Isolated ZVS Buck-Boost converter and control method and control circuit thereof

Abstract

The invention discloses an isolated ZVS Buck-Boost converter and a control method and a control circuit thereof. The primary side of the converter comprises a switching tube Q1, a switching tube Q3, a switching tube Q2, a switching tube Q4 and a transformer with leakage inductance; and the secondary side comprises synchronous rectifier tubes SR1, SR2, SR3 and SR4, a connecting inductor Lc and switch tubes Qb1 and Qb2. A synchronous rectifier tube is controlled to perform rectification regulation and control on a primary side current waveform, so that a primary side switching tube does not depend on energy stored by leakage inductance to realize ZVS in a full input, full output and full load range of the primary side switching tube any more, and meanwhile, an effective value of a primary side leakage inductance current is minimum; a secondary side switch tube adopts a PWM and phase shift control mode, the secondary side switch tube realizes ZVS in a full-input, full-output and full-load range by regulating and controlling the voltage at the two ends of a connecting inductor, and meanwhile, the effective value of secondary side inductor current is minimized. According to the invention, the converter can realize ZVS of a switching tube in a full-input, full-output and full-load range, the switching frequency and the power density are improved, the current effective value is reduced, and the converter has voltage regulation capability.

Description

Technical Field

[0001] The present invention belongs to the technical field of power converter control, and in particular relates to an isolated ZVS Buck-Boost converter and a control method and a control circuit thereof. Background Art

[0002] In recent years, with the continuous development of new energy technologies, traditional fossil energy is gradually being replaced, and the proportion of electric vehicles is also increasing. In order to meet user needs, the charging speed and charging power are constantly improving. In order to reduce losses, the bus voltage is constantly increasing, and the voltage platform of 400V and 800V has been achieved. The on-board charging power supply usually consists of an AC-DC converter plus a DC-DC converter. In order to ensure safety, the DC-DC converter usually uses an isolated converter. In order to reduce the size of the on-board charger and reduce charging losses, the on-board charger must have the characteristics of high power density and high efficiency.

[0003] At present, the DC-DC converter in the on-board charger usually adopts the topology of CLLC or DAB. For CLLC, it can achieve ZVS of the switch tube when working in DCX, and obtain higher conversion efficiency, but it does not have the ability to adjust the output voltage. If you want to adjust the output voltage, you need to change the switching frequency, which is not conducive to EMI design. For DAB, it cannot achieve ZVS of the switch tube when lightly loaded, which is not only not conducive to improving efficiency, but also not conducive to improving switching frequency and power density. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an isolated ZVS Buck-Boost converter and a control method and a control circuit thereof in view of the deficiencies of the above-mentioned prior art. The converter can achieve ZVS of the switching tube within the full input, full output and full load range, improve the switching frequency and power density, reduce the effective value of the current, and have the ability to regulate voltage.

[0005] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0006] An isolated ZVS Buck-Boost converter, wherein the primary side of the converter includes switch tubes Q1 and Q3, Q2 and Q4 and a transformer with leakage inductance, the transformer is respectively connected to the midpoint of the bridge arm of Q1 and Q3 and the midpoint of the bridge arm of Q2 and Q4, Q1 and Q3, Q2 and Q4 are all 180° complementary conduction; the primary side adopts phase shift control;

[0007] The secondary side of the converter is connected through a synchronous rectifier S R1 ,S R2 ,S R3 With S R4Rectification is performed to obtain a square wave voltage; the output of the synchronous rectifier is connected to the inductor L c One end, L c The other end is connected to the switch tube Q b1 With Q b2 The midpoint of the bridge arm, bridge arm Q b1 With Q b2 Connect output side; S R1 With S R4 Same opening and closing, S R3 With S R4 Same opening and closing, Q b1 With Q b2 Complementary conduction.

[0008] The control method of the isolated ZVS Buck-Boost converter controls the rectification and regulation of the primary current waveform by controlling the synchronous rectifier tube, so that the primary switch tube no longer relies on the energy stored in the leakage inductance to achieve ZVS within the full input, full output and full load range of the primary switch tube, and at the same time minimize the effective value of the primary leakage inductance current; the secondary switch tube adopts PWM plus phase shift control, and by regulating the size of the voltage across the connected inductor, the secondary switch tube achieves ZVS within the full input, full output and full load range, and at the same time minimizes the effective value of the secondary inductor current.

[0009] A control circuit for an isolated ZVS Buck-Boost converter, the control circuit comprising:

[0010] A primary side phase shift signal and drive signal generating module A, used to generate a phase shift signal between the primary sides Q1 and Q4 of the converter and drive signals for Q1, Q2, Q3 and Q4;

[0011] The driving signal generating module B is used to generate the secondary rectifier tube S R1 , S R2 , S R3 and S R4 The driving signal of

[0012] The drive signal generation module C is used to generate the secondary side switch tube Q b1 and Q b2 The driving signal of

[0013] Phase shift duty cycle circuit generation module D is used to generate switch tubes Q4 and Q b1 The phase difference between the turn-on times generates the phase-shifted duty cycle.

[0014] The primary side phase shift signal and driving signal generating module A comprises a voltage regulator, a comparator 1, an RS trigger 1 and a D trigger 1; wherein the input of the voltage regulator is the sampled value of the output voltage, the reference is the sampled value corresponding to the set output voltage, and the output of the voltage regulator is v vrAfter passing through comparator 1 with the sawtooth wave, a square wave signal is obtained, and after being combined with the clock signal CLK1 and passing through RS trigger 1 and D trigger 1 respectively, a phase shift signal between Q1 and Q4 is obtained, and the switch tubes Q1 and Q3, Q2 and Q4 are all 180° complementary turned on, thereby obtaining the driving signals of Q1 and Q3, Q2 and Q4, wherein the sawtooth wave is synchronized with the clock signal CLK1.

[0015] The driving signal generating module B determines the four rectifier tubes S on the secondary side under different working conditions through the calculation circuit 1, the comparator 2 and the D trigger 2. R1 , S R2 , S R3 and S R4 At the same time, the primary current is maintained at the minimum current I that can achieve ZVS. ZVS , reducing the effective value of the primary current; wherein the calculation circuit 1 calculates the formula (v ins v vr / v os )+v sita -2L c I ZVS / v os T s Get the output v SR , and sawtooth wave v saw The square wave signal is sent to comparator 2 to obtain the square wave signal. The narrow pulse corresponding to the falling moment of the square wave signal is input to D flip-flop 2. The output of D flip-flop 2 is logically ORed with the duty cycle of Q2 and Q4 respectively, so as to obtain the driving signal D of the secondary synchronous rectifier. s23 and D s14 , so that in S R1 and S R4 When the primary current drops to I ZVS When S R2 and S R3 , and turns off S when Q4 turns off R1 and S R4 ; Similarly, when S R2 and S R3 When the primary current rises to -I ZVS When S R1 and S R4 , and turns off S when Q2 turns off R2 and S R3

[0016] where v ins 、v os is the sampling value of input voltage and output voltage, v sita is the calculated value of phase shift duty cycle, L c is the inductance value, T s is the cycle size.

[0017] The driving signal generating module C generates the secondary switch tube Q through the comparator 3 and the RS trigger 2. b1 and Q b2 The input of comparator 3 is the secondary inductor current I LC and the minimum current I required to achieve soft switching ZVS , its output v comp The output of the OR gate with the CLK1 signal and the clock signal CLK2 are input into RS trigger 2; the secondary inductor current I LC The current I drops to the minimum level that can achieve soft switching. ZVS When comparator 3 outputs v comp The high potential resets RS flip-flop 2, Q b1 Set low to immediately shut down Q b1 , open Q b2 , to reduce current ripple.

[0018] The above-mentioned phase shift duty cycle circuit generation module D includes a calculation circuit 2 and a comparator 4, wherein the calculation circuit 2 generates the switch tubes Q4 and Q5 according to the principle of the minimum effective value of the secondary side inductor current. b1 The phase difference between the opening moments, specifically, the calculation circuit 2 uses the calculation formula av ins +bi os +c to get the calculated value of phase shift duty cycle v sita , and sawtooth wave v saw are sent to comparator 4 to obtain square wave signal Q θs , with Q θs The narrow pulse corresponding to the falling moment is used as the clock signal CLK2, which is input into the drive signal generating module C and used as Q b1 The opening signal;

[0019] Where a, b, c are coefficients, v ins 、i os It is the sampling value of input current and output current.

[0020] The present invention has the following beneficial effects:

[0021] The present invention fully considers the development needs of on-board chargers, which require high-efficiency and high-power-density on-board chargers, and proposes an isolated ZVS Buck-Boost converter and its control method and control circuit. The converter can minimize the effective value of the current on the basis of achieving ZVS of the switch tube within the full input, full output, and full load range, and can also adjust the output voltage when working at a fixed frequency. This can not only improve the working efficiency of the converter, but also increase its switching frequency, thereby increasing the power density of the converter.

[0022] The present invention makes the primary switch tube no longer rely on the energy stored in the leakage inductance to realize the soft switching of the switch tube, and reduces the effective value of the primary current on the basis of realizing the soft switching of the switch tube in the full input and full load range. At the same time, the secondary side adopts PWM plus phase shift control mode, and by adjusting the voltage across the inductor, the secondary side switch tube can also realize ZVS in the full load and full voltage change range, while minimizing the effective value of the secondary side inductor current. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the circuit structure diagram of the isolated ZVS Buck-Boost converter.

[0024] Figure 2 It is the main working waveform of the isolated ZVS Buck-Boost converter.

[0025] Figure 3a This is the circuit diagram of the primary side switch tube drive signal generating module.

[0026] Figure 3b This is the circuit diagram of the secondary side rectifier tube drive signal generating module.

[0027] Figure 3c This is the circuit diagram of the secondary side switch tube drive signal generating module.

[0028] Figure 3d For Q4 and Q b2 Circuit diagram of the phase difference generating module.

[0029] Figure 4a This is the simulation waveform diagram of the converter output voltage of 500V.

[0030] Figure 4b This is the simulation waveform diagram of the converter output voltage of 700V.

[0031] Figure 4c This is the simulation waveform diagram of the converter output voltage of 900V.

[0032] Figure 5 This is a load jump dynamic waveform diagram (output 700V, jump from 10% load to full load). DETAILED DESCRIPTION

[0033] The embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0034] An isolated ZVS Buck-Boost converter of the present invention has a circuit structure as shown in Figure 1 As shown, it mainly consists of six switch tubes Q1, Q2, Q3, Q4, Q b1 , Q b2 , four synchronous rectifier tubes S R1, S R2 , S R3 , S R4 , a transformer (including leakage inductance) and a filter inductor L c .

[0035] The primary side of the converter consists of four switching tubes and a transformer. The transformer (with leakage inductance L k ) are connected to the midpoints of the bridge arms of the switch tubes Q1 and Q3 and the midpoints of the bridge arms of Q2 and Q4 respectively, and Q1 and Q3, Q2 and Q4 are all 180° complementary conduction. The primary side adopts phase shift control.

[0036] The secondary side is connected through four synchronous rectifiers S R1 ,S R2 ,S R3 With S R4 Rectification is performed to obtain a square wave voltage. Filter inductor L c The two ends are connected to the output of the rectifier tube and the switch tube Q b1 , Q b2 The output side is connected to the bridge arm Q b1 With Q b2 . Rectifier tube S R1 With S R4 Same opening and closing, S R3 With S R4 The same opening and closing, the switch tube Q b1 With Q b2 Complementary conduction. The use of synchronous rectifiers can not only achieve bidirectional current flow, but also reduce conduction losses.

[0037] The input voltage is V in , the output voltage is V o , the output current is I o , the input voltage is sampled as v ins , the output voltage is sampled as v os , the output current sampling is i os .

[0038] In this topology, in order to make the primary switch tube no longer rely on the energy stored in the leakage inductance to achieve soft switching of the switch tube, a control method is proposed to adjust the primary current waveform by controlling the rectifier tube, so that the primary switch tube no longer relies on the energy stored in the leakage inductance to achieve zero voltage switching (zero voltage switching, ZVS) of the switch tube. On the basis of achieving soft switching of the switch tube in the full input and full load range, the effective value of the primary current is reduced. At the same time, the secondary switch tube Q b1 With Q b2By adopting PWM plus phase shift control method, the voltage across the inductor is adjusted to enable the secondary switch tube to achieve ZVS within the full load and full voltage range, while minimizing the effective value of the secondary inductor current.

[0039] After adopting this control method, the primary switch tube of the converter no longer relies on the energy stored in the leakage inductance to achieve ZVS. Based on the experimental ZVS of the primary and secondary switch tubes in the full input, full output, and full load range, the effective values ​​of the primary leakage inductance current and the secondary inductance current can also be minimized.

[0040] Since the primary side Q1 and Q3, Q2 and Q4 of the isolated Buck-Boost converter are all 180° complementary conduction, there is only one control variable on the primary side, that is, the phase difference between Q1 and Q4. R1 and S R4 Same opening and closing, S R2 and S R3 The secondary switch tube also has two control quantities, namely Q4 and Q b1 The phase difference between the opening times and Q b2 The duty cycle of the primary phase shift is D θp , rectifier tube S R1 and S R4 The duty cycle is D s14 , rectifier tube S R2 and S R3 The duty cycle is D s23 , Q4 and Q b1 The phase difference between the opening times is D θs , switch tube Q b2 The duty cycle is D y2 By properly controlling these degrees of freedom, it is possible to achieve output voltage regulation, ZVS of all switches on the primary and secondary sides within the full input, full output, and full load range, and minimize the effective value of the primary leakage inductance current and the secondary inductance current.

[0041] In order to realize the soft switching of the switch tube, it is necessary to ensure that the current discharges the junction capacitance of the switch tube to zero before the switch tube is turned on so that its reverse parallel diode is naturally turned on. b2 Before turning on, the current should be negative. When the switch tubes Q2, Q3, Q b1 The inductor current should be positive. Before the rectifier is turned on, the voltage across it is 0 to ensure the realization of ZVS.

[0042] Figure 2 This is the main working waveform of the isolated ZVS Buck-Boost. According to the proposed control method, the primary switch tube is 180° complementary conduction, and the secondary switch tube Q b1 and Qb2 Complementary conduction. S R1 and S R4 When the primary current drops to I ZVS When S R2 and S R3 , so that the current is maintained at I ZVS , and turns off S when Q4 turns off R1 and S R4 Similarly, when S R2 and S R3 When the primary current rises to -I ZVS When the current is maintained at -I ZVS , turn on S when Q2 is off R1 and S R4 This reduces the primary current and achieves ZVS of the primary and secondary switch tubes within the full input, full output, and full load range.

[0043] In one embodiment, the present invention proposes an isolated ZVS Buck-Boost converter and a control method and control circuit thereof, which realizes ZVS of the primary and secondary switch tubes and minimizes the effective value of the primary leakage inductance current and the secondary inductance current. Taking the analog control circuit as an example, the control circuit includes:

[0044] A primary side phase shift signal and drive signal generating module A, used to generate a phase shift signal between the primary sides Q1 and Q4 of the converter and drive signals for Q1, Q2, Q3 and Q4;

[0045] The driving signal generating module B is used to generate the secondary rectifier tube S R1 , S R2 , S R3 and S R4 The driving signal of

[0046] The drive signal generation module C is used to generate the secondary side switch tube Q b1 and Q b2 The driving signal of

[0047] Phase shift duty cycle circuit generation module D is used to generate switch tubes Q4 and Q b1 Phase difference between the opening times;

[0048] The schematic diagram of its principle is as follows Figure 3a to Figure 3d As shown, it mainly includes four components: the circuit diagram of the primary side switch tube drive signal generating module, the circuit diagram of the secondary side rectifier tube drive signal generating module, the circuit diagram of the secondary side switch tube drive signal generating module, Q4 and Q b2 The phase difference between the two is generated by the module circuit diagram. Some parameters in the figure are as follows: os is the output voltage sampling value; v ins is the input voltage sampling value; Vo_ref is the reference value of the voltage regulator; i Lc is the inductor current.

[0049] 1. Circuit diagram of primary switch tube drive signal generating module (primary phase shift signal and drive signal generating module A)

[0050] like Figure 3a As shown, module A includes a voltage regulator, a comparator 1, an RS flip-flop 1 and a D flip-flop 1. The input of the voltage regulator is the sampled value v of the output voltage. os The reference is the sampling value corresponding to the output voltage to be set. vr With sawtooth wave v saw It is sent to comparator 1 to get a square wave signal. After being sent to the phase shift generation circuit constructed by RS trigger 1 and D trigger 1, the phase shift signal between Q1 and Q4 can be obtained. Since the switch tubes Q1 and Q3, Q2 and Q4 are all 180° complementary conduction, the driving signals of the four switch tubes on the primary side can be obtained. It should be noted that v saw Synchronous with the clock signal CLK1, the CLK signal of the D flip-flop is also CLK1.

[0051] 2. Circuit diagram of the secondary rectifier tube drive signal generating module (drive signal generating module B)

[0052] like Figure 3b As shown, the drive signal generating module B includes a calculation circuit 1, a comparator 2 and a D flip-flop 2. The calculation circuit 1 determines the moment when the four rectifier tubes on the secondary side are turned on simultaneously under different working conditions, and its output v SR With sawtooth wave v saw The input signal CLK of D flip-flop 2 corresponds to the narrow pulse corresponding to the falling moment of the square wave signal output by comparator 2. The output of the flip-flop is logically ORed with the duty cycle of Q2 and Q4 respectively, so as to obtain the driving signal D of the secondary synchronous rectifier. s23 and D s14 . This maintains the primary current at the minimum current that can achieve ZVS, denoted as I ZVS , reducing the effective value of the primary current.

[0053] The calculation formula is as follows: R1 and S R4 When the primary current drops to I ZVS When S R2 and S R3 , and turns off S when Q4 turns off R1 and S R4 Similarly, when S R2 and S R3 When the primary current rises to -IZVS When S R2 and S R3 , and turns off S when Q2 turns off R2 and S R3 .

[0054] After adopting this control method, when the junction capacitance of the primary and secondary switch tubes is charged and discharged, the parasitic capacitance of the secondary synchronous rectifier tubes will also be charged and discharged, and the voltage across the transformer is not zero. Therefore, the soft switching of the primary switch tube is not completed by relying on the energy stored in the leakage inductance, and there is no problem of insufficient leakage inductance energy under light load, making it difficult to achieve soft switching. Thus, ZVS of the primary switch tube is achieved in the full input, full output, and full load range.

[0055] 3. Circuit diagram of the secondary side switch tube drive signal generating module (drive signal generating module C)

[0056] like Figure 3c As shown, the drive signal generating module C includes a comparator 3 and an RS trigger 2. The function of the module C is that when the secondary inductor current drops to the minimum current that can achieve soft switching, the comparator 3 outputs v comp The high potential resets RS flip-flop 2, Q b1 Set low to immediately shut down Q b1 , open Q b2 , to reduce current ripple. The CLK1 signal ensures that if the inductor current does not drop to the minimum current that can achieve soft switching at the end of the switching cycle, Q is forced to turn off. b1 To ensure the correctness of the switching timing.

[0057] 4. Q4 and Q b2 Phase difference generation module circuit diagram (phase shift duty cycle generation module D)

[0058] like Figure 3d As shown, the phase-shift duty cycle generation module D includes a calculation circuit 2 and a comparator 4. The phase-shift duty cycle circuit generation module is Q4 and Q b1 Phase difference between the opening moments: The phase difference is obtained based on the principle of the minimum effective value of the secondary inductor current and the calculation circuit. b1 The phase difference between the output of the circuit 2 and the sawtooth wave v saw Send to comparator 4 to get square wave signal Q θs . Generate clock signal CLK2 as Q θs The narrow pulse corresponding to the falling moment is input into the drive signal generating module C as Q b1 The generated phase shift duty ratio calculation value V sita , and sent to the calculation formula in module B to calculate the turn-on time of the secondary rectifier tube.

[0059] The control method of the isolated ZVS Buck-Boost converter proposed in the present invention is implemented based on the control circuit proposed above. In order to improve the working efficiency of the converter, all the switches on the primary and secondary sides achieve ZVS while minimizing the effective value of the primary and secondary currents.

[0060] Figure 3a In the example, the input is the output sampling voltage v os The output is the duty cycle of the primary switch tube, realizing closed-loop regulation of the output voltage. Figure 3b In the example, the input sampling voltage v ins , output voltage v os , and the regulator output v vr By calculating and obtaining the duty cycle of the secondary rectifier tube, the soft switching of the primary switch tube is no longer dependent on the energy stored in the leakage inductance. There is no problem of insufficient leakage inductance energy at light load, which makes it difficult to achieve soft switching. Thus, the ZVS of the primary switch tube can be achieved in the full input, full output, and full load range. At the same time, Figure 3c In the process, by sampling the inductor current i Lc and-I ZVS comparison, ensuring that the inductor current drops to -I ZVS Shutdown Q b1 , can reduce the effective value of the primary current and improve the efficiency of the converter. Furthermore, Figure 3d In the example, the input sampling voltage v ins and the output current i os Calculate and get Q b1 The turn-on signal CLK2 is used. By adjusting the secondary side phase shift duty cycle, the secondary side inductor current waveform can be optimized, and the effective value of the secondary side current can be minimized on the basis of achieving ZVS of the secondary side switch tube. On the basis of achieving ZVS of all switch tubes, the switching frequency, power density and working efficiency of the converter can be improved.

[0061] In order to further illustrate the superiority of the control method proposed in the present invention, a simulation example of the present invention is given below.

[0062] According to the 6kW isolated Buck-Boost converter parameters given in Table 1, a simulation circuit was built using Saber simulation software. Figure 4a-4c The simulation waveform of the four-tube Buck-Boost converter working in the forward direction at rated power is given, where: Figure 4a This is the simulation waveform diagram of the battery voltage at 500V full load; Figure 4b This is the simulation waveform diagram of the battery voltage at 700V under full load; Figure 4c This is the simulation waveform diagram under full load with a battery voltage of 900V. It can be seen that all switch tubes can achieve ZVS and the inductor current pulsation is small.

[0063] Figure 5 The dynamic waveform of the converter when the load changes (output 700V, from 10% load to full load). It can be seen that based on this control method, the dynamic performance of the converter is better, and the voltage drop and recovery time are shorter when the load changes.

[0064] Table 1 Main parameters of bidirectional converter

[0065] parameter Numeric parameter Numeric <![CDATA[Input V in > 400V <![CDATA[Output voltage V o > 500～900V Rated output power 6kW <![CDATA[Filter inductance value L c > 16μH <![CDATA[Primary side switching frequency f s > 250kHz <![CDATA[Secondary side switching frequency f s > 500kHz

[0066] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. Isolated ZVS Buck-Boost converter, characterized in that: The primary side of the converter includes switch tubes Q1 and Q3, Q2 and Q4 and a transformer with leakage inductance, the transformer is connected to the midpoint of the bridge arm of Q1 and Q3 and the midpoint of the bridge arm of Q2 and Q4 respectively, Q1 and Q3, Q2 and Q4 are all 180° complementary conduction; the primary side adopts phase shift control; The secondary side of the converter is connected through a synchronous rectifier S R1 ,S R2 ,S R3 With S R4 Rectification is performed to obtain a square wave voltage; the output of the synchronous rectifier is connected to the inductor L c One end, L c The other end is connected to the switch tube Q b1 With Q b2 The midpoint of the bridge arm, bridge arm Q b1 With Q b2 Connect output side; S R1 With S R4 Same opening and closing, S R3 With S R4 Same opening and closing, Q b1 With Q b2 Complementary conduction.

2. A control method for the isolated ZVS Buck-Boost converter according to claim 1, characterized in that: The output voltage is regulated by adjusting the phase-shift duty cycle of the primary switch tube and the duty cycle of the secondary switch tube; by adjusting the on-off moment of the rectifier tube, the soft switching of the primary switch tube is no longer dependent on the energy stored in the leakage inductance, and the ZVS of the primary switch tube in the full input, full output, and full load range is achieved, while reducing the effective value of the primary current; by adjusting the phase-shift duty cycle of the secondary switch tube, the secondary inductor current waveform is adjusted, and the effective value of the secondary current is minimized on the basis of achieving ZVS of the secondary switch tube.

3. A control circuit for the isolated ZVS Buck-Boost converter according to claim 1, characterized in that: The control circuit comprises: A primary side phase shift signal and drive signal generating module A, used to generate a phase shift signal between the primary sides Q1 and Q4 of the converter and drive signals for Q1, Q2, Q3 and Q4; The driving signal generating module B is used to generate the secondary rectifier tube S R1 , S R2 , S R3 and S R4 The driving signal of The drive signal generation module C is used to generate the secondary side switch tube Q b1 and Q b2 The driving signal of Phase shift duty cycle circuit generation module D is used to generate switch tubes Q4 and Q b1 The phase difference between the turn-on times generates the phase-shifted duty cycle.

4. The control circuit according to claim 3, characterized in that The primary side phase shift signal and driving signal generating module A comprises a voltage regulator, a comparator 1, an RS trigger 1 and a D trigger 1; wherein the input of the voltage regulator is the sampled value of the output voltage, the reference is the sampled value corresponding to the set output voltage, and the output of the voltage regulator is v vr After passing through comparator 1 with the sawtooth wave, a square wave signal is obtained, and after being combined with the clock signal CLK1 and passing through RS trigger 1 and D trigger 1 respectively, a phase shift signal between Q1 and Q4 is obtained, and the switch tubes Q1 and Q3, Q2 and Q4 are all 180° complementary turned on, thereby obtaining the driving signals of Q1 and Q3, Q2 and Q4, wherein the sawtooth wave is synchronized with the clock signal CLK1.

5. The control circuit according to claim 4, characterized in that The driving signal generating module B determines the four rectifier tubes S on the secondary side under different working conditions through the calculation circuit 1, the comparator 2 and the D trigger 2. R1 , S R2 , S R3 and S R4 At the same time, the primary current is maintained at the minimum current I that can achieve ZVS. ZVS , reducing the effective value of the primary current; wherein the calculation circuit 1 calculates the formula (v ins v vr / v os )+v sita -2L c I ZVS / v os T s Get the output v SR , and sawtooth wave v saw The square wave signal is sent to comparator 2 to obtain the square wave signal. The narrow pulse corresponding to the falling moment of the square wave signal is input to D flip-flop 2. The output of D flip-flop 2 is logically ORed with the duty cycle of Q2 and Q4 respectively, so as to obtain the driving signal D of the secondary synchronous rectifier. s23 and D s14 , so that in S R1 and S R4 When the primary current drops to I ZVS When S R2 and S R3 , and turns off S when Q4 turns off R1 and S R4 ; Similarly, when S R2 and S R3 When the primary current rises to -I ZVS When S R1 and S R4 , and turns off S when Q2 turns off R2 and S R3 where v ins 、v os is the sampling value of input voltage and output voltage, v sita is the calculated value of phase shift duty cycle, L c is the inductance value, T s is the cycle size.

6. The control circuit according to claim 5, characterized in that The driving signal generating module C generates the secondary side switch tube Q through the comparator 3 and the RS trigger 2 b1 and Q b2 The input of comparator 3 is the secondary inductor current I LC and the minimum current I required to achieve soft switching ZVS , its output v comp The output of the OR gate with the CLK1 signal and the clock signal CLK2 are input into RS trigger 2; the secondary inductor current I LC The current drops to the minimum I that can achieve soft switching. ZVS When comparator 3 outputs v comp is high, resetting RS flip-flop 2, Q b1 Set low to immediately shut down Q b1 , open Q b2 , to reduce current ripple.

7. The control circuit according to claim 6, characterized in that The phase shift duty cycle circuit generation module D includes a calculation circuit 2 and a comparator 4, wherein the calculation circuit 2 generates the switch tubes Q4 and Q5 according to the principle of the minimum effective value of the secondary inductor current. b1 The phase difference between the opening moments, specifically, the calculation circuit 2 uses the calculation formula av ins +bi os +c to get the calculated value of phase shift duty cycle v sita , and sawtooth wave v saw are sent to comparator 4 to obtain square wave signal Q θs , with Q θs The narrow pulse corresponding to the falling moment is used as the clock signal CLK2, which is input into the drive signal generating module C and used as Q b1 The opening signal; Where a, b, c are coefficients, v ins 、i os It is the sampling value of input current and output current.

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