A method for locating IGBT open circuit fault in FID submodule based on MIC

Abstract

The invention discloses a FID submodule IGBT open circuit fault locating method based on MIC, comprising: locating the faulty bridge arm and identifying the fault type based on the bridge arm output voltage and the predicted voltage difference; collecting a fundamental wave cycle of the faulty bridge arm submodule capacitor voltage; locating the faulty submodule based on the submodule capacitor voltage MIC value feature; when performing submodule IGBT open circuit fault detection, the invention avoids directly analyzing the relationship between the submodule capacitor voltage and a set voltage threshold, adopts the maximum information number, can fully utilize the capacitor voltage features of all submodules in the bridge arm, and improves the accuracy of fault locating.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics and power system application, and in particular to a method for locating an IGBT open-circuit fault of an FID submodule based on MIC. Background Art

[0002] The vigorous promotion of renewable energy, the rapid growth of loads and diversified access are changing the structure and operation characteristics of traditional distribution networks. The existing distribution system faces problems such as insufficient power supply capacity, difficult to ensure power quality, and reduced power supply reliability. The new power consumption situation has put forward higher requirements for intelligent distribution. How to efficiently utilize renewable energy and be compatible with diversified power demand, and improve power supply quality and reliability while ensuring the economical transmission and distribution of electricity is an important goal of the development of smart distribution networks.

[0003] In the late 1990s, with the rapid development of power electronic devices and control technology, flexible DC technology based on voltage source converter (VSC) has been widely used at the transmission network level. In recent years, in order to meet the supply demand of high-quality electricity, flexible DC technology has gradually expanded to the distribution level. Studies have shown that intelligent distribution technology based on flexible DC can effectively improve power quality, enhance power supply reliability, and improve the level of new energy consumption, and has broad development prospects. Among them, in view of the shortcomings of existing primary distribution equipment that is mostly limited by capacity, adjustment times and continuity, foreign scholars have proposed the concept of flexible interconnected equipment, including ring network flow controller, ring network power balancer, intelligent soft switch (soft open point, SOP), flexible DC link (DC link), etc.

[0004] FID can flexibly interconnect multiple distribution networks with different voltage frequencies, amplitudes and phases. Under normal conditions, FID can effectively balance the load, alleviate network congestion, and make full use of distribution assets by continuously adjusting the power output of each port. It can also reduce network losses, improve power quality, and achieve efficient and economical operation of the system. When a system fault occurs, FID can quickly isolate the fault without increasing the short-circuit current, and provide voltage and frequency support for the power outage area, thereby improving system safety and reliability. It can be seen that the flexible interconnection technology with FID as the core is an important means for the distribution network to achieve intelligent evolution.

[0005] Two-level / three-level VSC has been applied in medium and low voltage distribution systems and wind power generation systems due to its relatively simple structure and control method and low cost. However, as flexible interconnection gradually expands to the medium and high voltage distribution level, the two-level / three-level topology cannot meet the transmission requirements of high voltage, large capacity and high-quality output waveform. Modular multilevel converter (MMC) has the advantages of low loss, low footprint, low harmonic content, and no need for direct series connection of switching devices. At the same time, the modular characteristics of MMC are more conducive to large-scale production and assembly. Since it was proposed in 2002, MMC has been successfully applied in the field of flexible DC transmission. In 2016, NARI Relay Protection Electric Co., Ltd. successfully developed a 20kV~20MV MMC prototype, which provided a good foundation for the promotion of flexible interconnection of my country's distribution network.

[0006] Since the MMC system contains a large number of power electronic switching devices, and power semiconductor devices are considered to be one of the most vulnerable components in the power electronic system. It is estimated that 38% of the faults in the power conversion process are caused by semiconductor device failures. In general, semiconductor switching device failures can be divided into short-circuit failures and open-circuit failures. Short-circuit failures are highly destructive and may quickly damage the sub-module. The drive circuit is connected to the short-circuit protection circuit, which can quickly detect the fault and immediately shut down the device when the fault occurs. In contrast, open-circuit failures will not immediately damage the sub-module and may remain for a long time and cannot be detected; therefore, the main work of this paper is to study the rapid detection method of MMC sub-module IGBT open-circuit failures.

[0007] A lot of relevant research has been done at home and abroad on the location of MMC submodule IGBT open circuit faults. The diagnostic method proposed by some scholars can quickly detect and locate the open circuit fault submodule, but can only locate a single IGBT open circuit fault. It is not applicable to the situation where multiple IGBT faults occur in the bridge arm, which has certain limitations. The method proposed by some scholars can effectively solve the open circuit fault of one or more submodule IGBTs, but it takes a long time for the submodule capacitor voltage to increase to the given threshold, so the fault location takes a long time. The increase in capacitor voltage will further affect the normal operation of the MMC system. Some scholars have proposed a fault detection method based on a state observer, which takes 20-150ms to isolate the faulty submodule and has poor positioning speed. In the MMC system, in addition to output power or current control, the voltage balance and circulating current control of the submodule capacitor should also be realized at the same time. Model-predictive control (MPC) has a fast dynamic response and avoids complex controller design problems. It has been widely used in MMC control in recent years.

[0008] Most of the current sub-module IGBT open circuit fault location methods can only perform single sub-module IGBT open circuit fault diagnosis, and cannot quickly perform multiple sub-module IGBT open circuit fault diagnosis. The fault location method has many steps and is highly complex. Summary of the invention

[0009] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract of the specification and the title of the invention of this application to avoid blurring the purpose of this section, the abstract of the specification and the title of the invention, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0010] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0011] Therefore, the technical problem to be solved by the present invention is that most of the current sub-module IGBT open circuit fault locating methods can only perform single sub-module IGBT open circuit fault diagnosis, and cannot quickly perform multiple sub-module IGBT open circuit fault diagnosis. The fault locating method has many steps and high complexity.

[0012] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for locating an open-circuit fault of an FID submodule IGBT based on MIC, comprising:

[0013] The faulty bridge arm is located and the fault type is identified based on the difference between the bridge arm output voltage and the predicted voltage;

[0014] Collect a fundamental wave cycle of the capacitor voltage of the fault bridge arm submodule;

[0015] The faulty submodule is located based on the submodule capacitor voltage MIC value characteristics.

[0016] As a preferred solution of the MIC-based FID submodule IGBT open circuit fault locating method of the present invention, wherein: the fault bridge arm locating includes:

[0017] The voltage of each submodule capacitor is defined to be completely balanced, which can be achieved by the submodule capacitor voltage balancing solution. The standard deviation of the capacitor voltage error is defined as:

[0018]

[0019] Under normal conditions, the normalized capacitor voltage error is close to 0, and close to 1 or -1 when an IGBT open-circuit fault occurs in the submodule.

[0020] As a preferred solution of the MIC-based FID submodule IGBT open circuit fault locating method of the present invention, wherein:

[0021] Define the threshold Td to identify the health status of the MMC submodule:

[0022] When the normalized capacitor voltage error is within a predetermined threshold value Td, the MMC is in a normal working state;

[0023] When the normalized voltage error exceeds a predefined threshold value Td, the MMC is in a faulty operating state.

[0024] As a preferred solution of the MIC-based FID submodule IGBT open circuit fault locating method of the present invention, the fault type identification includes:

[0025] When an open-circuit fault occurs in one arm, the normalized voltage error of the corresponding arm will exceed the threshold value Td;

[0026] when When the threshold is exceeded, the open circuit fault is located in the upper arm, and when When the threshold is exceeded, the open circuit fault is located in the lower arm;

[0027] When the voltage error is close to −1, it indicates that an open-circuit fault occurs in the upper IGBT of the submodule. When the voltage error is close to 1, it indicates that an open-circuit fault occurs in the lower IGBT of the submodule.

[0028] As a preferred solution of the MIC-based FID submodule IGBT open circuit fault location method of the present invention, wherein: the bridge arm output voltage is calculated according to the input state by the submodule capacitor voltage collected by the sensor;

[0029] The predicted voltage difference is calculated by the controller according to the bridge arm current and the submodule input state collected by the sensor;

[0030] One fundamental wave period of the capacitor voltage of the faulty bridge arm submodule is collected by the sensor and sent to the controller.

[0031] As a preferred solution of the MIC-based FID submodule IGBT open circuit fault location method of the present invention, the submodule capacitor voltage balancing solution includes:

[0032] Determine the number of submodules required in the bridge arm;

[0033] The current state of the bridge arm at this time is determined. If it is in a charging state, a required number of sub-modules with a smaller capacitor voltage are put into use; if it is in a discharging state, a required number of sub-modules with a larger capacitor voltage are put into use.

[0034] As a preferred solution of the MIC-based FID submodule IGBT open circuit fault locating method of the present invention, wherein: the fault submodule locating includes:

[0035] Capacitor voltage samples are acquired based on a sliding window of one fundamental wave period. In normal operation, the maximum information number of any two capacitor voltages on the same arm will remain close to 1 with the same shape;

[0036] After an open circuit fault occurs, the capacitor voltage of the faulty submodule will operate abnormally, the maximum information between the capacitor of the faulty submodule and the voltage of the normal submodule will become smaller, while the maximum information number between the capacitor voltage of the normal submodule remains close to 1.

[0037] As a preferred solution of the MIC-based FID submodule IGBT open circuit fault location method of the present invention, the fault submodule judgment includes:

[0038] Traverse and calculate the maximum number of information between any two sub-modules;

[0039] Find a type of fault array whose maximum information number is much less than 1;

[0040] The repeated items in the fault array are faulty submodules.

[0041] As a preferred solution of the MIC-based FID submodule IGBT open circuit fault locating method described in the present invention, when the bridge arm current is greater than 0, the submodule output voltage is consistent with that when no upper tube fault occurs; when the bridge arm current is less than zero, under normal circumstances, the bridge arm current flows through the upper tube, and the output voltage is equal to the capacitor voltage; after an open circuit fault occurs in the upper tube of the submodule, the bridge arm current will flow through the lower tube, and at this time the SM output voltage is equal to 0, then the upper tube is faulty.

[0042] As a preferred solution of the MIC-based FID submodule IGBT open circuit fault locating method described in the present invention, when the bridge arm current is less than 0, the submodule output voltage is consistent with that when no lower tube fault occurs; when the bridge arm current is greater than zero, under normal circumstances, the bridge arm current flows through the lower tube and the output voltage is equal to 0; after an open circuit fault occurs in the lower tube of the submodule, the bridge arm current will flow through the upper tube, and at this time the SM output voltage is equal to the capacitor voltage, then the lower tube is faulty.

[0043] The beneficial effects of the present invention are as follows: the present invention avoids directly analyzing the relationship between the submodule capacitor voltage and the set voltage threshold when performing submodule IGBT open circuit fault detection, and adopts the maximum information number to fully utilize the capacitor voltage characteristics of all submodules in the bridge arm, thereby improving the accuracy of fault location. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0045] Figure 1 This is a single-phase MMC circuit topology diagram.

[0046] Figure 2 Diagrams of two types of IGBT open-circuit faults and current paths in SM.

[0047] Figure 3 This is a flow chart of the submodule fault diagnosis and location method.

[0048] Figure 4 This is the simulation waveform of the capacitor voltage of the sub-module with the open circuit fault of the upper tube IGBT of sub-module 1.

[0049] Figure 5 This is the simulation waveform diagram of the maximum number of information of the sub-module with the open circuit fault of the upper tube IGBT of sub-module 1.

[0050] Figure 6 This is the simulation waveform of the capacitor voltage of the sub-module 1 when the lower tube IGBT is open circuit fault.

[0051] Figure 7 This is the simulation waveform diagram of the maximum information number of the sub-module with the open circuit fault of the lower tube IGBT of sub-module 1. DETAILED DESCRIPTION

[0052] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0053] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0054] Secondly, the present invention is described in detail with reference to schematic diagrams. When describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0055] Furthermore, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0056] Example 1

[0057] Reference Figure 1 This embodiment provides a method for locating an open-circuit fault of an FID submodule IGBT based on MIC. Specifically, the present invention aims at the current research status of an open-circuit fault of an MMC submodule IGBT, analyzes the fault characteristics of the MMC under a submodule fault, and proposes a method for detecting and locating an open-circuit fault of an MMC submodule IGBT in a flexible interconnection device of a medium and low voltage distribution network based on the maximum information number of the submodule capacitor voltage, which can locate the IGBT fault of one or more MMC submodules.

[0058] The present invention is achieved through the following technical solutions:

[0059] When an S1 fault occurs in the submodule, when the bridge arm current is greater than 0, the output voltage of the submodule is consistent with that when no upper tube S1 fault occurs; when the bridge arm current is less than zero, under normal circumstances, the bridge arm current flows through the upper tube S1, and the output voltage is equal to the capacitor voltage; after an open circuit fault occurs in the upper tube S1 of the submodule, the bridge arm current will flow through the lower tube S2, and the SM output voltage is equal to 0 at this time.

[0060] When an S2 fault occurs in the submodule, when the bridge arm current is less than 0, the output voltage of the submodule is consistent with that when no lower tube S2 fault occurs; when the bridge arm current is greater than zero, under normal circumstances, the bridge arm current flows through the lower tube S2 and the output voltage is equal to 0; after an open circuit fault occurs in the lower tube S2 of the submodule, the bridge arm current will flow through the upper tube S1, and at this time the SM output voltage is equal to the capacitor voltage.

[0061] Based on the above analysis, the present invention uses the bridge arm predicted capacitor voltage and the actual capacitor voltage error to perform fault detection and fault type discrimination. The specific principle is as follows:

[0062] In order to simplify the analysis, it is defined that the voltage of each submodule capacitor is completely balanced, which can be achieved by the submodule capacitor voltage balancing solution. Define the capacitor voltage error standard deviation:

[0063]

[0064] Under normal conditions, the normalized capacitor voltage error is close to 0, and is close to 1 or -1 when an IGBT open-circuit fault occurs in the submodule. The threshold Td is defined to identify the health status of the MMC submodule. When the normalized capacitor voltage error is within the predetermined threshold Td, the MMC is in a normal operating state; when the normalized voltage error exceeds the predefined threshold Td, the MMC is in a faulty operating state. A higher Td value will reduce the probability of false alarms caused by transient interference and sampling noise.

[0065] The submodule capacitor voltage balancing solution is as follows:

[0066] The first step is to determine the number of submodules required in the bridge arm;

[0067] The second step is to determine the current state of the bridge arm at this time. If it is in the charging state, the required number of sub-modules with smaller capacitor voltages are put into operation; if it is in the discharging state, the required number of sub-modules with larger capacitor voltages are put into operation.

[0068] The input method is to give a switch trigger signal to the corresponding submodule.

[0069] When an open circuit fault occurs in one arm, the normalized voltage error of the corresponding arm will exceed the threshold value Td. When the threshold is exceeded, the open circuit fault is located in the upper arm, and when When the threshold is exceeded, the open circuit fault is located in the lower arm.

[0070] When the voltage error is close to −1, it indicates that an open circuit fault occurs in the upper tube S1 of the submodule, and when the voltage error is close to 1, it indicates that an open circuit fault occurs in the lower tube S2 of the submodule; therefore, by checking the standardized voltage error, the faulty bridge arm and the submodule IGBT open circuit fault type can be located.

[0071] Since the submodules in the MMC bridge arm are connected in series, an open circuit fault in one submodule and an open circuit fault in other submodules present the same characteristics at the terminal. Therefore, it is impossible to locate the exact faulty submodule by detecting the standard error of the capacitor voltage.

[0072] Fault submodule judgment includes:

[0073] Traverse and calculate the maximum number of information between any two sub-modules;

[0074] Find a type of fault array whose maximum information number is much less than 1;

[0075] The repeated items in the fault array are faulty submodules.

[0076] When an open circuit fault occurs, compared with the capacitor voltage of a normal submodule, the capacitor voltage of the faulty SM will operate abnormally due to the lack of a discharge circuit. Based on the above submodule capacitor voltage characteristics, the present invention proposes a submodule fault locating method based on the maximum information number of the bridge arm submodule capacitor voltage.

[0077] Specifically, capacitor voltage samples are obtained based on a sliding window of a fundamental wave period. In normal operation, the maximum information number of any two capacitor voltages with the same shape and on the same arm will remain close to 1. After an open circuit fault occurs, the capacitor voltage of the faulty submodule will operate abnormally, and the maximum information number between the capacitor of the faulty submodule and the voltage of the normal submodule will become smaller, while the maximum information number between the capacitor voltages of the normal submodules will remain close to 1.

[0078] Furthermore, MIC (maximum information number) measures the relevance of various variables by obtaining the maximum normalized mutual information under different grid divisions, which has high universality and fairness. Therefore, this paper adopts MIC as the relevance measurement standard for variable selection.

[0079] The basis of MIC is mutual information, and the formula of mutual information is:

[0080]

[0081] Where p(x,y) is the joint probability density function of variables x and y, which is difficult to calculate, but MIC can realize the calculation of p(x,y) through discrete methods. Assume that D(x,y) is a finite two-dimensional data set, divide the two-dimensional space into x segments and y segments in the X and Y directions respectively, forming an x´y grid G. Let the set of grids G formed by different division methods be W, then define:

[0082]

[0083] Where D|G represents the distribution of the data set D on the partitioned grid G.

[0084] The maximum normalized mutual information of the data set D under different partitioning methods is used to form the feature matrix M(D), and the element of the feature matrix is ​​defined as:

[0085]

[0086] Then MIC is defined as:

[0087]

[0088] Where B(n) is the upper limit of the number of grid divisions, which is a function of the number of samples in the data set n. Generally, the best effect is achieved when 0.6B(n)=n. The value range of MIC is [0,1]. The correlation coefficient is 1 in the case of perfect linear correlation, and all other cases are some values ​​in the open interval (0,1), indicating the degree of linear correlation between capacitor voltages. When it is close to zero, the relationship is small (closer to no correlation). The closer the coefficient is to 1, the stronger the correlation between capacitor voltages, that is, the larger the MIC value, the stronger the correlation.

[0089] The fault submodule location based on MIC includes:

[0090] Under normal circumstances, due to the series topology and capacitor voltage balance control, the maximum information number of any two capacitor voltages on the same arm is close to 1. Under open circuit fault conditions, the capacitor voltage of the faulty SM behaves abnormally, which means that it is not linearly related to the capacitor voltage of the normal SM.

[0091] Table 1 gives a fault diagnosis table for fault location when N=3 to illustrate the fault location method. For example, when the maximum information numbers among 1, 2, and 3 are all approximately equal to 1, it means that the capacitor voltages of the three are approximately equal, so it can be judged that the state at this time is normal; and when only one of the three maximum information numbers is close to 1, and the other two maximum information numbers are far less than 1, it means that a fault has occurred, and the fault item is the item with the repeated subscript in the two maximum information numbers far less than 1.

[0092] Table 1 Fault diagnosis in upper arm (N=3)

[0093]

[0094] Example 2

[0095] In order to verify the sub-module lower tube IGBT open circuit fault detection and diagnosis method proposed in this paper, a single-phase MMC simulation was carried out in Simulink software. The system parameters are shown in Table 2.

[0096] Table 2 Simulation parameters

[0097]

[0098] Reference Figure 1~2 The first embodiment of the present invention provides a submodule upper tube IGBT open circuit fault detection; submodule 1 is set to have an upper tube IGBT open circuit fault at 0.5s, and the upper bridge arm switch device has an upper tube IGBT open circuit fault result simulation result as shown in the figure. Figure 3~4 As shown. Figure 4 is the actual capacitor voltage of the submodule, Figure 5 It is the waveform diagram of the submodule capacitor voltage MIC.

[0099] from Figure 4 It can be clearly seen that at 0.506s, the capacitor voltage of submodule 1 is 402.7V. From 0.506s onwards, there is a significant difference between the capacitor voltage of submodule 1 and the other capacitor voltages, while the capacitor voltages of the other two submodules are basically the same. Based on the above capacitor voltage characteristics, Figure 5 It can be clearly seen that the maximum information number of the capacitor voltage of submodule 1 and submodule 2 is less than 1, the maximum information number of the capacitor voltage of submodule 1 and submodule 3 is less than 1, the maximum information number of the capacitor voltage of submodule 2 and submodule 3 is approximately equal to 1, and an open circuit fault occurs in submodule 1.

[0100] Reference Figure 1~2 The first embodiment of the present invention provides a submodule lower tube IGBT open circuit fault detection. Set submodule 1 to have a lower tube IGBT open circuit fault at 0.5s, and the upper bridge arm switch device to have a lower tube IGBT open circuit fault. The simulation results are as follows Figures 6 and 7 shown; Figure 6 is the actual capacitor voltage of the submodule, Figure 7 It is the waveform diagram of the submodule capacitor voltage MIC.

[0101] from Figure 6 It can be clearly seen that at 0.5s, the capacitor voltage of submodule 1 is 399.1. V. From 0.5s onwards, there is a significant difference between the capacitor voltage of submodule 1 and the other capacitor voltages, while the capacitor voltages of the other two submodules are basically the same. Based on the above capacitor voltage characteristics, Figure 7 It can be clearly seen that the maximum information number of the capacitor voltage of submodule 1 and submodule 2 is less than 1, the maximum information number of the capacitor voltage of submodule 1 and submodule 3 is less than 1, the maximum information number of the capacitor voltage of submodule 2 and submodule 3 is approximately equal to 1, and an open circuit fault occurs in submodule 1.

[0102] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for locating an open-circuit fault of an FID submodule IGBT based on MIC, characterized in that: include, The faulty bridge arm is located and the fault type is identified based on the difference between the bridge arm output voltage and the predicted voltage; Collect a fundamental wave cycle of the capacitor voltage of the faulty bridge arm submodule; Locate the faulty submodule based on the submodule capacitor voltage MIC value characteristics; The fault bridge arm positioning includes: Define that the voltage of each submodule capacitor is completely balanced, which can be achieved by the submodule capacitor voltage balancing solution; define the capacitor voltage error standard deviation: Under normal conditions, the standard deviation of the capacitor voltage error is close to 0, and close to 1 or -1 when an IGBT open-circuit fault occurs in the submodule; Define the threshold Td to identify the health status of the MMC submodule: When the capacitor voltage error standard deviation is within the predefined threshold value Td, the MMC is in normal working state; When the capacitor voltage error standard deviation exceeds the predefined threshold Td, the MMC is in a faulty operation state; The fault type identification includes: When an open circuit fault occurs in one arm, the standard deviation of the capacitance voltage error of the corresponding arm will exceed the threshold value Td; when When the threshold is exceeded, the open circuit fault is located in the upper arm, and when When the threshold is exceeded, the open circuit fault is located in the lower arm; When the standard deviation of the capacitor voltage error is close to −1, it indicates that an open circuit fault occurs in the upper tube IGBT of the submodule; when the standard deviation of the capacitor voltage error is close to 1, it indicates that an open circuit fault occurs in the lower tube IGBT of the submodule; Fault submodule judgment includes: Traverse and calculate the maximum number of information between any two sub-modules; Find a type of fault array whose maximum information number is much less than 1; The repeated items in the fault array are faulty submodules; The fault submodule positioning includes: Capacitor voltage samples are acquired based on a sliding window of one fundamental wave period. In normal operation, the maximum information number of any two capacitor voltages on the same arm will remain close to 1 with the same shape; After an open circuit fault occurs, the capacitor voltage of the faulty submodule will operate abnormally, and the maximum information number of the capacitor voltage of the faulty submodule and the normal submodule will become smaller.

2. The method for locating an open-circuit fault of an FID submodule IGBT based on MIC according to claim 1, characterized in that: The bridge arm output voltage is calculated based on the submodule capacitor voltage collected by the sensor according to the input state; The predicted voltage difference is calculated by the controller according to the bridge arm current and the submodule input state collected by the sensor; One fundamental wave period of the capacitor voltage of the faulty bridge arm submodule is collected by the sensor and sent to the controller.

3. The method for locating an open-circuit fault of an FID submodule IGBT based on MIC according to claim 2, characterized in that: The submodule capacitor voltage balancing solution includes: Determine the number of submodules required in the bridge arm; The current state of the bridge arm at this time is determined. If it is in a charging state, a required number of sub-modules with a smaller capacitor voltage are put into use; if it is in a discharging state, a required number of sub-modules with a larger capacitor voltage are put into use.

4. The method for locating an open-circuit fault of an FID submodule IGBT based on MIC according to claim 3, characterized in that: When the bridge arm current is greater than 0, the output voltage of the submodule is consistent with that when no upper tube failure occurs; when the bridge arm current is less than zero, under normal circumstances, the bridge arm current flows through the upper tube and the output voltage is equal to the capacitor voltage; after an open circuit failure occurs in the upper tube of the submodule, the bridge arm current will flow through the lower tube. At this time, the output voltage of the submodule is equal to 0, and the upper tube fails.

5. The method for locating an open-circuit fault of an FID submodule IGBT based on MIC according to claim 4, characterized in that: When the bridge arm current is less than 0, the output voltage of the submodule is consistent with that when no lower tube fault occurs; when the bridge arm current is greater than zero, under normal circumstances, the bridge arm current flows through the lower tube and the output voltage is equal to 0; after an open circuit fault occurs in the lower tube of the submodule, the bridge arm current will flow through the upper tube. At this time, the output voltage of the submodule is equal to the capacitor voltage, and the lower tube is faulty.

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