A grid-connected hybrid ANPC fault-tolerant system and control method thereof

Abstract

A grid-connected hybrid ANPC fault-tolerant system and a control method thereof, the system comprising a redundancy module, the redundancy module comprising an upper and a lower multiplexing redundancy unit, the upper multiplexing redundancy unit comprising a first multiplexing Si-IGBT device S1, a first thyristor T a1 , the second thyristor T b1 , the third thyristor T c1 The collector of S1 is connected to the common line on the parallel bridge arm, and the emitter of S1 is connected to T a1 The anode of a1 The cathode of the A phase bridge arm is clamped by the tube M a2 The drain of b1 The anode and T a1 The anode of b1 The cathode of the B phase bridge arm is clamped by the tube M b2 The drain of c1 The anode and T a1 The anode of c1 The cathode of the C phase bridge arm is clamped by tube M c2 The present invention has a small number of redundant components, a strong fault tolerance capability, and a wide range of fault tolerance situations.

Description

Technical Field

[0001] The present invention relates to the technical field of fault tolerance of power electronic converters, and in particular to a grid-connected hybrid ANPC fault-tolerant system and a control method thereof. Background Art

[0002] The hybrid active neutralpoint converter (ANPC) based on 4SiC&2Si heterogeneous devices per phase bridge arm has good application prospects in high-efficiency and high-power power conversion due to its high power density, low cost and low loss. However, in order to give full play to the advantages of low switching loss and high temperature resistance of SiC devices, they are in high-frequency working mode for a long time, which increases the probability of SiC device failure. Among them, the most common type of failure is device open circuit failure, which will lead to the asymmetry of the hybrid ANPC structure, greatly reduce the power quality of the equipment, and cause secondary system failures for long-term operation, resulting in large economic losses. Therefore, the corresponding fault-tolerant control strategy plays a vital role in the stable, reliable and efficient operation of the converter system.

[0003] At present, the types of fault-tolerant means based on three-level converters can be divided into hardware solutions and software solutions. The hardware solution compensates for the failure state of the converter by adding hardware circuits to maintain continuous power supply of the system, mainly including: parallel redundant switches, adding bidirectional thyristors at the output end of the bridge arm, and adding a fourth redundant bridge arm. However, the existing hardware solution adds a large number of redundant devices, which has the disadvantage of high cost; or the number of redundancies is small, which has the disadvantage of poor fault tolerance. The software solution uses its own redundant switch state to reconstruct the switch sequence to ensure the normal operation of the system. According to the type of failed switch and the switch state adopted by the fault-tolerant strategy, it can be divided into full two-level modulation, fault phase two-level modulation, switch state failure area two-level modulation, switch state replacement three-level modulation, and mixed level modulation. However, the fault types that can be tolerated based on the software solution are limited, and it cannot be implemented in some cases.

[0004] In summary, in order to achieve a compromise between fault-tolerant cost and performance, it is urgent to study a grid-connected hybrid ANPC fault-tolerant system with the characteristics of minimizing the number of redundant devices and maximizing the fault-tolerant capability. This is of great significance for improving system reliability and maintaining continuous and safe operation of the system. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the above-mentioned background technology and provide a grid-connected hybrid ANPC fault-tolerant system and a control method thereof, which has a small number of redundant components, strong fault-tolerant capability and a wide range of fault-tolerant situations.

[0006] The technical solution adopted by the present invention to solve the technical problem is a grid-connected hybrid ANPC fault-tolerant system, including a hybrid ANPC three-level circuit and a redundancy module, wherein the redundancy module includes an upper multiplexing redundancy unit and a lower multiplexing redundancy unit, wherein the upper multiplexing redundancy unit is composed of a first multiplexing Si-IGBT device S1, a first thyristor T a1 , the second thyristor T b1 , the third thyristor T c1 The collector of the first multiplexed Si-IGBT device S1 is connected to the common line on the parallel bridge arm, and the emitter of the first multiplexed Si-IGBT device S1 is connected to the first thyristor T a1 The anode of the first thyristor T a1 The cathode of the A phase bridge arm is clamped by the tube M a2 The drain of the second thyristor T b1 The anode of the first thyristor T a1 The anode of the second thyristor T b1 The cathode of the B phase bridge arm is clamped by the tube M b2 The drain of the third thyristor T c1 The anode of the first thyristor T a1 The anode of the third thyristor T c1 The cathode of the C phase bridge arm is clamped by tube M c2 The lower multiplexing redundant unit is composed of the second multiplexing Si-IGBT device S2, the fourth thyristor T a2 , the fifth thyristor T b2 , the sixth thyristor T c2 The emitter of the second multiplexed Si-IGBT device S2 is connected to the common line under the parallel bridge arm, and the collector of the second multiplexed Si-IGBT device S2 is connected to the fourth thyristor T a2 The cathode of the fourth thyristor T a2 The anode of the A phase bridge arm is clamped by the tube M a3 The source of the fifth thyristor T b2 The cathode of the fourth thyristor T a2 The cathode of the fifth thyristor T b2 The anode of the B phase bridge arm is clamped by the tube M b3 The source of the sixth thyristor T c2 The cathode of the fourth thyristor T a2 The cathode of the sixth thyristor T c2 The anode of the C phase bridge arm is clamped by the tube M c3 The source is connected.

[0007] Further, the hybrid ANPC three-level circuit includes a bridge arm module, a voltage stabilizing capacitor module and a filter module. After the bridge arm module and the voltage stabilizing capacitor module are connected in parallel, the output end is then connected in series with the filter module to form an ANPC three-level circuit topology; the bridge arm module includes three-phase parallel bridge arms, wherein each phase bridge arm includes four SiC-MOSFET devices M ki and 2 Si-IGBT devices S kj , each SiC-MOSFET device M ki Anti-parallel diode, each Si-IGBT device S kj Anti-parallel diode; 4 SiC-MOSFET devices M in each phase bridge arm ki For the upper outer tube M k1 , Upper clamp tube M k2 , lower clamp tube M k3 , lower outer tube M k4 The voltage stabilizing capacitor module is composed of two capacitors C1 and C2 connected in series, and the midpoint port is connected to the clamping point of each phase bridge arm; the filtering module is composed of a three-phase inductor L.

[0008] A control method for a grid-connected hybrid ANPC fault-tolerant system comprises the following steps:

[0009] Step S1: according to the open circuit fault device, start the corresponding redundant device and switch to the fault-tolerant topology;

[0010] Step S2: reconstructing the switch state logic of the device based on the fault type;

[0011] Step S3: Based on the modulation wave generated by the inverter closed-loop control and the zero-sequence voltage midpoint balance strategy, a PWM signal is generated using a co-phase carrier stacking modulation method to achieve fault-tolerant control of the system.

[0012] Further, in step S1, according to the open circuit fault device, the corresponding redundant device is started, and the specific method of switching to the fault-tolerant topology is as follows: when the upper external tube M k1 An open circuit fault occurs, turning on the thyristor T k1 , put the first multiplexing Si-IGBT device S1 into operation, and the upper multiplexing redundant unit operates; the lower external tube M k4 An open circuit fault occurs, turning on the thyristor T k2 , put the second multiplexing Si-IGBT device S2 into operation, and the lower multiplexing redundant unit starts working.

[0013] Further, in step S2, based on the fault type, the switching state logic of the device is reconstructed, and the fault type is specifically based on: according to the number and location of the SiC-MOSFET device faults, the faults are divided into single-tube faults, single-phase double-tube faults, single-phase multi-tube faults, out-of-phase double-tube faults, and out-of-phase multi-tube faults.

[0014] Further, in step S2, when a single-tube or single-phase dual-tube double outer tube fault occurs, the redundant device replaces the faulty device, and the switch state logic remains unchanged; when a double-tube fault occurs in an out-of-phase manner, the faulty phase bridge arm device and its redundant device operate according to the corresponding three-level switch state logic; when a single-phase multi-tube or single-phase dual-tube outer tube and clamping tube or out-of-phase multi-tube fault occurs, the healthy device of the faulty bridge arm and its redundant device operate according to the corresponding two-level switch state logic; the switch state logic of the healthy bridge arm device remains unchanged.

[0015] Further, in step S2, for a single-phase double-tube fault:

[0016] In single phase, when two outer tubes are open circuit, the upper outer tube M k1 With lower outer tube M k4 When the circuit is open, it is recorded as SD-I type fault. For SD-I type fault, according to the specific method of step S1, the corresponding redundant device is started, and the bridge arm of the fault phase performs hybrid ANPC three-level modulation according to the original switch state logic of the device. k1 The PWM signal is given to the first multiplexed Si-IGBT device S1, which originally has an external tube M k4 The PWM signal is given to the second multiplexed Si-IGBT device S2;

[0017] In a single phase, when one outer tube fails and one clamp tube opens, the upper outer tube M k1 With upper clamp tube M k2 Open circuit fault, or upper external tube M k1 With lower clamp tube M k3 Open circuit fault, or lower outer tube M k4 With upper clamp tube M k2 Open circuit fault, or lower outer tube M k4 With lower clamp tube M k3 When the circuit is open, it is recorded as SD-Ⅱ type fault. For SD-Ⅱ type fault, according to the specific method of step S1, the corresponding redundant device is started, and the bridge arm of the fault phase is modulated according to two levels; the upper external tube M k1 With upper clamp tube M k2 Open circuit fault, or upper external tube M k1 With lower clamp tube M k3 When an open circuit fault occurs, the corresponding device switch state logic is shown in Table C-1; k4 With upper clamp tube M k2 Open circuit fault, or lower outer tube M k4 With lower clamp tube M k3 In case of an open circuit fault, the corresponding device switch state logic is shown in Table C-2;

[0018] In a single phase, when two clamping tubes fail to open circuit, the upper clamping tube M k2 With lower clamp tube M k3In the case of an open circuit fault, it is recorded as an SD-III type fault. For an SD-III type fault, the redundant unit is not put into operation, and the faulty phase bridge arm operates in the traditional diode clamped three-level converter modulation mode.

[0019] Further, in step S2, for a single-phase multi-tube fault:

[0020] In single phase, when two outer tubes and one clamping tube open circuit fault, the upper outer tube M k1 , lower outer tube M k4 With upper clamp tube M k2 Open circuit fault, or upper external tube M k1 , lower outer tube M k4 With lower clamp tube M k3 When an open circuit fault occurs, it is recorded as an SM-I type fault. For an SM-I type fault, according to the specific method of step S1, the corresponding redundant device is started, and the fault phase bridge arm is modulated according to two levels. The corresponding device switch state logic is shown in Table C-3.

[0021] In a single phase, when one outer tube and two clamping tubes are open circuit fault, the upper outer tube M k1 , Upper clamp tube M k2 With lower clamp tube M k3 Open circuit fault, or lower outer tube M k4 , Upper clamp tube M k2 With lower clamp tube M k3 When the circuit is open, it is recorded as SM-Ⅱ type fault. For SM-Ⅱ type fault, according to the specific method of step S1, the corresponding redundant device is started, the bridge arm of the fault phase is modulated according to two levels, and the upper external tube M k1 , Upper clamp tube M k2 With lower clamp tube M k3 When an open circuit fault occurs, the corresponding device switch state logic is shown in Table C-1; k4 , Upper clamp tube M k2 With lower clamp tube M k3 In case of an open circuit fault, the corresponding device switch state logic is shown in Table C-2;

[0022] In single phase, when the two outer tubes and the two clamping tubes are open circuit fault, the upper outer tube M k1 , Upper clamp tube M k2 , lower clamp tube M k3 With lower outer tube M k4 In the case of an open circuit fault, it is recorded as an SM-III type fault. For an SM-III type fault, according to the specific method of step S1, the corresponding redundant device is started, and the faulty phase bridge arm is modulated according to two levels. The corresponding device switch state logic is shown in Table C-3.

[0023] Further, in step S2, for an out-of-phase double-tube fault:

[0024] When the x-phase external tube fails and the y-phase external tube fails, that is, the x-phase external tube M x1 With y phase upper outer tube M y1 Open circuit fault, or the external tube M on phase x x1 With y phase lower outer tube M y4 Open circuit fault, or the outer tube M of the x phase x4 With y phase upper outer tube M y1 Open circuit fault, or the outer tube M of the x phase x4 With y phase lower outer tube M y4 When the fault is open circuit, it is recorded as DPD-Ⅰ fault, and the external tube M on the x phase x1 With y phase upper outer tube M y1 In case of an open circuit fault, the fault phase is modulated according to the three-level modulation, and the corresponding device switch state logic is shown in Table C-4; x1 With y phase lower outer tube M y4 Open circuit fault, or the outer tube M of the x phase x4 With y phase upper outer tube M y1 When an open circuit fault occurs, the bridge arm of the faulty phase performs hybrid ANPC three-level modulation according to the original switch state logic of the device. x1 Or y phase upper outer tube M y1 The PWM signal is given to the first multiplexed Si-IGBT device S1, the original x-phase lower outer tube M x4 Or y phase lower outer tube M y4 The PWM signal is given to the second multiplexed Si-IGBT device S2; the x-phase lower outer tube M x4 With y phase lower outer tube M y4 In case of an open circuit fault, the fault phase is modulated according to three levels, and the corresponding device switch state logic is shown in Table C-5;

[0025] When the x-phase clamping tube fails and the y-phase clamping tube fails, that is, the x-phase upper clamping tube M x2 With the y-phase upper clamp tube M y2 Open circuit fault, or x-phase upper clamp tube M x2 With y phase down clamp tube M y3 Open circuit fault, or x-phase lower clamp tube M x3 With the y-phase upper clamp tube M y2 Open circuit fault, or x-phase lower clamp tube M x3 With y phase down clamp tube M y3 When there is an open circuit fault, it is recorded as a DPD-II fault. For the DPD-II fault, the x-phase and y-phase bridge arms work in the traditional diode clamped three-level converter modulation mode;

[0026] When the x-phase outer tube fails and the y-phase clamp tube fails, that is, the x-phase upper outer tube M x1 With the y-phase upper clamp tube M y2 Open circuit fault, or the external tube M on phase x x1With y phase down clamp tube M y3 Open circuit fault, or the outer tube M of the x phase x4 With the y-phase upper clamp tube M y2 Open circuit fault, or the outer tube M of the x phase x4 With y phase down clamp tube M y3 When the circuit is open, it is recorded as a DPD-III fault. For the DPD-III fault, according to the specific method of step S1, the corresponding redundant device is started, and the external tube M of the x-phase open fault is x1 The PWM signal is given to the first multiplexed Si-IGBT device S1, and the external tube M under the x-phase open circuit fault x4 The PWM signal is given to the second multiplexed Si-IGBT device S2, and the Y-phase clamping tube fault bridge arm works according to the traditional diode clamping type three-level converter modulation mode;

[0027] When the x-phase clamping tube fails and the y-phase external tube fails, the x-phase upper clamping tube M x2 With y phase upper outer tube M y1 Open circuit fault, or x-phase upper clamp tube M x2 With y phase lower outer tube M y4 Open circuit fault, or x-phase lower clamp tube M x3 With y phase upper outer tube M y1 Open circuit fault, or x-phase lower clamp tube M x3 With y phase lower outer tube M y4 When the fault is open circuit, it is recorded as DPD-Ⅳ type fault. For DPD-Ⅳ type fault, according to the specific method of step S1, the corresponding redundant device is started, and the external tube M of the y-phase open circuit fault is y1 The PWM signal is given to the first multiplexed Si-IGBT device S1, and the outer tube M under the y-phase open circuit fault y4 The PWM signal is given to the second multiplexed Si-IGBT device S2, and the x-phase clamping tube fault bridge arm operates according to the traditional diode clamping three-level converter modulation mode.

[0028] Further, in step S2, for out-of-phase multi-tube faults:

[0029] When the three phases are connected to the external tube, that is, the external tube M of the A phase a1 、B phase upper outer tube M b1 With C phase upper outer tube M c1 When an open circuit fault occurs, it is recorded as a DPM-Ⅰ type fault. For a DPM-Ⅰ type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-6;

[0030] When the three-phase lower outer tube fails, that is, the A phase lower outer tube M a4 、B phase lower outer tube M b4 With C phase lower outer tube Mc4 When an open circuit fault occurs, it is recorded as a DPM-Ⅱ type fault. For a DPM-Ⅱ type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-7;

[0031] When the double outer tube of phase x and the single outer tube of phase y fail, that is, the upper outer tube M of phase x x1 、x phase lower outer tube M x4 With y phase upper outer tube M y1 Open circuit fault, or the external tube M on phase x x1 、x phase lower outer tube M x4 With y phase lower outer tube M y4 When an open circuit fault occurs, it is recorded as a DPM-III type fault. For a DPM-III type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8;

[0032] When the upper outer tube of phase x fails, the upper outer tube of phase y fails, and the lower outer tube of phase z fails, that is, the upper outer tube M of phase x fails. x1 , y phase upper outer tube M y1 With z phase lower outer tube M z4 When an open circuit fault occurs, it is recorded as a DPM-Ⅳ type fault. For a DPM-Ⅳ type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8;

[0033] When the x-phase lower outer tube fails, the y-phase lower outer tube fails, and the z-phase upper outer tube fails, that is, the x-phase lower outer tube M x4 , y phase lower outer tube M y4 With z phase upper outer tube M z1 When an open circuit fault occurs, it is recorded as a DPM-V type fault. For a DPM-V type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8;

[0034] When the x-phase double outer tube fails, the y-phase single outer tube fails, and the z-phase single outer tube fails, that is, the x-phase upper outer tube M x1 、x phase lower outer tube M x4 , y phase upper outer tube M y1 With z phase upper outer tube M z1 Open circuit fault, or the external tube M on phase x x1 、x phase lower outer tube M x4 , y phase upper outer tube M y1 With z phase lower outer tube M z4Open circuit fault, or the external tube M on phase x x1 、x phase lower outer tube M x4 , y phase lower outer tube M y4 With z phase upper outer tube M z1 Open circuit fault, or the external tube M on phase x x1 、x phase lower outer tube M x4 , y phase lower outer tube M y4 With z phase lower outer tube M z4 When an open circuit fault occurs, it is recorded as a DPM-VI fault. For a DPM-VI fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8;

[0035] When the double outer tube of phase x fails and the double outer tube of phase y fails, that is, the upper outer tube M of phase x x1 、x phase lower outer tube M x4 , y phase upper outer tube M y1 With y phase lower outer tube M y4 In case of an open circuit fault, it is recorded as a DPM-VII fault. For a DPM-VII fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8;

[0036] When the upper outer tube of three phases fails and the lower outer tube of one phase fails, that is, the upper outer tube M of phase A a1 、B phase upper outer tube M b1 、C phase upper outer tube M c1 With x phase lower outer tube M x4 When an open circuit fault occurs, it is recorded as a DPM-VIII type fault. For a DPM-VIII type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8;

[0037] When the three-phase lower outer tube fails and one-phase upper outer tube fails, that is, the lower outer tube M of phase A a4 、B phase lower outer tube M b4 、C phase lower outer tube M c4 With x phase upper outer tube M x1 When an open circuit fault occurs, it is recorded as a DPM-IX fault. For a DPM-IX fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8;

[0038] When the three-phase upper outer tube fails and the two-phase lower outer tube fails, that is, the upper outer tube M of phase A a1 、B phase upper outer tube Mb1 、C phase upper outer tube M c1 、x phase lower outer tube M x4 With y phase lower outer tube M y4 When an open circuit fault occurs, it is recorded as a DPM-X type fault. For a DPM-X type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8;

[0039] When the three-phase lower outer tube fails and the two-phase upper outer tube fails, that is, the A phase lower outer tube M a4 、B phase lower outer tube M b4 、C phase lower outer tube M c4 、x phase upper outer tube M x1 With y phase upper outer tube M y1 When an open circuit fault occurs, it is recorded as a DPM-Ⅺ type fault. For a DPM-Ⅺ type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8;

[0040] When all outer tubes fail, that is, the outer tube M on phase A a1 、A phase lower outer tube M a4 、B phase upper outer tube M b1 、B phase lower outer tube M b4 、C phase upper outer tube M c1 With C phase lower outer tube M c4 In case of an open circuit fault, it is recorded as a DPM-XII fault. For a DPM-XII fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8.

[0041] Furthermore, in the logic table of all device switch states, a device switch state of 0 indicates that the gate drive signal to the device is at a low level and the device is off; a device switch state of 1 indicates that the gate drive signal to the device is at a high level and the device is on.

[0042] Compared with the prior art, the advantages of the present invention are as follows:

[0043] The redundant module designed by the present invention can reuse the multiplexed Si-IGBT devices S1 and S2 in the redundant unit in the scenario of multiple device open circuit failures, thereby reducing the number of redundant devices added, using fewer active devices, and realizing the fault tolerance of multiple types of device open circuit failures of the hybrid ANPC converter, which has the advantages of low cost, simple control, strong fault tolerance, and a wide range of fault tolerance situations. The fault-tolerant system is not only suitable for device open circuit failures under the full power range, and the system does not need to be derated, but also suitable for device open circuit failures in the rectification state or the inversion state of the converter, and has a wide range of applicable working conditions. The thyristor in the designed redundant unit can effectively isolate the healthy phase bridge arm from the faulty phase bridge arm, which will not affect the working state of the healthy phase bridge arm, and at the same time avoids the interference of energy transmission of each phase when the system is fault-tolerant. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a structural diagram of a grid-connected hybrid ANPC fault-tolerant system according to an embodiment of the present invention.

[0045] Figure 2 yes Figure 1 The fault-tolerant operation simulation waveforms of the fault-tolerant system shown in the figure; among them, (2a) is the fault-tolerant operation simulation waveform of SM-Ⅲ type fault, (2b) is the fault-tolerant operation simulation waveform of DPD-Ⅰ type fault, and (2c) is the fault-tolerant operation simulation waveform of DPM-Ⅵ type fault. DETAILED DESCRIPTION

[0046] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] Reference Figure 1 The grid-connected hybrid ANPC fault-tolerant system of this embodiment includes a hybrid ANPC three-level circuit and a redundancy module. The hybrid ANPC three-level circuit includes: a bridge arm module, a voltage-stabilizing capacitor module and a filter module. After the bridge arm module and the voltage-stabilizing capacitor module are connected in parallel, the output end is connected in series with the filter module to form an ANPC three-level circuit topology. The bridge arm module includes three-phase parallel bridge arms, where each phase bridge arm includes four SiC-MOSFET devices M ki (k=a, b, c, respectively represent phase A, phase B, phase C, i=1, 2, 3, 4) and 2 Si-IGBT devices S kj (j=1, 2), each SiC-MOSFET device M ki Anti-parallel diode, each Si-IGBT device S kj Anti-parallel diode. 4 SiC-MOSFET devices M in each phase bridge arm ki For the upper outer tube M k1 , Upper clamp tube M k2 , lower clamp tube M k3 , lower outer tube Mk4 The voltage stabilizing capacitor module is composed of two capacitors C1 and C2 connected in series, and the midpoint port is connected to the clamping point of each phase bridge arm; the filtering module is composed of three-phase inductors L.

[0048] The redundancy module includes an upper multiplexing redundancy unit and a lower multiplexing redundancy unit. The upper multiplexing redundancy unit is composed of a first multiplexing Si-IGBT device S1, a first thyristor T a1 , the second thyristor T b1 , the third thyristor T c1 The collector of the first multiplexed Si-IGBT device S1 is connected to the common line on the parallel bridge arm, and the emitter of the first multiplexed Si-IGBT device S1 is connected to the first thyristor T a1 The anode of the first thyristor T a1 The cathode of the A phase bridge arm is clamped by the tube M a2 The drain of the second thyristor T b1 The anode of the first thyristor T a1 The anode of the second thyristor T b1 The cathode of the B phase bridge arm is clamped by the tube M b2 The drain of the third thyristor T c1 The anode of the first thyristor T a1 The anode of the third thyristor T c1 The cathode of the C phase bridge arm is clamped by tube M c2 The first multiplexing Si-IGBT device S1 is a Si-IGBT device.

[0049] The lower multiplexing redundant unit is composed of the second multiplexing Si-IGBT device S2, the fourth thyristor T a2 , the fifth thyristor T b2 , the sixth thyristor T c2 The emitter of the second multiplexed Si-IGBT device S2 is connected to the common line under the parallel bridge arm, and the collector of the second multiplexed Si-IGBT device S2 is connected to the fourth thyristor T a2 The cathode of the fourth thyristor T a2 The anode of the A phase bridge arm is clamped by the tube M a3 The source of the fifth thyristor T b2 The cathode of the fourth thyristor T a2 The cathode of the fifth thyristor T b2 The anode of the B phase bridge arm is clamped by the tube M b3 The source of the sixth thyristor T c2 The cathode of the fourth thyristor T a2 The cathode of the sixth thyristor T c2 The anode of the C phase bridge arm is clamped by the tube M c3The second multiplexing Si-IGBT device S2 is a Si-IGBT device.

[0050] The control method of the grid-connected hybrid ANPC fault-tolerant system of this embodiment includes the following steps:

[0051] Step S1: According to the open circuit fault device, start the corresponding redundant device and switch to the fault-tolerant topology; the specific method is: when the system is connected to the external tube M k1 , lower outer tube M k4 When an open circuit fault occurs, the specific redundant device in the redundant unit is started according to Table A-1.

[0052] Table A-1 Action rules of redundant units for different open circuit fault devices

[0053] Faulty device Turn on the thyristor Put into reuse Si-IGBT devices <![CDATA[M k1 ]]> <![CDATA[T k1 ]]> <![CDATA[S1]]> <![CDATA[M k4 ]]> <![CDATA[T k2 ]]> <![CDATA[S2]]>

[0054] When the outer tube M k1 An open circuit fault occurs, turning on the thyristor T k1 , put the first multiplexing Si-IGBT device S1 into operation, and the upper multiplexing redundant unit operates; the lower external tube M k4 An open circuit fault occurs, turning on the thyristor T k2 , put the second multiplexing Si-IGBT device S2 into operation, and the lower multiplexing redundant unit starts working.

[0055] Step S2: Based on the fault type, reconstruct the switch state logic of the device. The specific method is as follows:

[0056] According to the number and location of SiC-MOSFET device failures, the faults are divided into single-tube failure, single-phase double-tube failure, single-phase multi-tube failure, out-of-phase double-tube failure, and out-of-phase multi-tube failure.

[0057] When a single-tube or single-phase dual-tube double outer tube fault occurs, the redundant device replaces the faulty device and the switch state logic remains unchanged; when an out-of-phase double-tube fault occurs, the faulty phase bridge arm device and its redundant device operate according to the corresponding three-level switch state logic; when a single-phase multi-tube or single-phase dual-tube outer tube and clamping tube or out-of-phase multi-tube fault occurs, the healthy device of the faulty bridge arm and its redundant device operate according to the corresponding two-level switch state logic; the switch state logic of the healthy bridge arm device remains unchanged.

[0058] In a single tube failure, if the upper clamp tube M k2 Or lower clamp tube M k3 If an open circuit fault occurs, the fault phase bridge arm operates in the traditional diode clamped three-level converter modulation mode; if the upper external tube M k1 Or lower outer tube M k4When an open circuit fault occurs, the corresponding redundant device is started according to the specific method of step S1, and the bridge arm of the faulty phase performs hybrid ANPC three-level modulation according to the original switch state logic of the device. k1 The PWM signal is given to the first multiplexed Si-IGBT device S1, or the original lower external tube M k4 The PWM signal is given to the second multiplexed Si-IGBT device S2.

[0059] Single-phase two-tube faults are further divided into types as shown in Table B-1.

[0060] Table B-1 Classification of single-phase double-tube faults

[0061]

[0062] In single phase, when two outer tubes are open circuit, the upper outer tube M k1 With lower outer tube M k4 When the circuit is open, it is recorded as SD-I type fault. For SD-I type fault, according to the specific method of step S1, the corresponding redundant device is started, and the bridge arm of the fault phase performs hybrid ANPC three-level modulation according to the original switch state logic of the device. k1 The PWM signal is given to the first multiplexed Si-IGBT device S1, which originally has an external tube M k4 The PWM signal is given to the second multiplexed Si-IGBT device S2.

[0063] In a single phase, when one outer tube fails and one clamp tube opens, the upper outer tube M k1 With upper clamp tube M k2 Open circuit fault, or upper external tube M k1 With lower clamp tube M k3 Open circuit fault, or lower outer tube M k4 With upper clamp tube M k2 Open circuit fault, or lower outer tube M k4 With lower clamp tube M k3 When the circuit is open, it is recorded as SD-Ⅱ type fault. For SD-Ⅱ type fault, according to the specific method of step S1, the corresponding redundant device is started, the bridge arm of the fault phase is modulated according to two levels, and the upper external tube M k1 With upper clamp tube M k2 Open circuit fault, or upper external tube M k1 With lower clamp tube M k3 When an open circuit fault occurs, the corresponding device switch state logic is shown in Table C-1; k4 With upper clamp tube M k2 Open circuit fault, or lower outer tube M k4 With lower clamp tube M k3 In case of an open circuit fault, the corresponding device switch state logic is shown in Table C-2.

[0064] Table C-1 Upper outer tube M in SD-Ⅱ type fault k1 With upper clamp tube M k2 Open circuit fault, or upper external tube M k1 With lower clamp tube M k3 The upper outer tube M in open circuit fault and SM-Ⅱ type fault k1 , Upper clamp tube M k2 With lower clamp tube M k3 Device switch state logic during open circuit fault

[0065]

[0066] Table C-2 Lower outer tube M in SD-Ⅱ type fault k4 With upper clamp tube M k2 Open circuit fault, or lower outer tube M k4 With lower clamp tube M k3 Open circuit fault and SM-Ⅱ fault in the lower outer tube M k4 , Upper clamp tube M k2 With lower clamp tube M k3 Device switch state logic during open circuit fault

[0067]

[0068]

[0069] In a single phase, when two clamping tubes fail to open circuit, the upper clamping tube M k2 With lower clamp tube M k3 In the case of an open circuit fault, it is recorded as an SD-III type fault. For an SD-III type fault, the redundant unit is not put into operation, and the faulty phase bridge arm operates in the traditional diode clamped three-level converter modulation mode.

[0070] Single-phase multi-tube faults are further divided into types as shown in Table B-2.

[0071] Table B-2 Classification of single-phase multi-tube faults

[0072]

[0073] In single phase, when two outer tubes and one clamping tube open circuit fault, the upper outer tube M k1 , lower outer tube M k4 With upper clamp tube M k2 Open circuit fault, or upper external tube M k1 , lower outer tube M k4 With lower clamp tube M k3 In the case of an open circuit fault, it is recorded as an SM-I type fault. For an SM-I type fault, according to the specific method of step S1, the corresponding redundant device is started, and the faulty phase bridge arm is modulated according to two levels. The corresponding device switch state logic is shown in Table C-3.

[0074] Table C-3 SM-Ⅰ and SM-Ⅲ fault device switch state logic

[0075]

[0076] In a single phase, when one outer tube and two clamping tubes are open circuit fault, the upper outer tube M k1 , Upper clamp tube M k2 With lower clamp tube M k3 Open circuit fault, or lower outer tube M k4 , Upper clamp tube M k2 With lower clamp tube M k3 When the circuit is open, it is recorded as SM-Ⅱ type fault. For SM-Ⅱ type fault, according to the specific method of step S1, the corresponding redundant device is started, the bridge arm of the fault phase is modulated according to two levels, and the upper external tube M k1 , Upper clamp tube M k2 With lower clamp tube M k3 When an open circuit fault occurs, the corresponding device switch state logic is shown in Table C-1; k4 , Upper clamp tube M k2 With lower clamp tube M k3 In case of an open circuit fault, the corresponding device switch state logic is shown in Table C-2.

[0077] In single phase, when the two outer tubes and the two clamping tubes are open circuit fault, the upper outer tube M k1 , Upper clamp tube M k2 , lower clamp tube M k3 With lower outer tube M k4 In the case of an open circuit fault, it is recorded as an SM-III type fault. For an SM-III type fault, according to the specific method of step S1, the corresponding redundant device is started, and the faulty phase bridge arm is modulated according to two levels. The corresponding device switch state logic is shown in Table C-3.

[0078] Out-of-phase double-tube faults are further divided into types as shown in Table B-3.

[0079] When the x-phase external tube fails and the y-phase external tube fails, that is, the x-phase external tube M x1 With y phase upper outer tube M y1 Open circuit fault, or the external tube M on phase x x1 With y phase lower outer tube M y4 Open circuit fault, or the outer tube M of the x phase x4 With y phase upper outer tube M y1 Open circuit fault, or the outer tube M of the x phase x4 With y phase lower outer tube M y4 When the fault is open circuit, it is recorded as DPD-Ⅰ fault, and the external tube M on the x phase x1 With y phase upper outer tube M y1In case of an open circuit fault, the fault phase is modulated according to the three-level modulation, and the corresponding device switch state logic is shown in Table C-4; x1 With y phase lower outer tube M y4 Open circuit fault, or the outer tube M of the x phase x4 With y phase upper outer tube M y1 When an open circuit fault occurs, the bridge arm of the faulty phase performs hybrid ANPC three-level modulation according to the original switch state logic of the device. x1 Or y phase upper outer tube M y1 The PWM signal is given to the first multiplexed Si-IGBT device S1, the original x-phase lower outer tube M x4 Or y phase lower outer tube M y4 The PWM signal is given to the second multiplexed Si-IGBT device S2. x4 With y phase lower outer tube M y4 In case of an open circuit fault, the faulty phase is modulated according to three levels, and the corresponding device switch state logic is shown in Table C-5.

[0080] When the x-phase clamping tube fails and the y-phase clamping tube fails, that is, the x-phase upper clamping tube M x2 With the y-phase upper clamp tube M y2 Open circuit fault, or x-phase upper clamp tube M x2 With y phase down clamp tube M y3 Open circuit fault, or x-phase lower clamp tube M x3 With the y-phase upper clamp tube M y2 Open circuit fault, or x-phase lower clamp tube M x3 With y phase down clamp tube M y3 In the case of an open circuit fault, it is recorded as a DPD-Ⅱ type fault. For the DPD-Ⅱ type fault, the x-phase and y-phase bridge arms operate according to the traditional diode clamped three-level converter modulation mode.

[0081] When the x-phase outer tube fails and the y-phase clamp tube fails, that is, the x-phase upper outer tube M x1 With the y-phase upper clamp tube M y2 Open circuit fault, or the external tube M on phase x x1 With y phase down clamp tube M y3 Open circuit fault, or the outer tube M of the x phase x4 With the y-phase upper clamp tube M y2 Open circuit fault, or the outer tube M of the x phase x4 With y phase down clamp tube M y3 When the circuit is open, it is recorded as a DPD-III fault. For the DPD-III fault, according to the specific method of step S1, the corresponding redundant device is started, and the external tube M of the x-phase open fault is x1 The PWM signal is given to the first multiplexed Si-IGBT device S1, and the external tube M under the x-phase open circuit fault x4The PWM signal is given to the second multiplexed Si-IGBT device S2, and the Y-phase clamped tube fault bridge arm operates according to the traditional diode clamped three-level converter modulation mode.

[0082] When the x-phase clamping tube fails and the y-phase external tube fails, the x-phase upper clamping tube M x2 With y phase upper outer tube M y1 Open circuit fault, or x-phase upper clamp tube M x2 With y phase lower outer tube M y4 Open circuit fault, or x-phase lower clamp tube M x3 With y phase upper outer tube M y1 Open circuit fault, or x-phase lower clamp tube M x3 With y phase lower outer tube M y4 When the fault is open circuit, it is recorded as DPD-Ⅳ type fault. For DPD-Ⅳ type fault, according to the specific method of step S1, the corresponding redundant device is started, and the external tube M of the y-phase open circuit fault is y1 The PWM signal is given to the first multiplexed Si-IGBT device S1, and the outer tube M under the y-phase open circuit fault y4 The PWM signal is given to the second multiplexed Si-IGBT device S2, and the x-phase clamped tube fault bridge arm works according to the traditional diode clamped three-level converter modulation mode. x = a, b or c, y = a, b or c, z = a, b or c, and x ≠ y ≠ z.

[0083] Table B-3 Classification of out-of-phase double-tube faults

[0084]

[0085] Table C-4DPD-Ⅰ fault x phase upper outer tube M x1 With y phase upper outer tube M y1 Device switch state logic during open circuit fault

[0086]

[0087] Table C-5DPD-Ⅰ type fault x phase lower outer tube M x4 With y phase lower outer tube M y4 Device switch state logic during open circuit fault

[0088]

[0089]

[0090] Out-of-phase multi-tube faults are further divided into types as shown in Table B-4.

[0091] When the three phases are connected to the external tube, that is, the external tube M of the A phase a1 、B phase upper outer tube M b1 With C phase upper outer tube M c1In case of an open circuit fault, it is recorded as a DPM-Ⅰ type fault. For a DPM-Ⅰ type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-6.

[0092] When the three-phase lower outer tube fails, that is, the A phase lower outer tube M a4 、B phase lower outer tube M b4 With C phase lower outer tube M c4 In case of an open circuit fault, it is recorded as a DPM-Ⅱ type fault. For a DPM-Ⅱ type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-7.

[0093] When the double outer tube of phase x and the single outer tube of phase y fail, that is, the upper outer tube M of phase x x1 、x phase lower outer tube M x4 With y phase upper outer tube M y1 Open circuit fault, or the external tube M on phase x x1 、x phase lower outer tube M x4 With y phase lower outer tube M y4 In case of an open circuit fault, it is recorded as a DPM-III type fault. For a DPM-III type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8.

[0094] When the upper outer tube of phase x fails, the upper outer tube of phase y fails, and the lower outer tube of phase z fails, that is, the upper outer tube M of phase x fails. x1 , y phase upper outer tube M y1 With z phase lower outer tube M z4 In case of an open circuit fault, it is recorded as a DPM-Ⅳ type fault. For a DPM-Ⅳ type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8.

[0095] When the x-phase lower outer tube fails, the y-phase lower outer tube fails, and the z-phase upper outer tube fails, that is, the x-phase lower outer tube M x4 , y phase lower outer tube M y4 With z phase upper outer tube M z1 In the case of an open circuit fault, it is recorded as a DPM-V type fault. For a DPM-V type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8.

[0096] When the x-phase double outer tube fails, the y-phase single outer tube fails, and the z-phase single outer tube fails, that is, the x-phase upper outer tube M x1 、x phase lower outer tube M x4 , y phase upper outer tube M y1 With z phase upper outer tube M z1 Open circuit fault, or the external tube M on phase x x1 、x phase lower outer tube M x4 , y phase upper outer tube M y1 With z phase lower outer tube M z4 Open circuit fault, or the external tube M on phase x x1 、x phase lower outer tube M x4 , y phase lower outer tube M y4 With z phase upper outer tube M z1 Open circuit fault, or the external tube M on phase x x1 、x phase lower outer tube M x4 , y phase lower outer tube M y4 With z phase lower outer tube M z4 In the case of an open circuit fault, it is recorded as a DPM-VI type fault. For a DPM-VI type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8.

[0097] When the double outer tube of phase x fails and the double outer tube of phase y fails, that is, the upper outer tube M of phase x x1 、x phase lower outer tube M x4 , y phase upper outer tube M y1 With y phase lower outer tube M y4 In the case of an open circuit fault, it is recorded as a DPM-VII type fault. For a DPM-VII type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8.

[0098] When the upper outer tube of three phases fails and the lower outer tube of one phase fails, that is, the upper outer tube M of phase A a1 、B phase upper outer tube M b1 、C phase upper outer tube M c1 With x phase lower outer tube M x4 In the case of an open circuit fault, it is recorded as a DPM-VIII type fault. For a DPM-VIII type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8.

[0099] When the three-phase lower outer tube fails and one-phase upper outer tube fails, that is, the lower outer tube M of phase A a4 、B phase lower outer tube M b4 、C phase lower outer tube M c4With x phase upper outer tube M x1 In the case of an open circuit fault, it is recorded as a DPM-IX type fault. For a DPM-IX type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8.

[0100] When the three-phase upper outer tube fails and the two-phase lower outer tube fails, that is, the upper outer tube M of phase A a1 、B phase upper outer tube M b1 、C phase upper outer tube M c1 、x phase lower outer tube M x4 With y phase lower outer tube M y4 In the case of an open circuit fault, it is recorded as a DPM-X type fault. For a DPM-X type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8.

[0101] When the three-phase lower outer tube fails and the two-phase upper outer tube fails, that is, the A phase lower outer tube M a4 、B phase lower outer tube M b4 、C phase lower outer tube M c4 、x phase upper outer tube M x1 With y phase upper outer tube M y1 In the case of an open circuit fault, it is recorded as a DPM-Ⅺ type fault. For a DPM-Ⅺ type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8.

[0102] When all outer tubes fail, that is, the outer tube M on phase A a1 、A phase lower outer tube M a4 、B phase upper outer tube M b1 、B phase lower outer tube M b4 、C phase upper outer tube M c1 With C phase lower outer tube M c4 In case of an open circuit fault, it is recorded as a DPM-XII fault. For a DPM-XII fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8.

[0103] In addition to the other types of faults mentioned above, including multi-tube faults not involving external tubes and mixed multi-tube faults involving external tubes and clamped tubes, which are recorded as OT-type faults (OT-type faults have many open-circuit fault devices and are difficult to list one by one, so they are not given in detail). When the multi-tube fault does not involve the external tube, the faulty phase bridge arm operates according to the traditional diode clamped three-level converter modulation mode. When the mixed multi-tube fault involves the external tube and the clamped tube, according to the specific method of step S1, the corresponding redundant device is started, and the faulty phase bridge arm is modulated according to two levels. The device switch state logic corresponding to the mixed multi-tube fault involving the upper external tube and the clamped tube is shown in Table C-6, the device switch state logic corresponding to the mixed multi-tube fault involving the lower external tube and the clamped tube is shown in Table C-7, and the device switch state logic corresponding to the mixed multi-tube fault involving the lower and upper dual external tubes and the clamped tube is shown in Table C-8.

[0104] Table B-4 Classification of out-of-phase multi-tube faults

[0105]

[0106]

[0107] Table C-6DPM-Ⅰ type fault device switch state logic

[0108]

[0109] Table C-7DPM-Ⅱ type fault device switch state logic

[0110] Table C-8 Switch state logic of DPM-Ⅲ, DPM-Ⅳ, DPM-Ⅴ, DPM-Ⅵ, DPM-Ⅶ, DPM-Ⅷ, DPM-Ⅸ, DPM-Ⅹ, DPM-Ⅺ, and DPM-Ⅻ fault devices

[0111]

[0112] In the switch state logic table of all devices, there are no devices or faulty devices involved, the pulse drive signal is set to 0, U dc is the DC side voltage, and the output voltage refers to the output voltage of the hybrid ANPC. In the logic table of all device switch states, the device switch state of 0 indicates that the gate drive signal to the device is low level and the device is turned off; the device switch state of 1 indicates that the gate drive signal to the device is high level and the device is turned on.

[0113] Step S3: Based on the modulation wave generated by the inverter closed-loop control and the zero-sequence voltage midpoint balance strategy, a PWM signal is generated using a co-phase carrier stacking modulation method to achieve fault-tolerant control of the system.

[0114] In the redundant module designed by the present invention, in the scenario of multiple device open circuit failure, the reused Si-IGBT devices S1 and S2 in the redundant unit can be shared (reused) by each phase bridge arm; thereby reducing the number of redundant devices (devices of the redundant module) added. The specific reuse situation is as follows: A phase upper external tube M a1 、B phase upper outer tube M b1 、C phase upper outer tube M c1 When open circuit faults occur at the same time, the first multiplexed Si-IGBT device S1 is multiplexed by the three-phase bridge arm, and can take over the functions (modulation tasks) of the above-mentioned faulty devices at the same time, thereby achieving fault tolerance of multiple device open circuit faults.

[0115] A phase lower outer tube M a4 、B phase lower outer tube M b4 、C phase lower outer tube M c4 When open circuit faults occur at the same time, the second multiplexed Si-IGBT device S2 is multiplexed by the three-phase bridge arm, and can take over the functions (modulation tasks) of the above-mentioned faulty devices at the same time, thereby achieving fault tolerance of multiple device open circuit faults.

[0116] x phase upper outer tube M x1 , y phase upper outer tube M y1 When open circuit faults occur simultaneously, the first multiplexed Si-IGBT device S1 is multiplexed by the x-phase and y-phase bridge arms, and can take over the functions (modulation tasks) of the above-mentioned faulty devices at the same time, thereby achieving fault tolerance of multiple device open circuit faults.

[0117] X phase lower outer tube M x4 , y phase lower outer tube M y4 When open circuit faults occur at the same time, the second multiplexed Si-IGBT device S2 is multiplexed by the x-phase and y-phase bridge arms, and can take over the functions (modulation tasks) of the above-mentioned faulty devices at the same time, thereby achieving fault tolerance of multiple device open circuit faults.

[0118] In terms of supported scenarios: the fault-tolerant system proposed in the present invention supports all fault scenarios involving an open circuit of an external tube, all fault scenarios involving an open circuit of a clamping tube, and all fault scenarios involving a combined open circuit of an external tube and a clamping tube. It has a wide range of fault-tolerant situations and does not require the converter to operate at a reduced rating.

[0119] Control aspect: the present invention can realize fault-tolerant control of the converter by only configuring corresponding redundant modules and simply reorganizing the switch states for the output level, without using complex voltage space vector reconstruction modulation strategy taking into account midpoint balance control.

[0120] Simulation Effect

[0121] In order to better demonstrate the effectiveness of the grid-connected hybrid ANPC fault-tolerant system proposed in the present invention, a fault-tolerant system model was built in MATLAB / Simulink, the open circuit fault simulation of related devices was set, and the fault-tolerant topology and strategy were verified. The specific circuit simulation parameters are shown in Table D-1.

[0122] Table D-1 Main circuit simulation parameters

[0123]

[0124]

[0125] Taking single-phase multi-tube SM-Ⅲ, out-of-phase dual-tube DPD-Ⅰ, and out-of-phase multi-tube DPM-Ⅵ faults as examples, the effectiveness of the fault-tolerant system is verified. In the simulation, the open-circuit fault of the device is simulated by blocking the switch pulse. Among them, the corresponding device is set to have an open-circuit fault at 0.4s, and the fault-tolerant strategy is implemented at 0.45s. The relevant simulation waveforms are as follows Figure 2 As shown, Figure 2 (a) is the fault-tolerant operation simulation waveform of SM-Ⅲ type fault. Figure 2 (b) is the fault-tolerant operation simulation waveform of DPD-Ⅰ fault. Figure 2 (c) is the fault-tolerant operation simulation waveform of DPM-VI fault. Figure 2 (a) with Figure 2 (c) It can be seen that after an open circuit fault occurs, the current waveform loses its symmetry; when the fault-tolerant control strategy is put into use, the waveform quality is reduced compared to normal operation, but the grid-connected current waveform restores the three-phase symmetric state, indicating that the equipment can stably and continuously transmit electric energy to the grid; Figure 2 (b) It can be seen that during the switch fault operation, the three-phase current waveform is greatly distorted. After the fault-tolerant control strategy is put into operation, the waveform quality is improved and the power can be effectively transmitted. It can be seen that the proposed three-level fault-tolerant topology is correct and effective.

[0126] The present invention uses fewer active devices to achieve fault tolerance of open-circuit faults of multiple types of devices in a hybrid ANPC converter, and has the advantages of low cost, simple control, strong fault tolerance, and a wide range of fault tolerance situations. The fault-tolerant system is not only suitable for device open-circuit faults under full power range conditions, and the system does not need to be derated for operation, but also suitable for device open-circuit faults in the rectification state or inversion state of the converter, and has a wide range of applicable working conditions. The thyristor in the designed redundant unit can effectively isolate the healthy phase bridge arm from the faulty phase bridge arm, and will not affect the working state of the healthy phase bridge arm, while avoiding interference in the energy transmission of each phase during the fault-tolerant operation of the system.

[0127] Those skilled in the art may make various modifications and variations to the present invention. If these modifications and variations are within the scope of the claims of the present invention and their equivalents, then these modifications and variations are also within the protection scope of the present invention.

[0128] The contents not described in detail in the specification are prior art known to those skilled in the art.

Claims

1. A grid-connected hybrid ANPC fault-tolerant system, comprising a hybrid ANPC three-level circuit and a redundancy module, characterized in that: The redundancy module includes an upper multiplexing redundancy unit and a lower multiplexing redundancy unit. The upper multiplexing redundancy unit is composed of a first multiplexing Si-IGBT device S1, a first thyristor T a1 , the second thyristor T b1 , the third thyristor T c1 The collector of the first multiplexed Si-IGBT device S1 is connected to the common line on the parallel bridge arm, and the emitter of the first multiplexed Si-IGBT device S1 is connected to the first thyristor T a1 The anode of the first thyristor T a1 The cathode of the A phase bridge arm is clamped by the tube M a2 The drain of the second thyristor T b1 The anode of the first thyristor T a1 The anode of the second thyristor T b1 The cathode of the B phase bridge arm is clamped by the tube M b2 The drain of the third thyristor T c1 The anode of the first thyristor T a1 The anode of the third thyristor T c1 The cathode of the C phase bridge arm is clamped by tube M c2 The lower multiplexing redundant unit is composed of the second multiplexing Si-IGBT device S2, the fourth thyristor T a2 , the fifth thyristor T b2 , the sixth thyristor T c2 The emitter of the second multiplexed Si-IGBT device S2 is connected to the common line under the parallel bridge arm, and the collector of the second multiplexed Si-IGBT device S2 is connected to the fourth thyristor T a2 The cathode of the fourth thyristor T a2 The anode of the A phase bridge arm is clamped by the tube M a3 The source of the fifth thyristor T b2 The cathode of the fourth thyristor T a2 The cathode of the fifth thyristor T b2 The anode of the B phase bridge arm is clamped by the tube M b3 The source of the sixth thyristor T c2 The cathode of the fourth thyristor T a2 The cathode of the sixth thyristor T c2 The anode of the C phase bridge arm is clamped by the tube M c3 The source is connected.

2. The grid-connected hybrid ANPC fault-tolerant system according to claim 1, characterized in that: The hybrid ANPC three-level circuit includes a bridge arm module, a voltage stabilizing capacitor module and a filter module. After the bridge arm module and the voltage stabilizing capacitor module are connected in parallel, the output end is connected in series with the filter module to form an ANPC three-level circuit topology; the bridge arm module includes three-phase parallel bridge arms, wherein each phase bridge arm includes four SiC-MOSFET devices M ki and 2 Si-IGBT devices S kj , each SiC-MOSFET device M ki Anti-parallel diode, each Si-IGBT device S kj Anti-parallel diode; 4 SiC-MOSFET devices M in each phase bridge arm ki For the upper outer tube M k1 , Upper clamp tube M k2 , lower clamp tube M k3 , lower outer tube M k4 The voltage stabilizing capacitor module is composed of two capacitors C1 and C2 connected in series, and the midpoint port is connected to the clamping point of each phase bridge arm; the filtering module is composed of a three-phase inductor L.

3. A control method for a grid-connected hybrid ANPC fault-tolerant system, applied to the grid-connected hybrid ANPC fault-tolerant system according to claim 1 or 2, characterized in that: The following steps are involved: Step S1: according to the open circuit fault device, start the corresponding redundant device and switch to the fault-tolerant topology; In step S1, according to the open circuit fault device, the corresponding redundant device is started, and the specific method of switching to the fault-tolerant topology is as follows: when the external tube M k1 An open circuit fault occurs, turning on the thyristor T k1 , put the first multiplexing Si-IGBT device S1 into operation, and the upper multiplexing redundant unit operates; the lower external tube M k4 An open circuit fault occurs, turning on the thyristor T k2 , put the second multiplexing Si-IGBT device S2 into operation, and the lower multiplexing redundant unit operates; Step S2: reconstructing the switch state logic of the device based on the fault type; In step S2, based on the fault type, the switch state logic of the device is reconstructed. Specifically, the fault type is based on: according to the number and location of the SiC-MOSFET device faults, the faults are divided into single-tube faults, single-phase double-tube faults, single-phase multi-tube faults, out-of-phase double-tube faults, and out-of-phase multi-tube faults; Step S3: Based on the modulation wave generated by the inverter closed-loop control and the zero-sequence voltage midpoint balance strategy, a PWM signal is generated using a co-phase carrier stacking modulation method to achieve fault-tolerant control of the system.

4. The control method of the grid-connected hybrid ANPC fault-tolerant system according to claim 3, characterized in that: In step S2, for a single tube failure, if the upper clamping tube M k2 Or lower clamp tube M k3 If an open circuit fault occurs, the fault phase bridge arm operates in the traditional diode clamped three-level converter modulation mode; if the upper external tube M k1 Or lower outer tube M k4 When an open circuit fault occurs, the corresponding redundant device is started according to the specific method of step S1, and the bridge arm of the faulty phase performs hybrid ANPC three-level modulation according to the original switch state logic of the device. k1 The PWM signal is given to the first multiplexed Si-IGBT device S1, or the original lower external tube M k4 The PWM signal is given to the second multiplexed Si-IGBT device S2.

5. The control method of the grid-connected hybrid ANPC fault-tolerant system according to claim 3, characterized in that: In step S2, for a single-phase double-tube fault: In single phase, when two outer tubes are open circuit, the upper outer tube M k1 With lower outer tube M k4 When the circuit is open, it is recorded as SD-I type fault. For SD-I type fault, according to the specific method of step S1, the corresponding redundant device is started, and the bridge arm of the fault phase performs hybrid ANPC three-level modulation according to the original switch state logic of the device. k1 The PWM signal is given to the first multiplexed Si-IGBT device S1, which originally has an external tube M k4 The PWM signal is given to the second multiplexed Si-IGBT device S2; In a single phase, when one outer tube fails and one clamp tube opens, the upper outer tube M k1 With upper clamp tube M k2 Open circuit fault, or upper external tube M k1 With lower clamp tube M k3 Open circuit fault, or lower outer tube M k4 With upper clamp tube M k2 Open circuit fault, or lower outer tube M k4 With lower clamp tube M k3 When the circuit is open, it is recorded as SD-Ⅱ type fault. For SD-Ⅱ type fault, according to the specific method of step S1, the corresponding redundant device is started, and the bridge arm of the fault phase is modulated according to two levels; the upper external tube M k1 With upper clamp tube M k2 Open circuit fault, or upper external tube M k1 With lower clamp tube M k3 When an open circuit fault occurs, the corresponding device switch state logic is shown in Table C-1; k4 With upper clamp tube M k2 Open circuit fault, or lower outer tube M k4 With lower clamp tube M k3 In case of an open circuit fault, the corresponding device switch state logic is shown in Table C-2; Table C-1 Upper outer tube M in SD-Ⅱ type fault k1 With upper clamp tube M k2 Open circuit fault, or upper external tube M k1 With lower clamp tube M k3 The upper outer tube M in open circuit fault and SM-Ⅱ type fault k1 , Upper clamp tube M k2 With lower clamp tube M k3 Device switch state logic during open circuit fault Table C-2 Lower outer tube M in SD-Ⅱ type fault k4 With upper clamp tube M k2 Open circuit fault, or lower outer tube M k4 With lower clamp tube M k3 Open circuit fault and SM-Ⅱ fault in the lower outer tube M k4 , Upper clamp tube M k2 With lower clamp tube M k3 Device switch state logic during open circuit fault In a single phase, when two clamping tubes fail to open circuit, the upper clamping tube M k2 With lower clamp tube M k3 In the case of an open circuit fault, it is recorded as an SD-III type fault. For an SD-III type fault, the redundant unit is not put into operation, and the faulty phase bridge arm operates in the traditional diode clamped three-level converter modulation mode.

6. The control method of the grid-connected hybrid ANPC fault-tolerant system according to claim 3, characterized in that: In step S2, for a single-phase multi-tube fault: In single phase, when two outer tubes and one clamping tube open circuit fault, the upper outer tube M k1 , lower outer tube M k4 With upper clamp tube M k2 Open circuit fault, or upper external tube M k1 , lower outer tube M k4 With lower clamp tube M k3 When an open circuit fault occurs, it is recorded as an SM-I type fault. For an SM-I type fault, according to the specific method of step S1, the corresponding redundant device is started, and the fault phase bridge arm is modulated according to two levels. The corresponding device switch state logic is shown in Table C-3. Table C-3 SM-Ⅰ and SM-Ⅲ fault device switch state logic In a single phase, when one outer tube and two clamping tubes are open circuit fault, the upper outer tube M k1 , Upper clamp tube M k2 With lower clamp tube M k3 Open circuit fault, or lower outer tube M k4 , Upper clamp tube M k2 With lower clamp tube M k3 When the circuit is open, it is recorded as SM-Ⅱ type fault. For SM-Ⅱ type fault, according to the specific method of step S1, the corresponding redundant device is started, the bridge arm of the fault phase is modulated according to two levels, and the upper external tube M k1 , Upper clamp tube M k2 With lower clamp tube M k3 When an open circuit fault occurs, the corresponding device switch state logic is shown in Table C-1; k4 , Upper clamp tube M k2 With lower clamp tube M k3 When an open circuit fault occurs, the corresponding device switch state logic is shown in Table C-2; in a single phase, when the two outer tubes and the two clamping tubes have an open circuit fault, that is, the upper outer tube M k1 , Upper clamp tube M k2 , lower clamp tube M k3 With lower outer tube M k4 In the case of an open circuit fault, it is recorded as an SM-III type fault. For an SM-III type fault, according to the specific method of step S1, the corresponding redundant device is started, and the faulty phase bridge arm is modulated according to two levels. The corresponding device switch state logic is shown in Table C-3.

7. The control method of the grid-connected hybrid ANPC fault-tolerant system according to claim 3, characterized in that: In step S2, for an out-of-phase double-tube fault: When the x-phase external tube fails and the y-phase external tube fails, that is, the x-phase external tube M x1 With y phase upper outer tube M y1 Open circuit fault, or the external tube M on phase x x1 With y phase lower outer tube M y4 Open circuit fault, or the outer tube M of the x phase x4 With y phase upper outer tube M y1 Open circuit fault, or the outer tube M of the x phase x4 With y phase lower outer tube M y4 When the fault is open circuit, it is recorded as DPD-Ⅰ fault, and the external tube M on the x phase x1 With y phase upper outer tube M y1 In case of an open circuit fault, the fault phase is modulated according to the three-level modulation, and the corresponding device switch state logic is shown in Table C-4; x1 With y phase lower outer tube M y4 Open circuit fault, or the outer tube M of the x phase x4 With y phase upper outer tube M y1 When an open circuit fault occurs, the bridge arm of the faulty phase performs hybrid ANPC three-level modulation according to the original switch state logic of the device. x1 Or y phase upper outer tube M y1 The PWM signal is given to the first multiplexed Si-IGBT device S1, the original x-phase lower outer tube M x4 Or y phase lower outer tube M y4 The PWM signal is given to the second multiplexed Si-IGBT device S2; the x-phase lower outer tube M x4 With y phase lower outer tube M y4 In case of open circuit fault, the fault phase is modulated according to three levels, and the corresponding device switch state logic is shown in Table C-5; Table C-4 DPD-Ⅰ type fault x phase upper external tube M x1 With y phase upper outer tube M y1 Device switch state logic during open circuit fault Table C-5DPD-Ⅰ type fault x phase lower outer tube M x4 With y phase lower outer tube M y4 Device switch state logic during open circuit fault When the x-phase clamping tube fails and the y-phase clamping tube fails, that is, the x-phase upper clamping tube M x2 With the y-phase upper clamp tube M y2 Open circuit fault, or x-phase upper clamp tube M x2 With y phase down clamp tube M y3 Open circuit fault, or x-phase lower clamp tube M x3 With the y-phase upper clamp tube M y2 Open circuit fault, or x-phase lower clamp tube M x3 With y phase down clamp tube M y3 When there is an open circuit fault, it is recorded as a DPD-II fault. For the DPD-II fault, the x-phase and y-phase bridge arms work in the traditional diode clamped three-level converter modulation mode; When the x-phase outer tube fails and the y-phase clamp tube fails, that is, the x-phase upper outer tube M x1 With the y-phase upper clamp tube M y2 Open circuit fault, or the external tube M on phase x x1 With y phase down clamp tube M y3 Open circuit fault, or the outer tube M of the x phase x4 With the y-phase upper clamp tube M y2 Open circuit fault, or the outer tube M of the x phase x4 With y phase down clamp tube M y3 When the circuit is open, it is recorded as a DPD-III fault. For the DPD-III fault, according to the specific method of step S1, the corresponding redundant device is started, and the external tube M of the x-phase open fault is x1 The PWM signal is given to the first multiplexed Si-IGBT device S1, and the external tube M under the x-phase open circuit fault x4 The PWM signal is given to the second multiplexed Si-IGBT device S2, and the Y-phase clamping tube fault bridge arm works according to the traditional diode clamping type three-level converter modulation mode; When the x-phase clamping tube fails and the y-phase external tube fails, the x-phase upper clamping tube M x2 With y phase upper outer tube M y1 Open circuit fault, or x-phase upper clamp tube M x2 With y phase lower outer tube M y4 Open circuit fault, or x-phase lower clamp tube M x3 With y phase upper outer tube M y1 Open circuit fault, or x-phase lower clamp tube M x3 With y phase lower outer tube M y4 When the fault is open circuit, it is recorded as DPD-Ⅳ type fault. For DPD-Ⅳ type fault, according to the specific method of step S1, the corresponding redundant device is started, and the external tube M of the y-phase open circuit fault is y1 The PWM signal is given to the first multiplexed Si-IGBT device S1, and the outer tube M under the y-phase open circuit fault y4 The PWM signal is given to the second multiplexed Si-IGBT device S2, and the x-phase clamping tube fault bridge arm operates according to the traditional diode clamping three-level converter modulation mode.

8. The control method of the grid-connected hybrid ANPC fault-tolerant system according to claim 3, characterized in that: In step S2, for out-of-phase multi-tube faults: When the three phases are connected to the external tube, that is, the external tube M of the A phase a1 、B phase upper outer tube M b1 With C phase upper outer tube M c1 When an open circuit fault occurs, it is recorded as a DPM-Ⅰ type fault. For a DPM-Ⅰ type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-6; Table C-6DPM-Ⅰ type fault device switch state logic When the three-phase lower outer tube fails, that is, the A phase lower outer tube M a4 、B phase lower outer tube M b4 With C phase lower outer tube M c4 When an open circuit fault occurs, it is recorded as a DPM-Ⅱ type fault. For a DPM-Ⅱ type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-7; Table C-7DPM-Ⅱ type fault device switch state logic When the double outer tube of phase x and the single outer tube of phase y fail, that is, the upper outer tube M of phase x x1 、x phase lower outer tube M x4 With y phase upper outer tube M y1 Open circuit fault, or the external tube M on phase x x1 、x phase lower outer tube M x4 With y phase lower outer tube M y4 When an open circuit fault occurs, it is recorded as a DPM-III type fault. For a DPM-III type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8; Table C-8 Switch state logic of DPM-Ⅲ, DPM-Ⅳ, DPM-Ⅴ, DPM-Ⅵ, DPM-Ⅶ, DPM-Ⅷ, DPM-Ⅸ, DPM-Ⅹ, DPM-Ⅺ, and DPM-Ⅻ fault devices When the upper outer tube of phase x fails, the upper outer tube of phase y fails, and the lower outer tube of phase z fails, that is, the upper outer tube M of phase x fails. x1 , y phase upper outer tube M y1 With z phase lower outer tube M z4 When an open circuit fault occurs, it is recorded as a DPM-Ⅳ type fault. For a DPM-Ⅳ type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8; When the x-phase lower outer tube fails, the y-phase lower outer tube fails, and the z-phase upper outer tube fails, that is, the x-phase lower outer tube M x4 , y phase lower outer tube M y4 With z phase upper outer tube M z1 When an open circuit fault occurs, it is recorded as a DPM-V type fault. For a DPM-V type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8; When the x-phase double outer tube fails, the y-phase single outer tube fails, and the z-phase single outer tube fails, that is, the x-phase upper outer tube M x1 、x phase lower outer tube M x4 , y phase upper outer tube M y1 With z phase upper outer tube M z1 Open circuit fault, or the external tube M on phase x x1 、x phase lower outer tube M x4 , y phase upper outer tube M y1 With z phase lower outer tube M z4 Open circuit fault, or the external tube M on phase x x1 、x phase lower outer tube M x4 , y phase lower outer tube M y4 With z phase upper outer tube M z1 Open circuit fault, or the external tube M on phase x x1 、x phase lower outer tube M x4 , y phase lower outer tube M y4 With z phase lower outer tube M z4 When an open circuit fault occurs, it is recorded as a DPM-VI fault. For a DPM-VI fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8; When the double outer tube of phase x fails and the double outer tube of phase y fails, that is, the upper outer tube M of phase x x1 、x phase lower outer tube M x4 , y phase upper outer tube M y1 With y phase lower outer tube M y4 In case of an open circuit fault, it is recorded as a DPM-VII fault. For a DPM-VII fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8; When the upper outer tube of three phases fails and the lower outer tube of one phase fails, that is, the upper outer tube M of phase A a1 、B phase upper outer tube M b1 、C phase upper outer tube M c1 With x phase lower outer tube M x4 When an open circuit fault occurs, it is recorded as a DPM-VIII type fault. For a DPM-VIII type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8; When the three-phase lower outer tube fails and one-phase upper outer tube fails, that is, the lower outer tube M of phase A a4 、B phase lower outer tube M b4 、C phase lower outer tube M c4 With x phase upper outer tube M x1 When an open circuit fault occurs, it is recorded as a DPM-IX fault. For a DPM-IX fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8; When the three-phase upper outer tube fails and the two-phase lower outer tube fails, that is, the upper outer tube M of phase A a1 、B phase upper outer tube M b1 、C phase upper outer tube M c1 、x phase lower outer tube M x4 With y phase lower outer tube M y4 When an open circuit fault occurs, it is recorded as a DPM-X type fault. For a DPM-X type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8; When the three-phase lower outer tube fails and the two-phase upper outer tube fails, that is, the A phase lower outer tube M a4 、B phase lower outer tube M b4 、C phase lower outer tube M c4 、x phase upper outer tube M x1 With y phase upper outer tube M y1 When an open circuit fault occurs, it is recorded as a DPM-Ⅺ type fault. For a DPM-Ⅺ type fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8; When all outer tubes fail, that is, the outer tube M on phase A a1 、A phase lower outer tube M a4 、B phase upper outer tube M b1 、B phase lower outer tube M b4 、C phase upper outer tube M c1 With C phase lower outer tube M c4 In case of an open circuit fault, it is recorded as a DPM-XII fault. For a DPM-XII fault, according to the specific method of step S1, the corresponding redundant device is started, the thyristor connected to the bridge arm of the external fault phase is turned on, and the bridge arm of the fault phase is modulated according to two levels. The corresponding device switch state logic is shown in Table C-8.

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