Power conversion circuit

Abstract

The present application discloses a power conversion circuit, which, through the on and off states of multiple switches in a first bridge arm and multiple switches in a second bridge arm, and the mutual coupling between a first resonant capacitor, a second resonant capacitor, a third resonant capacitor, and a first winding, a second winding, and a third winding of a transformer, enables the power conversion circuit to obtain different output voltage and input voltage gain ratios by adjusting the number of turns of the first winding and the number of turns of the second winding and the third winding. Therefore, the power conversion circuit of the present application can meet the requirements of different output voltage and input voltage gain ratios and has better applicability.

Description

Technical Field

[0001] The present application relates to a power conversion circuit, and more particularly to a power conversion circuit with a variable gain ratio between an input voltage and an output voltage. Background Art

[0002] With the rapid development of fixed-line and mobile communications, the demand for high-power DC / DC power converters (especially proportional converters) is also increasing. Figure 1 , an existing power conversion circuit with scalable duty cycle is shown, which has an input-output voltage gain ratio of 4:1 and has the advantage of high power density.

[0003] However, in this power conversion circuit, switches S1A, S2B, S1C and switches S2A, S1B, S2C are complementary and turned on, and the duty cycle is 50%, and the voltage on the two capacitors Cr is Vin / 2, and the voltage at points A and B on both sides of the winding T is a complementary square wave from 0 to Vin / 2, and the voltage at points A and B cannot be changed by adjusting the capacitance of the capacitors, so the input-output voltage gain ratio of this power conversion circuit cannot be changed. This power conversion circuit can only work in applications with an input-output voltage gain ratio of 4:1, and its applicability is poor.

[0004] Therefore, how to develop a power conversion circuit that can improve the above-mentioned prior art is an urgent need. Summary of the invention

[0005] The purpose of the present application is to provide a power conversion circuit which can change the gain ratio of input voltage and output voltage.

[0006] To achieve the above-mentioned purpose, the present application provides a power conversion circuit, comprising an input positive pole, an input negative pole, an output positive pole, an output negative pole, a first bridge arm, a second bridge arm, a transformer, a first resonant capacitor, a second resonant capacitor, a third resonant capacitor and an output capacitor. The input negative pole is connected to the output negative pole. The first bridge arm comprises a first switch, a second switch, a third switch and a fourth switch connected in series between the input positive pole and the input negative pole, the first switch is connected to the second switch to form a first connection point, the second switch is connected to the third switch to form a second connection point, and the third switch is connected to the fourth switch to form a third connection point. The second bridge arm comprises a fifth switch, a sixth switch, a seventh switch and an eighth switch connected in series between the input positive pole and the input negative pole, the fifth switch is connected to the sixth switch to form a fourth connection point, the sixth switch is connected to the seventh switch to form a fifth connection point, and the seventh switch is connected to the eighth switch to form a sixth connection point. The transformer comprises a first winding, a second winding and a third winding coupled to each other, the second winding is electrically connected between the third connection point and the output positive pole, and the third winding is electrically connected between the sixth connection point and the output positive pole. The first resonant capacitor is connected in series with the first winding and is electrically connected between the second connection point and the fifth connection point. The second resonant capacitor is electrically connected between the first connection point and the third connection point. The third resonant capacitor is electrically connected between the fourth connection point and the sixth connection point. The output capacitor is electrically connected between the output positive electrode and the output negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 The invention is an existing power conversion circuit with expandable duty cycle.

[0008] Figure 2A This is a schematic diagram of the circuit structure of the power conversion circuit of the first preferred embodiment of the present application.

[0009] Figure 2B for Figure 2A The power conversion circuit shown is a schematic diagram of a circuit structure having an equivalent excitation inductor and multiple series inductors.

[0010] Figure 3 for Figure 2B Schematic diagram of waveforms of some components of the power conversion circuit shown.

[0011] Figure 4A and Figure 4B for Figure 2B The power conversion circuit shown in Figure 3 Schematic diagram of working status in different time periods.

[0012] Figure 5 This is a schematic diagram of the circuit structure of a power conversion circuit according to the second preferred embodiment of the present application.

[0013] Figure 6This is a schematic diagram of the circuit structure of a power conversion circuit according to the third preferred embodiment of the present application.

[0014] Figure 7 This is a schematic diagram of the circuit structure of a power conversion circuit according to the fourth preferred embodiment of the present application.

[0015] Figure 8 for Figure 7 The voltage waveform of the power conversion circuit shown.

[0016] Fig. 9 This is a schematic diagram of the circuit structure of a power conversion circuit according to the fourth preferred embodiment of the present application.

[0017] Fig.10 for Fig. 9 Schematic diagram of waveforms of some components of the power conversion circuit shown.

[0018] FIG. 11A to FIG. 11D for Fig. 9 The power conversion circuit shown in Fig. 9 Schematic diagram of working status in different time periods.

[0019] The reference numerals are described as follows:

[0020] S1A, S2B, S1C, S2A, S1B, S2C: Switch

[0021] Cr: Capacitance

[0022] T: Winding

[0023] A, B: connection points

[0024] 1. 1a, 1b, 1c: Power conversion circuit

[0025] 11: Voltage Source

[0026] Vin: input voltage

[0027] Vin+: input positive

[0028] Vin-: input negative pole

[0029] Vo: output voltage

[0030] Vo+: output positive

[0031] Vo-: output negative pole

[0032] io: output current

[0033] 12: First bridge arm

[0034] S1: First switch

[0035] S2: Second switch

[0036] S3: The third switch

[0037] S4: The fourth switch

[0038] P1: First connection point

[0039] P2: Second connection point

[0040] P3: Third connection point

[0041] 13: Second bridge arm

[0042] S5: Fifth switch

[0043] S6: Sixth switch

[0044] S7: Seventh switch

[0045] S8: The eighth switch

[0046] P4: Fourth connection point

[0047] P5: Fifth connection point

[0048] P6: Sixth connection point

[0049] 14: Transformer

[0050] T1: First winding

[0051] T2: Second winding

[0052] T3: The third winding

[0053] Cr1: First resonant capacitor

[0054] Cr2: Second resonant capacitor

[0055] Cr3: The third resonant capacitor

[0056] Cin: input capacitance

[0057] Co: output capacitance

[0058] Lm: equivalent excitation inductance

[0059] iLm: Excitation current

[0060] Lr1: First series inductor

[0061] Lr2: Second series inductor

[0062] Lr3: The third series inductor

[0063] Vgs1 / 3 / 6 / 8: Gate-source voltage of the first switch, the third switch, the sixth switch, and the eighth switch

[0064] Vgs2 / 4 / 5 / 7: Gate-source voltage of the second switch, the fourth switch, the fifth switch, and the seventh switch

[0065] Vds1: drain-source voltage of the first switch

[0066] Vds2: drain-source voltage of the second switch

[0067] Vds3: drain-source voltage of the third switch

[0068] Vds4: drain-source voltage of the fourth switch

[0069] iLm: Excitation current flowing through the equivalent excitation inductance

[0070] iT1: First winding current

[0071] iT2: Second winding current

[0072] iT3: Third winding current

[0073] t0~t7: time

[0074] 2: Pre-charge circuit

[0075] R1: First resistor

[0076] R2: Second resistor

[0077] M: Auxiliary switch

[0078] Ma: First End

[0079] Mb: Second end

[0080] Mc: The third end

[0081] D1: First clamp switch

[0082] D2: Second clamp switch

[0083] D3: The third diode

[0084] Vg: Voltage at the second terminal of the auxiliary switch

[0085] 3: Startup circuit

[0086] Ss1: upper switch

[0087] Ss2: Lower switch

[0088] T4: Fourth winding

[0089] Lo: output inductance

[0090] Vgsu: Gate-source voltage of the upper switch

[0091] Vgsl: Gate-source voltage of the lower switch

[0092] iLo: Inductor current flowing through the output inductor

[0093] Vcr2: Terminal voltage of the second resonant capacitor

[0094] Vcr3: Terminal voltage of the third resonant capacitor

[0095] Vco: output capacitor voltage DETAILED DESCRIPTION

[0096] Some typical embodiments that embody the features and advantages of the present application will be described in detail in the following description. It should be understood that the present application can have various changes in different implementations without departing from the scope of the present application, and the descriptions and illustrations therein are essentially used for illustrative purposes rather than for limiting the present application.

[0097] Figure 2A The circuit structure diagram of the power conversion circuit of the first preferred embodiment of the present application. As shown in the figure, the power conversion circuit 1 is electrically connected to the voltage source 11 and the load, and is used to convert the input voltage Vin provided by the voltage source 11 to generate an output voltage Vo and an output current io to the load, wherein the power conversion circuit 1 has an input positive electrode Vin+, an input negative electrode Vin-, an output positive electrode Vo, an output negative electrode Vo-, a first bridge arm 12, a second bridge arm 13, a transformer 14, a first resonant capacitor Cr1, a second resonant capacitor Cr2, a third resonant capacitor Cr3 and an output capacitor Co. The input positive electrode Vin+ and the input negative electrode Vin- are electrically connected to the voltage source 11, and the power conversion circuit 1 receives the input voltage Vin via the input positive electrode Vin+ and the input negative electrode Vin-. The output positive electrode Vo+ and the output negative electrode Vo- are electrically connected to the load, and the power conversion circuit 1 outputs the output voltage Vo and the output current io to the load via the output positive electrode Vo+ and the output negative electrode Vo-.

[0098] The first bridge arm 12 includes a first switch S1, a second switch S2, a third switch S3, and a fourth switch S4 connected in series between an input positive electrode Vin+ and an input negative electrode Vin-. The first switch S1 and the fourth switch S4 are electrically connected to the input positive electrode Vin+ and the input negative electrode Vin-, respectively. The first switch S1 and the second switch S2 are connected in series to form a first connection point P1, the second switch S2 and the third switch S3 are connected in series to form a second connection point P2, and the third switch S3 and the fourth switch S4 are connected in series to form a third connection point P3, wherein all switches in the first bridge arm 12 may be, for example, but not limited to, MOSFETs, SiC switches, or GaN switches.

[0099] The second bridge arm 13 is connected in parallel with the first bridge arm 12, and includes a fifth switch S5, a sixth switch S6, a seventh switch S7 and an eighth switch S8 which are sequentially connected in series between the input positive electrode Vin+ and the input negative electrode Vin-. The fifth switch S5 and the eighth switch S8 are electrically connected to the input positive electrode Vin+ and the input negative electrode Vin-, respectively. The fifth switch S5 and the sixth switch S6 are connected in series to form a fourth connection point P4, the sixth switch S6 and the seventh switch S7 are connected in series to form a fifth connection point P5, and the seventh switch S7 and the eighth switch S8 are connected in series to form a sixth connection point P6, wherein all switches in the second bridge arm 13 may be, for example but not limited to, MOSFETs, SiC switches or GaN switches.

[0100] The transformer 14 includes a first winding T1, a second winding T2 and a third winding T3, and the first winding T1, the second winding T2 and the third winding T3 are wound on the same magnetic core (not shown) to couple with each other, wherein the number of turns of the first winding T1 is N1, and the number of turns of the second winding T2 and the third winding T3 are both N2, wherein N1 and N2 are both positive numbers. The first winding T1 and the first resonant capacitor Cr1 are connected in series between the second connection point P2 and the fifth connection point P5, and in this embodiment, the first end of the first winding T1 is electrically connected to the second connection point P2, the second end of the first winding T1 is electrically connected to the first end of the first resonant capacitor Cr1, and the second end of the first resonant capacitor Cr1 is electrically connected to the fifth connection point P5. The second winding T2 is electrically connected between the third connection point P3 and the output positive pole Vo+, and the third winding T3 is electrically connected between the output positive pole Vo+ and the sixth connection point P6. Specifically, the first end of the second winding T2 and the first end of the third winding T3 are electrically connected to the output positive electrode Vo+, the second end of the second winding T2 is electrically connected to the third connection point P3, and the second end of the third winding T3 is electrically connected to the sixth connection point P6. In this embodiment, the first end of the first winding T1, the first end of the second winding T2, and the second end of the third winding T3 are the same-named ends.

[0101] The second resonant capacitor Cr2 is electrically connected between the first connection point P1 and the third connection point P3. The third resonant capacitor Cr3 is electrically connected between the fourth connection point P4 and the sixth connection point P6. The output capacitor Co is electrically connected between the output positive electrode Vo+ and the output negative electrode Vo-. In this embodiment, the power conversion circuit 1 further includes an input capacitor Cin, which is electrically connected between the input positive electrode Vin+ and the input negative electrode Vin-.

[0102] Figure 2B for Figure 2A The power conversion circuit shown in FIG. 1 has a circuit structure diagram of an equivalent excitation inductor and multiple series inductors. Figure 2BAs shown, the transformer 14 of the power conversion circuit 1 has an equivalent excitation inductance Lm, and the equivalent excitation inductance Lm can be equivalent to being connected in parallel with the first winding T1, or can be equivalent to being connected in parallel with the second winding T2 or the third winding T3. In this embodiment, the equivalent excitation inductance Lm is equivalent to being connected in parallel with the first winding T1 as an example. In addition, the power conversion circuit 1 further includes a first series inductance Lr1, a second series inductance Lr2, and a third series inductance Lr3. The first series inductance Lr1, the first winding T1, and the first resonant capacitor Cr1 are connected in series and are electrically connected between the second connection point P2 and the fifth connection point P5, and the first series inductance Lr1 can be the leakage inductance of the transformer 14, or the first external inductance, or is composed of the leakage inductance of the transformer 14 and the first external inductance. The second series inductor Lr2 and the second winding T2 are connected in series and are electrically connected between the third connection point P3 and the output positive electrode Vo+, and the second series inductor Lr2 can be the leakage inductance of the transformer 14, or the second external inductance, or the leakage inductance and the second external inductance of the transformer 14. The third series inductor Lr3 and the third winding T3 are connected in series and are electrically connected between the sixth connection point P6 and the output positive electrode Vo+, and the third series inductor Lr3 can be the leakage inductance of the transformer 14, or the third external inductance, or the leakage inductance and the third external inductance of the transformer 14.

[0103] In this embodiment, the terminal voltages on the second resonant capacitor Cr2 and the third resonant capacitor Cr3 are the sum of the DC voltage component generated by the voltage source 11 and the oscillating AC voltage component generated by the transformer 14, wherein the DC voltage component is the difference between the input voltage Vin and twice the output voltage Vo. Preferably, the capacitance of the input capacitor Cin is much larger than the capacitance of the first resonant capacitor Cr1, the second resonant capacitor Cr2, and the third resonant capacitor Cr3, and the capacitance of the output capacitor Co is much larger than the capacitance of the first resonant capacitor Cr1, the second resonant capacitor Cr2, and the third resonant capacitor Cr3, so the influence of the input capacitor Cin and the output capacitor Co can be ignored in the following analysis of the circuit resonance.

[0104] Figure 3 for Figure 2B The waveform diagram of some components of the power conversion circuit shown in FIG. Figure 4A and Figure 4B for Figure 2B The power conversion circuit shown in Figure 3 Schematic diagram of working status in different time periods. Figure 3In the figure, Vgs1 / 3 / 6 / 8 are the gate-source voltages of the first switch S1, the third switch S3, the sixth switch S6 and the eighth switch S8, Vgs2 / 4 / 5 / 7 are the gate-source voltages of the second switch S2, the fourth switch S4, the fifth switch S5 and the seventh switch S7, Vds1 / Vds2 / Vds3 / Vds4 are the drain-source voltages of the first switch S1, the second switch S2, the third switch S3 and the fourth switch S4, iLm is the excitation current flowing through the equivalent excitation inductance Lm, iT1, iT2 and iT3 are the currents flowing through the first winding T1, the second winding T2 and the third winding T3, respectively. Figure 4A and Figure 4B In the figure, darker lines are used to show the circuits through which the current flows, and lighter lines are used to show the circuits through which the current does not flow. In addition, in order to simplify the analysis, in this embodiment, the inductance of the second series inductor Lr2 is equal to the inductance of the third series inductor Lr3, and the ratio K between the number of turns N1 of the first winding T1 and the number of turns N2 of the second winding T2 (or the number of turns N2 of the third winding T3) is a certain value.

[0105] like Figure 3 As shown, time t0 to t4 is a switching cycle, the first switch S1, the third switch S3, the sixth switch S6 and the eighth switch S8 are turned on and off synchronously, and the second switch S2, the fourth switch S4, the fifth switch S5 and the seventh switch S7 are turned on and off synchronously. The control signals received by the first switch S1, the third switch S3, the sixth switch S6 and the eighth switch S8 are 180 degrees out of phase with the control signals received by the second switch S2, the fourth switch S4, the fifth switch S5 and the seventh switch S7, and the duty ratios of the first switch S1, the second switch S2, the third switch S3, the fourth switch S4, the fifth switch S5, the sixth switch S6, the seventh switch S7 and the eighth switch S8 are 50% respectively. In actual control, due to the consideration of dead time, the duty ratio will be slightly less than 50%.

[0106] In addition, if Figure 3As shown, the period from time t1 to t2 and the period from time t3 to t4 are dead time. In the dead time, the excitation current iLm charges and discharges the parasitic capacitance of the corresponding switch, and causes the drain-source voltage of the switch to be turned on to drop to zero at the end of the dead time. Specifically, in the dead time of the first half cycle, that is, during the period from time t1 to t2, the excitation current iLm charges the parasitic capacitance of the first switch S1, the third switch S3, the sixth switch S6 and the eighth switch S8, and discharges the parasitic capacitance of the second switch S2, the fourth switch S4, the fifth switch S5 and the seventh switch S7, so that the drain-source voltage Vds2 / Vds4 of the second switch S2, the fourth switch S4, the fifth switch S5 and the seventh switch S7 to be turned on drops to zero at time t2, and the turn-off current of the second switch S2, the fourth switch S4, the fifth switch S5 and the seventh switch S7 at time t2 is also zero. In the dead time of the second half cycle, i.e., from time t3 to t4, the excitation current iLm charges the parasitic capacitance of the second switch S2, the fourth switch S4, the fifth switch S5 and the seventh switch S7, and discharges the parasitic capacitance of the first switch S1, the third switch S3, the sixth switch S6 and the eighth switch S8, so that the drain-source voltage Vds1 / Vds3 of the first switch S1, the third switch S3, the sixth switch S6 and the eighth switch S8 to be turned on drops to zero at time t4, and the turn-off current of the first switch S1, the third switch S3, the sixth switch S6 and the eighth switch S8 at time t2 is also zero. Accordingly, at the end of each dead time, such as time t2 and time t4, the drain-source voltage of the switch to be turned on is reduced to zero, so that the zero voltage turn-on of the switch can be achieved, reducing the turn-on loss of the switch. At the same time, since the dead time is shorter than the turn-on time of each switch to be described below, the changes of other variables in the dead time can be ignored.

[0107] See also Figure 3 and Figure 4A , during the period from time t0 to t1, the first switch S1, the third switch S3, the sixth switch S6 and the eighth switch S8 are in the on state, the second switch S2, the fourth switch S4, the fifth switch S5 and the seventh switch S7 are in the off state, and the excitation current iLm increases linearly, and the corresponding working mode is as follows Figure 4A In this working state, the power conversion circuit 1 can be equivalent to two resonant branches, namely the first resonant branch and the second resonant branch, wherein the first resonant branch is a branch formed by the second resonant capacitor Cr2 and the second series inductor Lr2 having a certain ratio in series. In terms of the equivalent circuit equation, the first resonant branch is Cr2 connected in series with Lr2*(K+4), and the first resonant frequency fs1 of the first resonant branch is:

[0108]

[0109] Cr2 is the capacitance of the second resonant capacitor, Lr2 is the inductance of the second series inductor, and K is the ratio between the number of turns N1 of the first winding T1 and the number of turns N2 of the second winding T2 (or the number of turns N2 of the third winding T3).

[0110] The second resonant branch is composed of the first resonant capacitor Cr1, the third resonant capacitor Cr3, the second series inductor Lr2 having a certain ratio and the first series inductor Lr1 in series. In terms of the equivalent circuit equation, the second resonant branch is Cr1 in series with Cr3 and Lr2*[(K+2)*(K+1)+2]+Lr1, and the second resonant frequency fs2 of the second resonant branch is:

[0111]

[0112] Wherein Cr1 is the capacitance of the first resonant capacitor, Cr3 is the capacitance of the third resonant capacitor, Lr1 is the inductance of the first series inductor, Lr2 is the inductance of the second series inductor, and K is the ratio between the number of turns N1 of the first winding T1 and the number of turns N2 of the second winding T2 (or the number of turns N2 of the third winding T3).

[0113] In order to make the power conversion circuit 1 reach a better working state, the capacitance of the first resonant capacitor Cr1, the second resonant capacitor Cr2 and the third resonant capacitor Cr3 can be selected so that the first resonant frequency fs1 is equal to the second resonant frequency fs2, and both resonant frequencies are equal to the switching frequencies of the first switch S1, the third switch S3, the sixth switch S6 and the eighth switch S8 in the on state. At this time, the current flowing through the first winding T1, the second winding T2 and the third winding T3 of the transformer 14 is the superposition of the excitation current and a sinusoidal current, and the waveform is approximately a sine wave, such as Figure 3 As shown in the first winding current iT1, the second winding current iT2 and the third winding current iT3.

[0114] Please continue reading Figure 4AIn this working state, there are three current branches in the power conversion circuit 1, namely, a first current branch, a second current branch and a third current branch, wherein the first current branch is formed by connecting the third resonant capacitor Cr3, the sixth switch S6, the first resonant capacitor Cr1, the first series inductor Lr1 (the first winding T1), the third switch S3, the second series inductor Lr2 (the second winding T2), the output positive electrode Vo+, the output negative electrode Vo- and the eighth switch S8 in sequence, and there is a first current on the first current branch, wherein in the first current branch, the energy stored in the third resonant capacitor Cr3 transfers energy to the output voltage Vo through the resonance of the first series inductor Lr1, the second series inductor Lr2 and the third resonant capacitor Cr3 and the first resonant capacitor Cr1. The second current branch is formed by connecting the input positive electrode Vin+, the first switch S1, the second resonant capacitor Cr2, the second winding T2, the second series inductor Lr2, the output positive electrode Vo+, the output negative electrode Vo- and the input negative electrode Vin- in sequence, and there is a second current on the second current branch, wherein in the second current branch, part of the energy of the input voltage Vin is stored in the second resonant capacitor Cr2, and at the same time, the energy is transferred to the output voltage Vo through the resonance of the second series inductor Lr2 and the second resonant capacitor Cr2. The third current branch is formed by connecting the third winding T3, the third series inductor Lr3, the output positive electrode Vo+, the output negative electrode Vo- and the eighth switch S8 in sequence, and there is a third current on the third current branch. As can be seen from the above, only the first current of the first current branch among the three current branches flows through the first winding T1, so the first winding current iT1 flowing through the first winding T1 is only composed of the first current, so the amplitude of the first winding current iT1 flowing through the first winding T1 is the amplitude of the first current. The first current of the first current branch and the second current of the second current branch among the three current branches flow through the second winding T2. Therefore, the second winding current iT2 flowing through the second winding T2 is composed of the first current and the second current. Therefore, the amplitude of the second winding current iT2 flowing through the second winding T2 is the sum of the amplitude of the first current and the amplitude of the second current. Since the amplitude of the first current is equal to the amplitude of the second current, the amplitude of the second winding current iT2 flowing through the second winding T2 is twice the amplitude of the first current or twice the amplitude of the second current. For the convenience of discussion, the following will be explained as the amplitude of the second winding current iT2 flowing through the second winding T2 is twice the amplitude of the second current (i.e., the input current).In addition, due to the coupling relationship between the first winding T1, the second winding T2 and the third winding T3 of the transformer 14, the amplitude of the third winding current iT3 flowing through the third winding T3 is K multiplied by the first current plus the first current plus the second current, where K is the ratio between the number of turns N1 of the first winding T1 and the number of turns N2 of the second winding T2 (or the number of turns N2 of the third winding T3), and since the amplitude of the first current is equal to the amplitude of the second current, the amplitude of the third winding current iT3 flowing through the third winding T3 is (K+2) times the amplitude of the first current or (K+2) times the amplitude of the second current. For the convenience of discussion, the following description will be based on the amplitude of the third winding current iT3 flowing through the third winding T3 being (K+2) times the amplitude of the second current. And according to. Figure 4A It can be seen that the output current io of the power conversion circuit 1 is the second winding current iT2 flowing through the second winding T2 plus the third winding current iT3 flowing through the third winding T3. Therefore, it can be seen that the amplitude of the output current io of the power conversion circuit 1 is twice the amplitude of the second current plus (K+2) times the amplitude of the second current, that is, (K+4) times the amplitude of the second current.

[0115] See also Figure 3 and Figure 4B , during the period from time t2 to t3, the second switch S2, the fourth switch S4, the fifth switch S5 and the seventh switch S7 are in the on state, the first switch S1, the third switch S3, the sixth switch S6 and the eighth switch S8 are in the off state, and the excitation current iLm decreases linearly. The corresponding working mode is as follows: Figure 4B In this working state, the power conversion circuit 1 can be equivalent to two resonant branches, and the two resonant branches are similar to Figure 4A The two resonant branches can also be made equal in frequency by selecting the capacitance of the first resonant capacitor Cr1, the second resonant capacitor Cr2 and the third resonant capacitor Cr3. At this time, the two resonant frequencies are equal to the switching frequencies of the second switch S2, the fourth switch S4, the fifth switch S5 and the seventh switch S7 which are in the on state, so they are not described in detail here.

[0116] Please continue reading Figure 4BIn this working state, there are three current branches in the power conversion circuit 1, namely, a first current branch, a second current branch and a third current branch, wherein the first current branch is formed by connecting the second resonant capacitor Cr2, the fourth switch S4, the output negative electrode Vo-, the output positive electrode Vo+, the third series inductor Lr3 (the third winding T3), the seventh switch S7, the first resonant capacitor Cr1, the first series inductor Lr1 (the first winding T1) and the second switch S2 in sequence, and there is a first current on the first current branch, wherein in the first current branch, the energy stored in the second resonant capacitor Cr2 transfers energy to the output voltage Vo through the resonance of the first series inductor Lr1, the third series inductor Lr3 and the second resonant capacitor Cr2 and the first resonant capacitor Cr1. The second current branch is formed by sequentially connecting the input positive electrode Vin+, the fifth switch S5, the third resonant capacitor Cr3, the third series inductor Lr3 (the third winding T3), the output positive electrode Vo+, the output negative electrode Vo- and the input negative electrode Vin-, and there is a second current on the second current branch, wherein in the second current branch, part of the energy of the input voltage Vin is stored in the third resonant capacitor Cr3, and at the same time, the energy is transferred to the output voltage Vo through the resonance of the third series inductor Lr3 and the third resonant capacitor Cr3. The third current branch is formed by sequentially connecting the second winding T2, the second series inductor Lr2, the output positive electrode Vo+, the output negative electrode Vo- and the fourth switch S4, and there is a third current on the third current branch. As can be seen from the above, among the three current branches, only the first current of the first current branch flows through the first winding T1, so the first winding current iT1 flowing through the first winding T1 is only composed of the first current, so the amplitude of the first winding current iT1 flowing through the first winding T1 is the amplitude of the first current. The first current of the first current branch and the second current of the second current branch among the three current branches flow through the second winding T2, so the third winding current iT3 flowing through the third winding T3 is composed of the first current and the second current, so the amplitude of the third winding current iT3 flowing through the third winding T3 is the sum of the amplitude of the first current and the amplitude of the second current, and because the amplitude of the first current is equal to the amplitude of the second current, the amplitude of the third winding current iT3 flowing through the third winding T3 is twice the amplitude of the first current or twice the amplitude of the second current. For the convenience of discussion, the following will be explained as the amplitude of the third winding current iT3 flowing through the third winding T3 is twice the amplitude of the second current (i.e., the input current).In addition, due to the coupling relationship between the first winding T1, the second winding T2 and the third winding T3 of the transformer 14, the amplitude of the second winding current iT2 flowing through the second winding T2 is K multiplied by the first current plus the first current plus the second current, where K is the ratio between the number of turns N1 of the first winding T1 and the number of turns N2 of the second winding T2 (or the number of turns N2 of the third winding T3), and since the amplitude of the first current is equal to the amplitude of the second current, the amplitude of the second winding current iT2 flowing through the second winding T2 is (K+2) times the amplitude of the first current or (K+2) times the amplitude of the second current. For the convenience of discussion, the following will be described with the amplitude of the second winding current iT2 flowing through the second winding T2 being (K+2) times the amplitude of the second current. According to. Figure 4A It can be seen that the output current io of the power conversion circuit 1 is the second winding current iT2 flowing through the second winding T2 plus the third winding current iT3 flowing through the third winding T3. Therefore, it can be seen that the amplitude of the output current io of the power conversion circuit 1 is twice the amplitude of the second current plus (K+2) times the amplitude of the first current, that is, (K+4) times the amplitude of the second current.

[0117] According to the on and off states of the multiple switches in the first bridge arm 12 and the multiple switches in the second bridge arm 13 of the above-mentioned power conversion circuit 1, and the mutual coupling between the first winding T1, the second winding T2 and the third winding T3 of the transformer 14, the output voltage Vo of the power conversion circuit 1 and the input voltage Vin have the following relationship: Vo=Vin / (K+4), wherein since K is the ratio between the number of turns N1 of the first winding T1 and the number of turns N2 of the second winding T2 (or the number of turns N2 of the third winding T3), the number of turns N1 of the first winding T1 and the number of turns N2 of the second winding T2 and the third winding T3 can be adjusted to obtain different gain ratios between the output voltage Vo and the input voltage Vin. For example, when K=N1 / N2=1, the gain ratio between the output voltage Vo and the input voltage Vin is 5:1. Therefore, the power conversion circuit 1 of the present application can meet the requirements of different gain ratios between the output voltage Vo and the input voltage Vin, and has better applicability. In some embodiments, when the ratio K between the number of turns N1 of the first winding T1 and the number of turns N2 of the second winding T2 (or the number of turns N2 of the third winding T3) is not equal to 1, the power conversion circuit 1 can still obtain different gain ratios between the output voltage Vo and the input voltage Vin according to different ratios K. According to the relationship between the output voltage Vo and the input voltage Vin, Vo = Vin / (K+4), the output voltage Vo and the input voltage Vin of the power conversion circuit 1 have the following general formula, Vo = Vin*[N2 / ((N1+N2*2)+2)].

[0118] In some embodiments, the resonant frequencies of the two resonant branches of the power conversion circuit 1 may not be equal to the switching frequency. In some embodiments, the power conversion circuit 1 may make the resonant frequencies of the two resonant branches unequal by selecting the capacitance of the first resonant capacitor Cr1, the second resonant capacitor Cr2, and the third resonant capacitor Cr3.

[0119] See also Figure 5 , which is a schematic diagram of the circuit structure of the power conversion circuit of the second preferred embodiment of the present application. The circuit configuration and control method of the power conversion circuit 1a of this embodiment are similar to Figure 2A The circuit configuration and control method of the power conversion circuit 1 are described in detail herein, and the power conversion circuit 1a of this embodiment is compared with Figure 2A In the power conversion circuit 1, only the setting positions of the first winding T1 and the first resonant capacitor Cr1 are swapped. In this embodiment, the first end of the first winding T1 is electrically connected to the second end of the first resonant capacitor Cr1, the second end of the first winding T1 is electrically connected to the fifth connection point P5, and the first end of the first resonant capacitor Cr1 is electrically connected to the second connection point P2.

[0120] See also Figure 6 , which is a schematic diagram of the circuit structure of the power conversion circuit of the third preferred embodiment of the present application. The circuit configuration and control method of the power conversion circuit 1b of this embodiment are similar to those of Figure 2A The circuit configuration and control method of the power conversion circuit 1 are described in detail herein, and the power conversion circuit 1b of this embodiment is compared with Figure 2A The power conversion circuit 1 only changes the setting position of the input capacitor Cin from Figure 2A The capacitor Cin shown in the embodiment is arranged between the input positive electrode Vin+ and the input negative electrode Vin- instead of being arranged between the input positive electrode Vin+ and the output positive electrode Vo+. Thus, the input capacitor Cin of the embodiment can adopt a capacitor with a smaller withstand voltage.

[0121] In some embodiments, in order to start the power conversion circuit, the second resonant capacitor Cr2 and the third resonant capacitor Cr3 need to be precharged to prevent the second resonant capacitor Cr2 and the third resonant capacitor Cr3 from causing impact damage to other devices during the startup process due to the low terminal voltage of the second resonant capacitor Cr2 and the third resonant capacitor Cr3. The power conversion circuit may also include a precharge circuit to increase the terminal voltage of the second resonant capacitor Cr2 and the third resonant capacitor Cr3. Figure 7 and Figure 8 ,in Figure 7 Schematic diagram of the circuit structure of the power conversion circuit of the fourth preferred embodiment of the present application, Figure 8 for Figure 7 The circuit configuration and control method of the power conversion circuit 1c of this embodiment are similar to those of Figure 2AThe circuit configuration and control method of the power conversion circuit 1 are not described here, and the power conversion circuit 1c of this embodiment further includes a first resistor R1, a second resistor R2, an auxiliary switch M, a first clamp switch D1 and a second clamp switch D2 constituting a pre-charging circuit 2, and the first clamp switch D1 and the second clamp switch D2 have a first end and a second end respectively. In the following embodiments, the first clamp switch D1 and the second clamp switch D2 are taken as an example to illustrate that the first clamp switch D1 and the second clamp switch D2 are respectively the first diode D1 and the second diode D2, wherein the first ends of the two clamp switches correspond to the anode of the diode, and the second ends of the two clamp switches correspond to the cathode of the diode, but this is not limited to this, as long as the switches with the same function are within this protection range.

[0122] The first resistor R1 and the second resistor R2 are connected in series between the input positive electrode Vin+ and the input negative electrode Vin-. The first end Ma of the auxiliary switch M is electrically connected to the input positive electrode Vin+, the second end Mb of the auxiliary switch M is electrically connected to the common connection point of the first resistor R1 and the second resistor R2, the third end Mc of the auxiliary switch M is electrically connected to the anode of the first diode D1 and the anode of the second diode D2, the cathode of the first diode D1 is electrically connected to the first connection point P1, and the cathode of the second diode D2 is electrically connected to the fourth connection point P4. In this embodiment, the pre-charging circuit 2 of the power conversion circuit 1c further includes a third diode D3, the cathode of the third diode D3 is electrically connected between the first resistor R1 and the second resistor R2, and the anode of the third diode D3 is electrically connected to the input negative electrode Vin-.

[0123] See also Figure 8 And cooperate Figure 7 When the voltage source 11 provides the input voltage Vin, the voltage Vg of the second terminal Mb of the auxiliary switch M will increase with the increase of the input voltage Vin to achieve self-conduction, and the input voltage Vin will pre-charge the second resonant capacitor Cr2 through the auxiliary switch M and the first diode D1, so that the terminal voltage Vcr2 of the second resonant capacitor Cr2 also increases with the increase of the input voltage Vin, and the input voltage Vin will pre-charge the third resonant capacitor Cr3 through the auxiliary switch M and the second diode D2, so that the terminal voltage Vcr3 of the third resonant capacitor Cr3 also increases with the increase of the input voltage Vin.

[0124] In this embodiment, the gate voltage Vg of the auxiliary switch M is formed by multiplying the input voltage Vin by the first resistor R1 and then dividing it by the sum of the first resistor R1 and the second resistor R2. In order to prevent the voltage Vg at the second end Mb of the auxiliary switch M from being too high, so that the terminal voltage Vcr2 of the second resonant capacitor Cr2 and the terminal voltage Vcr3 of the third resonant capacitor Cr3 exceed the steady-state operating voltage, the resistance ratio between the first resistor R1 and the second resistor R2 needs to be such that the relationship between the voltage Vg at the second end Mb of the auxiliary switch M and the input voltage Vin satisfies the following equation:

[0125] Vg <Vin*[1-2*N2 / ((N1+N2*2)+2)]+Vth,

[0126] Wherein Vg is the voltage of the second terminal Mb of the auxiliary switch M, Vin is the input voltage, N1 is the number of turns of the first winding T1, N2 is the number of turns of the second winding T2, the number of turns of the second winding T2 and the number of turns of the third winding T3 are the same, and Vth is the threshold voltage from the second terminal Mb to the third terminal Mc when the auxiliary switch M is turned on. The auxiliary switch M may be, for example but not limited to, a MOSFET, a BJT, a SiC or a GaN switch. In addition, taking the switches S1 to S8 as MOSFETs as an example, since the source of the first switch S1 and the source of the fifth switch S5 are electrically connected to the second resonant capacitor Cr2 and the third resonant capacitor Cr3 respectively, when the terminal voltage Vcr2 of the second resonant capacitor Cr2 and the terminal voltage Vcr3 of the third resonant capacitor Cr3 increase with the increase of the input voltage Vin, the drain-source voltage of the first switch S1 and the drain-source voltage of the fifth switch S5 can be reduced, so that the first switch S1 and the fifth switch S5 can select switch elements with lower withstand voltage, thereby improving the conversion efficiency of the power conversion circuit 1c during steady-state operation.

[0127] When the terminal voltage Vcr2 of the second resonant capacitor Cr2 and the terminal voltage Vcr3 of the third resonant capacitor Cr3 have reached the preset voltage, for example, when the terminal voltage Vcr2 of the second resonant capacitor Cr2 is equal to the difference between the input voltage Vin and twice the output voltage Vo, that is, Vin-2*Vo, and the terminal voltage Vcr3 of the third resonant capacitor Cr3 is equal to the difference between the input voltage Vin and twice the output voltage Vo, that is, Vin-2*Vo, the power conversion circuit 1c exits the pre-charging state and enters steady-state operation. At this time, the first diode D1 and the second diode D2 reversely block the electric energy transmitted by the auxiliary switch M, so that the pre-charging circuit 2 will no longer participate in the operation of the power conversion circuit 1c.

[0128] See also Fig. 9 , which is a schematic diagram of the circuit structure of the power conversion circuit of the fourth preferred embodiment of the present application. As shown in the figure, the circuit configuration and control method of the power conversion circuit 1c of this embodiment are similar to those of Figure 2AThe circuit configuration and control method of the power conversion circuit 1 are not described here, and the power conversion circuit 1c of this embodiment further includes a start-up circuit 3, which is used to control the resonant capacitors Cr2, Cr3 and the output capacitor Co of the power conversion circuit 1c to realize pre-charging at the same time, wherein the start-up circuit 3 includes an upper switch Ss1, a lower switch Ss2, a fourth winding T4 and an output inductor Lo. The upper switch Ss1 and the lower switch Ss1 are connected in series between the input positive electrode Vin+ and the input negative electrode Vin-, and the upper switch Ss1 and the lower switch Ss2 are complementary. The fourth winding T4 is coupled to the first winding T1, the second winding T2 and the third winding T3, wherein the position of the same-name end of the fourth winding T4 is not limited. The output inductor Lo is connected in series with the fourth winding T4 to form a series branch, one end of the series branch is electrically connected to the common connection point of the upper switch Ss1 and the lower switch Ss2, and the other end of the series branch is electrically connected to the output positive electrode Vo+, that is, the fourth winding T4 is electrically connected to the output positive electrode Vo+.

[0129] See also Fig.10 and FIG. 11A to FIG. 11D And cooperate Fig. 9 ,in Fig.10 for Fig. 9 The waveform diagram of some components of the power conversion circuit shown in FIG. FIG. 11A to FIG. 11D for Fig. 9 The power conversion circuit shown in Fig.10 Schematic diagram of the working state in different time periods. In this implementation, the upper switch Ss1 and the lower switch Ss2 are MOSFETs as an example. Fig.10 In the figure, Vgsu is the gate-source voltage of the upper switch Ss1, Vgsl is the gate-source voltage of the lower switch Ss2, iLo is the inductor current flowing through the output inductor Lo, Vcr2 and Vcr3 are the terminal voltage of the second resonant capacitor Cr2 and the terminal voltage of the third resonant capacitor Cr3, respectively, and Vco is the voltage of the output capacitor Co. Fig.10 As shown, the time from t0 to t4 is a switching cycle, and the upper switch Ss1 and the lower switch Ss2 are complementary turned on. FIG. 11A to FIG. 11D In the diagram, darker lines are used to show the paths through which current flows, and lighter lines are used to show the paths through which current does not flow.

[0130] See also Fig.10 and Fig.11ADuring the period from time t0 to t1, the upper switch Ss1 is in the on state, and the lower switch Ss2 is in the off state. At this time, the current in the startup circuit 3 flows through the upper switch Ss1, the output inductor Lo and the fourth winding T4, so that the inductor current iLo of the output inductor Lo rises linearly during the period from time t0 to t1, wherein the inductor current iLo of the output inductor Lo is smaller than the DC component on the output inductor Lo. At this time, the body diodes of the third switch S3 and the sixth switch S6 are turned on, and through the coupling of the fourth winding T4 with the first winding T1, the second winding T2 and the third winding T3, the coupling current flows through the third winding T3, the second winding T2, the third switch S3, the first winding T1, the first resonant capacitor Cr1, the sixth switch S6 and the third resonant capacitor Cr3 in sequence to precharge the third resonant capacitor Cr3.

[0131] See also Fig.10 and Fig. 11B , during the period from time t1 to t2, the upper switch Ss1 is in the on state, and the lower switch Ss2 is in the off state. At this time, the current in the startup circuit 3 flows through the upper switch Ss1, the output inductor Lo and the fourth winding T4, so that the inductor current iLo of the output inductor Lo rises linearly during the period from time t1 to t2, wherein the inductor current iLo of the output inductor Lo is greater than the DC component on the output inductor Lo. At this time, the inductor current iLo of the output inductor Lo flows to pre-charge the output capacitor Co. At the same time, the body diodes of the second switch S2 and the seventh switch S7 are turned on, and through the coupling of the fourth winding T4 with the first winding T1, the second winding T2 and the third winding T3, the coupling current flows through the second winding T2, the third winding T3, the seventh switch S7, the first resonant capacitor Cr1, the first winding T1, the second switch S2 and the second resonant capacitor Cr2 in sequence to pre-charge the second resonant capacitor Cr2.

[0132] See also Fig.10 and Fig. 11C , during the period from time t2 to t3, the upper switch Ss1 is in the off state, and the lower switch Ss2 is in the on state. At this time, the current in the startup circuit 3 flows through the lower switch Ss2, the output inductor Lo and the fourth winding T4, so that the inductor current iLo of the output inductor Lo decreases linearly during the period from time t2 to t3, wherein the inductor current iLo of the output inductor Lo is greater than the DC component on the output inductor Lo. At this time, the inductor current iLo of the output inductor Lo flows to the output capacitor Co for pre-charging. At the same time, the body diodes of the second switch S2 and the seventh switch S7 are turned on, and through the coupling of the fourth winding T4 with the first winding T1, the second winding T2 and the third winding T3, the coupling current flows through the second winding T2, the third winding T3, the seventh switch S7, the first resonant capacitor Cr1, the first winding T1, the second switch S2 and the second resonant capacitor Cr2 in sequence to pre-charge the second resonant capacitor Cr2.

[0133] See also Fig.10 and Fig.11D During the period from time t3 to t4, the upper switch Ss1 is in the off state, and the lower switch Ss2 is in the on state. At this time, the current in the startup circuit 3 flows through the lower switch Ss2, the output inductor Lo and the fourth winding T4, so that the inductor current iLo of the output inductor Lo decreases linearly during the period from time t3 to t4, wherein the inductor current iLo of the output inductor Lo is less than the DC component on the output inductor Lo. At this time, the body diodes of the second switch S2 and the seventh switch S7 are turned on, and through the coupling of the fourth winding T4 with the first winding T1, the second winding T2 and the third winding T3, the coupling current flows through the third winding T3, the second winding T2, the third switch S3, the first winding T1, the first resonant capacitor Cr1, the sixth switch S6 and the third resonant capacitor Cr3 in sequence to precharge the third resonant capacitor Cr3. The operation mode and working principle of other switching cycles can correspond to the operation mode and working principle of the above-mentioned time t0-t4, so they are not repeated here. Thereby, the power conversion circuit 1 c utilizes the start-up circuit 3 to pre-charge the second resonant capacitor Cr2 , the third resonant capacitor Cr3 and the output capacitor Co.

[0134] When the voltage across the second resonant capacitor Cr2, the third resonant capacitor Cr3 and the output capacitor Co reaches a preset value, the start-up circuit 3 exits the working state, and the switches S1-S8 enter the normal on and off state. The working state and principle are as follows: Figure 3 , Figure 4A and Figure 4B As shown, no further description is given here.

[0135] In summary, the power conversion circuit of the present application is coupled between the on and off states of the multiple switches in the first bridge arm and the multiple switches in the second bridge arm, the first resonant capacitor, the second resonant capacitor, the third resonant capacitor, and the first winding, the second winding, and the third winding of the transformer, so that the power conversion circuit can adjust the number of turns of the first winding and the number of turns of the second winding and the third winding to obtain different output voltage and input voltage gain ratios. Therefore, the power conversion circuit of the present application can meet the requirements of different output voltage and input voltage gain ratios and has better applicability. In addition, the power conversion circuit of the present application can also use a pre-charging circuit or a starting circuit to realize the pre-charging of the resonant capacitor and the output capacitor.

Claims

1. A power conversion circuit, comprising: An input positive electrode, an input negative electrode, an output positive electrode and an output negative electrode, wherein the input negative electrode and the output negative electrode are connected; a first bridge arm, comprising a first switch, a second switch, a third switch and a fourth switch connected in series between the input positive electrode and the input negative electrode, wherein the first switch is connected to the second switch to form a first connection point, the second switch is connected to the third switch to form a second connection point, and the third switch is connected to the fourth switch to form a third connection point; a second bridge arm, comprising a fifth switch, a sixth switch, a seventh switch and an eighth switch connected in series between the input positive electrode and the input negative electrode, the fifth switch and the sixth switch are connected to form a fourth connection point, the sixth switch and the seventh switch are connected to form a fifth connection point, and the seventh switch and the eighth switch are connected to form a sixth connection point; A transformer, comprising a first winding, a second winding and a third winding coupled to each other, wherein the second winding is electrically connected between the third connection point and the output positive electrode, and the third winding is electrically connected between the sixth connection point and the output positive electrode; a first resonant capacitor, connected in series with the first winding and electrically connected between the second connection point and the fifth connection point; a second resonant capacitor electrically connected between the first connection point and the third connection point; a third resonant capacitor electrically connected between the fourth connection point and the sixth connection point; and An output capacitor is electrically connected between the output positive electrode and the output negative electrode.

2. The power conversion circuit according to claim 1, in, A first end of the first winding is electrically connected to the second connection point, a second end of the first winding is electrically connected to the first resonant capacitor, a first end of the second winding and a first end of the third winding are electrically connected to the output positive pole, a second end of the second winding is electrically connected to the third connection point, and a second end of the third winding is electrically connected to the sixth connection point, wherein the first end of the first winding, the first end of the second winding, and the second end of the third winding are like-named ends.

3. The power conversion circuit according to claim 1, in, A first end of the first winding is electrically connected to the first resonant capacitor, a second end of the first winding is electrically connected to the fifth connection point, a first end of the second winding and a first end of the third winding are electrically connected to the output positive pole, a second end of the second winding is electrically connected to the third connection point, and a second end of the third winding is electrically connected to the sixth connection point, wherein the first end of the first winding, the first end of the second winding, and the second end of the third winding are like-named ends.

4. The power conversion circuit according to claim 1, in, The number of turns of the first winding is N1, and the number of turns of the second winding and the third winding are both N2, wherein N1 and N2 are both positive numbers.

5. The power conversion circuit according to claim 1, in, The power conversion circuit includes an input capacitor electrically connected between the input positive electrode and the input negative electrode, or electrically connected between the input positive electrode and the output positive electrode.

6. The power conversion circuit according to claim 1, in, The power conversion circuit includes a first series inductor, a second series inductor and a third series inductor, wherein the first series inductor, the first winding and the first resonant capacitor are connected in series and electrically connected between the second connection point and the fifth connection point, and the first series inductor is the leakage inductance of the transformer and / or a first external inductor, wherein the second series inductor and the second winding are connected in series and electrically connected between the third connection point and the output positive pole, and the second series inductor is the leakage inductance of the transformer and / or a second external inductor, wherein the third series inductor and the third winding are connected in series and electrically connected between the sixth connection point and the output positive pole, and the third series inductor is the leakage inductance of the transformer and / or a third external inductor.

7. The power conversion circuit according to claim 1, in, The transformer has an equivalent excitation inductance, which is equivalent to being connected in parallel with the first winding or the second winding or the third winding.

8. The power conversion circuit as claimed in claim 7, in, The multiple switches are turned on and off in a switching cycle, and there is a dead time in the switching cycle. During the dead time, an excitation current flowing through the equivalent excitation inductance charges and discharges the parasitic capacitance of the corresponding switch to achieve zero voltage switching.

9. The power conversion circuit according to claim 1, in, The first switch, the third switch, the sixth switch and the eighth switch are turned on and off synchronously, and the second switch, the fourth switch, the fifth switch and the seventh switch are turned on and off synchronously, and a control signal received by the first switch, the third switch, the sixth switch and the eighth switch is 180 degrees out of phase with the control signal received by the second switch, the fourth switch, the fifth switch and the seventh switch.

10. The power conversion circuit according to claim 9, in, Duty cycles of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, the sixth switch, the seventh switch, and the eighth switch are 50% respectively.

11. The power conversion circuit according to claim 9, in, When four of the first switch, the second switch, the third switch, the fourth switch, the fifth switch, the sixth switch, the seventh switch and the eighth switch are turned on, the power conversion circuit has two resonant branches, wherein the resonant frequencies of the two resonant branches are equal, and the resonant frequencies of the two resonant branches are equal to the switching frequencies of the four turned-on switches, and the current flowing through the first winding, the second winding and the third winding is the superposition of the excitation current and a sinusoidal current.

12. The power conversion circuit according to claim 1, in, The voltage between the input positive electrode and the input negative electrode is an input voltage, the voltage between the output positive electrode and the output negative electrode is an output voltage, and the relationship between the input voltage and the output voltage conforms to the following equation: Vo=Vin*[N2 / ((N1+N2*2)+2)] Wherein, Vo is the output voltage, Vin is the input voltage, N1 is the number of turns of the first winding, N2 is the number of turns of the second winding, and the number of turns of the second winding is the same as the number of turns of the third winding.

13. The power conversion circuit according to claim 1, in, The power conversion circuit includes a first resistor, a second resistor, an auxiliary switch, a first clamp switch and a second clamp switch, wherein the first resistor and the second resistor are connected in series between the input positive electrode and the input negative electrode, the first end of the auxiliary switch is electrically connected to the input positive electrode, the second end of the auxiliary switch is electrically connected to a common connection point of the first resistor and the second resistor, the third end of the auxiliary switch is electrically connected to the first end of the first clamp switch and the second end of the second clamp switch, the second end of the first clamp switch is electrically connected to the first connection point, and the second end of the second clamp switch is electrically connected to the fourth connection point, wherein the voltage between the input positive electrode and the input negative electrode is an input voltage, and the input voltage is used to charge the second resonant capacitor and the third resonant capacitor via the auxiliary switch, the first clamp switch and the second clamp switch.

14. The power conversion circuit according to claim 1, in, The power conversion circuit includes an upper switch, a lower switch, a fourth winding and an output inductor. The upper switch and the lower switch are connected in series between the input positive electrode and the input negative electrode. The fourth winding is coupled with the first winding, the second winding and the third winding. The output inductor and the fourth winding constitute a series branch. One end of the series branch is connected to a common connection point of the upper switch and the lower switch, and the other end of the series branch is connected to the output positive electrode. The second resonant capacitor, the third resonant capacitor and the output capacitor are pre-charged by controlling the opening and closing of the upper switch and the lower switch.

15. The power conversion circuit according to claim 14, in, The upper switch and the lower switch are complementary in conduction.

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