Cascade multi-level inverter switch tube open-circuit fault diagnosis method

Abstract

The invention discloses a cascade multi-level inverter switching tube open-circuit fault diagnosis method, which is characterized in that each phase of cascade H-bridge sub-modules is grouped, and a plurality of sub-modules in the group are monitored through a single voltage sensor. The method comprises the following steps: firstly, analyzing output voltage and current characteristics of a sub-module in normal and fault states, and constructing a fault characteristic value table; and then, sampling the output voltage and the driving signal, and when the theoretical output voltage is deviated from the actual output voltage, judging that a fault occurs. And finally, comparing the actual voltage and the theoretical voltage in different working states, and accurately positioning the fault switch tube in combination with the deviation and the phase voltage flow direction characteristics. According to the method, few sensors are needed, the cost is low, multiple fault states can be diagnosed at the same time, misdiagnosis is avoided during operation condition switching, and high robustness is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronic converter fault diagnosis, and in particular relates to a method for diagnosing open-circuit faults of switch tubes of a cascaded multi-level inverter. Background Art

[0002] Cascaded H-bridge multilevel inverters have been widely used in traction systems of electrified railways and urban rail transit, electric vehicles, photovoltaic grid-connected power generation systems, high-voltage DC transmission, AC motor drives and other occasions due to their advantages such as easy modularization, high voltage and large capacity, and low harmonic distortion. However, with the increase in the number of inverter modules in the system, as well as the complex and changeable operating conditions and the aging of the components themselves, the probability of failure also increases. According to relevant statistics and surveys, switch tube failures account for nearly one-third of the failures of the entire inverter system. Switch tube failures can generally be divided into open circuit failures and short circuit failures. Short circuit failures occur in a very short time and may cause irreparable damage to other components of the circuit before they have time to be discovered. Therefore, for short circuit failures, fast fuses are usually installed on the inverter, so that the short circuit failure can be directly replaced with an open circuit failure, which is then handled using the open circuit fault diagnosis method. In the case of an open circuit failure, the inverter system can continue to operate due to the inherent switch redundancy, but its output quality is reduced. However, this may increase the voltage stress of other healthy switches and may cause damage to the entire system. Therefore, it is of great practical significance to study the open circuit fault diagnosis method of the switch tube in the cascaded H-bridge multi-level inverter system.

[0003] Existing open-circuit fault diagnosis methods for multi-level inverters mainly include three types of methods: model-based, intelligent algorithm-based, and signal-based. Given the large number of switching devices contained in multi-level inverters, it is difficult to build an accurate and reliable fault diagnosis model, which makes it difficult to effectively implement model-based fault diagnosis methods in practical applications. In order to avoid the difficulties caused by modeling, relevant scholars have adopted fault diagnosis methods based on intelligent algorithms. Although this type of method can avoid the dependence of diagnostic accuracy on the system model, it has a large amount of calculation and is difficult to use for real-time online diagnosis. In order to achieve real-time online diagnosis, relevant scholars have adopted a signal-based fault diagnosis method. Compared with the first two methods, this type of method is simple to implement and easy to use in engineering.

[0004] However, existing signal-based fault diagnosis methods all require the installation of current or voltage sensors on each H-bridge module, which is costly and not easy to apply in engineering. Summary of the invention

[0005] The present invention proposes a method for diagnosing open-circuit faults of switch tubes of a cascaded multi-level inverter to solve the problems existing in the above-mentioned prior art.

[0006] To achieve the above object, the present invention provides a method for diagnosing an open circuit fault of a switch tube of a cascaded multi-level inverter, comprising the following steps:

[0007] The cascaded H-bridge submodules of each phase are grouped to obtain submodule groups, each group including a plurality of H-bridge submodules;

[0008] Several H-bridge submodules in the group are monitored by a single voltage sensor;

[0009] Based on the output voltage and current characteristics of the multi-level inverter under normal working state and faulty operating state, the variation law of the output voltage under different switch tube faults in the sub-module group is analyzed, and a fault characteristic value table is constructed;

[0010] The output voltage and driving signal of the submodule group are obtained, and when a deviation occurs between the theoretical output voltage and the actual output voltage of the submodule group, it is determined that a fault occurs;

[0011] When a fault occurs, the actual voltage of the submodule group in different working states is compared with the theoretical voltage. The open circuit fault of the switch tube is accurately located based on the deviation between the actual voltage and the theoretical voltage and the flow direction characteristics of the phase voltage.

[0012] Preferably, the grouping of the cascaded H-bridge submodules per phase comprises:

[0013] Each submodule of the H-bridge submodule group includes 4 switch tubes, 4 diodes respectively connected in anti-parallel with the 4 switch tubes, and 1 capacitor;

[0014] Every two adjacent sub-modules are divided into a group, and each group is equipped with a voltage sensor. The voltage sensor is installed at both ends of each group to measure the output voltage of each group of H-bridge sub-modules.

[0015] Preferably, an anti-interference coefficient is introduced when determining whether a fault occurs;

[0016] When the deviation between the actual output voltage and the expected output voltage is within the range of the anti-interference coefficient, the actual output voltage assignment rule is as follows:

[0017] When U o ∈((1-δ)*U dc ,(1+δ)*U dc ),U o =U dc ;

[0018] When U o ∈(-δ*U dc ,δ*U dc ),U o =0;

[0019] When U o∈(-(1+δ)*U dc , -(1-δ)*U dc ),U o =-U dc ;

[0020] Where U o represents the actual output voltage, δ represents the anti-interference coefficient, U dc Indicates the DC side voltage.

[0021] Preferably, accurately locating the open circuit fault of the switch tube includes:

[0022] When the phase current I i >0, the output voltage of the submodule group is compared according to the working condition to locate the fault;

[0023] When the phase current I i <0, the output voltages of the submodule groups are compared according to the operating conditions to locate the fault.

[0024] Preferably: the operating states include 12 kinds, each of which includes the operating states of 8 switch tubes S1-S8;

[0025] In working condition 1, the switches S2, S4, S6 and S8 are turned on;

[0026] In working condition 2, the switches S2, S4, S5 and S8 are turned on;

[0027] In working condition 3, the switches S1, S4, S6 and S8 are turned on;

[0028] In working condition 4, the switches S1, S3, S5 and S7 are turned on;

[0029] In working condition 5, the switches S1, S3, S5 and S8 are turned on;

[0030] In working condition 6, the switches S1, S4, S5 and S7 are turned on;

[0031] In working condition 7, the switches S2, S4, S6 and S8 are turned on;

[0032] In working condition 8, the switches S2, S4, S6 and S7 are turned on;

[0033] In working condition 9, the switches S2, S3, S6 and S8 are turned on;

[0034] In working condition 10, the switches S1, S3, S5 and S7 are turned on;

[0035] In working condition 11, the switches S1, S3, S6 and S7 are turned on;

[0036] In working condition 12, switch tubes S2, S3, S5 and S7 are turned on.

[0037] Preferably, the phase current I i >0, the specific working conditions and fault location include:

[0038] Condition 1: The expected output voltage is 0. If the actual output voltage U o =-U dc , it is determined that the switch tube S4 or S8 has an open circuit fault;

[0039] Working condition 2: The expected output voltage is U dc , if the actual output voltage U o =0, it is judged that the switch tube S4, S5 or S8 has an open circuit fault;

[0040] Working condition 3: expected output voltage is U dc , if the actual output voltage U o =0, it is judged that the switch tube S1, S5 or S8 has an open circuit fault;

[0041] Condition 4: The expected output voltage is 0. If the actual output voltage U o =-U dc , it is judged that the switch tube S1 or S5 has an open circuit fault;

[0042] Working condition 5: expected output voltage is U dc , if the actual output voltage U o =0, it is judged that the switch tube S1, S5 or S8 has an open circuit fault;

[0043] Working condition 6: expected output voltage is U dc , if the actual output voltage U o =0, it is determined that the switch tube S1, S4 or S5 has an open circuit fault.

[0044] Preferably, the phase current I i <0, the specific working conditions and fault location include:

[0045] Condition 7: The expected output voltage is 0. If the actual output voltage U o =+U dc , it is judged that the switch tube S2 or S6 has an open circuit fault;

[0046] Condition 8: Expected output voltage is -U dc , if the actual output voltage U o =0, it is judged that the switch tube S2, S6 or S7 has an open circuit fault;

[0047] Condition 9: Expected output voltage is -U dc , if the actual output voltage U o =0, it is judged that the switch tube S2, S3 or S6 has an open circuit fault;

[0048] Condition 10: The expected output voltage is 0. If the actual output voltage U o =+U dc , it is judged that the switch tube S3 or S7 has an open circuit fault;

[0049] Condition 11: Expected output voltage is -U dc , if the actual output voltage U o =0, it is judged that the switch tube S3, S6 or S7 has an open circuit fault;

[0050] Working condition 12: Expected output voltage is -U dc , if the actual output voltage U o =0, it is determined that the switch tube S2, S3 or S7 has an open circuit fault.

[0051] The present invention also provides a computer device, comprising a memory, a processor and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method.

[0052] The present invention also provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of the method are implemented.

[0053] The present invention also provides a computer program product, comprising a computer program, which implements the steps of the method when executed by a processor.

[0054] Compared with the prior art, the present invention has the following advantages and technical effects:

[0055] The present invention discloses a method for diagnosing an open-circuit fault of a switch tube of a cascaded multilevel inverter, comprising: grouping H-bridge submodules cascaded per phase, and monitoring multiple H-bridge submodules in the group through a single voltage sensor. First, based on the output voltage and current characteristics of the multilevel inverter in the normal working state and the faulty operating state, the variation law of the output voltage under different switch tube faults in the submodule group is analyzed, and then a fault characteristic value table is constructed. Then, the output voltage and drive signal of the submodule group are sampled, and when the theoretical output voltage and the actual output voltage of the submodule group deviate, it is determined that a fault occurs. Finally, after it is determined that a fault occurs, the actual voltage of the submodule group in different working states is compared with the theoretical voltage, and the accurate positioning of the open-circuit fault of the switch tube is achieved according to the size of the deviation and the flow direction characteristics of the phase voltage. The present invention reduces the number of voltage sensors required for fault diagnosis without affecting the diagnosis result, saves engineering costs, and is easy to apply in engineering. And it can realize the simultaneous diagnosis of multiple switch tube fault states. In addition, the present invention will not cause misdiagnosis due to the switching of the operating conditions of the cascaded H-bridge multilevel inverter, and has strong robustness. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0057] Figure 1 1 is a topological diagram of a cascaded H-bridge multi-level inverter system according to an embodiment of the present invention;

[0058] Figure 2 A schematic diagram of a fault diagnosis submodule group of a cascaded H-bridge multi-level inverter according to an embodiment of the present invention;

[0059] Figure 3 A topological structure diagram of a cascaded H-bridge multi-level inverter fault diagnosis submodule group and a voltage sensor circuit according to an embodiment of the present invention;

[0060] Figure 4 The present invention is a flowchart of fault location for a partial switch tube open circuit fault of a cascaded H-bridge multi-level inverter system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0061] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0062] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0063] Embodiment 1

[0064] like Figure 1 As shown, in the three-phase cascade H-bridge inverter structure involved in the present method, each phase of the inverter side is composed of n H-bridge units connected end to end, and the DC side of each H-bridge unit is connected to a mutually independent DC power supply. By inputting a control signal, different output voltages can be obtained. Each H-bridge inverter unit can output U dc ,0,-U dc Three different levels. Any submodule of the 3n submodules is denoted as submodule D ij , phase current I i , where i represents the phase sequence, i = a, b, c, j represents the serial number of each phase module, j = 1, 2....n; in submodule D ij It includes 4 switching tubes, 4 diodes connected in anti-parallel with the 4 switching tubes, and 1 capacitor. Figure 2As shown in FIG. 1 , the present invention groups every two adjacent submodules into a group and uses a single voltage sensor to diagnose the submodule group. The topological structure of a fault diagnosis circuit of a submodule group including a voltage sensor is shown in FIG. Figure 3 As shown, the submodule D ij The four switch tubes are denoted as S1, S2, S3 and S4 respectively, and the submodule D i(j+1) The switch tubes are respectively denoted as S5, S6, S7 and S8. When only one voltage sensor is used, the open circuit fault of the switch tube is diagnosed.

[0065] The H-bridge submodules of each bridge arm are grouped, and each group is equipped with a voltage sensor. The voltage sensors are installed at both ends of each group to measure the output voltage U of each group of H-bridge submodules. o The n H-bridge sub-modules of each bridge arm are divided into g groups, with 2 H-bridge sub-modules in each group.

[0066] Define the expected output voltage of the H-bridge submodule group as U * o , the actual output voltage is U o , the DC side voltage is U dc , real-time sampling of the output voltage and drive signal of the inverter module group, when the actual output voltage does not match the expected output voltage, it is determined that a fault has occurred. The anti-interference coefficient δ is introduced, δ = 0.5.

[0067] U o ∈((1-δ)*U dc ,(1+δ)*U dc ),remember U o =U dc ;

[0068] U o ∈(-δ*U dc ,δ*U dc ),remember U o =0;

[0069] U o ∈(-(1+δ)*U dc , -(1-δ)*U dc ),remember U o =-U dc ;

[0070] The present invention provides a method for diagnosing an open-circuit fault of a switch tube of a cascaded multi-level inverter, which is characterized by comprising the following steps:

[0071] The cascaded H-bridge submodules of each phase are grouped to obtain submodule groups, each group including a plurality of H-bridge submodules;

[0072] Several H-bridge submodules in the group are monitored by a single voltage sensor;

[0073] Based on the output voltage and current characteristics of the multi-level inverter under normal working state and faulty operating state, the variation law of the output voltage under different switch tube faults in the sub-module group is analyzed, and a fault characteristic value table is constructed;

[0074] The output voltage and driving signal of the submodule group are obtained, and when a deviation occurs between the theoretical output voltage and the actual output voltage of the submodule group, it is determined that a fault occurs;

[0075] When a fault occurs, the actual voltage of the submodule group in different working states is compared with the theoretical voltage. The open circuit fault of the switch tube is accurately located based on the deviation between the actual voltage and the theoretical voltage and the flow direction characteristics of the phase voltage.

[0076] Furthermore, based on the output voltage and current characteristics of the multilevel inverter under normal working state and faulty operating state, the variation law of the output voltage under different switch tube faults in the submodule group is analyzed, and then a fault characteristic value table is constructed, as shown in Table 1.

[0077] Table 1

[0078]

[0079] Furthermore, after determining that a fault has occurred, the actual voltage of the submodule group in different working states is compared with the theoretical voltage. With the help of the size of the deviation and the flow characteristics of the phase voltage, the open circuit fault of the switch tube can be accurately located. The fault location process is as follows: Figure 4 The specific process is as follows:

[0080] Phase current I i >0:

[0081] When the inverter is working in working condition 1, the expected output voltage of the H-bridge submodule group is 0. o =-U dc , it is judged that S4 or S8 has an open circuit fault. At this time, it is still impossible to determine the specific switch tube that has the open circuit fault. When the inverter runs to working condition 5, the output voltage of the submodule group is compared again. If U o = 0, it can be determined that the switch tube S8 has an open circuit fault. o =U dc , it can be determined that the open circuit fault occurs in the switch tube S4.

[0082] When the inverter is working in working condition 2, the expected output voltage of the H-bridge submodule group is U dc , if U o =0, it is judged that S4, S5 or S8 has an open circuit fault, and when the inverter runs to working condition 1, the output voltage of the submodule group is compared again. If Uo = 0, it is judged that S5 has an open circuit fault. If U o =-U dc , then continue to repeat working condition 1, U o =-U dc The judgment process.

[0083] When the inverter works in working condition 3, the expected output voltage of the H-bridge submodule group is U dc , if U o = 0, it is judged that S1, S5 or S8 has an open circuit fault, and when the inverter runs to working condition 1, the output voltage of the submodule group is compared again. If U o =0, it is judged that S1 has an open circuit fault. If U o =-U dc , then continue to repeat working condition 1, U o =-U dc The judgment process.

[0084] When the inverter is working in working condition 4, the expected output voltage of the H-bridge submodule group is 0. o =-U dc , it is judged that S1 or S5 has an open circuit fault. At this time, it is still impossible to determine the specific switch tube that has the open circuit fault. When the inverter runs to working condition 2, the output voltage of the submodule group is compared again. If U o = 0, it can be determined that the switch tube S5 has an open circuit fault. o =U dc , it can be determined that the open circuit fault occurs in the switch tube S1.

[0085] When the inverter is working in working condition 5, the expected output voltage of the H-bridge submodule group is U dc , if U o = 0, it is judged that S1, S5 or S8 has an open circuit fault, and when the inverter runs to working condition 4, the output voltage of the submodule group is compared again. If U o = 0, it is judged that S8 has an open circuit fault. If U o =-U dc , then continue to repeat working condition 4, U o =-U dc The judgment process.

[0086] When the inverter is working in working condition 6, the expected output voltage of the H-bridge submodule group is U dc , if U o = 0, it is judged that S1, S4 or S5 has an open circuit fault, and when the inverter runs to working condition 4, the output voltage of the submodule group is compared again. If U o = 0, it is judged that S4 has an open circuit fault. If Uo =-U dc , then continue to repeat working condition 4, U o =-U dc The judgment process.

[0087] Phase current I i <0 hours:

[0088] When the inverter is working in working condition 7, the expected output voltage of the H-bridge submodule group is 0. o =+U dc , it is judged that S2 or S6 has an open circuit fault. At this time, it is still impossible to determine the specific switch tube that has the open circuit fault. When the inverter runs to working condition 11, the output voltage of the submodule group is compared again. If U o = 0, it can be determined that the switch tube S6 has an open circuit fault. o =-U dc , it can be determined that the open circuit fault occurs in the switch tube S2.

[0089] When the inverter is working in working condition 8, the expected output voltage of the H-bridge submodule group is -U dc , if U o =0, it is judged that an open circuit fault occurs in S2, S6 or S7, and when the inverter runs to working condition 7, the output voltage of the submodule group is compared again. If U o =0, it is judged that S7 has an open circuit fault. If U o =+U dc , then continue to repeat working condition 7, U o =+U dc The judgment process.

[0090] When the inverter is working in working condition 9, the expected output voltage of the H-bridge submodule group is -U dc , if U o = 0, it is judged that an open circuit fault occurs in S2, S3 or S6, and when the inverter runs to working condition 7, the output voltage of the submodule group is compared again. If U o =0, it is judged that S3 has an open circuit fault. If U o =+U dc , then continue to repeat working condition 7, U o =+U dc The judgment process.

[0091] When the inverter is working in working condition 10, the expected output voltage of the H-bridge submodule group is 0. o =+U dc, it is judged that S3 or S7 has an open circuit fault. At this time, it is still impossible to determine the specific switch tube that has the open circuit fault. When the inverter runs to working condition 8, the output voltage of the submodule group is compared again. If U o = 0, it can be determined that the switch tube S7 has an open circuit fault. o =-U dc , it can be determined that the open circuit fault occurs in the switch tube S3.

[0092] When the inverter is working in working condition 11, the expected output voltage of the H-bridge submodule group is -U dc , if U o =0, it is judged that an open circuit fault occurs in S3, S6 or S7, and when the inverter runs to working condition 10, the output voltage of the submodule group is compared again. If U o = 0, it is judged that S6 has an open circuit fault. If U o =+U dc , then continue to repeat the working condition 10 times, U o =+U dc The judgment process.

[0093] When the inverter is working in working condition 12, the expected output voltage of the H-bridge submodule group is -U dc , if U o =0, it is judged that an open circuit fault occurs in S2, S3 or S7, and when the inverter runs to working condition 10, the output voltage of the submodule group is compared again. If U o =0, it is judged that S2 has an open circuit fault. If U o =+U dc , then continue to repeat the working condition 10 times, U o =+U dc The judgment process.

[0094] This embodiment further provides a computer device, including a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method.

[0095] This embodiment also provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of the method are implemented.

[0096] This embodiment also provides a computer program product, including a computer program, which implements the steps of the method when executed by a processor.

[0097] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for diagnosing an open-circuit fault of a switch tube of a cascaded multilevel inverter, characterized in that: The following steps are involved: The cascaded H-bridge submodules of each phase are grouped to obtain submodule groups, each group including a plurality of H-bridge submodules; Several H-bridge submodules in the group are monitored by a single voltage sensor; Based on the output voltage and current characteristics of the multi-level inverter under normal working state and faulty operating state, the variation law of the output voltage under different switch tube faults in the sub-module group is analyzed, and a fault characteristic value table is constructed; The output voltage and driving signal of the submodule group are obtained, and when a deviation occurs between the theoretical output voltage and the actual output voltage of the submodule group, it is determined that a fault occurs; When a fault occurs, the actual voltage of the submodule group in different working states is compared with the theoretical voltage. The open circuit fault of the switch tube is accurately located based on the deviation between the actual voltage and the theoretical voltage and the flow direction characteristics of the phase voltage.

2. The method according to claim 1, characterized in that The grouping of the cascaded H-bridge submodules per phase comprises: Each submodule of the H-bridge submodule group includes 4 switch tubes, 4 diodes respectively connected in anti-parallel with the 4 switch tubes, and 1 capacitor; Every two adjacent sub-modules are divided into a group, and each group is equipped with a voltage sensor. The voltage sensor is installed at both ends of each group to measure the output voltage of each group of H-bridge sub-modules.

3. The method according to claim 1, characterized in that Introduce the anti-interference coefficient when determining whether a fault has occurred; When the deviation between the actual output voltage and the expected output voltage is within the range of the anti-interference coefficient, the actual output voltage assignment rule is as follows: This U o ∈((1-δ)*U dc , (1+δ)*U dc ) time, U o = U dc ; This U o ∈(-δ*U dc , δ*U dc ) time, U o = 0; This U o ∈(-(1+δ)*U dc , -(1-δ)*U dc ) time, U o =-U dc ; Where U o represents the actual output voltage, δ represents the anti-interference coefficient, U dc Indicates the DC side voltage.

4. The method according to claim 1, characterized in that: Accurately locate the open circuit fault of the switch tube including: When the phase current I i >0, the output voltage of the submodule group is compared according to the working condition to locate the fault; When the phase current I i <0, the output voltages of the submodule groups are compared according to the operating conditions to locate the fault.

5. The method according to claim 4, characterized in that: The operating states include 12 types, each of which includes the operating states of 8 switch tubes S1-S8; In working condition 1, the switches S2, S4, S6 and S8 are turned on; In working condition 2, the switches S2, S4, S5 and S8 are turned on; In working condition 3, the switches S1, S4, S6 and S8 are turned on; In working condition 4, the switches S1, S3, S5 and S7 are turned on; In working condition 5, the switches S1, S3, S5 and S8 are turned on; In working condition 6, the switches S1, S4, S5 and S7 are turned on; In working condition 7, the switches S2, S4, S6 and S8 are turned on; In working condition 8, the switches S2, S4, S6 and S7 are turned on; In working condition 9, the switches S2, S3, S6 and S8 are turned on; In working condition 10, the switches S1, S3, S5 and S7 are turned on; In working condition 11, the switches S1, S3, S6 and S7 are turned on; In working condition 12, switch tubes S2, S3, S5 and S7 are turned on.

6. The method according to claim 5, characterized in that The phase current I i >0, the specific working conditions and fault location include: Condition 1: The expected output voltage is 0. If the actual output voltage U o =-U dc , it is determined that the switch tube S4 or S8 has an open circuit fault; Working condition 2: expected output voltage is U dc , if the actual output voltage U o =0, it is judged that the switch tube S4, S5 or S8 has an open circuit fault; Working condition 3: expected output voltage is U dc , if the actual output voltage U o =0, it is judged that the switch tube S1, S5 or S8 has an open circuit fault; Condition 4: The expected output voltage is 0. If the actual output voltage U o =-U dc , it is judged that the switch tube S1 or S5 has an open circuit fault; Working condition 5: expected output voltage is U dc , if the actual output voltage U o =0, it is judged that the switch tube S1, S5 or S8 has an open circuit fault; Condition 6: Expected output voltage is U dc , if the actual output voltage U o =0, it is determined that the switch tube S1, S4 or S5 has an open circuit fault.

7. The method according to claim 5, characterized in that The phase current I i <0, the specific working conditions and fault location include: Condition 7: The expected output voltage is 0. If the actual output voltage U o =+U dc , it is judged that the switch tube S2 or S6 has an open circuit fault; Condition 8: Expected output voltage is -U dc , if the actual output voltage U o =0, it is judged that the switch tube S2, S6 or S7 has an open circuit fault; Condition 9: Expected output voltage is -U dc , if the actual output voltage U o =0, it is judged that the switch tube S2, S3 or S6 has an open circuit fault; Condition 10: The expected output voltage is 0. If the actual output voltage U o =+U dc , it is judged that the switch tube S3 or S7 has an open circuit fault; Condition 11: Expected output voltage is -U dc , if the actual output voltage U o =0, it is judged that the switch tube S3, S6 or S7 has an open circuit fault; Working condition 12: Expected output voltage is -U dc , if the actual output voltage U o =0, it is determined that the switch tube S2, S3 or S7 has an open circuit fault.

8. A computer device comprising a memory, a processor and a computer program stored in the memory, characterized in that: The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 7.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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