A four-switch buck-boost bidirectional control method

Abstract

The application provides a four-switch Buck-Boost bidirectional control method in the field of power electronics, comprising the following steps: S10, setting voltage gain thresholds G1, G2, G3 and G4, and setting switch frequency thresholds fh and fl of a switch tube; S20, setting working modes including a high-frequency Buck mode, a low-frequency Buck mode, a low-frequency Buck-Boost mode, a low-frequency Boost mode and a high-frequency Boost mode, and matching each working mode with a voltage gain interval and a switch frequency; S30, after the output of a battery constant voltage loop and a battery constant current loop is switched and selected, inputting an inductor current reference value IL* to an inductor current loop; S40, the inductor current loop acquires an actual inductor current value IL, and outputs a voltage gain G based on the error between IL* and IL; S50, matching the working mode based on the voltage gain G; and S60, outputting pulse signals g1, g2, g3 and g4 based on the working mode and dead zone compensation duty ratio. The application has the advantages that the efficiency of working mode switching and the smoothness of charging and discharging transition are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a four-switch Buck-Boost bidirectional control method. Background Technology

[0002] The conventional topology for battery charging and discharging is a Buck circuit or a Boost circuit. The characteristics of this type of circuit are: it operates in Buck mode (buck operation) when charging and in Boost mode (boost operation) when discharging. It cannot achieve charging under boost voltage or discharging under buck voltage.

[0003] The four-switch Buck-Boost topology combines the advantages of Buck and Boost circuits, allowing for step-up / step-down operation based on the input and output voltage ranges, i.e., switching between operating modes. However, in traditional four-switch Buck-Boost topologies, during mode switching (Buck mode to Boost mode, or Boost mode to Buck mode), all four switches operate at higher switching frequencies, increasing switching losses and reducing overall efficiency. Furthermore, it is only suitable for cases where the inductor current is greater than 0 (charging mode) and does not consider cases where the inductor current is less than 0 (discharging mode).

[0004] Therefore, how to provide a four-switch Buck-Boost bidirectional control method to improve the efficiency of working mode switching and the smoothness of charge and discharge transition, especially when the input and output voltages are close, has become an urgent technical problem to be solved. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a four-switch Buck-Boost bidirectional control method to improve the efficiency of working mode switching and the smoothness of charge and discharge transition.

[0006] This invention is implemented as follows: a four-switch Buck-Boost bidirectional control method, comprising the following steps:

[0007] Step S10: Set voltage gain thresholds G1, G2, G3 and G4, where G1 < G2 < 1 < G3 < G4; Set switching frequency thresholds fh and fl of the switching transistor, where fh / 4 ≤ fl ≤ fh / 2;

[0008] Step S20: Set the operating modes of the four-switch Buck-Boost topology to include high-frequency Buck mode, low-frequency Buck mode, low-frequency Buck-Boost mode, low-frequency Boost mode and high-frequency Boost mode, and each operating mode is matched with a voltage gain range and a switching frequency, respectively.

[0009] Step S30: After the constant voltage and constant current switching selection is passed between the battery constant voltage loop and the battery constant current loop, the inductor current reference value IL* is input to the inductor current loop.

[0010] Step S40: The inductor current loop obtains the actual value IL of the inductor current of inductor L. The inductor current controller GiL of the inductor current loop outputs the voltage gain G to the mode control module based on the error between IL* and IL.

[0011] Step S50: The mode control module matches the corresponding operating mode based on the voltage gain G and the voltage gain range;

[0012] Step S60: Based on the operating mode and the dead-time compensation duty cycle output by the dead-time compensation module, the mode control module outputs pulse signals g1, g2, g3, and g4 to the four switching transistors respectively, thereby performing bidirectional control of the four-switch Buck-Boost topology.

[0013] Furthermore, in step S10, frequency hysteresis interval H1 and frequency hysteresis interval H2 are also set;

[0014] The frequency hysteresis interval H1 is used to prevent frequent switching between high-frequency Buck mode and low-frequency Buck mode; the frequency hysteresis interval H2 is used to prevent frequent switching between low-frequency Boost mode and high-frequency Boost mode.

[0015] Further, in step S20, the matching of each of the operating modes with a voltage gain range and a switching frequency specifically involves:

[0016] When the voltage gain G < voltage gain threshold G1, it operates in high-frequency Buck mode with the switching frequency threshold fh.

[0017] When the voltage gain threshold G1 ≤ voltage gain G < voltage gain threshold G2, it operates in low-frequency Buck mode with the switching frequency threshold fl.

[0018] When the voltage gain threshold G2 ≤ ​​voltage gain G < voltage gain threshold G3, it operates in low-frequency Buck-Boost mode with the switching frequency threshold fl.

[0019] When the voltage gain threshold G3 ≤ voltage gain G < voltage gain threshold G4, it operates in low-frequency Boost mode with the switching frequency threshold fl.

[0020] When the voltage gain G ≥ voltage gain threshold G4, it operates in high-frequency Boost mode with the switching frequency threshold fh.

[0021] Furthermore, in step S20, in the high-frequency Buck mode and the low-frequency Buck mode, the switching transistors Q1 and Q2 operate in a complementary PWM manner, and the switching transistor Q3 is in the on state while the switching transistor Q4 is in the off state.

[0022] In the low-frequency Buck-Boost mode, switching transistors Q1, Q2, Q3, and Q4 all operate in a complementary PWM mode, with Q1 and Q2 being complementary, and Q3 and Q4 being complementary; the low-frequency Buck-Boost mode is a combination of low-frequency Buck mode and low-frequency Boost mode operating alternately according to a preset ratio.

[0023] In the low-frequency Boost mode and the high-frequency Boost mode, the switching transistors Q3 and Q4 operate in a complementary PWM manner, with the switching transistor Q1 in the on state and the switching transistor Q2 in the off state.

[0024] Furthermore, in step S40, the voltage gain G has a value range of [0, 3].

[0025] Furthermore, in step S60, the pulse signals g1, g2, g3, and g4 are used to control the operation of the switching transistors Q1, Q2, Q3, and Q4, respectively.

[0026] Further, in step S60, the calculation process for the dead-zone compensation duty cycle is as follows:

[0027] Set the first inductor current threshold IL bu-dwlit Second inductor current threshold IL bu-uplit Third inductor current threshold IL bo-dwlit Fourth inductor current threshold IL bo-uplit ;

[0028] Real-time calculation of peak inductor current IL peak Inductor current valley value IL valley Average inductor current IL ave ;

[0029] When running in high-frequency Buck mode and low-frequency Buck mode:

[0030] When IL valley When ≥0, ΔD buck =T d / T s ;

[0031] When IL peak When ≤0, ΔD buck =-T d / T s ;

[0032] When IL valley <0, IL peak When the value is greater than 0, there are three possible scenarios:

[0033] When IL valley >IL bu-dwlit And IL peak >IL bu-uplit At that time, ΔD buck =(1-IL) valley / IL bu-dwlit )*(T d / T s );

[0034] When IL valley <IL bu-dwlit And IL peak >IL bu-uplit At that time, ΔD buck =0;

[0035] When IL valley <IL bu-dwlit And IL peak <IL bu-uplit At that time, ΔD buck =(IL peak / IL bu-uplit -1)*(T d / T s );

[0036] Where, ΔD buck Indicates the dead-zone compensation duty cycle of the Buck bridge arm; T d T represents the dead time; s Indicates the switching cycle of the switching transistor;

[0037] When running in low-frequency Boost mode and high-frequency Boost mode:

[0038] When IL valley When ≥0, ΔD boost =T d / T s ;

[0039] When IL peak When ≤0, ΔD boost =-T d / T s ;

[0040] When IL valley <0, IL peak When the value is greater than 0, there are three possible scenarios:

[0041] When ILvalley >IL bo-dwlit And IL peak >IL bo-uplit At that time, ΔD boost =(1-IL) valley / IL bo-dwlit )*(T d / T s );

[0042] When IL valley <IL bo-dwlit And IL peak >IL bo-uplit At that time, ΔD boost =0;

[0043] When IL valley <IL bo-dwlit And IL peak <IL bo-uplit At that time, ΔD boost =(IL peak / IL bo-uplit -1)*(T d / T s );

[0044] Where, ΔD boost This indicates the dead-time compensation duty cycle of the Boost bridge arm.

[0045] The advantages of this invention are:

[0046] 1. By setting the operating modes of the four-switch Buck-Boost topology to include high-frequency Buck mode, low-frequency Buck mode, low-frequency Buck-Boost mode, low-frequency Boost mode, and high-frequency Boost mode, and each operating mode is matched with a voltage gain range and switching frequency, that is, only two of the five operating modes operate at high frequency, while the rest operate at low frequency. This reduces the switching frequency of the switching transistors, greatly reduces the losses of the switching transistors, and thus greatly improves the efficiency of operating mode switching.

[0047] 2. By performing dead-zone compensation on the output of the mode control module, a smooth transition of dead-zone compensation is achieved under different charging and discharging conditions and different load currents, so that the calculated duty cycle is completely consistent with the actual duty cycle, thereby greatly improving the smoothness of the charging and discharging transition and greatly improving the stability of the four-switch Buck-Boost topology. Attached Figure Description

[0048] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0049] Figure 1This is a flowchart of a four-switch Buck-Boost bidirectional control method according to the present invention.

[0050] Figure 2 This is a circuit diagram of the four-switch Buck-Boost topology of this invention.

[0051] Figure 3 This is a flowchart illustrating the present invention.

[0052] Figure 4 This is a schematic diagram illustrating the switching of the working mode of the present invention.

[0053] Figure 5 This is a waveform diagram of the Buck bridge arm drive of the present invention.

[0054] Figure 6 This is a waveform diagram illustrating the first scenario of dead zone compensation duty cycle calculation according to the present invention.

[0055] Figure 7 This is a waveform diagram illustrating the second scenario of dead zone compensation duty cycle calculation according to the present invention.

[0056] Figure 8 This is a waveform diagram of the third case of dead zone compensation duty cycle calculation according to the present invention. Detailed Implementation

[0057] The overall idea of ​​the technical solution in this application embodiment is as follows: When switching between Buck mode and Boost mode, the switching frequency of the switching transistor is reduced to improve the efficiency of working mode switching; through the dead time compensation module, the dead time compensation duty cycle is calculated in real time to perform dead time compensation on the output of the mode control module, so that the calculated duty cycle is completely consistent with the actual duty cycle, thereby improving the smoothness of charging and discharging transition.

[0058] Please refer to Figures 1 to 8 As shown, this invention requires the use of a four-switch Buck-Boost topology, where switches Q1, Q2, Q3, and Q4 each form two bridge arms. Switches Q1 and Q2 form buck bridge arm 1, and switches Q3 and Q4 form boost bridge arm 2. The midpoints of the two bridge arms are connected by an inductor L. The input and output are respectively connected to capacitors Cin and Cout, and the input and output share a common ground. The output is directly connected to the battery system.

[0059] A preferred embodiment of the four-switch Buck-Boost bidirectional control method of the present invention includes the following steps:

[0060] Step S10: Set voltage gain thresholds G1, G2, G3 and G4, where G1 < G2 < 1 < G3 < G4; Set switching frequency thresholds fh and fl of the switching transistor, where fh / 4 ≤ fl ≤ fh / 2;

[0061] Step S20: Set the operating modes of the four-switch Buck-Boost topology to include high-frequency Buck mode, low-frequency Buck mode, low-frequency Buck-Boost mode, low-frequency Boost mode and high-frequency Boost mode, and each operating mode is matched with a voltage gain range and a switching frequency, respectively.

[0062] Step S30: After the constant voltage and constant current switching selection is passed between the battery constant voltage loop and the battery constant current loop, the inductor current reference value IL* is input to the inductor current loop.

[0063] Step S40: The inductor current loop obtains the actual value IL of the inductor current of inductor L. The inductor current controller GiL of the inductor current loop outputs the voltage gain G to the mode control module based on the error between IL* and IL.

[0064] Step S50: The mode control module matches the corresponding operating mode based on the voltage gain G and the voltage gain range;

[0065] Step S60: Based on the operating mode and the dead-time compensation duty cycle output by the dead-time compensation module, the mode control module outputs pulse signals g1, g2, g3, and g4 to the four switching transistors respectively, thereby performing bidirectional control of the four-switch Buck-Boost topology.

[0066] In step S10, frequency hysteresis interval H1 and frequency hysteresis interval H2 are also set.

[0067] The frequency hysteresis interval H1 is used to prevent frequent switching between high-frequency Buck mode and low-frequency Buck mode; the frequency hysteresis interval H2 is used to prevent frequent switching between low-frequency Boost mode and high-frequency Boost mode.

[0068] In step S20, each of the operating modes is specifically matched with a voltage gain range and a switching frequency as follows:

[0069] When the voltage gain G < voltage gain threshold G1, it operates in high-frequency Buck mode with the switching frequency threshold fh.

[0070] When the voltage gain threshold G1 ≤ voltage gain G < voltage gain threshold G2, it operates in low-frequency Buck mode with the switching frequency threshold fl.

[0071] When the voltage gain threshold G2 ≤ ​​voltage gain G < voltage gain threshold G3, it operates in low-frequency Buck-Boost mode with the switching frequency threshold fl.

[0072] When the voltage gain threshold G3 ≤ voltage gain G < voltage gain threshold G4, it operates in low-frequency Boost mode with the switching frequency threshold fl.

[0073] When the voltage gain G ≥ voltage gain threshold G4, it operates in high-frequency Boost mode with the switching frequency threshold fh.

[0074] In step S20, in the high-frequency Buck mode and the low-frequency Buck mode, the switching transistors Q1 and Q2 operate in a complementary PWM manner, and the switching transistor Q3 is in the on state while the switching transistor Q4 is in the off state.

[0075] In the low-frequency Buck-Boost mode, switching transistors Q1, Q2, Q3, and Q4 all operate in a complementary PWM mode, with Q1 and Q2 being complementary, and Q3 and Q4 being complementary. The low-frequency Buck-Boost mode involves alternating between low-frequency Buck mode and low-frequency Boost mode according to a preset ratio. For example, the first switching cycle operates in low-frequency Buck mode, and the next switching cycle operates in low-frequency Boost mode, and so on, in a cyclical alternation.

[0076] In the low-frequency Boost mode and the high-frequency Boost mode, the switching transistors Q3 and Q4 operate in a complementary PWM manner, with the switching transistor Q1 in the on state and the switching transistor Q2 in the off state.

[0077] In step S40, the voltage gain G has a value range of [0, 3].

[0078] In step S60, the pulse signals g1, g2, g3, and g4 are used to control the operation of the switching transistors Q1, Q2, Q3, and Q4, respectively.

[0079] In step S60, the calculation process for the dead-zone compensation duty cycle is as follows:

[0080] Taking the Buck bridge arm complementary PWM mode as an example, the principle of the Boost bridge arm working mode is similar.

[0081] Within the same bridge arm, to prevent shoot-through short circuits in the upper and lower switching transistors, a dead time is added to the driving of the upper and lower switching transistors. The driving waveform is as follows: Figure 5 As shown.

[0082] according to Figure 2 As shown by the direction of the medium current, during charging, the inductor current IL > 0. Within one switching cycle Ts, during the dead time 1 and dead time 2, the inductor current flows through the anti-parallel diode of the switching transistor Q2, causing the voltage at node U1 to be 0 during both dead time periods. The actual duty cycle of the switching transistor Q1 is...

[0083] During discharge, the inductor current IL < 0. During the time between dead zone 1 and dead zone 2, the inductor current flows through the anti-parallel diode of switch Q1, causing the voltage at node U1 to be Uin during the dead time. The actual duty cycle of switch Q1 is...

[0084] D is the duty cycle calculated by the mode control module. g1 This represents the actual duty cycle. It is evident that in charging and discharging mode, the dead time has diametrically opposed effects on the control performance. Furthermore, when switching between high and low frequencies, since the dead time remains constant but the switching cycle changes, without dead time compensation, the actual duty cycle will fluctuate drastically during high-frequency switching, causing instability.

[0085] The inductor current is a triangular wave within one cycle. Based on the waveform of the inductor current, we can derive:

[0086] IL peak +IL valley =2*IL ave ;

[0087] IL peak -IL valley =(U in -U out )*D*T s / L;

[0088] From the above formula, we can obtain:

[0089] IL peak =IL ave +(U in -U out )*D*T s / 2L;

[0090] IL valley =IL ave -(U in -U out )*D*T s / 2L;

[0091] Digital control is employed, and the drive pulse is generated using a symmetrical PWM method. This allows sampling at the moment of average inductor current to obtain the average inductor current. Due to dead-time compensation, the actual duty cycle D of the switching transistor Q1 can be calculated. Equivalent substitution. Uin and Uout are the input and output voltages. The peak and valley values ​​of the inductor current can be calculated in real time by the processor.

[0092] Set the first inductor current threshold IL bu-dwlit Second inductor current threshold IL bu-uplit Third inductor current threshold ILbo-dwlit Fourth inductor current threshold IL bo-uplit ;

[0093] Based on the above method, the peak inductor current IL is calculated in real time. peak Inductor current valley value IL valley Average inductor current IL ave ;

[0094] When running in high-frequency Buck mode and low-frequency Buck mode:

[0095] When IL valley When ≥0, ΔD buck =T d / T s ;

[0096] When IL peak When ≤0, ΔD buck =-T d / T s ;

[0097] When IL valley <0, IL peak When the value is greater than 0, there are three possible scenarios:

[0098] like Figure 6 As shown, when IL valley >IL bu-dwlit And IL peak >IL bu-uplit During the dead time 1, the voltage at node U1 is affected, and the lost duty cycle is T. d / T s However, within dead time 2, the increased duty cycle is (IL) valley / IL bu-dwlit )*(T d / T s Therefore, ΔD buck =(1-IL) valley / IL bu-dwlit )*(T d / T s );

[0099] like Figure 7 As shown, when IL valley <IL bu-dwlit And IL peak >IL bu-uplit During the dead time 1, the voltage at node U1 is affected, and the lost duty cycle is T. d / T s However, within the dead time 2, the increased duty cycle is T. d / T sIn the same switching cycle, the effects of the two dead times cancel each other out, so ΔD buck =0;

[0100] like Figure 8 As shown, when IL valley <IL bu-dwlit And IL peak <IL bu-uplit During the dead time 1, the voltage of node U1 is affected, and the lost duty cycle is (IL). peak / IL bu-uplit )*(T d / T s However, within the dead time 2, the increased duty cycle is T. d / T s Therefore, within the same switching cycle, ΔD buck =(IL peak / IL bu-uplit -1)*(T d / T s );

[0101] Where, ΔD buck Indicates the dead-zone compensation duty cycle of the Buck bridge arm; T d T represents the dead time; s Indicates the switching cycle of the switching transistor;

[0102] When running in low-frequency Boost mode and high-frequency Boost mode:

[0103] When IL valley When ≥0, ΔD boost =T d / T s ;

[0104] When IL peak When ≤0, ΔD boost =-T d / T s ;

[0105] When IL valley <0, IL peak When the value is greater than 0, there are three possible scenarios:

[0106] When IL valley >IL bo-dwlit And IL peak >IL bo-uplit At that time, ΔD boost =(1-IL) valley / IL bo-dwlit )*(T d / T s );

[0107] When IL valley <IL bo-dwlit And IL peak >IL bo-uplit At that time, ΔD boost =0;

[0108] When IL valley <IL bo-dwlit And IL peak <IL bo-uplit At that time, ΔD boost =(IL peak / IL bo-uplit -1)*(T d / T s );

[0109] Where, ΔD boost This indicates the dead-time compensation duty cycle of the Boost bridge arm.

[0110] Based on the high-frequency and low-frequency modes of mode control, T s The corresponding switching cycle should be selected so that smooth switching between high and low frequencies can be achieved.

[0111] In summary, the advantages of this invention are:

[0112] 1. By setting the operating modes of the four-switch Buck-Boost topology to include high-frequency Buck mode, low-frequency Buck mode, low-frequency Buck-Boost mode, low-frequency Boost mode, and high-frequency Boost mode, and each operating mode is matched with a voltage gain range and switching frequency, that is, only two of the five operating modes operate at high frequency, while the rest operate at low frequency. This reduces the switching frequency of the switching transistors, greatly reduces the losses of the switching transistors, and thus greatly improves the efficiency of operating mode switching.

[0113] 2. By performing dead-zone compensation on the output of the mode control module, a smooth transition of dead-zone compensation is achieved under different charging and discharging conditions and different load currents, so that the calculated duty cycle is completely consistent with the actual duty cycle, thereby greatly improving the smoothness of the charging and discharging transition and greatly improving the stability of the four-switch Buck-Boost topology.

[0114] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A four-switch Buck-Boost bidirectional control method, characterized in that: Includes the following steps: Step S10: Set voltage gain thresholds G1, G2, G3 and G4, where G1 < G2 < 1 < G3 < G4; Set switching frequency thresholds fh and fl of the switching transistor, where fh / 4 ≤ fl ≤ fh / 2; Step S20: Set the operating modes of the four-switch Buck-Boost topology to include high-frequency Buck mode, low-frequency Buck mode, low-frequency Buck-Boost mode, low-frequency Boost mode and high-frequency Boost mode, and each operating mode is matched with a voltage gain range and a switching frequency, respectively. Step S30: After the constant voltage and constant current switching selection is passed between the battery constant voltage loop and the battery constant current loop, the inductor current reference value IL* is input to the inductor current loop. Step S40: The inductor current loop obtains the actual value IL of the inductor current of inductor L. The inductor current controller GiL of the inductor current loop outputs the voltage gain G to the mode control module based on the error between IL* and IL. Step S50: The mode control module matches the corresponding operating mode based on the voltage gain G and the voltage gain range; Step S60: Based on the operating mode and the dead-time compensation duty cycle output by the dead-time compensation module, the mode control module outputs pulse signals g1, g2, g3, and g4 to the four switching transistors respectively, thereby performing bidirectional control on the four-switch Buck-Boost topology. The calculation process for the dead zone compensation duty cycle is as follows: Set the first inductor current threshold Second inductor current threshold Third inductor current threshold Fourth inductor current threshold ; Real-time calculation of inductor current peak Inductor current valley Average inductor current ; When running in high-frequency Buck mode and low-frequency Buck mode: when hour, ; when hour, ; when There are three possible scenarios: when hour, ; when hour, ; when hour, ; in, This indicates the dead zone compensation duty cycle of the Buck bridge arm; Indicates dead time; Indicates the switching cycle of the switching transistor; When running in low-frequency Boost mode and high-frequency Boost mode: when hour, ; when hour, ; when , There are three possible scenarios: when and hour, ; when and hour, ; when and hour, ; in, This indicates the dead-time compensation duty cycle of the Boost bridge arm.

2. The four-switch Buck-Boost bidirectional control method as described in claim 1, characterized in that: In step S10, frequency hysteresis interval H1 and frequency hysteresis interval H2 are also set. The frequency hysteresis interval H1 is used to prevent frequent switching between high-frequency Buck mode and low-frequency Buck mode; the frequency hysteresis interval H2 is used to prevent frequent switching between low-frequency Boost mode and high-frequency Boost mode.

3. The four-switch Buck-Boost bidirectional control method as described in claim 1, characterized in that: In step S20, each of the operating modes is specifically matched with a voltage gain range and a switching frequency as follows: When the voltage gain G < voltage gain threshold G1, it operates in high-frequency Buck mode with the switching frequency threshold fh. When the voltage gain threshold G1 ≤ voltage gain G < voltage gain threshold G2, it operates in low-frequency Buck mode with the switching frequency threshold fl. When the voltage gain threshold G2 ≤ ​​voltage gain G < voltage gain threshold G3, it operates in low-frequency Buck-Boost mode with the switching frequency threshold fl. When the voltage gain threshold G3 ≤ voltage gain G < voltage gain threshold G4, it operates in low-frequency Boost mode with the switching frequency threshold fl. When the voltage gain G ≥ voltage gain threshold G4, it operates in high-frequency Boost mode with the switching frequency threshold fh.

4. The four-switch Buck-Boost bidirectional control method as described in claim 1, characterized in that: In step S20, in the high-frequency Buck mode and the low-frequency Buck mode, the switching transistors Q1 and Q2 operate in a complementary PWM manner, and the switching transistor Q3 is in the on state while the switching transistor Q4 is in the off state. In the low-frequency Buck-Boost mode, switching transistors Q1, Q2, Q3, and Q4 all operate in a complementary PWM mode, with Q1 and Q2 being complementary, and Q3 and Q4 being complementary; the low-frequency Buck-Boost mode is a combination of low-frequency Buck mode and low-frequency Boost mode operating alternately according to a preset ratio. In the low-frequency Boost mode and the high-frequency Boost mode, the switching transistors Q3 and Q4 operate in a complementary PWM manner, with the switching transistor Q1 in the on state and the switching transistor Q2 in the off state.

5. The four-switch Buck-Boost bidirectional control method as described in claim 1, characterized in that: In step S40, the voltage gain G has a value range of [0, 3].

6. The four-switch Buck-Boost bidirectional control method as described in claim 1, characterized in that: In step S60, the pulse signals g1, g2, g3, and g4 are used to control the operation of the switching transistors Q1, Q2, Q3, and Q4, respectively.

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