Multi - frequency and multi - load wireless power transfer system and its current - tracking PWM control method

Abstract

The present invention provides a multi-frequency and multi-load wireless power transmission system and its current-tracking PWM control method. In this method, a current acquisition circuit is arranged on the primary side of the multi-frequency and multi-load wireless power transmission system to collect the output current of the high-frequency inverter, and a current-tracking PWM control circuit is set up to perform current-tracking PWM control on the output current of the high-frequency inverter based on a preset command current. By utilizing the relationship between the output power of the system and the magnitude of the command current, the command current is designed, and by setting the magnitude of the command current, the power on the load side can be controlled, thereby matching the power requirements of different loads. The magnitude of each frequency component of the command current can be set independently, realizing independent control between loads of different frequencies. Moreover, since the frequency in the command current can be adjusted according to actual application requirements, it can adapt to the power supply requirements of loads with different operating frequencies.

Description

Technical Field

[0001] The present invention relates to a multi - frequency and multi - load wireless power transmission system, and particularly to a multi - frequency and multi - load wireless power transmission system and its current - tracking PWM control method. Background Art

[0002] Multi - frequency hybrid power supplies are applied to multi - load wireless power transmission scenarios under different frequency standards. In current multi - frequency hybrid power supply technologies, methods such as phase - shift control, parallel operation of multiple inverters, and transmitting energy using the fundamental wave and harmonics output by the inverter are usually adopted to output multi - frequency electric energy to achieve multi - frequency and multi - load wireless power transmission. However, the existing technologies have the following deficiencies:

[0003] 1. For the method of preparing multi - frequency hybrid signals using phase - shift control, the voltage regulation range of the inverter is not wide enough. If an additional voltage regulation link is added for adjustment, it will affect the overall efficiency of the system and increase the system volume and cost;

[0004] 2. For the method of supplying power using the fundamental frequency and several harmonics output by the inverter, there is coupling between the output multi - frequency hybrid signals, and the number of supported frequencies is small, making it difficult to achieve flexible multi - frequency load wireless power supply;

[0005] 3. Existing multi - frequency and multi - load wireless power transmission systems with a single - transmitter structure on the primary side generally have a large amount of reactive power, so the power factor of the system is low. Summary of the Invention

[0006] Object of the Invention: The present invention aims to propose a multi - frequency and multi - load wireless power transmission system and a current - tracking PWM control method to achieve multi - frequency and multi - load wireless power transmission, independent load control, and efficient wireless power transmission within a relatively wide power adjustment range.

[0007] Technical Solution: To achieve the above object, in the first aspect of the present invention, a current - tracking PWM control method for a multi - frequency and multi - load wireless power transmission system is proposed. This method is used to perform current - tracking PWM control on the current flowing through the primary coil of the multi - frequency and multi - load wireless power transmission system based on a preset command current; the design method of the command current includes the steps:

[0008] (1) Determine the operating frequency f i of the loads in each secondary receiving circuit of the multi - frequency and multi - load wireless power transmission system, where i = 1, 2,..., n, and n is the total number of secondary receiving circuits;

[0009] (2) Calculate the amplitude parameter a i of the sub - command current of each secondary receiving circuit:

[0010]

[0011] Among them, P oi represents the load power of the i-th secondary receiving circuit, and R Li represents the load equivalent resistance of the i-th secondary receiving circuit, and M psi represents the mutual inductance between the primary coil and the receiving coil in the i-th secondary receiving circuit;

[0012] (3) Set up an optimization model:

[0013]

[0014]

[0015] Among them, represents the amplitude parameter of the sub-instruction current of the i-th secondary receiving circuit, T represents the cycle duration, f min and f max are the preset minimum tracking frequency and maximum tracking frequency, i * (t) represents the function of the instruction current with respect to time t, and I max represents the maximum current value that the system can track, and h max represents the maximum current change rate of the system;

[0016] (4) Solve the optimization model to obtain the phase parameters of the sub-instruction currents of the secondary receiving circuits;

[0017] (5) Calculate the instruction current as:

[0018]

[0019] Among them, i * represents the value of the instruction current, represents the value of the sub-instruction current of the i-th secondary receiving circuit.

[0020] The second aspect of the present invention proposes a multi-frequency and multi-load wireless power transmission system, including a DC power supply, a high-frequency inverter, and a transmitting coil that are arranged on the primary side of the system and connected in sequence, and a plurality of receiving circuits arranged on the secondary side of the system; characterized in that it further includes a current tracking PWM control circuit and a current acquisition circuit arranged on the primary side of the system; the current acquisition circuit is used to acquire the output current of the high-frequency inverter; the current tracking PWM control circuit is used to perform current tracking PWM control based on the output current and a preset instruction current, and the instruction current is set by using the current tracking PWM control method of the multi-frequency and multi-load wireless power transmission system.

[0021] As an alternative embodiment of the second aspect of the present invention, the receiving circuit includes a resonant network and a load corresponding to a frequency; the resonant network is used to extract sub-electromagnetic waves of a corresponding resonant frequency from the composite electromagnetic waves emitted by the primary side of the system, and convert them into electrical energy to supply power to the load connected thereto.

[0022] As an alternative embodiment of the second aspect of the present invention, a compensation capacitor is further provided in the primary side circuit of the system, and the value of the compensation capacitor can be designed as: where Q sys represents the overall reactive power of the multi-frequency and multi-load wireless power transmission system, represents the peak value of the primary current corresponding to the secondary receiving circuit with a working frequency of f i . By outputting capacitive reactive power through the compensation capacitor, the inductive reactive power existing in the system can be compensated.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0024] 1. Design the command current parameters according to the load requirements, and at the same time, the command current parameters can be adjusted according to the load state. The voltage regulation range is wide and no additional voltage regulation circuit is added, saving costs;

[0025] 2. The command current frequency is given according to the load requirements. When designing each frequency component, there is no need to follow the relationship between the fundamental wave and the harmonic, and they can be designed independently. The frequency selection is flexible, and flexible multi-frequency load wireless power supply can be realized;

[0026] 3. Thanks to the current tracking PWM control, the primary side of the system has the characteristics of a current source. Therefore, adding a compensation capacitor does not affect the energy transmission of the multi-frequency electrical energy required by the system. At the same time, the capacitive reactive power of the compensation capacitor can be used to reduce the overall reactive power of the system and improve the power factor. Description of the Drawings

[0027] Figure 1 is the schematic diagram of the current tracking PWM control method for the multi-frequency and multi-load wireless power transmission system involved in the embodiment;

[0028] Figure 2 is the waveform diagram of the primary current flowing through the transmitting coil in the simulation result involved in the embodiment;

[0029] Figure 3 is the FFT analysis result of the primary current flowing through the transmitting coil in the simulation result involved in the embodiment;

[0030] Figure 4 (a) is the voltage waveform diagram of the load R L1 in the simulation result involved in the embodiment; Figure 4 (b) is the load R in the simulation result involved in the embodiment L2Voltage waveform diagram on

[0031] Figure 5 (a) In the simulation results related to the embodiment, after changing the amplitude of the 80 kHz component in the command current, the load R L1 Voltage waveform diagram on Figure 5 (b) In the simulation results related to the embodiment, after changing the amplitude of the 80 kHz component in the command current, the load R L2 Voltage waveform diagram on. Detailed implementation manners

[0032] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0033] Those skilled in the art of the present technology can understand that, unless specifically stated otherwise, the terms "first", "second", etc. used herein are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. In the description of the present invention, "a plurality of" means two or more, unless otherwise specifically defined.

[0034] Those skilled in the art of the present technology can understand that in the embodiments of the present application, the various numerical numbers involved are only for the convenience of description and are not used to limit the scope of the embodiments of the present application.

[0035] Those skilled in the art of the present technology can understand that, unless specifically stated otherwise, the singular forms "a", "an", "the" and "said" used herein may also include the plural forms. It should be further understood that the term "including" used in the description of the present application means that there are the described features, integers, steps, operations, elements and / or components, but does not exclude the existence or addition of one or more other features, integers, steps, operations, elements, components and / or their combinations.

[0036] Those skilled in the art of the present technology can understand that, unless otherwise clearly defined and limited, the terms "connected" and "connected" should be understood in a broad sense. For example, they can be directly connected or indirectly connected through an intermediate medium. They can be the internal connection of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0037] Those skilled in the art can understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as the general understanding of those of ordinary skill in the art to which this application belongs. It should also be understood that terms such as those defined in a general dictionary should be understood to have a meaning consistent with the meaning in the context of the prior art, and will not be interpreted in an idealized or overly formal sense unless specifically defined as in the embodiments of this application.

[0038] The purpose of this embodiment is to propose a multi-frequency and multi-load wireless power transmission system and its current-tracking PWM control method in view of the deficiencies of the prior art.

[0039] Reference Figure 1 , Figure 1 schematically shows a circuit structure of the multi-frequency and multi-load wireless power transmission system described in this embodiment and a schematic diagram of the current-tracking PWM control of the system. Figure 1 It includes: a DC power supply, a high-frequency inverter, a transmitting coil Lp, a current-tracking PWM control circuit, and a current acquisition circuit provided on the primary side of the system, and n receiving circuits provided on the secondary side of the system, where n is an integer and n>0.

[0040] The DC power supply is used to supply power to the high-frequency inverter, the current-tracking PWM control circuit, and the current acquisition circuit.

[0041] The current acquisition circuit is used to acquire the output current of the high-frequency inverter and transmit it to the current-tracking PWM control circuit.

[0042] The current-tracking PWM control circuit is used to perform a hysteresis comparison between the acquired current and a preset command current through a controller to generate a PWM pulse control sequence, thereby performing current-tracking PWM control on the high-frequency inverter. According to the conventional maximum switching frequency formula of current-tracking PWM control: U d is the DC-side voltage of the inverter, and h is the hysteresis width of the current-tracking PWM control; the hysteresis width during the current-tracking process can be comprehensively adjusted according to the maximum switching frequency supported by the switching device in the actual system and the tracking accuracy requirements.

[0043] The high-frequency inverter is used to generate a multi-frequency composite current required by the load according to the PWM pulse control sequence. In this embodiment, the high-frequency inverter is implemented by a full-bridge inverter circuit composed of 4 switching tubes.

[0044] The transmitting coil Lp is used to convert the multi-frequency composite current into a multi-frequency composite electromagnetic wave.

[0045] The receiving circuit is used to extract electromagnetic waves of corresponding frequencies from the multi-frequency composite electromagnetic wave, convert them into electrical energy, and then supply power to the load. In this embodiment, each secondary receiving circuit is exemplarily implemented by an LCR series resonance circuit, and the resonance frequency of the i-th secondary receiving circuit is f i .

[0046] In this embodiment, the command current is set according to the load side demand, and its functional expression is:

[0047]

[0048] where, i1 * to i n * are the sub-command current functions of the 1st to the n-th secondary receiving circuits respectively, f1 to f n are the operating frequencies of the loads in the 1st to the n-th secondary receiving circuits respectively, a1 to a n are the amplitude parameters of the respective sub-command currents respectively, is the phase parameter of the respective sub-command currents.

[0049] This system realizes multi-frequency and multi-load wireless power transfer and control based on current tracking PWM control. The magnitude of the system output power is positively correlated with the magnitude of the command current. Therefore, by setting the magnitude of the command current, the power on the load side can be controlled, and then it can be matched with the power demands of different loads. The magnitude of each frequency component of the command current can be set independently, realizing independent control between loads of different frequencies. And by changing the frequency components in the command current, it can adapt to the power supply demands of loads with different operating frequencies according to actual application requirements.

[0050] From the above working principle, it can be seen that the present invention has at least the following advantages:

[0051] The present invention is based on current tracking PWM control, which controls the output current waveform of the high-frequency inverter to always maintain the desired output waveform. By changing the frequencies and magnitudes of the frequency components of the command current in the current tracking PWM controller, the directional power transfer and control for loads of any specific frequency can be realized. The entire system has a simple structure and strong robustness, and can directly output the current required by the load at each operating frequency, which can not only meet the fast and stable power supply demands of multi-frequency and multi-load, realize flexible adjustment of wide-range power, but also realize independent power supply and control for each load, improving the power supply flexibility and compatibility of the system compared with the existing control methods.

[0052] Figure 1The current tracking PWM control method for the shown circuit is as follows: The current flowing through the transmitting coil Lp is collected in real time by the current acquisition circuit set on the primary side, and then the collected current is sent into the current tracking PWM control circuit for hysteresis comparison with the pre-set command current. The hysteresis controller in the current tracking PWM control circuit generates a PWM control sequence according to the comparison result to control the on-off of each switching tube in the high-frequency inverter, thereby realizing the tracking of the command current.

[0053] The design method of the command current parameters is as follows: First, determine the frequency parameters, then determine the amplitude parameters according to the load power demand, and finally, based on the design conditions of the frequency parameters and the amplitude parameters, establish an optimization model of the command current function, and design the phase parameters according to the solution of the model. The specific design process includes the following steps:

[0054] (1) Determine the operating frequencies f1 to fn of each load in the 1st to nth secondary receiving circuits n ;

[0055] (2) The amplitude parameters in the sub-command current are determined respectively according to the actual power demand of the loads in each secondary receiving circuit. Establish a system circuit model, and equivalent the primary circuit to the secondary side. The expression of the load voltage in the ith secondary receiving circuit can be obtained as:

[0056]

[0057] where, U Li is the load voltage in the ith secondary receiving circuit, R Li is the equivalent resistance of the load in the ith secondary receiving circuit, M psi is the mutual inductance value between the primary coil and the receiving coil in the ith secondary receiving circuit, I i represents the effective value of the primary current corresponding to the operating frequency of the ith secondary receiving circuit, L si is the inductance value of the resonant inductor in the ith secondary receiving circuit, and C si is the capacitance value of the resonant capacitor in the ith secondary receiving circuit.

[0058] (3) The parameter design criterion of the secondary receiving circuit is to improve the quality factor as much as possible to obtain better frequency selection characteristics. Therefore, the load voltage can be further simplified at the operating frequency of the secondary receiving circuit as:

[0059] U Li = jω i M psi I i

[0060] (4) Also, based on the load power expression as:

[0061]

[0062] Combining the load voltage and power expressions with the relationship between the frequency parameter in the corresponding sub-instruction current function, a function expression between the amplitude parameter of the sub-instruction current corresponding to the i-th secondary receiving circuit and the system parameters can be established: i Combined with the relationship between the load voltage and power expressions and the frequency parameter in the corresponding sub-instruction current function, a function expression between the amplitude parameter of the sub-instruction current corresponding to the i-th secondary receiving circuit and the system parameters can be established:

[0063]

[0064] (5) The first derivative function expression of the command current function is obtained as:

[0065]

[0066] (6) The phase parameter design criterion is that the command current function is minimized within the period. Combining the determined amplitude parameter and frequency parameter, the constraint of the amplitude condition is that the amplitude of the command current function is less than the system current tracking threshold, and the constraint of the signal change rate is that the instantaneous change rate of the signal is less than the system maximum tracking frequency. Solve the phase combination that satisfies the constraint conditions within the phase parameter change range to determine the phase parameter. Therefore, the optimization model:

[0067]

[0068]

[0069] where, T represents the period duration, f min and f max are the preset minimum tracking frequency and maximum tracking frequency, i * (t) represents the function of the command current with respect to time t, I max represents the maximum current value that the system can track, h max represents the maximum current change rate of the system; Solving the above optimization model, the obtained solution is the phase parameter of the sub-instruction current corresponding to each secondary receiving circuit

[0070] Continue to refer to Figure 1 , Figure 1 As shown in, the primary side of the multi-frequency and multi-load wireless power transmission system is a current source type system. Therefore, a power compensation capacitor can be added to the primary side, which can effectively improve the power factor of the system and achieve efficient wireless power transmission for multi-frequency and multi-load.

[0071] The parameter design method of the power compensation capacitor is as follows:

[0072] Based on the current hysteresis tracking PWM control, the output current of the high-frequency inverter is determined by the command current. Therefore, the primary side can be equivalently regarded as the superposition of several current sources, and the parameters of the power compensation capacitor can be determined according to the current reactive power level of the system and its corresponding reactive power compensation strategy. The superposition theorem can be used for analysis during design.

[0073] Reference Figure 1 , according to the system circuit model, the secondary impedance can be transformed to the primary side. When the impedance of the j-th secondary receiving circuit is transformed to the primary side, the corresponding system model expression at the working frequency f i is as follows:

[0074]

[0075] where, is the equivalent impedance of the j-th load loop transformed to the primary side at the working frequency f i .

[0076] The reactive power of the system at the corresponding working frequency is:

[0077]

[0078] where, is the effective value of the primary side current at the working frequency f i , and is the primary side impedance of the system at the working frequency f i , and the expression is:

[0079]

[0080] The expression of the overall reactive power of the system is:

[0081]

[0082] where, represents the reactive power of the system at the working frequency f i .

[0083] If the reactive power to be generated by the compensation capacitor for complete reactive power compensation is:

[0084]

[0085] where, C P represents the capacitance value of the electric energy compensation capacitor.

[0086] Since over-compensation may increase the system current during reactive power compensation, a full compensation strategy is often not adopted, but an under-compensation method is used. Therefore, the reactive power can be compensated according to 90% to 95% of the required compensation amount. Thus, the value of the electric energy compensation capacitor can be:

[0087]

[0088] where, Q sys represents the overall reactive power of the multi-frequency and multi-load wireless power transmission system, Indicates the peak value of the primary current corresponding to the secondary receiving circuit with a working frequency of f i .

[0089] To verify the technical effects of the present invention, the following simulation results are given for illustration.

[0090] Continue to refer to Figure 1 , in the circuit shown in Figure 1 , two secondary receiving loops are set. The first secondary receiving circuit includes a receiving coil L S1 , a resonant capacitor C S1 , a resistor R S1 , and a load R L1 . The working frequency of the first secondary receiving circuit is set to 20 kHz. The inductance value of the receiving coil L S1 of the first secondary receiving loop is 88.6 μH, the equivalent internal resistance of the receiving coil L S1 is 0.13 Ω, and the load R L1 is set as a resistive load with an impedance of 3 Ω. The second secondary receiving circuit includes a receiving coil L S2 , a resonant capacitor C S2 , a resistor R S2 , and a load R L2 . The working frequency of the second secondary receiving circuit is set to 80 kHz. The parameters of the receiving coil L S2 of the second secondary receiving loop are 89.05 μH, the equivalent internal resistance of the receiving coil L S2 is 0.1 Ω, and the second load R L2 is set as a resistive load with an impedance of 10 Ω.

[0091] The DC side voltage of the high-frequency inverter is set to 120 V. The parameters of the primary transmitting coil L P are set to 29.1 μH, and the equivalent impedance is set to 0.07 Ω. The mutual inductance value between the transmitting coil L p and the receiving coil L S1 is 17.08 μH, the mutual inductance value between the transmitting coil L p and the receiving coil L S2 is 16.6 μH, the cross mutual inductance value between the receiving coil L S1 and the receiving coil L S2 is 0.125 μH, and the value of the power compensation capacitor C p is set to 0.47 μF.

[0092] The secondary receiving circuit adopts a series compensation strategy. For the first secondary receiving circuit, the working frequency of the load R L1 is 20 kHz, then ω1 = 2·20000·π. When the circuit is in series resonance, there is a relationship ωL = 1 / ωC. Therefore, the resonant capacitor C S1The value of is 0.6918 μF. Similarly, for the second secondary receiving circuit, the load R L2 has an operating frequency of 80 kHz, then ω2 = 2·80000·π, and the resonant capacitor C S2 has a value of 0.04752 μF. The power demand of Load 1 is 17 W, and the power demand of Load 2 is 12 W.

[0093] Based on the above parameter settings, the command current can be calculated as:

[0094] i * = 5·sin(2π·20000·t + 0.942) + 2·sin(2π·80000·t + 0.541) A.

[0095] Reference Figure 2 , Figure 2 is the waveform diagram of the primary current flowing through the transmitting coil in the above simulation circuit. It can be seen from the current waveform that the primary current is not a regular single-frequency sine wave, but a waveform after the superposition of several frequencies. Its frequency components can be analyzed by performing FFT analysis on it. Figure 3 is the FFT analysis result of the primary current. The fundamental frequency in the FFT analysis tool is set to 20 kHz. The result shows that the main frequency components in the primary current are 20 kHz and 80 kHz components. The interference of other frequencies is extremely low compared with the main frequencies, so it can be ignored. Since the frequency setting in this design method is completely based on the function frequency parameters of the load demand and does not depend on the harmonic frequencies existing in the inverter output square wave, it can better adapt to the load frequency demand. This shows that the method proposed in the embodiment of the present invention can achieve the effect of generating a power supply with a preset frequency mixed superposition.

[0096] Figure 4 (a) is the voltage waveform of the load R L1 . It can be seen that the waveform is a relatively regular sine wave, with a frequency of 20 kHz and a voltage peak reaching 10 V. Figure 4 (b) is the voltage waveform of the load R L2 . The waveform is a relatively regular sine wave, with a frequency of 80 kHz and an amplitude of 15 V. The load current waveforms are all sine waves. It can be seen from this that the multi-frequency and multi-load wireless power transmission system proposed in the embodiment of the present invention can simultaneously achieve wireless power transmission of multiple frequencies.

[0097] Figure 5 (a) is the voltage waveform of the load R L1 after changing the amplitude of the 80 kHz component in the command current. It can be seen that the waveform is a relatively regular sine wave, with a frequency of 20 kHz and the amplitude still being 10 V, and the waveform hardly changes. Figure 5 (b) is the voltage waveform of the load RL2 The voltage waveform is a relatively regular sine wave with a frequency of 80 kHz, and its amplitude changes linearly with the command current. It can be seen from this that the multi-frequency and multi-load wireless power transmission system proposed in the embodiments of the present invention can achieve the individual control of a frequency component by changing the amplitude of a frequency component in the command current, thereby realizing flexible power transmission and control.

[0098] In the description of the present invention, a large number of specific details are set forth. However, it is understood that the embodiments of the present invention may be practiced without these specific details. In some instances, well-known methods, structures, and technologies have not been shown in detail so as not to obscure the understanding of this specification.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered by the scope of the claims and the specification of the present invention.

Claims

1. Current tracking PWM control method for multi - frequency and multi - load wireless power transfer system, characterized in that The method is used to perform current tracking PWM control on the current flowing through the primary coil of the multi - frequency and multi - load wireless power transmission system based on a preset command current; the design method of the command current includes the steps: (1) Determine the operating frequency f of the loads in each secondary receiving circuit of the multi-frequency and multi-load wireless power transmission system i , where i = 1, 2, …, n, and n is the total number of the secondary receiving circuits; (2) Calculate the amplitude parameter a of the sub-instruction current of each secondary receiving circuit i : Among them, P oi represents the load power of the i-th secondary receiving circuit, and R Li represents the load equivalent resistance of the i-th secondary receiving circuit, and M psi represents the mutual inductance between the primary coil and the receiving coil in the i-th secondary receiving circuit; (3) Set up an optimization model: Among them, represents the amplitude parameter of the sub-instruction current of the i-th said secondary receiving circuit, T represents the cycle duration, f min and f max are the preset minimum tracking frequency and maximum tracking frequency, i * (t) represents the function of the said instruction current with respect to time t, I max represents the maximum current value that the system can track, h max represents the maximum current change rate of the system; (4) Solve the optimization model to obtain the phase parameters of the sub - command currents of each secondary receiving circuit; (5) Calculate the command current as: where, i * represents the instruction current value, represents the sub-instruction current value of the i-th secondary receiving circuit.

2. A multi-frequency and multi-load wireless power transmission system, characterized in that, It includes a DC power supply, a high - frequency inverter, and a transmitting coil that are sequentially connected on the primary side of the system, and multiple receiving circuits on the secondary side of the system; characterized in that it further includes a current tracking PWM control circuit and a current acquisition circuit provided on the primary side of the system; the current acquisition circuit is used to acquire the output current of the high - frequency inverter; the current tracking PWM control circuit is used to perform current tracking PWM control based on the output current and a preset command current, and the command current is set by the method described in claim 1.

3. The multi-frequency and multi-load wireless power transmission system according to claim 2, wherein The receiving circuit includes a resonant network and a load corresponding to the frequency; the resonant network is used to extract sub - electromagnetic waves with corresponding resonant frequencies from the composite electromagnetic waves transmitted from the primary side of the system and convert them into electrical energy to supply power to the load connected to this end.

4. The multi-frequency and multi-load wireless power transmission system according to claim 3, characterized in that, A compensation capacitor is further provided in the primary - side circuit of the system.

5. The multi-frequency and multi-load wireless power transmission system according to claim 4, wherein The value of the compensation capacitance is as follows: where Q sys represents the overall reactive power of the multi-frequency and multi-load wireless power transmission system, represents the peak value of the primary current corresponding to the secondary receiving circuit with the operating frequency of f i ​

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