A method for controlling the shutdown of a switch failure in an ANPC three-level inverter

Abstract

The invention relates to the technical field of power electronics, and specifically discloses a method for controlling the switch tube failure of an ANPC type three-level inverter. The method utilizes the characteristics of a CPLD module with fast processing speed and many pins, and inputs the fault signals of 18 switch tubes into the CPLD module. During operation, the driving circuit only uploads the fault, and does not directly perform a switch tube shutdown operation. Instead, the CPLD module performs the switch tube shutdown control. When the CPLD module receives the switch tube fault signal uploaded by the driving circuit, the CPLD module performs a fault detection on each switch tube, and then performs a corresponding switch tube shutdown operation according to the position of each switch tube and the current action logic of other switch tubes, so as to realize fast and accurate switch tube shutdown and better protect the switch tube. Moreover, the CPLD control of the switch tube shutdown timing response is fast and flexible, and fault-tolerant operation and stable parking can also be realized.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a method for controlling a switch failure of an ANPC type three-level inverter. Background Art

[0002] An inverter is a converter that converts DC power (battery, storage bottle) into constant frequency and voltage or frequency and voltage regulated AC power. Inverters for high voltage and high power applications usually use an active neutral-point-clamped (ANPC) three-level inverter topology. The main circuit of an ANPC three-level inverter generally includes two DC bus support capacitors and three bridge arms of the same structure connected in parallel. The connection method of each bridge arm is the same. Taking one phase as an example, the topology of the main circuit of an ANPC three-level inverter is as follows: Figure 1 As shown, it includes a DC bus support capacitor C1, a DC bus support capacitor C2, switches S1-S6, and diodes connected in anti-parallel with the switches S1-S6, respectively. The switches S1 and S4 are outer bridge arm tubes, and the switches S2 and S3 are inner bridge arm tubes. The input end of the switch S1 is connected to the positive pole of the DC bus, and the output end is connected to the input end of the switches S2 and S5; the output end of the switch S4 is connected to the negative pole of the DC bus, and the input end is connected to the output end of the switches S3 and S6 respectively; the output end of the switch S5 is connected to the input end of the switch S6, and the output end of the switch S2 is connected to the input end of the switch S3; the output end of the switch S5 and the input end of the switch S6 are both connected to the midpoint O of the DC bus; the DC bus support capacitor C1 is connected between the positive pole and the midpoint O of the DC bus; the DC bus support capacitor C2 is connected between the negative pole and the midpoint O of the DC bus; the output end U of the switch S2 is used as the AC output end. The control ends of the switch tubes S1 - S6 are respectively connected to the output ends of the drive circuit, and the drive circuit outputs gate drive signals to control the on and off of the switch tubes S1 - S6.

[0003] In the existing ANPC type three-level inverter, when the switch tube fails, the driving circuit of the switch tube usually directly outputs the corresponding gate drive signal to directly close the failed switch tube, and the driving circuit uploads the fault signal to the DSP (digital signal processor) module for corresponding fault processing. Usually, all the switch tube faults are combined into the same fault signal, and the tubes are closed according to a unified closing sequence after the fault occurs. There are two problems: First, if only the inner tube of the bridge arm (switch tube 2 and switch tube S3) fails and is automatically closed by the driving circuit, if the outer tube of the bridge arm (switch tube S1 and switch tube S4) is still in the on state, switch tube 2 and switch tube S3 may be damaged by full pressure; Second, the unified closing sequence is slow to respond and not flexible enough. Summary of the invention

[0004] The object of the present invention is to provide a method for controlling the shutdown of a switch tube failure of an ANPC type three-level inverter, which can protect the switch tube from being damaged due to improper shutdown timing, and the shutdown timing response is fast and flexible.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A method for controlling a switch failure of an ANPC type three-level inverter. The ANPC type three-level inverter has three bridge arms corresponding to three phases, each of which has a switch S1 to a switch S6. A control unit is used to control the switch S1 to the switch S6 in each bridge arm according to various switch failure conditions.

[0007] The control unit includes a DSP module, a CPLD module and a drive circuit, wherein the DSP module is bidirectionally connected to the CPLD module, and the CPLD module is bidirectionally connected to the drive circuit; the DSP module performs algorithm operation according to the control instruction issued by the main control unit, and the bus voltage signal and output current signal of the inverter collected, generates three groups of level signals and three direction signals and outputs them to the CPLD module; the CPLD module calculates six switch signals of each phase of the inverter according to the three groups of level signals and the three direction signals, and the CPLD module outputs 18 drive signals to the drive circuit; each output end of the drive circuit is respectively connected to the control end of the switch tube S1 to the switch tube S6, and is used to output the gate drive signal to control the conduction and closing of the switch tube S1 to the switch tube S6; the drive circuit is also used to process the fault detection signal of the switch tube S1 to the switch tube S6, and output the switch tube fault signal to the CPLD module, and then the CPLD module outputs the fault and alarm information to the DSP module, and the DSP module displays the fault and disconnects the enable;

[0008] When working, the driving circuit only uploads the fault and does not directly shut down the tube. Instead, the CPLD module performs the shut-down control. When the CPLD module receives the switch tube fault signal uploaded by the driving circuit, the CPLD module performs fault detection on each switch tube, and then performs the corresponding shut-down operation according to the position of each switch tube and the current action logic of other switch tubes, so as to better protect the switch tube.

[0009] Furthermore, for the fault condition where only one switch tube in one bridge arm is faulty, the following method is used to perform tube shut-down control:

[0010] When the CPLD module determines that the fault occurs in the switch tube S1 or the switch tube S4, the switch tube S1 or the switch tube S4 is directly turned off, and then the switch tubes S5 and S6 are turned on after an interval of 5us, and then the switch tubes S2 and S3 are turned off after an interval of 5us, and finally the switch tubes S5 and S6 are turned off after an interval of 5us;

[0011] When the CPLD module determines that the fault occurs in the switch tube S2, the switch tube S1 is directly turned off first, and then the switch tube S2 is turned off after an interval of 2us to protect the switch tube S2 from being damaged; finally, the switch tubes in the on state among the switch tubes S3, S4, S5 and S6 are turned off;

[0012] When the CPLD module determines that the fault occurs in the switch tube S3, the switch tube S4 is directly turned off first, and then the switch tube S3 is turned off after an interval of 2us to protect the switch tube S3 from being damaged; finally, the switch tubes in the on state among the switch tubes S1, the switch tube S2, the switch tube S5 and the switch tube S6 are turned off;

[0013] When the CPLD module determines that the fault occurs in switch tube S5 or switch tube S6, it directly turns off switch tube S5 or switch tube S6, then adjusts the zero-level switch timing, and outputs fault and alarm information to the DSP module to keep running, thereby achieving fault-tolerant operation or normal deceleration and parking.

[0014] Furthermore, in the case where two or more switch tubes in one bridge arm are faulty, the following method is used to perform tube shut-down control:

[0015] When the CPLD module determines that the failed switch tubes are the switch tubes S5 and S6 of the same bridge arm, the switch tubes S5 and S6 of the bridge arm are directly turned off. In this case, the topology of the bridge arm is switched from ANPC to NPC circuit, and the control algorithm of the DSP module and the CPLD module for the bridge arm is switched to NPC type control mode to achieve fault-tolerant operation or smooth parking;

[0016] When the CPLD module determines that the failed switch tubes are the switch tubes S5 and S6 of different bridge arms, the failed switch tubes S5 and S6 are directly turned off, and then the zero-level switch timing of the corresponding bridge arm is adjusted to achieve fault-tolerant operation or smooth parking;

[0017] When the CPLD module determines that the faulty switch tubes include switch tube S2 and switch tube S3, the switch tube S1 and switch tube S4 of the corresponding bridge arm and the faulty switch tubes other than switch tube S2 and switch tube S3 in the corresponding bridge arm are directly turned off first; then the faulty switch tube S2 and switch tube S3 are turned off again after an interval of 2us; finally, the CPLD module turns off all the switch tubes, outputs a fault signal, displays the fault and disconnects the enable;

[0018] When the CPLD module determines that the faulty switch tube is two or more of the switch tube S1, the switch tube S4, the switch tube S5 or the switch tube S6, fault-tolerant operation is not considered in this case. The faulty switch tube is directly turned off first, and the switch tubes S1 and the switch tube S4 that have not failed in the three bridge arms are also turned off. After an interval of 5us, the switch tubes S5 and the switch tube S6 that have not failed in each bridge arm are turned on to clamp the output voltage at the zero level. After an interval of 5us, all the switch tubes S2 and all the switch tubes S3 in the three bridge arms are turned off. Finally, the CPLD module turns off all the switch tubes, outputs a fault signal, displays the fault and disconnects the enable.

[0019] After adopting the above scheme, the present invention uses the characteristics of fast processing speed and many pins of the CPLD module to input the fault signals of 18 switch tubes into the CPLD module. When working, the driving circuit only uploads the fault and does not directly perform the tube shut-off control. Instead, the CPLD module performs the tube shut-off control. When the CPLD module receives the switch tube fault signal uploaded by the driving circuit, the CPLD module will perform fault detection on each switch tube, and then perform the corresponding tube shut-off operation according to the position of each switch tube and the current action logic of other switch tubes, so as to achieve fast and accurate tube shut-off and better protect the switch tube. Moreover, the CPLD control tube shut-off timing response is fast and flexible, and fault-tolerant operation and stable parking can also be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A topological structure diagram of the main circuit of the ANPC type three-level inverter in the prior art;

[0021] Figure 2 It is a circuit principle block diagram of a control unit of an ANPC type three-level inverter in the present invention;

[0022] Figure 3 This is a timing flow chart of shutting down a single switch tube when it fails in the present invention;

[0023] Figure 4 This is a timing flow chart of shutting down multiple switch tubes due to faults in the present invention. DETAILED DESCRIPTION

[0024] The present invention discloses a method for controlling the shutdown of a switch tube failure of an ANPC type three-level inverter. The main circuit of the ANPC type three-level inverter adopts the same topology as the prior art, including two DC bus support capacitors and three bridge arms corresponding to three phases with the same structure and connected in parallel. The connection mode of each bridge arm is the same, and each bridge arm has six switch tubes. The six switch tubes in each bridge arm are controlled to be shut down accordingly according to various switch tube failure conditions by a control unit.

[0025] Since the structure and connection method of each bridge arm are the same, take one phase as an example. Figure 1 As shown, it includes a DC bus support capacitor C1, a DC bus support capacitor C2, switches S1-S6, and diodes connected in anti-parallel with the switches S1-S6, respectively. The switches S1 and S4 are outer bridge arm tubes, and the switches S2 and S3 are inner bridge arm tubes. The input end of the switch S1 is connected to the positive pole of the DC bus, and the output end is connected to the input end of the switches S2 and S5; the output end of the switch S4 is connected to the negative pole of the DC bus, and the input end is connected to the output end of the switches S3 and S6 respectively; the output end of the switch S5 is connected to the input end of the switch S6, and the output end of the switch S2 is connected to the input end of the switch S3; the output end of the switch S5 and the input end of the switch S6 are both connected to the midpoint O of the DC bus; the DC bus support capacitor C1 is connected between the positive pole and the midpoint O of the DC bus; the DC bus support capacitor C2 is connected between the negative pole and the midpoint O of the DC bus; the output end U of the switch S2 is used as the AC output end.

[0026] like Figure 2As shown, the control unit includes a DSP module, a CPLD module and a drive circuit, the DSP module is bidirectionally connected to the CPLD module, and the CPLD module is bidirectionally connected to the drive circuit; the DSP module performs algorithm operation according to the control instruction issued by the main control unit, and the bus voltage signal and output current signal of the inverter collected, generates three groups of level signals and three direction signals and outputs them to the CPLD module, the CPLD module calculates six switch signals of each phase of the inverter according to the three groups of level signals and three direction signals, and the CPLD module outputs 18 drive signals to the drive circuit, each output end of the drive circuit is respectively connected to the control end of the switch tube S1-switch tube S6, which is used to output the gate drive signal to control the conduction and closing of the switch tube S1-switch tube S6, and the drive circuit is also used to process the fault detection signal of the switch tube S1-switch tube S6, and output the switch tube fault signal to the CPLD module, and then the CPLD module outputs the fault and alarm information to the DSP module, and the DSP module displays the fault and disconnects the enable. The driving circuit adopts the existing well-known and commonly used driving circuit 1QP0335V45-Q, which is internally provided with a detection circuit, and is connected to each switch tube through the detection circuit to detect whether each switch tube has a fault.

[0027] In the present invention, by setting the working mode of the driving circuit and turning off the automatic shut-off function, the driving circuit only uploads the fault during operation and does not directly perform shut-off control. Instead, the CPLD module performs shut-off control. When the CPLD module receives the switch tube fault signal uploaded by the driving circuit, the CPLD module performs fault detection on each switch tube, and then performs corresponding shut-off operations according to the position of each switch tube and the current action logic of other switch tubes, so as to better protect the switch tube.

[0028] Furthermore, for the fault situation where only one switch tube in a bridge arm is faulty, such as Figure 3 As shown, the following method is used for closing control:

[0029] When the CPLD module receives the switch fault signal uploaded by the drive circuit and determines that the fault occurs in the switch tube S1 or the switch tube S4, the CPLD module outputs a drive signal to the drive circuit to control the drive circuit to directly turn off the switch tube S1 or the switch tube S4, and then turn on the switch tube S5 and the switch tube S6 after an interval of 5us, and then turn off the switch tube S2 and the switch tube S3 after an interval of 5us, and finally turn off the switch tube S5 and the switch tube S6 after another interval of 5us;

[0030] When the CPLD module receives the switch fault signal uploaded by the drive circuit and determines that the fault occurs in the switch tube S2, the CPLD module outputs a drive signal to the drive circuit to control the drive circuit to directly turn off the switch tube S1 first, and then turn off the switch tube S2 after an interval of 2us to protect the switch tube S2 from damage; finally, the switch tubes in the on state among the switch tubes S3, S4, S5 and S6 are turned off;

[0031] When the CPLD module receives the switch fault signal uploaded by the drive circuit and determines that the fault occurs in the switch tube S3, the CPLD module outputs a drive signal to the drive circuit to control the drive circuit to directly turn off the switch tube S4 first, and then turn off the switch tube S3 after an interval of 2us to protect the switch tube S3 from damage; finally, the switch tubes in the on state among the switch tubes S1, S2, S5 and S6 are turned off;

[0032] When the CPLD module receives the switch fault signal uploaded by the drive circuit and determines that the fault occurs in the switch tube S5 or the switch tube S6, the CPLD module outputs a drive signal to the drive circuit to control the drive circuit to directly turn off the switch tube S5 or the switch tube S6, and then adjusts the zero-level switch timing. Because the zero-level switch timing has a total of four switch states, that is, there is a redundant state. Please refer to the table below for the output level and the switch state, so the two zero-level switch timings corresponding to the switch tube S5 or the switch tube S6 that has not failed can be selected. In this case, only a warning prompt is given, and the CPLD module outputs an alarm message to the DSP module to keep running and achieve fault-tolerant operation.

[0033]

[0034] At this time, the DSP module can also process according to the alarm information and perform normal deceleration and smooth parking under appropriate working conditions. It should be noted that due to the existence of a certain zero-level switch state that cannot be used, although it has little effect on the operation of the equipment, it has some impact on the switch loss balance and commutation circuit, so this processing method is generally only used as an emergency solution rather than a long-term solution.

[0035] Furthermore, for the fault situation where two or more switch tubes in one bridge arm are faulty, such as Figure 4 As shown, the following method is used for closing control:

[0036] When the CPLD module receives the switch fault signal uploaded by the drive circuit and determines that the failed switch tubes are the switch tubes S5 and S6 of the same bridge arm, the CPLD module outputs a drive signal to the drive circuit to control the drive circuit to directly turn off the switch tubes S5 and S6 of this bridge arm. In this case, the topology of this bridge arm is switched from ANPC to NPC circuit, and the control algorithm of the DSP module and the CPLD module for this bridge arm is switched to NPC type control mode, and the corresponding switch timing is also output according to NPC to achieve fault-tolerant operation or smooth parking;

[0037] When the CPLD module receives the switch fault signal uploaded by the drive circuit and determines that the failed switch tubes are the switch tubes S5 and S6 of different bridge arms, the CPLD module outputs a six-phase drive signal to the drive circuit to control the drive circuit to directly turn off the failed switch tubes S5 and S6, and then adjust the zero-level switch timing of the corresponding bridge arm (that is, among the four zero-level switch timings, select the two zero-level switch timings of the switch tubes S5 or S6 that have not failed) to achieve fault-tolerant operation or smooth parking;

[0038] When the CPLD module receives the switch fault signal uploaded by the drive circuit and determines that the switch tubes that have failed include the switch tubes S2 and S3, the CPLD module outputs a drive signal to the drive circuit to control the drive circuit to directly turn off the switch tubes S1 and S4 of the corresponding bridge arm and the switch tubes that have failed except the switch tubes S2 and S3 in the corresponding bridge arm; then turn off the switch tubes S2 and S3 that have failed at an interval of 2us; finally, the CPLD module turns off all the switch tubes, and outputs a fault and alarm signal to the DSP module, and the DSP module displays the fault and disconnects the enable;

[0039] When the CPLD module receives the switch fault signal uploaded by the drive circuit, it is determined that the faulty switch tube is two or more of the switch tube S1, the switch tube S4, the switch tube S5 or the switch tube S6. In this case, fault-tolerant operation is not considered. The CPLD module outputs a drive signal to the drive circuit to control the drive circuit to directly turn off the faulty switch tube first, and also turn off the switch tubes S1 and the switch tube S4 that are not faulty in the three bridge arms. After an interval of 5us, the switch tubes S5 and the switch tube S6 that are not faulty in each bridge arm are turned on to clamp the output voltage at zero level. After an interval of 5us, all the switch tubes S2 and all the switch tubes S3 in the three bridge arms are turned off. Finally, the CPLD module turns off all the switch tubes and outputs a fault and alarm signal to the DSP module. The DSP module displays the fault and disconnects the enable.

[0040] After adopting the above scheme, the present invention adopts a method for controlling the switch tube failure of an ANPC type three-level inverter. By utilizing the characteristics of the CPLD module with fast processing speed and many pins, the fault signals of 18 switch tubes are input to the CPLD module. The time for the drive circuit to transmit the switch tube fault signal to the CPLD module is within 100ns. The CPLD module processes in real time, so it is completely feasible to use the CPLD module to perform the switch tube failure operation. During operation, the drive circuit only uploads the fault signal and does not directly perform the switch tube failure control. Instead, the CPLD module performs the switch tube failure control. When the CPLD module receives the switch tube failure signal uploaded by the drive circuit, the CPLD module performs fault detection on each switch tube, and then performs the corresponding switch tube failure operation according to the position of each switch tube and the current action logic of other switch tubes, so as to realize fast and accurate switch tube failure and better protect the switch tube. Moreover, the CPLD control of the switch tube failure timing response is fast and flexible, and fault-tolerant operation and stable parking can also be realized.

[0041] The above description is only a preferred embodiment of the present invention, and therefore cannot be used to limit the scope of implementation of the present invention. That is, equivalent changes and modifications made according to the scope of the patent application of the present invention and the contents of the specification should still fall within the scope covered by the patent of the present invention.

Claims

1. A method for controlling the shut-down of a switch failure of an ANPC type three-level inverter, wherein the ANPC type three-level inverter has three bridge arms corresponding to three phases, each bridge arm has a switch S1 to a switch S6, and is characterized in that: The control unit performs corresponding shutdown control on the switch tubes S1 to S6 in each bridge arm according to various switch tube fault conditions; The control unit includes a DSP module, a CPLD module and a drive circuit, wherein the DSP module is bidirectionally connected to the CPLD module, and the CPLD module is bidirectionally connected to the drive circuit; the DSP module performs algorithm operation according to the control instruction issued by the main control unit, and the bus voltage signal and output current signal of the inverter collected, generates three groups of level signals and three direction signals and outputs them to the CPLD module; the CPLD module calculates six switch signals of each phase of the inverter according to the three groups of level signals and the three direction signals, and the CPLD module outputs 18 drive signals to the drive circuit; each output end of the drive circuit is respectively connected to the control end of the switch tube S1 to the switch tube S6, and is used to output the gate drive signal to control the conduction and closing of the switch tube S1 to the switch tube S6; the drive circuit is also used to process the fault detection signal of the switch tube S1 to the switch tube S6, and output the switch tube fault signal to the CPLD module, and then the CPLD module outputs the fault and alarm information to the DSP module, and the DSP module displays the fault and disconnects the enable; When working, the driving circuit only uploads the fault information and does not directly shut down the switch. Instead, the CPLD module performs the shut down control. When the CPLD module receives the switch failure signal uploaded by the driving circuit, the CPLD module performs fault detection on each switch, and then performs the corresponding shut down operation according to the position of each switch and the current action logic of other switch to better protect the switch; In the case where only one switch tube in a bridge arm is faulty, the following method is used to shut down the tube: When the CPLD module determines that the fault occurs in the switch tube S1 or the switch tube S4, the switch tube S1 or the switch tube S4 is directly turned off, and then the switch tubes S5 and S6 are turned on after an interval of 5us, and then the switch tubes S2 and S3 are turned off after an interval of 5us, and finally the switch tubes S5 and S6 are turned off after an interval of 5us; When the CPLD module determines that the fault occurs in the switch tube S2, the switch tube S1 is directly turned off first, and then the switch tube S2 is turned off after an interval of 2us to protect the switch tube S2 from being damaged; finally, the switch tubes in the on state among the switch tubes S3, S4, S5 and S6 are turned off; When the CPLD module determines that the fault occurs in the switch tube S3, the switch tube S4 is directly turned off first, and then the switch tube S3 is turned off after an interval of 2us to protect the switch tube S3 from being damaged; finally, the switch tubes in the on state among the switch tubes S1, the switch tube S2, the switch tube S5 and the switch tube S6 are turned off; When the CPLD module determines that the fault occurs in switch tube S5 or switch tube S6, it directly turns off switch tube S5 or switch tube S6, then adjusts the zero-level switch timing, and outputs fault and alarm information to the DSP module to keep running, thereby achieving fault-tolerant operation or normal deceleration and parking.

2. A method for controlling the shut-down of a switch failure of an ANPC type three-level inverter, wherein the ANPC type three-level inverter has three bridge arms corresponding to three phases, each bridge arm has a switch S1 to a switch S6, characterized in that: The control unit performs corresponding shutdown control on the switch tubes S1 to S6 in each bridge arm according to various switch tube fault conditions; The control unit includes a DSP module, a CPLD module and a drive circuit, wherein the DSP module is bidirectionally connected to the CPLD module, and the CPLD module is bidirectionally connected to the drive circuit; the DSP module performs algorithm operation according to the control instruction issued by the main control unit, and the bus voltage signal and output current signal of the inverter collected, generates three groups of level signals and three direction signals and outputs them to the CPLD module; the CPLD module calculates six switch signals of each phase of the inverter according to the three groups of level signals and the three direction signals, and the CPLD module outputs 18 drive signals to the drive circuit; each output end of the drive circuit is respectively connected to the control end of the switch tube S1 to the switch tube S6, and is used to output the gate drive signal to control the conduction and closing of the switch tube S1 to the switch tube S6; the drive circuit is also used to process the fault detection signal of the switch tube S1 to the switch tube S6, and output the switch tube fault signal to the CPLD module, and then the CPLD module outputs the fault and alarm information to the DSP module, and the DSP module displays the fault and disconnects the enable; When working, the driving circuit only uploads the fault information and does not directly shut down the switch. Instead, the CPLD module performs the shut down control. When the CPLD module receives the switch failure signal uploaded by the driving circuit, the CPLD module performs fault detection on each switch, and then performs the corresponding shut down operation according to the position of each switch and the current action logic of other switch to better protect the switch; In the case where two or more switch tubes in a bridge arm are faulty, the following method is used to shut down the tubes: When the CPLD module determines that the failed switch tubes are the switch tubes S5 and S6 of the same bridge arm, the switch tubes S5 and S6 of the bridge arm are directly turned off. In this case, the topology of the bridge arm is switched from ANPC to NPC circuit, and the control algorithm of the DSP module and the CPLD module for the bridge arm is switched to NPC type control mode to achieve fault-tolerant operation or smooth parking; When the CPLD module determines that the failed switch tubes are the switch tubes S5 and S6 of different bridge arms, the failed switch tubes S5 and S6 are directly turned off, and then the zero-level switch timing of the corresponding bridge arm is adjusted to achieve fault-tolerant operation or smooth parking; When the CPLD module determines that the faulty switch tubes include switch tube S2 and switch tube S3, the switch tube S1 and switch tube S4 of the corresponding bridge arm and the faulty switch tubes other than switch tube S2 and switch tube S3 in the corresponding bridge arm are directly turned off first; then the faulty switch tube S2 and switch tube S3 are turned off again after an interval of 2us; finally, the CPLD module turns off all the switch tubes, outputs a fault signal, displays the fault and disconnects the enable; When the CPLD module determines that the fault condition of the faulty switch tube does not belong to the three fault conditions described above, fault-tolerant operation is not considered in this case. The faulty switch tube is directly turned off first, and the switch tubes S1 and S4 that have not failed in the three bridge arms are also turned off. After an interval of 5us, the switch tubes S5 and S6 that have not failed in each bridge arm are turned on to clamp the output voltage at zero level. After an interval of 5us, all the switch tubes S2 and all the switch tubes S3 in the three bridge arms are turned off. Finally, the CPLD module turns off all the switch tubes, outputs a fault signal, displays the fault and disconnects the enable.

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