Modular multilevel matrix converter device open-circuit fault diagnosis method and system

Abstract

This invention relates to the field of M3C fault diagnosis technology, and particularly to a method and system for diagnosing open-circuit faults in modular multilevel matrix converter devices. The method involves acquiring capacitor voltages, constructing fault discrimination indicators, and identifying faulty submodules. It calculates the bridge arm current residual; when the residual is greater than a positive threshold, it is diagnosed as a Type I fault; when it is less than a negative threshold, it is diagnosed as a Type II fault, and a faulty switch pair is identified. After identifying the faulty switch pair, a preset bypass switch state test signal corresponding to the faulty switch pair type is briefly injected into the faulty submodule, and the trend of the residual is calculated. This uniquely identifies the specific device experiencing the open-circuit fault. Based on the M3C topology, this method designs a new state equation model, which can achieve accurate tracking of bridge arm currents with small errors, enabling rapid and accurate location of faulty power devices.

Description

Technical Field

[0001] This invention relates to the field of M3C fault diagnosis technology, and in particular to a method and system for diagnosing open-circuit faults in modular multilevel matrix converter devices. Background Technology

[0002] Modular multilevel matrix converters (M3Cs), with their excellent modularity, high voltage level adaptability, and four-quadrant operation, have become the core topology for high-voltage, high-power applications such as low-frequency power transmission and offshore wind power grid connection. M3Cs consist of nine bridge arms and numerous cascaded full-bridge submodules. While the large number of power devices improves power quality, it also significantly increases the probability of system failure. As one of the most vulnerable power devices, an open-circuit fault in an IGBT, although not immediately causing overcurrent shutdown, can lead to submodule capacitor voltage imbalance, output current distortion, and increased system stress. If not addressed promptly, this can result in serious secondary faults. Therefore, developing a fast, robust fault diagnosis strategy that can accurately pinpoint specific switching transistors is crucial for the stable operation of M3Cs. Existing fault diagnosis methods for M3Cs include data-driven and model-based approaches. In recent years, artificial intelligence algorithms, represented by convolutional neural networks and long short-term memory networks, have been introduced into the field of fault diagnosis. By mining deep features of current or voltage waveforms, high diagnostic accuracy has been achieved without relying on precise system parameters. However, data-driven methods are often accompanied by complex computations and are highly sensitive to the completeness of training data. In systems like the M3C with complex dynamic characteristics, obtaining a fault sample set covering all operating conditions remains an unsolved problem. Model-based methods have attracted considerable attention due to their lack of additional hardware requirements and clear physical meaning. These methods typically use observers or analytical models to estimate the system's state variables and identify faults by comparing the residuals generated by the estimates with the actual values. Most existing model-based methods can only locate faulty submodules or faulty switch pairs, failing to achieve precise location of specific power devices. Summary of the Invention

[0003] This invention aims to at least solve one of the technical problems existing in related technologies. To this end, this invention provides a method and system for diagnosing open-circuit faults in modular multilevel matrix converter devices, which achieves accurate tracking of bridge arm currents with small errors, and enables rapid and accurate location of faulty power devices.

[0004] This invention provides a method for diagnosing open-circuit faults in power devices of a modular multilevel matrix converter, comprising: S1: Collect the capacitor voltage of each sub-module on the bridge arm to be diagnosed, construct a fault discrimination index for each sub-module based on the capacitor voltage, compare the fault discrimination index values ​​of each sub-module, and determine the sub-module corresponding to the smallest fault discrimination index value as the fault sub-module. S2: Calculate the theoretical value of the arm current based on the current switch status and grid operating conditions. Calculate the arm current residual based on the actual collected arm current and the theoretical value of the arm current. When the arm current residual is greater than the positive threshold, it is diagnosed as a Type I fault and determined to be a faulty switch pair. When the arm current residual is less than the negative threshold, it is diagnosed as a Type II fault and determined to be a faulty switch pair. S3: After identifying the faulty switch pair, a preset bypass switch state test signal corresponding to the type of the faulty switch pair is injected into the faulty submodule for a short time. The bridge arm current residual data sequence is collected within the injection window, and the trend of the residual within the injection interval is calculated. Based on the sign polarity of the trend and the fault type of the switch pair, the specific device that has experienced an open circuit fault is determined.

[0005] According to the present invention, a method for diagnosing open-circuit faults in power devices of a modular multilevel matrix converter is provided, wherein the calculation process of the fault discrimination index is as follows: in, Let m be the fault detection index for the m-th submodule. Let be the total number of submodules, i be the ordinal number of the first submodule, j be the ordinal number of the second submodule, and m be the ordinal number of the submodule. Let be the capacitor voltage of the i-th submodule. Let be the capacitor voltage of the j-th submodule.

[0006] According to the present invention, a method for diagnosing open-circuit faults in power devices of a modular multilevel matrix converter is provided, and the process of step S2 is as follows: S21: The current in the arm branch is calculated based on the current state equation of the M3C arm. S22: Define the current sign variable according to the current of the bridge arm branch; S23: Calculate the bridge arm voltage based on the current sign variable and the effective operating state; S24: Calculate the theoretical value of the bridge arm current based on the bridge arm voltage, calculate the bridge arm current residual based on the theoretical value of the bridge arm current and the actual collected bridge arm current, and compare and diagnose the fault switch pair.

[0007] According to the present invention, a method for diagnosing open-circuit faults in power devices of a modular multilevel matrix converter is provided, wherein the calculation formula for the M3C bridge arm current state equation is as follows: in, The three bridge arms connected to the output voltage, representing the inductance value, are defined as a sub-converter Y. Let Y be the current in the first branch corresponding to the sub-converter Y. The input-side voltage source voltage, For the resistance value, This represents the voltage of the first branch corresponding to sub-converter Y. This represents the current in the second branch corresponding to sub-converter Y. This refers to the third branch current corresponding to sub-converter Y. This is the voltage of the second branch corresponding to sub-converter Y. This is the voltage of the third branch corresponding to the sub-converter Y.

[0008] According to the method for diagnosing open-circuit faults in power devices of a modular multilevel matrix converter provided by the present invention, the calculation formula for step S22 is as follows: in, Let x be the current sign variable of the xth branch of the sub-converter connected to the yth phase output voltage source. Let x be the current sign variable of the x-th branch of the sub-converter connected to the y-th phase output voltage source at the previous time step, where y is the output voltage source ordinal number and x is the branch ordinal number. Let x be the current in the x-th branch of the sub-converter connected to the output voltage source of phase y. The anti-jitter threshold is defined as follows: u is the first phase output voltage source, v is the second phase output voltage source, w is the third phase output voltage source, a is the first branch, b is the second branch, and c is the third branch.

[0009] According to the present invention, a method for diagnosing open-circuit faults in power devices of a modular multilevel matrix converter is provided, wherein the method for calculating the bridge arm voltage is as follows: in, This represents the current-weighted level number. Let be the capacitor voltage of the m-th submodule. The output voltage of the m-th submodule in the x-th branch of the sub-converter connected to the output voltage source of the y-th phase is... This is the drive signal for the first power device in the submodule. This is the drive signal for the second power device in the submodule. This is the drive signal for the third power device in the submodule. This is the drive signal for the fourth power device in the submodule.

[0010] According to the method for diagnosing open-circuit faults in power devices of a modular multilevel matrix converter provided by the present invention, the process of step S24 is as follows: S241: The formula for calculating the bridge arm current residual is as follows: in, For the bridge arm current residual, This is the calculated value for the bridge arm current; S242: Determine the fault type based on the bridge arm current residual and identify the fault switch pair: in, The fault judgment thresholds are: Type I faults are faults of the first and fourth transistors, and Type II faults are faults of the second and third transistors.

[0011] According to the present invention, a method for diagnosing open-circuit faults in power devices of a modular multilevel matrix converter includes step S3 as follows: When the fault switch identifies a Type I fault, it injects test signals into the fault submodule within the interval where the bridge arm current is less than zero. These signals turn on the first transistor T1 and the third transistor T3, and turn off the second transistor T2 and the fourth transistor T4. By analyzing the trend of the residual within the injected interval, it distinguishes between the fault of the first transistor T1 and the fault of the fourth transistor T4. If the trend of the residual is greater than or equal to 0, the faulty device is determined to be the first transistor T1. If the trend of the residual is less than 0, the faulty device is determined to be the fourth transistor T4. When the fault switch is identified as a Type II fault, a test signal is injected into the fault submodule within the range where the bridge arm current is greater than zero. This signal turns on the second transistor T2 and the fourth transistor T4, and turns off the first transistor T1 and the third transistor T3. By analyzing the trend of the residual within the injected range, the faults of the second transistor T2 and the third transistor T3 are distinguished. If the trend of the residual is greater than or equal to 0, the faulty device is determined to be the third transistor T3. If the trend of the residual is less than 0, the faulty device is determined to be the second transistor T2.

[0012] According to the present invention, a method for diagnosing open-circuit faults in power devices of a modular multilevel matrix converter is provided, wherein the method for calculating the trend of the residual is as follows: S31: At a fixed length Collect bridge arm current residual data sequence within the injection window of each sampling point; S32: Select the first few steps of the residual sequence respectively Each sampling point and subsequent The mean is calculated for each sampling point; γ is defined as the proportion of the mean window within the injection interval: Mean of the first-stage residuals The calculation formula is: Mean of residuals in the later stage The calculation formula is: in, This represents the number of sampling points in the mean window between the preceding and following segments. This is a sequence of current residual sampling data. The sampling sequence number; S33: Define the trend of the residual as The calculation formula is: .

[0013] This invention also provides a modular multilevel matrix converter power device open-circuit fault diagnosis system, comprising: Fault Submodule Judgment Module: Used to collect the capacitor voltage of each submodule on the bridge arm to be diagnosed, construct a fault discrimination index for each submodule based on the capacitor voltage, compare the fault discrimination index values ​​of each submodule, and determine the submodule with the smallest fault discrimination index value as the fault submodule. Fault switch pair judgment module: It is used to calculate the theoretical value of the arm current based on the current switch status and power grid operating conditions, and calculate the arm current residual based on the actual collected arm current and the theoretical value of the arm current. When the arm current residual is greater than the positive threshold, it is diagnosed as a type I fault and determined as a fault switch pair. When the arm current residual is less than the negative threshold, it is diagnosed as a type II fault and determined as a fault switch pair. Fault Device Judgment Module: After identifying a faulty switch pair, it briefly injects a preset bypass switch state test signal corresponding to the type of the faulty switch pair into the fault submodule, collects the bridge arm current residual data sequence within the injection window, calculates the trend of the residual within the injection interval, and determines the specific device that has experienced an open circuit fault based on the sign polarity of the trend and the fault type of the switch pair.

[0014] The above-described one or more technical solutions in the embodiments of the present invention have at least one of the following technical effects: (1) The method proposed in this invention does not require additional sensors; diagnosis can be completed using existing sensors, which can effectively reduce costs and can be directly applied to existing M3C systems. Compared with detection methods that require additional hardware, it can effectively reduce system costs.

[0015] (2) The fault diagnosis method proposed in this paper adopts a hierarchical and progressive diagnostic approach, proceeding step by step in the order of fault submodule location, fault switch location, and specific power device location. This makes the diagnostic objectives and criteria clear at each step, thereby avoiding a single criterion from undertaking multiple diagnostic tasks simultaneously and reducing the risk of misdiagnosis.

[0016] (3) The present invention can quickly lock the faulty device in a relatively short control cycle and complete the diagnosis before the overvoltage or overcurrent causes physical damage to the device. This not only minimizes the impact of the fault on the system, but also significantly improves the stability of M3C, saving time for subsequent fault-tolerant control strategies.

[0017] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a flowchart illustrating a method for diagnosing open-circuit faults in power devices of a modular multilevel matrix converter.

[0020] Figure 2 This is the topology diagram of M3C.

[0021] Figure 3 This is a waveform diagram of the capacitor voltage of the three sub-modules after a Type I fault occurs in the power device of the bridge arm.

[0022] Figure 4 This is a waveform diagram of the capacitor voltage of the three sub-modules after the power device of the Type II fault bridge arm fails.

[0023] Figure 5 The waveform diagram shows the bridge arm of the M3C experiencing a Type I fault.

[0024] Figure 5 (a) is the current waveform of the bridge arm when a type I fault occurs in M3C.

[0025] Figure 5 (b) is the residual waveform of the bridge arm current when a Type I fault occurs in M3C.

[0026] Figure 6 The waveform diagram of the bridge arm when the M3C experiences a type II fault.

[0027] Figure 6 (a) is the current waveform of the bridge arm when M3C experiences a type II fault.

[0028] Figure 6 (b) is the residual waveform of the bridge arm current when M3C experiences a type II fault.

[0029] Figure 7 The waveform diagram is shown after the second transistor T2 experiences an open-circuit fault.

[0030] Figure 7 (a) is the capacitor voltage waveform after the second transistor T2 experiences an open-circuit fault.

[0031] Figure 7 (b) is a waveform diagram of the fault identification index of the submodule after the second transistor T2 has an open circuit fault.

[0032] Figure 7 (c) is a submodule fault flag bitmap after the second transistor T2 experiences an open-circuit fault.

[0033] Figure 7 (d) is the waveform diagram of the switch to the fault flag bit after the second transistor T2 has an open circuit fault.

[0034] Figure 7 (e) is the current diagram after the second transistor T2 experiences an open-circuit fault.

[0035] Figure 7 The diagram in (f) shows the residual waveform of the bridge arm current after the second transistor T2 experiences an open-circuit fault.

[0036] Figure 7 (g) is a partial enlarged view of the bridge arm current residual waveform after the second transistor T2 experiences an open-circuit fault.

[0037] Figure 7 The middle (h) is the fault flag bitmap of the switching transistor after the second transistor T2 has an open circuit fault.

[0038] Figure 8 This is a block diagram of a modular multilevel matrix converter power device open-circuit fault diagnosis system.

[0039] Figure label: 101. Fault submodule judgment module; 102. Fault switch pair judgment module; 103. Fault device judgment module. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. The following embodiments are used to illustrate this invention but cannot be used to limit the scope of this invention.

[0041] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0042] The following is combined with Figures 1 to 8 This invention is described.

[0043] Example like Figure 1 As shown, Figure 1 A flowchart illustrating a method for diagnosing open-circuit faults in power devices of a modular multilevel matrix converter is shown, including: S1: Collect the capacitor voltage of each sub-module on the bridge arm to be diagnosed, construct a fault discrimination index for each sub-module based on the capacitor voltage, compare the fault discrimination index values ​​of each sub-module, and determine the sub-module corresponding to the smallest fault discrimination index value as the fault sub-module. S2: Calculate the theoretical value of the arm current based on the current switch status and grid operating conditions. Calculate the arm current residual based on the actual collected arm current and the theoretical value of the arm current. When the arm current residual is greater than the positive threshold, it is diagnosed as a Type I fault and determined to be a faulty switch pair. When the arm current residual is less than the negative threshold, it is diagnosed as a Type II fault and determined to be a faulty switch pair. S3: After identifying the faulty switch pair, a preset bypass switch state test signal corresponding to the type of the faulty switch pair is injected into the faulty submodule for a short time. The bridge arm current residual data sequence is collected within the injection window, and the trend of the residual within the injection interval is calculated. Based on the sign polarity of the trend and the fault type of the switch pair, the specific device that has experienced an open circuit fault is determined.

[0044] Specifically, such as Figure 2As shown, Figure 2 The main circuit topology of a modular multilevel matrix converter (M3C) constructed from nine symmetrical bridge arms is shown, directly connecting the three-phase input power supply and the three-phase output power supply. Each bridge arm connecting the input and output phases includes a bridge arm inductor and N=3 cascaded full-bridge submodules. Variable u xy and i xy These represent the combined output voltage and instantaneous bridge arm current of the bridge arm, respectively. , The full-bridge submodule is the core power unit of the M3C, and its topology is as follows: Figure 1 As shown. Each submodule contains a DC capacitor and two half-bridge branches consisting of four insulated-gate bipolar transistors (transistor T1, transistor T2, transistor T3, and transistor T4) and their anti-parallel diodes (diodes D1, D2, D3, and D4). To avoid capacitor short circuits and damage to power devices, the upper and lower switches of the same half-bridge branch are controlled by complementary gate drive signals. SM represents the submodule, SM1-SM2. k This represents the first to the kth submodules. The total number of submodules.

[0045] Specifically, the calculation process for the fault identification index is as follows: in, Let be the fault detection index for the m-th submodule, where i is the ordinal number of the first submodule, j is the ordinal number of the second submodule, and m is the ordinal number of the submodule. Let be the capacitor voltage of the i-th submodule. Let be the capacitor voltage of the j-th submodule.

[0046] like Figure 3 and Figure 4 As shown, when an open-circuit fault occurs in a submodule IGBT, the faulty submodule is first located. Due to the unidirectional blocking effect of the faulty bridge arm current path, the capacitor voltage of the faulty submodule will exhibit characteristics of continuous accumulation or abnormal fluctuation, resulting in a significant deviation from the voltage trajectory of the healthy submodules. Based on the physical characteristic that the voltages of healthy submodules are highly consistent while the voltages of faulty submodules deviate, this embodiment proposes a location algorithm based on voltage cross-validation.

[0047] in, This reflects the voltage consistency of the remaining submodules after removing the m-th submodule. When the removed submodule is a faulty submodule, the remaining submodules are all healthy submodules, with the lowest voltage dispersion. The minimum value is obtained. Therefore, the location of the faulty submodule can be determined. In this method, the submodules in each arm of the bridge are k=3, then: According to the above definition, for a bridge arm containing three submodules, when the first submodule fails, the capacitor voltages of the remaining two healthy submodules... and It still maintains a high degree of consistency, therefore the corresponding deviation index This will converge to a minimum (ideally close to zero). Conversely, the deviation index involving the faulty submodule will increase significantly. Similarly, when the second or third submodule fails, the following will occur: or To obtain the minimum value. Therefore, the criterion for locating the faulty submodule can be expressed as: finding the set of indicators { , , The minimum value in the interval} is used, and the index m corresponding to this minimum value is the number of the faulty submodule. This method requires no additional sensors and can achieve rapid location using only existing capacitor voltage sampling values.

[0048] Specifically, the process of step S2 is as follows: S21: The current in the arm branch is calculated based on the current state equation of the M3C arm. S22: Define the current sign variable according to the current of the bridge arm branch; S23: Calculate the bridge arm voltage based on the current sign variable and the effective operating state; S24: Calculate the theoretical value of the bridge arm current based on the bridge arm voltage, calculate the bridge arm current residual based on the theoretical value of the bridge arm current and the actual collected bridge arm current, and compare and diagnose the fault switch pair.

[0049] The formula for calculating the current state equation of the M3C bridge arm is as follows: in, The three bridge arms connected to the output voltage, representing the inductance value, are defined as a sub-converter Y. Let Y be the current in the first branch corresponding to the sub-converter Y. The input-side voltage source voltage, For the resistance value, This represents the voltage of the first branch corresponding to sub-converter Y. This represents the current in the second branch corresponding to sub-converter Y. This refers to the third branch current corresponding to sub-converter Y. This is the voltage of the second branch corresponding to sub-converter Y. This is the voltage of the third branch corresponding to the sub-converter Y.

[0050] Specifically, the calculation formula for step S22 is as follows: in, Let x be the current sign variable of the xth branch of the sub-converter connected to the yth phase output voltage source. Let x be the current sign variable of the x-th branch of the sub-converter connected to the y-th phase output voltage source at the previous time step, where y is the output voltage source ordinal number and x is the branch ordinal number. Let x be the current in the x-th branch of the sub-converter connected to the output voltage source of phase y. The anti-jitter threshold is defined as follows: u is the first phase output voltage source, v is the second phase output voltage source, w is the third phase output voltage source, a is the first branch, b is the second branch, and c is the third branch.

[0051] Specifically, the calculation method for the bridge arm voltage is as follows: in, This represents the current-weighted level number. Let be the capacitor voltage of the m-th submodule. The output voltage of the m-th submodule in the x-th branch of the sub-converter connected to the output voltage source of the y-th phase is... This is the drive signal for the first power device in the submodule. This is the drive signal for the second power device in the submodule. This is the drive signal for the third power device in the submodule. This is the drive signal for the fourth power device in the submodule.

[0052] Specifically, the process of step S24 is as follows: S241: The formula for calculating the bridge arm current residual is as follows: in, For the bridge arm current residual, This is the calculated value for the bridge arm current; S242: Determine the fault type based on the bridge arm current residual and identify the fault switch pair: in, The fault judgment thresholds are: Type I faults are faults of the first and fourth transistors, and Type II faults are faults of the second and third transistors.

[0053] The trend of the residual current after T1 fault is as follows Figure 5 As shown, Figure 5 Figure (a) shows the current waveform of the bridge arm when a type I fault occurs in the M3C. Figure 5 Figure (b) shows the residual waveform of the bridge arm current during a Type I fault in the M3C. It can be seen that the residual increases when the bridge arm current is less than 0 and gradually decreases when the bridge arm current is greater than 0. The residual changes rapidly, with an overall trend greater than 0. After detecting a faulty submodule, the fault switch can be quickly detected. The fourth transistor T4, like T1, suffers a Type I fault, and its residual trend is similar to that of T1. When the residual exceeds the threshold... When a Type I fault occurs, it is diagnosed as a Type I fault. After a Type II fault occurs, the analysis is the same as above; the residual trend of T2 during an open-circuit fault is as follows. Figure 6 As shown, Figure 6 (a) is the current waveform of the bridge arm when a type II fault occurs in M3C. Figure 6 (b) is the residual waveform of the arm current during a Type II fault in the M3C. When the residual is less than the threshold... At that time, it was diagnosed as a Type II fault.

[0054] Specifically, step S3 includes: When the fault switch identifies a Type I fault, it injects test signals to turn on T1 and the third transistor T3, and turn off T2 and the fourth transistor T4 into the fault submodule within the interval where the bridge arm current is less than zero. By analyzing the trend of the residual within the injected interval, it distinguishes between the T1 fault and the fourth transistor T4 fault. If the trend of the residual is greater than or equal to 0, the faulty device is determined to be T1; if the trend of the residual is less than 0, the faulty device is determined to be the fourth transistor T4. When the fault switch is identified as a Type II fault, test signals are injected into the fault submodule within the range where the bridge arm current is greater than zero. These signals enable T2 and the fourth transistor T4, and disable T1 and the third transistor T3. By analyzing the trend of the residual within the injected range, the faults of T2 and the third transistor T3 are distinguished. If the trend of the residual is greater than or equal to 0, the faulty device is determined to be the third transistor T3. If the trend of the residual is less than 0, the faulty device is determined to be T2.

[0055] The specific method for calculating the trend of the residual is as follows: S31: At a fixed length Collect bridge arm current residual data sequence within the injection window of each sampling point; S32: Select the first few steps of the residual sequence respectively Each sampling point and subsequent Calculate the mean value from each sampling point; define... The percentage of the mean window injected within the interval: In particular, with As the value increases, the robustness of the residual mean calculation increases, but... The larger the value, the smaller the effective separation between the two segments, and the less obvious the trend of residual change will be. The effect is best when the value is 0.25.

[0056] Mean of the first-stage residuals The calculation formula is: Mean of residuals in the later stage The calculation formula is: in, This represents the number of sampling points in the mean window between the preceding and following segments. This is a sequence of current residual sampling data. The sampling sequence number; S33: Define the trend of the residual as The calculation formula is: .

[0057] When the switch T2 in the first submodule of bridge arm 1 experiences an open-circuit fault, the experimental results are as follows: Figure 7 As shown in (a)-(h), where, This refers to the current in the first branch of the sub-converter connected to the first phase output voltage source. This is the calculated value of the bridge arm current for the first branch of the first phase output voltage source. The bridge arm current residual of the first branch of the first phase output voltage source, when the submodule is in negative input mode and When the current is >0, the current cannot flow through T2, the original current path is disrupted, and the current can only flow through the anti-parallel diodes D1 and T3. At this time, the submodule output voltage is 0, and the SM capacitor neither charges nor discharges. When the submodule is in the cut-off (T2, fourth transistor T4 is on) working mode and... When the current is greater than 0, the current cannot flow through T2, disrupting the original current path. The current can only flow through the anti-parallel diode D1, the capacitor, and the anti-parallel diode D4. At this time, the submodule output voltage is high, and the capacitor is in a charging state. In summary, when the bridge arm current is greater than 0, the fault will affect the normal operation of the M3C. The fault will cause abnormal charging and discharging of the capacitor, resulting in a capacitor voltage higher than the other two submodules, such as... Figure 7 As shown, the deviation index at this time It converges to a minimum value, and the other two deviation indices increase significantly, such as Figure 7 As shown, at this time, the positioning submodule 1 malfunctions, and the submodule fault flag F is set. smSet it to 1, and then enter the bridge arm current calculation module through the enable module. This way, only one bridge arm current needs to be calculated, greatly reducing the computational load of this method. From Figure 7 As can be seen, before the fault occurred at T2, the calculated value of the bridge arm current closely followed the actual value, and the current residual remained near 0. After the fault occurred at T2, in the fault-sensitive region, the flow path of the actual value of the bridge arm current was disrupted, the current residual rapidly increased negatively, and exceeded the threshold. At this time, the switch sets the fault flag F. S Setting it to 2 indicates a Type II fault. The switch is set to fault flag F. S After setting to 2, the switch signal injection program is immediately started, injecting a (0101) signal for 0.05 cycles. Within the signal injection interval, the absolute value of the current residual continues to increase. <0 indicates that an open-circuit fault has been diagnosed in switch T2 within a very short time, and the switch fault flag F is set. r Setting 2, overall diagnosis time It takes 3.72ms.

[0058] like Figure 8 As shown below, a modular multilevel matrix converter power device open-circuit fault diagnosis system provided by the present invention will be described. The modular multilevel matrix converter power device open-circuit fault diagnosis system described below can be referred to in correspondence with the modular multilevel matrix converter power device open-circuit fault diagnosis method described above.

[0059] Fault Submodule Judgment Module 101: Used to collect the capacitor voltage of each submodule on the bridge arm to be diagnosed, construct a fault discrimination index for each submodule based on the capacitor voltage, compare the fault discrimination index values ​​of each submodule, and determine the submodule corresponding to the smallest fault discrimination index value as the fault submodule. Fault switch pair judgment module 102: It is used to calculate the theoretical value of the bridge arm current based on the current switch status and power grid operating conditions, and to calculate the bridge arm current residual based on the actual collected bridge arm current and the theoretical value of the bridge arm current. When the bridge arm current residual is greater than the positive threshold, it is diagnosed as a type I fault and determined as a fault switch pair. When the bridge arm current residual is less than the negative threshold, it is diagnosed as a type II fault and determined as a fault switch pair. Fault Device Judgment Module 103: After identifying a faulty switch pair, it briefly injects a preset bypass switch state test signal corresponding to the type of the faulty switch pair into the fault submodule, collects the bridge arm current residual data sequence within the injection window, calculates the trend of the residual within the injection interval, and determines the specific device that has experienced an open circuit fault based on the sign polarity of the trend and the fault type of the switch pair.

[0060] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0061] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0063] It should be noted that the embodiments of this disclosure can be implemented using hardware, software, or a combination of both. The hardware portion can be implemented using dedicated logic; the software portion can be stored in memory and executed by a suitable instruction execution system, such as a microprocessor or dedicated-design hardware. Those skilled in the art will understand that the above-described devices and methods can be implemented using computer-executable instructions and / or included in processor control code, for example, such code provided on a programmable memory or a data carrier such as an optical or electronic signal carrier.

[0064] Furthermore, although the operation of the methods of this disclosure is described in a specific order in the accompanying drawings, this does not require or imply that these operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. Rather, the steps depicted in the flowcharts may be performed in a different order. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps. It should also be noted that the features and functions of two or more devices according to this disclosure may be embodied in one device. Conversely, the features and functions of one device described above may be further divided and embodied by multiple devices.

[0065] While this disclosure has been described with reference to several specific embodiments, it should be understood that this disclosure is not limited to the specific embodiments disclosed. This disclosure is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A method for diagnosing open-circuit faults in power devices of a modular multilevel matrix converter, characterized in that, include: S1: Collect the capacitor voltage of each sub-module on the bridge arm to be diagnosed, construct a fault discrimination index for each sub-module based on the capacitor voltage, compare the fault discrimination index values ​​of each sub-module, and determine the sub-module corresponding to the smallest fault discrimination index value as the fault sub-module. S2: Calculate the theoretical value of the arm current based on the current switch status and grid operating conditions. Calculate the arm current residual based on the actual collected arm current and the theoretical value of the arm current. When the arm current residual is greater than the positive threshold, it is diagnosed as a Type I fault and determined to be a faulty switch pair. When the arm current residual is less than the negative threshold, it is diagnosed as a Type II fault and determined to be a faulty switch pair. The formula for calculating the bridge arm current residual is as follows: in, Let x be the current in the x-th branch of the sub-converter connected to the y-th phase output voltage source, where y is the output voltage source number and x is the branch number. For the bridge arm current residual, This is the calculated value for the bridge arm current; The fault type is determined based on the bridge arm current residual, and the fault switch pair is identified: in, The fault judgment thresholds are: Type I faults are faults of the first and fourth transistors, and Type II faults are faults of the second and third transistors. S3: After identifying the faulty switch pair, a preset bypass switch state test signal corresponding to the type of the faulty switch pair is injected into the faulty submodule for a short time. The bridge arm current residual data sequence is collected within the injection window, and the trend of the residual within the injection interval is calculated. Based on the sign polarity of the trend and the fault type of the switch pair, the specific device experiencing the open-circuit fault is determined. Step S3 includes: When the fault switch is identified as a Type I fault, test signals are injected into the fault submodule within the interval where the bridge arm current is less than zero. These signals turn on the first transistor T1 and the third transistor T3, and turn off the second transistor T2 and the fourth transistor T4. By analyzing the trend of the residual within the injected interval, the faults of the first transistor T1 and the fourth transistor T4 are distinguished. If the trend of the residual is greater than or equal to 0, the faulty device is determined to be the first transistor T1. If the trend of the residual is less than 0, the faulty device is determined to be the fourth transistor T4. When the fault switch is identified as a Type II fault, test signals are injected into the fault submodule within the range where the bridge arm current is greater than zero. These signals turn on the second transistor T2 and the fourth transistor T4, and turn off the first transistor T1 and the third transistor T3. By analyzing the trend of the residual within the injected range, the faults of the second transistor T2 and the third transistor T3 are distinguished. If the trend of the residual is greater than or equal to 0, the faulty device is determined to be the third transistor T3. If the trend of the residual is less than 0, the faulty device is determined to be the second transistor T2. The specific method for calculating the trend of the residual is as follows: S31: At a fixed length Collect bridge arm current residual data sequence within the injection window of each sampling point; S32: Select the first few steps of the residual sequence respectively Each sampling point and subsequent The mean is calculated for each sampling point; γ is defined as the proportion of the mean window within the injection interval: Mean of the first-stage residuals The calculation formula is: Mean of residuals in the later stage The calculation formula is: in, This represents the number of sampling points in the mean window between the preceding and following segments. This is a sequence of current residual sampling data. The sampling sequence number; S33: Define the trend of the residual as The calculation formula is: 。 2. The method for diagnosing open-circuit faults in power devices of a modular multilevel matrix converter according to claim 1, characterized in that, The calculation process for the fault discrimination index is as follows: in, Let m be the fault detection index for the m-th submodule. Let be the total number of submodules, i be the ordinal number of the first submodule, j be the ordinal number of the second submodule, and m be the ordinal number of the submodule. Let be the capacitor voltage of the i-th submodule. Let be the capacitor voltage of the j-th submodule.

3. The method for diagnosing open-circuit faults in power devices of a modular multilevel matrix converter according to claim 2, characterized in that, The process for step S2 is as follows: S21: The current in the arm branch is calculated based on the current state equation of the M3C arm. S22: Define the current sign variable according to the current of the bridge arm branch; S23: Calculate the bridge arm voltage based on the current sign variable and the effective operating state; S24: Calculate the theoretical value of the bridge arm current based on the bridge arm voltage, calculate the bridge arm current residual based on the theoretical value of the bridge arm current and the actual collected bridge arm current, and compare and diagnose the fault switch pair.

4. The method for diagnosing open-circuit faults in power devices of a modular multilevel matrix converter according to claim 3, characterized in that, The formula for calculating the M3C bridge arm current state equation is as follows: in, The three bridge arms connected to the output voltage, representing the inductance value, are defined as a sub-converter Y. Let Y be the current in the first branch corresponding to the sub-converter Y. The input-side voltage source voltage, For the resistance value, This represents the voltage of the first branch corresponding to sub-converter Y. This represents the current in the second branch corresponding to sub-converter Y. This refers to the third branch current corresponding to sub-converter Y. This is the voltage of the second branch corresponding to sub-converter Y. This is the voltage of the third branch corresponding to the sub-converter Y.

5. The method for diagnosing open-circuit faults in power devices of a modular multilevel matrix converter according to claim 4, characterized in that, The calculation formula for step S22 is as follows: in, Let x be the current sign variable of the xth branch of the sub-converter connected to the yth phase output voltage source. Let x be the current sign variable of the x-th branch of the sub-converter connected to the y-th phase output voltage source at the previous time step, where y is the output voltage source ordinal number and x is the branch ordinal number. Let x be the current in the x-th branch of the sub-converter connected to the output voltage source of phase y. The anti-jitter threshold is defined as follows: u is the first phase output voltage source, v is the second phase output voltage source, w is the third phase output voltage source, a is the first branch, b is the second branch, and c is the third branch.

6. The method for diagnosing open-circuit faults in power devices of a modular multilevel matrix converter according to claim 5, characterized in that, The method for calculating the bridge arm voltage is as follows: in, This represents the current-weighted level number. Let be the capacitor voltage of the m-th submodule. The output voltage of the m-th submodule in the x-th branch of the sub-converter connected to the output voltage source of the y-th phase is... This is the drive signal for the first power device in the submodule. This is the drive signal for the second power device in the submodule. This is the drive signal for the third power device in the submodule. This is the drive signal for the fourth power device in the submodule.

7. A modular multilevel matrix converter power device open-circuit fault diagnosis system, used to execute the modular multilevel matrix converter power device open-circuit fault diagnosis method as described in any one of claims 1 to 6, characterized in that, include: Fault Submodule Judgment Module: Used to collect the capacitor voltage of each submodule on the bridge arm to be diagnosed, construct a fault discrimination index for each submodule based on the capacitor voltage, compare the fault discrimination index values ​​of each submodule, and determine the submodule with the smallest fault discrimination index value as the fault submodule. Fault switch pair judgment module: It is used to calculate the theoretical value of the arm current based on the current switch status and power grid operating conditions, and calculate the arm current residual based on the actual collected arm current and the theoretical value of the arm current. When the arm current residual is greater than the positive threshold, it is diagnosed as a type I fault and determined as a fault switch pair. When the arm current residual is less than the negative threshold, it is diagnosed as a type II fault and determined as a fault switch pair. Fault device judgment module: After identifying the fault switch pair, it briefly injects a preset bypass switch state test signal corresponding to the type of the fault switch pair into the fault submodule, collects the bridge arm current residual data sequence within the injection window, and calculates the trend of the residual within the injection interval. Based on the sign polarity of the trend quantity and the fault type of the switch pair, the specific device that experienced an open-circuit fault is determined.

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