Three-level rectifier DC / DC converter

Abstract

This case provides a three-level rectifier DC / DC converter, which includes a primary circuit, a resonant cavity circuit, and a secondary circuit. The voltage between the two primary ends of the resonant cavity circuit is the first voltage, and the voltage between the two secondary ends is the second voltage. The secondary circuit includes two clamping switches, a switch bridge arm, and a capacitor bridge arm. The switch bridge arm includes four switches connected in series. The two clamping switches are connected in series between the node between the first and second switches and the node between the third and fourth switches. The two secondary ends are respectively connected between the second and third switches and between the two output capacitors of the capacitor bridge arm, and the node between the two clamping switches is connected between the two output capacitors. During the change period of the first voltage, the second switch conducts for a preset duration after the falling edge, and the third switch conducts for a preset duration after the rising edge.

Description

Technical Field

[0001] This case relates to a DC / DC converter, especially a three-level rectifier DC / DC converter. Background Art

[0002] Low-voltage / DC / DC converters, bidirectional OBCs (on-board chargers), and traction inverters are the three main power conversion units of electric vehicles. Among them, the OBC, as an energy conversion unit between AC and DC, supplies energy to the power battery and is indispensable in the configuration of electric vehicles. In recent years, with the continuous improvement of the endurance of electric vehicles, the battery voltage is changing from the traditional 400V to 800V, and the OBC is gradually transitioning from traditional single-phase charging to three-phase charging. Therefore, the rectified voltage from AC to DC will reach 800V. It can be seen that both the primary and secondary sides of the DC / DC converter will involve 800V applications.

[0003] In the case where traditional devices with a withstand voltage of 650V cannot be used, SiC devices with a withstand voltage of 1200V need to be adopted. However, their cost is relatively high, and the resulting high dv / dt will also cause problems related to EMI (electromagnetic interference). In addition, as the development trend of future power devices, wide-bandgap semiconductor devices GaN are difficult to be directly applied in high-voltage working scenarios such as 800V due to their limited withstand voltage. The use of multi-level technology can break this limitation, thereby expanding the development and application of actual products.

[0004] In addition, for applications with a wide output voltage range in actual engineering, in order to meet the requirements of high efficiency and high output voltage gain, fixed-frequency PWM (pulse width modulation) control based on a dual active bridge (DAB) and resonant soft-switching variable-frequency control based on an LLC circuit are usually adopted.

[0005] For the dual active bridge circuit, multiple phase-shift techniques are usually adopted to achieve the switching ZVS (zero-voltage switching) operation in the case of a wide output range. However, its control is relatively complex, and due to the large turn-off current, it is easy to cause high turn-off stress and EMI problems.

[0006] For the LLC circuit, variable-frequency control is usually adopted, so that all switches can achieve ZVS operation, and its control implementation method is relatively simple. However, the LLC circuit is difficult to meet the bidirectional working requirements in actual applications.

[0007] Therefore, it is an urgent need at present to develop a three-level rectifying DC / DC converter that can improve the above-known technologies. Summary of the Invention

[0008] The purpose of this case is to provide a three-level rectifying DC / DC converter, which has the characteristics of a resonant circuit and can also meet the requirements of bidirectional operation. In addition, it has the energy storage characteristics of secondary short circuit, and can achieve high voltage gain output by this means.

[0009] To achieve the above purpose, this case provides a three-level rectifying DC / DC converter, which includes a primary circuit, a resonant cavity circuit and a secondary circuit. The primary circuit receives an input voltage and includes a plurality of primary switches. The resonant cavity circuit includes a resonant inductor, a resonant capacitor and a transformer. The first primary end and the second primary end of the resonant cavity circuit are electrically connected to the primary circuit, the primary winding of the transformer is electrically connected between the first primary end and the second primary end, and the secondary winding of the transformer is electrically connected between the first secondary end and the second secondary end of the resonant cavity circuit. The voltage between the first primary end and the second primary end is the first voltage, and the voltage between the first secondary end and the second secondary end is the second voltage. The secondary circuit includes two clamping switches, a switch bridge arm and a capacitor bridge arm. The switch bridge arm includes a first secondary switch, a second secondary switch, a third secondary switch and a fourth secondary switch connected in series in sequence. The two clamping switches are connected in series between the node between the first secondary switch and the second secondary switch and the node between the third secondary switch and the fourth secondary switch. The node between the second secondary switch and the third secondary switch is connected to the first secondary end. The capacitor bridge arm includes a first output capacitor and a second output capacitor connected in series, and the node between the first output capacitor and the second output capacitor is connected to the node between the two clamping switches and the second secondary end. The two ends of the capacitor bridge arm are respectively connected to the two ends of the switch bridge arm, and the voltage between the two ends of the capacitor bridge arm is the output voltage. The second secondary switch is in the on state at least within a preset time period after the falling edge in the change period of the first voltage, and the third secondary switch is in the on state at least within a preset time period after the rising edge in the change period of the first voltage. Description of the Drawings

[0010] Figure 1 Schematic diagram of the circuit architecture of the three-level rectifying DC / DC converter according to a preferred embodiment of this case;

[0011] Figure 2 Shows Figure 1 The equivalent circuit of the three-level rectifying DC / DC converter;

[0012] Figure 3A And Figure 3B Is Figure 1 The variation example of the three-level rectifying DC / DC converter;

[0013] Figure 4 is Figure 1 a schematic diagram of key waveforms of a three-level rectifying DC / DC converter;

[0014] Figures 5A to 5F shows Figure 1 the operating states of a three-level rectifying DC / DC converter within one period of its secondary side switch;

[0015] Figure 6A shows Figure 1 the equivalent circuit of a three-level rectifying DC / DC converter during the period when its primary side first voltage is at high level and its secondary side switch conducts forward;

[0016] Figure 6B shows Figure 1 the equivalent circuit of a three-level rectifying DC / DC converter during the period when its primary side first voltage is at low level and its secondary side switch conducts forward;

[0017] Figure 7 is Figure 1 a schematic diagram of key waveforms of a three-level rectifying DC / DC converter when its secondary side switch adopts full synchronous rectification;

[0018] Figure 8A is a control block diagram for Figure 1 a three-level rectifying DC / DC converter when adopting variable frequency control;

[0019] Figure 8B is a control block diagram for Figure 1 a three-level rectifying DC / DC converter when adopting fixed frequency control;

[0020] Figure 9 illustrates Figure 1 a specific implementation aspect of a resonant cavity circuit;

[0021] Figure 10 illustrates Figure 1 a specific implementation aspect of a primary side circuit;

[0022] Figure 11 is Figure 10 a schematic diagram of key waveforms of a three-level rectifying DC / DC converter;

[0023] Figure 12 is Figure 10 a schematic diagram of key waveforms of a three-level rectifying DC / DC converter when its secondary side switch adopts full synchronous rectification;

[0024] Figure 13 illustrates Figure 1 another specific implementation aspect of a primary side circuit;

[0025] Figure 14 For Figure 13 Schematic diagram of key waveforms of a three-level rectifier DC / DC converter;

[0026] Figure 15 For Figure 13 Schematic diagram of key waveforms of a three-level rectifier DC / DC converter when its secondary side switches adopt full synchronous rectification.

[0027]

Symbol Explanation

[0028] 1: Three-level rectifier DC / DC converter

[0029] 11: Primary circuit

[0030] 12: Resonant cavity circuit

[0031] Lr: Resonant inductor

[0032] Cr: Resonant capacitor

[0033] Tr: Transformer

[0034] Np: Primary winding

[0035] Ns: Secondary winding

[0036] 121: First primary terminal

[0037] 122: Second primary terminal

[0038] 123: First secondary terminal

[0039] 124: Second secondary terminal

[0040] 13: Secondary circuit

[0041] D1, D2: Clamping switches

[0042] S21: First secondary switch

[0043] S22: Second secondary switch

[0044] S23: Third secondary switch

[0045] S24: Fourth secondary switch

[0046] Co1: First output capacitor

[0047] Co2: Second output capacitor

[0048] A, B, C, D: Nodes

[0049] VAB: First voltage

[0050] VCD: Second voltage

[0051] Ip: Primary side current

[0052] Is: Secondary side current

[0053] Vin: Input voltage

[0054] Vo: Output voltage

[0055] is21, is22, is23, is24, iD1, iD2: Currents

[0056] t0, t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11, t12: Moments

[0057] 14a, 14b: Control modules

[0058] 141: Regulator

[0059] 142: Voltage-controlled oscillator

[0060] 143: Controller

[0061] 144: PWM controller

[0062] Io: Output current

[0063] Vin_FB: Input voltage signal

[0064] Vo_FB: Output voltage signal

[0065] Io_FB: Output current signal

[0066] Vo_ref: Output reference voltage

[0067] Io_ref: Output reference current

[0068] fs: Switching frequency

[0069] n: Turns ratio

[0070] Ton: Conduction time

[0071] Lrp: Primary side resonant inductor

[0072] Lrs: Secondary side resonant inductor

[0073] Crp: Primary side resonant capacitor

[0074] Crs: Secondary side resonant capacitor

[0075] 11a, 11b: Primary side circuit

[0076] Cin: Input capacitor

[0077] S11: First primary side switch

[0078] S12: The second primary switch

[0079] S13: The third primary switch

[0080] S14: The fourth primary switch

[0081] D3, D4: Primary clamping switches

[0082] C1: The first input capacitor

[0083] C2: The second input capacitor Detailed implementation manners

[0084] Some typical embodiments embodying the features and advantages of this case will be described in detail in the following description. It should be understood that this case can have various changes in different aspects, all of which do not depart from the scope of this case, and the descriptions and illustrations therein are essentially for illustrative purposes rather than for limiting this case.

[0085] Figure 1 It is a schematic circuit diagram of a three-level rectifying DC / DC converter as a preferred embodiment of this case. Figure 2 Shows Figure 1 The equivalent circuit of the three-level rectifying DC / DC converter. As Figure 1 And Figure 2 Shown, the three-level rectifying DC / DC converter 1 includes a primary circuit 11, a resonant cavity circuit 12 and a secondary circuit 13, which can meet the requirements of bidirectional operation while having the characteristics of a resonant-type circuit.

[0086] The primary circuit 11 receives the input voltage Vin and includes a plurality of primary switches, and is configured to provide a first voltage VAB. It should be noted that since the actual aspect of the primary circuit 11 is not limited, in this embodiment, the primary circuit 11 is only schematically represented by a voltage source providing the first voltage VAB, and the specific implementation aspects of the primary circuit 11 will be illustrated in the following description.

[0087] The resonant cavity circuit 12 includes a resonant inductor Lr, a resonant capacitor Cr and a transformer Tr. The first primary terminal 121 and the second primary terminal 122 of the resonant cavity circuit 12 are electrically connected to the primary circuit 11, the primary winding Np of the transformer Tr is electrically connected between the first primary terminal 121 and the second primary terminal 122, and the secondary winding Ns of the transformer Tr is electrically connected between the first secondary terminal 123 and the second secondary terminal 124 of the resonant cavity circuit 12. The voltage between the first primary terminal 121 and the second primary terminal 122 is the first voltage VAB, and the voltage between the first secondary terminal 123 and the second secondary terminal 124 is the second voltage VCD. In Figure 1 And Figure 2 Ip is the primary current and Is is the secondary current.

[0088] The secondary circuit 13 includes two clamping switches D1 and D2, a switch bridge arm, and a capacitor bridge arm. The switch bridge arm includes a first secondary switch S21, a second secondary switch S22, a third secondary switch S23, and a fourth secondary switch S24 connected in series in sequence. The two clamping switches D1 and D2 are connected in series between the node between the first secondary switch S21 and the second secondary switch S22 and the node between the third secondary switch S23 and the fourth secondary switch S24. The node C between the second secondary switch S22 and the third secondary switch S23 is connected to the first secondary terminal 123. The capacitor bridge arm includes a first output capacitor Co1 and a second output capacitor Co2 connected in series, where the node between the first output capacitor Co1 and the second output capacitor Co2 is connected to the node D between the two clamping switches D1 and D2 and the second secondary terminal 124. Both ends of the capacitor bridge arm are respectively connected to both ends of the switch bridge arm, and the voltage between these two ends of the capacitor bridge arm is the output voltage Vo.

[0089] In Figure 1 the illustrated embodiment, the first secondary switch S21, the second secondary switch S22, the third secondary switch S23, and the fourth secondary switch S24 are all active switch tubes. In some other embodiments, for example Figure 3A as shown, the first secondary switch S21 and the fourth secondary switch S24 can also be a first diode and a second diode respectively, where the anode and cathode of the first diode are electrically connected to the second secondary switch S22 and the first output capacitor Co1 respectively, and the anode and cathode of the second diode are electrically connected to the second output capacitor Co2 and the third secondary switch S23 respectively.

[0090] In addition, in Figure 1 the illustrated embodiment, the clamping switches D1 and D2 are a third diode and a fourth diode respectively, where the anode and cathode of the third diode are electrically connected to the cathode of the fourth diode and the node between the first secondary switch S21 and the second secondary switch S22 respectively, and the anode of the fourth diode is electrically connected to the node between the third secondary switch S23 and the fourth secondary switch S24. In some other embodiments, for example Figure 3B as shown, the clamping switches D1 and D2 can also be active switch tubes.

[0091] Figure 4 is Figure 1 a schematic diagram of the key waveforms of a three-level rectifier DC / DC converter. In Figure 4Among them, S21, S22, S23, and S24 respectively represent the driving signals of the first secondary switch S21, the second secondary switch S22, the third secondary switch S23, and the fourth secondary switch S24. is21, is22, is23, and is24 respectively represent the currents flowing through the first secondary switch S21, the second secondary switch S22, the third secondary switch S23, and the fourth secondary switch S24. iD1 and iD2 respectively represent the currents flowing through the clamping switches D1 and D2. As Figure 4 shown, the second secondary switch S22 is in the on state within a preset time period after the falling edge in the change period of the first voltage VAB, and the third secondary switch S23 is in the on state within a preset time period after the rising edge in the change period of the first voltage VAB. The first secondary switch S21 and the fourth secondary switch S24 are in the diode rectification mode and remain in the off state. The second secondary switch S22 and the third secondary switch S23 have the same switching frequency, and their switching frequency is equal to the frequency of the first voltage VAB. The phases of the second secondary switch S22 and the third secondary switch S23 differ by 180 degrees. All of these secondary switches in the secondary circuit 13 can achieve zero-voltage turn-on. The aforementioned preset time period is obtained based on the input voltage Vin and the output voltage Vo. By controlling the preset time period, the duty cycle of each secondary switch can be adjusted, and thus the gain of the output voltage Vo can be controlled. In addition, the first voltage VAB is a square wave that is high-level in one half-cycle and low-level in the other half-cycle, where the high level and the low level can be equal to +VAB / 2 and -VAB / 2 respectively, or equal to +VAB and 0 respectively.

[0092] In Figure 4 , the time period from time t0 to t6 can be regarded as one cycle of the secondary switch. Figures 5A to 5F shows Figure 1 the operating states of the three-level rectifier DC / DC converter within one cycle of its secondary switch. Specifically, Figures 5A to 5F shows the switching states and current flow directions of the three-level rectifier DC / DC converter 1 at each time period within one cycle. The time period from time t1 to t2 ( Figure 5B ) and the time period from time t4 to t5 ( Figure 5E ) respectively correspond to the time periods when the third secondary switch S23 and the second secondary switch S22 are conducting forward. Figure 5B and 5E show the corresponding operating states of the three-level rectifier DC / DC converter 1. The equivalent circuit of the three-level rectifier DC / DC converter 1 during the time period from time t1 to t2 is as shown in Figure 6A , and the equivalent circuit of the three-level rectifier DC / DC converter 1 during the time period from time t4 to t5 is as shown in Figure 6B . From Figure 5B , 5EAs can be seen from FIGS. 6A and 6B, during the period when the third secondary switch S23 and the second secondary switch S22 are conducting forward, the secondary circuit 13 is equivalent to being in a short - circuit state. At this time, the resonant inductor Lr stores energy through the first voltage VAB, thereby preparing for the high - gain energy output in the next period.

[0093] As described above, in the three - level rectifier DC / DC converter 1 of this case, by controlling the four secondary switches, energy can be stored in the resonant inductor Lr during operation, thereby achieving a high - gain voltage output.

[0094] In some embodiments, to further improve the working efficiency of the three - level rectifier DC / DC converter 1, a synchronous rectification control method can be adopted for the secondary switches, that is, a drive is applied to the secondary switches during the period when the current flows in the reverse direction, thereby reducing the conduction loss of the secondary switches.

[0095] Figure 7 For Figure 1 Schematic diagram of the key waveforms of the three - level rectifier DC / DC converter when its secondary switches adopt full - synchronous rectification. As Figure 7 shown, when full - synchronous rectification is adopted, the first secondary switch S21, the second secondary switch S22, the third secondary switch S23, and the fourth secondary switch S24 are in the conducting state not only during the conducting period shown in Figure 4 but also during all periods when the current of the first secondary switch S21, the second secondary switch S22, the third secondary switch S23, and the fourth secondary switch S24 flows in the reverse direction. In this embodiment, the drive signals of the second secondary switch S22 and the third secondary switch S23 are complementary, and the duty cycles are both 50%. The phases of the first secondary switch S21 and the fourth secondary switch S24 differ by 180 degrees, and the phases of the second secondary switch S22 and the third secondary switch S23 differ by 180 degrees.

[0096] In addition, according to whether the switching frequency of the primary switch changes or not, the control methods for the three - level rectifier DC / DC converter 1 of this case can be classified into variable - frequency control and fixed - frequency control.

[0097] Figure 8A For Figure 1 Control block diagram of the three - level rectifier DC / DC converter when variable - frequency control is adopted. When variable - frequency control is adopted, as Figure 8AAs shown, the three-level rectifier DC / DC converter 1 further includes a control module 14a, where the control module 14a is configured to obtain, through sensing, an input voltage signal Vin_FB, an output voltage signal Vo_FB, and an output current signal Io_FB that respectively reflect the input voltage Vin, the output voltage Vo, and the output current Io, and control the operation of all primary switches and secondary switches. The control module 14a includes a regulator 141, where the regulator 141 generates a regulation signal based on the output voltage signal Vo_FB, the output current signal Io_FB, the output reference voltage Vo_ref, and the output reference current Io_ref. In this embodiment, the control module 14a further includes a voltage-controlled oscillator 142 and a controller 143. The voltage-controlled oscillator 142 is electrically connected to the regulator 141 and generates the switching frequency fs of all primary switches based on the regulation signal. The controller 143 is electrically connected to the voltage-controlled oscillator 142 and generates the on-time Ton of all secondary switches based on the input voltage signal Vin_FB, the output voltage signal Vo_FB, and the switching frequency fs of all primary switches. When the turns ratio n of the transformer Tr is constant, the relationship between the on-time Ton of all secondary switches, the input voltage Vin, the output voltage Vo, and the switching frequency fs of all primary switches conforms to Figure 8A the relationship curve shown therein. In practical applications, the on-time Ton of the secondary switches can be obtained through calculation or by looking up a table.

[0098] Figure 8B For Figure 1 the three-level rectifier DC / DC converter, the control block diagram when using fixed-frequency control is shown. When using fixed-frequency control, the switching frequency fs of all primary switches is fixed and greater than the resonant frequency of the resonant cavity circuit 12. As Figure 8B shown, the three-level rectifier DC / DC converter 1 further includes a control module 14b, where the control module 14b is configured to obtain, through sensing, an input voltage signal Vin_FB, an output voltage signal Vo_FB, and an output current signal Io_FB that respectively reflect the input voltage Vin, the output voltage Vo, and the output current Io, and control the operation of all primary switches and secondary switches. The control module 14b includes a regulator 141, where the regulator 141 generates a regulation signal based on the output voltage signal Vo_FB, the output current signal Io_FB, the output reference voltage Vo_ref, and the output reference current Io_ref. In this embodiment, the control module 14b further includes a PWM controller 144, where the PWM controller 144 is electrically connected to the regulator 141 and generates drive signals for all primary switches and secondary switches based on the regulation signal.

[0099] In addition, in the three-level rectifier DC / DC converter 1 of this case, there are various implementation forms for the resonant inductor Lr and the resonant capacitor Cr of the resonant cavity circuit 12. Figure 9Exemplifies a specific embodiment of a resonant cavity circuit 12. In Figure 9 the illustrated embodiment, the resonant inductor Lr, the primary winding Np, and the resonant capacitor Cr are sequentially connected in series between the first primary end 121 and the second primary end 122. However, this is not limited thereto. For example, the resonant capacitor Cr can also be connected in series between the secondary winding Ns and the second secondary end 124, and the resonant inductor Lr can also be connected in series between the secondary winding Ns and the first secondary end 123. Furthermore, for example Figure 10 as shown, in some embodiments, the resonant inductor Lr includes a primary resonant inductor Lrp and a secondary resonant inductor Lrs, where the primary resonant inductor Lrp is connected in series between the primary winding Np and the first primary end 121, and the secondary resonant inductor Lrs is connected in series between the secondary winding Ns and the first secondary end 123; in some embodiments, the resonant capacitor Cr includes a primary resonant capacitor Crp and a secondary resonant capacitor Crs, where the primary resonant capacitor Crp is connected in series between the primary winding Np and the second primary end 122, and the secondary resonant capacitor Crs is connected in series between the secondary winding Ns and the second secondary end 124.

[0100] Furthermore, in the three-level rectifying DC / DC converter 1 of this case, the actual circuit topology of the primary circuit is not limited and can be, for example but not limited to, a full-bridge circuit, a half-bridge circuit, a series half-bridge circuit, a flying capacitor three-level circuit, or a neutral point clamped three-level circuit. Two actual circuit topologies of the primary circuit will be exemplified below.

[0101] In some embodiments, as Figure 10 shown, the primary circuit 11a is a full-bridge circuit, where the primary circuit 11a includes an input capacitor Cin, a first bridge arm, and a second bridge arm that are connected in parallel with each other. The voltage across the input capacitor Cin is the input voltage Vin. The first bridge arm includes a first primary switch S11 and a second primary switch S12 connected in series, and the node B between the first primary switch S11 and the second primary switch S12 is connected to the second primary end 122. The second bridge arm includes a third primary switch S13 and a fourth primary switch S14 connected in series, and the node A between the third primary switch S13 and the fourth primary switch S14 is connected to the first primary end 121. The primary switches in the primary circuit 11a can all achieve zero-voltage turn-on. Figure 11 is Figure 10 a schematic diagram of the key waveforms of the three-level rectifying DC / DC converter. Figure 12 is Figure 10 a schematic diagram of the key waveforms of the three-level rectifying DC / DC converter when its secondary switch adopts full synchronous rectification.

[0102] In some embodiments, as Figure 13As shown, the primary circuit 11b is a neutral-point-clamped three-level circuit. The primary circuit 11b includes two primary clamping switches D3 and D4, a first arm and a second arm. The voltage between the two ends of the first arm is the input voltage Vin, and the two ends of the first arm are respectively connected to the two ends of the second arm. The first arm includes a first input capacitor C1 and a second input capacitor C2 connected in series. The second arm includes a first primary switch S11, a second primary switch S12, a third primary switch S13, and a fourth primary switch S14 connected in series in sequence. The two primary clamping switches D3 and D4 are connected in series between the node between the first primary switch S11 and the second primary switch S12 and the node between the third primary switch S13 and the fourth primary switch S14. The node A between the second primary switch S12 and the third primary switch S13 is connected to the first primary terminal 121, and the node between the first input capacitor C1 and the second input capacitor C2 is connected to the node B between the two primary clamping switches D3 and D4 and the second primary terminal 122. All the primary switches in the primary circuit 11b can achieve zero-voltage turn-on. Figure 14 is Figure 13 a schematic diagram of the key waveforms of a three-level rectifier DC / DC converter. Figure 15 is Figure 13 a schematic diagram of the key waveforms of a three-level rectifier DC / DC converter when its secondary switches adopt full synchronous rectification.

[0103] In summary, this case provides a three-level rectifier DC / DC converter, which can meet the requirements of bidirectional operation while having the characteristics of a resonant circuit. In addition, it has the characteristic of secondary short-circuit energy storage, which can be used to achieve high-voltage gain output. The highest voltage across the secondary switching device is half of the output voltage, and devices with lower breakdown voltage can be selected, which is conducive to the selection of switching devices and cost reduction. In addition, by controlling the four secondary switches, the resonant inductor can be energized through the equivalent short circuit of the secondary circuit during operation, so as to achieve high-gain voltage output.

[0104] It should be noted that the above is only a preferred embodiment proposed to illustrate this case. This case is not limited to the described embodiment, and the scope of this case is determined by the appended claims. And this case can be variously modified by those skilled in this technology, but all do not exceed the scope to be protected by the appended claims.

Claims

1. A three-level rectifier DC / DC converter, characterized in that, Comprising: A primary circuit that receives an input voltage and includes a plurality of primary switches; A resonant cavity circuit that includes a resonant inductor, a resonant capacitor, and a transformer. The first primary terminal and the second primary terminal of the resonant cavity circuit are electrically connected to the primary circuit. The primary winding of the transformer is electrically connected between the first primary terminal and the second primary terminal. The secondary winding of the transformer is electrically connected between the first secondary terminal and the second secondary terminal of the resonant cavity circuit. And the voltage between the first primary terminal and the second primary terminal is a first voltage, and the voltage between the first secondary terminal and the second secondary terminal is a second voltage; and A secondary circuit that includes two clamping switches, a switch bridge arm, and a capacitor bridge arm. The switch bridge arm includes a first secondary switch, a second secondary switch, a third secondary switch, and a fourth secondary switch that are sequentially connected in series. The two clamping switches are connected in series between the node between the first secondary switch and the second secondary switch and the node between the third secondary switch and the fourth secondary switch. The node between the second secondary switch and the third secondary switch is connected to the first secondary terminal; the capacitor bridge arm includes a first output capacitor and a second output capacitor connected in series. The node between the first output capacitor and the second output capacitor is connected to the node between the two clamping switches and the second secondary terminal. The two ends of the capacitor bridge arm are respectively connected to the two ends of the switch bridge arm, and the voltage between the two ends of the capacitor bridge arm is the output voltage, wherein, when the first secondary switch and the fourth secondary switch are always maintained in the off state, the second secondary switch switches from the off state to the on state at the falling edge in the change period of the first voltage and remains in the on state for a preset time period after the falling edge. The third secondary switch switches from the off state to the on state at the rising edge in the change period of the first voltage and remains in the on state for the preset time period after the rising edge.

2. The three-level rectifying DC / DC converter according to claim 1, wherein, The phases of the second secondary switch and the third secondary switch differ by 180 degrees.

3. The three-level rectifying DC / DC converter according to claim 1, wherein The switching frequencies of the second secondary switch and the third secondary switch are equal to the frequency of the first voltage.

4. The three-level rectifier DC / DC converter according to claim 1, characterized in that, When the first secondary switch and the fourth secondary switch are not always maintained in the off state, the first secondary switch, the second secondary switch, the third secondary switch, and the fourth secondary switch are respectively in the on state during all time periods when the first secondary switch, the second secondary switch, the third secondary switch, and the fourth secondary switch are in the period of reverse current flow.

5. The three-level rectifier DC / DC converter according to claim 4, wherein, The drive signals of the second secondary switch and the third secondary switch are complementary.

6. The three-level rectifying DC / DC converter according to claim 1, wherein, The preset time period is obtained based on the input voltage and the output voltage.

7. The three-level rectifying DC / DC converter according to claim 1, characterized in that, The primary switches and the secondary switches are turned on with zero voltage.

8. The three-level rectifier DC / DC converter according to claim 1, characterized in that, The first voltage is a square wave that is high level for half a cycle and low level for the other half cycle.

9. The three-level rectifier DC / DC converter according to claim 1, wherein The first secondary switch and the fourth secondary switch are active switch tubes.

10. The three-level rectifier DC / DC converter according to claim 1, wherein, The first secondary switch and the fourth secondary switch are a first diode and a second diode respectively. The anode and cathode of the first diode are electrically connected to the second secondary switch and the first output capacitor respectively. The anode and cathode of the second diode are electrically connected to the second output capacitor and the third secondary switch respectively.

11. The three-level rectifying DC / DC converter according to claim 1, characterized in that, The two clamping switches are active switching tubes.

12. The three-level rectifying DC / DC converter according to claim 1, characterized in that, The two clamping switches are a third diode and a fourth diode respectively. The anode and cathode of the third diode are electrically connected to the cathode of the fourth diode and the node between the first secondary switch and the second secondary switch respectively. The anode of the fourth diode is electrically connected to the node between the third secondary switch and the fourth secondary switch.

13. The three-level rectifying DC / DC converter according to claim 1, wherein The primary circuit includes an input capacitor, a first arm and a second arm connected in parallel with each other. The voltage across the input capacitor is the input voltage. The first arm includes a first primary switch and a second primary switch connected in series. The node between the first primary switch and the second primary switch is connected to the second primary terminal. The second arm includes a third primary switch and a fourth primary switch connected in series. The node between the third primary switch and the fourth primary switch is connected to the first primary terminal.

14. The three-level rectifier DC / DC converter according to claim 1, wherein The primary circuit includes two primary clamping switches, a first arm and a second arm. The voltage between the two ends of the first arm is the input voltage, and the two ends of the first arm are respectively connected to the two ends of the second arm. The first arm includes a first input capacitor and a second input capacitor connected in series. The second arm includes a first primary switch, a second primary switch, a third primary switch and a fourth primary switch connected in series in sequence. The two primary clamping switches are connected in series between the node between the first primary switch and the second primary switch and the node between the third primary switch and the fourth primary switch. The node between the second primary switch and the third primary switch is connected to the first primary terminal; the node between the first input capacitor and the second input capacitor is connected to the node between the two primary clamping switches and the second primary terminal.

15. The three-level rectifying DC / DC converter according to claim 1, wherein In the resonant cavity circuit, the resonant inductor, the primary winding and the resonant capacitor are connected in series between the first primary terminal and the second primary terminal.

16. The three-level rectifying DC / DC converter according to claim 1, characterized in that, It further includes a control module. The control module is configured to sense an input voltage signal, an output voltage signal and an output current signal respectively reflecting the input voltage, the output voltage and an output current, and control the operation of the primary switches and the secondary switches; the control module includes a regulator, and the regulator generates a regulation signal according to the output voltage signal, the output current signal, an output reference voltage and an output reference current.

17. The three-level rectifying DC / DC converter according to claim 16, wherein The control module further includes a voltage-controlled oscillator and a controller. The voltage-controlled oscillator is electrically connected to the regulator and generates the switching frequencies of the primary switches according to the regulation signal. The controller is electrically connected to the voltage-controlled oscillator and generates the conduction times of the secondary switches according to the input voltage signal, the output voltage signal and the switching frequencies of the primary switches.

18. The three-level rectifying DC / DC converter according to claim 16, wherein The control module further includes a PWM controller. The PWM controller is electrically connected to the regulator and generates drive signals for the primary switches and the secondary switches according to the regulation signal.

19. The three-level rectifier DC / DC converter according to claim 18, characterized in that, The switching frequencies of the primary switches are fixed and greater than the resonant frequency of the resonant cavity circuit.

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