Table lookup-free closed-loop control method for four-switch Buck-Boost converter with optimal variable load circuit

Abstract

The invention discloses a table lookup-free closed-loop control method for a four-switch Buck-Boost converter with an optimal variable load line, and belongs to the technical field of power generation, power transformation or power distribution. The method comprises an optimal variable load circuit control strategy, a driving signal triggering strategy and a quadrilateral inductor current modulation strategy. According to the optimal variable load line control strategy, quadrilateral inductive current time parameters meeting soft switching conditions are accurately calculated within a given switching frequency range, and the driving signal triggering strategy compensates the quadrilateral inductive current time parameters of all switching periods so that the minimum value of the quadrilateral inductive current can be kept at a given value. The quadrilateral inductor current modulation strategy realizes the generation of switching tube driving signals in each switching period, soft switching can be realized in a full-load range, and the effective value of the quadrilateral inductor current is minimum.

Description

Technical Field

[0001] The invention discloses a table-lookup-free closed-loop control method for a four-switch Buck-Boost converter with an optimal load-changing circuit, relates to power electronics technology, and belongs to the technical field of power generation, power transformation or power distribution. Background Art

[0002] In the field of photovoltaic energy storage, bidirectional non-isolated converters play a vital role. Among them, the four-switch Buck-Boost has comprehensive advantages over other non-isolated DC-DC converters. For example, the voltage and current stress of the four switch tubes of the four-switch Buck-Boost converter is low, both bidirectional buck and boost can be achieved, there are few passive inductor and capacitor components, the input and output voltage and current polarity are the same, there are many control variables and the control method can be flexible and changeable.

[0003] In the traditional four-switch Buck-Boost converter control, the multi-mode control method of three-mode or four-mode control is mostly used, and there is a problem of switching between different modes. The quadrilateral inductor current modulation method proposed in 2013 solves the mode switching problem in multi-mode control, but this method converts continuous three-dimensional data into discrete table data in closed-loop control and stores it in the memory of the MCU, thereby increasing the memory requirements of closed-loop control, resulting in an increase in control costs. At present, the method based on quadrilateral inductor current modulation is based on frequency conversion. Frequent frequency conversion increases the difficulty of system control and increases the difficulty of designing the front-stage EMC circuit. In addition, the existing quadrilateral inductor current modulation method cannot achieve the minimum effective value of the quadrilateral inductor current in the full load range.

[0004] The present application aims to propose a table-lookup-free closed-loop control method for a four-switch Buck-Boost converter with an optimal load-changing circuit to overcome the above-mentioned defects. Summary of the invention

[0005] The purpose of the present invention is to address the deficiencies of the above-mentioned background technology and propose a table-lookup-free closed-loop control method for a four-switch Buck-Boost converter with an optimal variable load circuit. The switch tube drive control signal is compensated by an optimal variable load circuit control strategy that achieves the minimum effective value of the quadrilateral inductor current in the full load range under the optimal soft switching condition, thereby achieving the purpose of the invention of the table-lookup-free closed-loop control of the four-switch Buck-Boost converter and solving the technical problems that the existing table-lookup control method has high requirements for MCU memory and the frequency conversion control strategy is complex and cannot achieve the minimum effective value of the quadrilateral inductor current in the full load range.

[0006] The present invention adopts the following technical solutions to solve the technical problems:

[0007] A table-free closed-loop control method for a four-switch Buck-Boost converter with an optimal load-changing circuit includes:

[0008] The optimal variable load line control strategy is to set the maximum and minimum switching frequency within the frequency range, take the minimum effective value of the quadrilateral inductor current as the control target, and calculate the quadrilateral inductor current time parameter within the frequency range according to the quadrilateral inductor current peak value, on the premise that the quadrilateral inductor current time parameter is clamped to a value that satisfies the zero voltage switching condition;

[0009] A driving signal triggering strategy is used to compare the inductor current sampling value with the minimum value of the given inductor current, and to compensate the inductor discharge phase duration parameter and the inductor current holding phase duration parameter calculated by the optimal variable load line control strategy according to the comparison result; and,

[0010] The quadrilateral inductor current modulation strategy generates drive signals for four switch tubes based on the inductor charging phase duration parameters, energy transmission phase duration parameters, inductor discharge phase duration parameters compensated by the drive signal trigger strategy, and inductor current holding phase duration parameters calculated according to the optimal variable load line control strategy.

[0011] As a further optimization scheme for the table-less closed-loop control method of a four-switch Buck-Boost converter with an optimal variable load circuit, when the four-switch Buck-Boost converter operates in Buck mode, the optimal variable load circuit control strategy takes the minimum effective value of the quadrilateral inductor current as the control target within the frequency range determined by setting the maximum and minimum values ​​of the switching frequency, and calculates the quadrilateral inductor current time parameter within the frequency range according to the quadrilateral inductor current peak value, on the premise that the duration parameter of the inductor charging stage is clamped to a value that satisfies the zero voltage switching condition.

[0012] As a further optimization scheme for the table-lookup-free closed-loop control method of a four-switch Buck-Boost converter with an optimal variable load line, when the four-switch Buck-Boost converter operates in the Boost mode, the optimal variable load line control strategy takes the minimum effective value of the quadrilateral inductor current as the control target within the frequency range determined by setting the maximum and minimum values ​​of the switching frequency, and calculates the quadrilateral inductor current time parameter within the frequency range according to the quadrilateral inductor current peak value, on the premise that the duration parameter of the inductor discharge phase is clamped to a value that satisfies the zero voltage switching condition.

[0013] As a further optimization scheme of the table-lookup-free closed-loop control method of the four-switch Buck-Boost converter with an optimal variable load line, the inductor charging stage duration parameter is clamped to a value that satisfies the zero voltage switching condition. Specifically, the inductor charging stage duration parameter is clamped to the minimum inductor charging stage duration or the minimum inductor charging stage duration that satisfies the zero voltage switching condition.

[0014] As a further optimization scheme for the table-lookup-free closed-loop control method of a four-switch Buck-Boost converter with an optimal variable load line, the inductor discharge phase duration parameter is clamped at a value that satisfies the zero voltage switching condition. Specifically, the inductor discharge phase duration parameter is clamped at the minimum value of the inductor discharge phase duration parameter or the minimum inductor discharge phase duration that satisfies the zero voltage switching condition.

[0015] As a further optimization scheme of the closed-loop control method without table lookup for the four-switch Buck-Boost converter with optimal variable load circuit, the optimal variable load circuit control strategy calculates the quadrilateral inductor current time parameter within the frequency range according to the quadrilateral inductor current peak value, specifically: the converter successively experiences output power P within the frequency range 1 , P 2 , P 3 and P 4 The four stages of P 1 <P 2 <P 3 <P 4 ,

[0016] In the first stage, the converter operates at the set maximum switching frequency, and the duration parameter of the inductor charging stage is clamped to a value that satisfies the zero voltage switching condition. Then T 1 =(2*I ZVS )*L / V in , T 2 =(V pi -I zvs )*L / (V in -V out ), T` 3 =(V pi +I zvs )*L / V out , T` 4 =1 / f max -T 1 -T 2 -T` 3 , where T 1 is the duration parameter of the inductor charging phase, T 2 is the duration parameter of the energy transfer phase, T 3 ' is the duration parameter of the inductor discharge phase, T'4 is the duration parameter of the inductor current holding phase, I zvs is the maximum value of the given inductor current, L is the inductance value of the converter, V in is the input voltage of the converter, V pi is the peak value of the quadrilateral inductor current, V out is the output voltage of the converter, f max To set the maximum switching frequency,

[0017] In the second stage, the converter operates at the set maximum switching frequency, and the duration parameter of the inductor charging stage is clamped to a value that satisfies the zero voltage switching condition. Then, the duration parameter of the inductor charging stage, the duration parameter of the energy transfer stage, and the duration parameter of the inductor discharging stage are the same as those in the first stage, and the duration parameter of the inductor current holding stage is zero.

[0018] In the third stage, the converter operating frequency is reduced, and the duration parameter of the inductor charging stage is clamped to a value that satisfies the zero voltage switching condition. Then T 1 =(2*I ZVS )*L / V in , T 2 =(V pi -I zvs )*L / (V in -V out ), f is the operating frequency,

[0019] In the fourth stage, the converter operating frequency is reduced to the set minimum switching frequency, and the value that satisfies the zero voltage switching condition is raised. The inductor charging phase duration parameter is clamped to the minimum inductor charging phase duration that satisfies the zero voltage switching condition after the increase. Then T′ 4 =0,I a_const and I b_const They are respectively when the converter operating frequency reaches the set switching frequency minimum value T 1 The maximum value of the inductor current at the end time, T′ 3 The maximum value of the inductor current at the beginning.

[0020] As a further optimization scheme of the closed-loop control method without table lookup for the four-switch Buck-Boost converter with optimal variable load circuit, the expression of the minimum inductor charging phase duration that satisfies the zero voltage switching condition in the fourth stage is: Where ΔIa is T 1 The rise of the inductor current at the end time, ΔIb is T′ 3 The amount of inductor current rise at the beginning.

[0021] As a further optimization scheme of the table-less closed-loop control method of the four-switch Buck-Boost converter with an optimal variable load circuit, the method for obtaining the peak current of the quadrilateral inductor is: comparing the output voltage sampling value with the output voltage reference value, and performing PI adjustment on the comparison result.

[0022] As a further optimization scheme of the closed-loop control method without table lookup of the four-switch Buck-Boost converter with optimal variable load circuit, the inductor current at the start time of the duration parameter of the inductor discharge phase after the compensation of the driving signal trigger strategy is equal to the minimum value of the given inductor current.

[0023] The present invention adopts the above technical solution and has the following beneficial effects:

[0024] (1) Cost advantage: Compared with the common quadrilateral inductor current modulation, the control method proposed in the present invention does not need to query a three-dimensional table to obtain the four time parameters of the quadrilateral inductor current, and has lower memory requirements for the MCU, thereby reducing costs.

[0025] (2) Performance advantages: Compared with ordinary quadrilateral inductor current modulation, the closed-loop control method proposed in the present invention accurately calculates the quadrilateral inductor current time parameters that meet the soft switching conditions within a given switching frequency range through the optimal variable load line control strategy, and compensates the quadrilateral inductor current time parameters of each switching cycle through the drive signal trigger strategy to keep the minimum value of the quadrilateral inductor current within the specified power range at a given value. The quadrilateral inductor current modulation strategy is used to generate the switch tube drive signal for each switching cycle within the specified power range. Soft switching can be achieved within the full load range and the effective value of the quadrilateral inductor current is minimized, thereby reducing operating losses and achieving better efficiency.

[0026] (3) Easy to integrate: The control method proposed in the present invention does not require external injection signals, and the frequency conversion control within a small range is friendly to the design of the previous stage EMC circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The invention provides a block diagram of a table-lookup-free closed-loop control method for a four-switch Buck-Boost converter with an optimal load-changing circuit.

[0028] Figure 2 It is the quadrilateral inductor current waveform of the four-switch Buck-Boost converter in Buck mode.

[0029] Figure 3 It is the quadrilateral inductor current waveform of the four-switch Buck-Boost converter in Boost mode.

[0030] Figure 4 It is a flow chart of the control method proposed in this invention.

[0031] Figure 5 It is a schematic diagram of the optimal variable load line control strategy proposed by the present invention.

[0032] Figure 6 This is a quadrilateral inductor current waveform diagram under the closed-loop control method proposed in the present invention.

[0033] Figure 7 The variable load line is raised I a The quadrilateral inductor current waveform after.

[0034] Figure 8 T 3 The analog circuit portion that drives the trigger circuit.

[0035] Fig. 9 T 3 The digital circuit part that drives the trigger circuit.

[0036] Fig.10 The effective value of the quadrilateral inductor current and the duration parameter T of the inductor charging stage 1 relationship diagram.

[0037] Description of the symbols in the figure: S 1 , the first switch tube, S 2 , the second switch tube, S 3 , the third switch tube, S 4 , the fourth switch tube, L, the inductor, C O , output filter capacitor, R L ,load. DETAILED DESCRIPTION

[0038] The present invention proposes a table-lookup-free closed-loop control method for a four-switch Buck-Boost converter with an optimal load-changing circuit. To make the purpose, technical solution and effect of the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings.

[0039] In view of the problems existing in the existing table lookup control method, the present invention proposes a method such as Figure 1 The four-switch Buck-Boost converter with an optimal load-changing circuit is shown in the table-free closed-loop control method. The four-switch Buck-Boost converter includes: a first switch tube S 1 , the second switch tube S 2 , the third switch tube S 3 , the fourth switch tube S 4 , inductor L, output filter capacitor C O 、Load R L , the first switch tube S 1 and the second switch tube S 2 The first bridge arm connected in series is connected to the input voltage V in, the third switch tube S 3 and the fourth switch tube S 4 The second bridge arm is connected in series, the inductor L is connected between the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the output filter capacitor C O Connected in parallel at both ends of the second bridge arm, load R L With the output filter capacitor C O in parallel.

[0040] The control method proposed by the present invention is to control the output voltage V out With a given output voltage V ref The difference is calculated by PI operation to obtain the quadrilateral inductor current peak value V pi , quadrilateral inductor current peak value V pi In such Figure 2 Buck mode shown is I b ,exist Figure 3 In the Boost mode shown, I a , following the principle that the effective value of the quadrilateral inductor current is the smallest during load changes, according to the quadrilateral inductor current peak value V pi The various time parameters that meet the soft switching conditions can be obtained. Figure 4 The control flow chart of the method is shown in Figure 1. The method is divided into two parts: digital control and analog control, and the two parts are executed simultaneously. Finally, the driving signal generated by the quadrilateral inductor current time parameters obtained by the digital control part and the analog control part acts on the four switch tubes in the four-switch Buck-Boost circuit. The method includes: optimal variable load line control strategy, driving signal triggering strategy and quadrilateral inductor current modulation strategy. The following describes the control strategies of each part of the method.

[0041] 1. Optimal load-variable line control strategy

[0042] In most cases, the power P is within a variable range, so it is necessary to discuss how the quadrilateral inductor current can be changed to minimize its effective value within a certain power range. In Buck mode, the optimal variable load line control strategy proposed is as follows Figure 5 As shown. Figure 5 There are four stages 1 to 4, corresponding to power P 1 , P 2 , P 3 and P 4 , the power size of the four stages is ranked as P 1 <P 2 <P 3 <P 4As the load power increases, the frequency will also increase. The change of frequency is not conducive to the design and operation of the circuit, and the wider the frequency change, the more difficult it is to design the front-end EMC circuit. Therefore, we comprehensively consider limiting the frequency within a certain range [f min , f max ] where f s is the switching frequency, f max To set the maximum switching frequency, f min This variable load circuit can keep the quadrilateral inductor current at a minimum in a wide power range of the FSBB converter and limit the frequency change to ensure stability to a certain extent.

[0043] In order to ensure the stability of the output voltage, PI control is required, in which the detected output voltage is compared with the set output voltage value. The comparison value is considered to be the peak value V of the quadrilateral inductor current after PI operation. pi ,like Figure 6 As shown, where T 4 When the time is not equal to 0, the four time parameters can be calculated by the following formula, which corresponds to stage 1 in the optimal variable load line control strategy:

[0044] T 1 =(2*I ZVS )*L / V in

[0045] T 2 =(V pi -I zvs )*L / (V in -V out )

[0046] T` 3 =(V pi +I zvs )*L / V out

[0047] T` 4 =1 / f max -T 1 -T 2 -T` 3

[0048] The duration parameter T of the inductor charging phase in the optimal variable load line control strategy stage 2 1 , Energy transfer phase duration parameter T 2 , Inductor discharge phase duration parameter T′ 3 Same as stage 1, the inductor current is maintained at the stage duration parameter T′ 4 =0.

[0049] In the optimal load-variable line control strategy, the third stage T 1 Maintain the optimal soft switching conditions and meet the power demand by reducing the frequency. At this time, the three time parameters and frequency can be obtained by the following formula:

[0050] T 1 =(2*I ZVS )*L / V in

[0051] T 2 =(V pi -I zvs )*L / (V in -V out )

[0052] T` 3 =(V pi +I zvs )*L / V out

[0053]

[0054] In the optimal variable load line control strategy stage 4, the frequency has reached the minimum value, so the optimal soft switch clamping value needs to be raised, such as Figure 7 As shown, T 1 At this time, it is greater than T 1_s The lifting relationship can be obtained through plane geometric relationship. a_const and I b_const When the frequency reaches the minimum, T 1 The maximum value of the inductor current at the end time, T 3 ′The inductor current reaches its maximum value at the beginning.

[0055]

[0056] In stage 4, the three time parameters can be calculated by the following formula:

[0057]

[0058] The above formulas are obtained in Buck mode. The Boost mode is similar and will not be described here. Since the logic is negative feedback, V pi It will stabilize to the peak value of the corresponding quadrilateral inductor current.

[0059] 2. Driving signal trigger strategy

[0060] Since the above analysis is under ideal conditions and does not take into account the system loss, when the system has a certain loss, if the input power is fixed, the power transmitted to the output side will be reduced, resulting in a decrease in the output voltage, that is, other balances will be reached in the open loop, which will cause the minimum value of the quadrilateral inductor current to not be maintained at -I zvs In order to ensure the minimization of the effective value of the quadrilateral inductor current and the soft switching of the switch tube, that is, T 3 When turned on, the inductor current should be at -I zvs , you can pass Figure 8 The comparator circuit shown compares the sensed inductor current with a given -I zvs Perform amplification and comparison to determine whether the inductor current is equal to the minimum value of the quadrilateral inductor current - I zvs The judgment result of Ti L ,pass Fig. 9 The driving signal trigger circuit shown in the figure is combined with the optimal variable load line control strategy to obtain T 3 ′、T 4 ′ and the judgment result Ti L , and get T 3 、T 4 , according to T 3 、T 4 The third switch tube S can be obtained 3 and the fourth switch tube S 4 The compensation waveform of the driving signal can ensure that the minimum value of the quadrilateral inductor current will not be less than or greater than -I zvs , in closed-loop control, the soft switching characteristics of the switch tube can be guaranteed and the output voltage can be stabilized at a given value.

[0061] 3. Quadrilateral inductor current modulation strategy

[0062] For a quadrilateral inductor current of a given frequency, the four time parameters in the quadrilateral inductor current modulation can be solved by the following formula:

[0063] V in (T 1 +T 2 )=V o (T 2 +T 3 )

[0064]

[0065] T 1 +T 2 +T 3 +T 4 =T s

[0066] V o *T3 =2*L*I x

[0067] The four time parameters of the quadrilateral inductor current are solved, and the duty ratios of the two bridge arms are: D 1 =(T 1 +T 2 ) / T s , D 2 =(T 2 +T 3 ) / T s , the phase shift time of the two bridge arms is T 1 The waveform of the quadrilateral inductor current in Buck mode is as follows: Figure 2 As shown in the figure, the waveform in Boost mode is as follows Figure 3 shown.

[0068] By reasoning from the above formula, we can get the quadrilateral inductor current and T 1 The relationship between Fig.10 As shown, the switching frequency f = 300kHz, the inductance L = 10uH, and the input voltage is V in =270V.

[0069] like Fig.10 As shown, the three different lines represent the output voltage V out The quadrilateral inductor current RMS waveform at 160V, 270V, and 200V. It can be seen from the figure that when T 1 The smaller the value, the smaller the effective value of the quadrilateral inductor current will be. Fig. 9 The dashed line in the middle represents the minimum T that can achieve soft switching. 1_s , if T 1 Less than T 1_s Then soft switching cannot be achieved. In other words, in Buck mode, T 1 The minimum inductor charging phase duration T that meets the zero voltage switching condition is clamped 1_s or T 1 Take the minimum duration of the inductor charging phase T 1_min It is an effective method to achieve the minimum effective value of quadrilateral inductor current while ensuring soft switching boundary conditions. 3 The minimum inductor discharge phase duration T that meets the zero voltage switching condition is clamped 3_s or T 3 Take the minimum duration of the inductor discharge phase T 3_min It is an effective method to achieve the minimum effective value of quadrilateral inductor current while ensuring soft switching boundary conditions.

[0070] Therefore, the quadrilateral inductor current modulation strategy accurately controls the on and off time of the four switch tubes, so that the inductor current forms a quadrilateral trajectory in each switching cycle, effectively improving the efficiency and power density of the power supply while reducing switching losses and electromagnetic interference.

[0071] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A four-switch Buck-Boost converter with an optimal load-changing circuit without table lookup closed-loop control method, characterized in that: include: The optimal variable load line control strategy is to set the maximum and minimum switching frequency within the frequency range, take the minimum effective value of the quadrilateral inductor current as the control target, and calculate the quadrilateral inductor current time parameter within the frequency range according to the quadrilateral inductor current peak value, on the premise that the quadrilateral inductor current time parameter is clamped to a value that satisfies the zero voltage switching condition; A driving signal triggering strategy is used to compare the inductor current sampling value with the minimum value of the given inductor current, and to compensate the inductor discharge phase duration parameter and the inductor current holding phase duration parameter calculated by the optimal variable load line control strategy according to the comparison result; and, The quadrilateral inductor current modulation strategy generates drive signals for four switch tubes according to the inductor charging phase duration parameters, energy transmission phase duration parameters calculated by the optimal variable load line control strategy, and the inductor discharge phase duration parameters and inductor current holding phase duration parameters compensated by the drive signal trigger strategy.

2. The method for closed-loop control of a four-switch Buck-Boost converter with an optimal load-changing circuit without table lookup according to claim 1, characterized in that: When the four-switch Buck-Boost converter operates in the Buck mode, the optimal variable load line control strategy takes the minimum effective value of the quadrilateral inductor current as the control target within the frequency range determined by setting the maximum and minimum values ​​of the switching frequency, and calculates the quadrilateral inductor current time parameter within the frequency range according to the quadrilateral inductor current peak value, on the premise that the duration parameter of the inductor charging stage is clamped to a value that satisfies the zero voltage switching condition.

3. The method for closed-loop control of a four-switch Buck-Boost converter with an optimal load-changing circuit without table lookup according to claim 1, characterized in that: When the four-switch Buck-Boost converter operates in the Boost mode, the optimal variable load line control strategy takes the minimum effective value of the quadrilateral inductor current as the control target within the frequency range determined by setting the maximum and minimum values ​​of the switching frequency, and calculates the quadrilateral inductor current time parameter within the frequency range according to the quadrilateral inductor current peak value, on the premise that the duration parameter of the inductor discharge stage is clamped to a value that satisfies the zero voltage switching condition.

4. The method for closed-loop control of a four-switch Buck-Boost converter with an optimal load-changing circuit without table lookup according to claim 2, characterized in that: The clamping of the inductor charging phase duration parameter to a value satisfying the zero voltage switching condition is specifically: clamping the inductor charging phase duration parameter to a minimum inductor charging phase duration value or a minimum inductor charging phase duration satisfying the zero voltage switching condition.

5. The method for closed-loop control of a four-switch Buck-Boost converter with an optimal load-changing circuit without table lookup according to claim 3, characterized in that: The clamping of the inductor discharge phase duration parameter to a value satisfying the zero voltage switching condition is specifically: clamping the inductor discharge phase duration parameter to a minimum value of the inductor discharge phase duration parameter or a minimum inductor discharge phase duration satisfying the zero voltage switching condition.

6. The method for closed-loop control of a four-switch Buck-Boost converter with an optimal load-changing circuit without table lookup according to claim 4, characterized in that: The optimal variable load line control strategy calculates the quadrilateral inductor current time parameter within the frequency range according to the quadrilateral inductor current peak value, specifically: the converter sequentially undergoes four stages of output power P1, P2, P3 and P4 within the frequency range, P1 <P2<P3<P4, In the first stage, the converter operates at the set maximum switching frequency, and the duration parameter of the inductor charging stage is clamped to a value that satisfies the zero voltage switching condition, then T1 = (2*I ZVS )*L / V in , T2=(V pi -I zvs )*L / (V in -V out ), T`3=(V pi +I zvs )*L / V out , T`4=1 / f max -T1-T2-T3, where T1 is the duration parameter of the inductor charging phase, T2 is the duration parameter of the energy transfer phase, T3′ is the duration parameter of the inductor discharging phase, T4′ is the duration parameter of the inductor current holding phase, I zvs is the maximum value of the given inductor current, L is the inductance value of the converter, V in is the input voltage of the converter, V pi is the peak value of the quadrilateral inductor current, V out is the output voltage of the converter, f max To set the maximum switching frequency, In the second stage, the converter operates at the set maximum switching frequency, and the duration parameter of the inductor charging stage is clamped to a value that satisfies the zero voltage switching condition. Then, the duration parameter of the inductor charging stage, the duration parameter of the energy transfer stage, and the duration parameter of the inductor discharging stage are the same as those in the first stage, and the duration parameter of the inductor current holding stage is zero. In the third stage, the converter operating frequency is reduced, and the duration parameter of the inductor charging stage is clamped to a value that satisfies the zero voltage switching condition, then T1 = (2*I ZVS )*L / V in , T2=(V pi -I zvs )*L / (V in -V out ), f is the operating frequency, In the fourth stage, the converter operating frequency is reduced to the set minimum switching frequency, the value that satisfies the zero voltage switching condition is raised, and the inductor charging stage duration parameter is clamped to the minimum inductor charging stage duration that satisfies the zero voltage switching condition after the raising, then T4′=0,I a_const and I b_const They are respectively the maximum value of the inductor current at the end of T1 and the maximum value of the inductor current at the beginning of T3′ when the converter operating frequency reaches the set minimum switching frequency.

7. The method for closed-loop control of a four-switch Buck-Boost converter with an optimal load-changing circuit without table lookup according to claim 6, characterized in that: In the fourth stage, the expression for raising the minimum inductor charging stage duration that satisfies the zero voltage switching condition is: Wherein, ΔIa is the increase in the inductor current at the end of T1, and ΔIb is the increase in the inductor current at the start of T3′.

8. The method for closed-loop control of a four-switch Buck-Boost converter with an optimal load-changing circuit without table lookup according to any one of claims 1 to 7, characterized in that: The method for obtaining the quadrilateral inductor current peak value is: comparing the output voltage sampling value with the output voltage reference value, and performing PI regulation on the comparison result.

9. The method for closed-loop control of a four-switch Buck-Boost converter with an optimal load-changing circuit without table lookup according to any one of claims 1 to 7, characterized in that: At the start time of the duration parameter of the inductor discharge phase compensated by the drive signal triggering strategy, the inductor current is equal to the minimum value of the given inductor current.

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