Fault-tolerant device, power conversion device, power supply system, and fault-tolerant method

Abstract

The present application provides a fault-tolerant device, a power conversion device, a power supply system, and a fault-tolerant method for a power conversion circuit. The fault-tolerant device is applied to the power conversion circuit, and the power conversion circuit includes a primary bridge circuit, a transformer, and a secondary bridge circuit. The fault-tolerant device includes a fault-tolerant protection circuit, and the fault-tolerant protection circuit is connected between the secondary side of the transformer and the secondary bridge circuit. Wherein, when the outer tube control signals of the two outer tubes of the secondary bridge circuit are both off control signals, and / or when the inner tube control signals of the two inner tubes of the secondary bridge circuit are both off control signals, the fault-tolerant protection circuit is in a conducting state to provide freewheeling for the secondary current on the secondary side and absorb the energy of the secondary current, thereby reducing the risk of overstress of the secondary switching tubes and ensuring the operation of the power conversion circuit.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and particularly to a fault-tolerant device, a power conversion device, a power supply system, and a fault-tolerant method for a power conversion circuit. Background Art

[0002] In the field of new energy, dual-active-bridge micro-inverters are increasingly widely used due to their advantages such as small size, low cost, and high efficiency. In practical applications, dual-active-bridge micro-inverters may have incorrect control timing of the secondary side switching tubes due to hardware or software problems under various complex working conditions, resulting in the inability of the secondary side current to flow continuously normally, leading to the risk of stress damage to the secondary side switching tubes and affecting the operation of the dual-active-bridge micro-inverters. Therefore, it is necessary to propose a control fault-tolerant design for dual-active-bridge micro-inverters. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, this application provides a fault-tolerant device, a power conversion device, a power supply system, and a fault-tolerant method for a power conversion circuit, which can ensure the safety of the secondary side switching tubes and the normal operation of the power conversion circuit when the control timing of the secondary side switching tubes is incorrect.

[0004] In the first aspect of this application, a fault-tolerant device is provided, which is applied to a power conversion circuit. The power conversion circuit includes a primary bridge circuit, a transformer, and a secondary bridge circuit. The first end of the primary bridge circuit is connected to the primary side of the transformer, the second end of the primary bridge circuit is used to connect a DC power supply or a DC load, the first end of the secondary bridge circuit is connected to the secondary side of the transformer, and the second end of the secondary bridge circuit is used to connect an AC load or an AC power supply; wherein the secondary bridge circuit includes a first secondary bridge arm and a second secondary bridge arm connected in parallel. The first secondary bridge arm includes two bidirectional switches connected in series, and both bidirectional switches include an outer tube and an inner tube connected in reverse series. The second secondary bridge arm includes a first capacitor and a second capacitor connected in series. The fault-tolerant device includes a fault-tolerant protection circuit, which is connected between the secondary side of the transformer and the secondary bridge circuit. Among them, when the outer tube control signals of the two outer tubes are both off control signals at the same time, and / or when the inner tube control signals of the two inner tubes are both off control signals at the same time, the fault-tolerant protection circuit is in a conducting state to provide a freewheeling path for the secondary side current on the secondary side and absorb the energy of the secondary side current.

[0005] In an embodiment, when the outer tube control signals of the two outer tubes are not both off control signals at the same time, and the inner tube control signals of the two inner tubes are not both off control signals at the same time, the fault-tolerant protection circuit is in an open state to enable the secondary bridge circuit to provide a freewheeling path for the secondary side current on the secondary side.

[0006] In one embodiment, a fault-tolerant protection circuit is connected between the secondary side of a transformer and the first end of a secondary-side bridge circuit. The fault-tolerant protection circuit includes a control switch and an absorption circuit connected to each other. The fault-tolerant device further includes a controller connected to the control switch. The controller is configured to obtain the outer-tube control signal and the inner-tube control signal of the secondary-side bridge circuit, and when the outer-tube control signals of the two outer tubes are both off-control signals at the same time, and / or when the inner-tube control signals of the two inner tubes are both off-control signals at the same time, control the control switch to close, so that the secondary-side current continues to flow through the control switch and the absorption circuit, and the energy of the secondary-side current is absorbed by the absorption circuit; and when the outer-tube control signals of the two outer tubes are not both off-control signals at the same time, and the inner-tube control signals of the two inner tubes are not both off-control signals at the same time, control the control switch to open.

[0007] In one embodiment, the number of fault-tolerant protection circuits is two. The two fault-tolerant protection circuits are both connected between the secondary side of the transformer and the second end of the secondary-side bridge circuit, and are connected in parallel with two bidirectional switches in one-to-one correspondence. Each fault-tolerant protection circuit includes a control switch and an absorption circuit connected to each other. The fault-tolerant device further includes a controller connected to the control switches of the two fault-tolerant protection circuits. The controller is configured to obtain the outer-tube control signal and the inner-tube control signal of the secondary-side bridge circuit, and when the outer-tube control signals of the two outer tubes are both off-control signals at the same time, and / or when the inner-tube control signals of the two inner tubes are both off-control signals at the same time, control the control switches to close, so that the secondary-side current continues to flow through the control switches and the absorption circuit, and the energy of the secondary-side current is absorbed by the absorption circuit; and when the outer-tube control signals of the two outer tubes are not both off-control signals at the same time, and the inner-tube control signals of the two inner tubes are not both off-control signals at the same time, control the control switches to open.

[0008] In one embodiment, the absorption circuit includes an absorption resistor and a buffer capacitor. The absorption resistor and the buffer capacitor in the same fault-tolerant protection circuit are connected to the control switch.

[0009] In one embodiment, the absorption resistor, the buffer capacitor and the control switch in the same fault-tolerant protection circuit are connected in series; or, the absorption resistor and the buffer capacitor in the same fault-tolerant protection circuit are connected in parallel, and the control switch in the same fault-tolerant protection circuit is connected in series with the parallel-connected absorption resistor and buffer capacitor.

[0010] The second aspect of the present application provides a power conversion device. The power conversion device includes a power conversion circuit and a fault tolerance protection circuit. The power conversion circuit includes a primary bridge circuit, a transformer, and a secondary bridge circuit. The first end of the primary bridge circuit is connected to the primary side of the transformer, and the second end of the primary bridge circuit is used to connect to a DC power supply or a DC load. The first end of the secondary bridge circuit is connected to the secondary side of the transformer, and the second end of the secondary bridge circuit is used to connect to an AC load or an AC power supply. Among them, the secondary bridge circuit includes a first secondary bridge arm and a second secondary bridge arm connected in parallel. The first secondary bridge arm includes two bidirectional switches connected in series, and both bidirectional switches include an outer tube and an inner tube connected in reverse series. The second secondary bridge arm includes a first capacitor and a second capacitor connected in series. The fault tolerance protection circuit is connected between the secondary side of the transformer and the secondary bridge circuit. Among them, when the outer tube control signals of the two outer tubes are both off control signals at the same time, and / or when the inner tube control signals of the two inner tubes are both off control signals at the same time, the fault tolerance protection circuit is in a conducting state to provide a freewheeling path for the secondary current on the secondary side and absorb the energy of the secondary current.

[0011] In one embodiment, when the outer tube control signals of the two outer tubes are not both off control signals at the same time, and the inner tube control signals of the two inner tubes are not both off control signals at the same time, the fault tolerance protection circuit is in an open state, so that the secondary bridge circuit provides a freewheeling path for the secondary current on the secondary side.

[0012] In one embodiment, the fault tolerance protection circuit is connected between the secondary side of the transformer and the first end of the secondary bridge circuit. The fault tolerance protection circuit includes a control switch and an absorption circuit connected to each other. The power conversion device further includes a controller connected to the control switch. The controller is used to obtain the outer tube control signal and the inner tube control signal of the secondary bridge circuit, and when the outer tube control signals of the two outer tubes are both off control signals at the same time, and / or when the inner tube control signals of the two inner tubes are both off control signals at the same time, control the control switch to close, so that the secondary current freewheels through the control switch and the absorption circuit, and the energy of the secondary current is absorbed by the absorption circuit. And when the outer tube control signals of the two outer tubes are not both off control signals at the same time, and the inner tube control signals of the two inner tubes are not both off control signals at the same time, control the control switch to open.

[0013] In one embodiment, the number of fault-tolerant protection circuits is two. The two fault-tolerant protection circuits are both connected between the secondary side of the transformer and the second end of the secondary side bridge circuit, and are connected in parallel with two bidirectional switches one by one. Each fault-tolerant protection circuit includes a control switch and an absorption circuit connected to each other. The power conversion device further includes a controller, which is connected to the control switches of the two fault-tolerant protection circuits. The controller is configured to obtain the outer tube control signal and the inner tube control signal of the secondary side bridge circuit, and when the outer tube control signals of the two outer tubes are both off control signals, and / or when the inner tube control signals of the two inner tubes are both off control signals, control the control switches to be closed, so that the secondary side current continues to flow through the control switches and the absorption circuit, and the energy of the secondary side current is absorbed by the absorption circuit; and when the outer tube control signals of the two outer tubes are not both off control signals and the inner tube control signals of the two inner tubes are not both off control signals, control the control switches to be opened.

[0014] In one embodiment, the voltages applied across the outer tubes and the voltages applied across the inner tubes are always within a preset safe voltage range.

[0015] In one embodiment, the controller is further connected to the power conversion circuit, and the controller is further configured to generate control signals for the power conversion circuit, where the control signals for the power conversion circuit include a primary side control signal, an outer tube control signal, and an inner tube control signal. The primary side control signal is used to control the on / off states of the switching tubes in the primary side bridge circuit, the outer tube control signal is used to control the on / off states of the outer tubes in the secondary side bridge circuit, and the inner tube control signal is used to control the on / off states of the inner tubes in the secondary side bridge circuit.

[0016] In one embodiment, the primary side bridge circuit includes a first primary side bridge arm and a second primary side bridge arm connected in parallel. The first primary side bridge arm includes a first primary side switching tube and a second primary side switching tube connected in series, and the second primary side bridge arm includes a third primary side switching tube and a fourth primary side switching tube connected in series.

[0017] The third aspect of the present application provides a power supply system, which includes: a DC power supply and the power conversion device described in the second aspect or any one of the embodiments in the second aspect. The DC power supply is connected to the second end of the primary side bridge circuit, and the second end of the secondary side bridge circuit is connected to a common coupling point. The DC power supply includes at least one of an energy storage device and a photovoltaic power generation device, and the common coupling point is used to connect at least one of a power grid and an AC load.

[0018] The fourth aspect of the present application provides a fault tolerance method for a power conversion circuit. The power conversion circuit includes a primary side bridge circuit, a transformer, and a secondary side bridge circuit. The first end of the primary side bridge circuit is connected to the primary side of the transformer, the second end of the primary side bridge circuit is used to connect to a DC power supply or a DC load, the first end of the secondary side bridge circuit is connected to the secondary side of the transformer, the second end of the secondary side bridge circuit is used to connect to an AC load or an AC power supply, and a fault tolerance protection circuit is also connected between the secondary side of the transformer and the secondary side bridge circuit; wherein the secondary side bridge circuit includes a first secondary side bridge arm and a second secondary side bridge arm connected in parallel. The first secondary side bridge arm includes two bidirectional switches connected in series, and both bidirectional switches include an outer tube and an inner tube connected in reverse series. The second secondary side bridge arm includes a first capacitor and a second capacitor connected in series. The fault tolerance method for the power conversion circuit includes: obtaining the outer tube control signal and the inner tube control signal of the secondary side bridge circuit; when the outer tube control signals of the two outer tubes are both off control signals, and / or when the inner tube control signals of the two inner tubes are both off control signals, controlling the fault tolerance protection circuit to be in a conducting state, so that the fault tolerance protection circuit can provide freewheeling for the secondary side current on the secondary side and absorb the energy of the secondary side current.

[0019] In one embodiment, the fault tolerance method further includes: when the outer tube control signals of the two outer tubes are not both off control signals and the inner tube control signals of the two inner tubes are not both off control signals, controlling the fault tolerance protection circuit to be in an open state.

[0020] In one embodiment, the fault tolerance protection circuit is connected between the secondary side of the transformer and the first end of the secondary side bridge circuit, and the fault tolerance protection circuit includes a control switch and an absorption circuit connected together. Correspondingly, when the outer tube control signals of the two outer tubes are both off control signals, and / or when the inner tube control signals of the two inner tubes are both off control signals, the process of controlling the fault tolerance protection circuit to be in a conducting state so that the fault tolerance protection circuit can provide freewheeling for the secondary side current on the secondary side and absorb the energy of the secondary side current includes: when the outer tube control signals of the two outer tubes are both off control signals, and / or when the inner tube control signals of the two inner tubes are both off control signals, controlling the control switch to close, so that the secondary side current can freewheel through the control switch and the absorption circuit, and the energy of the secondary side current is absorbed by the absorption circuit. Correspondingly, when the outer tube control signals of the two outer tubes are not both off control signals and the inner tube control signals of the two inner tubes are not both off control signals, the process of controlling the fault tolerance protection circuit to be in an open state includes: when the outer tube control signals of the two outer tubes are not both off control signals and the inner tube control signals of the two inner tubes are not both off control signals, controlling the control switch to open.

[0021] In one embodiment, the number of fault-tolerant protection circuits is two. The two fault-tolerant protection circuits are both connected between the secondary side of the transformer and the second end of the secondary-side bridge circuit, and are connected in parallel with the two bidirectional switches one by one. Each fault-tolerant protection circuit includes a control switch and an absorption circuit connected to each other. Correspondingly, when the outer-tube control signals of the two outer tubes are both off-control signals at the same time, and / or when the inner-tube control signals of the two inner tubes are both off-control signals at the same time, the fault-tolerant protection circuit is controlled to be in a conducting state, so that the process of the fault-tolerant protection circuit for freewheeling the secondary-side current on the secondary side and absorbing the energy of the secondary-side current includes: when the outer-tube control signals of the two outer tubes are both off-control signals at the same time, and / or when the inner-tube control signals of the two inner tubes are both off-control signals at the same time, the control switches are controlled to be closed, so that the secondary-side current freewheels through the control switches and the absorption circuit, and the energy of the secondary-side current is absorbed by the absorption circuit. Correspondingly, when the outer-tube control signals of the two outer tubes are not both off-control signals at the same time, and the inner-tube control signals of the two inner tubes are not both off-control signals at the same time, the process of controlling the fault-tolerant protection circuit to be in an open state includes: when the outer-tube control signals of the two outer tubes are not both off-control signals at the same time, and the inner-tube control signals of the two inner tubes are not both off-control signals at the same time, the control switches are controlled to be opened.

[0022] In one embodiment, the fault-tolerant method further includes: when the outer-tube control signals of the two outer tubes are both at the first level at the same time, it is determined that the outer-tube control signals of the two outer tubes are both off-control signals at the same time. When the outer-tube control signals of the two outer tubes are both at the second level, or when one outer-tube control signal is at the first level and the other outer-tube control signal is at the second level, it is determined that the outer-tube control signals of the two outer tubes are not both off-control signals at the same time. When the inner-tube control signals of the two inner tubes are both at the first level at the same time, it is determined that the inner-tube control signals of the two inner tubes are both off-control signals at the same time. When the inner-tube control signals of the two inner tubes are both at the second level, or when one inner-tube control signal is at the first level and the other inner-tube control signal is at the second level, it is determined that the inner-tube control signals of the two inner tubes are not both off-control signals at the same time. Wherein, the first level is different from the second level, the first level is used to drive the switch tube to turn off, and the second level is used to drive the switch tube to turn on.

[0023] Compared with the prior art, the present application has at least the following advantages:

[0024] 1. By adding a fault tolerance device to the power conversion circuit, in the case where the secondary side control signal wrongly drives both external transistors to turn off, and / or in the case where the secondary side control signal wrongly drives both internal transistors to turn off, the fault tolerance protection circuit in the fault tolerance device can be in a conducting state, enabling the secondary side current to flow through the fault tolerance protection circuit for freewheeling. Therefore, even if a control timing error occurs, the power conversion circuit will not have the problem of over-stress damage to the external transistors caused by the freewheeling boost of the parasitic capacitance of the secondary side switching transistors. Thus, the present application can achieve fault tolerance protection for the secondary side switching transistors and the power conversion circuit, ensuring the operation of the power conversion circuit.

[0025] 2. The fault tolerance device of the present application can ensure the freewheeling of the secondary side current in the case of a wrong secondary side control signal, and can also not affect the normal freewheeling of the secondary side current and the normal operation of the secondary side bridge circuit in the case of a normal secondary side control signal.

[0026] 3. The present application is applicable to the case where the secondary side control signal wrongly drives both external transistors to turn off, or the secondary side control signal wrongly drives both internal transistors to turn off, or the secondary side control signal wrongly drives both internal and external transistors to turn off. That is to say, the present application can be applicable to various cases of control timing errors. Therefore, the present application has a wide application range. Moreover, the present application directly controls the fault tolerance protection circuit without changing the original control logic of the external and internal transistors. Therefore, the control is simple, the control complexity of the external and internal transistors will not be increased, and it is not easy to have control logic chaos.

[0027] 4. The fault tolerance protection circuit of the present application is a hardware protection circuit, and the fault tolerance protection for the power conversion circuit is more reliable and stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic structural diagram of a power supply system provided by an embodiment of the present application.

[0029] Figure 2 is Figure 1 a schematic connection diagram of the power conversion circuit and the fault tolerance device in

[0030] Figure 3 is Figure 1 a circuit diagram of the power conversion circuit in

[0031] Figure 4 is Figure 3 a working waveform diagram when the power conversion circuit shown is operating normally.

[0032] Figure 5 is in the case where the fault tolerance device of the embodiment of the present application is not set, Figure 3 a current flow diagram of the secondary side current when the control timing of the power conversion circuit shown goes wrong.

[0033] Figure 6 In the case where the fault tolerance device of the embodiment of the present application is not set, Figure 3 Another current flow diagram of the secondary side current when the control timing of the shown power conversion circuit goes wrong.

[0034] Figure 7 In the case where the fault tolerance device of the embodiment of the present application is not set, Figure 3 A waveform diagram of the voltage stress borne by the secondary side switch tube when the control timing of the shown power conversion circuit goes wrong.

[0035] Figure 8 It is Figure 7 A partial enlarged view of a part near a zero crossing of the shown waveform.

[0036] Figure 9 A circuit diagram of the power conversion circuit and the fault tolerance protection circuit provided in Embodiment 1.

[0037] Figure 10 It is Figure 9 A current flow diagram of the secondary side current of the shown power conversion circuit.

[0038] Figure 11 It is Figure 9 Another current flow diagram of the secondary side current of the shown power conversion circuit.

[0039] Figure 12 It is Figure 9 A waveform diagram of the voltage stress borne by the secondary side switch tube of the shown power conversion circuit.

[0040] Figure 13 It is Figure 12 A partial enlarged view of a part near a zero crossing of the shown waveform.

[0041] Figure 14 A circuit diagram of the power conversion circuit and the fault tolerance protection circuit provided in Embodiment 2.

[0042] Figure 15 It is Figure 14 A current flow diagram of the secondary side current of the shown power conversion circuit.

[0043] Figure 16 It is Figure 14 Another current flow diagram of the secondary side current of the shown power conversion circuit.

[0044] Figure 17 It is Figure 14 A waveform diagram of the voltage stress borne by the secondary side switch tube of the shown power conversion circuit.

[0045] Figure 18 It is Figure 17 A partial enlarged view of a part near a zero crossing of the shown waveform.

[0046] Figure 19 It is a flowchart of a fault tolerance method for a power conversion circuit provided by an embodiment of the present application.

[0047] Description of main component symbols

[0048] 100 - power supply system, 10 - DC power supply, 11 - energy storage device, 12 - photovoltaic power generation device, 20 - power conversion device,

[0049] 21 - power conversion circuit, 211 - primary side bridge circuit, 2111 - first primary side bridge arm, 2112 - second primary side bridge arm,

[0050] 212 - transformer, 213 - resonant inductor, 214 - secondary side bridge circuit, 2141 - first secondary side bridge arm,

[0051] 2142 - second secondary side bridge arm, 22 - fault tolerance device, 23, 23A, 23B - fault tolerance protection circuit, 24 - controller,

[0052] 30 - common coupling point, 40 - power grid, 50 - AC load. Detailed implementation manners

[0053] In order to enable those skilled in the art to better understand the solution of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present application. Without conflict, the following different embodiments and the features in the embodiments can be combined with each other.

[0054] Please refer to Figure 1 , which shows the topology diagram of the power supply system 100 provided by the embodiment of the present application.

[0055] As Figure 1 shown, the power supply system 100 includes a DC power supply 10 and a power conversion device 20. For convenience of description, it is taken as an example that the DC power supply 10 is an energy storage device 11 and a photovoltaic power generation device 12. At this time, the power supply system 100 can also be called a photovoltaic energy storage charging system.

[0056] It should be understood that in other scenarios, only the photovoltaic power generation device 12 or the energy storage device 11 can also be used as the DC power supply 10, or other devices that can provide direct current can be used as the DC power supply 10. Among them, in the scenario where only the photovoltaic power generation device 12 is used as the DC power supply 10, the power supply system 100 can also be called a photovoltaic system. In the scenario where only the energy storage device 11 is used as the DC power supply 10, the power supply system 100 can also be called an energy storage system or a storage and charging system.

[0057] The power conversion device 20 is a single-stage micro-inverter. The power conversion device 20 includes a power conversion circuit 21. One end of the power conversion circuit 21 is connected to the energy storage device 11 and the photovoltaic power generation device 12. The energy storage device 11 includes an energy storage battery that can be charged and discharged. The other end of the power conversion circuit 21 is connected to the point of common coupling 30 (abbreviated as PCC). The point of common coupling 30 can be used to connect to the power grid 40 and the AC load 50.

[0058] In the embodiments of the present application, please refer to Figure 2 , the power conversion circuit 21 includes a primary bridge circuit 211, a transformer 212, and a secondary bridge circuit 214. Among them, the primary bridge circuit 211 can adopt a full-bridge structure or a half-bridge structure, and the secondary bridge circuit 214 adopts a half-bridge structure. Therefore, the power conversion circuit 21 can also be called a dual active bridge (DAB) conversion circuit.

[0059] For the convenience of description, in the embodiments of the present application, Figure 3 the shown primary bridge circuit 211 is a full-bridge structure, and the secondary bridge circuit 214 is a half-bridge structure for exemplary illustration.

[0060] As Figure 3 shown, the primary bridge circuit 211 includes a first primary bridge arm 2111 and a second primary bridge arm 2112 connected in parallel. The first primary bridge arm 2111 includes a first primary switch tube Q1 and a second primary switch tube Q2 connected in series. The second primary bridge arm 2112 includes a third primary switch tube Q3 and a fourth primary switch tube Q4 connected in series. The midpoints of the first primary bridge arm 2111 and the second primary bridge arm 2112 together form the first end of the primary bridge circuit 211. The first end of the primary bridge circuit 211 is connected to the primary side of the transformer 212. The two ends of the first primary bridge arm 2111 and the two ends of the second primary bridge arm 2112 form the second end of the primary bridge circuit 211. The second end of the primary bridge circuit 211 can be connected to the capacitor Cdc and can also be used to connect to the DC power supply 10 or the DC load.

[0061] The secondary side bridge circuit 214 includes a first secondary side bridge arm 2141 and a second secondary side bridge arm 2142 connected in parallel. The first secondary side bridge arm 2141 includes two bidirectional switches connected in series, namely a first bidirectional switch and a second bidirectional switch. The first bidirectional switch includes two secondary side switching tubes Q5 and Q6 connected in reverse series, and the second bidirectional switch includes two secondary side switching tubes Q7 and Q8 connected in reverse series. Among them, Q6 and Q7 are located between Q5 and Q8. Q5 can also be called the first outer tube, Q8 can also be called the second outer tube, Q6 can also be called the first inner tube, and Q7 can also be called the second inner tube. The second secondary side bridge arm 2142 includes a first capacitor Cr1 and a second capacitor Cr2 connected in series. The midpoints of the first secondary side bridge arm 2141 and the second secondary side bridge arm 2142 together constitute the first end of the secondary side bridge circuit 214, and the first end of the secondary side bridge circuit 214 is connected to the secondary side of the transformer 212.

[0062] Among them, the switching tubes Q1~Q8 can adopt corresponding types of semiconductor switching devices according to actual needs. For the convenience of description, Figure 3 in the example, the switching tubes Q1~Q8 all adopt MOSFETs for display. The turns ratio between the secondary side and the primary side of the transformer 212 is n:1, where n>1. The transformer 212 has a secondary side leakage inductance, and the secondary side leakage inductance can be independent of the transformer 212 and is located between the midpoint of the first secondary side bridge arm 2141 and the secondary side of the transformer 212. The secondary side leakage inductance can be used as the resonant inductor 213. For the convenience of description, Figure 3 in the example, the resonant inductor 213 (corresponding to Figure 3 Lr in it) is displayed. In some embodiments, the resonant inductor Lr can form a resonant circuit alone. In some other embodiments, it can also be that the resonant inductor Lr, the first capacitor Cr1 and the second capacitor Cr2 together form a resonant circuit.

[0063] The two ends of the first secondary side bridge arm 2141 and the two ends of the second secondary side bridge arm 2142 constitute the second end of the secondary side bridge circuit 214. The second end of the secondary side bridge circuit 214 can be used to connect to the common coupling point 30, so as to connect to an AC power supply or an AC load 50. A filter or a filter circuit can be provided between the second end of the secondary side bridge circuit 214 and the common coupling point 30, such as Figure 3 the filter inductor Lf in it.

[0064] Based on such a design, when the power supply system 100 operates, the energy storage device 11 can serve as the DC power supply 10, and the power conversion circuit 21 can transfer the power provided by the energy storage device 11 to the AC load 50 and / or the power grid 40. Among them, when the power conversion circuit 21 feeds power to the power grid 40, the power grid 40 can be regarded as the AC load 50 at this time. Conversely, the energy storage device 11 can also serve as a DC load, the power grid 40 serves as an AC power supply, and the power conversion circuit 21 can transfer the power provided by the power grid 40 to the energy storage device 11 to charge the energy storage device 11.

[0065] In the embodiments of the present application, the process of transferring power from the primary bridge circuit 211 to the secondary bridge circuit 214 can be referred to as the forward operation process of the power conversion circuit 21, and the process of transferring power from the secondary bridge circuit 214 to the primary bridge circuit 211 can be referred to as the reverse operation process of the power conversion circuit 21. In other embodiments, the forward and reverse can also be reversed, which is not specifically limited herein.

[0066] Among them, the primary bridge circuit 211 constitutes a DC / AC conversion circuit, and the secondary bridge circuit 214 constitutes an AC / AC conversion circuit. The voltage at the second end of the primary bridge circuit 211 is the DC voltage Vdc, the voltage at the second end of the secondary bridge circuit 214 is the AC voltage Vac, and the current at the second end of the secondary bridge circuit 214 is the AC current iac.

[0067] The transformer 212 is used to isolate and couple the primary bridge circuit 211 and the secondary bridge circuit 214. The resonant circuit is used to store and transfer energy. The voltage on the primary side of the transformer 212 can be referred to as the primary voltage Vp. The primary voltage Vp is also the voltage generated at the first end of the primary bridge circuit 211, or the voltage between the midpoint of the first primary bridge arm 2111 and the midpoint of the second primary bridge arm 2112 of the primary bridge circuit 211. The current on the secondary side of the transformer 212 can be referred to as the secondary current is. The secondary current is is also the inductor current flowing through the resonant inductor Lr. The voltage generated on the secondary side of the transformer 212 can be referred to as the secondary voltage Vs. The secondary voltage Vs is also the voltage at the first end of the secondary bridge circuit 214, or the voltage between the midpoint of the first secondary bridge arm 2141 and the midpoint of the second secondary bridge arm 2142 of the secondary bridge circuit 214.

[0068] The control terminals of switching transistors Q1 to Q8 are used to receive control signals, which are used to control the on / off states of switching transistors Q1 to Q8. When the control signal of a switching transistor is at a first level, the control signal is a turn-on control signal and can be used to drive the switching transistor to turn on; when the control signal of a switching transistor is at a second level, the control signal is a turn-off control signal and can be used to drive the switching transistor to turn off. Herein, the first level is different from the second level. For ease of description, in the embodiments of the present application, it is taken as an example that the first level is a low level (e.g., 0) and the second level is a high level (e.g., 1).

[0069] In the embodiments of the present application, the control signal of the first primary switching transistor Q1 is S1, the control signal of the second primary switching transistor Q2 is S2, the control signal of the third primary switching transistor Q3 is S2, and the control signal of the fourth primary switching transistor Q4 is S4. The control signal of the first outer transistor Q5 is S5, the control signal of the first inner transistor Q6 is S6, the control signal of the second inner transistor Q7 is S7, and the control signal of the second outer transistor Q8 is S8. For ease of description, S1 to S4 can all be referred to as primary control signals, and S5 to S8 can all be referred to as secondary control signals. Further, the control signal S6 of the first inner transistor Q6 and the control signal S7 of the second inner transistor Q7 can both be referred to as inner transistor control signals, and the control signal S5 of the first outer transistor Q5 and the control signal S8 of the second outer transistor Q8 can both be referred to as outer transistor control signals.

[0070] Under normal circumstances, for the primary bridge circuit 211, under the control of the control signals S1 and S2, the first primary switching transistor Q1 and the second primary switching transistor Q2 conduct alternately at a high frequency; under the control of the control signals S3 and S4, the third primary switching transistor Q3 and the fourth primary switching transistor Q4 conduct alternately at a high frequency.

[0071] Under normal circumstances, for the secondary bridge circuit 214, please refer to Figure 4 , the secondary switching transistors switch states at the zero-crossing point of the AC voltage Vac. Among them, when the real-time AC voltage Vac is positive, under the control of the control signals S5 and S7, the first outer transistor Q5 and the second inner transistor Q7 conduct alternately at a high frequency; under the control of the control signals S6 and S8, the first inner transistor Q6 and the second outer transistor Q8 are always on. To avoid the direct connection of the first secondary bridge arm, the control signals S5 and S7 have a dead time. During this dead time, both the first outer transistor Q5 and the second inner transistor Q7 are turned off. When the real-time AC voltage Vac is negative, under the control of the control signals S6 and S8, the first inner transistor Q6 and the second outer transistor Q8 conduct alternately at a high frequency; under the control of the control signals S5 and S7, the first outer transistor Q5 and the second inner transistor Q7 are always on. To avoid the direct connection of the first secondary bridge arm, the control signals S6 and S8 have a dead time. During this dead time, both the first inner transistor Q6 and the second outer transistor Q8 are turned off.

[0072] However, in practical applications, due to hardware or software problems, the power conversion device 20 may have incorrect control timing of the secondary side switching transistors under various complex operating conditions. For example, Q5~Q8 may all incorrectly switch to the off state; or, Q6 and Q7 switch on and off normally, while Q5 and Q8 have incorrect switching timing, resulting in both being in the off state; or, Q5 and Q8 switch on and off normally, while Q6 and Q7 have incorrect switching timing, resulting in both being in the off state.

[0073] As Figure 5 shown by the thick black line (the arrow indicates the current flow direction) in

[0074] Similarly, as Figure 6 shown by the thick black line (the arrow indicates the current flow direction) in

[0075] Taking Figure 7 and Figure 8 as an example of the simulation signal waveform diagram shown. Figure 7 shows the waveform diagram of the voltages across Q5~Q8, that is, the voltage stress waveform diagram of Q5~Q8, when incorrect control timing occurs where both Q5 and Q8 are off and / or both Q6 and Q7 are off during the operation of the power conversion circuit 21 shown in Figure 3 . Figure 8 shows a partial enlarged view of the part near the zero crossing within the elliptical dashed box of the waveform shown in Figure 7 . From Figure 7 and Figure 8It can be seen that when Q5 to Q8 are all switched to the off state, a large spike will appear near the voltage zero-crossing point in the waveform. The spike voltage is approximately 150V to 200V, indicating that the voltage stress of Q5 and Q8 near the voltage zero-crossing point reaches about 150V to 200V. Similarly, when Q6 and Q7 in Q5 to Q8 are both switched to the off state, there is also a spike of about 150V to 200V near the voltage zero-crossing point in the waveform, indicating that the voltage stress of Q6 and Q7 near the voltage zero-crossing point reaches about 150V to 200V. From Figure 7 It can be seen that when Q5 to Q8 are all turned off, the stress of Q5 is as high as about 800V at this time, and the stresses of Q6, Q7, and Q8 are all as high as 500V or exceed 500V.

[0076] It can be understood that excessive voltage stress will cause over-stress damage to the secondary side switching transistors, affecting the operation of the power conversion circuit 21. Therefore, please refer to Figure 1 and Figure 2 again. The embodiment of the present application proposes a fault-tolerant device 22, which can be applied to the power conversion circuit 21 to ensure the continuous flow of the secondary side current when a control timing error occurs in the secondary side switching transistors of the power conversion circuit 21, and achieve fault-tolerant protection for the secondary side switching transistors and the power conversion circuit 21.

[0077] Specifically, as Figure 1 shown, the fault-tolerant device 22 can be arranged in the power conversion device 20. The fault-tolerant device 22 includes a fault-tolerant protection circuit 23 and a controller 24. Among them, as Figure 2 shown, the fault-tolerant protection circuit 23 is connected between the secondary side of the transformer 212 and the secondary side bridge circuit 214. The controller 24 is connected to the power conversion circuit 21 and the fault-tolerant protection circuit 23.

[0078] Furthermore, the fault-tolerant protection circuit 23 includes a control switch and an absorption circuit. The control switch can be any kind of electrically controlled switch. The electrically controlled switch can be, for example, a relay, a contactor, a semiconductor switch or a combination thereof, etc., and no special limitation is made here. The absorption circuit can include a resistor for energy consumption and a capacitor for energy storage, etc. The control switch is connected to the absorption circuit. When the power conversion circuit is operating, when the control switch is turned on, the fault-tolerant protection circuit 23 is in a conducting state, and when the control switch is turned off, the fault-tolerant protection circuit 23 is in an open state.

[0079] The controller 24 can be a microcontroller unit (MCU), a digital signal processor (DSP), or other control elements or circuits. The controller 24 can be connected to the control terminals of the switching transistors Q1 - Q8 in the power conversion circuit 21, and is used to modulate and generate control signals for the switching transistors Q1 - Q8 and output them to the switching transistors Q1 - Q8 to control the on - off states of the switching transistors Q1 - Q8, thereby realizing the control of the operation of the power conversion circuit 21.

[0080] The controller 24 can be used to connect to the control switch in the fault - tolerant protection circuit 23, and is used to output a control signal for the control switch to the control switch to control the on - off state of the control switch, thereby controlling the connection situation of the fault - tolerant protection circuit 23.

[0081] Among them, in the case of control timing errors, when the outer - transistor control signals of two outer transistors are both off - control signals at the same time, or when the inner - transistor control signals of two inner transistors are both off - control signals at the same time, or when the outer - transistor control signals of two outer transistors are both off - control signals and the inner - transistor control signals of two inner transistors are both off - control signals at the same time, the controller 24 can be used to control the control switch in the fault - tolerant protection circuit 23 to conduct, so that the fault - tolerant protection circuit 23 is in a conducting state.

[0082] It can be understood that when the outer - transistor control signals S5 and S8 are both off - control signals, the outer transistors Q5 and Q8 are both off. Referring to the foregoing Figure 6 description, the secondary - side current is flowing in the reverse direction can only free - wheel through the parasitic capacitances of the outer transistor Q5 and the outer transistor Q8 at this time, resulting in high voltage stress on Q5 and Q8 and a high risk of stress damage. In the embodiment of the present application, the controller 24 actively controls the fault - tolerant protection circuit 23 to conduct at this time, so that the secondary side of the transformer 212 is connected to the secondary - side bridge circuit 214 through the conducting fault - tolerant protection circuit 23. Furthermore, the secondary - side current is flowing in the forward or reverse direction can flow into the fault - tolerant protection circuit 23, that is, free - wheel through the fault - tolerant protection circuit 23, thereby reducing the current flowing into the parasitic capacitances of the outer transistors Q5 and Q8, suppressing the voltage boost caused by the free - wheeling of the parasitic capacitances of Q5 and Q8. Therefore, the over - stress risk of Q5 and Q8 can be reduced. At the same time, the absorption circuit in the fault - tolerant protection circuit 23 can also absorb the energy of the secondary - side current is during free - wheeling, further reducing the over - stress risk of Q5 and Q8.

[0083] Similarly, when the inner - transistor control signals S6 and S7 are both off - control signals, the inner transistors Q6 and Q7 are both off. Referring to the foregoing Figure 5In the description, the forward flowing secondary current is can only freewheel through the parasitic capacitances of the inner transistor Q6 and the inner transistor Q7 at this time, resulting in high voltage stress on Q6 and Q7 and a high risk of stress damage. However, the controller 24 in the embodiment of the present application actively controls the conduction of the fault tolerance protection circuit 23 at this time, so that the secondary side of the transformer 212 is connected to the secondary side bridge circuit 214 through the conducting fault tolerance protection circuit 23. Furthermore, the secondary current is flowing forward or backward can flow to the fault tolerance protection circuit 23, that is, freewheel through the fault tolerance protection circuit 23, thereby reducing the current flowing to the parasitic capacitances of the inner transistors Q6 and Q7 and suppressing the voltage boost caused by the freewheeling of the parasitic capacitances of Q6 and Q7. Therefore, the overstress risk of Q6 and Q7 can be reduced. At the same time, the absorption circuit in the fault tolerance protection circuit 23 can also absorb the energy of the secondary current is during freewheeling, further reducing the overstress risk of Q6 and Q7.

[0084] It can be seen from this that based on the fault tolerance device 22 in the embodiment of the present application, in the case of incorrect control timing of the secondary side switching transistors, whether the secondary current is flows forward or backward, the fault tolerance protection circuit 23 can freewheel the secondary current is, suppress the voltage boost caused by the freewheeling of the parasitic capacitance, and further reduce the voltage stress of the secondary side switching transistors, preventing overstress damage to the secondary side switching transistors, thereby ensuring the operation of the power conversion circuit 21.

[0085] Therefore, through the fault tolerance device 20, it is possible to avoid overstress damage to the secondary side switching transistors caused by the inability of the secondary current to freewheel due to incorrect control timing of the power conversion circuit 21, and thus the fault tolerance protection of the secondary side switching transistors and the power conversion circuit 21 can be achieved.

[0086] In addition, under normal conditions, the outer transistors Q5 and Q8 conduct alternately at high frequency and Q6 and Q8 are always on, or Q6 and Q8 conduct alternately at high frequency and Q5 and Q8 are always on. Therefore, under normal control timing, the control timing of the outer transistors Q5 and Q8 may be: the outer transistor control signals of the two outer transistors are both conduction control signals at the same time, or one of the outer transistor control signals is a disconnection control signal and the other outer transistor control signal is a conduction control signal. In these cases, Q5 and Q8 are not both disconnected at the same time, and at least one outer transistor is conducting. Therefore, the reverse flowing secondary current is can still freewheel normally through the channel of the conducting outer transistor, and there will be no problem of overstress damage to the outer transistor caused by the voltage boost of the parasitic capacitances of Q5 and Q8, which affects the operation of the power conversion circuit 21.

[0087] Similarly, under normal control timing, the control timing of the inner tubes Q6 and Q7 may be: the inner tube control signals of the two inner tubes are both on-control signals at the same time, or, one of the inner tube control signals is an off-control signal and the other inner tube control signal is an on-control signal. And in these cases, Q6 and Q7 are not both off at the same time, and at least one inner tube is on. Therefore, the forward flowing secondary current is can still flow through the channel of the on outer tube normally for freewheeling, and there will be no problem that the outer tube is damaged due to overstress caused by the freewheeling boost of the parasitic capacitance of Q6 and Q7, which affects the operation of the power conversion circuit 21.

[0088] That is to say, in the above cases, the power conversion circuit 21 can operate normally. Therefore, the fault-tolerant device 22 of the embodiment of the present application will not interfere with the freewheeling of the secondary current. That is, when the outer tube control signals of the two outer tubes are not both off-control signals at the same time, and the inner tube control signals of the two inner tubes are not both off-control signals at the same time, the controller 24 can be used to control the control switch in the fault-tolerant protection circuit 23 to disconnect, so that the fault-tolerant protection circuit 23 is in an open circuit state. At this time, the secondary current on the secondary side flows through the secondary bridge circuit 214 for freewheeling.

[0089] It can be seen that the power conversion device 20 of the embodiment of the present application can not only enable the fault-tolerant device 22 to freewheel the secondary current is when the control timing error affects the normal operation of the secondary bridge circuit 214, realize the fault-tolerant protection of the secondary switching tube, and ensure that the secondary bridge circuit 214 can continue to operate, but also deactivate the fault-tolerant device 22 when the control timing of the secondary bridge circuit 214 is normal, so as to avoid affecting the freewheeling of the secondary current is by the secondary bridge circuit 214, thereby affecting the power conversion of the power conversion circuit 21. With such a design, regardless of whether the control timing is incorrect or correct, the power conversion device 20 can always freewheel the secondary current is. Based on this, the voltage applied across the outer tube and the voltage applied across the inner tube can always be maintained within a preset safe voltage (for example, about 90% of the breakdown voltage of the switching tube), ensuring that the secondary bridge circuit 214 can continue to operate normally. Moreover, compared with the fault-tolerant protection implemented by pure software, the fault-tolerant device 22 belongs to hardware fault-tolerant protection, and the fault-tolerant protection of the power conversion circuit 21 is more reliable and stable.

[0090] It should be understood that in other embodiments, the controller 24 in the fault-tolerant device 22 can also be set independently, or integrated with other circuits / modules / devices. In other embodiments, the fault-tolerant protection circuit 23 and the power conversion circuit 21 can also be controlled by different controllers 24 respectively.

[0091] For better understanding, the fault-tolerant device 22 of the embodiment of the present application will be further described below with reference to Embodiment 1 and Embodiment 2.

[0092] Embodiment 1

[0093] Please refer to Figure 9 , which shows a circuit diagram of the fault - tolerance protection circuit 23 in the fault - tolerance device 22 of the first embodiment connected to the power conversion circuit 21. For simplicity of illustration, Figure 9 the controller 24 is not shown in

[0094] As Figure 9 shown, the fault - tolerance protection circuit 23 is connected between the secondary side of the transformer 212 and the first end of the secondary - side bridge circuit 214. Specifically, it can be connected between the mid - point of the secondary side of the transformer 212 and the first secondary - side bridge arm 2141, or between the secondary side of the transformer 212 and the inner tube Q6 of the first bidirectional switch. The leakage inductance Lr of the secondary side of the transformer 212 in this embodiment is also located between the mid - point of the first secondary - side bridge arm 2141 and the secondary side of the transformer 212. At this time, the fault - tolerance protection circuit 23 can be connected in parallel with the secondary - side leakage inductance Lr.

[0095] The fault - tolerance protection circuit 23 includes a control switch Ks and an absorption circuit. The control switch Ks is connected to the controller 24 and its switching state is controlled by the controller 24. The absorption circuit includes an absorption resistor Rs and a buffer capacitor Cs, and the absorption resistor Rs, the buffer capacitor Cs are connected to the control switch Ks.

[0096] In the first embodiment, an example is shown where the absorption resistor Rs, the control switch Ks, and the buffer capacitor Cs are connected in series in sequence. It should be understood that in other embodiments, the specific positions and connection relationships of the absorption resistor Rs, the control switch Ks, and the buffer capacitor Cs can be adjusted according to the actual situation, and are not limited to the positions and connection relationships shown in the first embodiment.

[0097] Based on such a structural design, when the outer - tube control signals of the two outer tubes Q5 and Q8 are both off - control signals at the same time, and / or when the inner - tube control signals of the two inner tubes Q6 and Q7 are both off - control signals at the same time, the controller 24 can control the control switch Ks to close to turn on the fault - tolerance protection circuit 23.

[0098] At this time, as Figure 10 shown by the thick black line (the arrow indicates the current flow direction) in Figure 11As shown by the thick black line (with the arrow indicating the current flow direction), if the secondary current is flows in the reverse direction, the fault-tolerant protection circuit 23 can also form a freewheeling branch, enabling the secondary current is to flow into the fault-tolerant protection circuit. Among them, the energy of the current flowing through the buffer capacitor Cs will first be stored in the buffer capacitor Cs and then released to the absorption resistor Rs. The energy of the current flowing through the absorption resistor Rs will be consumed by the absorption resistor Rs. That is to say, the buffer capacitor Cs can buffer the energy of the secondary current is, and the absorption resistor Rs can absorb the energy of the secondary current is, thereby reducing the voltage stress on the secondary switching tube and protecting the secondary switching tube.

[0099] When the outer tube control signals of the two outer tubes Q5 and Q8 are not both off control signals, and the inner tube control signals of the two inner tubes Q6 and Q7 are not both off control signals, the controller 24 can control the control switch Ks to open to disconnect the fault-tolerant protection circuit 23.

[0100] In addition, while controlling the operation of the secondary bridge circuit 214, the controller 24 also controls the operation of the primary bridge circuit 211. Therefore, in this embodiment, the controller 24 can also control the first primary switching tube Q1 and the second primary switching tube Q2 to conduct alternately, and control the third primary switching tube Q3 and the fourth primary switching tube Q4 to conduct alternately.

[0101] It should be understood that in other embodiments, if the primary bridge circuit 211 of the power conversion circuit 21 is a primary half-bridge circuit, that is Figure 3 when some of the primary switching tubes in the primary full-bridge circuit are replaced with capacitors, the primary switching tubes in the primary half-bridge circuit are turned on and off according to the on-off logic of the same primary switching tubes in the primary full-bridge circuit, so it will not be elaborated here.

[0102] In addition, to verify the effect of reducing the stress on the secondary switching tube in Embodiment 1, the present application embodiment also conducts a simulation experiment on the power conversion device 20.

[0103] Please refer to Figure 12 and Figure 13 the shown simulation signal waveform diagrams, where Figure 12 shows the waveform diagram of the voltage across Q5-Q8, that is, the voltage stress waveform diagram of Q5-Q8, when control timing errors occur during the operation of the power conversion circuit 21 shown in Figure 9 where both Q5 and Q8 are off, and / or both Q6 and Q7 are off; Figure 13 shows Figure 12 a partial enlarged view of the part near the zero crossing point within the elliptical dashed box of the waveform shown.

[0104] It can be understood that Figure 12 the corresponding simulation experiment and Figure 7 the corresponding simulation experiment have the same experimental conditions, except thatFigure 7 In the corresponding experiment, the fault-tolerant device 22 of the first embodiment was not provided in the power conversion device 20. Figure 12 In the corresponding experiment, the power conversion device 20 was provided with the fault-tolerant device 22 shown in the first embodiment, and the fault-tolerant device 22 provided fault-tolerant protection.

[0105] From Figure 12 It can be seen that when Q5 to Q8, both Q5 and Q8 are switched to the off state, the voltage stress waveforms of Q5 and Q8 can still transition smoothly near the voltage zero-crossing point. When Q6 and Q7 among Q5 to Q8 are both switched to the off state, the voltage stress waveforms of Q6 and Q7 can also transition smoothly near the voltage zero-crossing point. From Figure 13 It can be seen that the voltage stress of Q5 and Q8, Q6 and Q7 near the voltage zero-crossing point is less than 25V, which is significantly less than Figure 8 the stress exceeding 150V shown. When Q5 to Q8 are all turned off, since the fault-tolerant protection circuit 23 of the embodiment of the present application can be turned on, therefore, at this time, the voltage stress of Q5 to Q8 is still significantly less than Figure 7 the stress shown. For example, the stress of Q5, Q6, and Q7 is lower than 400V, and the stress of Q8 is lower than 200V.

[0106] Thus, based on the fault-tolerant device 22 of the first embodiment, it is possible to reduce the voltage stress of the secondary side switching transistors Q5 to Q8 in the case of incorrect control timing of the secondary side switching transistors, so that the voltage stress of Q5 to Q8 (that is, the voltage applied across Q5 to Q8) is always within a preset safe voltage range, thereby ensuring the safety of the secondary side switching transistors and the normal operation of the power conversion circuit 21.

[0107] Embodiment 2

[0108] Please refer to Figure 14 , which shows a circuit diagram of the fault-tolerant protection circuit 23 in the fault-tolerant device 22 of Embodiment 2 connected to the power conversion circuit 21. For simplicity of illustration, Figure 14 the controller 24 is not shown in

[0109] The main difference between Embodiment 2 and Embodiment 1 lies in the quantity, position, and connection relationship of the fault-tolerant protection circuit 23.

[0110] Specifically, as Figure 14As shown, the number of fault-tolerant protection circuits 23 in the second embodiment is two, namely the first fault-tolerant protection circuit 23A and the second fault-tolerant protection circuit 23B. The structures and component parameters of the two fault-tolerant protection circuits 23 are the same. The two fault-tolerant protection circuits 23 are both connected between the secondary side of the transformer 212 and the second end of the secondary side bridge circuit 214, and the two fault-tolerant protection circuits 23 are connected in parallel with two bidirectional switches respectively. For example, the first fault-tolerant protection circuit 23A is connected in parallel with the first bidirectional switch, and the second fault-tolerant protection circuit 23B is connected in parallel with the second bidirectional switch.

[0111] The first fault-tolerant protection circuit 23A includes a control switch Ks1 and an absorption circuit, and the second fault-tolerant protection circuit 23B includes a control switch Ks2 and an absorption circuit. The control switch Ks1 and the control switch Ks2 are respectively connected to the controller 24, and their switching states are controlled by the controller 24. In this embodiment, the switching states of the control switch Ks1 and the control switch Ks2 are the same. The absorption circuit in the first fault-tolerant protection circuit 23A includes an absorption resistor Rs1 and a buffer capacitor Cs1, and the absorption resistor Rs1, the buffer capacitor Cs1 are connected to the control switch Ks1. The absorption circuit in the second fault-tolerant protection circuit 23B includes an absorption resistor Rs2 and a buffer capacitor Cs2, the absorption resistor Rs1, the buffer capacitor Cs1 are connected to the control switch Ks1, and the absorption resistor Rs2, the buffer capacitor Cs2 are connected to the control switch Ks2.

[0112] In the second embodiment, taking the absorption resistor Rs1 and the buffer capacitor Cs1 being connected in parallel, the control switch Ks1 being connected in series with the parallel-connected absorption resistor Rs1 and buffer capacitor Cs1 and also connected to the midpoint of the first secondary side bridge arm, the absorption resistor Rs2 and the buffer capacitor Cs2 being connected in parallel, and the control switch Ks2 being connected in series with the parallel-connected absorption resistor Rs2 and buffer capacitor Cs2 and also connected to the midpoint of the first secondary side bridge arm as an example for display. It should be understood that in other embodiments, the specific positions and connection relationships of the absorption resistor, the control switch, and the buffer capacitor in the same fault-tolerant protection circuit 23 can be adjusted accordingly according to the actual situation, and are not limited to the positions and connection relationships shown in the second embodiment.

[0113] Based on such a structural design, when the outer tube control signals of the two outer tubes Q5 and Q8 are both off control signals at the same time, and / or when the inner tube control signals of the two inner tubes Q6 and Q7 are both off control signals at the same time, the controller 24 can control the control switches Ks1 and Ks2 to be both closed to turn on the fault-tolerant protection circuits 23A and 23B.

[0114] At this time, as Figure 15As shown by the thick black line (with the arrow indicating the current flow direction), if the secondary side current \(i_s\) flows in the positive direction, the fault-tolerant protection circuit 23A can form a freewheeling branch, and the fault-tolerant protection circuit 23B can form another freewheeling branch, enabling the secondary side current \(i_s\) to flow into the fault-tolerant protection circuits 23A and 23B. As Figure 16 As shown by the thick black line (with the arrow indicating the current flow direction), if the secondary side current \(i_s\) flows in the reverse direction, the fault-tolerant protection circuits 23A and 23B can also form two freewheeling branches, enabling the secondary side current \(i_s\) to flow into the fault-tolerant protection circuits 23A and 23B. Among them, the buffer capacitors \(C_{s1}\) and \(C_{s2}\) can buffer the energy of the secondary side current \(i_s\), and the absorption resistors \(R_{s1}\) and \(R_{s2}\) can absorb the energy of the secondary side current \(i_s\), thereby reducing the voltage stress on the secondary side switching tubes and protecting the secondary side switching tubes.

[0115] When the external control signals of the two external tubes Q5 and Q8 are not both off control signals, and the internal control signals of the two internal tubes Q6 and Q7 are not both off control signals, the controller 24 can control the control switches \(K_{s1}\) and \(K_{s2}\) to be both turned on to disconnect the fault-tolerant protection circuits 23A and 23B.

[0116] In addition, to verify the effect of reducing the stress on the secondary side switching tubes in Embodiment 2, the embodiment of the present application also conducts a simulation experiment on the power conversion device 20.

[0117] Please refer to Figure 17 and Figure 18 the shown simulation signal waveform diagram, where Figure 17 shows Figure 14 during the operation of the power conversion circuit 21 shown, when there are control timing errors where both Q5 and Q8 are off, and / or both Q6 and Q7 are off, the waveform diagram of the voltage across Q5 - Q8, that is, the voltage stress waveform diagram of Q5 - Q8; Figure 18 shows Figure 17 a partial enlarged view of the part near the zero crossing point within the elliptical dashed box of the waveform shown.

[0118] It can be understood that Figure 17 the corresponding simulation experiment and Figure 7 the corresponding simulation experiment have the same experimental conditions, except that Figure 7 in the experiment corresponding to Figure 17 the power conversion device 20 is not provided with the fault-tolerant device 22 shown in Embodiment 2,

[0119] From Figure 17It can be seen that when both Q5 and Q8 in Q5~Q8 are switched to the off state, the voltage stress waveforms of Q5 and Q8 can still smoothly transition near the voltage zero-crossing point. When both Q6 and Q7 in Q5~Q8 are switched to the off state, the voltage stress waveforms of Q6 and Q7 can also smoothly transition near the voltage zero-crossing point. From Figure 18 It can be seen that the voltage stress of Q5 and Q8, Q6 and Q7 near the voltage zero-crossing point is less than 2.5V and can be nearly 0, which is significantly less than Figure 8 the stress exceeding 150V shown. When Q5~Q8 are all turned off, since the fault-tolerant protection circuit 23 of the embodiment of the present application can be turned on, therefore, at this time, the voltage stress of Q5~Q8 is still significantly less than Figure 7 the stress shown. For example, the stress of Q5 and Q6 is 0, and the stress of Q7 and Q8 is less than 150V.

[0120] It can be seen that based on the fault-tolerant device 22 of Embodiment 2, it is possible to reduce the voltage stress of the secondary side switching transistors Q5~Q8 in the case of incorrect control timing of the secondary side switching transistors, so that the voltage stress of Q5~Q8 (that is, the voltage applied across Q5~Q8) is always within a preset safe voltage range, thereby ensuring the safety of the secondary side switching transistors and the normal operation of the power conversion circuit 21.

[0121] It should be understood that other descriptions of Embodiment 2 can also refer to Embodiment 1 and will not be repeated here.

[0122] In addition, based on Figure 1 the scenario shown, the embodiment of the present application also provides a fault-tolerant method for a power conversion circuit. This fault-tolerant method can be executed by the controller 24 in the fault-tolerant device 22, and can achieve fault-tolerant protection for the secondary side switching transistors and the power conversion circuit 21 through the fault-tolerant protection circuit 23 in the case of incorrect control timing of the secondary side switching transistors of the power conversion circuit 21. It should be understood that in other embodiments, this fault-tolerant method can also be executed by other modules or devices with control functions, and can be specifically selected according to actual situations and will not be specifically limited here.

[0123] Specifically, please refer to Figure 19 , the fault-tolerant method for the power conversion circuit of the embodiment of the present application includes the following steps:

[0124] Step S100, obtain the outer transistor control signal and the inner transistor control signal of the secondary side bridge circuit.

[0125] It can be understood that the control signals S1 to S8 of the power conversion circuit 21 can all be generated by the modulation circuit. The modulation circuit can be integrated in the controller 24 or set independently. Therefore, in step S100, the controller 24 can obtain the outer transistor control signal S5 of the outer transistor Q5, the outer transistor control signal S8 of the outer transistor Q8, the inner transistor control signal S6 of the inner transistor Q6, and the inner transistor control signal S7 of the inner transistor Q7 from the modulation circuit.

[0126] Step S200: When the outer transistor control signals of the two outer transistors are simultaneously off control signals, and / or when the inner transistor control signals of the two inner transistors are simultaneously off control signals, control the fault tolerance protection circuit to be in a conducting state, so that the fault tolerance protection circuit conducts the current of the secondary side and absorbs the energy of the secondary side current.

[0127] Exemplarily, in the first embodiment, the fault tolerance device 22 is provided with a fault tolerance protection circuit 23, and the fault tolerance protection circuit 23 includes a connected control switch Ks and an absorption circuit. Therefore, step S200 can be specifically:

[0128] When the outer transistor control signals of the two outer transistors are simultaneously off control signals, and / or when the inner transistor control signals of the two inner transistors are simultaneously off control signals, control the control switch Ks to close, so that the secondary side current conducts through the control switch Ks and the absorption circuit, and the energy of the secondary side current is absorbed by the absorption circuit.

[0129] Exemplarily again, in the second embodiment, the fault tolerance device 22 is provided with two fault tolerance protection circuits, namely 23A and 23B. The fault tolerance protection circuit 23A includes a connected control switch Ks1 and an absorption circuit, and the fault tolerance protection circuit 23B includes a connected control switch Ks2 and an absorption circuit. Therefore, step S200 can be specifically:

[0130] When the outer transistor control signals of the two outer transistors are simultaneously off control signals, and / or when the inner transistor control signals of the two inner transistors are simultaneously off control signals, control both the control switches Ks1 and Ks2 to close, so that the secondary side current conducts through the control switch Ks1 and its connected absorption circuit, and conducts through the control switch Ks2 and its connected absorption circuit, and the energy of the secondary side current is absorbed by the two absorption circuits.

[0131] In the embodiment of the present application, the first level is used to drive the switch transistor to turn off, and the second level is used to drive the switch transistor to turn on. Therefore, before step S20, the fault tolerance method can further include:

[0132] When the outer transistor control signals S5 and S8 of the outer transistors Q5 and Q8 are simultaneously the first level, determine that the outer transistor control signals S5 and S8 of these two outer transistors are simultaneously off control signals.

[0133] When the inner tube control signals S6 and S7 of the inner tubes Q6 and Q7 are both at the first level simultaneously, it is determined that the inner tube control signals S6 and S7 of these two inner tubes are both disconnection control signals.

[0134] On the contrary, when the outer tube control signals S5 and S8 of the outer tubes Q5 and Q8 are both at the second level simultaneously, or when one of the outer tube control signals is at the first level and the other outer tube control signal is at the second level, for example, S5 is at the first level and S8 is at the second level, or for another example, S8 is at the first level and S5 is at the second level, it is determined that the outer tube control signals S5 and S8 of these two outer tubes are not both disconnection control signals simultaneously.

[0135] When the inner tube control signals S6 and S7 of the inner tubes Q6 and Q7 are both at the second level simultaneously, or when one of the inner tube control signals is at the first level and the other inner tube control signal is at the second level, for example, S6 is at the first level and S7 is at the second level, or for another example, S7 is at the first level and S6 is at the second level, it is determined that the inner tube control signals S6 and S7 of these two inner tubes are not both disconnection control signals simultaneously.

[0136] In summary, based on the method of the embodiment of the present application, in the case of incorrect control timing of the secondary side switching tube, regardless of whether the secondary side current is flows forward or backward, the fault tolerance protection circuit 23 can provide freewheeling for the secondary side current is, suppress the boost of the parasitic capacitance freewheeling, and further reduce the voltage stress of the secondary side switching tube, prevent the secondary side switching tube from being damaged due to overstress, and thus ensure the operation of the power conversion circuit 21.

[0137] In addition, under normal control timing, the reversely flowing secondary side current is can still flow through the channel of the conducting outer tube for normal freewheeling, and there will be no problem that the outer tube is damaged due to overstress caused by the boost of the parasitic capacitance of Q5 and Q8, affecting the circuit operation. Similarly, under normal control timing, the forwardly flowing secondary side current is can still flow through the channel of the conducting outer tube for normal freewheeling, and there will be no problem that the outer tube is damaged due to overstress caused by the boost of the parasitic capacitance of Q6 and Q7, affecting the circuit operation. Therefore, please continue to refer to Figure 9 The fault tolerance method of the embodiment of the present application may further include the following steps:

[0138] Step S300, when the outer tube control signals of the two outer tubes are not both disconnection control signals simultaneously, and the inner tube control signals of the two inner tubes are not both disconnection control signals simultaneously, control the fault tolerance protection circuit to be in an open circuit state.

[0139] That is to say, when both S5 and S8 are at the second level, or when S5 is at the second level and S8 is at the first level, or when S8 is at the second level and S5 is at the first level, the controller 24 controls the fault-tolerant protection circuit 23 to disconnect, so that the secondary side of the transformer 212 cannot be connected to the secondary side bridge circuit 214 through the fault-tolerant protection circuit 23. Furthermore, the secondary side current is flowing in the forward or reverse direction flows to the first secondary side bridge arm 2141, that is, through the secondary side bridge circuit 214 for normal freewheeling.

[0140] Exemplarily, in the first embodiment, step S200 may be specifically:

[0141] When the outer tube control signals of the two outer tubes are not both disconnect control signals, and the inner tube control signals of the two inner tubes are not both disconnect control signals, control the control switch Ks to turn on.

[0142] Also exemplarily, in the second embodiment, step S200 may be specifically:

[0143] When the outer tube control signals of the two outer tubes are not both disconnect control signals, and the inner tube control signals of the two inner tubes are not both disconnect control signals, control both the control switches Ks1 and Ks2 to turn on.

[0144] It should be understood that "step S200" and "step S300" are only for distinguishing two different situations and do not limit the execution order.

[0145] In addition, based on Figure 3 the power conversion circuit 21 shown, the fault-tolerant method of the embodiment of the present application further includes the step of controlling the operation of the primary side bridge circuit 211, which may specifically be:

[0146] Control the first primary side switch tube Q1 and the second primary side switch tube Q2 to conduct alternately, and control the third primary side switch tube Q3 and the fourth primary side switch tube Q4 to conduct alternately.

[0147] Generally speaking, in the case where the control timing of the power conversion circuit 21 goes wrong and affects the normal operation of the secondary side bridge circuit 214, the fault-tolerant protection circuit 23 can provide freewheeling for the secondary side current is, realizing the fault-tolerant protection of the secondary side switching tube, thereby ensuring that the secondary side bridge circuit 214 can continue to operate. In addition, when the control timing of the secondary side bridge circuit 214 is normal, it can ensure that the secondary side bridge circuit 214 provides normal freewheeling for the secondary side current is, avoiding the influence of the fault-tolerant protection circuit 23 on the freewheeling of the secondary side bridge circuit 214, and thus avoiding affecting the power conversion of the power conversion circuit 21. Therefore, whether the control timing is wrong or correct, the power conversion device 20 can always provide freewheeling for the secondary side current is, so that the voltage applied across the outer tube and the voltage applied across the inner tube can always be maintained within the preset safe voltage range, ensuring that the power conversion circuit 21 can continue to operate normally.

[0148] Moreover, the fault-tolerant protection and fault-tolerant method proposed in the embodiments of the present application can be implemented relying on the hardware structure. Compared with relying on pure software programs, such an implementation method is more reliable and has higher control efficiency. The fault-tolerant method proposed in the embodiments of the present application does not need to change the original control logic of the outer tube and the inner tube, so the control is simple, does not increase the control complexity of the outer tube and the inner tube, and is not prone to control logic confusion.

[0149] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit them. Although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A fault-tolerant device, characterized in that: Applied to a power conversion circuit, the power conversion circuit includes a primary bridge circuit, a transformer and a secondary bridge circuit, the first end of the primary bridge circuit is connected to the primary side of the transformer, the second end of the primary bridge circuit is used to connect a DC power supply or a DC load, the first end of the secondary bridge circuit is connected to the secondary side of the transformer, and the second end of the secondary bridge circuit is used to connect an AC load or an AC power supply; wherein the secondary bridge circuit includes a first secondary bridge arm and a second secondary bridge arm connected in parallel, the first secondary bridge arm includes two bidirectional switches connected in series, the two bidirectional switches each include an outer tube and an inner tube connected in reverse series, and the second secondary bridge arm includes a first capacitor and a second capacitor connected in series; The fault-tolerant device comprises a fault-tolerant protection circuit, and the fault-tolerant protection circuit is connected between the secondary side of the transformer and the secondary side bridge circuit, wherein: When the outer tube control signals of the two outer tubes are disconnection control signals at the same time, and / or when the inner tube control signals of the two inner tubes are disconnection control signals at the same time, the fault-tolerant protection circuit is in a conduction state to continue the secondary current on the secondary side and absorb the energy of the secondary current.

2. The fault-tolerant device according to claim 1, characterized in that: When the outer tube control signals of the two outer tubes are not disconnection control signals at the same time, and the inner tube control signals of the two inner tubes are not disconnection control signals at the same time, the fault-tolerant protection circuit is in an open circuit state, so that the secondary side bridge circuit continues the secondary side current on the secondary side.

3. The fault-tolerant device according to claim 1, characterized in that: The fault-tolerant protection circuit is connected between the secondary side of the transformer and the first end of the secondary side bridge circuit, and the fault-tolerant protection circuit includes a connected control switch and an absorption circuit; The fault-tolerant device further includes a controller, the controller is connected to the control switch, the controller is used to obtain the outer tube control signal and the inner tube control signal of the secondary bridge circuit, and when the outer tube control signals of the two outer tubes are disconnection control signals at the same time, and / or when the inner tube control signals of the two inner tubes are disconnection control signals at the same time, control the control switch to close, so that the secondary current continues to flow through the control switch and the absorption circuit, and the energy of the secondary current is absorbed by the absorption circuit; and, When the outer tube control signals of the two outer tubes are not disconnection control signals at the same time, and the inner tube control signals of the two inner tubes are not disconnection control signals at the same time, the control switch is controlled to be opened.

4. The fault-tolerant device according to claim 1, characterized in that: The number of the fault-tolerant protection circuits is two, and the two fault-tolerant protection circuits are both connected between the secondary side of the transformer and the second end of the secondary side bridge circuit, and are connected in parallel with the two bidirectional switches in a one-to-one correspondence, and each of the fault-tolerant protection circuits includes a connected control switch and an absorption circuit; The fault-tolerant device further includes a controller, the controller is connected to the control switches of the two fault-tolerant protection circuits, the controller is used to obtain the outer tube control signal and the inner tube control signal of the secondary bridge circuit, and when the outer tube control signals of the two outer tubes are disconnection control signals at the same time, and / or when the inner tube control signals of the two inner tubes are disconnection control signals at the same time, control the control switches to be closed, so that the secondary current continues to flow through the control switch and the absorption circuit, and the energy of the secondary current is absorbed by the absorption circuit; and, When the outer tube control signals of the two outer tubes are not disconnection control signals at the same time, and the inner tube control signals of the two inner tubes are not disconnection control signals at the same time, the control switches are controlled to be opened.

5. The fault-tolerant device according to claim 3 or 4, characterized in that: The absorption circuit includes an absorption resistor and a buffer capacitor. The absorption resistor and the buffer capacitor in the same fault-tolerant protection circuit are connected to the control switch.

6. The fault-tolerant device according to claim 5, characterized in that: The absorption resistor, the buffer capacitor and the control switch in the same fault-tolerant protection circuit are connected in series; or, The absorption resistor in the same fault-tolerant protection circuit is connected in parallel with the buffer capacitor, and the control switch in the same fault-tolerant protection circuit is connected in series with the parallel-connected absorption resistor and the buffer capacitor.

7. A power conversion device, characterized in that: The power conversion device comprises a power conversion circuit and a fault-tolerant protection circuit, wherein the power conversion circuit comprises a primary bridge circuit, a transformer and a secondary bridge circuit, wherein the first end of the primary bridge circuit is connected to the primary side of the transformer, the second end of the primary bridge circuit is used to connect a DC power supply or a DC load, the first end of the secondary bridge circuit is connected to the secondary side of the transformer, and the second end of the secondary bridge circuit is used to connect an AC load or an AC power supply; wherein the secondary bridge circuit comprises a first secondary bridge arm and a second secondary bridge arm connected in parallel, wherein the first secondary bridge arm comprises two bidirectional switches connected in series, and both of the two bidirectional switches comprise an outer tube and an inner tube connected in reverse series, and the second secondary bridge arm comprises a first capacitor and a second capacitor connected in series; The fault-tolerant protection circuit is connected between the secondary side of the transformer and the secondary side bridge circuit, wherein: When the outer tube control signals of the two outer tubes are disconnection control signals at the same time, and / or when the inner tube control signals of the two inner tubes are disconnection control signals at the same time, the fault-tolerant protection circuit is in a conduction state to continue the secondary current on the secondary side and absorb the energy of the secondary current.

8. The power conversion device according to claim 7, characterized in that When the outer tube control signals of the two outer tubes are not disconnection control signals at the same time, and the inner tube control signals of the two inner tubes are not disconnection control signals at the same time, the fault-tolerant protection circuit is in an open circuit state, so that the secondary side bridge circuit continues the secondary side current on the secondary side.

9. The power conversion device according to claim 7, characterized in that The fault-tolerant protection circuit is connected between the secondary side of the transformer and the first end of the secondary side bridge circuit, and the fault-tolerant protection circuit includes a connected control switch and an absorption circuit; The power conversion device further includes a controller, the controller is connected to the control switch, the controller is used to obtain the outer tube control signal and the inner tube control signal of the secondary bridge circuit, and when the outer tube control signals of the two outer tubes are disconnection control signals at the same time, and / or when the inner tube control signals of the two inner tubes are disconnection control signals at the same time, control the control switch to close, so that the secondary current continues to flow through the control switch and the absorption circuit, and the energy of the secondary current is absorbed by the absorption circuit; and, When the outer tube control signals of the two outer tubes are not disconnection control signals at the same time, and the inner tube control signals of the two inner tubes are not disconnection control signals at the same time, the control switch is controlled to be opened.

10. The power conversion device according to claim 7, characterized in that The number of the fault-tolerant protection circuits is two, and the two fault-tolerant protection circuits are both connected between the secondary side of the transformer and the second end of the secondary side bridge circuit, and are connected in parallel with the two bidirectional switches in a one-to-one correspondence, and each of the fault-tolerant protection circuits includes a connected control switch and an absorption circuit; The power conversion device further includes a controller, the controller is connected to the control switches of the two fault-tolerant protection circuits, the controller is used to obtain the outer tube control signal and the inner tube control signal of the secondary bridge circuit, and when the outer tube control signals of the two outer tubes are disconnection control signals at the same time, and / or when the inner tube control signals of the two inner tubes are disconnection control signals at the same time, control the control switches to be closed, so that the secondary current continues to flow through the control switch and the absorption circuit, and the energy of the secondary current is absorbed by the absorption circuit; and, When the outer tube control signals of the two outer tubes are not disconnection control signals at the same time, and the inner tube control signals of the two inner tubes are not disconnection control signals at the same time, the control switches are controlled to be opened.

11. The power conversion device according to claim 7, characterized in that The voltage applied to both ends of the outer tube and the voltage applied to both ends of the inner tube are always within a preset safe voltage range.

12. The power conversion device according to claim 7, characterized in that The power conversion device also includes a controller, which is connected to the power conversion circuit and is used to generate a control signal for the power conversion circuit, wherein the control signal for the power conversion circuit includes a primary control signal, an external tube control signal and an internal tube control signal, the primary control signal is used to control the on-off state of the switch tube in the primary bridge circuit, the external tube control signal is used to control the on-off state of the external tube in the secondary bridge circuit, and the internal tube control signal is used to control the on-off state of the inner tube in the secondary bridge circuit.

13. The power conversion device according to claim 7, characterized in that The primary bridge circuit includes a first primary bridge arm and a second primary bridge arm connected in parallel, the first primary bridge arm includes a first primary switch tube and a second primary switch tube connected in series, and the second primary bridge arm includes a third primary switch tube and a fourth primary switch tube connected in series.

14. A power supply system, characterized in that: The power supply system comprises: a DC power supply and a power conversion device as described in any one of claims 7 to 13, the DC power supply is connected to the second end of the primary bridge circuit, the second end of the secondary bridge circuit is connected to a common coupling point, the DC power supply comprises at least one of an energy storage device and a photovoltaic power generation device, and the common coupling point is used to connect at least one of a power grid and an AC load.

15. A fault-tolerant method for a power conversion circuit, characterized in that: The power conversion circuit includes a primary bridge circuit, a transformer and a secondary bridge circuit, wherein the first end of the primary bridge circuit is connected to the primary side of the transformer, the second end of the primary bridge circuit is used to connect a DC power supply or a DC load, the first end of the secondary bridge circuit is connected to the secondary side of the transformer, the second end of the secondary bridge circuit is used to connect an AC load or an AC power supply, and a fault-tolerant protection circuit is also connected between the secondary side of the transformer and the secondary bridge circuit; wherein the secondary bridge circuit includes a first secondary bridge arm and a second secondary bridge arm connected in parallel, the first secondary bridge arm includes two bidirectional switches connected in series, the two bidirectional switches each include an outer tube and an inner tube connected in reverse series, and the second secondary bridge arm includes a first capacitor and a second capacitor connected in series; the fault-tolerant method includes: Obtaining an outer tube control signal and an inner tube control signal of the secondary side bridge circuit; When the outer tube control signals of the two outer tubes are disconnection control signals at the same time, and / or when the inner tube control signals of the two inner tubes are disconnection control signals at the same time, the fault-tolerant protection circuit is controlled to be in a conduction state so that the fault-tolerant protection circuit continues the secondary current on the secondary side and absorbs the energy of the secondary current.

16. The fault-tolerant method according to claim 15, characterized in that: The fault-tolerant method further comprises: When the outer tube control signals of the two outer tubes are not disconnection control signals at the same time, and the inner tube control signals of the two inner tubes are not disconnection control signals at the same time, the fault-tolerant protection circuit is controlled to be in an open circuit state.

17. The fault-tolerant method according to claim 16, wherein: The fault-tolerant protection circuit is connected between the secondary side of the transformer and the first end of the secondary side bridge circuit, and the fault-tolerant protection circuit includes a connected control switch and an absorption circuit; When the outer tube control signals of the two outer tubes are disconnection control signals at the same time, and / or when the inner tube control signals of the two inner tubes are disconnection control signals at the same time, controlling the fault-tolerant protection circuit to be in a pass state so that the fault-tolerant protection circuit continues the secondary current on the secondary side and absorbs the energy of the secondary current, comprising: When the outer tube control signals of the two outer tubes are disconnection control signals at the same time, and / or when the inner tube control signals of the two inner tubes are disconnection control signals at the same time, the control switch is controlled to be closed, so that the secondary current continues to flow through the control switch and the absorption circuit, and the energy of the secondary current is absorbed by the absorption circuit; When the outer tube control signals of the two outer tubes are not disconnection control signals at the same time, and the inner tube control signals of the two inner tubes are not disconnection control signals at the same time, controlling the fault-tolerant protection circuit to be in an open circuit state includes: When the outer tube control signals of the two outer tubes are not disconnection control signals at the same time, and the inner tube control signals of the two inner tubes are not disconnection control signals at the same time, the control switch is controlled to be opened.

18. The fault-tolerant method according to claim 16, wherein: The number of the fault-tolerant protection circuits is two, and the two fault-tolerant protection circuits are both connected between the secondary side of the transformer and the second end of the secondary side bridge circuit, and are connected in parallel with the two bidirectional switches in a one-to-one correspondence, and each of the fault-tolerant protection circuits includes a connected control switch and an absorption circuit; When the outer tube control signals of the two outer tubes are disconnection control signals at the same time, and / or when the inner tube control signals of the two inner tubes are disconnection control signals at the same time, controlling the fault-tolerant protection circuit to be in a pass state so that the fault-tolerant protection circuit continues the secondary current on the secondary side and absorbs the energy of the secondary current, comprising: When the outer tube control signals of the two outer tubes are disconnection control signals at the same time, and / or when the inner tube control signals of the two inner tubes are disconnection control signals at the same time, the control switches are controlled to be closed, so that the secondary current continues to flow through the control switch and the absorption circuit, and the energy of the secondary current is absorbed by the absorption circuit; When the outer tube control signals of the two outer tubes are not disconnection control signals at the same time, and the inner tube control signals of the two inner tubes are not disconnection control signals at the same time, controlling the fault-tolerant protection circuit to be in an open circuit state includes: When the outer tube control signals of the two outer tubes are not disconnection control signals at the same time, and the inner tube control signals of the two inner tubes are not disconnection control signals at the same time, the control switches are controlled to be opened.

19. The fault-tolerant method according to claim 15 or 16, characterized in that: The fault-tolerant method further comprises: When the external tube control signals of the two external tubes are at the first level at the same time, determining that the external tube control signals of the two external tubes are disconnection control signals at the same time; When the external tube control signals of the two external tubes are at the second level at the same time, or when one of the external tube control signals is at the first level and the other external tube control signal is at the second level, determining that the external tube control signals of the two external tubes are not disconnection control signals at the same time; When the inner tube control signals of the two inner tubes are at the first level at the same time, determining that the inner tube control signals of the two inner tubes are disconnection control signals at the same time; When the inner tube control signals of the two inner tubes are at the second level at the same time, or when one of the inner tube control signals is at the first level and the other inner tube control signal is at the second level, determining that the inner tube control signals of the two inner tubes are not disconnection control signals at the same time; The first level is different from the second level, the first level is used to drive the switch tube to turn off, and the second level is used to drive the switch tube to turn on.

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