Resonance type wireless power transmission system based on fixed-width frequency modulation control

Abstract

The invention discloses a resonant wireless power transmission system based on fixed-width frequency modulation control. The resonant wireless power transmission system comprises a direct-current power supply, a high-frequency inverter circuit, a loose coupling transformer, a rectifying circuit, an output load and a control system, the high-frequency inverter circuit is composed of four MOSFETs, a direct-current bus side diode is added to a transmitting end, an anti-series switch tube is added to a receiving end, and the rectifier circuit is connected with an output load through a direct-current side filter capacitor Cd; the beneficial effects of the invention are that when the system is in the interruption time, the coil current of the receiving end can be ensured to continuously follow current, so that the purpose of always ensuring simultaneous resonance of the transmitting end and the receiving end is achieved. Through a fixed-width frequency modulation control strategy, the problems of system offset resonant frequency point, system detuning, narrow soft switching range and the like are solved.

Description

Technical Field

[0001] The present application relates to the field of wireless power transmission, and in particular to a resonant wireless power transmission circuit based on fixed-width frequency modulation control. Background Art

[0002] Traditional wired power supply methods have safety hazards such as exposed plugs, damaged cables, and aging lines, and are also less adaptable to harsh environments such as underwater and humid environments. Wireless power transmission technology does not require physical contact and achieves electrical insulation between the primary and secondary sides, completely solving the problem of traditional plug-and-play charging's dependence on conductors. Therefore, compared to traditional wired charging, wireless power transmission technology has the advantages of flexibility, convenience, electrical isolation, maintenance-free, and strong environmental adaptability, and is expected to be widely used in smart homes, electric vehicles, industrial robots, logistics and transportation, and other fields.

[0003] The components of the wireless power transmission system mainly include DC power supply, high-frequency inverter circuit, loosely coupled transformer, transmitter and receiver compensation network, rectifier circuit and output load. The wireless power transmission system uses high-frequency alternating magnetic field as the medium for transmitting electric energy, converts electric energy into magnetic field energy at the transmitter, and converts magnetic field energy into electric energy at the receiver, so as to realize wireless transmission of electric energy. In order to realize the efficient transmission of electric energy, it is necessary to increase the frequency of the alternating magnetic field. The industrial frequency power supply used in daily life cannot meet the requirements, so a rectifier inverter is usually required to generate high-frequency alternating current. Since the wireless power transmission system uses a loosely coupled transformer and there is a certain distance between the transmitter and the receiver coils, the coupling coefficient is small, and a large leakage magnetic field will be generated during the operation of the system, which is reflected in the circuit as the power supply needs to provide a large amount of reactive power for the system. Therefore, both the transmitter and the receiver of the wireless power transmission system need to add compensation circuits to reduce the reactive power in the system, thereby improving the efficiency and power transmission capacity of the system.

[0004] In wireless power transmission systems, when using traditional complementary pulses, when the switch tube is turned off, intermittent time is added, and voltage reduction regulation can be achieved by inserting intermittent time without changing the system resonant frequency. Similarly, in order to avoid the anti-parallel diode of the switching device being turned on during the intermittent time to form a resonant circuit, a DC bus side diode is added to prevent the reverse flow of current, thereby achieving soft switching of the system. However, if only a DC bus side diode is added to the transmitting end, when the system is in the intermittent time, the transmitting end stops resonating, while the receiving end continues to resonate, and the system resonates out of sync, which affects the efficiency of the system.

[0005] In a wireless power transmission system, if the transmitter resonates and the receiver does not resonate, in addition to being unable to ensure that the system maintains the maximum energy transmission efficiency, it will also cause a large amount of energy loss during the transmission process, and these losses are usually manifested as heat losses, causing the system to generate additional heat losses. In addition, it may cause circuit impedance mismatch, increase the risk of circuit oscillation or unstable operation, and affect the normal operation of the system. And there may be a mismatch in current and voltage between the transmitter and the receiver, resulting in an increased risk of equipment damage, overload or breakdown of circuit components, and thus damage to the equipment. The main problems are:

[0006] (1) The state of the wireless power transmission system is affected by the compensation elements at the receiving end. When both the transmitter and the receiver of the wireless power transmission system are at the resonant frequency point, the maximum energy transmission efficiency can be achieved. When the resonant frequency does not match or the receiving end does not continue to flow, the system is detuned, which greatly reduces the transmission efficiency and reduces the performance and reliability of the system.

[0007] (2) Since the operating frequency of the converter in the traditional wireless power transmission system is high, the use of resonant conversion technology to achieve soft switching of power devices can effectively reduce device switching losses and improve energy conversion efficiency, making high-frequency resonant systems widely used. However, the variable frequency voltage regulation control commonly used in resonant systems often has problems such as system deviation from the resonant frequency point, system detuning, and narrow soft switching range.

[0008] (3) Currently, the output voltage of the wireless power transmission system is regulated by adjusting the switching frequency. This method will increase the voltage stress of the switching device.

[0009] In summary, in order to solve the above problems and improve the efficiency and reliability of the wireless power transmission system, it is necessary to study and improve the wireless power transmission system. Summary of the invention

[0010] The present application is designed to solve the above-mentioned technical problems and is a resonant wireless power transmission system based on fixed-width frequency modulation control.

[0011] The technical solution adopted by this application to solve its technical problem is:

[0012] A resonant wireless power transmission system based on fixed-width frequency modulation control, comprising a DC power supply, a high-frequency inverter circuit, a loosely coupled transformer, a rectifier circuit, an output load and a control system; the DC power supply input voltage is U inThe high-frequency inverter circuit is composed of four MOSFET tubes T1, T2, T3 and T4. The transmitter self-inductance coil L1 of the loosely coupled transformer is connected to the high-frequency inverter circuit through the resonant capacitor C1 and the resistor R1 to form a transmitter compensation network. The receiver self-inductance coil L2 of the loosely coupled transformer is connected to the rectifier circuit through the resonant capacitor C2 and the resistor R2 to form a receiver compensation network; the rectifier circuit is connected to the DC side filter capacitor C d Connect the output load;

[0013] The transmitter compensation network is connected to the DC power supply through the absorption capacitor C and the absorption resistor R connected in series, and the diode D in The anode is connected to the positive pole of the DC power supply, and the diode D in The cathode is connected to the drain of MOSFET tubes T1 and T2;

[0014] The receiving end compensation network is connected to anti-series switch tubes T5 and T6, the drain of the switch tube T5 is connected to the same-name end of the receiving end self-inductance coil L2, and the drain of the switch tube T6 is connected to the opposite-name end of the receiving end self-inductance coil L2 through the resistor R2;

[0015] The control system controls the working states of four MOSFET tubes T1, T2, T3 and T4, and switch tubes T5 and T6 in the high-frequency inverter circuit respectively.

[0016] In the resonant wireless power transmission system based on fixed-width frequency modulation control, the loosely coupled transformer also includes a receiving end detection coil L3, which is coupled to the receiving end self-inductance coil L2. The detection coil L3 collects the zero-crossing instantaneous information of the voltage u2 of the receiving end self-inductance coil L2, and then the control system controls the working states of the anti-series switch tubes T5 and T6.

[0017] The resonant wireless power transmission system based on fixed-width frequency modulation control collects the system output voltage U through the voltage sampling module 1 out , the system output voltage U out With the set reference voltage U ref The error signal ΔU1 is input into the proportional integral PI controller to generate a PI adjustment signal ΔT p ; The system input voltage U in With the set reference voltage U ref Enter the feedforward G f (s) In the controller, a feedforward control signal ΔT is generated f ; The PI adjustment signal ΔT p With the feedforward regulation signal ΔT f Add together to generate a sawtooth wave signal ΔS w The sawtooth wave signal ΔSw Enter the fixed-width frequency modulation control module, and then the fixed-width frequency modulation control algorithm in the module generates the intermittent time ΔT required by the system; the system collects the transmitting coil current i1 through the current sampling and zero-crossing comparison module to generate the current comparison result ΔI1; the intermittent time ΔT and the current comparison result ΔI1 enter the drive signal 1 module to generate the drive signals GT1, GT2, GT3 and GT4 for regulating the operation of the system switches T1, T2, T3 and T4; the system collects the voltage u at both ends of the detection coil through the voltage sampling 2 and the zero-crossing comparison module A , generating a voltage comparison result ΔU A The intermittent time ΔT and the voltage comparison result ΔU A Enter the drive signal 2 module to generate drive signals GT5 and GT6 for regulating the operation of the system switches T5 and T6; thereby adjusting the switching frequency of the inverter so that the system always operates near the resonant frequency, ensuring a stable output voltage when the load changes;

[0018] The current sampling and zero-crossing comparison module collects the transmitting coil current i1 to obtain its zero-crossing moment, at which time the inverter tubes T1 to T4 are all turned off; when the transmitting coil current i1 crosses zero from positive to negative, the switch tubes T1 and T4 are turned off; when i1 crosses zero from negative to positive, the switch tubes T2 and T3 are turned off;

[0019] The voltage sampling 2 and zero-crossing comparison module detects the voltage u at both ends of the coil. A Collect and find the voltage zero point, voltage u A When the voltage crosses zero from positive voltage to negative voltage and from negative voltage to positive voltage, the anti-series switch tubes T5 and T6 are turned on to keep the current at the receiving end flowing in the coil loop;

[0020] The voltage u across the detection coil A The phase is the same as the transmitting coil current i1, and the voltage u A The same as the zero-crossing point of the current i1, at this time, the action of each switch tube can satisfy the synchronous stop of resonance of the receiving end and the transmitting end;

[0021] The intermittent time ΔT is passed through the drive signal 1 module and the drive signal 2 module, thereby changing the length of the on and off time of all switch tubes, thereby adjusting the system output voltage, providing a protection function, and preventing the switches from being turned on at the same time.

[0022] The resonant wireless power transmission system based on fixed-width frequency modulation control, the fixed-width frequency modulation control takes the resonant frequency as a reference, and realizes frequency tracking and power regulation by adjusting the switching frequency of the inverter; the fixed-width frequency modulation control algorithm can keep the system working at the optimal resonant point to realize efficient and stable wireless power transmission.

[0023] The resonant wireless power transmission system based on fixed-width frequency modulation control includes a feedforward G f (s) controller, incremental proportional integral PI controller and fixed width frequency modulation control module; input voltage and U in With a given reference voltage U ref For comparison, after feedforward G f (s) ΔT obtained after the controller is tuned f ;

[0024] Load voltage U out With a given reference voltage U ref For comparison, the incremental proportional integral PI controller is tuned to obtain ΔT p , ΔT obtained by superimposing feedforward control f Get the sawtooth wave signal ΔS w The sawtooth wave signal ΔS w Enter the fixed-width frequency modulation control module to obtain the intermittent time ΔT, and the intermittent time ΔT generates the drive signals GT1 to GT4 of the inverter bridge switch tube through the drive signal 1 module; by controlling the length of the intermittent time of the switch tube, the system output voltage is controlled to a given reference output voltage value; after the output voltage fluctuation information is added to the feedforward control, the control requirements of the PI closed loop can be reduced, and the dynamic response of the system can be greatly improved; the expression of the feedforward controller is calculated as follows:

[0025]

[0026] Among them, T r is the resonant period of the D-LLC circuit.

[0027] The resonant wireless power transmission system based on fixed-width frequency modulation control, the voltage regulation strategy of the system control is: the pulse width variation range in the fixed-width frequency modulation control is determined to be 40kHz according to the load demand and system design parameters, and the frequency range is 85kHz to 125kHz; the pulse width does not change with the load, but the output is adjusted by changing the switching frequency; by real-time sampling of the voltage and comparing it with the reference value, the input voltage and the reference voltage enter the feedforward G f (s) The controller performs calculation to obtain ΔT s , output voltage U out With reference voltage U ref Enter the incremental proportional integral PI controller to calculate ΔT p ; ΔT s and ΔT p After adding, we get the sawtooth wave signal ΔS w , ΔS wThe intermittent time ΔT is obtained through the fixed-width frequency modulation module, and the intermittent time ΔT is used to adjust the length of the intermittent time of the system switch tube to maintain output stability and ensure that the voltage reaches the predetermined target; an incremental proportional integral PI controller is used to effectively reduce the calculation time of the control system;

[0028] Working status includes:

[0029] The transmitting coil current i1 is sampled to obtain its zero-crossing moment, at which time the inverter tubes T1 to T4 are all turned off;

[0030] When the transmitting coil current i1 passes through zero from positive to negative, the switch tubes T1 and T4 are turned off; when i1 passes through zero from negative to positive, the switch tubes T2 and T3 are turned off;

[0031] Voltage u across the detection coil A After the voltage detection circuit and zero-crossing comparison, the voltage zero-crossing point is found, which is the pulse opening moment of the reverse series switch tubes T5 and T6 at the receiving end;

[0032] When the voltage u A When the voltage passes through zero from positive voltage to negative voltage and vice versa, the anti-series switch tubes T5 and T6 are turned on to keep the current at the receiving end flowing continuously in the coil loop.

[0033] The resonant wireless power transmission system based on fixed-width frequency modulation control, the fixed-width frequency modulation control algorithm comprises the following steps:

[0034] S100: Feed-forward G f (s) controller, incremental proportional integral PI controller after tuning, in the algorithm it is a sawtooth wave signal ΔS with a variable peak value w ; Digital clock frequency f clk is 150MHz; due to fixed-width frequency modulation control, the given pulse width T on Set to 5 microseconds; switching frequency f PWM The range is 85kHz to 125kHz;

[0035] S200: Given a constant comparison value A and a variable comparison value B that changes with the input amount, and the sum of the variable comparison value B and the constant comparison value A is equal to the sawtooth wave signal ΔS w The peak value of the inverter bridge is ensured to be constant during the opening time; where:

[0036]

[0037] The constant comparison value A is determined to be 375 by formula (16), and the variable comparison value B is determined to be in the range of 600 to 882 by formula (17). The sum of the variable comparison value B and the constant comparison value A is equal to the peak value of the sawtooth wave signal, ensuring the constant opening time of the inverter bridge.

[0038] S300: When the algorithm is in the upward counting mode, when the sawtooth wave signal is less than or equal to the comparison value A, a high level is output, which is the turn-on time of the inverter bridge switches T1 and T4; when the algorithm is in the downward counting mode, when the sawtooth wave signal is greater than or equal to the comparison value B, a high level is output, which is the turn-on time of the inverter bridge switches T2 and T3;

[0039] S400: when the algorithm is in the upward counting mode and the sawtooth wave signal is greater than the comparison value A, and when the algorithm is in the downward counting mode and the sawtooth wave signal is less than the comparison value B, both output a high level as the turn-on time of the anti-series switch tubes T5 and T6;

[0040] S500: Due to the voltage u across the detection coil A The phase is the same as the transmitting coil current i1, and the voltage u A The same as the zero-crossing point of the current i1, at this time, the action of each switch tube can satisfy the synchronization between the receiving end and the transmitting end and stop the resonance.

[0041] The resonant wireless power transmission system based on fixed-width frequency modulation control, the system also includes an operating condition detection process, the loosely coupled transformer has an excitation inductance, the operating condition detection process can realize the prompting of the transformer energy transmission efficiency, the system operating condition detection process is: after the system operating condition detection starts, the given voltage reference value is compared with the system output voltage value:

[0042] When the given voltage reference value is greater than the system output voltage value, the system is in a boost condition; the intermittent time ΔT obtained by the fixed-width frequency modulation control algorithm is compared with the excitation current i m Critical time t for continuous or intermittent operation c Compare; when the intermittent time ΔT is less than the critical time t c , the system needs to perform fixed-width frequency modulation control; when the intermittent time ΔT is greater than the critical time t c , the system does not need fixed-width frequency modulation control;

[0043] When the given voltage reference value is less than the system output voltage value, it means that the system is in a voltage reduction state; the intermittent time ΔT obtained by the fixed-width frequency modulation control algorithm is compared with the excitation current i m Critical time t for continuous or intermittent operation c When the intermittent time ΔT is greater than the critical time t c , the system needs to perform fixed-width frequency modulation control; when the intermittent time ΔT is less than the critical time t c , the system does not need fixed-width frequency modulation control;

[0044] When the given voltage reference value is equal to the system output voltage, it means that the system does not need fixed-width frequency modulation control.

[0045] At least one of the above technical solutions adopted in the embodiments of the present application can achieve the following beneficial effects:

[0046] (1) To address the problem of non-continuous current at the receiving end of a wireless power transmission system, the present invention adds a DC bus side diode at the transmitting end and an anti-series switch tube at the receiving end to ensure that when the system is in the intermittent time, the coil current at the receiving end can continue to flow, thereby achieving the purpose of ensuring simultaneous resonance at the transmitting end and the receiving end.

[0047] (2) Since the operating frequency of the converter in the traditional wireless power transmission system is high, the use of resonant conversion technology to achieve soft switching of power devices can effectively reduce device switching losses and improve energy conversion efficiency, making high-frequency resonant systems widely used. However, the variable frequency voltage regulation control commonly used in resonant systems often has problems such as system deviation from the resonant frequency point, system detuning, and narrow soft switching range. This paper proposes a fixed-width frequency modulation control strategy that enables the wireless power transmission system to achieve a wide gain range while ensuring soft switching. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0049] Figure 1 It is a topology diagram of a resonant wireless power transmission system based on fixed-width frequency modulation control;

[0050] Figure 2 It is a waveform diagram of a resonant wireless power transmission system based on fixed-width frequency modulation control;

[0051] Figure 3(a) is a schematic diagram of the system's operating state when T2 and T3 are turned on;

[0052] Figure 3(b) is a schematic diagram of the system's operating state when T2 and T3 are turned off;

[0053] Figure 3(c) is a schematic diagram of the system's operating state when T1 and T4 are turned on;

[0054] Figure 3(d) is a schematic diagram of the system's operating state when T1 and T4 are turned off;

[0055] Figure 4 This is the structure diagram of the detection coil;

[0056] Figure 5 This is the fundamental wave equivalent circuit schematic diagram of fixed-width frequency modulation control;

[0057] Figure 6 This is the PI control principle diagram;

[0058] Figure 7 This is the fixed width frequency modulation control block diagram;

[0059] Figure 8 It is a control block diagram of a resonance type wireless power transmission system based on fixed-width frequency modulation;

[0060] Fig. 9 It is a flow chart of the control algorithm of the resonant wireless power transmission system based on fixed-width frequency modulation;

[0061] Fig.10 This is the system operation condition detection flow chart. DETAILED DESCRIPTION

[0062] In order to make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be clearly and completely described below in combination with the specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0063] The technical solutions provided by various embodiments of the present application are described in detail below in conjunction with the accompanying drawings.

[0064] In order to facilitate the understanding of the various embodiments of the present application, Figure 1 A resonant wireless power transmission system based on fixed-width frequency modulation control is shown, comprising a DC power supply, a high-frequency inverter circuit, a loosely coupled transformer, a rectifier circuit, an output load and a control system; the DC power supply input voltage is U in The high-frequency inverter circuit is composed of four MOSFET tubes T1, T2, T3 and T4. The transmitter self-inductance coil L1 of the loosely coupled transformer is connected to the high-frequency inverter circuit through the resonant capacitor C1 and the resistor R1 to form a transmitter compensation network. The receiver self-inductance coil L2 of the loosely coupled transformer is connected to the rectifier circuit through the resonant capacitor C2 and the resistor R2 to form a receiver compensation network; the rectifier circuit is connected to the DC side filter capacitor C d Connect the output load;

[0065] The transmitter compensation network is connected to the DC power supply through the absorption capacitor C and the absorption resistor R connected in series, and the diode D in The anode is connected to the positive pole of the DC power supply, and the diode D in The cathode is connected to the drain of MOSFET tubes T1 and T2;

[0066] The receiving end compensation network is connected to anti-series switch tubes T5 and T6, the drain of the switch tube T5 is connected to the same-name end of the receiving end self-inductance coil L2, and the drain of the switch tube T6 is connected to the opposite-name end of the receiving end self-inductance coil L2 through the resistor R2;

[0067] The control system controls the working states of four MOSFET tubes T1, T2, T3 and T4, and switch tubes T5 and T6 in the high-frequency inverter circuit respectively.

[0068] In the resonant wireless power transmission system based on fixed-width frequency modulation control, the loosely coupled transformer also includes a receiving end detection coil L3, which is coupled to the receiving end self-inductance coil L2. The detection coil L3 collects the zero-crossing instantaneous information of the voltage u2 of the receiving end self-inductance coil L2, and then the control system controls the working states of the anti-series switch tubes T5 and T6.

[0069] The resonant wireless power transmission system based on fixed-width frequency modulation control receives an external DC power source Ui n The input voltage is filtered through the absorption capacitor C to suppress the voltage fluctuation and high-frequency noise at the input end, output a stable DC voltage, and provide input power for the subsequent inverter circuit.

[0070] The transmitter full-bridge inverter includes four power switch tubes T1, T2, T3 and T4. By controlling the on-off state of the four switch tubes, the input DC voltage U in Converted into high-frequency AC voltage to form a square wave voltage u AB The switch drive signal of the inverter is controlled by fixed-width frequency modulation to ensure that the AC voltage output by the inverter operates at the resonant frequency, thereby improving system efficiency.

[0071] The resonant network consists of a coupled inductor M1 and a resonant capacitor, which is used to convert the square wave voltage output by the full-bridge inverter into an AC voltage u close to a sine wave. AB , and works at the resonant frequency to maximize power transfer efficiency, transferring energy from the transmitter to the receiver. The design of the resonant network ensures that the system can maintain efficient transmission under varying load conditions.

[0072] The receiving end rectification and filtering circuit includes two power switch tubes T5 and T6, four diode rectifiers D1, D2, D3 and D4, and a filtering capacitor C d The high-frequency AC voltage output by the resonant network is rectified by the rectifier circuit and converted into a DC voltage U out , and then through the filter capacitor C d Further smoothing provides a stable output voltage.

[0073] The resonant wireless power transmission system based on fixed-width frequency modulation control collects the system output voltage U through the voltage sampling module 1 out , the system output voltage U out With the set reference voltage U refThe error signal ΔU1 is input into the proportional integral PI controller to generate a PI adjustment signal ΔT p ; The system input voltage U in With the set reference voltage U ref Enter the feedforward G f (s) In the controller, a feedforward control signal ΔT is generated f ; The PI adjustment signal ΔT p With the feedforward regulation signal ΔT f Add together to generate a sawtooth wave signal ΔS w The sawtooth wave signal ΔS w Enter the fixed-width frequency modulation control module, and then the fixed-width frequency modulation control algorithm in the module generates the intermittent time ΔT required by the system; the system collects the transmitting coil current i1 through the current sampling and zero-crossing comparison module to generate the current comparison result ΔI1; the intermittent time ΔT and the current comparison result ΔI1 enter the drive signal 1 module to generate the drive signals GT1, GT2, GT3 and GT4 for regulating the operation of the system switches T1, T2, T3 and T4; the system collects the voltage u at both ends of the detection coil through the voltage sampling 2 and the zero-crossing comparison module A , generating a voltage comparison result ΔU A The intermittent time ΔT and the voltage comparison result ΔU A Enter the drive signal 2 module to generate drive signals GT5 and GT6 for regulating the operation of the system switches T5 and T6; thereby adjusting the switching frequency of the inverter so that the system always operates near the resonant frequency, ensuring a stable output voltage when the load changes;

[0074] The current sampling and zero-crossing comparison module collects the transmitting coil current i1 to obtain its zero-crossing moment, at which time the inverter tubes T1 to T4 are all turned off; when the transmitting coil current i1 crosses zero from positive to negative, the switch tubes T1 and T4 are turned off; when i1 crosses zero from negative to positive, the switch tubes T2 and T3 are turned off;

[0075] The voltage sampling 2 and zero-crossing comparison module detects the voltage u at both ends of the coil. A Collect and find the voltage zero point, voltage u A When the voltage crosses zero from positive voltage to negative voltage and from negative voltage to positive voltage, the anti-series switch tubes T5 and T6 are turned on to keep the current at the receiving end flowing in the coil loop;

[0076] The voltage u across the detection coil A The phase is the same as the transmitting coil current i1, and the voltage u A The same as the zero-crossing point of the current i1, at this time, the action of each switch tube can satisfy the synchronous stop of resonance of the receiving end and the transmitting end;

[0077] The intermittent time ΔT is passed through the drive signal 1 module and the drive signal 2 module, thereby changing the length of the on and off time of all switch tubes, thereby adjusting the system output voltage, providing a protection function, and preventing the switches from being turned on at the same time.

[0078] u AB is the AC voltage passing through the high-frequency inverter bridge, u ab is the voltage before the rectifier bridge, i1 is the transmitting coil current, i2 is the receiving coil current, I out is the DC current flowing through the load, U out The DC voltage at its two ends. Points A and B are the inverter output terminals, and points C and D are the rectifier network terminals. Compared with the traditional SS-type WPT system, the SS-type wireless power transmission system based on fixed-width frequency modulation adds a diode D on the DC bus side. in , add anti-series switching tubes T5 and T6 at the receiving end coil.

[0079] 1. Working Principle

[0080] The switching tube drive signal and system voltage and current waveform of the resonant wireless power transmission system based on fixed-width frequency modulation control are as follows: Figure 2 The fixed width refers to the resonant period T of the system. r unchanged, that is Figure 2 The length of t0~t1 and t2~t3 is defined as R in this paper, which corresponds to the resonant state of the system. The time when all inverter tubes are turned off is the intermittent time ΔT, that is, Figure 2 In this paper, t1~t2 and t3~t4 are defined as Z, which corresponds to the discontinuous state of the system. The sum of the resonant period and the discontinuous time is the switching period T s ,for Figure 2 t0~t4 in.

[0081] As shown in Figure 3, within one working cycle, the transmitting coil current i1 resonates to zero twice. At t1, after the positive half-cycle resonance of the system ends, the transmitting coil current i1 resonates to zero for the first time, and the intermittent time ΔT is inserted at this time. At the end of the negative half-cycle resonance of the system, the transmitting coil current i1 resonates to zero again, and the intermittent time ΔT is also inserted at this time. Since the system does not transfer energy when it is in the intermittent time, the output voltage U can be adjusted by controlling the length of the intermittent time and the ratio of the system switching cycle. out .

[0082] exist Figure 2 In the figure, t0 to t4 constitute a complete operation cycle, which includes four operation modes. The circuit operation analysis in each mode is as follows.

[0083] Mode 1 [t0~t1] The equivalent circuit of this mode is shown in Figure 3(a). At t0, T2 and T3 are turned on, and the input current i1 passes through the DC bus side diode D in The energy flows into the compensation network and is transferred from the transmitting end to the receiving end through the coupling coil. The rectifier tubes D2 and D3 at the receiving end are turned on and the load is charged. The inverter bridge output voltage u AB Equal to input voltage U in , the transmitting coil L1 resonates with the transmitting resonant capacitor C1, the receiving coil L2 resonates with the receiving resonant capacitor C2, the transmitting coil current i1 and the receiving coil current i2 are both sinusoidal waves in half a cycle, with a phase difference of 90°, that is, the system is in a resonant state. At the end of this mode, at time t1, the transmitting coil current i1 resonates to 0, the receiving coil current i2 resonates to the maximum value, and the transmitting resonant capacitor voltage u C1 Increase to the maximum value U C1max .

[0084] Mode 2 [t1~t2] The equivalent circuit of this mode is shown in Figure 3(b). At t1, T1~T4 are all turned off, T5 and T6 are turned on, energy is no longer transmitted through the coupling coil, the receiving end rectifier tubes D1~D4 are turned off, and the load current is provided by the filter capacitor. The DC bus side diode D m Reverse bias, the transmitting coil current cannot flow in the reverse direction and is clamped to 0. According to the KVL theorem, the inverter bridge output voltage u AB Equal to the maximum value of the transmitting end resonant capacitor voltage U C1max Since the transmitting coil current i1 has resonated to 0 in the previous state, the inverter tube can achieve ZCS shutdown at this time; and there is no current flowing in the anti-series switch tube loop in the previous state, so T5 and T6 tubes can achieve ZCS opening. T5, T6 tubes and the receiving coil L2 form a loop, and the receiving coil current i2 continues to flow and maintains the maximum value unchanged.

[0085] Mode 3 [t2~t3] The equivalent circuit of this mode is shown in Figure 3(c). At time t2, T1 and T4 are turned on, T5 and T6 are turned off, and the input side diode D in The forward bias and conduction, energy is transferred from the transmitting end of the power supply to the receiving end. This is the working mode of the system under reverse resonance, and its working principle is the same as that of mode 1. In the previous mode, the transmitting coil current i1 is affected by the DC bus side diode D in The influence of always remains 0, so at time t2, both inverter tubes T1 and T4 can achieve ZCS opening.

[0086] Mode 4 [t3~t4] The equivalent circuit of this mode is shown in Figure 3(d). At t3, T1~T4 are all turned off, T5 and T6 are turned on, and energy is no longer transmitted through the transformer. The receiving end rectifier tubes D1~D4 are turned off, and the load current is provided by the filter capacitor. The DC bus side diode D in Reverse bias, the transmitting coil current cannot flow in the reverse direction and is clamped to 0. According to the KVL theorem, the inverter bridge output voltage u AB Equal to the maximum value of the transmitting end resonant capacitor voltage U Clmax At this point the system works exactly the same as Mode 2.

[0087] Since a pair of anti-series switch tubes are added to the receiving end, it is necessary to control the on and off of the switch tubes. In order to realize the simultaneous control of the transmitting end and the receiving end of the system, it is necessary to install a detection coil L3 on the receiving end coil to collect the zero-crossing moment of the receiving end coil voltage u2, such as Figure 4 shown.

[0088] Since the system adds a detection coil L3 when applying fixed-width frequency modulation control, the transmission characteristics of the resonant wireless power transmission system with the detection coil added will be analyzed. The basic equivalent circuit of the resonant wireless power transmission system using the detection coil is as follows: Figure 5 shown.

[0089] Among them, C1 and C2 are the resonant capacitors at the transmitting end and the resonant capacitors at the receiving end, respectively, u1, u2, u A are the voltage source of the transmitting end, the coil voltage of the receiving end and the port voltage of the detection coil, respectively; i1, i2, i3 are the coil currents of the transmitting end, the receiving end and the detection coil, respectively; L1, L2, L3 are the self-inductance coils of the transmitting end, the receiving end and the detection coil, respectively; M, M 13 、M 23 are the mutual inductances between the transmitting and receiving coils, the transmitting and detecting coils, and the receiving and detecting coils, respectively. eq is the equivalent resistance of the rectifier bridge. According to Kirchhoff's voltage theorem, we can get:

[0090]

[0091] Among them, X1 and X2 are:

[0092]

[0093] Since the detection coil L3 is unloaded, there is no current in the coil, so I3 = 0, so:

[0094]

[0095] According to the above formula, we can get:

[0096]

[0097] Therefore, the detection coil will not affect the magnitude and phase of the current at the system transmitter and receiver. When the system transmitter and receiver are both in a resonant state, X1 = 0 and X2 = 0, the current expressions of the system transmitter and receiver can be obtained as:

[0098]

[0099] The voltage expression of the detection coil and the receiving coil is:

[0100]

[0101] Since the detection coil L3 and the receiving coil L2 are wound together, according to equation (8), the receiving coil voltage u2 and the detection coil voltage u A There is only a difference in amplitude, while the phase and polarity are exactly the same. A Whether it changes from positive to negative or from negative to positive, the zero-crossing moment corresponds to the conduction time of the switch tubes T5 and T6. The conduction duration of T5 and T6 is also ΔT, which is the same as the intermittent time ΔT of the inverter tube at the transmitting end.

[0102] In addition, when the system coil is offset, the coil's transmitting end self-inductance L1, receiving end self-inductance L2, mutual inductance M, M 13 、M 23 will change, but according to formula (8), since the coil offset only causes the voltage amplitude to change and does not affect the phase relationship between the transmitting and receiving coils, even if the coil is offset, the detection coil can still make a phase judgment on the on-time of the anti-series switch tubes T5 and T6 at the receiving end of the system.

[0103] The resonant wireless power transmission system based on fixed-width frequency modulation control, the fixed-width frequency modulation control takes the resonant frequency as a reference, and realizes frequency tracking and power regulation by adjusting the switching frequency of the inverter; the fixed-width frequency modulation control algorithm can keep the system working at the optimal resonant point, and realize efficient and stable wireless power transmission;

[0104] 2. Fixed-width frequency modulation control scheme for wireless power transmission system

[0105] 2.1PI controller design

[0106] The proportional integral (PI) controller has the characteristics of clear theory, easy implementation and strong stability. The PI closed-loop control model of the wireless power transmission system is as follows: Figure 6As shown in the figure, r(t) is the input reference voltage, y(t) is the actual value of the output voltage, e(t) is the error between the output voltage and the input voltage, and u(t) is the input of the controlled object. After the error signal e(t) is processed by the PI controller, the input of the controlled object u(t) is obtained, which means that the PI closed-loop control is realized.

[0107] PI regulation control can be expressed as:

[0108]

[0109] The regulation of the system requires the coordination of proportional control and integral control to keep the system in the best working state. Increasing the proportional coefficient can speed up the response speed, but there may be problems with system oscillation; increasing the time constant of the integral link can shorten the regulation time, but may increase the overshoot.

[0110] The commonly used positional and incremental algorithms are analyzed separately below.

[0111]

[0112] Formula (10) discretizes the integral link, and formula (11) is expressed in incremental form. The discretized PI expression is:

[0113]

[0114] In the formula, k represents the sampling point, T I is the time constant of the integral link, u(k) is the output voltage after adjustment, let K I is the time constant of the integral link, we can get:

[0115]

[0116] The above is a positional PI control algorithm, and the adjustment amount is related to the previous state. When the system is running, the output deviation continues to accumulate, resulting in an increase in the computational load. The following will analyze the incremental PI control algorithm.

[0117] From formula (12), we can get:

[0118]

[0119] Δu(k)=u(k)-u(k-1)=K p [e(k)-e(k-1)]+ΔtK I e(k) (15)

[0120] The output voltage u(k) expression is:

[0121] u(k)=u(k-1)+Δu(k)=u(k-1)+K p [e(k)-e(k-1)]+ΔtK I e(k) (16)

[0122] It can be seen from the formula that incremental PI control does not require time accumulation and is only related to the latest sampling value and control increment Δu(k), which greatly reduces the calculation time and solves the delay problem.

[0123] 2.2 Feedforward controller design

[0124] The PI controller mainly offsets the steady-state error through the integral term, but its response capability is limited to sudden, high-frequency disturbances, and may be at the expense of response speed. In some rapidly changing systems, using only PI control may not meet the demand for fast response. In summary, using only PI control may not meet the requirements for system performance, stability, and response speed. Therefore, the present invention chooses to add feedforward control to compensate for the limitations of PI control. The fixed-width frequency modulation control schematic is shown in Figure 1. Figure 7 As shown, it includes a PI controller and a feedforward controller.

[0125] Load voltage U out With a given reference voltage U ref For comparison, the ΔT obtained after PI adjustment p , ΔT obtained by superimposing feedforward control f The intermittent time reference value ΔT is obtained, and the drive signal G of the inverter bridge switch tube is generated through the modulation circuit. T1 ~~G T4 By controlling the length of the switch intermittent time, the system output voltage is controlled to a given reference output voltage value. After the output voltage fluctuation information is added to the feedforward control, the control requirements of the PI closed loop can be reduced and the dynamic response of the system can be greatly improved.

[0126] The resonant wireless power transmission system based on fixed-width frequency modulation control includes a feedforward G f (s) controller, incremental proportional integral PI controller and fixed width frequency modulation control module; input voltage and U in With a given reference voltage U ref For comparison, after feedforward G f (s) ΔT obtained after the controller is tuned f ;

[0127] Load voltage U out With a given reference voltage U ref For comparison, the incremental proportional integral PI controller is tuned to obtain ΔT p , ΔT obtained by superimposing feedforward controlf The intermittent time reference value ΔT is obtained, and the drive signal G of the inverter bridge switch tube is generated through the modulation circuit. T1 ~G T4 ; By controlling the length of the switch intermittent time, the system output voltage is controlled to a given reference output voltage value; after the output voltage fluctuation information is added to the feedforward control, the control requirements of the PI closed loop can be reduced and the dynamic response of the system can be greatly improved; the expression of the feedforward controller is calculated as follows:

[0128]

[0129] Among them, T r is the resonant period of the D-LLC circuit.

[0130] The resonant wireless power transmission system based on fixed-width frequency modulation control, the voltage regulation strategy of the system control is: the pulse width variation range in the fixed-width frequency modulation control is determined to be 40kHz according to the load demand and system design parameters, and the frequency range is 85kHz to 125kHz; the pulse width does not change with the load, but the output is adjusted by changing the switching frequency; by real-time sampling of the voltage and comparing it with the reference value, the input voltage and the reference voltage enter the feedforward G f (s) The controller performs calculation to obtain ΔT s , output voltage U out With reference voltage U ref Enter the incremental proportional integral PI controller to calculate ΔT p ; ΔT s and ΔT p After adding, we get the sawtooth wave signal ΔS w , ΔS w The intermittent time ΔT is obtained through the fixed-width frequency modulation module, and the intermittent time ΔT is used to adjust the length of the intermittent time of the system switch tube to maintain output stability and ensure that the output voltage reaches the predetermined target; the use of an incremental proportional integral PI controller can effectively reduce the control system calculation time;

[0131] Working status includes:

[0132] The transmitting coil current i1 is sampled to obtain its zero-crossing moment, at which time the inverter tubes T1 to T4 are all turned off;

[0133] When the transmitting coil current i1 passes through zero from positive to negative, the switch tubes T1 and T4 are turned off; when i1 passes through zero from negative to positive, the switch tubes T2 and T3 are turned off;

[0134] Voltage u across the detection coil A After the voltage detection circuit and zero-crossing comparison, the voltage zero-crossing point is found, which is the pulse opening moment of the reverse series switch tubes T5 and T6 at the receiving end;

[0135] When the voltage u A When the voltage passes through zero from positive voltage to negative voltage and vice versa, the anti-series switch tubes T5 and T6 are turned on to keep the current at the receiving end flowing continuously in the coil loop.

[0136] Frequency regulation is the core of this control method. The frequency is adjusted based on the output deviation, and the output power is balanced by increasing or decreasing the switching frequency.

[0137] The resonant wireless power transmission system based on fixed-width frequency modulation control, the fixed-width frequency modulation control algorithm comprises the following steps:

[0138] S100: Feed-forward G f (s) controller, incremental proportional integral PI controller after tuning, in the algorithm it is a sawtooth wave signal ΔS with a variable peak value w ; Digital clock frequency f clk is 150MHz; due to fixed-width frequency modulation control, the given pulse width T on Set to 5 microseconds; switching frequency f PWM The range is 85kHz to 125kHz;

[0139] S200: Given a constant comparison value A and a variable comparison value B that changes with the input amount, and the sum of the variable comparison value B and the constant comparison value A is equal to the sawtooth wave signal ΔS w The peak value of the inverter bridge is ensured to be constant during the opening time; where:

[0140]

[0141] The constant comparison value A is determined to be 375 by formula (16), and the variable comparison value B is determined to be in the range of 600 to 882 by formula (17). The sum of the variable comparison value B and the constant comparison value A is equal to the sawtooth wave signal ΔS at the same time. w The peak value ensures the constant opening time of the inverter bridge;

[0142] S300: When the algorithm is in the upward counting mode, when the sawtooth wave signal is less than or equal to the comparison value A, a high level is output, which is the turn-on time of the inverter bridge switches T1 and T4; when the algorithm is in the downward counting mode, when the sawtooth wave signal is greater than or equal to the comparison value B, a high level is output, which is the turn-on time of the inverter bridge switches T2 and T3;

[0143] S400: when the algorithm is in the upward counting mode and the sawtooth wave signal is greater than the comparison value A, and when the algorithm is in the downward counting mode and the sawtooth wave signal is less than the comparison value B, both output a high level as the turn-on time of the anti-series switch tubes T5 and T6;

[0144] S500: Due to the voltage u across the detection coilA The phase is the same as the transmitting coil current i1, and the voltage u A The same as the zero-crossing point of the current i1, at this time, the action of each switch tube can satisfy the synchronization between the receiving end and the transmitting end and stop the resonance.

[0145] The resonant wireless power transmission system based on fixed-width frequency modulation control, the system also includes an operating condition detection process, the loosely coupled transformer has an excitation inductance, the operating condition detection process can realize the prompting of the transformer energy transmission efficiency, the system operating condition detection process is: after the system operating condition detection starts, the given voltage reference value is compared with the system output voltage value:

[0146] When the given voltage reference value is greater than the system output voltage value, the system is in a boost condition; the intermittent time ΔT obtained by the fixed-width frequency modulation control algorithm is compared with the excitation current i m Critical time t for continuous or intermittent operation c Compare; when the intermittent time ΔT is less than the critical time t c , the system needs to perform fixed-width frequency modulation control; when the intermittent time ΔT is greater than the critical time t c , the system does not need fixed-width frequency modulation control;

[0147] When the given voltage reference value is less than the system output voltage value, it means that the system is in a voltage reduction state; the intermittent time ΔT obtained by the fixed-width frequency modulation control algorithm is compared with the excitation current i m Critical time t for continuous or intermittent operation c When the intermittent time ΔT is greater than the critical time t c , the system needs to perform fixed-width frequency modulation control; when the intermittent time ΔT is less than the critical time t c , the system does not need fixed-width frequency modulation control;

[0148] When the given voltage reference value is equal to the system output voltage, it means that the system does not need fixed-width frequency modulation control.

[0149] 2.3 System control scheme design

[0150] The voltage regulation strategy based on the fixed-width frequency modulation control principle mentioned above is as follows Figure 8 As shown. The resonant frequency is determined according to the parameters of the resonant elements of the system. According to the relationship between the given value and the actual value of the output voltage, the intermittent time ΔT required by the system is obtained through the feedforward control algorithm, that is, by controlling the length of the switch tube off time, the system output voltage is controlled to a given reference output voltage value. The transmitting coil current i1 is sampled to obtain its zero-crossing moment, at which time the inverter tubes T1 to T4 are all turned off. When the transmitting coil current i1 passes through zero from positive to negative, the switch tubes T1 and T4 are turned off; when i1 passes through zero from negative to positive, the switch tubes T2 and T3 are turned off. The voltage u at both ends of the detection coilA After the voltage detection circuit and zero-crossing comparison, the voltage zero-crossing point is found, which is the pulse opening moment of the reverse series switch tubes T5 and T6 at the receiving end. A When the voltage crosses zero from positive voltage to negative voltage and vice versa, the anti-series switch tubes T5 and T6 are turned on to keep the current at the receiving end flowing in the coil loop. The on-time is obtained through the feedforward control algorithm to obtain the intermittent time ΔT required by the system. The flow chart of the fixed-width frequency modulation control algorithm is as follows: Fig. 9 shown.

[0151] After adding a feedforward controller and performing PI tuning, the data is the input of the fixed-width frequency modulation algorithm, which is a sawtooth wave signal with a variable peak value in the algorithm. A constant comparison value A and a variable comparison value B that changes with the input are given, and the sum of the variable comparison value B and the constant comparison value A is equal to the peak value of the sawtooth wave signal at all times, so as to ensure the constancy of the inverter bridge opening time. When the algorithm is in the upward counting mode, when the sawtooth wave signal is less than or equal to the comparison value A, a high level is output, which is the opening time of the inverter bridge switches T1 and T4; when the algorithm is in the downward counting mode, when the sawtooth wave signal is greater than or equal to the comparison value B, a high level is output, which is the opening time of the inverter bridge switches T2 and T3. When the algorithm is in the upward counting mode, when the sawtooth wave signal is greater than the comparison value A, and when the algorithm is in the downward counting mode, when the sawtooth wave signal is less than the comparison value B, a high level is output as the opening time of the anti-series switches T5 and T6. Since the voltage u across the detection coil is A The phase is the same as the transmitting coil current i1, and the voltage u A The same as the zero-crossing point of the current i1, the action of each switch tube at this time can satisfy the synchronous cessation of resonance of the receiving end and the transmitting end.

[0152] Due to the existence of excitation inductance in the resonant wireless charging system, the energy in the transformer excitation inductance has a great influence on the energy transmission of the system. The system operation condition detection flow chart is as follows: Fig.10 When the given voltage reference value is greater than the system output voltage, it means that the system is in a boost condition. If the intermittent time obtained by the fixed-width frequency modulation control algorithm is greater than or equal to the excitation current i m If the intermittent time is less than the critical time of the continuous or intermittent working condition, the system stops running; when the given voltage reference value is less than the system output voltage, it means that the system is in a step-down working condition. If the intermittent time obtained by the fixed-width frequency modulation control algorithm is less than or equal to the excitation current i m When the critical time of continuous or intermittent working conditions is exceeded, the system stops running; when the given voltage reference value is equal to the system output voltage, it indicates that the system does not need fixed-width frequency modulation control.

[0153] The above is only an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A resonant wireless power transmission system based on fixed-width frequency modulation control, comprising a DC power supply, a high-frequency inverter circuit, a loosely coupled transformer, a rectifier circuit, an output load and a control system; characterized in that: The DC power supply input voltage is U in The high-frequency inverter circuit is composed of four MOSFET tubes T1, T2, T3 and T4. The transmitter self-inductance coil L1 of the loosely coupled transformer is connected to the high-frequency inverter circuit through the resonant capacitor C1 and the resistor R1 to form a transmitter compensation network. The receiver self-inductance coil L2 of the loosely coupled transformer is connected to the rectifier circuit through the resonant capacitor C2 and the resistor R2 to form a receiver compensation network; the rectifier circuit is connected to the DC side filter capacitor C d Connect the output load; The transmitter compensation network is connected to the DC power supply through the absorption capacitor C and the absorption resistor R connected in series, and the diode D in The anode is connected to the positive pole of the DC power supply, and the diode D in The cathode is connected to the drain of MOSFET tubes T1 and T2; The receiving end compensation network is connected to anti-series switch tubes T5 and T6, the drain of the switch tube T5 is connected to the same-name end of the receiving end self-inductance coil L2, and the drain of the switch tube T6 is connected to the opposite-name end of the receiving end self-inductance coil L2 through the resistor R2; The control system controls the working states of four MOSFET tubes T1, T2, T3 and T4, and switch tubes T5 and T6 in the high-frequency inverter circuit respectively.

2. The resonant wireless power transmission system based on fixed-width frequency modulation control according to claim 1, characterized in that: The loosely coupled transformer also includes a receiving end detection coil L3, which is coupled to the receiving end self-inductance coil L2. The detection coil L3 collects the zero-crossing instant information of the voltage u2 of the receiving end self-inductance coil L2, and then controls the working state of the anti-series switch tubes T5 and T6 through the control system.

3. The resonant wireless power transmission system based on fixed-width frequency modulation control according to claim 1, characterized in that: The system collects the system output voltage U through the voltage sampling module 1 out , the system output voltage U out With the set reference voltage U ref The error signal ΔU1 is input into the proportional integral PI controller to generate a PI adjustment signal ΔT p ; The system input voltage U in With the set reference voltage U ref Enter the feedforward G f (s) In the controller, a feedforward control signal ΔT is generated f ; The PI adjustment signal ΔT p With the feedforward regulation signal ΔT f Add together to generate a sawtooth wave signal ΔS w The sawtooth wave signal ΔS w Enter the fixed-width frequency modulation control module, and then the fixed-width frequency modulation control algorithm in the module generates the intermittent time ΔT required by the system; the system collects the transmitting coil current i1 through the current sampling and zero-crossing comparison module to generate the current comparison result ΔI1; the intermittent time ΔT and the current comparison result ΔI1 enter the drive signal 1 module to generate the drive signals GT1, GT2, GT3 and GT4 for regulating the operation of the system switches T1, T2, T3 and T4; the system collects the voltage u at both ends of the detection coil through the voltage sampling 2 and the zero-crossing comparison module A , generating a voltage comparison result ΔU A The intermittent time ΔT and the voltage comparison result ΔU A Enter the drive signal 2 module to generate drive signals GT5 and GT6 for regulating the operation of the system switches T5 and T6; thereby adjusting the switching frequency of the inverter so that the system always operates near the resonant frequency, ensuring a stable output voltage when the load changes; The current sampling and zero-crossing comparison module collects the transmitting coil current i1 to obtain its zero-crossing moment, at which time the inverter tubes T1 to T4 are all turned off; when the transmitting coil current i1 crosses zero from positive to negative, the switch tubes T1 and T4 are turned off; when i1 crosses zero from negative to positive, the switch tubes T2 and T3 are turned off; The voltage sampling 2 and zero-crossing comparison module detects the voltage u at both ends of the coil. A Collect and find the voltage zero point, voltage u A When the voltage crosses zero from positive voltage to negative voltage and from negative voltage to positive voltage, the anti-series switch tubes T5 and T6 are turned on to keep the current at the receiving end flowing in the coil loop; The voltage u across the detection coil A The phase is the same as the transmitting coil current i1, and the voltage u A The same as the zero-crossing point of the current i1, at this time, the action of each switch tube can satisfy the synchronous stop of resonance of the receiving end and the transmitting end; The intermittent time ΔT is passed through the drive signal 1 module and the drive signal 2 module, thereby changing the length of the on and off time of all switch tubes, thereby adjusting the system output voltage, providing a protection function, and preventing the switches from being turned on at the same time.

4. The resonance type wireless power transmission system based on fixed-width frequency modulation control according to claim 3 is characterized in that: The fixed-width frequency modulation control uses the resonant frequency as a reference and realizes frequency tracking and power regulation by adjusting the switching frequency of the inverter; the fixed-width frequency modulation control algorithm can keep the system working at the optimal resonant point to achieve efficient and stable wireless power transmission.

5. The resonance type wireless power transmission system based on fixed-width frequency modulation control according to claim 3 is characterized in that: The fixed-width frequency modulation control includes a feedforward G f (s) controller, incremental proportional integral PI controller and fixed width frequency modulation control module; input voltage and U in With a given reference voltage U ref For comparison, after feedforward G f (s) ΔT obtained after the controller is tuned f ; Load voltage U out With a given reference voltage U ref For comparison, the incremental proportional integral PI controller is tuned to obtain ΔT p , ΔT obtained by superimposing feedforward control f Get the sawtooth wave signal ΔS w The sawtooth wave signal ΔS w Enter the fixed-width frequency modulation control module to obtain the intermittent time ΔT, and the intermittent time ΔT generates the drive signals GT1 to GT4 of the inverter bridge switch tube through the drive signal 1 module; by controlling the length of the intermittent time of the switch tube, the system output voltage is controlled to a given reference output voltage value; after the output voltage fluctuation information is added to the feedforward control, the control requirements of the PI closed loop can be reduced, and the dynamic response of the system can be greatly improved; the expression of the feedforward controller is calculated as follows: Among them, T r is the resonant period of the D-LLC circuit.

6. The resonance type wireless power transmission system based on fixed-width frequency modulation control according to claim 3, characterized in that: The voltage regulation strategy of the system control is: the pulse width variation range in the fixed-width frequency modulation control is determined to be 40kHz according to the load demand and system design parameters, and the frequency range is 85kHz to 125kHz; the pulse width does not change with the load, but the output is adjusted by changing the switching frequency; the voltage is sampled in real time and compared with the reference value, where the input voltage and the reference voltage enter the feedforward G f (s) The controller performs calculation to obtain ΔT s , output voltage U out With reference voltage U ref Enter the incremental proportional integral PI controller to calculate ΔT p ; ΔT s and ΔT p After adding, we get the sawtooth wave signal ΔS w , ΔS w The intermittent time ΔT is obtained through the fixed-width frequency modulation module, and the intermittent time ΔT is used to adjust the length of the intermittent time of the system switch tube to maintain output stability and ensure that the voltage reaches the predetermined target; Use incremental proportional integral PI controller to effectively reduce the control system calculation time; Working status includes: The transmitting coil current i1 is sampled to obtain its zero-crossing moment, at which time the inverter tubes T1 to T4 are all turned off; When the transmitting coil current i1 passes through zero from positive to negative, the switch tubes T1 and T4 are turned off; when i1 passes through zero from negative to positive, the switch tubes T2 and T3 are turned off; The voltage uA at both ends of the detection coil passes through the voltage detection circuit and zero-crossing comparison to find the voltage zero-crossing point, which is the pulse opening moment of the reverse series switch tubes T5 and T6 at the receiving end; When the voltage u A When the voltage passes through zero from positive voltage to negative voltage and vice versa, the anti-series switch tubes T5 and T6 are turned on to keep the current at the receiving end flowing continuously in the coil loop.

7. The resonance type wireless power transmission system based on fixed-width frequency modulation control according to claim 3 is characterized in that: The fixed-width frequency modulation control algorithm comprises the following steps: S100: Feed-forward G f (s) controller, incremental proportional integral PI controller after tuning, in the algorithm is a sawtooth wave signal ΔS with a variable peak value w ; Digital clock frequency f clk is 150MHz; due to fixed-width frequency modulation control, the given pulse width T on Set to 5 microseconds; switching frequency f PWM The range is 85kHz to 125kHz; S200: Given a constant comparison value A and a variable comparison value B that changes with the input amount, and the sum of the variable comparison value B and the constant comparison value A is equal to the sawtooth wave signal ΔS w The peak value of the inverter bridge is ensured to be constant during the opening time; where: The constant comparison value A is determined to be 375 by formula (16), and the variable comparison value B is determined to be in the range of 600 to 882 by formula (17). The sum of the variable comparison value B and the constant comparison value A is equal to the peak value of the sawtooth wave signal, ensuring the constant opening time of the inverter bridge. S300: When the algorithm is in the upward counting mode, when the sawtooth wave signal is less than or equal to the comparison value A, a high level is output, which is the turn-on time of the inverter bridge switches T1 and T4; when the algorithm is in the downward counting mode, when the sawtooth wave signal is greater than or equal to the comparison value B, a high level is output, which is the turn-on time of the inverter bridge switches T2 and T3; S400: when the algorithm is in the upward counting mode and the sawtooth wave signal is greater than the comparison value A, and when the algorithm is in the downward counting mode and the sawtooth wave signal is less than the comparison value B, both output a high level as the turn-on time of the anti-series switch tubes T5 and T6; S500: Due to the voltage u across the detection coil A The phase is the same as the transmitting coil current i1, and the voltage u A The same as the zero-crossing point of the current i1, at this time, the action of each switch tube can satisfy the synchronization between the receiving end and the transmitting end and stop the resonance.

8. The resonance type wireless power transmission system based on fixed-width frequency modulation control according to claim 1, characterized in that: The system also includes an operating condition detection process. The loosely coupled transformer has an excitation inductance. The operating condition detection process can realize the prompting of the transformer energy transmission efficiency. The system operating condition detection process is: after the system operating condition detection starts, the given voltage reference value is compared with the system output voltage value: When the given voltage reference value is greater than the system output voltage value, the system is in boost condition; The intermittent time ΔT obtained by the fixed-width frequency modulation control algorithm is compared with the excitation current i m Critical time t for continuous or intermittent operation c Compare; when the intermittent time ΔT is less than the critical time t c , the system needs to perform fixed-width frequency modulation control; when the intermittent time ΔT is greater than the critical time t c , the system does not need fixed-width frequency modulation control; When the given voltage reference value is less than the system output voltage value, it means that the system is in a voltage reduction state; the intermittent time ΔT obtained by the fixed-width frequency modulation control algorithm is compared with the excitation current i m Critical time t for continuous or intermittent operation c When the intermittent time ΔT is greater than the critical time t c , the system needs to perform fixed-width frequency modulation control; when the intermittent time ΔT is less than the critical time t c , the system does not need fixed-width frequency modulation control; When the given voltage reference value is equal to the system output voltage, it means that the system does not need fixed-width frequency modulation control.

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