Transmission line having variable impedance

Abstract

Apparatus for a transmission line, comprises conductors each being separated from one or more other of the conductors by a dielectric material, and electrical connections for the conductors to a supply side of a power source and / or a return side of the power source. The apparatus can be switched between at least first and second modes. In the first mode, one or more of the conductors are connected to the supply side of the power source but not to the return side of the power source, and one or more of the conductors are connected to the return side of the power source but not to the supply side of the power source. In the second mode any one, more than one or all of: (i) a different one or more of the conductors is connected to the supply side of the power source but not to the return side of the power source compared with the first mode; (ii) a different one or more of the conductors is connected to the return side of the power source but not to the supply side of the power source compared with the first mode; (iii) one or more of the conductors that is connected in the first mode to the supply side of the power source but not to the return side of the power source, or to the return side of the power source but not to the supply side of the power source, is isolated; and (iv) one or more of the conductors is connected to the supply side and to the return side.

Description

[0001] TRANSMISSION LINE HAVING VARIABLE IMPEDANCE

[0002] Introduction

[0003] The present invention relates to a transmission line and to uses thereof in transmitting / transferring power. In particular, the invention relates to a transmission line the configuration of which can be modified to change the impedance, type and / or topology of the transmission line and / or a power transmission system of which the transmission line forms a part.

[0004] In certain embodiments, the present invention relates to a coil for wireless power transfer and to uses thereof in transferring power, especially for wireless charging of electric vehicles. In particular, the invention relates to a power transfer coil and to a method of wirelessly transmitting power comprising using such a power transfer coil.

[0005] Background

[0006] Power transmission systems traditionally use a conventional transmission line, such as a conventional cable, to transmit power between a power source and a load. It is known that, in such systems, impedance arises along the length of the transmission line when the transmission line is in use, transmitting power. This impedance affects the efficiency of power transmission along the length of the transmission line. It will be appreciated that the impedance required for optimal power transmission may differ for different loads, e.g. loads that draw different amounts of power from the power source. Conventionally, the load to which power is supplied by the transmission line does not change, and thus the transmission line can be constructed to have optimal impedance for that load and the impedance does not thereafter need to be monitored or adjusted. However, in some prior art systems, it is possible to change the load. For example, a conventional wireless electric vehicle charging system comprises a power source connected to a converter, which converts an approximately 50 Hz or 60 Hz alternating current input from the power source to an approximately 70-95 kHz output, which is in turn connected to a ground pad. In this system, the converter supplies alternating current at a high frequency, e.g. about 85 kHz, to a transmitting coil in the ground pad, which then wirelessly transmits power to a receiving coil in a car pad in an electric vehicle parked at or near the ground pad. It will be appreciated that, in this system, the electric vehicle parked at or near the ground pad may change. It is therefore desirable to provide alternative, and preferably improved, circuits for power transmission systems wherein a power source is connected to one or more load(s) by a transmission line, such as a cable.

[0007] Some prior art power transmission systems comprising transmission lines have systems for modifying the impedance thereof in accordance with changing loads. An example of such a prior art power transmission system is described in PCT / EP2024 / 064946. However, a problem with such prior art systems is that these typically require one or more additional components, such as one or more capacitor(s), inductor(s), and / or resistor(s), to be connected to the transmission line to enable the impedance to be modified. This is problematic because such components can be expensive and their inclusion increases the overall complexity of the system, which is undesirable. It is therefore desirable to provide a power transmission system and transmission lines therefor having variable impedance but which do not require such additional components to be included in the electrical circuit.

[0008] It also is desirable in general to provide alternative, and preferably improved, power transmission systems, as well as transmission lines and other components therefor. Wireless power transfer (“WPT”) utilises conductive coils which generate a magnetic field to transfer energy between a transmitting coil and a receiving coil via electromagnetic induction. To increase the efficiency of the system, capacitively reactive compensation, i.e. additional capacitance, can be added into, or removed from, the circuit to balance the inductive reactance generated by the coils. This is traditionally achieved with capacitors connected in series or in parallel with the coils. Inductors connected in series or in parallel with the coils can also be used to adjust the inductive reactance. By balancing the capacitive reactance and the inductive reactance of the circuit, the impedance is reduced, allowing power to be transferred with lower losses.

[0009] A capacitive coil for charging of electric vehicles is known from WO 2024 / 042136 providing two parallel conductors, separated from each other by dielectric material and wound into a coil / winding, one conductor connected just to source and the other just to load. This is effective and addresses other problems in the art, related e.g. to the high frequency alternating current used in such systems, e.g. as described in WO 2022 / 258782.

[0010] Nevertheless, challenges with WPT remain in practice, including coil misalignment, variable distance between the transmitting and receiving coils, and varying power transfer (i.e. load demand or coil design choice). These lead to changes in the inductive reactance of the system, and therefore to changes in the amount of capacitive compensation required.

[0011] Known coils have limitation, however, in ability and / or timeliness of providing compensation. Known coils use an external capacitor bank, which adds to costs and size I weight of those systems. All such systems preferably have provision to monitor for and react to faults; reducing the type or frequency or likelihood of faults is desirable.

[0012] Known systems can also be complex physically and electronically, which can impact negatively on reliability.

[0013] It is known to include a capacitive coupling between layers of a coil. However, this does not provide desired flexibility during coil use to address the problems identified.

[0014] An aim of the invention is to provide an alternative coil for WPT, and an aim of preferred embodiments is to provide an improved WPT coil e.g. with greater options for use and control over its operation.

[0015] Summary of the Invention

[0016] Embodiments of the present invention provides a transmission line for a power transmission system which has variable impedance but does not require, or at least has reduced requirement for (compared to prior art systems), additional components, such as capacitors, inductors, and resistors, to be included in the electrical circuit to facilitate variation of the impedance. Instead, impedance is varied by switching the configuration of one or more conductors of the transmission line between modes. Embodiments are thus advantageous because this can facilitate variable impedance without the additional cost associated with these additional electrical components, and enables impedance to be varied without increasing the overall complexity of the system.

[0017] Another advantage of the transmission line may be that various electrical parameters of the transmission line and the power transmission system it forms a part of can be varied. Examples of such parameters include AC resistance, DC resistance, inductance, shunt capacitance, quality factor, distributed capacitance (both series and parallel), and the profile (i.e. intensity and / or direction) of currents generated in, and / or magnetic fields generated around, the transmission line and / or other components of the power transmission system.

[0018] The transmission line may also be advantageous because the transmission line may not need to be changed for a different transmission line having a different impedance every time the load, and thus the optimal impedance, is changed. This can reduce costs and improves convenience for operators of power transmission systems which comprise transmission lines.

[0019] Another advantage of the transmission line may be that the load can be monitored continuously and impedance of the transmission line continuously or regularly modified in response to a change in the load and / or in anticipation of a change in the load. Being able to monitor the load and constantly or regularly modifying the impedance of the transmission line in this manner can be advantageous because this can ensure the impedance is maintained at or near the optimum, which may, for example, maximise the efficiency of the system or reduce the risk of a fault becoming hazardous.

[0020] Yet another advantage of the transmission line of the invention is that the impedance can be modified to reduce the electrical burden on the dielectric material of the transmission line, which reduces the risk of the dielectric material becoming damaged when the transmission line is in use, transmitting power.

[0021] In certain embodiments, a power transfer / transmission coil is provided with variable capacitance and / or inductance, addressing one or more of all of the issues with known coils.

[0022] Embodiments provides a coil that can be switched between modes having varying capacitance and / or inductance, and thus also reactance. The capacitance / inductance can be varied statically or dynamically, i.e. in real time and in accordance with changing power demand.

[0023] Methods of power transmission are provided wherein the coil is switched between modes during charging.

[0024] Embodiments may allow the inherent capacitance and / or inductance and / or resistance of the power transfer coil to be modified, which can reduce or eliminate the need to include additional capacitors / inductors connected in series or in parallel with the coil to provide capacitive / inductive compensation. However, the invention also allows such additional capacitors / inductors to be used in combination with changing the inherent capacitance and / or inductance of the coil, which can provide a further degree of control over the impedance of the coil.

[0025] In a first aspect, the invention provides a transmission line, comprising:

[0026] (a) a plurality of sets of first and second conductors, the conductors of each set separated by a dielectric material, and

[0027] (b) electrical connections for the conductors to a supply side of a power source and / or either a load or a return side of the power source, wherein the transmission line can be switched between at least first and second modes, wherein in the first mode, one or more or all of the first conductors are connected to the supply side of the power source but not to the load or the return side of the power source, and one or more or all of the second conductors are connected to the load or the return side of the power source but not to the supply side of the power source, and wherein in the second mode (i) the number of the first conductors that are connected to the supply side of the power source but not to the load or the return side of the power source is different compared with the first mode, or (ii) the number of the second conductors that are connected to the load or the return side of the power source but not to the supply side of the power source is different compared with the first mode, or (iii) both (i) and (ii).

[0028] As used herein, the term “transmission line” is intended to mean an electrical component for transmitting power from a first node in an electrical circuit, such as a power source, to a second node in the electrical circuit, such as a load. Examples of transmission lines include cables and traces on printed circuit boards. In the invention, preferably the transmission line is a cable.

[0029] The transmission line of the invention suitably comprises one or more switches that can be operated to switch the line between the first and second modes.

[0030] The conductors of each set may each be wound into a winding.

[0031] The transmission line may be for a power transmission system. The transmission line may be a power transfer / transmission coil and / or the power transmission system may be a wireless electric vehicle charging system. Hence, the invention provides, in a particular embodiment, a power transfer / transmission coil, comprising:

[0032] (a) a plurality of sets of first and second conductors, the conductors of each set separated by a dielectric material and each wound into a winding, and

[0033] (b) electrical connections for the conductors to a supply side of a power source and / or a return side of the power source, wherein the power transfer coil can be switched between at least first and second modes, wherein in the first mode, one or more or all of the first conductors are connected to the supply side of the power source but not to the return side of the power source, and one or more or all of the second conductors are connected to the return side of the power source but not to the supply side of the power source, and wherein in the second mode (i) the number of the first conductors that are connected to the supply side of the power source but not to the return side of the power source is different compared with the first mode, or (ii) the number of the second conductors that are connected to the return side of the power source but not to the supply side of the power source is different compared with the first mode, or (iii) both (i) and (ii).

[0034] The ability to selectively switch between modes gives a choice of capacitance I capacitive reactance to the user during use, e.g., and especially for coils of the invention, for wireless charging of a battery.

[0035] The power transfer coil may be for use as a transmitting coil or a receiving coil in a WPT system, such as a wireless electric vehicle charging system. Thus, in embodiments wherein the coil is for use as a receiving coil, the electrical connections may be for connection to a load, rather than the power source.

[0036] A transmission line of the invention can be switched to a mode in which only one of the first conductors is connected to the supply side of the power source but not to the load or the return side of the power source. Similarly, a transmission line according to the invention can be switched to a mode in which only one of the second conductors is connected to the load or the return side of the power source but not to the supply side of the power source. This can provide for minimum capacitance operation.

[0037] It is preferred that the transmission line can be switched to a mode in which all of the first conductors are connected to the supply side of the power source but not to the load or the return side of the power source. Again, it is also preferred that the transmission line can be switched to a mode in which all of the second conductors are connected to the load or the return side of the power source but not to the supply side of the power source. This can provide for maximum capacitance operation, with all conductors, e.g. windings, connected capacitively.

[0038] Another option for modes is to enable shorting out of one or more conductors / windings, stopping their function as a capacitive conductor / winding and / or switching them from capacitive to conventional mode. Hence, transmission lines of preferred embodiments can be switched to a mode in which one or more of the first conductors is connected to the supply side of the power source and to the load or the return side of the power source. This shorts out the first conductor(s) into galvanic connection, optionally making it(them) function conventionally, e.g. as an inductive coil if the transmission line is a power transfer coil. This additional option further expands the range of operating modes for the transmission line. Still further, it is also preferred that in a further mode one or more of the second conductors is connected to the supply side of the power source and to the load or the return side of the power source. In this way the ability to short out one or more or all of the second conductors is added to the transmission line functionality.

[0039] Thus, in particular embodiments, the transmission line has the ability to operate with one or more or all conductors / windings in capacitive mode, with one or more or all conductors / windings in conventional mode or with a combination, also referred to as a hybrid mode, namely with one or more conductors / windings in capacitive mode and one or more conductors / windings in conventional mode.

[0040] It is added that the transmission line has been described as having the option to have all conductors / windings in conventional mode. It is nevertheless a feature of preferred embodiments that at least one first conductor and at least one second conductor are capacitively connected; thus, preferably, at all times during operation at least one of the first conductors is connected to the supply side of the power source but not to the load or the return side of the power source, and at least one of the second conductors is connected to the load or the return side of the power source but not to the supply side of the power source.

[0041] Particularly preferred transmission lines and / or control systems therefor are configured so that in all modes there is at least one set of first and second conductors that are capacitively connected to, i.e. in capacitive relationship with, each other, the first conductor being connected to the supply side of the power source but not to the load or the return side of the power source, and the second conductor being connected to the load or the return side of the power source but not to the supply side of the power source.

[0042] In general, the coils and windings are not limited to shape, size or form, and can have any shape while accounting for frequency driven factors such as parasitic losses, depth, thickness, etc and / or the coil’s figure of merit, i.e. its coupling coefficient, quality factor, alignment sensitivity, power transfer efficiency, and / or the distance between the transmitting and receiving coils. Coils and windings are well-known, and known in varying geometries and in a range of suitable conducting materials. In embodiments, and as described below in more detail, the first and second conductors are wound into substantially planar, spiral windings. Electrical connections to supply and / or return may be provided for winding ends and / or at intermediate distances along the length of each conductor. Those connections can interfere with layer-by-layer stacking of adjacent windings. Preferred windings comprise a space or void at or towards their centre so that connections, e.g. wires or other conductors, from the winding central ends can pass through aligned spaces I voids and exit at the top or bottom of a stack.

[0043] The first and second conductors may be wound into coplanar windings electrically separated from each other by a dielectric material. First and second conductors of each capacitive winding are in the same plane and wound around each other in a twin spiral. The first and second conductors may be wound into similar windings located one atop the other and electrically separated from each other by a layer of dielectric material. These first and second conductor windings can be more or less identical (apart from, in some cases, the locations of exterior and / or interior connection ends) when viewed from above, just spaced apart in separate layers. The first and second conductors are suitably located in a stack of substantially planar layers, the stack having a central lumen for location of electrical connections between the windings and the power source / supply.

[0044] The first and second conductors of each set may be wound together into a winding.

[0045] In a second aspect of the invention there is a single set of first and second conductors. Hence, in a third aspect the invention also provides a transmission line, comprising:

[0046] (a) first and second conductors, separated by a dielectric material, and

[0047] (b) electrical connections for the conductors to a supply side of a power source and a load or a return side of the power source, wherein the transmission line can be switched between at least first and second modes, wherein in the first mode, the first conductor is connected to the supply side of the power source but not to the load or the return side of the power source, and the second conductor is connected to the load or the return side of the power source but not to the supply side of the power source, and wherein in the second mode at least one of the first and second conductors is connected to both the supply side of the power source and the load or the return side of the power source.

[0048] In such embodiments, the first and second conductors may each be wound into a winding. Thus, the single set of first and second conductors may be a single capacitive winding. The transmission line may be a power transfer / transmission coil.

[0049] Again, the power transfer coil may be for use as a transmitting coil or a receiving coil in a WPT system, such as a wireless electric vehicle charging system. Thus, in embodiments wherein the coil is for use as a receiving coil, the electrical connections may be for connection to a load, rather than the power source.

[0050] The first and second conductors may be wound together into a winding.

[0051] The transmission line of this embodiment can be switched to a third mode, being a derivative of the second mode, wherein in the third mode both of the first and second conductors are connected to both the supply side of the power source and the load or the return side of the power source. One or more switches are suitably included that can be operated to switch the transmission line between the first, second and third modes. Each winding may comprise any number of turns. However, generally in transmission lines herein, each winding comprises at least five turns, preferably at least ten turns, or at least twenty turns. Specific embodiments, described in the examples, have approximately six and eleven turns respectively, though the number of turns can vary greatly and significantly higher numbers of turns are expected in further applications of the invention to power transfer / transmission. The exact number of turns used may depend on facts such as the application for which the transmission line is used, power demand, and / or frequency of power transmission.

[0052] In the second mode, one of the first conductors and one of the second conductors may be shorted out, i.e. electrically / galvanically connected to each other, so that they are both connected to the supply side of the power source and also to the load or the return side of the power source. The first and second conductors that are shorted out in the second mode may be of the same set or may be from adjacent sets. Switches may be provided that can be operated to short out one or more of the first and second conductors.

[0053] First and second conductors from two sets may be shorted out. In such embodiments, the first and second sets may be located symmetrically within the transmission line and the shorting out may result in an even redistribution of impedance within the transmission line. Alternatively, the first and second sets may be located asymmetrically within the transmission line and the shorting out may result in an uneven redistribution of impedance within the transmission line.

[0054] The first and second conductors may be shorted out at or near ends of the conductors or at a point along a length of each conductor, such as at a midpoint of the conductors. Shorting out at the midpoint, rather than the end, of a conductor allows changing of the inductance I inductive reactance of the conductors and thus the transmission line, in addition to the capacitance I capacitive reactance. This provides an additional degree of control over the impedance of the transmission line compared to modifying the capacitance I capacitive reactance only. There may be a plurality of points along the length of each conductor at which shorting out can occur; having a greater number of such points enables finer tuning of the inductance I inductive reactance compared to only having one or two points to choose from.

[0055] The conductors / coils / windings can be formed by providing a trace of conductive material in the form of a conductor / coil / winding, e.g. a metal or alloy trace on an insulating support such as copper or aluminium on a printed circuit board (“PCB”). The support can constitute the dielectric layer between adjacent layers.

[0056] Power transfer coils of the invention also suitably comprise an outer ferrite layer, in accordance with ferrite layers in conventional such coils, and also suitably are used with other components of such power transmission systems, such as a conductive shielding plate.

[0057] Transmission lines of the invention also suitably comprise electrical connections to an electrical circuitry for control of the switching between operating modes, as well as connectors for connection to a power source, again as is conventional in the field.

[0058] The power transfer coils of the invention can be used for wireless power transfer / transmission with the ability for alternative, and preferably improved, control of charging, e.g. alternative, and preferably improved, compensation in dynamic system states and thus improved efficiency. In a fourth aspect the invention also provides a transmission line, comprising:

[0059] (a) a plurality of sets of first and second conductors, the conductors of each set separated by a dielectric material, and

[0060] (b) electrical connections for the conductors to a supply side of a power source and / or either a load or a return side of the power source, wherein the first conductors are connected to the supply side of the power source, wherein the second conductors are connected to either the load or the return side of the power source, wherein the transmission line can be switched between at least first and second modes, wherein in the first mode, one or more of the sets of conductors is / are connected as a signal line and one or more of the sets of conductors is / are connected as a return line, and wherein in the second mode, (i) the set(s) of conductors that is / are connected as the signal line is different compared with the first mode, and (ii) the set(s) of conductors that is / are connected as the return line is different compared with the first mode.

[0061] Preferably, a first half of the sets of first and second conductors are connected as the signal line and a second half of the sets of first and second conductors are connected as the return line in each of the first and second modes.

[0062] The transmission line may comprise at least six sets of first and second conductors. This can be advantageous because this enables the cable to be used to transmit power in a multi-phase manner, especially in a three-phase manner. Thus, the transmission line may be for transmitting power in a multi-phase manner, especially in a three-phase manner. Switching between different choices for which sets of conductors are for the signal line and which are for the return line can be used to modify cable impedance.

[0063] The transmission line may be a capacitive cable. Each set of first and second conductors may be configured as a sub-cable I core of the capacitive cable. Each sub-cable I core may be a capacitive sub-cable I capacitive core.

[0064] Apparatus of the invention is provided, comprising the transmission line and / or transmission coil and further comprising one or more or all of other components described herein for use with the line and / or coil, such as one or more switches for switching between modes, one or more connectors for connection of conductors to supply or load or return, one or more switches for shorting out of first and / or second conductors and and one or more additional capacitors and / or inductors.

[0065] The invention also provides a method of transferring / transmitting power comprising using a transmission line of the invention and switching the transmission line between modes, e.g. to vary the capacitance I capacitive reactance and / or the inductance I inductance reactance thereof. In use the invention offers the advantage to vary the reactance I impedance during power transmission and to provide the ability to inject compensation by way of varied capacitance I capacitive reactance, inductance I inductive reactance, and / or resistance.

[0066] The method may be a method of wirelessly transferring / transmitting power. The transmission line may be a power transfer / transmission coil.

[0067] As set out in more detail in examples below, a variable impedance coil of the present invention thus uses at least two conductive layers in a capacitive winding, the conductive layers being separated by a dielectric layer. The capacitive winding is for power transfer as either the transmitting coil, receiving coil, or both. These conductor layers are galvanically isolated from each other forming a capacitive coupling and can be galvanically connected to each other with use of a switch. By stacking multiple pairs of conductive layers, the coil can balance the inductive reactance with the inherent capacitive reactance from the capacitive properties of the layers.

[0068] The inherent capacitance / inductance within the transmission line can be adjusted based on factors described above, e.g. by closing one or more of the switches between each layer. This way, when there is a change in inductive reactance due to the factors described above, the system can adjust its capacitance and / or inductance to balance the reactance and reduce the overall impedance. Use of the invention can benefit from dynamic reactance balancing using inherent capacitance between layers.

[0069] Further, in use of the invention, one advantage that can be realised is reduced or no need for an external capacitor bank, as capacitance / inductance / impedance interventions are achieved using the switchable transmission line components. The invention generally reduces transmission line complexity, leading to savings on component costs, system weight and footprint. An increase in system I transmission line impedance also has the benefit of reducing the risk of fault due to excessive current. Fewer components in systems I transmission lines of the invention leads also to increased reliability.

[0070] Coils and methods comprising using coils of the invention are suitably for wireless charging in general, and especially for wireless charging of electric vehicles. The invention can also advantageously be used for charging of implanted medical devices, for charging of unmanned aerial vehicles (“UAVs”, e.g. drones) and for communication services.

[0071] Embodiments have broad application, for example for in underground or overhead power transmission lines, control cables, communications lines, in transformers, motors, generators, solenoids, electromagnets, antennas, filters (e.g. in HiFi), furnaces, heaters, chargers, wireless power transfer systems (e.g. wireless charger) and / or dynamos.

[0072] Brief Description of Figures

[0073] Embodiments of the invention are now illustrated by way of the following examples, with reference to the accompanying drawings, in which:

[0074] Fig. 1 shows a schematic view of a power transfer coil of the invention having just one set of first and second conductors, i.e. a single capacitive winding, and having variable capacitance I capacitive reactance;

[0075] Fig. 2 shows a schematic view of switching options for a further power transfer coil of the invention having variable capacitance I capacitive reactance and having N sets of first and second conductors - five sets are shown (each with two conductors);

[0076] Fig. 3 shows three schematic views of a still further power transfer coil of the invention having twelve sets of first and second conductors (each with two conductors);

[0077] Fig. 4 shows a schematic view of a power transfer coil of the invention having just one set of first and second conductors, i.e. a single capacitive winding, and having variable inductance I inductive reactance;

[0078] Fig. 5 shows a schematic view of switching options for a further power transfer coil of the invention having variable inductance I inductive reactance and having N sets of first and second conductors - five sets are shown (each with two conductors)

[0079] Fig. 6 shows a schematic cross-sectional end view of a transmission line of the invention;

[0080] Fig. 7 shows a schematic view of switching options for the transmission line of Figure 6; Fig. 8 shows a magnetic field profile obtained by computational modelling of the transmission line of Figure 6 in a first mode;

[0081] Fig. 9 shows a magnetic field profile obtained by computational modelling of the transmission line of Figure 6 in a second mode; and

[0082] Fig. 10 shows a magnetic field profile obtained by computational modelling of the transmission line of Figure 6 in a third mode;

[0083] Figure 11 is a schematic view of a cross-section of a cable according to an embodiment, including a conductive core and concentric conductive layers around the core;

[0084] Figure 12 is a schematic view of a series connection of two of the cables of Figure 11 ; Figure 13 is a schematic view of a series connection of two of the cables of Figure 6; Figures 14A and 14B show how different conductor assignment in the cable of Figure 6 for phase components of a three-phase signal effects magnetic field profile;

[0085] Figure 15 shows switching options for capacitive live / signal and return / neutral cables in accordance with an embodiment;

[0086] Figures 16 to 18 each indicate switching configuration for a respective mode for the cables in Figure 15 in accordance with an embodiment;

[0087] Figures 19 to 24 each indicate a switching configuration in switching networks connected to multiple conductors, in accordance with another embodiment;

[0088] Figures 25 to 27 are each a schematic view of apparatus having a curved, loop or ring shape and a switching configuration in accordance with a respective mode;

[0089] Figures 28 to 33 are each a schematic view of switching networks connected to multiple conductors, and switching configurations in accordance with different modes;

[0090] Figure 34 is a schematic view illustrating distributed series and parallel capacitive conductor components connected in series;

[0091] Figures 35 to 38 are each a schematic view of a coil with switches, to illustrate how current through a part of coil can be prevented using switches and how direction of current through a portion of a coil can be changed;

[0092] Figures 39 to 41 are each a schematic view of a circuit in accordance with another embodiment with different switching configurations in accordance with different modes; and

[0093] Figure 42 is a schematic view of illustrating options for placement of terminals.

[0094] Detailed Description of Embodiments

[0095] Embodiments of the invention relate to a transmission line. The transmission line may comprise a power transfer coil. The transmission line comprises conductors, each of which is separated from at least one other by a dielectric material. The transmission line also comprises electrical connections for the conductors to a supply side of a power source and / or either a load or a return side of a power source. The transmission line can be switched between at least first and second modes in which one or more characteristics or use of the transmission line is different. The electrical connections to the supply side may comprise switches (a first switching network). The electrical connections to the load or return side may also comprise switches (second switching network).

[0096] The transmission line may comprise at least two conductor components (or segments) connected in series. Each conductor component may comprise have respective first and second switching networks

[0097] Different embodiments are described below with reference to examples. A title of “example” should not be taken to be limiting - more than one embodiment may be described following such a title. Example 1 - Power Transfer Coil Having a Single Capacitive Winding and Variable Capacitance / Capacitive Reactance

[0098] Referring to Figure 1 , a device comprises a power transfer coil of substantially planar form having two conductors, separated by dielectric and each wound into a winding. The first conductor comprises a first conductor winding that is connected to the power source via junction terminal A from where it is continuous through a spiral winding beginning centrally as shown and expanding clockwise, radially outwards in six and a bit turns, then terminating at junction terminal B, not being onwardly connected in a return line to the other side of the power source. The second conductor comprises a second conductor winding and is not connected to the power source via junction terminal A but begins electrically at junction terminal A, from where it is continuous through a spiral winding beginning centrally as shown and expanding outwards in six and a bit turns, then connecting to junction position B and is, in contrast to the first conductor, onwardly connected in a return line to the other side of the power source.

[0099] The two windings are located side-by-side as approximately parallel (or twin) spiral windings that follow or match each other’s course, spaced apart by a dielectric material and not galvanically connected to each other. The windings form a capacitive winding (also referred to as two coils forming a single capacitive coil) and when operated generate a magnetic field for transmission of power to, or are suitable for receipt of power from, another coil; that other coil, referred to as the receiving coil or transmitting coil (depending upon direction of power transfer), can be of like capacitive type or can be a conventional coil.

[0100] The two windings are formed by flat, electrically conducting traces on a non-conducting PCB support. Note that if the conductors are encased by dielectric then the support is optional. The diagram is schematic and in practice the two windings lie flat next to each other and the connections of the central beginnings of the windings to terminals A and B are located underneath the two flat windings. In other examples, one of which is described below, a plurality of windings are stacked on top of each other in flat layers with connections to A and B or their equivalent passing through a central region and not interfering with the layer-by-layer stacking of the windings on top of each other.

[0101] At junction terminals A and B, the connections can be switched so that, at A, the first winding or the second winding or both can be connected to the power supply and, at B, the first winding or the second winding or both can be connected back to the return side of power supply.

[0102] Modes of operation of the device are as in Table A:

[0103] Table A:

[0104] Example 2 - Power Transfer Coil Having N Capacitive Windings and Variable Capacitance / Capacitive Reactance

[0105] Referring to Figure 2, a composite device comprises windings in layers and their connections to a supply side and a return side of a power source, shown schematically in a circuit diagram for up to N flat capacitive winding layers (thus each flat layer having two wound conductors in a capacitive winding). The N winding layers are stacked on top of each other, in substantially horizontal, flat layers, connections to their winding beginnings passing through apertures in each layer which form a common central stack channel.

[0106] Terminal A is connected to its layer 1 , layers numbered from the top of the stack, and according to the position of the outer switches shown on the left-hand side of the circuit diagram can be electrically connected in parallel to one or two or three or up to all of the other (N-1) Terminal A layers, descending through the stack.

[0107] Terminal B is connected to its layer 1 , layers numbered from the bottom of the stack, and according to the position of the outer switches shown on the right-hand side of the circuit diagram can be electrically connected in parallel to one or two or three or up to all of the other (N-1) Terminal B layers, ascending through the stack.

[0108] The Terminal B layer 1 winding thus forms a capacitive winding with the Terminal A layer N winding, and the Terminal B layer 2 winding thus forms a capacitive winding with Terminal A layer N-1 winding, and this continues through the stack to the top, where the Terminal B layer N winding thus forms a capacitive winding with the Terminal A layer 1 winding.

[0109] Inner switches, shown on the left- and right-hand sides of Figure 2, located inside the outer switches described above, allow each of the capacitive windings in the stack to be selectively shorted out, i.e. shorted to form a galvanic rather than a capacitive connection between respective first and second conductors of that layer. Hence the composition can operate with one or more or all layers in capacitive mode or with one or more or all layers in conventional mode, or with a blend of varying amounts of each, As mentioned above, it is preferred that there is at least one capacitive connection within the layers of the multi-layer composite device.

[0110] Variation of capacitance I capacitive reactance is achieved according to the positions of the switches. In more detail, through a combination of switching on I operating the outer switches of windings(s) of layers 1 , or 1 and 2, or 1 , 2 and 3 etc, via Terminal A and the outer switches of windings(s) of layers 1 , or 1 and 2, or 1 , 2 and 3 etc, via Terminal B, together with the inner switches for shorting out windings layer-by-layer the user selects which layers in the stack are operating as capacitive windings and which conductors in which layers are selectively shorted- out, thus varying the capacitive reactance and impedance of the composite coil. Specifically, the coil can be operated so as to provide for equal (re)distribution of CSA (lateral) between the Input (A) & Output (B) terminals, or to provide unequal (re)distribution of CSA (lateral) between A & B terminals. Referring to the circled arrows, these indicate shorting options with like arrow / circle combinations indicating a pair of shorting operations that can be used at the same time. Referring to the top left and bottom right like-arrowed circles (large circle, solid line; Terminal A layer 1 and Terminal B layer 1), an equal distribution can be achieved by shorting between those conductors. Similarly, referring to the smaller circle, solid line arrows (Terminal A layer 1 and Terminal B layer N-1) an equal distribution can be achieved by shorting between those conductors.

[0111] Referring to the larger circle, dotted line arrows (Terminal B layers 1 and N) an unequal distribution can be achieved by shorting between those conductors. Similarly, referring to the smaller circle, dotted line arrows (Terminal A layers 1 and 2) an unequal distribution can be achieved by shorting between those conductors.

[0112] Example 3 - Power Transfer Coil Having Twelve Sets of First and Second Conductors

[0113] Referring to Figure 3, a second composite device of the invention is shown schematically in three related views; the top view shows the composite device from above, the middle view shows a cross-section F-F of the composite device and the lower view shows detail of the portion circled “G” in the middle view.

[0114] Referring to all three, the composite device has an upper ferrite layer 4 then twelve layers each having (i) a first dielectric layer 1 , (ii) a first conductor winding layer 2, (iii) a second dielectric layer 1 , and (iv) a second conductor winding layer 3. Hence, there are twenty-four dielectric layers in total. A bottom insulating or support layer is present but not shown.

[0115] Starting from the top of the device, after the ferrite layer 4 and adjacent the first dielectric layer 1 is a first conductor 2 in the form of a spiral winding beginning centrally as shown in the top view and expanding radially outwards, anticlockwise in eleven and a bit turns, then terminating at a junction at the left-hand side of the top view of Figure 3. Continuing down the stack there is a second dielectric layer 1 and next the second conductor 3 in the form of a similar spiral winding beginning centrally and expanding radially outwards, anticlockwise in eleven and a bit turns, then terminating at a junction at the left-hand side of the top view of Figure 3. The second conductor 3 is not visible in the top view (as it is obscured by the top first conductor when viewed from above) but its terminating end is staggered relative to the first conductor 2, and hence just its end is visible; the staggered ends facilitate connection to power and switching circuitry of respective first and second conductor windings. Next, there is a further, third dielectric layer 1 and then the pattern of first conductor, dielectric layer, second conductor, dielectric layer continues to the bottom.

[0116] The first and second conductor windings are in this device of similar size and shape and axially spaced apart by and separated by the dielectric layers. The conductor windings form a capacitive winding (also referred to as two coils forming a single capacitive coil) and when operated generate a magnetic field for transmission of power to, or are for receipt of power from, another coil.

[0117] Electrical connections and switching of the windings, and optional shorting-out of the windings is as per the diagram in Figure 2 (N= 12) .

[0118] With the option for selective use of first and second conductor windings as capacitive windings or convention windings, and / or for selectively not using all windings, by shorting one or more adjacent windings, the invention thus provides a power transfer coil having variable capacitance I capacitive reactance and thus impedance. Example 4 - Power Transfer Coil Having a Single Capacitive Winding and Variable Inductance / Inductive Reactance

[0119] Referring to Figure 4, a device comprises a power transfer coil similar to that of Example 1 (shown in Figure 1) but configured to readily vary inductance I inductive reactance.

[0120] The first and second conductors of this coil are each wound into spiral windings like the coil of Example 1 and each have N turns. At one end of the windings, the first conductor is connected to a supply side of the power source via connection at Terminal A, whilst the second conductor is not. In contrast, via connection at Terminal B, the second conductor is connected to a return side of the power source, whilst the first conductor is not.

[0121] The point along the second conductor at which Terminal B connects the second conductor to the return side of the power source is variable. In other words, Terminal B can connect the return side of the power source to the second conductor at Turn 2, Turn 5, Turn N-1 , or Turn N. It will be appreciated that Terminal B could be connected at any of the other turns but that these connection points are not shown in Figure 4.

[0122] Thus, by varying which Turn of the second conductor is connected to the return side of the power source at Terminal B, the inductance I inductive reactance, and thus also the impedance, of the power transfer coil can be modified.

[0123] Example 5 - Power Transfer Coil Having N Capacitive Windings and Variable Inductance / Inductive Reactance

[0124] Referring to Figure 5, a composite device comprises a power transfer coil similar to that of Example 2 (shown in Figure 2) but configured to readily vary inductance I inductive reactance.

[0125] Like the coil of Example 2 above, this power transfer coil has switches allowing the capacitance I capacitive reactance of the coil to be varied by adjusting which switches are open / inactive and / or closed / active at any given time. However, unlike the coil of Example 2, this power transfer coil is configured such that the conductor layers of each capacitive winding can be shorted out, i.e. connected to each other, using switches positioned at a plurality of points along the lengths of these windings.

[0126] By changing the position at which the shorting out occurs, the inductance I inductive reactance of each capacitive winding, and thus also of the power transfer coil as a whole, can be adjusted, which can provide an additional degree of control for modifying the reactance, and thus the impedance, compared to modifying the capacitance I capacitive reactance only.

[0127] Example 6 - Switchable Capacitive Cable

[0128] Referring to Figure 6, a transmission line, which is a capacitive cable, comprises six sets 1 , 2, 3, 4, 5, 6 of first and second conductors arranged in a ring around a former. Each set of first and second conductors is configured as a capacitive sub-cable / core of the capacitive cable.

[0129] Each of the cores can be switched between being connected as part of a signal line or being connected as part of a return line of a power transmission system. A switching network which can be used to switch each core between signal and return is shown in Figure 7. In a first mode, three of the cores 1 , 3, 5 are connected as a signal line and three of the cores 2, 4, 6 are connected as a return line. In this mode, the cores alternate between signal and return as one progresses around the ring of cores shown in Figure 6.

[0130] In a second mode, three of the cores 2, 3, 5 are connected as a signal line and three of the cores 1 , 4, 6 are connected as a return line. Thus, the signal cores are concentrated on the right-hand side of the cable shown in Figure 6, whilst the return cores are concentrated on the left-hand side instead.

[0131] In a third mode, three of the cores 1 , 5, 6 are connected as a signal line and three of the cores 2, 3, 4 are connected as a return line. Thus, the signal cores are concentrated on the left-hand side of the cable shown in Figure 6, whilst the return cores are concentrated on the right-hand side instead.

[0132] In each of the three modes, the cable has a different impedance to each of the other two modes, and thus switching between modes can be used to modify the impedance of the cable. In one or more modes, the cable may have a different conductor property (AC resistance, inductance and / or shunt capacitance) than in other of the modes. A greater or lesser number of cores may be used as signal than return. The mode of the cable may be changed for balancing.

[0133] Example 7 - Modelling of the Cable of Example 6

[0134] COMSOL Multiphysics software was used to produce a computational model of the cable of Example 6 above operating at a frequency of 50 Hz.

[0135] When the first mode of this cable was modelled, the cable was predicted to have an overall AC resistance for each of the signal and return lines of 514.29 mQ / km, an overall inductance for each of the signal and return lines of 0.044424 mH / km, and a shunt capacitance between the cores constituting the signal and return lines of 1.3483 pF / km.

[0136] When the second mode of this cable was modelled, the cable was predicted to have an overall AC resistance for each of the signal and return lines of 514.77 mQ / km, an overall inductance for each of the signal and return lines of 0.080333 mH / km, and a shunt capacitance between the cores constituting the signal and return lines of 1.1320 pF / km.

[0137] When the third mode of this cable was modelled, the cable was predicted to have an overall AC resistance for each of the signal and return lines of 515.03 mQ / km, an overall inductance for each of the signal and return lines of 0.14195 mH / km, and a shunt capacitance between the cores constituting the signal and return lines of 0.91229 pF / km.

[0138] The magnetic fields generated around the cable in each mode were also modelled using this software. The magnetic field profiles for each mode are shown in Figures 8 to 10, with Figure 8 showing the magnetic field profile for the first mode, Figure 9 showing the magnetic field profile for the second mode, and Figure 10 showing the magnetic field profile for the third mode.

[0139] Accordingly, computational modelling confirmed that switching which cores are used as the signal line and which cores are used as the return line results in various electrical parameters of the cable changing, including its AC resistance, inductance, shunt capacitance, and magnetic field profile, and thus also its impedance. Example 8 - Modulation of a Series Capacitive Cable

[0140] Referring to Figure 11 , a capacitive conductor component (or “cable”), which may be part of a transmission line, comprises a set of six conductors, indicated at conductive layers 1-6, five dielectric layers 1-5 and outer layers. The conductive layer 1 is central and the subsequent layers are arranged concentrically around this layer. The dielectric layers 1-5 are also arranged concentrically around the former, with each dielectric layer 1-5 being located between respective adjacent conductive layers. The outer layers comprise separation layers 101 , 102, an insulation layer 103, a metallic sheath 104 and an outer layer 100. The separation layer 101 is arranged around conductive layer 6. The insulation layer 103 is arranged around the separation layer 101. The separation layer 102 is arranged around the insulation layer 103. The metallic sheath 104 is arranged around the separation 102. The outer layer 105 is arranged around the metallic sheath 104. Embodiments are not limited to the number of conductor and dielectric layers.

[0141] Electrical connections at input and output terminals of the transmission line include, respectively, a set of first switches and a set of second switches (not shown in Figure 11). The first and second switches can be operated to change mode of the transmission line. For example, in a first mode one or more of the conductors (first conductors) are connected to a supply side of a power supply and not to a return side of the power supply, and one or more other of the conductors (second conductors) are connected to the return side of the power supply and not to supply side. In operation, capacitive power transfer thus occurs. In another mode one or more of the conductors (first conductors) different to those in the first mode are connected to a supply side of the power supply and not to a return side, and / or one or more other of the conductors (second conductors) different to those in the first mode can be connected to the return side of the power supply and not to the supply side. In different modes, the cross-sectional area (CSA) of the first conductors and / or the second conductors is different. In one of the modes (which may be one of the first or second modes), all conductors on one side (inner or outer) of one of the dielectric layers may be first conductors and all conductors on the other side (other of inner and outer) may be second conductors. In another mode (which may be one of the first and second modes), all conductors on one side (inner or outer) of a different one of the dielectric layers may be first conductors and all conductors on the other side (other of inner and outer) may be second conductors.

[0142] Each conductor layer 1-6 is formed of a plurality of conductive strands, although this is not essential and the conductor layers 1-6 may be alternatively formed or configured. Table B indicates the cross-sectional of conductive layers 1-6 in a specific example, and the proportion that each layer contributes to the overall CSA.

[0143] Table B: Thus, in different modes, a respective one of the dielectric layers may be selected and the electrical connections arranged so that conductor(s) within the selected dielectric layer are first conductors, and conductor(s) outside the selected dielectric layer are second conductors (or vice versa). In this case, the first conductors are electrically connected to a supply side and the second conductors are electrically connected to the load or return side. The CSA is different in different modes.

[0144] In one or more modes, any one or more of the conductive layers may be connected to the supply side and the return side for galvanic (non-capacitive) conduction.

[0145] Table C indicates different CSAs in different modes, and simulated capacitance in each of these modes, for the specific cable having properties set out in Table C:

[0146] Thus, the cable 100 can be operated to modify an amount of distributed capacitance, and as a result, the capacitive compensation. Also, the cable 100 can be operated to modify a ratio of conductor density or CSA between input and output terminals.

[0147] Referring to Figure 12, two of the cables 100a, 100b are connected in series. The transmission line includes for the cable 100a electrical connections including a first set of switches 110a at an input terminal and a second set of switches 112a at an output terminal. The transmission line includes for the cable 100b electrical connections including a first set of switches 110b at an input terminal and a second set of switches 112b at an output terminal. The input terminal 110a of the first transmission line is connected to a supply. The output terminal 112a is connected to a load circuit and also to the input terminal 110a. The output terminal 112b is connected to a load circuit. Embodiments are not limited to any number of conductor components being connected in series, with first and second sets of switches controllable to change characteristics of any one or more of the lines.

[0148] Return transmission lines, although not shown in Figure 12, may be provided alongside the transmission lines for a signal. Electrical connections including first switches may be located at 118 for a first return transmission line and at 116 for the second transmission line). Electrical connection including second switches may be located at 116 and 114 for a second return transmission line.

[0149] Additionally and / or alternatively, parallel transmission lines may be provided where indicated at 114, 116, 118 for power transmission where the supply is multiple phase, where transmission lines 100a, 100b carry 1 phase and further phases are carried by other transmission lines.

[0150] Selective allocation of the conductors as first and second conductors can result in a reduction in thermal and electrical losses compared to losses due to distribution in a conventional distributed series capacitive transmission line.

[0151] Example 9 - Property Manipulation for a three-phase Capacitive Cable

[0152] In another embodiment, cables like those described in relation to Figure 6 are connected in series. Electrical connections including first switches are connected at inputs terminals and second switches are connected at output terminals. The first and second switches may be configured like those described in relation to Figure 12, while being connected to side-by-side conductors in a cable rather than to concentrically layered conductors, thereby enabling different longitudinal segments of a transmission line to be assigned different modes in which different segments have different properties.

[0153] Referring to Figure 13, a transmission comprises conductor components (cables) like those described in relation to Figures 11 and 12. Electrical connections differ in that they connect the transmission line to a 3-phase power supply. Each cable is independently configurable in that each conductor in each cable can be assigned any one of the three phases by operation of the switches. Table D indicates inductance, AC resistance, and shunt capacitance for each of the three phases at each of operating frequencies of 50Hz and 400Hz, in each of five modes.

[0154] Referring to Figures 14A and 14B, assignment of different phases and conductors is illustrated, with corresponding magnetic-field profiles for the different modes where the operating frequency is 50Hz. A central core is earthed or used as a neutral line.

[0155] By changing the assignment of conductors for each phase in a 3-phase arrangement, properties can be modulated. In different modes, the number of conductors assigned any one of the phases can be different in one of the cables compared to the other. Thus, each phase may be assigned conductors in an equal (like in figures 14A and 14B) or unequal manner, so that the CSA of the conductors for different phases is different. Where the phases are distributed so that the conductor CSA is equal in different modes one or more of the phases may result in a different conductor property (AC resistance, inductance and / or shunt capacitance) from each other. In this case the phases are imbalanced. Also, in different modes, relative positions of multiple conductors assigned for different phases can be different in one of the cables compared to the other. The mode of each of the cables in a transmission line comprising such cables in series can be changed such that the phase is transposed, which may be performed for balancing.

[0156] Different modes can be selected to modulate design characteristics and improve performance and efficiency, and loss and heat dissipation profile. Such selection also enables improvement in harmonic filtration processing. Also, the power capacity of the transmission line and thus the installed network can be increased or decreased.

[0157] Further, in some embodiments, the electrical connections can selectively connect the input terminal of the cable to at least two of a 1 -phase, 3-phase and 6-phase power support. In this case, selection between each of these, as well as selection of a respective at least one core for each phase, can be achieved. Thus, the number of modes available is also dependent on selection of power supply.

[0158] Example 10 - Manipulation of Properties of Capacitive Cables by Assignment of Terminals

[0159] In embodiments, a transmission line comprises a first capacitive cable, which is a signal / live cable, comprising first and second conductors 120a, 122a. Referring to Figure 15, the first and second conductors 120a, 122a are concentrically arranged with the first conductor 120a being a core and the second conductor 122a being arranged around the core. A second capacitive cable, which is the return / neutral line, comprises first and second conductors 120a, 122b arranged in the same way. Embodiments are not limited to the first and second conductors 120a, 120b, 122a, 122b of either cable being so arranged. The transmission line comprises electrical connections including switches, arranged to selectively connect the first and second conductors of each cable to a power source and to a load circuit with the cables remaining capacitive.

[0160] Referring to Figure 16, in a first mode the power supply is electrically connected to: the second conductor 122a of the first cable and the first conductor 120b of the second cable. The power supply is not electrically connected to the first conductor 120a of the first cable and the second conductor 122b of the second cable. The load circuit is electrically connected to the first conductor 120a of the first cable and to the second conductor 122b of the second cable. The load circuit is not electrically connected to the second conductor 122a of the first cable or to the first cable 120b of the second cable.

[0161] Referring to Figure 17, in a second mode, the power supply is electrically connected to the first conductor 120a of the first cable and to the first conductor 120b of the second cable. The power supply is not electrically connected to the second conductor 122a of the first cable or to the first conductor 120b of the second cable. The load circuit is electrically connected to the second conductor 122b of the first cable and to the second conductor 122b of the second cable. The load circuit is not electrically connected to the first conductor 120a of the first cable or to the second conductor 122b of the second cable.

[0162] Referring to Figure 18, in a third mode, the power supply is electrically connected to the second conductor 122a of the first cable and to the second conductor 122b of the second cable. The power supply is not electrically connected to the first conductor 120a of the first cable or to the first conductor 120b of the second cable. The load circuit is electrically connected to the first conductor 120a of the first cable and to the first conductor 120b of the second cable. The load circuit is not electrically connected to the second conductor 122a of the first cable or to the second conductor 122b of the second cable.

[0163] In the different modes, the pairs of cables have different conductor properties and thus different performance profiles. Changing of mode changes these properties and performance parameters. The properties and performance profile of each of the first and cable changes according to mode, but also interaction between the cables causes change. Where the cables run alongside other cables, for example where a power supply is multi phase and each phase is carried by a separate cable, properties and performance profile of the cables will be impacted by the other cables and mode can be changes in view of this.

[0164] Conductors of different embodiments may be of different shape, dimension and / or material. Mode can be selected in view of operational (performance and loss) parameters.

[0165] In an experimental example, the transmission line includes such first and second cables, the cables being for capacitive power transfer and the cable being a CTS HF Mk.l cable for 85kHz operation as produced by Enertechnos under equal input operating conditions. The length of each cable is, by way of example only, 108 metres and a single pair of wireless power transfer (WPT) charging pads are connected at the receiving end (108-metre) of the two cables.

[0166] Data relating to the three modes of operation are in Table E, which indicates AC performance characteristics of the 1-ph cable operating at 85.22kHz in the three different modes but with near equal input voltage conditions. Table E:

[0167] Advantages observed include better regulation of the voltage across the cable such as reduction in voltage rise (attributed to Ferranti effect during low load conditions) at the receiving end of the cable by selection of mode based on present load configuration (e.g., position of the load(s), impedance of the load(s), quantity of the loads, power rating of the loads). Furthermore, performance efficiency and losses in the cable arrangement changes based on the selected mode.

[0168] Change of mode with such first and second cables can modify the shunt capacitance established between the cables. This is also the case where multiple phases are carried.

[0169] Table F indicates performance of the unit equivalent to an EV DC load i.e., a battery (post HF signal rectification) connected at the receiving end of the 1-ph cable (108-metre) for each of the three modes.

[0170] Additionally, the effects and benefits apply to multi-phase applications and other types of conductors (parallel distributed capacitive conductor, conventional / uncompensated or a hybrid conductor).

[0171] A transmission line may include a plurality of such cables as segments connected in series, where one of the modes can be independently selected for each cable.

[0172] Example 11 - Switching between Series Capacitive Compensation, Parallel Capacitive Compensation and Uncompensated Circuits.

[0173] According to other embodiments, a conductor component in the form of a cable comprises a plurality of conductors separated by insulation, and a transmission line includes the cable, a first switching network having electrical connections including switches, arranged to controllably connect a power source to a first terminal of the cable, and a second switching network having electrical connections including switches, arranged to controllably connect a load to a second terminal of the cable, the first and second switching networks being controllably to change between modes in which the cable / conductors have different properties.

[0174] Referring to Figure 19, in an example a cable includes first, second, third and fourth conductors 132a, 132b, 134a, 134b, switches 136a-139a, 140a-143a, 144a-145a of the first switching network 130a, and switches 136b-139b, 140b-143b, 144b-145b of the second switching network 130a. A first set of the switches 136a-139a are connected to, respectively, a terminal of each of the four conductors. Each of a second set of the switches 140a-143a are respectively connected in series to a respective one of the switches of the first set 136a-139a. A respective electrical connection is present between pairs of first and second switches that are in series.

[0175] A further electrical connection connects between the electrical connection between the pair of switches connected to the terminal of the first conductor 132a and the electrical connection between the pair of switches connected to the terminal of the third conductor 132b. The switch 144a of a third set is located in that further electrical connection controllable to permit or prevent flow of electricity.

[0176] Similarly, a further electrical connection connects between the electrical connection between the pair of switches connected to the terminal of the second conductor 134a and the electrical connection between the pair of switches connected to the terminal of the fourth conductor 134b. The switch 145a of a third set is located in a further electrical connection, such that the switch is controllable to permit or prevent flow of electricity.

[0177] The second switching network 130b is configured in the same way as the first switching network 130a, except inputs to the second switching network 130b are connected to the other terminals of the conductors and an output is to a load circuit.

[0178] In a first mode, which is illustrated in Figure 19, the switches of the first set are closed in both the first and second switching networks 130a, 130b. In the second set, the set 140a and 142a are closed, and switches 141a and 143a are open. The switches 144a and 145a are closed. The switches of the second switching network 130b are in mirror image. First and third conductors are thus connected together in both the first and second switching networks, and connected to the power supply but not to the load circuit. Second and fourth conductors are thus connected together in both the first and second switching networks, and connected to the load circuit but not to the power supply. In operation, power is thus transferred capacitively from the first and second conductors to the second and fourth conductors. In this mode, the conductors form collectively a distributed parallel capacitive conductor.

[0179] Selected output / load sub-conductors are shorted at both the receiving and sending ends connected to the load (circuit) terminal but not connected to the source circuit.

[0180] Referring to Figure 20, in a second mode, in the first switching network, in the first set switches 137a-139a are open and switch 136a is closed. In the second set the switch 140a is closed and switches 141a, 142a, 143a are open. In the third set, switches 144a, 145a are open. In the second switch network, in the first set switches 136b-138b are open and switch 139b is closed, in the second set switches 140b-142b are open and switch 143b is closed. In the third set switches 144b, 145b are open.

[0181] This results in the first conductor 132a being connected to the power supply and not to the load circuit, and the fourth conductor 134b being connected to the load circuit and not to the power supply. In operation, power is thus transferred capacitively from the first conductor to the fourth conductor. The second and third conductors are both galvanically isolated (floating). In this mode, the cable is a distributed series capacitive power transfer cable, with floating conductors. Referring to Figure 21 , in a third mode, in the first switching network 130a in the first set switches 136a, 138a are closed and switches 137a, 139a are open. In the second set, switches 140a and 142a are closed and switches 141a and 143a are open. Both switches 144a, 145a are open. In the second switching network 130a, switches in the first and third sets are open / closed in mirror image to those in the first set. In the second set, switches 140b and 142b are open and switches 141 b and 143b are closed. The configuration of switches in the third mode is like that in the first mode except for the switches in the third sets being open. Thus, first and third conductors are only connected at a supply side and second and fourth are only connected at the return side. In operation, power is transferred capacitively from the first and second conductors to the second and fourth conductors. In this mode, the cable is a distributed series capacitive power transfer cable, with compensation.

[0182] Referring to Figure 22, in a fourth mode, all switches in the first and second switching networks 130a, 130b are closed. Power is thus not transmitted capacitively. All conductors are thus shorted together. The conductors are collectively uncompensated.

[0183] Referring to Figure 23, in a fifth mode, all switches in the first and second switching networks 130a, 130b are open. Power is thus not transmitted.

[0184] Referring to Figure 24, in a sixth mode, the switches are like in the first mode, except that the switch 144a in the first switching set 130a and the switch 142b in the second switching set 130b are open. In operation, power is transferred capacitively from the first and third conductors to the second and fourth conductors. In this mode, the conductors form collectively a distributed parallel capacitive conductor having different conductor properties to those in the first mode.

[0185] Embodiments are not limited to the cable comprising four conductors. There may in practice be a greater number, the same principles of operation being applicable.

[0186] The power supply and the load circuit may be multi-phase or single phase.

[0187] The conductors may be modified to form windings of an electromagnetic coil (for example a power transfer coil). In this case the first and second switching networks 130a, 130b may be provided at terminals of the coil, per turn, or for any one or more lengths of the windings. Parallel

[0188] In some embodiments, conductors may follow a looped or ring-like path, such that terminals at the supply side and the return side are located near one another. Referring to Figure 25, apparatus (e.g. a cable or electromagnetic coil (e.g. a WPT coil)) comprises first and second conductors 150, 152 are separated by an insulator 154. Electric connections connect the first conductor 150 to a power source, and the second conductor 152 to a power source. The electrical connections include a first switch 156, this electrical connection with the first switch being arranged to controllably connect or disconnect, at a supply side, a second terminal of the second conductor 152 and a first terminal of the first conductor 150. The electrical connections include a second switch 158, this electrical connection with the second switch being arranged to controllably connect or disconnect, at a return side, a first terminal of the second conductor 152 and a second terminal of the first conductor 150. The electrical connections include a third switch 160, this electrical connection with the third switch being arranged to controllably connect or disconnect the second terminal of the second conductor 152 with the first terminal of the first conductor 150. The electrical connections include a fourth switch 162, this electrical connection with the fourth switch being arranged to controllably connect or disconnect the first terminal of the first conductor with the first terminal of the second conductor 152.

[0189] The first and second conductors may be 1 or multi-phase.

[0190] In a first mode, all of the first, second, third and fourth switches 156, 158, 160, 162 are open. In operation, the first and second conductors, with the insulator, function as an uncompensated distributed series capacitor.

[0191] In a second mode, the first and second switches 156, 158 are closed, such that the first terminal of the first conductor 150 and the second terminal of the second conductor 152 are electrically connected, and the second terminal of the first conductor 150 and the first terminal of the first conductor 152 are electrically connected. The third and fourth switches 160, 162 are open. In operation, the first and second conductors, with the insulator, function as an uncompensated conductor.

[0192] In a third mode, the third and fourth switches 160, 162 are closed, such that the first terminals of the first and second conductors 150, 152 are connected. The first and second switches 156, 158 are open. In operation, power transfer takes place capacitively from the first conductor 150 to the second conductor with characteristics of self-compensation.

[0193] Example 13 - Switching including Hybrid Compensation

[0194] In other embodiments, apparatus comprises a conductor component in the form of an electromagnetic coil or a cable, the conductor component including a plurality of conductors separated by an insulator. In these embodiments, series and parallel compensation may be integrated, which is advantageous with respect to AC machine applications, for example electromagnetic coils used for wireless power transfer. Quality factor, coupling coefficient, resonance freguency and mutual inductance may be improved, and versatility of the conductor component increased for various operational scenarios.

[0195] Referring to Figure 28, a plurality of conductors are layered, although in alternative examples they may be otherwise arranged. The apparatus comprises electrical connections including switches, switches between supply side terminals of the conductors and a power supply being of a first switching network 170a and switches between return side terminals of the conductors and the load circuit being of a second switching network 170b. Switches in the first switching network 170a that are each connected to a terminal of a respective conductor are of a first set. Switches in the first switching network 170a of a second set are each located between a respective switch of the first set and the power supply, connected in series to the respective switch of the first set. Switches in the first switching network 170a of a third set are each arranged to connect or disconnect alternate conductors, that is, not to connect one conductor with an adjacent conductor, but a next of the conductors.

[0196] In a first mode, an example of which is at Figure 28, some of switches of the first and second sets are shorted (closed) only at the first switching network 170a (that is, that the sending-end), such that one or more of the conductors are connected to the power supply. In the second switching network 170b, for each of those one or more conductors, the connected switch of the first set or second set in the second switching network 170b is open. The one or more conductors are not connected elsewhere by switches in the first set in the third switching network. Some of the switches of the first and second sets are shorted only at the second switching network 170b (that is, the receiving-end), such that different one or more of the conductors are connected to the load circuit. In the first switching network 170a, for each of those one or more (different) conductors, the connected switch of the first set or second set in the first switching network 170a is open. The one or more conductors are not connected elsewhere by switches in the third set in the second switching network.

[0197] In operation, power transfer occurs capacitively from the one or more conductors to one or more different conductors, through series capacitance.

[0198] Also in the first mode, two or more further of the conductors are connected to the power supply through corresponding switches in the first and second sets of the first switching network being shorted, but are not connected to the load circuit (associated switches in the second switching network being open). The two or more further of the conductors are electrically connected in parallel by a switch in the third set in the first and second switch networks, which connects then, being shorted. Also, two or more different further of the conductors are connected to the load circuit through corresponding switches in the first and second sets of the first switching network being shorted, but are not connected to the power supply (associated switches in the first switching network being open). The two or more different further of the conductors are electrically connected in parallel by a switch in the third set in the first and second switch networks, which connects then, being shorted.

[0199] In operation, power transfer occurs from the two or more further conductors to the two or more different further conductors through parallel capacitance.

[0200] The apparatus indicates in Figures 28 to 33 relates to a single phase of a multi-phase conductor component - the apparatus may be replicated for each additional phase for use with a multiphase power source. The apparatus may also be used for each of a live / signal line and a neutral / return line.

[0201] In a second mode, an example of which is at Figure 29, one or more of the conductors may be isolated. The isolated conductors may be located between conductors through which series capacitance occurs. In the second mode illustrated, the switches are open or shorted like in the first mode, save for switches that are open to isolate two conductors. In operation, series and parallel capacitance occurs like in the first mode, but properties are changed by isolation of conductors.

[0202] A third mode, an example of which is at Figure 30, differs to the first mode in that none of the conductors is used for power transfer through parallel capacitance, and in that one or more of the conductors are shorted such that conduction can occur non-capacitively as well as through series capacitance. As can be seen in the figure, switches in the first and second sets of the first and second switching networks are shorted to this end.

[0203] A fourth mode, an example of which is at Figure 31 , differs to the first mode in that none of the conductors is used for power transfer through series capacitance, and in that one or more of the conductors are shorted such that conduction can occur non-capacitively as well as through parallel capacitance. As can be seen in the figure, switches in the first and second sets of the first and second switching networks are shorted to this end. A fifth mode, an example of which is at Figure 32, conductors are used for power transfer through distributed series capacitance and parallel capacitance, and through one or more of the conductors being shorted such that conduction can occur non-capacitively.

[0204] A sixth mode, an example of which is at Figure 33, conductors are used for power transfer through distributed series capacitance and parallel capacitance, and through one or more of the conductors being shorted such that conduction can occur non-capacitively. Further, one or more of the conductors is isolated.

[0205] Referring to Figure 34, in a variant, a transmission line is arranged to include a distributed series capacitive conductor component and a distributed parallel capacitive conductor component (cables). The transmission line comprises the cables components, a first switching network 180, an intermediate switching network 182 and a second switching network 184. The first switching network 180 is between supply side terminals of conductors of the series capacitive conductor component and a power supply. The intermediate switching network 182 is between other terminals of the series capacitive conductor component and supply side terminals of the parallel capacitive conductor component. The second switching network is between return side terminals of conductors of the parallel capacitive conductor component and a load circuit. Switches in the first switching network 180 and the intermediate switching network 182 are configured to enable power transfer through the series capacitive conductor component. Switches in the second switching network 184 and the intermediate switching network 182 are configured to enable power transfer through the parallel capacitive conductor component. Configuration of switches can be understood from description in relation to Figures 28 to 33.

[0206] Example 14 - Change of Current Direction and selection of Coil Sections

[0207] In another embodiment, pathway and / or direction of current flow can be changed in some coils or cable configurations by selective switching operations. This alters shape and intensity of the electromagnetic field.

[0208] Referring to Figures 35 to 39, in a specific example pathway and / or direction of current flow is changed in a double-D (DD) electromagnetic coil. The coil thereof comprises a CTS / Series capacitive coil. In figure 35, a first conductor is connected to a power supply and a second conductor is electrically connected to outputs. In Figure 35 all switches are open, which is a non- operational switch configuration. A first winding is on a left side and a second winding is on a right side.

[0209] Referring to Figure 36, in a first mode switches are shorted or open such that the first winding is operational and the second winding is isolated.

[0210] Referring to Figure 37, in a second mode switches are shorted or open such that both windings are operational and current can flow in a same direction in the two windings.

[0211] Referring to Figure 38, in a third mode switches are shorted or open such that current flows in opposite directions in the two windings.

[0212] In operation, different modes can be selected to alter shape and intensity of the electromagnetic field. Example 15 - Interchanging Connection of Load Terminals to Different Current Carrying Components of a Conductor Component

[0213] In another embodiment, an alternative configuration of allows power to be transferred to and / or from a load circuit in a compensated or uncompensated manner by control of switches.

[0214] Referring to Figure 39, in a first mode, power is transferred to the load circuit capacitively and connections to outputs are non-capacitive.

[0215] Referring to Figure 40, in a second mode power is transferred to the load circuit by a non- capacitive electrical connection and connections to outputs are capacitive.

[0216] Referring to Figure 41 , power is transferred to the load circuit by a non-capacitive electrical connection and capacitively. Current flows to the outputs by a non-capacitive electrical connection and capacitively.

[0217] Example 16 - Balance & Imbalance 1-Phase & Multi-Phase Conductors

[0218] In some embodiments, each line in a 1-phase conductor or phase in a multi-phase conductor component can have a different impedance property either via changing the type, topology or degree of passive elements in the conductor component by inclusion and operation of switches. A result of such operation is to modulate the balance between the phases, and lines in a 1-ph conductor component, and by extension a system.

[0219] The conductor component can be configured by use of switches to be unbalanced. Benefits of being unbalanced including increased flexibility, in that an unbalanced system can allow for more flexibility in terms of the types of loads that can be connected to it, and it can allow for the use of non-symmetrical loads. Also, cost-efficient load distribution may result in networks where 3-phase loads are rare or only 1-phase eguipment is used. This may avoid need for upgrades.

[0220] Example 17 - Example of Coil with Terminal Placements

[0221] In embodiments, an electromagnetic coil may be provided with multiple terminals for first and second conductors and one of these may be selected for the first and / or second conductor using a switching network, such that the length of the first and / or second conductor can be changed. Terminals may be located at different angular positions around the coil. Examples are shown in Figure 42.

[0222] Any of the embodiments of the invention described above may be used over a wide bandwidth.

[0223] Unless otherwise stated, all individual features and / or steps of all embodiments described herein are disclosed in isolation and any combination of two or more such features is also disclosed, to the extent that such features or steps or combinations of features and / or steps are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features.

Claims

Claims1 . Apparatus for a transmission line, comprising:(a) conductors each being separated from one or more other of the conductors by a dielectric material, and(b) electrical connections for the conductors to a supply side of a power source and / or a return side of the power source, wherein the apparatus can be switched between at least first and second modes, wherein in the first mode, one or more of the conductors are connected to the supply side of the power source but not to the return side of the power source, and one or more of the conductors are connected to the return side of the power source but not to the supply side of the power source, and wherein in the second mode any one, more than one or all of: (i) a different one or more of the conductors is connected to the supply side of the power source but not to the return side of the power source compared with the first mode; (ii) a different one or more of the conductors is connected to the return side of the power source but not to the supply side of the power source compared with the first mode; (iii) one or more of the conductors that is connected in the first mode to the supply side of the power source but not to the return side of the power source, or to the return side of the power source but not to the supply side of the power source, is isolated; and (iv) one or more of the conductors is connected to the supply side and to the return side.

2. The apparatus of claim 1 , wherein the electrical connections comprise one or more switches operable to switch the apparatus between the at least first and second modes.

3. The apparatus of claim 1 or claim 2, which can be switched to a mode in which only one of the conductors is connected to the supply side of the power source but not to the return side of the power source and / or which can be switched to a mode in which only one of the conductors is connected to the return side of the power source but not to the supply side of the power source.

4. The apparatus of any one of the preceding claims, wherein in (i) the number of the one or more conductors that are connected to the supply side of the power source but not to the return side of the power source is different compared with the first mode, and / or in (ii) the number of the conductors that are connected to the return side of the power source but not to the supply side of the power source is different compared with the first mode,5. The apparatus of any one of the preceding claims, wherein the conductors comprise a plurality of sets of first and second conductors, the conductors of each set being separated by a dielectric material, wherein in the first mode, one, more or all of the first conductors are connected to the supply side of the power source but not to the return side of the power source, and one or more or all of the second conductors are connected to the return side of the power source but not to the supply side of the power source, and wherein in the second mode (i) the number of the first conductors that are connected to the supply side of the power source but not to the return side of the power source is different compared with the first mode, or (ii) the number of the second conductors that are connected to the return side of the power source but not to the supply side of the power source is different compared with the first mode, or (iii) both (i) and (ii).

6. The apparatus of claim 5, which can be switched to a mode in which all of the first conductors are connected to the supply side of the power source but not to the return side of the power source and / or which can be switched to a mode in which all of the second conductors are connected to the return side of the power source but not to the supply side of the power source.

7. The apparatus of claim 5 or claim 6, which can be switched to a mode in which one or more of the first conductors is connected to the supply side of the power source and to the return side of the power source, and / or which can be switched to a mode in which one or more of the second conductors is connected to the supply side of the power source and to the return side of the power source.

8. The apparatus of any one of claims 5 to 7, configured so that in all modes there is at least one set of first and second conductors that are capacitively connected to each other, the first conductor being connected to the supply side of the power source but not to the return side of the power source, and the second conductor being connected to the return side of the power source but not to the supply side of the power source.

9. The apparatus of any one of claims 5 to 8, wherein the first and second conductors are wound into substantially planar, spiral windings.

10. The apparatus of any one of claims 5 to 9, wherein the first and second conductors are located in a stack of substantially planar layers, the stack having a central lumen for location of electrical connections between the windings and the power source.

11. The apparatus of any one of claims 5 to 10, wherein in the second mode one of the first conductors and one of the second conductors are shorted out so that they are both connected to the supply side of the power source and also to the return side of the power source.

12. The apparatus of claim 11 , wherein the first and second conductors that are shorted out in the second mode are of the same set.

13. The apparatus as claimed in claim 12, wherein the first and second conductors that are shorted out in the second mode are from adjacent sets.

14. The apparatus as claimed in any one of claims 5 to 13, wherein first and second conductors from two sets are shorted out.

15. The apparatus as claimed in claim 14, wherein the first and second sets are located symmetrically within the coil and the shorting out results in an even redistribution of impedance within the coil.

16. The apparatus as claimed in claim 14, wherein the first and second sets are located asymmetrically within the coil and the shorting out results in an uneven redistribution of impedance within the coil.

17. The apparatus of any one of the preceding claims, wherein, in a mode (such as the first mode, the second mode of a different mode), at least two of the conductors are connected to the supply side of the power source but not to the return side of the power source, wherein the electrical connections also electrically connect in parallel, and / or at least two of the conductorsare connected to the return side of the power source but not to the supply side of the power source, wherein the electrical connections also electrically connect in parallel.

18. The apparatus of any one of the preceding claims, wherein conductors are arranged in layers (for example concentric or planar layers), adjacent layers being separated by a layer of the dielectric material, wherein in the first mode one or more of the conductors on a first side of one of the layers of dielectric material is connected to the supply side of the power source but not to the return side of the power source, and none of the conductors on the first side of the one layer are connected to the return side of the power source, and one of more of the conductors on the second side of the one layer are connected to the return side of the power source, and none of the conductors on the second side are connected to the supply side of the power source, wherein in the second mode one or more of the conductors on a first side of a different one of the layers of dielectric material are connected to the supply side of the power source but not to the return side of the power source, and none of the conductors on the first side of the different layer are connected to the return side of the power source, and one of more of the conductors on the second side of the different layer are connected to the return side of the power source, and none of the conductors on the second side are connected to the supply side of the power source.

19. The apparatus of any one of the preceding claims, wherein conductors are arranged in layers (for example concentric or planar layers), adjacent layers being separated by a layer of the dielectric material, wherein, in a mode (for example the first mode, the second mode or a different mode), (a) one of the conductors in a respective layer is connected to the supply side of the power source but not to the return side of the power source, wherein another of the conductors in a respective layer is also connected to the supply side of the power source but not to the return side of the power source, and wherein a yet other of the conductors in a respective layer between the layers of the one and other of the conductors is connected to the return side of the power source but not to the supply side of the power source, and / or(b) one of the conductors in a respective layer is connected to the return side of the power source but not to the supply side of the power source, wherein another of the conductors in a respective layer is also connected to the return side of the power source but not to the supply side of the power source, and wherein a yet other of the conductors in a respective layer between the layers of the one and other of the conductors is connected to the supply side of the power source but not to the return side of the power source.

20. The apparatus of claim 19, wherein in (a) one of the electrical connections electrically connects the one and other conductors at the return side, wherein in (b) one of the electrical connections electrically connects the one and other conductors at the supply side.

21. The apparatus of any one of the preceding claims, wherein the one or more conductors connected to the supply side of the power source and the one or more conductors connected to the return side of the power source are arranged, in at least the first mode, for capacitive power transfer.

22. Apparatus for a transmission line, comprising:(a) first and second conductors, separated by a dielectric material and each wound into one or more windings, and(b) electrical connections for the conductors to a supply side of a power source and a return side of the power source, wherein the apparatus can be switched between at least first and second modes, wherein in the first mode, the first conductor is connected to the supply side of the power source but not to the return side of the power source, and the second conductor is connected to the return side of the power source but not to the supply side of the power source, and wherein in the second mode at least one of: (i) at least one of the first and second conductors is connected to both the supply side and the return side of the power source; (ii) a portion (for example one or more of the windings) of the first and second conductors is isolated; (iii) direction of current flow in one or more of the windings is reversed.

23. The apparatus of claim 22, further comprising one or more switches operable to switch the power transfer coil between the at least first and second modes.

24. The apparatus of any one of the preceding claims, wherein the transmission line is a power transfer coil.

25. Apparatus for a transmission line, comprising:(a) a plurality of sets of first and second conductors, the conductors of each set separated by a dielectric material, and(b) electrical connections for the first and second conductors to a supply side of a power source and / or a return side of the power source, the power source supplying power having a plurality of phase components (for example being 3- or 6-phase), wherein the apparatus can be switched between at least first and second modes, wherein in the first mode, for each phase component, one or more of the first conductors are connected to the supply side of the power source for supply of the respective phase component, but not to the return side of the power source, and one or more or all of the second conductors are connected to the return side of the power source but not to the supply side of the power source, and wherein, in the second mode, for at least one of the phase components, different one or more of the first conductors are connected to the supply side of the power source for supply of the at least one phase component, but not to the return side of the power source compared with the first mode.

26. The apparatus of claim 25, wherein, in the second mode, for at least one of the phase components, the number of the first conductors that are connected to the supply side for supply of the at least one phase component but not to the return side of the power source is different compared with the first mode.

27. Apparatus comprising: a first conductor section comprising the apparatus of any one of the preceding claims; a second conductor section comprising the apparatus of any one of the preceding claims, wherein the electrical connections of the first and second conductor sections are connected in series.

28. The apparatus of claim 27, wherein first and second conductor sections are in different ones of the modes.

29. Apparatus for a transmission line, comprising: at least two conductor components, wherein each of the conductor components comprises a plurality of conductors and dielectric material, wherein conductors of the conductor components can be connected in series; at input and output sides of each of the conductor components, electrical connections including switches for assignment of each of the conductors for one of: capacitive power transmission connected at a supply side, capacitive power transmission connected at a return / load side, isolation and non-capacitive power transmission; and / or transmission of a phase component of a multi-phase power source, wherein the switches for each of the conductor components are independently configurable such that conductor properties of any two of the conductor components can be different.

30. A method of wirelessly transmitting power comprising using the apparatus as claimed in any one of claims 1 to 28 and switching between modes to vary the magnetic field, capacitance and / or reactance thereof.31 . The method of claim 30, further comprising operating the one or more switches to switch the apparatus or the coil between modes.

32. The method of claim 31 , further comprising operating the one or more switches to switch one or more connections between the conductors and / or between the conductors and the supply and / or return and / or load, so as to switch the apparatus between modes.

33. The method of claim 32, wherein the operating is performed during power supply through the transmission line.

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