Inductive power transfer transmitter and system

Abstract

1. An inductive power transfer transmitter comprising: an inverter subcircuit including at least one inverter; and a regulated circuit comprising a plurality of components, the components comprising at least a transmit coil, a first tuning network comprising an inductor and a capacitor, and a second tuning network comprising a first additional component, the plurality of components being arranged such that the regulated circuit is capable of varying a current through the transmit coil to compensate for variations in a K factor and is capable of providing an output current from the inverter subcircuit independent of a transmit coil current.

Description

[Technical field]

[0001] The present invention relates to an inductive power transfer transmitter, an inductive power transfer system and method. [Background technology]

[0002] Inductive power transfer is the transfer of electrical energy without a physical or wired connection. A typical inductive power transfer system includes an inductive power transfer transmitter or primary device that generates an electromagnetic field, which is used to transfer power across space to an inductive power transfer receiver or secondary device, which extracts power from the electromagnetic field and delivers it to a load. A typical inductive power transfer transmitter is driven by a power source and includes an inverter, a primary conditioning network, and a primary coil. A typical inductive power transfer receiver includes a secondary coil, a secondary conditioning network, a rectifier, and a load.

[0003] The system uses a magnetic field to wirelessly transfer power from a primary coil to a secondary coil. The magnetic field is generated by inputting an AC current into the primary coil. The secondary coil, when placed within the magnetic field generated by the primary coil, generates an AC voltage across its terminals to drive or power a connected load. Inductive power transfer can eliminate the use of wires and batteries, thus increasing the mobility, convenience, and safety of electronic devices.

[0004] References herein to patents, other external documents, or other sources of information are generally for the purpose of providing a context for discussing features of the present invention, and unless otherwise expressly stated, references to such external documents should not be construed as an admission that such documents or such sources are prior art or form part of the common general knowledge in the art in any jurisdiction. Summary of the Invention

[0005] It is an object of at least some preferred embodiments of the present invention to provide wireless power transmitters and systems, and / or at least provide the public with a useful alternative.

[0006] In one aspect, the invention is an inductive power transfer transmitter comprising: an inverter subcircuit including at least one inverter; and a tuned circuit comprising a plurality of components, the components comprising at least a transmit coil, a first tuning network comprising an inductor and a capacitor, and a second tuning network comprising a first additional component, the components being arranged such that the tuned circuit is capable of varying a current through the transmit coil to compensate for changes in K factor and is capable of providing an output current from the inverter subcircuit independent of the transmit coil current.

[0007] Optionally, the output current from the inverter sub-circuit is different from the transmit coil current.

[0008] Optionally, the output current from the inverter sub-circuit is less than the transmit coil current.

[0009] Optionally, power losses in the inverter sub-circuit are reduced.

[0010] Also, as described, First additional component Inductors Capacitors One or more of the inverter subcircuit output current and / or the transmit coil current are disposed in the regulated circuit to provide a current flow for the transmit coil current in addition to the inverter subcircuit output current and to provide sufficient current to the transmit coil.

[0011] Also, as described, a first additional component is in parallel with the transmit coil to provide a current source to the transmit coil in addition to the inverter subcircuit output current to supply sufficient current to the transmit coil.

[0012] Also, as described, an inductor and / or capacitor is in parallel with the transmitting coil to provide a current source to the transmitting coil in addition to the inverter subcircuit output current to supply sufficient current to the transmitting coil.

[0013] Also, as described, the output current from the inverter sub-circuit is smaller than the transmit coil current, and the current flow provided by the first additional component and / or inductor and / or capacitor provides current compensation by providing a current equal to the difference between the transmit coil current and the output current from the inverter sub-circuit.

[0014] Optionally, the regulated circuit further comprises at least one further additional component for improving the power factor of the power supplied from the inverter sub-circuit to the transmit coil.

[0015] Optionally, said at least one further additional component is a variable component for varying a power factor.

[0016] Optionally, the variable component is a variable capacitor and / or a variable inductor.

[0017] Optionally, an inductor and / or a capacitor and / or a first additional component is disposed in the regulated circuit to provide filtering.

[0018] Optionally, the regulated circuit may filter out harmonics in the output current from the inverter sub-circuit to improve EMI performance.

[0019] Optionally, the variable component is a variable capacitor and / or a variable inductor.

[0020] Optionally, the regulated circuit comprises a variable component that is variable for varying the portion of the current through the transmit coil.

[0021] Optionally, the variable component is a variable capacitor and / or a variable inductor.

[0022] Optionally, the transmit coil, the inductor, the capacitor and the first additional component are each located on a separate branch of the regulated circuit.

[0023] Optionally, an inductor is placed at the output of the inverter sub-circuit.

[0024] Optionally, a capacitor is placed at the output of the inverter sub-circuit.

[0025] Optionally, the branch in which the capacitor is located intersects with the branch in which the inductor is located.

[0026] Optionally, the capacitor, the first additional component and the transmit coil are connected in parallel.

[0027] Optionally, the inductor, the first additional component and the transmit coil are connected in parallel.

[0028] Optionally, a number of components are placed on the tuned circuit such that the tuned circuit can be modified as if the transmit coil were series tuned such that the tuned circuit can vary the current through the transmit coil to compensate for changes in the K factor.

[0029] Optionally, both the first tuning network and the second tuning network are Norton and Thevenin equivalents of a series tuned circuit and vary the current through the transmit coil to compensate for K-factor changes, while optionally comprising one or more components in parallel with the transmit coil to decouple the inverter from the transmit coil.

[0030] Optionally, the regulated circuit can be adapted by applying Norton's Theorem to transform the parallel connection of a voltage source (supplied by the inverter sub-circuit voltage), a series connection of a current source of an inductor and a capacitor, and a parallel connection of an inductor and a capacitor, creating the appearance of a first regulating network supplying the current source to the transmitting coil, and applying Thevenin's Theorem to transform the parallel connection of the current source, the first additional component, and the transmitting coil into a series connection of a voltage source, the first additional component, and the transmitting coil, such that the transmitting coil appears to be series regulated.

[0031] Optionally, the inductor and capacitor each have an absolute reactance such that the absolute reactance of the inductor is substantially the same as the absolute reactance of the capacitor, such that the combined impedance of the inductor and capacitor creates the appearance of an open circuit component such that the first tuning network appears to supply a current source to the transmitting coil.

[0032] Optionally, the first tuning network further comprises a second inductor.

[0033] Optionally, a second inductor is located at the output of the inverter sub-circuit, the second inductor being located in a branch separate from the branch of the first inductor.

[0034] Optionally, a branch of the capacitor intersects with a branch of the first inductor at one end and with a branch of the second inductor at the other end.

[0035] Optionally, the tuned circuit can be modified by applying Norton's Theorem to transform the series connection of a voltage source (supplied by the inverter sub-circuit voltage), a first and second inductor and a capacitor into a parallel connection of a current source, a first and second inductor and a capacitor, the inductor and capacitor each having an absolute reactance such that the combined absolute reactance of the inductor and capacitor is substantially the same as the absolute reactance of the capacitor, such that the combined impedance of the inductor and capacitor creates the appearance of an open circuit component such that the first tuning network appears to supply said current source to the transmitting coil, and by applying Thevenin's Theorem to transform the parallel connection of the current source, the first additional component and the transmitting coil into a series connection of a voltage source, the first additional component and the transmitting coil, such that the transmitting coil appears to be series tuned.

[0036] Optionally, the first tuning network further comprises a second capacitor.

[0037] Optionally, a second capacitor is placed at the output of the inverter sub-circuit, the second capacitor being placed in a branch separate from the branch of the first capacitor.

[0038] Optionally, a branch of the inductor intersects with a branch of the first capacitor at one end and with a branch of the second capacitor at the other end.

[0039] Optionally, the tuned circuit can be modified by applying Norton's Theorem to transform the series connection of a voltage source (supplied by the inverter sub-circuit voltage), a first and second capacitor and an inductor into a parallel connection of a current source, a first and second capacitor and an inductor, the inductor and capacitor having absolute reactances, respectively, such that the combined absolute reactance of the capacitors is substantially the same as the absolute reactance of the inductor, so that the combined impedance of the inductor and the capacitors creates the appearance of an open circuit component such that the first tuning network appears to supply a current source to the transmitting coil, and by applying Thevenin's Theorem to transform the parallel connection of the current source, the first additional component and the transmitting coil into a series connection of a voltage source, the first additional component and the transmitting coil, so that the transmitting coil appears to be series tuned.

[0040] Optionally, the regulated circuit further comprises a second additional component.

[0041] Optionally, a second additional component is disposed on a branch that intersects the branch on which the capacitor is disposed.

[0042] Optionally, a second additional component is located on a branch that intersects the branch on which the inductor is located.

[0043] Optionally, the branch on which the first additional component is located intersects the branch on which the second additional component is located.

[0044] Optionally, the branch in which the transmit coil is located intersects with the branch in which the first additional component is located.

[0045] Optionally, the regulated circuit further comprises a third additional component.

[0046] Optionally, the third additional component is disposed on a branch separate from the branch of the second additional component, the branch of the third additional component intersecting with the branch of the capacitor at one end and with the branch of the first additional component at the other end.

[0047] Optionally, the third additional component is disposed on a branch separate from the branch of the second additional component, the branch of the third additional component intersecting with the branch of the inductor at one end and with the branch of the first additional component at the other end.

[0048] Optionally, a first inductor; a second inductor; and A capacitor; a first additional component; and a second additional component; and a third additional component; and One or more of may be adjustable or fixed in any combination.

[0049] Optionally, the first additional component is a capacitor, and / or an inductor, and / or a combination of one or more capacitors and one or more inductors.

[0050] Optionally, the second additional component is an inductor, and / or a capacitor, and / or a combination of one or more capacitors and one or more inductors.

[0051] Optionally, the third additional component is an inductor, and / or a capacitor, and / or a combination of one or more capacitors and one or more inductors.

[0052] As used herein, "high power applications" refers to applications with high power ratings (inductive power transfer applications), which may be, for example, about 10 kW or greater.

[0053] As used herein, "low power applications" refers to applications with low power ratings (inductive power transfer applications), which may be, for example, about 10 kW or less.

[0054] As used herein, "wireless charging of electric vehicles" refers to wireless charging of electric vehicles large enough for industrial / commercial use, which is distinct from in-home wireless charging of electric vehicles, which may or may not have different design considerations than the inductive power transfer systems described herein.

[0055] The term "capacitor" is a term well understood in the art. However, as used herein, "capacitor" may refer to any component that has a capacitive reactance. "Capacitor" may also refer to any combination of components (which may or may not include any capacitors) arranged such that the net reactance of the combination of components is capacitive, and thus may be modified to a capacitor. A non-limiting example may be a combination of one or more capacitors and one or more inductors that are electrically equivalent to the capacitor.

[0056] The term "inductor" is a term well understood in the art. However, as used herein, "inductor" may refer to any component having an inductive reactance. "Inductor" may also refer to any combination of components (which may or may not include any inductors) arranged such that the net reactance of the combination of components is inductive and thus may be remodeled into an inductor. A non-limiting example may be a combination of one or more capacitors and one or more inductors that are electrically equivalent to the inductor.

[0057] As used herein, the term "LCL tuning" refers to a type of tuning that can be applied to the primary / transmitting coil as well as the secondary / receiving coil of an inductive power transfer system. An example of LCL tuning of a primary / transmitting coil is shown in FIG. 2C, where the first "L" in "LCL" refers to block 1 having a net inductive reactance, the "C" in "LCL" refers to block 2 having a net capacitive reactance, and the second "L" in "LCL" refers to block 3 having a net inductive reactance (supplied by the inductance of the primary / transmitting coil). It is desirable for the reactances of each of blocks 1-3 to be the same in absolute value. For example, blocks 1 and 3 each have an inductive reactance of +X, and block 2 has a capacitive reactance of -X. Blocks 1 and 3 can have series capacitors if desired, but blocks 1 and 3 should have a net inductive reactance even though they both have capacitors.

[0058] As used herein, the terms "series regulated" / "LC series regulated" refer to a type of regulation that can be applied to the primary / transmitting coil as well as the secondary / receiving coil of an inductive power transfer system.

[0059] While the inductive power transfer system described below can be used in a variety of applications, it should be noted that the inductive power transfer system (including the described embodiments and the sub-circuits that make up the inductive power transfer system) is designed to have high power applications, including, for example, wireless charging of electric vehicles in an industrial / commercial environment (as opposed to a domestic environment). Such designs should be distinguished from inductive power transfer systems that have only lower power applications (such as, for example, wireless charging of electronic devices such as mobile phones) even if the electronic circuits appear similar on a schematic diagram. Inductive power transfer systems with high power applications have certain design considerations that are not applicable when designing inductive power transfer systems with low power applications. For example, inductive power transfer systems with high power applications have significantly greater problems with heat dissipation and power efficiency that, at least in some cases, cannot be adequately addressed using techniques known to those skilled in the art. Some of these specific design considerations (and their respective solutions) are discussed later in the detailed description.

[0060] Regarding the terms "comprising" and "consisting at least part of" as used herein, each statement in this specification should be interpreted such that when an independent claim is presented containing the term "comprising", there may be other features present than the term or features preceded by that term. Related terms such as "comprise" and "comprises" should be interpreted in the same manner.

[0061] Reference to a numerical range disclosed herein (e.g., 1-10) also includes reference to every reasonable number within that range (e.g., 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9, and 10), as well as any reasonable numerical range within that range (e.g., 2-8, 1.5-5.5, and 3.1-4.7), and thus all subranges of every range explicitly disclosed herein are expressly disclosed herein. These are merely specifically intended examples, and all possible combinations of numerical values ​​between the lowest and highest values ​​recited are considered to be expressly described in this application in a similar manner.

[0062] The present invention may also be broadly described as consisting of any or all combinations of the parts, elements and features referred to or indicated in the specification of this application, individually or collectively, and any two or more of said parts, elements or features, and where a specific integer having known equivalents in the art to which the invention pertains is referred to herein, such known equivalents are deemed to be incorporated herein as if individually set forth.

[0063] The embodiments are described with reference to the following drawings. [Brief description of the drawings]

[0064] [Figure 1] 1 shows an overview of an inductive power transfer system. [Figure 2A] 1 shows different types of inverters. [Figure 2B] 1 shows different types of inverters. [Figure 2C] 1 shows different types of LCL adjustments. [Figure 3A] 1 shows different types of regulated circuits on the inductive power transfer transmitter side. [Figure 3B] 1 shows different types of regulated circuits on the inductive power transfer transmitter side. [Figure 4A] 1 shows different types of regulated circuits on the inductive power transfer receiver side. [Figure 4B]1 shows different types of regulated circuits on the inductive power transfer receiver side. [Figure 5A] 1 shows a generalized secondary side. [Figure 5B] 1 shows a generalized secondary side. [Figure 6A] 1 shows an outline of an inductive power transfer transmitter. [Figure 6B] 1 shows an outline of an inductive power transfer transmitter. [Figure 6C] 1 shows a first general embodiment of an inductive power transfer transmitter. [Figure 6D] 2 shows a second general embodiment of an inductive power transfer transmitter. [Figure 7] 1 shows a first exemplary embodiment of a first general embodiment of a regulated circuit. [Figure 8] FIG. 8 illustrates how the embodiment of FIG. 7 can be modified to appear series regulated. [Figure 9] The embodiment of FIG. 7 is shown as part of an inductive power transfer system. [Figure 10] 2 illustrates a second exemplary embodiment of the first general embodiment of the regulated circuit. [Figure 11] 1 shows a third exemplary embodiment of the first general embodiment of the regulated circuit. [Figure 12A] 1 illustrates an exemplary embodiment of a first tuning network of a first general embodiment of a tuned circuit. [Figure 12B] 1 illustrates an exemplary embodiment of a first regulating network of a second general embodiment of a regulated circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] [1. Overview of Inductive Power Transfer System] An overview of inductive power transfer systems is first provided to provide background information to the invention described herein. While the inductive power transfer systems described below can be used in a variety of applications, it should be noted that the inductive power transfer systems (including the described embodiments and the sub-circuits that make up the inductive power transfer systems) are designed to have high power applications, including, for example, wireless charging of electric vehicles in industrial / commercial environments (as opposed to domestic environments). Such designs should be distinguished from inductive power transfer systems that have only lower power applications (such as, for example, wireless charging of electronic devices such as mobile phones) even if the electronic circuits appear similar on a schematic diagram. Inductive power transfer systems with high power applications have certain design considerations that are not applicable when designing inductive power transfer systems with low power applications. For example, inductive power transfer systems with high power applications have significantly greater problems with heat dissipation and power efficiency that, at least in some cases, cannot be adequately addressed using techniques known to those skilled in the art. Some of these specific design considerations (and their respective solutions) are discussed later in the detailed description.

[0066] 1 shows an overview of an inductive power transfer system 1 that wirelessly transmits power from a power input 10 to supply power to a load 12. The inductive power transfer system includes an inductive power transfer transmitter 35 (also referred to as a "primary device," "transmitter circuit," "transmitter side," or "transmitter module") and an inductive power transfer receiver 36 (also referred to as a "secondary device," "receiver circuit," "receiver side," or "receiver module"). The inductive power transfer transmitter 35 is the portion of the inductive power transfer system 1 that wirelessly transmits power. The inductive power transfer receiver 36 is the portion of the inductive power transfer system 1 that wirelessly receives power.

[0067] First, we turn to the inductive power transfer transmitter 35. The inductive power transfer system 1 in the inductive power transfer transmitter 35 comprises a power input 10. The power input 10 can be a voltage and / or current input. For example, the power input 10 can provide a DC voltage, which can be generated from a power factor correction (PFC) unit, a DC-DC converter, a battery, or other type of DC source. The inductive power transfer system 1 in the inductive power transfer transmitter 35 also comprises an inverter subcircuit 14, which is used to convert the direct current of the power input to an alternating current output. The inverter subcircuit 14 includes at least one inverter, but may be two or more. The inverters that make up the inverter subcircuit 14 can be half-bridge (FIG. 2A), full-bridge (FIG. 2B), another switching mechanism, or a combination of the above. The inverter subcircuit 14 can be considered a modular stand-alone component. Those skilled in the art will understand that if the power input already has an alternating current, the inverter subcircuit 14 is not required. The inductive power transfer system 1 in the inductive power transfer transmitter 35 also comprises a primary coil 18 (interchangeably referred to as a "transmitting coil") that is used to wirelessly transfer power. The primary coil 18 may have multiple coils combined in series or parallel, but may be collectively referred to as a "primary coil 18". The primary coil 18 is regulated by a regulating subcircuit 20 such that the primary coil 18 and the regulating subcircuit 20 form a regulated circuit 22. The regulated circuit 22 may be considered to be modular. The regulated circuit 22 may be a series regulated circuit (e.g., FIG. 3A) with a capacitor to which the regulating subcircuit 20 tunes the primary coil 18. Alternatively, the regulated circuit 22 may be a (parallel) LC regulated circuit with a capacitor to which the regulating subcircuit 20 provides regulation. However, the regulated circuit 22 is preferably an LCL regulated circuit (e.g., FIG. 3B). In the LCL regulated circuit 22, the regulating subcircuit 20 provides a capacitor and an inductor for the primary coil 18, which is the LCL regulated circuit. The capacitors used in the LCL regulated circuit 22 are provided by the regulating subcircuit 20 .In addition to the primary coil 18 , the inductor used for LCL tuning 22 may be supplied by the tuning subcircuit 20 .

[0068] Reference is now made to the inductive power transfer receiver 36. The inductive power transfer system 1 in the inductive power transfer receiver 36 also comprises a secondary coil 24 (interchangeably referred to as a "receiving coil") for receiving the wirelessly transferred power from the primary coil 18. The secondary coil 24 may have multiple coils combined in series or parallel, but may be collectively referred to as the "secondary coil 24". Similar to the primary coil 18, the secondary coil 24 is tuned by a tuning subcircuit 26 to form a tuned circuit 28. The tuned circuit 28 may be considered to be modular. The tuned circuit 28 may be an LCL tuned circuit (e.g., FIG. 4A) having an inductor and a capacitor for the tuning subcircuit 26 to provide tuning. Alternatively, the tuned circuit 28 may be a (parallel) LC tuned circuit having a capacitor for the tuning subcircuit 26 to provide tuning. However, the tuned circuit 28 is preferably a series tuned circuit (e.g., FIG. 4B). In the series tuned circuit 28, it is the tuning subcircuit 26 that provides the capacitor for the secondary coil 24 to be series tuned. Inductive power transfer system 1 also includes a rectifier subcircuit 32 within inductive power transfer receiver 36 for converting an AC input to a DC output. Rectifier subcircuit 32 may be considered modular. Inductive power transfer system 1 also includes a load 12 within inductive power transfer receiver 36. Those skilled in the art will appreciate that it is desirable to have a rectifier subcircuit 32 in situations where it is desirable to supply DC current to load 12.

[0069] [1.1 Power transmission and alignment] An inductive power transfer system 1, of which the present invention may form a part, allows electrical energy to be transferred without physical contact. The inductive power transfer system 1 should be able to operate to generate a constant output for receipt at a load 12. For example, this may be to achieve a good user experience for applications such as wireless charging of electric vehicles.

[0070] As will be described in more detail in this embodiment, this involves controlling the power that the primary device provides from the primary coil 18 in response to changes in the secondary device 36. For example, such changes may be related to a particular amount of mismatch between the primary coil 18 and the secondary coil 24 and / or changes in the load 12 connected to the secondary device 36.

[0071] The inductive power transfer system 1 transfers power optimally when the primary coil 18 and secondary coil 24 are properly aligned. The alignment is such that the secondary coil 24 is within the strongest portion of the electromagnetic field generated by the primary coil 18. Any misalignment between the primary coil 18 and secondary coil 24 can lead to less than optimal power transfer from the primary device 35 to the secondary device 36.

[0072] Misalignment may refer to the distance between the transmitter 35 and the receiver 36 not being close enough and / or the orientation between the transmitter 35 and the receiver 36 being incorrect. For example, misalignment between the primary coil 18 and the secondary coil 24 may occur because, for example, an electric vehicle may have different ground clearances depending on its load, or the secondary coil 24 located within the electric vehicle may be difficult to park so as to be well aligned with the primary coil 18 each time the electric vehicle is charged. As another example, there may be a tilt between the transmitter 35 and the receiver 36 such that a misalignment occurs.

[0073] Mismatch between the primary coil 18 and the secondary coil 24 may change the magnetic coupling coefficient (k factor) between the primary coil 18 and the secondary coil 24. The change in the coupling coefficient k may then change the power at the secondary device 36. The change in k affects both the power level and the efficiency of the wireless power transfer system.

[0074] For example, the power in the secondary coil 24 and output increases as the value of magnetic coupling increases, e.g., as the primary coil 18 and secondary coil 24 become better aligned. In other examples, using different types of tuning, the power in the secondary coil 24 may decrease as the coupling coefficient k (also referred to as the "magnetic coupling coefficient") increases.

[0075] Inductive power transfer systems operate over a wide range of coupling coefficient k and load conditions. Variations in the coupling coefficient k are due to physical misalignments between the primary coil 18 and secondary coil 24, because it is difficult to perfectly align both the transmitter coil 18 and receiver coil 24 for each charge, and because vehicle ground clearance varies with load and tire pressure. Typically, the magnetic coupling coefficient (k factor) can vary by a factor of two or more. For example, the k factor can vary from a value of 0.15 at the furthest distance between the primary coil 18 and secondary coil 24 to a value of 0.3 at the closest position between the primary coil 18 and secondary coil 24 in the context of a wireless electric vehicle charging application.

[0076] Alternatively, the secondary device 36 may be modified in a manner that is unrelated to a mismatch in the coils 18, 24 but that causes more or less power to be required or drawn by the secondary device 36. In one such example situation, the load 12 connected to the secondary device may be changed, which will also change the amount of power drawn by the load 12. Thus, the secondary device 36 may require more or less power to be drawn from the primary device 35 in order to provide sufficient power to the load 12 in response to this change.

[0077] [2. K-factor compensation] In the inductive power transfer system 1, the output power provided by the secondary device 36 is preferably kept constant in order to maintain the power to the load 12. Therefore, power control is desired to maintain constant power at the output of the secondary device 36. Typically, this power control may be implemented in both the primary device 35 and the secondary device 36, for example to compensate for changes in the coupling coefficient k.

[0078] With regard to the ability to compensate for changes in the coefficient k, inductive power transfer systems 1 can be divided into two groups depending on whether or not power control is implemented on the secondary device 36. Both will be discussed.

[0079] [2.1 K-factor compensation without power control of secondary devices] For a system 1 without power control on the secondary device 36, changes in power level due to changes in k are typically compensated for by adjusting the primary coil current (Ipt) in the opposite direction of the change in k, so that their product remains largely unchanged. That is, power control in the primary device 35 typically requires supplying a current to the primary coil 18 such that the power supplied by the primary coil 18 changes in correlation with changes in the system. For example, power control in the primary device 35 may take the form of controlling the current supplied to the primary coil 18 in relation to changes in the coupling coefficient k with the secondary coil 24, so that the product of these two variables, i.e., the power received by the secondary device 36 from the primary device 35, remains largely unchanged.

[0080] For example, as the secondary coil 22 moves further away from the primary coil 18, the coupling coefficient k decreases and therefore the primary device 35 supplies more current to the primary coil 18 to generate more power. This increase in power coincides with the change in the coupling coefficient k. Thus, the secondary device 36 does not see the effect of the change in the coupling coefficient k because the increased power from the primary coil 18 offsets the change in the coupling coefficient k.

[0081] To wirelessly transmit power via a magnetic field, the transmitter 35 needs to inject an AC current (Ipt) into the transmitting coil Lpt to set up a magnetic field. The secondary coil needs to be placed within this magnetic field to wirelessly receive the energy. More specifically, the magnetic field induces a voltage in series with the secondary coil, which is measured in an open circuit condition. It is therefore typically known as the secondary coil open circuit voltage Voc.

[0082]

number

[0083] where Lpt and Lst are the primary secondary coil inductances, ω=2πf, and f is the operating frequency of the wireless power transfer system.

[0084] According to this definition, Voc is related to the operating frequency, the primary coil current, the coupling coefficient k, and the coil inductance.

[0085] For a given secondary circuit, Voc determines the amount of power transferred from the primary to the secondary. Primary circuits and pads can also be configured as Voc.

[0086] Since the coil inductance typically does not change significantly with mismatch, and the frequency is typically fixed or has a small range of variation for EV charging applications (to maintain good tuning), Voc is directly controlled by the product of Ipt and k. Therefore, if the product of Ipt and k can be kept constant, Voc and the power level can be kept constant.

[0087] Due to mismatch, k can typically change by a factor of two or more, which means that to maintain constant power, the primary coil current must change in the opposite direction by the same factor.

[0088] [2.1.1 LCL Adjustable Primary Coil] For an LCL regulated primary coil, the primary coil current is defined as:

[0089]

number

[0090] Here, X is the characteristic impedance of the LCL network, which is equal to the absolute reactance of Cpt (Figure 3) or the combined reactance of all components between the inverter and Cpt, and Vinv is the inverter output voltage.

[0091] Vinv is typically used to control the primary coil current. Vinv can be changed by changing the inverter's input DC voltage (VDC) or phase shift percentage (θ) using the following formula:

[0092]

number

[0093] Here, θ can be varied from 0 to 100% to reduce Vinv.

[0094] VDC is generated by either a single-phase or three-phase power factor correction unit which has a very limited range of variation (typically less than 1.3 times) and therefore cannot be used alone to vary Vinv by more than a factor of 2 to compensate for the large k variations in the LCL regulated primary.

[0095] Inverter phase shift can be used to vary Vinv, but operating at a large phase shift percentage (i.e., a lower inverter output voltage) increases the inverter current, which results in higher inverter conduction and switching losses, and therefore reduces operating efficiency.

[0096] Therefore, it is difficult to vary the primary coil current over a large range to compensate for changes in k of the LCL regulated primary.

[0097] [2.1.2 Series Adjustable Primary Coil] For a series regulated primary, Vinv does not need to change as much as an LCL regulated primary to change Ipt by many times. It is therefore possible to rely on limited changes in Vdc to compensate for power level changes due to large k changes, and it may be possible to operate the inverter with 0% minimum phase shift to reduce switching and conduction losses. This concept is explained below with the help of Figure 5, which shows a series regulated primary and a generalized secondary driven by Voc. On the secondary side, the impedance Voc includes the secondary coil inductor in series with the rest of the secondary circuit. It is denoted Z_Voc in this paper. For efficiency reasons, Z_Voc is typically designed to be primarily real. For simplicity, we will assume it is a resistor.

[0098] The secondary circuit can be represented and formed using a reflected impedance Zr as shown in FIG. 5, where:

[0099]

number

[0100] The primary and secondary coil inductances (Lpt, Lst) typically do not vary significantly with k, and the frequency may be fixed, for example, for EV charging applications. Thus, according to this equation, Zr is larger for larger k and smaller for smaller k. Assuming Vinv is fixed, it is clear that a higher Zr (as a result of a higher k) will reduce the primary coil current and vice versa. This desirable relationship between Ipt and k is shown in the equation below and helps to stabilize Voc for varying k (as Voc is the product of Ipt and k).

[0101]

number

[0102] Thus, a series regulated primary can compensate for changes in k by automatically changing its primary coil current. It is possible to design an IPT system with a series regulated primary to fully compensate for a range of changes in k such that Voc and system power remain nearly unchanged even with a fixed inverter output voltage. Practical limitations may reduce the effectiveness of such compensation, so that Vinv may still need to be changed only slightly to aid in compensation.

[0103] However, series regulated primaries have two major drawbacks that make them less attractive for high power applications. First, high power applications typically require large primary coil currents, and the series configuration means that this large current must flow through the inverter, which can create large losses. Second, the series regulated network is a poorer filter compared to an LCL network, which means that more of the higher order harmonics generated by the normal operation of the inverter can reach the primary coil and radiate into nearby space, creating potential EMI challenges.

[0104] [2.2 K factor compensation by power control of secondary device] For systems with power control implemented on the secondary device 36, changes in k do not need to be fully compensated for by the primary coil current. The power control implemented on the secondary device 36 may partially adjust the output power level. However, implementing power control on the secondary device 36 adds cost and complexity to the secondary device, which may be undesirable.

[0105] Large k changes can also detune the system, causing higher reactive currents in various components such as inverters, inductors, and capacitors, which reduces system efficiency and increases costs by requiring components with higher current and voltage ratings and more expensive thermal management.

[0106] 2.3 Transmitter topology design to compensate for k-factor variations The remainder of the detailed description describes a topology for inductive power transfer transmitter 35 that allows the primary coil current to automatically vary over a large range to compensate for changes in k (similar to a series regulated primary) such that the required inverter voltage range is reduced, while providing output current from the inverter sub-circuit independent of the transmit coil current (making the topology more advantageous than a true series regulated primary), and optionally achieving other results including, for example, one or more of the following: Achieve high efficiency (in terms of the ability to keep the power factor of the inverter output voltage close to unity) Achieve high EMI performance Achieve control of the current through the transmitting coil.

[0107] The above results make the inductive power transfer transmitter 35 (described herein) advantageous over the various topologies of k-factor compensation described above.

[0108] 3. General embodiment of an inductive power transfer transmitter [3.1 Overview] A general embodiment of an inductive power transfer transmitter 35 will now be described. The general embodiment of the inductive power transfer transmitter 35 can form part of the inductive power transfer system 1.

[0109] 6A shows a schematic of an inductive power transfer transmitter 35. The inductive power transfer transmitter 35 has a (DC) power input 10. The power input 10 connects to an inverter subcircuit 14 for converting DC power (received from the (DC) power input 10) to AC power. The inverter subcircuit 14 has one or more inverters 38. The inductive power transfer transmitter 35 also has a regulated circuit 22 that comprises a number of components.

[0110] Next, the regulated circuit 22 shown in Figure 6A will be described. The regulated circuit 22 shown in Figure 6A comprises a transmitter coil 18, a first tuning network 37, and a second tuning network 39. At one end of the regulated circuit 22 is the first tuning network 37, which is located (directly) at the output of the inverter subcircuit 14. At the other end of the regulated circuit 22 is the transmitter coil 18. The second tuning network 39 is located between the first tuning network 37 and the transmitter coil 18.

[0111] The purpose of the first and second tuning networks is to allow the tuned circuit 22 to be retrofitted into the circuit equivalent of a series-tuned transmit coil 18; as discussed in section 2.1.2, having a series-tuned transmit coil 18 means that the tuned circuit 22 allows for automatic changes in the current through the transmit coil 18 to compensate for changes in the k-factor: The function of the first regulating network is to convert a voltage source Vinv (the inverter output) into a current source (I_X) that flows into the second regulating network. As will be explained later, the first regulating network comprises at least one inductor and at least one capacitor. The function of the second tuning network is to convert the current source (I_X) back to a second voltage source, and the second tuning network is tuned in series with the transmit coil (Lpt) driven by the second voltage source. Although the second tuning network is shown in FIG. 6A as being in parallel with the transmit coil (Lpt), in reality it is in series with the transmit coil (Lpt) driven by the second voltage source. As will be described below, the second tuning network comprises at least one electronic component. For example, the electronic component can be, but is not limited to, a resistor, an inductor, or a capacitor.

[0112] Thus, the structure of FIG. 6A has the k-compensation characteristic of the series regulated primary coil described in section 2.1.2, but because the first and second regulating networks of regulated circuit 22 provide a current source for the transmit coil (as each of these regulating networks provides a branch that provides current flow to the transmit coil), the current in the inverter can be much smaller than the current in the transmit coil (Lpt). That is, having both the first regulating network 37 and the second regulating network 39 between inverter subcircuit 14 and transmit coil 18 "decouples" the inverter subcircuit output current from the transmit coil current, thus allowing regulated circuit 22 to be designed to have independent inverter subcircuit output and transmit coil currents. That is, the currents may be the same or different. This allows the inverter subcircuit output current and the transmit coil current to be designed independently. Thus, regulated circuit 22 is particularly suited for high power wireless systems, which typically require large transmit coil currents to set up large magnetic fields for power transfer, and optimal (e.g., minimum) inverter currents to reduce inverter subcircuit losses. The output current of the inverter subcircuit is easier to design to be much lower than the transmit coil current (i.e., when the inverter subcircuit has a high input voltage). This reduces power losses in the inverter subcircuit. In a series regulated primary, such advantages realized in regulated circuit 22 are not possible because the inverter output current is connected directly to the transmit coil, forcing the inverter current to be the same as the transmit coil current. This gives regulated circuit 22 an advantage over a true series regulated transmit coil.

[0113] FIG. 6B shows an embodiment of FIG. 6A as an example. The embodiment of the regulated circuit 22 of FIG. 6B is similar to the regulated circuit 22 of FIG. 6B, but the regulated circuit embodiment 22 also includes one or more inverter power factor correction networks 45, 47 inserted between the first and second regulating networks to help improve the power factor of the inverter. Such a network would be considered to be placed in series with the first current source (the voltage source transformed by the first regulating network). This inverter power factor correction network decouples the inverter power factor control from the power control, since the first constant current source is not affected by the changes of the inverter power factor correction network. The first power factor correction network 45 and the second power factor correction network 47 each include one or more components for improving the power factor of the power supplied from the inverter subcircuit 14. Both the first power factor correction network 45 and the second power factor correction network 47 are optional and are not required to be included in the regulated circuit 22.

[0114] Various embodiments of regulated circuit 22 will now be described. As will become apparent, the regulated circuit 22 embodiments described herein include at least one inductor and at least one capacitor in the first regulation network. The regulated circuit embodiments described herein also include at least one additional component 44 in the second regulation network. The regulated circuit 22 embodiments described herein also include a transmit coil 18.

[0115] The various embodiments described herein fall into one of two general embodiments. A first general embodiment is shown in FIG. 6C, and a second general embodiment is shown in FIG. 6D. The difference between the first and second general embodiments is in the respective first tuning networks 37, where the positions of the inductors and capacitors in the first tuning networks are effectively "swapped around": 6C, the first tuning network of a first general embodiment has at least one inductor located at the output of the inverter subcircuit 14. There is also at least one capacitor located on a separate branch from the inductor(s). Based on the relative positions of the inductor and capacitor, this general embodiment can be referred to as an "LC embodiment." In contrast, referring to FIG. 6D, the first regulation network of the second general embodiment has at least one capacitor located at the output of the inverter subcircuit 14. There is also at least one inductor located on a separate branch from the capacitor(s). Based on the relative locations of the inductor and capacitor, this general embodiment can be referred to as the “CL embodiment.”

[0116] 4. First (LC) General Embodiment of the Adjusted Circuit [4.1 Overview] Next, a first general embodiment of the regulated circuit will be described with reference to FIG. 6C.

[0117] First, the adjusted circuit 22 according to the first general embodiment will be described at the "block level."

[0118] The regulated circuit 22 shown in FIG. 6C includes a transmit coil 18, a first regulating network 37, a second regulating network 39, a first inverter power factor correction network 45, and a second power factor correction network 47. At one end of the regulated circuit 22 is the first regulating network 37 located (directly) at the output of the inverter subcircuit 14. At the other end of the regulated circuit 22 is the transmit coil 18. The second regulating network 39 is located between the first regulating network 37 and the transmit coil 18. The first inverter power factor correction network 45 and the second inverter power factor correction network 47 are located between the first regulating network 37 and the second regulating network 39.

[0119] The regulated circuit shown in FIG. A first tuning network 37 including inductors 40a and 40b and a capacitor 42b A second regulation network including an additional component 44 a first inverter power factor correction network including at least an additional component 46; A second inverter power factor correction network comprising at least additional components 48 Transmitting coil 18 Includes.

[0120] The components that form the regulated circuit of FIG. 6C will now be described in more detail.

[0121] The regulated circuit 22 has inductors 40a and 40b arranged at the output of the inverter subcircuit 14. The inductors 40a and 40b are arranged on separate branches. Either of the inductors 40a, 40b can be adjustable so that its inductance can be changed. The regulated circuit 22 also has a capacitor 42 connected between the inductors 40a and 40b. The capacitor 42 can be adjustable so that its capacitance can be changed. The regulated circuit 22 has three parallel branches in which the capacitor 42, the additional component 44, and the transmit coil 18 are connected in parallel with each other. The regulated circuit 22 also has additional components 46 and 48 connected between the parallel branches of the capacitor 42 and the additional component 44. The additional components 46 and 48 are arranged on separate branches with each other.

[0122] The additional components 44, 46, 48 are components that have impedances that are resistive and / or reactive. For example, any of the additional components 44, 46, 48 can be resistors, capacitors, or inductors. Any of the additional components 44, 46, 48 can have a fixed impedance. Alternatively, any of the additional components 44, 46, 48 can be adjustable such that its impedance can be changed. If any of the additional components 44, 46, 48 have a resistive impedance, the additional component can be adjusted to change its resistance. If any of the additional components 44, 46, 48 have a reactive impedance, the additional component can be adjusted to change its reactance. The reactance can be changed between inductive and capacitive.

[0123] Although the additional components 44, 46, 48 can have resistive impedances, it is preferred that these components have only reactive impedances, or at least, have minimal resistance. Thus, it is preferred that the additional components 44, 46, 48 are capacitors or inductors, rather than being resistors. More preferably, the additional component 44 is a capacitor and the additional components 46, 48 are inductors, such that the additional components 44, 46, 48 provide filtering to filter out higher order harmonics generated from the inverter subcircuit output and / or provide filtering to improve the power factor of the power output from the inverter subcircuit. Furthermore, it is even more preferred that the additional component 44 is a capacitor with an adjustable capacitance. Having the additional component 44 as a variable capacitor helps to filter out higher order harmonics generated from the inverter subcircuit output and / or improve the power factor of the power output from the inverter subcircuit. Having the additional component 44 as a variable capacitor also helps to control the current provided to the transmit coil 18.

[0124] In the first general embodiment of the regulated circuit 22, it is not necessary to have all the components shown in FIG. 6C. However, in this general embodiment, the regulated circuit 22 should at least include the transmit coil 18, a first tuning network 37 comprising at least one inductor (either inductor 40a or 40b is sufficient, but both inductors 40a, 40b may be optionally incorporated) and one capacitor (such as, for example, capacitor 42), a second tuning network 39 comprising an additional component 44, and further additional components that may be either additional component 46 or additional component 48 (but both additional components 46, 48 may be optionally incorporated). This allows the regulated circuit 22 to vary the current through the transmit coil to compensate for changes in the K factor. Preferably, the regulated circuit 22 also has additional components (such as, for example, components 46, 48) to improve the power factor of the power supplied to the transmit coil and / or to control the current through the transmit coil 18. This will be explained in more detail in the next section.

[0125] [4.2 Design Considerations] We now discuss various design considerations for a first general embodiment of regulated circuit 22. The design considerations are as follows: Provides output current from the inverter subcircuit independent of the transmit coil current (advantageous over series regulated primary), while automatically varying the primary coil current over a large range to compensate for changes in k (similar to series regulated primary) so that the required inverter output voltage range is reduced Achieve improved EMI performance Achieve improved efficiency (in terms of the ability to keep the power factor of the inverter output voltage close to unity) Controlling the transmit coil current.

[0126] Each of these advantages is described in the context of what it can provide as an advantage over the regulated circuit topologies described in Sections 2.1 and 2.2. Each advantage is described separately in detail.

[0127] [4.2.1 Automatic change of primary coil current to compensate for k-factor change] The inductive power transfer transmitter 35 preferably has a regulated circuit 22 comprising a number of components arranged such that the regulated circuit 22 can be retrofitted to a series regulated primary coil arrangement via a combination of Thevenin and Norton circuit analysis. By allowing the regulated circuit 22 to be retrofitted to a series regulated primary coil arrangement, the regulated circuit 22 can automatically adjust the current through the primary coil 18 in response to changes in the k-factor in the same manner as described above in section 2.1.1.

[0128] To achieve this desired result, a first general embodiment of regulated circuit 22 should have at least a first tuning network 37 comprising at least an inductor (in the example of FIG. 6C, it is sufficient to have either inductor 40a or inductor 40b) and a capacitor 42, and a second tuning network 39 comprising a first additional component 44 and a second additional component (which can be either additional component 46 or 48). Having two inductors is optional but not required. Having additional components 46, 48 is optional but not required.

[0129] The remainder of this section provides a description of how the components in first tuning network 37 and second tuning network 39 enable the first general embodiment of tuned circuit 22 to provide automatic changes in the transmit coil current to compensate for changes in the k-factor.

[0130] The inductors and capacitors (in the first tuning network 37) allow the application of Norton's theorem to transform the regulated circuit 22 from a series connection of a voltage source (supplied by the inverter subcircuit voltage), an inductor and a capacitor to a (circuit equivalent) parallel connection of a current source, an inductor and a capacitor. By having a (circuit equivalent) parallel connection of a current source, an inductor and a capacitor, the combined impedance of the inductors and capacitors creates a large impedance appearance (preferably an open circuit appearance) to the parallel connected current sources (e.g., when the absolute reactances of the inductors and capacitors are similar). Preferably, the absolute capacitive reactance of the capacitors is substantially equal to the absolute inductive reactance of the inductors, or substantially equal to the absolute combined inductive reactance of the inductors if both inductors 40a, 40b are used in the regulated circuit 22. Thus, the first tuning network 37 becomes a constant current source.

[0131] Following the transformation into a constant current source supplied by the first tuning network 37, the regulated circuit 22 can be further transformed by applying Thevenin's theorem. This is possible due to the presence of the first additional component 44 (in the second tuning network 39). Applying Thevenin's theorem transforms the parallel connection of the current source, the first additional component 44, and the transmit coil 18 into a (circuit equivalent) series connection of the voltage source, the first additional component 44, and the transmit coil 18. The (circuit equivalent) series connection provides the appearance of a series regulated transmit coil 18, and as explained in section 2.1.2, having a series regulated transmit coil 18 means that the regulated circuit 22 allows for automatic changes in the current through the transmit coil 18 to compensate for changes in the k-factor.

[0132] Furthermore, in the first general embodiment of the regulated circuit 22, the first regulating network 37 has a capacitor 42 connected to provide a current flow to the transmit coil 18, and the second regulating network 39 has an additional component 44 to provide a current flow to the transmit coil 18. The current flows provided by the capacitor 42 and the additional component 44, respectively, are added to the current provided from the output of the inverter subcircuit. This means that the current output of the inverter subcircuit is independent of the transmit coil current. That is, the inverter subcircuit 14 does not have to match the current through the transmit coil 18, but can differ. In contrast, in an actual series regulated transmit coil circuit, the inverter subcircuit is always the same as the transmit coil current.

[0133] This difference provides the regulated circuit 22 with an advantage over a real series regulated transmit coil circuit and can be described as follows. The design of the regulated circuit 22 allows the transmit coil current to be sourced from the inverter subcircuit output, but also allows for the current to be sourced from the current flowing through the capacitor 42 and / or the current flowing through the additional component 44. By sourcing a portion of the transmit coil current from other components and not only from the inverter subcircuit output, the inverter subcircuit output current can be designed to be less than the transmit coil current. This allows the output current of the inverter subcircuit to be reduced. This reduces the power loss in the inverter subcircuit. While this described advantage is particularly applicable to high power applications, one skilled in the art will appreciate that the described advantage can be implemented even when high power applications are not considered.

[0134] As explained, the current flowing out of the first tuning network 37 can be considered as a current source whose magnitude is determined by I_X=Vinv / X, where X is the impedance of one or more inductors (e.g., inductors 40a and / or 40b) or capacitor 42. This magnitude remains unchanged regardless of how the rest of the circuit changes. Thus, the first tuning network can be considered as a constant current source. If we ignore the additional components 46 and 48 (because they are in series with the current source), the current source flows through both the additional component 44 and the transmitting coil 18. However, the current distribution between the additional component 44 and the transmitting coil 18 is entirely dependent on the impedance of the additional component 44, the impedance of the transmitting coil 18, and the reflected impedance, which changes with power. The current I_inv at the inverter is I_inv=power / Vinv at unity power factor, where Vinv can change with the input voltage and phase shift of the inverter subcircuit. Thus, the current in the inverter subcircuit is independent of the current in the primary coil.

[0135] In some embodiments, there may be one or more capacitors in series with an inductor in the first tuning network 37. Alternatively, or in addition, there may be one or more inductors in series with a capacitor in the first tuning network 37. FIG. 12A illustrates a general example of this, where the first tuning network 37 has at least an inductor 40a and a capacitor 42, and may also have (depending on the value of c) a capacitor 41a in series with the inductor 40a, and an inductor 43 in series with the capacitor 42. In such a situation, it is desirable for the combined reactance of the components at the output of the inverter subcircuit 14 to be substantially the same as the combined reactance of the components connected in parallel with the transmit coil 18, so that the first general embodiment of the tuned circuit 22 can be adapted as a series tuned transmit coil, such that K compensation is provided by automatic changes in current.

[0136] An example of this can be seen in FIG. 12A, where the combined reactance between terminals a and e is X, indicating that the combined impedance is inductive. Note that the constant c ranges from 0 to 1. When c=0, an inductor (reactance X) is connected between terminals a and e, and a capacitor (reactance -X) is connected between terminals e and f. When C>0, both an inductor and a capacitor are present between these terminals. The combined reactance between terminals e and f is -X, indicating that the combined impedance is capacitive. Also, if the sum of the reactance between terminals a and e and the reactance between terminals b and f is X, then a portion of the reactance X (between a and e) may shift between terminals b and f.

[0137] In the context of this general embodiment, arranging components in the adjusted circuit 22 or a circuit equivalent of an LCL adjusted transmit coil to generate an LCL adjusted transmit coil should be avoided for reasons discussed in section 2.1.1. It also prevents the adjusted circuit 22 from being converted into a series adjusted transmit coil to realize the advantage of automatically varying the transmit coil current to compensate for changes in the k-factor. With reference to the example of FIG. 6C, if either the capacitor 42, the first additional component 44, or the second additional component (which can be either the additional component 46 or the additional component 48) is omitted from the adjusted circuit 22, the adjusted circuit 22 will look like an LCL adjusted transmit coil (or its circuit equivalent), and such a circuit configuration is undesirable since it cannot provide automatic changes in the primary coil current to compensate for changes in the k-factor.

[0138] Further specific information can be found in Section 4.3.1, and in particular the accompanying description of Figures 8A-F. Although Section 4.3.1 is described in the context of a first exemplary embodiment, those skilled in the art will recognize that the principles described in Section 4.3.1 apply to this general embodiment as well as the other exemplary embodiments.

[0139] [4.2.2 Improving EMI performance] It is also desirable for the inductive power transfer transmitter 35 to have a regulated circuit 22 that includes a number of components arranged such that the regulated circuit 22 improves EMI performance in the inductive power transfer transmitter 35. As discussed in Section 2.1.2, having a regulated circuit with a series regulated transmit coil is problematic because the regulated circuit provides insufficient filtering and does not adequately address the issue of high order harmonics generated from the inverter subcircuit 14 that lead to EMI performance issues. Therefore, to provide improved EMI performance in the inductive power transfer transmitter 35, it is desirable for the regulated circuit 22 to act as a filter that filters out high order harmonics generated from the inverter subcircuit 14, or at least provide better filtering than could be achieved from a regulated circuit with a series regulated circuit.

[0140] Therefore, it is preferable to have an inductor (either inductor 40a or inductor 40b will suffice) and capacitor 42 in regulated circuit 22 to provide improved filtering. Placing an inductor at the output of inverter subcircuit 14 along with capacitor 42 provides a filter that diverts higher order harmonics away from transmit coil 18, thus improving EMI performance in inductive power transfer transmitter 35.

[0141] To filter out higher order harmonics, both inductors (i.e., inductor 40a and inductor 40b) are preferably used in conjunction with capacitor 42. Also, first additional component 44 is preferably capacitive. A second additional component in the regulated circuit (which may be either additional component 46 or additional component 48) is preferably an inductor. Even more preferably, both additional components 46 and 48 are present in regulated circuit 22 and both additional components are inductors.

[0142] [4.2.3 Power factor improvement] Inductive power transfer transmitter 35 also desirably has regulated circuit 22 with a number of components arranged such that regulated circuit 22 can improve the power factor of the power provided by inverter subcircuit 14 to improve the power efficiency of inverter subcircuit 14. In this context, improved power factor refers to an inverter subcircuit output power factor approaching unity. A power factor of unity means that the inverter subcircuit output current is in phase with the inverter subcircuit output voltage, such that the effective value of the inverter subcircuit output current is a minimum for a given power level output by the inverter subcircuit.

[0143] To achieve this desired result, regulated circuit 22 may have either additional component 46 or additional component 48, but that is not required, to improve the inverter power factor towards unity or to make the overall impedance of regulated circuit 22 (slightly) inductive. Optionally, regulated circuit can have both additional component 46 and additional component 48, to improve the inverter power factor towards unity or to make the overall impedance of regulated circuit 22 (slightly) inductive. The impedance of additional component 46 and / or additional component 48 is preferably tunable.

[0144] Components in regulated circuit 22 may be optionally tunable for purposes of improving the power factor. For example, one or more of inductor 40a, inductor 40b, capacitor 42, additional component 44, additional component 46, and additional component 48 may be tunable. That is, the impedance of each may be adjusted to improve the power factor of the power delivered to transmit coil 18.

[0145] [4.2.4 Control of transmitting coil current] It is also desirable for the inductive power transfer transmitter 35 to have a tuned circuit 22 that includes a first additional component 44 that is variable, such as a variable capacitor or inductor. Because the total current flowing through the additional component 44 and the transmit coil 18 is fixed by a constant current source provided by the first tuning network 37, varying the impedance of the additional component 44 varies the portion of the current (provided by the first tuning network 37) that flows through the transmit coil 18.

[0146] 4.3 Exemplary embodiments of an inductive power transfer transmitter Next, we will describe exemplary embodiments that fall within the scope of the first general embodiment of regulated circuit 22. More generally, these exemplary embodiments fall within the scope of the general embodiment of inductive power transfer transmitter 35.

[0147] 4.3.1 First Exemplary Embodiment A first exemplary embodiment of an inductive power transfer transmitter will now be described with reference to Figures 7 and 8A-F. The first exemplary embodiment shown in Figures 7 and 8A-F comprises the following features: Inductive power transfer transmitter 135, which corresponds to inductive power transfer transmitter 35 Power input 110 corresponds to power input 10 Inverter subcircuit 114 corresponding to inverter subcircuit 14 Inverter 138, which corresponds to Inverter 38 Adjusted circuit 122 corresponding to adjusted circuit 22 A first regulation network 137 corresponding to the first regulation network 37 A second regulation network 139 corresponding to the second regulation network 39 A first inverter power factor correction network 145 corresponding to the first inverter power factor correction network 45 A second inverter power factor correction network 147 corresponding to the second inverter power factor correction network 47 Inductor 140a ("L1A"), which corresponds to inductor 40a Inductor 140b ("L1B"), which corresponds to inductor 40b Capacitor 141a ("C1A"), which corresponds to capacitor 41a Capacitor 141b ("C1B"), which corresponds to capacitor 41b Capacitor 142 ("C2"), which corresponds to capacitor 42 A capacitor 144 ("C3") corresponding to the first additional component 44 An adjustable impedance 146 ("X2A") corresponding to the second additional component 46 · An adjustable impedance 148 (“X2B”) corresponding to the third additional component 48 .

[0148] Features of the first exemplary embodiment are as follows: The inverter operates at a fixed frequency f (but is not limited to a fixed frequency). The combined impedance of L1A, L1B, C1A and C1B is (effectively) +X at frequency f. The impedance of C2 is (effectively) -X at frequency f. · The adjustable impedances X2A and X2B are variable reactance elements that can be either inductive or capacitive, or change between capacitive and inductive. Their unique location in the circuit allows for effective control of the power factor of the inverter output voltage Vinv without affecting the power level of the system. The power factor can be determined by measuring the phase difference between Vinv and Iinv, or the phase difference between Iinv and I_X2. The impedances of X2A and X2B can then be adjusted to improve the inverter power factor towards unity, or make the overall impedance of the regulated circuit slightly inductive. X2A and X2B may each be implemented using a variable capacitor, a variable inductor, a fixed inductor in series with a variable capacitor, a variable inductor in series with a fixed capacitor, or any other combination of variable or fixed inductors and capacitors. The input DC voltage can be varied to control the primary coil current Ipt and power. The inverter phase shift can also be varied to control the primary coil current Ipt and power. The regulated topology can operate either as LCL regulated, series regulated secondary, or any other secondary topology. The regulated network is a better harmonic filter than LCL and series regulated topologies in preventing inverter generated higher harmonics from reaching and radiating into the primary coil, therefore it has better EMI performance than LCL or series regulated primary. Capacitors C1A, C1B, C4A, and C4B are optional. Capacitors C1A or C1B can be placed in series with L1A or L1B, respectively. Using one or both of these capacitors can help reduce the overall net inductance from L1A and L1B, so that the overall net inductance can effectively cancel the capacitance of C, as discussed later in this section. Either of the capacitors C4A and C4B can be placed in series with the transmit coil. Adding these capacitors in series with the transmit coil reduces the overall reactance of the branch in which the transmit coil is placed, and therefore increases the current supplied to the transmit coil. The regulating network behaves similarly to a series regulated primary in terms of its ability to automatically adjust the primary coil current to compensate for changes in Voc and power level due to changes in k. As a result, the required range of Vinv can be significantly reduced compared to an LCL regulated primary; thus avoiding high inverter currents. This special property is illustrated using Figure 8 A-F, which demonstrates how the proposed circuit can be converted into a series regulated primary.

[0149] FIG. 8A shows the topology of the first exemplary embodiment, and FIG. 8B shows its equivalent circuit by expressing certain components by their impedance. According to Norton's theorem, the series connection of Vinv and the composite impedance (X / 2) of L1A / B and C1A / B can be transformed into a parallel equivalent where a current source is in parallel with an impedance of (substantially) +X, as shown in FIG. 8C. The magnitude of the current is Vinv / X. The parallel connection of (substantially) X and (substantially) -X results in (or converges to) an infinite impedance, since their composite impedance is substantially -X^2 / (XX). The denominator of zero is infinity. Thus, in FIG. 8D, both +X and -X are (substantially) eliminated. Since X2A and X2B cannot change the magnitude of the current source, these two variable impedance blocks can also be eliminated, leading to the circuit of FIG. 8E, where the current source is placed in parallel with the capacitor C3, and according to Thévenin's theorem, it can be transformed again into a voltage source in series with an impedance, as shown in FIG. 8F. The magnitude of the voltage is Veq = Vinv / X*XC3.

[0150] F in Figure 8 is obviously a series regulated circuit, and the primary coil current Ipt is expressed as:

[0151]

number

[0152] As can be seen, the proposed circuit behaves similarly to a series regulated primary circuit in terms of its ability to automatically vary Ipt to compensate for changes in power and Voc due to changes in k, with a larger k leading to a smaller Ipt and vice versa. Finally, it is worth mentioning that since the tunable impedances X2A and X2B are in series with the current sources, varying their values ​​does not change the magnitude of the current sources and therefore the power levels, but their inherent position in the circuit allows them to control the power factor of the inverter output very effectively. The decoupling between the power and the inverter power factor simplifies the control algorithm.

[0153] FIG. 9 shows a first exemplary embodiment as part of an inductive power transfer system 1 .

[0154] 4.3.2 Second Exemplary Embodiment Next, a second exemplary embodiment of an inductive power transmission transmitter will be described, which is shown in Fig. 10. The second exemplary embodiment shown in Fig. 10 comprises the following features: Inductive power transfer transmitter 235 corresponding to inductive power transfer transmitter 35 Power input 210 corresponds to power input 10 Inverter subcircuit 214 corresponding to inverter subcircuit 14 Inverter 238 corresponding to inverter 38 An adjusted circuit 222 corresponding to the adjusted circuit 22 A first regulation network 237 corresponding to the first regulation network 37 A second regulation network 239 corresponding to the second regulation network 39 A first inverter power factor correction network 245 corresponding to the first inverter power factor correction network 45 A second inverter power factor correction network 247 corresponding to the second inverter power factor correction network 47 Inductor 240a ("L1A"), which corresponds to inductor 40a Inductor 240b ("L1B"), which corresponds to inductor 40b Capacitor 241a ("C1A"), which corresponds to capacitor 41a Capacitor 241b ("C1B"), which corresponds to capacitor 41b Capacitor 242 ("C2"), which corresponds to capacitor 42 An adjustable impedance 244 ("X3") corresponding to the first additional component 44 An adjustable impedance 246 ("X2A") corresponding to the second additional component 46 · An adjustable impedance 248 (“X2B”) corresponding to the third additional component 48 .

[0155] The second exemplary embodiment differs from the first exemplary embodiment in that the capacitor C3 in FIG. 7 is replaced with an adjustable impedance X3.

[0156] Features of this second exemplary embodiment are as follows: 1. The primary coil current and power level can also be controlled by varying the impedance of X3 in addition to the inverter output voltage. As a result, the inverter phase shift and input DC voltage range can be further reduced.

[0157] 2. Impedances X2A and X2B are used to control the inverter power factor.

[0158] 3. X3 can be either inductive or capacitive.

[0159] 4.3.3 Third Exemplary Embodiment Next, a third exemplary embodiment of an inductive power transmission transmitter will be described, which is shown in Fig. 11. The third exemplary embodiment shown in Fig. 11 comprises the following features: Inductive power transfer transmitter 335 corresponding to inductive power transfer transmitter 35 Power input 310 corresponds to power input 10 Inverter subcircuit 314 corresponding to inverter subcircuit 14 Inverter 338, which corresponds to Inverter 38 Adjusted circuit 322 corresponding to adjusted circuit 22 A first regulation network 337 corresponding to the first regulation network 37 A second regulation network 339 corresponding to the second regulation network 39 A first inverter power factor correction network 345 corresponding to the first inverter power factor correction network 45 A second inverter power factor correction network 347 corresponding to the second inverter power factor correction network 47 An (inductive) tunable impedance 340a ("X1A") that corresponds to inductor 40a An (inductive) tunable impedance 340b ("X1B") corresponding to inductor 40b Capacitor 342 ("C2"), which corresponds to capacitor 42 An adjustable impedance 344 ("X3") corresponding to the first additional component 44 An adjustable impedance 346 ("X2A") corresponding to the second additional component 46 · An adjustable impedance 348 (“X2B”) corresponding to the third additional component 48 .

[0160] A third exemplary embodiment shows that X1A and X1B are adjustable, which (1) helps control the power factor of the inverter output voltage and (2) helps control the primary coil current and power level.

[0161] 5. Second (CL) General Embodiment of the Adjusted Circuit [5.1 Overview] A second general embodiment of the regulated circuit will now be described. The purpose of the following description is intended to highlight the differences between the first and second general embodiments of the regulated circuit 22. Any description of the first general embodiment of the regulated circuit 22 should be assumed to apply to the second general embodiment, unless otherwise explained in this section.

[0162] A second general embodiment of a regulated circuit will now be described with reference to FIG. 6D.

[0163] The adjusted circuit 22 according to the second general embodiment will first be described at the "block level."

[0164] The regulated circuit 22 shown in FIG. 6D has a transmit coil 18, a first regulating network 37, a second regulating network 39, a first inverter power factor correction network 45, and a second power factor correction network 47. At one end of the regulated circuit 22 is the first regulating network 37 located (directly) at the output of the inverter subcircuit 14. At the other end of the regulated circuit 22 is the transmit coil 18. The second regulating network 39 is located between the first regulating network 37 and the transmit coil 18. The first inverter power factor correction network 45 and the second inverter power factor correction network 47 are located between the first regulating network 37 and the second regulating network 39.

[0165] The regulated circuit shown in FIG. A first tuning network 37 comprising capacitors 51a and 51b and an inductor 53b A second regulation network including an additional component 44 a first inverter power factor correction network including at least an additional component 46; A second inverter power factor correction network comprising at least additional components 48 Transmitting coil 18 Includes.

[0166] The components that form the regulated circuit of FIG. 6D will now be described in more detail.

[0167] The regulated circuit 22 has capacitors 51a and 51b arranged at the output of the inverter subcircuit 14. The capacitors 51a and 51b are arranged on separate branches. Either of the capacitors 51a, b is adjustable so that its capacitance can be changed. The regulated circuit 22 also has an inductor 53 connecting between the capacitors 51a and 51b. The inductor 53 can be adjustable so that its inductance can be changed. The regulated circuit 22 has three parallel branches in which the inductor 53, the additional component 44, and the transmission coil 18 are connected in parallel with each other. The regulated circuit 22 also has additional components 46 and 48 connected between the parallel branch of the capacitor 42 and the additional component 44. The additional components 46 and 48 are arranged on separate branches with each other.

[0168] In the second general embodiment of the regulated circuit 22, it is not necessary to have all the components shown in Figure 6D. However, in this general embodiment, the regulated circuit 22 should at least include the transmit coil 18, a first tuning network 37 comprising at least one capacitor (either capacitor 51a or 51b is sufficient, but both capacitors 51a, 51b may be optionally incorporated) and one inductor (such as inductor 53), and a second tuning network 39 comprising additional components 44. This allows the regulated circuit 22 to vary the current through the transmit coil to compensate for variations in the K factor.

[0169] [5.2 Design Considerations] We now discuss various design considerations for a second general embodiment of regulated circuit 22. The design considerations are as follows: Provides output current from the inverter subcircuit independent of the transmit coil current (advantageous over series regulated primary), while automatically varying the primary coil current over a large range to compensate for changes in k (similar to series regulated primary) so that the required inverter output voltage range is reduced Achieve improved EMI performance Achieve improved efficiency (in terms of the ability to keep the power factor of the inverter output voltage close to unity) Controlling the transmit coil current Improve current stability.

[0170] Each of these three advantages will be described in the context as it can provide an advantage over the regulated circuit topologies described in Sections 2.1 and 2.2.

[0171] [5.2.1 Automatic change of primary coil current to compensate for k-factor change] The inductive power transfer transmitter 35 preferably has a regulated circuit 22 comprising a number of components arranged such that the regulated circuit 22 can be retrofitted to a series regulated primary coil arrangement via a combination of Thevenin and Norton circuit analysis. By allowing the regulated circuit 22 to be retrofitted to a series regulated primary coil arrangement, the regulated circuit 22 can automatically adjust the current through the primary coil 18 in response to changes in the k-factor in the same manner as described above in section 2.1.1.

[0172] To achieve this desired result, a second general embodiment of regulated circuit 22 should have at least a first tuning network 37 comprising at least a capacitor (in the example of FIG. 6D, it is sufficient to have either capacitor 51a or capacitor 51b) and an inductor 53, and a second tuning network 39 comprising a first additional component 44. Having two capacitors is optional but not required. Having additional components 46, 48 is optional but not required.

[0173] The remainder of this section provides a description of how the components in first tuning network 37 and second tuning network 39 enable the second general embodiment of tuned circuit 22 to provide automatic changes in the transmit coil current to compensate for changes in the k-factor.

[0174] The inductors and capacitors (in the first tuning network 37) allow the application of Norton's theorem to transform the regulated circuit 22 from a series connection of a voltage source (supplied by the inverter sub-circuit voltage), an inductor and a capacitor to a (circuit equivalent) parallel connection of a current source, an inductor and a capacitor. By having a (circuit equivalent) parallel connection of a current source, an inductor and a capacitor, the combined impedance of the inductors and capacitors creates a large impedance appearance (preferably an open circuit appearance) to the parallel connected current sources (e.g., when the absolute reactances of the inductors and capacitors are substantially the same). Preferably, the absolute inductive reactance of the inductors is substantially equal to the absolute capacitive reactance of the capacitors, or substantially equal to the absolute combined capacitive reactance of the capacitors if both capacitors 51a,b are used in the regulated circuit 22. Thus, the first tuning network 37 becomes a constant current source.

[0175] Following the transformation into a constant current source supplied by the first tuning network 37, the regulated circuit 22 can be further transformed by applying Thévenin's theorem. This is possible due to the presence of the first additional component 44 (in the second tuning network 39). Applying Thévenin's theorem transforms the parallel connection of the current source, the first additional component 44, and the transmitting coil 18 into a (circuit equivalent) series connection of the voltage source, the first additional component 44, and the transmitting coil 18. The (circuit equivalent) series connection provides the appearance of a series regulated transmitting coil 18, and as we did in section 2.1.2, having a series regulated transmitting coil 18 means that the regulated circuit 22 allows for automatic changes in the current through the transmitting coil 18 to compensate for changes in the k-factor.

[0176] Furthermore, in the second general embodiment of the regulated circuit 22, the first regulating network 37 has an inductor 53 connected to provide a current flow to the transmit coil 18, and the second regulating network 39 has an additional component 44 to provide a current flow to the transmit coil 18. The current flow provided by the inductor 53 and the additional component 44, respectively, is added to the current provided from the output of the inverter subcircuit. This means that the current output of the inverter subcircuit is independent of the transmit coil current. That is, the inverter subcircuit 14 does not have to match the current through the transmit coil 18, but can differ. In contrast, in an actual series regulated transmit coil circuit, the inverter subcircuit is always the same as the transmit coil current.

[0177] This difference provides the regulated circuit 22 with an advantage over the actual series regulated transmit coil circuit and can be described as follows. The design of the regulated circuit 22 allows the transmit coil current to be sourced from the inverter subcircuit output, but also allows for the current to be sourced from the current flowing through the inductor 53 and / or the current flowing through the additional component 44. By sourcing a portion of the transmit coil current from other components and not only from the inverter subcircuit output, the inverter subcircuit output current can be designed to be less than the transmit coil current. This allows the output current of the inverter subcircuit to be reduced. This reduces the power loss in the inverter subcircuit. This described advantage is particularly applicable to high power applications, but one skilled in the art will understand that the described advantage can be implemented even when high power applications are not considered.

[0178] As explained, the current flowing out of the first tuning network 37 can be considered as a current source whose magnitude is determined by I_X=Vinv / X, where X is the impedance of one or more inductors (e.g., capacitors 51a and / or 51b) or inductor 53. This magnitude remains unchanged regardless of how the rest of the circuit changes. The first tuning network can therefore be considered as a constant current source. If we ignore the additional components 46 and 48 (because they are in series with the current source), the current source flows through both the additional component 44 and the transmitting coil 18. However, the current distribution between the additional component 44 and the transmitting coil 18 is entirely dependent on the reflected impedance, which changes with power. The current I_inv at the inverter is I_inv=power / Vinv at unity power factor, where Vinv can vary with the input voltage and phase shift of the inverter subcircuit. Therefore, the current in the inverter subcircuit is independent of the current in the primary coil.

[0179] In some embodiments, there may be one or more inductors in series with a capacitor in the first tuning network 37. Alternatively, or in addition, there may be one or more capacitors in series with an inductor in the first tuning network 37. FIG. 12B illustrates a general example of this, where the first tuning network 37 has at least a capacitor 51a and an inductor 53, and may also have (depending on the value of c) an inductor 50a in series with the capacitor 51a, and a capacitor 52 in series with the inductor 53. In such a situation, it is desirable for the combined reactance of the components at the output of the inverter subcircuit 14 to be substantially the same as the combined reactance of the components connected in parallel with the transmit coil 18, so that the second general embodiment of the tuned circuit 22 can be adapted as a series tuned transmit coil, such that K compensation is provided by automatic changes in current.

[0180] An example of this can be seen in FIG. 12B, where the combined reactance between terminals a and e is -X, indicating that the combined impedance is capacitive. Note that the constant c ranges from 0 to 1. When c=0, a capacitor (reactance -X) is connected between terminals a and e, and an inductor (reactance X) is connected between terminals e and f. When C>0, both a capacitor and an inductor are present between these terminals. The combined reactance between terminals e and f is X, indicating that the combined impedance is inductive. Also, if the sum of the reactance between terminals a and e and the reactance between terminals b and f is -X, then a portion of the reactance X (between a and e) may shift between terminals b and f.

[0181] Further specific information can be found in Section 4.3.1, and in particular the accompanying description of Figures 8A-F. Although Section 4.3.1 is described in the context of a first exemplary embodiment, those skilled in the art will recognize that the principles described in Section 4.3.1 apply to this general embodiment as well.

[0182] [5.2.2 Improving EMI performance] It is also desirable for the inductive power transfer transmitter 35 to have a regulated circuit 22 that includes a number of components arranged such that the regulated circuit 22 improves EMI performance in the inductive power transfer transmitter 35. As discussed in Section 2.1.2, having a regulated circuit with a series regulated transmit coil is problematic because the regulated circuit provides insufficient filtering and does not adequately address the issue of high order harmonics generated from the inverter subcircuit 14 that lead to EMI performance issues. Therefore, to provide improved EMI performance in the inductive power transfer transmitter 35, it is desirable for the regulated circuit 22 to act as a filter that filters out high order harmonics generated from the inverter subcircuit 14, or at least provide better filtering than could be achieved from a regulated circuit with a series regulated circuit.

[0183] Although not required, it is preferred to provide improved filtering in regulated circuit 22 by having an inductor in series with capacitor 51a and / or capacitor 51b (while ensuring a net capacitive impedance along the branch including capacitors 51a and / or 51b in this general embodiment) and by having a capacitor in series with inductor 53 (while ensuring a net inductive impedance along the branch including inductor 53 in this general embodiment). Placing an inductor at the output of inverter subcircuit 14 along with capacitor 42 provides a filter that diverts higher harmonics away from transmit coil 18, thus improving EMI performance in inductive power transfer transmitter 35.

[0184] Although not required, in order to filter out higher order harmonics, an inductor in series with both capacitor 51a and capacitor 51b is preferably used along with a capacitor in series with inductor 53. Also, it is preferred that first additional component 44 is capacitive. It is preferred that a second additional component in the regulated circuit (which may be either additional component 46 or additional component 48) is capacitive. Even more preferably, both additional components 46 and 48 are present in regulated circuit 22 and both additional components are capacitive.

[0185] [5.2.3 Power factor improvement] Inductive power transfer transmitter 35 also desirably has regulated circuit 22 with a number of components arranged such that regulated circuit 22 can improve the power factor of the power provided by inverter subcircuit 14 to improve the power efficiency of inverter subcircuit 14. The techniques used to improve the power factor in the first general embodiment of regulated circuit 22 also apply to the second general embodiment.

[0186] [5.2.4 Control of transmitting coil current] For the same reasons as described with respect to the first general embodiment of the regulated circuit 22, it is also desirable for the inductive power transfer transmitter 35 to have a regulated circuit 22 that includes a first additional component 44 that is a variable capacitor.

[0187] [5.2.5 Improving current stability] It is also preferable to place an inductor in series with capacitor 51a and / or capacitor 51b (while ensuring, in this general embodiment, a net capacitive impedance along the branch containing capacitor 51a and / or 51b). The series inductor with capacitor 51a and / or 51b limits the rate of current change to improve operational stability.

Claims

1. 1. An inductive power transfer transmitter comprising: an inverter subcircuit including at least one inverter; and a regulated circuit comprising a plurality of components, the components including at least A transmitting coil; a first tuning network comprising an inductor and a capacitor; a second tuning network comprising a first additional component; Here, the plurality of components include the adjusted circuit: To be able to vary the current through the transmit coil to compensate for variations in the K factor, to provide an output current from the inverter subcircuit independent of the transmit coil current; 2. An inductive power transfer transmitter comprising:

2. 2. The inductive power transfer transmitter of claim 1, wherein the output current from the inverter subcircuit is less than the transmit coil current.

3. 2. The inductive power transfer transmitter of claim 1, wherein the current output from the inverter subcircuit is reduced as a result of the two conditioning networks decoupling the inverter from the transmit coil.

4. 2. The inductive power transfer transmitter of claim 1, wherein power losses in the inverter subcircuit are reduced.

5. 2. The inductive power transfer transmitter of claim 1, wherein the regulated circuit further comprises at least one further additional component for improving a power factor of the power supplied from the inverter subcircuit to the transmit coil.

6. 6. An inductive power transfer transmitter as claimed in claim 5, characterised in that the at least one further additional component is a variable component for varying the power factor.

7. 7. An inductive power transfer transmitter according to claim 6, characterized in that the variable components are variable capacitors and / or variable inductors.

8. 2. An inductive power transfer transmitter as claimed in claim 1, characterised in that the inductor and / or capacitor and / or the first additional component and / or second additional component are arranged in the regulated circuit to provide filtering.

9. 9. The inductive power transfer transmitter of claim 8, wherein the regulated circuit is capable of filtering out harmonics in the output current from the inverter subcircuit to improve EMI performance.

10. 2. An inductive power transfer transmitter as claimed in claim 1, characterized in that the regulated circuit comprises a variable component which is variable for varying the portion of the current passing through a transmitting coil.

11. 11. An inductive power transfer transmitter according to claim 10, characterized in that the variable components are variable capacitors and / or variable inductors.

12. 2. The inductive power transfer transmitter of claim 1, wherein the transmitting coil, the inductor, the capacitor, and the first additional component are each disposed on a separate branch of the regulated circuit.

13. 13. An inductive power transfer transmitter as claimed in claim 12, wherein the inductor is disposed at the output of the inverter sub-circuit.

14. 13. An inductive power transfer transmitter as claimed in claim 12, wherein the capacitor is located at the output of the inverter sub-circuit.

15. 13. An inductive power transfer transmitter according to claim 12, characterized in that the branch in which the capacitor is located intersects the branch in which the inductor is located.

16. 2. The inductive power transfer transmitter of claim 1, wherein the capacitor, the first additional component, and the transmit coil are connected in parallel.

17. 2. The inductive power transfer transmitter of claim 1, wherein the inductor, the first additional component, and the transmit coil are connected in parallel.

18. 2. The inductive power transfer transmitter of claim 1, wherein the components are arranged on the tuned circuit such that the tuned circuit can be modified as if the transmit coil were series tuned so that the tuned circuit can vary the current through the transmit coil to compensate for variations in K-factor.

19. 2. The inductive power transfer transmitter of claim 1, wherein the first and second tuning networks are both Norton and Thevenin equivalents of series tuned circuits for varying the current through a transmit coil to compensate for K-factor variations while optionally comprising one or more components in parallel with the transmit coil to decouple the inverter from the transmit coil.

20. The regulated circuit is applying Norton's theorem to transform a voltage source provided by the inverter subcircuit voltage, the series connection of the inductor and the capacitor into a current source, the parallel connection of the inductor and the capacitor, generating the appearance of a first regulating network that supplies the current source to the second regulating network; applying Thevenin's theorem to transform the parallel connection of the current source, the first additional component, and the transmitter coil into a series connection of a voltage source, the first additional component, and the transmitter coil, so that the transmitter coil appears to be series regulated; 2. An inductive power transfer transmitter according to claim 1, characterized in that it can be retrofitted by

21. 21. The inductor of claim 20, wherein the inductor and the capacitor each have an absolute reactance such that the absolute reactance of the inductor is substantially the same as the absolute reactance of the capacitor such that a combined impedance of the inductor and the capacitor creates the appearance of an open circuit component such that the first tuning network appears to supply the current source to the second tuning network.

22. the first tuning network further comprising a second inductor; 2. The inductive power transfer transmitter of claim 1, wherein the second inductor is located at an output of the inverter subcircuit, the second inductor being located in a branch separate from a branch of the first inductor.

23. the first tuning network further comprising a second capacitor; 2. The inductive power transfer transmitter of claim 1, wherein the second capacitor is located at an output of the inverter subcircuit, the second capacitor being located in a branch separate from the branch of the first capacitor.

24. the regulated circuit further comprises a second additional component; the second additional component is disposed on a branch that intersects the branch on which the capacitor is disposed; the second additional component is located on a branch that intersects the branch on which the inductor is located; and / or 13. An inductive power transfer transmitter according to claim 12, characterized in that the branch on which the first additional component is located intersects the branch on which the second additional component is located.

25. The first inductor; The second inductor; The capacitor; the first additional component; and the second additional component; and the third additional component; and 25. An inductive power transfer transmitter according to any one of claims 1 to 24, characterized in that one or more of are adjustable or fixed in any combination.

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