Multi-frequency multi-load wireless power transmission system based on midpoint clamping multi-level inverter

Abstract

This invention relates to the field of wireless power transmission technology, specifically disclosing a multi-frequency, multi-load wireless power transmission system based on a midpoint clamped multilevel inverter. By employing a midpoint clamped multilevel inverter as the core power conversion unit and combining it with a multi-frequency modulation strategy, multiple AC voltages of different frequencies are generated simultaneously on a single inverter. This eliminates the need for multiple independent inverters to drive multiple transmitting coils with different resonant frequencies, significantly simplifying the topology of the multi-frequency, multi-load wireless power transmission system. It also effectively suppresses cross-interference between different frequency channels, ensuring that each load receives a stable, low-harmonic energy supply. This improves the transmission efficiency and reliability when multiple loads are powered simultaneously. While achieving wireless power transmission for multiple loads of different frequencies from a single inverter, it also considers system simplicity, power quality, and operational stability.

Description

Technical Field

[0001] This invention relates to the field of wireless power transmission technology, and in particular to a multi-frequency, multi-load wireless power transmission system based on midpoint clamping multi-level inverter. Background Technology

[0002] Wireless power transfer (WPT) technology, with its advantages of being contactless, safe, and flexible, has been increasingly widely used in consumer electronics, medical devices, industrial robots, and electric vehicles. However, as application scenarios become more complex, single-frequency, single-load wireless power transfer systems are no longer sufficient to meet practical requirements such as simultaneous power supply to multiple devices, different power levels, and compatibility with different resonant frequencies. Therefore, multi-frequency, multi-load wireless power transfer systems have become a current research hotspot.

[0003] Most existing multi-frequency, multi-load wireless power transfer systems utilize full-bridge or half-bridge superimposed inverters. Although existing technologies can achieve multi-frequency output from these inverters, the following shortcomings still exist:

[0004] 1. High harmonic content in inverter output: Traditional full-bridge or half-bridge inverters output two-level voltages, which have high harmonic content. The presence of non-target harmonics makes it difficult to design the resonant network of the transmitter and receiver in a multi-frequency, multi-load wireless power transmission system, and also greatly affects the efficiency from the transmitter to the receiver. Furthermore, if non-target harmonics cannot be separated, it also affects the energy quality of the equipment.

[0005] 2. Limited inverter output power, unable to adapt to high-power scenarios: Because the switching devices of the inverter have certain rated voltage and current, this limits the maximum current and voltage that the inverter can withstand, thus limiting the maximum power transmission capability of the inverter. Summary of the Invention

[0006] The multi-frequency, multi-load wireless power transmission system based on midpoint clamping multi-level inverter provided by this invention solves the technical problem of how to enable a single inverter to output multi-frequency energy simultaneously while avoiding frequency interference, so as to simplify the structure of the multi-frequency, multi-load wireless power transmission system and improve its performance.

[0007] To address the above technical problems, this invention provides a multi-frequency, multi-load wireless power transmission system based on a midpoint-clamped multilevel inverter, comprising a DC power supply and a midpoint-clamped multilevel inverter, wherein the DC power supply includes a DC voltage. , connected in series with DC voltage The first DC-side capacitor and the second DC-side capacitor between the positive and negative terminals;

[0008] The midpoint clamping multilevel inverter includes eight MOSFETs, with the first, second, third, and fourth MOSFETs connected in series in series with the DC voltage. Between the positive and negative terminals, the fifth, sixth, seventh, and eighth MOSFETs are connected in series in series with the DC voltage. Between the positive and negative terminals, the first diode and the second diode are connected in reverse series between the common terminals of the first MOSFET and the second MOSFET, and between the common terminals of the third MOSFET and the fourth MOSFET. The third diode and the fourth diode are connected in reverse series between the common terminals of the fifth MOSFET and the sixth MOSFET, and between the common terminals of the seventh MOSFET and the eighth MOSFET. The common terminals of the first DC-side capacitor and the second DC-side capacitor, the common terminals of the first diode and the second diode, and the common terminals of the third diode and the fourth diode are connected.

[0009] Preferably, the system further includes a secondary receiving device, the secondary receiving device comprising a corresponding... Each load terminal has a resonant frequency and includes a receiving coil, a secondary compensation capacitor, and a load connected in a loop.

[0010] Preferably, the system further includes a PWM modulation control circuit connected to the midpoint clamped multilevel inverter. The PWM modulation control circuit controls the on / off state of eight MOSFETs in the midpoint clamped multilevel inverter, and, in conjunction with the midpoint clamping effect of the first to fourth diodes, enables the inverter output to obtain... , 0 , There are five discrete level levels.

[0011] Preferably, the PWM modulation control circuit generates a voltage with the same frequency as the resonant frequency of the n load terminals based on the different operating frequency requirements of the n load terminals. It then determines the amplitude of each voltage according to the energy demand of each receiving load. After discretizing the voltages corresponding to each load terminal, the circuit superimposes and maps them to a vector space to obtain the corresponding multi-frequency composite reference voltage. Finally, it uses hybrid multi-frequency space vector modulation technology to generate a switching drive signal that acts on the midpoint clamping multilevel inverter, so that the midpoint clamping multilevel inverter outputs a five-level multi-frequency composite reference voltage containing the signals required by the n load terminals.

[0012] Preferably, the system further includes a primary-side transmitting device, which comprises primary-side compensation capacitors connected in series. and transmitting coil .

[0013] Preferably, the primary-side compensation capacitor The parameter design process is as follows:

[0014] Determine the operating frequency of each load terminal according to the requirements of the load side;

[0015] Calculate the total reflected impedance from all load terminals to the primary transmitting device based on the operating frequency, receiving coil inductance, secondary compensation capacitor, receiving coil internal resistance, and load parameters for each load terminal. ;

[0016] Based on total reflection impedance Calculate the self-impedance of the primary-side series resonant network and the expression for the total input impedance of the primary-side series resonant network;

[0017] Setting the imaginary part of the expression for the total input impedance of the primary-side series resonant network to zero, we can solve for the primary-side compensation capacitor. Theoretical value;

[0018] Based on practical engineering considerations, the primary-side compensation capacitor is... The theoretical value is optimized to obtain the primary-side compensation capacitor. The optimal value.

[0019] Preferably, the first The receiving coil at each load end Secondary side compensation capacitor satisfy: , For the first The resonant frequency of each load terminal.

[0020] Preferably, the parameter design process for the first DC-side capacitor and the second DC-side capacitor is as follows:

[0021] Determine the rated withstand voltage of the capacitors based on the DC bus voltage, ensuring that each capacitor can withstand approximately half of the bus voltage over a long period of time, with a voltage margin of 1.5 to 2 times.

[0022] With the system's rated output power, fundamental frequency, switching frequency, and allowable midpoint potential fluctuation range as constraints, and based on the theory of midpoint current second harmonic component and DC bus voltage ripple, the capacitance requirements to satisfy midpoint potential balance and bus voltage stability are derived respectively, and the larger value of the two calculated results is taken as the DC side capacitor.

[0023] This invention provides a multi-frequency, multi-load wireless power transmission system based on a midpoint-clamped multilevel inverter. By employing a midpoint-clamped multilevel inverter as the core power conversion unit and combining it with a multi-frequency modulation strategy, multiple AC voltages of different frequencies are simultaneously generated on a single inverter. This eliminates the need for multiple independent inverters to drive multiple transmitting coils with different resonant frequencies, significantly simplifying the topology of the multi-frequency, multi-load wireless power transmission system and reducing system size and hardware costs. Because the midpoint-clamped multilevel inverter itself has inherent advantages such as low output voltage harmonic distortion and low voltage stress on switching devices, combined with multi-frequency modulation technology, the purity of each frequency component in the output power is high, effectively suppressing cross-interference between different frequency channels. This ensures that each load receives a stable, low-harmonic energy supply, improving transmission efficiency and reliability when multiple loads are powered simultaneously. Furthermore, multi-level output reduces the requirements for the transmitting end filter network, allowing for a smaller size of the filter inductor and capacitor, further increasing the system's power density. In summary, this invention achieves wireless power transmission for multiple loads at different frequencies using a single inverter, while also ensuring system simplicity, power quality, and operational stability. Attached Figure Description

[0024] Figure 1 This is a diagram of a multi-frequency, multi-load wireless power transmission system based on midpoint clamping multi-level inverter provided in an embodiment of the present invention;

[0025] Figure 2 This is a flowchart of the PWM modulation control circuit generating PWM control signals provided in an embodiment of the present invention;

[0026] Figure 3 The primary-side resonant compensation capacitor C provided in this embodiment of the invention. P Parameter design flowchart;

[0027] Figure 4 This is an equivalent model diagram of the dual-frequency dual-load wireless power transmission system provided in the embodiments of the present invention;

[0028] Figure 5 This is a simulation output waveform diagram of the midpoint clamping multilevel inverter provided in an embodiment of the present invention. Figure 5 Figure (a) shows the inverter output voltage waveform. Figure 5 (b) shows the inverter output current waveform.

[0029] Figure 6 This is a simulation output waveform diagram of the load receiver provided in an embodiment of the present invention. Figure 6 Figure (a) shows the output current waveform of the load receiving circuit at 20kHz. Figure 6 (b) shows the output current waveform of the 60kHz load receiving circuit;

[0030] Figure 7 This is a simulation harmonic analysis diagram of the midpoint clamping multilevel inverter provided in an embodiment of the present invention. Figure 7 Figure (a) shows the harmonic analysis diagram of the 20kHz load receiving circuit. Figure 7 Figure (b) shows the harmonic analysis diagram of the 60kHz load receiving circuit. Detailed Implementation

[0031] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The embodiments are given for illustrative purposes only and should not be construed as limiting the present invention. The accompanying drawings are for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0032] The multi-frequency, multi-load wireless power transmission system based on midpoint clamping multi-level inverter provided in this embodiment of the invention has the following circuit topology: Figure 1 As shown, it includes a DC power supply 1, a midpoint clamped multilevel inverter 2, a primary-side transmitter 3, a secondary-side receiver 4, and a PWM modulation control circuit connected to the midpoint clamped multilevel inverter 2. Figure 1 (Not shown in the image).

[0033] like Figure 1 As shown, DC power supply 1 includes DC voltage. , connected in series with DC voltage The first DC-side capacitor between the positive and negative terminals (Voltage is) ) and second DC side capacitor (Voltage is) ).

[0034] like Figure 1 As shown, the midpoint clamped multilevel inverter 2 includes 8 MOSFETs, wherein the MOSFETs (First MOSFET) (Second MOSFET) (Third MOSFET) (The fourth MOSFET) is connected in series with the DC voltage. Between the positive and negative terminals, the MOSFET (Fifth MOSFET) (Sixth MOSFET) (Seventh MOSFET) (Eighth MOSFET) is connected in series with DC voltage. Between the positive and negative terminals, the MOSFET and common terminal, MOSFET and A diode is connected in reverse order between the common terminals. (First diode) and (Second diode), MOSFET and common terminal, MOSFET and A diode is connected in reverse order between the common terminals. (Third diode) and (Fourth diode). Capacitor and Common terminal (connection point O), diode and common terminal, diode and Connected to the common terminal, the current is .

[0035] like Figure 1 As shown, the primary-side transmitting device 3 includes primary-side compensation capacitors connected in series. and transmitting coil (Current is expressed as) The secondary receiving device 4 includes a corresponding... The load terminal at the resonant frequency, each load terminal (the first) One load terminal, resonant frequency This includes receiving coils connected in a loop. Secondary side compensation capacitor and load Transmitting coil and receiving coil The mutual induction between them is represented as The current at n load terminals is expressed as .

[0036] In this embodiment, the midpoint clamped multilevel inverter 2 consists of two sets of symmetrical bridge arms, and the voltage values ​​of each DC-side capacitor are equal, i.e. By controlling the on / off state of the switching transistors in the two bridge arms, and in conjunction with the midpoint clamping effect of the clamping diodes, the inverter output can obtain... , 0 , There are five discrete voltage levels, so the inverter outputs five voltage levels.

[0037] Figure 2 A flowchart illustrating the generation of PWM control signals for a PWM modulation control circuit. (Example:) Figure 2 As shown, the PWM modulation control circuit uses different operating frequencies in n receiving loops ( To meet the requirements, a voltage with a frequency consistent with the resonant frequencies of n receiving loops (load ends) is generated. The amplitude of each voltage is determined based on the energy demand of each receiving load. Then, the voltages corresponding to each receiving loop are discretized and superimposed (the mixed frequency vector is represented as...). And map it to vector space to obtain the corresponding multi-frequency composite reference voltage. Finally, the switching drive signal of the midpoint clamping multilevel inverter 2 is generated by using hybrid multi-frequency space vector modulation technology (sector judgment, vector selection, determination of reference vector action time, and using a hybrid vector modulation controller), so that the midpoint clamping multilevel inverter 2 can output a five-level multi-frequency composite reference voltage containing the signals required by n receiving circuits.

[0038] The mathematical expression for the multi-frequency composite reference voltage is:

[0039] ,

[0040] in, For the first The voltage vector corresponding to each receiving loop , , The first The magnitude and phase of the voltage vector corresponding to each receiving loop, f i Let t represent the frequency of the voltage vector corresponding to each receiving circuit, and t represent the time.

[0041] Finally, the method for generating the switching drive signal of the midpoint clamping multilevel inverter using hybrid multi-frequency space vector modulation technology is as follows: the action time and action sequence of the multi-frequency composite reference voltage vector are controlled to synthesize a reference voltage vector, and then the synthesized reference voltage vector is modulated to generate 8 drive signals, thereby enabling the midpoint clamping inverter to generate multi-frequency composite power with five levels.

[0042] The secondary receiving coil receives the multi-frequency composite magnetic field from the transmitting coil to generate a multi-frequency voltage, and then separates the frequency electrical energy required by each receiving load from the multi-frequency composite energy through the resonant network of each receiving circuit.

[0043] The multi-frequency, multi-load wireless power transfer system employs an S-type compensation structure on both the primary and secondary sides. Based on the resonance relationship, the parameters satisfy the following:

[0044] .

[0045] Therefore, the method for determining the secondary compensation capacitor is as follows: based on the frequency requirements of the load in each receiving circuit, combined with the self-inductance of each receiving coil, to satisfy the resonance condition. The compensation capacitor values ​​corresponding to each receiving circuit on the secondary side are calculated.

[0046] Because the primary side contains multi-frequency electrical energy, the primary side compensation capacitor... The selection criteria for the primary capacitor cannot be referenced by those for the secondary capacitor; the primary capacitor... The primary goal of the primary capacitor is to compensate for reactive power in the system and improve the overall power factor. However, its selection should not have too much impact on the overall system efficiency or the power transmission efficiency at each frequency. Therefore, the primary capacitor... The selection must also take into account the frequency of each power channel.

[0047] Figure 3 Primary-side resonant compensation capacitor The parameter design flowchart. (See attached flowchart.) Figure 3 As shown, the operating frequency f required by the system to be compatible with different standards is first determined based on the load-side requirements. i Then, based on the operating frequency of each load end... Calculate the total reflected impedance of all load terminals reflected to the primary transmitting device (3) based on the self-inductance of the receiving coil, the secondary compensation capacitor, the internal resistance of the receiving coil, and the load parameters. Subsequently, based on the total reflection impedance Self impedance of the primary-side series resonant network ( Calculate the total input impedance expression for the primary-side series resonant network (assuming the internal resistance of the transmitting coil); then set the imaginary part of the input impedance of the primary-side series resonant network to zero to achieve primary-side resonance and zero-voltage switching, and derive the solution accordingly. The theoretical value; finally, combined with engineering realities such as load fluctuations and parameter deviations, the theoretical value is... Optimization can yield the primary-side compensation capacitor. The optimal value.

[0048] The parameter values ​​for the first DC-side capacitor and the second DC-side capacitor also need to be determined. The parameter design process is as follows:

[0049] Determine the rated withstand voltage of the capacitors based on the DC bus voltage, ensuring that each capacitor can withstand approximately half of the bus voltage over a long period of time, with a voltage margin of 1.5 to 2 times.

[0050] With the system's rated output power, fundamental frequency, switching frequency, and allowable midpoint potential fluctuation range as constraints, and based on the theory of midpoint current second harmonic component and DC bus voltage ripple, the capacitance requirements to satisfy midpoint potential balance and bus voltage stability are derived respectively, and the larger value of the two calculated results is taken as the DC side capacitor.

[0051] Next, based on the inherent resonant frequency and power requirements of each receiving circuit load, as well as the number of loads, the number, frequency, and amplitude of the superimposed voltages are determined. The various voltages are superimposed to obtain a multi-frequency composite reference voltage, and hybrid multi-frequency space vector modulation technology is used to generate the switching drive signal for the midpoint clamped multilevel inverter, thereby enabling the midpoint clamped multilevel inverter to output better multi-frequency composite high-frequency power.

[0052] The multi-frequency, multi-load wireless power transmission system based on midpoint-clamped multilevel inverter provided in this invention uses a midpoint-clamped multilevel inverter as the core power conversion unit, combined with a multi-frequency modulation strategy, to simultaneously generate multiple AC voltages of different frequencies on a single inverter. This eliminates the need for multiple independent inverters to drive multiple transmitting coils with different resonant frequencies, significantly simplifying the topology of the multi-frequency, multi-load wireless power transmission system and reducing system size and hardware costs. Because the midpoint-clamped multilevel inverter itself has inherent advantages such as low output voltage harmonic distortion and low voltage stress on switching devices, combined with multi-frequency modulation technology, the purity of each frequency component in the output power is high, effectively suppressing cross-interference between different frequency channels. This ensures that each load end receives a stable, low-harmonic energy supply, improving transmission efficiency and reliability when multiple loads are powered simultaneously. Furthermore, multi-level output reduces the requirements for the transmitting end filter network, allowing for a smaller size of the filter inductor and capacitor, further increasing the system's power density. In summary, this invention achieves wireless power transmission for multiple loads at different frequencies using a single inverter, while also ensuring system simplicity, power quality, and operational stability.

[0053] The following section uses specific parameters and experimental analysis to further verify the technical effectiveness of this invention.

[0054] The verification will take a dual-frequency, dual-load circuit as an example, building the corresponding simulation circuit and setting the DC voltage. DC side capacitor When the capacitor voltages are equal, then The resonant frequency of the secondary receiving circuit Set to 20kHz and 60kHz; self-inductance of the primary-side transmitting coil It is 136.0 μH, internal resistance The primary-side compensation capacitor C is 0.05Ω, determined through theoretical analysis. P The selected value is 51.73nF; the self-inductance of the secondary 20kHz receiving coil is... It is 236.7 μH, and its internal resistance is 236.7 μH. It is 0.27 resonant capacitance value The mutual inductance is 267.54 nF, and the mutual inductance of the transmitting coil is... The self-inductance of the secondary 60kHz receiving coil is 8.5μH. The internal resistance is 233.38 μH. It is 0.05 resonant capacitance value The mutual inductance of the transmitting coil is 30.15 nF. The mutual inductance is 8.2 μH; since the two receiving coils are placed on opposite sides of the transmitting coil, the mutual inductance between the two receiving coils is... Neglecting this. Set two discretized voltage amplitudes. It is 0.45.

[0055] Based on the above data, combined with Figure 4 The equivalent model of the dual-frequency dual-load wireless power transfer system shown can be used to calculate the effective values ​​of the two frequency voltages output by the midpoint clamped multilevel inverter:

[0056] ,

[0057] The discretized sampling voltage angular frequency is:

[0058] .

[0059] Solve using Kirchhoff's voltage law. Figure 3 From the circuit model shown, we can obtain:

[0060] ,

[0061] in, , , (i=1,2) represent frequencies respectively. and Input impedances of the primary and secondary sides:

[0062] .

[0063] Thus, the primary and secondary circuit currents of the system can be solved:

[0064] ,

[0065] in, , , (i=1,2) represent frequencies respectively. and The current generated in the primary transmitting circuit and the secondary receiving circuit i.

[0066] The overall system output power is calculated as follows:

[0067] ,

[0068] in, , (i=1,2) represent frequencies respectively. and The output power of the secondary receiving circuit i below.

[0069] The total power loss of the system is calculated as follows:

[0070] ,

[0071] in, Secondary receiving loop Power loss.

[0072] The total active power of the system is calculated as follows:

[0073] .

[0074] The system efficiency is:

[0075] .

[0076] Substituting the relevant system parameters, the system efficiency can be obtained as follows: This simulation result demonstrates that the proposed scheme achieves high-efficiency multi-frequency, multi-load power transmission while maintaining system simplicity.

[0077] Figure 5 This is the simulated output waveform of a midpoint clamped multilevel inverter. Figure 5 In the middle (a), the inverter output voltage waveform is shown. Figure 5 (b) shows the inverter output current waveform. Figure 5 It can be seen that the inverter output voltage is a high-frequency mixed multi-level pulse voltage; the transmitting circuit current is a high-frequency current composed of 20kHz and 60kHz currents, thus verifying that the embodiment of the present invention has the function of outputting multi-frequency mixed power after passing through the midpoint clamped multi-level inverter.

[0078] Figure 6 This is the simulated output waveform of the load receiver. Figure 6 In diagram (a), the output current waveform of the load receiving circuit is shown in the diagram (20kHz). Figure 6 (b) shows the output current waveform of the load receiving circuit at 60kHz. Figure 6 It can be seen that the output current of the power receiving circuit is a sine wave, and the waveform is smooth and the amplitude is relatively stable.

[0079] Figure 7 This is a simulation harmonic analysis of a midpoint clamped multilevel inverter. Figure 7 (a) shows the harmonic analysis of the 20kHz load receiving circuit. Figure 7 (b) shows the harmonic analysis of the 60kHz load receiving circuit. Figure 7 It can be seen that the two load circuits receive power at 20kHz and 60kHz respectively, thus verifying that the embodiment of the present invention has the power receiving function of the load circuit.

[0080] It is evident from the above experiments that the multi-frequency, multi-load wireless power transmission system based on a midpoint clamping multi-level inverter proposed in this embodiment of the invention can improve the efficiency from the transmitter to the receiver. The hybrid multi-frequency space vector modulation technique used can realize the multi-frequency output of the inverter and enable independent control of each output channel.

[0081] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A multi-frequency, multi-load wireless power transmission system based on midpoint clamping multi-level inverter, characterized in that: The system includes a DC power supply (1) and a midpoint clamping multilevel inverter (2), wherein the DC power supply (1) includes a DC voltage. , connected in series with DC voltage The first DC-side capacitor and the second DC-side capacitor between the positive and negative terminals; The midpoint clamped multilevel inverter (2) includes eight MOSFETs, with the first, second, third, and fourth MOSFETs connected in series in series with the DC voltage. Between the positive and negative terminals, the fifth, sixth, seventh, and eighth MOSFETs are connected in series in series with the DC voltage. Between the positive and negative terminals, the first diode and the second diode are connected in reverse series between the common terminals of the first MOSFET and the second MOSFET, and between the common terminals of the third MOSFET and the fourth MOSFET. The third diode and the fourth diode are connected in reverse series between the common terminals of the fifth MOSFET and the sixth MOSFET, and between the common terminals of the seventh MOSFET and the eighth MOSFET. The common terminals of the first DC-side capacitor and the second DC-side capacitor, the common terminals of the first diode and the second diode, and the common terminals of the third diode and the fourth diode are connected.

2. The multi-frequency, multi-load wireless power transmission system based on midpoint clamping multi-level inverter according to claim 1, characterized in that: The system also includes a secondary receiving device (4), which includes a corresponding... Each load terminal has a resonant frequency and includes a receiving coil, a secondary compensation capacitor, and a load connected in a loop.

3. The multi-frequency, multi-load wireless power transmission system based on midpoint clamping multi-level inverter according to claim 2, characterized in that: The system also includes a PWM modulation control circuit connected to the midpoint clamp multilevel inverter (2). The PWM modulation control circuit controls the on / off state of the eight MOS transistors in the midpoint clamp multilevel inverter (2), and, in conjunction with the midpoint clamping effect of the first to fourth diodes, enables the inverter output to obtain... , 0 , There are five discrete level levels.

4. The multi-frequency, multi-load wireless power transmission system based on midpoint clamping multi-level inverter according to claim 3, characterized in that: The PWM modulation control circuit generates a voltage with the same frequency as the resonant frequency of the n load terminals according to the different operating frequency requirements of the n load terminals. It determines the amplitude of each voltage according to the energy demand of each receiving load. Then, it discretizes the voltages corresponding to each load terminal, superimposes them, and maps them to the vector space to obtain the corresponding multi-frequency composite reference voltage. Finally, it uses hybrid multi-frequency space vector modulation technology to generate a switching drive signal that acts on the midpoint clamping multilevel inverter (2), so that the midpoint clamping multilevel inverter (2) outputs a five-level multi-frequency composite reference voltage containing the signals required by the n load terminals.

5. The multi-frequency, multi-load wireless power transmission system based on midpoint clamping multi-level inverter according to claim 4, characterized in that: The system also includes a primary-side transmitter (3), which comprises a primary-side compensation capacitor connected in series. and transmitting coil .

6. The multi-frequency, multi-load wireless power transmission system based on midpoint clamping multi-level inverter according to claim 5, characterized in that, The primary-side compensation capacitor The parameter design process is as follows: Determine the operating frequency of each load terminal according to the requirements of the load side; Calculate the total reflection impedance of all load terminals reflected to the primary transmitting device (3) based on the operating frequency of each load terminal, the self-inductance of the receiving coil, the secondary compensation capacitor, the internal resistance of the receiving coil, and the load parameters. ; Based on total reflection impedance Calculate the self-impedance of the primary-side series resonant network and the expression for the total input impedance of the primary-side series resonant network; Setting the imaginary part of the expression for the total input impedance of the primary-side series resonant network to zero, we can solve for the primary-side compensation capacitor. Theoretical value; Based on practical engineering considerations, the primary-side compensation capacitor is... The theoretical value is optimized to obtain the primary-side compensation capacitor. The optimal value.

7. The multi-frequency, multi-load wireless power transmission system based on midpoint clamping multi-level inverter according to claim 6, characterized in that, No. The receiving coil at each load end Secondary side compensation capacitor satisfy: , For the first The resonant frequency of each load terminal.

8. The multi-frequency, multi-load wireless power transmission system based on midpoint clamping multi-level inverter according to any one of claims 1 to 7, characterized in that, The parameter design process for the first DC-side capacitor and the second DC-side capacitor is as follows: Determine the rated withstand voltage of the capacitors based on the DC bus voltage, ensuring that each capacitor can withstand approximately half of the bus voltage over a long period of time, with a voltage margin of 1.5 to 2 times. With the system's rated output power, fundamental frequency, switching frequency, and allowable midpoint potential fluctuation range as constraints, and based on the theory of midpoint current second harmonic component and DC bus voltage ripple, the capacitance requirements to satisfy midpoint potential balance and bus voltage stability are derived respectively, and the larger value of the two calculated results is taken as the DC side capacitor.

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