Constant-voltage output three-coil wireless power transmission system and parameter determination method thereof

Abstract

The invention discloses a constant-voltage output three-coil wireless power transmission system and a parameter determination method thereof, and the system consists of a Buck-Boost circuit, a high-frequency full-bridge inverter circuit, a transmitting / relay / receiving resonator, a rectification filter circuit and a variable load, and is provided with a control unit. The Buck-Boost circuit adjusts output voltage, the high-frequency inverter circuit converts direct current into high-frequency alternating current, and energy wireless transmission is achieved through the three resonators. The system is characterized in that current and voltage parameters are analyzed by using a non-Hermite physics theory, so that the optimal output voltage value of the Buck-Boost circuit is determined, high-efficiency and stable voltage output is realized under different load conditions, and bilateral communication or receiving side control is not needed. According to the design, the system complexity is simplified, and meanwhile the energy transmission efficiency and stability are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless energy transmission, and in particular relates to a constant voltage output three-coil wireless energy transmission system and a parameter determination method thereof. Background Art

[0002] Wireless power transfer (WPT) technology usually refers to a power transmission method that uses electromagnetic fields as relay energy to transmit electric energy from the transmitter to the receiver in a non-contact manner. This technology can effectively solve many problems caused by traditional wired power transmission methods, such as cable wear, safety hazards, and wiring difficulties in special environments. With the rapid development of power electronics technology, electromagnetic field theory, microwave technology and other fields, wireless power transmission technology has made significant progress. In particular, the introduction of magnetically coupled resonant wireless power transmission technology has laid a solid foundation for the practical application of wireless power transmission technology. Magnetic coupled resonant wireless power transmission is a relatively popular wireless power transmission method. Its principle is that when the resonant system frequencies of the transmitter and the receiver match, efficient transmission of electric energy can be achieved. This method has a long transmission distance and is not affected by non-magnetic obstacles. It is suitable for medium-distance power transmission. With the popularization of modern electronic products such as portable electronic devices, electric vehicles, and implantable medical devices, there is an urgent need for safe, convenient and efficient charging methods. Wireless power transmission technology has become an ideal choice to meet these needs with its advantages such as no need for physical connection, ability to penetrate various obstacles, and suitability for a variety of complex environments. However, in existing wireless power transmission systems, traditional SiC NMOS transistors are generally used as key components of full-bridge inverter circuits. Due to inherent physical limitations, such transistors have insufficient performance in terms of operating frequency, switching loss, thermal performance, and power density, resulting in low system efficiency and difficulty in achieving stable constant voltage output. In addition, traditional wireless power transmission systems rely on bilateral communication and receiving-side control to adjust the output voltage, which increases the complexity and cost of the system. More importantly, when the load changes, this design has a slow response speed and cannot accurately predict and adapt to the dynamic changes of the load in a timely manner, affecting the efficiency and stability of power transmission. Therefore, when faced with different load conditions, it is difficult for existing technologies to simultaneously ensure high efficiency and stable output voltage, especially in the application scenario of medium-distance wireless power transmission, where these shortcomings are particularly prominent. Summary of the invention

[0003] The purpose of the embodiment of the present invention is to provide a constant voltage output three-coil wireless power transmission system, which adopts GaN transistors and a transmitting side control strategy to achieve high-efficiency and stable constant voltage output wireless power transmission under different load conditions without the need for bilateral communication and receiving side control.

[0004] The second object of the present invention is to provide a method for determining the parameters of a constant-voltage output three-coil wireless power transmission system.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is that a constant-voltage output three-coil wireless power transmission system includes:

[0006] A main circuit unit, including a Buck-Boost circuit, a full-bridge inverter circuit, a transmitting resonator, a relay resonator, a receiving resonator, and a variable load R connected in sequence L ;

[0007] And,

[0008] A transmitting-side control unit, including an output voltage control module and a negative resistance control module;

[0009] The input end of the Buck-Boost circuit is connected to a DC power supply, and the output end is connected to the input end of the full-bridge inverter circuit;

[0010] The input end of the transmitting resonator is connected to the output end of the full-bridge inverter circuit, and a relay resonator is arranged between the output end of the transmitting resonator and the input end of the receiving resonator; the relay resonator realizes energy transmission through magnetic field energy coupling;

[0011] The output end of the receiving resonator is provided with a variable load R L 。

[0012] Further, the Buck-Boost circuit specifically includes:

[0013] A storage inductor L0, a switching tube S0, a diode D0, and an output filter capacitor C0, where: the gate G0 of the switching tube S0 is connected to the transmitting-side control unit, and the on and off of the switching tube S0 form two loops: the first loop is composed of the storage inductor L0 and the DC voltage V IN Connected in series, the second loop is composed of the storage inductor L0 in series with the diode D0, and then in series with a circuit formed by the parallel connection of the capacitor C0 and the three-coil magnetic coupling resonance circuit.

[0014] Further, the transmitting resonator includes a series loop composed of a transmitting inductor L1 and a first tuning capacitor C1;

[0015] The relay resonator includes a series loop composed of a relay inductor L2 and a second tuning capacitor C2;

[0016] The receiving resonator includes a series loop composed of a receiving inductor L3 and a third tuning capacitor C3;

[0017] The full-bridge inverter circuit includes:

[0018] The center point between the left and right bridge arms of the full-bridge inverter circuit is connected in parallel with the series circuit composed of the transmitting coil L1 and the first tuning capacitor C1;

[0019] Among them, the transmitting coil L1 is coupled in the same direction as the relay coil L2, and the relay coil L2 is coupled in the same direction as the receiving coil L3.

[0020] Furthermore, the full-bridge inverter circuit uses GaN transistors to construct a full-bridge topology.

[0021] Furthermore, the negative resistance control unit includes a current sampler, a differential amplifier, a filter, a zero-crossing comparator, and a dead-time generation circuit connected in sequence; the output voltage control unit includes a digital signal processor.

[0022] A method for determining the parameters of a constant-voltage output three-coil wireless power transmission system includes the following processes:

[0023] S1. Design the parameters of the three-coil magnetic coupling resonance circuit and the relationships between the parameters according to the rated load and output voltage on the receiving side;

[0024] S2. Design the coil size, spatial structure, and winding method according to the parameters of the three-coil magnetic coupling resonance circuit and in combination with the coil transmission distance;

[0025] S3. Determine the load -R N on the transmitting side of the three-coil magnetic coupling resonance circuit, and sample the amplitude and phase information of the voltage and current on the transmitting side to complete the estimation of the actual load size and determine the optimal output voltage value of the Buck-Boost circuit;

[0026] S4. Determine the parameters of each component of the Buck-Boost circuit, including the energy storage inductor L0 and the output filter capacitor C0;

[0027] S5. Design the system according to the parameters of each component of the three-coil wireless power transmission system determined in S4 and conduct experimental verification, and adjust the parameters of each component of the three-coil wireless power transmission system through the experimental results;

[0028] S6. According to the experimental data obtained in S5, use the data fitting method to determine the model between the output voltage and the operating frequency of the Buck-Boost circuit, and modify the output voltage value of the Buck-Boost circuit based on the curve to make the power transmission system output a constant voltage.

[0029] Furthermore, the specific process of S1 is as follows:

[0030] S101. Determine the self-inductance L and mutual inductance M of the resonator coil ij :

[0031]

[0032] Among them, μ0 is the magnetic permeability of vacuum, μ r is the relative magnetic permeability of the medium where the coil is located, N is the number of turns of the coil, A is the cross-sectional area of the coil, and l is the average perimeter of the coil;

[0033]

[0034] Among them, k ij is the coupling coefficient;

[0035] S102. Determine the relationship between the diameter d of the Litz wire and the coil resistance:

[0036] The DC resistance R of the coil dc and the AC resistance R of the coil ac :

[0037]

[0038] Among them, ρ is the resistivity of the Litz wire, l total is the total length of the Litz wire, A wire is the effective cross-sectional area of the Litz wire, and A eff is the effective cross-sectional area affected by the skin effect;

[0039] S103. Determine the relationship between the tuning capacitors C1, C2, C3, the self-inductance L of the coil, and the operating frequency f:

[0040] f = 2πL i ·C i , i = 1, 2, 3

[0041]

[0042] Among them, i and j are index variables.

[0043] Furthermore, the specific process of the S2 is as follows:

[0044] First, determine that the winding mode of the coil is spiral forward, the compensation mode of the tuning capacitor is segmented compensation, and determine the diameter D c , the number of turns N:

[0045]

[0046] Among them, L is the self-inductance of the coil, μ0 is the magnetic permeability of vacuum, and π is the ratio of the circumference of a circle to its diameter; finally, verify through simulation tool experiments and determine the coil turn spacing s according to the simulation results.

[0047] Furthermore, the specific process of the S3 is as follows:

[0048] S301. Determine the relationships among the inductance, tuning capacitance, current, and input voltage of the transmitting resonator, relay resonator, and receiving resonator:

[0049]

[0050] Among them, L1, L2, and L3 are the inductances of the transmitting resonator, relay resonator, and receiving resonator respectively, and v C1 , v C2 , v C3 are the voltages across the capacitors in the transmitting resonator, relay resonator, and receiving resonator respectively, and i1, i2, and i3 are the currents of the transmitting resonator, relay resonator, and receiving resonator respectively; M 12 is the mutual inductance between the transmitting resonator and the relay resonator, and M 23 represents the mutual inductance between the relay resonator and the receiving resonator; C1, C2, and C3 are the tuning capacitors of the transmitting resonator, relay resonator, and receiving resonator respectively, r1, r2, and r3 are the parasitic resistances of the transmitting resonator, relay resonator, and receiving resonator respectively, and v1 is the input voltage of the transmitting resonator; R L is the variable load resistance;

[0051] S302. Determine the voltage v L across the coil:

[0052]

[0053] Among them, θ is the phase of the resonator, i represents the actual current flowing through the coil, I represents the maximum value of the current, ω represents the resonance frequency, and t represents time;

[0054] S303. Define the energy mode of an independent LC resonator without mutual coupling as:

[0055]

[0056] Among them, A represents the amplitude of the energy mode, a represents the energy mode of the resonator, + is the phase symbol, j is the imaginary symbol, and e is the base of the natural logarithm;

[0057] S304. Determine that the third-order wireless power transfer system satisfies the equation according to the energy definition in S303:

[0058]

[0059]

[0060] H is the effective Hamiltonian operator, a represents the energy mode of the resonator, + is the phase, γ refers to the total loss of the receiving resonator, and γ sn(n = 1, 2, 3) represents the inherent loss of the resonator, k 12 represents the coupling coefficient between the transmitting resonator and the relay resonator, k 23 represents the coupling coefficient between the relay resonator and the receiving resonator, g represents the net gain of the system, ω0 is the self-resonant frequency of the resonator,

[0061] S305. Solve the equations of the third-order wireless power transfer system to determine the eigenvalues:

[0062] ω s1 = ω0

[0063]

[0064] where c2 and c0 are intermediate parameters, ω s1 , ω s2,3 , ω s4,5 are the different operating frequencies of the system;

[0065] S306. Use Fourier transform to represent the amplitude V 1m of the fundamental component of the voltage of the load on the voltage transmitting side as:

[0066]

[0067] S307. Accurately determine the negative resistance value R N of the load on the voltage transmitting side according to the DC voltage and the transmitted current:

[0068]

[0069] where V DC is the output voltage of the Buck - Boost circuit, I 1m represents the current amplitude of the transmitting resonator;

[0070] S308. Determine the total loss γ of the receiving resonator in different modes:

[0071]

[0072] a = g - r s2

[0073]

[0074] where a, b, and c are intermediate coefficients;

[0075] Obtain the predicted value R L,est of the load resistance size as:

[0076] R L,est = ω0L3(γ - γ s3 )

[0077] The current relationship between the transmitter and the receiver can be obtained through the circuit equations:

[0078]

[0079] where ω is the actual operating frequency of the circuit, and G I13 is an intermediate parameter representing the relationship between the current amplitudes of the transmitting resonator and the receiving resonator, and I 3m represents the current amplitude of the receiving resonator.

[0080] According to the required DC output voltage V L for the load R L,set , the required current amplitude of the receiver is determined as:

[0081]

[0082] where V 3m,set is the target amplitude of the fundamental frequency component of the actual voltage of the receiving resonator, and R L,est is the estimated load;

[0083] S309. Determine the DC voltage V DC,set to be set:

[0084]

[0085] where V 1m,set is the target amplitude of the fundamental frequency component of the actual voltage of the transmitting resonator.

[0086] where the specific process of S4 is as follows:

[0087] S401. Assume that the switching transistor and the diode are ideal devices, with zero voltage drop when conducting, capable of instantaneous conduction or instantaneous cut-off, and no leakage current when cut-off; the inductor and capacitor are ideal components, the inductor operates in the linear region without saturation, the parasitic resistance is 0, and the equivalent series resistance of the capacitor is also 0;

[0088] S402. After the switching transistor S0 is turned on, the diode D0 is reverse-biased and cut off, and the input voltage V IN is applied across the inductor L0, with the polarity positive at the top and negative at the bottom, and the energy stored in the inductor current increases. Among them, the increase in the inductor current is:

[0089]

[0090] where D is the duty cycle of the pulse wave, T0 is the period of the pulse wave, T ON represents the switching-on time within one period, and L c is the critical inductance value;

[0091] S403. After the switch tube S0 is turned off, the inductor current decreases, and the inductor coil generates a self-induced back electromotive force, which is negative at the top and positive at the bottom. The diode D0 conducts under the forward voltage. The inductor charges the capacitor through the diode, and the capacitor stores energy to discharge to the load to maintain the load output V when the switch tube is turned on. DC The voltage remains unchanged. Among them, the reduction amount of the inductor current is:

[0092]

[0093] S404. Determine the critical inductance value L c and the size of the energy storage inductor L0:

[0094]

[0095] L0 = 1.3×L c

[0096] S405. In the continuous inductor current mode of the Buck - Boost DC conversion circuit, if the ripple voltage requirement is ΔU, the value of the output - side filter capacitor is:

[0097]

[0098] Among them, I o is the average value of the output current of the Buck - Boost circuit.

[0099] Compared with the prior art, the beneficial effects of the present invention are as follows: By optimizing the control algorithm and circuit design, the present invention realizes stable voltage output in a wide load range, solves the problem of output voltage fluctuation caused by load change in the existing three - coil system, and improves the applicability and reliability of the system. Using a gallium nitride switch - tube full - bridge inverter circuit as the inverter power supply for three - coil wireless power transmission improves the working frequency and response speed of the wireless power transmission system, and effectively addresses the limitations of the traditional bridge - type inverter circuit in medium - distance wireless power transmission applications. In addition, compared with traditional SiC NMOS transistors, gallium nitride switch tubes have better performance in terms of working frequency, switching loss, thermal performance, and power density, which helps to improve system efficiency and achieve more stable constant - voltage output. This technology reduces the dependence on bilateral communication and the control of the receiving side to adjust the output voltage, simplifies the system structure, reduces costs, and enhances the response speed and adaptability of the system to dynamic load changes, thereby improving the efficiency and stability of power transmission. Especially in the application scenario of medium - distance wireless power transmission, these improvements significantly enhance the overall performance of the system. Description of the Drawings

[0100] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0101] Figure 1 is the circuit schematic diagram of a three - coil wireless power transfer system.

[0102] Figure 2 shows the load characteristics based on non - Hermitian theory; among them, (a) is the real and imaginary parts of the normalized eigenvalue, and (b) is the corresponding gain of the system.

[0103] Figure 3 is the mapping of the system gain and the normalized eigenvalue based on the frequency response and energy minimization principle; among them, (a) is the real and imaginary parts of the normalized eigenvalue, and (b) is the corresponding gain of the system.

[0104] Figure 4 Schematic diagram of the negative resistance control unit, where (a) is the equivalent circuit of the full - bridge inverter and the control schematic diagram of the negative resistance control unit, and (b) is the actual control circuit of the self - feedback negative resistance.

[0105] Figure 5 is the system block diagram of the output voltage closed - loop control unit.

[0106] Figure 6 is the scatter plot of the system operating frequency f when the load changes.

[0107] Figure 7 is the output voltage V of the system when the load changes 3,RMS and the comparison diagram of the theoretical and actual efficiency.

[0108] Figure 8 is the load resistance R L When it is 10Ω, the voltage - current waveforms of the transmitting side and the receiving side.

[0109] Figure 9 is the load resistance R L When it is 35Ω, the voltage - current waveforms of the transmitting side and the receiving side.

[0110] Figure 10 is the load resistance R L When it is 40Ω, the voltage - current waveforms of the transmitting side and the receiving side.

[0111] Figure 11 is the load resistance R L When it is 75Ω, the voltage - current waveforms of the transmitting side and the receiving side.

[0112] Figure 12 is a circuit schematic diagram of a three - coil system containing a negative resistance -R N . Specific implementation manners

[0113] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0114] As Figure 1 This embodiment provides a constant - voltage output three - coil wireless power transfer system, specifically a constant - voltage output three - coil wireless power transfer system based on transmitter - side control. Using GaN (gallium nitride) transistors to replace traditional SiC (silicon carbide) NMOS transistors in the full - bridge inverter circuit significantly improves the performance of the system. The system in this embodiment can monitor the voltage and current parameters at the transmitter end in real time, and use the coupled - mode theory to estimate the load changes, and then automatically adjust the output voltage of the Buck - Boost converter to meet the expected output voltage requirements, without relying on bilateral communication or receiver - side control mechanisms throughout the process.

[0115] As Figure 1 , in some specific implementation manners, the constant - voltage output three - coil wireless power transfer system consists of a main - circuit unit and a transmitter - side control unit. The main circuit includes a Buck - Boost circuit, a high - frequency full - bridge inverter circuit, a transmitting resonator, a relay resonator, a receiving resonator, and a variable load R L . The Buck - Boost circuit is connected to an external DC power supply and is used for step - up and step - down conversion; the input end of the high - frequency full - bridge inverter circuit is connected to the output end of the Buck - Boost circuit and is used for converting direct current into high - frequency alternating current; the input end of the transmitting resonator is connected to the output end of the high - frequency full - bridge inverter circuit, the relay resonator realizes energy transfer through magnetic - field energy coupling, and the receiving resonator is connected to the variable load R L and is used for adjusting and compensating the output power of the high - frequency full - bridge inverter circuit.

[0116] The transmitter - side control unit determines the optimal output voltage value of the Buck - Boost circuit by sampling the current and voltage parameters in the actual circuit and using non - Hermitian physics theory, so as to achieve the purpose of constant - voltage output of the system, without the need for bilateral communication and receiver - side control, and can achieve high transmission efficiency and stable output voltage under different load conditions.

[0117] In some specific embodiments, the Buck - Boost circuit includes a DC input power supply, a storage inductor L0, a switching transistor S0, a diode D0, and an output filter capacitor C0. Among them: the gate G0 of the switching transistor S0 is connected to the transmitting - side control unit. The conduction and turn - off of the switching transistor S0 form two loops: the first loop is composed of the series connection of the storage inductor L0 and the DC voltage V in in series, and the second loop is composed of the series connection of the storage inductor L0, the diode D0, and then the series connection of a circuit formed by the parallel connection of the capacitor C0 and the three - coil magnetic - coupling resonance circuit.

[0118] In some specific embodiments, the center point between the left and right arms of the high - frequency full - bridge inverter circuit is connected to a series loop composed of a transmitting inductor L1 and a first tuning capacitor C1. The transmitting inductor L1 is coupled in the same direction as the relay inductor L2. The relay inductor L2 and the second tuning capacitor C2 form a series loop. The relay coil L2 is coupled in the same direction as the receiving inductor L3. The receiving inductor L3 and the third tuning capacitor C3 form a series loop.

[0119] In some specific embodiments, the transmitting - side control system includes an output - voltage control unit and a negative - resistance control unit; the specific structure is as shown in Figure 4 , Figure 5. Among them, the core of the negative - resistance control unit is to make the output port of the inverter present a pure - resistive impedance characteristic through real - time closed - loop regulation, realize the in - phase relationship between the output voltage and the current, and eliminate the reactive component; Figure 5 Shown in is the Buck - Boost output - voltage control strategy. It adopts a multi - parameter sampling and detection technique. By real - time collecting the working - state parameters of the converter (including input voltage, inductor current, output voltage, etc.), and determining them using non - Hermitian physics theory, to set the optimal output - voltage value of the Buck - Boost circuit; in some possible embodiments, the output - voltage control unit uses a TMS320F28335 digital signal processor to complete the control function.

[0120] In some possible embodiments, the negative - resistance control unit first samples the transmitting current through a current - sampling unit CU8965 and converts it into a voltage signal. Subsequently, a square - wave signal is generated through a zero - crossing comparator TL3016. Then, the driver Si8271 outputs driving signals G 1,4 and G 2,3 . In addition, in order to achieve impedance matching and signal amplification, this embodiment uses a differential amplifier OPA690. The propagation delay of the control circuit is compensated by a phase - compensator, and the dead - time generation circuit (74VHC132) is responsible for converting the square - wave signal into two complementary driving signals with dead - time.

[0121] This embodiment also provides a method for determining the parameters of each component of the constant-voltage-output three-coil wireless power transmission system circuit, specifically:

[0122] Step S1: Design the parameters of the three-coil magnetically coupled resonant circuit according to the rated load and output voltage on the receiving side, including the self-inductance of the coil, the mutual inductance of the coils, the wire diameter of the Litz wire used for the coil, and the size of the tuning capacitor;

[0123] In the three-coil magnetically coupled resonant circuit, the three coils are the transmitting coil (coil 1), the relay coil (coil 2), and the receiving coil (coil 3). In this embodiment, the specifications of the three coils are basically the same. The parameters of the three-coil magnetically coupled resonant circuit are designed according to the following relationship and in combination with actual needs (meeting the transmission distance and providing the energy required by the load):

[0124] 1. Determination of coil self-inductance and mutual inductance

[0125] For each coil, its self-inductance L can be approximately determined by the following formula:

[0126]

[0127] where μ0 is the permeability of free space, μ r is the relative permeability of the medium where the coil is located, N is the number of turns of the coil, A is the cross-sectional area of the coil, and l is the average perimeter of the coil.

[0128] The mutual inductance M between two coils ij can be determined by the following formula:

[0129]

[0130] It can be seen that the mutual inductance is proportional to the geometric mean of the self-inductances of the two interacting coils and is affected by the coupling coefficient. When the coupling coefficient is larger, the mutual inductance is larger; vice versa.

[0131] 2. Determine the relationship between the wire diameter d of the Litz wire and the coil resistance R

[0132] The Litz wire is composed of multiple strands of fine wires twisted together. Its wire diameter directly affects the resistance of the coil. In principle, the smaller the wire diameter of the Litz wire used for the coil, the better. The specific selection needs to be combined with actual needs. The DC resistance R of the coil dc and the AC resistance R ac can be estimated by the following formula:

[0133]

[0134] where ρ is the resistivity of the Litz wire, l total is the total length of the Litz wire, A wire is the effective cross-sectional area of the Litz wire, A effIt is the effective cross-sectional area under the influence of the skin effect. By reasonably selecting the wire diameter d and the number of turns N of the Litz wire, the DC resistance and AC resistance of the coil can be optimized, thereby improving the performance of the wireless energy transmission system.

[0135] 3. Relationship between the tuning capacitors C1, C2, C3, the self-inductance of the coil, and the operating frequency f

[0136] To make the three coils reach the resonant state, tuning capacitors need to be connected in parallel across each coil. The size of the tuning capacitor can be determined by the following resonance condition:

[0137] f = 2πL i ·C i , i = 1, 2, 3

[0138]

[0139] It can be seen that the tuning capacitor is inversely proportional to the self-inductance of the coil and inversely proportional to the square of the operating frequency. When the self-inductance of the coil is larger, the required tuning capacitor is smaller; vice versa. At the same time, the higher the operating frequency, the smaller the required tuning capacitor.

[0140] For example, in the design process, first determine that the transmission distance is 80 cm, that is, the distance between the coils is 40 cm, the operating frequency is 1 MHz, the actual Litz wire is selected as 1500 strands of copper wire with a wire diameter of 0.05 mm, and the self-inductance of the coil and the size of the tuning capacitor are determined to be 106.32 μH and 243.08 pF respectively. The rest of the parameter values are estimated values and are affected by the actual spatial structure.

[0141] Step S2: According to the parameters of the three-coil magnetic coupling resonance circuit, combined with the coil transmission distance, design the coil size, spatial structure, and winding method;

[0142] In some specific embodiments, the relationship between the self-inductance and the tuning capacitor of the coil is determined based on the resonance relationship formula among the self-inductance of the coil, the tuning capacitor, and the resonance frequency of the coil; according to the energy transfer efficiency model between the coils in the three-coil system, the specific values of the self-inductance and mutual inductance of the coil are determined; after determining the self-inductance of the coil, the size of the tuning capacitor is deduced backward according to the resonance frequency formula, and finally, according to the electromagnetic field theory, it is determined how to wind this coil to meet the requirements of the self-inductance of the coil. According to the requirements of the transmission distance, the geometric structure and relative position of the coil are further adjusted to determine the size of the mutual inductance of the coil; in this embodiment, designing the parameters of the three-coil magnetic coupling resonance circuit is a process that comprehensively considers the rated load, output voltage, transmission distance, self-inductance and mutual inductance of the coil, the wire diameter of the Litz wire, and the size of the tuning capacitor. These parameters are interrelated and need to be iterated and optimized to achieve the best power transmission efficiency and system performance. The final design scheme should ensure that the system can operate stably under specified conditions and achieve efficient wireless energy transmission.

[0143] In this embodiment, it is first determined that the winding mode of the coil is spiral forward, and the compensation mode of the tuning capacitor is segmented compensation. Currently, the parameters to be determined are the coil diameter D c , the number of turns N, and the coil turn spacing s. Among them, the selection of the coil diameter D c is relatively free and reasonable. We choose the coil diameter to be 40 cm. The selection of the number of turns is related to the self-inductance diameter of the coil, and its determination method is as follows:

[0144]

[0145] It is determined that the number of turns of the coil is 13. A tuning capacitor is connected in series with each turn of the coil. Finally, through simulation tools (such as ANSYS Maxwell, COMSOL, etc.) and experimental verification, the coil turn spacing s is determined, and the design parameters are optimized and iterated to achieve the best power transfer efficiency and system performance.

[0146] Step S3: According to the non-Hermitian physics theory of the three-coil system, determine the load - R on the transmitting side of the three-coil magnetic coupling resonance circuit N , and sample the amplitude and phase information of the voltage and current on the transmitting side to complete the estimation of the actual load size, and further determine the optimal output voltage value of the Buck - Boost circuit;

[0147] The equivalent circuit of the three-coil series-compensated WPT system is as Figure 12 shown. The negative resistance - R in the system N acts as a gain element and can provide a stable input voltage v1. In addition, L n , C n , r n and i n (n = 1, 2, 3) represent the inductance, tuning capacitor, parasitic resistance, and current of the transmitter, relay, and receiver resonators respectively. Among them, the mutual inductance M 12 and M 23 between adjacent resonators are represented, while the mutual inductance M 12 between the transmitter and receiver resonators is assumed to be negligible. v3 represents the output voltage across the load resistance R L .

[0148] The transmitter resonator, relay resonator, and receiver resonator are respectively composed of inductance (L1, L2, L3), tuning capacitor (C1, C2, C3), parasitic resistance (r1, r2, r3), and current (i1, i2, i3). R L is the load resistance, and v1 is the voltage provided by the midpoint of two bridge arms of the full-bridge inverter to the transmitting coil, that is, the input voltage of the transmitter resonator; among them, M 12 and M 23represents the mutual inductance between adjacent resonators, while the mutual inductance between the transmitter and the receiver (i.e., M 13 ) is assumed to be negligible. For a third-order series resonant system (this system), v C1 v C2 v C3 are the voltages across the capacitors in the transmitting resonator, the relay resonator, and the receiving resonator respectively. There is the following system of equations:

[0149]

[0150] In an LC series resonant circuit with a resonant frequency ω, once the current in the resonator is determined, the voltage across the inductor can be determined.

[0151]

[0152] where θ is the phase of the resonator, i represents the actual current flowing through the coil, I represents the maximum value of the current, ω represents the resonant frequency, and t represents time;

[0153] Based on the coupled mode theory (CMT), the energy mode of an independent LC resonator without mutual coupling in this embodiment can be defined as:

[0154]

[0155] where A represents the amplitude of the energy mode, a represents the energy mode of the resonator, + is the phase symbol, j is the imaginary symbol, and e is the base of the natural logarithm; this indicates that the phase of the resonator is associated with the amplitude of the energy mode. Accordingly, another conclusion can be further inferred in this embodiment: the interaction between resonators can be described by a specific relationship. To simplify the model, three resonators with the same natural resonant frequency are designed in this embodiment to construct a third-order wireless power transfer (WPT) system. Under the assumption that the coupling coefficients are equal, the actual third-order system can be simplified to the following system of first-order differential equations by the coupled mode theory:

[0156]

[0157] H is the effective Hamiltonian operator. In this embodiment, a = [a1, a2, a3] T represents the energy mode of the resonator, g = g N -γ s1 = (R N - r1) / (ω0L1) represents the net gain of the system, γ = γ l +γ s3 = (R Leq + r3) / (ω0L3) refers to the total loss of the receiving resonator, γsn = r n / (ω0L n )(n = 1, 2, 3) represents the inherent loss of the resonator, and and respectively represent the coupling coefficients between adjacent resonators, where -R N is the equivalent resistance of the output port of the full-bridge inverter circuit (i.e., the load on the transmitting side of the three-coil magnetic coupling resonance circuit), which is used as the input of the three-order wireless power transmission system in this embodiment, and ω0 is the self-resonant frequency of the transmitting, relay, and receiving resonators.

[0158] To determine the eigenvalues of the system, the characteristic equation must be solved. By simplifying the equation det(ωI - H) = 0 (where I represents the identity matrix), we can obtain:

[0159]

[0160] where is the frequency perturbation, is the normalized eigenvalue, c = g - γ s2 -γ. By setting the real and imaginary parts to zero respectively to solve the equation, we can obtain:

[0161]

[0162] Combining the above two equations, we can obtain:

[0163]

[0164] By solving the characteristic equation, the eigenvalues can be obtained, and their expression is:

[0165] ω s1 = ω0

[0166]

[0167] where Different system parameters, such as coupling coefficients, resonant frequencies, and losses, determine the characteristic modes of the system, and each mode has its unique eigenvalue and gain. According to the principle of energy minimization, the system tends to operate in the mode with the minimum gain. When the load resistance is less than the critical value under the condition of a fixed coupling coefficient in the three-coil wireless power transmission system, the steady-state mode of the system is ω s1 ; when the load resistance is greater than the critical value, the steady-state mode of the system is ω s2 or ω s3 . The theoretical determination results of its operating frequency and system gain (principle of energy minimization) with respect to the load are shown in Figure 2 and 3 .

[0168] In some possible embodiments, the process of determining the output voltage of the Buck-Boost circuit on the transmitting side is as follows: The entire constant-voltage output three-coil wireless power transfer system is controlled by the transmitting side. By sampling the current I1 of the transmitting resonator and using the phase information of its current zero-crossing point to drive the four GaN (gallium nitride) switching tubes of the full-bridge inverter circuit, frequency feedback and phase tracking can be achieved, and the pure resistive characteristic of the equivalent resistance at the output port of the full-bridge inverter circuit can be satisfied to a great extent. Moreover, the negative resistance value -R can be accurately determined according to the DC voltage and the transmitted current. N ; Additionally, by sampling the output voltage V of the Buck-Boost circuit DC , the current amplitude I of the transmitting resonator 1m , the frequency ω, and the desired constant-voltage output voltage V L,set (rms value), the output voltage V of the Buck-Boost circuit can be determined. The specific circuit control scheme is as shown in DC,set Figs. Figure 4 (a), (b), Figure 5 etc.

[0169] Using Fourier transform, the amplitude of the fundamental component of the voltage v1 can be expressed as:

[0170]

[0171] Through the automatic tracking of the frequency, this embodiment ensures that the steady-state input impedance of the third-order system remains purely resistive. Therefore, this embodiment can accurately determine the negative resistance value according to the DC voltage and the transmitted current:

[0172]

[0173] Through the circuit equations, the relationships between the gain, loss, and coupling coefficient can be obtained. Based on these relationships, the corresponding losses of the system in different modes can be deduced.

[0174]

[0175] where a = g - r s2 , Thus, the predicted value of the load resistance size can be obtained as:

[0176] R L,est = ω0L3(γ - γ s3 )

[0177] Through the circuit equations, the current relationship between the transmitter and the receiver can be obtained:

[0178]

[0179] where ω is the actual operating frequency of the circuit, ω0 is the self-resonant frequency of the resonator, and G I13 is an intermediate parameter representing the relationship between the current amplitudes of the transmitting resonator and the receiving resonator, and I 3m represents the current amplitude of the receiving resonator.

[0180] According to the required AC output voltage of V L,set (rms value), the required current amplitude I 3m,set of the receiver is:

[0181]

[0182] where V 3m,set is the target amplitude of the fundamental frequency component of the actual voltage v3 of the receiving resonator, and R L,est is the estimated load. Based on the above equations, the DC voltage to be set is determined.

[0183]

[0184] where V 1m,set is the target amplitude of the fundamental frequency component of the actual voltage of the transmitting resonator.

[0185] The output voltage stable control strategy avoids complex bilateral wireless communication between the transmitter and the receiver, thus simplifying the system design and improving the response speed. This closed-loop control method, with appropriate adjustment, can also be applied to application scenarios that require constant current or constant power output.

[0186] Step S4: According to the frequency requirement of the inverter circuit and the input voltage ripple limit of the inverter side, determine the parameters of each component of the Buck-Boost circuit, including the energy storage inductor L0 and the output filter capacitor C0;

[0187] First, given the input voltage V IN , the output voltage V DC , according to the duty cycle D = V DC / (V DC + V IN )(which holds under the condition of continuous conduction mode CCM of the inductor current), given the switching period as T0, assuming the equivalent load at the output port of the Buck-Boost circuit is R, in order to facilitate the analysis of the steady-state characteristics of the boost circuit and simplify the derivation process of the formula, the following assumptions are made:

[0188] 1) The switching transistor and the diode are both ideal devices, that is, the voltage drop during conduction is not considered, and they can conduct or cut off instantaneously, and no leakage current is generated when they are cut off.

[0189] 2) Inductors and capacitors are ideal components. The inductor operates in a linear region approaching saturation with a parasitic resistance of 0, and the equivalent series resistance of the capacitor is also 0.

[0190] The critical inductor value L is determined through the following process c , the magnitudes of the energy storage inductor L0 and the output filter capacitor C0:

[0191] 1) After the switch S0 is turned on, the diode D0 is reverse-biased and cut off, and the input voltage V IN is applied across the inductor L0 with the polarity being positive at the top and negative at the bottom, and the energy stored in the inductor current increases. The increase in the inductor current is:

[0192]

[0193] where D is the duty cycle of the pulse wave, T0 is the period of the pulse wave, and T ON is the switch-on time within one period. Here, L c is the critical inductor value to ensure that the inductor operates in the DCM mode;

[0194] 2) After the switch S0 is turned off, the inductor current decreases, and the inductor coil generates a self-induced back electromotive force with the polarity being negative at the top and positive at the bottom. The diode D0 is forward-biased and conducts, and the inductor charges the capacitor through the diode. The capacitor stores energy to discharge to the load to maintain the load output voltage V DC constant when the switch is turned on. During this process, the decrease in the inductor current is:

[0195]

[0196] Within the entire switching period, the increase in the inductor current is equal to the decrease in the inductor current. In the critical state, i L = 2I o , I o = V DC / R = 2, and I o is the average value of the output current of the Buck - Boost circuit. The "-" is the phase symbol. In practical applications, the actual value of the inductor is generally taken as 1.2 - 1.3 times the critical value of the inductor.

[0197]

[0198] L0 = 1.3 × L c

[0199] In the Buck - Boost DC conversion circuit in the continuous inductor current mode, if the ripple voltage requirement is ΔU, the value of the output - side filter capacitor is:

[0200]

[0201] where VDC is the output voltage of the Buck - Boost circuit, and R is the load of the buck - boost circuit

[0202] Step S5: Design the system according to the determined parameters of each component in the circuit of the three - coil wireless power transfer system and conduct experimental verification. Further adjust the parameters of each component in the circuit of the three - coil wireless power transfer system based on the experimental results, including the dead - time generation circuit of the gallium nitride full - bridge inverter circuit, the transmitting - coil current leading - compensation module (i.e., Figure 4 (the filter in (b))), and the coil capacitance compensation parameters. The theoretical determination and experimental comparison results of the system in this embodiment are as Figure 6 , shown in Fig. 7. The oscilloscope waveforms under different loads are as Figures 8 - 11 shown, mainly including the input voltage and current waveforms of the transmitting coil (upper) and the load voltage and current waveforms (lower).

[0203] S6: According to the experimental data obtained in step S5, use the method of data fitting to obtain the mathematical model of the output voltage of the Buck - Boost circuit at the second operating frequency (i.e., when the load is relatively large). Through the analysis of the curve, modify the output voltage value of the Buck - Boost circuit in this case, and correct the error of the model at the second operating frequency to achieve the purpose of constant - voltage output.

[0204] Figures 8 - 11 shows the main measured waveforms at different load resistance values. It can be found that the voltage and current of the inverter are in the same phase, and soft - switching is achieved, thus providing an efficient switching - mode negative - resistance characteristic. Since the switching frequency is as high as MHz, gallium nitride transistors are used to minimize the switching losses, achieve faster switching speeds, and higher power densities. To reduce switching oscillations and minimize related losses, the parasitic inductance in the circuit layout must be minimized. Therefore, the full - bridge inverter in the system uses the first inner layer of the PCB as the power return path, which is located directly below the top - power loop to achieve the smallest power loop. From Figure 8 and Figure 9 it can be seen that a constant output voltage can be maintained within the low - loss region, which is consistent with our theoretical analysis. In addition, Figure 10 and 11 show another state of the system when operating in the high - loss region, that is, the efficiency decreases due to the oscillation - frequency deviation.

[0205] Figure 6 、 7Shows the operating frequency, transmission efficiency, overall efficiency, and output voltage at different load resistance values. The measured frequency, efficiency, and output voltage shown are in good agreement with the determined results. At the phase transition point, the operating frequency f changes by 0.01 MHz, which is consistent with the theoretical analysis. Over a wide load range, the change in the system frequency is small, thus reducing the requirement for the operating frequency range of the inverter. This provides the possibility for the application of high-frequency and high-efficiency inverters (such as class E inverters) in the self-excited oscillation wireless power transfer system. Interestingly, after switching to the high-loss region, the system efficiency does not decrease significantly, but when R L is close to zero, the efficiency drops rapidly. From this point of view, if the requirement for the stability of the operating frequency is not high, the system can have a wider high-efficiency load range. When R L = 35 Ω, the system has a peak transmission efficiency of 94.3%.

[0206] It can be seen from Figure 7 that the effective value of the output voltage based on the closed-loop control method remains at 48 V in the low-loss region, but increases with the increase of the load resistance in the high-loss region. The reason for this difference is that the coupled-mode theory ignores the influence of the high-order terms in the system characteristic equation. Therefore, when the operating frequency deviates from the natural resonance frequency, the estimated value of the load resistance is inaccurate, which leads to the deviation of the system output from the expected value. Therefore, the system controlled by the transmitting end is preferably operated in the ω1 mode. If the system mode can be adjusted by other methods to expand the load range or the coupling coefficient range of the ω1 mode, the stability and transmission efficiency of the system will be greatly improved. In addition, if the numerical solution can be derived according to the circuit model or the error correction can be carried out, the system output in the ω2 mode can be accurately controlled.

[0207] The system of this embodiment first accurately designs the key parameters of the three-coil magnetic coupling resonance circuit according to the rated load and output voltage on the receiving side, including the self-inductance of the coil, mutual inductance, the wire diameter of the litz wire, and the size of the tuning capacitor. The quality factor Q of the coil is 900. When the transmission distance of the coil is 80 cm, the transmission efficiency of the coil is around 90% when varying with the load, and the measured transmission power can reach 240 W, solving the problem of efficient energy transmission under medium-distance conditions.

[0208] According to the non-Hermitian physics theory of the three-coil system, determine the load - R N on the transmitting side of the three-coil magnetic coupling resonance circuit, and then match the output voltage of the Buck-Boost circuit according to the load size. This step provides a theoretical basis for the subsequent circuit design and achieves a constant voltage output under the variable load condition of 10 Ω - 75 Ω.

[0209] This embodiment proposes and implements an efficient third-order self-excited oscillation circuit system based on switched-mode negative resistance and transmitter output voltage control for wireless power transfer. A novel analysis method combining the coupled-mode model and circuit analysis is adopted to analyze the power transfer characteristics of the system. The proposed system can provide a nearly constant output voltage over a wide load variation range and achieve an efficiency of 94.3% at a transmission distance of 80 cm. The experimental results confirm the theoretical analysis and design steps. Based on non-Hermitian design, the operating frequency of the system is stable at around 1 MHz throughout the designed load region without any active regulation, thus providing great convenience for multi-type load access, system status detection, and electromagnetic compatibility design. This also provides a reliable and scalable framework for the practical application of wireless power transfer technology.

[0210] Each embodiment in this specification is described in a related manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and reference can be made to the relevant parts of the method embodiments for the relevant content.

[0211] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A constant-voltage-output three-coil wireless power transfer system, characterized in that Including: The main circuit unit includes a Buck-Boost circuit, a full-bridge inverter circuit, a transmitting resonator, a relay resonator, a receiving resonator, and a variable load R, which are connected in sequence L ; And, The transmitting side control unit includes an output voltage control module and a negative resistance control module; The input end of the Buck - Boost circuit is connected to a DC power supply, and the output end is connected to the input end of the full - bridge inverter circuit; The input end of the transmitting resonator is connected to the output end of the full - bridge inverter circuit, and a relay resonator is arranged between the output end of the transmitting resonator and the input end of the receiving resonator; The relay resonator realizes energy transmission through magnetic field energy coupling; A variable load R is provided at the output end of the receiving resonator L .

2. The constant - voltage output three - coil wireless power transmission system according to claim 1, characterized in that The Buck - Boost circuit specifically includes: Energy storage inductor L0, switching transistor S0, diode D0, output filter capacitor C0, where: the gate G0 of the switching transistor S0 is connected to the control unit on the emitter side, and the conduction and cutoff of the switching transistor S0 form two loops: the first loop is composed of the series connection of the energy storage inductor L0 and the DC voltage V IN in series, and the second loop is composed of the series connection of the energy storage inductor L0, the diode D0, and then the series connection of a circuit formed by the parallel connection of the capacitor C0 and the three-coil magnetic coupling resonance circuit.

3. A constant-voltage-output three-coil wireless power transmission system according to claim 1, characterized in that, The transmitting resonator includes a series circuit composed of a transmitting inductor L1 and a first tuning capacitor C1; The relay resonator includes a series circuit composed of a relay inductor L2 and a second tuning capacitor C2; The receiving resonator includes a series circuit composed of a receiving inductor L3 and a third tuning capacitor C3; The full - bridge inverter circuit includes: The center point between the left and right bridge arms of the full - bridge inverter circuit is connected in parallel with the series circuit composed of the transmitting coil L1 and the first tuning capacitor C1; Among them, the transmitting coil L1 and the relay coil L2 are coupled in the same direction, and the relay coil L2 and the receiving coil L3 are coupled in the same direction.

4. A constant-voltage-output three-coil wireless power transmission system according to claim 1, wherein The full - bridge inverter circuit uses GaN transistors to construct a full - bridge topology.

5. A constant-voltage-output three-coil wireless power transmission system according to claim 1, characterized in that, The negative resistance control unit includes a current sampler, a differential amplifier, a filter, a zero - crossing comparator, and a dead - time generation circuit connected in sequence; the output voltage control unit includes a digital signal processor.

6. A method for determining parameters of a constant-voltage-output three-coil wireless power transmission system according to any one of claims 1 to 5, characterized in that Including the following process: S1. Design the parameters of the three - coil magnetic - coupling resonance circuit and the relationships between the parameters according to the rated load and output voltage on the receiving side; S2. Design the coil size, spatial structure, and winding method according to the parameters of the three - coil magnetic - coupling resonance circuit and in combination with the coil transmission distance; S3. Determine the load - R on the transmitting side of the three - coil magnetically coupled resonant circuit N , and sample the voltage and current amplitudes and phase information on the transmitting side to complete the estimation of the actual load size and determine the optimal output voltage value of the Buck - Boost circuit; S4. Determine the parameters of each component of the Buck - Boost circuit, including the energy - storage inductor L0 and the output filter capacitor C0; S5. Design the system according to the parameters of each component of the circuit of the three - coil wireless power transmission system determined in S4 and conduct experimental verification, and adjust the parameters of each component of the circuit of the three - coil wireless power transmission system through the experimental results; S6. According to the experimental data obtained in S5, determine the model between the output voltage and the operating frequency of the Buck - Boost circuit by means of data fitting, and modify the output voltage value of the Buck - Boost circuit based on the curve so that the power transmission system has a constant - voltage output.

7. A method for determining the parameters of a constant-voltage-output three-coil wireless power transmission system according to claim 6, characterized in that, The specific process of S1 is as follows: S101. Determine the self-inductance L and mutual inductance M of the resonator coil ij : where μ0 is the magnetic permeability of vacuum, μ r is the relative magnetic permeability of the medium where the coil is located, N is the number of turns of the coil, A is the cross-sectional area of the coil, and l is the average perimeter of the coil; where k ij is the coupling coefficient; S102. Determine the relationship between the diameter d of the Litz wire and the coil resistance: DC resistance R of the coil dc and AC resistance R of the coil ac : Among them, ρ is the resistivity of the Litz wire, l total is the total length of the Litz wire, A wire is the effective cross-sectional area of the Litz wire, A eff is the effective cross-sectional area affected by the skin effect; S103. Determine the relationships between the tuning capacitors C1, C2, C3 and the coil self - inductance L and the operating frequency f: f = 2πL i ·C i , i = 1, 2, 3 Where i and j are index variables.

8. The method for determining the parameters of the constant - voltage output three - coil wireless power transmission system according to claim 6, the specific process of S2 is as follows: First, determine that the winding mode of the coil is spiral forward, the compensation mode of the tuning capacitor is segmented compensation, and determine the diameter D c , the number of turns N: Among them, L is the coil self - inductance, μ0 is the vacuum permeability, and π is the pi; finally, verify through a simulation tool experiment, and determine the coil turn - to - turn spacing s according to the simulation results.

9. A method for determining the parameters of a constant-voltage-output three-coil wireless power transmission system according to claim 6, characterized in that, The specific process of S3 is as follows: S301. Determine the relationships among the inductance, tuning capacitance, current, and input voltage of the transmitting resonator, relay resonator, and receiving resonator: Among them, L1, L2, and L3 are the inductances of the transmitting resonator, the relay resonator, and the receiving resonator respectively, v C1 , v C2 , v C3 are the voltages across the capacitors in the transmitting resonator, the relay resonator, and the receiving resonator respectively, i1, i2, and i3 are the currents of the transmitting resonator, the relay resonator, and the receiving resonator respectively; M 12 is the mutual inductance between the transmitting resonator and the relay resonator, M 23 represents the mutual inductance between the relay resonator and the receiving resonator; C1, C2, and C3 are the tuning capacitors of the transmitting resonator, the relay resonator, and the receiving resonator respectively, r1, r2, and r3 are the parasitic resistances of the transmitting resonator, the relay resonator, and the receiving resonator respectively, v1 is the input voltage of the transmitting resonator; R L is the variable load resistance; S302. Determine the voltage v across the coil ends L : where θ is the phase of the resonator, i represents the actual current flowing through the coil, I represents the maximum value of the current, ω represents the resonant frequency, and t is time; S303. Define the energy mode of an independent LC resonator without mutual coupling as: where A represents the amplitude of the energy mode, a represents the energy mode of the resonator, + is the phase symbol, j is the imaginary symbol, and e is the base of the natural logarithm; S304. Determine the equation satisfied by the third-order wireless power transfer system according to the energy definition in S303: H is the effective Hamiltonian operator, γ refers to the total loss of the receiving resonator, γ sn (n = 1, 2, 3) represents the intrinsic loss of the resonator, k 12 represents the coupling coefficient between the transmitting resonator and the relay resonator, k 23 represents the coupling coefficient between the relay resonator and the receiving resonator, g represents the net gain of the system, ω0 is the self-resonant frequency of the resonator, S305. Solve the equation of the third-order wireless power transfer system to determine the eigenvalues: ω s1 = ω0 where c2 and c0 are intermediate parameters, ω s1 , ω s2,3 , ω s4,5 are different operating frequencies of the system; S306. Using Fourier transform, the amplitude V of the fundamental component of the voltage of the load on the voltage transmission side is expressed as: 1m as follows: S307. Accurately determine the negative resistance value R of the load on the voltage transmission side based on the DC voltage and the transmission current N : Among them, V DC is the output voltage of the Buck-Boost circuit, and I 1m represents the current amplitude of the transmitting resonator; S308. Determine the total loss γ of the receiving resonator in different modes: a = g - r s2 where a, b, and c are intermediate coefficients; Obtain the predicted value R of the load resistance L,est is: R L,est = ω0L3(γ - γ s3 ) The current relationship between the transmitter and the receiver can be obtained through the circuit equation: where ω is the actual operating frequency of the circuit, and G I13 is an intermediate parameter representing the relationship between the current amplitudes of the transmitting resonator and the receiving resonator, and I 3m represents the current amplitude of the receiving resonator; According to the load R L The required DC output voltage is V L,set , and the required receiver current amplitude is determined to be: where V 3m,set is the target amplitude of the fundamental frequency component of the actual voltage of the receiving resonator, and R L,est is the estimated load; S309. Determine the DC voltage V to be set DC,set : where V 1m,set is the target amplitude of the fundamental frequency component of the actual voltage of the transmitting resonator.

10. A method for determining the parameters of a constant-voltage-output three-coil wireless power transmission system according to claim 6, characterized in that, The specific process of S4 is as follows: S401. Assume that the switching transistors and diodes are ideal devices, with zero voltage drop when conducting, capable of instantaneously turning on or off, and no leakage current when turned off; the inductors and capacitors are ideal components, the inductors operate in the linear region without saturation, the parasitic resistance is 0, and the equivalent series resistance of the capacitors is also 0; S402. After the switch tube S0 is turned on, the diode D0 is reverse-biased and cut off, and the input voltage V IN is applied across the inductor L0 with the polarity being positive at the top and negative at the bottom. The energy stored in the inductor current increases. Among them, the increase in the inductor current is: where D is the duty cycle of the pulse wave, T0 is the period of the pulse wave, and T ON represents the switch-on time within one period, and L c is the critical inductance value; S403. After the switching transistor S0 is turned off, the inductor current decreases, and the inductor coil generates a self-induced back electromotive force, which is negative at the top and positive at the bottom. The diode D0 conducts under the forward voltage. The inductor charges the capacitor through the diode, and the capacitor stores energy to discharge to the load to maintain the load output V when the switching transistor is turned on. DC The voltage remains unchanged. Among them, the reduction amount of the inductor current is: S404. Determine the critical inductance value L c The magnitude of the energy storage inductor L0: L0 = 1.3 × L c S405. In the continuous inductor current mode of the Buck - Boost DC conversion circuit, when the ripple voltage requirement is ΔU, the value of the output - side filter capacitor is: Among them, I o is the average value of the output current of the Buck-Boost circuit.

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