Multi-frequency multi-load wireless power transmission system based on cascaded h-bridge multi-level inverter

Abstract

The application discloses a kind of based on cascaded h bridge multilevel inverter's multi-frequency multi-load wireless power transmission system, including n direct current power supply, cascaded h bridge inverter, primary side transmitting device, secondary side receiving device, PWM generation circuit, PWM generation circuit is arranged in primary side transmitting device, and the switch driving signal of cascaded h bridge inverter is generated using the carrier same direction laminated modulation mode of multiple modulation wave compound, so that cascaded h bridge inverter generates the composite multilevel voltage of different load operating frequency of receiving side, and through transmitting coil, electric energy is converted into magnetic energy;System secondary side receiving coil converts magnetic energy into electric energy, and through resonant network, the electric energy of other frequency is filtered out, and the electric energy of self-resonant frequency is supplied to load.This application not only realizes the multi-frequency electric energy output of cascaded h bridge multilevel inverter, but also realizes multi-frequency multi-load independent electric energy transmission and control, while realizing the transmission of high-power electric energy.

Description

Technical Field

[0001] This invention relates to the fields of wireless power transmission and power converters, specifically to a multi-frequency, multi-load wireless power transmission system based on a cascaded h-bridge multilevel inverter. Background Technology

[0002] Wireless power transfer systems, with their inherent advantage of using soft media in space for contactless power transfer, have been widely applied in fields such as electric vehicles, smart devices, underwater equipment, and drones.

[0003] Currently, due to the lack of a unified design standard for wireless charging devices, wireless charging products from different vendors are not compatible with each other, and different wireless charging transmitters cannot charge different electrical devices. Therefore, researching wireless power transfer systems capable of simultaneously powering loads at multiple frequencies has broad prospects. Most existing multi-frequency, multi-load wireless power transfer systems utilize full-bridge or half-bridge superimposed inverter structures. 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] Objective: To overcome the shortcomings of existing technologies, this invention provides a multi-frequency, multi-load wireless power transmission system based on a cascaded H-bridge multilevel inverter. It employs a multi-modulation wave composite carrier in-direction cascade modulation method to generate the switching drive signal for the cascaded H-bridge inverter. This allows the cascaded H-bridge inverter to generate composite multilevel voltages at different load operating frequencies on the receiving side, and converts electrical energy into magnetic energy through the transmitting coil. The secondary receiving coil converts magnetic energy into electrical energy, and filters out electrical energy of other frequencies through the resonant network of its respective receiving circuit, using the electrical energy at its own resonant frequency to power the load. This system can improve the system efficiency of both the transmitting and receiving ends, enable independent control of the power of each receiving circuit, and achieve high-power multi-frequency, multi-load wireless power transmission.

[0007] Technical solution: To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0008] A multi-frequency, multi-load wireless power transmission system based on a cascaded h-bridge multilevel inverter includes n DC power supplies, a cascaded h-bridge inverter, a primary-side transmitter, a secondary-side receiver, and a PWM generation circuit. The n DC power supplies, the cascaded h-bridge inverter, and the primary-side transmitter are connected in series. The primary-side transmitter includes a primary-side compensation capacitor and a primary-side transmitting coil connected in series. The secondary-side receiver includes n power receiving loops, each including a receiving coil, a secondary-side compensation capacitor, and a load connected in series. The receiving coil is positioned opposite to the primary-side transmitting coil. The number of DC power supplies is the same as the number of h-bridges, n. The number of output levels of the cascaded h-bridge inverter is 2n+1. The system has m receiving loops and loads operating at different frequencies.

[0009] The PWM generation circuit is located in the primary-side transmitting device. The PWM generation circuit generates a modulation wave signal with the same frequency as the resonant frequency of the m receiving loops based on the different operating frequency requirements of the m receiving loops. The amplitude of each modulation wave signal is determined according to the energy demand of each receiving load. The modulation waves corresponding to each receiving loop are then superimposed to obtain a composite modulation signal. Finally, the composite modulation signal is compared with the carrier superimposed modulation method to generate the switching drive signal of the cascaded h-bridge multilevel inverter, so that the inverter can output a multi-frequency composite voltage with 2n+1 levels and containing the signals required by the m receiving loops.

[0010] Preferably, the transfer functions of the two transmission channels of the system are:

[0011]

[0012]

[0013] in, This represents the transfer function of transmission channel one. Represents complex variables in the complex plane. This indicates that the receiving coil and the transmitting coil are mutually inducted. This indicates the mutual inductance between the receiving coil and the transmitting coil. This represents the impedance of the receiving circuit. This represents the two impedances of the receiving circuit. This indicates the mutual inductance between the receiving coils. This indicates the load value of transmission channel one. Indicates the primary impedance. This represents the transfer function of transmission channel two. This indicates the load value of transmission channel two.

[0014] Preferred method for generating composite modulation signal: Based on the inherent resonant frequency and power requirements of each receiving circuit, determine the frequency and amplitude of the corresponding modulation wave, and add all modulation waves together to obtain the final composite modulation signal.

[0015] The preferred formula for calculating the composite modulation signal is:

[0016] .

[0017] in, It is a composite modulation signal. The modulated wave corresponding to each receiving loop, , Indicates the number of receiving loops. This represents the amplitude of the modulated wave corresponding to each receiving loop. The frequency of the modulation wave corresponding to each receiving circuit. Indicates the time.

[0018] Preferred method: The method of generating the switching drive signal of the cascaded h-bridge multilevel inverter by comparing the composite modulation signal with the co-directionally stacked carriers using carrier-in-the-direction stacked modulation is as follows: 2n triangular carriers with the same amplitude, frequency, and phase are arranged in a stacked manner, with n triangular carriers located in the positive half of the coordinate axis and n triangular carriers located in the lower half of the coordinate axis. 2n drive signals are generated by modulating the composite modulation wave with the composite modulation wave. The drive signal modulated by one layer of carriers and the composite modulation wave, as well as its complementary signal, are used to drive one bridge arm, thereby enabling the cascaded h-bridge inverter to generate multi-frequency composite power with 2n+1 levels.

[0019] Preferably, 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 end load from the multi-frequency composite energy through the resonant network of each receiving circuit.

[0020] Preferably, the cascaded h-bridge inverter is an inverter circuit composed of n cascaded h-bridges consisting of 4n switching transistors.

[0021] Preferably, both the primary and secondary sides of the multi-frequency, multi-load wireless power transmission system adopt an S-shaped compensation structure.

[0022] The preferred 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, the resonance condition is satisfied. The compensation capacitor values ​​corresponding to each receiving loop on the secondary side are calculated, where: The resonant frequency, This is a secondary-side compensation capacitor. This is the self-inductance of the receiving coil.

[0023] Preferred method for determining the primary-side compensation capacitor: Considering the overall system power, overall system transmission efficiency, and transmission efficiency of each frequency channel, the priority relationship is as follows: prioritize meeting the overall system power requirement, ensuring high efficiency of the main frequency transmission channels while preventing other frequency channels from becoming too inefficient, and maintaining a high overall system efficiency. This will yield the desired primary-side compensation capacitor. The optimal value.

[0024] Preferably, when adjusting the amplitude of the modulation wave, the amplitude of the final superimposed composite modulation signal should not be higher than the maximum value of the co-directional stacked carrier.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. The cascaded h-bridge multilevel inverter used in this invention has low harmonic content in its output power, so there is no need to consider the influence of non-target frequency power when designing the system resonant network, which simplifies the design of the system resonant network and improves the transmission efficiency from the system transmitter to the receiver.

[0027] 2. This invention uses carrier-coupled modulation technology based on composite modulation waves to obtain multi-frequency power output, wherein the power ratio of each frequency can be independently controlled, thereby realizing independent power supply to loads of different frequencies.

[0028] 3. The cascaded h-bridge multilevel inverter structure used in this invention allows the power to be distributed among the n h-bridges, thereby further improving the maximum input power of the system, enabling the system to achieve a larger power output and supply power to larger power loads.

[0029] 4. This invention enables multi-frequency power output from cascaded h-bridge multi-level inverters, realizes independent power transmission and control for multiple frequencies and loads, improves transmission efficiency from transmitter to receiver, enhances energy quality, and enables high-power power transmission. Attached Figure Description

[0030] Figure 1 This is the overall circuit schematic diagram of the multi-frequency, multi-load wireless power transmission system based on a cascaded h-bridge multilevel inverter involved in the embodiment.

[0031] Figure 2 This is a flowchart of the carrier co-directional stacked modulation process based on composite modulation waves in the embodiment.

[0032] Figure 3 This is a circuit simulation diagram involved in the embodiment.

[0033] Figure 4 It is the system equivalent model.

[0034] Figure 5 This is the simulated output voltage waveform of a cascaded h-bridge multilevel inverter, where... Figure 5 Figure (a) shows the inverter output voltage waveform. Figure 5 Figure (b) shows the system output voltage waveform.

[0035] Figure 6 This is a simulation harmonic analysis of a cascaded h-bridge multilevel inverter, in which... Figure 6 Figure (a) shows the harmonic analysis of the 20kHz channel. Figure 6 Figure (b) shows the harmonic analysis of the 60kHz channel. Detailed Implementation

[0036] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the invention. After reading this invention, any modifications of the invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0037] A multi-frequency, multi-load wireless power transfer system based on a cascaded h-bridge multilevel inverter, such as Figure 1 As shown, the system includes n DC power supplies 1, cascaded h-bridge inverters 2, a primary-side transmitter, a secondary-side receiver, and a PWM generation circuit. The n DC power supplies 1, cascaded h-bridge inverters 2, and primary-side transmitters are connected in series. The cascaded h-bridge inverters 2 are inverter circuits composed of n cascaded h-bridges consisting of 4n switching transistors. The primary-side transmitter includes a primary-side compensation capacitor and a primary-side transmitter coil 3 connected in series. The secondary-side receiver includes n power receiving loops 4. Each receiving loop 4 includes a receiving coil, a secondary-side compensation capacitor, and a load connected in series. The receiving coil is positioned opposite to the primary-side transmitter coil 3. The number of DC power supplies is the same as the number of h-bridges n. The number of output levels of the cascaded h-bridge inverters is 2n+1. The system has m receiving loops and loads operating at different frequencies.

[0038] In this embodiment, the number of h-bridges in the cascaded h-bridge inverter 2 is n, which corresponds to the number of DC power supplies 1, and the voltage values ​​of each DC power supply are equal. Then the number of output levels of the cascaded h-bridge inverter is 2n+1.

[0039] The PWM generation circuit is set in the primary side transmitter. The PWM generation circuit generates a modulation wave signal with the same frequency as the resonant frequency of the m receiving loops according to the different operating frequency requirements of the m receiving loops. The amplitude of each modulation wave signal is determined according to the energy demand of each receiving load. The modulation waves corresponding to each receiving loop are superimposed to obtain a composite modulation signal. Finally, the composite modulation signal is compared with the carrier stacked modulation method (the number of carrier layers is 2n) to generate the switching drive signal of the cascaded h-bridge multilevel inverter, so that the inverter can output a multi-frequency composite voltage with 2n+1 levels and containing the signals required by the m receiving loops.

[0040] The transfer functions of the two transmission channels of the system are:

[0041]

[0042]

[0043] in, This represents the transfer function of transmission channel one. Represents complex variables in the complex plane. This indicates that the receiving coil and the transmitting coil are mutually inducted. This indicates the mutual inductance between the receiving coil and the transmitting coil. This represents the impedance of the receiving circuit. This represents the two impedances of the receiving circuit. This indicates the mutual inductance between the receiving coils. This indicates the load value of transmission channel one. Indicates the primary impedance. This represents the transfer function of transmission channel two. This represents the load value of transmission channel two. Electrical energy of different frequencies between the two channels may interfere with each other, thus affecting the output power of each channel. The degree of interference between different channels is closely related to the frequency selectivity characteristics of the primary and secondary resonant network. This invention analyzes the effectiveness of the two channels in suppressing electrical energy of the opposite frequency by calculating the transfer functions G1(s) and G2(s) of the two channels and by plotting Bode plots.

[0044] Figure 2 The paper illustrates a carrier-in-direction stacked modulation technique based on composite modulated waves. The method for generating the composite modulated signal is as follows: based on the inherent resonant frequency and power requirements of each receiving circuit, the frequency and amplitude of the corresponding modulated wave are determined, and all modulated waves are added together to obtain the final composite modulated signal.

[0045] The formula for calculating composite modulated signals is:

[0046] .

[0047] in, It is a composite modulation signal. The modulated wave corresponding to each receiving loop, , Indicates the number of receiving loops. This represents the amplitude of the modulated wave corresponding to each receiving loop. The frequency of the modulation wave corresponding to each receiving circuit. Indicates the time.

[0048] Finally, a carrier-in-direction stacked modulation method is adopted to generate the switching drive signal for the cascaded H-bridge inverter by modulating the composite modulation wave and 2n layers of carriers. The composite modulation signal and the drive signal generated by one layer of carriers are used to drive one bridge arm, thereby enabling the cascaded H-bridge multilevel inverter to generate high-frequency composite power containing the frequency and power requirements of all power receiving circuits. Specifically, the method of generating the switching drive signal for the cascaded H-bridge multilevel inverter by comparing the composite modulation signal with the co-directional stacked carriers is as follows: 2n triangular carriers with the same amplitude, frequency, and phase are arranged in a stacked manner, with n triangular carriers located in the positive half of the coordinate axis and n triangular carriers located in the lower half of the coordinate axis. These are modulated with the composite modulation wave to generate 2n drive signals. The drive signal modulated by one layer of carriers and the composite modulation wave, along with its complementary signal, are used to drive one bridge arm, thereby enabling the cascaded H-bridge inverter to generate multi-frequency composite power with 2n+1 levels.

[0049] 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.

[0050] The primary and secondary sides of the multi-frequency, multi-load wireless power transmission system both employ an S-shaped compensation structure. The secondary-side receiving device includes n power receiving loops, each containing a receiving coil, a compensation capacitor, and a load. Figure 1 In the system shown, , The resonant network, connected in series, forms the first receiving loop, with a resonant frequency of . . , The resonant network, connected in series, forms the second receiving circuit, with a resonant frequency of... And so on. , Series connection to form a receiving circuit The resonant network has a resonant frequency of And all parameters satisfy:

[0051]

[0052] 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 loop on the secondary side are calculated, where: The resonant frequency, This is a secondary-side compensation capacitor. This is the self-inductance of the receiving coil.

[0053] Because the primary side contains multi-frequency electrical energy, therefore 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.

[0054] Therefore, the method for determining the primary-side compensation capacitor is as follows: considering the overall system power, overall system transmission efficiency, and transmission efficiency of each frequency channel, the priority relationship among them is: firstly, ensuring that the overall system power meets the standard; secondly, ensuring that the efficiency of the main frequency transmission channels is high, while preventing the efficiency of other frequency channels from being too low, thus ensuring that the overall system efficiency remains at a high level. This will yield the primary-side compensation capacitor. The optimal value.

[0055] The working principle of the multi-frequency, multi-load wireless power transfer system based on a cascaded h-bridge multilevel inverter involved in this implementation is as follows: First, the system parameters are designed, with a focus on the selection of capacitors on the primary and secondary sides. Specifically:

[0056] (1) Based on the requirements of the load in each receiving circuit for the operating frequency, and combined with the self-inductance of each receiving coil, the resonance condition is satisfied. Therefore, the corresponding compensation capacitor values ​​in each receiving circuit on the secondary side can be calculated.

[0057] (2) The selection of the primary-side compensation capacitor needs to take into account the overall power factor of the system, the overall transmission efficiency of the system, and the transmission efficiency of each frequency channel. The priority relationship among them is: first, to meet the system power factor target; second, to ensure that the efficiency of the main frequency transmission channels is high, and third, to ensure that the efficiency of other frequency channels is not too low, so as to ensure that the overall system efficiency remains at a high level. The primary-side compensation capacitor can be obtained through system modeling calculation. The optimal value.

[0058] Next, based on the load's frequency and power requirements, as well as the number of loads, the number, amplitude, and frequency of the modulation waves are determined. The modulation waves are then superimposed to obtain a composite modulation wave, and a switching drive signal is generated using a carrier-in-the-direction stacking modulation method. When adjusting the modulation wave amplitude, care must be taken to ensure that the amplitude of the final superimposed composite modulation wave does not exceed the maximum value of the carrier waves stacked in the same direction; otherwise, distortion of the inverter output waveform will occur. The inverter's switching frequency is closely related to the carrier frequency. An excessively high carrier frequency will lead to frequent inverter switching, resulting in higher inverter losses, while an excessively low carrier frequency will increase harmonics in the inverter output. Furthermore, to reduce low-frequency harmonics, the carrier frequency is generally set to the least common multiple of the resonant frequencies of each receiving circuit. This allows the cascaded h-bridge multilevel inverter to output better composite high-frequency power.

[0059] The following section uses specific parameters and experimental analysis to further verify the technical effectiveness of this invention.

[0060] The verification will take a dual-frequency, dual-load circuit as an example, and its simulation circuit is as follows: Figure 3 As shown, its system equivalent model is as follows: Figure 4 As shown, set the DC voltage. The resonant frequency of the secondary receiving circuit Set to 20kHz and 60kHz; self-inductance of the primary-side transmitting coil It is 29.1 internal resistance It is 0.05 Through theoretical analysis of the primary-side compensation capacitor Choose a value of 1.8 ; Secondary 20kHz receiving coil self-inductance It is 88.6 internal resistance It is 0.08 resonant capacitance value It is 0.715 The mutual inductance value of the transmitting coil It is 17.1 ; Self-inductance of the secondary 60kHz receiving coil It is 89.1 internal resistance It is 0.08 resonant capacitance value It is 0.079 The mutual inductance of the transmitting coil It is 16.6 Since the two receiving coils are placed on opposite sides of the transmitting coil, the mutual inductance between the two receiving coils is negligible.

[0061] The carrier wave is composed of four in-phase carrier waves with an amplitude of 0.25 and a frequency of 360kHz, stacked together to achieve a carrier amplitude between -2 and 2. Two modulation wave amplitudes are set. The value is 0.64, and the composite modulation amplitude is 1.971. At this time, the ratio of the composite modulation amplitude to the carrier amplitude is approximately 0.9855.

[0062] Based on the above data, the dual-frequency dual-load wireless power transmission system is analyzed as follows:

[0063] a. The effective values ​​of the two frequency voltages output by the cascaded h-bridge multilevel inverter:

[0064]

[0065]

[0066] The modulation wave angular frequency is:

[0067] ,

[0068] b. Impedance analysis of the primary and secondary sides of the system

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075] in, , , For frequency The electrical energy in the system corresponds to the primary and secondary impedances. , , For frequency The electrical energy in the system corresponds to the primary and secondary impedances.

[0076] c. System primary and secondary currents

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083] in, For frequency The electrical energy generates current in the primary-side transmitting coil. For frequency The electrical energy at the secondary resonant frequency is The current generated in the receiving circuit, For frequency The electrical energy at the secondary resonant frequency is The current generated in the receiving circuit; For frequency The electrical energy generates current in the primary-side transmitting coil. For frequency The electrical energy at the secondary resonant frequency is The current generated in the receiving circuit, For frequency The electrical energy at the secondary resonant frequency is The current generated in the receiving circuit.

[0084] d. System active power analysis

[0085]

[0086]

[0087]

[0088]

[0089]

[0090]

[0091] in, For the frequency in the system is At the resonant frequency The output power in the receiving circuit, The intermediate frequency is At the resonant frequency The output power in the receiving circuit, For frequency The electrical energy is lost in the primary side and all secondary side receiving circuits. For the frequency in the system is At the resonant frequency The output power in the receiving circuit, The intermediate frequency is At the resonant frequency The output power in the receiving circuit, For frequency The electrical energy is lost in the primary side and all secondary side receiving circuits.

[0092] Therefore, the overall output power of the system is:

[0093]

[0094] Total system losses:

[0095]

[0096] e. System power factor

[0097] System reactive power:

[0098]

[0099]

[0100] in, For frequency The electrical energy has resonant frequencies at the primary and secondary sides. The reactive power generated in the receiving circuit, For frequency The electrical energy has resonant frequencies at the primary and secondary sides. The reactive power generated in the receiving circuit.

[0101] Therefore, the total reactive power of the system is:

[0102]

[0103] The total active power of the system is:

[0104]

[0105] Therefore, the system power factor is:

[0106]

[0107] f. System efficiency

[0108]

[0109] g. Consider the impact of harmonics on system efficiency

[0110] like Figure 5 , 6As shown, compared with the traditional full-bridge inverter structure, the cascaded h-bridge multilevel inverter used in this invention can significantly reduce low-frequency harmonics. This invention considers several harmonic frequencies with high content: 220kHz, 300kHz, 340kHz, 380kHz and 420kHz, with contents of 21.89%, 36.45%, 52.38%, 49.62% and 33.89% of 20kHz, respectively.

[0111] The efficiency of the system if harmonic effects are present is calculated as follows: .

[0112] It is evident that the multi-frequency, multi-load wireless power transmission system based on a cascaded h-bridge multi-level inverter proposed in this invention can improve the efficiency from the transmitter to the receiver. The carrier co-directional stacking technology based on composite modulation waves can realize multi-frequency output of the inverter and independent control of each output channel. In addition, the input power is shunted in the h-bridge, thus making high-power transmission possible.

[0113] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A multi-frequency, multi-load wireless power transmission system based on a cascaded h-bridge multilevel inverter, characterized in that, The system includes n DC power supplies (1), cascaded h-bridge inverters (2), primary-side transmitters, secondary-side receivers, and PWM generation circuits. The n DC power supplies (1), cascaded h-bridge inverters (2), and primary-side transmitters are connected in series. The primary-side transmitter includes a primary-side compensation capacitor and a primary-side transmitter coil (3) connected in series. The secondary-side receiver includes n power receiving circuits (4). Each power receiving circuit (4) includes a receiver coil, a secondary-side compensation capacitor, and a load connected in series. The receiver coil is positioned opposite to the primary-side transmitter coil (3). The number of DC power supplies is the same as the number of h-bridges n. The number of output levels of the cascaded h-bridge inverters is 2n+1. The system has m receiver circuits and loads operating at different operating frequencies. The PWM generation circuit is set in the primary side transmitter. The PWM generation circuit generates a modulation wave signal with the same frequency as the resonant frequency of the m receiving loops according to the different operating frequency requirements of the m receiving loops. The amplitude of each modulation wave signal is determined according to the energy demand of each receiving load. The modulation waves corresponding to each receiving loop are superimposed to obtain a composite modulation signal. Finally, the composite modulation signal is compared with the carrier superimposed modulation method to generate the switching drive signal of the cascaded h-bridge multilevel inverter, so that the inverter can output a multi-frequency composite voltage with 2n+1 level numbers and containing the signals required by the m receiving loops. The method of generating the switching drive signal of the cascaded h-bridge multilevel inverter by comparing the composite modulation signal with the co-directionally stacked carriers using the carrier in the same direction is as follows: 2n triangular carriers with the same amplitude, frequency and phase are arranged in a stacked manner, with n triangular carriers located in the positive half of the coordinate axis and n triangular carriers located in the lower half of the coordinate axis. 2n drive signals are generated by modulating the composite modulation wave with the composite modulation wave. The drive signal modulated by one layer of carriers and the composite modulation wave, as well as its complementary signal, are used to drive one bridge arm, thereby enabling the cascaded h-bridge inverter to generate multi-frequency composite power with 2n+1 levels.

2. The multi-frequency, multi-load wireless power transmission system based on a cascaded h-bridge multilevel inverter according to claim 1, characterized in that, The transfer functions of the two transmission channels of the system are: Where G1(s) represents the transfer function of transmission channel one, s represents the complex variable in the complex plane, and M s1p M represents the mutual inductance between the receiving coil and the transmitting coil. s2p Z represents the mutual inductance between the receiving coil and the transmitting coil. s1 (s) represents the impedance of the receiving circuit, Z s2 (s) represents the two impedances of the receiving circuit, M s1s2 R represents the mutual inductance between the receiving coils. L1 Z represents the load value of transmission channel one. p (s) represents the primary impedance, G2(s) represents the transfer function of transmission channel two, and R L2 This indicates the load value of transmission channel two.

3. The multi-frequency, multi-load wireless power transmission system based on a cascaded h-bridge multilevel inverter according to claim 2, characterized in that: The method for generating a composite modulation signal is as follows: based on the inherent resonant frequency and power requirements of each receiving circuit, determine the frequency and amplitude of the corresponding modulation wave, and add all the modulation waves together to obtain the final composite modulation signal.

4. The multi-frequency, multi-load wireless power transmission system based on a cascaded h-bridge multilevel inverter according to claim 3, characterized in that, The formula for calculating composite modulated signals is: u r (a1 sin 2πf1t + a2 sin 2πf2t + a3 sin 2πf3t + ...a) m sin 2πf m t; Among them, u r For composite modulation signals, u ri Let i = 1, 2, ..., m, where m represents the number of receiving loops, and a i f represents the amplitude of the modulated wave corresponding to each receiving loop. i Let t represent the frequency of the modulated wave corresponding to each receiving loop, and t represent the time.

5. The multi-frequency, multi-load wireless power transmission system based on a cascaded h-bridge multilevel inverter according to claim 4, characterized in that: The secondary receiving coil receives the multi-frequency composite magnetic field from the transmitting coil and generates a multi-frequency voltage. Then, through the resonant network of each receiving circuit, the frequency power required by each receiving load is separated from the multi-frequency composite energy.

6. The multi-frequency, multi-load wireless power transmission system based on a cascaded h-bridge multilevel inverter according to claim 5, characterized in that: The cascaded h-bridge inverter (2) is an inverter circuit composed of n cascaded h-bridges consisting of 4n switching transistors; The primary and secondary sides of the multi-frequency, multi-load wireless power transmission system both adopt an S-shaped compensation structure.

7. The multi-frequency, multi-load wireless power transmission system based on a cascaded h-bridge multilevel inverter according to claim 6, characterized in that, The method for determining the secondary-side compensation capacitor is as follows: Based on the frequency requirements of the load in each receiving circuit, and combined with the self-inductance of each receiving coil, the resonance condition (2πf) is satisfied. i ) 2 L i C i =1, calculate the corresponding compensation capacitor value in each receiving circuit on the secondary side, where: f i C is the resonant frequency. i For secondary-side compensation capacitor, L i This is the self-inductance of the receiving coil.

8. The multi-frequency, multi-load wireless power transmission system based on a cascaded h-bridge multilevel inverter according to claim 7, characterized in that: The method for determining the primary-side compensation capacitor requires consideration of the overall system power factor, overall system transmission efficiency, and the transmission efficiency of each frequency channel. The priority relationship among these factors is as follows: Prioritize achieving the target overall system power factor; while ensuring high efficiency for the main frequency transmission channels, avoid excessively low efficiency for other frequency channels, thus maintaining a high overall system transmission efficiency. The primary-side compensation capacitor C can be obtained through system modeling and calculation. p The optimal value.

9. The multi-frequency, multi-load wireless power transmission system based on a cascaded h-bridge multilevel inverter according to claim 8, characterized in that: When adjusting the amplitude of the modulation wave, do not make the amplitude of the final superimposed composite modulation signal higher than the maximum value of the same-direction stacked carrier.

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