An Improved SS-Type Wireless Charging System with Single-Order Frequency and Voltage Modulation and Its Control Method

Abstract

This invention relates to an improved S-S type wireless charging system and its control method using single-order frequency modulation and voltage regulation, belonging to the field of wireless charging. The invention achieves an improved S-S type wireless charging system by connecting a diode in series before the DC-AC inverter unit and a set of anti-series switches in parallel after the receiving coil L2, enabling the transmitter and receiver to simultaneously stop resonating in a zero-resonance state. The system performs tuning control under resonant offset conditions, and then, while maintaining resonance, adjusts the voltage by changing the duty cycle corresponding to the high and low levels, thereby achieving synchronous regulation of the system resonance and output voltage. Further, the voltage adjustment by changing the duty cycle corresponding to the high and low levels is achieved through constant-width frequency modulation (VFM) control; this VFM control, under the premise of a fixed resonant frequency, changes the total control period by inserting a zero-resonance state, thereby changing the equivalent frequency.

Description

Technical Field

[0001] This disclosure relates to the field of wireless charging, and in particular to an improved SS-type wireless charging system with single-stage frequency and voltage modulation and its control method. Background Technology

[0002] Wireless charging systems are power supply systems that utilize electromagnetic induction between transmitting and receiving coils to transfer energy. They enable mechanical isolation between power generation and consumption equipment, reduce the use of sockets and cables, and have broad application prospects in areas such as electric vehicle charging. Due to the loose coupling characteristics of the transmitting and receiving coils, a resonant compensation network needs to be added to the wireless charging system to bring it into a resonant state in order to improve system transmission performance and quality factor. In the resonant state, the voltage received by the load is higher, the system's reactive power is lower, and the system's output active power and energy transfer efficiency are greater.

[0003] In practical operation of wireless charging systems, changes in parameters such as the relative position of the coupling coils and the equivalent impedance of the load, along with variations in the application scenario, can cause shifts in resonant parameters such as coil self-inductance, mutual inductance, and coupling coefficient. This disrupts the system's resonant state, leading to changes in the transmitter's resonant frequency, increased reactive power in the transmitter circuit, and decreased active power transmission, while also posing risks of overvoltage and overcurrent. Current wireless charging system design focuses on improving the system's maximum tolerance to coil position shifts, enabling relatively stable wireless energy transmission within a relatively wide range of coupling coefficient variations, ensuring minimal fluctuations in charging voltage or current. This research direction is crucial for expanding the application of wireless charging energy supply to more scenarios. This goal can only be achieved when the wireless charging system consistently operates near its resonant frequency without significant deviations from the resonant point. Therefore, to ensure the transmitter always operates in a resonant state, the operating frequency of the transmitter's inverter circuit must consistently track the transmitter's resonant frequency.

[0004] Frequency adjustment ("FM") is one of the basic methods of tuning, directly adjusting the operating frequency of the transmitter inverter circuit to match the system's transmitter resonant frequency. As an efficiency optimization method, it ensures high output power and transmission efficiency by real-time controlling and optimizing the system's operating frequency. However, most existing frequency tracking algorithms use hardware comparators to measure the voltage and current phase difference of the inverter and then control the inverter's operating frequency to track the resonant frequency. Due to high-frequency noise and other factors, the measurement error of the voltage and current phase difference is relatively large, resulting in poor frequency tracking performance. To avoid problems caused by voltage and current measurement errors, the research team at Zhejiang University proposed a frequency tracking control method based on the maximum received voltage (Frequency Tracking Technology and Control Method for Wireless Power Transmission Systems, Journal of Electrical Machines and Control, 2020, 24(09): 22-29). This method detects the load voltage at the receiving end in real time and automatically adjusts the transmitter frequency [J] to ensure that the system is always in the maximum power transmission state. The received power and transmission efficiency are improved by 19.25% and 10.56%, respectively. Zhang Yufan of Chongqing University (Optimization Analysis and Frequency Tracking Control of Non-Contact Inductive Coupled Power Transmission System [D], Chongqing University, 2011) addressed the problem that the system transmission efficiency is sensitive to changes in system parameters by adopting a phase-locked loop frequency tracking control method with the energy efficiency product as the optimization index, achieving a better efficiency optimization effect. In contrast, the frequency tracking tuning method for the transmitter end of a wireless charging system based on the minimum voltage value proposed in Patent 1 (CN 104135085 A, A Frequency Tracking Tuning Method for the Transmitter End of a Wireless Power Transmission Device) can only perform tuning and cannot achieve system voltage regulation without an external DC-DC converter. Compared to Patent 2 (CN 209448509 U, Automatic Voltage Regulation Resonant Wireless Power Transmission Device Using Buck Converter), which considers that most wireless charging systems need to operate in constant voltage source mode, in order to reduce power loss and increase system efficiency, an additional Buck converter is added at the receiving end for switching regulation to achieve control of output voltage and power.

[0005] In summary, while existing wireless charging system tuning methods offer some insights, they all require additional DC-DC converters for output control. Currently, there is no single-order wireless charging topology or corresponding control strategy that simultaneously achieves tuning and output control as resonant parameters change. Therefore, in practical applications, a specific control method is needed to maintain the system in a resonant state while ensuring adjustable output. Since the load is often equivalent to a resistive load in system analysis and calculation, the direct physical quantity for output control is the load voltage; therefore, "output control" here is more intuitively referred to as "voltage regulation." Summary of the Invention

[0006] In view of the fact that there is currently no single-order wireless charging system topology and corresponding control strategy that can simultaneously achieve tuning and voltage regulation functions, the purpose of this invention is to propose an improved SS-type wireless charging system with single-order frequency and voltage regulation. It can realize the tuning and output control of the wireless charging system simultaneously without adding an additional DC-DC converter circuit, and effectively improves the power density of the system while achieving the same tuning and output control functions.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows.

[0008] In a first aspect, this invention proposes an improved SS-type wireless charging system with single-order frequency and voltage modulation. The system is a magnetically coupled resonant wireless charging system, comprising a transmitter and a receiver. At the transmitter, the input DC voltage is converted into high-frequency AC power by a DC-AC inverter unit, and then provides power to the receiver through a transmitter resonant unit composed of a transmitter resonant capacitor C1 and a transmitter coil L1. At the receiver, the high-frequency AC power, which serves as power, is received by a receiver resonant unit composed of a resonant capacitor C2 and a receiver coil L2, and then converted into DC power suitable for supplying the load through an AC-DC converter unit. By connecting a diode in series before the DC-AC inverter unit and a set of anti-series switches in parallel after the receiver coil L2, the transmitter and receiver can simultaneously stop resonating in a zero-resonance state, thus obtaining the improved SS-type wireless charging system. The system performs tuning control under resonant offset conditions, and then, while maintaining resonance, adjusts the voltage by changing the duty cycle corresponding to the high and low levels, thereby achieving synchronous regulation of the system resonance and output voltage.

[0009] In the above technical solution, the voltage regulation is achieved by changing the duty cycle corresponding to the high and low levels, which is realized through constant width frequency modulation control.

[0010] The fixed-width frequency modulation control is based on a fixed resonant frequency, which changes the total control period by inserting a zero-resonance state, thereby causing the equivalent frequency to change.

[0011] In the above technical solution, tuning control under the condition of resonance offset includes the following steps:

[0012] When the coupling parameters change, determine whether the current frequency satisfies the system resonance.

[0013] If the system does not resonate, when the resonant frequencies of the transmitting and receiving ends are the same, change the system switching frequency to the resonant frequency so that the system returns to the resonant state.

[0014] When the resonant frequencies of the transmitter and receiver are different, the transmitter uses frequency conversion to achieve tuning, and the receiver uses an adjustable resonant capacitor to compensate for the resonant offset, so that the system returns to the resonant state.

[0015] In the above technical solution, determining whether the current frequency satisfies system resonance is specifically as follows:

[0016] Check the output voltage U of the DC-AC inverter unit in-ac Whether it is in phase with the transmitting current I1, and the voltage U on the receiving resonant capacitor C2. c2 Is it in phase with the transmitter current I1?

[0017] In the above technical solution, after fixed-width frequency modulation control, the system output voltage U′ out It becomes:

[0018] When the resonant frequency of the system remains constant:

[0019] The resonant frequency of the system is determined by ω s Transform into ω r In the following circumstances:

[0020]

[0021] In the formula: U out ΔT represents the system output voltage before fixed-width frequency modulation control, T represents the duration of each cycle before adding the zero-resonance state, and ΔT represents the insertion duration of a single zero-resonance state.

[0022] In the above technical solution, the DC-AC inverter unit includes a filter capacitor C. d Load resistance R L rectifier;

[0023] The rectifier consists of four diodes, or MOSFETs, or IGBTs, D1, D2, D3, and D4;

[0024] D1 and D2 are connected in series, then in parallel with D3 and D4 (which are also connected in series), and then connected to the filter capacitor C respectively. d Load resistance R L in parallel;

[0025] The positive terminal of the receiving end resonant unit is connected to the connection point of D1 and D2, and the negative terminal of the receiving end resonant unit is connected to the connection point of D3 and D4.

[0026] Secondly, this invention proposes a control method for an improved SS-type wireless charging system with single-order frequency and voltage modulation, the method comprising the following steps:

[0027] A diode is connected in series before the DC-AC inverter unit of the SS-type wireless charging system, and a set of anti-series switching transistors are connected in parallel after the receiving coil L2, so that the transmitting end and the receiving end can stop resonating at the same time in the zero-resonance state, thereby obtaining an improved SS-type wireless charging system.

[0028] Tuning control is performed when the system resonance is offset, and then voltage regulation is achieved by changing the duty cycle corresponding to the high and low levels while maintaining resonance, thereby realizing the synchronous regulation of system resonance and output voltage.

[0029] In the above technical solution, the voltage regulation is achieved by changing the duty cycle corresponding to the high and low levels, which is realized through constant width frequency modulation control.

[0030] The fixed-width frequency modulation control is based on a fixed resonant frequency, which changes the total control period by inserting a zero-resonance state, thereby causing the equivalent frequency to change.

[0031] In the above technical solution, tuning control under the condition of resonance offset includes the following steps:

[0032] When the coupling parameters change, determine whether the current frequency satisfies the system resonance.

[0033] If the system does not resonate, when the resonant frequencies of the transmitting and receiving ends are the same, change the system switching frequency to the resonant frequency so that the system returns to the resonant state.

[0034] When the resonant frequencies of the transmitter and receiver are different, the transmitter uses frequency conversion to achieve tuning, and the receiver uses an adjustable resonant capacitor to compensate for the resonant offset, so that the system returns to the resonant state.

[0035] In the above technical solution, determining whether the current frequency satisfies system resonance is specifically as follows:

[0036] Check the output voltage U of the DC-AC inverter unit in-ac Whether it is in phase with the transmitting current I1, and the voltage U on the receiving resonant capacitor C2. c2 Are the transmitter currents I1 in phase?

[0037] The improved SS-type wireless charging system and implementation method with single-stage frequency and voltage modulation proposed in this invention can simultaneously achieve system tuning and output control without adding an additional DC-DC converter circuit. While achieving the same tuning and output control functions, it effectively improves the power density of the system. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1A schematic diagram of the improved SS-type wireless charging system topology in one specific embodiment;

[0040] Figure 2 A schematic diagram comparing the transmitting end drive pulse and the transmitting end resonant waveform in one specific embodiment;

[0041] Figure 3 A schematic diagram of the anti-series switch drive pulse and the voltage and current waveforms detected at the receiving end in one specific embodiment;

[0042] Figure 4 A schematic diagram of the anti-series switch drive pulse and the resonant waveform at the receiving end in one specific embodiment;

[0043] Figure 5 A schematic diagram of a fixed-width frequency modulation control strategy in one specific implementation. Detailed Implementation

[0044] Tuning of wireless charging systems plays a crucial role in improving their active power transmission and efficiency. Traditional wireless charging system tuning methods only maintain the system's resonant state, requiring the addition of an additional DC-DC converter (i.e., a DC / DC converter) at the transmitter or receiver for output voltage and power control (hereinafter referred to as "output control"). Currently, there is no single-order wireless charging system topology and corresponding control strategy that simultaneously achieves tuning and voltage regulation. The purpose of this invention is to propose an improved SS-type wireless charging system with single-order frequency and voltage regulation, which can simultaneously achieve wireless charging system tuning and output control without adding an additional DC-DC converter circuit, effectively improving the system's power density while achieving the same tuning and output control functions.

[0045] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0046] join Figure 1 This is a schematic diagram of the topology of an improved SS-type wireless charging system. The improved SS-type wireless charging system is a magnetically coupled resonant wireless charging system. The input DC voltage U... in_dcThe AC power is converted into high-frequency AC through a full-bridge inverter circuit (T1-T4) consisting of four MOSFETs. This AC power then powers the receiver via a transmitter resonant unit composed of transmitter resonant capacitor C1 and transmitter coil L1. The receiver resonant unit consists of receiver resonant capacitor C2 and receiver coil L2. The high-frequency AC power received at the receiver is then converted into DC power suitable for supplying the load through a full-bridge rectifier circuit (D1, D2, D3, D4) composed of four diodes and a series of subsequent processing steps. R1 is the internal resistance of the transmitter coil, R2 is the internal resistance of the receiver coil, and C... d For the filter capacitor, R L Let M be the load resistance and M be the mutual inductance of the inductor coil. To ensure that the transmitter and receiver can simultaneously stop resonating in the zero-resonance state of the system, a diode D is connected in series before the inverter of the SS-type wireless charging topology. in Its positive terminal is connected to the positive terminal of the input power supply, and its negative terminal is connected to the drain of the switching transistor T1. A set of anti-series switching transistors (T5, T6) is connected in parallel after the receiving coil to ensure that the original receiving end can stop resonating at the same time when the zero resonance state is reached.

[0047] In the above topology, the topology of the resonant capacitor C2 connected in series at the receiving end can be changed, such as a switched capacitor, a phase-controlled capacitor, or a phase-controlled inductor. All these topologies can realize the resonant offset compensation function of the resonant capacitor C2.

[0048] In the above topology, the DC-AC inverter unit includes a filter capacitor C. d Load resistance R L There are four diodes: D1, D2, D3, and D4. D1 and D2 are connected in series, then in parallel with the series-connected D3 and D4, and then connected to the filter capacitor C. d Load resistance R L In parallel connection, the positive terminal of the receiving end resonant unit is connected to the positive terminal of D1, and the negative terminal of the receiving end resonant unit is connected to the negative terminal of D4. The four diodes D1, D2, D3, and D4 can also be replaced with MOSFETs or IGBTs to transform the rectifier bridge into a synchronous rectification circuit.

[0049] The system performs tuning control when there is a resonance offset, and then adjusts the voltage by changing the duty cycle corresponding to the high and low levels while maintaining the resonance state, thereby achieving synchronous adjustment of the system resonance and output voltage.

[0050] In this embodiment, voltage regulation is achieved by changing the duty cycle corresponding to the high and low levels through fixed-width frequency modulation control. Figure 2 This is a schematic diagram of the key waveforms for a fixed-width frequency modulation (VFM) strategy. The "width" in "fixed-width frequency modulation" refers to the pulse width at which the switching transistor in the transmitter's inverter circuit is turned on. "Fixed width" means that the resonant frequency of the system's resonant elements remains constant. Figure 2In this context, t0-t1 and t2-t3 represent the same length, both being the time the system is in a resonant state, meaning the system is always in a resonant state. Fixed-width frequency modulation (VFM) control, under the premise of a fixed resonant frequency, changes the total control cycle length by inserting zero-resonant states (i.e., t1-t2, t3-t4, t5-t6). Figure 2 The expression represents the moment when the transmitter current resonates to 0 twice in one switching cycle. At time t1, the transmitter current resonates to 0 for the first time, and a zero-resonance state t1-t2 is introduced at this time. At time t3, the transmitter current resonates to 0 for the second time, and a zero-resonance state t3-t4 is introduced at this time, thereby changing the total control duration and thus achieving the regulation of the output voltage.

[0051] Because the fixed-width frequency modulation control inserts a zero-resonance state, theoretically the inverter output voltage should be 0. However, due to the charge on the resonant capacitor at the transmitter, the voltage across the resonant capacitor will reverse. At this time, the inverter bridge output voltage waveform is as follows: Figure 2 As shown, T1 and T2 are complementary pulses of the inverter bridge, U in-ac I is the output voltage of the inverter bridge, and I1 is the transmitter current.

[0052] The resonant waveform at the transmitter of the system is as follows Figure 3 As shown. The resonant waveform at the system receiver is as follows. Figure 4 As shown, G is the drive pulse waveform of the anti-series switching transistors (i.e., T5 and T6) at the receiving end, and U... c2 I1 is the voltage across the resonant capacitor C2 at the receiving end, and I2 is the current at the transmitting end.

[0053] Figure 5 This is a specific implementation method for synchronously regulating the system resonance and output voltage by adjusting the duty cycle corresponding to the high and low levels while maintaining resonance, in order to perform tuning control under resonant offset conditions and then adjust the voltage while maintaining resonance.

[0054] Specifically, first observe whether the coupling parameters change: when the system parameters shift, check the inverter bridge output voltage U. in-ac Check if the transmitter current I1 is in phase to determine if the system transmitter can resonate at the current switching frequency. If the transmitter does not resonate, change the system switching frequency to the resonant frequency to bring the transmitter back to the resonant state. Further check the voltage U across the resonant capacitor C2 at the receiver. c2The system's ability to resonate at the receiver is determined by checking if the current I1 at the transmitting end is in phase. If the receiver does not meet the resonance condition, an adjustable resonant capacitor is used to compensate for the resonance offset, bringing the system back to the resonant state and enabling soft switching of the inverter even with resonance offset. At different reference frequencies, the system is subjected to constant-width modulation (PWM) control. By adding a zero-resonance state, the equivalent frequency changes, altering the duty cycle corresponding to the high and low levels. This allows for synchronous regulation of system resonance and output voltage without the need for an additional DC-DC converter.

[0055] In the initial state, the resonance parameters are:

[0056]

[0057] When the coupling parameters change, the coil parameters become L′1 and L′2, and the resonant frequency becomes ω. r That is, under fixed-width frequency modulation control, the equivalent frequency of high and low levels is ω. r .

[0058] According to the resonance formula:

[0059]

[0060] The resonant frequency, i.e., the parameters of the adjustable resonant capacitor at the receiving end, are determined as follows:

[0061]

[0062] With the system's resonant frequency remaining constant, the output voltage changes after constant-width frequency modulation control as follows:

[0063]

[0064] In the formula: U out ΔT represents the system output voltage before fixed-width frequency modulation control, T represents the duration of each cycle before adding the zero-resonance state, and ΔT represents the insertion duration of a single zero-resonance state.

[0065] The resonant frequency of the system is determined by ω s Transform into ω r Under these conditions, after performing fixed-width frequency modulation control, the system output voltage changes as follows:

[0066]

[0067] In summary, based on the above formula and Figure 5 It enables simultaneous frequency modulation (tuning) and voltage regulation (output control) functions.

[0068] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of the present invention, and all of these are within the scope of protection of the present invention.

Claims

1. An improved S-S type wireless charging system of single frequency modulation and voltage regulation, the system is a magnetic coupling resonant type wireless charging system, comprising a transmitting end and a receiving end; at the transmitting end, an input DC voltage becomes a high-frequency AC through a DC-AC inversion unit, and provides power for the receiving end through a transmitting end resonance unit composed of a transmitting coil 1 and a transmitting resonance capacitor C 1 L 1 ; at the receiving end, the high-frequency AC received as power through a receiving end resonance unit composed of a receiving coil 2 and a receiving resonance capacitor C 2 and a receiving resonance capacitor L 2 , is converted into a DC through an AC-DC conversion unit, which can supply power to a load; characterized in that: By connecting a diode in series in front of the DC-AC inverter unit, and connecting a group of anti-series switch tubes in parallel after the receiving end coil L 2, the transmitting end and the receiving end can stop resonance at the same time in the zero resonance state, so as to obtain an improved S-S type wireless charging system. The system carries out tuning control in the case of resonance deviation, then realizes voltage regulation by changing the duty cycle corresponding to high and low levels in the case of keeping resonance state, so as to realize synchronous regulation of system resonance and output voltage.

2. The system of claim 1, wherein, The changing of the duty cycle corresponding to high and low levels realizes voltage regulation through fixed-width frequency control; The fixed-width frequency control is to change the total cycle length of control by inserting zero resonance state under the premise of fixed resonance frequency, so as to change the equivalent frequency.

3. The system of claim 1, wherein, The tuning control in the case of resonance deviation includes the following steps: When the coupling parameter changes, it is judged whether the current frequency satisfies system resonance; If the system is not resonant, the system switching frequency is changed to the resonance frequency when the resonance frequencies of the transmitting end and the receiving end are the same, so that the system returns to the resonant state; When the resonance frequencies of the transmitting end and the receiving end are different, the transmitting end adopts frequency conversion to realize tuning, and the receiving end adopts an adjustable resonance capacitor to realize compensation of resonance deviation, so that the system returns to the resonant state.

4. The system of claim 3, wherein, It is judged whether the current frequency satisfies system resonance, specifically: Check the output voltage of the DC-AC inverter unit. U in-ac With the transmitter current I 1. Whether they are in phase, and the resonant capacitance at the receiving end. C voltage on 2 U c2 Emitter current I 1. Are they in phase? 5. The system of claim 2, wherein, After the constant-width frequency modulation control, the output voltage of the system becomes: The resonant frequency of the system does not change: The resonance frequency of the system is given by becomes in the case of In the formula: Vsys is the system output voltage before the fixed-width frequency modulation control, T is the length of each cycle before the addition of the zero resonance state, T is the length of the single zero resonance state insertion.

6. The system of claim 1, characterized in that: The DC-AC inverter unit includes a filter capacitor C d , a load resistor R L , a rectifier The rectifier is composed of four diodes D1, D2, D3 and D4 or MOSFET or IGBT switch tube; Wherein, D1, D2 in series and D3, D4 in series are connected in parallel, and then respectively with filter capacitor C d , load resistance R L parallel; The positive pole of the receiving end resonance unit is connected to the connection point of D1 and D2, and the negative pole of the receiving end resonance unit is connected to the connection point of D3 and D4.

7. A method for regulating a single-stage frequency-modulated voltage-regulated improved S-S type wireless charging system, the system being a magnetic coupling resonant type wireless charging system, comprising a transmitting end and a receiving end; at the transmitting end, an input direct current voltage is converted into high-frequency alternating current by a direct current-alternating current inversion unit, and the high-frequency alternating current is provided to the receiving end through a transmitting end resonant unit composed of a transmitting resonant capacitor C 1 and a transmitting coil L 1 ; at the receiving end, the high-frequency alternating current as electric energy is received through a receiving end resonant unit composed of a receiving resonant capacitor C 2 and a receiving coil L 2, and is converted into direct current that can supply power to a load through an alternating current-direct current conversion unit; characterized in that, The method includes the following steps: In the S-S type wireless charging system, a diode is connected in series before the DC-AC inversion unit, and a group of anti-series connection switch tubes are connected in parallel after the receiving end coil L 2, so that the transmitting end and the receiving end can stop resonance at the same time in the zero resonance state, thereby obtaining an improved S-S type wireless charging system. The system carries out tuning control in the case of resonance deviation, then realizes voltage regulation by changing the duty cycle corresponding to high and low levels in the case of keeping resonance state, so as to realize synchronous regulation of system resonance and output voltage.

8. The method of claim 7, wherein, The changing of the duty cycle corresponding to high and low levels realizes voltage regulation through fixed-width frequency control; The fixed-width frequency control is to change the total cycle length of control by inserting zero resonance state under the premise of fixed resonance frequency, so as to change the equivalent frequency.

9. The method of claim 7, wherein, The tuning control in the case of resonance deviation includes the following steps: When the coupling parameter changes, it is judged whether the current frequency satisfies system resonance; If the system is not resonant, the system switching frequency is changed to the resonance frequency when the resonance frequencies of the transmitting end and the receiving end are the same, so that the system returns to the resonant state; When the resonance frequencies of the transmitting end and the receiving end are different, the transmitting end adopts frequency conversion to realize tuning, and the receiving end adopts an adjustable resonance capacitor to realize compensation of resonance deviation, so that the system returns to the resonant state.

10. The method of claim 9, wherein, It is judged whether the current frequency satisfies system resonance, specifically: Checking the output voltage of a dc-ac inverter unit U in-ac whether the transmit end current I 1 is in phase, and the voltage on the receive end resonance capacitor C 2 U c2 whether the transmit end current I 1 is in phase.

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