Method and device for improving dynamic characteristics of two-stage resonant converter based on virtual resistor

Abstract

The invention discloses a method and a device for improving dynamic characteristics of a two-stage resonant converter based on a virtual resistor, and in the converter, a front-stage Buck converter and a rear-stage LLC resonant converter are connected through a common DC bus; the dynamic characteristic improvement method comprises the following steps: inputting bus capacitor voltage on a common direct current bus into an active damping inner ring controller, and simulating a virtual resistor accessed to a converter through output; the difference value between the output voltage of the resonant converter and the reference voltage is input into a voltage outer loop proportional-integral controller; and subtracting the output signals of the active damping controller and the voltage outer loop controller to obtain an improved duty ratio of the preceding-stage Buck converter for controlling a switching device. By adopting the above technical scheme, through a control mode of combining voltage outer loop control and active damping inner loop control, the double-resonance peak in the voltage loop is suppressed, and the bandwidth of the voltage loop is effectively expanded.

Description

Technical Field

[0001] The present invention relates to the field of power electronic converter control, and particularly to a method and device for improving the dynamic characteristics of a two-stage resonant converter based on a virtual resistor. Background Art

[0002] Although the single-stage resonant converter has the advantages of simple structure, high efficiency, high energy density, etc., it has obvious limitations: on the one hand, the voltage gain range of the single-stage resonant converter is relatively narrow, making it difficult to meet the requirements of wide input voltage or large-range load jumps; on the other hand, the single-stage resonant converter usually adopts pulse width frequency modulation, making it difficult to optimize the parameters of its resonant elements and the magnetic integration complexity is high, which limits its application range. In contrast, the two-stage resonant converter has the advantages of wide voltage gain and easy optimization of resonant parameters, and has received more and more extensive attention.

[0003] The two-stage resonant converter is composed of a front-stage PWM (Pulse Width Modulation, PWM) converter and a rear-stage DCX-LLC (DC Transformer, DCX) resonant converter. The front-stage PWM converter is used to regulate the voltage to give full play to the advantage of wide voltage gain; the rear-stage DCX-LLC resonant converter plays the role of electrical isolation.

[0004] However, there are double resonant peaks in the voltage loop of the two-stage resonant converter, that is, there are multiple peaks in the gain curve of the control loop near the resonant frequency, which reduces the gain margin and phase margin of the system, resulting in insufficient bandwidth of the traditional voltage single-loop control and reducing the dynamic characteristics of the converter.

[0005] Although the virtual resistor active damping technology provided by the prior art can suppress the resonant peaks, these technologies are mainly aimed at systems with single resonant peaks, such as LCL-type grid-connected converters or LC-type uninterruptible power supplies, and cannot solve the problem of double resonant peaks in the two-stage resonant converter. Summary of the Invention

[0006] Object of the Invention: The present invention provides a method and device for improving the dynamic characteristics of a two-stage resonant converter based on a virtual resistor, aiming to solve the technical problem of double resonant peaks existing in the voltage loop of the two-stage resonant converter in the prior art.

[0007] Technical solution: The present invention provides a method for improving the dynamic characteristics of a two-stage resonant converter based on a virtual resistor, including: The two-stage resonant converter includes a front-stage Buck converter and a rear-stage LLC resonant converter. Among them, the positive and negative terminals of the output side of the front-stage Buck converter are respectively connected to both ends of the common DC bus, and the positive and negative terminals of the input side of the rear-stage LLC resonant converter are respectively connected to both ends of the common DC bus; the output side of the two-stage resonant converter is connected to the load; a bus capacitor is provided on the common DC bus; The method for improving the dynamic characteristics includes: using the bus capacitor voltage of the bus capacitor as an input signal and inputting it into the active damping inner-loop controller, and the active damping inner-loop controller outputs an analog virtual resistor connected to the converter; using the difference between the output voltage loaded on the load at the output side of the converter and the reference voltage as an input signal and inputting it into the voltage outer-loop proportional-integral controller; subtracting the output signal of the active damping inner-loop controller from the output signal of the voltage outer-loop proportional-integral controller, calculating the improved duty ratio of the front-stage Buck converter, and controlling the closing and turning off of the switching device of the front-stage Buck converter according to the control signal obtained from the improved duty ratio.

[0008] Specifically, the switching frequency of the switching device of the rear-stage LLC resonant converter is controlled to be fixed and equal to the resonant frequency of the rear-stage LLC resonant converter.

[0009] Specifically, the active damping inner-loop controller simulates a virtual resistor connected in parallel with the bus capacitor.

[0010] Specifically, the characteristic polynomial of the active damping inner-loop corresponding to the virtual resistor connected in parallel with the bus capacitor is as follows: det(sI 4×4 -A m ) = 0, where det represents the determinant of the matrix, s represents the complex frequency variable, I 4×4 represents the 4×4 identity matrix, and A m represents the state matrix of the two-stage resonant converter.

[0011] Specifically, convert the characteristic polynomial of the active damping inner-loop into the root locus formula of the active damping inner-loop with respect to the virtual resistor; based on the root locus formula of the active damping inner-loop with respect to the virtual resistor, combined with the poles of the active damping inner-loop root locus function, obtain the corresponding virtual resistor value.

[0012] Specifically, obtaining the virtual resistor value includes: among the poles of the active damping inner-loop root locus function, taking the virtual resistor value corresponding to the maximum damping of the two-stage resonant converter as the applied virtual resistor value.

[0013] Specifically, the root locus formula of the active damping inner-loop with respect to the virtual resistor is as follows: 1 + Rv T Rv (s) = 0, wherein, R v represents a virtual resistor, T Rv (s) represents the active damping inner - loop root - locus function, , wherein, C dc1 represents the bus capacitor, C dc2 represents the output capacitor connected in parallel on the output side of the two - stage resonant converter, L e represents the equivalent inductor of the front - stage Buck converter, L eq represents the equivalent inductor of the rear - stage LLC resonant converter, R L represents the load, and N represents the transformer turns ratio of the rear - stage LLC resonant converter.

[0014] Specifically, the closed - loop transfer function G pm (s) of the active damping inner - loop is as follows: G pm (s)=C(sI 4×4 - A m )B u , wherein, C = [0, 0, 0, 1], B u =[M(D)e(s) / L b , 0, 0, 0] T , M(D) represents the voltage gain of the front - stage Buck converter, e(s) represents the controlled voltage - source coefficient of the front - stage Buck converter, and L b represents the filter inductor of the front - stage Buck converter.

[0015] Specifically, the voltage - outer - loop loop - gain function under the active damping inner - loop control is as follows: T pm (s)=G PI (s)G pm (s), wherein, T pm (s) represents the voltage - outer - loop loop - gain, G PI (s) represents the voltage - outer - loop proportional - integral controller function, G PI (s)=k p +k i / s, k p represents the proportional gain, k i represents the integral gain; When the voltage - outer - loop loop - gain satisfies that the gain margin is greater than 4 dB and the phase margin is greater than 45°, the corresponding proportional gain and integral gain of the voltage outer - loop are used as the applied proportional gain and integral gain.

[0016] The present invention also provides a device for improving the dynamic characteristics of a two-stage resonant converter based on a virtual resistor, including: a signal acquisition unit and a signal processing unit, wherein: the two-stage resonant converter includes a front-stage Buck converter and a rear-stage LLC resonant converter. Among them, the positive and negative terminals of the output side of the front-stage Buck converter are respectively connected to both ends of the common DC bus, the positive and negative terminals of the input side of the rear-stage LLC resonant converter are respectively connected to both ends of the common DC bus, and the output side of the rear-stage LLC resonant converter is connected to a load; a bus capacitor is arranged on the common DC bus; the signal acquisition unit is used to take the bus capacitor voltage of the bus capacitor as an input signal and input it into an active damping inner-loop controller, and the active damping inner-loop controller outputs an analog virtual resistor connected to the converter; the difference between the output voltage loaded on the load at the output side of the converter and the reference voltage is used as an input signal and input into a voltage outer-loop proportional-integral controller; the signal processing unit is used to subtract the output signal of the active damping inner-loop controller from the output signal of the voltage outer-loop proportional-integral controller, calculate the improved duty cycle of the front-stage Buck converter, and control the closing and opening of the switching device of the front-stage Buck converter according to the control signal obtained from the improved duty cycle.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: Through the control method combining voltage outer-loop control and active damping inner-loop control, it is possible to suppress the double resonant peaks in the voltage loop, effectively expand the voltage loop bandwidth, improve the dynamic response ability, significantly shorten the control time of the output voltage, and enable it to be applicable to various working conditions such as sudden load changes. Description of the Drawings

[0018] Figure 1 It is a schematic diagram of the topology structure of the two-stage resonant converter and active damping control provided by the present invention; Figure 2 It is a schematic diagram of the equivalent circuit of the topology of the two-stage resonant converter provided by the present invention; Figure 3 It is a schematic diagram of the connection mode of the virtual resistor provided by the present invention; Figure 4 It is a schematic diagram of the derivation process of the active damping controller with respect to the virtual resistor provided by the present invention; Figure 5 It is a schematic diagram of the derivation process of the active damping controller with respect to the virtual resistor and the filter inductor provided by the present invention; Figure 6 It is a schematic diagram of the derivation process of the active damping controller provided by the present invention; Figure 7 It is a schematic diagram of the root locus of the active damping inner-loop pole with respect to the virtual resistor provided by the present invention; Figure 8The Bode plot of the voltage loop gain provided by the present invention; Figure 9 The voltage and current waveforms of a two-stage resonant converter when applying the voltage single-loop control in the prior art; Figure 10 The voltage and current waveforms applying the virtual-resistance active damping control provided by the present invention. Specific embodiments

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0020] Refer to Figure 1 , which is a schematic diagram of the topology structure and active damping control of the two-stage resonant converter provided by the present invention.

[0021] As Figure 1 shown, the two-stage resonant converter includes a front-stage Buck converter and a rear-stage LLC resonant converter. The front-stage Buck converter includes a filter inductor L b , a diode D b , and a switching transistor S b , and an input voltage v in ; the rear-stage LLC resonant converter includes a resonant capacitor C r , a resonant inductor L r , an exciting inductor L m , a high-frequency transformer with a turns ratio of N, switching transistors S1 to S4, and diodes D R1 to D R4 ; the front-stage and rear-stage converters are connected through a common DC bus (intermediate DC bus), and a bus capacitor is provided on the common DC bus; the output side (rectification side) of the rear-stage LLC resonant converter is connected to a load R L ; the front-stage Buck converter adjusts the output voltage v b of the two-stage resonant converter topology by controlling the duty cycle d y of the switching device S dc2 , that is, the voltage applied to the load R L .

[0022] In the embodiment of the present invention, the switching frequency f s of the switching device of the rear-stage LLC resonant converter is fixed and equal to the resonant frequency f r of the rear-stage LLC resonant converter.

[0023] In a specific implementation, the switching frequency of the switching device of the subsequent LLC resonant converter is controlled to be equal to its resonant frequency, enabling it to operate in the DCX (DC Transformer) mode, achieving a fixed voltage conversion ratio between the input and output, ensuring that the LLC resonant converter operates at the optimal efficiency operating point, and providing electrical isolation simultaneously.

[0024] The method for improving the dynamic characteristics provided by the present invention includes: using the bus capacitor voltage v of the bus capacitor dc1 as an input signal and inputting it into the active damping inner loop controller G ad (s), and the active damping inner loop controller outputs an analog virtual resistor connected to the converter; using the difference between the output voltage v dc2 loaded on the load at the output side of the converter and the reference voltage v dc2_ref as an input signal and inputting it into the voltage outer loop proportional-integral controller G PI (s); subtracting the output signal of the active damping inner loop controller from the output signal of the voltage outer loop proportional-integral controller to calculate the improved duty ratio of the pre-stage Buck converter, and obtaining a control signal according to the improved duty ratio (by inputting the duty ratio into the PWM module) to control the closing and turning off of the switching device S b of the pre-stage Buck converter.

[0025] Refer to Figure 2 , which is a schematic diagram of the equivalent circuit of the two-stage resonant converter topology provided by the present invention.

[0026] Figure 2 It can be known that the two-stage resonant converter includes 4 state variables, namely the inductor current i of the Buck converter Lb , the bus capacitor voltage v of the intermediate DC bus dc1 , the rectifier side current i of the subsequent LLC resonant converter rect and the output voltage v dc2 . The subsequent LLC resonant converter includes an equivalent inductor L r formed by the series connection of the resonant capacitor C r and the resonant inductor L eq , and the expression is: L eq =L r π 2 / 4N 2 , formula (1). L e represents the equivalent inductor of the pre-stage Buck converter.

[0027] The expression of the controlled voltage source coefficient e(s) of the pre-stage Buck converter is: e(s)= V dc1 / D y 2, formula (2), where V dc1 represents the steady-state value of the intermediate DC bus capacitor voltage, and D y represents the steady-state value of the duty cycle of the front-stage Buck converter.

[0028] The voltage gain M(D) of the front-stage Buck converter is: M(D)= D y , formula (3).

[0029] According to the selected state variables and the calculated parameters above, the state-space model of the two-stage resonant converter is as follows: x’=A0x+B u d y +B v +B io i o , formula (4).

[0030] In formula (4), x’ represents the calculated state vector, and i o represents the output current of the two-stage resonant converter. Other symbols are as follows: x=[i Le ,v dc1 ,i rect ,v dc2 T ,B u =[M(D)e(s) / L b ,0,0,0] T ,B v =[M(D) / L b ,0,0,0] T ,B io =[0,0,0,-1 / C dc2 T , formula (5), where i Le represents the output current of the front-stage Buck converter, C dc2 represents the output capacitor connected in parallel on the output side of the two-stage resonant converter, and T represents matrix transpose.

[0031] , formula (6), where C dc1 represents the bus capacitor provided on the common DC bus.

[0032] Refer to Figure 3 , which is a schematic diagram of the virtual resistor connection method provided by the present invention.

[0033] In the embodiment of the present invention, the active damping inner-loop controller simulates a virtual resistor R connected in parallel with the bus capacitor C dc1 ​​​v .

[0034] Refer to Figures 4 to 6 , which are respectively the derivation process of the active damping controller provided by the present invention with respect to the virtual resistor, the derivation process of the active damping controller with respect to the virtual resistor and the filter inductor, and the schematic diagram of the derivation process of the active damping controller.

[0035] In a specific implementation, when using R v in parallel with C dc1 , and the intermediate DC bus capacitor voltage v dc1 is used as the active damping feedback variable, the expression of the active damping inner-loop controller G ad (s) is: G ad (s)=(L b / M(D)e(s)R v )(ω ad s / (ω ad +s)), formula (7), where ω ad represents the corner frequency of the first-order high-pass filter, which usually needs to be much greater than the high-frequency resonance frequency of the two-stage resonant converter, and s represents the complex frequency variable. It can be seen from Figure 6 that the derived active damping controller contains a differential operator, which will amplify the high-frequency interference in the feedback signal. Therefore, in practical engineering, it is replaced by a first-order high-pass filter, as shown in formula (7).

[0036] After adopting the connection method of the virtual resistor with R v in parallel with C dc1 , the system state matrix A m of the two-stage resonant converter is: , formula (8).

[0037] Furthermore, after adopting the connection method of the virtual resistor in parallel with the bus capacitor, the characteristic polynomial of the active damping inner loop is: det(sI 4×4 -A m ) = 0, formula (9), where det represents the determinant of the matrix, s represents the complex frequency variable, I 4×4 represents the 4×4 identity matrix, and A m represents the state matrix of the two-stage resonant converter.

[0038] In a specific implementation, formula (9) can be converted into the formula of the root locus of the active damping inner loop with respect to the virtual resistor R v as follows: 1 + R v T Rv(s) = 0, Equation (10), where T Rv (s) represents the active damping inner - loop root - locus function.

[0039] , Equation (11), where C dc1 represents the bus capacitor, C dc2 represents the output capacitor connected in parallel on the output side of the two - stage resonant converter, L e represents the equivalent inductor of the front - stage Buck converter, L eq represents the equivalent inductor of the rear - stage LLC resonant converter, R L represents the load, and N represents the transformer turns ratio of the rear - stage LLC resonant converter.

[0040] In the embodiments of the present invention, based on the root - locus formula of the active damping inner - loop with respect to the virtual resistance and combined with the poles of the active damping inner - loop root - locus function, the corresponding virtual - resistance value is obtained.

[0041] In the embodiments of the present invention, among the poles of the active damping inner - loop root - locus function, the virtual - resistance value corresponding to the maximum damping of the two - stage resonant converter is used as the applied virtual - resistance value.

[0042] Refer to Figure 7 , which is a schematic diagram of the root - locus of the active damping inner - loop poles with respect to the virtual resistance provided by the present invention.

[0043] As Figure 7 shown, according to T Rv (s), the root - locus of the active damping inner - loop with respect to R v is plotted. It can be seen from Figure 7 that the damping ζ of the active damping inner - loop poles first increases and then decreases with R v , and when R v = R v,op , the damping of the active damping inner - loop poles reaches the maximum value. Therefore, select R v,op as the final value of R v .

[0044] In the embodiments of the present invention, the closed - loop transfer function G pm (s) of the active damping inner - loop is as follows: G pm (s)=C(sI 4×4 - A m )B u , Equation (12), where C = [0,0,0,1], B u = [M(D)e(s) / L b ,0,0,0] T, M(D) represents the voltage gain of the front - end Buck converter, e(s) represents the controlled voltage source coefficient of the front - end Buck converter, and L b represents the filter inductor of the front - end Buck converter.

[0045] In the embodiments of the present invention, the voltage outer - loop loop - gain function under active - damping inner - loop control is as follows: T pm (s)= G PI (s)G pm (s), where, T pm (s) represents the voltage outer - loop loop - gain, G PI (s) represents the voltage outer - loop proportional - integral controller function, and G PI (s)=k p +k i / s, k p represents the proportional gain, and k i represents the integral gain.

[0046] Refer to Figure 8 , which is the Bode plot of the voltage loop - gain T pm (s) provided by the present invention.

[0047] In specific implementation, adjust the proportional gain k p and the integral gain k i . When the voltage outer - loop loop - gain satisfies that the gain margin is greater than 4 dB (preferably greater than 4.5 dB), ensure that the control system can still maintain sufficient stability under factors such as model error, non - linearity, and perturbation; the phase margin is greater than 45°, ensure that the control system has good dynamic response and sufficient robustness, and avoid excessive oscillation or instability. Take the corresponding proportional gain and integral gain of the voltage outer - loop as the applied proportional gain and integral gain.

[0048] Thus, the design of all control parameters is completed.

[0049] In specific implementation, conduct experimental verification on the method for improving the dynamic characteristics of the two - stage resonant converter provided by the present invention. The system parameters of the two - stage resonant converter are as follows: L b = 1 mH, C dc1 = 800 μF, N = 1:1, L m = 100 μH, L r = 24 μH, C r = 0.42 μF, C dc2 = 800 μF. The rated input voltage and output voltage of the system are both 200 V, and the rated output power is 2 kW. When the output power of the two - stage resonant converter steps from 1 kW to 2 kW, compare the voltage fluctuation range and the stabilization time under different control schemes.

[0050] As Figure 9 shown, it is the voltage and current waveform diagram of a two-stage resonant converter when adopting voltage single-loop control in the prior art. When the output power undergoes a step change, it can be seen that the output voltage fluctuation range is from 195.5V to 204.3V, and there are also double resonant peaks, and the settling time is 170ms.

[0051] As Figure 10 shown, it is the voltage and current waveform diagram corresponding to the virtual-resistance-based active damping control provided by the present invention under the same experimental conditions. It can be seen that the output voltage fluctuation range is from 198.1V to 200.3V. It should be particularly noted that while suppressing the double resonant peaks, the settling time is only 1.12ms. Therefore, the control scheme provided by the present invention has better dynamic characteristics compared with the traditional voltage single-loop control scheme.

[0052] The present invention also provides a device for improving the dynamic characteristics of a two-stage resonant converter based on a virtual resistance, including: a signal acquisition unit and a signal processing unit, wherein: the two-stage resonant converter includes a front-stage Buck converter and a rear-stage LLC resonant converter. Among them, the positive and negative terminals of the output side of the front-stage Buck converter are respectively connected to both ends of the common DC bus, the positive and negative terminals of the input side of the rear-stage LLC resonant converter are respectively connected to both ends of the common DC bus, and the output side of the rear-stage LLC resonant converter is connected to the load; a bus capacitor is arranged on the common DC bus; the signal acquisition unit is used to take the bus capacitor voltage of the bus capacitor as an input signal and input it to the active damping inner-loop controller, and the active damping inner-loop controller outputs and simulates a virtual resistance connected to the converter; the difference between the output voltage loaded on the load at the output side of the converter and the reference voltage is used as an input signal and input to the voltage outer-loop proportional-integral controller; the signal processing unit is used to subtract the output signal of the active damping inner-loop controller and the output signal of the voltage outer-loop proportional-integral controller, calculate the improved duty ratio of the front-stage Buck converter, and control the closing and turning off of the switching device of the front-stage Buck converter according to the control signal obtained from the improved duty ratio.

[0053] For the device for improving the dynamic characteristics of a two-stage resonant converter based on a virtual resistance provided by the present invention, for the unit that executes the method, steps or functions, the method, steps or functions it executes can refer to the method for improving the dynamic characteristics of a two-stage resonant converter based on a virtual resistance provided by the present invention.

Claims

1. A method for improving the dynamic characteristics of a two-stage resonant converter based on a virtual resistor, characterized in that, including: The two-stage resonant converter includes a front-stage Buck converter and a rear-stage LLC resonant converter. Among them, the positive and negative terminals of the output side of the front-stage Buck converter are respectively connected to both ends of the common DC bus, and the positive and negative terminals of the input side of the rear-stage LLC resonant converter are respectively connected to both ends of the common DC bus; the output side of the two-stage resonant converter is connected to the load; a bus capacitor is provided on the common DC bus; The dynamic characteristic improvement method includes: Taking the bus capacitor voltage of the bus capacitor as an input signal and inputting it into the active damping inner-loop controller, and the active damping inner-loop controller outputs an analog virtual resistor connected to the converter; taking the difference between the output voltage loaded on the load at the output side of the converter and the reference voltage as an input signal and inputting it into the voltage outer-loop proportional-integral controller; Subtracting the output signal of the active damping inner-loop controller from the output signal of the voltage outer-loop proportional-integral controller, calculating the improved duty ratio of the front-stage Buck converter, and controlling the closing and turning off of the switching device of the front-stage Buck converter according to the control signal obtained from the improved duty ratio.

2. The method for improving the dynamic characteristics of a two-stage resonant converter based on a virtual resistor according to claim 1, wherein Controlling the switching frequency of the switching device of the rear-stage LLC resonant converter to be fixed and equal to the resonant frequency of the rear-stage LLC resonant converter.

3. The method for improving the dynamic characteristics of a two-stage resonant converter based on a virtual resistor according to claim 1, wherein The active damping inner-loop controller simulates a virtual resistor connected in parallel with the bus capacitor.

4. The method for improving the dynamic characteristics of a two-stage resonant converter based on a virtual resistor according to claim 3, characterized in that The characteristic polynomial of the active damping inner-loop corresponding to the virtual resistor connected in parallel with the bus capacitor is as follows: det(sI 4×4 -A m ) = 0, where det represents the matrix determinant, s represents the complex frequency variable, I 4×4 represents the 4×4 identity matrix, and A m represents the state matrix of the two-stage resonant converter.

5. The method for improving the dynamic characteristics of a two-stage resonant converter based on a virtual resistor according to claim 4, characterized in that Converting the characteristic polynomial of the active damping inner-loop into a root locus formula of the active damping inner-loop with respect to the virtual resistor; Based on the root locus formula of the active damping inner-loop with respect to the virtual resistor and combining the poles of the root locus function of the active damping inner-loop, obtaining the corresponding virtual resistor value.

6. The method for improving the dynamic characteristics of a two-stage resonant converter based on a virtual resistor according to claim 5, characterized in that, The obtaining of the virtual resistor value includes: Among the poles of the root locus function of the active damping inner-loop, taking the virtual resistor value corresponding to the maximum damping of the two-stage resonant converter as the applied virtual resistor value.

7. The method for improving the dynamic characteristics of a two-stage resonant converter based on a virtual resistor according to claim 5, characterized in that, The root locus formula of the active damping inner-loop with respect to the virtual resistor is as follows: 1+R v T Rv (s)=0, Among them, R v represents a virtual resistor, and T Rv (s) represents the active damping inner-loop root locus function. ， Among them, C dc1 represents the bus capacitor, and C dc2 represents the output capacitor connected in parallel on the output side of the two-stage resonant converter. L e represents the equivalent inductance of the front-stage Buck converter, and L eq represents the equivalent inductance of the rear-stage LLC resonant converter. R L represents the load, and N represents the transformer turns ratio of the rear-stage LLC resonant converter.

8. The method for improving the dynamic characteristics of a two-stage resonant converter based on a virtual resistor according to claim 7, characterized in that, The closed-loop transfer function G pm (s) of the active damping inner loop is as follows: G pm (s)=C(sI 4×4 -A m )B u , Among them, C = [0, 0, 0, 1], B u = [M(D)e(s) / L b , 0, 0, 0] T , M(D) represents the voltage gain of the pre-stage Buck converter, e(s) represents the controlled voltage source coefficient of the pre-stage Buck converter, and L b represents the filter inductor of the pre-stage Buck converter.

9. The method for improving the dynamic characteristics of a two-stage resonant converter based on a virtual resistor according to claim 8, characterized in that The voltage outer-loop loop gain function under the control of the active damping inner-loop is as follows: T pm (s)= G PI (s)G pm (s), Among them, T pm (s) represents the voltage outer loop gain, G PI (s) represents the voltage outer loop proportional integral controller function, G PI (s)=k p +k i / s, k p represents the proportional gain, k i represents the integral gain; When the voltage outer-loop loop gain satisfies that the gain margin is greater than 4 dB and the phase margin is greater than 45°, taking the corresponding proportional gain and integral gain of the voltage outer-loop as the applied proportional gain and integral gain.

10. A device for improving the dynamic characteristics of a two-stage resonant converter based on a virtual resistor, characterized in that including: A signal acquisition unit and a signal processing unit, where: The two-stage resonant converter includes a front-stage Buck converter and a rear-stage LLC resonant converter. Among them, the positive and negative terminals of the output side of the front-stage Buck converter are respectively connected to both ends of the common DC bus, and the positive and negative terminals of the input side of the rear-stage LLC resonant converter are respectively connected to both ends of the common DC bus, and the output side of the rear-stage LLC resonant converter is connected to the load; a bus capacitor is provided on the common DC bus; The signal acquisition unit is used to take the bus capacitor voltage of the bus capacitor as an input signal and input it into the active damping inner-loop controller, and the active damping inner-loop controller outputs an analog virtual resistor connected to the converter; taking the difference between the output voltage loaded on the load at the output side of the converter and the reference voltage as an input signal and inputting it into the voltage outer-loop proportional-integral controller; The signal processing unit is configured to subtract the output signal of the active damping inner loop controller from the output signal of the voltage outer loop proportional integral controller, calculate the improved duty ratio of the pre-stage Buck converter, and control the closing and turning off of the switching device of the pre-stage Buck converter according to the control signal obtained from the improved duty ratio.

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