MMC-based open-circuit fault diagnosis method and system for medium-voltage direct-current converter

Abstract

An MMC-based open-circuit fault diagnosis method and system for a medium-voltage direct-current converter. The method comprises: acquiring on / off states and voltage and current signal data of a sub-module in a modular multilevel converter when the sub-module is in a normal operating state and a fault state; establishing different types of fault determination logic on the basis of the on / off states and the voltage and current signal data of the sub-module when same is in the normal operating state and the fault state, and establishing a fault indicator on the basis of different types of fault determination logic; establishing a sub-module capacitor current observation equation on the basis of the structure of the sub-module in the modular multilevel converter, and determining the relationship between an actual value and a predicted value of a capacitor current and a first threshold value; and on the basis of a determination result regarding the relationship between the actual value and the predicted value of the capacitor current and the first threshold value, displaying an open-circuit fault diagnosis result in combination with the fault indicator. In the method and the system, a capacitor current path and on / off state information are used to perform fault diagnosis quickly and accurately when a fault occurs, thereby providing a solution for actual engineering application.

Description

A method and system for diagnosing open-circuit faults of medium-voltage DC converters based on MMC Technical Field

[0001] The present invention relates to the technical field of medium voltage DC converter open circuit fault diagnosis, and in particular to a medium voltage DC converter open circuit fault diagnosis method and system based on MMC. Background Art

[0002] Medium-voltage DC-to-DC converters are important power conversion devices widely used in power systems, industrial control, transportation, and other fields. However, during operation, medium-voltage DC-to-DC converters may experience open-circuit failures due to various reasons such as component aging, environmental influences, or operational errors.

[0003] Open-circuit faults can severely impact the normal operation and stability of medium-voltage DC converters, potentially even causing system downtime and damage. Therefore, quickly and accurately detecting and locating open-circuit faults is crucial for improving the operational reliability of medium-voltage DC converters.

[0004] Diagnostic methods and strategies for open-circuit faults in medium-voltage DC converters have been extensively researched. Traditional fault diagnosis methods primarily rely on analog and digital monitoring parameters, but suffer from low diagnostic accuracy and limited real-time performance. Furthermore, some methods require system recalibration after a fault occurs, increasing maintenance costs and downtime.

[0005] Summary of the Invention

[0006] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of this application to avoid obscuring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions should not be used to limit the scope of the present invention.

[0007] In view of the above existing problems, the present invention is proposed.

[0008] Therefore, the present invention provides a method and system for diagnosing open-circuit faults of a medium-voltage DC converter based on MMC, which can solve the problems mentioned in the background technology.

[0009] To solve the above technical problems, the present invention provides the following technical solution: a method for diagnosing open-circuit faults of a medium-voltage DC converter based on MMC, comprising:

[0010] Obtaining the switch status, voltage and current signal data of the submodules in the modular multilevel converter when they are in normal working state and fault state;

[0011] Establish different fault judgment logics based on the switch states, voltage and current signal data of the submodules in normal working state and fault state, and establish a fault indicator based on the different fault judgment logics;

[0012] Establishing a submodule capacitor current observation equation according to the structure of the submodule in the modular multilevel converter, and determining a relationship between an actual value and a predicted value of the capacitor current and a first threshold value;

[0013] According to the judgment result of the relationship between the actual value and the predicted value of the capacitor current and the first threshold, the open circuit fault diagnosis result is displayed in combination with the fault indicator.

[0014] As a preferred solution of the MMC-based medium voltage DC converter open circuit fault diagnosis method of the present invention, wherein: the sub-module capacitance current observation equation is established according to the structure of the sub-module in the modular multi-level converter, including:

[0015] Modular multilevel converter submodule switching function S xi Expressed as:

[0016] Among them, S1 represents the upper tube IGBT in the submodule, and S2 represents the lower tube IGBT in the submodule;

[0017] When the switch function S xi =1, the submodule is in operation and the output voltage is equal to the capacitor voltage;

[0018] When the switch function S xi =0, the submodule is in bypass operation and the output voltage is 0.

[0019] As a preferred solution of the MMC-based medium voltage DC converter open circuit fault diagnosis method of the present invention, wherein: the establishment of the submodule capacitance current observation equation according to the structure of the submodule in the modular multilevel converter further includes:

[0020] The actual value of the capacitive current of the modular multilevel converter submodule is expressed as:

[0021] Among them, u cm (k) and u cm (k-1) represents the actual value of the submodule capacitor voltage collected by the sensor at time k and time k-1, respectively, and C represents the submodule capacitance value;

[0022] The predicted value of the capacitor current of the modular multilevel converter submodule is expressed as:

[0023] Among them, u cpre (k+1) and ucpre (k-1) represents the predicted values ​​of the submodule capacitor voltage at time k+1 and k-1 respectively.

[0024] As a preferred solution of the MMC-based medium voltage DC converter open circuit fault diagnosis method of the present invention, the determination of the relationship between the actual value and the predicted value of the capacitor current and the first threshold value includes:

[0025] When the actual capacitance current of the submodule is not less than the first positive threshold I th When the actual capacitance current of the submodule is not greater than the negative first threshold -I th When , set the current path state to 1;

[0026] When the actual capacitor current of the submodule is between the positive first threshold and the negative first threshold, the current path state is set to 0;

[0027] When the submodule predicts that the capacitor current is not less than the first positive threshold I th When the submodule predicts that the capacitor current is not greater than the negative first threshold -I th When , set the current path state to 1;

[0028] When the submodule predicts that the capacitor current is between the positive first threshold and the negative first threshold, the current path state is set to 0.

[0029] As a preferred embodiment of the MMC-based medium voltage DC converter open circuit fault diagnosis method of the present invention, the judgment result based on the relationship between the actual value and the predicted value of the capacitor current and the first threshold value, combined with the display of the open circuit fault diagnosis result on the fault indicator, includes:

[0030] Define a normal state indicator X1 as follows:

[0031] Among them, X1 is the indicator of normal state, Indicates "XOR", X1=0 indicates that the MMC is running in normal state, X1=1 indicates that the MMC is running in fault state;

[0032] When the switch state S=1, the bridge arm current i x When <0, the upper IGBT is considered faulty and recorded as T1 fault. The T1 fault indicator is defined as follows:

[0033] X2=S·X1

[0034] Among them, X2 is a T1 fault indicator, “·” represents “AND”, X2=1 indicates that a T1 fault exists in the submodule, and X2=0 indicates that no T1 fault exists in the submodule.

[0035] As a preferred embodiment of the method for diagnosing an open circuit fault of a medium voltage DC converter based on MMC according to the present invention, the judgment result based on the relationship between the actual value and the predicted value of the capacitor current and the first threshold value, combined with the display of the open circuit fault diagnosis result by a fault indicator, further comprises:

[0036] In the switching state S=0, the bridge arm current i x >0, the lower IGBT is considered to be faulty and recorded as T2 fault. The T2 fault indicator is defined as follows:

[0037] Among them, X3 is a T2 fault indicator, “-” means “not”, X3=1 indicates that a T2 fault exists in the submodule, and X3=0 indicates that a T2 fault does not exist in the submodule.

[0038] As a preferred embodiment of the method for diagnosing an open circuit fault of a medium voltage DC converter based on MMC according to the present invention, the judgment result based on the relationship between the actual value and the predicted value of the capacitor current and the first threshold value, combined with the display of the open circuit fault diagnosis result by a fault indicator, further comprises:

[0039] The total fault indicator X is defined as follows:

[0040] X=(X1,X2,X3)

[0041] Among them, X1, X2 and X3 are normal status indicator, T1 fault indicator and T2 fault indicator respectively;

[0042] When the total fault indicator X is equal to (0, 0, 0), there is no fault in the MMC system;

[0043] When the total fault indicator X is not equal to (0, 0, 0) and lasts for at least one cycle, it means that a fault has occurred;

[0044] Compare the total fault indicator X with (1, 1, 0) and (1, 0, 1) in sequence. If the total fault indicator X is equal to (1, 1, 0) and the fault duration is greater than the second threshold T c When , it is judged as T1 failure;

[0045] If the fault duration is less than the second threshold T c When , it is determined whether the total fault indicator X is equal to (1, 0, 1);

[0046] If they are equal, and the fault duration is greater than the second threshold T c When , it is judged as T2 fault;

[0047] If they are equal, and the fault duration is less than the second threshold T c When , the judgment ends;

[0048] If they are not equal, the judgment ends.

[0049] A medium voltage DC converter open circuit fault diagnosis system based on MMC, characterized by comprising: a data acquisition module, a logic establishment module, a judgment module and a fault result display module,

[0050] A data acquisition module, the data acquisition module is used to obtain switch status, voltage and current signal data of the submodules in the modular multilevel converter when they are in normal working state and fault state;

[0051] a logic establishment module, the logic establishment module being used to establish different fault judgment logics according to the switch states, voltage and current signal data of the submodules in normal working state and fault state, and to establish a fault indicator according to the different fault judgment logics;

[0052] a judgment module, the judgment module being configured to establish a submodule capacitor current observation equation according to the structure of the submodule in the modular multilevel converter, and to judge a relationship between an actual value and a predicted value of the capacitor current and a first threshold;

[0053] A fault result display module is used to display the open circuit fault diagnosis result in combination with a fault indicator based on the judgment result of the relationship between the actual value and the predicted value of the capacitor current and the first threshold.

[0054] A computer device includes a memory and a processor, wherein the memory stores a computer program, and wherein the processor implements the steps of the above method when executing the computer program.

[0055] A computer-readable storage medium stores a computer program thereon, wherein the computer program implements the steps of the method described above when executed by a processor.

[0056] Beneficial effects of the present invention: The present invention proposes a method and system for diagnosing open-circuit faults of medium-voltage DC converters based on MMC, which obtains the switch state, voltage, and current signal data of the submodules in the normal working state and the fault state of the modular multi-level converter; establishes different fault judgment logics based on the switch state, voltage, and current signal data of the submodules in the normal working state and the fault state, and establishes a fault indicator based on the different fault judgment logics; establishes a submodule capacitor current observation equation based on the structure of the submodules in the modular multi-level converter, and judges the relationship between the actual value and predicted value of the capacitor current and the first threshold; displays the open-circuit fault diagnosis result in combination with the fault indicator based on the judgment result of the relationship between the actual value and predicted value of the capacitor current and the first threshold. This patent utilizes the capacitor current path and switch state information, and can quickly and accurately perform fault diagnosis when a fault occurs, providing a feasible solution for practical engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort. Among them:

[0058] FIG1 is a flow chart of a method and system for diagnosing an open-circuit fault of a medium-voltage DC converter based on MMC according to an embodiment of the present invention;

[0059] FIG2 is a topological diagram of an MMC DC converter according to an MMC-based medium voltage DC converter open circuit fault diagnosis method and system provided by one embodiment of the present invention;

[0060] FIG3 is a current path diagram of an upper tube IGBT fault in a medium voltage DC converter open circuit fault diagnosis method and system based on MMC provided by one embodiment of the present invention, (a) a schematic diagram of current path 1, and (b) a schematic diagram of current path 2;

[0061] FIG4 is a current path diagram of a method and system for diagnosing an open-circuit fault of a medium-voltage DC converter based on MMC under a faulty lower-side IGBT according to an embodiment of the present invention, (c) a schematic diagram of current path 3, and (d) a schematic diagram of current path 4;

[0062] FIG5 is a flowchart of an open-circuit fault diagnosis method and system for a medium-voltage DC converter based on MMC according to an embodiment of the present invention;

[0063] FIG6 is a diagram showing a simulation waveform of an open-circuit fault of an IGBT on a submodule 1 of an MMC-based medium-voltage DC converter open-circuit fault diagnosis method and system provided by one embodiment of the present invention, (a) a diagram showing the actual and predicted capacitor current of the submodule 1, (b) a diagram showing the error between the actual and predicted capacitor current of a normal submodule, (c) a diagram showing the switch state of the submodule 1, and (d) a diagram showing the triggering time of the fault indicator of the submodule 1;

[0064] FIG7 is a diagram showing a simulation waveform of an open-circuit fault of the lower tube IGBT of submodule 1 of an MMC-based medium-voltage DC converter open-circuit fault diagnosis method and system provided by one embodiment of the present invention, (a) a diagram showing the actual and predicted capacitor current of submodule 1, (b) a diagram showing the error value of the actual and predicted capacitor current of a normal submodule, (c) a diagram showing the switch state of submodule 1, and (d) a diagram showing the triggering time of the fault indicator of submodule 1;

[0065] FIG8 is an internal structure diagram of a computer device of an MMC-based medium voltage DC converter open circuit fault diagnosis method and system provided by one embodiment of the present invention. DETAILED DESCRIPTION

[0066] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, the following detailed description of the specific embodiments of the present invention is given in conjunction with the accompanying drawings. It is obvious that the described embodiments are only part of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in this field without creative work should fall within the scope of protection of the present invention.

[0067] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0068] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0069] The present invention is described in detail with reference to schematic diagrams. For ease of illustration, cross-sectional views of device structures may be partially enlarged and not to scale when describing embodiments of the present invention. Furthermore, the schematic diagrams are merely illustrative and should not limit the scope of the present invention. Furthermore, in actual production, the three-dimensional dimensions of length, width, and depth should be included.

[0070] Furthermore, in the description of the present invention, it should be noted that the terms "upper, lower, inner, and outer" and other references to orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first, second, or third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0071] In this disclosure, unless otherwise specified or limited, the terms "mounted," "connected," and "connected" should be interpreted broadly. For example, they may refer to fixed, removable, or integral connections. They may also refer to mechanical, electrical, or direct connections, indirect connections through an intermediary, or internal communication between two components. Those skilled in the art will understand the specific meanings of these terms in this disclosure.

[0072] Example 1

[0073] 1-8 , which illustrate a first embodiment of the present invention, provide a method and system for diagnosing an open-circuit fault of a medium-voltage DC converter based on an MMC, including:

[0074] Obtaining the switch status, voltage and current signal data of the submodules in the modular multilevel converter when they are in normal working state and fault state;

[0075] Furthermore, different fault judgment logics are established based on the switch states, voltage and current signal data of the submodules in normal working state and fault state, and fault indicators are established based on the different fault judgment logics;

[0076] Furthermore, a submodule capacitor current observation equation is established according to the structure of the submodule in the modular multilevel converter, and a relationship between the actual value and the predicted value of the capacitor current and the first threshold is determined;

[0077] Among them, the sub-module capacitance current observation equation is established according to the structure of the sub-module in the modular multi-level converter, including:

[0078] Modular multilevel converter submodule switching function S xi Expressed as:

[0079] Among them, S1 represents the upper tube IGBT in the submodule, and S2 represents the lower tube IGBT in the submodule;

[0080] It should be noted that when the switch function S xi =1, the submodule is in operation and the output voltage is equal to the capacitor voltage;

[0081] It should be noted that when the switch function S xi =0, the submodule is in bypass operation and the output voltage is 0.

[0082] Furthermore, according to the structure of the sub-modules in the modular multi-level converter, the sub-module capacitance current observation equation is established, which also includes:

[0083] The actual value of the capacitive current of the modular multilevel converter submodule is expressed as:

[0084] Among them, u cm (k) and u cm (k-1) represents the actual value of the submodule capacitor voltage collected by the sensor at time k and time k-1, respectively, and C represents the submodule capacitance value;

[0085] Furthermore, the predicted value of the capacitor current of the modular multilevel converter submodule is expressed as:

[0086] Among them, u cpre (k+1) and u cpre (k-1) represents the predicted values ​​of the submodule capacitor voltage at time k+1 and k-1 respectively.

[0087] It should be noted that determining the relationship between the actual value and the predicted value of the capacitor current and the first threshold value includes:

[0088] When the actual capacitance current of the submodule is not less than the first positive threshold I th When the actual capacitance current of the submodule is not greater than the negative first threshold -I th When , set the current path state to 1;

[0089] When the actual capacitor current of the submodule is between the positive first threshold and the negative first threshold, the current path state is set to 0;

[0090] When the submodule predicts that the capacitor current is not less than the first positive threshold I th When the submodule predicts that the capacitor current is not greater than the negative first threshold -I th When , set the current path state to 1;

[0091] When the submodule predicts that the capacitor current is between the positive first threshold and the negative first threshold, the current path state is set to 0.

[0092] Furthermore, based on the judgment result of the relationship between the actual value and the predicted value of the capacitor current and the first threshold, the open circuit fault diagnosis result is displayed in combination with the fault indicator.

[0093] The method of determining the relationship between the actual value and the predicted value of the capacitor current and the first threshold value and displaying the open circuit fault diagnosis result in combination with the fault indicator includes:

[0094] Define a normal state indicator X1 as follows:

[0095] Among them, X1 is the indicator of normal state, Indicates "XOR", X1=0 indicates that the MMC is running in normal state, X1=1 indicates that the MMC is running in fault state;

[0096] Furthermore, when the switch state S=1, the bridge arm current i x When <0, the upper IGBT is considered faulty and recorded as T1 fault. The T1 fault indicator is defined as follows:

[0097] X2=S·X1

[0098] Among them, X2 is a T1 fault indicator, “·” represents “AND”, X2=1 indicates that a T1 fault exists in the submodule, and X2=0 indicates that no T1 fault exists in the submodule.

[0099] Furthermore, based on the judgment result of the relationship between the actual value and the predicted value of the capacitor current and the first threshold, the open circuit fault diagnosis result displayed by the fault indicator also includes:

[0100] In the switching state S=0, the bridge arm current i x >0, the lower IGBT is considered to be faulty and recorded as T2 fault. The T2 fault indicator is defined as follows:

[0101] Among them, X3 is a T2 fault indicator, “-” means “not”, X3=1 indicates that a T2 fault exists in the submodule, and X3=0 indicates that a T2 fault does not exist in the submodule.

[0102] Furthermore, based on the judgment result of the relationship between the actual value and the predicted value of the capacitor current and the first threshold, the open circuit fault diagnosis result displayed by the fault indicator also includes:

[0103] The total fault indicator X is defined as follows:

[0104] X=(X1,X2,X3)

[0105] Among them, X1, X2 and X3 are normal status indicator, T1 fault indicator and T2 fault indicator respectively;

[0106] It should be noted that when the total fault indicator X is equal to (0, 0, 0), there is no fault in the MMC system;

[0107] It should be noted that when the total fault indicator X is not equal to (0, 0, 0) and lasts for at least one cycle, it means that a fault has occurred;

[0108] It should be noted that the total fault indicator X is compared with (1, 1, 0) and (1, 0, 1) in sequence. If the total fault indicator X is equal to (1, 1, 0) and the fault duration is greater than the second threshold T c When , it is judged as T1 failure;

[0109] It should be noted that if the fault duration is less than the second threshold T c When , it is determined whether the total fault indicator X is equal to (1, 0, 1);

[0110] It should be noted that if they are equal and the fault duration is greater than the second threshold T c When , it is judged as T2 fault;

[0111] It should be noted that if they are equal and the fault duration is less than the second threshold T c When , the judgment ends;

[0112] It should be noted that if they are not equal, the judgment is terminated.

[0113] It should be noted that when a submodule fails, there will be inconsistency between the actual current of the submodule and the current predicted by the model, which will eventually lead to a significant error between the capacitor voltage of the submodule and the capacitor voltage predicted by the model.

[0114] It should be noted that by promptly detecting and locating open-circuit faults, this patent allows for rapid repair, preventing the fault from escalating and impacting the entire system, and improving system reliability and stability. This method can quickly diagnose and locate the problem when it occurs, reducing troubleshooting time and human resources, and lowering maintenance costs.

[0115] It should be noted that the fault display uses advanced signal processing technology to quickly and accurately diagnose module open-circuit faults and provide detailed fault location information. Based on power information and other relevant parameters, a designed algorithm determines whether an open-circuit fault exists and locates the submodule where the fault occurs.

[0116] In summary, the present invention proposes a method for diagnosing open-circuit faults of medium-voltage DC converters based on MMC, which obtains the switch state, voltage, and current signal data of the submodules in the normal working state and the fault state of the modular multi-level converter; establishes different fault judgment logics based on the switch state, voltage, and current signal data of the submodules in the normal working state and the fault state, and establishes a fault indicator based on the different fault judgment logics; establishes a submodule capacitor current observation equation based on the structure of the submodules in the modular multi-level converter, and judges the relationship between the actual value and predicted value of the capacitor current and the first threshold; based on the judgment result of the relationship between the actual value and predicted value of the capacitor current and the first threshold, the open-circuit fault diagnosis result is displayed in combination with the fault indicator. This patent utilizes the capacitor current path and switch state information, and can quickly and accurately perform fault diagnosis when a fault occurs, providing a feasible solution for practical engineering applications.

[0117] In a preferred embodiment, a medium voltage DC converter open circuit fault diagnosis system based on MMC includes: a data acquisition module, a logic establishment module, a judgment module and a fault result display module.

[0118] A data acquisition module is used to obtain switch status, voltage and current signal data of the submodules in the modular multilevel converter when they are in normal working state and fault state;

[0119] A logic establishment module is used to establish different fault judgment logics based on the switch states, voltage and current signal data of the submodules in normal working state and fault state, and to establish fault indicators based on the different fault judgment logics;

[0120] A judgment module, the judgment module is used to establish a sub-module capacitor current observation equation according to the structure of the sub-module in the modular multi-level converter, and to judge the relationship between the actual value and the predicted value of the capacitor current and the first threshold value;

[0121] The fault result display module is used to display the open circuit fault diagnosis result in combination with the fault indicator based on the judgment result of the relationship between the actual value and the predicted value of the capacitor current and the first threshold.

[0122] The above-mentioned unit modules may be embedded in or independent of the processor in the computer device in the form of hardware, or may be stored in the memory of the computer device in the form of software, so that the processor can call and execute the operations corresponding to the above-mentioned modules.

[0123] In one embodiment, a computer device is provided. The computer device may be a terminal, and its internal structure diagram may be as shown in FIG8 . The computer device includes a processor, memory, a communication interface, a display screen, and an input device connected via a system bus. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and computer program in the non-volatile storage medium. The communication interface of the computer device is used to communicate with an external terminal via wired or wireless communication. The wireless communication may be achieved via Wi-Fi, a carrier network, NFC (near-field communication), or other technologies. When executed by the processor, the computer program implements an MMC-based method for diagnosing open-circuit faults in medium-voltage DC converters. The display screen of the computer device may be a liquid crystal display or an electronic ink display. The input device of the computer device may be a touch screen covering the display screen, or may be buttons, a trackball, or a touchpad provided on the computer device housing, or may be an external keyboard, touchpad, or mouse.

[0124] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the following steps are implemented:

[0125] Obtaining the switch status, voltage and current signal data of the submodules in the modular multilevel converter when they are in normal working state and fault state;

[0126] According to the switch status, voltage and current signal data of the submodule in normal working state and fault state, different fault judgment logics are established, and fault indicators are established according to the different fault judgment logics;

[0127] Establishing a submodule capacitor current observation equation according to the structure of the submodule in the modular multilevel converter, and determining a relationship between an actual value and a predicted value of the capacitor current and a first threshold value;

[0128] The open circuit fault diagnosis result is displayed in combination with the fault indicator based on the judgment result of the relationship between the actual value and the predicted value of the capacitor current and the first threshold.

[0129] Example 2

[0130] 2-7 , which is an embodiment of the present invention, provides a method and system for diagnosing open-circuit faults of a medium-voltage DC converter based on MMC. To verify the beneficial effects of the present invention, scientific demonstration is conducted through experiments.

[0131] The simulation results of setting the upper tube IGBT open circuit fault in submodule 1 at 0.5s and the lower tube IGBT open circuit fault in the upper bridge arm switching device are shown in Figure 6.

[0132] The upper IGBT open-circuit fault occurred at 0.5s. A comparison of the expected and predicted values ​​of the submodule capacitor current before and after the fault, as well as the simulation results of the submodule switching states, are shown in Figure 6. Figures 6(a) and 6(b) clearly show that the actual capacitor current state of faulty submodule 1 at 0.508s is bypass, while the predicted capacitor current state is discharge. The actual capacitor current paths of the remaining submodules are essentially consistent with the model-predicted capacitor current paths. Based on these current path differences and the submodule switching states in Figure 6(c), submodule 1 is detected and located as faulty, and the fault diagnosis time is 8ms.

[0133] Figure 7 is a simulation diagram of the open-circuit fault result of the lower tube IGBT of submodule 1. The open-circuit fault of the lower tube IGBT occurs at 0.5s. It can be clearly seen in Figures 7(a) and 7(b) that the actual capacitor current state of the faulty submodule 1 at 0.501s is charging, and the predicted capacitor current state is bypass. The actual capacitor current paths of the other submodules are basically consistent with the capacitor current paths predicted by the model. Based on the differences in their current paths and combined with the switching states of the submodules in Figure 7(c), submodule 1 is detected and located as a fault, and the fault diagnosis time is 6.2ms.

[0134] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

[0135] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code. The scheme in the embodiment of the present application can be implemented in various computer languages, for example, object-oriented programming language Java and literal translation scripting language JavaScript, etc.

[0136] The present application is described with reference to the flow chart and / or block diagram of the method, device (system), and computer program product according to the embodiment of the present application. It should be understood that each flow process and / or box in the flow chart and / or block diagram and the combination of the flow process and / or box in the flow chart and / or block diagram can be realized by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processing machine or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device produce a device for realizing the function specified in one flow chart flow or multiple flows and / or one box or multiple boxes of the block diagram.

[0137] These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce a product including an instruction device that implements the functions specified in one or more processes in the flowchart and / or one or more boxes in the block diagram.

[0138] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more processes in the flowchart and / or one or more boxes in the block diagram.

[0139] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0140] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A method for diagnosing open circuit faults of medium voltage DC converters based on MMC, characterized in that: include: Obtain switch status, voltage and current signal data of submodules in a modular multilevel converter when they are in normal working state and fault state; Establish different fault judgment logics according to the switch states, voltage and current signal data of the submodules in normal working state and fault state, and establish a fault indicator according to the different fault judgment logics; Establishing a submodule capacitor current observation equation according to the structure of the submodule in the modular multilevel converter, and determining the relationship between the actual value and the predicted value of the capacitor current and the first threshold value; The open circuit fault diagnosis result is displayed in combination with the fault indicator according to the judgment result of the relationship between the actual value and the predicted value of the capacitor current and the first threshold.

2. The method for diagnosing open circuit faults of medium voltage DC converters based on MMC according to claim 1, characterized in that: The establishing of the submodule capacitance current observation equation according to the structure of the submodule in the modular multilevel converter comprises: Modular multilevel converter submodule switching function S xi It is expressed as: Among them, S1 represents the upper tube IGBT in the submodule, and S2 represents the lower tube IGBT in the submodule; When the switch function S xi =1, the submodule is in operation, and the output voltage is equal to the capacitor voltage; When the switch function S xi =0, the submodule is in bypass operation and the output voltage is 0.

3. The method for diagnosing open circuit faults of medium voltage DC converters based on MMC according to claim 2, characterized in that: The establishing of the submodule capacitance current observation equation according to the structure of the submodule in the modular multilevel converter further comprises: The actual value of the capacitive current of the modular multilevel converter submodule is expressed as: Among them, u cm (k) and u cm (k-1) represents the actual value of the submodule capacitor voltage collected by the sensor at time k and time k-1, respectively, and C represents the submodule capacitance value; The predicted value of the capacitor current of the modular multilevel converter submodule is expressed as: Among them, u cpre (k+1) and u cpre (k-1) represents the predicted values ​​of the submodule capacitor voltage at time k+1 and k-1 respectively.

4. The method for diagnosing open circuit faults of medium voltage DC converters based on MMC according to claim 3, characterized in that: The determining of the relationship between the actual value and the predicted value of the capacitor current and the first threshold value includes: When the actual capacitor current of the submodule is not less than the first positive threshold I th When the actual capacitance current of the submodule is not greater than the negative first threshold value -I th When , set the current path state to 1; When the actual capacitor current of the submodule is between the positive first threshold and the negative first threshold, the current path state is set to 0; When the submodule predicts that the capacitor current is not less than the positive first threshold I th When the submodule predicts that the capacitor current is not greater than the negative first threshold -I th When , set the current path state to 1; When the submodule predicts that the capacitor current is between the positive first threshold and the negative first threshold, the current path state is set to 0.

5. The method for diagnosing open circuit faults of medium voltage DC converters based on MMC according to claim 4, characterized in that: The judgment result based on the relationship between the actual value and the predicted value of the capacitor current and the first threshold value, combined with the fault indicator to display the open circuit fault diagnosis result includes: Define a normal state indicator X1 as follows: Among them, X1 is the indicator of normal state, Indicates "XOR", X1=0 indicates that the MMC is running in normal state, and X1=1 indicates that the MMC is running in fault state; When the switch state S = 1, the bridge arm current i x When <0, the upper IGBT is considered to be faulty and recorded as T1 fault. The T1 fault indicator is defined as follows: X2=S·X1 Among them, X2 is a T1 fault indicator, "·" represents "and", X2=1 represents that a T1 fault exists in the submodule, and X2=0 represents that a T1 fault does not exist in the submodule.

6. The method for diagnosing open circuit faults of medium voltage DC converters based on MMC according to claim 5, characterized in that: The judgment result based on the relationship between the actual value and the predicted value of the capacitor current and the first threshold value, combined with the fault indicator to display the open circuit fault diagnosis result, also includes: When the switch state S = 0, the bridge arm current i x >0, the lower IGBT is considered to be faulty and recorded as T2 fault. The T2 fault indicator is defined as follows: Among them, X3 is a T2 fault indicator, "-" means "not", X3=1 means that the submodule has a T2 fault, and X3=0 means that the submodule does not have a T2 fault.

7. The method for diagnosing open circuit faults of medium voltage DC converters based on MMC according to claim 6, characterized in that: The judgment result based on the relationship between the actual value and the predicted value of the capacitor current and the first threshold value, combined with the fault indicator to display the open circuit fault diagnosis result, also includes: The overall fault indicator X is defined as follows: X=(X1,X2,X3) Among them, X1, X2 and X3 are normal status indicator, T1 fault indicator, T2 fault indicator respectively; When the total fault indicator X is equal to (0, 0, 0), the MMC system has no fault; When the total fault indicator X is not equal to (0, 0, 0) and lasts for at least one cycle, it means that a fault has occurred; The total fault indicator X is compared with (1, 1, 0) and (1, 0, 1) in sequence. If the total fault indicator X is equal to (1, 1, 0) and the fault duration is greater than the second threshold T c When , it is judged as T1 failure; If the fault duration is less than the second threshold T c When , it is determined whether the total fault indicator X is equal to (1, 0, 1); If they are equal, and the fault duration is greater than the second threshold T c When , it is judged as T2 fault; If they are equal, and the fault duration is less than the second threshold T c When , the judgment ends; If they are not equal, the judgment ends.

8. A medium voltage DC converter open circuit fault diagnosis system based on MMC, characterized in that: include: Data acquisition module, logic establishment module, judgment module and fault result display module, A data acquisition module, the data acquisition module is used to obtain switch states, voltage and current signal data of submodules in a normal working state and a fault state of the modular multilevel converter; A logic establishment module, the logic establishment module is used to establish different fault judgment logics according to the switch states, voltage and current signal data of the submodules in normal working state and fault state, and establish a fault indicator according to the different fault judgment logics; A judgment module, the judgment module is used to establish a submodule capacitor current observation equation according to the structure of the submodule in the modular multi-level converter, and judge the relationship between the actual value and the predicted value of the capacitor current and the first threshold value; A fault result display module is used to display the open circuit fault diagnosis result in combination with the fault indicator according to the judgment result of the relationship between the actual value and the predicted value of the capacitor current and the first threshold.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

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

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