Synchronous Buck converter main circuit based on zero-voltage switch multi-resonant circuit and control method thereof

Abstract

The invention discloses a synchronous Buck converter main circuit based on a zero-voltage switch multi-resonant circuit and a control method of the synchronous Buck converter main circuit. The synchronous Buck converter main circuit based on the zero-voltage switch multi-resonant circuit comprises a direct-current power supply Vin, a first resonant capacitor Cr1, a main switch tube Q1, a resonant inductor Lr, a first branch circuit, a second branch circuit and a PWM control circuit. The PWM control circuit comprises a data processing module and a self-adaptive PID (Proportion Integration Differentiation) controller; the first resonant capacitor Cr1 is connected in parallel with the main switching tube Q1, then is connected in series with the resonant inductor Lr, and is connected to a first branch and a second branch which are connected in parallel; the first branch comprises a second resonant capacitor Cr2 and a synchronous tube Q2 which are connected in parallel; the second branch comprises an output capacitor C and a load resistor R which are connected in parallel, and the output capacitor C and the load resistor R are connected in series with the filter inductor L after being connected in parallel. By introducing a multi-resonant network formed by the resonant inductor Lr and the resonant capacitors Cr1 and Cr2, ideal switching conditions are created for all switching tubes, and a foundation is laid for improving efficiency and frequency.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, in particular to a synchronous Buck converter main circuit based on a zero-voltage switching multi-resonant circuit and a control method thereof. BACKGROUND

[0002] With the rapid development of power electronics technology, switching power supplies have become an indispensable key device in modern production and life due to their high efficiency and energy saving characteristics, and are widely used in new energy vehicles, rail transit, motor speed regulation systems and other fields. As a typical representative of DC / DC converters, they bear the core task of efficient transmission and conversion of electric energy. As a wide bandgap semiconductor material, gallium nitride (GaN) is becoming an ideal device for realizing high-frequency and high-efficiency power conversion due to its high breakdown voltage, fast electron drift speed and excellent temperature stability.

[0003] In view of the high power density and high frequency operation requirements of laser load equipment (such as individual, vehicle-mounted, airborne, etc.) for driving sources, the traditional pump source driving system based on silicon (Si) devices has faced a bottleneck in performance, and generally has problems such as low power density, large switching loss, strong electromagnetic interference, etc. The low on-resistance and high switching speed of GaN transistors (HEMT) provide great potential for designing high-frequency and high-power density power supply systems.

[0004] In order to overcome the switching loss at high frequency, soft switching technology is widely researched and applied. This technology can significantly reduce the voltage and current overlap loss in the switching process, thereby improving system efficiency and operating frequency, while helping to reduce the size of passive components, enhance system reliability and reduce electromagnetic interference. However, the existing mainstream soft switching schemes each have their limitations: Active auxiliary resonant soft switching technology: such as zero switching PWM circuit and zero conversion PWM circuit, which requires the introduction of additional active switching devices to control the starting time of the resonant process. This not only increases the complexity and cost of the circuit, but also brings difficulties to the design of the control strategy.

[0005] Quasi-resonant soft switching technology: for example, zero-current switching quasi-resonant circuit (ZCS-QRC), the switching tube bears a large current stress, and its soft switching condition is sensitive to the load range, and may fail when the load is too heavy; zero-voltage switching quasi-resonant circuit (ZVS-QRC) has the problem of large voltage stress of the switching tube, and also has requirements for the load range, and it is difficult to achieve soft switching when the load is too light.

[0006] In summary, the existing technology is difficult to achieve high efficiency and high power density soft switching operation in a wide load range without adding additional active devices. SUMMARY

[0007] The application aims at solving the problem that the prior art is difficult to realize high-efficiency soft switching in a wide load range without adding additional active devices.

[0008] In order to achieve the above-mentioned purpose, the application provides a synchronous Buck converter main circuit based on a zero-voltage switching multi-resonant circuit, comprising a direct-current power supply Vin, a first resonant capacitor Cr1, a main switch Q1, a resonant inductor Lr, a first branch, a second branch, and a PWM control circuit. The first resonant capacitor Cr1 is connected in parallel with the main switch Q1, and then connected in series with the resonant inductor Lr, and connected to the parallel first branch and the second branch. The first branch comprises a second resonant capacitor Cr2 and a synchronous tube Q2 connected in parallel, and the second branch comprises a filter inductor L, an output capacitor C, and a load resistor R connected in series.

[0009] Optionally, the drain D1 of the main switch is connected with the direct-current power supply Vin, the source S1 is connected with the resonant inductor Lr, and the gate G1 is connected with the PWM control circuit. Optionally, the drain D2 of the synchronous tube is connected with the resonant inductor Lr, the source S2 is connected with the direct-current power supply Vin, and the gate G2 is connected with the PWM control circuit.

[0010] Optionally, the resonant inductor Lr, the first resonant capacitor Cr1, and the second resonant capacitor Cr2 form a multi-resonant network, and soft switching is realized through resonance when the main switch Q1 is turned on, the synchronous tube Q2 is turned on, and the synchronous tube Q2 is turned off.

[0011] Optionally, the main switch Q1 and the synchronous tube Q2 are both composed of a plurality of GaN power transistors connected in parallel.

[0012] Optionally, the main switch Q1 and the synchronous tube Q2 are both composed of two GaN power transistors connected in parallel, and the GaN power transistors are GS66516 transistors of GaN Systems Company.

[0013] The application further provides a control method of the above-mentioned synchronous Buck converter main circuit based on a zero-voltage switching multi-resonant circuit, and the method comprises the following steps: Step S1, constructing the synchronous Buck converter main circuit based on a zero-voltage switching multi-resonant circuit; Step S2, the data processing module real-time acquisition of current flowing through the load resistance, compared with the reference value after the adaptive PID controller generates PWM signal, control main switch Q1, Q2 synchronous tube working state; Step S3, the resonant inductor Lr, the first resonant capacitor Cr1, the second resonant capacitor Cr2 constitute a multi resonant network, in the main switch Q1 open, synchronous tube Q2 open and off through the resonance to realize soft switch; Wherein, the resonant angle frequency of the multi resonant network ω r Expression is: , L r The inductance of resonant inductor Lr, C r1 The capacitance of the first resonant capacitor Cr1, C r2 The capacitance of the second resonant capacitor Cr2.

[0014] Optionally, the characteristic impedance expression of the multi resonant network is: , Z r1 The characteristic impedance of resonant inductor Lr and the first resonant capacitor Cr1, Z r2 The characteristic impedance of resonant inductor Lr and the second resonant capacitor Cr2.

[0015] Optionally, in a switching cycle, the synchronous Buck converter main circuit based on zero voltage switching multi resonant circuit includes four stages: t0-t1 stage: when the main switch Q1 starts to conduct, the resonant inductor current i Lr From zero linearly, meet the relationship: , i Lr (t) is the current of resonant inductor at t, i Lr (t0) is the current of resonant inductor at t0, V in The DC power supply voltage, V0 is the voltage across the load resistor, t-t0 is the time difference between t and t0, when i Lr Reaches the preset output current I0, the synchronous tube Q2 is naturally off under zero current condition; t1-t2 stage: the resonant inductor Lr and the second resonant capacitor Cr2 begin to resonate, the resonant process inductance current and voltage satisfy: , V Cr2 The voltage across the second resonant capacitor Cr2, t-t1 is the time difference between t and t1, V Lr (t) is the voltage of resonant inductor at t, i r(t1) is the current of the load resistance at t1; t2-t3 stage: the resonant inductor Lr resonates with the first resonant capacitor Cr1 and the second resonant capacitor Cr2, when the voltage across the second resonant capacitor Cr2 resonates to zero, the synchronous tube Q2 is turned on at zero voltage; t3-t4 stage: the resonant inductor Lr continues to resonate with the first resonant capacitor Cr1, when the voltage across the first resonant capacitor Cr1 resonates to zero, the main switch tube Q1 is turned on again at zero voltage, completing a complete switching cycle.

[0016] Compared with the prior art, the beneficial effects of the present application are: (1) high-efficiency soft switching is realized, and the loss is significantly reduced: The present application introduces resonant inductor Lr and resonant capacitors Cr1 and Cr2 to form a multi-resonant network, providing soft switching conditions for all switching devices, realizing zero-voltage turn-on of the main switch tube Q1 and zero-voltage turn-on and zero-current turn-off of the synchronous tube Q2. This fundamentally solves the core problem of high switching loss of traditional hard switching technology at high frequency, laying the foundation for improving efficiency and frequency.

[0017] (2) the topology structure is simple, and no additional active devices are needed: The present application is based on the improved topology structure of the synchronous Buck converter, only adding passive devices (resonant inductor Lr and resonant capacitors Cr1 and Cr2), compared with zero switching / zero conversion PWM circuit which needs active assistance, no active devices are needed, simplifying the circuit structure, reducing cost and control complexity.

[0018] (3) effectively utilizing the high-frequency advantage of GaN devices: The present application makes full use of the high-frequency characteristics of GaN transistors (such as GS66516), overcomes the switching loss bottleneck in high-frequency applications through soft switching technology, so that the high-frequency potential of GaN devices can be fully utilized, realizing high-frequency and high-efficiency operation.

[0019] (4) the present application adopts adaptive PID control strategy to adjust the PWM of the switch tube in real time, so that the system can maintain high efficiency operation in a wide load range. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The present application is based on the principle diagram of the main circuit and control circuit of the synchronous Buck converter of the multi-resonant circuit based on zero-voltage switching.

[0021] Figure 2 The key waveform diagram of the resonant drive of the multi-resonant network.

[0022] Figure 3 The comparison diagram of the measured waveforms of the soft switching of the main switch tube and the synchronous tube.

[0023] Figure 4 It is a system control block diagram.

[0024] Figure 5 It is a hard switch and soft switch conversion efficiency comparison curve diagram.

[0025] Figure 6 It is a physical diagram of an experimental prototype. DETAILED DESCRIPTION

[0026] The technical solutions of the application are further described below in combination with the drawings and examples.

[0027] As shown in Figure 1 The application provides a synchronous Buck converter main circuit based on a zero-voltage switching multi-resonant circuit, which comprises a direct current power supply Vin, a first resonant capacitor Cr1, a main switch tube Q1, a resonant inductor Lr, a first branch, a second branch, and a PWM control circuit. The first resonant capacitor Cr1 is connected in parallel with the main switch tube Q1, and then connected in series with the resonant inductor Lr, and is connected to the parallelly connected first branch and second branch. The first branch comprises a second resonant capacitor Cr2 and a synchronous tube Q2 connected in parallel, and the second branch comprises a filter inductor L, an output capacitor C, and a load resistor R connected in series.

[0028] The application introduces a multi-resonant network composed of a resonant inductor Lr and resonant capacitors Cr1 and Cr2 on the basis of a conventional synchronous Buck converter, combines the high-frequency characteristics of GaN devices, realizes high efficiency and high power density, creates ideal switching conditions for all switch tubes (the main switch tube Q1 and the synchronous tube Q2), and realizes zero-voltage turn-on (ZVS) of the main switch tube Q1 and zero-voltage turn-on and zero-current turn-off (ZCS) of the synchronous tube Q2. This fundamentally solves the core problem of large switching loss of conventional hard switching technology at high frequency, and lays a foundation for improving efficiency and frequency.

[0029] In some embodiments, the drain D1 of the main switch tube is connected with the direct current power supply Vin, the source S1 is connected with the resonant inductor Lr, the gate G1 is connected with the PWM control circuit, the drain D2 of the synchronous tube is connected with the resonant inductor Lr, the source S2 is connected with the direct current power supply Vin, and the gate G2 is connected with the PWM control circuit.

[0030] In some embodiments, the main switch Q1 and the synchronous switch Q2 each adopts two GS66516 transistors of GaN Systems in parallel, and the key parameters are as follows: VDS is 650V, ID is 60A, and RDS(on) is 25mΩ.

[0031] In some embodiments, the resonant inductor Lr is selected as 800nH, and the first resonant capacitor Cr1 and the second resonant capacitor Cr2 are both 4.3nF.

[0032] In some embodiments, the filter inductor L is composed of two inductors with a value of 6.8μH in series. The output capacitor C is composed of 24 ceramic capacitors in parallel, and the total capacitance is 50μF.

[0033] The main circuit of the synchronous Buck converter based on the zero-voltage switching multi-resonant circuit (ZVS-MRC) of the application adopts a two-stage integrated structure, integrates an LLC resonant cavity and an isolation rectifier circuit on the four-switch Buck-Boost rear bridge arm of two-phase interleaved parallel connection, and can realize an extremely wide voltage ratio. In order to enable all switch tubes to realize soft switching in the full voltage and load range, a set of control methods is proposed for the above new circuit, including the following steps: Step S1, main circuit construction: constructing the main circuit of the synchronous Buck converter based on the zero-voltage switching multi-resonant circuit.

[0034] Step S2, control strategy: the data processing module acquires the current flowing through the load resistor in real time, compares it with the reference value, and generates PWM through an adaptive PID controller.

[0035] Step S3, soft switching implementation: the resonant inductor Lr, the first resonant capacitor Cr1, and the second resonant capacitor Cr2 form a multi-resonant network, and soft switching is realized through resonance when the main switch Q1 is turned on, the synchronous switch Q2 is turned on and turned off, including the output capacitance of the main switch Q1 and the synchronous switch Q2 and the leakage inductance of the line, which provides good switching conditions for all switch devices. In one switching cycle, the circuit operation is divided into four stages: [t0-t1] is the charging stage of the resonant inductor Lr; [t1-t2] is the first resonant stage, in which the resonant inductor Lr and the second resonant capacitor Cr2 start to resonate; [t2-t3] is the second resonant stage, in which the resonant inductor Lr and the first resonant capacitor Cr1 and the second resonant capacitor Cr2 jointly resonate; [t3-t4] is the third resonant stage, in which the resonant inductor Lr and the first resonant capacitor Cr1 continue to resonate.

[0036] Step S4, soft start and protection: soft start is realized by slowly increasing the closed-loop current reference value; input under-voltage, output over-voltage, over-current and over-temperature protection functions are set, when abnormal parameters are detected, the converter stops working and reports fault codes through CAN communication.

[0037] Embodiment The embodiment provides a control method of a synchronous Buck converter main circuit based on a zero-voltage switching multi-resonant circuit, and the control method comprises the following steps: Step S1, main circuit construction: the synchronous Buck converter main circuit based on the zero-voltage switching multi-resonant circuit is constructed.

[0038] Step S2, control strategy: in order to realize accurate control of the system, the adaptive PID control strategy as shown in the figure is adopted in the embodiment, the data processing module collects output current in real time, and after comparison with a reference value, a PWM signal is generated through the adaptive PID controller. The discrete form of the PID controller is as follows: Figure 4 , Among them, 、 PID controller output of the current period and the last period are respectively represented by u(k) and u(k-1), 、 、 Error signals of the current period, the last period and the previous two periods are respectively represented by e(k), e(k-1) and e(k-2), and q0, q1 and q2 respectively represent weights of the error signals of the current period, the last period and the previous two periods.

[0039] The continuous domain transfer function G c (s) of the PID controller is designed as:

[0040] Among them, the gain coefficient K=14.12, the zero point frequency fz1=1.5 kHz and fz2=3 kHz, and the pole point frequency fp1=18 kHz. s is a complex variable, ω z1 、ω z2 are the angular frequencies of the zero point Z1 and the zero point Z2, and ω p1 represents the angular frequency of the pole point P1. The control strategy can automatically adjust parameters according to the system running state, and realizes fast and stable dynamic response.

[0041] ​Step S3, soft switch implementation: the resonant inductor Lr, the first resonant capacitor Cr1, and the second resonant capacitor Cr2 constitute a multi-resonant network, which absorbs the parasitic parameters in the main circuit of the synchronous Buck converter based on the zero-voltage switching multi-resonant circuit, including the output capacitances of the main switch Q1 and the synchronous tube Q2 and the leakage inductance of the line, to provide good switching conditions for all switching devices. In one switching cycle, the circuit operation is divided into four stages, and the key theoretical waveforms are as shown in Figure 2 [t0-t1] is the charging stage of the resonant inductor Lr: when the main switch Q1 starts to conduct, the resonant inductor current i Lr starts to rise linearly from zero, satisfying the relationship: , i Lr (t) is the current of the resonant inductor at t, i Lr (t0) is the current of the resonant inductor at t0, V in is the DC power supply voltage, V0 is the voltage across the load resistor, and t-t0 is the time difference between t and t0. When i Lr reaches the preset output current I0, the synchronous tube Q2 naturally turns off under zero current conditions; [t1-t2] is the first resonant stage, Lr and Cr2 start to resonate: during the resonant process, the inductor current and voltage satisfy: , V Cr2 is the voltage across the second resonant capacitor Cr2, t-t1 is the time difference between t and t1, V Lr (t) is the voltage of the resonant inductor at t, i r (t1) is the current of the load resistor at t1; The resonant angular frequency ω r of the multi-resonant network is expressed as: , L r is the inductance of the resonant inductor Lr, C r1 is the capacitance of the first resonant capacitor Cr1, and C r2 is the capacitance of the second resonant capacitor Cr2; The characteristic impedance expression is: , Z r1 is the characteristic impedance when the resonant inductor Lr and the first resonant capacitor Cr1 resonate, and Z r2 is the characteristic impedance when the resonant inductor Lr and the second resonant capacitor Cr2 resonate; [t2-t3] is the second resonant stage, Lr and Cr1, Cr2 jointly resonate: when the voltage across the second resonant capacitor Cr2 resonates to zero, the synchronous tube Q2 conducts under zero voltage; ​[t3-t4] is a resonant third stage, Lr and Cr1 continue to resonate: when the first resonant capacitor Cr1 both ends voltage resonant to zero, the main switch Q1 is turned on again at zero voltage, a complete switching cycle is completed.

[0042] Step S4, soft start and protection: the soft start process gradually increases the closed-loop current reference value, so that the output current gradually increases, and finally reaches the rated output value.

[0043] The current reference value update algorithm in the soft start process is:

[0044] Where, I ref (k) is the current reference value of the current period, I ref (k-1) is the current reference value of the last period, ΔI step is the current step increment; when I ref (k)≥I target , stop the soft start process, wherein I target is the preset target current value.

[0045] The protection function includes setting input under-voltage, output over-voltage, over-current and over-temperature, when detecting abnormal parameters, the converter stops working and reports fault code through CAN communication.

[0046] The judgment conditions of each protection threshold are: Input under-voltage protection: V in <V underthreshold Input over-voltage protection: V in >V overthreshold Output over-current protection: I out >I overthreshold Over-temperature protection: T device >T maxthreshold Where, V underthreshold is the lower limit of the preset voltage threshold, V overthreshold is the upper limit of the preset voltage threshold, I out is the current flowing through the load resistor, I overthreshold is the upper limit of the preset current threshold, T device is the current temperature of the switch tube, T maxthreshold is the upper limit of the preset temperature threshold.

[0047] The working of the synchronous Buck converter main circuit based on the zero-voltage switching multi-resonant circuit is in continuous conduction mode (CCM), and the voltage gain ratio M (CCM→Mode) is expressed as:

[0048] wherein R out is the load resistance, D is the duty cycle, L r is the inductance of the resonant inductor Lr, V out is the voltage across the load resistance, V in is the DC supply voltage; inductance current ripple Δi Lr(CCM) is calculated by the formula: .

[0049] The resonant inductor peak current i L(Peak-CCM) is calculated by the formula:

[0050] The resonant inductor average current i L(Avg-CCM) is calculated by the formula:

[0051] wherein t sw is the switching period, f sw is the switching frequency.

[0052] The calculation of the switching tube loss of the present application includes: the conduction loss P cond :

[0053] the switching loss P sw :

[0054] the parasitic capacitance P coss loss:

[0055] wherein I rms is the current effective value of the switching tube, R DS(on) is the on-resistance of the switching tube, V DS is the drain-source breakdown voltage of the switching tube, I D is the continuous drain current of the switching tube, t on , t off are the turn-on and turn-off times of the switching tube, C oss is the output capacitance of the switching tube.

[0056] To verify the technical effects of the present application, an experimental prototype as shown in Figure 6 is made. The prototype size is 105mm x 50mm x 14mm, the weight is 98g, the power density reaches 20.35kW / kg, and the power density P d is calculated by the formula: , Pout Pm is the output power of the prototype, m is the mass of the prototype.

[0057] The test is carried out under the conditions of input voltage 120V~170V, output voltage 114V±5V, and output current 0A-25A±0.2A, and the obtained soft-switching actual waveform is as shown in Figure 3 The test results show that the main switch tube Q1 realizes zero-voltage turn-on (Vds(Q1) has been resonated to zero before the rising edge of the driving signal Vgs(Q1) arrives), and the synchronous tube Q2 realizes zero-voltage turn-on and zero-current turn-off at the same time (Vds(Q2) starts to rise after the current drops to zero when turning off).

[0058] Figure 5 The efficiency comparison curves of the present application and the traditional hard switch are shown, the orange column chart represents the present application, and the blue column chart represents the traditional hard switch. When the output current is 25A under the conditions of 200kHz switching frequency, input voltage 120V, 150V and 170V, the conversion efficiency of the present application is maintained at more than 97.5%, the highest efficiency reaches 98.8%, and the output current ripple is less than 200mA, which is significantly higher than that of the traditional hard switch scheme. The conversion efficiency η calculation formula is: P in is the input power of the converter, I in is the input current of the converter.

[0059] In addition, the dynamic response test of the system shows that under the adaptive PID control, the starting time is shortened to 2ms, and there is no overshoot phenomenon, which shows excellent followability and stability.

[0060] The present application can realize high-frequency and high-efficiency power conversion without increasing additional active devices, and is particularly suitable for laser driving, aerospace and other occasions with high requirements for power density and efficiency.

[0061] Although the content of the present application has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the present application. After reading the above content, various modifications and alternatives of the present application will be obvious to those skilled in the art. Therefore, the protection scope of the present application should be defined by the appended claims.

Claims

1. A synchronous Buck converter main circuit based on a zero-voltage switching multi-resonant circuit, characterized by, The synchronous Buck converter comprises a direct current power supply Vin, a first resonant capacitor Cr1, a main switch Q1, a resonant inductor Lr, a first branch, a second branch and a PWM control circuit. The first resonant capacitor Cr1 is connected in parallel with the main switch Q1, and then connected in series with the resonant inductor Lr, and then connected to the first branch and the second branch in parallel. The first branch comprises a second resonant capacitor Cr2 and a synchronous transistor Q2 connected in parallel. The second branch comprises a filter inductor L, an output capacitor C and a load resistor R connected in series.

2. The zero-voltage-switching multi-resonant circuit based synchronous Buck converter main circuit according to claim 1, characterized in that, The drain D1 of the main switch is connected to the direct current power supply Vin, the source S1 is connected to the resonant inductor Lr, and the gate G1 is connected to the PWM control circuit.

3. The zero-voltage-switching multi-resonant circuit based synchronous Buck converter main circuit according to claim 1, wherein, The drain D2 of the synchronous transistor is connected to the resonant inductor Lr, the source S2 is connected to the direct current power supply Vin, and the gate G2 is connected to the PWM control circuit.

4. The zero-voltage-switching multi-resonant circuit based synchronous Buck converter main circuit according to claim 1, characterized by, The resonant inductor Lr, the first resonant capacitor Cr1 and the second resonant capacitor Cr2 form a multi-resonant network, and soft switching is realized through resonance when the main switch Q1 is turned on, the synchronous transistor Q2 is turned on and turned off.

5. The zero-voltage-switching multi-resonant circuit based synchronous Buck converter main circuit according to claim 1, wherein, The main switch Q1 and the synchronous transistor Q2 are both composed of a plurality of GaN power transistors connected in parallel.

6. The zero-voltage-switching multi-resonant circuit based synchronous Buck converter main circuit according to claim 5, characterized by, The main switch Q1 and the synchronous transistor Q2 are both composed of two GaN power transistors connected in parallel.

7. The zero-voltage-switching multi-resonant circuit based synchronous Buck converter main circuit according to claim 6, characterized by, The GaN power transistor is a GS66516 transistor.

8. A control method of a synchronous Buck converter main circuit based on a zero-voltage switching multi-resonant circuit according to any one of claims 1 to 7, characterized by, The method comprises the following steps: Step S1, constructing a synchronous Buck converter main circuit based on a zero-voltage switching multi-resonant circuit; Step S2, the data processing module collects the current flowing through the load resistor in real time, compares it with the reference value, and then generates a PWM signal through the adaptive PID controller to control the working state of the main switch Q1 and the synchronous transistor Q2; Step S3, the resonant inductor Lr, the first resonant capacitor Cr1 and the second resonant capacitor Cr2 form a multi-resonant network, and soft switching is realized through resonance when the main switch Q1 is turned on, the synchronous transistor Q2 is turned on and turned off; wherein the resonant angular frequency ω of the multi-resonant network is r The expression is: , L r is an inductance of the resonant inductor Lr, C r1 is a capacitance of the first resonant capacitor Cr1, C r2 is a capacitance of the second resonant capacitor Cr2.

9. The control method according to claim 8, characterized by, The characteristic impedance expression of the multi-resonant network is: , Z r1 is the characteristic impedance when the resonant inductance Lr resonates with the first resonant capacitor Cr1, Z r2 is the characteristic impedance when the resonant inductance Lr resonates with the second resonant capacitor Cr2.

10. The control method according to claim 9, characterized by, In one switching cycle, the working of the synchronous Buck converter main circuit based on the zero-voltage switching multi-resonant circuit comprises four stages: t0-t1 stage: when the main switch tube Q1 starts to conduct, the resonant inductance current i Lr Linearly rising from zero, satisfying the relationship: , i Lr (t) is the current of the resonant inductor at time t, i Lr (t0) is the current of the resonant inductor at time t0, V in is the DC power supply voltage, V0 is the voltage across the load resistor, t-t0 is the time difference between time t and time t0, when i Lr reaches the preset output current I0, the synchronous tube Q2 is naturally turned off under zero current condition; t1-t2 stage: the resonant inductor Lr and the second resonant capacitor Cr2 start to resonate, and the inductor current and voltage satisfy: ， V Cr2 V is the voltage across the second resonant capacitor Cr2, t-t1 is the time difference between t and t1, V Lr (t) is the voltage across the resonant inductor at t, i r (t1) is the current through the load resistor at t1; t2-t3 stage: the resonant inductor Lr and the first resonant capacitor Cr1 and the second resonant capacitor Cr2 jointly resonate, and when the voltage across the second resonant capacitor Cr2 resonates to zero, the synchronous transistor Q2 is turned on at zero voltage; t3-t4 stage: the resonant inductor Lr and the first resonant capacitor Cr1 continue to resonate, and when the voltage across the first resonant capacitor Cr1 resonates to zero, the main switch Q1 is turned on again at zero voltage, completing a complete switching cycle.

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