Method and device for improving stability of output voltage of full-bridge frequency-conversion phase-shift LLC (Logical Link Control)

Abstract

The invention discloses a method for improving the stability of the output voltage of a full-bridge variable-frequency phase-shift LLC, and the method comprises the steps: carrying out the improvement of a transfer function of a PID controller of the full-bridge variable-frequency phase-shift LLC through employing a fuzzy PID controller in a variable-frequency mode, carrying out the improvement of a sliding-mode PID controller in a phase-shift mode, adding the supplement amount of a compensation loop, and carrying out the equalization processing, thereby achieving the improvement of the stability of the output voltage of the full-bridge variable-frequency phase-shift LLC. And combining the improved PID transfer function with a three-type compensation loop transfer function and a full-bridge frequency conversion phase shift LLC transfer function to obtain an improved output voltage of the system. A transfer function of the system is demonstrated through KEIL5 programming software and a SIMULINK simulation platform, and it is found that the dynamic performance and stability of the system are greatly improved, and expected requirements are met.

Description

Technical Field

[0001] The invention relates to the field of switching power supplies, and in particular to a method and a device for improving the output voltage stability of a full-bridge frequency conversion phase shift LLC. Background Art

[0002] The full-bridge LLC variable frequency phase-shift resonant converter is a highly efficient power conversion technology that maintains high efficiency and stability under different load conditions by adjusting the operating frequency and phase shift angle. The design of this converter allows soft switching within a wide input voltage range, reducing switching losses and electromagnetic interference. At the same time, the phase shift control is achieved by adjusting the phase of the control signal, which has high flexibility and stability. The variable frequency control allows the converter to automatically adjust the operating frequency according to the load demand, further optimizing the efficiency. However, the full-bridge LLC variable frequency phase-shift resonant converter still has many shortcomings, such as slow dynamic response, poor stability, reduced efficiency, overshoot and undershoot, difficulty in achieving precise control, sensitivity to parameter changes, and lack of flexibility. In addition, when the system processor processes data for the full-bridge LLC variable frequency phase-shift resonant converter, the data processing is too cumbersome because the transfer function is phased in frequency conversion and phase shift. Summary of the invention

[0003] Purpose of the invention: The present invention improves the overall performance and reliability of the system by improving the PID control function in different modes and combining a type III compensation network (TYPEIII) to form a new full-bridge LLC variable frequency phase-shift resonant converter output voltage transfer function, so that the converter can have extremely high dynamic stability regardless of whether it is in variable frequency mode or phase-shift mode.

[0004] Technical solution: A method for improving the output voltage stability of a full-bridge variable frequency phase-shift LLC. The transfer function of the PID controller of the full-bridge variable frequency phase-shift LLC is improved by a fuzzy PID controller in the variable frequency mode and by a sliding mode PID controller in the phase-shift mode. The improved PID transfer function is then averaged after adding the supplementary amount of the compensation loop to obtain an improved PID transfer function. The improved PID transfer function is then combined with the three-type compensation loop transfer function and the full-bridge variable frequency phase-shift LLC transfer function to obtain the improved output voltage of the system.

[0005] Furthermore, the improvement of using the fuzzy PID controller in the variable frequency mode is specifically as follows:

[0006] A fuzzy PID controller is used, and the proportional gain, integral gain, and differential gain of the fuzzy PID controller are adjusted using a neural network, and the control signal is calculated using the adjusted proportional gain, integral gain, and differential gain;

[0007] The transfer function G2(S) of the fuzzy PID controller in variable frequency mode is:

[0008]

[0009] Where w is the output of the control signal, K P3、 K i3、 K d3 are the proportional gain, integral gain, and differential gain of the fuzzy PID controller, respectively, and S is the complex variable of the Laplace transform;

[0010] Furthermore, the improvement of using the sliding mode PID controller in the phase shift mode is specifically as follows:

[0011] Using the sliding mode PID controller, the transfer function of the sliding mode PID controller is expressed as:

[0012] G4(S)=K p4 +K i4 +K d4 +K s sign(e)

[0013] K s is the sliding mode control gain, sign(e) is the sign function of the error, K P4、 K i4、 K d4 They are the proportional gain, integral gain and differential gain of the sliding mode PID controller respectively.

[0014] Furthermore, the averaging process after adding the compensation loop supplement is specifically as follows: the PID transfer functions of the variable frequency mode and the phase shift mode in different time periods are averaged and improved and the compensation amount K is added. h sign(e) v ;

[0015] The improved PID transfer function is Z(s)

[0016]

[0017] t1 and t2 are the start and end times of acquisition in frequency conversion mode, t3 and t4 are the start and end times of acquisition in phase shift mode, K h is the gain constant, v is the power of sign(e);

[0018] K in the above formula h In the frequency conversion mode, the value is 1, and the voltage in the frequency conversion mode is incrementally compensated. In the phase shift mode, the value is -1, and the voltage in the phase shift mode is attenuated.

[0019] Furthermore, the improved PID transfer function is combined with the three-type compensation loop transfer function to obtain the system transfer function H(S):

[0020]

[0021] Among them, G(S) is the transfer function of the three-type compensation network when using an ideal operational amplifier, R1, R2, R3 are resistors, and C1, C2, C3 are capacitors.

[0022] Furthermore, the transfer function U(s) of the system obtained by combining the improved PID transfer function with the three-type compensation loop transfer function and the full-bridge variable frequency phase-shift LLC transfer function is:

[0023]

[0024] G LLC (S) is the full-bridge variable frequency phase-shift LLC transfer function. At this time, the output voltage transfer function Y(S) of the improved full-bridge variable frequency phase-shift LLC system is:

[0025]

[0026] In the above formula, V out is the output voltage of the full-bridge LLC resonant converter after phase shift and frequency conversion, V in is the input voltage of the system, ω r is the resonant frequency, ω Z is the zero frequency, and K is the gain constant.

[0027] A device for improving the stability of full-bridge variable frequency phase-shift LLC output voltage, comprising a PID controller module and a three-type compensation loop module;

[0028] A fuzzy PID controller is used to improve the transfer function in the variable frequency mode, and a sliding mode PID controller is used to improve the transfer function in the phase shift mode. The improved PID transfer function is obtained by adding the supplementary amount of the compensation loop and performing averaging processing. The improved PID transfer function is then combined with the transfer function of the three-type compensation loop module and the full-bridge variable frequency phase-shift LLC transfer function to obtain the improved output voltage of the system.

[0029] Beneficial effects: The present invention demonstrates the transfer function of the system through KEIL5 programming software and SIMULINK simulation platform, and finds that the dynamic performance and stability of the system have been greatly improved, meeting the expected requirements. The present invention has stronger dynamic stability and faster response speed, and the system improves the PID controller in different modes, and through the addition amount, the improved system can use a unified transfer function to represent the output voltage in both modes. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the square wave signal diagram of the 3KW full-bridge phase-shifted frequency-converting LLC resonant converter;

[0031] Figure 2 Output voltage variation diagram of 3KW full-bridge phase-shifted variable frequency LLC resonant converter using traditional PID control algorithm;

[0032] Figure 3 This is the PID system adjustment block diagram under voltage frequency conversion mode;

[0033] Figure 4 It is a PID controller in variable frequency mode of full-bridge variable frequency LLC resonant converter;

[0034] Figure 5 is the output voltage error after adjustment by the PID controller in variable frequency mode;

[0035] Figure 6 This is the PID system adjustment block diagram in voltage phase shift mode;

[0036] Figure 7 It is a PID controller in phase-shift mode of full-bridge variable frequency LLC resonant converter;

[0037] Figure 8 is the output voltage error after adjustment by the PID controller in the phase shift mode;

[0038] Fig. 9 It is the fuzzy PID simulation model in variable frequency mode;

[0039] Fig.10 It is a visualization diagram of fuzzy rules;

[0040] Fig.11 It is the output voltage error signal of fuzzy PID in variable frequency mode;

[0041] Fig.12 It is the sliding mode PID control framework in phase shift mode;

[0042] Fig.13 It is the output voltage error signal of the sliding mode PID in the phase shift mode;

[0043] Fig.14 To improve the error signal of the output voltage after PID;

[0044] Fig.15 It is the structure diagram of the three-type compensation network;

[0045] Fig.16 It is the bode diagram of the phase margin of LLC resonant converter;

[0046] Fig.17 It is the simulation diagram of the three-type compensation network;

[0047] Fig.18 This is the output voltage waveform diagram under the improved variable frequency mode;

[0048] Fig.19 To improve the output voltage waveform in the rear phase shift mode;

[0049] Fig. 20 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0050] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0051] The present invention provides a technical solution:

[0052] A control system for improving the output voltage stability of a full-bridge LLC variable frequency phase-shift resonant converter. The system uses a PID controller to reduce the error between the actual output voltage of the full-bridge LLC variable frequency phase-shift resonant converter and the reference voltage, and cooperates with a three-type compensation network to perform loop compensation on the output voltage of the full-bridge LLC adjusted by the PID controller, so as to reduce the error between the output voltage and the reference voltage again in a shorter time, thereby improving the stability of the system.

[0053] The working principle of the full-bridge LLC variable frequency phase-shift resonant converter is: using a power switch and a resonant cavity to convert the DC voltage into a high-frequency square wave, and then outputting a stable DC power through a transformer and a diode rectifier. It is a high-efficiency converter. It combines frequency conversion control and phase shift control to optimize efficiency and dynamic response, and uses soft switching characteristics to reduce switching losses and improve efficiency. It also realizes effective energy transmission in different working modes and is suitable for high-performance power supply design.

[0054] The specific parameters of the known 3KW full-bridge LLC variable frequency phase-shift resonant converter are as follows:

[0055] System power: P = 3KW;

[0056] Input voltage: Vin = 250V ~ 500V;

[0057] Output voltage: Vo = 360V;

[0058] Output full load current: Iomax = 8.3A;

[0059] Maximum switching frequency: fsmax=120KHZ

[0060] Resonant inductance: Lr1 = 14.6 μH

[0061] Resonant capacitor: Cr1 = 110nF

[0062] Excitation inductance: Lm1 = 64.4 μH

[0063] Switching frequency: fr1 = 50 kHz

[0064] Resonant frequency: fr2 = 120 kHz

[0065] Secondary resistor 1: Rf1 = 43.37Ω

[0066] Secondary resistor 2: Rf2 = 50Ω

[0067] When the input voltage is less than 360V, the full-bridge LLC resonant converter automatically switches to variable frequency control. When the input voltage is greater than 360V, the full-bridge LLC resonant converter automatically switches to phase-shift control.

[0068] The system transfer function of the full-bridge phase-shifted frequency-converting LLC resonant converter is obtained by small signal analysis method:

[0069]

[0070] In the above formula, V out is the output voltage of the full-bridge LLC resonant converter after phase shift and frequency conversion, V in is the input voltage of the system, ω r is the resonant frequency, ω Z is the zero frequency, and K is the gain constant.

[0071] in:

[0072]

[0073] Combining the known parameters, we can get:

[0074] ω r =120kHZ

[0075]

[0076] To simplify the calculation, When the input voltage during frequency conversion is set to the minimum voltage of 250V, the optimal gain K1 is:

[0077]

[0078] Substituting the above results into equation (1), we can get the transfer function of the minimum output voltage V out (S) is:

[0079]

[0080] When the input voltage during phase shifting is set to the maximum voltage of 500V, the gain K2 = 0.72, and the transfer function of the maximum output voltage G LLC2 (S) is equal to the minimum output voltage transfer function.

[0081] The square wave signal diagram of the 3KW full-bridge phase-shifted frequency-converting LLC resonant converter is as follows: Figure 1shown.

[0082] The output voltage simulink simulation diagram of the 3KW full-bridge phase-shifted variable-frequency LLC resonant converter using the traditional PID control algorithm is shown in the figure below. Figure 2 shown.

[0083] It can be observed from the figure that although the full-bridge phase-shifted frequency-converting LLC resonant converter has converted the DC voltage into a high-frequency square wave, there is an error between the actual output voltage and the reference voltage 360V and the response speed is slow. Therefore, this design is committed to designing a system that improves the PID control algorithm and combines it with a three-type compensator to obtain a new output voltage transfer function. It can solve the problems of large errors between the output voltage and the reference voltage of the full-bridge phase-shifted frequency-converting LLC resonant converter for a long time and slow response speed due to switching losses, external temperature and other factors, thereby improving the stability of the system. The system can also be used to improve the stability of other switching power supply systems and has great application prospects.

[0084] Traditional PID control algorithm:

[0085] The output signal u(t) of the PID controller is:

[0086]

[0087] The transfer function G of the PID controller pid (S) is:

[0088]

[0089] in

[0090]

[0091] K d =K P T D

[0092] e(t) is the error between the output voltage signal and the reference voltage signal, K p is the proportional gain, K i is the integral gain, K d is the differential gain.

[0093] Combined with the known parameters, the full-bridge LLC resonant converter is designed through simulink simulation. The system block diagram and PID controller of the full-bridge LLC resonant converter in the voltage frequency conversion mode are shown as follows: Figure 3 , Figure 4 shown.

[0094] From the figure we can see that:

[0095] K p1=0.001,K i1 =0.8,K d1 =0

[0096] The transfer function G of the PID controller in variable frequency mode is p1 (s):

[0097]

[0098] At this time, the output voltage error signal u(t) adjusted by the PID controller is:

[0099]

[0100] In an ideal state, the output voltage is equal to the reference voltage, so the error voltage e(t) = V out -360V.

[0101] Substituting the error voltage into equation (2) yields the output voltage error signal u(t), whose waveform is shown in Figure 5 shown.

[0102] from Figure 5 It can be seen that the error voltage σ(t) of the full-bridge variable frequency LLC resonant converter is controlled within 1.1V after adjustment by the PID controller.

[0103] The system block diagram in voltage phase shift mode is as follows: Figure 6 As shown; the PID controller in voltage phase shift mode, such as Figure 7 shown.

[0104] From the figure we can see that:

[0105] K p2 =0.001,K i2 =3.5,K d2 =0

[0106] The transfer function G of the PID controller in variable frequency mode is p1 (s):

[0107]

[0108] At this time, the output voltage error after the PID controller is adjusted is:

[0109]

[0110] Similarly, substituting the error voltage e(t) into equation (3), the waveform of the output voltage error signal u(t) is as follows: Figure 8 shown.

[0111] from Figure 8It can be observed that the error σ(t) between the output voltage and the reference voltage is controlled within 0.7V.

[0112] From the above results, although the PID control algorithm does control the system error within a smaller range, the system is still in a state of slow response and unstable output voltage. Therefore, it is necessary not only to improve the PID transfer function of the full-bridge phase-shifted frequency conversion LLC, but also to add a compensation loop so that the error between the output voltage and the reference voltage of the improved transfer function continues to decrease regardless of the frequency conversion or phase shift stage, so that the system is in a stable state.

[0113] First, we consider improving the PID transfer function in variable frequency mode. The PID in variable frequency mode adopts the BP neural network structure. The improved BP neural network PID simulation model in variable frequency mode is as follows: Fig. 9 shown.

[0114] The transfer function G2(S) of the fuzzy PID controller is:

[0115]

[0116] Where w is the output of the fuzzy rule, K P3、 K i3、 K d3 They are the proportional gain, integral gain and differential gain of the fuzzy PID controller respectively.

[0117] Visualization of fuzzy rules Fig.10 As shown, the color depth represents the correlation of gain, which can be based on Fig.10 Adjust the parameters.

[0118] At this time, the output voltage error signal in the frequency conversion mode is as follows Fig.11 As shown. Fig.11 It can be seen that the error voltage is stable at around 0.22V.

[0119] Secondly, the PID transfer function in the phase-shifting mode is improved. The sliding mode PID controller is used in the phase-shifting mode. The sliding mode PID controller combines sliding mode control and PID control to improve the robustness and rapidity of the system. The transfer function of the sliding mode PID controller can be expressed as:

[0120] G4(S)=K p4 +K i4 +K d4 +K s sign(e)

[0121] Ks is the sliding mode control gain, sign(e) is the sign function of the error, K P4、 K i4、 Kd4 They are the proportional gain, integral gain and differential gain of the sliding mode PID controller respectively.

[0122] where sign(e) is equal to the sum of the derivative of the error and the error times the gain, i.e.:

[0123] sign(e)=e(t),+e(t)(K p4 +K i4 +K d4 +K s )

[0124] The simulation framework of sliding mode PID in phase shift mode is as follows Fig.12 shown.

[0125] At this time, the output voltage error signal in the phase shift mode is as follows Fig.13 shown.

[0126] Considering that frequency conversion and phase shifting is a complete system, it is necessary to improve the PID control functions of frequency conversion and phase shifting in different time periods and add compensation K h sign(e) v , so that the system can be made more stable through a unified transfer function regardless of whether it is in frequency conversion or phase shift mode, and the workload inside the MCU when the system is working can be greatly reduced. Now assume that the improved PID transfer function is Z(s).

[0127]

[0128] t1 and t2 are the sampling times in the frequency conversion state, t3 and t4 are the sampling times in the phase shift state, K h is the gain constant, and v is the power of sign(e).

[0129] K in the above formula h When the frequency is changed, it takes 1 to perform incremental compensation on the voltage in the frequency conversion mode. When the phase is shifted, it takes -1 to perform attenuation compensation on the voltage in the phase shift mode.

[0130] At this time, the error signal of the system is Fig.14 shown.

[0131] The meaning of the improved phase-shifted frequency conversion PID transfer function is: the system performs code programming through the internal chip, and takes two signal segments that are in the frequency conversion and phase shift phase in a very short time respectively, first adds the integrated signals and then performs average differentiation processing, that is, takes the average of the two. In this way, the improved transfer function can represent the changes of the full-bridge frequency conversion phase-shift LLC in the entire stage.

[0132] The structure diagram of the three-type compensation network is as follows Fig.15As shown, R1, R2, R3 are resistors, C1, C2, C3 are capacitors, V O is the voltage after being adjusted by the PID controller, V comp To obtain the final output voltage after improvement, V Ref is the reference voltage, R BIAS is the total load resistance of the secondary side. O is the input voltage when the system uses the three-type loop compensator. Its magnitude is equal to the sum of the output voltage and the output voltage error obtained after the system uses the PID controller, that is: V O =V LLC1 +u(t).

[0133] The transfer function G(S) of the three-type compensation network when using an ideal op amp is:

[0134]

[0135] The calculation formulas for each capacitor and resistor in the above formula are:

[0136]

[0137]

[0138] Therefore, the new transfer function H(S) of the system after combining the improved PID control algorithm and the three-type compensator is:

[0139]

[0140] Combined with the known parameters, the H(s) applied to the 3KW full-bridge variable frequency phase-shifted LLC resonant converter is verified through simulink simulation and KEIL5 software programming to test whether the new transfer function can improve the system stability.

[0141] First, determine the transfer function of the three-type compensation network. Based on the known parameters of the 3KW full-bridge phase-shifted frequency conversion LLC and the phase margin bode diagram of the LLC resonant converter after PID adjustment, see Fig.16 , and the parameter setting method of the three-type compensator used in the full-bridge phase-shifted variable-frequency LLC resonant converter: zero frequency f p1 , f p2 Placed between 1 / 10 and 1 / 5 of the switching frequency, the pole frequency f z1 , f z2 The right half plane pole f p0 Place it in the high frequency band, away from the crossover frequency, to obtain the specific zero-pole frequency. Fig.17 This is the simulation diagram of the three-type compensation network.

[0142] The two zero frequencies of this system are:

[0143] f p1 =5kHZ

[0144] f p2 =7kHZ

[0145] The two pole frequencies are:

[0146] f z1 =3kHZ

[0147] f z2 =4kHZ

[0148] The right half plane poles are:

[0149] f p0 =30kHZ

[0150] When the zero-pole frequency is the above data, the gain of the type III compensation loop is maximum.

[0151] The gain constant K3 of the type III compensator is calculated by the K factor method = 2.33

[0152] The transfer function U(s) of the full-bridge variable frequency phase-shifted LLC system combining the improved PID control algorithm and the three-type compensator is:

[0153]

[0154] At this time, the output voltage transfer function Y(S) of the improved full-bridge frequency conversion phase shifting system is:

[0155]

[0156] Substituting the output voltage transfer function H(s) with known parameters, we can get the output voltage waveform under phase shift and frequency conversion state. The output voltage waveform under the improved frequency conversion mode is shown in the figure below: Fig.18 shown.

[0157] Depend on Fig.18 It can be seen that the improved system can reduce the output error in a very short time and make the output voltage infinitely close to the reference voltage, which greatly improves the dynamic stability of the original system in the variable frequency mode.

[0158] The output voltage waveform in the improved phase-shift mode is as follows Fig.19 shown.

[0159] comprehensive Fig.18 , Fig.19 and Figure 2By comparison, it was found that after the system used the improved PID control algorithm and combined with the three-type compensation loop to improve the full-bridge variable frequency phase-shifted LLC resonant converter, the dynamic stability of the system was greatly enhanced. Therefore, the improved output voltage transfer function can be applied to the full-bridge LLC, and the design scheme is feasible.

Claims

1. A method for improving the output voltage stability of a full-bridge frequency conversion phase-shift LLC, characterized in that: The transfer function of the PID controller of the full-bridge variable frequency phase-shift LLC is improved by a fuzzy PID controller in the variable frequency mode and by a sliding mode PID controller in the phase-shift mode. The improved PID transfer function is then averaged after adding the supplementary amount of the compensation loop to obtain the improved PID transfer function. The improved PID transfer function is then combined with the three-type compensation loop transfer function and the full-bridge variable frequency phase-shift LLC transfer function to obtain the improved output voltage of the system.

2. A method for improving the output voltage stability of a full-bridge frequency conversion phase-shift LLC according to claim 1, characterized in that: The improvement of using fuzzy PID controller in variable frequency mode is specifically as follows: A fuzzy PID controller is used, and the proportional gain, integral gain, and differential gain of the fuzzy PID controller are adjusted using a neural network, and the control signal is calculated using the adjusted proportional gain, integral gain, and differential gain; The transfer function G2(S) of the fuzzy PID controller in variable frequency mode is: Where w is the output of the control signal, K P3、 K i3、 K d3 They are the proportional gain, integral gain and differential gain of the fuzzy PID controller respectively, and S is the complex variable of Laplace transform.

3. A method for improving the output voltage stability of a full-bridge frequency conversion phase-shift LLC according to claim 1, characterized in that: The improvement of using sliding mode PID controller in phase shift mode is specifically as follows: Using the sliding mode PID controller, the transfer function of the sliding mode PID controller is expressed as: G4(S)=K p4 +K i4 +K d4 +K s sign(s) K s is the sliding mode control gain, sign(e) is the sign function of the error, K P4、 K i4、 K d4 They are the proportional gain, integral gain and differential gain of the sliding mode PID controller respectively.

4. The method for improving the output voltage stability of a full-bridge frequency conversion phase shift LLC according to claim 1, characterized in that: The averaging process after adding the compensation loop supplement is specifically as follows: the PID transfer functions of the variable frequency mode and the phase shift mode in different time periods are averaged and improved and the compensation amount K is added. h sign(e) v ; The improved PID transfer function is Z(s) t1 and t2 are the start and end times of acquisition in frequency conversion mode, t3 and t4 are the start and end times of acquisition in phase shift mode, K h is the gain constant, v is the power of sign(e); K in the above formula h In the frequency conversion mode, the value is 1, and the voltage in the frequency conversion mode is incrementally compensated. In the phase shift mode, the value is -1, and the voltage in the phase shift mode is attenuated.

5. A method for improving the output voltage stability of a full-bridge frequency conversion phase-shift LLC according to claim 4, characterized in that: The improved PID transfer function is combined with the three-type compensation loop transfer function to obtain the system transfer function H(S): Among them, G(S) is the transfer function of the three-type compensation network when using an ideal operational amplifier, R1, R2, R3 are resistors, and C1, C2, C3 are capacitors.

6. A method for improving the output voltage stability of a full-bridge frequency conversion phase-shift LLC according to claim 5, characterized in that: The transfer function U(s) of the system obtained by combining the improved PID transfer function with the three-type compensation loop transfer function and the full-bridge variable frequency phase-shift LLC transfer function is: G LLC (S) is the full-bridge variable frequency phase-shift LLC transfer function. At this time, the output voltage transfer function Y(S) of the improved full-bridge variable frequency phase-shift LLC system is: In the above formula, V out is the output voltage of the full-bridge LLC resonant converter after phase shift and frequency conversion, V in is the input voltage of the system, ω r is the resonant frequency, ω Z is the zero frequency, and K is the gain constant.

7. A device for improving the output voltage stability of a full-bridge frequency conversion phase-shift LLC, characterized in that: Including PID controller module and three-type compensation loop module; A fuzzy PID controller is used to improve the transfer function in the variable frequency mode, and a sliding mode PID controller is used to improve the transfer function in the phase shift mode. The improved PID transfer function is obtained by adding the supplementary amount of the compensation loop and performing averaging processing. The improved PID transfer function is then combined with the transfer function of the three-type compensation loop module and the full-bridge variable frequency phase-shift LLC transfer function to obtain the improved output voltage of the system.

8. The device for improving the output voltage stability of a full-bridge frequency conversion phase-shift LLC according to claim 7, characterized in that: The averaging process after adding the compensation loop supplement is specifically as follows: the PID transfer functions of the variable frequency mode and the phase shift mode in different time periods are averaged and improved and the compensation amount K is added. h sign(e) v ; The improved PID transfer function is Z(s) t1 and t2 are the start and end times of acquisition in frequency conversion mode, t3 and t4 are the start and end times of acquisition in phase shift mode, K h is the gain constant, v is the power of sign(e); w is the output of the control signal, K P3、 K i3、 K d3 are the proportional gain, integral gain and differential gain of the fuzzy PID controller respectively, S is the complex variable of Laplace transform; K s is the sliding mode control gain, sign(e) is the sign function of the error, K P4、 K i4、 K d4 They are proportional gain, integral gain and differential gain of the sliding mode PID controller respectively; K in the above formula h In the frequency conversion mode, the value is 1, and the voltage in the frequency conversion mode is incrementally compensated. In the phase shift mode, the value is -1, and the voltage in the phase shift mode is attenuated.

9. The device for improving the output voltage stability of a full-bridge frequency conversion phase-shift LLC according to claim 8, characterized in that: The improved PID transfer function is combined with the three-type compensation loop transfer function to obtain the system transfer function H(S): Among them, G(S) is the transfer function of the three-type compensation network when using an ideal operational amplifier, R1, R2, R3 are resistors, and C1, C2, C3 are capacitors.

10. The device for improving the output voltage stability of a full-bridge frequency conversion phase-shift LLC according to claim 9, characterized in that: The transfer function U(s) of the system obtained by combining the improved PID transfer function with the three-type compensation loop transfer function and the full-bridge variable frequency phase-shift LLC transfer function is: G LLC (S) is the full-bridge variable frequency phase-shift LLC transfer function. At this time, the output voltage transfer function Y(S) of the improved full-bridge variable frequency phase-shift LLC system is: In the above formula, V out is the output voltage of the full-bridge LLC resonant converter after phase shift and frequency conversion, V in is the input voltage of the system, ω r is the resonant frequency, ω Z is the zero frequency, and K is the gain constant.

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