A method and system for diagnosing faults of flexible direct current converter valve submodules

Abstract

The present invention discloses a method for diagnosing faults of submodules of flexible direct current converter valves, comprising: obtaining an output sequence of a capacitor voltage sensor of each submodule, calculating a submodule autocorrelation coefficient using a capacitor voltage output sequence of adjacent periods, and comparing the submodule autocorrelation coefficient with a set autocorrelation coefficient threshold value, wherein the judgment comprises whether a submodule fails; when a submodule fails, calculating an effective value of a capacitor voltage increment, an output average value of a capacitor voltage sensor, and a difference between a positive zero crossing number and a negative zero crossing number of a capacitor voltage increment, to obtain a calculation result; according to the calculation result, identifying the fault type, and performing joint fault diagnosis using only the information of the submodule capacitor voltage itself, wherein the algorithm is simple, does not require communication with a main controller, and reduces the burden of hardware cost.

Description

Technical Field

[0001] The present invention relates to the technical field of multi-type fault monitoring of MMC flexible direct current converter valves, and in particular to a flexible direct current converter valve submodule fault diagnosis method and system. Background Art

[0002] The large-scale access of renewable energy and the construction of new power systems have led to a continuous increase in the proportion of flexible direct current transmission in the power system. As a key energy conversion device in flexible direct current transmission, the operation reliability of flexible direct current converter valves is particularly important. Compared with conventional direct current transmission equipment based on thyristors, flexible direct current converter valves have more complex structures, a large number of submodules, and significantly higher operation and maintenance costs, and their fault monitoring and diagnosis requirements are constantly increasing. The existing fault diagnosis methods for flexible direct current converter valves have the disadvantages of long detection delay, low online diagnosis accuracy, and often only targeting a certain type of fault. The actual flexible direct current converter valve system may contain hundreds of submodules, and various types of faults may occur inside each submodule, including open / short circuit faults of the insulated gate bipolar transistor (IGBT) switch of the submodule, and various types of faults of the submodule sensor. Existing research has difficulty in effectively distinguishing different types of faults. Some of the above-mentioned different types of faults have similar fault characteristics. How to effectively distinguish and identify various types of converter valve faults and reduce detection delay and false alarm rate has become a difficulty in fault location diagnosis and identification.

[0003] In summary, in response to the problem of multiple types of faults in existing flexible DC converter valve sub-modules, the present invention proposes a joint diagnosis method for flexible DC converter valve sub-module switch open circuit faults and voltage sensor faults based on the capacitor voltage information of a single sub-module. This method does not require communication with other sub-modules and the main controller to achieve fault location by identifying the fault type of the flexible DC converter valve. Summary of the invention

[0004] In view of the above-mentioned problems, the present invention is proposed.

[0005] Therefore, the technical problem solved by the present invention is: the present invention solves the problems of the existing flexible direct current converter valve fault diagnosis method, such as long detection delay, low online diagnosis accuracy, and often only targeting a certain type of fault.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] In a first aspect, the present invention provides a method for diagnosing faults of a flexible direct current converter valve submodule, comprising:

[0008] Obtaining the output sequence of the capacitance and voltage sensor of each submodule, calculating the submodule autocorrelation coefficient using the capacitance and voltage output sequence of the previous adjacent cycle, and comparing the submodule autocorrelation coefficient with a set autocorrelation coefficient threshold to determine whether the submodule fails;

[0009] When a submodule fails, the effective value of the capacitor voltage increment of the failed submodule, the output average value of the capacitor voltage sensor, and the difference between the positive zero crossing times and the negative zero crossing times of the capacitor voltage increment are calculated to obtain a calculation result;

[0010] According to the calculation result, the fault type is identified.

[0011] As a preferred solution of the flexible direct current converter valve submodule fault diagnosis method of the present invention, the submodule autocorrelation coefficient is calculated by using the capacitor voltage output sequence of the previous adjacent cycle, including:

[0012] The submodule voltage sensor output sequence within a cycle is stored in a sliding manner, and the autocorrelation coefficient is calculated with the submodule capacitor voltage output sequence of the previous cycle. The normalized autocorrelation coefficient is expressed as:

[0013] ,

[0014] in, is the sliding window length, is the average value of the capacitor voltage of the flexible direct current converter valve submodule under normal working conditions, is the capacitor voltage output sequence value in the previous cycle, It is the capacitor voltage output sequence value in the current cycle.

[0015] As a preferred solution of the method for diagnosing faults of flexible direct current converter valve submodules of the present invention, the comparison and judgment of the submodule autocorrelation coefficient with a set autocorrelation coefficient threshold comprises:

[0016] When the absolute value of the submodule autocorrelation coefficient is less than the set autocorrelation coefficient threshold, the counter performs a self-increment operation. When the counter value is greater than the set number of times, the submodule fails and the fault position of the submodule is marked.

[0017] As a preferred solution of the fault diagnosis method of the flexible direct current converter valve submodule of the present invention, when a submodule fails, the effective value of the capacitor voltage increment of the faulty submodule, the output average value of the capacitor voltage sensor, and the difference between the positive zero crossing number and the negative zero crossing number of the capacitor voltage increment are calculated to obtain the calculation result, including:

[0018] The effective value of the capacitor voltage increment during two cycles is calculated as:

[0019] ,

[0020] in, is the period of the AC signal, is the square of the discrete form of the submodule capacitor voltage increment, is the current sampling point of the accumulation process, is the total number of sampling points;

[0021] The output average value of the capacitor voltage sensor is expressed as:

[0022] ,

[0023] in, is the current sampling point of the accumulation process, is the total number of sampling points, For the The capacitor voltage value at each sampling point is is the period of the AC signal;

[0024] The difference between the number of positive zero crossings and the number of negative zero crossings of the capacitor voltage increment is expressed as: ,in, is the number of positive zero crossings of the capacitor voltage increment, is the number of negative zero crossings.

[0025] As a preferred solution of the method for diagnosing faults of flexible direct current converter valve submodules of the present invention, the method for identifying the fault type according to the calculation result includes:

[0026] when , it is determined that the fault at this time is a type A fault, and the type A fault is a sensor stuck fault or a sensor disconnection fault;

[0027] when , it is determined that the fault at this time is a type B fault, and the type B fault is an upper switch fault of the submodule switch tube, a lower switch fault of the switch tube, or a sensor gain fault.

[0028] As a preferred solution of the method for diagnosing faults of flexible direct current converter valve submodules of the present invention, wherein: according to the calculation result, identifying the fault type further comprises:

[0029] When a type A fault occurs, calculate the output average of the submodule capacitor voltage sensor ;

[0030] like , then the sensor is disconnected;

[0031] like , the sensor is stuck.

[0032] As a preferred solution of the fault diagnosis method of the flexible direct current converter valve submodule of the present invention, the difference between the number of positive zero crossings and the number of negative zero crossings of the capacitor voltage increment includes:

[0033] When a type B fault occurs, the output average value of the submodule capacitor voltage sensor is calculated. If the output average value is lower than the average value of the capacitor voltage of the flexible direct current converter valve submodule under normal working conditions, a sensor gain fault occurs;

[0034] If the output average value is higher than the average value of the capacitor voltage of the flexible direct current converter valve submodule under normal working conditions, the difference between the positive and negative zero crossing times of the submodule capacitor voltage increment is calculated. ;

[0035] when If it is greater than 0, an upper switch failure of the insulated gate bipolar transistor of the submodule occurs;

[0036] when If it is equal to 0, a lower switch failure of the insulated gate bipolar transistor of the submodule occurs;

[0037] when If it is less than 0, a sensor gain fault occurs.

[0038] In a second aspect, the present invention provides a flexible direct current converter valve submodule fault diagnosis system, comprising:

[0039] A judgment module is used to obtain the output sequence of the capacitance and voltage sensor of each submodule, calculate the submodule autocorrelation coefficient by using the capacitance and voltage output sequence of the previous adjacent cycle, and compare the submodule autocorrelation coefficient with a set autocorrelation coefficient threshold to determine whether the submodule fails;

[0040] A calculation module, used for calculating the effective value of the capacitor voltage increment of the faulty submodule, the output average value of the capacitor voltage sensor, and the difference between the number of positive zero crossings of the capacitor voltage increment and the number of negative zero crossings of the capacitor voltage increment when a submodule fails, to obtain a calculation result;

[0041] The identification module is used to identify the fault type according to the calculation result.

[0042] In a third aspect, the present invention provides a computing device, comprising:

[0043] Memory and processor;

[0044] The memory is used to store computer executable instructions, and the processor is used to execute the computer executable instructions. When the computer executable instructions are executed by the processor, the steps of the flexible direct current converter valve submodule fault diagnosis method are implemented.

[0045] In a fourth aspect, the present invention provides a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the steps of the flexible direct current converter valve submodule fault diagnosis method.

[0046] Beneficial effects of the present invention: the flexible direct current converter valve submodule fault diagnosis method proposed in the present invention can jointly and simultaneously diagnose the MMC flexible direct current converter valve submodule IGBT open circuit fault, voltage sensor disconnection fault, stuck fault, and gain fault, and realize fault type identification and fault location of different faults; the fault position can be located within 20ms, and the fault type can be identified within 40ms on the basis of fault location, including submodule IGBT upper switch fault, submodule IGBT lower switch fault, voltage sensor stuck fault, voltage sensor disconnection fault, and voltage sensor gain fault; the fault diagnosis process only depends on the voltage sensor information of this submodule, and does not require other submodule capacitor voltage or bridge arm current, circulating current, output phase current and other information, so there is no need to communicate with other submodules or the main controller, reducing the hardware burden and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0048] Figure 1 An overall flow chart of a fault diagnosis method for a flexible direct current converter valve submodule provided by the present invention;

[0049] Figure 2 A waveform diagram of switch fault location on the IGBT of a flexible direct current converter valve submodule fault diagnosis method provided by the present invention;

[0050] Figure 3 A waveform diagram of the IGBT lower switch fault location of a flexible direct current converter valve submodule fault diagnosis method provided by the present invention;

[0051] Figure 4 A voltage sensor disconnection fault location waveform diagram of a flexible direct current converter valve submodule fault diagnosis method provided by the present invention;

[0052] Figure 5 A waveform diagram of a voltage sensor stuck fault location in a flexible direct current converter valve submodule fault diagnosis method provided by the present invention;

[0053] Figure 6A voltage sensor high-gain fault location waveform diagram of a flexible direct current converter valve submodule fault diagnosis method provided by the present invention;

[0054] Figure 7 A voltage sensor low gain fault location waveform diagram of a flexible direct current converter valve submodule fault diagnosis method provided by the present invention;

[0055] Figure 8 A waveform diagram of switch fault diagnosis on IGBT of a flexible direct current converter valve submodule fault diagnosis method provided by the present invention;

[0056] Fig. 9 A waveform diagram of IGBT lower switch fault diagnosis of a flexible direct current converter valve submodule fault diagnosis method provided by the present invention;

[0057] Fig.10 A voltage sensor disconnection fault diagnosis waveform diagram of a flexible direct current converter valve submodule fault diagnosis method provided by the present invention;

[0058] Fig.11 A voltage sensor stuck fault diagnosis waveform diagram of a flexible direct current converter valve submodule fault diagnosis method provided by the present invention;

[0059] Fig.12 A voltage sensor high-gain fault diagnosis waveform diagram of a flexible direct current converter valve submodule fault diagnosis method provided by the present invention;

[0060] Fig.13 A voltage sensor low gain fault diagnosis waveform diagram of a flexible direct current converter valve submodule fault diagnosis method provided by the present invention;

[0061] Fig.14 A schematic diagram of the flow path of the switch fault current on the MMC submodule of a flexible direct current converter valve submodule fault diagnosis method provided by the present invention;

[0062] Fig.15 A schematic diagram of the flow path of the switch fault current under the MMC submodule of a flexible direct current converter valve submodule fault diagnosis method provided by the present invention. DETAILED DESCRIPTION

[0063] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0064] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0065] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0066] The present invention is described in detail with reference to schematic diagrams. When describing the embodiments of the present invention, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0067] At the same time, in the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "upper, lower, inner and outer" are based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first, second or third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0068] In the present invention, unless otherwise clearly specified and limited, the terms "install, connect, connect" should be understood in a broad sense, for example: it can be a fixed connection, a detachable connection or an integral connection; it can also be a mechanical connection, an electrical connection or a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0069] Example 1 Reference Figure 1-Figure 15 , is an embodiment of the present invention, and provides a method for diagnosing faults of a flexible direct current converter valve submodule, comprising:

[0070] S100: Obtain the output sequence of the capacitance and voltage sensor of each submodule, calculate the submodule autocorrelation coefficient by using the capacitance and voltage output sequence of the previous adjacent cycle, compare the submodule autocorrelation coefficient with the set autocorrelation coefficient threshold, and determine whether the submodule fails;

[0071] In the embodiment of the present application, the submodule voltage sensor output sequence within one cycle is stored in a sliding manner, and the autocorrelation coefficient is calculated with the submodule capacitor voltage output sequence of the previous cycle. The normalized autocorrelation coefficient is expressed as:

[0072] ,

[0073] in, is the sliding window length, is the average value of the capacitor voltage of the flexible direct current converter valve submodule under normal working conditions, is the capacitor voltage output sequence value in the previous cycle, It is the capacitor voltage output sequence value in the current cycle.

[0074] For example, if the AC side cycle is , the sampling frequency is , then the sliding window selects sampling points, the length of each slide is , The selection should balance the computational cost and positioning speed. When , the length of each slide is 20 sampling points, and the frequency of calculating the autocorrelation coefficient is .

[0075] Specifically, in the MMC flexible direct current converter valve, each bridge arm contains Half-bridge submodule units, each submodule capacitor voltage is ,in, , representing three groups of ABC, ,in, For the upper bridge arm, is the lower bridge arm, , is the submodule serial number in the bridge arm;

[0076] = / ,in, is the sampling frequency, is the AC side frequency, From 0 to , respectively traverse the capacitor voltage value output sequence value in an AC cycle, and slide each time the autocorrelation coefficient is calculated cycles, The appropriate value can be selected according to the sampling frequency; Is it within the specified range, i.e. , is the set autocorrelation coefficient threshold;

[0077] Autocorrelation coefficient threshold The value is between 0.4-0.75;

[0078] It should be noted that the autocorrelation coefficient threshold It reflects the distortion of the submodule capacitor voltage waveform in the two AC cycles before and after. The closer the value is to 1, the faster the fault identification speed will be, but it will increase the misjudgment rate. The closer the value is to 0, the greater the waveform distortion will be in the two AC cycles before and after, which will improve the accuracy of fault identification but reduce the fault identification rate. Considering that fault location is the basis for subsequent fault type identification, the autocorrelation coefficient threshold is set to The value is between 0.4 and 0.75, which ensures the fault response rate and fault identification accuracy.

[0079] In an embodiment of the present application, when the absolute value of the submodule autocorrelation coefficient is less than the set autocorrelation coefficient threshold, the counter performs a self-increment operation. When the counter value is greater than the set number of times, the submodule fails and the fault location of the submodule is marked.

[0080] Specifically, when a submodule fails, the submodule flag is set to 1, and the simulation results are as follows: Figure 2-Figure 7 As shown, first is the schematic diagram of the capacitor voltage waveform of the faulty submodule, which fails at 0.7, and then the calculated waveform of the autocorrelation coefficient of the faulty submodule. At the moment of the fault, the autocorrelation coefficient drops sharply and fluctuates. Secondly, the counter count value when the autocorrelation coefficient of the faulty submodule is lower than the threshold, and finally the fault flag bit. At the moment when the counter counts to the threshold, the fault flag bit is 1, realizing the positioning of the faulty submodule. The low autocorrelation coefficient for a period of time reflects the sudden change of the capacitor voltage value of the submodule;

[0081] The number of times set is selected according to the sampling frequency;

[0082] It should be noted that when the absolute value of the autocorrelation coefficient is lower than the set threshold, the counter is automatically superimposed, providing an early warning mechanism for the fault, allowing the system to take preventive measures before the fault occurs. Once the counter value exceeds the set number of times, the system can determine that a submodule has failed, and by setting the submodule flag position to 1, the specific location of the fault is clarified, thereby improving the reliability and stability of the system and reducing maintenance costs.

[0083] S200: When a submodule fails, the effective value of the capacitor voltage increment of the failed submodule, the output average value of the capacitor voltage sensor, and the difference between the number of positive zero crossings of the capacitor voltage increment and the number of negative zero crossings of the capacitor voltage increment are calculated to obtain a calculation result;

[0084] In the embodiment of the present application, the submodule capacitor voltage increment is expressed as:

[0085] ,

[0086] The discrete form is expressed as:

[0087] The effective value of the capacitor voltage increment during two cycles is calculated as:

[0088] ,

[0089] in, is the voltage change rate, is the current through the capacitor, is the capacitance value, is the capacitor voltage at the current sampling point, is the capacitor voltage at the previous sampling point, is the sampling period, is the period of the AC signal, is the square of the discrete form of the submodule capacitor voltage increment, is the current sampling point of the accumulation process, is the total number of sampling points.

[0090] Specifically, after locating the specific fault submodule, the fault type identification program of the corresponding submodule is executed according to the fault flag bit, and the effective value of the capacitor voltage increment, the output average value of the capacitor voltage sensor, and the difference between the positive zero crossing number and the negative zero crossing number of the capacitor voltage increment are calculated respectively.

[0091] In the embodiment of the present application, when , it is determined that the fault at this time is a type A fault, and a type A fault is a sensor stuck fault or a sensor disconnection fault;

[0092] when , it is determined that the fault at this time is a type B fault, and the type B fault is an upper switch fault of the submodule switch tube, a lower switch fault of the switch tube, or a sensor gain fault.

[0093] Specifically, It can be set to 2% of the effective value of the capacitor voltage increment when the MMC flexible DC converter valve is operating normally. The fault criterion is expressed as:

[0094] ,

[0095] In the embodiment of the present application, when a type A fault occurs, the output average value of the submodule capacitor voltage sensor is expressed as:

[0096] ,

[0097] in, is the current sampling point of the accumulation process, is the total number of sampling points, For the The capacitor voltage value at each sampling point is is the period of the AC signal;

[0098] like , then the sensor is disconnected;

[0099] like , the sensor is stuck.

[0100] Specifically, The average value of the submodule capacitor voltage during normal operation of the MMC flexible DC converter valve can be taken as 2%. At this time, a sensor disconnection fault occurs. Otherwise, it is considered that a sensor stuck fault occurs. The stuck value is the output voltage of the voltage sensor at this time. The fault judgment criterion is expressed as:

[0101] ,

[0102] In the embodiment of the present application, when a type B fault occurs, the output average value of the submodule capacitor voltage sensor is calculated. If the output average value is lower than the average value of the capacitor voltage of the flexible direct current converter valve submodule under normal working conditions, a sensor gain fault occurs;

[0103] If the output average value is higher than the average value of the capacitor voltage of the flexible direct current converter valve submodule under normal working conditions, the difference between the positive and negative zero crossing times of the submodule capacitor voltage increment is calculated and expressed as: ,in, is the number of positive zero crossings of the capacitor voltage increment, is the number of negative zero crossings;

[0104] when If it is greater than 0, an upper switch failure of the insulated gate bipolar transistor of the submodule occurs;

[0105] when If it is equal to 0, a lower switch failure of the insulated gate bipolar transistor of the submodule occurs;

[0106] when If it is less than 0, a sensor gain fault occurs.

[0107] Specifically, the fault criterion is expressed as:

[0108] ,

[0109] Specifically, the fault type identification simulation results are as follows: Figure 8-Figure 13As shown, the upper left represents the capacitor voltage waveform of the faulty submodule, the upper right is the fault flag position 1 of the faulty submodule after fault location, the middle left is the effective value of the capacitor voltage increment within two AC cycles calculated from the fault flag position 1, the middle right is the average capacitor voltage within two AC cycles calculated from the fault flag position 1, and compared with the average capacitor voltage of the submodule during normal operation, the lower left is the number of positive and negative zero crossings of the capacitor voltage increment and the difference in the number of times within two AC cycles after the fault flag position 1, the lower right is the diagnosis flag of various fault types, DF represents the voltage sensor disconnection fault flag, SF represents the voltage sensor stuck fault flag, LGF represents the voltage sensor low gain fault flag, USF represents the submodule upper switch open circuit fault flag, DSF represents the submodule lower switch open circuit fault flag, HGF represents the voltage sensor high gain fault flag.

[0110] It should be noted that the fault diagnosis process only relies on the capacitor voltage sensor information of this sub-module, and does not require information such as the capacitor voltage of other sub-modules or the bridge arm current, circulating current, output phase current, etc. Therefore, there is no need to communicate with other sub-modules or the main controller, which reduces the hardware burden and cost and speeds up the fault location and fault type identification.

[0111] S300: Identify the fault type according to the calculation result.

[0112] Specifically, the switch on the submodule IGBT is open circuit fault;

[0113] Assuming that only one component failure occurs in the MMC flexible DC converter valve system at the same time, and the submodule adopts a half-bridge structure, when a switch failure occurs on the submodule IGBT, such as Fig.14 As shown;

[0114] When a switch failure occurs on the submodule IGBT, the switch signal And the bridge arm current , the submodule is in the on state, and the current flows through the anti-parallel diode D1 and capacitor of Q1 itself, and then flows out of the submodule. At this time, the open circuit fault of Q1 has no effect on the working state of the submodule, which is the same as the normal operation. The current path is shown by the green dotted line.

[0115] When the switch signal Bridge arm current , at this time, the submodule is in the cut-off state, the current flows through Q2, and then flows out of the submodule. At this time, the Q1 open circuit fault has no effect on the working state of the submodule. The same as the normal operation, the current path is shown as the green dotted line.

[0116] When the switch signal And the bridge arm current When the current is turned on, it should flow through the capacitor and Q1 and finally out of the submodule. However, due to the open circuit failure of the upper switch tube Q1, the current flows out of the submodule through Q2's own anti-parallel diode D2. Its current path is shown by the red dotted line. The submodule fails to be put into operation and is forced to be removed. At this time, the capacitor current is 0, and the submodule capacitor cannot form a discharge circuit. The capacitor can only be charged but not discharged. The submodule capacitor voltage rises, and the sum of the capacitor voltages of this bridge arm increases.

[0117] When the switch signal And the bridge arm current At this time, the submodule is in the cut-off state, and its current path is shown as the green dotted line. At this time, the Q1 open circuit fault has no effect on the working state of the submodule, which is the same as the normal operation.

[0118] In summary, the impact of the switch open circuit failure on the submodule itself is: when the bridge arm current is less than 0 and it should be discharged, it cannot be discharged, it can only be charged but not discharged, and the submodule capacitor voltage will increase.

[0119] When the control algorithm of sorting and equalizing voltage is adopted, when the bridge arm current When the bridge arm current is When the upper tube of a submodule is open-circuited, the submodule in the bridge arm current When the fault occurs, an abnormality will occur and the capacitor voltage of the faulty submodule will not be able to be put into operation and discharged. As a result, the capacitor voltage of the faulty submodule will continue to rise intermittently within several cycles of the fault. At this time, the capacitor voltage of other normal submodules is slightly lower than that of the faulty submodule. When the normal submodule that should be removed is charged because its capacitor voltage is lower than the capacitor voltage of the faulty submodule, a sufficient number of normal submodules are selected for charging in one switching cycle, so that the normal submodule will rise synchronously with the capacitor voltage of the faulty submodule. When the capacitor voltage of the faulty submodule rises to the highest, if the bridge arm contains redundant submodules, the capacitor of the faulty submodule will no longer be charged in the charging cycle, and the capacitor of the faulty submodule cannot be discharged in the discharging cycle due to the upper switch failure, and the capacitor voltage of the faulty submodule will remain constant afterwards.

[0120] Therefore, when an open-circuit fault occurs on the IGBT switch, the submodule capacitor voltage increment will only have positive values ​​(charging period, capacitor voltage increment positive zero crossing point > 0), no negative values ​​(unable to discharge, capacitor voltage increment negative zero crossing point = 0), the submodule capacitor voltage increment effective value ,therefore , and the average capacitor voltage at this time is greater than the average capacitor voltage during normal operation. When the faulty submodule is charged to the highest voltage, it will no longer be charged. At this time, the capacitor voltage is a constant value, and the capacitor voltage increment will remain unchanged at 0.

[0121] The lower switch is faulty;

[0122] When a switch failure occurs on the submodule IGBT, such as Fig.15 As shown;

[0123] When the lower tube Q2 has an open circuit fault, and When , the submodule is in the charging state, and the current flows through the anti-parallel diode D2 of the Q1 switch tube, the submodule capacitor C, and then flows out. At this time, the open circuit failure of the Q2 tube has no effect on the working state of the submodule, which is the same as the normal operation. The current path is shown by the green dotted line. and When , the submodule is in the state of discharge, and the current flows through the submodule capacitor C, Q1 switch tube, and then flows out. At this time, the open circuit failure of Q2 tube has no effect on the working state of the submodule, which is the same as the normal operation. The current path is shown by the green dotted line.

[0124] when When the bridge arm current , which is the same as the normal operation, and the current path is shown by the green dotted line; if the bridge arm current Since Q2 is open, the current is forced to flow through the anti-parallel diode D1 of Q1 to charge the capacitor. The submodule capacitor voltage rises, and its current path is shown by the red dotted line. The submodule output voltage becomes the capacitor voltage, instead of 0 in normal state. The submodule capacitor changes from the normal cut-off charging state to the charged state, so the fault submodule capacitor voltage will rise, and the bridge arm voltage will also rise. , the actual number of submodules put into operation increased by 1. Due to the increase in the voltage of the faulty submodule, the current When the bridge arm current When T2 is open-circuited, the current will be forced to flow through the internal diode of Q1 to charge the submodule capacitor. Therefore, the voltage waveform of the faulty submodule capacitor will show a trend of alternating charging and discharging, but the overall voltage will rise. The positive and negative zero crossing times of the capacitor voltage increment will be one in each cycle. , , the switch open circuit fault under the sub-module IGBT can be identified and diagnosed based on this criterion.

[0125] Sensor stuck fault;

[0126] When a submodule sensor is stuck, the voltage sensor output is a constant value. The average value of the capacitor voltage is not 0, and the effective value of the capacitor voltage increment will fluctuate around zero (considering various sampling errors, zero drift and other factors), that is: the effective value of the capacitor voltage increment , average capacitor voltage , determine whether a submodule voltage sensor stuck fault occurs. Depending on the different output values ​​of the voltage sensor when stuck, the system will produce different responses. When stuck at a position greater than the average value of the submodule capacitor voltage, the voltage value sampled at this time is higher. Under the action of the sorting and voltage-equalizing algorithm, the faulty submodule will be put into discharge all the time, and charging will be cut off, resulting in a decrease in the actual capacitor voltage value of the faulty submodule. When stuck at a position less than the average value of the submodule capacitor voltage, the voltage value sampled at this time is lower. Under the action of the sorting and voltage-equalizing algorithm, the faulty submodule will be put into charging all the time, and discharging will be cut off, resulting in an increase in the actual capacitor voltage value of the faulty submodule. When stuck at a position equal to the average value of the submodule capacitor voltage, the voltage value sampled at this time is moderate. Under the action of the sorting and voltage-equalizing algorithm, the faulty submodule will be put into discharge and charging at the same frequency. At this time, the actual capacitor voltage value does not change much, and the external impact is small.

[0127] Sensor disconnect failure;

[0128] When a submodule sensor disconnection failure occurs, the voltage sensor output is 0, the capacitor voltage average value fluctuates around zero (considering various sampling errors, zero drift and other factors), and the capacitor voltage increment effective value will also remain at 0 without changing, that is, , Determine whether a submodule voltage sensor disconnection fault occurs.

[0129] Since the voltage sensor output value is 0, under the capacitor voltage balancing sorting algorithm, when the bridge arm current When the charging cycle is 100%, the submodule with lower capacitor voltage value will be put into charge first. Therefore, the faulty submodule will be put into charge and will be charged continuously, and the normal submodule that should be put into charge will be cut off, which will cause the actual capacitor voltage of the faulty submodule to rise during the charging cycle, and the actual capacitor voltage of the normal submodule to drop during the charging cycle.

[0130] When the bridge arm current When the bridge arm contains redundant sub-modules, the sub-module with higher capacitor voltage value will be put into discharge first. Since the output value of the voltage sensor of the faulty sub-module is 0, it will be in the cut-off state, and the normal sub-module that should have been cut off will be put into discharge. This will cause the actual capacitor voltage of the faulty sub-module to remain unchanged during the discharge cycle, and the actual capacitor voltage of the normal sub-module to decrease during the discharge cycle.

[0131] Sensor gain failure;

[0132] When a submodule sensor gain fault occurs, consider the fault gain or , at this time, the voltage sensor output is the gain times of the normal submodule capacitor voltage. Depending on whether the gain is greater than 1 when the gain fails, the voltage sensor output value is different, and the system will also produce different responses.

[0133] When the gain value 1, the output value of the voltage sensor of the faulty submodule will be significantly lower than the capacitor voltage value of other normal submodules. Under the action of the sorting and voltage balancing algorithm, the faulty submodule will be continuously charged until the capacitor voltage value after sampling is consistent with the capacitor voltage value of other normal submodules. According to the above criteria, the low gain fault of the submodule can be identified.

[0134] When the gain value 1, the output value of the voltage sensor of the faulty submodule will be significantly higher than the capacitor voltage value of other normal submodules. Under the action of the sorting and voltage balancing algorithm, the faulty submodule will be continuously discharged for several cycles. At this time, the capacitor voltage increment of the faulty submodule will only have negative values, no positive values, that is, the number of positive zero crossings =0, negative zero crossing times 0, the difference between the number of positive and negative zero crossings ,According to the judgment criteria, the high gain fault of the submodule can be identified.

[0135] The above is a schematic scheme of a flexible direct current converter valve submodule fault diagnosis method of this embodiment. It should be noted that the technical scheme of the flexible direct current converter valve submodule fault diagnosis device and the technical scheme of the flexible direct current converter valve submodule fault diagnosis method described above belong to the same concept, and the details of the technical scheme of the flexible direct current converter valve submodule fault diagnosis device not described in detail in this embodiment can all be referred to the description of the technical scheme of the flexible direct current converter valve submodule fault diagnosis method described above.

[0136] The fault diagnosis device for the flexible direct current converter valve submodule in this embodiment includes:

[0137] A judgment module is used to obtain the output sequence of the capacitance and voltage sensor of each submodule, calculate the submodule autocorrelation coefficient by using the capacitance and voltage output sequence of the previous adjacent cycle, and compare the submodule autocorrelation coefficient with a set autocorrelation coefficient threshold to determine whether the submodule fails;

[0138] A calculation module, used for calculating the effective value of the capacitor voltage increment of the faulty submodule, the output average value of the capacitor voltage sensor, and the difference between the number of positive zero crossings of the capacitor voltage increment and the number of negative zero crossings of the capacitor voltage increment when a submodule fails, to obtain a calculation result;

[0139] The identification module is used to identify the fault type according to the calculation result.

[0140] This embodiment further provides a computing device, which is applicable to the fault diagnosis of the flexible direct current converter valve submodule, and includes:

[0141] Memory and processor; the memory is used to store computer executable instructions, and the processor is used to execute computer executable instructions to implement the fault diagnosis method of the flexible direct current converter valve submodule as proposed in the above embodiment.

[0142] This embodiment also provides a storage medium on which a computer program is stored. When the program is executed by a processor, the method for diagnosing faults of a flexible direct current converter valve submodule as proposed in the above embodiment is implemented.

[0143] The storage medium proposed in this embodiment and the method for implementing fault diagnosis of the flexible direct current converter valve submodule proposed in the above embodiment belong to the same inventive concept. The technical details not fully described in this embodiment can be referred to the above embodiment, and this embodiment has the same beneficial effects as the above embodiment.

[0144] Through the above description of the implementation mode, the technicians in the relevant field can clearly understand that the present invention can be implemented by means of software and necessary general hardware, and of course can also be implemented by hardware, but in many cases the former is a better implementation mode. Based on such an understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, a read-only memory (ROM), a random access memory (RAM), a flash memory (FLASH), a hard disk or an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods of various embodiments of the present invention.

[0145] Embodiment 2 is different from the first embodiment in that it provides a verification test of a flexible direct current converter valve submodule fault diagnosis method to verify and illustrate the technical effects adopted in the method.

[0146] Build a Simulink simulation model, with a DC side input voltage of 5500V, a half-bridge submodule structure, 22 submodules in each bridge arm, a submodule bypass capacitor of 10mF, a submodule initial voltage of 250V, a bridge arm inductance of 13.5mF, a DC side capacitor of 1mF, a three-phase AC grid side frequency of 50Hz, a line voltage effective value of 3300V, a capacitor voltage balance using a sorting voltage balancing algorithm, circulating current suppression using PIR control, and a resonant angular frequency of ,bandwidth , resonant gain , proportionality coefficient , integral coefficient ; The PWM modulation method adopts the nearest level approximation modulation strategy, and the feedforward decoupling double closed-loop middle power outer loop for , for , in the inner current loop for , for , coupling for .

[0147] First, write a fault location program for each submodule, calculate the autocorrelation coefficient between the output value of its own voltage sensor and the previous cycle, and compare and locate the fault. This step uses the output value of the submodule capacitor voltage sensor to slide and store the submodule capacitor voltage value sequence in the previous cycle. When the MMC system works normally and stably, the voltage sensor measurement value moves back and forth around 250V. When a fault occurs, depending on the type of fault, the measurement value of the voltage sensor will quickly deviate from 250V, or get stuck and no longer change. The capacitor voltage sequence of the previous cycle and the capacitor voltage sequence in this cycle are calculated to obtain the autocorrelation coefficient, and count when exceeding the threshold. If the threshold is exceeded for a certain number of times continuously, it can be considered that the submodule has a fault, and the fault is located to a specific submodule.

[0148] On the basis of fault location, the fault type is identified and differentiated by calculating the effective value of the submodule capacitor voltage increment, the number of positive and negative zero crossings of the capacitor voltage increment, and the average capacitor voltage value and comparing it with the average capacitor voltage value during normal operation. The specific fault type identification process is as follows: Figure 1 This step requires calculating the output value sequence of the capacitor voltage sensor of the faulty submodule and determining the specific fault type by comparison.

[0149] Compared with the traditional method, the present invention takes into account both the MMC submodule switch open circuit fault and the typical voltage sensor fault, and for different types of faults, only uses the information of the submodule capacitor voltage itself for joint fault diagnosis. The algorithm is simple, does not need to communicate with the main controller, and reduces the hardware cost burden.

[0150] 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.

Claims

1. A method for diagnosing faults of a flexible direct current converter valve submodule, characterized in that: include: Obtaining the output sequence of the capacitance and voltage sensor of each submodule, calculating the submodule autocorrelation coefficient using the capacitance and voltage output sequence of the previous adjacent cycle, and comparing the submodule autocorrelation coefficient with a set autocorrelation coefficient threshold to determine whether the submodule fails; When a submodule fails, the effective value of the capacitor voltage increment of the failed submodule, the output average value of the capacitor voltage sensor, and the difference between the positive zero crossing times and the negative zero crossing times of the capacitor voltage increment are calculated to obtain a calculation result; According to the calculation result, the fault type is identified; The submodule autocorrelation coefficients calculated using the capacitor voltage output sequence of the previous adjacent cycle include: The submodule voltage sensor output sequence within a cycle is stored in a sliding manner, and the autocorrelation coefficient is calculated with the submodule capacitor voltage output sequence of the previous cycle. The normalized autocorrelation coefficient is expressed as: Among them, L sw is the sliding window length, U c-Normal-mean is the average value of the capacitor voltage of the flexible direct current converter valve submodule under normal working conditions, U c [k] is the capacitor voltage output sequence value in the previous cycle, U c [k+L sw ] is the capacitor voltage output sequence value in the current cycle; The effective value of the capacitor voltage increment of the fault submodule, the output average value of the capacitor voltage sensor, and the difference between the positive zero crossing times and the negative zero crossing times of the capacitor voltage increment are calculated to obtain the calculation results, including: The effective value of the capacitor voltage increment during two cycles is calculated as: Among them, T AC is the period of the AC signal, is the square of the discrete form of the submodule capacitor voltage increment, i is the current sampling point of the accumulation process, and 2n is the total number of sampling points; The output average value of the capacitor voltage sensor is expressed as: Among them, i is the current sampling point of the accumulation process, 2n is the total number of sampling points, U c [i] is the capacitor voltage value at the i-th sampling point, T AC is the period of the AC signal; The difference between the number of positive zero crossings and the number of negative zero crossings of the capacitor voltage increment is expressed as: N0 = N + -N - , where N + N is the number of positive zero crossings of the capacitor voltage increment, - is the number of negative zero crossings.

2. The method for diagnosing faults of a flexible direct current converter valve submodule according to claim 1, characterized in that: Comparing the submodule autocorrelation coefficient with a set autocorrelation coefficient threshold value comprises: When the absolute value of the submodule autocorrelation coefficient is less than the set autocorrelation coefficient threshold, the counter performs a self-increment operation. When the counter value is greater than the set number of times, the submodule fails and the fault position of the submodule is marked.

3. The method for diagnosing faults of a flexible direct current converter valve submodule according to claim 1, characterized in that: According to the calculation result, identifying the fault type includes: When U c-incre-RMS ∈[0,ξ], the fault at this time is determined to be a type A fault, and the type A fault is a sensor stuck fault or a sensor disconnection fault; when The fault at this time is determined to be a type B fault, and the type B fault is an upper switch fault of the submodule switch tube, a lower switch fault of the switch tube, or a sensor gain fault.

4. The method for diagnosing faults of a flexible direct current converter valve submodule according to claim 1, characterized in that: According to the calculation result, identifying the fault type further includes: When a type A fault occurs, calculate the output average value U of the submodule capacitor voltage sensor c-Fault-mean ; like The sensor is disconnected. like The sensor is stuck.

5. The method for diagnosing faults of a flexible direct current converter valve submodule according to claim 3 or 4, characterized in that: According to the calculation result, identifying the fault type further includes: When a type B fault occurs, the output average value of the submodule capacitor voltage sensor is calculated. If the output average value is lower than the average value of the capacitor voltage of the flexible direct current converter valve submodule under normal working conditions, a sensor gain fault occurs; If the output average value is higher than the average value of the capacitor voltage of the flexible direct current converter valve submodule under normal working conditions, the difference N0 between the positive and negative zero crossing times of the submodule capacitor voltage increment is calculated; When N0 is greater than 0, an upper switch failure of the insulated gate bipolar transistor of the submodule occurs; When N0 is equal to 0, a lower switch failure of the submodule insulated gate bipolar transistor occurs; When N0 is less than 0, a sensor gain fault occurs.

6. A system applied to the fault diagnosis method of flexible direct current converter valve submodule according to claims 1 to 5, characterized in that: include: A judgment module is used to obtain the output sequence of the capacitance and voltage sensor of each submodule, calculate the submodule autocorrelation coefficient by using the capacitance and voltage output sequence of the previous adjacent cycle, and compare the submodule autocorrelation coefficient with a set autocorrelation coefficient threshold to determine whether the submodule fails; A calculation module, used for calculating the effective value of the capacitor voltage increment of the faulty submodule, the output average value of the capacitor voltage sensor, and the difference between the number of positive zero crossings of the capacitor voltage increment and the number of negative zero crossings of the capacitor voltage increment when a submodule fails, to obtain a calculation result; The identification module is used to identify the fault type according to the calculation result.

7. An electronic device, characterized in that: The device comprises: processor; a memory for storing processor-executable instructions; The processor is configured to call the instructions stored in the memory to execute the method according to any one of claims 1 to 5.

8. A computer-readable storage medium having computer program instructions stored thereon, characterized in that: When the computer program instructions are executed by a processor, the method according to any one of claims 1 to 5 is implemented.

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