Constant-frequency constant-voltage output wireless charging system based on capacitance switching and control method

Abstract

The invention provides a fixed-frequency constant-voltage output wireless charging system based on capacitance switching and a control method, and is used for solving the problem that the coupling coefficient fluctuation range is relatively large when the transmission distance of a WPT system is changed and a coil cannot be aligned. The system comprises a transmitting end and a receiving end, the transmitting end comprises a primary side push-pull inverter, and the receiving end comprises a secondary side push-pull inverter; the primary side push-pull inverter comprises a primary side first push-pull circuit and a primary side second push-pull circuit which are arranged in parallel, the secondary side push-pull inverter comprises a secondary side first push-pull circuit and a secondary side second push-pull circuit which are arranged in parallel, and the primary side first push-pull circuit, the primary side second push-pull circuit, the secondary side first push-pull circuit and the secondary side second push-pull circuit each comprise a push-pull compensation inductor and a push-pull module which are arranged in series. The push-pull module is provided with a plurality of switch tube sub-circuits which are arranged in parallel. Each switch tube sub-circuit comprises a switch compensation capacitor and a first MOSFET tube which are arranged in series. The WPT system can work under the conditions of constant frequency, wide coupling coefficient and load, and stable steady-state output is achieved.

Description

Technical Field

[0001] The present invention relates to the field of wireless power transmission, and in particular to a capacitor switching-based fixed-frequency constant-voltage output wireless charging system and a control method. Background Art

[0002] Currently, wireless power transfer (WPT) systems, which transmit electricity through electromagnetic induction without any physical contact, have been implemented in various applications. It is usually necessary to keep the coupling coefficient of the WPT system stable. However, changes in the relative position between coils often change the coupling conditions of the WPT system, resulting in changes in the system transmission characteristics and parameters. When charging a mobile electric vehicle, not only does the transmission distance change, but the coils cannot be fully aligned, and the coupling coefficient fluctuates over a large range. Summary of the invention

[0003] The purpose of the present invention is to provide a constant frequency and constant voltage output wireless charging system and control method based on capacitor switching, which is used to solve the technical problem that the coupling coefficient of the existing wireless power transmission system fluctuates greatly when the transmission distance changes and the coil cannot be aligned.

[0004] A constant-frequency and constant-voltage output wireless charging system based on capacitor switching, comprising a transmitting end and a receiving end for transmitting electric energy through magnetic coupling, wherein the transmitting end comprises a primary-side push-pull inverter, and the receiving end comprises a secondary-side push-pull inverter;

[0005] The primary push-pull inverter includes a primary first push-pull circuit and a primary second push-pull circuit arranged in parallel, and the secondary push-pull inverter includes a secondary first push-pull circuit and a secondary second push-pull circuit arranged in parallel. The first and second primary push-pull circuits and the first and second secondary push-pull circuits all include a push-pull compensation inductor and a push-pull module arranged in series. The push-pull module includes a plurality of switch tube circuits arranged in parallel, and the switch tube circuit includes a switch compensation capacitor and a first MOSFET tube arranged in series.

[0006] Optionally, the transmitting end further includes a DC power supply, a primary compensation inductor, a primary compensation capacitor and a transmitting coil;

[0007] The DC power supply and the primary compensation inductor are connected in series to form a first series module, and two ends of the first series module are respectively connected to two ends of the primary first and second push-pull circuits connected in parallel. The primary compensation capacitor and the transmitting coil are connected in parallel to form a first parallel module, and two ends of the first parallel module are respectively connected to two output ends of the primary push-pull inverter. The connection end of the push-pull compensation inductor and the push-pull module in the primary push-pull inverter is its output end.

[0008] Optionally, the receiving end further includes a receiving coil, a secondary side compensation capacitor, a secondary side compensation inductor and a load;

[0009] The secondary compensation inductor and the load are connected in series to form a second series module. The two ends of the second series module are respectively connected to the two ends after the parallel connection of the first and second push-pull circuits on the secondary side. The receiving coil and the secondary compensation capacitor are connected in parallel to form a second parallel module. The two ends of the second parallel module are respectively connected to the two input ends of the secondary push-pull inverter. The connection end of the push-pull compensation inductor and the push-pull module in the secondary push-pull inverter is its input end.

[0010] Optionally, the first and second primary push-pull circuits further include a second MOSFET tube connected in parallel with a plurality of switch tube circuits.

[0011] Optionally, the first and second secondary push-pull circuits further include a diode connected in parallel with a plurality of switch tube circuits.

[0012] Optionally, the transmitting end and the receiving end adopt the same electrical parameters, and the transmitting end and the receiving end satisfy the PT symmetry condition.

[0013] A control method for a wireless charging system with fixed-frequency constant-voltage output based on capacitor switching, characterized in that it is used to control the above-mentioned wireless charging system with fixed-frequency constant-voltage output based on capacitor switching. The specific steps are as follows:

[0014] S1: Determine whether the wireless charging system meets the tuning condition. If it meets, go to step S2. If it does not meet, immediately turn off the system;

[0015] S2: Turn on a first MOSFET tubes in the push-pull module to connect all a switch compensation capacitors to the circuit, where: 0 < a < n, and n is the number of switch tube circuits in the push-pull module;

[0016] S3: Maintain the system operation for b cycles, detect the capacitor voltage, and measure the phase angle of the capacitor voltage;

[0017] S4: Determine the phase angle of the capacitor voltage:

[0018] If the phase angle of the current capacitor voltage is less than m1, the circuit compensation is insufficient. Add a group of switch tube circuits to the circuit and return to step S3;

[0019] If the phase angle of the current capacitor voltage is greater than or equal to m1 and less than or equal to m2, maintain the current output;

[0020] If the phase angle of the current capacitor voltage is greater than m2, the circuit compensation is excessive. Remove a group of switch tube circuits from the circuit and return to step S3.

[0021] Optionally, the specific steps for determining whether the wireless charging system meets the tuning condition in step S1 are as follows:

[0022] S1.1: Turn on all the first MOSFETs in the push-pull module so that all the switch compensation capacitors are connected to the circuit;

[0023] S1.2: Maintain the system operation for b cycles, detect the capacitor voltage, and measure the phase angle of the capacitor voltage to determine whether the system phase angle is less than m1. If so, the system does not meet the tuning conditions and shuts down the system immediately. If not, go to step S1.3;

[0024] S1.3: Turn off all first MOSFETs in the push-pull module so that all switch compensation capacitors are not connected to the circuit;

[0025] S1.4: Maintain the system operation for b cycles, detect the capacitor voltage, and measure the phase angle of the capacitor voltage to determine whether the system phase angle is greater than m2. If so, the system does not meet the tuning conditions and shuts down the system immediately. If not, go to step S2.

[0026] Optionally, in step S3, m1 is 175° and m2 is 179.5°.

[0027] Due to the adoption of the above technical solution, the present invention has the following advantages:

[0028] 1. The present application enables the PT-symmetrical wireless power transmission system to achieve stable steady-state output at a constant frequency and under a wide range of coupling coefficients and load conditions. For other variable-frequency PT-symmetrical wireless power transmission systems, the system uses push-pull fixed-frequency control, and the control scheme is simple and effective.

[0029] 2. The inherent resonant frequency of the wireless charging system of the present application tracks the operating frequency, and the fixed frequency control simplifies the operation and minimizes EMI.

[0030] 3. For dynamically changing loads, the wireless charging system of the present application always maintains a constant voltage output and achieves zero voltage switching (ZVS) during the entire power transmission process to ensure high efficiency.

[0031] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings of the present invention are as follows.

[0033] Figure 1 It is a structural schematic diagram of the wireless charging system of the present invention.

[0034] Figure 2 Flow chart of the wireless charging system control method of the present invention.

[0035] Figure 3 FIG. 4 is an equivalent circuit diagram of the push-pull system of the present invention.

[0036] Figure 4 This is the circuit diagram of the present invention when the transmitting end has a forward pulse and a reverse pulse.

[0037] Figure 5 This is a waveform diagram of the resonant circuit when the present invention sends a pulse to the switch tube.

[0038] Figure 6 This is a simulation waveform diagram of the present invention when the transmitting and receiving coils are 30.9 μH at 58.8 kHz.

[0039] Figure 7 It is a simulation diagram of the system natural frequency under different coupling coefficients of the present invention.

[0040] Figure 8 This is a simulation waveform diagram of the output voltage when the coupling coefficient of the present invention changes.

[0041] Fig. 9 This is a simulation trend diagram of the coupling coefficient of the present invention changing with the air gap.

[0042] Fig.10 It is a simulation curve diagram of the output voltage in the uncontrolled system of the present invention.

[0043] Fig.11 It is a simulation curve diagram of the output voltage in the controlled system of the present invention.

[0044] Fig.12 It is the voltage waveform diagram at both ends of the transmitting coil of the present invention. DETAILED DESCRIPTION

[0045] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0046] Embodiment 1:

[0047] like Figure 1 A constant-frequency constant-voltage output wireless charging system based on capacitor switching is shown, comprising a transmitting end and a receiving end for transmitting electric energy through magnetic coupling, wherein the transmitting end further comprises a DC power supply, a primary compensation capacitor, a primary push-pull inverter, a primary compensation capacitor and a transmitting coil, and the receiving end comprises a receiving coil, a secondary compensation capacitor, a secondary push-pull inverter, a secondary compensation inductor and a load;

[0048] The DC power supply and the primary compensation inductor are connected in series to form a first series module, and two ends of the first series module are respectively connected to two ends of the primary first and second push-pull circuits connected in parallel, and the primary compensation capacitor and the transmitting coil are connected in parallel to form a first parallel module, and two ends of the first parallel module are respectively connected to two output ends of the primary push-pull inverter, and the connection end of the push-pull compensation inductor and the push-pull module in the primary push-pull inverter is its output end;

[0049] The secondary side compensation inductor and the load are connected in series to form a second series module, and two ends of the second series module are respectively connected to the two ends of the secondary side first and second push-pull circuits connected in parallel. The receiving coil and the secondary side compensation capacitor are connected in parallel to form a second parallel module, and two ends of the second parallel module are respectively connected to the two input ends of the secondary side push-pull inverter. The connection end of the push-pull compensation inductor and the push-pull module in the secondary side push-pull inverter is its input end.

[0050] In this embodiment, if Figure 1 As shown, the DC power supply at the transmitter is U dc , the primary compensation capacitor is L dc-in , the primary compensation capacitor is C P and the transmitting coil L P The receiving coil at the receiving end is L S , the secondary side compensation capacitor is C S , secondary side compensation inductor L dc-out and load R L In this embodiment, the DC power supply is U dc The primary compensation capacitor is L dc-in A quasi-current source is formed.

[0051] like Figure 1 As shown, the primary push-pull inverter includes a primary first push-pull circuit and a primary second push-pull circuit arranged in parallel, the secondary push-pull inverter includes a secondary first push-pull circuit and a secondary second push-pull circuit, the primary first and second push-pull circuits and the secondary first and second push-pull circuits all include a push-pull compensation inductor and a push-pull module arranged in series, the push-pull module includes a plurality of switch tube circuits arranged in parallel, and the switch tube circuit includes a switch compensation capacitor and a first MOSFET tube arranged in series.

[0052] The first and second push-pull circuits on the primary side also include a second MOSFET tube arranged in parallel with a plurality of switch tube circuits, and the first and second push-pull circuits on the secondary side also include a diode arranged in parallel with a plurality of switch tube circuits.

[0053] In this embodiment, if Figure 1 As shown, the push-pull compensation inductor in the first push-pull circuit of the primary side is L P1 The push-pull compensation inductor in the second push-pull circuit of the primary side is LP2 The switch compensation capacitor in the switch tube circuit of the first push-pull circuit on the primary side is C PA1 -C PAn , the first MOSFET is S PA1 -S PAn The switch compensation capacitor in the switch tube circuit in the second push-pull circuit of the primary side is C PB1 -C PBn , the first MOSFET is S PB1 -S PBn The push-pull compensation inductor in the first push-pull circuit of the secondary side is L S1 The push-pull compensation inductor in the second push-pull circuit of the secondary side is L S2 The switch compensation capacitor in the switch tube circuit of the first push-pull circuit on the secondary side is C SAi and the first MOSFET is S SAi The switch compensation capacitor in the switch tube circuit of the second push-pull circuit on the secondary side is C SBi , the first MOSFET is S SBi Where i∈n, n is the number of switch tube circuits in the first and second push-pull circuits on the primary side and the first and second push-pull circuits on the secondary side. In this embodiment, the push-pull compensation inductor L P1 And push-pull compensation inductor L P2 The DC power supply U dc The provided DC current is split into two current sources.

[0054] In this embodiment, if Figure 1 As shown, the second MOSFET tubes in the first and second push-pull circuits of the primary side are S A and S B The diodes in the first and second push-pull circuits of the secondary side are respectively D A and D B .

[0055] In this embodiment, the transmitting end and the receiving end use the same circuit structure and parameters, which conforms to the PT symmetry principle. The switch compensation capacitor of the switch tube circuit is connected in series with the first MOSFET tube to achieve the fixed frequency self-tuning function. The system's inherent resonant frequency tracks the operating frequency.

[0056] In this embodiment, the source terminal of the MOSFET in the push-pull inverter is directly grounded, which is convenient for control. Compared with the class E inverter, the push-pull inverter makes the switch bear lower voltage stress, so that a higher power level can be achieved. It is relatively complex to implement ZVS in the class E circuit, and various circuit component parameters such as the primary and secondary compensation capacitors and compensation inductors need to be designed in detail. In contrast, the push-pull topology is much simpler in this regard. The equivalent topology of the push-pull system is as follows: Figure 3 As shown. In the push-pull system, Ldc-in The inductance value of is designed to be much larger than the inductance value of the resonant inductor, so it can usually be ignored. P1 and L P2 Designed to maintain a relatively constant current, it can be modeled as a DC current source. When the switch is open, the associated DC inductor is charged, and when the switch is closed, the inductor releases its current into the resonant LC circuit. By alternately opening and closing the two switches of the converter, the system oscillates around the resonance point in a steady state.

[0057] Analyze the system:

[0058] 1. Analyze the circuit operation process:

[0059] Since the push-pull circuit is relatively stable, it consists of two stages. Take the transmitter as an example. Figure 4 (a) and Figure 4 (b) shows the two states, and the transmitter circuit switches between the two state stages. Figure 4 (a) is the equivalent circuit diagram of the transmitting end of the system in the positive half cycle of the pulse. Figure 4 (b) is the equivalent circuit diagram of the transmitting end of the system during the negative half cycle of the pulse. Figure 4 (a) The capacitance value C involved in the resonance tuning =C PA1 +C P , Figure 4 (b) The capacitance value C involved in the resonance tuning =C PB1 +C P . Send pulses to the switch tubes on both sides respectively to compensate the capacitor C P The voltage is Figure 5 As shown. There may be three situations: Figure 5 (a) The compensation capacitor is too small to be tuned. At this time, the impedance is inductive and the capacitor voltage becomes zero at time t1. However, from the characteristics of the capacitor, it can be seen that the capacitor current is not zero at this time. Therefore, the diode begins to conduct electricity and forms a loop with the capacitor, which is equivalent to a capacitor short circuit. The current immediately becomes zero. Figure 5 (b) For perfect tuning, when the capacitor voltage is zero, the switching pulse is zero, truly achieving ZPA. Figure 5 (c) The compensation capacitor is too large. At this time, the impedance is capacitive. When the switch pulse is zero, the capacitor voltage has not been released. If it is suddenly turned off, a large peak current will be generated. In summary, Figure 5 (a) and Figure 5 (c) The voltage waveform will be distorted. Choose the appropriate capacitor value to make the circuit run in 5(b), and Figure 5 (c) will generate a spike current that will damage the circuit, so this situation should be avoided as much as possible.

[0060] 2. Analyze the zero voltage switch of the system:

[0061] The wireless charging system of this application uses a 50% switching duty cycle to track the zero phase angle. The fundamental wave approximation method can be used to effectively analyze the system in the phasor domain. The input DC voltage and AC voltage of the driving compensation network are:

[0062]

[0063] In formula (1), U in is the input voltage, T is the system operation cycle time, T on is the conduction time of the system switch tube, f sw is the switching frequency of the system switch tube, U ac is the system inverter voltage.

[0064] The impedance Z reflected from the receiving circuit to the transmitting circuit ref It can be expressed as:

[0065]

[0066] In formula (2), M is the mutual inductance between the transmitting coil and the receiving coil, R L (ac) is the equivalent AC impedance of the load.

[0067] Input impedance seen from the transmitter It is expressed as:

[0068]

[0069] Input current I seen from the primary in for:

[0070]

[0071] Short-circuit current I when the secondary circuit is short-circuited sc for:

[0072]

[0073] The output voltage U out for:

[0074]

[0075] The equivalent AC load at the input of the rectifier can be calculated by applying the power balance between the input and output of the rectifier:

[0076]

[0077] so:

[0078]

[0079] The gain of the input and output impedances can be expressed as:

[0080]

[0081] If the system is to achieve ZVS, the input impedance must be a pure resistor:

[0082] Im{Z in}=0 (10)

[0083] This equation can be simplified to:

[0084]

[0085] in:

[0086] a=L P R L 2

[0087]

[0088] d=-C P C S 2 L P 2 L s 2 R L 2 +2C P C S 2 L P L s M 2 R L 2 -C P C S 2 M 4 R L 2

[0089] The seventh-order polynomial in the numerator of the equation (11) can be simplified to a cubic polynomial in one variable:

[0090]

[0091] Right now:

[0092]

[0093] This type of cubic equation in one variable can be solved using Cardano's formula.

[0094]

[0095] in:

[0096]

[0097] When Δ>0, the equation has one real root and two non-real complex conjugate roots.

[0098]

[0099] When Δ<0, due to the interaction between the coils, equation (16) obtains three different real roots, namely ω1, ω2 and ω3, as shown below:

[0100]

[0101] in:

[0102]

[0103] 3. Analyze the constant pressure model of the system:

[0104] In order to satisfy the PT symmetry condition, the transmitter and receiver use the same parameters, namely L P =L S =L, C P =C S = C. By neglecting parasitic effects, the required capacitance value corresponding to the change in coupling coefficient can be derived.

[0105] When frequency splitting occurs, the system exhibits three stable resonant frequencies, two of which are only present when k>k c When k c for:

[0106]

[0107] in:

[0108]

[0109] according to Figure 3 The equivalent circuit of the push-pull system shown in the figure can be written as follows:

[0110]

[0111] in:

[0112]

[0113] Where α = ω / ω o ;X o =(L / C) 1 / 2 When k>k cWhen , the system operating frequency and the nominal tuning frequency can be found and the ABCD matrix parameters are:

[0114]

[0115] so:

[0116]

[0117] It can be concluded that:

[0118] U in =U out (twenty four)

[0119] 4. Analyze the system tuning capacitor:

[0120] Based on equations (10) and (11), the required capacitance value for adjustment can be deduced as:

[0121]

[0122] like Figure 6 As shown in Figure 1, the transmitter and receiver coils are simulated at 58.8kHz with an inductance of 30.9μH. It can be observed that when k>k c There are three possible tuning capacitor values, including ω1 and ω2, which are both CV output modes. In actual operation, it is sufficient to ensure that the system continuously follows a single tuning capacitor curve as the coupling coefficient changes, such as Figure 1 As shown in the figure, as long as there are enough parallel capacitor branches, the system can maintain ZVS and always keep a constant voltage output.

[0123] 5. Analyze the frequency bifurcation of the system:

[0124] In this embodiment, in the WPT system, in order to improve the system performance, compensation capacitors with appropriate parameters are usually added to the main and auxiliary components of the system. This method can ensure that the system operates in a resonant state and maintain the total impedance at the maximum pure resistance level, thereby achieving the highest efficiency. However, as the system parameters change, multiple resonant frequencies may appear. This phenomenon is called frequency bifurcation. Frequency bifurcation will cause the system to switch to other operating states during operation, resulting in reduced robustness, performance, and efficiency, which are unacceptable. Frequency bifurcation often occurs when the coupling coefficient is high or the load is light. The fixed-frequency PT system of the present application effectively alleviates the negative impact of frequency bifurcation. By maintaining a fixed operating frequency and adopting complex parameter design, the system can reliably oscillate at a single frequency point, ensuring stable and robust system performance. As Figure 7 As shown in Figure 2, the simulation k changes from 0.24 to 0.72. The results show that the natural frequency of the system is basically consistent with the set operating frequency of 58.8kHz.

[0125] In summary, the inherent resonant frequency of the wireless charging system of the present application tracks the operating frequency, and the fixed-frequency control simplifies the operation and minimizes EMI. For a dynamically changing load, a constant voltage output is always maintained. At the same time, the present application achieves zero-voltage switching (ZVS) throughout the power transmission process, ensuring high efficiency.

[0126] Embodiment 2:

[0127] As Figure 2 shown, a control method for a fixed-frequency constant-voltage output wireless charging system based on capacitor switching is used to control the fixed-frequency constant-voltage output wireless charging system described in Embodiment 1. The specific steps are as follows:

[0128] S1: Determine whether the wireless charging system meets the tuning condition. If it meets, go to step S2; if not, immediately turn off the system. The specific steps are as follows:

[0129] S1.1: Turn on all the first MOSFET tubes in the push-pull module so that all the switching compensation capacitors are connected to the circuit.

[0130] S1.2: Maintain the system operation for a time of b cycles, detect the capacitor voltage, and measure the phase angle of the capacitor voltage. Determine whether the system phase angle is less than m1. If so, the system does not meet the tuning condition, and immediately turn off the system. If not, go to step S1.3.

[0131] S1.3: Turn off all the first MOSFET tubes in the push-pull module so that all the switching compensation capacitors are not connected to the circuit.

[0132] S1.4: Maintain the system operation for a time of b cycles, detect the capacitor voltage, and measure the phase angle of the capacitor voltage. Determine whether the system phase angle is greater than m2. If so, the system does not meet the tuning condition, and immediately turn off the system. If not, go to step S2.

[0133] S2: Turn on a first MOSFET tubes in the push-pull module so that a switching compensation capacitors are connected to the circuit, where: 0 < a < n, and n is the number of switch transistor sub-circuits in the push-pull module.

[0134] S3: Maintain the system operation for a time of b cycles, detect the capacitor voltage, and measure the phase angle of the capacitor voltage.

[0135] S4: Determine the phase angle of the capacitor voltage:

[0136] If the phase angle of the current capacitor voltage is less than m1, the circuit compensation is insufficient. Add a group of switch transistor sub-circuits to the circuit and return to step S3.

[0137] If the phase angle of the current capacitor voltage is greater than or equal to m1 and less than or equal to m2, the current output is maintained;

[0138] If the phase angle of the current capacitor voltage is greater than m2, the circuit is over-compensated, a set of switch tube circuits in the circuit is removed, and the process returns to step S3.

[0139] In this embodiment, m1 is 175°, m2 is 179.5°, b is 10, and the system is maintained for 10 cycles to stabilize the system. In this embodiment, the initial time is set to n / 2.

[0140] In this embodiment, a corresponding control simulation is established in PSIM. When the coupling coefficient k changes from 0.24 to 0.72, the system output voltage is as follows: Figure 8 As shown, it can be observed that the voltage fluctuates between 9.5V and 10.5V.

[0141] S5: Simulation verification: Design system parameters that meet the requirements, and the parameters are shown in Table 1.

[0142] Table 1 Parameters of the proposed WPT system

[0143]

[0144]

[0145] The system uses the parameters shown in Table 1 and builds a wireless power transmission system with a power of 10W. Fig. 9 The coupling coefficient k changes with the air gap. Without any control, as the air gap increases and the coupling coefficient decreases, the output voltage gradually decreases, such as Fig.10 After the control is implemented, the output voltage waveform is as follows Fig.11 It can be observed that after a tuning process, the voltage remains stable at the output. Fig.12 is the voltage across the primary compensation capacitor. When the coupling coefficient changes, the system undergoes a self-tuning process and transitions from an under-compensated state to a normal tuning state. Figure 5 The circuit analysis is consistent with .

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A constant frequency and constant voltage output wireless charging system based on capacitor switching, comprising a transmitting end and a receiving end for power transmission through magnetic coupling, characterized in that: The transmitting end includes a primary push-pull inverter, and the receiving end includes a secondary push-pull inverter; The primary push-pull inverter includes a primary first push-pull circuit and a primary second push-pull circuit arranged in parallel. The secondary push-pull inverter includes a secondary first push-pull circuit and a secondary second push-pull circuit arranged in parallel. The primary first and second push-pull circuits and the secondary first and second push-pull circuits each include a push-pull compensation inductor and a push-pull module arranged in series. The push-pull module is composed of a plurality of switch tube circuits arranged in parallel. The switch tube circuit includes a switch compensation capacitor and a first MOSFET tube arranged in series.

2. According to claim 1, a constant frequency and constant voltage output wireless charging system based on capacitor switching is characterized in that: The transmitting end further includes a DC power supply, a primary compensation inductor, a primary compensation capacitor, and a transmitting coil; The DC power supply and the primary compensation inductor are connected in series to form a first series module. The two ends of the first series module are respectively connected to the two ends after the parallel connection of the primary first and second push-pull circuits. The primary compensation capacitor and the transmitting coil are connected in parallel to form a first parallel module. The two ends of the first parallel module are respectively connected to the two output ends of the primary push-pull inverter. The connection end of the push-pull compensation inductor and the push-pull module in the primary push-pull inverter is its output end.

3. A constant frequency and constant voltage output wireless charging system based on capacitor switching according to claim 2, characterized in that: The receiving end further includes a receiving coil, a secondary compensation capacitor, a secondary compensation inductor, and a load; The secondary compensation inductor and the load are connected in series to form a second series module. The two ends of the second series module are respectively connected to the two ends after the parallel connection of the secondary first and second push-pull circuits. The receiving coil and the secondary compensation capacitor are connected in parallel to form a second parallel module. The two ends of the second parallel module are respectively connected to the two input ends of the secondary push-pull inverter. The connection end of the push-pull compensation inductor and the push-pull module in the secondary push-pull inverter is its input end.

4. According to claim 2, a constant frequency and constant voltage output wireless charging system based on capacitor switching is characterized in that: The primary first and second push-pull circuits further include a second MOSFET tube arranged in parallel with a plurality of switch tube circuits.

5. The constant frequency and constant voltage output wireless charging system based on capacitor switching according to claim 3, characterized in that: The secondary first and second push-pull circuits further include a diode arranged in parallel with a plurality of switch tube circuits.

6. The constant frequency and constant voltage output wireless charging system based on capacitor switching according to claim 3, characterized in that: The transmitting end and the receiving end adopt the same electrical parameters, and the transmitting end and the receiving end satisfy the PT symmetry condition.

7. A control method for a constant frequency and constant voltage output wireless charging system based on capacitor switching, characterized in that: Used to control a wireless charging system with fixed-frequency constant-voltage output based on capacitor switching as described in claims 1-6. The specific steps are as follows: S1: Determine whether the wireless charging system meets the tuning condition. If it meets, go to step S2. If it does not meet, immediately turn off the system; S2: Turn on a first MOSFET tubes in the push-pull module to connect a switch compensation capacitors to the circuit, where: 0 < a < n, and n is the number of switch tube circuits in the push-pull module; S3: Maintain the system operation for b cycles, detect the capacitor voltage, and measure the phase angle of the capacitor voltage; S4: Determine the phase angle of the capacitor voltage: If the current phase angle of the capacitor voltage is less than m1, the circuit compensation is insufficient. Add a group of switch tube circuits to the circuit and return to step S3; If the current phase angle of the capacitor voltage is greater than or equal to m1 and less than or equal to m2, maintain the current output; If the current phase angle of the capacitor voltage is greater than m2, the circuit compensation is excessive. Remove a group of switch tube circuits from the circuit and return to step S3.

8. The control method of a constant frequency and constant voltage output wireless charging system based on capacitor switching according to claim 7, characterized in that: The specific steps of determining whether the wireless charging system meets the tuning condition in step S1 are: S1.1: Turn on all the first MOSFETs in the push-pull module so that all the switch compensation capacitors are connected to the circuit; S1.2: Maintain the system operation for b cycles, detect the capacitor voltage, and measure the phase angle of the capacitor voltage to determine whether the system phase angle is less than m1. If so, the system does not meet the tuning conditions and shuts down the system immediately. If not, go to step S1.3; S1.3: Turn off all first MOSFETs in the push-pull module so that all switch compensation capacitors are not connected to the circuit; S1.4: Maintain the system operation for b cycles, detect the capacitor voltage, and measure the phase angle of the capacitor voltage to determine whether the system phase angle is greater than m2. If so, the system does not meet the tuning conditions and shuts down the system immediately. If not, go to step S2.

9. The control method of a constant frequency and constant voltage output wireless charging system based on capacitor switching according to claim 7 or 8, characterized in that: In step S3, m1 is 175° and m2 is 179.5°.

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