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

Abstract

The invention discloses a multi-frequency multi-load wireless electric energy transmission system based on a cascaded h-bridge multi-level inverter, which comprises n direct-current power supplies, the cascaded h-bridge inverter, a primary side transmitting device, a secondary side receiving device and a PWM (Pulse Width Modulation) generation circuit, and is characterized in that the PWM generation circuit is arranged on the primary side transmitting device; the method comprises the following steps: generating a switch driving signal of a cascaded h-bridge inverter by adopting a multi-modulation wave composite carrier same-direction laminated modulation mode, so that the cascaded h-bridge inverter generates composite multi-level voltage with different load working frequencies on a receiving side, and converting electric energy into magnetic energy through a transmitting coil; the secondary receiving coil of the system converts magnetic energy into electric energy, filters the electric energy of other frequencies through a resonant network, and supplies energy to a load through the electric energy of the resonant frequency of the system. According to the invention, not only is multi-frequency electric energy output of the cascaded h-bridge multi-level inverter realized, but also multi-frequency multi-load independent electric energy transmission and control are realized, and meanwhile, high-power electric energy transmission is realized.

Description

Technical Field

[0001] The present invention relates to the fields of wireless power transmission and power converters, and particularly to a multi-frequency and multi-load wireless power transmission system based on a cascaded H-bridge multilevel inverter. Background Art

[0002] The wireless power transmission system itself has the advantage of non-contact power transmission using spatial soft media, and has been widely applied to fields such as electric vehicles, smart devices, underwater devices, and drones.

[0003] Currently, due to the lack of a unified design standard for wireless charging devices, the wireless charging products of various manufacturers cannot be mutually compatible, and different wireless charging transmitting devices cannot charge different electrical devices. Therefore, researching a wireless power transmission system that can supply power to loads of multiple frequencies simultaneously has broad prospects. Most of the existing multi-frequency and multi-load wireless power transmission systems use full-bridge structures or half-bridge stacked structure inverters. Although existing technologies can achieve multi-frequency output of such inverters, there are still the following deficiencies:

[0004] 1. The harmonic content of the inverter output is relatively high: The outputs of traditional full-bridge or half-bridge structure inverters are both two-level voltages, and their harmonic content is relatively high. The existence of non-target harmonics brings difficulties to the design of the resonant networks at the transmitting and receiving ends of the multi-frequency and multi-load wireless power transmission system, greatly affects the efficiency from the transmitting end to the receiving end, and if the non-target harmonics cannot be separated, it also affects the energy usage quality of the device.

[0005] 2. The output power of the inverter is limited and cannot adapt to scenarios with relatively large power: Since the switching devices of the inverter have certain rated voltages and currents, this limits the maximum current and voltage that the inverter can withstand, thereby limiting the maximum power transmission capacity of the inverter. Summary of the Invention

[0006] Object of the Invention: In order to overcome the deficiencies existing in the prior art, the present invention provides a multi-frequency and multi-load wireless power transmission system based on a cascaded H-bridge multilevel inverter, which uses a carrier co-directional stacked modulation method with multi-modulation waves to generate the switching drive signals of the cascaded H-bridge inverter, enabling the cascaded H-bridge inverter to generate a composite multi-level voltage with different load operating frequencies on the receiving side, and converting electrical energy into magnetic energy through the transmitting coil; the receiving coil on the secondary side of the system converts magnetic energy into electrical energy, filters out the electrical energy of other frequencies through the resonant networks of their respective receiving circuits, and supplies power to the load with the electrical energy of the resonant frequency of the receiving circuit itself. This system can achieve improving the system efficiency of the transmitting and receiving ends, independently controlling the power of each receiving circuit, and realizing multi-frequency and multi-load wireless power transmission with relatively large power.

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

[0008] A multi-frequency and multi-load wireless power transmission system based on a cascaded H-bridge multilevel inverter, comprising n DC power supplies, a cascaded H-bridge inverter, a primary side transmitting device, a secondary side receiving device, and a PWM generation circuit. The n DC power supplies, the cascaded H-bridge inverter, and the primary side transmitting device are connected in series. The primary side transmitting device includes a primary side compensation capacitor and a primary side transmitting coil connected in series. The secondary side receiving device includes n power receiving circuits, and each receiving circuit includes a receiving coil, a secondary side compensation capacitor, and a load connected in series. The receiving coil is disposed opposite to the primary side transmitting coil. Among them, 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, and there are m receiving circuits and loads operating at different operating frequencies in the system.

[0009] The PWM generation circuit is disposed on the primary side transmitting device. The PWM generation circuit generates a modulation wave signal with a frequency consistent with the resonance frequencies of the m receiving circuits according to the requirements of different operating frequencies in the m receiving circuits, and determines the amplitudes of the modulation wave signals according to the energy consumption requirements of the loads on each receiving side. Then, the modulation waves corresponding to the determined receiving circuits are superimposed to obtain a composite modulation signal. Finally, the composite modulation signal is compared with the carrier wave stacked in the same direction by using the carrier wave same-direction layer stacking modulation method to generate a switching drive signal for 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 circuits.

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

[0011]

[0012]

[0013] Among them, represents the transfer function of transmission channel 1, represents the complex variable in the complex plane, represents the mutual inductance between the first receiving coil and the transmitting coil, represents the mutual inductance between the second receiving coil and the transmitting coil, represents the impedance of receiving circuit 1, represents the impedance of receiving circuit 2, represents the mutual inductance between the receiving coils, represents the load value of transmission channel 1, represents the primary side impedance, represents the transfer function of transmission channel 2, represents the load value of transmission channel 2.

[0014] Preferably, the method for generating the composite modulation signal is as follows: according to the inherent resonance frequencies and power requirements of each receiving loop, determine the frequencies and amplitudes of the corresponding modulation waves, and add all the modulation waves to obtain the final composite modulation signal.

[0015] Preferably, the calculation formula for the composite modulation signal is:

[0016] .

[0017] Wherein, is the composite modulation signal, is the modulation wave corresponding to each receiving loop, , represents the number of receiving loops, is the amplitude of the modulation wave corresponding to each receiving loop, is the frequency of the modulation wave corresponding to each receiving loop, represents the time.

[0018] Preferably, the method for generating the switching drive signals of the cascaded H-bridge multilevel inverter by comparing the composite modulation signal with the carrier waves in the same direction stacked modulation manner is as follows: arrange 2n triangular carrier waves with the same amplitude, the same frequency, and the same phase in a stacked manner, and among them, n triangular carrier waves are located in the positive half part of the coordinate axis, and another n triangular carrier waves are located in the negative half part of the coordinate axis. Modulate 2n drive signals through the composite modulation wave. The drive signals and their complementary signals modulated by one layer of carrier wave and the composite modulation wave are used to drive one bridge arm, so that the cascaded H-bridge inverter generates multi-frequency composite electric energy 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 electric energy required by each receiving-end load from the multi-frequency composite energy through the resonance network of each receiving loop.

[0020] Preferably, the cascaded H-bridge inverter is an inverter circuit formed by cascading n H-bridges composed of 4n switching tubes.

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

[0022] Preferably, the method for determining the secondary compensation capacitor: according to the requirements of the load for the power consumption frequency in each receiving loop, combined with the self-inductance of each receiving coil, to meet the resonance condition , calculate the values of the compensation capacitors corresponding to each receiving loop on the secondary side, where: is the resonance frequency, is the secondary compensation capacitor, is the self-inductance of the receiving coil.

[0023] Preferred: Method for determining the primary side compensation capacitor: Considering the overall system power, the overall system transmission efficiency, and the transmission efficiency of each frequency channel, where the priority relationship among them is: First, ensure that the overall system power meets the standard. Under the condition of ensuring a relatively high efficiency of the main frequency transmission channel, do not make the efficiency of other frequency channels too low, and ensure that the overall system efficiency remains at a relatively high level, then the optimal value of the primary side compensation capacitor can be obtained.

[0024] Preferred: When adjusting the amplitude of the modulation wave, do not make the amplitude of the finally superimposed composite modulation signal higher than the maximum value of the in-phase stacked carrier wave.

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

[0026] 1. The electric energy output by the cascaded H-bridge multilevel inverter used in the present invention has less harmonic content. Therefore, when designing the system resonance network, there is no need to consider the influence of non-target frequency electric energy too much, which simplifies the design of the system resonance network and also improves the transmission efficiency from the system transmitter to the receiver.

[0027] 2. The present invention uses the carrier in-phase stacking modulation technology based on the composite modulation wave to obtain multi-frequency electric energy output, and the proportion of each frequency electric energy can be independently controlled, thus realizing independent power supply for different frequency loads.

[0028] 3. The structure of the cascaded H-bridge multilevel inverter used in the present invention enables the power to be distributed among n H-bridges, thereby further increasing the maximum input power of the system, that is, enabling the system to output a relatively large power and supply power to relatively large power loads.

[0029] 4. The present invention realizes the multi-frequency electric energy output of the cascaded H-bridge multilevel inverter, realizes the independent electric energy transmission and control of multi-frequency and multi-loads, improves the transmission efficiency from the transmitter to the receiver, improves the energy utilization quality, and realizes the transmission of high-power electric energy. Brief Description of the Drawings

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

[0031] Figure 2 is the flow block diagram of the carrier in-phase stacking modulation based on the composite modulation wave in the embodiment.

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

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

[0034] Figure 5 It is the simulated output voltage waveform of the cascaded H-bridge multilevel inverter, where Figure 5 In Figure (a), it is the output voltage waveform of the inverter, Figure 5 In Figure (b), it is the output voltage waveform of the system.

[0035] Figure 6 It is the simulation harmonic analysis of the cascaded H-bridge multilevel inverter, where Figure 6 In Figure (a), it is the harmonic analysis of the 20 kHz channel, Figure 6 In Figure (b), it is the harmonic analysis of the 60 kHz channel. Specific embodiments

[0036] The present invention will be further clarified below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. After reading the present invention, those skilled in the art's various equivalent modifications of the present invention fall within the scope defined by the appended claims of this application.

[0037] A multi-frequency and multi-load wireless power transmission system based on a cascaded H-bridge multilevel inverter, as Figure 1 shown, includes n DC power supplies 1, a cascaded H-bridge inverter 2, a primary side transmitting device, a secondary side receiving device, and a PWM generation circuit. The n DC power supplies 1, the cascaded H-bridge inverter 2, and the primary side transmitting device are connected in series. The cascaded H-bridge inverter 2 is an inverter circuit formed by cascading n H-bridges composed of 4n switching tubes. The primary side transmitting device includes a primary side compensation capacitor and a primary side transmitting coil 3 connected in series. The secondary side receiving device includes n power receiving circuits 4. Each receiving circuit 4 includes a receiving coil, a secondary side compensation capacitor, and a load connected in series. The receiving coil is disposed opposite to the primary side transmitting coil 3. Among them, 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, and there are m receiving circuits and loads operating at different operating frequencies in the system.

[0038] In this embodiment, the number of H-bridges in the cascaded H-bridge inverter 2 is n, then the number of corresponding DC power supplies 1 is n, and the voltage values of each DC power supply are equal, that is , then the number of levels output by the cascaded H-bridge inverter is 2n + 1.

[0039] The PWM generation circuit is arranged in the primary side emission device. The PWM generation circuit generates a modulation wave signal with a frequency consistent with the resonance frequencies of the m receiving circuits according to the requirements of different operating frequencies in the m receiving circuits, determines the amplitudes of the modulation wave signals according to the energy consumption requirements of the loads on each receiving side, then superimposes the modulation waves corresponding to the determined receiving circuits to obtain a composite modulation signal, and finally uses the carrier in-phase stacking modulation method (the number of carrier layers is 2n) to compare the composite modulation signal with the in-phase stacked carriers to generate the switching drive signals 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 circuits.

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

[0041]

[0042]

[0043] Among them, represents the transfer function of transmission channel 1, represents the complex variable in the complex plane, represents the mutual inductance between the first receiving coil and the transmitting coil, represents the mutual inductance between the second receiving coil and the transmitting coil, represents the impedance of the first receiving circuit, represents the impedance of the second receiving circuit, represents the mutual inductance between the receiving coils, represents the load value of transmission channel 1, represents the primary side impedance, represents the transfer function of transmission channel 2, represents the load value of transmission channel 2. The electric 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 selection characteristics of the primary and secondary resonance networks. The present invention analyzes the effects of the two channels in suppressing the electric energy of each other's frequencies by calculating the transfer functions G1(s) and G2(s) of the two channels and by plotting the Bode diagram.

[0044] Figure 2 Illustrates the carrier in-phase stacking modulation technology based on the composite modulation wave. The generation method of the composite modulation signal is as follows: According to the natural resonance frequencies and power requirements of each receiving circuit, determine the frequencies and amplitudes of the corresponding modulation waves, and add all the modulation waves to obtain the final composite modulation signal.

[0045] The calculation formula of the composite modulation signal is:

[0046] .

[0047] Among them, is a composite modulation signal, is the modulation wave corresponding to each receiving loop, , represents the number of receiving loops, is the amplitude of the modulation wave corresponding to each receiving loop, is the frequency of the modulation wave corresponding to each receiving loop, represents the time.

[0048] Finally, the carrier in-phase stacking modulation method is adopted to modulate the composite modulation wave and the 2n-layer carrier to generate the switching drive signal of the cascaded H-bridge inverter. Among them, the drive signal generated by the composite modulation signal and one layer of carrier is used to drive one bridge arm, so that the cascaded H-bridge multilevel inverter generates high-frequency composite electric energy containing the frequency and power requirements of all electric energy receiving loops. Specifically, the method of using the carrier in-phase stacking modulation method to compare the composite modulation signal with the in-phase stacked carrier to generate the switching drive signal of the cascaded H-bridge multilevel inverter is as follows: Arrange 2n triangular carriers with the same amplitude, the same frequency, and the same phase in a stacked manner, and among them, n triangular carriers are located in the positive half part of the coordinate axis, and another n triangular carriers are located in the negative half part of the coordinate axis. Modulate with the composite modulation wave to generate 2n drive signals. The drive signal and its complementary signal modulated by one layer of carrier and the composite modulation wave are used to drive one bridge arm, so that the cascaded H-bridge inverter generates multi-frequency composite electric energy with 2n + 1 level quantities.

[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 electric energy required by each receiving-end load from the multi-frequency composite energy through the resonant network of each receiving loop.

[0050] Both the primary side and the secondary side of the multi-frequency multi-load wireless power transmission system adopt the S-type compensation structure. Among them, the secondary receiving device includes n electric energy receiving loops, and each receiving loop includes a receiving coil, a compensation capacitor, and a load. In Figure 1 the system shown, , are connected in series to form the resonant network of receiving loop one, and the resonant frequency is . , are connected in series to form the resonant network of receiving loop two, and the resonant frequency is . And so on, , are connected in series to form the resonant network of receiving loop , and the resonant frequency is , and each parameter satisfies:

[0051]

[0052] Therefore, the method for determining the secondary compensation capacitor is as follows: According to the requirements of the loads in each receiving loop for the power consumption frequency, combined with the self-inductance of each receiving coil, the resonance condition is satisfied , and the corresponding compensation capacitor values in each receiving loop on the secondary side are calculated, where: is the resonance frequency, is the secondary compensation capacitor, is the self-inductance of the receiving coil.

[0053] Since there is multi-frequency electric energy on the primary side, therefore the selection of cannot refer to the selection criteria of the secondary capacitor. The main purpose of the primary capacitor is to compensate for the reactive power of the system and improve the overall power factor of the system. However, its selection should not have too much impact on the overall system efficiency and the transmission efficiency of each frequency of electric energy. Therefore, the primary capacitor should also be selected in combination with the frequencies of each power channel.

[0054] Therefore, the method for determining the primary compensation capacitor is as follows: Considering the overall power 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, ensure that the overall power of the system meets the standard. Under the condition of ensuring a relatively high efficiency of the main frequency transmission channel, do not make the efficiency of other frequency channels too low, and ensure that the overall system efficiency remains at a relatively high level, then the optimal value of the primary compensation capacitor can be obtained.

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

[0056] (1) According to the requirements of the loads in each receiving loop for the power consumption frequency, combined with the self-inductance of each receiving coil, the resonance condition is satisfied , and thus the corresponding compensation capacitor values in each receiving loop on the secondary side can be calculated.

[0057] (2) The selection of the primary compensation capacitor needs to consider 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, ensure that the power factor of the system meets the standard. Under the condition of ensuring a relatively high efficiency of the main frequency transmission channel, do not make the efficiency of other frequency channels too low, and ensure that the overall system efficiency remains at a relatively high level. Through system modeling and calculation, the optimal value of the primary compensation capacitor can be obtained.

[0058] Next, according to the power consumption demands of the load for frequency and power, as well as the number of loads, determine the number, amplitude, and frequency of the modulation waves. Superimpose the modulation waves to obtain a composite modulation wave, and use the modulation method of carrier in-phase stacking to generate the switching drive signal. When adjusting the amplitude of the modulation wave, it should be noted not to make the amplitude of the finally superimposed composite modulation wave higher than the maximum value of the in-phase stacked carrier, otherwise waveform distortion of the inverter output will occur. The switching frequency of the inverter is closely related to the carrier frequency. An excessively high carrier frequency will cause the inverter to switch frequently, resulting in higher inverter losses, while an excessively low carrier frequency will lead to an increase in harmonics output by the inverter. In addition, to reduce low-frequency harmonics, the carrier frequency is generally set to the least common multiple of the resonance frequencies of each receiving circuit. Thus, the cascaded H-bridge multilevel inverter outputs better composite high-frequency electric energy.

[0059] Next, specific parameters are substituted, and the technical effects of the present invention are further verified through experimental analysis.

[0060] The verification will take the dual-frequency and dual-load as an example. Its simulation circuit is as Figure 3 shown, and its system equivalent model is as Figure 4 shown. Set the DC voltage ; the resonance frequencies of the secondary receiving circuits are set to 20 kHz and 60 kHz; the self-inductance of the primary transmitting coil is 29.1 , and the internal resistance is 0.05 . Through theoretical analysis, the value of the primary compensation capacitor is selected as 1.8 ; the self-inductance of the secondary 20 kHz receiving coil is 88.6 , the internal resistance is 0.08 , the resonance capacitance value is 0.715 , and the mutual inductance value with the transmitting coil is 17.1 ; the self-inductance of the secondary 60 kHz receiving coil is 89.1 , the internal resistance is 0.08 , the resonance capacitance value is 0.079 , and the mutual inductance value with the transmitting coil is 16.6 . Since the two receiving coils are respectively placed on both sides of the transmitting coil, the mutual inductance between the two receiving coils is negligible.

[0061] The carrier is formed by stacking four in-phase carrier layers with an amplitude of 0.25 and a frequency of 360 kHz, so that the carrier amplitude is between -2 and 2. Set the amplitudes of the two modulation waves to be 0.64. At this time, the amplitude of the composite modulation wave is 1.971, and the ratio of the amplitude of the composite modulation wave to the carrier amplitude is about 0.9855.

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

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

[0064]

[0065]

[0066] The angular frequency of the modulation wave is:

[0067] ,

[0068] b. Analysis of the primary and secondary impedances of the system

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075] Among them, 、 、 are the primary and secondary impedances corresponding to the electrical energy with frequency in the system, 、 、 are the primary and secondary impedances corresponding to the electrical energy with frequency in the system.

[0076] c. The primary and secondary currents of the system

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083] wherein, is the current generated by the electric energy with frequency in the primary side transmitting coil, is the current generated by the electric energy with frequency in the secondary side receiving loop with the resonance frequency ; is the current generated by the electric energy with frequency in the secondary side receiving loop with the resonance frequency ; is the current generated by the electric energy with frequency in the primary side transmitting coil, is the current generated by the electric energy with frequency in the secondary side receiving loop with the resonance frequency ; is the current generated by the electric energy with frequency in the secondary side receiving loop with the resonance frequency .

[0084] d. System active power analysis

[0085]

[0086]

[0087]

[0088]

[0089]

[0090]

[0091] wherein, is the output power in the receiving loop with the resonance frequency in the system at the frequency ; is the output power in the receiving loop with the resonance frequency in the system at the frequency ; is the loss caused by the electric energy with the frequency in the primary side and all secondary side receiving loops. is the frequency in the system at the resonance frequency The output power in the receiving circuit with a frequency of at the resonant frequency The output power in the receiving circuit is the power loss caused by the electric energy with a frequency of in the primary side and all secondary side receiving circuits

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

[0093]

[0094] The total system loss is

[0095]

[0096] e. System power factor

[0097] The reactive power of the system is

[0098]

[0099]

[0100] wherein is the reactive power generated by the electric energy with a frequency of in the primary side and the receiving circuit with a secondary side resonant frequency of and is the reactive power generated by the electric energy with a frequency of in the primary side and the receiving circuit with a secondary side resonant frequency of

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

[0102]

[0103] Also, the total active power of the system is

[0104]

[0105] Therefore, the system power factor is

[0106]

[0107] f. System efficiency

[0108]

[0109] g. Considering the influence of harmonics on system efficiency

[0110] Such as Figure 5 、 6 ​As shown, compared with the traditional full-bridge inverter structure, the cascaded H-bridge multilevel inverter adopted in the present invention can significantly reduce low-frequency harmonics. The present invention considers several harmonic frequencies with relatively high contents: 220 kHz, 300 kHz, 340 kHz, 380 kHz, and 420 kHz, and their contents are 21.89%, 36.45%, 52.38%, 49.62%, and 33.89% of that of 20 kHz respectively.

[0111] By calculation, if there are harmonics affecting the system efficiency, it is .

[0112] It can be easily seen from this that the multi-frequency and multi-load wireless power transmission system based on the cascaded H-bridge multilevel inverter proposed in the present invention can improve the efficiency from the transmitter end to the receiver end of the system. The carrier co-directional stacking technology based on the composite modulation wave adopted can achieve multi-frequency output of the inverter and can realize 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 are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A multi-frequency and multi-load wireless power transmission system based on cascaded H-bridge multi-level inverters, characterized in that: The system comprises n DC power supplies (1), cascaded H-bridge inverters (2), a primary transmitting device, a secondary receiving device, and a PWM generating circuit, wherein the n DC power supplies (1), the cascaded H-bridge inverters (2), and the primary transmitting devices are connected in series, and the primary transmitting device comprises a primary compensation capacitor and a primary transmitting coil (3) connected in series; the secondary receiving device comprises n electric energy receiving circuits (4), each receiving circuit (4) comprises a receiving coil, a secondary compensation capacitor, and a load connected in series, and the receiving coil is arranged opposite to the primary transmitting coil (3), wherein the number of DC power supplies is consistent with the number of H-bridges n, the number of output levels of the cascaded H-bridge inverters is 2n+1, and there are m receiving circuits and loads operating at different operating frequencies in the system; A PWM generating circuit is arranged in a primary transmitting device. The PWM generating circuit generates a modulation wave signal having a frequency consistent with the resonance frequency of the m receiving circuits according to the requirements of different working frequencies in the m receiving circuits, and determines the amplitude of each modulation wave signal according to the energy demand of each receiving side load, and then superimposes the modulation waves corresponding to each determined receiving circuit to obtain a composite modulation signal. Finally, the composite modulation signal is compared with the carrier stacked in the same direction by using the carrier stacking modulation mode to generate a switch driving signal of the cascaded H-bridge multi-level 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 circuits.

2. The multi-frequency and multi-load wireless power transmission system based on cascaded H-bridge multi-level inverter according to claim 1, characterized in that: The transfer function of the two transmission channels of the system is: in, represents the transfer function of transmission channel one, represents a complex variable in the complex plane, represents the mutual inductance between the receiving coil 1 and the transmitting coil, represents the mutual inductance between the receiving coil 2 and the transmitting coil, Represents the receiving loop impedance. Represents the second impedance of the receiving loop, represents the mutual inductance between the receiving coils, Indicates the load value of transmission channel 1, represents the primary impedance, represents the transfer function of transmission channel 2, Indicates the load value of transmission channel 2.

3. The multi-frequency and multi-load wireless power transmission system based on cascaded H-bridge multi-level inverter according to claim 2, characterized in that: The method for generating the composite modulated signal is as follows: according to the inherent resonant frequency and power requirement of each receiving circuit, the frequency and amplitude of the corresponding modulated wave are determined, and all the modulated waves are added together to obtain the final composite modulated signal.

4. The multi-frequency and multi-load wireless power transmission system based on cascaded H-bridge multi-level inverter according to claim 3 is characterized in that: The calculation formula of the composite modulated signal is: ； in, is a composite modulated signal, is the modulation wave corresponding to each receiving circuit, , Indicates the number of receiving loops, is the amplitude of the modulation wave corresponding to each receiving circuit, is the frequency of the modulation wave corresponding to each receiving circuit, Indicates time.

5. The multi-frequency and multi-load wireless power transmission system based on cascaded H-bridge multi-level inverters according to claim 4, characterized in that: The method of using the carrier co-directional stacking modulation method to compare the composite modulation signal with the co-directional stacked carrier to generate the switch drive signal of the cascaded H-bridge multi-level inverter is as follows: 2n triangular carriers with the same amplitude, frequency and phase are arranged in a stacked manner, and n of the triangular carriers are located in the positive half of the coordinate axis, and n of the triangular carriers are located in the lower half of the coordinate axis, and 2n drive signals are modulated by the composite modulation wave. The drive signal modulated by a layer of carrier and the composite modulation wave and its complementary signal are used to drive a bridge arm, so that the cascaded H-bridge inverter generates 2n+1 levels of multi-frequency composite electric energy.

6. The multi-frequency and multi-load wireless power transmission system based on cascaded H-bridge multi-level inverters according to claim 5, characterized in that: 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.

7. The multi-frequency and multi-load wireless power transmission system based on cascaded H-bridge multi-level inverters according to claim 6, characterized in that: The cascaded H-bridge inverter (2) is an inverter circuit formed by cascading n H-bridges composed of 4n switch tubes; the primary side and the secondary side of the multi-frequency multi-load wireless power transmission system both adopt an S-type compensation structure.

8. The multi-frequency and multi-load wireless power transmission system based on cascaded H-bridge multi-level inverters according to claim 7, characterized in that: Method for determining the secondary compensation capacitor: According to the requirements of the load on the power frequency in each receiving circuit, combined with the self-inductance of each receiving coil, the resonance condition is met. , calculate the corresponding compensation capacitance value in each receiving circuit of the secondary side, where: is the resonant frequency, is the secondary side compensation capacitor, is the self-inductance of the receiving coil.

9. The multi-frequency and multi-load wireless power transmission system based on cascaded H-bridge multi-level inverters according to claim 8, characterized in that: The method for determining the primary compensation capacitor is as follows: considering the overall system power, the overall system transmission efficiency, and the transmission efficiency of each frequency channel, the priority relationship between them is: give priority to meeting the overall system power standard, while ensuring the efficiency of the main frequency transmission channel, while ensuring the efficiency of other frequency channels, the primary compensation capacitor can be obtained. The best value.

10. The multi-frequency and multi-load wireless power transmission system based on cascaded H-bridge multi-level inverters according to claim 9, 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 co-directionally stacked carrier.

Images