High frequency wireless power transmission system, transmitter and receiver therefor

Abstract

The load independent inverter comprises a switch-mode zero voltage switching (ZVS) amplifier comprising a pair of circuits comprising at least one transistor and at least one capacitor arranged in parallel and at least one inductor arranged in series with the transistor and capacitor, the amplifier further comprising only one ZVS inductor connected to the pair of circuits, and at least one pair of capacitors connected to the ZVS inductor and arranged in series with the at least one inductor and at least one resistor.

Description

[Technical field]

[0001] The present disclosure relates generally to wireless power transfer, and more particularly to high frequency wireless power transfer systems and transmitters and receivers therefor. [Background technology]

[0002] Wireless charging and wireless power transfer systems are becoming an increasingly important technology enabling the next generation of devices. The potential benefits and advantages offered by this technology are evident with an increasing number of manufacturers and companies investing in the technology.

[0003] Various types of wireless power transmission systems are known. A typical wireless power transmission system includes a power source electrically connected to a wireless power transmitter, and a wireless power receiver electrically connected to a load.

[0004] In a magnetic induction system, a transmitter has a coil with an inductance that transfers electrical energy from a power source to a receiving coil with an inductance. Power transfer occurs through magnetic field coupling between the transmitter and receiver inductors. These magnetic induction systems have a limited range, and the transmitter and receiver inductors must be optimally aligned for power transfer.

[0005] There are also resonant magnetic systems in which power is transferred by coupling of a magnetic field between the inductors of the transmitter and receiver. In resonant magnetic systems, the inductors are made to resonate using at least one capacitor. In resonant magnetic systems, the transmitter is self-resonant and the receiver is self-resonant. The range of power transfer in resonant magnetic systems is increased over that of magnetic induction systems and alignment problems are corrected. Although electromagnetic energy is generated in magnetic induction and resonant magnetic systems, the majority of power transfer occurs through magnetic fields. Little, if any, power is transferred through electrical induction or resonant electrical induction.

[0006] The Qi wireless charging standard is an exemplary implementation of a magnetic induction system. The Qi wireless charging standard is used for low-power consumer electronics such as smartphones and wearable devices. Furthermore, low-cost power converters, coils and integrated circuits are available for use with the Qi wireless charging standard. The Qi wireless charging standard operates in the kHz frequency range. Accordingly, devices operating according to the Qi wireless charging standard have a limited coupling range, require precise coil alignment, and use ferrite-based coils, which can be heavy and fragile. As a result, the application range of the Qi wireless charging standard is limited.

[0007] In an electrical induction system, the transmitter and receiver have capacitive electrodes. Power transfer occurs due to coupling of an electric field between the capacitive electrodes of the transmitter and receiver. Similar to resonant magnetic systems, there are resonant electrical systems in which the capacitive electrodes of the transmitter and receiver are made to resonate using at least one inductor. In resonant electrical systems, the transmitter is self-resonant and the receiver is self-resonant. Resonant electrical systems have an increased range of power transfer compared to that of electrical induction systems, and alignment problems are rectified. Although electromagnetic energy is generated in electrical induction and resonant electrical systems, the majority of power transfer occurs via electric fields. Little, if any, power is transferred via magnetic induction or resonant magnetic induction.

[0008] Applications of magnetic and electric induction systems, commonly referred to as inductive power transfer (IPT) systems, can operate in the tens of MHz frequency range, where the topologies of direct current (DC)-alternating current (AC) inverters used in the transmitters of these systems are typically based on class E or class EF2 inverter configurations. Although these configurations are power efficient and easy to build, optimal switching behavior can only be maintained for fixed loads. Thus, such configurations are highly dependent on fixed loads. As a result, IPT systems using class E or class EF2 inverters typically only operate efficiently over a narrow load range with a fixed coil separation distance.

[0009] As described in "Load-independent Class E Power Inverters: Part I. Theoretical Development," RE Zulinski and KJ Grady, IEEE Trans. Circuits Syst. I, Reg. Papers, Vol. 37, No. 8, pp. 1010-1018, August 1990, and "Design of Single-switch Inverters for Variable Resistance / load Modulation Operation," L. Roslaniec, AS Jurkov, A. Al Bastami and DJ Perreault, IEEE Trans. Power Electron., Vol. 30, No. 6, pp. 3200-3214, June 2015, relevant portions of which are incorporated herein by reference, class E and class EF2 inverters can be designed such that they achieve zero voltage switching (ZVS) to produce a constant output voltage as the load resistance varies when used with a finite DC inductor instead of a choke.

[0010] Such designs can extend the load range over which a class E or class EF2 inverter can operate efficiently, from infinite load resistance (open circuit) to some minimum load resistance. While these designs may be applied in some applications, such as high frequency DC / DC converters, they generally cannot be used efficiently in IPT systems where the distance between the coils / electrodes varies. In an IPT system, the load ranges from zero resistance (short circuit), where the coils / electrodes are completely isolated from each other, to some maximum load resistance where the coils / electrodes are closest to each other.

[0011] As previously mentioned, IPT systems can operate in the tens of MHz frequency range. By utilizing wide bandgap devices such as GaN and SiC, switching in the tens of MHz frequency range can be achieved. As described in “Load-independent Class E / EF Inverters and Rectifiers for MHz-Switching Applications,” S. Aldhaher, D. C. Yates, and P. D. Mitcheson, IEEE Trans. Power Electron., Vol. 33, No. 10, pp. 8270-8287, October 2018, and “High-frequency, High-power Resonant Inverter with eGaN FETs for Wireless Power Transfer,” J. Choi, D. Tsukiyama, Y. Tsuruda, and J. M. R. Davila, IEEE Trans. Power Electron., Vol. 33, No. 3, pp. 1890-1896, March 2018, relevant portions of which are incorporated herein by reference, recent developments in resonant converters and soft-switching topologies such as class E and class EF allow true utilization of wide bandgap devices, providing designers with topologies and circuit configurations to use to achieve high performance / power density converters.

[0012] Operating at tens of MHz frequencies for wireless power transfer increases the maximum air gap distance and improves tolerance to coil misalignment, thus allowing the receiver to be placed anywhere in the charging area without strict alignment requirements. This wireless power transfer also allows high-Q single-turn air-core coils to be used that are lightweight, compact, and can be implemented on low-cost FR4 PCBs. Such features were demonstrated by wirelessly powering a small drone as described in “Light-weight Wireless Power Transfer for Mid-air Charging of Drones,” by S. Aldhaher, PD Mitcheson, JM Arteaga, G. Kkelis, and DC Yates, 11th European Conf. Antennas Propagation, March 2017, pp. 336-340, the relevant portions of which are incorporated herein by reference. [Prior art documents] [Non-patent literature]

[0013] [Non-Patent Document 1] "Load-independent Class E Power Inverters: Part I. Theoretical Development," RE Zulinski and KJ Grady, IEEE Trans. Circuits Syst. I, Reg. Papers, Vol. 37, No. 8, pp. 1010-1018, August 1990. [Non-Patent Document 2] "Design of Single-switch Inverters for Variable Resistance / load Modulation Operation," L. Roslaniec, AS Jurkov, A. Al Bastami and DJ Perreault, IEEE Trans. Power Electron., Vol. 30, No. 6, pp. 3200-3214, June 2015.

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 6

Non-Patent Document 7

[0014] Although wireless power transfer techniques are known, improvements are desirable. It is therefore an object to provide novel wireless power transfer systems, transmitters and receivers therefor, and methods of wirelessly transferring power. [Means for solving the problem]

[0015] It should be appreciated that this Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to be used to limit the scope of the claimed subject matter.

[0016] Thus, in one aspect, there is provided a load independent inverter comprising a switch mode zero voltage switching (ZVS) amplifier, the switch mode ZVS amplifier being a pair of circuits comprising at least one transistor and at least one capacitor arranged in parallel and at least one inductor arranged in series with the transistor and capacitor, only one ZVS inductor connected to the pair of circuits, and at least one pair of capacitors connected to the ZVS inductor and arranged in series with the at least one inductor and at least one resistor.

[0017] In one or more embodiments, the load independent inverter comprises at least two capacitors connected to the ZVS inductor, hi one or more embodiments, the at least two capacitors are arranged in series with the at least one inductor and resistor.

[0018] In one or more embodiments, the minimum value of the load resistance normalized to the characteristic impedance of the switch mode ZVS amplifier is between 0.585 and 0.975.

[0019] In one or more embodiments, the q value of the load independent inverter is between 0.739 and 1.231.

[0020] In one or more embodiments, the residual reactance normalized to the characteristic impedance of the load independent inverter is between 0.194 and 0.323.

[0021] In one or more embodiments, the voltage gain value of the load independent inverter is between 2.349 and 3.915.

[0022] In one or more embodiments, the normalized output power of the load independent inverter is between 4.700 and 7.834.

[0023] In one or more embodiments, the load independent inverter has a constant voltage output. In one or more embodiments, the load independent inverter has a load range of 5.625 ohms to infinite or open circuit load. In one or more embodiments, the load independent inverter further comprises an impedance inverter circuit configured to convert the load independent inverter from a constant voltage output to a constant current output.

[0024] In one or more embodiments, the load independent inverter has a constant current output. In one or more embodiments, the load independent inverter has a load range from zero ohms or a short circuit load to 9.375 ohms.

[0025] In one or more embodiments, the load independent inverter is configured to detect a metal object. In one or more embodiments, the load independent inverter further comprises a peak detection circuit configured to measure a peak value of a voltage across a transistor of the load independent inverter, and a comparator configured to compare the peak value of the voltage with a threshold voltage and output a detection signal if the peak value of the voltage exceeds the threshold voltage. In one or more embodiments, the load independent inverter further comprises a voltage divider configured to convert the peak value of the voltage before measurement by the peak detection circuit.

[0026] In one or more embodiments, the switch mode ZVS amplifier is a radio frequency (RF) amplifier.

[0027] In one or more embodiments, the load independent inverter is a class E inverter.

[0028] In one or more embodiments, the load independent inverter is a direct current (DC) to alternating current (AC) inverter.

[0029] According to another aspect, a transmitter is provided that includes a load independent inverter that includes a switch mode zero voltage switching (ZVS) amplifier and a transmit coil or electrode connected to the load independent inverter, the transmit coil or electrode configured to transmit power to a receiver via magnetic or electric field coupling.

[0030] In one or more embodiments, the transmitter is non-resonant or not self-resonant.

[0031] In one or more embodiments, the transmit coil is configured to transfer power via magnetic field coupling.

[0032] In one or more embodiments, the transmit electrode is configured to transmit power via electric field coupling.

[0033] In one or more embodiments, the transmitter further comprises a power source.

[0034] In one or more embodiments, the transmitter further comprises a power converter configured to convert the power signal from the power source prior to reception by the inverter.

[0035] According to another aspect, there is provided a wireless power transfer system comprising: a load independent inverter comprising a switch mode zero voltage switching (ZVS) amplifier; a transmitter comprising a transmitting coil or electrode connected to the load independent inverter, the transmitting coil or electrode configured to transmit power to the receiver via magnetic field or electric field coupling; and a receiver comprising a receiving coil or electrode configured to extract power from the receiver via magnetic field or electric field coupling.

[0036] In one or more embodiments, the transmitter is non-resonant or not self-resonant and the receiver is resonant, hi one or more embodiments, the receiver is resonant at the operating frequency of the transmitter.

[0037] In one or more embodiments, the transmit coil is configured to transmit power via magnetic field coupling, and the receive coil is configured to extract power via magnetic field coupling.

[0038] In one or more embodiments, the transmitting electrodes are configured to transmit power via electric field coupling, and the receiving electrodes are configured to extract power via electric field coupling.

[0039] In one or more embodiments, the receiver further comprises a rectifier connected to the receiving coil or electrodes.

[0040] In one or more embodiments, the receiver further comprises a load connected to the receiving coil or the electrodes.

[0041] Embodiments will now be described more fully with reference to the accompanying drawings. [Brief description of the drawings]

[0042] [Figure 1] FIG. 1 is a block diagram of a wireless power transmission system. [Figure 2A] FIG. 1 is a block diagram of a resonant magnetic wireless power transfer system. [Figure 2B] FIG. 1 is a block diagram of a resonant electrical wireless power transfer system. [Diagram 3] FIG. 1 is a block diagram of a high frequency magnetic wireless power transfer system according to one aspect of the present disclosure. [Figure 4A] 4 is a partial schematic layout diagram of an inductive link of the high frequency magnetic wireless power transmission system of FIG. 3. [Figure 4B] 4 is a partial schematic layout diagram of an equivalent circuit seen by the transmitter of the high frequency magnetic wireless power transfer system of FIG. 3. [Diagram 5] 4 is a schematic layout diagram of a DC / AC inverter of the high frequency magnetic wireless power transmission system of FIG. 3. [Figure 6] 6 is an equivalent circuit of the DC / AC inverter in FIG. 5. [Figure 7] 7 is a series of graphs of a simulation of the equivalent circuit of FIG. 6. [Figure 8] FIG. 6 is a schematic layout diagram of another embodiment of the DC / AC inverter of FIG. [Figure 9] FIG. 6 is a schematic layout diagram of another embodiment of the DC / AC inverter of FIG. [Figure 10] FIG. 6 is a schematic layout diagram of another embodiment of the DC / AC inverter of FIG. [Figure 11] FIG. 6 is a block diagram of another embodiment of the DC / AC inverter of FIG. [Figure 12] FIG. 6 is a block diagram of another embodiment of the DC / AC inverter of FIG. [Figure 13] 13 is a graph of the voltage across the transistors of the DC / AC inverter of FIG. 12 with and without the presence of a metal object. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] In addition to the summary above, the following detailed description of certain examples will be better understood when read in conjunction with the accompanying drawings. As used herein, an element or feature introduced in the singular and preceded by the word "a" or "an" should be understood as not necessarily excluding a plural of the same element or feature. Furthermore, reference to "one example" or "one embodiment" is not intended to be interpreted as excluding the existence of additional examples or embodiments that also incorporate the described element or feature. Moreover, unless expressly stated otherwise, an example or embodiment that "comprises" or "has" or "includes" an element or feature or elements or features having a particular property may include additional elements or features that do not have that property. It will also be recognized that the terms "comprise", "have", and "include" mean "including without limitation" and that the terms "comprise", "have", and "include" have equivalent meanings. It will also be recognized that similar reference numerals are used to refer to similar elements throughout the description and drawings.

[0044] As used herein, the terms "adapted" and "configured" mean that an element, component, or other object is designed and / or intended to perform a given function. As such, use of the terms "adapted" and "configured" should be interpreted to mean that a given element, component, or other object is specifically selected, created, implemented, utilized, and / or designed for performing a given function, rather than merely being "capable" of performing the given function. It is also within the scope of this application that an element, component, and / or other object described as being adapted to perform a particular function may additionally or alternatively be described as being configured to perform that function, and vice versa. Similarly, an object described as being configured to perform a particular function may additionally or alternatively be described as operating to perform that function.

[0045] When an element is referred to as being "adjacent," "attached," "connected," "coupled," "in contact," or the like, to another element, it will be understood that it can be directly adjoined, attached, connected, coupled, or in contact with the other element, or intervening elements may be present.

[0046] Use of the word "exemplary" should be understood to mean "as an example" or "one example" rather than to imply a preferred or optimal design or implementation, unless otherwise stated.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0048] For purposes of this disclosure, the switching frequency ω sis defined. The switching frequency may be supplied from an external signal source such as a function generator or may be generated using an oscillator. The switching signal based on the switching frequency is the main "clock" of the wireless power transfer system. Therefore, the fundamental frequency components of all other voltage and current signals of the relevant components will be equal to the switching frequency.

[0049] For purposes of this disclosure, the resonant frequency ω is defined as the frequency at which a circuit network has zero reactive impedance. o is defined. The resonant frequency of a series LCR circuit is given by Equation 1:

[0050]

number

[0051] where L is the inductance and C is the capacitance.

[0052] The resonant frequency of a parallel RLC circuit is given by Equation 2:

[0053]

number

[0054] where R is the load. The switching frequency is not necessarily equal to the resonant frequency. Different operating modes can be obtained by operating the inverter at switching frequencies above, below or equal to the resonant frequency.

[0055] For the purposes of this disclosure, ZVS is the switching of a transistor from an off state to an on state when the voltage across the transistor is zero. As a result, no energy is lost during this off-to-on transition. In reality, some energy is lost due to the finite time of the transition period. However, the energy loss is substantially lower than non-ZVS circuits. ZVS enables efficient operation of power inverters, especially in the MHz frequency range. ZVS is achieved by using a combination of passive components, such as capacitors and inductors, with certain values.

[0056] For purposes of this disclosure, the characteristic impedance (Z) of the inverter's resonant network is given by Equation 3:

[0057]

number

[0058] where ω is the frequency, L is the inductance of the inverter's resonant network, and C is the capacitance of the resonant network.

[0059] 1, there is illustrated a wireless power transfer system generally identified by the reference numeral 100. The wireless power transfer system 100 comprises a transmitter 110 comprising a power source 112 electrically connected to a transmitting element 114, and a receiver 120 comprising a receiving element 124 electrically connected to a load 122. Power is transferred from the power source 112 to the transmitting element 114. The power is then transferred from the transmitting element 114 to the receiving element 124 via resonant or non-resonant electric or magnetic field coupling. The power is then transferred from the receiving element 124 to the load 122.

[0060] Turning now to FIG. 2A, an IPT system is illustrated. In this embodiment, the IPT system is a resonant magnetic wireless power transfer system generally identified by reference character 200. The resonant magnetic wireless power transfer system 200 comprises a transmitter 210 comprising a power source 212 electrically connected to a transmit resonator 214. The transmit resonator 214 comprises a transmit resonator coil 216 and is electrically connected to the power source 212 via a capacitor 218. The magnetic resonant wireless power transfer system 200 further comprises a receiver 220 comprising a receive resonator 224 electrically connected to a load 222. The receive resonator 224 is tuned to the resonant frequency of the transmit resonator 214. The receive resonator 224 comprises a receive resonator coil 226 and is electrically connected to the load 222 via a capacitor 228.

[0061] During operation of the resonant magnetic wireless power transfer system 200, power is transferred from the power source 212 to the transmit resonator coil 216 via the capacitor 218. In particular, the power signal from the power source 212 transferred to the transmit resonator coil 216 via the capacitor 218 excites the transmit resonator 214, causing it to generate a magnetic field. The receiver 220 is tuned to the same resonant frequency as the transmitter 210, and when placed in the magnetic field, the receive resonator 224 extracts power from the transmit resonator 214 via resonant magnetic field coupling. The extracted power is then transferred from the receive resonator 224 to the load 222. Because the power transfer is highly resonant, the transmit resonator coil 216 and the receive resonator coil 226 do not need to be as close together or well aligned, respectively, as in a non-resonant magnetic system. Although the transmit resonator 214 may generate an electric field, little, if any, power is transferred via electric field coupling.

[0062] Turning now to FIG. 2B, another IPT system is illustrated. In this embodiment, the IPT system is a resonant electrical wireless power transfer system generally identified by reference character 250. The resonant electrical wireless power transfer system 250 comprises a transmitter 260 comprising a power source 262 electrically connected to a transmit resonator 264. The transmit resonator 264 comprises a transmit resonator electrode 266, which is electrically connected to the power source 262 via one or more inductors 268. The resonant electrical wireless power transfer system 250 further comprises a receiver 270 comprising a receive resonator 274, which is electrically connected to a load 272. The receive resonator 274 is tuned to a resonant frequency of the transmit resonator 264. The receive resonator 274 comprises a receive resonator electrode 276, which is electrically connected to the load 272 via one or more inductors 278.

[0063] During operation of the resonant electrical wireless power transfer system 250, power is transferred from the power source 262 to the transmit resonator electrode 266 via the inductor 268. In particular, the power signal from the power source 262 transferred to the transmit resonator electrode 266 via the inductor 268 excites the transmit resonator 264, causing it to generate an electric field. The receiver 270 is tuned to the same resonant frequency as the transmitter 260, and when placed within the electric field, the receive resonator 274 extracts power from the transmit resonator 264 via resonant electric field coupling. The extracted power is then transferred from the receive resonator 274 to the load 272. Because the power transfer is highly resonant, the transmit resonator electrode 266 and the receive resonator electrode 276 do not need to be as close together or well aligned, respectively, as in a non-resonant electrical system. Although the transmit resonator 264 may generate a magnetic field, little, if any, power is transferred via magnetic field coupling.

[0064] 3, there is illustrated a high frequency wireless power transfer system according to one embodiment of the present disclosure and generally identified as reference numeral 300. The high frequency wireless power transfer system 300 comprises a transmitter 302 and a receiver 304. As described below, the high frequency wireless power transfer system 300 operates by transferring power from the transmitter 302, which is non-resonant or not self-resonant, to the receiver 304, which is resonant at the operating frequency of the transmitter 302.

[0065] The transmitter 302 is configured to transfer power wirelessly via high frequency magnetic inductive coupling as described below. Electric fields may also be generated, but little, if any, power is transferred via electric field coupling.

[0066] The transmitter 302 comprises a power supply 306, a transmitter DC / DC converter 308, a DC / AC inverter 310 and a transmit coil 312. The power supply 306 is electrically connected to the transmitter DC / DC converter 308. The power supply 306 is configured to generate a DC power signal. The power supply 306 is configured to output the DC power signal to the transmitter DC / DC converter 308. In this embodiment, the DC power signal is between 24V and 48V. The transmitter DC / DC converter 308 is electrically connected to the power supply 306. The transmitter DC / DC converter 308 is electrically connected to the DC / AC inverter 310. The transmitter DC / DC converter 308 interfaces the power supply 306 to the DC / AC inverter 310. The transmitter DC / DC converter 308 is configured to convert the DC power signal from the power supply 306 to a voltage level for transmission to the DC / AC inverter 310.

[0067] The DC / AC inverter 310 is electrically connected to the transmitter DC / DC converter 308. The DC / AC inverter 310 is electrically connected to the transmit coil 312. The DC / AC inverter 310 is configured to convert a DC power signal from the transmitter DC / DC converter 308 into a sinusoidal radio frequency (RF) power signal. The sinusoidal RF power signal is output from the DC / AC inverter 310 to the transmit coil 312.

[0068] Although the transmitter 302 has been described as including a transmitter DC / DC converter 308, one skilled in the art will recognize that other configurations are possible. In another embodiment, the transmitter 302 does not include a transmitter DC / DC converter 308. In this embodiment, the power supply 306 is electrically connected to a DC / AC inverter 310. The power supply 306 is configured to generate a DC power signal that is acceptable to the DC / AC inverter 310.

[0069] The receiver 304 is configured to extract power from the transmitter 302 via high frequency magnetic inductive coupling, as described below. Electric fields may also be generated, but little, if any, power is extracted via electric field coupling.

[0070] The receiver 304 includes a receive coil 314, an AC / DC rectifier 316, a receiver DC / DC converter 318, and a load 320. The receive coil 314 is electrically connected to the AC / DC rectifier 316. The receive coil 314 is configured to receive power from the transmitter 302 via the transmit coil 312 using high frequency magnetic coupling. In this embodiment, the receive coil 314 has the same dimensions and number of turns as the transmit coil 312.

[0071] The AC / DC rectifier 316 is electrically connected to the receive coil 314. The AC / DC rectifier 316 is electrically connected to a receiver DC / DC converter 318. The AC / DC rectifier 316 is configured to convert the sinusoidal RF power signal from the receive coil 314 into a DC power signal. The AC / DC rectifier 316 is configured to output the DC power signal to the receiver DC / DC converter 318.

[0072] The receiver DC / DC converter 318 is electrically connected to the AC / DC rectifier 316. The receiver DC / DC converter 318 is electrically connected to a load 320. A DC power signal is output from the AC / DC rectifier 316 to the receiver DC / DC converter 318. The receiver DC / DC converter 318 interfaces the AC / DC rectifier 316 to the load 320. The receiver DC / DC converter 318 is configured to convert the received DC power signal. The converted DC power signal is output from the receiver DC / DC converter 318 to the load 320. The load 320 is electrically connected to the receiver DC / DC converter 318. The load 320 may be a fixed or variable load.

[0073] Although receiver 304 has been described as including a receiver DC / DC converter 318, one skilled in the art will recognize that other configurations are possible. In another embodiment, receiver 304 does not include a receiver DC / DC converter 318. In this embodiment, AC / DC rectifier 316 is electrically connected to load 320. AC / DC rectifier 316 is configured to generate a DC power signal that is acceptable to load 320.

[0074] The transmitter 302 operates at a given frequency. In this embodiment, the operating frequency of the transmitter 302 is 13.56 MHz. Moreover, in this embodiment, the transmit coil 312 and the receive coil 314 each have dimensions of 23.4 cm by 26.2 cm. The coils 312 and 314 each consist of two turns of copper trace with a width of 14 mm on an FR4 printed circuit board (PCB). The coils 312 and 314 have an inductance of approximately 1.50 uH. The reflected load seen by the transmit coil 312 varies from 0 ohms at no load 320 to 7 ohms at full load 320. The maximum power required by the load 320 is 30 W.

[0075] The receiver 304 operates at a given frequency. In this embodiment, the operating frequency of the receiver 304 is the operating frequency of the transmitter 302. In this embodiment, the operating frequency of the receiver 304 is 13.56 MHz.

[0076] As previously mentioned, the DC / AC inverter 310 is configured to convert the DC power signal from the transmitter DC / DC converter 308 into a sinusoidal RF power signal. The sinusoidal RF power signal is output from the DC / AC inverter 310 to the transmit coil 312.

[0077] In particular, the DC / AC inverter 310 drives the transmit coil 312 with a sinusoidal alternating current (AC). The transmit coil 312 is configured to generate an inductive (magnetic) field and to transfer power via high frequency inductive (magnetic) field coupling. The DC / AC inverter 310 receives a DC input voltage and converts it to a high frequency AC current to drive the transmit coil 312.

[0078] The DC / AC inverter 310 is affected by changes in load conditions, changes in the placement of the system 300, and external distances (i.e., environmental influences) such as the presence of metallic objects near the system 300. It is therefore desirable for the DC / AC inverter 310 to be robust and resistant to these changes, and also for the DC / AC inverter 310 to operate at MHz frequencies.

[0079] As mentioned above, class E and class EF2 inverters can be designed to achieve ZVS and generate a constant output voltage as the load resistance varies when used with a finite DC inductor instead of a choke. Such designs can extend the load range in which a class E or class EF2 inverter can operate efficiently from infinite load resistance (open circuit) to some minimum load resistance. Although these designs can be applied to some applications such as high frequency DC / DC converters, they generally cannot be used efficiently in the high frequency wireless power transfer system 300 because the distance between the coils 312 and 314 varies and the load ranges from zero resistance (short circuit), where the coils 312 and 314 are completely separated from each other, to some maximum load resistance, where the coils 312 and 314 are closest to each other.

[0080] Moreover, in some applications of IPT systems operating at tens of MHz, the topology of the DC / AC inverter 310 is based on class E or class E2 configurations, as described in “Load-independent Class E / EF Inverters and Rectifiers for MHz-Switching Applications,” S. Aldhaher, D. C. Yates, and P. D. Mitcheson, IEEE Trans. Power Electron., Vol. 33, No. 10, pp. 8270-8287, October 2018, and “Maximizing DC-to-load Efficiency for Inductive Power Transfer,” M. Pinuela, D. C. Yates, S. Lucyszyn, and P. D. Mitcheson, IEEE Trans. Power Electron., Vol. 28, No. 5, pp. 2437-2447, May 2013, the relevant portions of which are incorporated herein by reference. Although these configurations are power efficient and easy to build, they can only maintain optimal switching behavior for fixed loads and are therefore highly dependent on the load value.

[0081] Consequently, this limits IPT systems with class E or class EF2 DC / AC inverters to function efficiently only for a narrow load range with a fixed coil separation distance.

[0082] To overcome the aforementioned challenges when using inverters based on class E or class EF2 configurations and to allow for variable distance between the transmit coil 312 and the receive coil 314, the DC / AC inverter 310 is load independent. The load independent DC / AC inverter 310 enables class E and class EF inverters to maintain efficient operation by achieving ZVS regardless of the load resistance value. In addition, unlike typical class E and EF2, the load independent class E and class EF inverters can provide a constant output AC voltage or current that does not change with the load, which is more suitable for IPT applications.

[0083] A discussion regarding the efficiency of the coupling and / or inductive link between coils 312 and 314 is useful when considering the design of DC / AC inverter 310. As previously mentioned, high frequency wireless power transfer system 300 includes a transmitter 302 and a receiver 304. Transmitter 302 includes, among other elements, a transmit coil 312, and receiver 304 includes, among other elements, a receive coil 314.

[0084] The coils 312 and 314 are separated from each other by a gap. The transmit coil 312 is driven by a sinusoidal AC at a fixed frequency, the operating frequency of the transmitter 302. An alternating magnetic field is generated that couples to the receive coil 314 and induces a sinusoidal voltage across the terminals of the receive coil 314 at the same frequency of the current in the transmit coil 312. Any load, such as load 320, connected across the terminals of the receive coil 314 will result in a current flowing into the load. The coupling coefficient k indicates the amount of coupling between the two coils 312 and 314 as defined in Equation 4:

[0085]

number

[0086] In the formula, L p is the inductance of the transmitting coil 312, and L s is the inductance of the receiving coil 314, and M is the mutual inductance between coils 312 and 314.

[0087] Turning now to FIG. 4A, there is illustrated a partial schematic layout of an inductive link of a high frequency magnetic wireless power transfer system 300. FIG. 4A includes a circuit representation of two coupled coils 312 and 314. Resistor R L Resistor 402 with capacitance C s A capacitor 404 having a capacitance of Ref is given by Equation 5:

[0088]

number

[0089] where M is the mutual inductance between coils 312 and 314, ω is the operating frequency, and jX Ls is the impedance of the receiving coil 314 at the frequency of operation, and jX Cs is the impedance of the series capacitor 404 at the frequency of operation.

[0090] The reflected impedance is a measure of how much of the real load is seen by the transmitter 302. It is a function of the mutual inductance between the coils 312 and 314 and is affected by the distance between the coils 312 and 314. The closer the coils 312 and 314 are to each other, the higher the mutual inductance and the higher the reflected impedance. The farther the coils 312 and 314 are from each other, the lower the mutual inductance and the lower the reflected impedance.

[0091] As shown in Equation 5, the reflected impedance is inversely proportional to the load resistance and the magnitude of the impedance of the receive coil 314. Maximizing the reflected impedance allows power to be delivered to the load 320 at a lower current. Furthermore, the DC / AC inverter 310 can operate at a lower current and therefore has lower conduction and resistive losses and higher efficiency.

[0092] The reflected impedance in Equation 5 is calculated using the reactance term X LS The reactance term reflects the resistive load on the transmitter 302. This reduces the reactance term to 1 / (ω 2 L s ) at the operating frequency. With this capacitance value, Equation 5 becomes Equation 6:

[0093]

number

[0094] Turning now to FIG. 4B, there is illustrated a partial schematic layout of the equivalent circuit seen by the transmitter 302 of the high frequency magnetic wireless power transfer system 300. FIG. 4B illustrates the resonance (i.e., jX Ls =jX Cs 3 illustrates an equivalent circuit of the transmit coil 312 when operating with a receive coil 314 tuned at 100 kHz. The circuit has an inductance L p Inductor 406 and resistor R Ref As seen in Equation 6, when using series resonance, the reflected impedance remains resistive regardless of the load resistance value. This is different from the case of a parallel-tuned receive coil 314 or secondary coil, as described in "Inductive Powering: Basic Theory and Application to Biomedical Systems," K. V. Schuylenbergh and R. Puers, 1st Edition, Springer Publishing Company, Incorporated, 2009, relevant portions of which are incorporated herein by reference.

[0095] The reflected impedance remains resistive, ensuring that the DC / AC inverter 310 is not detuned from its optimum operating condition. Series resonance, however, causes the parasitic capacitance of the receive coil 314 to resonate during operation with the capacitor C s This can limit the maximum frequency of operation since it cannot be absorbed into the

[0096] As previously mentioned, the receive coil 314 may be operating at resonance or near resonance, but the transmit coil 312 is not operating at resonance (i.e., the transmit coil 312 is not self-resonant). This is in contrast to many IPT systems in which the transmit coil 312 is operating at resonance.

[0097] From the above equations, the link efficiency of the high frequency wireless power transfer system 300 can be determined. The link efficiency of the high frequency wireless power transfer system 300 is defined as the power delivered to the AC secondary load (load 320) divided by the power input to the transmit coil 312. When the receive coil 314 is operated at resonance and with an optimal load for maximum efficiency, the link efficiency (n) is given by Equation 7:

[0098]

number

[0099] In the formula, Q Lp and Q Ls are the unloaded quality factors of the transmit coil 312 and the receive coil 314, respectively.

[0100] 5, there is shown a schematic diagram of the DC / AC inverter 310 of the high frequency magnetic wireless power transfer system 300. The DC / AC inverter 310 is configured to generate an AC output voltage that has a constant amplitude independent of the load while maintaining ZVS.

[0101] As mentioned above, the DC / AC inverter 310 is load independent. In this embodiment, the DC / AC inverter 310 is a push-pull inverter. In this embodiment, the DC / AC inverter 310 is a class E inverter. The DC / AC inverter 310 has a voltage mode output. The voltage mode output indicates that the DC / AC inverter 310 has a constant voltage output.

[0102] The DC / AC inverter 310 includes a switch mode ZVS amplifier, as described below. The amplifier is a radio frequency (RF) amplifier.

[0103] As shown in FIG. 5, a switch-mode ZVS amplifier operates with an input voltage V inThe inductor 502 includes series inductors 502 and 518 having inductances L1 and L2, respectively, receiving a load. Each inductor 502, 518 is connected in series with a combination of a transistor 512 and 520 (Q1 and Q2) (or switch) and a capacitor 514 and 522, respectively. The capacitors 514 and 522 have capacitances C1 and C2, respectively. Specifically, the transistor 512 and the capacitor 514 are arranged in parallel and connected to the inductor 502. The transistor 520 and the capacitor 522 are arranged in parallel and connected to the inductor 518. Both the transistor 512, 520 and the capacitor 514, 522 pairs are connected to ground. The inductances L ZVS An inductor 516 having an inductance L RESa Inductor 532 with capacitance C 3a a capacitor 504 having an inductance L3, an inductor 506 having an inductance L3, and a resistor R L Resistor 508 with capacitance C 3b A capacitor 510 having an inductance L RESb is arranged in series with and connected in parallel to inductor 516. Inductor 506 represents the inductance of the transmit coil 312, and resistor 508 represents the reflected load of the receive coil 314. Inductors 532, 534 represent the residual inductance of the receive coil 314.

[0104] To derive the design equations for the DC / AC inverter 310, a state-space modeling approach was used as described in “Design and optimization of switched-mode circuits for inductive links”, S. Aldhaher, Ph.D. dissertation, Cranfield University, 2014, relevant portions of which are incorporated herein by reference.

[0105] Following a state space modeling approach, an equivalent circuit of the DC / AC inverter 310 illustrated in Figure 5 has been generated. Turning now to Figure 6, an equivalent circuit of the DC / AC inverter 310 is illustrated. As illustrated in Figure 6, the voltage V in Two voltage sources 602 and 622 having a capacitance L1 feed two inductors 604 and 624 having an inductance L1 on either side of the equivalent circuit. Specifically, one voltage source 602 feeds one inductor 604, and another voltage source 622 feeds another inductor 624. Each voltage source 602, 622 and inductor 604, 624 pair is connected to a resistor 606 or 626 having a resistance R1 or R2, respectively, in a parallel arrangement. Each voltage source 602, 622 and inductor 604, 624 pair is further connected to a capacitor 608, 628 in a parallel arrangement. Each capacitor has a capacitance C1. Specifically, the voltage source 602 and inductor 604 pair is connected to the resistor 606 and the capacitor 608. The other voltage source 622 and inductor 624 pair is connected to the resistor 626 and the capacitor 628. The inductors 604 and 624 have an inductance L ZVS and resistor R LZVS The inductor 610 and resistor 612 are connected in series with a capacitor 614 having a capacitance C3, an inductor 616 having an inductance L3, and a resistor R L The capacitor 614, inductor 616 and resistor 618 form an output network. The capacitance C3 of the capacitor 614 is equal to the capacitance (C 3a and C 3b 5 are replaced with resistors 606 and 626 having resistances R1 and R2, respectively.

[0106] The equivalent circuit in Figure 6 has a load value R L = 6.25, 12.5, 25 and 100 ohms. The results of these simulations are shown in the graph of FIG. 7. As shown in FIG. 7, the input voltage V inThe ratio of the voltage across the transistor / switch 512 to the load value R L is equal to 6.25 ohms. Similarly, the input voltage V in The ratio of the voltage of the transistor / switch 520 to the load value R L is maximized when is equal to 6.25 ohms.

[0107] Furthermore, as illustrated in FIG. 7, the DC / AC inverter 310 maintains ZVS for different load conditions from an open circuit load condition to a minimum load resistance. The amplitude and phase of the output AC voltage across the load remain constant regardless of the load value. Although the shapes of the various waveforms may vary, ZVS is approximately maintained, and the amplitude and phase of the output voltage are approximately constant. Additionally, the current in the transistors 512 and 520 at turn-off has a negative slope as the load resistance decreases. The negative slope at turn-off may minimize the turn-off time of the transistors 512 and 520 and may counteract the effect of the parasitic inductance.

[0108] As mentioned above, a state-space modeling approach was used to derive the design equations for the equivalent circuit of Figure 6. The design equations discussed can be used to construct an AC / DC inverter 310 for a particular set of requirements such as load impedance, resonator impedance, frequency of operation and input DC voltage. The following design equations were derived: q value, residual reactance X res , voltage gain, load resistance R L and output power P out .

[0109] The q value that sets the resonant frequency of the DC / AC inverter 310 to the frequency of operation is given by Equation 8:

[0110]

number

[0111] The q value is specific to each inverter class and topology. For an operating frequency of 13.56 MHz and optimal performance of the high frequency wireless power transfer system 300, the q value is approximately 0.985. This is expected since the transmitter 302 is non-resonant (or not self-resonant), and the q value should not be equal to 1.

[0112] Those skilled in the art will recognize that the q value may not be exactly equal to 0.985 and the high frequency wireless power transfer system 300 may still function, however the load range may be reduced and performance may be negatively affected. In some embodiments, the q value may vary by as much as plus or minus 25% of 0.985 (e.g., between about 0.739 and 1.231) and still provide acceptable performance.

[0113] The capacitor 614 is made up of an inductor 616 and a resistor 618, and the capacitance C3 of the capacitor 614 is equal to the sum of the capacitances of the capacitors 504 and 510 (C3=C 3a +C 3b ) The output network is not tuned to the resonant frequency of the transmitter 302. As a result, the output network has a residual reactance X at the frequency of operation given by Equation 9. res You will have:

[0114]

number

[0115] As with the q value, X res The value of is specific to the inverter class and topology. For AC / DC inverter 310, the value of X normalized to the characteristic impedance of inverter 310 is res The ratio of is given by Equation 10:

[0116]

number

[0117] This is expected since the transmitter 302 is non-resonant (or not self-resonant) and res The value should not be equal to zero (0). Although not shown, one skilled in the art will recognize that residual inductance may also be present, as represented by inductors 532, 534 in FIG.

[0118] X res Those skilled in the art will recognize that the value may not be exactly equal to 0.258 and the high frequency wireless power transfer system 300 will still function, however performance will be negatively affected. res The value may vary by as much as plus or minus 25% of 0.258 (eg, about 0.194 to 0.323) and still provide acceptable performance.

[0119] The characteristic impedance of the AC / DC inverter 310 is given by Equation 11:

[0120]

number

[0121] The voltage gain is expressed as the input DC voltage V IN Load R L For this AC / DC inverter 310, the voltage gain is given by Equation 12:

[0122]

number

[0123] For an operating frequency of 13.56 MHz and optimal performance of the high frequency wireless power transfer system 300, the voltage gain is approximately 3.132.

[0124] Those skilled in the art will recognize that the voltage gain value may not be exactly equal to 3.132 and the high frequency wireless power transfer system 300 may still function, however performance may be negatively affected. In some embodiments, the voltage gain value may vary by as much as plus or minus 25% of 3.132 (e.g., between about 2.349 and 3.915) and still provide acceptable performance.

[0125] As previously mentioned, the DC / AC inverter 310 has a voltage mode output, i.e., a constant voltage output. The DC / AC inverter 310 is connected to a load resistor R L R Lmin , ∞}. L R Lmin If it decreases below that, the DC / AC inverter 310 will no longer operate efficiently, ie, ZVS operation will be lost, and the output voltage of the DC / AC inverter 310 will fluctuate.

[0126] This is because the voltage across the transistors will swing below zero volts, which in effect means that the body diodes of transistors Q1 and Q2 will conduct, thus disrupting the operation of the DC / AC inverter 310. Lmin corresponds to the load to which the DC / AC inverter can deliver maximum power (when operating in voltage mode), where R normalized to the characteristic impedance Z Lmin The value of is given by Equation 13:

[0127]

number

[0128] Normalized R Lmin One skilled in the art will recognize that the value of R may not be exactly equal to 0.780 and the high frequency wireless power transfer system 300 will still function, however performance will be negatively affected. LminThe value of may vary by as much as plus or minus 25% of 0.780 (eg, between 0.585 and 0.975) and still provide acceptable performance.

[0129] Combining Equation 12 and Equation 13, we obtain the output power P of the DC / AC inverter 310 at minimum load resistance for a particular input DC voltage: out The normalized output power P out is given by Equation 14:

[0130]

number

[0131] Normalized output power P out Those skilled in the art will recognize that may not be exactly equal to 6.267 and the high frequency wireless power transfer system 300 will still function, however performance will be negatively affected. out may vary by as much as plus or minus 25% of 6.267 (e.g., from about 4.700 to 7.834) and still provide acceptable performance.

[0132] Implementing the DC / AC inverter 310 according to the derived design equations results in a DC / AC inverter that is more efficient and robust than other configurations. In particular, Table 1 lists the differences between the DC / AC inverter 310 and other configurations.

[0133] [Table 1A]

[0134] [Table 1B]

[0135] In operation, the DC / AC inverter 310 generates a constant AC voltage or current that does not vary with the load. As previously mentioned, in this embodiment, the DC / AC inverter 310 has a voltage-mode output, so that a constant AC voltage is generated.

[0136] The reflected resistance of the DC / AC inverter 310 is zero (0) when there is no coupling between the transmit coil 312 and the receive coil 314 or when the receiver 304 is unloaded. However, during operation, the reflected resistance exists because there is coupling between the coils 312 and 314. Specifically, as the coupling between the coils 312 and 314 increases, the reflected resistance increases. A current sensing and feedback system may be used to regulate the output current of the DC / AC inverter 310.

[0137] As will be described below, instead of a current sensing and feedback system, the voltage mode output (constant voltage output) may be converted to a current mode output (constant current output) to eliminate reflected resistance.

[0138] Although a particular DC / AC inverter 310 has been described, one skilled in the art will recognize that other configurations are possible. Turning now to Figure 8, there is shown a schematic layout diagram of another embodiment of a DC / AC inverter, generally identified by reference character 800. In this embodiment, the DC / AC inverter 800 comprises a load independent circuit 802 and an impedance inverter circuit 804. The DC / AC inverter 800 is a current mode output (constant output current).

[0139] The load independent circuit 802 is configured to convert an input DC signal to an output AC signal. The load independent circuit 802 is a voltage mode output (constant output voltage). The load independent circuit 802 is configured to convert an input DC signal to an output AC signal. inThe inductors 810, 830 have inductances L1 and L2, respectively, and receive an input voltage having a capacitance C1, C2. Each inductor 810, 830 is connected in series with a combination of a transistor 812, 832 (Q1 and Q2), respectively, and a capacitor 814, 834, respectively, having a capacitance C1, C2. Specifically, the transistor 812 and the capacitor 814 are arranged in parallel and connected to the inductor 810. The transistor 832 and the capacitor 834 are arranged in parallel and connected to the inductor 830. Both transistor 812, 832 and capacitor 814, 834 pairs are grounded. The inductances L ZVS An inductor 840 having a capacitance of

[0140] The impedance inverter circuit 804 is configured to convert the load independent circuit 802 from a voltage mode output (constant output voltage) to a current mode output (constant output current). RESa +L 3a , L RESb +L 3b and L3, a capacitor 870 having a capacitance C3, and a resistor R L The inductors 850 and 852 are connected in series with the inductor 840. The inductance L3 is 3a and inductance L 3b (L3=L 3a +L 3b ). Inductance L RESa and L RESb represents the residual inductance.

[0141] 5, capacitor 870 is connected in parallel with inductor 840. Inductor 860 and resistor 880 are connected in series, and together they are connected in parallel with capacitor 870. The output current in inductor 860 is given by Equation 15:

[0142]

number

[0143] As previously mentioned, the value of inductance L3 is given by Equation 16.

[0144]

number

[0145] The current in the inductor 860 is constant regardless of the reflected load. The impedance inverter circuit 804 is configured to convert the output of the load independent circuit 802 from a voltage mode output (constant output voltage) to a current mode output (constant output current), but the value of the output current is dependent on the input voltage and the inductance of the transmit coil 312. The output current cannot be changed without changing either the input voltage or the inductance of the transmit coil 312.

[0146] Although specific DC / AC inverters 310 and 800 have been described, one skilled in the art will recognize that other configurations are possible. Turning now to Figure 9, there is illustrated a schematic layout diagram of another embodiment of a DC / AC inverter, generally identified by reference character 900. In this embodiment, the DC / AC inverter 900 comprises a load independent circuit 902 and an impedance inverter circuit 904. The DC / AC inverter 900 is a current mode output (constant output current).

[0147] The load independent circuit 902 is configured to convert an input DC signal to an output AC signal. The load independent circuit 902 is a voltage mode output (constant output voltage). The load independent circuit 902 outputs a voltage V inThe inductors 910, 930 have inductances L1 and L2 and receive an input voltage having a capacitance of 1. Each inductor 910, 930 is connected in series with a combination of a transistor 912, 932 (Q1 and Q2), respectively, and a capacitor 914, 934, respectively. The capacitors 914, 934 have capacitances C1 and C2, respectively. Specifically, the transistor 912 and the capacitor 914 are arranged in parallel and connected to the inductor 910. The transistor 932 and the capacitor 934 are arranged in parallel and connected to the inductor 930. Both transistor 912, 932 and capacitor 914, 934 pairs are grounded. The inductances L ZVS An inductor 940 having a capacitance of

[0148] The impedance inverter circuit 904 is configured to invert the load independent circuit 902 from a voltage mode output (constant output voltage) to a current mode output (constant output current). The impedance inverter circuit 904 has a T network topology. The impedance inverter circuit 904 includes an inductance L RESa +L 3a , L RESb +L 3b and L3, respectively, inductors 950, 952, 976, capacitance C 3a Capacitors 954, 958 each having a capacitance C 3b a capacitor 970 having a capacitance C4, and a resistor R L The inductance L3 has an inductance L 3a and inductance L 3b (L3=L 3a +L 3b ). Inductance L RESa and L RESbrepresents the residual inductance. Each inductor 950, 952 is connected in series with a capacitor 954, 956, respectively. The inductor / capacitor pairs 950, 954 and 952, 956 are connected across the inductor 940 of the load independent circuit 902. A capacitor 970 is connected in parallel with the inductor 940. Additionally, the capacitor 958, the inductor 976, the resistor 980 and the capacitor 960 are connected in series, and together they are connected in parallel with the capacitor 970. The capacitance C3 is dependent on the capacitance C4 and is given by Equation 17:

[0149]

number

[0150] The output current in inductor 976 is given by Equation 18:

[0151]

number

[0152] As shown in Equation 18, the output current in inductor 976 is proportional to the capacitance C4 of capacitor 970 and the input voltage V in depends on.

[0153] As previously mentioned, the inductance L3 of inductor 976 is given by Equation 19.

[0154]

number

[0155] However, the capacitance C3 is given by Equation 20:

[0156]

number

[0157] Although specific DC / AC inverters 310, 800 and 900 have been described, one skilled in the art will recognize that other configurations are possible. Turning now to Figure 10, there is shown a schematic layout diagram of another embodiment of a DC / AC inverter, generally identified by reference numeral 700. In this embodiment, the DC / AC inverter 700 comprises a load independent circuit 702 and an impedance inverter circuit 704. The DC / AC inverter 700 is a current mode output (constant output current).

[0158] The load independent circuit 702 is configured to convert an input DC signal to an output AC signal. The load independent circuit 702 is a voltage mode output (constant output voltage). The load independent circuit 702 converts a voltage V in The inductors 710, 730 have inductances L1 and L2 and receive an input voltage having a capacitance of 1. Each inductor 710, 730 is connected in series with a combination of a transistor 712, 732 (Q1 and Q2), respectively, and a capacitor 714, 734, respectively. The capacitors 714, 734 have capacitances C1 and C2, respectively. Specifically, the transistor 712 and the capacitor 714 are arranged in parallel and connected to the inductor 710. The transistor 732 and the capacitor 734 are arranged in parallel and connected to the inductor 730. Both transistor 712, 732 and capacitor 714, 734 pairs are grounded. The inductances L ZVS An inductor 740 having a capacitance of

[0159] The impedance inverter circuit 704 is configured to convert the load independent circuit 702 from a voltage mode output (constant output voltage) to a current mode output (constant output current). In contrast to the impedance inverter circuit 904, the impedance inverter circuit 704 has a pi network circuit configuration. The impedance inverter circuit 704 is RESa +L 3a , L RESb +L 3b and L3, respectively, inductors 750, 752, 770, capacitance C 4a, C 4b Capacitors 760, 762, each having a resistor R L A resistor 780 having a capacitance C 3a A capacitor 764 having a capacitance C 3b A capacitor 766 having a capacitance Vref = 1 ...

[0160] Inductance L3 is inductance L 3a and inductance L 3b (L 3= L 3a +L 3b ). Inductance L RESa and L RESb represents the residual inductance. The capacitance C 3a is the capacitance C 3b and equal to capacitance C3. The relationship between capacitances C3 and C4 is given by Equation 21:

[0161]

number

[0162] The capacitance C3 is given by Equation 22:

[0163]

number

[0164] The capacitance C4 is the capacitance C 4a , C 4b is given by Equation 23:

[0165]

number

[0166] The inductance L3 is given by Equation 24:

[0167]

number

[0168] Residual inductance L RES is given by Equation 25:

[0169]

number

[0170] In the formula, X res is the residual reactance and w is the operating frequency.

[0171] The output current in the inductor 770 or in the resistor 780 is the current in the transmit coil 312 and is thus given by Equation 26:

[0172]

number

[0173] The DC / AC inverter 700 allows the current in the transmit coil 312 to be set independent of the input DC voltage and the inductance of the transmit coil 312. The DC / AC inverter 700 is suitable for operation at high MHz frequencies, e.g., 6.78 MHz and above, since the self-capacitance of the transmit coil 312 can be absorbed into the capacitor 766.

[0174] As previously mentioned, in operation, the DC / AC inverter 310 generates a constant AC voltage or current that does not change with the load. However, a metal object in close proximity to the transmitter 302 will detune the transmitter 302, leading to increased losses. The magnetic field generated by the transmit coil 312 will induce eddy currents in the metal object, leading to losses in power transmission. The strength of the induced eddy currents is proportional to the surface area of ​​the metal object, the magnetic field density, and the frequency of operation.

[0175] Because the DC / AC inverter 310 is load independent, the DC / AC inverter 310 maintains ZVS when the load resistance varies. However, if there is a change in the load reactance, the DC / AC inverter 310 may lose ZVS switching. The receiver 304 is tuned at a frequency of operation such that the reflected load of the load 320 seen by the DC / AC inverter 310 is always real when the wireless power transfer coupling or the DC value of the load 320 changes.

[0176] However, when a metal object is introduced between the transmitter 302 and the receiver 304 or anywhere near the transmitter 302, the reflected load seen by the transmitter 302 is no longer real and will include reactive components due to eddy currents induced in the metal object. Thus, the DC / AC inverter 310 will no longer achieve ZVS. Furthermore, the voltage waveforms across the transistors 512, 520 (Q1 and Q2) of the DC / AC inverter 310 will be different.

[0177] Turning now to Figure 11, there is illustrated another embodiment of a DC / AC inverter, generally identified by the reference character 1000. The DC / AC inverter 1000 is configured to detect the presence of a metal object.

[0178] In this embodiment, the DC / AC inverter 1000 includes the same components as the previously described DC / AC inverter 310. Additionally, the DC / AC inverter 1000 includes a peak detection circuit 1008, a comparator 1010, and a threshold setter 1012. The peak detection circuit 1008 is electrically connected to the DC / AC inverter 310. The comparator 1010 is electrically connected to the threshold setter 1012 and the peak detection circuit 1008. The threshold setter 1012 is connected to the comparator 1010.

[0179] The peak detector circuit 1008 is configured to measure the peak value of the voltage across the transistor 512 (Q1) of the DC / AC inverter 310.

[0180] The threshold setter 1012 is configured to set a threshold voltage for comparison with the peak value of the measured voltage across the transistor 512 (Q1) of the DC / AC inverter 310.

[0181] The comparator 1010 is configured to compare a set threshold voltage with the peak value of the measured voltage across the transistor 512 (Q1) of the DC / AC inverter 310. If the measured peak voltage exceeds the threshold voltage, the comparator 1010 is configured to output a detection signal. If the measured peak voltage does not exceed the threshold voltage, the comparator 1010 does not output a detection signal.

[0182] Although a particular DC / AC inverter 1000 configured to detect the presence of a metal object has been described, one skilled in the art will recognize that other configurations are possible. Turning now to Figure 12, another embodiment of a DC / AC inverter, generally identified by the reference numeral 1100, is illustrated.

[0183] In this embodiment, the DC / AC inverter 1100 includes the same components as the previously described DC / AC inverter 310. Additionally, the DC / AC inverter 1100 includes a resistive voltage divider 1106, a peak detection circuit 1108, a comparator 1110, a threshold setter 1112, and an indicator 1114.

[0184] The resistive voltage divider 1106 is connected to the DC / AC inverter 310. The resistive voltage divider 1106 is connected to a peak detection circuit 1108. The peak detection circuit 1108 is connected to the resistive voltage divider 1106. The peak detection circuit 1108 is connected to a comparator 1110. The comparator 1110 is connected to a threshold setter 1112 and the peak detection circuit 1108. The comparator 1110 is connected to an indicator 1114. The threshold setter 1112 is connected to the comparator 1110. The indicator 1114 is connected to the comparator 1110.

[0185] The resistive voltage divider 1106 is configured to convert the voltage at the transistor Q1 of the DC / AC inverter 310 to a safe level. Specifically, the resistive voltage divider 1106 is configured to step down the voltage at the transistor 512 (Q1) of the DC / AC inverter 310 to a safe level. The resistive voltage divider is configured to divide the voltage at the transistor 512 (Q1) of the DC / AC inverter 310.

[0186] The peak detector circuit 1108 is configured to measure the peak value of the divided voltage from the resistive divider 1106. The peak detector circuit 1108 outputs the measured peak value to a comparator 1110.

[0187] The threshold setter 1112 is configured to set a threshold voltage for comparison with the measured peak value of the divided voltage.

[0188] The comparator 1110 is configured to compare a set threshold voltage with the measured peak value of the divided voltage. If the measured peak value of the divided voltage exceeds the threshold voltage, the comparator 1110 is configured to output a detection signal to the indicator 1114. If the measured peak value of the divided voltage does not exceed the threshold voltage, the comparator 1110 does not output a detection signal to the indicator 1114.

[0189] The indicator 1114 is configured to receive the detection signal from the comparator 1110. The indicator 1114 is configured to trip or set a fault indicator in response to receiving the detection signal, such that detection of a metal object is indicated.

[0190] Now, the operation of the AC / DC inverter 1100 will be described. FIG. 13 is a graph of the voltage at the transistor 512 (Q1) of the DC / AC inverter 1100 when a metal object is present and not present during the operation of the AC / DC inverter 1100. FIG. 13 further includes a threshold set by the threshold setter 1112. In this embodiment, the DC / AC inverter 1100 has an operating frequency of 6.78 MHz. As illustrated in FIG. 13, the peak voltage increases when a metal object is present. Additionally, when a metal object is present, the voltage reaches zero voltage before the transistor 512 (Q1) is turned on. The voltage reaching zero voltage before the transistor 512 (Q1) is turned on may indicate that the body of the transistor 512 (Q1) begins to conduct, resulting in increased power loss and reduced efficiency.

[0191] Furthermore, the difference between the voltages when a metal object is present and absent is proportional to the strength of the induced eddy currents. The larger the induced eddy currents, the more they can raise the peak voltage of transistor 512 (Q1). This raised peak voltage can reach the breakdown voltage of transistor Q1, which can permanently damage the DC / AC inverter 310.

[0192] In operation, the resistive divider 1106 receives and converts the voltage at the transistor 512 (Q1) of the DC / AC inverter 310 to a safe level. The peak detection circuit 1108 measures the peak value of the divided voltage from the resistive divider 1106. As shown in FIG. 13, as a result of the reactance reflected by a metal object being capacitive, the voltage waveform across the transistor 512 (Q1) of the DC / AC inverter 310 becomes narrower and higher compared to the voltage waveform when no metal object is present. The comparator 1110 receives the measured peak value of the divided voltage from the peak detection circuit 1108 and the set threshold voltage from the threshold setter 1112. As shown in FIG. 13, the measured peak value is obviously higher than the set threshold voltage when a metal object is present. Because the measured peak value is obviously higher than the set threshold voltage, the comparator 1110 outputs a detection signal to the indicator 1114. The indicator 1114 trips the fault indicator. This shuts down the DC / AC inverter 1100 and the entire high frequency wireless power transmission system 300 of which the DC / AC inverter 1100 is a part. This prevents not only damage to the DC / AC inverter 1100, but also possible heating of metal objects due to induced eddy currents.

[0193] As mentioned above, the transmitter 302 operates at a given frequency. In this embodiment, the operating frequency of the transmitter 302 is 13.56 MHz. Moreover, in this embodiment, the transmit coil 312 and receive coil 314 each have dimensions of 23.4 cm by 26.2 cm. The coils 312 and 314 each consist of two turns of copper trace with a width of 14 mm on an FR4 printed circuit board (PCB). The coils 312 and 314 have an inductance of approximately 1.50 uH. The reflected load seen by the transmit coil 312 varies from 0 ohms at no load 320 to 7 ohms at full load 320. The maximum power required by the load 320 is 30 W. Considering these operating parameters, consider now the design examples of the various presented DC / AC inverter embodiments.

[0194] We now describe an exemplary design embodiment of the DC / AC inverter 310 illustrated in Figure 5. In this embodiment, the transmit coil 312 and receive coil 314 have an inductance of 1.5uH, so inductance L3=1.5uH. The reflected load seen by the transmit coil 312 varies from 0 ohms at no load 320 to 7 ohms at full load 320. The maximum power required by the load 320 is 30W.

[0195] Based on the above formula, various parameters can be determined. According to the maximum reflected load (7 ohms) and the required power (30 W), the current required for the transmit coil 312 is 2.93 A (i.e., P max =1 / 2I L3 2 R L , and therefore I L3 =2.93A). The characteristic impedance Z0 is 8.9744 ohms (i.e. R Lmin / Z0=0.78, so Z0=8.9744). Furthermore, L ZVS and the values ​​of C1 and C2 are L ZVS The DC input voltage V is 107nH for C1 and 1.33nF for C2. The value of the residual reactance is 27.58nH (i.e. 0.258*Z0=2.3154 ohms). in is 6.546V.

[0196] We now describe an exemplary design embodiment of the DC / AC inverter 800 illustrated in Figure 8. In this embodiment, the transmit coil 312 and receive coil 314 have an inductance of 1.5uH, so inductance L3=1.5uH. The reflected load seen by the transmit coil 312 varies from 0 ohms at no load 320 to 7 ohms at full load 320. The maximum power required by the load 320 is 30W.

[0197] Based on the above formula, various parameters can be determined. According to the maximum reflected load (7 ohms) and the required power (30 W), the current required for the transmit coil 312 is 2.93 A (i.e., P max =1 / 2I L3 2 R L , and therefore I L3 =2.93A). DC input voltage V in is 119V (i.e. I L3 =3.132×V in / w L3 ). The characteristic impedance Z0 is 2989 ohms. Furthermore, L ZVS and the values ​​of C1 and C2 are L ZVS 35.6uH for C1 and 4pF for C2.

[0198] We now describe an exemplary design embodiment of the DC / AC inverter 900 illustrated in FIG. 9. In this embodiment, the transmit coil 312 and receive coil 314 have an inductance of 1.5 uH, so the inductance L3=1.5 uH. The reflected load seen by the transmit coil 312 varies from 0 ohms at no load 320 to 7 ohms at full load 320. The maximum power required by the load 320 is 30W. Based on the above formulas, various parameters can be determined. According to the maximum reflected load (7 ohms) and the required power (30W), the current required for the transmit coil 312 is 2.93A (i.e., P max =1 / 2I L3 2 R L , and therefore I L3 =2.93A). DC input voltage V in may be set to any voltage. In this embodiment, the DC input voltage V in is 24 V. Capacitance C4 is determined to be 457.5 pF. Capacitance C3 is determined to be 115 pF. Capacitance C 3b is the capacitance C 3a It is the same as the capacitance C 3a and C 3bis twice the capacitance C3, or 230 pF, according to Equation 20. DC input voltage V in And the characteristic impedance Z0 for a power of 30 W is 120.63 ohms. ZVS and the values ​​of C1 and C2 are L ZVS and 1.4375uH for C1 and 99pF for C2. The residual reactance is 31.12 ohms.

[0199] Although the high frequency wireless power transfer system 300 has been described as comprising a transmitter 302 configured to transfer power wirelessly via high frequency magnetic inductive coupling and a receiver 304 configured to extract power from the transmitter 302 via high frequency magnetic inductive coupling, one skilled in the art will recognize that other configurations are possible. In another embodiment, the transmitter 302 is configured to transfer power wirelessly via high frequency electrical inductive coupling, and the receiver 304 is configured to extract power from the transmitter 302 via high frequency electrical inductive coupling. In this embodiment, the transmitter 302 comprises a transmitting electrode rather than a transmitting coil 312, and the receiver 304 comprises a receiving electrode rather than a receiving coil 314.

[0200] Although embodiments have been described above with reference to the figures, those skilled in the art will recognize that variations and modifications can be made without departing from the scope thereof, as defined by the appended claims. [Explanation of symbols]

[0201] 100 Wireless power transmission system 110 Transmitter 112 Power supply 114 Sending elements 120 Receiver 122 Load 124 Receiving elements 200 Resonant Magnetic Wireless Power Transfer System 210 Transmitter 212 Power supply 214 Transmitting resonator 216 Transmitting resonator coil 218 Capacitor 220 Receiver 222 Load 224 Receiving resonator 226 Receiver resonator coil 228 Capacitor 250 Resonant Electrical Wireless Power Transfer System 260 Transmitter 262 Power supply 264 Transmitting Resonator 266 Transmitting resonator electrode 268 Inductor 270 Receiver 272 Load 274 Receiving Resonator 276 Receiving resonator electrode 278 Inductor 300 High Frequency Wireless Power Transmission System 302 Transmitter 304 Receiver 306 Power supply 308 Transmitter DC / DC Converter 310 DC / AC Inverter 312 Transmitting Coil 314 Receiver Coil 316 AC / DC Rectifier 318 Receiver DC / DC Converter 320 Load 402 resistor 404 Capacitor 406 Inductor 408 resistor 502 Inductor 504 Capacitor 506 Inductor 508 resistor 510 Capacitor 512 Transistor 514 Capacitor 516 Inductor 518 Inductor 520 Transistor 522 Capacitor 532 Inductor 534 Inductor 602 Voltage Source 604 Inductor 606 resistor 608 Capacitor 610 Inductor 612 resistor 614 Capacitor 616 Inductor 618 resistor 622 Voltage Source 624 Inductor 626 resistor 628 Capacitor 700 DC / AC Inverter 702 Load independent circuit 704 Impedance Inverter Circuit 710 Inductor 712 Transistor 714 Capacitor 730 Inductor 732 Transistor 734 Capacitor 740 Inductor 750 Inductor 752 Inductor 760 Capacitor 762 Capacitor 764 Capacitor 766 Capacitor 770 Inductor 780 resistor 800 DC / AC Inverter 802 Load independent circuit 804 Impedance Inverter Circuit 810 Inductor 812 Transistor 814 Capacitor 830 Inductor 832 Transistor 834 Capacitor 840 Inductor 850 Inductor 852 Inductor 860 Inductor 870 Capacitor 880 resistor 900 DC / AC Inverter 902 Load independent circuit 904 Impedance Inverter Circuit 910 Inductor 912 Transistor 914 Capacitor 930 Inductor 932 Transistor 934 Capacitor 940 Inductor 950 Inductor 952 Inductor 954 Capacitor 956 Capacitor 958 Capacitor 960 Capacitor 970 Capacitor 976 Inductor 980 resistor 1000 DC / AC Inverter 1008 Peak detection circuit 1010 Comparator 1012 Threshold setting device 1100 DC / AC Inverter 1106 Resistor Divider 1108 Peak detection circuit 1110 Comparator 1112 Threshold setting device 1114 Display

Claims

1. 1. A load independent inverter comprising a switch mode zero voltage switching (ZVS) amplifier, the switch mode ZVS amplifier comprising: A pair of circuits, at least one transistor and at least one capacitor arranged in parallel; a pair of circuits comprising at least one inductor disposed in series with the transistor and a capacitor; a single ZVS inductor connected to the pair of circuits, the capacitor and the inductor of the pair of circuits having values ​​such that the inverter operates in ZVS; at least one capacitor connected to the ZVS inductor and disposed in series with at least one inductor and at least one resistor; the q value of the load independent inverter is between 0.739 and 1.231; the residual reactance normalized to the characteristic impedance of the load independent inverter is between 0.194 and 0.323; The voltage gain value of the load independent inverter is between 2.349 and 3.915 and the minimum value of the load resistance normalized to the characteristic impedance of the switch mode ZVS amplifier is between 0.585 and 0.975, or the normalized output power of the load independent inverter is between 4.700 and 7.834; Load independent inverter.

2. 2. The load independent inverter of claim 1, comprising at least two capacitors connected to the ZVS inductor.

3. 3. The load independent inverter of claim 2, wherein the at least two capacitors are placed in series with the at least one inductor and resistor.

4. 4. A load independent inverter as claimed in claim 1, wherein the load independent inverter has a constant voltage output.

5. 5. The load independent inverter of claim 4, wherein the load independent inverter has a load range from 5.625 ohms to infinite or open circuit load.

6. 6. The load independent inverter of claim 4 or 5, further comprising an impedance inverter circuit configured to convert the load independent inverter from a constant voltage output to a constant current output.

7. 7. The load independent inverter of claim 6, wherein the impedance inverter circuit has a T-network topology or a Pi-network topology.

8. 4. A load independent inverter as claimed in claim 1, wherein the load independent inverter has a constant current output.

9. 9. The load independent inverter of claim 8, wherein the load independent inverter has a load range from zero ohms or a short circuit load to 9.375 ohms.

10. 10. The load independent inverter of claim 1, wherein the load independent inverter is configured to detect metal objects.

11. a peak detection circuit configured to measure a peak value of a voltage across a transistor of the load independent inverter; a comparator configured to compare the peak value of the voltage with a threshold voltage and output a detection signal if the peak value of the voltage exceeds the threshold voltage; The load independent inverter of claim 10 further comprising:

12. a voltage divider configured to convert the peak value of the voltage before being measured by the peak detection circuit; The load independent inverter of claim 11 further comprising:

13. 13. The load independent inverter of claim 1, wherein the switch mode ZVS amplifier is a radio frequency (RF) amplifier.

14. 14. A load independent inverter as claimed in any one of claims 1 to 13, wherein the load independent inverter is a class E inverter.

15. The load independent inverter of any one of claims 1 to 13, wherein the load independent inverter is a direct current (DC) to alternating current (AC) inverter.

16. A load independent inverter comprising a switch mode zero voltage switching (ZVS) amplifier, A pair of circuits, at least one transistor and at least one capacitor arranged in parallel; a pair of circuits comprising at least one inductor disposed in series with the transistor and a capacitor; a single ZVS inductor connected to the pair of circuits, the capacitor and the inductor of the pair of circuits having values ​​such that the inverter operates in ZVS; at least one capacitor connected to the inductor and disposed in series with the at least one inductor and the at least one resistor; the q value of the load independent inverter is between 0.739 and 1.231; the residual reactance normalized to the characteristic impedance of the load independent inverter is between 0.194 and 0.323; The voltage gain value of the load independent inverter is between 2.349 and 3.915 and the minimum value of the load resistance normalized to the characteristic impedance of the switch mode ZVS amplifier is between 0.585 and 0.975, or the normalized output power of the load independent inverter is between 4.700 and 7.834; A load independent inverter; a transmitting coil or electrode connected to the load independent inverter, the transmitting coil or electrode being configured to transmit power to a receiver via magnetic field or electric field coupling; A transmitter comprising:

17. The transmitter of claim 16 , wherein the transmitter is non-resonant or not self-resonant.

18. 18. The transmitter of claim 16 or 17, wherein the transmit coil is configured to transfer power via magnetic field coupling.

19. 18. The transmitter of claim 16 or 17, wherein the transmitting electrode is configured to transfer power via electric field coupling.

20. 20. The transmitter of claim 16, further comprising a power source.

21. 21. The transmitter of claim 20, wherein the transmitter further comprises a power converter configured to convert a power signal from the power source prior to reception by the inverter.

22. A wireless power transmission system, A load independent inverter comprising a switch mode zero voltage switching (ZVS) amplifier, A pair of circuits, at least one transistor and at least one capacitor arranged in parallel; a pair of circuits comprising at least one inductor disposed in series with the transistor and a capacitor; a single ZVS inductor connected to the pair of circuits, the capacitor and the inductor of the pair of circuits having values ​​such that the inverter operates in ZVS; at least one capacitor connected to the inductor and disposed in series with the at least one inductor and the at least one resistor; Equipped with the q value of the load independent inverter is between 0.739 and 1.231; the residual reactance normalized to the characteristic impedance of the load independent inverter is between 0.194 and 0.323; The voltage gain value of the load independent inverter is between 2.349 and 3.915 and the minimum value of the load resistance normalized to the characteristic impedance of the switch mode ZVS amplifier is between 0.585 and 0.975, or the normalized output power of the load independent inverter is between 4.700 and 7.834; A load independent inverter; a transmitting coil or electrode connected to the load independent inverter, the transmitting coil or electrode configured to transmit power to a receiver via magnetic field or electric field coupling; A transmitter comprising: A receiving coil or electrode configured to extract power from the receiver via magnetic or electric field coupling. and the receiver comprising:

23. 23. The wireless power transfer system of claim 22, wherein the transmitter is non-resonant or not self-resonant and the receiver is resonant.

24. 24. The wireless power transfer system of claim 23, wherein the receiver is resonant at an operating frequency of the transmitter.

25. 25. The wireless power transfer system of claim 22, wherein the transmitting coil is configured to transmit power via magnetic field coupling and the receiving coil is configured to extract power via magnetic field coupling.

26. 25. The wireless power transfer system of claim 22, wherein the transmitting electrodes are configured to transmit power via electric field coupling and the receiving electrodes are configured to extract power via electric field coupling.

27. 27. The wireless power transfer system of claim 22, wherein the receiver further comprises a rectifier connected to the receiving coil or electrode.

28. 28. The wireless power transfer system of claim 22, wherein the receiver further comprises a load connected to the receiving coil or electrode.

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