High frequency wireless power transfer system and its transmitter and receiver

Abstract

A load independent inverter includes a switched mode zero voltage switching (ZVS) amplifier. The switched mode ZVS amplifier includes: a circuit pair including: at least a transistor and at least a capacitor arranged in parallel; and at least an inductor arranged in series with the transistor and capacitor. The amplifier further includes: only one ZVS inductor connected to the circuit pair; and at least a pair of capacitors connected to the ZVS inductor and arranged in series with at least the inductor and at least a resistor.

Description

Technical Field

[0001] This invention relates generally to wireless power transmission, and more particularly to high-frequency wireless power transmission systems and their transmitters and receivers. Background Technology

[0002] Wireless charging and wireless power transfer systems are becoming increasingly important technologies supporting next-generation devices. The growing number of manufacturers and companies investing in this technology demonstrates its potential benefits and advantages.

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

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

[0005] There also exist resonant magnetic systems, where power is transferred due to magnetic field coupling between the inductors of the transmitter and receiver. In a resonant magnetic system, the inductors resonate using at least one capacitor. In a resonant magnetic system, both the transmitter and receiver are self-resonant. The power transfer range in a resonant magnetic system is increased compared to that in a magnetic induction system, and alignment issues are corrected. Although electromagnetic energy is generated in both magnetic induction and resonant magnetic systems, most of the power transfer occurs via the magnetic field. Power transferred via induction or resonant induction, if any, is minimal.

[0006] The Qi wireless charging standard is an exemplary implementation of a magnetic induction system. It is used in low-power consumer electronics such as smartphones and wearable devices. Furthermore, low-cost power converters, coils, and integrated circuits are available for the Qi wireless charging standard. The Qi wireless charging standard operates in the kHz frequency range. Therefore, 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. Consequently, the application scope of the Qi wireless charging standard is limited.

[0007] In an inductive system, both the transmitter and receiver have capacitive electrodes. Power transfer occurs due to electric field coupling between the capacitive electrodes of the transmitter and receiver. Similar to a resonant magnetic system, there exists a resonant electric system in which at least one inductor is used to make the capacitive electrodes of the transmitter and receiver resonate. In a resonant electric system, both the transmitter and receiver are self-resonant. Resonant electric systems offer an increased power transfer range compared to inductive systems, and alignment issues are corrected. Although electromagnetic energy is generated in both inductive and resonant electric systems, most of the power transfer occurs via the electric field. The power transferred via magnetic induction or resonant magnetic induction, if any, is minimal.

[0008] Applications of electromagnetic induction systems, commonly referred to as inductive power transfer (IPT) systems, can operate in the tens of MHz frequency range. In this range, the topologies of the DC-to-AC inverters used in the transmitters of these systems are typically based on Class E or EF2 inverter configurations. While these configurations are power efficient and simple to construct, optimal switching operation may only be maintained for stationary loads. Therefore, this configuration is highly dependent on stationary loads. Consequently, IPT systems using Class E or EF2 inverters typically operate efficiently only within a fixed coil spacing and a narrow load range.

[0009] As described in “Load-independent Class E Power Inverters: Part I. Theoretical Development” by REZulinski and KJ Grady in IEEE Trans. Circuits Syst. I, Reg. Papers, Vol. 37, No. 8, pp. 1010-1018 in August 1990, and “Design of Single-switch Inverters for Variable Resistance / load Modulation Operation” by L. Roslaniec, A.S. Jurkov, A. Albastami, and D.J. Erreault in IEEE Trans. Power Electron., Vol. 30, No. 6, pp. 3200-3214 in June 2015, Class E and Class EF2 inverters can be designed to achieve zero-voltage switching (ZVS) and produce a constant output voltage as the load resistance changes when used with finite DC inductors instead of chokes, relevant portions of these articles are incorporated herein by reference.

[0010] This design extends the load range for efficient operation of Class E or EF2 inverters from infinite load resistance (open circuit) to a minimum load resistance. While these designs can be applied to several applications, such as high-frequency DC / DC converters, they are generally not efficient for IPT systems where the distance between the coils / electrodes varies. In IPT systems, the load range extends from zero resistance (short circuit) when the coils / electrodes are completely separated to a maximum load resistance when the coils / electrodes are closest to each other.

[0011] As mentioned earlier, IPT systems can operate within a frequency range of tens of MHz. Switching within this frequency range can be achieved by utilizing wide-bandgap devices such as GaN and SiC. Recent developments in resonant converters and soft-switching topologies, such as Class E and Class EF, as described in “Load-independent Class E / EF Inverters and Rectifiers for MHz-Switching Applications” by S. Aldhaher, DCYates, and PDMitcheson in IEEE Trans. Power Electron., Vol. 33, No. 10, pp. 8270-8287 in October 2018, and “High-frequency, High-power Resonant Inverter with eGaN FET for Wireless Power Transfer” by J. Choi, D. Tsukiyama, Y. Tsuruda, and JMR Davila in IEEE Trans. Power Electron., Vol. 33, No. 3, pp. 1890-1896 in March 2018, allow for the development of truly wide-bandgap devices and provide designers with topologies and circuit configurations for realizing high-performance / power-density converters. Relevant sections of these articles are incorporated herein by reference.

[0012] Wireless power transfer operating at frequencies in the tens of MHz increases the maximum air gap distance, improves the tolerance for coil misalignment, and therefore allows the receiver to be placed anywhere in the charging area without precise alignment. This wireless power transfer also allows the use of high-Q single-turn air-core coils, which are lightweight, compact, and can be implemented on low-cost FR4 PCBs. Demonstrations of these capabilities by wirelessly powering micro-drones are described in “Light-weight Wireless Power Transfer for Mid-air Charging of Drones,” published by S. Aldhaher, P.D. Mitcheson, J.M. M ...

[0013] Although wireless power transfer technology is known, it still needs improvement. Therefore, the aim is to provide a novel wireless power transfer system, its transmitter and receiver, and a method for wirelessly transmitting power. Summary of the Invention

[0014] It should be understood that this summary is provided to introduce some concepts in a simplified form, which will be further described in the detailed embodiments below. This summary is not intended to limit the scope of the claimed subject matter.

[0015] Therefore, on one hand, a load-independent inverter is provided, which includes a switch-mode zero-voltage switching (ZVS) amplifier, the switch-mode zero-voltage switching amplifier including: a pair of circuits including: at least a transistor and at least a capacitor arranged in parallel; and at least an inductor arranged in series with the transistor and the capacitor; only one ZVS inductor connected to the pair of circuits; and at least a pair of capacitors connected to the ZVS inductor and arranged in series with the at least inductor and at least a resistor.

[0016] In one or more embodiments, the load-independent inverter includes at least two capacitors connected to a ZVS inductor. In one or more embodiments, the at least two capacitors are arranged in series with at least one inductor and a resistor.

[0017] In one or more embodiments, the minimum value of the load resistance normalized relative to the characteristic impedance of the switch-mode ZVS amplifier is between 0.585 and 0.975.

[0018] In one or more embodiments, the q-value of the load-independent inverter is between 0.739 and 1.231.

[0019] 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.

[0020] In one or more embodiments, the voltage gain of the load-independent inverter is between 2.349 and 3.915.

[0021] In one or more embodiments, the normalized output power of the load-independent inverter is between 4,700 and 7,834.

[0022] 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 from 5.625 ohms to infinite or open-circuit loads. In one or more embodiments, the load-independent inverter further includes an impedance inverter circuit configured to convert the load-independent inverter from a constant voltage output to a constant current output.

[0023] 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 0 ohms or short-circuit load to 9.375 ohms.

[0024] In one or more embodiments, the load-independent inverter is configured to detect metallic objects. In one or more embodiments, the load-independent inverter further includes: a peak detection circuit configured to measure a peak voltage across a transistor of the load-independent inverter; and a comparator configured to compare the peak voltage with a threshold voltage and output a detection signal if the peak voltage exceeds the threshold voltage. In one or more embodiments, the load-independent inverter further includes: a voltage divider configured to convert the peak voltage before it is measured by the peak detection circuit.

[0025] In one or more embodiments, the switch-mode ZVS amplifier is a radio frequency (RF) amplifier.

[0026] In one or more embodiments, the load-independent inverter is a Class E inverter.

[0027] In one or more embodiments, the load-independent inverter is a DC-to-AC inverter.

[0028] According to another aspect, a transmitter is provided, comprising: a load-independent inverter including a switch-mode zero-voltage switching (ZVS) amplifier; and a transmitter coil or electrode connected to the load-independent inverter, the transmitter coil or electrode being configured to transmit power to a receiver via magnetic or electric field coupling.

[0029] In one or more embodiments, the transmitter is non-resonant or non-self-resonant.

[0030] In one or more embodiments, the transmitter coil is configured to transmit power via magnetic field coupling.

[0031] In one or more embodiments, the transmitter electrodes are configured to transmit power via electric field coupling.

[0032] In one or more embodiments, the transmitter also includes a power source.

[0033] In one or more embodiments, the transmitter further includes a power converter configured to convert the power signal from the power source before it is received by the inverter.

[0034] According to another aspect, a wireless power transmission system is provided, comprising: a transmitter including: a load-independent inverter including a switch-mode zero-voltage switching (ZVS) amplifier; and a transmitter coil or electrode connected to the load-independent inverter, the transmitter coil or electrode being configured to transmit power to a receiver via magnetic field or electric field coupling; and a receiver including: a receiver coil or electrode configured to extract power from the receiver via magnetic field or electric field coupling.

[0035] In one or more embodiments, the transmitter is non-resonant or non-self-resonant, and the receiver is resonant. In one or more embodiments, the receiver resonates at the operating frequency of the transmitter.

[0036] In one or more embodiments, the transmitter coil is configured to transmit power via magnetic field coupling, and the receiver coil is configured to extract power via magnetic field coupling.

[0037] In one or more embodiments, the transmitter electrodes are configured to transmit power via electric field coupling, and the receiver electrodes are configured to extract power via electric field coupling.

[0038] In one or more embodiments, the receiver further includes a rectifier connected to the receiver coil or electrodes.

[0039] In one or more embodiments, the receiver further includes a load connected to the receiver coil or electrodes. Attached Figure Description

[0040] The embodiments will now be described more fully with reference to the accompanying drawings, in which:

[0041] Figure 1 This is a block diagram of a wireless power transmission system;

[0042] Figure 2AThis is a block diagram of a resonant magnetic wireless power transmission system;

[0043] Figure 2B This is a block diagram of a resonant wireless power transmission system;

[0044] Figure 3 This is a block diagram of a high-frequency magnetic wireless power transmission system according to one aspect of this disclosure;

[0045] Figure 4A yes Figure 3 A partial schematic layout of the inductive link of a high-frequency magnetic wireless power transmission system;

[0046] Figure 4B yes Figure 3 A partial schematic layout of the equivalent circuit as seen from the transmitter of a high-frequency magnetic wireless power transmission system.

[0047] Figure 5 yes Figure 3 Schematic layout of DC / AC inverter for high-frequency magnetic wireless power transmission system;

[0048] Figure 6 yes Figure 5 The equivalent circuit of a DC / AC inverter;

[0049] Figure 7 yes Figure 6 A series of analog curves of the equivalent circuit;

[0050] Figure 8 yes Figure 5 A schematic layout of another embodiment of a DC / AC inverter;

[0051] Figure 9 yes Figure 5 A schematic layout of another embodiment of a DC / AC inverter;

[0052] Figure 10 yes Figure 5 A schematic layout of another embodiment of a DC / AC inverter;

[0053] Figure 11 yes Figure 5 A block diagram of another embodiment of a DC / AC inverter;

[0054] Figure 12 yes Figure 5 A block diagram of another embodiment of the DC / AC inverter; and

[0055] Figure 13 It refers to the presence and absence of a metallic object. Figure 12 Voltage curves at the transistors of a DC / AC inverter. Detailed Implementation

[0056] The foregoing description of the invention and the following detailed description of specific examples will be better understood when read in conjunction with the accompanying drawings. As used herein, elements or features introduced in the singular and preceded by the word "a" or "an" should be understood to not necessarily exclude multiple elements or features. Furthermore, references to "an example" or "an embodiment" are not intended to be construed as excluding the existence of additional examples or embodiments that also incorporate the described elements or features. Moreover, unless explicitly stated otherwise, examples or embodiments that "comprise," "have," or "include" one element or feature or multiple elements or features having a particular attribute may include additional elements or features that do not have that attribute. Similarly, it should be understood that the terms "comprise," "have," and "include" mean "including but not limited to," and the terms "comprise," "have," and "include" have equivalent meanings. It should also be understood that throughout the specification and drawings, the same reference numerals will be used to refer to the same elements.

[0057] As used herein, the terms “suitable” and “configured” mean that an element, component, or other subject is designed and / or intended to perform a given function. Therefore, the use of the terms “suitable” and “configured” should not be construed as meaning that a given element, component, or other subject is simply “capable” of performing a given function, but rather that the element, component, and / or other subject is specifically selected, created, implemented, utilized, and / or designed to perform that function. Elements, components, and / or other subjects described as suitable for performing a particular function are also within the scope of this application and may additionally or alternatively be described as configured to perform that function, and vice versa. Similarly, subjects described as configured to perform a particular function may additionally or alternatively be described as operable to perform that function.

[0058] It should be understood that when a component is referred to as "located on", "attached to", "connected to", "coupled to", "contact", etc., another component may be directly located on, attached to, connected to, coupled to, or in contact with another component, or there may be an intermediate component.

[0059] It should be understood that, unless otherwise stated, the use of the word "exemplary" means "by example" or "an example," and not a preferred or best design or implementation.

[0060] 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 the subject matter pertains.

[0061] For the purpose of making the topic public, the switching frequency, w sThe switching frequency is defined as the frequency at which the switch is turned on and off. The switching frequency can be provided by an external signal source, such as a function generator, or generated using an oscillator. The switching signal based on the switching frequency is the master "clock" of the wireless power transmission system. Therefore, the fundamental frequency component of all other voltage and current signals of the relevant components will be equal to the switching frequency.

[0062] For the purpose of disclosing the subject matter, the resonant frequency w o The resonant frequency is defined as the frequency at which the circuit network has zero reactance impedance. The resonant frequency of a series LCR circuit is given by Equation 1:

[0063]

[0064] Where L is inductance and C is capacitance.

[0065] The resonant frequency of the parallel RLC circuit is given by Equation 2:

[0066]

[0067] 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 higher than, lower than, or equal to the resonant frequency.

[0068] For the purpose of disclosure, ZVS switches the transistor from the off state to the on state when the voltage across the transistor is zero. Therefore, there is no energy loss during the transition from the off state to the on state. In reality, there is some energy loss due to the finite duration of the transition. However, the energy loss is significantly lower than in non-ZVS circuits. ZVS allows for efficient operation of power inverters, especially in the MHz frequency range. ZVS is achieved using a combination of passive components such as capacitors and inductors with specific values.

[0069] For the purpose of disclosing the subject matter, the characteristic impedance (Zo) of the inverter resonant network is given by Equation 3:

[0070]

[0071] Where w is the frequency, L is the inductance of the inverter resonant network, and C is the capacitance of the resonant network.

[0072] Turn now Figure 1This figure illustrates a wireless power transfer system, generally identified by reference numeral 100. The wireless power transfer system 100 includes a transmitter 110 and a receiver 120. The transmitter 110 includes a power supply 112 electrically connected to a transmitting element 114, and the receiver 120 includes a receiving element 124 electrically connected to a load 122. Power is transferred from the power supply 112 to the transmitting element 114. Power is then transferred from the transmitting element 114 to the receiving element 124 via resonant or non-resonant electric or magnetic field coupling. Power is then transferred from the receiving element 124 to the load 122.

[0073] Turn now Figure 2A The figure illustrates an IPT system. In this embodiment, the IPT system is a resonant magnetic wireless power transmission system, generally identified by reference numeral 200. The resonant magnetic wireless power transmission system 200 includes a transmitter 210, which includes a power supply 212 electrically connected to a transmitting resonator 214. The transmitting resonator 214 includes a transmitting resonator coil 216 electrically connected to the power supply 212 via a capacitor 218. The magnetic resonant wireless power transmission system 200 also includes a receiver 220, which includes a receiving resonator 224 electrically connected to a load 222. The receiving resonator 224 is tuned to the resonant frequency of the transmitting resonator 214. The receiving resonator 224 includes a receiving resonator coil 226 electrically connected to the load 222 via a capacitor 228.

[0074] During operation of the resonant magnetic wireless power transmission system 200, power is transferred from power source 212 to transmitting resonator coil 216 via capacitor 218. Specifically, the power signal from power source 212 transmitted to transmitting resonator coil 216 via capacitor 218 excites transmitting resonator 214, causing transmitting resonator 214 to generate a magnetic field. When receiver 220, tuned to the same resonant frequency as transmitter 210, is placed within the magnetic field, receiving resonator 224 extracts power from transmitting resonator 214 via resonant magnetic field coupling. The extracted power is then transmitted from receiving resonator 224 to load 222. Because the power transmission is highly resonant, transmitting resonator 216 and receiving resonator coil 226 do not need to be as close or well aligned as in the case of a non-resonant magnetic system. Although transmitting resonator 214 can generate an electric field, the power transmitted via electric field coupling is minimal, if any.

[0075] Turn now Figure 2BAnother IPT system is illustrated. In this embodiment, the IPT system is a resonant electrical wireless power transfer system, generally identified by reference numeral 250. The resonant electrical wireless power transfer system 250 includes a transmitter 260, which includes a power supply 262 electrically connected to a transmitting resonator 264. The transmitting resonator 264 includes transmitting resonator electrodes 266 electrically connected to the power supply 262 via one or more inductors 268. The resonant electrical wireless power transfer system 250 also includes a receiver 270, which includes a receiving resonator 274 electrically connected to a load 272. The receiving resonator 274 is tuned to the resonant frequency of the transmitting resonator 264. The receiving resonator 274 includes receiving resonator electrodes 276 electrically connected to the load 272 via one or more inductors 278.

[0076] During operation of the resonant wireless power transmission system 250, power is transferred from power source 262 to transmitting resonator electrode 266 via inductor 268. Specifically, a power signal from power source 262 transmitted to transmitting resonator electrode 266 via inductor 268 excites transmitting resonator 264, causing transmitting resonator 264 to generate an electric field. When receiver 270, tuned to the same resonant frequency as transmitter 260, is placed within the electric field, receiving resonator 274 extracts power from transmitting resonator 264 via resonant electric field coupling. The extracted power is then transmitted from receiving resonator 274 to load 272. Because the power transmission is highly resonant, transmitting resonator 266 and receiving resonator electrode 276 do not need to be as close or well aligned as in the case of a non-resonant electrical system. Although transmitting resonator 264 can generate a magnetic field, the power transmitted via magnetic field coupling is minimal, if any.

[0077] Turn now Figure 3 This illustration shows a high-frequency wireless power transmission system 300, one aspect of which is disclosed in this subject matter and is generally identified by reference numeral 300. The high-frequency wireless power transmission system 300 includes a transmitter 302 and a receiver 304. As will be described, the high-frequency wireless power system 300 operates by transmitting power from a non-resonant or non-self-resonant transmitter 302 to a receiver 304 that resonates at the operating frequency of the transmitter 302.

[0078] Transmitter 302 is configured to wirelessly transmit power via high-frequency magnetic induction coupling as described below. Although an electric field may also be generated, the power transmitted via electric field coupling, if any, is very small.

[0079] Transmitter 302 includes a power supply 306, a transmitter DC / DC converter 308, a DC / AC inverter 310, and a transmitter coil 312. Power supply 306 is electrically connected to transmitter DC / DC converter 308. Power supply 306 is configured to generate a DC power signal. Power supply 306 is configured to output a DC power signal to transmitter DC / DC converter 308. In this embodiment, the DC power signal is between 24V and 48V. Transmitter DC / DC converter 308 is electrically connected to power supply 306. Transmitter DC / DC converter 308 is electrically connected to DC / AC inverter 310. Transmitter DC / DC converter 308 connects power supply 306 to DC / AC inverter 310. Transmitter DC / DC converter 308 is configured to convert the DC power signal from power supply 306 into a voltage level for transmission to DC / AC inverter 310.

[0080] The DC / AC inverter 310 is electrically connected to the transmitter DC / DC converter 308. The DC / AC inverter 310 is also electrically connected to the transmitter coil 312. The DC / AC inverter 310 is configured to convert the 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 converter 310 to the transmitter coil 312.

[0081] Although transmitter 302 has been described as including transmitter DC / DC converter 308, those skilled in the art will understand that other configurations are possible. In another embodiment, transmitter 302 does not include transmitter DC / DC converter 308. In this embodiment, power supply 306 is electrically connected to DC / AC inverter 310. Power supply 306 is configured to generate a DC power signal acceptable to DC / AC inverter 310.

[0082] Receiver 304 is configured to extract power from transmitter 302 via high-frequency magnetic induction coupling as described below. Although an electric field may also be generated, the power extracted via electric field coupling, if any, is very small.

[0083] Receiver 304 includes receiver coil 314, AC / DC rectifier 316, receiver DC / DC converter 318, and load 320. Receiver coil 314 is electrically connected to AC / DC rectifier 316. Receiver coil 314 is configured to receive power from transmitter 302 via transmitter coil 312 using high-frequency magnetic coupling. In this embodiment, receiver coil 314 has the same dimensions and number of turns as transmitter coil 312.

[0084] AC / DC rectifier 316 is electrically connected to receiver coil 314. AC / DC rectifier 316 is also electrically connected to receiver DC / DC converter 318. AC / DC rectifier 316 is configured to convert a sinusoidal RF power signal from receiver coil 314 into a DC power signal. AC / DC rectifier 316 is configured to output a DC power signal to receiver DC / DC converter 318.

[0085] The receiver DC / DC converter 318 is electrically connected to the AC / DC rectifier 316. The receiver DC / DC converter 318 is also electrically connected to the 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 connects the AC / DC rectifier 316 to the load 320 via an interface. 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 can be a fixed load or a variable load.

[0086] Although receiver 304 is described as including receiver DC / DC converter 318, those skilled in the art will understand that other configurations are possible. In another embodiment, receiver 304 does not include 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 acceptable to load 320.

[0087] Transmitter 302 operates at a given frequency. In this embodiment, the operating frequency of transmitter 302 is 13.56 MHz. Furthermore, in this embodiment, transmitter coil 312 and receiver coil 314 each have dimensions of 23.4 cm × 26.2 cm. Coils 312 and 314 are each composed of two 14 mm wide copper traces on an FR4 printed circuit board (PCB). Coils 312 and 314 have an inductance of approximately 1.50 μH. The reflected load seen by transmitter coil 312 varies from 0 ohms when there is no load 320 to 7 ohms when there is a full load 320. The maximum power required by load 320 is 30 W.

[0088] Receiver 304 operates at a given frequency. In this embodiment, the operating frequency of receiver 304 is the operating frequency of transmitter 302. In this embodiment, the operating frequency of receiver 304 is 13.56 MHz.

[0089] As previously described, the DC / AC inverter 310 is configured to convert a 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 converter 310 to the transmitter coil 312.

[0090] Specifically, the DC / AC inverter 310 drives the transmitter coil 312 with sinusoidal alternating current (AC). The transmitter coil 312 is configured to generate an induced (magnetic) field and transmit power via high-frequency induced (magnetic) field coupling. The DC / AC inverter 310 acquires a DC input voltage and converts the acquired DC input voltage into a high-frequency AC current to drive the transmitter coil 312.

[0091] The DC / AC inverter 310 is affected by variations in load conditions, changes in the geometry of the system 300, and external distances (i.e., environmental influences), such as the presence of metallic objects near the system 300. Therefore, it is desirable for the DC / AC inverter 310 to be robust and tolerant to these variations, and it is desirable for the DC / AC inverter 310 to operate at a frequency of MHz.

[0092] As previously mentioned, Class E and Class EF2 inverters can be designed to achieve zero resistance (ZVS) and produce a constant output voltage as the load resistance varies when used with finite DC inductors instead of chokes. This design extends the range of loads over which Class E or Class EF2 inverters can operate efficiently from an infinite load resistance (open circuit) to a minimum load resistance. While these designs can be applied to several applications, such as high-frequency DC / DC converters, they are generally not efficient for use in high-frequency wireless power transfer systems 300 because of the varying distance between coils 312 and 314, and because the load range extends from zero resistance (short circuit) when coils 312 and 314 are completely separated to a maximum load resistance when coils 312 and 314 are closest to each other.

[0093] Furthermore, 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” by S. Aldhaher, DCYates, and P.D. Mitcheson in IEEE Trans., Power Electronics, Vol. 33, No. 10, pp. 8270-8287, October 2018, and “Maximizing DC-to-load Efficiency for Inductive Power Transfer” by M. Pinuela, DCYates, S. Lucyszyn, and P.D. Mitcheson in IEEE Trans., Power Electronics, Vol. 28, No. 5, pp. 2437-2447, May 2013, relevant sections of which are incorporated herein by reference. While these configurations are power efficient and simple to construct, they maintain their optimal switching operation only for stationary loads and are therefore highly dependent on the load value.

[0094] Therefore, this limits IPT systems with Class E or Class EF2 DC / AC inverters to operate efficiently only at fixed coil spacing and narrow load ranges.

[0095] To overcome the challenges discussed earlier when using inverters based on Class E or EF2 configurations, and to allow for variable distance between the transmitter coil 312 and receiver coil 314, the DC / AC inverter 310 is load-independent. The load-independent DC / AC inverter 310 allows Class E and EF inverters to maintain efficient operation by achieving ZVS independent of load resistance. Furthermore, unlike typical Class E and EF2 inverters, load-independent Class E and EF inverters can deliver a constant output AC voltage or current that does not change with the load, making them more suitable for IPT applications.

[0096] When considering the design of the DC / AC inverter 310, it is beneficial to discuss the efficiency of the coupling and / or inductive link between coils 312 and 314. As previously mentioned, the high-frequency wireless power transmission system 300 includes a transmitter 302 and a receiver 304. The transmitter 302 includes a transmitter coil 312 and other components, and the receiver 304 includes a receiver coil 314 and other components.

[0097] Coils 312 and 314 are spaced apart by a certain gap. Transmitter coil 312 is driven by a sinusoidal AC current at a fixed frequency (the operating frequency of transmitter 302). An alternating magnetic field coupled to receiver coil 314 is generated, inducing a sinusoidal voltage at the same frequency as the current in transmitter coil 312 across the terminals of receiver coil 314. Any load across the terminals of receiver coil 314, such as load 320, will cause current to flow into the load. The coupling coefficient k represents the amount of coupling between the two coils 312 and 314, as defined in Equation 4:

[0098]

[0099] Where L p It is the inductance of transmitter coil 312, L s M is the inductance of receiver coil 314, and M is the mutual inductance between coils 312 and 314.

[0100] Turn now Figure 4A This shows a partial schematic layout of the inductive link of the high-frequency magnetic wireless power transmission system 300. Figure 4A The circuit representation includes two coupled coils, 312 and 314. It has a resistor R. L Resistor 402 represents the AC load resistance. Capacitor 404, with capacitance Cs, is connected in series with receiver coil 314 to make receiver coil 314 resonate at the operating frequency. The reflected impedance Z seen by transmitter coil 312 is... Ref As given by Equation 5:

[0101]

[0102] Where M is the mutual inductance between coils 312 and 314, w is the operating frequency, and jX is the operating frequency. Ls It is the impedance of receiver coil 314 at the operating frequency, jX Cs It is the impedance of the series capacitor 404 at the operating frequency.

[0103] Reflected impedance is a measure of how much of the actual load is seen by transmitter 302. It is a function of the mutual inductance between coils 312 and 314, and is affected by the distance between them. The closer coils 312 and 314 are to each other, the higher the mutual inductance and the higher the reflected impedance. The farther apart coils 312 and 314 are, the lower the mutual inductance and the lower the reflected impedance.

[0104] As shown in Equation 5, the reflected impedance is inversely proportional to the load resistance and the impedance of the receiver 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, thus exhibiting lower conduction and ohmic losses and higher efficiency.

[0105] The reflection impedance in Equation 5 can be reduced by eliminating the reactance term X of the receiver coil 314. LS To maximize this. The reactance term reflects the resistive load of transmitter 302. This can be achieved at the operating frequency by setting the reactance term to be equal to 1 / (W). 2 L s This is achieved through [the following]. With this capacitance value, equation 5 becomes equation 6:

[0106]

[0107] Turn now Figure 4B The diagram shows a partial schematic layout of the equivalent circuit as seen from the transmitter 302 of the high-frequency magnetic wireless power transmission system 300. Figure 4B This shows the transmitter coil 312 tuned to resonance (i.e., jX) in the receiver coil 314. Ls =jX Cs The equivalent circuit when ) is used. This circuit includes an inductor L p Inductor 406 and having resistor R Ref Resistor 408. As shown in Equation 6, when using series resonance, the reflected impedance remains resistive regardless of the load resistance value. This differs from the case of parallel tuned receiver coil 314 or secondary coil described by K.V. Chuylenbergh and R. Puers in "Inductive Powering: Basic Theory and Application to Biomedical Systems," Springer, 2009, 1st edition, the relevant sections of which are incorporated herein by reference.

[0108] The reflected impedance remains resistive, ensuring that the DC / AC inverter 310 does not deviate from optimal operating conditions. However, series resonance limits the maximum operating frequency because the parasitic capacitance of the receiver coil 314 is not absorbed by the resonant capacitor C during operation. s middle.

[0109] As previously stated, while the receiver coil 314 can operate at or near resonance, the transmitter coil 312 does not operate at resonance (i.e., the transmitter coil 312 is not self-resonant). This contrasts with many IPT systems where the transmitter coil 312 operates at resonance.

[0110] Based on the above equation, the link efficiency of the high-frequency wireless power transmission system 300 can be determined. The link efficiency of the high-frequency wireless power transmission system 300 is defined as the power delivered to the AC secondary load (load 320) divided by the power input to the transmitter coil 312. With the receiver coil 314 operating at resonance and having the optimal load for maximum efficiency, the link efficiency (η) is given by Equation 7:

[0111]

[0112] Q Lp and Q Ls These are the unloaded quality factors of the transmitter coil 312 and the receiver coil 314, respectively.

[0113] Turn now Figure 5 A schematic diagram of the DC / AC inverter 310 of the high-frequency magnetic wireless power transmission system 300 is shown. The DC / AC inverter 310 is configured to generate an AC output voltage with a constant amplitude regardless of the load, while maintaining ZVS.

[0114] As previously stated, 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. Voltage-mode output indicates that the DC / AC inverter 310 has a constant voltage output.

[0115] The DC / AC inverter 310 includes a switch-mode ZVS amplifier as described below. The amplifier is a radio frequency (RF) amplifier.

[0116] like Figure 5 As shown, the switch-mode ZVS amplifier includes series inductors 502 and 518, which have inductances L1 and L2 respectively, and receive input voltage V. in Each inductor 502, 518 is connected in series with a combination of transistors 512 and 520 (Q1 and Q2) (or switches) and capacitors 514 and 522, respectively. Capacitors 514 and 522 have capacitances C1 and C2, respectively. Specifically, transistor 512 and capacitor 514 are arranged in parallel and connected to inductor 502. Transistor 520 and capacitor 522 are arranged in parallel and connected to inductor 518. The pairs of transistors 512 and capacitor 514, and transistor 520 and capacitor 522, are grounded. An inductor L... ZVS Inductor 516 is connected in parallel between inductors 502 and 518. It has an inductance L... RESa Inductor 532, with capacitor C 3aCapacitor 504, inductor 506 with inductance L3, resistor R L Resistor 508, with capacitor C 3b Capacitor 510 and having inductance L RESb Inductor 534 is arranged in series and connected in parallel to inductor 516. Inductor 506 represents the inductance of transmitter coil 312, and resistor 508 represents the reflected load of receiver coil 314. Inductors 532 and 534 represent the residual inductance of receiver coil 314.

[0117] The state-space modeling method described by S. Aldhaher in his 2014 doctoral dissertation at Cranfield University, “Design and optimization of switched-mode circuits for inductive links,” is used to derive the design equations for the DC / AC inverter 310. Relevant parts of that dissertation are incorporated herein by reference.

[0118] Figure 5 The equivalent circuit of the DC / AC inverter 310 shown is produced according to the state-space modeling method. Now turn to... Figure 6 The equivalent circuit of the DC / AC inverter 310 is shown. For example... Figure 6 As shown, it has a voltage V in Two voltage sources 602 and 622 feed signals to two inductors 604 and 624, each having an inductance L1 on either side of the equivalent circuit. Specifically, one voltage source 602 feeds to one inductor 604, and the other voltage source 622 feeds to the other inductor 624. Each of the voltage source 602 and inductor 604 pairs, and the voltage source 622 and inductor 624 pairs, is connected in parallel to a resistor 606 or 626 having resistances R1 or R2. Each of the voltage source 602 and inductor 604 pairs, and the voltage source 622 and inductor 624 pairs, is also connected in parallel to capacitors 608 and 628. Each capacitor has a capacitance C1. Specifically, the voltage source 602 and inductor 604 pair is connected to resistor 606 and capacitor 608. Another voltage source 622 and inductor 624 are connected to resistor 626 and capacitor 628. Inductors 604 and 624 are connected in series to a resistor with inductance L. ZVS Inductor 610 and having resistor R LZVS Resistor 612. Inductor 610 and resistor 612 are connected in parallel to capacitor 614 with capacitance C3, inductor 616 with inductance L3, and resistor R. LResistor 618. Capacitor 614, inductor 616, and resistor 618 form the output network. The capacitance C3 of capacitor 614 is equal to the sum of the capacitances of capacitors 504 and 510 (C... 3a and C 3b ). Figure 5 Transistors 512 and 520 have been replaced by resistors 606 and 626, which have resistances R1 and R2 respectively.

[0119] For load value R L =6.25 ohms, 12.5 ohms, 25 ohms and 100 ohms simulated Figure 6 The equivalent circuit. The results of these simulations are as follows: Figure 7 The graph is shown below. Figure 7 As shown, when the load value R L When the resistance is equal to 6.25 ohms, the voltage across the transistor / switch 512 is equal to the input voltage V. in The ratio is the largest. Similarly, when the load value R... L When the resistance is equal to 6.25 ohms, the voltage across the transistor / switch 520 is equal to the input voltage V. in The ratio is the largest.

[0120] In addition, such as Figure 7 As shown, the DC / AC inverter 310 maintains ZVS under various load conditions, ranging from open-circuit load conditions to minimum load resistance. Regardless of the load value, the amplitude and phase of the output AC voltage across the load remain constant. Although the shapes of various waveforms may change, ZVS generally remains constant, and the amplitude and phase of the output voltage are typically constant. Furthermore, when the load resistance decreases, the currents in transistors 512 and 520 exhibit a negative slope during turn-off. This negative slope during turn-off minimizes the turn-off time of transistors 512 and 520 and eliminates the effects of parasitic inductance.

[0121] As mentioned earlier, the state-space modeling method is used for derivation. Figure 6 Design equations for the equivalent circuit. The design equations discussed can be used to construct the AC / DC inverter 310 to meet a specific set of requirements, such as load impedance, resonator impedance, operating frequency, and input DC voltage. The following design equations are derived: q value, residual reactance X res Voltage gain, load resistance R L and output power P out .

[0122] The resonant frequency of the DC / AC inverter 310 is set to the operating frequency. The value of q is given by Equation 8:

[0123]

[0124] The q-value is unique for each inverter class and topology. For optimal performance of the 13.56MHz operating frequency and the high-frequency wireless power transmission system 300, the q-value is approximately 0.985. This is expected because the transmitter 302 is non-resonant (or non-self-resonant), so the q-value should not be equal to 1.

[0125] Those skilled in the art will understand that the q-value may not be exactly equal to 0.985, and the high-frequency wireless power transmission system 300 may still operate; however, the load range will be reduced, and performance will be negatively affected. In some embodiments, the q-value may vary by up to plus or minus 25% of 0.985 (e.g., approximately 0.739 to 1.231) while still providing acceptable performance.

[0126] The output network consists of capacitor 614, inductor 616, and resistor 618. The capacitance C3 of capacitor 614 is equal to the sum of the capacitances of capacitor 504 and capacitor 510 (C3 = C...). 3a +C 3b The frequency of the transmitter 302 is not tuned to its resonant frequency. Therefore, at the operating frequency given in Equation 9, the output network will have a residual reactance X. res :

[0127]

[0128] Similar to the q-value, X res The value of X is unique for the inverter type and topology. For AC / DC inverter 310, X is normalized relative to the characteristic impedance of inverter 310. res The ratio is given by Equation 10:

[0129]

[0130] This is expected because transmitter 302 is non-resonant (or non-self-resonant), so X res The value should not be equal to zero (0). Although not described, it will be understood by those skilled in the art that, as Figure 5 As shown in inductors 532 and 534, residual inductance may also exist.

[0131] Those skilled in the art will understand that X res The value may not be exactly equal to 0.258, and the high-frequency wireless power transmission system 300 will still function; however, performance will be negatively affected. In some embodiments, X res The value can vary by up to 25% plus or minus 0.258 (e.g., from approximately 0.194 to 0.323) while still providing acceptable performance.

[0132] The characteristic impedance of AC / DC inverter 310 is given by equation 11:

[0133]

[0134] Voltage gain is the load R L The amplitude of the AC voltage across the terminals is related to the input DC voltage V. IN The ratio. For this AC / DC inverter 310, the voltage gain is given by Equation 12:

[0135]

[0136] For optimal performance of the 13.56MHz operating frequency and the high-frequency wireless power transmission system 300, the voltage gain is approximately 3.132.

[0137] Those skilled in the art will understand that the voltage gain value may not be exactly equal to 3.132, and the high-frequency wireless power transmission system 300 may still function; however, performance will be negatively affected. In some embodiments, the voltage gain value may vary by up to plus or minus 25% of 3.132 (e.g., approximately 2.349 to 3.915) while still providing acceptable performance.

[0138] As mentioned earlier, the DC / AC inverter 310 features voltage-mode output, i.e., constant voltage output. When the load resistance R... L In {R Lmin The DC / AC inverter 310 can operate efficiently within the range of ∞. If the load resistance R... L Reduced to below R Lmin The DC / AC inverter 310 will no longer operate efficiently, i.e., ZVS operation will be lost, and the output voltage of the DC / AC inverter 310 will change.

[0139] This is because the voltage across the transistors will swing below zero volts, which effectively means that the body diodes of transistors Q1 and Q2 will conduct, thus interrupting the operation of the DC / AC inverter 310. Minimum load resistance R Lmin This corresponds to the load that the DC / AC inverter can deliver at its maximum power (when operating in voltage mode). Here, R is normalized relative to the characteristic impedance Z0. Lmin The value is given by Equation 13:

[0140]

[0141] Those skilled in the art will understand that, for R Lmin The value, after normalization, may not exactly equal 0.780, and the high-frequency wireless power transmission system 300 will still function; however, performance will be negatively affected. In some embodiments, for R... LminThe value can be normalized to vary by up to 25% plus or minus 0.780 (e.g., between 0.585 and 0.975) while still providing acceptable performance.

[0142] By combining equations 12 and 13, the output power P of the DC / AC inverter 310 at the minimum load resistance under a specific input DC voltage can be determined. out Regarding the output power P out Normalization is given by Equation 14:

[0143]

[0144] Those skilled in the art will understand that, for the output power P out Normalization may not result in an exact value of 6.267, and the high-frequency wireless power transmission system 300 will still function; however, performance will be negatively impacted. In some embodiments, the output power P... out Normalization can vary up to 6.267 by plus or minus 25% (e.g., from approximately 4.700 to 7.834) while still providing acceptable performance.

[0145] Implementing the DC / AC inverter 310 according to the derived design equations produces a more efficient and robust DC / AC inverter 310 than other configurations. In particular, Table 1 lists the differences between the DC / AC inverter 310 and other configurations.

[0146] Table 1

[0147]

[0148]

[0149] Table 1

[0150] During operation, the DC / AC inverter 310 generates a constant AC voltage or current that does not change with the load. As previously described, in this embodiment, the DC / AC inverter 310 has a voltage-mode output, thus generating a constant AC voltage.

[0151] When there is no coupling between the transmitter coil 312 and the receiver coil 314, or when the receiver 304 is unloaded, the reflected resistance of the DC / AC inverter 310 is zero (0). However, during operation, a reflected resistance exists due to the coupling between coils 312 and 314. Specifically, the reflected resistance increases as the coupling between coils 312 and 314 increases. A current sensing and feedback system can be used to regulate the output current of the DC / AC inverter 310.

[0152] As described below, as an alternative to current sensing and feedback systems, voltage-mode output (constant voltage output) can be converted to current-mode output (constant current output) to eliminate reflective resistance.

[0153] Although a specific DC / AC inverter 310 has been described, those skilled in the art will understand that other configurations are possible. Now turning to... Figure 8 The figure shows a schematic layout of another embodiment of a DC / AC inverter, typically identified by reference numeral 800. In this embodiment, the DC / AC inverter 800 includes load-independent circuitry 802 and impedance inverter circuitry 804. The DC / AC inverter 800 is a current-mode output (constant output current).

[0154] The load-independent circuit 802 is configured to convert an input DC signal into an output AC signal. The load-independent circuit 802 is a voltage-mode output (constant output voltage). The load-independent circuit 802 includes inductors 810 and 830, each having inductances L1 and L2 respectively, which receive signals having a voltage V. in The input voltage. Each inductor 810, 830 is connected in series with a combination of transistors 812, 832 (Q1 and Q2) and capacitors 814, 834, each having capacitances C1 and C2. Specifically, transistor 812 and capacitor 814 are arranged in parallel and connected to inductor 810. Transistor 832 and capacitor 834 are arranged in parallel and connected to inductor 830. The pair of transistors 812 and capacitor 814, and the pair of transistors 832 and capacitor 834, are grounded. With inductance L ZVS Inductor 840 is connected in parallel between inductors 810 and 830.

[0155] Impedance inverter circuit 804 is configured to convert load-independent circuit 802 from voltage-mode output (constant output voltage) to current-mode output (constant output current). Impedance inverter circuit 804 includes circuits with inductors L... RESa +L 3a L RESa +L 3b Inductors 850, 852, and 860 with L3; capacitor 870 with capacitance C3; and resistor R L Resistor 880. Inductors 850 and 852 are connected in series with inductor 840. Inductance L3 is equal to inductance L. 3a With inductor L 3b The sum (L3 = L) 3a +L 3b Inductance L RESa and L RESb This indicates residual inductance.

[0156] and Figure 5 Compared to the AC / DC inverter 310 shown, capacitor 870 is connected in parallel with inductor 840. Inductor 860 is connected in series with resistor 880, and together they are connected in parallel with capacitor 870. The output current in inductor 860 is given by Equation 15:

[0157]

[0158] As mentioned earlier, the value of inductance L3 is given by Equation 16.

[0159] L3 = L 3a +L 3b (16)

[0160] The current in inductor 860 is constant regardless of the reflected load. Although 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), the value of the output current depends on the input voltage and the inductance of the transmitter coil 312. The output current cannot be changed without altering the input voltage or the inductance of the transmitter coil 312.

[0161] Although specific DC / AC inverters 310 and 800 have been described, those skilled in the art will understand that other configurations are also possible. Now turning to... Figure 9 The figure shows a schematic layout of another embodiment of a DC / AC inverter, typically identified by reference numeral 900. In this embodiment, the DC / AC inverter 900 includes load-independent circuitry 902 and impedance inverter circuitry 904. The DC / AC inverter 900 is a current-mode output (constant output current).

[0162] The load-independent circuit 902 is configured to convert an input DC signal into an output AC signal. The load-independent circuit 902 is a voltage-mode output (constant output voltage). The load-independent circuit 902 includes inductors 910 and 930 with inductances L1 and L2, which receive signals having a voltage V. in The input voltage. Each inductor 910, 930 is connected in series with a combination of transistors 912, 932 (Q1 and Q2) and capacitors 914, 934, respectively. Capacitors 914 and 934 have capacitances C1 and C2, respectively. Specifically, transistor 912 and capacitor 914 are arranged in parallel and connected to inductor 910. Transistor 932 and capacitor 934 are arranged in parallel and connected to inductor 930. The pair of transistors 912 and capacitor 914, and the pair of transistors 932 and capacitor 934, are grounded. An inductor L... ZVS Inductor 940 is connected in parallel between inductors 910 and 912.

[0163] Impedance inverter circuit 904 is configured to convert load-independent circuit 902 from voltage-mode output (constant output voltage) to current-mode output (constant output current). Impedance converter circuit 904 has a T-network circuit configuration. Impedance inverter circuit 904 includes circuits with inductors L... RESa + L3a L RESa +L 3b The inductors 950, 952, and 976 of L3 each have a capacitor C. 3a Capacitors 954 and 958; each has a capacitance C 3b Capacitors 956 and 960; capacitor 970 with capacitance C4; and capacitor with resistance R L The resistor is 980. The inductor L3 is equal to the inductor L. 3a With inductor L 3b The sum (L3 = L) 3a +L 3b Inductance L RESa and L RESb This represents residual inductance. Each inductor 950, 952 is connected in series with capacitors 954, 956, respectively. Inductor / capacitor pairs 950, 954 and 952, 956 are connected to either end of inductor 940 in load-independent circuit 902. Capacitor 970 is connected in parallel with inductor 940. Furthermore, capacitor 958, inductor 976, resistor 980, and capacitor 960 are connected in series, and together they are connected in parallel with capacitor 970. Capacitance C3 depends on capacitance C4, as given by Equation 17:

[0164]

[0165] The output current in inductor 976 is given by equation 18:

[0166]

[0167] As shown in Equation 18, the output current in inductor 976 depends on the capacitance C4 of capacitor 970 and the input voltage V. in .

[0168] As mentioned earlier, the inductance L3 of inductor 376 is given by Equation 19.

[0169] L3 = L 3a +L 3b (19)

[0170] However, capacitor C3 is given by equation 20:

[0171]

[0172] While specific DC / AC inverters 310, 800, and 900 have been described, those skilled in the art will understand that other configurations are also possible. Now turning to... Figure 10 The figure shows a schematic layout of another embodiment of a DC / AC inverter, typically identified by reference numeral 700. In this embodiment, the DC / AC inverter 700 includes load-independent circuitry 702 and impedance inverter circuitry 704. The DC / AC inverter 700 is a current-mode output (constant output current).

[0173] The load-independent circuit 702 is configured to convert an input DC signal into an output AC signal. The load-independent circuit 702 is a voltage-mode output (constant output voltage). The load-independent circuit 702 includes inductors 710 and 730 with inductances L1 and L2, which receive signals having a voltage V. in The input voltage. Each inductor 710, 730 is connected in series with a combination of transistors 712, 732 (Q1 and Q2) and capacitors 714, 734, respectively. Capacitors 714, 734 have capacitances C1 and C2, respectively. Specifically, transistor 712 and capacitor 714 are arranged in parallel and connected to inductor 710. Transistor 732 and capacitor 734 are arranged in parallel and connected to inductor 730. The pair of transistors 712 and capacitor 714, and the pair of transistors 732 and capacitor 734, are grounded. With inductance L ZVS Inductor 740 is connected in parallel between inductors 710 and 712.

[0174] Impedance inverter circuit 704 is configured to convert load-independent circuit 702 from voltage-mode output (constant output voltage) to current-mode output (constant output current). Unlike impedance inverter circuit 904, impedance converter circuit 704 has a pi-network circuit configuration. Impedance inverter circuit 704 includes circuits with inductors L... RESa +L 3a L RESa +L 3b Inductors 750, 752, and 770 of L3; each has a capacitor C 4a C 4b Capacitors 760 and 762; and capacitors with resistor R L The resistor is 780Ω. It has a capacitor C. 3a Capacitor 764 is connected in parallel to inductors 750 and 752. It has a capacitance C. 3b Capacitor 766 is connected in parallel to capacitors 760 and 762. Inductor 770 and resistor 780 are connected in series, and together they are connected in parallel to capacitor 766.

[0175] Inductance L3 equals inductance L 3a With inductor L 3bThe sum (L3 = L) 3a +L 3b Inductance L RESa and L RESb Represents residual inductance. Capacitor C 3a Equal to capacitance C 3b And it is equal to capacitance C3. The relationship between capacitances C3 and C4 is given by equation 21:

[0176]

[0177] Capacitor C3 is given by Equation 22:

[0178] C3 = C 3a =C 3b (twenty two)

[0179] According to capacitance C 4a C 4b The capacitance C4 is given by equation 23:

[0180]

[0181] Inductance L3 is given by Equation 24:

[0182] L3 = L 3a +L 3b (twenty four)

[0183] Residual inductance L RES Given by Equation 25:

[0184]

[0185] Where Xres is the residual reactance and w is the operating frequency.

[0186] The output current in inductor 770 or resistor 780, i.e. the current in transmitter coil 312, is therefore given by equation 26:

[0187]

[0188] The DC / AC inverter 700 allows the current in the transmitter coil 312 to be set independently of the input DC voltage and the inductance of the transmitter coil 312. Because the self-capacitance of the transmitter coil 312 can be absorbed into the capacitor 766, the DC / AC inverter 700 is suitable for operation at higher MHz frequencies, such as 6.78MHz and above.

[0189] As previously described, during operation, the DC / AC inverter 310 generates a constant AC voltage or current that does not change with the load. However, a metallic object adjacent to the transmitter 302 will detune the transmitter 302 and lead to increased losses. The magnetic field generated by the transmitter coil 312 will induce eddy currents in the metallic object, resulting in power transmission losses. The intensity of the induced eddy currents is proportional to the surface area of ​​the metallic object, the magnetic field density, and the operating frequency.

[0190] Because the DC / AC inverter 310 is independent of the load, it maintains ZVS when the load resistance changes. However, if the load reactance changes, the DC / AC inverter 310 may lose ZVS switching. The receiver 304 is tuned to the operating frequency such that if the wireless power transfer coupling of the load 320 or the DC value changes, the reflected load of the load 320 seen by the DC / AC inverter 310 is always real.

[0191] However, when a metallic object is introduced anywhere between the transmitter 302 and the receiver 304 or near the transmitter 302, the reflected load seen by the transmitter 302 will no longer be real and will include a reactance component due to eddy currents induced in the metallic object. Therefore, the DC / AC inverter 310 no longer achieves ZVS. Furthermore, the voltage waveforms across transistors 512 and 520 (Q1 and Q2) of the DC / AC inverter 310 will be different.

[0192] Turn now Figure 11 This illustrates another embodiment of a DC / AC inverter, typically identified by reference numeral 1000. The DC / AC inverter 1000 is configured to detect the presence of a metallic object.

[0193] In this embodiment, the DC / AC inverter 1000 includes the same components as the aforementioned DC / AC inverter 310. Furthermore, 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 both the threshold setter 1012 and the peak detection circuit 1008. The threshold setter 1012 is connected to the comparator 1010.

[0194] The peak detection circuit 1008 is configured to measure the peak voltage across transistor 512 (Q1) of DC / AC inverter 310.

[0195] The threshold setter 1012 is configured to set a threshold voltage for comparison with the measured peak voltage across transistor 512 (Q1) of the DC / AC inverter 310.

[0196] Comparator 1010 is configured to compare a set threshold voltage with a measured peak voltage across transistor 512 (Q1) of DC / AC inverter 310. If the measured peak voltage exceeds the threshold voltage, comparator 1010 is configured to output a detection signal. If the measured peak voltage does not exceed the threshold voltage, comparator 1010 does not output a detection signal.

[0197] While a specific DC / AC inverter 1000 configured to detect the presence of a metallic object has been described, those skilled in the art will understand that other configurations are possible. Now turning to... Figure 12 This illustrates another embodiment of a DC / AC inverter, typically identified by reference numeral 1100 in the accompanying drawings.

[0198] In this embodiment, the DC / AC inverter 1100 includes the same components as the aforementioned DC / AC inverter 310. Furthermore, the DC / AC inverter 1100 includes a resistor divider 1106, a peak detection circuit 1108, a comparator 1110, a threshold setter 1112, and an indicator 1114.

[0199] Resistor divider 1106 is connected to DC / AC inverter 310. Resistor divider 1106 is connected to peak detection circuit 1108. Peak detection circuit 1108 is connected to resistor divider 1106. Peak detection circuit 1108 is connected to compressor 1110. Comparator 1110 is connected to threshold setter 1112 and peak detection circuit 1108. Comparator 1110 is connected to indicator 1114. Threshold setter 1112 is connected to comparator 1110. Indicator 1114 is connected to comparator 1110.

[0200] Resistive voltage divider 1106 is configured to convert the voltage at transistor Q1 of DC / AC inverter 310 to a safe level. Specifically, resistive voltage divider 1106 is configured to reduce the voltage at transistor 512 (Q1) of DC / AC inverter 310 to a safe level. The resistive voltage divider is configured to divide the voltage at transistor 512 (Q1) of DC / AC inverter 310.

[0201] Peak detection circuit 1108 is configured to measure the peak value of the voltage divider 1106. Peak detection circuit 1108 outputs the measured peak value to comparator 1110.

[0202] Threshold setter 1112 is configured to set a threshold voltage for comparison with the measured peak value of the voltage divider.

[0203] Comparator 1110 is configured to compare a set threshold voltage with the measured peak value of the voltage divider. If the measured peak value of the voltage divider exceeds the threshold voltage, comparator 1110 is configured to output a detection signal to indicator 1114. If the measured peak value of the voltage divider does not exceed the threshold voltage, comparator 1110 does not output a detection signal to indicator 1114.

[0204] Indicator 1114 is configured to receive a detection signal from comparator 1110. Indicator 1114 is configured to trigger or set a fault indicator upon receiving a detection signal. In this way, the detection of a metal object is clearly indicated.

[0205] The operation of the AC / DC inverter 1100 will now be discussed. Figure 13 This is a voltage curve at transistor 512 (Q1) of the DC / AC inverter 1100 during operation, with and without a metal object. Figure 13 It also includes a threshold set by threshold setter 1112. In this embodiment, the DC / AC inverter 1100 has an operating frequency of 6.78 MHz. Figure 13 As shown, the peak voltage increases in the presence of a metallic object. Furthermore, the voltage reaches zero before transistor 512 (Q1) turns on when a metallic object is present. This zero-voltage condition before transistor 512 (Q1) turns on can indicate that the body of transistor 512 (Q1) begins to conduct, leading to increased power loss and reduced efficiency.

[0206] Furthermore, the voltage difference between the presence and absence of a metallic object is proportional to the intensity of the induced eddy current. A larger induced eddy current can cause a further increase in the peak voltage of transistor 512 (Q1). This increased peak voltage may reach the breakdown voltage of transistor Q1, potentially permanently damaging the DC / AC inverter 310.

[0207] In operation, the resistive voltage divider 1106 receives the voltage from transistor 512 (Q1) of the DC / AC inverter 310 and converts this voltage to a safe level. The peak detection circuit 1108 measures the peak value of the voltage divided by the resistive voltage divider 1106. Figure 13 As shown, the reactance reflected by the metallic object is capacitive, which causes the voltage waveform across transistor 512 (Q1) of the DC / AC inverter 310 to be narrower and higher compared to the voltage waveform when the metallic object is absent. Comparator 1110 receives the measured peak value from the voltage divider of peak detection circuit 1108 and the set threshold voltage from threshold setter 1112. Figure 13As shown, when a metallic object is present, the measured peak value is significantly higher than the set threshold voltage. When the measured peak value is significantly higher than the set threshold voltage, comparator 1110 outputs a detection signal to indicator 1114. Indicator 1114 triggers a fault indicator. This disables the DC / AC inverter 1100 and the entire high-frequency wireless power transmission system 300, of which the DC / AC inverter 1100 is part. This not only prevents damage to the DC / AC inverter 1100 but also prevents heating of the metallic object due to induced eddy currents.

[0208] As previously described, transmitter 302 operates at a given frequency. In this embodiment, the operating frequency of transmitter 302 is 13.56 MHz. Furthermore, in this embodiment, transmitter coil 312 and receiver coil 314 each have dimensions of 23.4 cm × 26.2 cm. Coils 312 and 314 are each composed of two 14 mm wide copper traces on an FR4 printed circuit board (PCB). Coils 312 and 314 have an inductance of approximately 1.50 μH. The reflected load seen by transmitter coil 312 varies from 0 ohms at no load 320 to 7 ohms at full load 320. The maximum power required by load 320 is 30 W. Given these operating parameters, design examples of various presented DC / AC inverter embodiments will now be considered.

[0209] Now we will discuss Figure 5 The diagram illustrates an exemplary design embodiment of the DC / AC inverter 310. In this embodiment, the transmitter coil 312 and receiver coil 314 have an inductance of 1.5uH, therefore inductance L3 = 1.5uH. The reflected load seen by the transmitter coil 312 varies from 0 ohms at no load 320 to 7 ohms at full load 320. The maximum power required by load 320 is 30W.

[0210] Based on the aforementioned equations, various parameters can be determined. According to the maximum reflective load (7 ohms) and the required power (30W), the current required for transmitter coil 312 is 2.93A (i.e., P...). max =1 / 2I L3 2 R L Therefore I L3 =2.93A). The characteristic impedance Z0 is 8.9744 ohms (i.e., R = 2.93A). Lmin / Z0=0.78, therefore Z0=8.9744). Furthermore, L ZVS The values ​​of C1 and C2 are L ZVS The capacitance is 107nH, and C1 and C2 are 1.33nF. The residual reactance is 27.58nH (i.e., 0.258 * Z0 = 2.3154 ohms). The DC input voltage V...in It is 6.546V.

[0211] The discussion will now begin. Figure 8 The diagram illustrates an exemplary design embodiment of the DC / AC inverter 800. In this embodiment, the transmitter coil 312 and receiver coil 314 have an inductance of 1.5uH, therefore inductance L3 = 1.5uH. The reflected load seen by the transmitter coil 312 varies from 0 ohms when there is no load 320 to 7 ohms when there is a full load 320. The maximum power required by the load 320 is 30W.

[0212] Based on the aforementioned equations, various parameters can be determined. According to the maximum reflective load (7 ohms) and the required power (30W), the current required for transmitter coil 312 is 2.93A (i.e., P...). max = 1 / 2I L3 2 R L Therefore I L3 =2.93A). DC input voltage V in It is 119V (i.e., I L3 =3.132×V in / w L3 The characteristic impedance Z0 is 2989 ohms. Furthermore, L... ZVS The values ​​of C1 and C2 are L ZVS The value is 35.6uH, and C1 and C2 are 4pF.

[0213] The discussion will now begin. Figure 9 The diagram illustrates an exemplary design embodiment of a DC / AC inverter 900. In this embodiment, the transmitter coil 312 and receiver coil 314 have an inductance of 1.5uH, therefore inductance L3 = 1.5uH. The reflected load seen by the transmitter coil 312 varies from 0 ohms when there is no load 320 to 7 ohms when there is a full load 320. The maximum power required by the load 320 is 30W. Based on the equations described above, various parameters can be determined. According to the maximum reflected load (7 ohms) and the required power (30W), the current required by the transmitter coil 312 is 2.93A (i.e., P...). max = 1 / 2I L3 2 R L Therefore I L3 =2.93A). DC input voltage V in It can be set to any voltage. In this embodiment, the DC input voltage V in It is 24V. Capacitor C4 is determined to be 457.5pF. Capacitor C3 is determined to be 115pF. Capacitor C 3b With capacitor C 3aSame. According to Equation 20, capacitance C 3a and C 3b It is twice the capacitance of C3, i.e., 230pF. For a DC input voltage of 24V V... in With a power rating of 30W, the characteristic impedance Z0 is 120.63 ohms. ZVS And the values ​​of C1 and C2 are L ZVS The capacitance is 1.4375uH, and C1 and C2 are 99pF. The residual reactance is 31.12 ohms.

[0214] While the high-frequency wireless power system 300 is described as including a transmitter 302 configured to wirelessly transmit power via high-frequency magnetic inductive coupling and a receiver 304 configured to extract power from the transmitter 302 via high-frequency magnetic inductive coupling, those skilled in the art will understand that other configurations are possible. In another embodiment, the transmitter 302 is configured to wirelessly transmit power via high-frequency electro-coupling, and the receiver 304 is configured to extract power from the transmitter 302 via high-frequency electro-coupling. In this embodiment, the transmitter 302 includes transmitter electrodes instead of a transmitter coil 312, and the receiver 304 includes receiver electrodes instead of a receiver coil 314.

[0215] Although the embodiments have been described above with reference to the accompanying drawings, those skilled in the art should understand that changes and modifications can be made without departing from the scope defined by the appended claims.

Claims

1. A load-independent inverter including a switch-mode zero-voltage switching (ZVS) amplifier, the switch-mode ZVS amplifier comprising: The circuit pair includes: At least transistors and at least capacitors arranged in parallel; and At least an inductor arranged in series with a transistor and a capacitor; Only one inductor is connected to the circuit pair, wherein the capacitor and the inductor of the circuit pair have values ​​that cause the inverter to operate at ZVS; and At least one capacitor is connected to the single inductor and arranged 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 relative to the characteristic impedance of the load-independent inverter, is between 0.194 and 0.

323. in: The voltage gain of the load-independent inverter is between 2.349 and 3.915, and the minimum load resistance normalized relative to the characteristic impedance of the switch-mode ZVS amplifier is between 0.585 and 0.

975. The normalized output power of the load-independent inverter is between 4.700 and 7.

834.

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

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

4. The load-independent inverter according to any one of claims 1 to 3, wherein the load-independent inverter has a constant voltage output.

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 loads.

6. The load-independent inverter of claim 4 further includes an impedance inverter circuit configured to convert the load-independent inverter from a constant voltage output to a constant current output.

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

8. The load-independent inverter according to any one of claims 1 to 3, wherein the load-independent inverter has a constant current output.

9. The load-independent inverter of claim 8, wherein the load-independent inverter has a load range from 0 ohms or short-circuit load to 9.375 ohms.

10. The load-independent inverter according to any one of claims 1 to 3, wherein the load-independent inverter is configured to detect a metallic object.

11. The load-independent inverter according to claim 10, further comprising: The peak detection circuit is configured to measure the peak voltage across the transistors of a load-independent inverter. and The comparator is configured to compare the voltage peak with a threshold voltage, and output a detection signal if the voltage peak exceeds the threshold voltage.

12. The load-independent inverter according to claim 11, further comprising: The voltage divider is configured to convert the voltage peak before it is measured by the peak detection circuit.

13. The load-independent inverter according to any one of claims 1 to 3, wherein the switch-mode ZVS amplifier is a radio frequency (RF) amplifier.

14. The load-independent inverter according to any one of claims 1 to 3, wherein the load-independent inverter is a Class E inverter.

15. The load-independent inverter according to any one of claims 1 to 3, wherein the load-independent inverter is a DC to AC inverter.

16. A transmitter, comprising: A load-independent inverter, including a switch-mode zero-voltage switching (ZVS) amplifier, wherein the switch-mode ZVS amplifier comprises: The circuit pair includes: At least transistors and at least capacitors arranged in parallel; and At least an inductor arranged in series with a transistor and a capacitor; Only one inductor is connected to the circuit pair, wherein the capacitor and the inductor of the circuit pair have values ​​that cause the inverter to operate at ZVS; and At least one capacitor is connected to the inductor and arranged in series with at least the inductor and at least the resistor. The q-value of the load-independent inverter is between 0.739 and 1.

231. The residual reactance, normalized relative to the characteristic impedance of the load-independent inverter, is between 0.194 and 0.

323. in: The voltage gain of the load-independent inverter is between 2.349 and 3.915, and the minimum load resistance normalized relative to the characteristic impedance of the switch-mode ZVS amplifier is between 0.585 and 0.

975. The normalized output power of the load-independent inverter is between 4.700 and 7.834; and A transmitter coil or electrode connected to the load-independent inverter is configured to transmit power to a receiver via magnetic field coupling or electric field coupling.

17. The transmitter of claim 16, wherein the transmitter is non-resonant or non-self-resonant.

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

19. The transmitter of claim 16 or 17, wherein the electrodes are configured to transmit power via electric field coupling.

20. The transmitter of claim 16 or 17, wherein the transmitter further comprises a power source.

21. The transmitter of claim 20, wherein the transmitter further comprises a power converter configured to convert a power signal from a power source before the inverter receives it.

22. A wireless power transmission system, comprising: The transmitter includes: A load-independent inverter, including a switch-mode zero-voltage switching (ZVS) amplifier, said switch-mode ZVS amplifier comprising: The circuit pair includes: At least transistors and at least capacitors arranged in parallel; and At least an inductor arranged in series with a transistor and a capacitor; Only one inductor is connected to the circuit pair, wherein the capacitor and the inductor of the circuit pair have values ​​that cause the inverter to operate at ZVS; and At least one capacitor is connected to the inductor and arranged in series with at least the inductor and at least the resistor. The q-value of the load-independent inverter is between 0.739 and 1.

231. The residual reactance, normalized relative to the characteristic impedance of the load-independent inverter, is between 0.194 and 0.

323. in: The voltage gain of the load-independent inverter is between 2.349 and 3.915, and the minimum load resistance normalized relative to the characteristic impedance of the switch-mode ZVS amplifier is between 0.585 and 0.

975. The normalized output power of the load-independent inverter is between 4.700 and 7.834; and A transmitter coil or electrode, connected to the load-independent inverter, is configured to transmit power to the receiver via magnetic field coupling or electric field coupling; and The receiver includes: The receiver coil or electrode is configured to extract power from the field via magnetic field coupling or electric field coupling.

23. The wireless power transmission system of claim 22, wherein the transmitter is non-resonant or non-self-resonant, and the receiver is resonant.

24. The wireless power transmission system of claim 23, wherein the receiver resonates at the operating frequency of the transmitter.

25. The wireless power transmission system according to any one of claims 22 to 24, wherein the transmitter coil is configured to transmit power via magnetic field coupling, and the receiver coil is configured to extract power via magnetic field coupling.

26. The wireless power transmission system according to any one of claims 22 to 24, wherein the electrodes of the transmitter are configured to transmit power via electric field coupling, and the electrodes of the receiver are configured to extract power via electric field coupling.

27. The wireless power transmission system according to any one of claims 22 to 24, wherein the receiver further comprises a rectifier connected to the receiver coil or electrode.

28. The wireless power transmission system according to any one of claims 22 to 24, wherein the receiver further comprises a load connected to the receiver coil or electrode.

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