Soft switching control method and controller for six-transistor Buck-Boost converter

Abstract

This invention discloses a soft-switching control method and controller for a six-transistor Buck-Boost converter, belonging to the field of power electronics conversion and control. The method includes: For a six-transistor Buck-Boost converter, using two inductor current cycles as one switching cycle, a switching sequence is designed to achieve soft switching of all switching devices over a wide input voltage and load range. With minimizing inductor current ripple as the goal and soft switching of each switch as a constraint, the phase shift angle and duty cycle of each switch are calculated. This method can achieve zero-voltage turn-on of all six-transistor Buck-Boost switching devices. Duty cycle control and phase shift control are also used to reduce inductor current ripple, thereby improving converter efficiency.

Description

Technical Field

[0001] The present invention belongs to the field of power electronic conversion and control, and more particularly, relates to a soft switching control method and a controller for a six-tube Buck-Boost converter. Background Art

[0002] In common energy storage systems, bidirectional DC / DC converters are key devices for voltage conversion and power transmission. As the voltage level of energy storage devices increases, higher voltage-bearing requirements are placed on the bidirectional DC / DC energy storage-side ports. Therefore, a three-level bridge arm is often used to replace the two-level bridge arm in the traditional four-transistor Buck-Boost converter, forming a new six-transistor Buck-Boost converter. Compared to midpoint-clamped three-level and cascaded three-level structures, the flying capacitor three-level six-transistor Buck-Boost converter has the advantages of a common input and output ground and unrestricted switching timing, making it more suitable for high-voltage and high-power applications.

[0003] Currently, research on six-switch buck-boost converters focuses on model predictive control (MPC) and multi-mode control, both of which are hard-switching control strategies. To overcome the high switching losses and low device efficiency associated with traditional hard-switching control in high-voltage, high-power operating scenarios, zero-voltage switching (ZVS) can be employed to eliminate losses during switch turn-on. Without adding additional auxiliary soft-switching circuits, implementing soft switching of all switching devices increases inductor current ripple and conduction losses compared to traditional hard-switching methods.

[0004] Therefore, in order to improve the working efficiency and power density of the six-switch Buck-Boost converter, how to achieve soft switching control of the entire device and reduce the inductor current ripple on this basis is of great research significance. Summary of the Invention

[0005] In response to the shortcomings of the existing technology and the need for improvement, the present invention provides a soft switching control method and controller for a six-transistor Buck-Boost converter. Its purpose is to reduce switching losses while lowering conduction losses caused by inductor current pulsation, thereby improving the operating efficiency and power density of the six-transistor Buck-Boost converter.

[0006] To achieve the above object, according to one aspect of the present invention, a soft switching control method for a six-transistor Buck-Boost converter is provided. The six-transistor Buck-Boost converter includes a three-level bridge arm, a two-level bridge arm, an inductor, and a flying capacitor; the three-level bridge arm includes a switching tube Q connected in sequence. A1 , Q A2 , Q A3 and Q A4The two-level bridge arm includes the switch tubes Q connected in sequence B1 and Q B2 ; One end of the inductor is connected to Q A2 and Q A3 The other end is connected to Q B1 and Q B2 The connection point of the flying capacitor is Q A1 and Q A2 The other end is connected to Q A3 and Q A4 The method includes: taking two inductor current cycles as one switching cycle, and in each switching cycle, Q A4 and Q A1 Complementary conduction, Q A3 and Q A2 Complementary conduction, Q B2 and Q B1 Complementary conduction; in the first inductor current cycle of each switching cycle, the starting time Q A1 and Q A2 At the same time, Q A1 After the first period of conduction, it turns off, Q A2 After the second period of conduction, it is turned off and the starting time Q B1 Shutdown, at Q A3 and Q A4 Before turning on Q B1 , in Q A4 The absolute value of the source current is greater than the zero voltage turn-on current and turns off Q B1 ; In the second inductor current cycle of each switching cycle, Q A1 , Q A2 The driving signals correspond to the first inductor current cycle Q A2 , Q A1 The driving signal is the same, starting at Q B1 Shutdown, at Q A3 and Q A4 Before turning on Q B1 , in Q A4 The absolute value of the source current is greater than the zero voltage turn-on current and turns off Q B1 ; Wherein, the first time period and the second time period are obtained by the following method: taking the minimum pulsation of the inductor current as the goal and the soft switching of each switch tube as the constraint, and calculating them.

[0007] Furthermore, the calculation method of the first time period and the second time period specifically includes: SA1, according to the input voltage V in , output voltage V out and the output current reference value I out, determine its working condition; SA2, according to the working condition of the six-tube Buck-Boost converter, with the goal of minimizing the pulsation of the inductor current and the soft switching of each switch tube as the constraint, calculate the proportion of each mode in an inductor current cycle; SA3, based on 0.5V in The difference between the voltage of the flying capacitor and the duty cycle is controlled by PI. The result of PI control is limited to obtain the duty cycle compensation value △D, which is used to compensate for the proportion of the third mode. SA4 calculates Q according to the proportion of the first mode, the proportion of the second mode and the proportion of the compensated third mode. A1 The on-duty cycle D A1 and Q A2 The on-duty cycle D A2 , where the first mode refers to V A =V in And V B = 0 mode, the second mode refers to V A =V in And V B =V out The third mode is V A =0.5V in And V B =V out The mode, V A is the output voltage of the three-level bridge arm, V B is the output voltage of the two-level bridge arm; SA5, calculate D A1 The corresponding first time period, and D A2 The corresponding second time period.

[0008] Furthermore, the SA1 specifically includes: when V in >V out When I out >I out1 The six-tube Buck-Boost converter is in the first operating state. If I out2 out ≤I out1 In the second working condition, if I out ≤I out2 In the third working condition; when V in ≤V out When I out >I out3 The six-tube Buck-Boost converter is in the fourth operating state. If I out ≤I out3 In the fifth working condition; I out1 , I out2 and I out3 They are:

[0009] ​

[0010] Among them, I out1 is the first boundary current, I out2 is the second boundary current, I out3 is the third boundary current, k is the ratio of output voltage to input voltage, I ZVS is the zero voltage turn-on current, L is the inductance value, T s is the inductor current period.

[0011] Furthermore, the proportion of the third mode after compensation is:

[0012] D 3_1 =D3+△D

[0013] D A1 and D A2 They are:

[0014] D A1 =D1+D2

[0015] D A2 =D1+D2+D 3_1

[0016] Among them, D 3_1 is the proportion of the third mode after compensation, D3 is the proportion of the third mode before compensation, D2 is the proportion of the second mode, and D1 is the proportion of the first mode.

[0017] Furthermore, the proportion of the third mode after compensation is:

[0018] D 3_1 =D3-△D

[0019] D A1 and D A2 They are:

[0020] D A1 =D1+D2+D 3_1

[0021] D A2 =D1+D2

[0022] Among them, D 3_1 is the proportion of the third mode after compensation, D3 is the proportion of the third mode before compensation, D2 is the proportion of the second mode, and D1 is the proportion of the first mode.

[0023] Furthermore, the method further comprises: calculating Q B1 Duty cycle D B1 and conduction phase shift angle φ B1 , according to D B1 and Control Q B1 On / off, DB1 and They are:

[0024] D B1 =D2+D 3_1 +D4

[0025]

[0026] Among them, D1 is the proportion of the first mode, D2 is the proportion of the second mode, and D 3_1 is the proportion of the third mode after compensation, and D4 is the proportion of the fourth mode.

[0027] Furthermore, the control switch Q A1 , Q A2 , Q A3 , Q A4 , Q B1 and Q B2 During the on-off process, a dead time is set.

[0028] According to another aspect of the present invention, a soft switching controller for a six-transistor Buck-Boost converter is provided, which is used to execute the soft switching control method for the six-transistor Buck-Boost converter described above.

[0029] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0030] (1) A soft switching control method for a six-tube Buck-Boost converter is provided. For the six-tube Buck-Boost converter, the method takes the realization of zero voltage conduction of each switch tube as a constraint, utilizes the degree of freedom of the duty cycle and phase shift angle of the switching device, optimizes the inductor current ripple to minimize it, and controls the on and off of each switch tube according to the method. Under the premise of achieving full-range soft switching, the inductor current ripple is reduced, the conduction loss caused by the inductor current ripple is reduced, and the conduction loss of the inductor and the switching device is effectively reduced, the inductor volume is reduced, and the power density is improved;

[0031] (2) A specific calculation method for the duty cycle of a driving signal is provided. The input voltage, output voltage and output power reference values ​​are used to judge the working condition of the converter. The input voltage, output power and working area signal are used to calculate the duty cycle and phase shift angle of each switch tube. The switch duty cycle is compensated through the flying capacitor voltage closed-loop control to achieve flying capacitor voltage following. According to the compensated switch tube duty cycle and phase shift angle, a carrier and a modulation wave are generated to control the on and off of each switch tube, thereby improving the working efficiency of the converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1A topological diagram of a six-transistor Buck-Boost converter provided in an embodiment of the present invention;

[0033] Figure 2 A control block diagram of a six-transistor Buck-Boost converter provided in an embodiment of the present invention;

[0034] Figure 3 A schematic diagram of the division of different working conditions provided by an embodiment of the present invention;

[0035] Figure 4 A switching timing diagram of an inductor current cycle provided by an embodiment of the present invention;

[0036] Figure 5 A switching timing diagram of a switching cycle provided by an embodiment of the present invention;

[0037] Figure 6 The control method provided by the embodiment of the present invention is V in >V out Schematic diagram of inductor current change when load size changes;

[0038] Figure 7 The control method provided by the embodiment of the present invention is V in ≤V out Schematic diagram of inductor current change when load size changes;

[0039] Figure 8 The working waveform under the first working condition when the control method provided by the embodiment of the present invention is adopted;

[0040] Figure 9 The working waveform under the second working condition when the control method provided by the embodiment of the present invention is adopted;

[0041] Figure 10 The working waveform under the third working condition when the control method provided by the embodiment of the present invention is adopted;

[0042] Figure 11 The operating waveform under the fourth working condition when the control method provided by the embodiment of the present invention is adopted;

[0043] Figure 12 The working waveform under the fifth working condition when the control method provided by the embodiment of the present invention is adopted;

[0044] Figure 13 This is the working waveform when the input voltage changes when the control method provided by the embodiment of the present invention is adopted. DETAILED DESCRIPTION

[0045] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0046] In the present invention, the terms "first", "second", etc. (if any) in the present invention and the drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0047] Example 1

[0048] A soft switching control method for a six-switch Buck-Boost converter, see Figures 1-13 , the soft switching control method for the six-transistor Buck-Boost converter in this embodiment is described in detail.

[0049] The six-tube Buck-Boost converter includes a three-level bridge arm, a two-level bridge arm, an inductor and a flying capacitor. The three-level bridge arm includes a switch tube Q connected in sequence. A1 , Q A2 , Q A3 and Q A4 The two-level bridge arm includes a switch tube Q connected in sequence B1 and Q B2 One end of the inductor is connected to Q A2 and Q A3 The other end is connected to Q B1 and Q B2 One end of the flying capacitor is connected to Q A1 and Q A2 The other end is connected to Q A3 and Q A4 connection point.

[0050] See Figure 1 The three-level bridge arm includes the upper bridge arm outer tube Q A1 、Upper arm inner tube Q A2 、Lower bridge arm inner tube Q A3 、Lower bridge arm outer tube Q A4 And the flying capacitor C fly Composition, among which C fly One end and Q A1 Source, Q A2 The drain is connected to the node, and the other end is connected to the Q A3 Source, Q A4 The node connected to the drain is connected, and the output port is Q A2 Source and Q A3The connection point of the drain. The two-level bridge arm consists of the upper bridge arm switch tube Q B1 With the lower bridge arm switch tube Q B2 The output port is Q B1 With Q B2 The two ends of the inductor L are connected to the output port of the three-level bridge arm and the output port of the two-level bridge arm respectively. Output filter capacitor C o The two ends are connected to the switch tube Q B1 The drain is connected to ground. Figure 2 The control block diagram shown implements this method.

[0051] The soft switching control method for the six-transistor Buck-Boost converter is as follows. Two inductor current cycles constitute one switching cycle. When operating in steady state, the inductor currents in the two inductor current cycles are exactly the same. In each switching cycle, Q A4 and Q A1 Complementary conduction, Q A3 and Q A2 Complementary conduction, Q B2 and Q B1 Complementary conduction. In the first inductor current cycle of each switching cycle, the starting time Q A1 and Q A2 At the same time, Q A1 After the first period of conduction, it turns off, Q A2 After the second period of conduction, it is turned off and the starting time Q B1 Shutdown, at Q A3 and Q A4 Before turning on Q B1 , in Q A4 The absolute value of the source current is greater than the zero voltage turn-on current and turns off Q B1 In the second inductor current cycle of each switching cycle, Q A1 , Q A2 The driving signals correspond to the first inductor current cycle Q A2 , Q A1 The driving signal is the same, starting at Q B1 Shutdown, at Q A3 and Q A4 Before turning on Q B1 , in Q A4 The absolute value of the source current is greater than the zero voltage turn-on current and turns off Q B1 The first time period and the second time period are obtained by the following method: taking the minimum pulsation of the inductor current as the goal and the soft switching of each switch tube as the constraint, the timing of each switch tube in a switching cycle is calculated as follows: Figure 5 shown.

[0052] Preferably, the calculation method of the first time period and the second time period specifically includes the following operations SA1 to SA5.

[0053] Operation SA1, according to the input voltage V in , output voltage V out and the output current reference value I out , determine its working conditions.

[0054] See Figure 2 , sample output voltage V out With the reference output voltage V out_ref After comparison, the output voltage error value is obtained, which is input into the PI controller PI1, and the power reference value P is output through PI1. ref According to P ref Calculate the output current reference value I out =P ref / V out .

[0055] V in >V out When the load changes, the inductor current is as follows: Figure 6 As shown, V in ≤V out When the load changes, the inductor current is as follows: Figure 7 See Figure 6 and Figure 7 , it can be seen that when V in >V out When Q A1 With Q A2 The turn-off time is the same. When the load current decreases, it enters the fifth working condition from the fourth working condition. The fifth working condition has Q A3 , Q A4 With Q B2 The switching mode of simultaneous conduction is not present in the fourth operating condition; when V in ≤V out When the load current decreases, it enters the second working condition from the first working condition, and the second working condition has Q A1 With Q A2 One of them is on at a constant duty cycle, and the current at point B is constant at I zvs When the load current is further reduced, it enters the third working condition from the second working condition. The third working condition has Q A3 , Q A4 With Q B2 The switching mode is turned on at the same time, but not in the first and second working conditions. The current at point B is constant at I zvs .

[0056] See Figure 3The working conditions of the six-tube Buck-Boost converter are divided into five categories, and the working conditions are judged by the input voltage boundary value and the output current boundary value. The specific judgment method is as follows: When V in >V out When I out >I out1 The six-tube Buck-Boost converter is in the first operating state. If I out2 out ≤I out1 In the second working condition, if I out ≤I out2 In the third working condition; when V in ≤V out When I out >I out3 The six-tube Buck-Boost converter is in the fourth operating state. If I out ≤I out3 In the fifth working condition.

[0057] I out1 , I out2 and I out3 They are:

[0058]

[0059] Among them, I out1 is the first boundary current, I out2 is the second boundary current, I out3 is the third boundary current, k is the ratio of output voltage to input voltage, I ZVS is the zero voltage turn-on current, L is the inductance value, T s is the inductor current period.

[0060] In operation SA2, based on the operating conditions of the six-transistor Buck-Boost converter, with the goal of minimizing inductor current ripple and the soft switching of each switch as a constraint, calculate the proportion of each mode within an inductor current cycle.

[0061] Under the first working condition, the proportions of each mode in one inductor current cycle are:

[0062]

[0063] W1=-I zvs 2 L 2 +2I zvs LT s V in (k+1)+2I out LT s V in (k 2 ​+k+1)-T s 2 V in 2 k

[0064] Among them, D1, D2, D3, D4, and D5 are the proportions of the first mode, the second mode, the third mode, the fourth mode, and the fifth mode in one inductor current cycle, respectively, and W1 is the first intermediate parameter.

[0065] The first mode is V A =V in And V B = 0 mode, the second mode refers to V A =V in And V B =V out The third mode is V A =0.5V in And V B =V out The fourth mode is V A =0 and V B =V out The fifth mode is V A =0 and V B = 0 mode, V A is the output voltage of the three-level bridge arm, V B is the output voltage of the two-level bridge arm. The first mode, the second mode, the third mode, the fourth mode, and the fifth mode correspond to Figure 4 T1, T2, T3, T4, and T5.

[0066] Under the second working condition, the proportions of each mode in one inductor current cycle are:

[0067]

[0068] D5=0

[0069] W2=(-4I zvs 2 L 2 (k 2 +k)+LT s V in (I zvs (4k 2 -2)-2I out )-T s 2 V in 2 (k 2 -k)) (1 / 2)

[0070] Under the third working condition, the proportions of each mode in one inductor current cycle are:

[0071]

[0072] W3=(L 2 I zvs 2 +I out LT s V in (-4k 2 +6k-2)) (1 / 2)

[0073] Under the fourth working condition, the proportions of each mode in one inductor current cycle are:

[0074]

[0075]

[0076] D3=0

[0077]

[0078] D5=0

[0079] W4=(I zvs 2 L 2 -2I zvs LT s V in (k+1)-2I out LT s V in (k 2 +k+1)+T s 2 V in 2 k) (1 / 2)

[0080] Under the fifth working condition, the proportions of each mode in one inductor current cycle are:

[0081]

[0082] D3=0

[0083]

[0084] W5=(L 2 I zvs 2 -2I out T s LV in (1-k)) (1 / 2)

[0085] Among them, W2, W3, W4, and W5 are the second intermediate parameter, the third intermediate parameter, the fourth intermediate parameter, and the fifth intermediate parameter respectively.

[0086] Operate SA3, according to 0.5V in The difference between the voltage of the flying capacitor and the duty cycle is controlled by PI. The result of the PI control is limited to obtain the duty cycle compensation value △D, and the proportion of the third mode is compensated by △D.

[0087] Operation SA4 calculates Q based on the proportion of the first mode, the proportion of the second mode, and the proportion of the third mode after compensation. A1 The on-duty cycle D A1 and Q A2 The on-duty cycle D A2 .

[0088] In one embodiment of the present invention, the proportion of the third mode after compensation is:

[0089] D 3_1 =D3+△D

[0090] D A1 and D A2 They are:

[0091] D A1 =D1+D2

[0092] D A2 =D1+D2+D 3_1

[0093] In this embodiment, Q A4 Hysteresis Q A3 Activated.

[0094] In another embodiment of the present invention, the proportion of the third mode after compensation is:

[0095] D 3_1 =D3-△D

[0096] D A1 and D A2 They are:

[0097] D A1 =D1+D2+D 3_1

[0098] D A2 =D1+D2

[0099] In this embodiment, Q A4 Advance Q A3 Open. D 3_1is the proportion of the third mode after compensation, D3 is the proportion of the third mode before compensation, D2 is the proportion of the second mode, and D1 is the proportion of the first mode.

[0100] Operation SA5, calculate D A1 The corresponding first time period, and D A2 The corresponding second time period. Specifically, the first time period is equal to D A1 The product of the inductor current period, the second time period is equal to D A2 The product of the inductor current period.

[0101] According to an embodiment of the present invention, the method further includes: calculating Q B1 Duty cycle D B1 and conduction phase shift angle According to D B1 and Control Q B1 On-off, D B1 and They are:

[0102] D B1 =D2+D 3_1 +D4

[0103]

[0104] Among them, D1 is the proportion of the first mode, D2 is the proportion of the second mode, and D 3_1 is the proportion of the third mode after compensation, and D4 is the proportion of the fourth mode.

[0105] Preferably, in this embodiment, the control switch tube Q A1 , Q A2 , Q A3 , Q A4 , Q B1 and Q B2 In the switching process, a dead time is set. Specifically, the PWM duty cycle and phase shift angle of each switch tube are modulated, and the dead time is set to obtain the driving signal of each switch tube.

[0106] Under steady-state conditions, in two adjacent cycles, Q in the latter inductor current cycle is A1 , Q A4 Respectively with Q in the previous inductor current cycle A2 , Q A3 The driving signals are exactly the same; the Q A2 , Q A3 The drive signal is respectively the same as the Q in the previous inductor current cycle A1 , Q A4 The drive signals are exactly the same.

[0107] by Figure 1 、 Figure 2 The main parameters in the test example shown are set as follows to verify the effectiveness of this method: Rated capacity P N =6.6kW, switching frequency is 100kHz, minimum input DC voltage V inmin =500V, maximum input DC voltage V inmax =1500V, output voltage value V out =750V, flying capacitor value C fly =120μF, inductance value L = 75μH, output filter capacitor capacitance value C f =80μF, DC input capacitor value C in =200μF, output capacitance of the switching device C oss =200pF, zero voltage turn-on current I zvs =2A, dead time t dead =200ns.

[0108] Under the above parameter settings, the key waveforms of the six-tube Buck-Boost converter in the first, second, third, fourth and fifth working conditions are as follows: Figure 8 、 9 , 10, 11, 12. See Figures 8-12 It can be seen that the present method can effectively realize zero-voltage turn-on of all switching devices.

[0109] Under the above parameter settings, when the input voltage of the six-transistor Buck-Boost converter changes, the inductor current waveform and the flying capacitor voltage waveform are as follows: Figure 13 See Figure 13 It can be seen that this method can effectively achieve the capacitor voltage tracking 0.5 times the input voltage. Figures 8-13 , which verifies the effectiveness of this method.

[0110] The soft-switching control method for a six-transistor buck-boost converter provided by an embodiment of the present invention employs a switching sequence that enables soft switching of all switching devices over a wide input voltage and load range. The converter's operating condition is determined based on the output power reference value and input voltage obtained through a closed-loop output voltage control. The duty cycle of each operating mode in the soft-switching sequence is calculated based on the operating condition, input voltage, and output power. The flying capacitor's charge and discharge mode time is compensated using closed-loop control of the flying capacitor. The compensated switching mode time is used to calculate the switch duty cycle and phase shift angle, generating a carrier and modulation wave to produce a drive signal. This method achieves zero-voltage turn-on of all six-transistor buck-boost devices. Duty cycle control and phase shift control also reduce inductor current ripple, improving converter efficiency.

[0111] Example 2

[0112] A soft switching controller for a six-transistor Buck-Boost converter is used to implement the above-mentioned soft switching control method for a six-transistor Buck-Boost converter. The related technical solutions are the same as those in the first embodiment and will not be described in detail here.

[0113] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A soft switching control method for a six-transistor Buck-Boost converter, wherein the six-transistor Buck-Boost converter comprises a three-level bridge arm, a two-level bridge arm, an inductor, and a flying capacitor; the three-level bridge arm comprises a switching tube Q connected in sequence; A1 , Q A2 , Q A3 and Q A4 The two-level bridge arm includes the switch tubes Q connected in sequence B1 and Q B2 ; One end of the inductor is connected to Q A2 and Q A3 The other end is connected to Q B1 and Q B2 The connection point of the flying capacitor is Q A1 and Q A2 The other end is connected to Q A3 and Q A4 connection point; characterized in that, Methods include: Two inductor current cycles are considered as one switching cycle. In each switching cycle, Q A4 and Q A1 Complementary conduction, Q A3 and Q A2 Complementary conduction, Q B2 and Q B1 complementary conduction; In the first inductor current cycle of each switching cycle, the starting time Q A1 and Q A2 At the same time, Q A1 After the first period of conduction, it turns off, Q A2 After the second period of conduction, it is turned off and the starting time Q B1 Shutdown, at Q A3 and Q A4 Before turning on Q B1 , in Q A4 The absolute value of the source current is greater than the zero voltage turn-on current and turns off Q B1 ; During the second inductor current cycle of each switching cycle, Q A1 , Q A2 The driving signals correspond to the first inductor current cycle Q A2 , Q A1 The driving signal is the same, starting at Q B1 Shutdown, at Q A3 and Q A4 Before turning on Q B1 , in Q A4 The absolute value of the source current is greater than the zero voltage turn-on current and turns off Q B1 ; The first time period and the second time period are obtained by calculation with the goal of minimizing the pulsation of the inductor current and the soft switching of each switch tube as a constraint.

2. The soft switching control method for a six-transistor Buck-Boost converter according to claim 1, wherein: The calculation method of the first time period and the second time period specifically includes: SA1, based on the input voltage V in , output voltage V out and the output current reference value I out , judge its working condition; SA2, based on the operating conditions of the six-transistor Buck-Boost converter, with the goal of minimizing the inductor current ripple and the soft switching of each switch as a constraint, calculates the proportion of each mode within an inductor current cycle; SA3, based on 0.5V in The difference between the voltage of the flying capacitor and the duty cycle is controlled by PI. The result of the PI control is limited to obtain the duty cycle compensation value △D, which is used to compensate for the proportion of the third mode. SA4, calculate Q based on the proportion of the first mode, the proportion of the second mode, and the proportion of the third mode after compensation A1 The on-duty cycle D A1 and Q A2 The on-duty cycle D A2 , where the first mode refers to V A =V in And V B = 0 mode, the second mode refers to V A =V in And V B =V out The third mode is V A =0.5V in And V B =V out The mode, V A is the output voltage of the three-level bridge arm, V B is the output voltage of the two-level bridge arm; SA5, calculate D A1 The corresponding first time period, and D A2 The corresponding second time period.

3. The soft switching control method for a six-transistor Buck-Boost converter according to claim 2, wherein: The SA1 specifically includes: When V in >V out When I out >I out1 The six-tube Buck-Boost converter is in the first operating state. If I out2 out ≤I out1 In the second working condition, if I out ≤I out2 In the third working condition;​ When V in ≤V out When I out >I out3 The six-tube Buck-Boost converter is in the fourth operating state. If I out ≤I out3 In the fifth working condition; I out1 , I out2 and I out3 They are: Among them, I out1 is the first boundary current, I out2 is the second boundary current, I out3 is the third boundary current, k is the ratio of output voltage to input voltage, I ZVS is the zero voltage turn-on current, L is the inductance value, T s is the inductor current period.

4. The soft switching control method for a six-transistor Buck-Boost converter according to claim 2, wherein: The proportion of the third mode after compensation is: D 3_1 =D3+△D D A1 and D A2 They are: D A1 =D1+D2 D A2 =D1+D2+D 3_1 Among them, D 3_1 is the proportion of the third mode after compensation, D3 is the proportion of the third mode before compensation, D2 is the proportion of the second mode, and D1 is the proportion of the first mode.

5. The soft switching control method for a six-transistor Buck-Boost converter according to claim 2, wherein: The proportion of the third mode after compensation is: D 3_1 =D3-△D D A1 and D A2 They are: D A1 =D1+D2+D 3_1 D A2 =D1+D2 Among them, D 3_1 is the proportion of the third mode after compensation, D3 is the proportion of the third mode before compensation, D2 is the proportion of the second mode, and D1 is the proportion of the first mode.

6. The soft switching control method for a six-transistor Buck-Boost converter according to any one of claims 2 to 5, wherein: The method further includes: calculating Q B1 Duty cycle D B1 and conduction phase shift angle According to D B1 and Control Q B1 On / off, D B1 and They are: D B1 =D2+D 3_1 +D4 Among them, D1 is the proportion of the first mode, D2 is the proportion of the second mode, and D 3_1 is the proportion of the third mode after compensation, and D4 is the proportion of the fourth mode.

7. The soft switching control method for a six-transistor Buck-Boost converter according to claim 1, wherein: Control switch Q A1 , Q A2 , Q A3 , Q A4 , Q B1 and Q B2 During the on-off process, a dead time is set.

8. A soft-switching controller for a six-transistor Buck-Boost converter, characterized in that: Used to execute the soft switching control method for a six-transistor Buck-Boost converter as claimed in any one of claims 1 to 7.

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