Method and Device for Open-Circuit Fault Diagnosis of Half-Bridge Submodule in Three-Phase MMC System Based on dq Coordinate Transformation

Abstract

This invention discloses a method and apparatus for diagnosing open-circuit faults in half-bridge submodules of a three-phase MMC system based on dq coordinate transformation. The method includes: acquiring the capacitor voltage of half-bridge submodules located at the same position in each phase of the three-phase MMC system and performing dq coordinate transformation to obtain d-axis and q-axis components; constructing complex numbers using the d-axis and q-axis components as imaginary and real parts respectively, and calculating the magnitude and principal argument of the complex numbers; determining whether a half-bridge submodule fault exists by checking if the magnitude of the complex number is greater than or equal to a threshold; if a half-bridge submodule fault occurs, identifying the faulty phase by determining the interval of the principal argument of the corresponding complex number, and determining the faulty submodule and normal submodule within the faulty phase; and determining the fault type by the consistency of the intervals of the principal argument of the complex numbers corresponding to the faulty and normal submodules. This invention requires no additional sensors and has high detection accuracy.

Description

Technical Field

[0001] This invention relates to the field of fault diagnosis, specifically to a method and apparatus for diagnosing open-circuit faults in a half-bridge submodule of a three-phase MMC system based on dq coordinate transformation. Background Technology

[0002] Thanks to the highly modular power units, modular multilevel converters (MMCs) offer advantages over other multilevel circuits, including ease of redundancy and maintenance, low output voltage harmonic content, and small output filter size. However, the cascading of numerous modular power units means that a failure in the switching devices of even one submodule can affect the normal operation of the entire system and equipment safety. Therefore, analyzing open-circuit faults in MMC systems and researching fault diagnosis methods is of great significance.

[0003] Currently, methods for diagnosing open-circuit faults in submodules of modular multilevel converters can be mainly categorized into signal processing-based methods, mathematical model-based methods, and artificial intelligence-based methods. Signal processing-based methods often require additional hardware circuitry to acquire extra circuit signals to aid in diagnosis and fault location, increasing circuit complexity and diagnostic costs. Mathematical model-based methods are susceptible to limitations in model accuracy, and robustness and diagnostic accuracy are key issues that need to be addressed. Artificial intelligence-based methods typically require extensive offline data training and place high performance demands on the core controller.

[0004] Therefore, there is a need for a method to diagnose open-circuit faults in MMC system submodules that requires no additional sensor configuration, does not have high requirements for model accuracy, and has a simple and efficient diagnostic algorithm. Summary of the Invention

[0005] The purpose of this application is to overcome the aforementioned technical problems. Therefore, it proposes a method and device for diagnosing open-circuit faults in a three-phase MMC system half-bridge submodule based on dq coordinate transformation, which requires no additional sensor configuration, has low requirements for model accuracy, and features a simple and efficient diagnostic algorithm.

[0006] In a first aspect, the present invention provides a method for diagnosing open-circuit faults in a half-bridge submodule of a three-phase MMC system based on dq coordinate transformation, comprising the following steps:

[0007] The capacitor voltages of the half-bridge submodules located at the same position in each phase of the three-phase MMC system are obtained and dq coordinate transformations are performed to obtain the d-axis and q-axis components. The d-axis and q-axis components are used as the imaginary and real parts to construct complex numbers, respectively. The half-bridge submodules located at the same position in each phase of the three-phase MMC system constitute a group of half-bridge submodules. The modulus and principal argument of the complex number corresponding to each group of half-bridge submodules are calculated.

[0008] The presence of a faulty half-bridge module in the three-phase MMC system is determined by whether the modulus of the complex number corresponding to the half-bridge submodule group is greater than or equal to a threshold.

[0009] In response to a fault in a half-bridge submodule in a three-phase MMC system, the faulty phase is determined by the range of the principal argument value of the complex number corresponding to the half-bridge submodule group, and the faulty submodule and normal submodule within the faulty phase are identified.

[0010] The fault type is determined by the consistency of the range of the principal argument values ​​of the complex numbers corresponding to the half-bridge submodule groups where the faulty submodule and the normal submodule are located.

[0011] Preferably, the three-phase MMC system has three bridge arms to form three phases. Each phase includes an upper bridge arm and a lower bridge arm. The upper bridge arm and the lower bridge arm are respectively equipped with a bridge arm resistor and a bridge arm inductor. The midpoint of the upper bridge arm and the lower bridge arm is led out to the load of each phase. Each upper bridge arm and the lower bridge arm contain N half-bridge sub-modules. Each phase has a total of 2N half-bridge modules. There are a total of 2N groups of half-bridge sub-modules in the three-phase MMC system.

[0012] Preferably, the capacitor voltages of the half-bridge submodules located at the same position in each phase of the three-phase MMC system are obtained and subjected to dq coordinate transformation to obtain the d-axis and q-axis components. The d-axis and q-axis components are used as the imaginary and real parts, respectively, to construct complex numbers. The half-bridge submodules located at the same position in each phase of the three-phase MMC system constitute a group of half-bridge submodules. The modulus and principal argument of the complex number corresponding to each group of half-bridge submodules are calculated, specifically including:

[0013] Select the capacitor voltage u of three half-bridge submodules located in different phases but at the same position in a three-phase MMC system. cjk These form a set of three-phase voltage quantities, where j = a, b, c, representing phase a, phase b, and phase c respectively; k = 1 to 2N, representing the number of the half-bridge sub-module, forming a total of 2N sets of three-phase voltage quantities;

[0014] The dq coordinate transformations of the 2N groups of three-phase voltages are shown in the following equations:

[0015]

[0016] Among them, v dk and v qk The d-axis and q-axis components of the capacitor voltages of the three half-bridge submodules in the k-th half-bridge submodule group of the three-phase MMC system are obtained after dq coordinate transformation; λ is the angle between the d-axis and the phase reference axis, and λ is the initial phase angle of phase a.

[0017] The complex number Z is constructed from the d-axis and q-axis components obtained after the dq coordinate transformation using the following formula.k That is, let v dk As the imaginary part of a complex number, v qk As the real part of a complex number:

[0018] Z k =v qk +i*v dk ;

[0019] The complex number Z corresponding to the kth half-bridge submodule group during the operation of the three-phase MMC system is calculated based on the modulus calculation formula. k The modulus M k for:

[0020]

[0021] The complex number Z corresponding to the kth group of half-bridge submodules k Principal argument ε k for:

[0022] ε k =arg(Z) k ).

[0023] Preferably, the presence of a faulty half-bridge submodule in the three-phase MMC system is determined by whether the modulus of the complex number corresponding to the half-bridge submodule group is greater than or equal to a threshold. Specifically, this includes:

[0024] In response to determining that the modulus of the complex number corresponding to the kth half-bridge submodule group in the three-phase MMC system is greater than or equal to a threshold, it is determined that one of the half-bridge submodules in the three-phase MMC system has a single tube open circuit fault.

[0025] Preferably, the fault phase is determined by the range of the principal argument value of the complex number corresponding to the half-bridge submodule group, specifically including:

[0026] In response to determining the principal argument of the complex number corresponding to the k-th half-bridge submodule group in the three-phase MMC system at 60°

[0027] If the temperature range is within ~120° or -120° to -60°, then it is determined that the switch in one of the half-bridge submodules of phase a in the three-phase MMC system has an open-circuit fault.

[0028] In response to determining that the principal argument of the complex number corresponding to the kth half-bridge submodule group in the three-phase MMC system is within the range of -60° to 0° or 120° to 180°, it is determined that an open-circuit fault has occurred in one of the half-bridge submodules of the bth phase in the three-phase MMC system.

[0029] In response to the determination that the principal argument of the complex number corresponding to the k-th half-bridge submodule group of phase c in the three-phase MMC system is within the range of -180° to -120° or 0° to 60°, it is determined that an open-circuit fault has occurred in one of the half-bridge submodules of phase c in the three-phase MMC system.

[0030] Preferably, the faulty submodules and normal submodules within the faulty phase are identified, specifically including:

[0031] The half-bridge submodule with the highest location capacitor voltage in the faulty phase is the faulty submodule, and the other half-bridge submodules in the upper or lower bridge arm where the faulty submodule is located in the faulty phase are normal submodules.

[0032] Preferably, the fault type is determined by the consistency of the range of the principal argument values ​​of the complex numbers corresponding to the half-bridge submodule groups containing the faulty submodule and the normal submodule, specifically including:

[0033] In response to the fact that the principal argument value of the complex number corresponding to the half-bridge submodule group where the faulty submodule is located is within the same range as the principal argument value of the complex number corresponding to the half-bridge submodule group where the normal submodule is located, the fault type of the faulty submodule is determined to be an open circuit fault of the switch transistor T1.

[0034] If the principal argument value of the complex number corresponding to the half-bridge submodule group where the faulty submodule is located is in a different range from the principal argument value of the complex number corresponding to the half-bridge submodule group where the normal submodule is located, then the fault type of the faulty submodule is determined to be an open circuit fault of the switch transistor T2.

[0035] Secondly, the present invention provides a three-phase MMC system half-bridge submodule open-circuit fault diagnosis device based on dq coordinate transformation, comprising:

[0036] The coordinate transformation module is configured to acquire the capacitor voltage of the half-bridge submodule located at the same position in each phase of the three-phase MMC system and perform dq coordinate transformation to obtain the d-axis component and q-axis component. The d-axis component and q-axis component are used as the imaginary part and real part respectively to construct a complex number. The half-bridge submodules located at the same position in each phase of the three-phase MMC system constitute a group of half-bridge submodules. The module and principal argument of the complex number corresponding to each group of half-bridge submodules are calculated.

[0037] The fault determination module is configured to determine whether a half-bridge module in the three-phase MMC system is faulty by checking whether the modulus of the complex number corresponding to the half-bridge submodule group is greater than or equal to a threshold.

[0038] The fault phase and fault submodule determination module is configured to, in response to the presence of a faulty half-bridge submodule in the three-phase MMC system, determine the faulty phase by the interval of the principal argument value of the complex number corresponding to the half-bridge submodule group, and determine the faulty submodule and normal submodule within the faulty phase.

[0039] The fault type determination module is configured to determine the fault type by the consistency of the range of the principal argument values ​​of the complex numbers corresponding to the half-bridge submodule groups where the faulty submodule and the normal submodule are located.

[0040] Thirdly, the present invention provides an electronic device including one or more processors; and a storage device for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the method as described in any implementation of the first aspect.

[0041] Fourthly, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method as described in any of the implementations of the first aspect.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) The open circuit fault diagnosis method of the half-bridge submodule of the three-phase MMC system based on dq coordinate transformation proposed in this invention transforms the capacitor voltage of the half-bridge submodule of the three-phase MMC system into dq coordinates, and constructs a complex number by taking the obtained d-axis component and q-axis component as the imaginary part and real part respectively. The open circuit fault is detected and located by calculating the magnitude and principal value of the complex number.

[0044] (2) The open-circuit fault diagnosis method for half-bridge submodules of three-phase MMC system based on dq coordinate transformation proposed in this invention can quickly detect faults, effectively locate faulty submodules, and accurately identify fault types. It does not require additional sensor configuration, accurate mathematical models, or complex diagnostic algorithms, thus reducing the cost of fault diagnosis.

[0045] (3) The open circuit fault diagnosis method of half-bridge submodule of three-phase MMC system based on dq coordinate transformation proposed in this invention performs coordinate transformation on the capacitor voltage of half-bridge module. No additional sensor configuration is required. The diagnosis process is simple and efficient. It can accurately identify the phase where the open circuit fault is located and its fault type. Theoretically, it can be applied to MMC system with any number of levels. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a flowchart illustrating an embodiment of the three-phase MMC system half-bridge submodule open-circuit fault diagnosis method based on dq coordinate transformation.

[0048] Figure 2 The topology diagram of the three-phase MMC system in the three-phase MMC system half-bridge submodule open circuit fault diagnosis method based on dq coordinate transformation according to an embodiment of this application is shown.

[0049] Figure 3 The topology diagram of the half-bridge module in the three-phase MMC system half-bridge submodule open-circuit fault diagnosis method based on dq coordinate transformation according to an embodiment of this application is shown.

[0050] Figure 4 This is a schematic diagram of the capacitor voltage grouping standard of the half-bridge module in the three-phase MMC system half-bridge sub-module open-circuit fault diagnosis method based on dq coordinate transformation, which is an embodiment of this application.

[0051] Figure 5 This is a flowchart illustrating the open-circuit fault diagnosis process of the IGBT switching transistor in the half-bridge module of the three-phase MMC system based on dq coordinate transformation, as an embodiment of this application.

[0052] Figure 6 This is a schematic diagram of the interval division of the principal argument value under fault conditions in the three-phase MMC system half-bridge submodule open-circuit fault diagnosis method based on dq coordinate transformation, which is an embodiment of this application.

[0053] Figure 7 The half-bridge submodule SM in the embodiments of this application a1 Waveform of the capacitor voltage of phase a half-bridge submodule when T1 open circuit fault occurs;

[0054] Figure 8 The half-bridge submodule SM in the embodiments of this application a1 Calculation results of the principal values ​​of the modulus and argument when an open-circuit fault (T1) occurs;

[0055] Figure 9 The half-bridge submodule SM in the embodiments of this application a1 Waveform of the capacitor voltage of phase a half-bridge submodule when T2 open circuit fault occurs;

[0056] Figure 10The half-bridge submodule SM in the embodiments of this application a1 Calculation results of the modulus and principal argument values ​​when a T2 open-circuit fault occurs;

[0057] Figure 11 The half-bridge submodule SM in the embodiments of this application a1 Diagram showing the fault diagnosis and location results when an open-circuit fault (T1) occurs;

[0058] Figure 12 The half-bridge submodule SM in the embodiments of this application b1 Diagram showing the fault diagnosis and location results when a T2 open circuit fault occurs;

[0059] Figure 13 This is a schematic diagram of an open-circuit fault diagnosis device for a three-phase MMC system half-bridge submodule based on dq coordinate transformation, as an embodiment of this application.

[0060] Figure 14 This is a schematic diagram of the hardware structure of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of the present invention more apparent, the present invention will be further described in detail below with reference to the accompanying drawings. It is apparent that the embodiments described are only some, not all, of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0062] Figure 1 This application illustrates an embodiment of a method for diagnosing open-circuit faults in a half-bridge submodule of a three-phase MMC system based on dq coordinate transformation, comprising the following steps:

[0063] S1. Obtain the capacitor voltage of the half-bridge submodule located at the same position in each phase of the three-phase MMC system and perform dq coordinate transformation to obtain the d-axis component and q-axis component. Use the d-axis component and q-axis component as the imaginary part and real part respectively to construct a complex number. The half-bridge submodule located at the same position in each phase of the three-phase MMC system constitutes a group of half-bridge submodules. Calculate the modulus and principal argument of the complex number corresponding to each group of half-bridge submodules.

[0064] In a specific embodiment, the three-phase MMC system has three bridge arms to form three phases. Each phase includes an upper bridge arm and a lower bridge arm. The upper bridge arm and the lower bridge arm are respectively provided with a bridge arm resistor and a bridge arm inductor. The midpoint of the upper bridge arm and the lower bridge arm is led out to the load of each phase. Each upper bridge arm and the lower bridge arm contain N half-bridge sub-modules. Each phase has a total of 2N half-bridge modules. There are a total of 2N groups of half-bridge sub-modules in the three-phase MMC system.

[0065] For details, please refer to Figure 2 A three-phase MMC system has three bridge arms forming three phases. Each phase includes an upper bridge arm and a lower bridge arm. Both the upper and lower bridge arms include N half-bridge submodules (HBSMs), one bridge arm resistor, and one inductor. The midpoint between the upper and lower bridge arms is connected to the load of each phase. dc i is the DC bus voltage. uj with i lj Let R be the current in the upper arm of phase j (j = a, b, c) and the current in the lower arm of phase j, respectively. uj With R lj Let L be the arm resistance of the upper arm of phase j and the arm resistance of the lower arm of phase j, respectively. uj With L lj Let i be the inductance of the upper arm of phase j and the lower arm of phase j, respectively. oj For the load-side output current, L oj With R oj For AC-side loads, the neutral point of the three-phase MMC system is O.

[0066] refer to Figure 3 Each half-bridge submodule includes two IGBT switching transistors, T1 and T2, two diodes, D1 and D2, connected in anti-parallel to the IGBTs, and a capacitor C for charging and discharging. sm i is the port voltage of the half-bridge submodule. sm For the current flowing into the half-bridge submodule, u c This is the capacitor voltage of the half-bridge submodule. (Reference) Figure 4 The 2N half-bridge submodules in each phase are grouped into groups: the N half-bridge submodules of the upper arm are group 1 to group N, and the N half-bridge submodules of the lower arm are group N+1 to group 2N.

[0067] In a specific embodiment, the capacitor voltages of the half-bridge submodules located at the same position in each phase of the three-phase MMC system are obtained and subjected to dq coordinate transformation to obtain d-axis and q-axis components. The d-axis and q-axis components are used as the imaginary and real parts, respectively, to construct complex numbers. The half-bridge submodules located at the same position in each phase of the three-phase MMC system constitute a group of half-bridge submodules. The modulus and principal argument of the complex number corresponding to each group of half-bridge submodules are calculated, specifically including:

[0068] For a three-phase MMC system in normal operation, the capacitor voltage u of the half-bridge submodule at the same position of the three phases is... c The AC components satisfy the condition that their amplitudes are equal and their phases differ by 120° sequentially; therefore, the capacitor voltages u of three half-bridge submodules located in different phases but at the same position in the three-phase MMC system are selected. cjkThese form a set of three-phase voltage quantities, where j = a, b, c, representing phase a, phase b, and phase c respectively; k = 1 to 2N, representing the number of the half-bridge sub-module, forming a total of 2N sets of three-phase voltage quantities;

[0069] The dq coordinate transformations of the 2N groups of three-phase voltages are shown in the following equations:

[0070]

[0071] Among them, v dk and v qk The d-axis and q-axis components of the capacitor voltages of the three half-bridge submodules in the k-th half-bridge submodule group of the three-phase MMC system are obtained after dq coordinate transformation; λ is the angle between the d-axis and the phase reference axis, and λ is the initial phase angle of phase a.

[0072] The complex number Z is constructed from the d-axis and q-axis components obtained after the dq coordinate transformation using the following formula. k That is, let v dk As the imaginary part of a complex number, v qk As the real part of a complex number:

[0073] Z k =v qk +i*v dk ;

[0074] The complex number Z corresponding to the kth half-bridge submodule group during the operation of the three-phase MMC system is calculated based on the modulus calculation formula. k The modulus M k for:

[0075]

[0076] The complex number Z corresponding to the kth group of half-bridge submodules k Principal argument ε k for:

[0077] ε k =arg(Z) k ).

[0078] Specifically, for a three-phase MMC (Modular Multilevel Converter) system in normal operation, the capacitor voltage u at the same position of the three phases... c The AC components satisfy the condition that the amplitudes are equal and the phases differ by 120° sequentially. Therefore, the capacitor voltages u of three half-bridge submodules with different phases but at the same position can be selected. cjk (j = a, b, c, representing phase; k = 1~2N, representing the number of the half-bridge submodule), such as u ca1 u cb1 with u cc1 Perform coordinate transformation on a set of three-phase voltage quantities.

[0079] When the three-phase MMC system is in normal operation, the capacitor current of the half-bridge submodule is approximately sinusoidal, which is denoted as:

[0080]

[0081] Among them, I cjk This represents the amplitude of the capacitor current. Let be the phase angle. Then, in a three-phase MMC system, the capacitor voltage u of each half-bridge module in the k-th group of the j-th phase half-bridge submodules is... cjk It can be represented as:

[0082]

[0083] Let the initial phase angle of phase a be 0°, and then... Substitution By simplifying the process, we can obtain the capacitor voltage u of each half-bridge module in the k-th group of the j-th phase half-bridge sub-modules in a three-phase MMC system. cjk The expression is shown below:

[0084]

[0085] By performing a dq coordinate transformation on the capacitor voltage of each half-bridge module in the k-th group of the j-th phase half-bridge submodules in a three-phase MMC system, the following equation is obtained:

[0086]

[0087] Where E is the capacitance of each half-bridge module in the k-th half-bridge sub-module group of the three-phase MMC system during each charge and discharge cycle. c The magnitude of change. The d-axis component v obtained after coordinate transformation. dk and q-axis component v qk Constructing complex number Z k That is, let the d-axis component v dk As the imaginary part of a complex number, the q-axis component v qk As the real part of a complex number.

[0088] The formula for calculating the modulus is that the modulus equals the d-axis component v. dk With q-axis component v qk The square root of the sum of squares is used to calculate the complex number Z corresponding to the k-th half-bridge submodule group when the three-phase MMC system is in normal operation, according to the modulus calculation formula. k The modulus M k for:

[0089]

[0090] When the three-phase MMC system is in normal operation, the complex number Z corresponding to the k-th half-bridge submodule group k Principal argument ε k for:

[0091]

[0092] Based on the above two equations, when no fault occurs in the three-phase MMC system, the complex number Z corresponding to the k-th group of half-bridge submodules is... k The modulus M k It will fluctuate within a certain numerical range, with relatively small changes in value, while the complex number Z corresponding to the k-th group of half-bridge submodules... k Principal argument ε k It then varies continuously between -180° and 180°. However, when an open-circuit fault occurs in the IGBT switching transistor of one of the half-bridge submodules in a three-phase MMC system, the u used for coordinate transformation... cjk The values ​​will change. Because the three phases in the MMC three-phase system are completely symmetrical and independent, when an open-circuit fault occurs in any phase, only the capacitor voltage waveform of the half-bridge submodule of the faulty phase changes. Taking an open-circuit fault of any type of switch transistor in any half-bridge submodule of phase a as an example, the capacitor voltage u of each half-bridge submodule in the k-th group of phase j in the three-phase MMC system will change. cjk Represented as:

[0093]

[0094] In the above formula, because the capacitor voltage of the kth half-bridge submodule of phase a cannot be charged and discharged normally, the initial capacitor voltage u of the capacitor voltage of the kth half-bridge submodule of phase a in each charge and discharge cycle is reduced. cak (0) It shows a continuous increasing or decreasing trend, and DH represents the initial capacitor voltage u of the kth half-bridge submodule of phase a after the fault. cak The offset of (0). The sign of D depends on the changing trend of the capacitor voltage of the kth half-bridge submodule of phase a, that is, it is positive when the capacitor voltage of the kth half-bridge submodule of phase a rises and negative when the capacitor voltage of the kth half-bridge submodule of phase a falls, and it increases continuously with the increase of fault time. H is the fixed increment of the kth half-bridge submodule of phase a for each charging cycle.

[0095] Performing a synchronous rotation coordinate transformation on the above equation, the d-axis component v is obtained. dk With q-axis component v qk As shown in the following formula:

[0096]

[0097] Based on the results of the above formula, calculate the modulus M of the complex number corresponding to the k-th group of half-bridge submodules. kand the principal value of the argument ε k for:

[0098]

[0099] S2 determines whether a half-bridge submodule in the three-phase MMC system is faulty by checking whether the modulus of the complex number corresponding to the half-bridge submodule group is greater than or equal to a threshold.

[0100] In a specific embodiment, S2 specifically includes:

[0101] In response to determining that the modulus of the complex number corresponding to the kth half-bridge submodule group in the three-phase MMC system is greater than or equal to a threshold, it is determined that one of the half-bridge submodules in the three-phase MMC system has a single tube open circuit fault.

[0102] For details, please refer to Figure 5 The modulus M of the complex number corresponding to the kth half-bridge submodule group in the three-phase MMC system is calculated. k Principal value of argument ε k Then, using the modulus M k Principal value of argument ε k Fault diagnosis can be divided into four stages: fault detection, fault phase identification, fault submodule confirmation, and fault type determination. In the fault detection stage, the modulus M of the complex number corresponding to each half-bridge submodule group is compared with a set threshold T. If a fault exists... k If the threshold value is ≥T, then one of the half-bridge submodules in the three-phase MMC system is considered faulty. The selection of the threshold value T should balance diagnostic accuracy and speed; too small a value can easily lead to false positives, while too large a value will result in slow diagnosis. In the fault phase identification stage, the principal argument value ε of the complex number corresponding to the k-th group of half-bridge submodules is used. k Combination Figure 6 The first step is to determine the phase in which the open-circuit fault occurs. Then, in the fault submodule confirmation stage, the faulty submodule can be located by finding the half-bridge submodule number corresponding to the maximum capacitor voltage within the faulty phase. Finally, the fault type determination stage begins. If the faulty submodule is in the upper bridge arm, the fault type is determined by the uniformity of the principal argument value intervals of the complex numbers corresponding to each group of half-bridge submodules in the upper bridge arm. Conversely, the uniformity of the principal argument value intervals of the corresponding half-bridge submodules in the lower bridge arm is used to determine the fault type. If the principal argument values ​​are in the same interval, it is a T1 fault; otherwise, it is a T2 fault. T1 refers to the upper transistor of the half-bridge submodule, and T2 refers to the lower transistor of the half-bridge submodule.

[0103] From the modulus M k From the formula, we can see that after an open-circuit fault occurs, the capacitor voltage of the kth half-bridge submodule in phase a continuously deviates from the normal value, and the modulus M... k It will also increase accordingly, so the modulus M can be... kUsed to determine the occurrence of a fault. If M k If the value is ≥T, then one of the half-bridge submodules in the three-phase MMC system is considered to have failed. However, it is not possible to determine which half-bridge submodule in the three phases has failed at this time. Further determination is required based on the principal argument value.

[0104] S3, in response to a fault in a half-bridge submodule in a three-phase MMC system, determines the faulty phase by the range of the principal argument value of the complex number corresponding to the half-bridge submodule group, and identifies the faulty submodule and normal submodule within the faulty phase.

[0105] In a specific embodiment, the fault phase is determined by the range of the principal argument value of the complex number corresponding to the half-bridge submodule group, specifically including:

[0106] In response to determining the principal argument of the complex number corresponding to the k-th half-bridge submodule group in the three-phase MMC system at 60°

[0107] If the temperature range is within ~120° or -120° to -60°, then it is determined that the switch in one of the half-bridge submodules of phase a in the three-phase MMC system has an open-circuit fault.

[0108] In response to determining that the principal argument of the complex number corresponding to the kth half-bridge submodule group in the three-phase MMC system is within the range of -60° to 0° or 120° to 180°, it is determined that an open-circuit fault has occurred in one of the half-bridge submodules of the bth phase in the three-phase MMC system.

[0109] In response to the determination that the principal argument of the complex number corresponding to the k-th half-bridge submodule group of phase c in the three-phase MMC system is within the range of -180° to -120° or 0° to 60°, it is determined that an open-circuit fault has occurred in one of the half-bridge submodules of phase c in the three-phase MMC system.

[0110] Specifically, the principal argument ε k The formula shows that when an open-circuit fault occurs in phase a, the capacitor voltage u of the kth half-bridge submodule in phase a... cak It shows an upward trend, that is, when D>0, v dk / v qk The overall value will tend towards positive infinity, with the principal argument value approaching 90°, corresponding to π / 2 radians; while the capacitor voltage u of the kth half-bridge submodule of phase a... cak It shows a downward trend, that is, when D < 0, v dk / v qk The overall value tends towards negative infinity, therefore the principal argument value is close to -90°, corresponding to -π / 2 radians. Similarly, when an open-circuit fault occurs in phase b, the capacitor voltage u of the k-th half-bridge submodule in phase b... cbkWhen the trend is upward, the principal value of the argument is close to -33°, corresponding to approximately -0.577 radians; while when the capacitor voltage u of the kth half-bridge submodule of phase b... cbk When the trend is downward, the principal argument value is close to 147°, corresponding to approximately 2.56 radians; when an open-circuit fault occurs in phase c, the capacitor voltage u of the kth half-bridge submodule in phase c... cck When the trend is upward, the principal argument value is close to -147°, corresponding to approximately -2.56 radians; while when the capacitor voltage u of the kth half-bridge submodule of phase c... cck When the trend is downward, the principal value of the argument is close to 33°, corresponding to approximately 0.577 radians.

[0111] Therefore, when an open-circuit fault occurs, the range of the principal argument value of the corresponding half-bridge submodule group is as follows: Figure 6 As shown, the system can be divided into six intervals. When the calculated principal argument value falls within a certain fixed interval, the phase in which the open-circuit fault occurs can be determined by interval comparison. The phase in which the open-circuit fault occurs is the faulty phase. By finding the number of the half-bridge submodule corresponding to the maximum capacitor voltage within the faulty phase, the faulty half-bridge submodule in that phase can be located, thus identifying the faulty submodule. The remaining half-bridge submodules located in the same upper or lower bridge arm as the faulty submodule are normal submodules.

[0112] S4 determines the fault type by the consistency of the range of the principal argument values ​​of the complex numbers corresponding to the half-bridge submodule groups where the faulty submodule and the normal submodule are located.

[0113] In a specific embodiment, S4 specifically includes:

[0114] In response to the fact that the principal argument value of the complex number corresponding to the half-bridge submodule group where the faulty submodule is located is within the same range as the principal argument value of the complex number corresponding to the half-bridge submodule group where the normal submodule is located, the fault type of the faulty submodule is determined to be an open circuit fault of the switch transistor T1.

[0115] If the principal argument value of the complex number corresponding to the half-bridge submodule group where the faulty submodule is located is in a different range from the principal argument value of the complex number corresponding to the half-bridge submodule group where the normal submodule is located, then the fault type of the faulty submodule is determined to be an open circuit fault of the switch transistor T2.

[0116] Specifically, when an open-circuit fault exists in the upper bridge arm, the capacitor voltage changes of the faulty submodule and the normal submodule in the same upper bridge arm show the same trend, which is reflected in the consistent range of ε values ​​in the principal argument value. When an open-circuit fault exists in the lower bridge arm, the capacitor voltage changes of the faulty submodule and the normal submodule in the same lower bridge arm show different trends, which is reflected in the different ranges of ε values ​​in the principal argument value. Therefore, by judging the consistency of the range of the principal argument value, the type of open-circuit fault can be effectively identified. Taking the open-circuit fault of the half-bridge submodule with each phase number 1 as an example, the criteria for judging the type of open-circuit fault are shown in Table 1.

[0117] Table 1. Principal values ​​of argument angle ε for each phase's first group of half-bridge submodules under different open-circuit fault types. k Interval distribution

[0118]

[0119] Example

[0120] The following describes this technology in further detail with reference to specific implementation methods:

[0121] The main circuit structure diagram of the three-phase MMC system in this embodiment is as follows: Figure 2 As shown, its half-bridge submodule structure is as follows: Figure 3 As shown in Table 2, the parameters of each part of the three-phase MMC system are shown in Table 2, and the threshold T is set to 15.

[0122] Table 2 Three-phase MMC main circuit parameters

[0123]

[0124] In the event of a fault in the upper bridge arm, due to the faulty upper bridge arm's normal submodule (SM) a2 -SM a4 ) and fault submodule SM a1 The capacitor voltage changes in the same trend, such as Figure 7 As shown, the calculated principal argument values ​​are in the same interval, such as... Figure 8 As shown; for lower-transistor type faults, because the capacitor voltage change trends of the normal submodule and the faulty submodule of the upper bridge arm are inconsistent, such as... Figure 9 As shown, the calculated principal argument values ​​fall within different intervals, such as... Figure 10 As shown.

[0125] The open-circuit fault diagnosis method for half-bridge submodules of a three-phase MMC system based on dq coordinate transformation proposed in the embodiments of this application calculates the modulus M of the complex number corresponding to each group of half-bridge submodules in each phase in step S1. k Principal value of argument ε k The result is as follows Figure 11As shown, since the modulus M1 of the complex number corresponding to the first group of half-bridge submodules begins to rise at time t0, a fault occurs at time t0. At time t1, the modulus M1 reaches the threshold T, meaning M1 ≥ T, confirming an open-circuit fault in the half-bridge submodule. Therefore, the fault diagnosis method proposed in this application can detect the fault, and the fault detection flag Fault is set to 1. Since the calculated principal argument values ​​of the complex numbers corresponding to each group of half-bridge submodules all fall within interval 3, phase a is determined to be the fault phase. Furthermore, since the principal argument values ​​of the complex numbers corresponding to the faulty submodule and the normal submodule in the faulty phase both belong to the same interval, the fault type is determined to be a T1 open-circuit fault. (Reference) Figure 12 Since the calculated principal argument values ​​of the complex numbers corresponding to each group of half-bridge submodules all fall within intervals 2 or 5, phase b is determined to be the faulty phase. Furthermore, since the principal argument values ​​of the complex numbers corresponding to the half-bridge submodule groups containing the faulty submodule and the normal submodule in the faulty phase do not belong to the same interval, the fault type is determined to be a T2 open-circuit fault.

[0126] The above results show that the three-phase MMC system half-bridge submodule open-circuit fault diagnosis method based on dq coordinate transformation proposed in this invention can accurately and effectively locate the faulty submodule and identify the fault type, with an average diagnosis time of within three power frequency cycles.

[0127] If v qk As the imaginary part of a complex number, v dk As the real part of a complex number, constructing a complex number can still achieve the fault detection stage, and is also within the protection scope of this application. That is, v qk and v dk One of them is used as the imaginary part of the complex number, and the other is used as the real part of the complex number. If v qk As the imaginary part of a complex number, v dk As the real part of the complex number, the interval corresponding to the fault phase identification stage needs to be adjusted, while the fault submodule confirmation stage and the fault type judgment stage remain unchanged.

[0128] Further reference Figure 13 As an implementation of the methods shown in the above figures, this application provides an embodiment of a three-phase MMC system half-bridge submodule open-circuit fault diagnosis device based on dq coordinate transformation. This device embodiment is similar to... Figure 1 Corresponding to the method embodiments shown, this device can be specifically applied to various electronic devices.

[0129] This application provides a device for diagnosing open-circuit faults in a half-bridge submodule of a three-phase MMC system based on dq coordinate transformation, comprising:

[0130] Coordinate transformation module 1 is configured to acquire the capacitor voltage of the half-bridge submodule located at the same position in each phase of the three-phase MMC system and perform dq coordinate transformation to obtain the d-axis component and q-axis component. The d-axis component and q-axis component are used as the imaginary part and real part respectively to construct a complex number. The half-bridge submodules located at the same position in each phase of the three-phase MMC system constitute a group of half-bridge submodules. The modulus and principal argument of the complex number corresponding to each group of half-bridge submodules are calculated.

[0131] Fault determination module 2 is configured to determine whether a half-bridge module in the three-phase MMC system is faulty by whether the modulus of the complex number corresponding to the half-bridge submodule group is greater than or equal to a threshold.

[0132] The fault phase and fault submodule determination module 3 is configured to, in response to the presence of a faulty half-bridge submodule in the three-phase MMC system, determine the faulty phase by the interval of the principal argument value of the complex number corresponding to the half-bridge submodule group, and determine the faulty submodule and normal submodule within the faulty phase.

[0133] The fault type determination module 4 is configured to determine the fault type by the consistency of the range of the principal argument values ​​of the complex numbers corresponding to the half-bridge submodule groups where the faulty submodule and the normal submodule are located.

[0134] Figure 14 This is a schematic diagram of the hardware structure of an electronic device provided in an embodiment of the present invention. For example... Figure 14 As shown, the electronic device in this embodiment includes a processor 1401 and a memory 1402; wherein the memory 1402 is used to store computer execution instructions; and the processor 1401 is used to execute the computer execution instructions stored in the memory to implement the various steps performed by the electronic device in the above embodiment. For details, please refer to the relevant descriptions in the foregoing method embodiments.

[0135] Alternatively, the memory 1402 can be either standalone or integrated with the processor 1401.

[0136] When the memory 1402 is set up independently, the electronic device also includes a bus 1403 for connecting the memory 1402 and the processor 1401.

[0137] This invention also provides a computer storage medium storing computer execution instructions, which, when executed by the processor 1401, implement the above method.

[0138] This invention also provides a computer program product, including a computer program that, when executed by a processor 1401, implements the above-described method.

[0139] In the embodiments provided by this invention, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative; for instance, the division of modules is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple modules may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be indirect coupling or communication connection through some interfaces, devices, or modules, and may be electrical, mechanical, or other forms.

[0140] The modules described as separate components may or may not be physically separate. The components shown as modules 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 implement the solution of this embodiment according to actual needs.

[0141] Furthermore, the functional modules in the various embodiments of the present invention can be integrated into one processing unit, or each module can exist physically separately, or two or more modules can be integrated into one unit. The unit composed of the above modules can be implemented in hardware or in the form of hardware plus software functional units.

[0142] The integrated modules implemented as software functional modules described above can be stored in a computer-readable storage medium. These software functional modules, stored in a storage medium, include several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) or processor 1401 to execute certain steps of the methods of the various embodiments of this application.

[0143] It should be understood that the processor 1401 described above can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), etc. The general-purpose processor can be a microprocessor, or the processor 1401 can be any conventional processor 1401. The steps of the method disclosed in this invention can be directly manifested as the hardware processor 1401 executing the steps, or as a combination of hardware and software modules within the processor 1401 executing the steps.

[0144] The memory 1402 may include high-speed RAM memory, and may also include non-volatile memory NVM, such as at least one disk storage, and may also be a USB flash drive, portable hard drive, read-only memory, disk or optical disc, etc.

[0145] Bus 1403 can be an Industry Standard Architecture (ISA), a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus, etc. Bus 1403 can be divided into address bus, data bus, control bus, etc. For ease of illustration, the bus 1403 in the accompanying drawings of this application is not limited to only one bus 1403 or one type of bus 1403.

[0146] The aforementioned storage medium can be implemented from any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk. The storage medium can be any available medium accessible to general-purpose or special-purpose computers.

[0147] An exemplary storage medium is coupled to a processor 1401, enabling the processor 1401 to read information from and write information to the storage medium. Alternatively, the storage medium can be an integral part of the processor 1401. The processor 1401 and the storage medium can reside in an application-specific integrated circuit (ASIC). Alternatively, the processor 1401 and the storage medium can exist as discrete components in an electronic device or a host device.

[0148] Those skilled in the art will understand that all or part of the steps of the above-described method embodiments can be implemented by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When executed, the program performs the steps of the above-described method embodiments; and the aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks.

[0149] Finally, 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for diagnosing open-circuit faults in a half-bridge submodule of a three-phase MMC system based on dq coordinate transformation, characterized in that, Includes the following steps: The capacitor voltages of the half-bridge submodules located at the same position in each phase of the three-phase MMC system are obtained and dq coordinate transformations are performed to obtain the d-axis and q-axis components. The d-axis and q-axis components are used as the imaginary and real parts to construct complex numbers, respectively. The three-phase MMC system has three bridge arms to form three phases. Each phase includes an upper bridge arm and a lower bridge arm. The upper and lower bridge arms are respectively provided with bridge arm resistors and bridge arm inductors. The midpoint of the upper and lower bridge arms is led out to the load of each phase. Each upper and lower bridge arm contains N half-bridge submodules, and there are a total of 2N half-bridge submodules per phase. There are 2N groups of half-bridge submodules in the three-phase MMC system. The half-bridge submodules located at the same position in each phase of the three-phase MMC system form a group of half-bridge submodules. The modulus and principal argument of the complex number corresponding to each group of half-bridge submodules are calculated. The system determines whether a half-bridge submodule in the three-phase MMC system is faulty by checking whether the modulus of the complex number corresponding to the half-bridge submodule group is greater than or equal to a threshold. Specifically, this includes: In response to determining that the modulus of the complex number corresponding to the kth half-bridge submodule group in the three-phase MMC system is greater than or equal to a threshold, it is determined that one of the half-bridge submodules in the three-phase MMC system has a single tube open circuit fault. In response to a fault in a half-bridge submodule in the three-phase MMC system, the faulty phase is determined by the range of the principal argument value of the complex number corresponding to the half-bridge submodule group, specifically including: In response to determining that the principal argument of the complex number corresponding to the kth half-bridge submodule group in the three-phase MMC system is within the range of 60°~120° or -120°~-60°, it is determined that an open-circuit fault has occurred in one of the half-bridge submodules of the a-th phase in the three-phase MMC system. In response to determining that the principal argument value of the complex number corresponding to the kth half-bridge submodule group in the three-phase MMC system is within the range of -60° to 0° or 120° to 180°, it is determined that an open-circuit fault has occurred in one of the half-bridge submodules of the bth phase in the three-phase MMC system. In response to determining that the principal argument of the complex number corresponding to the k-th half-bridge submodule group of the c-th phase in the three-phase MMC system is within the range of -180° to -120° or 0° to 60°, it is determined that the switch in one of the half-bridge submodules of the c-th phase in the three-phase MMC system has an open-circuit fault, and the faulty submodule and normal submodule in the faulty phase are determined. The fault type is determined by the consistency of the range of the principal argument values ​​of the complex numbers corresponding to the half-bridge submodule groups where the faulty submodule and the normal submodule are located.

2. The method for diagnosing open-circuit faults in a half-bridge submodule of a three-phase MMC system based on dq coordinate transformation according to claim 1, characterized in that, The process involves acquiring the capacitor voltage of the half-bridge submodule located at the same position in each phase of the three-phase MMC system and performing dq coordinate transformation to obtain the d-axis and q-axis components. These components are then used as the imaginary and real parts, respectively, to construct a complex number. The half-bridge submodules located at the same position in each phase of the three-phase MMC system form a group of half-bridge submodules. The modulus and principal argument of the complex number corresponding to each group of half-bridge submodules are calculated, specifically including: Select the capacitor voltage u of three half-bridge submodules located in different phases but at the same position in the three-phase MMC system. cjk These form a set of three-phase voltage quantities, where j=a, b, c, representing phase a, phase b, and phase c respectively; k=1~2N, representing the number of the half-bridge sub-module, forming a total of 2N sets of three-phase voltage quantities; The 2N groups of three-phase voltages are transformed using dq coordinates, as shown in the following equations: ； in, and The d-axis and q-axis components of the capacitor voltages of the three half-bridge submodules in the k-th half-bridge submodule group of the three-phase MMC system are obtained after dq coordinate transformation; λ is the angle between the d-axis and the phase reference axis. The complex number Z is constructed from the d-axis and q-axis components obtained after the dq coordinate transformation using the following formula. k That is, let v dk As the imaginary part of a complex number, v qk As the real part of a complex number: ； The complex number Z corresponding to the k-th half-bridge submodule group is calculated according to the modulus calculation formula when the three-phase MMC system is running. k The modulus M k for: ； The complex number Z corresponding to the kth group of half-bridge submodules k Principal argument ε k for: 。 3. The method for diagnosing open-circuit faults in a half-bridge submodule of a three-phase MMC system based on dq coordinate transformation according to claim 1, characterized in that, The determination of the faulty submodule and normal submodule within the faulty phase specifically includes: The half-bridge submodule with the highest location capacitor voltage within the faulty phase is the faulty submodule, and the remaining half-bridge submodules in the upper or lower bridge arm where the faulty submodule is located within the faulty phase are normal submodules.

4. The method for diagnosing open-circuit faults in a half-bridge submodule of a three-phase MMC system based on dq coordinate transformation according to claim 1, characterized in that, The method of determining the fault type by the consistency of the intervals in which the principal argument values ​​of the complex numbers corresponding to the half-bridge submodule groups containing the faulty submodule and the normal submodule are located specifically includes: In response to determining that the principal argument value of the complex number corresponding to the half-bridge submodule group where the faulty submodule is located is within the same range as the principal argument value of the complex number corresponding to the half-bridge submodule group where the normal submodule is located, the fault type of the faulty submodule is determined to be an open circuit fault of the switching transistor T1. In response to determining that the principal argument value of the complex number corresponding to the half-bridge submodule group where the faulty submodule is located is in a different range from the principal argument value of the complex number corresponding to the half-bridge submodule group where the normal submodule is located, the fault type of the faulty submodule is determined to be an open circuit fault of the switch transistor T2.

5. A diagnostic device for open-circuit faults in a half-bridge submodule of a three-phase MMC system based on dq coordinate transformation, characterized in that, include: The coordinate transformation module is configured to acquire the capacitor voltage of the half-bridge submodule located at the same position in each phase of the three-phase MMC system and perform dq coordinate transformation to obtain the d-axis component and q-axis component. The d-axis component and q-axis component are used as the imaginary part and real part to construct a complex number. The three-phase MMC system has three bridge arms to form three phases. Each phase includes an upper bridge arm and a lower bridge arm. The upper bridge arm and the lower bridge arm are respectively provided with a bridge arm resistor and a bridge arm inductor. The midpoint of the upper bridge arm and the lower bridge arm is led out to the load of each phase. Each upper bridge arm and the lower bridge arm contain N half-bridge submodules. There are a total of 2N half-bridge submodules in each phase. There are 2N groups of half-bridge submodules in the three-phase MMC system. The half-bridge submodules located at the same position in each phase of the three-phase MMC system form a group of half-bridge submodules. The module calculates the modulus and principal argument of the complex number corresponding to each group of half-bridge submodules. The fault determination module is configured to determine whether a half-bridge submodule in the three-phase MMC system is faulty by checking whether the modulus of the complex number corresponding to the half-bridge submodule group is greater than or equal to a threshold. Specifically, this includes: In response to determining that the modulus of the complex number corresponding to the kth half-bridge submodule group in the three-phase MMC system is greater than or equal to a threshold, it is determined that one of the half-bridge submodules in the three-phase MMC system has a single tube open circuit fault. The fault phase and fault submodule determination module is configured to, in response to a fault in a half-bridge submodule in the three-phase MMC system, determine the fault phase by the interval of the principal argument value of the complex number corresponding to the half-bridge submodule group, specifically including: In response to determining that the principal argument of the complex number corresponding to the kth half-bridge submodule group in the three-phase MMC system is within the range of 60°~120° or -120°~-60°, it is determined that an open-circuit fault has occurred in one of the half-bridge submodules of the a-th phase in the three-phase MMC system. In response to determining that the principal argument value of the complex number corresponding to the kth half-bridge submodule group in the three-phase MMC system is within the range of -60° to 0° or 120° to 180°, it is determined that an open-circuit fault has occurred in one of the half-bridge submodules of the bth phase in the three-phase MMC system. In response to determining that the principal argument of the complex number corresponding to the k-th half-bridge submodule group of the c-th phase in the three-phase MMC system is within the range of -180° to -120° or 0° to 60°, it is determined that the switch in one of the half-bridge submodules of the c-th phase in the three-phase MMC system has an open-circuit fault, and the faulty submodule and normal submodule in the faulty phase are determined. The fault type determination module is configured to determine the fault type by the consistency of the range of the principal argument values ​​of the complex numbers corresponding to the half-bridge submodule groups where the faulty submodule and the normal submodule are located.

6. An electronic device, comprising: One or more processors; Storage device for storing one or more programs. When the one or more programs are executed by the one or more processors, the one or more processors implement the method as described in any one of claims 1-4.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method as described in any one of claims 1-4.

Images