A self-excitation frequency control method and system for a series-series compensation type WPT system

Abstract

The present application relates to the technical field of wireless power transmission, and specifically discloses a self-excitation frequency control method and system for a series-series compensation type WPT system, which obtains the current working state of the system by detecting the coupling coefficient, takes the power transmission characteristics as the optimization target, switches to the ideal and appropriate self-excitation oscillation frequency by setting the threshold or making the system be in the detuned state, and continues charging when the coupling mechanism position is determined, i.e. the working state of the system no longer changes, until the charging is completed. The present application realizes the free switching of the self-excitation frequency of the series-series compensation type WPT system, and is not affected by the initial state of the system, is convenient to operate, simple to control, improves the power transmission characteristics, and enables the system to output relatively stably under the condition of varying coupling coefficient, while working in weak inductance. Compared with the existing single-resonance frequency system design method, the present application can significantly improve the system offset adaptability.

Description

Technical Field

[0001] This invention relates to the field of wireless power transmission technology, and in particular to a self-excited frequency control method and system for a string-to-string compensated WPT system. Background Technology

[0002] With the accumulation of technology in recent years, wireless power transfer technology has become increasingly mature, and research results in the laboratory are gradually being industrialized. Many high-tech products, such as new energy vehicles, implantable devices, and intelligent drones, have adopted wireless power transfer technology. While wireless power transfer technology has brought much convenience to people's daily lives, some problems still exist in its use. Due to the loose coupling between the primary and secondary sides of a wireless power transfer system, resonant switching circuits are typically used in the main circuits of both sides to improve the power transfer capability. This leads to high-order nonlinear characteristics of the system, making its dynamic behavior very complex. Consequently, under certain special circumstances, the wireless power transfer system may exhibit self-excited frequency jumps.

[0003] Currently, to address the aforementioned issues, numerous academic papers and patents have researched and proposed corresponding solutions. Tang Chunsen, in his doctoral dissertation "Research and Application of Soft Switching Operating Point in Non-Contact Power Transmission System," proposed a power control approach based on multiple resonant points of the system. The core idea is to allow the system to switch back and forth between multiple resonant points based on error feedback information, thereby achieving power control. This control method has a simple structure and high conversion efficiency, but its output current exhibits ripple, making it unsuitable for applications requiring high voltage waveform quality. Tan Jianping et al., in their patent "A Method for Synchronous Transmission of Power and Signal Based on Frequency Splitting in Wireless Power Transmission," used a current zero-crossing detection method to switch between two autonomous stable frequencies of resonance to achieve frequency modulation transmission of the signal. The zero-crossing detection method is beneficial for reliable signal transmission, but it has certain drawbacks; it is significantly affected by the initial values ​​of the system, and different initial values ​​will influence the selection of the resonant frequency. Summary of the Invention

[0004] This invention provides a self-excited frequency control method for a series-compensated WPT system. The technical problem it solves is that the current zero-crossing detection method is greatly affected by the selection of the initial value of the system in realizing the free switching of the self-excited frequency of the series-compensated WPT system.

[0005] To address the above technical problems, this invention provides a self-excited frequency control method for a string-compensated WPT system, comprising the following steps:

[0006] S1. Detect the coupling coefficient of the string-compensated WPT system, and obtain the working state of the string-compensated WPT system based on the coupling coefficient;

[0007] S2. Determine whether the working state of the string-to-string compensation type WPT system is single-mode or multi-mode at this time. If it is multi-mode, proceed to step S3; if it is single-mode, return to step S1.

[0008] S3. Detect the primary current i1 and inverter output voltage v1 of the string-compensated WPT system, generate the amplitude-frequency phase curve of i1 / v1, and determine the first and second resonant frequency points from low to high based on the amplitude-frequency phase curve.

[0009] S4. Determine whether the difference between the amplitude of the first resonant frequency point and the amplitude of the second resonant frequency point is greater than a preset value. If yes, proceed to steps S5 and S6; otherwise, proceed to step S7.

[0010] S5. Set the first threshold for the first resonant frequency point and the second threshold for the second resonant frequency point according to the phase curve in the amplitude-frequency phase curve of i1 / v1.

[0011] S6. Using the first threshold or the second threshold as the threshold for primary current detection, control the primary inverter circuit of the string-compensated WPT system so that the resonant frequency of the system is stabilized at the first resonant frequency point or the second resonant frequency point.

[0012] S7. Set the threshold for primary current detection to 0, and adjust the effective value of the primary resonant capacitor or secondary resonant capacitor of the series-compensated WPT system to stabilize the resonant frequency of the system at the third resonant frequency point or the fourth resonant frequency point.

[0013] Further, in step S5, the first threshold is set to the sine value of the phase angle at the maximum point of the phase curve in the amplitude-frequency phase curve, and the second threshold is set to the sine value of the phase angle at the minimum point of the phase curve in the amplitude-frequency phase curve.

[0014] Furthermore, in step S7, when the effective value of the secondary resonant circuit capacitor is adjusted to be A times the initial capacitor value, the resonant frequency of the control system stabilizes at the third resonant frequency point, where A < 1. The third resonant frequency point is the resonant frequency point with a larger amplitude in the amplitude-frequency phase curve of i1 / / v1 after adjusting the effective value of the secondary resonant circuit capacitor.

[0015] Furthermore, in step S7, when the effective value of the secondary resonant circuit capacitor is adjusted to be B times the initial capacitor value, the resonant frequency of the control system stabilizes at the fourth resonant frequency point, where B > 1. The fourth resonant frequency point is the resonant frequency point with a larger amplitude in the amplitude-frequency phase curve of i1 / / v1 after adjusting the effective value of the secondary resonant circuit capacitor.

[0016] Furthermore, in step S1, by sampling the transmitter current and DC input voltage and calculating their effective values, and combining other known system parameters and the derivation formula of the coupling coefficient, the coupling coefficient between the coupling mechanisms is estimated in real time.

[0017] Furthermore, the step S7 is followed by the following step:

[0018] S8. Determine whether the working state of the string-to-string compensation type WPT system has changed. If not, continue charging until charging is complete. If yes, return to step S1.

[0019] The present invention also provides a self-excited frequency control system for a series-compensated WPT system, the key of which is: including a primary-side current and voltage acquisition module and a primary-side controller;

[0020] The primary-side current and voltage acquisition module is used to acquire the primary-side current i1 and inverter output voltage v1 of the string-compensated WPT system and send them to the primary-side controller.

[0021] The primary-side controller is used to execute steps S1 to S8 in the above method.

[0022] This invention provides a self-excited frequency control method and system for a series-compensated WPT system. The method obtains the current operating state of the system by detecting the coupling coefficient, and then, using power transfer characteristics as the optimization target, sets a threshold or adjusts the resonant capacitor value to put the system in a detuned state, thereby switching to the ideal self-excited oscillation frequency. When the position of the coupling mechanism is determined, i.e., the system operating state no longer changes, charging continues until charging is complete. This invention achieves free switching of the self-excited frequency of the series-compensated WPT system, unaffected by the initial state of the system. It is convenient to operate and simple to control, enabling the system to output more stably under varying coupling coefficients, while operating in a weakly inductive state. Compared with existing single-resonant frequency system control methods, it significantly improves the system's offset adaptability. Attached Figure Description

[0023] Figure 1 This is a circuit diagram of a string-compensated WPT system provided in an embodiment of the present invention;

[0024] Figure 2 This is provided by the embodiments of the present invention. Figure 1 The equivalent circuit diagram;

[0025] Figure 3 This is provided by the embodiments of the present invention. Figure 2 The equivalent circuit diagram;

[0026] Figure 4(a) is a system amplitude-frequency phase curve diagram corresponding to mutual inductance M = 10μH provided in the embodiment of the present invention;

[0027] Figure 4(b) is a system amplitude-frequency phase curve diagram corresponding to mutual inductance M = 40μH provided in the embodiment of the present invention;

[0028] Figure 5 This is a flowchart of a self-excited frequency control method for a string-compensated WPT system provided in an embodiment of the present invention;

[0029] Figure 6 This is a verification result diagram of the first method provided in the embodiments of the present invention when the initial value is arbitrary;

[0030] Figure 7(a) shows the C2=C provided in the embodiment of the present invention. s The corresponding amplitude-frequency-phase curve;

[0031] Figure 7(b) shows the C2=C provided in the embodiment of the present invention. s The corresponding system autonomous stability frequency diagram;

[0032] Figure 8(a) shows the C2 = 0.8 * C provided in the embodiment of the present invention. s The corresponding amplitude-frequency-phase curve;

[0033] Figure 8(b) shows the C2 = 0.8 * C provided in the embodiment of the present invention. s The corresponding system autonomous stability frequency diagram;

[0034] Figure 9(a) shows the C2 = 1.2 * C provided in the embodiment of the present invention. s The corresponding amplitude-frequency-phase curve;

[0035] Figure 9(b) shows the C2 = 1.2 * C provided in the embodiment of the present invention. s The corresponding system autonomous stability frequency diagram. Detailed Implementation

[0036] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The embodiments are given for illustrative purposes only and should not be construed as limiting the present invention. The accompanying drawings are for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0037] Figure 1 The diagram shown is a structural diagram of a series-to-series compensated WPT system, also known as a series-to-series compensated WPT system. Figure 1 As can be seen, the series-compensated WPT system includes a transmitter and a receiver. The transmitter includes a DC power supply, a high-frequency inverter, a primary-side series compensation capacitor C1, and a transmitting coil L1 connected in sequence. The receiver includes a receiving coil L2, a secondary-side series compensation capacitor C2, and a rectifier and filter circuit (consisting of a rectifier and a filter capacitor C1) connected in sequence. f Composition), load resistance R oThe corresponding current and voltage are also indicated. Figure 1 The corresponding position, including the inverter input current I dc Inverter output voltage v1, primary current i1, secondary current i2, rectifier input voltage v2, rectifier output current I r System output current I o System output voltage V o .

[0038] against Figure 1 The series-series compensated WPT system shown, due to its inherent high-order nonlinear characteristics, exhibits multiple soft-switching operating points and potentially multiple resonant operating points. By replacing the DC voltage source and inverter module with a square wave voltage source, replacing the coupling effect with two controlled voltage sources, and replacing the rectifier bridge with a square wave source and a DC current source, the following can be achieved: Figure 1 Equivalent to Figure 2 Where R1 and R2 represent the equivalent resistances of the primary and secondary sides, respectively, and M represents the mutual inductance between the transmitting and receiving coils. The WPT system is modeled based on... Figure 2 The equivalent circuit analysis is shown. To facilitate the analysis of system behavior, the load resistance is mapped to the resistance in the secondary loop and represented as R. eq Equivalent resistance R eq Approximately:

[0039]

[0040] Based on the equivalent resistance of the load, further... Figure 2 The equivalent circuit is simplified to Figure 3 .

[0041] According to Kirchhoff's laws Figure 3 The behavior of the equivalent circuit shown can be described by the following equation:

[0042]

[0043] ω represents the system's operating angular frequency.

[0044] After canceling out i2 in the above equation, we can further obtain the ratio G between the primary current i1 and the inverter output voltage v1:

[0045]

[0046] Where z1 represents the primary impedance and z2 represents the secondary impedance. z1 and z2 are specifically represented as follows:

[0047]

[0048] This embodiment mainly studies the dynamic behavior of the system based on the relationship between the amplitude and phase of G and the switching frequency. Simulation experiments show that as the coupling coefficient increases, the number of resonant frequency points of the system is no longer unique. Figure 4(a) shows the system amplitude-frequency phase curve when the mutual inductance M = 10 μH, and Figure 4(b) shows the system amplitude-frequency phase curve when the mutual inductance M = 40 μH. Comparing Figure 4(a) and Figure 4(b), it can be found that when the coupling coefficient is large enough, the number of resonant points of the system becomes two. As can be seen from Figure 4(b), the two resonant frequencies are 169.20 kHz and 256.34 kHz, respectively. If the system amplitudes corresponding to the two resonant frequencies are similar and both can exist stably in floating frequency mode, there is still a problem that the switching element cannot freely switch between the two resonant frequencies. Compared with a system with only one resonant frequency, the multi-resonant system structure, with its multiple resonant frequencies matched together, can obtain a rich variety of transmission characteristics.

[0049] The key problem this invention aims to solve is how to freely switch the system's autonomous stable frequency without being affected by the system's initial values. To address this problem, this embodiment proposes a self-excited frequency control method for a series-compensated WPT system, such as... Figure 5 As shown, the specific steps include:

[0050] S1. Detect the coupling coefficient of the string-compensated WPT system and obtain the working state of the string-compensated WPT system based on the coupling coefficient;

[0051] S2. Determine whether the working state of the serial-to-serial compensation type WPT system is single-mode or multi-mode at this time. If it is multi-mode, proceed to step S3; if it is single-mode, return to step S1.

[0052] S3. Detect the primary current i1 and inverter output voltage v1 of the series-compensated WPT system, generate the amplitude-frequency phase curve of i1 / v1, and determine the first and second resonant frequency points from low to high based on the amplitude-frequency phase curve.

[0053] S4. Determine whether the difference between the amplitude of the first resonant frequency point and the amplitude of the second resonant frequency point is greater than a preset value. If yes, proceed to steps S5 and S6; otherwise, proceed to step S7.

[0054] S5. Set the first threshold and the second threshold according to the phase curve in the amplitude-frequency phase curve of i1 / v1;

[0055] S6. Using the first threshold or the second threshold as the threshold for primary current detection, control the primary inverter circuit of the series-compensated WPT system so that the resonant frequency of the system is stabilized at the first resonant frequency point or the second resonant frequency point.

[0056] S7. Set the threshold of primary current detection to 0, and adjust the effective value of the primary resonant capacitor or secondary resonant capacitor of the series-compensated WPT system to stabilize the resonant frequency of the system at the third resonant frequency point or the fourth resonant frequency point.

[0057] S8. Determine whether the working state of the string-to-string compensation type WPT system has changed. If not, continue charging until charging is complete. If yes, return to step S1.

[0058] Regarding step S4, when the amplitudes at the first and second resonant frequencies differ significantly, frequency switching can be achieved by changing the current detection threshold (the first method). (Here, the threshold refers to the ratio of the current value at the switching point to the current peak value, i.e., the sine of the phase angle between the two resonant frequencies). Other parameters remain unchanged. By selecting the threshold, the system can switch from the multi-mode region to the single-mode region, thus solving the problem of frequency jumps. Compared to the current zero-crossing detection method, changing the current detection threshold does not switch the system's autonomous stable frequency at the current zero-crossing point, but rather switches at a set threshold, causing the phase angle to change from multi-mode (one-to-many) to single-mode (one-to-one). This allows for free switching of the system's autonomous stable frequency, unaffected by the system's initial value x.

[0059] The threshold value is determined based on the system's phase curve, as shown in Figure 4(b). The phase curve intersects the zero axis at three points, with the point corresponding to the middle frequency being unstable; only the other two stable resonant points are considered. The phase corresponding to the two extreme points in the curve is the boundary between single-mode and multi-mode operation. The threshold value can be determined by converting the sine of the phase angle between these two extreme points. It is worth noting that the threshold setting considers the free switching of the self-excited frequency, unaffected by the system's initial value, thereby improving the transmission characteristics of the wireless power transmission system. Therefore, it is best to select a threshold value close to or equal to the threshold value. In this embodiment, the threshold value is directly selected as the current detection threshold. Calculations show that the threshold values ​​corresponding to the two resonant frequency points of 169.20kHz and 256.34kHz shown in Figure 4(b) are +0.4 and -0.26, respectively.

[0060] against Figure 1 In the WPT system shown, when the threshold is set to zero and the initial system state is not zero, the autonomous frequency cannot be freely switched. However, by setting an appropriate threshold σ, the autonomous frequency can be freely switched regardless of the initial system state. To verify the effectiveness of the proposed method, the verification results are as follows: Figure 6 As shown, Figure 6 In the waveform, the lower amplitude in the middle section represents the primary current, while the higher amplitude waveform represents the inverter output voltage. From Figure 6It can be seen that when the threshold σ(tol) = 0 (the initial state of the system is not zero), the autonomous frequency cannot be freely switched, and the system's autonomous stable frequency is 246.61 kHz. When the threshold σ(tol) = +0.4, the system's autonomous stable frequency of 169.20-40 kHz is selected, which is the first resonant frequency point in Figure 4(b). When the threshold σ = -0.26, the system's autonomous stable frequency of 256.34 kHz is selected, which is the second resonant frequency point in Figure 4(b). This verifies the effectiveness of the first method proposed in this embodiment.

[0061] When the amplitudes at the first and second resonant frequencies are relatively small, the second method is used. This second method involves primary-side or secondary-side detuning control. When the system amplitudes at the two resonant frequencies are similar, the system cannot freely switch between its two autonomous stable frequencies. In this case, the effective capacitance or inductance value in the primary or secondary resonant circuit can be adjusted to put the system in a detuned state. This detuning weakens the amplitude of one resonant frequency, while the amplitude of the other resonant frequency is relatively larger. This allows for free switching of the system's autonomous stable frequencies according to specific needs, unaffected by the initial system values. For a series-to-series compensated WPT system, the value of the secondary resonant circuit capacitor C2 is adjusted (assuming its original value is C). s It can freely control the switching of the system's autonomous stable frequency, and is not affected by the system's initial value.

[0062] In step S7, when the effective value of the secondary resonant circuit capacitor is adjusted to be A times the initial capacitance value, the resonant frequency of the control system stabilizes at the third resonant frequency point, where A < 1. The third resonant frequency point is the resonant frequency point with the larger amplitude in the amplitude-frequency phase curve of i1 / v1 after adjusting the effective value of the secondary resonant circuit capacitor. When the effective value of the secondary resonant circuit capacitor is adjusted to be B times the initial capacitance value, the resonant frequency of the control system stabilizes at the fourth resonant frequency point, where B > 1. The fourth resonant frequency point is the resonant frequency point with the larger amplitude in the amplitude-frequency phase curve of i1 / v1 after adjusting the effective value of the secondary resonant circuit capacitor. The values ​​of A and B need to ensure that the amplitudes of the two resonant frequency points in the amplitude-frequency phase curve after adjusting the capacitance value differ significantly.

[0063] With arbitrary initial system values, the verification results are shown in Figures 7(a), 7(b), 8(a), 8(b), 9(a), and 9(b). Figures 7(a) and 7(b) show C2 = C s The corresponding amplitude-frequency-phase curves and the corresponding system autonomous stable frequency diagrams, Figure 8(a) and Figure 8(b), respectively show C2 = 0.8 * C s (i.e., A = 0.8) The amplitude-frequency phase curve and the corresponding system autonomous stable frequency diagram are shown in Figures 9(a) and 9(b), respectively, for C2 = 1.2 * Cs The amplitude-frequency phase curves and the corresponding system autonomous stable frequency diagrams for (i.e., B = 1.2) are shown in Figures 7(a) and 7(b). As can be seen from Figures 7(a) and 7(b), when the threshold tol is uniformly set to 0, the system has two resonant frequency points, but the system cannot switch frequencies, resulting in the system's autonomous stable frequency stabilizing at 246.60 kHz. As can be seen from Figures 8(a) and 8(b), when the secondary resonant capacitor is reduced to 0.8 times the initial capacitance value, the two resonant frequency points of the system change. At this point, there is a resonant frequency point with a significantly larger amplitude (179.61 kHz), which is then used as the third resonant frequency point, and the system is switched to this third resonant frequency point (the system's autonomous stable frequency). As can be seen from Figures 9(a) and 9(b), when the secondary resonant capacitor is increased to 1.2 times the initial capacitance value, the two resonant frequency points of the system change. At this point, there is a resonant frequency point with a significantly larger amplitude (239.79 kHz), which is then used as the fourth resonant frequency point, and the system is switched to this fourth resonant frequency point (the system's autonomous stable frequency). When the system first switches, it is unstable, and you can see that the system's resonant frequency is slightly different from the corresponding third and fourth resonant frequency points.

[0064] Comparing Figures 7(a), 7(b), 8(a), 8(b), 9(a), and 9(b), when the threshold tol is uniformly set to 0, changing the effective value of the secondary resonant circuit capacitor allows for free control of the switching of the system's autonomous stable frequency, unaffected by the system's initial value. This verifies the effectiveness of the second method proposed in this embodiment.

[0065] This invention can be applied to scenarios where the receiver's position is not fixed and may change, such as wireless charging for drones and UUVs (Unmanned Aerial Vehicles). For a wireless charging system for a drone or underwater robot, the transmitter and receiver are typically not perfectly aligned, and the coupling mechanism often experiences misalignment and other suboptimal operating states. These different operating states directly determine the system's power transmission capability and efficiency. In situations with a large range of coupling mechanism misalignment, the ability to freely switch the self-excited frequency is particularly important, significantly improving the system's misalignment adaptability compared to existing single-resonant-frequency system design methods.

[0066] When a multiresonant system is operating normally, its current operating state is obtained by detecting the coupling coefficient. In practical applications, directly measuring the offset between the transmitting and receiving coils is difficult, making direct measurement of the coupling coefficient challenging. This patent addresses this by sampling the transmitting current and DC input voltage and calculating their effective values. Combined with other known system parameters and the derivation formula for the coupling coefficient, the coupling coefficient between the two coils can be estimated in real time. Furthermore, using power transfer characteristics as the optimization objective, the microcontroller sets a threshold or detunes the system, thereby switching to an ideal and suitable self-excited oscillation frequency. Once the coupling mechanism position is determined, meaning the system's operating state no longer changes, charging continues until completion.

[0067] Corresponding to the above system, the present invention also provides a self-excited frequency control system for a string-compensated WPT system, including a primary-side current and voltage acquisition module and a primary-side controller.

[0068] The primary current and voltage acquisition module is used to acquire the primary current i1 and inverter output voltage v1 of the string-compensated WPT system and send them to the primary controller.

[0069] The primary-side controller is used to execute steps S1 to S8 in the above method.

[0070] In summary, the self-excited frequency control method and system for a series-compensated WPT system provided by this invention obtains the current operating state of the system by detecting the coupling coefficient. Then, using power transfer characteristics as the optimization target, the system is brought into a detuned state by setting a threshold or adjusting the resonant capacitor value, thereby switching to the ideal self-excited oscillation frequency. When the position of the coupling mechanism is determined, i.e., the system operating state no longer changes, charging continues until charging is complete. This invention enables free switching of the self-excited frequency of the series-compensated WPT system, unaffected by the initial state of the system. It is convenient to operate and simple to control, enabling the system to output more stably under varying coupling coefficients, while operating in a weakly inductive state. Compared with existing single-resonant frequency system control methods, it can significantly improve the system's offset adaptability.

[0071] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A self-excited frequency control method for a string-compensated WPT system, characterized in that, Including the following steps: S1. Detect the coupling coefficient of the string-compensated WPT system and obtain the working state of the string-compensated WPT system based on the coupling coefficient; S2. Determine whether the working state of the string-to-string compensation type WPT system is single-mode or multi-mode at this time. If it is multi-mode, proceed to step S3; if it is single-mode, return to step S1. S3. Detect the primary current of the string-compensated WPT system. With inverter output voltage ,generate / The amplitude-frequency phase curve is used to determine the first and second resonant frequency points from low to high. S4. Determine whether the difference between the amplitude of the first resonant frequency point and the amplitude of the second resonant frequency point is greater than a preset value. If yes, proceed to steps S5 and S6; otherwise, proceed to step S7. S5, according to / The phase curve in the amplitude-frequency phase curve is set with a first resonant frequency point, a first threshold, and a second resonant frequency point, a second threshold; the first threshold is set to the sine value of the phase angle at the maximum point of the phase curve in the amplitude-frequency phase curve, and the second threshold is set to the sine value of the phase angle at the minimum point of the phase curve in the amplitude-frequency phase curve. S6. Using the first threshold or the second threshold as the threshold for primary-side current detection, control the primary-side inverter circuit of the string-compensated WPT system so that the resonant frequency of the system is stabilized at the first resonant frequency point or the second resonant frequency point. S7. Set the threshold for primary current detection to 0, and adjust the effective value of the primary or secondary resonant capacitor of the series-compensated WPT system to stabilize the system's resonant frequency at the third or fourth resonant frequency point; when the effective value of the secondary resonant circuit capacitor is adjusted to A times the initial capacitance value, the system's resonant frequency stabilizes at the third resonant frequency point, where A < 1. The third resonant frequency point is the value after adjusting the effective value of the secondary resonant circuit capacitor. / The resonant frequency point with a larger amplitude in the amplitude-frequency-phase curve; when the effective value of the secondary resonant circuit capacitor is adjusted to be B times the initial capacitance value, the resonant frequency of the control system stabilizes at the fourth resonant frequency point, where B >

1. The fourth resonant frequency point is the resonant frequency point after adjusting the effective value of the secondary resonant circuit capacitor. / The resonant frequency point with a larger amplitude in the amplitude-frequency phase curve.

2. The self-excited frequency control method for a string-to-string compensated WPT system according to claim 1, characterized in that: In step S1, the coupling coefficient between the coupling mechanisms is estimated in real time by sampling the transmitter current and DC input voltage and calculating their effective values, combined with other known system parameters and the derivation formula of the coupling coefficient.

3. The self-excited frequency control method for a string-to-string compensated WPT system according to claim 1, characterized in that, The step S7 is followed by the following step: S8. Determine whether the working state of the string-to-string compensation type WPT system has changed. If not, continue charging until charging is complete. If yes, return to step S1.

4. A self-excited frequency control system for a series-compensated WPT system, characterized in that: Includes a primary-side current and voltage acquisition module and a primary-side controller; The primary current and voltage acquisition module is used to acquire the primary current of the string-compensated WPT system. With inverter output voltage And send it to the primary edge controller; The primary-side controller is used to execute steps S1 to S7 as described in any one of claims 1 to 3.

5. The self-excited frequency control system for a series-compensated WPT system according to claim 4, characterized in that: The primary-side controller is also used to perform step S8 as described in claim 3.

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