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

Abstract

The present invention discloses an isolated ZVS Buck-Boost converter and a control method and a control circuit thereof. The primary side of the converter includes switch tubes Q1 and Q3, Q2 and Q4 and a transformer with leakage inductance; the secondary side includes a synchronous rectifier tube S R1 ,S R2 ,S R3 With S R4 , connection inductor L c , switch tube Q b1 With Q b2 . By controlling the synchronous rectifier tube to rectify and regulate the primary current waveform, 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, while minimizing 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, while minimizing the effective value of the secondary inductor current. The present invention enables the converter to achieve ZVS of the switch 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.

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 fuels are being gradually replaced, and the proportion of electric vehicles is also increasing. To meet user needs, charging speed and power are constantly improving. To reduce losses, bus voltage is constantly increasing, and voltage platforms of 400V and 800V are now achieved. On-board charging power supplies typically consist of an AC-DC converter and a DC-DC converter. To ensure safety, the DC-DC converter is usually an isolated converter. To reduce the size of the on-board charger and minimize charging losses, the charger must have high power density and high efficiency.

[0003] Currently, DC-DC converters in on-board chargers typically use either CLLC or DAB topologies. CLLC can achieve zero-voltage switching (ZVS) of the switching transistors when operating in DCX mode, resulting in higher conversion efficiency, but it lacks the ability to adjust the output voltage. Adjusting the output voltage requires varying the switching frequency, which is detrimental to EMI design. DAB, on the other hand, cannot achieve zero-voltage switching (ZVS) of the switching transistors under light loads, hindering not only efficiency gains but also increases in switching frequency and power density. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned existing technologies and provide an isolated ZVS Buck-Boost converter and its control method and control circuit. 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 switches Q1 and Q3, Q2 and Q4, and a transformer with a leakage inductor. The transformer is connected to the midpoints of the bridge arms of Q1 and Q3, and the midpoints of the bridge arms of Q2 and Q4, respectively. Q1 and Q3, and Q2 and Q4 are all 180° complementary conduction. The primary side adopts phase-shift control.

[0007] The secondary side of the converter is connected to the 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 primary current waveform by controlling the synchronous rectifier tube to rectify and regulate the primary current waveform, 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, while minimizing the effective value of the primary leakage inductance current; the secondary switch tube adopts PWM plus phase shift control method, 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, while minimizing the effective value of the secondary inductor current.

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

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

[0011] Drive signal generating module B, used to generate secondary rectifier tube S R1 、S R2 、S R3 and S R4 The driving signal;

[0012] Drive signal generating module C is used to generate the secondary side switch tube Q b1 and Q b2 The driving signal;

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

[0014] The primary side phase shift signal and drive 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. After being combined with the clock signal CLK1 and passing through RS trigger 1 and D trigger 1 respectively, a phase-shifted signal between Q1 and Q4 is obtained, and the switch tubes Q1 and Q3, Q2 and Q4 are all complementary turned on at 180 degrees, thereby obtaining the driving signals of Q1 and Q3, Q2 and Q4, where 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, and the narrow pulse corresponding to the falling moment of the square wave signal is input to D trigger 2. The output of D trigger 2 is logically ORed with the duty cycle of Q2 and Q4 respectively, thereby obtaining the driving signal D of the secondary synchronous rectifier tube. 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 side switch 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 the RS trigger 2; the secondary inductor current I LC Drop to the minimum current I that can achieve soft switching ZVS When comparator 3 outputs v comp The potential is high, which resets the RS trigger 2. b1 Set low to immediately shut down Q b1 , open Q b2 , to reduce current pulsation.

[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 switching 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 the Q b1 The opening signal;

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

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

[0021] This invention fully considers the development needs of on-board chargers, which require high efficiency and high power density. It proposes an isolated ZVS Buck-Boost converter, its control method, and control circuit. This converter achieves ZVS switching across the full input, output, and load ranges, while minimizing the effective current. It also regulates the output voltage during fixed-frequency operation. This not only improves the converter's efficiency but also increases its switching frequency, thereby increasing its power density.

[0022] This invention eliminates the need for primary-side switches to rely on energy stored in leakage inductance to achieve soft switching. This reduces the RMS value of the primary current while ensuring soft switching across the full input and full load range. Simultaneously, the secondary side utilizes PWM plus phase-shift control to regulate the voltage across the inductor, enabling the secondary-side switches to achieve zero-voltage switching (ZVS) across the full load and voltage range, while minimizing the RMS value of the secondary 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 generation module.

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

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

[0028] Figure 3d For Q4 and Q b2 Phase difference generation module circuit diagram.

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

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

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

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

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

[0034] An isolated ZVS Buck-Boost converter of the present invention has a circuit structure as shown in FIG. 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 switches Q1 and Q3, and Q2 and Q4, respectively. Q1 and Q3, and Q2 and Q4 are all conducting at 180° complementary angles. The primary side uses phase-shift control.

[0036] The secondary side is connected through four synchronous rectifier tubes S R1 ,S R2 ,S R3 With S R4 Rectify and get 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 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 sampling is 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 side 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 regulate the primary side current waveform by controlling the rectifier tube. This method makes the primary side switch tube no longer rely on the energy stored in the leakage inductance to achieve 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 side current is reduced. At the same time, the secondary side switch tube Q b1 With Q b2By adopting PWM plus phase-shift control mode and adjusting the voltage across the inductor, the secondary side switch tube can also achieve ZVS under full load and full voltage variation range, while minimizing the effective value of the secondary side inductor current.

[0039] After adopting this control method, the primary-side switching 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-side switching tubes under the full input, full output, and full load range, the effective values of the primary-side leakage inductance current and the secondary-side 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 quantity 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 time and Q b2 The duty cycle of the primary side 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 over the full input, full output, and full load ranges, and minimize the effective values of the primary leakage current and the secondary inductor 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 the 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 enables ZVS of the primary and secondary switches within the full input, full output, and full load range.

[0043] In one embodiment, the present invention provides an isolated ZVS Buck-Boost converter and its control method and circuit, which achieve ZVS of the primary and secondary switching transistors and minimize the effective values of the primary leakage inductor current and the secondary inductor current. Taking an analog control circuit as an example, the control circuit includes:

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

[0045] Drive signal generating module B, used to generate secondary rectifier tube S R1 、S R2 、S R3 and S R4 The driving signal;

[0046] Drive signal generating module C is used to generate the secondary side switch tube Q b1 and Q b2 The driving signal;

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

[0048] The schematic diagram of its principle is as follows Figures 3a to 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 circuit diagram of the phase difference generation module between the two. 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 the primary side switch tube drive signal generation module (primary side phase shift signal and drive signal generation 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 of the output voltage v os , the reference is the sampling value corresponding to the output voltage to be set, and the output v vr With sawtooth wave v saw It is sent to comparator 1 to obtain a square wave signal. After being sent to the phase shift generation circuit built 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 side rectifier tube drive signal generation module (drive signal generation 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 at the same time under different working conditions, and its output v SR With sawtooth wave v saw The D flip-flop 2 input signal CLK 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 to obtain the driving signal D of the secondary synchronous rectifier. s23 and D s14 . Thus, the primary current is maintained at the minimum current that can achieve ZVS, which is recorded as I ZVS , reducing the effective value of the primary current.

[0053] The calculation formula is: 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] With this control method, as the junction capacitance of the primary-side and secondary-side switches charges and discharges, the parasitic capacitance of the secondary-side synchronous rectifier also charges and discharges, causing the voltage across the transformer to be non-zero. Therefore, soft switching of the primary-side switches is achieved without relying on energy stored in the leakage inductance. The problem of insufficient leakage inductance energy under light loads, which makes soft switching difficult, is eliminated. This ensures ZVS (zero voltage switching) of the primary-side switches across the full input, full output, and full load range.

[0055] 3. Circuit diagram of the secondary side switch tube drive signal generation module (drive signal generation 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 to output v when the secondary inductor current drops to the minimum current that can achieve soft switching. comp The potential is high, which resets the RS trigger 2. 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 generating module D includes a calculation circuit 2 and a comparator 4. The phase-shift duty cycle circuit generating module is Q4 and Q b1 Phase difference between the opening moments: The phase difference is obtained based on the principle of minimum effective value of the secondary inductor current and the calculation circuit. b1 The output of the phase difference calculation circuit 2 between the opening time and the sawtooth wave v saw Send it 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 cycle calculation value V sita , and input it into the calculation formula in module B to calculate the turn-on time of the secondary side 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 side 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 side 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 no longer relies on the energy stored in the leakage inductance. There is no problem of insufficient leakage inductance energy under light load, which makes 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. At the same time, Figure 3c In the process, by sampling the inductor current i Lc and-I ZVS Comparison to ensure 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 secondary-side phase-shift duty cycle is adjusted to optimize the secondary-side inductor current waveform, minimizing the RMS secondary current while achieving zero-voltage (ZVS) across all secondary switches. This improves the converter's switching frequency, power density, and efficiency.

[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. Figures 4a-4c The simulation waveforms of the four-tube Buck-Boost converter in forward operation at rated power are 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 The simulation waveform diagram is when the battery voltage is 900V and the battery is fully loaded. It can be seen that all switches can achieve ZVS and the inductor current pulsation is small.

[0063] Figure 5 The following figure shows the converter's dynamic waveform during a load transition (output 700V, transitioning from 10% load to full load). It can be seen that this control method provides better dynamic performance, with shorter voltage drops and recovery times during load transitions.

[0064] Table 1 Main parameters of bidirectional converter

[0065] parameter Numerical parameter Numerical <![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 merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. Isolated ZVS Buck-Boost converter, characterized by: The primary side of the converter includes switches Q1 and Q3, Q2 and Q4, and a transformer with leakage inductance. The transformer is connected to the midpoints of the bridge arms of Q1 and Q3 and the midpoints of the bridge arms 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 to the 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 R2 Same opening and closing, Q b1 With Q b2 complementary conduction; Drive signal generating module B, used to generate secondary rectifier tube S R1 、S R2 、S R3 and S R4 The driving signal; 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, comparator 2 and 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, and the narrow pulse corresponding to the falling moment of the square wave signal is input to D trigger 2. The output of D trigger 2 is logically ORed with the duty cycle of Q2 and Q4 respectively, thereby obtaining the driving signal D of the secondary synchronous rectifier tube. 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.

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-side switch and the duty cycle of the secondary-side switch. By adjusting the on / off moments of the rectifier, the soft switching of the primary-side switch is no longer dependent on the energy stored in the leakage inductance, achieving ZVS of the primary-side switch within the full input, full output, and full load range while reducing the effective value of the primary current. By adjusting the phase-shift duty cycle of the secondary-side switch, the waveform of the secondary-side inductor current is adjusted, minimizing the effective value of the secondary current while achieving ZVS of the secondary-side switch.

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

4. The control circuit according to claim 3, characterized in that The primary side phase shift signal and drive signal generating module A includes 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 voltage regulator output v vr After passing through comparator 1 with the sawtooth wave, a square wave signal is obtained. After being combined with the clock signal CLK1 and passing through RS trigger 1 and D trigger 1 respectively, a phase-shifted signal between Q1 and Q4 is obtained, and the switch tubes Q1 and Q3, Q2 and Q4 are all complementary turned on at 180 degrees, thereby obtaining the driving signals of Q1 and Q3, Q2 and Q4, where 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 C generates the secondary side switch tube Q through the comparator 3 and 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 the 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 The potential is high, which resets the RS trigger 2. b1 Set low to immediately shut down Q b1 , open Q b2 , to reduce current pulsation.

6. The control circuit according to claim 5, 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 switching tubes Q4 and Q5 according to the principle of 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 the Q b1 The opening signal; Where a, b, c are coefficients, v ins 、i os are the sampling values of input current and output current.

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