A frequency multiplication control strategy for wireless power transmission systems

Abstract

The present invention provides a frequency doubling control strategy suitable for wireless power transmission systems, which is different from the traditional phase shift control strategy: the duty cycle of the leading bridge arm and the lagging bridge arm is always 0.5, the operating frequency of the resonant tank is the same as the switching frequency, and the voltage at both ends of the load is regulated by controlling the phase shift angle. The frequency doubling control strategy controls the duty cycle of the two switch tubes in the same bridge arm to 0.25 and 0.75, and the phase angles of the two bridge arms differ by 180 degrees, thereby achieving a multiplication effect of the operating frequency of the resonant tank at the same switching frequency compared with the traditional phase shift control strategy, thereby improving the efficiency of the wireless power transmission system. When regulating the voltage, the dual-frequency control strategy is combined to control the output voltage by adjusting the duty cycle d of the control frequency, and the voltage regulation logic is simple. At the same time, because the parasitic capacitance of the switch tube involved in each switching action of the frequency doubling control strategy is two, which is half of the traditional phase shift control strategy, the soft switching condition is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless energy transmission, which converts electric energy into a magnetic field by means of magnetic coupling and converts the electric energy into electric energy on a receiving side after transmission, and in particular to a frequency multiplication control strategy applicable to a wireless power transmission system. Background Art

[0002] Wireless power transmission technology achieves complete electrical isolation between the power supply and the power-consuming equipment, and solves the problems of circuit aging, tip discharge, and spark generation in traditional power supply. It has many advantages such as safety, flexibility, and reliability, and is widely used in electric vehicles, drones, underwater submersibles, medical equipment, etc. Although wireless power transmission has the above advantages, it is limited by existing technical research. The current wireless power transmission system still has problems with transmission power, efficiency, and distance, as well as electromagnetic compatibility and biosafety. Among them, power transmission efficiency is the most basic and most important problem, which limits the promotion and application of this technology in other fields.

[0003] At present, the strategies commonly used by wireless power transmission systems to improve system efficiency are: (1) Adding relay coils: Adding relay coils can greatly increase the excitation current, amplify the alternating magnetic field between the coils, and improve the efficiency of the wireless power transmission system. (2) Adding magnetic isolation sheets: The magnetic isolation sheets can guide the alternating magnetic field generated by the primary coil, so that the magnetic field energy generated by the primary coil acts on the secondary coil as much as possible, thereby improving the coupling coefficient of the magnetic coupling system and optimizing the efficiency of the wireless power transmission system.

[0004] However, these traditional strategies often only consider improving the coupling coefficient M of the magnetic coupling system. Adding relay coils or additional magnetic isolation sheets increases the hardware complexity of the wireless power transmission system and increases the overall cost of the system.

[0005] Therefore, the present invention aims to seek a technology that can achieve good energy transmission efficiency without increasing the complexity of the wireless power transmission system. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a frequency doubling control strategy suitable for a wireless power transmission system, which realizes a doubling effect of the operating frequency of the resonant slot at the same switching frequency compared with a traditional phase shift control strategy, thereby improving the efficiency of the wireless power transmission system.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] A frequency multiplication control strategy applicable to a wireless power transmission system comprises the following steps:

[0009] S1, set the duty cycle of the drive signal of the inverter circuit switch tubes S1 and S4 to 0.25, the duty cycle of the drive signal of the switch tubes S2 and S3 to 0.75, the phase angle difference of the two bridge arm drive signals is 180 degrees, and the system working pulse F1 is generated, and the frequency of the working pulse F1 is f1;

[0010] S2. Due to the characteristics of the frequency doubling control strategy: the square wave frequency output by the inverter circuit is twice the switching frequency of the switch tube, and the resonant frequency f0 of the magnetic coupling resonance system is twice the working pulse frequency f1. According to the following formula,

[0011]

[0012] S3, set the inverter circuit to output control pulse F2, the control pulse F2 frequency is f2, and the voltage across the load is adjusted by changing the control frequency F2 duty cycle d according to the following formula:

[0013]

[0014] S4. Use the control frequency F2 to modulate the working pulse F1, and use the modulated four drive signals to drive the four switch tubes of the inverter circuit, so that the load operates under a stable voltage.

[0015] Preferably, due to the frequency multiplication effect of the frequency multiplication modulation strategy, the frequency of the square wave output by the inverter circuit is twice the frequency f1 of the working pulse F1 and is the same as the inherent resonant frequency f0 of the resonant circuit, thereby ensuring high-efficiency operation of the system in the working range.

[0016] Preferably, the control pulse F2 controls the working pulse F1 at a lower frequency f2. When the control pulse F2 outputs a high level, the working pulse F1 drives the inverter circuit switch tube to operate normally. When the control pulse F2 outputs a low level, the working pulse F1 driving the inverter circuit switch tube is effectively disabled.

[0017] Preferably, the formula in S3 is derived as follows:

[0018] According to Kirchhoff's circuit theory, the mesh equation of the transmitter circuit is:

[0019]

[0020] The mesh equation of the receiving side circuit is:

[0021]

[0022] When the transmission system is in resonance:

[0023]

[0024] Formula (1) and formula (2) can be simplified to:

[0025]

[0026] The currents on the transmitting and receiving sides are:

[0027]

[0028] The voltage transfer ratio is:

[0029]

[0030] Without considering the switching loss of the inverter circuit and only considering the efficiency of the magnetic coupling system, the transmission efficiency η of the entire system is:

[0031]

[0032] From formula (7), it can be seen that the transmission efficiency of the wireless power transmission system can be improved by increasing the coupling coefficient M and the resonant frequency f of the magnetic coupling system. The frequency doubling control strategy can double the output resonant voltage frequency under the same switching frequency, thereby achieving the purpose of improving the system transmission efficiency.

[0033] Expand the voltage waveform of the unipolar voltage V1 output by the inverter circuit under the frequency doubling control strategy into a Fourier series:

[0034]

[0035] When only the fundamental component is considered and the duty cycle of the control frequency F2 is d, the input voltage on the transmitting side is The effective value of U1 becomes:

[0036]

[0037] The duty cycle d of the control pulse F2 and the receiving side voltage U L The relationship is:

[0038]

[0039] It can be seen from formula (10) that when the DC input voltage U in When the coupling coefficient M remains unchanged, the voltage U at both ends of the load can be controlled by changing the duty cycle d of the control pulse F2. L control.

[0040] Compared with the prior art, the present invention has at least the following beneficial effects:

[0041] (1) Compared with the traditional phase-shift control strategy, under the same switching frequency, the frequency doubling control strategy doubles the operating frequency of the resonant tank, thereby improving the efficiency of the wireless power transmission system.

[0042] (2) In terms of soft switching: Because the frequency doubling control strategy involves two parasitic capacitors of the switch tube in each switching action, which is half of the traditional phase-shift control strategy, the conditions for soft switching are reduced, making it easier to achieve soft switching.

[0043] (3) When adjusting the voltage, the dual-frequency control strategy is combined to control the output voltage by adjusting the duty cycle d of the control frequency, and the voltage regulation logic is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a graph showing the relationship between resonant frequency and transmission efficiency.

[0045] Figure 2 It is a system block diagram of the wireless power transmission system of the present invention.

[0046] Figure 3 This is a circuit model of the wireless power transmission system of the present invention.

[0047] Figure 4 is a flow chart of the wireless power transmission system of the present invention.

[0048] Figure 5 It is the waveform diagram of working pulse F1 and control pulse F2 in the frequency doubling control strategy.

[0049] Figure 6 This is the efficiency comparison curve between the frequency doubling control strategy and the traditional phase shifting control strategy.

[0050] Figure 7 It is the mutual inductance equivalent model of wireless energy transmission power conversion system.

[0051] Figure 8 1 is a control waveform diagram showing the switching transistors S1 to S4 of the first embodiment.

[0052] Fig. 9 1 is a diagram showing the load voltage and inverter circuit output waveforms of Example 1.

[0053] Fig.10 1 is a control waveform diagram showing the switching transistors S1 to S4 of the first embodiment.

[0054] Fig.11 1 is a diagram showing the load voltage and inverter circuit output waveforms of Example 1.

[0055] Fig.12 1 is a control waveform diagram showing the switching transistors S1 to S4 of the first embodiment.

[0056] Fig.13 1 is a diagram showing the load voltage and inverter circuit output waveforms of Example 1.

[0057] Fig.14 1 is a control waveform diagram showing the switching transistors S1 to S4 of the first embodiment.

[0058] Fig.15 1 is a diagram showing the load voltage and inverter circuit output waveforms of Example 1. DETAILED DESCRIPTION

[0059] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0060] An embodiment of the present invention provides a frequency multiplication control strategy applicable to a wireless power transmission system, comprising the following steps:

[0061] S1, set the duty cycle of the drive signal of the inverter circuit switch tubes S1 and S4 to 0.25, the duty cycle of the drive signal of the switch tubes S2 and S3 to 0.75, the phase angle difference of the two bridge arm drive signals is 180 degrees, and the system working pulse F1 is generated, and the frequency of the working pulse F1 is f1;

[0062] S2. Due to the characteristics of the frequency doubling control strategy: the frequency of the inverter circuit outputting the square wave is twice the switching frequency of the switch tube. The resonant frequency f0 of the magnetic coupling resonance system is twice the operating pulse frequency f1. According to the following formula,

[0063]

[0064] S3, set the inverter circuit to output control pulse F2, the control pulse F2 frequency is f2, and the voltage across the load is adjusted by changing the control frequency F2 duty cycle d according to the following formula:

[0065]

[0066] S4. Use the control frequency F2 to modulate the working pulse F1, and use the modulated four drive signals to drive the four switch tubes of the inverter circuit, so that the load operates under a stable voltage.

[0067]

Composition of wireless energy transmission system

[0068] like Figure 2 As shown, it is mainly composed of a high-frequency inverter circuit, a coupled resonant network and a full-bridge rectifier. The high-frequency inverter circuit converts DC power into high-frequency AC power and inputs it into the transmitting coil. The receiving coil couples with the transmitting coil magnetic field to generate an induced current, which is consumed by the load through the full-bridge rectifier.

[0069] like Figure 3As shown, there are four switching tubes, a transmitting side coil, a receiving side coil, two resonant capacitors, four rectifier diodes, a filter capacitor, and a load.

[0070] like Figure 4 As shown, it includes a DC power supply, an auxiliary power supply, a high-frequency inverter circuit, a magnetic coupling system, a digital signal processor DSP, a rectifier circuit and a variable load.

[0071]

Soft switch

[0072] The condition for the switch tube to achieve soft switching is that I1 crosses zero in the positive direction after the rising edge of the inverter circuit output voltage V1, that is, φ>0. At this time, the anti-parallel diode of the lagging arm switch tube has been turned on by the reverse current I1 before the turn-on signal is applied, and the zero voltage turn-on of the lagging arm switch tube can be achieved, that is, a sufficiently long dead time is guaranteed so that the resonant current can completely drain the charge in the parasitic capacitance of the switch tube, so that the voltage of the switch tube to be turned on drops to zero, that is,

[0073]

[0074] i mp is the peak value of the excitation current, which occurs when the switch is in action, C zvs It is the sum of the capacitance values ​​of all the switch tubes involved in a commutation, V in is the DC power supply input voltage. For the traditional phase-shift control strategy, each switching action involves 4 switch tubes, while for the frequency-doubling control strategy, each switching action involves only 2 switch tubes, so the capacitor value involved in one commutation is half of that of the traditional phase-shift control strategy. At the same switching frequency, the dead time should be the same. From formula (11), it can be seen that the excitation current required by the frequency-doubling control strategy is smaller, indicating that soft switching is easier to achieve.

[0075]

Wireless power transmission system efficiency

[0076] right Figure 7 The mutual inductance equivalent model, according to Kirchhoff circuit theory, the mesh equation of the transmitter side circuit is:

[0077]

[0078] The mesh equation of the receiving side circuit is:

[0079]

[0080] When the transmission system is in resonance:

[0081]

[0082] Formula (1) and formula (2) can be simplified to:

[0083]

[0084] The currents on the transmitting and receiving sides are:

[0085]

[0086] The voltage transfer ratio is:

[0087]

[0088] Without considering the switching loss of the inverter circuit and only considering the efficiency of the magnetic coupling system, the transmission efficiency η of the entire system is:

[0089]

[0090] From formula (7), it can be seen that the transmission efficiency of the wireless power transmission system can be improved by increasing the coupling coefficient M and the resonant frequency f of the magnetic coupling system.

[0091] The core innovation of this patent is that the frequency doubling control strategy can double the output resonant voltage frequency under the same switching frequency, thereby achieving the purpose of improving the system transmission efficiency.

[0092] Example 1

[0093] When the DC power input voltage U in When the voltage is 400V, the switching frequency is set to 100kHz, the control pulse F2 frequency is 2kHz, and the natural resonant frequency of the resonant tank is 200kHz, which is twice the switching frequency. The duty cycle d = 0.2, and the control waveforms of the switch tubes S1 to S4 are as follows: Figure 8 As shown in the figure, when the control pulse F2 is in a high level state, the duty cycle of the drive signal of the inverter circuit switch tubes S1 and S4 is 0.25, the duty cycle of the drive signal of the switch tubes S2 and S3 is 0.75, and the phase angle of the two bridge arm drive signals differs by 180 degrees. When the control pulse F2 is in a low level state, all the switch tubes are in the off state, and the inverter circuit output is always zero.

[0094] The driving signals of the four switch tubes are as follows: Fig.11 As shown, the inverter circuit output voltage and load voltage waveforms are as follows Fig. 9 As shown, the load voltage U L The value is 52.5V.

[0095] Example 2

[0096] When the DC power input voltage U inWhen the voltage is 400V, the switching frequency is set to 100kHz, the control pulse F2 frequency is 2kHz, and the natural resonant frequency of the resonant tank is 200kHz, which is twice the switching frequency. The duty cycle d = 0.4, and the control waveforms of the switch tubes S1 to S4 are as follows: Fig.10 As shown in the figure, when the control pulse F2 is in a high level state, the duty cycle of the drive signal of the inverter circuit switch tubes S1 and S4 is 0.25, the duty cycle of the drive signal of the switch tubes S2 and S3 is 0.75, and the phase angle of the two bridge arm drive signals differs by 180 degrees. When the control pulse F2 is in a low level state, all the switch tubes are in the off state, and the inverter circuit output is always zero.

[0097] The driving signals of the four switch tubes are as follows: Fig.11 As shown, the inverter circuit output voltage and load voltage waveforms are as follows Fig. 9 As shown, the load voltage U L The value is 76.5V.

[0098] Example 3

[0099] When the input DC voltage is 80V, the duty cycle of the control pulse F2 is set to f = 2kHz, the duty cycle d = 0.7, and the control waveforms of the switch tubes S1 ~ S4 are as follows Fig.12 As shown, when the control pulse F2 is in a high level state, the switch tubes S1 to S4 are controlled by the working pulse F1. When the control pulse F2 is in a low level state, the switch tubes S1 and S3 are in the on state, and the switch tubes S2 and S4 are in the off state. The output of the inverter circuit is always zero.

[0100] The output voltage V1, current I1 and load voltage V of the inverter circuit L The waveform is as Fig.13 As shown, the load voltage U L The value is 112.3V.

[0101] Example 4

[0102] When the DC power input voltage U in When the voltage is 400V, the switching frequency is set to 100kHz, the control pulse F2 frequency is 2kHz, and the natural resonant frequency of the resonant tank is 200kHz, which is twice the switching frequency. The duty cycle d = 0.8, and the control waveforms of the switch tubes S1 to S4 are as follows: Fig.14 As shown in the figure, when the control pulse F2 is in a high level state, the duty cycle of the drive signal of the inverter circuit switch tubes S1 and S4 is 0.25, the duty cycle of the drive signal of the switch tubes S2 and S3 is 0.75, and the phase angle of the two bridge arm drive signals differs by 180 degrees. When the control pulse F2 is in a low level state, all the switch tubes are in the off state, and the inverter circuit output is always zero.

[0103] The output voltage V1, current I1 and load voltage V of the inverter circuit L The waveform is as Fig.15 As shown, the load voltage U L The value is 146.3V.

[0104] The technical solution provided by the present invention is that the inverter circuit switch tube driving signal no longer has the same driving timing but is 180 degrees different, and the duty cycle is not the traditional 0.5 but is 0.75 and 0.25 respectively, so that the inverter output frequency is twice the switching frequency, and the resonant tank operating frequency is doubled. When regulating the voltage, the control frequency F2 is introduced to control the operating frequency F1. When F2 is in a high level state, the inverter circuit switch tube will switch. When the control pulse F2 is in a low level state, the inverter circuit switch tube is not in action. The output voltage is controlled by adjusting the control pulse duty cycle d;

[0105] Compared with the traditional phase-shift control strategy, under the same switching frequency, the doubling of the resonant tank operating frequency under the frequency-doubling control strategy improves the efficiency of the wireless power transmission system;

[0106] In terms of soft switching: because the frequency doubling control strategy involves two parasitic capacitors of the switch tube in each switching action, which is half of the traditional phase-shift control strategy, the soft switching conditions are reduced, which makes it easier to achieve soft switching;

[0107] When regulating the voltage, the dual-frequency control strategy is combined to control the output voltage by adjusting the duty cycle d of the control frequency, and the voltage regulation logic is simple.

[0108] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A frequency multiplication control strategy applicable to a wireless power transmission system, characterized in that: The steps include: S1, set the duty cycle of the drive signal of the inverter circuit switch tubes S1 and S4 to 0.25, the duty cycle of the drive signal of the switch tubes S2 and S3 to 0.75, the phase angle difference of the two bridge arm drive signals is 180 degrees, and the system working pulse F1 is generated, and the frequency of the working pulse F1 is f1; S2. Due to the characteristics of the frequency doubling control strategy: the square wave frequency output by the inverter circuit is twice the switching frequency of the switch tube, and the resonant frequency f0 of the magnetic coupling resonance system is twice the working pulse frequency f1. According to the following formula, S3, set the inverter circuit to output control pulse F2, the control pulse F2 frequency is f2, and the voltage across the load is adjusted by changing the control frequency F2 duty cycle d according to the following formula: S4. Use the control frequency F2 to modulate the working pulse F1, and use the modulated four drive signals to drive the four switch tubes of the inverter circuit, so that the load operates under a stable voltage.

2. The frequency multiplication control strategy applicable to the wireless power transmission system according to claim 1, characterized in that: According to S1 and S2, due to the frequency doubling effect of the frequency doubling modulation strategy, the frequency of the square wave output by the inverter circuit is twice the frequency f1 of the working pulse F1, and is the same as the inherent resonant frequency f0 of the resonant circuit, ensuring high-efficiency operation of the system in the working range.

3. The frequency multiplication control strategy applicable to the wireless power transmission system according to claim 1, characterized in that: According to S3 and S4, it can be known that the control pulse F2 controls the working pulse F1 at a lower frequency f2. When the control pulse F2 outputs a high level, the working pulse F1 drives the inverter circuit switch tube to operate normally. When the control pulse F2 outputs a low level, the working pulse F1 driving the inverter circuit switch tube is effectively disabled.

4. The frequency multiplication control strategy applicable to the wireless power transmission system according to claim 1, characterized in that: The formula in S3 is derived as follows: According to Kirchhoff's circuit theory, the mesh equation of the transmitter circuit is: The mesh equation of the receiving side circuit is: When the transmission system is in resonance: Formula (1) and formula (2) can be simplified to: The currents on the transmitting and receiving sides are: The voltage transfer ratio is: Without considering the switching loss of the inverter circuit and only considering the efficiency of the magnetic coupling system, the transmission efficiency η of the entire system is: From formula (7), it can be seen that the transmission efficiency of the wireless power transmission system can be improved by increasing the coupling coefficient M and the resonant frequency f of the magnetic coupling system. The frequency doubling control strategy can double the output resonant voltage frequency under the same switching frequency, thereby achieving the purpose of improving the system transmission efficiency. Expand the voltage waveform of the unipolar voltage V1 output by the inverter circuit under the frequency doubling control strategy into a Fourier series: When only the fundamental component is considered and the duty cycle of the control frequency F2 is d, the input voltage on the transmitting side is The effective value of U1 becomes: The duty cycle d of the control pulse F2 and the receiving side voltage U L The relationship is: It can be seen from formula (10) that when the DC input voltage U in When the coupling coefficient M remains unchanged, the voltage U at both ends of the load can be controlled by changing the duty cycle d of the control pulse F2. L control.

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