A soft-switching four-transistor Cuk converter and its modulation method

Abstract

The present invention discloses a soft-switching four-tube Cuk converter, comprising a power supply V in , inductor L1, inductor L2, switch tube Q1 and its anti-parallel diode and junction capacitance, switch tube Q2 and its anti-parallel diode and junction capacitance, switch tube Q3 and its anti-parallel diode and junction capacitance, switch tube Q4 and its anti-parallel diode and junction capacitance, output capacitor C f and the intermediate capacitor C b The soft-switching four-tube Cuk converter includes 8 switching modes. By controlling the on and off of the switch tubes Q1, Q2, Q3, and Q4, the current i L1 Or the current i of inductor L2 L2 The control is a quadrilateral, sequentially charging and discharging the two junction capacitors in one of the switch arms. The four switches are sequentially turned on at zero voltage, and the inductor current ripple decreases as the load decreases. This invention can achieve ZVS for all switches across the entire range, significantly reducing switching losses.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic power converter topology, and in particular to a soft-switching four-tube Cuk converter and a modulation method thereof. Background Art

[0002] For applications with a wide input voltage range and an output voltage between these ranges, a buck-boost converter is required. The Cuk buck-boost converter is widely used due to its characteristics of opposite input and output voltage polarity, minimal input current ripple, and minimal current ripple before the filter capacitor. To increase the power density of the converter, it is often necessary to increase the switching frequency to reduce the size of passive components such as the filter inductor and filter capacitor. However, when the switching tube is a hard switch, its switching losses increase with increasing switching frequency, resulting in reduced converter efficiency. To reduce switching losses, it is necessary to implement soft switching of the switching tube.

[0003] Existing research proposes reducing the inductor current ripple to increase its current ripple, causing the inductor current to become overly negative, thereby achieving zero voltage switching (ZVS) of the switching tube. Due to the large inductor current ripple, when the load is reduced, the inductor current becomes more overly negative, resulting in low light-load efficiency of the converter.

[0004] Therefore, how to reduce the inductor current ripple while ensuring soft switching becomes a key issue to further improve the conversion efficiency, power density and reliability of the Cuk converter. Summary of the Invention

[0005] The purpose of the present invention is to propose a soft-switching four-tube Cuk converter and its modulation method, which can achieve soft switching of all switch tubes in the entire domain (the entire input voltage variation range and the entire load variation range) to greatly reduce switching losses and inductor current ripple, thereby significantly improving the conversion efficiency, power density and reliability of the Cuk converter.

[0006] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0007] A soft-switching four-tube Cuk converter, the soft-switching four-tube Cuk converter includes a power supply V in , inductor L1, inductor L2, switch tube Q1 and its anti-parallel diode and junction capacitance, switch tube Q2 and its anti-parallel diode and junction capacitance, switch tube Q3 and its anti-parallel diode and junction capacitance, switch tube Q4 and its anti-parallel diode and junction capacitance, output capacitor C f and the intermediate capacitor C b ;

[0008] The switch tubes Q1 and Q2 are complementary turned on to form a first switch bridge arm; the switch tubes Q3 and Q4 are complementary turned on to form a second switch bridge arm;

[0009] The power supply V in The positive electrode of the switch is connected to the drain of the switch tube Q3, the source of the switch tube Q3 is connected to the drain of the switch tube Q4 and one end of the inductor L1, and the other end of the inductor L1 is connected to the drain of the switch tube Q1 and the intermediate capacitor C b The anode of the middle capacitor C b The cathode of the switch tube Q2 is connected to the source and one end of the inductor L2, and the other end of the inductor L2 is connected to the output capacitor C f The cathode and load R Ld The negative terminal of the power supply V in The negative electrode of the switch tube Q4, the source of the switch tube Q1, the drain of the switch tube Q2, and the output capacitor C f The anode and load R Ld The positive end is connected;

[0010] The soft-switching four-tube Cuk converter includes 8 switching modes, which controls the on and off of the switch tubes Q1, Q2, Q3 and Q4 to change the current i of the inductor L1 to L1 The control is a quadrilateral, charging and discharging the two junction capacitors in one of the switch bridge arms in turn, turning on the four switch tubes in sequence with zero voltage, and the inductor current ripple decreases as the load decreases.

[0011] Furthermore, the soft-switching four-switch Cuk converter includes 8 switching modes: switching mode 1 in the period [t0, t1], switching mode 2 in the period [t1, t2], switching mode 3 in the period [t2, t3], switching mode 4 in the period [t3, t4], switching mode 5 in the period [t4, t5], switching mode 6 in the period [t5, t6], switching mode 7 in the period [t6, t7] and switching mode 8 in the period [t7, t8].

[0012] When in switching mode 1, the switch tube Q3 and the switch tube Q1 are turned on at the same time, and the voltage V AB V in , inductor current i L1 The voltage V applied across the inductor L2 rises linearly. CD V Cb -V o , inductor current i L2 linear rise;

[0013] When in switching mode 2, at time t1, the switch tube Q1 is turned off, and the inductor current i L1The junction capacitance C1 of the switch tube Q1 is charged, and the junction capacitance C2 of the switch tube Q2 is discharged at the same time. At time t2, the voltage of the junction capacitance C1 is charged to V Cb At the same time, the voltage of the junction capacitor C2 is reduced to zero, the anti-parallel diode D2 of the switch tube Q2 is naturally turned on, and the switch tube Q2 is turned on at zero voltage;

[0014] When in switching mode 3, the switch tube Q3 and the switch tube Q2 are turned on at the same time, and the voltage V AB V in -V Cb , inductor current i L1 The voltage V across the inductor L2 increases or decreases linearly. CD -V o , inductor current i L2 Linear decline;

[0015] When in switching mode 4, at time t3, the switch tube Q3 is turned off, and the inductor current i L1 The junction capacitance C3 of the switch tube Q3 is charged, and the junction capacitance C4 of the switch tube Q4 is discharged at the same time. At time t4, the voltage of the junction capacitance C3 is charged to V in At the same time, the voltage of the junction capacitor C4 is reduced to zero, the anti-parallel diode D4 of the switch tube Q4 is naturally turned on, and the switch tube Q4 is turned on at zero voltage;

[0016] When in switching mode 5, the switch tube Q4 and the switch tube Q2 are turned on at the same time, and the voltage V AB -V Cb , inductor current i L1 It decreases linearly and drops to a negative value before t5. The voltage V CD -V o , inductor current i L2 Continue to decline linearly;

[0017] When in switching mode 6, at time t5, the switch tube Q2 is turned off, and the inductor current i L1 The junction capacitance C2 of the switch tube Q2 is charged, and the junction capacitance C1 of the switch tube Q1 is discharged at the same time. At time t6, the voltage of the junction capacitance C2 is charged to V Cb At the same time, the voltage of the junction capacitor C1 is reduced to zero, the anti-parallel diode D1 of the switch tube Q1 is naturally turned on, and the switch tube Q1 is turned on at zero voltage;

[0018] When in switching mode 7, the switch tube Q4 and the switch tube Q1 are turned on at the same time, and the voltage V AB is 0, the inductor current i L1 The voltage V across the inductor L2 remains unchanged. CD V Cb-V o , inductor current i L2 linear increase;

[0019] When in switching mode 8, at time t7, the switch tube Q4 is turned off, and the inductor current i L1 The junction capacitance C4 of the switch tube Q4 is charged, and the junction capacitance C3 of the switch tube Q3 is discharged at the same time. At time t8, the voltage of the junction capacitance C4 is charged to V in At the same time, the voltage of the junction capacitor C3 is reduced to zero, the anti-parallel diode D3 of the switch tube Q3 is naturally turned on, and the switch tube Q3 is turned on at zero voltage.

[0020] Furthermore, the output voltage polarity is opposite to the input voltage, and the relationship between the intermediate capacitor voltage and the absolute value of the input and output voltages is:

[0021]

[0022]

[0023] Where D y1 is the duty cycle of the switch tube Q1, D y2 is the duty cycle of the switch tube Q4.

[0024] In a second aspect, the present invention further discloses a modulation method for a soft-switching four-transistor Cuk converter. Based on the soft-switching four-transistor Cuk converter proposed in the first aspect, the modulation method comprises the following steps:

[0025] A modulation cycle is divided into 8 time periods, namely, time period [t0, t1], time period [t1, t2], time period [t2, t3], time period [t3, t4], time period [t4, t5], time period [t5, t6], time period [t6, t7] and time period [t7, t8];

[0026] In the period [t0, t1], the switch tube Q3 and the switch tube Q1 are turned on at the same time, and the voltage V AB V in , inductor current i L1 The voltage V applied across the inductor L2 rises linearly. CD V Cb -V o , inductor current i L2 linear rise;

[0027] At time t1, the switch tube Q1 is turned off and the inductor current i L1 The junction capacitance C1 of the switch tube Q1 is charged, and the junction capacitance C2 of the switch tube Q2 is discharged at the same time. At time t2, the voltage of the junction capacitance C1 is charged to V CbAt the same time, the voltage of the junction capacitor C2 is reduced to zero, the anti-parallel diode D2 of the switch tube Q2 is naturally turned on, and the switch tube Q2 is turned on at zero voltage;

[0028] During the period [t2, t3], the switch tubes Q3 and Q2 are turned on at the same time, and the voltage V AB V in -V Cb , inductor current i L1 The voltage V across the inductor L2 increases or decreases linearly. CD -V o , inductor current i L2 Linear decline;

[0029] At t3, the switch tube Q3 is turned off, and the inductor current i L1 The junction capacitance C3 of the switch tube Q3 is charged, and the junction capacitance C4 of the switch tube Q4 is discharged at the same time. At time t4, the voltage of the junction capacitance C3 is charged to V in At the same time, the voltage of the junction capacitor C4 is reduced to zero, the anti-parallel diode D4 of the switch tube Q4 is naturally turned on, and the switch tube Q4 is turned on at zero voltage;

[0030] During the period [t4, t5], the switch tubes Q4 and Q2 are turned on at the same time, and the voltage V AB -V Cb , inductor current i L1 It decreases linearly and drops to a negative value before t5. The voltage V CD -V o , inductor current i L2 Continue to decline linearly;

[0031] At t5, the switch tube Q2 is turned off, and the inductor current i L1 The junction capacitance C2 of the switch tube Q2 is charged, and the junction capacitance C1 of the switch tube Q1 is discharged at the same time. At time t6, the voltage of the junction capacitance C2 is charged to V Cb At the same time, the voltage of the junction capacitor C1 is reduced to zero, the anti-parallel diode D1 of the switch tube Q1 is naturally turned on, and the switch tube Q1 is turned on at zero voltage;

[0032] During the period [t6, t7], the switch tubes Q4 and Q1 are turned on at the same time, and the voltage V AB is 0, the inductor current i L1 The voltage V across the inductor L2 remains unchanged. CD V Cb -V o , inductor current i L2 linear increase;

[0033] At t7, the switch tube Q4 is turned off, and the inductor current i L1 The junction capacitance C4 of the switch tube Q4 is charged, and the junction capacitance C3 of the switch tube Q3 is discharged at the same time. At time t8, the voltage of the junction capacitance C4 is charged to V in At the same time, the voltage of the junction capacitor C3 is reduced to zero, the anti-parallel diode D3 of the switch tube Q3 is naturally turned on, and the switch tube Q3 is turned on at zero voltage.

[0034] In a third aspect, the present invention discloses a soft-switching four-tube Cuk converter, wherein the soft-switching four-tube Cuk converter includes a power supply V in , inductor L1, inductor L2, switch tube Q1 and its anti-parallel diode and junction capacitance, switch tube Q2 and its anti-parallel diode and junction capacitance, switch tube Q3 and its anti-parallel diode and junction capacitance, switch tube Q4 and its anti-parallel diode and junction capacitance, output capacitor C f and the intermediate capacitor C b ;

[0035] The switch tubes Q1 and Q2 are complementary turned on to form a first switch bridge arm; the switch tubes Q3 and Q4 are complementary turned on to form a second switch bridge arm;

[0036] The power supply V in The positive electrode is connected to one end of the inductor L1, and the other end of the inductor L1 is connected to the drain of the switch tube Q1 and the intermediate capacitor C b The anode of the middle capacitor C b The cathode of the switch is connected to the source of the switch tube Q2 and one end of the inductor L2. The other end of the inductor L2 is connected to the source of the switch tube Q3 and the drain of the switch tube Q4. The source of the switch tube Q4 is connected to the output capacitor C f The cathode and load R Ld The negative terminal of the power supply V in The negative electrode of the switch tube Q1, the source of the switch tube Q2, the drain of the switch tube Q3, and the output capacitor C f The anode and load R Ld The positive end is connected;

[0037] The soft-switching four-tube Cuk converter includes 8 switching modes, which controls the on and off of the switch tubes Q1, Q2, Q3 and Q4 to change the current i of the inductor L2 to L2 The control is a quadrilateral, charging and discharging the two junction capacitors in one of the switch bridge arms in turn, turning on the four switch tubes in sequence with zero voltage, and the inductor current ripple decreases as the load decreases.

[0038] Furthermore, the soft-switching four-switch Cuk converter includes 8 switching modes: switching mode 1 in the period [t0, t1], switching mode 2 in the period [t1, t2], switching mode 3 in the period [t2, t3], switching mode 4 in the period [t3, t4], switching mode 5 in the period [t4, t5], switching mode 6 in the period [t5, t6], switching mode 7 in the period [t6, t7] and switching mode 8 in the period [t7, t8].

[0039] When in switching mode 1, the switch tube Q1 and the switch tube Q3 are turned on at the same time, and the voltage V AB V in , inductor current i L1 The voltage V applied across the inductor L2 rises linearly. CD V Cb , inductor current i L2 linearly increases; during this period, the load is composed of the output capacitor C f powered by;

[0040] When in switching mode 2, at time t1, the switch tube Q3 is turned off, and the inductor current i L2 The junction capacitance C3 of the switch tube Q3 is charged, and the junction capacitance C4 of the switch tube Q4 is discharged at the same time. At time t2, the voltage of the junction capacitance C3 is charged to V o At the same time, the voltage of the junction capacitor C4 is reduced to zero, the anti-parallel diode D4 of the switch tube Q4 is naturally turned on, and the switch tube Q4 is turned on at zero voltage;

[0041] When in switching mode 3, the switch tube Q1 and the switch tube Q4 are turned on at the same time, and the voltage V AB V in , inductor current i L1 Continue to rise linearly, the voltage V applied across the inductor L2 CD V Cb -V o , inductor current i L2 linear increase or decrease;

[0042] When in switching mode 4, at time t3, the switch tube Q1 is turned off, and the inductor current i L1 To charge the junction capacitance C1 of the switch tube Q1, the inductor current i L2 Discharge the junction capacitance C2 of the switch tube Q2; at time t4, the voltage of the junction capacitance C1 is charged to V Cb At the same time, the voltage of the junction capacitor C2 is reduced to zero, the anti-parallel diode D2 of the switch tube Q2 is naturally turned on, and the switch tube Q2 is turned on at zero voltage;

[0043] When in switching mode 5, the switch tubes Q2 and Q4 are turned on at the same time, and the voltage V AB V in -V Cb , inductor current i L1 Linearly decreases, the voltage V applied across the inductor L2 CD -V o , inductor current i L2 It decreases linearly and reaches a negative value before t5;

[0044] When in switching mode 6, at time t5, the inductor current i L2 The junction capacitance C4 of the switch tube Q4 is charged, and the junction capacitance C3 of the switch tube Q3 is discharged at the same time. At time t6, the voltage of the junction capacitance C4 is charged to V o At the same time, the voltage of the junction capacitor C3 is reduced to zero, the anti-parallel diode D3 of the switch tube Q3 is naturally turned on, and the switch tube Q3 is turned on at zero voltage;

[0045] When in switching mode 7, the switch tubes Q2 and Q3 are turned on at the same time, and the voltage V AB V in -V Cb , inductor current i L1 Linearly decreases, the voltage V applied across the inductor L2 CD is 0, the inductor current i L2 remains unchanged; during this period, the load is composed of the output capacitor C f powered by;

[0046] When in switching mode 8, at time t7, the switch tube Q2 is turned off; the inductor current i L2 The junction capacitance C2 of the switch tube Q2 is charged, and at the same time the inductor current i L1 Discharge the junction capacitance C1 of the switch tube Q1; at time t8, the voltage of the junction capacitance C2 is charged to V Cb At the same time, the voltage of the junction capacitor C1 is reduced to zero, the anti-parallel diode D1 of the switch tube Q1 is naturally turned on, and the switch tube Q1 is turned on at zero voltage.

[0047] Furthermore, the output voltage polarity is opposite to the input voltage, and the relationship between the intermediate capacitor voltage and the absolute value of the input and output voltages is:

[0048]

[0049]

[0050] Where D y1 is the duty cycle of the switch tube Q1, D y2 is the duty cycle of the switch tube Q4.

[0051] In a fourth aspect, the present invention further discloses a modulation method for a soft-switching four-transistor Cuk converter. Based on the soft-switching four-transistor Cuk converter topology of the third aspect, the modulation method comprises the following steps:

[0052] A modulation cycle is divided into 8 time periods, namely, time period [t0, t1], time period [t1, t2], time period [t2, t3], time period [t3, t4], time period [t4, t5], time period [t5, t6], time period [t6, t7] and time period [t7, t8];

[0053] In the period [t0, t1], the switch tube Q1 and the switch tube Q3 are turned on at the same time, and the voltage V AB V in , inductor current i L1 The voltage V applied across the inductor L2 rises linearly. CD V Cb , inductor current i L2 linearly increases; during this period, the load is composed of the output capacitor C f powered by;

[0054] At time t1, the switch tube Q3 is turned off, and the inductor current i L2 The junction capacitance C3 of the switch tube Q3 is charged, and the junction capacitance C4 of the switch tube Q4 is discharged at the same time. At time t2, the voltage of the junction capacitance C3 is charged to V o At the same time, the voltage of the junction capacitor C4 is reduced to zero, the anti-parallel diode D4 of the switch tube Q4 is naturally turned on, and the switch tube Q4 is turned on at zero voltage;

[0055] During the period [t2, t3], the switch tubes Q1 and Q4 are turned on at the same time, and the voltage V AB V in , inductor current i L1 Continue to rise linearly, the voltage V applied across the inductor L2 CD V Cb -V o , inductor current i L2 linear increase or decrease;

[0056] At t3, the switch tube Q1 is turned off and the inductor current i L1 To charge the junction capacitance C1 of the switch tube Q1, the inductor current i L2 Discharge the junction capacitance C2 of the switch tube Q2; at time t4, the voltage of the junction capacitance C1 is charged to V Cb At the same time, the voltage of the junction capacitor C2 is reduced to zero, the anti-parallel diode D2 of the switch tube Q2 is naturally turned on, and the switch tube Q2 is turned on at zero voltage;

[0057] During the period [t4, t5], the switch tubes Q2 and Q4 are turned on at the same time, and the voltage V AB V in -V Cb , inductor current i L1 Linearly decreases, the voltage V applied across the inductor L2 CD -V o , inductor current i L2 It decreases linearly and reaches a negative value before t5;

[0058] At t5, the inductor current i L2 The junction capacitance C4 of the switch tube Q4 is charged, and the junction capacitance C3 of the switch tube Q3 is discharged at the same time. At time t6, the voltage of the junction capacitance C4 is charged to V o At the same time, the voltage of the junction capacitor C3 is reduced to zero, the anti-parallel diode D3 of the switch tube Q3 is naturally turned on, and the switch tube Q3 is turned on at zero voltage;

[0059] During the period [t6, t7], the switch tubes Q2 and Q3 are turned on at the same time, and the voltage V AB V in -V Cb , inductor current i L1 Linearly decreases, the voltage V applied across the inductor L2 CD is 0, the inductor current i L2 remains unchanged; during this period, the load is composed of the output capacitor C f powered by;

[0060] At t7, the switch tube Q2 is turned off; the inductor current i L2 The junction capacitance C2 of the switch tube Q2 is charged, and at the same time the inductor current i L1 Discharge the junction capacitance C1 of the switch tube Q1; at time t8, the voltage of the junction capacitance C2 is charged to V Cb At the same time, the voltage of the junction capacitor C1 is reduced to zero, the anti-parallel diode D1 of the switch tube Q1 is naturally turned on, and the switch tube Q1 is turned on at zero voltage.

[0061] Compared with the prior art, the present invention has the following beneficial effects:

[0062] First, the soft-switching four-tube Cuk converter and its modulation method of the present invention retain the buck-boost function of the traditional converter without changing the polarity of the output voltage. At the same time, it can achieve ZVS of all switching tubes in the entire domain (the entire input voltage variation range and the entire load variation range), which can greatly reduce switching losses.

[0063] Second, the soft-switching four-transistor Cuk converter and its modulation method of the present invention control the current of inductor L1 or inductor L2 into a quadrilateral, and the inductor current ripple decreases as the load decreases, thereby ensuring the minimum effective value of the inductor current and improving light-load efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 Figure 2 is the circuit structure diagram of the soft-switching four-transistor Cuk converter, where (a) is the circuit structure diagram of the soft-switching four-transistor Cuk converter topology 1, and (b) is the circuit structure diagram of the soft-switching four-transistor Cuk converter topology 2.

[0065] Figure 2a The working waveform of the soft-switching four-transistor Cuk converter topology 1 (V in >V Cb ).

[0066] Figure 2b The working waveform of the soft-switching four-transistor Cuk converter topology 1 (V in <V Cb ).

[0067] Figure 3a This is the equivalent circuit diagram of the soft-switching four-tube Cuk converter topology in switching mode 1.

[0068] Figure 3b This is the equivalent circuit diagram of the soft-switching four-tube Cuk converter topology one switching mode 2.

[0069] Figure 3c This is the equivalent circuit diagram of the soft-switching four-tube Cuk converter topology in switching mode 3.

[0070] Figure 3d This is the equivalent circuit diagram of the soft-switching four-tube Cuk converter topology and switching mode 4.

[0071] Figure 3e This is the equivalent circuit diagram of the soft-switching four-tube Cuk converter topology one switching mode 5.

[0072] Figure 3f This is the equivalent circuit diagram of the soft-switching four-tube Cuk converter topology in switching mode 6.

[0073] Figure 3g This is the equivalent circuit diagram of the soft-switching four-tube Cuk converter topology in switching mode 7.

[0074] Figure 3h This is the equivalent circuit diagram of the soft-switching four-tube Cuk converter topology in switching mode 8.

[0075] Figure 4a The working waveform of the soft-switching four-transistor Cuk converter topology 2 (V in >VCb ).

[0076] Figure 4b The working waveform of the soft-switching four-transistor Cuk converter topology 2 (V in <V Cb ).

[0077] Figure 5a This is the equivalent circuit diagram of the soft-switching four-tube Cuk converter topology two switching mode 1.

[0078] Figure 5b This is the equivalent circuit diagram of the soft-switching four-tube Cuk converter topology two switching mode 2.

[0079] Figure 5c This is the equivalent circuit diagram of the soft-switching four-tube Cuk converter topology two switching mode 3.

[0080] Figure 5d This is the equivalent circuit diagram of the soft-switching four-tube Cuk converter topology two switching mode 4.

[0081] Figure 5e This is the equivalent circuit diagram of the soft-switching four-tube Cuk converter topology two switching mode 5.

[0082] Figure 5f This is the equivalent circuit diagram of the soft-switching four-tube Cuk converter topology two switching mode 6.

[0083] Figure 5g This is the equivalent circuit diagram of the soft-switching four-tube Cuk converter topology two switching mode 7.

[0084] Figure 5h This is the equivalent circuit diagram of the soft-switching four-tube Cuk converter topology two switching mode 8.

[0085] Figure 6 The simulation waveforms of the 500W soft-switching four-transistor Cuk converter topology 1 are given.

[0086] Figure 7 The simulation waveforms of the 500W soft-switching four-transistor Cuk converter topology 2 are given. DETAILED DESCRIPTION

[0087] The embodiments of the present invention are described in further detail below with reference to the accompanying drawings.

[0088] The embodiment of the present invention discloses a soft-switching four-tube Cuk converter, which includes a power supply V in , inductor L1, inductor L2, switch tube Q1 and its anti-parallel diode and junction capacitance, switch tube Q2 and its anti-parallel diode and junction capacitance, switch tube Q3 and its anti-parallel diode and junction capacitance, switch tube Q4 and its anti-parallel diode and junction capacitance, output capacitor C fand the intermediate capacitor C b The soft-switching four-tube Cuk converter of this embodiment has two topological structures. In both topological structures, the switch tubes Q1 and Q2 are complementary turned on to form the first switch bridge arm; the switch tubes Q3 and Q4 are complementary turned on to form the second switch bridge arm. The soft-switching four-tube Buck-Boost converter includes 8 switching modes. By controlling the on and off of the switch tubes Q1, Q2, Q3, and Q4, the current i L1 Or the current i of inductor L2 L2 The control is quadrilateral, sequentially charging and discharging the two junction capacitors in one of the switch arms. The four switches are sequentially turned on at zero voltage, and the inductor current ripple decreases as the load decreases. This enables the soft-switching four-switch Cuk converter to achieve soft switching of all switches across the entire input voltage and load ranges, significantly reducing switching losses and inductor current ripple. This invention significantly improves the conversion efficiency, power density, and reliability of the Cuk converter.

[0089] The two topological structures and corresponding modulation methods are described in detail below with reference to the accompanying drawings.

[0090] Figure 1 Part (a) is the circuit structure diagram of the soft-switching four-transistor Cuk converter topology 1. Figure 1 Part (b) is the circuit structure diagram of the soft-switching four-transistor Cuk converter topology 2. Each topology includes a power supply V in , inductor L1, inductor L2, switch tube Q1 and its anti-parallel diode and junction capacitance, switch tube Q2 and its anti-parallel diode and junction capacitance, switch tube Q3 and its anti-parallel diode and junction capacitance, switch tube Q4 and its anti-parallel diode and junction capacitance, output capacitor C f and the intermediate capacitor C b In the soft-switching four-tube Cuk converter, the switch tubes Q1 and Q2 are complementary turned on, and the switch tubes Q3 and Q4 are complementary turned on.

[0091] In topology 1, the power supply V in The positive electrode of the switch is connected to the drain of the switch tube Q3, the source of the switch tube Q3 is connected to the drain of the switch tube Q4 and one end of the inductor L1, and the other end of the inductor L1 is connected to the drain of the switch tube Q1 and the intermediate capacitor C b The anode of the middle capacitor C b The cathode of the switch tube Q2 is connected to the source and one end of the inductor L2, and the other end of the inductor L2 is connected to the output capacitor C f The cathode and load R Ld The negative terminal of the power supply V inThe negative electrode of the switch tube Q4, the source of the switch tube Q1, the drain of the switch tube Q2, and the output capacitor C f The anode and load R Ld The positive end is connected to .

[0092] In topology 2, the power supply V in The positive electrode is connected to one end of the inductor L1, and the other end of the inductor L1 is connected to the drain of the switch tube Q1 and the intermediate capacitor C b The anode of the middle capacitor C b The cathode of the switch is connected to the source of the switch tube Q2 and one end of the inductor L2. The other end of the inductor L2 is connected to the source of the switch tube Q3 and the drain of the switch tube Q4. The source of the switch tube Q4 is connected to the output capacitor C f The cathode and load R Ld The negative terminal of the power supply V in The negative electrode of the switch tube Q1, the source of the switch tube Q2, the drain of the switch tube Q3, and the output capacitor C f The anode and load R Ld The positive end is connected to .

[0093] The soft-switching four-tube Cuk converter topology disclosed in the present invention includes 8 switching modes. Figure 2a-2b This is the working waveform of the soft-switching four-transistor Cuk converter topology 1. Figures 3a-3h Figure 1 is the equivalent circuit diagram of the soft-switching four-transistor Cuk converter topology under different switching modes. The eight switching modes are:

[0094] like Figure 3a , Switching mode 1 [t0, t1]: Switch tube Q3 and switch tube Q1 are turned on at the same time, and the voltage V applied across the inductor L1 is AB V in , inductor current i L1 The voltage V applied across the inductor L2 rises linearly. CD V Cb -V o , inductor current i L2 Linear increase.

[0095] like Figure 3b , switching mode 2 [t1, t2]: At t1, the switch tube Q1 is turned off, and the inductor current i L1 The junction capacitance C1 of the switch tube Q1 is charged, and the junction capacitance C2 of the switch tube Q2 is discharged. Since the mode time is very short, i L1 Approximately constant. At t2, the voltage of the junction capacitor C1 is charged to V Cb At the same time, the voltage of the junction capacitor C2 is reduced to zero, and the anti-parallel diode D2 of the switch tube Q2 is naturally turned on. At this time, the zero voltage turns on the switch tube Q2.

[0096] like Figure 3c , Switching mode 3 [t2, t3]: In this mode, the switch tube Q3 and the switch tube Q2 are turned on at the same time, and the voltage V AB V in -V Cb , inductor current i L1 Linear increase (V in >V Cb ) or drop (V in <V Cb ), the voltage V applied across the inductor L2 CD -V o , inductor current i L2 Linear decrease.

[0097] like Figure 3d , switching mode 4 [t3, t4]: At t3, the switch tube Q3 is turned off, and the inductor current i L1 The junction capacitance C3 of the switch tube Q3 is charged, and the junction capacitance C4 of the switch tube Q4 is discharged. At time t4, the voltage of the junction capacitance C3 is charged to V in At the same time, the voltage of the junction capacitor C4 is reduced to zero, and the anti-parallel diode D4 of the switch tube Q4 is naturally turned on. At this time, the switch tube Q4 can be turned on at zero voltage.

[0098] like Figure 3e , Switching mode 5 [t4, t5]: In this mode, the switch tube Q4 and the switch tube Q2 are turned on at the same time, and the voltage V AB -V Cb , inductor current i L1 It decreases linearly and drops to a negative value before t5. The voltage V CD V o , inductor current i L2 Continue to decline linearly.

[0099] like Figure 3f , switching mode 6 [t5, t6]: At t5, the switch tube Q2 is turned off, and the inductor current i L1 The junction capacitance C2 of the switch tube Q2 is charged, and the junction capacitance C1 of the switch tube Q1 is discharged. At time t6, the voltage of the junction capacitance C2 is charged to V Cb At the same time, the voltage of the junction capacitor C1 is reduced to zero, and the anti-parallel diode D1 of the switch tube Q1 is naturally turned on. At this time, the switch tube Q1 can be turned on at zero voltage.

[0100] like Figure 3g , Switching mode 7 [t6, t7]: In this mode, the switch tube Q4 and the switch tube Q1 are turned on at the same time, and the voltage V AB is 0, the inductor current i L1The voltage V across the inductor L2 remains unchanged. CD V Cb -V o , inductor current i L2 Linear increase.

[0101] like Figure 3h , Switching mode 8 [t7, t8]: At t7, the switch tube Q4 is turned off. The inductor current i L1 The junction capacitance C4 of the switch tube Q4 is charged, and the junction capacitance C3 of the switch tube Q3 is discharged. At time t8, the voltage of the junction capacitance C4 is charged to V in At the same time, the voltage of the junction capacitor C3 is reduced to zero, and the anti-parallel diode D3 of the switch tube Q3 is naturally turned on. At this time, the switch tube Q3 can be turned on at zero voltage.

[0102] The present invention discloses a soft-switching four-transistor Cuk converter topology 2 including 8 switching modes. Figure 4a-4b This is the working waveform of the soft-switching four-transistor Cuk converter topology 2. Figures 5a-5h The equivalent circuit diagram of the soft-switching four-transistor Cuk converter topology 2 under different switching modes is shown in Figure 2. The eight switching modes are:

[0103] like Figure 5a , Switching mode 1 [t0, t1]: Switch tube Q1 and switch tube Q3 are turned on at the same time, and the voltage V applied across the inductor L1 is AB V in , inductor current i L1 The voltage V applied across the inductor L2 rises linearly. CD V Cb , inductor current i L2 During this period, the load is composed of the output capacitor C f powered by.

[0104] like Figure 5b , switching mode 2 [t1, t2]: At t1, the switch tube Q3 is turned off, and the inductor current i L2 The junction capacitance C3 of the switch tube Q3 is charged, and the junction capacitance C4 of the switch tube Q4 is discharged. Since the mode time is very short, i L2 Approximately constant. At t2, the voltage of the junction capacitor C3 is charged to V o At the same time, the voltage of the junction capacitor C4 is reduced to zero, and the anti-parallel diode D4 of the switch tube Q4 is naturally turned on. At this time, the zero voltage turns on the switch tube Q4.

[0105] like Figure 5c , Switching mode 3 [t2, t3]: In this mode, the switch tube Q1 and the switch tube Q4 are turned on at the same time, and the voltage V AB V in, inductor current i L1 Continue to rise linearly, the voltage V applied across the inductor L2 CD V Cb -V o , inductor current i L2 Linear increase (V Cb >V o ) or drop (V Cb <V o ).

[0106] like Figure 5d , switching mode 4 [t3, t4]: At t3, the switch tube Q1 is turned off, and the inductor current i L1 To charge the junction capacitance C1 of the switch tube Q1, the inductor current i L2 Discharge the junction capacitance C2 of the switch tube Q2. At time t4, the voltage of the junction capacitance C1 is charged to V Cb At the same time, the voltage of the junction capacitor C2 is reduced to zero, and the anti-parallel diode D2 of the switch tube Q2 is naturally turned on. At this time, the switch tube Q2 can be turned on at zero voltage.

[0107] like Figure 5e , Switching mode 5 [t4, t5]: In this mode, the switch tube Q2 and the switch tube Q4 are turned on at the same time, and the voltage V AB V in -V Cb , inductor current i L1 Linearly decreases, the voltage V applied across the inductor L2 CD -V o , inductor current i L2 It decreases linearly and reaches a negative value before time t5.

[0108] like Figure 5f , switching mode 6 [t5, t6]: At t5, the switch tube Q4 is turned off, and the inductor current i L2 The junction capacitance C4 of the switch tube Q4 is charged, and the junction capacitance C3 of the switch tube Q3 is discharged. At time t6, the voltage of the junction capacitance C4 is charged to V o At the same time, the voltage of the junction capacitor C3 is reduced to zero, and the anti-parallel diode D3 of the switch tube Q3 is naturally turned on. At this time, the switch tube Q3 can be turned on at zero voltage.

[0109] like Figure 5g , Switching mode 7 [t6, t7]: In this mode, the switch tube Q2 and the switch tube Q3 are turned on at the same time, and the voltage V AB V in -V Cb , inductor current i L1 Linearly decreases, the voltage V applied across the inductor L2 CDis 0, the inductor current i L2 During this period, the load is composed of the output capacitor C f powered by.

[0110] like Figure 5h , Switching mode 8 [t7, t8]: At t7, the switch tube Q2 is turned off. The inductor current i L2 The junction capacitance C2 of the switch tube Q2 is charged, and at the same time the inductor current i L1 Discharge the junction capacitance C1 of the switch tube Q1. At time t8, the voltage of the junction capacitance C2 is charged to V Cb At the same time, the voltage of the junction capacitor C1 is reduced to zero, and the anti-parallel diode D1 of the switch tube Q1 is naturally turned on. At this time, the switch tube Q1 can be turned on at zero voltage.

[0111] A soft-switching four-tube Cuk converter and its modulation strategy. In topology 1, the duty cycles of switch tube Q1 and switch tube Q4 are defined as D y1 and D y2 , then the average voltage at points A, B, C, and D is and They are:

[0112]

[0113]

[0114]

[0115]

[0116] Where V in is the input voltage, V o is the output voltage.

[0117] In steady-state operation, the average voltage across the inductor during each switching cycle is zero, so:

[0118]

[0119]

[0120] From the above six equations, we can get the relationship between the voltage of the intermediate capacitor and the absolute value of the input and output voltages in the soft-switching four-transistor Cuk converter topology, namely:

[0121]

[0122]

[0123] A modulation strategy for a soft-switching four-transistor Cuk converter. In topology 2, the duty cycles of switch Q1 and switch Q4 are defined as D and D respectively. y1 and D y2 , then the average voltage at points A, B, C, and D is and They are:

[0124]

[0125]

[0126]

[0127]

[0128] Where V in is the input voltage, V o is the output voltage.

[0129] In steady-state operation, the average voltage across the inductor during each switching cycle is zero, so:

[0130]

[0131]

[0132] From the above six equations, we can get the relationship between the intermediate capacitor voltage and the absolute value of the input and output voltages in the soft-switching four-transistor Cuk converter topology 2, namely:

[0133]

[0134]

[0135] In order to further illustrate the advantages of this topology and its modulation strategy, two simulation examples of the present invention are given below.

[0136] According to the main parameters of the 500W soft-switching four-transistor Cuk converter topology given in Table 1, a simulation circuit was built using Saber simulation software. Figure 6 The simulation waveform of 500W soft switching converter topology 1 is given. Figure 6 It can be seen that, taking the switch tube Q1 as an example, before the switch tube Q1 is turned on, the inductor current i L1 It has dropped to a negative value, which can realize the zero voltage turn-on of the switch tube Q1. Similarly, the ZVS of the switch tubes Q2, Q3 and Q4 can also be realized.

[0137] Table 1 Main parameters of soft-switching four-transistor Cuk converter topology 1

[0138] parameter symbol Numerical parameter symbol Numerical Input voltage <![CDATA[V in ]]> 160V Inductor 1 <![CDATA[L1]]> 8.5μH Output voltage <![CDATA[V o ]]> 120V Inductor 2 <![CDATA[L2]]> 20μH Switching frequency <![CDATA[f s ]]> 500kHz Intermediate capacitor <![CDATA[C b ]]> 60μF Output power <![CDATA[P o ]]> 500W Output capacitor <![CDATA[C f ]]> 30μF

[0139] According to the main parameters of the 500W soft-switching four-transistor Cuk converter topology 2 given in Table 2, a simulation circuit was built using Saber simulation software. Figure 7 The simulation waveform of the 500W soft switching converter topology 2 is given. Figure 7 It can be seen that, taking the switch tube Q3 as an example, before the switch tube Q3 is turned on, the inductor current i L2 It has dropped to a negative value, which can realize the zero voltage turn-on of the switch tube Q3. Similarly, the ZVS of the switch tubes Q1, Q2 and Q4 can also be realized.

[0140] Table 2 Main parameters of soft-switching four-transistor Cuk converter topology 2

[0141]

[0142]

[0143] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code. The scheme in the embodiment of the present application can be implemented in various computer languages, for example, object-oriented programming language Java and literal translation scripting language JavaScript, etc.

[0144] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0145] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0146] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions for executing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0147] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0148] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A soft-switching four-transistor Cuk converter, characterized in that: The soft-switching four-tube Cuk converter includes a power supply V in , inductor L1, inductor L2, switch tube Q1 and its anti-parallel diode and junction capacitance, switch tube Q2 and its anti-parallel diode and junction capacitance, switch tube Q3 and its anti-parallel diode and junction capacitance, switch tube Q4 and its anti-parallel diode and junction capacitance, output capacitor C f and the intermediate capacitor C b ; The switch tubes Q1 and Q2 are complementary turned on to form a first switch bridge arm; the switch tubes Q3 and Q4 are complementary turned on to form a second switch bridge arm; The power supply V in The positive electrode of the switch is connected to the drain of the switch tube Q3, the source of the switch tube Q3 is connected to the drain of the switch tube Q4 and one end of the inductor L1, and the other end of the inductor L1 is connected to the drain of the switch tube Q1 and the intermediate capacitor C b The anode of the middle capacitor C b The cathode of the switch tube Q2 is connected to the source and one end of the inductor L2, and the other end of the inductor L2 is connected to the output capacitor C f The cathode and load R Ld The negative terminal of the power supply V in The negative electrode of the switch tube Q4, the source of the switch tube Q1, the drain of the switch tube Q2, and the output capacitor C f The anode and load R Ld The positive end is connected; The soft-switching four-tube Cuk converter includes 8 switching modes, which controls the on and off of the switch tubes Q1, Q2, Q3 and Q4 to change the current i of the inductor L1 to L1 The control is a quadrilateral, charging and discharging the two junction capacitors in one of the switch bridge arms in turn, turning on the four switch tubes in sequence with zero voltage, and the inductor current ripple decreases as the load decreases.

2. The soft-switching four-transistor Cuk converter according to claim 1, characterized in that: The soft-switching four-transistor Cuk converter includes 8 switching modes: switching mode 1 in the period [t0, t1], switching mode 2 in the period [t1, t2], switching mode 3 in the period [t2, t3], switching mode 4 in the period [t3, t4], switching mode 5 in the period [t4, t5], switching mode 6 in the period [t5, t6], switching mode 7 in the period [t6, t7] and switching mode 8 in the period [t7, t8]. When in switching mode 1, the switch tube Q3 and the switch tube Q1 are turned on at the same time, and the voltage V AB V in , inductor current i L1 The voltage V applied across the inductor L2 rises linearly. CD V Cb -V o , inductor current i L2 linear rise; When in switching mode 2, at time t1, the switch tube Q1 is turned off, and the inductor current i L1 The junction capacitance C1 of the switch tube Q1 is charged, and the junction capacitance C2 of the switch tube Q2 is discharged at the same time. At time t2, the voltage of the junction capacitance C1 is charged to V Cb At the same time, the voltage of the junction capacitor C2 is reduced to zero, the anti-parallel diode D2 of the switch tube Q2 is naturally turned on, and the switch tube Q2 is turned on at zero voltage; When in switching mode 3, the switch tube Q3 and the switch tube Q2 are turned on at the same time, and the voltage V AB V in -V Cb , inductor current i L1 The voltage V across the inductor L2 increases or decreases linearly. CD -V o , inductor current i L2 Linear decline; When in switching mode 4, at time t3, the switch tube Q3 is turned off, and the inductor current i L1 The junction capacitance C3 of the switch tube Q3 is charged, and the junction capacitance C4 of the switch tube Q4 is discharged at the same time. At time t4, the voltage of the junction capacitance C3 is charged to V in At the same time, the voltage of the junction capacitor C4 is reduced to zero, the anti-parallel diode D4 of the switch tube Q4 is naturally turned on, and the switch tube Q4 is turned on at zero voltage; When in switching mode 5, the switch tube Q4 and the switch tube Q2 are turned on at the same time, and the voltage V AB -V Cb , inductor current i L1 It decreases linearly and drops to a negative value before t5. The voltage V CD -V o , inductor current i L2 Continue to decline linearly; When in switching mode 6, at time t5, the switch tube Q2 is turned off, and the inductor current i L1 The junction capacitance C2 of the switch tube Q2 is charged, and the junction capacitance C1 of the switch tube Q1 is discharged at the same time. At time t6, the voltage of the junction capacitance C2 is charged to V Cb At the same time, the voltage of the junction capacitor C1 is reduced to zero, the anti-parallel diode D1 of the switch tube Q1 is naturally turned on, and the switch tube Q1 is turned on at zero voltage; When in switching mode 7, the switch tube Q4 and the switch tube Q1 are turned on at the same time, and the voltage V AB is 0, the inductor current i L1 The voltage V across the inductor L2 remains unchanged. CD V Cb -V o , inductor current i L2 linear increase; When in switching mode 8, at time t7, the switch tube Q4 is turned off, and the inductor current i L1 The junction capacitance C4 of the switch tube Q4 is charged, and the junction capacitance C3 of the switch tube Q3 is discharged at the same time. At time t8, the voltage of the junction capacitance C4 is charged to V in At the same time, the voltage of the junction capacitor C3 is reduced to zero, the anti-parallel diode D3 of the switch tube Q3 is naturally turned on, and the switch tube Q3 is turned on at zero voltage.

3. The soft-switching four-transistor Cuk converter according to claim 1, characterized in that: The output voltage polarity is opposite to the input voltage, and the relationship between the intermediate capacitor voltage and the absolute value of the input and output voltages is: Where D y1 is the duty cycle of the switch tube Q1, D y2 is the duty cycle of the switch tube Q4.

4. A modulation method based on the soft-switching four-transistor Cuk converter according to any one of claims 1 to 3, characterized in that: The modulation method comprises the following steps: A modulation cycle is divided into 8 time periods, namely, time period [t0, t1], time period [t1, t2], time period [t2, t3], time period [t3, t4], time period [t4, t5], time period [t5, t6], time period [t6, t7] and time period [t7, t8]; In the period [t0, t1], the switch tube Q3 and the switch tube Q1 are turned on at the same time, and the voltage V AB V in , inductor current i L1 The voltage V applied across the inductor L2 rises linearly. CD V Cb -V o , inductor current i L2 linear rise; At time t1, the switch tube Q1 is turned off and the inductor current i L1 The junction capacitance C1 of the switch tube Q1 is charged, and the junction capacitance C2 of the switch tube Q2 is discharged at the same time. At time t2, the voltage of the junction capacitance C1 is charged to V Cb At the same time, the voltage of the junction capacitor C2 is reduced to zero, the anti-parallel diode D2 of the switch tube Q2 is naturally turned on, and the switch tube Q2 is turned on at zero voltage; During the period [t2, t3], the switch tubes Q3 and Q2 are turned on at the same time, and the voltage V AB V in -V Cb , inductor current i L1 The voltage V across the inductor L2 increases or decreases linearly. CD -V o , inductor current i L2 Linear decline; At t3, the switch tube Q3 is turned off, and the inductor current i L1 The junction capacitance C3 of the switch tube Q3 is charged, and the junction capacitance C4 of the switch tube Q4 is discharged at the same time. At time t4, the voltage of the junction capacitance C3 is charged to V in At the same time, the voltage of the junction capacitor C4 is reduced to zero, the anti-parallel diode D4 of the switch tube Q4 is naturally turned on, and the switch tube Q4 is turned on at zero voltage; During the period [t4, t5], the switch tubes Q4 and Q2 are turned on at the same time, and the voltage V AB -V Cb , inductor current i L1 It decreases linearly and drops to a negative value before t5. The voltage V CD -V o , inductor current i L2 Continue to decline linearly; At t5, the switch tube Q2 is turned off, and the inductor current i L1 The junction capacitance C2 of the switch tube Q2 is charged, and the junction capacitance C1 of the switch tube Q1 is discharged at the same time. At time t6, the voltage of the junction capacitance C2 is charged to V Cb At the same time, the voltage of the junction capacitor C1 is reduced to zero, the anti-parallel diode D1 of the switch tube Q1 is naturally turned on, and the switch tube Q1 is turned on at zero voltage; During the period [t6, t7], the switch tubes Q4 and Q1 are turned on at the same time, and the voltage V AB is 0, the inductor current i L1 The voltage V across the inductor L2 remains unchanged. CD V Cb -V o , inductor current i L2 linear increase; At t7, the switch tube Q4 is turned off, and the inductor current i L1 The junction capacitance C4 of the switch tube Q4 is charged, and the junction capacitance C3 of the switch tube Q3 is discharged at the same time. At time t8, the voltage of the junction capacitance C4 is charged to V in At the same time, the voltage of the junction capacitor C3 is reduced to zero, the anti-parallel diode D3 of the switch tube Q3 is naturally turned on, and the switch tube Q3 is turned on at zero voltage.

5. A soft-switching four-transistor Cuk converter, characterized in that: The soft-switching four-tube Cuk converter includes a power supply V in , inductor L1, inductor L2, switch tube Q1 and its anti-parallel diode and junction capacitance, switch tube Q2 and its anti-parallel diode and junction capacitance, switch tube Q3 and its anti-parallel diode and junction capacitance, switch tube Q4 and its anti-parallel diode and junction capacitance, output capacitor C f and the intermediate capacitor C b ; The switch tubes Q1 and Q2 are complementary turned on to form a first switch bridge arm; the switch tubes Q3 and Q4 are complementary turned on to form a second switch bridge arm; The power supply V in The positive electrode is connected to one end of the inductor L1, and the other end of the inductor L1 is connected to the drain of the switch tube Q1 and the intermediate capacitor C b The anode of the middle capacitor C b The cathode of the switch is connected to the source of the switch tube Q2 and one end of the inductor L2. The other end of the inductor L2 is connected to the source of the switch tube Q3 and the drain of the switch tube Q4. The source of the switch tube Q4 is connected to the output capacitor C f The cathode and load R Ld The negative terminal of the power supply V in The negative electrode of the switch tube Q1, the source of the switch tube Q2, the drain of the switch tube Q3, and the output capacitor C f The anode and load R Ld The positive end is connected; The soft-switching four-tube Cuk converter includes 8 switching modes, which controls the on and off of the switch tubes Q1, Q2, Q3 and Q4 to change the current i of the inductor L2 to L2 The control is a quadrilateral, charging and discharging the two junction capacitors in one of the switch bridge arms in turn, turning on the four switch tubes in sequence with zero voltage, and the inductor current ripple decreases as the load decreases.

6. The soft-switching four-transistor Cuk converter according to claim 5, characterized in that: The soft-switching four-transistor Cuk converter includes 8 switching modes: switching mode 1 in the period [t0, t1], switching mode 2 in the period [t1, t2], switching mode 3 in the period [t2, t3], switching mode 4 in the period [t3, t4], switching mode 5 in the period [t4, t5], switching mode 6 in the period [t5, t6], switching mode 7 in the period [t6, t7] and switching mode 8 in the period [t7, t8]. When in switching mode 1, the switch tube Q1 and the switch tube Q3 are turned on at the same time, and the voltage V AB V in , inductor current i L1 The voltage V applied across the inductor L2 rises linearly. CD V Cb , inductor current i L2 linearly increases; during this period, the load is composed of the output capacitor C f powered by; When in switching mode 2, at time t1, the switch tube Q3 is turned off, and the inductor current i L2 The junction capacitance C3 of the switch tube Q3 is charged, and the junction capacitance C4 of the switch tube Q4 is discharged at the same time. At time t2, the voltage of the junction capacitance C3 is charged to V o At the same time, the voltage of the junction capacitor C4 is reduced to zero, the anti-parallel diode D4 of the switch tube Q4 is naturally turned on, and the switch tube Q4 is turned on at zero voltage; When in switching mode 3, the switch tube Q1 and the switch tube Q4 are turned on at the same time, and the voltage V AB V in , inductor current i L1 Continue to rise linearly, the voltage V applied across the inductor L2 CD V Cb -V o , inductor current i L2 linear increase or decrease; When in switching mode 4, at time t3, the switch tube Q1 is turned off, and the inductor current i L1 To charge the junction capacitance C1 of the switch tube Q1, the inductor current i L2 Discharge the junction capacitance C2 of the switch tube Q2; at time t4, the voltage of the junction capacitance C1 is charged to V Cb At the same time, the voltage of the junction capacitor C2 is reduced to zero, the anti-parallel diode D2 of the switch tube Q2 is naturally turned on, and the switch tube Q2 is turned on at zero voltage; When in switching mode 5, the switch tubes Q2 and Q4 are turned on at the same time, and the voltage V AB V in -V Cb , inductor current i L1 Linearly decreases, the voltage V applied across the inductor L2 CD -V o , inductor current i L2 It decreases linearly and reaches a negative value before t5; When in switching mode 6, at time t5, the inductor current i L2 The junction capacitance C4 of the switch tube Q4 is charged, and the junction capacitance C3 of the switch tube Q3 is discharged at the same time. At time t6, the voltage of the junction capacitance C4 is charged to V o At the same time, the voltage of the junction capacitor C3 is reduced to zero, the anti-parallel diode D3 of the switch tube Q3 is naturally turned on, and the switch tube Q3 is turned on at zero voltage; When in switching mode 7, the switch tubes Q2 and Q3 are turned on at the same time, and the voltage V AB V in -V Cb , inductor current i L1 Linearly decreases, the voltage V applied across the inductor L2 CD is 0, the inductor current i L2 remains unchanged; during this period, the load is composed of the output capacitor C f powered by; When in switching mode 8, at time t7, the switch tube Q2 is turned off; the inductor current i L2 The junction capacitance C2 of the switch tube Q2 is charged, and at the same time the inductor current i L1 Discharge the junction capacitance C1 of the switch tube Q1; at time t8, the voltage of the junction capacitance C2 is charged to V Cb At the same time, the voltage of the junction capacitor C1 is reduced to zero, the anti-parallel diode D1 of the switch tube Q1 is naturally turned on, and the switch tube Q1 is turned on at zero voltage.

7. The soft-switching four-transistor Cuk converter according to claim 5, characterized in that: The output voltage polarity is opposite to the input voltage, and the relationship between the intermediate capacitor voltage and the absolute value of the input and output voltages is: Where D y1 is the duty cycle of the switch tube Q1, D y2 is the duty cycle of the switch tube Q4.

8. A modulation method based on the soft-switching four-transistor Cuk converter according to any one of claims 5 to 7, characterized in that: The modulation method comprises the following steps: A modulation cycle is divided into 8 time periods, namely, time period [t0, t1], time period [t1, t2], time period [t2, t3], time period [t3, t4], time period [t4, t5], time period [t5, t6], time period [t6, t7] and time period [t7, t8]; In the period [t0, t1], the switch tube Q1 and the switch tube Q3 are turned on at the same time, and the voltage V AB V in , inductor current i L1 The voltage V applied across the inductor L2 rises linearly. CD V Cb , inductor current i L2 linearly increases; during this period, the load is composed of the output capacitor C f powered by; At time t1, the switch tube Q3 is turned off, and the inductor current i L2 The junction capacitance C3 of the switch tube Q3 is charged, and the junction capacitance C4 of the switch tube Q4 is discharged at the same time. At time t2, the voltage of the junction capacitance C3 is charged to V o At the same time, the voltage of the junction capacitor C4 is reduced to zero, the anti-parallel diode D4 of the switch tube Q4 is naturally turned on, and the switch tube Q4 is turned on at zero voltage; During the period [t2, t3], the switch tubes Q1 and Q4 are turned on at the same time, and the voltage V AB V in , inductor current i L1 Continue to rise linearly, the voltage V applied across the inductor L2 CD V Cb -V o , inductor current i L2 linear increase or decrease; At t3, the switch tube Q1 is turned off and the inductor current i L1 To charge the junction capacitance C1 of the switch tube Q1, the inductor current i L2 Discharge the junction capacitance C2 of the switch tube Q2; at time t4, the voltage of the junction capacitance C1 is charged to V Cb At the same time, the voltage of the junction capacitor C2 is reduced to zero, the anti-parallel diode D2 of the switch tube Q2 is naturally turned on, and the switch tube Q2 is turned on at zero voltage; During the period [t4, t5], the switch tubes Q2 and Q4 are turned on at the same time, and the voltage V AB V in -V Cb , inductor current i L1 Linearly decreases, the voltage V applied across the inductor L2 CD -V o , inductor current i L2 It decreases linearly and reaches a negative value before t5; At t5, the inductor current i L2 The junction capacitance C4 of the switch tube Q4 is charged, and the junction capacitance C3 of the switch tube Q3 is discharged at the same time. At time t6, the voltage of the junction capacitance C4 is charged to V o At the same time, the voltage of the junction capacitor C3 is reduced to zero, the anti-parallel diode D3 of the switch tube Q3 is naturally turned on, and the switch tube Q3 is turned on at zero voltage; During the period [t6, t7], the switch tubes Q2 and Q3 are turned on at the same time, and the voltage V AB V in -V Cb , inductor current i L1 Linearly decreases, the voltage V applied across the inductor L2 CD is 0, the inductor current i L2 remains unchanged; during this period, the load is composed of the output capacitor C f powered by; At t7, the switch tube Q2 is turned off; the inductor current i L2 The junction capacitance C2 of the switch tube Q2 is charged, and at the same time the inductor current i L1 Discharge the junction capacitance C1 of the switch tube Q1; at time t8, the voltage of the junction capacitance C2 is charged to V Cb At the same time, the voltage of the junction capacitor C1 is reduced to zero, the anti-parallel diode D1 of the switch tube Q1 is naturally turned on, and the switch tube Q1 is turned on at zero voltage.

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