Further, the switches of the switching circuit may simultaneously be determined to be operating as expected if current flows as expected. However, if a switch fault occurs, there may be an open circuit or short circuit caused by that faulty switch. Accordingly, the controller may arrange a series configuration of cells which includes and excludes the (suspected) faulty switch. The controller may be configured to do so if current is above or below what might be expected from any particular cell combination.

[0329] Referring to Figure 7, if, for example, switch 411 was to have a shorted fault condition, then cells 421 and 422 would always be connected, and closing switch 415 would cause a shorting of the cells 421 and 422. The controller may be configured to determine an output voltage from the closing of switch 415, and if the voltage was lower than expected, as caused by the shorted cells, then a fault would be noted.

[0330] In the above examples, reactive current with a low or zero power factor may be generated in the system with the external load disconnected. Components in the system can advantageously be tested by passing the reactive current through a particular circuit configuration, measuring the voltage, and comparing that voltage to that expected. Further, the controller can deduce the health of a particular component by the configuration of a first and second circuit, where the circuits contain one or more shared components, and deduce that if a voltage from each circuit matches an expected voltage, then the shared component is healthy.

[0331] Accordingly, in some embodiments, the controller is configured to determine the health status of a combination of one or more switches in the switching circuit and one or more battery cells by a process which includes controlling the switching circuit to create a reactive current between a first series configuration of one or more battery cells and one or more switches of the switching circuit, determining a reactive current operating in the circuit based on the control of the switching circuit, and determine the health status of at least one of a switch and a battery cell based on the determined reactive current. In some embodiments, the controller is configured to control the switching circuit to configure a second series configuration of one or more battery cells and one or more switches of the switching circuit, where at least one switch or battery cell is shared with the first series configuration.

[0332] For each of the first and second series configurations, the controller is configured to compare generated voltages and / or reactive currents with predetermined expected reactive currents. Where the generated current substantially matches the expected current, the controller is configured to determine that at least the component shared between the first and second series configurations is operational. However, in instances where there is an unexpected reactive current measurement, indicated by the current not substantially matching a predetermined expected current, the controller can determine the faulty component by arrangement of circuit paths including different combinations of cells and switches, with the combinations sharing different components, to thereby isolate the component which is at fault. Alternatively, the controller can treat the segment of the circuit as faulty, and remove that segment from further circuit configurations. In this way, the problem component can be avoided while maintaining an output to a load.

[0333] Therefore, in one embodiment the controller is configured to determine the health status of a select circuit configuration including a particular combination of one or more switches in the switching circuit and one or more battery cells by the steps of:

[0334] • controlling the switching circuit to drive a reactive current in a select circuit configuration;

[0335] • determining a voltage and / or reactive current operating in the select circuit based on the control of the switching circuit, and

[0336] • determining the health status of at least one of a switch and a battery cell in the select circuit based on the determined reactive current or voltage.

[0337] In one embodiment, the controller is further configured to determine an operational health status of at least one cell or at least one switch in a reconfigurable battery system by executing a method including the steps of:

[0338] • configuring a series connection of a first group of components, the first group comprising one or more cells and a plurality of switches.

[0339] • configuring a series connection of a second group of components, the first group comprising one or more cells and a plurality of switches, where the first and second group share a component;

[0340] • connecting the determined at least one cell in antiseries, with one or more other battery cells and the resonance circuit and rapidly alternating the polarity of the cells, to thereby control the transfer of reactive current in the battery pack.

[0341] • comparing the reactive current to a predetermined reactive current, and

[0342] • determining a health status of the component shared by the first and second group based on the comparison.

[0343] Figure 25 shows an exemplary voltage (solid line) and reactive current (broken line) for ten different select circuit configurations. Figures 26(A)-26(J) each show a particular configuration of a circuit based on a circuit module from the battery system of Figure 7. Figure 25 shows an expected voltage for the ten circuit configurations which correspond to the configurations shown in Figures 26(A)-26(J). In particular,

[0344] • Figure 26(A) shows a circuit configuration including a current path including switch 2 and switch 3;

[0345] • Figure 26(B) shows a circuit configuration including a current path including switch 3 and the body diode of switch 4;

[0346] • Figure 26(C) shows a circuit configuration including a current path including switch 4 and switch 4;

[0347] • Figure 26(D) shows a circuit configuration including a current path including switch 4 and the body diode of switch 1 ;

[0348] • Figure 26(E) shows a circuit configuration including a current path including switch 1 and switch 4;

[0349] • Figure 26(F) shows a circuit configuration including a current path including switch 1 and switch 4;

[0350] • Figure 26(G) shows a circuit configuration including a current path including switch 1 and the body diode of switch 2; • Figure 26(H) shows a circuit configuration including a current path including switch 1 and switch 2;

[0351] • Figure 26(l) shows a circuit configuration including a current path including switch 2 and the body diode of switch 3;

[0352] • Figure 26(J) shows a circuit configuration including a current path including switch 2 and the body diode of switch 3;

[0353] Adjacent each of the above circuit configurations is the expected voltage, the combination of which are shown by Figure 25. The controller is configured to compare the expected voltage to a predetermined voltage, based on the voltage of the battery cell module and accounting for any voltage drop from a body diode. Based on the measured voltage of the select circuit configuration, the health status of the circuit components can be deduced.

[0354] A target component may be any of those in the circuit path, including a cell module, a switch (MOSFET, IGBT etc.) and its driven circuit (Gate driver), body diodes, the voltage sensor, the current sensor. Further, other operational components includes firmware and / or software for the switching mechanism, communication interfaces and channels between circuits and wire connections.

[0355] While the invention has been described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.

Claims

1. Claims1 . A battery system configured to manage reactive energy transfer between battery cells, the system comprising: a plurality of battery cell modules; a reactive circuit; a switching circuit configured to: selectively connect any one or more the battery cell modules with the reactive circuit, and configure the relative polarity of each battery cell module connected with the reactive circuit; and a controller configured to operate the switching circuit in a first mode and a second mode, wherein: in the first mode, the controller is configured to connect one or more of the battery cell modules through the reactive circuit to an output for an external load, and in the second mode, the controller is configured to: disconnect the battery cell modules from the output, and drive a reactive current in the reactive circuit by alternately connecting selected one or more battery cell modules with the reactive circuit in a polarity that influences the reactive alternating current phase, thereby enabling interaction between the reactive current and selected one or more battery cell modules.

2. The battery system of claim 1 , wherein the controller is further configured, in the second mode, for one or more of: determining a state of health of the selected battery cell modules, measuring electrical characteristics of the selected battery cell modules, generating heat within the selected battery cell modules, and a condition or health of one or more switches in the switching circuit.

3. The system of claim 1 or claim 2, wherein the controller is configured to: determine a phase angle of the reactive current; connect a target battery cell module to the reactive current with an opposite polarity based on the determined phase angle; measure a voltage drop across the target battery cell module for a period upon connection; and determine a state of health of the target battery cell module based on the measured voltage drop.

4. The system as claimed in claim 3, wherein the voltage drop is measured over a time period of up to 10 ms.

5. The system as claimed in claim 3 or claim 4, wherein the measure of the target cell state of health is based on a determination of a cell impedance according to Vcell(drop) I Icell.

6. The system as claimed in any one of claims 3 to 5, wherein the phase angle includes the phase and polarity of the reactive current, and the target cell is connected with an opposing polarity to the reactive current.

7. The system as claimed in any one of claims 3 to 6, wherein the controller is further configured to control the voltage drop based on one or more of:• the number of cells to configured to drive the reactive current in the reactive circuit,• a connection interval of cell modules connected drive the reactive current in the reactive circuit,• a connection interval and phase angle of the one or more cell modules meeting at least a temperature criteria, and• the alternation frequency.

8. The system of any one of claims 1 to 7, wherein the controller is configured to: alternate the polarity of the connection of at least a target battery cell module at a plurality of test frequencies;for each frequency, determine a dataset comprising: amplitude of the voltage, amplitude of the reactive current, and phase angle between the voltage and current; and determine a measure of the state of health of the target battery cell module based on the dataset.

9. The system as claimed in claim 8, wherein the controller is configured to determine the cell impedance based on FFT analysis of the magnitude and phase of the impedance in the frequency domain.

10. The system as claimed in any one of claims 8 or 9, wherein the controller is configured to apply a phase analyser to the determined dataset to thereby deduce the real and imaginary impedance of the target cell module, wherein the cell impedance is based on the real impedance when the imaginary impedance is zero.11 . The system as claimed in any one of claims 8 to 10, wherein the controller is configured to determine an equivalent circuit including the target cell impedance, the circuit comprising a R, L and C curve fit.

12. The system as claimed in any one of claims 8 to 11 , wherein, in the first mode, the controller is configured to control the connection of the target cell module with the external load based on the state of health measurement.

13. The system as claimed in any one of claims 8 to 12, wherein, in the first mode, the controller is configured to control the cell contribution of a voltage output based on the state of health measurement.

14. The system of any one of claims 1 to 13, wherein the controller is configured to: identify one or more battery cell modules to be heated based on a temperature criterion, and control the rate of cell heating by adjusting one or more of: the number of cell modules connected in series, the alternation frequency of the polarity change, the phase angle of the connection relative to the current phase angle, and the phase duration of the connection.

15. The system as claimed in claim 14, wherein the temperature criteria comprises one or more of: a temperature of one or more battery cells is below a predetermined temperature threshold, and a rate of change of temperature is below a predetermined temperature threshold.

16. The system as claimed in claim 14 or 15, wherein the controller is further configured to remove one or more cells from the connection of any one or more cell modules when a cell temperature reaches one or more of:• the predetermined temperature threshold,• the predetermined rate of temperature increase, and• a voltage threshold.

17. The system as claimed in any one of claims 14 to 16, wherein the controller is further configured to identify one or more cell modules to be heated based on meeting a state of charge criteria.

18. The system of any one of claims 1 to 17, wherein the controller is configured to: control the switching circuit to create a select circuit path including a switch and one or more battery cell modules; determine one or more of a voltage or reactive current within the select circuit; and determine a fault or degradation condition of the switch or the battery cell module based on the determined characteristic.

19. The system as claimed in claim 18, wherein the controller is configured to determine an operational health status of at least one cell module of the or at least one switch of the switching circuit, wherein, in the second mode, the controller is configured to:• configure a series connection of a first group of components, the first group comprising a one or more cells and a plurality of switches.• configure a series connection of a second group of components, the first group comprising one or more cells and a plurality of switches, where the first and second group share a component;• connect the determined at least one cell in antiseries, with one or more other battery cells and the resonance circuit and rapidly alternating the polarity of the cells, to thereby control the transfer of reactive current in the battery pack.• compare the reactive current to a predetermined reactive current, and• determine the health status of the component shared by the first and second group based on the comparison.

20. The system as claimed in claim 18 or claim 19, wherein the controller is configured to, in the first mode, connect the one or more cell modules to an output for an external load by configuration of the switching circuit based on the determined health status of the at least one of a switch and a battery cell module.21 . The system as claimed in any one of claims 18 to 20, wherein the select circuit comprises one or more of the following components:• a cell module;• a switch;• a switch driver circuit;• body diodes;• a voltage sensor;• a current sensor; and• wire connections between the controller and a component; and the controller is configured to determine the health status of any one or more of the components.

22. The system as claimed in any one of claims 1 to 21 , wherein the reactive circuit is configured, at least in part, as a low pass filter for output from the plurality of battery cells when the output connection is connected to the load.

23. The system as claimed in any one of claims 1 to 22, wherein the switching circuit comprises one or more switching circuits, each configured to:• selectively connect zero, one or more cell modules in a series connection with the reactive filter,• selectively bypass cell modules from a series connection with other cells, and• selectively control the forward or reverse polarity of one or more cell modules in the series connection.

24. The system as claimed in claim 23, wherein the controller is further configured to modulate the connection of one or more cell modules in the series connection based on one or more modulation parameters.

25. The system as claimed in claim 23 or 24, wherein the controller is configured to:• determine a measured reactive current,• compare the measured reactive current to a target reactive current, and,• based on the comparison, change at least one of: o an alternation frequency, and o a number of series connected cell modules.

26. The system as claimed in any one of claims 1 to 25, wherein the controller is configured to determine a target reactive current, and control the target reactive current by one or more of:• determining a number of cell modules based on one or more of: o the target reactive current, ando a state of charge criteria of at least some cell modules,• determining an alternation frequency based on the target reactive current, and• controlling the switching circuit and the connection of cell modules at the determined alternation frequency.

27. The system as claimed in any one of claims 1 to 26, wherein the controller is configured to:• determine a measured reactive current, and• change at least the alternation frequency based on a comparison between the target current and the measured reactive current.

28. The system as claimed in any one of claims 1 to 27, wherein the controller is configured to modulate a number of series connected cell modules to control the magnitude of reactive current.

29. The system as claimed in any one of claims 1 to 28, wherein the controller is configured to determine a measured reactive current, and change a number of connected cell modules based on the one or more criteria comprising a comparison between a target current and the measured reactive current.

30. The system as claimed in any one of claims 1 to 29, wherein the controller is configured to modulate the connection of one or more cell modules, the modulation comprising a PWM or PDM based connection duty cycle within a connection interval based on the relative phase angle of the reactive current.

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