Fault identification method and device for multiple direct current systems, storage medium and equipment

Abstract

The invention discloses a fault identification method and device for a multi-direct-current system, a storage medium and computer equipment, and the method comprises the steps: obtaining an estimated first fault type under the condition that a target multi-direct-current system has a fault, and carrying out the calculation of a mode voltage from a mode voltage calculation formula corresponding to a plurality of preset fault types based on the first fault type, determining a target calculation formula matched with the first fault category; based on the target calculation formula, calculating a line mode voltage and a zero mode voltage corresponding to a current-limiting actuator on a fault generation line in the target multi-DC system, and determining a target coordinate point according to the line mode voltage and the zero mode voltage, determining a second fault category corresponding to the target multi-direct-current system according to the position of the target coordinate point in a preset four-quadrant modal voltage interval; and determining a target fault category corresponding to the target multi-DC system according to the first fault category and the second fault category.

Description

Technical Field

[0001] The present application relates to the field of direct current transmission control technology, and in particular to a fault identification method and device, a storage medium, and a computer device for a multi-direct current system. Background Art

[0002] With the continuous development of power systems, DC transmission technology has shown unique advantages in long-distance large-capacity transmission and asynchronous power grid interconnection. Therefore, multi-DC transmission systems (referred to as multi-DC systems) are increasingly widely used in power grids. However, the complexity of multi-DC systems also brings higher failure risks. According to the type of fault, the faults of multi-DC systems can be divided into pole-to-pole faults and pole-to-ground faults. According to the location of the fault, the faults of multi-DC systems can be divided into internal faults, external faults, etc. If these faults cannot be accurately identified and handled, they may have a serious impact on the stable operation of the power system.

[0003] Traditional fault identification methods mainly rely on manual experience judgment, which has the problem of low accuracy in fault judgment. Especially when a fault occurs in a multi-DC system, due to the mutual influence between the DC systems, the fault characteristics are often more complex, and manual judgment methods often have difficulty in accurately determining the fault type and location. Summary of the invention

[0004] In view of this, the present application provides a fault identification method and device, storage medium, and computer equipment for a multi-DC system. The fault identification method is based on the line mode voltage and zero mode voltage of the current limiting actuator of the fault-occurring line, and a preset four-quadrant modal voltage range. The method can effectively and easily verify the accuracy of manually predicted faults, thereby significantly improving the fault identification accuracy of the multi-DC system after a fault occurs.

[0005] According to one aspect of the present application, a fault identification method for a multi-DC system is provided, comprising:

[0006] In the case where a fault occurs in the target multi-DC system, an estimated first fault category is obtained, and based on the first fault category, a target calculation formula matching the first fault category is determined from mode voltage calculation formulas corresponding to a plurality of preset fault categories;

[0007] Based on the target calculation formula, a line mode voltage and a zero mode voltage corresponding to the current limiting actuator on the fault-occurring line in the target multi-DC system are calculated, and a target coordinate point is determined according to the line mode voltage and the zero mode voltage, and a second fault category corresponding to the target multi-DC system is determined according to a position of the target coordinate point in a preset four-quadrant modal voltage interval, wherein the preset four-quadrant modal voltage interval includes a plurality of sub-intervals, and each sub-interval indicates a fault category;

[0008] A target fault category corresponding to the target multi-DC system is determined according to the first fault category and the second fault category.

[0009] According to another aspect of the present application, a fault identification device for a multi-DC system is provided, comprising:

[0010] a first fault category acquisition module, configured to acquire an estimated first fault category when a fault occurs in a target multi-DC system, and determine, based on the first fault category, a target calculation formula matching the first fault category from among mode voltage calculation formulas corresponding to a plurality of preset fault categories;

[0011] a second fault category determination module, configured to calculate, based on the target calculation formula, a line mode voltage and a zero mode voltage corresponding to a current limiting actuator on a fault-occurring line in the target multi-DC system, and determine a target coordinate point according to the line mode voltage and the zero mode voltage, and determine a second fault category corresponding to the target multi-DC system according to a position of the target coordinate point in a preset four-quadrant modal voltage interval, wherein the preset four-quadrant modal voltage interval includes a plurality of sub-intervals, and each sub-interval indicates a fault category;

[0012] A target fault category determination module is used to determine a target fault category corresponding to the target multi-DC system according to the first fault category and the second fault category.

[0013] According to another aspect of the present application, a storage medium is provided, on which a computer program is stored, and when the program is executed by a processor, the fault identification method of the multi-DC system is implemented.

[0014] According to another aspect of the present application, a computer device is provided, including a storage medium, a processor, and a computer program stored on the storage medium and executable on the processor, wherein the processor implements the above-mentioned multi-DC system fault identification method when executing the program.

[0015] By means of the above technical scheme, the present application provides a method and device for fault identification of a multi-DC system, a storage medium, and a computer device. When a fault occurs in a target multi-DC system, a preliminary fault identification is first performed manually to obtain a first fault category of the target multi-DC system. Then, according to the first fault category estimated manually, a target calculation formula matching the first fault category can be selected from the mode voltage calculation formulas corresponding to the preset multiple fault categories. Next, the line mode voltage and zero mode voltage of the current limiting actuator are calculated using the target calculation formula in combination with the current limiting actuator parameters and real-time measurement data on the fault-occurring line. Afterwards, a target coordinate point is determined within a preset four-quadrant modal voltage interval based on the calculated line mode voltage and zero mode voltage values. The second fault category corresponding to the target multi-DC system is determined based on the sub-interval to which the target coordinate point belongs in the preset four-quadrant modal voltage interval. Finally, the target fault category corresponding to the target multi-DC system is determined in combination with the estimated first fault category and the second fault category. The embodiment of the present application proposes a fault identification method based on the line mode voltage and zero mode voltage of the current limiting actuator of the fault-occurring line, and a preset four-quadrant modal voltage range. The method can effectively and simply verify the accuracy of manually predicted faults, thereby significantly improving the fault identification accuracy of multiple DC systems after a fault occurs.

[0016] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0018] Figure 1 A schematic flow chart of a fault identification method for a multi-DC system provided in an embodiment of the present application is shown;

[0019] Figure 2 A schematic diagram of a four-quadrant modal voltage interval provided in an embodiment of the present application is shown;

[0020] Figure 3 A schematic diagram of a determination process of an impedance fault type provided by an embodiment of the present application is shown;

[0021] Figure 4 A schematic diagram of a simplified model of a multi-level converter provided in an embodiment of the present application is shown;

[0022] Figure 5 A simulation circuit topology diagram of a four-terminal DC system provided in an embodiment of the present application is shown;

[0023] Figure 6 A schematic diagram of a system equivalent model of MMC1 and MMC2 parts provided in an embodiment of the present application is shown;

[0024] Figure 7 The circuit mode voltage according to the fault equivalent resistance R provided by the embodiment of the present application is shown. f Schematic diagram of the curve that changes with changes;

[0025] Figure 8 A schematic structural diagram of a fault identification device for a multi-DC system provided in an embodiment of the present application is shown;

[0026] Fig. 9 A schematic diagram of the device structure of a computer device provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0027] The present application will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict.

[0028] In this embodiment, a fault identification method for a multi-DC system is provided. Figure 1 As shown, the method includes:

[0029] Step 101, when a target multi-DC system fails, obtain an estimated first fault category, and based on the first fault category, determine a target calculation formula matching the first fault category from mode voltage calculation formulas corresponding to a plurality of preset fault categories.

[0030] A fault identification method for a multi-DC system provided in an embodiment of the present application can manually predict the fault after a fault occurs in the multi-DC system, and then further verify whether the result of the manual prediction is accurate, thereby determining the final target fault category of the multi-DC system.

[0031] When a fault occurs in the target multi-DC system, a preliminary fault identification is first performed manually to obtain the first fault category of the target multi-DC system. Then, according to the manually estimated first fault category, a target calculation formula matching the first fault category can be selected from the mode voltage calculation formulas corresponding to the preset multiple fault categories. These preset mode voltage calculation formulas can be derived based on the system parameters and system structure simulation results of the multi-DC system, or derived through the system structure of the target multi-DC system, and can reflect the mode voltage characteristics of the current limiting actuator under different fault categories. Here, the multiple fault categories can include internal positive pole to ground fault category, internal negative pole to ground fault category, external forward pole to ground fault category, external reverse pole to ground fault category, internal pole to pole fault category, and external pole to pole fault category. Each fault category is pre-set with a mode voltage calculation formula. It should be noted that each mode voltage calculation formula includes two formulas, one for calculating the line mode voltage corresponding to the current limiting actuator, and one for calculating the zero mode voltage corresponding to the current limiting actuator. For example, if the first fault category is an internal negative pole to ground fault category, then the mode voltage calculation formula corresponding to the internal negative pole to ground fault category can be found from the mode voltage calculation formulas corresponding to the preset multiple fault categories as the target calculation formula.

[0032] Step 102: based on the target calculation formula, calculate the line mode voltage and the zero mode voltage corresponding to the current limiting actuator on the fault-occurring line in the target multi-DC system, determine the target coordinate point according to the line mode voltage and the zero mode voltage, and determine the second fault category corresponding to the target multi-DC system according to the position of the target coordinate point in a preset four-quadrant modal voltage interval, wherein the preset four-quadrant modal voltage interval includes a plurality of sub-intervals, and each sub-interval indicates a fault category.

[0033] In this embodiment, next, the target calculation formula is used to combine the current limiting actuator parameters and real-time measurement data on the fault line to calculate the line mode voltage and zero mode voltage of the current limiting actuator. These two voltage values ​​reflect the electrical characteristics and fault characteristics of the fault line. Afterwards, a target coordinate point is determined within the preset four-quadrant modal voltage interval according to the calculated line mode voltage and zero mode voltage values. Due to different fault types, the current limiting actuator corresponds to different line mode voltages and zero mode voltages. Therefore, the four-quadrant modal voltage interval can be made according to multiple fault types and the line mode voltage range and zero mode voltage range of the current limiting actuator under each fault type. The preset four-quadrant modal voltage interval may include multiple sub-intervals, and each sub-interval is used to indicate a fault category. The horizontal coordinate of the four-quadrant modal voltage interval may be the zero mode voltage, and the vertical coordinate may be the line mode voltage. Specifically, after obtaining the line mode voltage and zero mode voltage corresponding to the current limiting actuator, the zero mode voltage can be used as the horizontal coordinate of the target coordinate point, and the line mode voltage can be used as the vertical coordinate of the target coordinate point to obtain the target coordinate point.

[0034] Next, the second fault category corresponding to the target multi-DC system is determined according to the sub-interval to which the target coordinate point belongs in the preset four-quadrant modal voltage interval. That is, the fault category corresponding to the sub-interval to which the target coordinate point belongs is taken as the second fault category corresponding to the target multi-DC system.

[0035] Step 103: Determine a target fault category corresponding to the target multi-DC system according to the first fault category and the second fault category.

[0036] In this embodiment, the target fault category corresponding to the target multi-DC system is determined in combination with the estimated first fault category and the second fault category. Specifically, it can be determined whether the first fault category is consistent with the second fault category. If the first fault category and the second fault category are consistent, it means that the estimated first fault category is accurate. At this time, the first fault category or the second fault category can be used as the target fault category of the multi-DC system. If the first fault category and the second fault category are inconsistent, it means that there is a deviation in the estimated first fault category. At this time, a new first fault category can be manually re-estimated, and the above steps 101 to 103 are repeated until the first fault category and the second fault category are consistent.

[0037] By applying the technical solution of this embodiment, when a fault occurs in the target multi-DC system, a preliminary fault identification is first performed manually to obtain the first fault category of the target multi-DC system. Then, according to the manually estimated first fault category, a target calculation formula matching the first fault category can be selected from the mode voltage calculation formulas corresponding to the preset multiple fault categories. Next, the line mode voltage and zero mode voltage of the current limiting actuator are calculated using the target calculation formula in combination with the current limiting actuator parameters and real-time measurement data on the fault-occurring line. Afterwards, a target coordinate point is determined within the preset four-quadrant modal voltage interval based on the calculated line mode voltage and zero mode voltage values. The second fault category corresponding to the target multi-DC system is determined based on the sub-interval to which the target coordinate point belongs in the preset four-quadrant modal voltage interval. Finally, the target fault category corresponding to the target multi-DC system is determined in combination with the estimated first fault category and the second fault category. The embodiment of the present application proposes a fault identification method based on the line mode voltage and zero mode voltage of the current limiting actuator of the fault-occurring line, and a preset four-quadrant modal voltage range. The method can effectively and simply verify the accuracy of manually predicted faults, thereby significantly improving the fault identification accuracy of multiple DC systems after a fault occurs.

[0038] In an embodiment of the present application, optionally, the preset four-quadrant modal voltage interval includes an easily misidentified subinterval; step 103 includes: when the target coordinate point is located in a subinterval outside the easily misidentified subinterval, and the first fault category is consistent with the second fault category, taking the first fault category as the target fault category corresponding to the target multi-DC system; when the target coordinate point is located in the easily misidentified subinterval, and the first fault category is consistent with the second fault category, calculating the DC voltage change rate on the DC transmission line in the target multi-DC system, and judging the magnitude relationship between the DC voltage change rate and a preset evaluation trigger event threshold; when the DC voltage change rate is less than or equal to the evaluation trigger event threshold, taking the first fault category as the target fault category of the target multi-DC system; when the DC voltage change rate is greater than the evaluation trigger event threshold, judging whether the first fault category is a pole-to-pole fault, and determining the impedance fault type corresponding to the target multi-DC system according to the judgment result.

[0039] In this embodiment, the preset four-quadrant modal voltage interval includes a sub-interval that is easy to be misidentified, such as Figure 2 As shown in the figure, a schematic diagram of a four-quadrant modal voltage range is given, where U Lmn_l represents the line mode voltage of the current limiting actuator between line m and line n, U Lmn_0It represents the zero-mode voltage of the current limiting actuator between line m and line n. According to the line mode voltage range and zero-mode voltage range corresponding to different fault categories, their sub-intervals can be marked as 1, 2, 3, 4, 5.1 (5.2), 6 and 7, which represent internal positive pole-to-ground fault, internal negative pole-to-ground fault, external forward pole-to-ground fault, external reverse pole-to-ground fault, internal pole-to-pole fault (easy to misidentify area), external pole-to-pole fault and no fault.

[0040] If it is found through judgment that the target coordinate point is located in a sub-interval other than the easily misidentified sub-interval (for example, the sub-intervals marked as 1, 2, 3, 4, 5.1, 6 and 7 above), and the first fault category is consistent with the second fault category at this time, then it means that the judgment of the first fault category is accurate and there is no misjudgment. At this time, the first fault category (or the second fault category) is used as the target fault category corresponding to the target multi-DC system.

[0041] If it is found through judgment that the target coordinate point is located in a subinterval that is easy to misidentify (for example, the subinterval marked as 5.2 above), and at this time the first fault category is consistent with the second fault category, then it means that there may be a misjudgment of the first fault category. At this time, the subsequent fault judgment can be made based on the DC voltage change rate on the DC transmission line in the target multi-DC system. Here, the evaluation trigger event threshold can be determined based on the empirical value. In a four-terminal DC system, the evaluation trigger event threshold can be set to a typical value of -100kV / ms. The evaluation trigger event threshold can be further judged whether there is a misjudgment of the fault category.

[0042] In an embodiment of the present application, optionally, the "determining the impedance fault type corresponding to the target multi-DC system according to the judgment result" includes: in the case where the first fault category is a pole-to-pole fault, if the DC voltage change rate is greater than a first preset change rate threshold, then the impedance fault type corresponding to the target multi-DC system is determined to be an internal high impedance fault, otherwise, the impedance fault type corresponding to the target multi-DC system is determined to be an external low impedance fault; in the case where the first fault category is not a pole-to-pole fault, if the DC voltage change rate is greater than a second preset change rate threshold, then the impedance fault type corresponding to the target multi-DC system is determined to be an internal high impedance fault, otherwise, the impedance fault type corresponding to the target multi-DC system is determined to be an external low impedance fault, wherein the absolute value of the first preset change rate threshold is greater than the absolute value of the second preset change rate threshold.

[0043] In this embodiment, the first preset change rate threshold and the second preset change rate threshold are voltage change rate thresholds for pole-to-pole faults and pole-to-ground faults, respectively. In a four-terminal DC system, typical values ​​of the first preset change rate threshold and the second preset change rate threshold may be -300 kV / ms and -150 kV / ms, respectively. Specifically, both the first preset change rate threshold and the second preset change rate threshold may be negative values, and the absolute value of the first preset change rate threshold is greater than the absolute value of the second preset change rate threshold.

[0044] like Figure 3 As shown, a schematic diagram of a judgment process of an embodiment of the present application is shown. Figure 3 As shown, first, after a fault occurs, the target calculation formula is determined according to the predicted fault category (i.e., the first fault category). Then, the target calculation formula is used to calculate U L12_l (i.e. line mode voltage) and U L12_0 (That is, zero mode voltage). L12_l and U L12_0 (ie zero mode voltage) to determine the target coordinate point and determine the target coordinate point (U L12_l , U L12_0 ) In the sub-interval of the preset four-quadrant modal voltage interval, the second fault category is determined according to the fault category corresponding to the sub-interval. Afterwards, it is determined whether the first fault category is consistent with the second fault category. If not, the first fault category is re-determined, and the target calculation formula and the second fault category are re-determined until the first fault category is consistent with the second fault category. When the first fault category and the second fault category are consistent, it is determined that dU dc The relationship between / dt and the preset evaluation trigger event threshold (D): If dU dc / dt≤D, then the first fault category can be directly used as the final target fault category; if dU dc / dt>D, indicating that there is a misjudgment, then it can be further determined whether the first fault category is a pole-to-pole fault. For example, if the first fault category is consistent with the second fault category, and the first fault category is an internal pole-to-pole fault or an external pole-to-pole fault, then it can be determined that the first fault category is a pole-to-pole fault.

[0045] If the first fault type is a pole-to-pole fault, then dU can be directly determined. dc / dt and the first preset change rate threshold (M set1 ) between the size relationship: if dU dc / dt>M set1 , then it can be determined that the target fault type is an internal high impedance fault; if dU dc / dt≤M set1 , then it can be determined that the target fault category is an external low impedance fault.

[0046] If the first fault type is not a pole-to-pole fault, then dU can be directly determined. dc / dt and a second preset rate of change threshold (M set2 ) between the size relationship: if dU dc / dt>M set2 , then it can be determined that the target fault type is an internal high impedance fault; if dU dc / dt≤M set2 , then it can be determined that the target fault category is an external low impedance fault. The embodiment of the present application uses the above determination method to further determine which target fault category it is when the target coordinate point is located in the easily misidentified sub-interval, thereby greatly improving the recognition accuracy of the target fault category.

[0047] In an embodiment of the present application, optionally, before "determining a target calculation formula matching the first fault category" in step 101, the method further includes: determining a target analysis area from the target multi-DC system according to the fault-occurring line, and simplifying the structure of the multilevel converter in the system model corresponding to the target analysis area through a multilevel converter simplification model to obtain a system equivalent model corresponding to the target analysis area, and obtaining initial voltage calculation formulas and phase modal transformation expressions corresponding to multiple fault categories based on the system equivalent model; and obtaining mode voltage calculation formulas corresponding to the multiple fault categories based on the initial voltage calculation formula and the phase modal transformation expression.

[0048] In this embodiment, first, a target analysis area is determined in a target multi-DC system according to the line where the fault occurs. Specifically, the parameters required for analyzing the line mode voltage and zero mode voltage of the current limiting actuator can be determined based on the current limiting actuator in the fault-occurring line, and the target analysis area can be determined according to these parameters, so that the line mode voltage and zero mode voltage of the current limiting actuator can be calculated according to the part of the target analysis area. After the target analysis area is determined, the simplified model of the multilevel converter can be used to simplify the structure of the multilevel converter in the target analysis area. The purpose of this step is to reduce the complexity of the system model and facilitate subsequent analysis and calculation. Through the above simplification, a system equivalent model corresponding to the target analysis area can be obtained. This equivalent model can retain the main characteristics of the original system while simplifying the calculation process. On the basis of the system equivalent model, initial voltage calculation formulas are derived for a variety of possible fault categories. These formulas will be used to describe the line mode voltage and zero mode voltage of the current limiting actuator when the fault occurs. At the same time, phase mode transformation expressions are derived, which are used to convert the voltage from one representation form (such as time domain) to another (such as modal domain) so as to more easily analyze the dynamic behavior of the system. Finally, the mode voltage calculation formulas corresponding to various fault categories are derived using the initial voltage calculation formula and phase mode transformation expression obtained above. Specifically, the phase mode transformation expression can be substituted into the initial voltage calculation formula under each fault category to obtain the mode voltage calculation formula under each fault category. The embodiment of the present application goes through a series of logical steps, starting from determining the target analysis area, to simplifying the model, deriving the formula, and finally obtaining the mode voltage calculation formula under different fault categories, which can simplify complex system problems and make the analysis more efficient and accurate. At the same time, through the derived formula, the line mode voltage and zero mode voltage of the current limiting actuator under different faults can be easily calculated and analyzed.

[0049] In the embodiment of the present application, optionally, the simplified model of the multilevel converter is expressed by the following formula:

[0050] R MMC =(2 / 3)(R+ΣR ON )

[0051] L MMC =(2 / 3)L

[0052] C MMC =6(C / N)

[0053] Among them, R MMC represents the equivalent resistance of the multilevel converter, L MMC represents the equivalent inductance of the multilevel converter, C MMCrepresents the equivalent capacitance of the multilevel converter, R represents the sum of the arm resistances of all bridge arms of the multilevel converter, ΣR ON represents the sum of the on-state resistances of all IGBT modules of the multilevel converter, L represents the sum of the bridge arm inductances of all bridge arms of the multilevel converter, C represents the submodule capacitance corresponding to any submodule of the multilevel converter, and N represents the number of submodules of any bridge arm.

[0054] In this embodiment, if Figure 4 A simplified model of a multi-level converter provided in an embodiment of the present application is shown. Figure 4 The left side is a normal system model, and the right side is a simplified system equivalent model. MMC1 represents a multilevel converter 1, which can be specifically simplified into a form consisting of an equivalent resistor, an equivalent inductor, and an equivalent capacitor. Figure 4 Middle U L12_p and U L12_n They represent the positive line mode voltage and the negative line mode voltage respectively, p represents the positive pole, n represents the negative pole, and i represents the positive pole. L12_p and i L12_n Represents the current passing through the positive and negative electrodes of the current limiting actuator, i s1p and i s1n It is a current source of positive and negative poles. By equating the detailed circuit structure of the multi-level converter to an external characteristic equivalent network of a current source and an internal impedance in series, the subsequent calculation and analysis are simplified.

[0055] In the embodiment of the present application, optionally, when the target multi-DC system is a four-terminal DC system, the phase mode transformation expression is expressed by the following formula:

[0056]

[0057] The four-terminal DC system includes four multilevel converters, one end of each of the multilevel converters is connected to a section of overhead line through a current limiting actuator; the overhead lines corresponding to multilevel converter 1 are line 1 and line 4, the overhead lines corresponding to multilevel converter 2 are line 1 and line 2, the overhead lines of multilevel converter 3 are line 2 and line 3, and the overhead lines of multilevel converter 4 are line 3 and line 4; Z 14 Represents the equivalent impedance between line 1 and line 4, Z 23 represents the equivalent impedance between line 2 and line 3, L 41 Indicates the equivalent inductance between line 1 and line 4, L 23 Indicates the equivalent inductance between line 2 and line 3, L T41 Indicates the equivalent inductance of the transformer between line 1 and line 4, L T23It represents the transformer equivalent inductance between line 2 and line 3, L MMC3 is the equivalent inductance of the multilevel converter 3, L MMC4 is the equivalent inductance of the multilevel converter 4, R 41 Represents the line equivalent resistance between line 1 and line 4, R 23 Represents the equivalent resistance between line 2 and line 3, R MMC3 is the equivalent resistance of the multilevel converter 3, R MMC4 is the equivalent resistance of the multilevel converter 4, L mn is the self-inductance between line m and line n, M mn is the mutual inductance between line m and line n, L mn_l is the line mode inductance between line m and line n, L mn_0 is the zero-mode component inductance between line m and line n;

[0058] The calculation formulas for the initial voltages corresponding to the various fault types are as follows:

[0059] In the case of internal positive-to-ground fault, the initial voltage calculation formula is as follows:

[0060]

[0061] Under the internal negative pole to ground fault category, the initial voltage calculation formula is as follows:

[0062]

[0063] Among them, U L12_l (jω) and U L12_0 (jω) are the line mode voltage and zero mode voltage of the current limiting actuator between line 1 and line 2, respectively, L T12 Indicates the equivalent inductance of the transformer between line 1 and line 2, U dc represents the rated DC voltage of the target multi-DC system before fault, R f represents the fault equivalent resistance of the target multi-DC system, Z1, Z2, Z3 and Z4 are impedance values ​​related to frequency, R MMC1 represents the equivalent resistance of the multilevel converter 1, R MMC2 represents the equivalent resistance of the multilevel converter 2, d represents the duty cycle of the multilevel converter;

[0064] Under the external forward pole-to-ground fault category, the initial voltage calculation formula is as follows:

[0065]

[0066] Under the external reverse pole-to-ground fault category, the initial voltage calculation formula is as follows:

[0067]

[0068] Among them, L MMC1 is the equivalent inductance of multilevel converter 1, L MMC2 is the equivalent inductance of the multilevel converter 2, Z5, Z6, Z7, Z8, Z9, Z 10 It is the impedance value related to frequency;

[0069] Under the internal pole-to-pole fault category, the initial voltage calculation formula is as follows:

[0070]

[0071] Under the external pole-to-pole fault category, the initial voltage calculation formula is as follows:

[0072]

[0073] The mode voltage calculation formulas corresponding to the multiple fault types are obtained according to the initial voltage calculation formula and the phase mode transformation expression, including:

[0074] Substituting the phase mode transformation expression into the initial voltage calculation formula, the mode voltage calculation formulas corresponding to the multiple fault types are obtained.

[0075] In this embodiment, according to the simplified model of the multilevel converter, the system equivalent model of the target multi-DC system under the pole-to-ground fault can be obtained. In order to decouple the inter-pole dependence of the transmission line under the pole-to-ground fault, the phase transformation can be incorporated into the system equivalent network of the target multi-DC system. It should be noted that the duty cycles of different multilevel converters in the above four-terminal DC system are the same.

[0076] like Figure 5 As shown, a simulation circuit topology diagram of a four-terminal DC system according to an embodiment of the present application is given. Figure 6 The schematic diagram of the system equivalent model of the MMC1 and MMC2 parts corresponding to the above simulation circuit topology diagram is given. According to the simplified model of the multilevel converter, the system equivalent model of the four-terminal DC system under fault is derived and transformed, which provides the basis for calculating the line mode voltage and zero mode voltage of the current limiting actuator.

[0077] like Figure 5 and Figure 6 The four-terminal DC system shown in the figure can obtain the above phase mode transformation expression and the initial voltage calculation formula corresponding to various fault types. T'12When calculating the line mode voltage and zero mode voltage of the current limiting actuator, the above initial voltage calculation formula and phase mode transformation expression can be used for calculation. It should be noted that for a four-terminal DC system, the line mode voltage and zero mode voltage of the current limiting actuator at different positions can be calculated by the above initial voltage calculation formula and phase mode transformation formula.

[0078] In the embodiment of the present application, optionally, the method further includes:

[0079] For each fault category, based on the line mode voltage calculated under the fault category and the quantitative relationship formula between the line mode voltage and the fault equivalent resistance, determine a first curve of the line mode voltage changing with the fault equivalent resistance under the fault category, map the first curve corresponding to each fault category to the same coordinate system, determine a first curve with an overlapping range of values ​​under the line mode voltage coordinate axis, determine a first easily misidentified area according to the overlapping range, and determine a line mode voltage range corresponding to the first easily misidentified area based on the maximum fault equivalent resistance under the target multi-DC system; and / or,

[0080] For each fault category, based on the line mode voltage calculated under the fault category and the quantitative relationship formula between the line mode voltage and the current limiting actuator inductance, determine a second curve of the line mode voltage changing with the current limiting actuator inductance under the fault category, map the second curve corresponding to each fault category to the same coordinate system, determine a second curve with an overlapping range of values ​​under the line mode voltage coordinate axis, determine a second easily misidentified area based on the overlapping range, and determine a line mode voltage range corresponding to the second easily misidentified area based on the maximum current limiting actuator inductance under the target multi-DC system;

[0081] The quantitative relationship between the line mode voltage and the fault equivalent resistance is as follows:

[0082]

[0083] R f0 is the fault equivalent resistance in zero mode, γ=1+(Z1 / Z2), ΔR f is the small change of fault equivalent resistance;

[0084] The quantitative relationship between line mode voltage and current limiting actuator inductance is as follows:

[0085]

[0086] β=(L MMC / 2L T′12 +L MMC );

[0087] L T'12 is the inductance of the current limiting actuator between line 1 and line 2, L T'120 is the inductance of the current limiting actuator between Line 1 and Line 2 in zero mode.

[0088] In this embodiment, according to the fault equivalent resistance and the inductance of the current limiting actuator, a sensitivity function for analyzing the influence of the fault equivalent resistance and the inductance of the current limiting actuator on the line mode voltage of the current limiting actuator is proposed. The sensitivity function The formula can be as follows:

[0089]

[0090] Where G(jω) is the mode voltage, p i is the circuit parameter (R f , L T'mn etc., L. T'mn is the inductance of the current limiting actuator between line m and line n).

[0091] By adding R f , L T'mn Substituting into the above equation, we can get:

[0092]

[0093] Further, the line mode voltage of the current limiting actuator and the fault equivalent resistance R f The sensitivity relationship between small changes, the line mode voltage of the current limiting actuator and the inductance L of the current limiting actuator T'mn Furthermore, according to the above sensitivity relationship, the quantitative relationship formula between the line mode voltage and the fault equivalent resistance, and the quantitative relationship formula between the line mode voltage and the inductance of the current limiting actuator can be obtained.

[0094] like Figure 7 As shown, a line mode voltage with fault equivalent resistance R provided in an embodiment of the present application is shown. f The curves that change with the change of (only the curves under the two fault categories with overlapping value ranges of line mode voltage are shown). Figure 7 It can be seen that the line mode voltage is related to R f Therefore, the line mode voltage range of the easily misidentified area can be determined according to the fault equivalent resistance that can be achieved in actual projects. For example, in actual projects, only R f The maximum value is 600Ω. Therefore, it is only necessary to set the lower limit threshold of the easy-to-misidentify area to the line mode voltage value of the pole-to-pole fault when 600Ω is used, instead of setting it to R f= 1000Ω, the lower threshold is 200kV. This method provides a theoretical basis for optimizing the design of the protection device and the threshold setting. Similarly, the line mode voltage range of the easily misidentified area can be determined according to the current limiting actuator inductance that may be achieved in the actual project, which will not be repeated here. The embodiment of the present application can calculate the line voltage mode range suitable for the actual project through the sensitivity function, which can effectively avoid equipment damage or grid instability.

[0095] Further, as Figure 1 The specific implementation of the method, the embodiment of the present application provides a fault identification device for a multi-DC system, such as Figure 8 As shown, the device comprises:

[0096] a first fault category acquisition module, configured to acquire an estimated first fault category when a fault occurs in a target multi-DC system, and determine, based on the first fault category, a target calculation formula matching the first fault category from among mode voltage calculation formulas corresponding to a plurality of preset fault categories;

[0097] a second fault category determination module, configured to calculate, based on the target calculation formula, a line mode voltage and a zero mode voltage corresponding to a current limiting actuator on a fault-occurring line in the target multi-DC system, and determine a target coordinate point according to the line mode voltage and the zero mode voltage, and determine a second fault category corresponding to the target multi-DC system according to a position of the target coordinate point in a preset four-quadrant modal voltage interval, wherein the preset four-quadrant modal voltage interval includes a plurality of sub-intervals, and each sub-interval indicates a fault category;

[0098] A target fault category determination module is used to determine a target fault category corresponding to the target multi-DC system according to the first fault category and the second fault category.

[0099] Optionally, the preset four-quadrant modal voltage interval includes a sub-interval that is prone to misidentification; and the target fault category determination module is used to:

[0100] When the target coordinate point is located in a subinterval outside the easily misidentified subinterval, and the first fault category is consistent with the second fault category, taking the first fault category as the target fault category corresponding to the target multi-DC system;

[0101] When the target coordinate point is located in the easily misidentified sub-interval and the first fault category is consistent with the second fault category, the DC voltage change rate on the DC transmission line in the target multi-DC system is calculated, and the magnitude relationship between the DC voltage change rate and the preset evaluation trigger event threshold is determined; when the DC voltage change rate is less than or equal to the evaluation trigger event threshold, the first fault category is used as the target fault category of the target multi-DC system; when the DC voltage change rate is greater than the evaluation trigger event threshold, it is determined whether the first fault category is a pole-to-pole fault, and the impedance fault type corresponding to the target multi-DC system is determined according to the judgment result.

[0102] Optionally, the target fault category determination module is further used to:

[0103] In the case where the first fault type is a pole-to-pole fault, if the DC voltage change rate is greater than a first preset change rate threshold, it is determined that the impedance fault type corresponding to the target multi-DC system is an internal high impedance fault; otherwise, it is determined that the impedance fault type corresponding to the target multi-DC system is an external low impedance fault;

[0104] In the case where the first fault category is not a pole-to-pole fault, if the DC voltage change rate is greater than a second preset change rate threshold, the impedance fault type corresponding to the target multi-DC system is determined to be an internal high impedance fault; otherwise, the impedance fault type corresponding to the target multi-DC system is determined to be an external low impedance fault, wherein the absolute value of the first preset change rate threshold is greater than the absolute value of the second preset change rate threshold.

[0105] Optionally, the device further comprises a formula determination module; the formula determination module is used to:

[0106] Before determining the target calculation formula matching the first fault category, a target analysis area is determined from the target multi-DC system according to the fault-occurring line, and a multilevel converter in a system model corresponding to the target analysis area is structurally simplified through a multilevel converter simplified model to obtain a system equivalent model corresponding to the target analysis area, and initial voltage calculation formulas and phase mode transformation expressions corresponding to multiple fault categories are obtained according to the system equivalent model;

[0107] According to the initial voltage calculation formula and the phase mode transformation expression, the mode voltage calculation formulas corresponding to the multiple fault types are obtained.

[0108] Optionally, the simplified model of the multilevel converter is expressed by the following formula:

[0109] R MMC =(2 / 3)(R+ΣRON )

[0110] L MMC =(2 / 3)L

[0111] C MMC =6(C / N)

[0112] Among them, R MMC represents the equivalent resistance of the multilevel converter, L MMC represents the equivalent inductance of the multilevel converter, C MMC represents the equivalent capacitance of the multilevel converter, R represents the sum of the arm resistances of all bridge arms of the multilevel converter, ΣR ON represents the sum of the on-state resistances of all IGBT modules of the multilevel converter, L represents the sum of the bridge arm inductances of all bridge arms of the multilevel converter, C represents the submodule capacitance corresponding to any submodule of the multilevel converter, and N represents the number of submodules of any bridge arm.

[0113] Optionally, when the target multi-DC system is a four-terminal DC system, the phase mode transformation expression is expressed by the following formula:

[0114]

[0115] The four-terminal DC system includes four multilevel converters, one end of each of the multilevel converters is connected to a section of overhead line through a current limiting actuator; the overhead lines corresponding to multilevel converter 1 are line 1 and line 4, the overhead lines corresponding to multilevel converter 2 are line 1 and line 2, the overhead lines of multilevel converter 3 are line 2 and line 3, and the overhead lines of multilevel converter 4 are line 3 and line 4; Z 14 Represents the equivalent impedance between line 1 and line 4, Z 23 represents the equivalent impedance between line 2 and line 3, L 41 Indicates the equivalent inductance between line 1 and line 4, L 23 Indicates the equivalent inductance between line 2 and line 3, L T41 Indicates the equivalent inductance of the transformer between line 1 and line 4, L T23 It represents the transformer equivalent inductance between line 2 and line 3, L MMC3 is the equivalent inductance of the multilevel converter 3, L MMC4 is the equivalent inductance of the multilevel converter 4, R 41 Represents the line equivalent resistance between line 1 and line 4, R 23 Represents the equivalent resistance between line 2 and line 3, R MMC3 is the equivalent resistance of the multilevel converter 3, R MMC4is the equivalent resistance of the multilevel converter 4, L mn is the self-inductance between line m and line n, M mn is the mutual inductance between line m and line n, L mn_l is the line mode inductance between line m and line n, L mn_0 is the zero-mode component inductance between line m and line n;

[0116] The calculation formulas for the initial voltages corresponding to the various fault types are as follows:

[0117] In the case of internal positive-to-ground fault, the initial voltage calculation formula is as follows:

[0118]

[0119] Under the internal negative pole to ground fault category, the initial voltage calculation formula is as follows:

[0120]

[0121] Among them, U L12_l (jω) and U L12_0 (jω) are the line mode voltage and zero mode voltage of the current limiting actuator between line 1 and line 2, respectively, L T12 Indicates the equivalent inductance of the transformer between line 1 and line 2, U dc represents the rated DC voltage of the target multi-DC system before fault, R f represents the fault equivalent resistance of the target multi-DC system, Z1, Z2, Z3 and Z4 are impedance values ​​related to frequency, R MMC1 represents the equivalent resistance of the multilevel converter 1, R MMC2 represents the equivalent resistance of the multilevel converter 2, d represents the duty cycle of the multilevel converter;

[0122] Under the external forward pole-to-ground fault category, the initial voltage calculation formula is as follows:

[0123]

[0124] Under the external reverse pole-to-ground fault category, the initial voltage calculation formula is as follows:

[0125]

[0126] Among them, L MMC1 is the equivalent inductance of multilevel converter 1, L MMC2 is the equivalent inductance of the multilevel converter 2, Z5, Z6, Z7, Z8, Z9, Z 10 It is the impedance value related to frequency;

[0127] Under the internal pole-to-pole fault category, the initial voltage calculation formula is as follows:

[0128]

[0129] Under the external pole-to-pole fault category, the initial voltage calculation formula is as follows:

[0130]

[0131] The formula determination module is also used for:

[0132] Substituting the phase mode transformation expression into the initial voltage calculation formula, the mode voltage calculation formulas corresponding to the multiple fault types are obtained.

[0133] Optionally, the device further includes a voltage range determination module; the voltage range determination module is configured to:

[0134] For each fault category, based on the line mode voltage calculated under the fault category and the quantitative relationship formula between the line mode voltage and the fault equivalent resistance, determine a first curve of the line mode voltage changing with the fault equivalent resistance under the fault category, map the first curve corresponding to each fault category to the same coordinate system, determine a first curve with an overlapping range of values ​​under the line mode voltage coordinate axis, determine a first easily misidentified area according to the overlapping range, and determine a line mode voltage range corresponding to the first easily misidentified area based on the maximum fault equivalent resistance under the target multi-DC system; and / or,

[0135] For each fault category, based on the line mode voltage calculated under the fault category and the quantitative relationship formula between the line mode voltage and the current limiting actuator inductance, determine a second curve of the line mode voltage changing with the current limiting actuator inductance under the fault category, map the second curve corresponding to each fault category to the same coordinate system, determine a second curve with an overlapping range of values ​​under the line mode voltage coordinate axis, determine a second easily misidentified area based on the overlapping range, and determine a line mode voltage range corresponding to the second easily misidentified area based on the maximum current limiting actuator inductance under the target multi-DC system;

[0136] The quantitative relationship between the line mode voltage and the fault equivalent resistance is as follows:

[0137]

[0138] R f0 is the fault equivalent resistance in zero mode, γ=1+(Z1 / Z2), ΔR f is the small change of fault equivalent resistance;

[0139] The quantitative relationship between line mode voltage and current limiting actuator inductance is as follows:

[0140]

[0141] β=(L MMC / 2L T′12 +L MMC );

[0142] L T'12 is the inductance of the current limiting actuator between line 1 and line 2, L T'120 is the inductance of the current limiting actuator between Line 1 and Line 2 in zero mode.

[0143] It should be noted that for other corresponding descriptions of the functional units involved in the fault identification device for a multi-DC system provided in the embodiment of the present application, reference can be made to Figures 1 to 7 The corresponding description in the method will not be repeated here.

[0144] The present application also provides a computer device, which may be a personal computer, a server, a network device, etc. Fig. 9 As shown, the computer device includes a bus, a processor, a memory and a communication interface, and may also include an input and output interface and a display device. Among them, 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 an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store location information. The network interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, the steps in each method embodiment are implemented.

[0145] Those skilled in the art will understand that Fig. 9 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components.

[0146] In one embodiment, a computer-readable storage medium is provided. The computer-readable storage medium may be non-volatile or volatile, and stores a computer program thereon. When the computer program is executed by a processor, the steps in the above-mentioned method embodiments are implemented.

[0147] In one embodiment, a computer program product is provided, including a computer program, which implements the steps in the above method embodiments when executed by a processor.

[0148] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties.

[0149] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited to this. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but are not limited to this.

[0150] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0151] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A fault identification method for a multi-DC system, characterized in that: include: In the case where a fault occurs in the target multi-DC system, an estimated first fault category is obtained, and based on the first fault category, a target calculation formula matching the first fault category is determined from mode voltage calculation formulas corresponding to a plurality of preset fault categories; Based on the target calculation formula, a line mode voltage and a zero mode voltage corresponding to the current limiting actuator on the fault-occurring line in the target multi-DC system are calculated, and a target coordinate point is determined according to the line mode voltage and the zero mode voltage, and a second fault category corresponding to the target multi-DC system is determined according to a position of the target coordinate point in a preset four-quadrant modal voltage interval, wherein the preset four-quadrant modal voltage interval includes a plurality of sub-intervals, and each sub-interval indicates a fault category; A target fault category corresponding to the target multi-DC system is determined according to the first fault category and the second fault category.

2. The method according to claim 1, characterized in that The preset four-quadrant modal voltage interval includes a sub-interval that is easy to be misidentified; The determining, according to the first fault category and the second fault category, a target fault category corresponding to the target multi-DC system includes: When the target coordinate point is located in a subinterval outside the easily misidentified subinterval, and the first fault category is consistent with the second fault category, taking the first fault category as the target fault category corresponding to the target multi-DC system; When the target coordinate point is located in the easily misidentified sub-interval and the first fault category is consistent with the second fault category, the DC voltage change rate on the DC transmission line in the target multi-DC system is calculated, and the magnitude relationship between the DC voltage change rate and the preset evaluation trigger event threshold is determined; when the DC voltage change rate is less than or equal to the evaluation trigger event threshold, the first fault category is used as the target fault category of the target multi-DC system; when the DC voltage change rate is greater than the evaluation trigger event threshold, it is determined whether the first fault category is a pole-to-pole fault, and the impedance fault type corresponding to the target multi-DC system is determined according to the judgment result.

3. The method according to claim 2, characterized in that The determining, according to the judgment result, the impedance fault type corresponding to the target multi-DC system includes: In the case where the first fault type is a pole-to-pole fault, if the DC voltage change rate is greater than a first preset change rate threshold, it is determined that the impedance fault type corresponding to the target multi-DC system is an internal high impedance fault; otherwise, it is determined that the impedance fault type corresponding to the target multi-DC system is an external low impedance fault; In the case where the first fault category is not a pole-to-pole fault, if the DC voltage change rate is greater than a second preset change rate threshold, the impedance fault type corresponding to the target multi-DC system is determined to be an internal high impedance fault; otherwise, the impedance fault type corresponding to the target multi-DC system is determined to be an external low impedance fault, wherein the absolute value of the first preset change rate threshold is greater than the absolute value of the second preset change rate threshold.

4. The method according to claim 1, characterized in that: Before determining the target calculation formula matching the first fault category, the method further includes: According to the fault occurrence line, a target analysis area is determined from the target multi-DC system, and a multilevel converter in a system model corresponding to the target analysis area is structurally simplified through a multilevel converter simplified model to obtain a system equivalent model corresponding to the target analysis area, and initial voltage calculation formulas and phase mode transformation expressions corresponding to multiple fault categories are obtained according to the system equivalent model; According to the initial voltage calculation formula and the phase mode transformation expression, the mode voltage calculation formulas corresponding to the multiple fault types are obtained.

5. The method according to claim 4, characterized in that The simplified model of the multilevel converter is expressed by the following formula: R MMC =(2 / 3)(R+ΣR ON ) L MMC =(2 / 3)L C MMC =6(C / N) The current transformer is used in the following ways: MM feel C , Table C shows MM Place C The description of the multi-level converter is shown in Figure 1. The multi-level converter is used to describe the effective resistance of the converter. MM Allow C , R represents the sum of the arm resistances of all the bridge arms of the multi-level converter, ΣR ON represents the sum of the on-state resistances of all IGBT modules of the multilevel converter, L represents the sum of the bridge arm inductances of all bridge arms of the multilevel converter, C represents the submodule capacitance corresponding to any submodule of the multilevel converter, and N represents the number of submodules of any bridge arm.

6. The method according to claim 4 or 5, characterized in that: When the target multi-DC system is a four-terminal DC system, the phase mode transformation expression is expressed by the following formula: The four-terminal DC system includes four multilevel converters, one end of each of the multilevel converters is connected to a section of overhead line through a current limiting actuator; the overhead lines corresponding to multilevel converter 1 are line 1 and line 4, the overhead lines corresponding to multilevel converter 2 are line 1 and line 2, the overhead lines of multilevel converter 3 are line 2 and line 3, and the overhead lines of multilevel converter 4 are line 3 and line 4; Z 14 It represents the equivalent impedance between line 1 and line 4, Z 23 represents the equivalent impedance between line 2 and line 3, L 41 Indicates the equivalent inductance between line 1 and line 4, L 23 Indicates the equivalent inductance between line 2 and line 3, L T41 Indicates the equivalent inductance of the transformer between line 1 and line 4, L T23 It represents the transformer equivalent inductance between line 2 and line 3, L MMC3 is the equivalent inductance of the multilevel converter 3, L MMC4 is the equivalent inductance of the multilevel converter 4, R 41 Represents the line equivalent resistance between line 1 and line 4, R 23 Represents the equivalent resistance between line 2 and line 3, R MMC3 is the equivalent resistance of the multilevel converter 3, R MMC4 is the equivalent resistance of the multilevel converter 4, L mn is the self-inductance between line m and line n, M mn is the mutual inductance between line m and line n, L mn_l is the line mode inductance between line m and line n, L mn_0 is the zero-mode component inductance between line m and line n; The calculation formulas for the initial voltages corresponding to the various fault types are as follows: In the case of internal positive-to-ground fault, the initial voltage calculation formula is as follows: Under the internal negative pole to ground fault category, the initial voltage calculation formula is as follows: Among them, U L12_l (jω) and U L12_0 (jω) are the line mode voltage and zero mode voltage of the current limiting actuator between line 1 and line 2, respectively, L T12 Indicates the equivalent inductance of the transformer between line 1 and line 2, U dc represents the rated DC voltage of the target multi-DC system before fault, R f represents the fault equivalent resistance of the target multi-DC system, Z1, Z2, Z3 and Z4 are impedance values ​​related to frequency, R MMC1 represents the equivalent resistance of the multilevel converter 1, R MMC2 represents the equivalent resistance of the multilevel converter 2, d represents the duty cycle of the multilevel converter; Under the external forward pole-to-ground fault category, the initial voltage calculation formula is as follows: Under the external reverse pole-to-ground fault category, the initial voltage calculation formula is as follows: Among them, L MMC1 is the equivalent inductance of multilevel converter 1, L MMC2 is the equivalent inductance of the multilevel converter 2, Z5, Z6, Z7, Z8, Z9, Z 10 It is the impedance value related to frequency; Under the internal pole-to-pole fault category, the initial voltage calculation formula is as follows: Under the external pole-to-pole fault category, the initial voltage calculation formula is as follows: The mode voltage calculation formulas corresponding to the multiple fault types are obtained according to the initial voltage calculation formula and the phase mode transformation expression, including: Substituting the phase mode transformation expression into the initial voltage calculation formula, the mode voltage calculation formulas corresponding to the multiple fault types are obtained.

7. The method according to claim 6, characterized in that The method further comprises: For each fault category, based on the line mode voltage calculated under the fault category and the quantitative relationship formula between the line mode voltage and the fault equivalent resistance, determine a first curve of the line mode voltage changing with the fault equivalent resistance under the fault category, map the first curve corresponding to each fault category to the same coordinate system, determine a first curve with an overlapping range of values ​​under the line mode voltage coordinate axis, determine a first easily misidentified area according to the overlapping range, and determine a line mode voltage range corresponding to the first easily misidentified area based on the maximum fault equivalent resistance under the target multi-DC system; and / or, For each fault category, based on the line mode voltage calculated under the fault category and the quantitative relationship formula between the line mode voltage and the current limiting actuator inductance, determine a second curve of the line mode voltage changing with the current limiting actuator inductance under the fault category, map the second curve corresponding to each fault category to the same coordinate system, determine a second curve with an overlapping range of values ​​under the line mode voltage coordinate axis, determine a second easily misidentified area based on the overlapping range, and determine a line mode voltage range corresponding to the second easily misidentified area based on the maximum current limiting actuator inductance under the target multi-DC system; The quantitative relationship between the line mode voltage and the fault equivalent resistance is as follows: R f0 is the fault equivalent resistance in zero mode, γ=1+(Z1 / Z2), ΔR f is the small change of fault equivalent resistance; The quantitative relationship between line mode voltage and current limiting actuator inductance is as follows: β=(L MMC / 2L T′12 +L MMC ); L T'12 is the inductance of the current limiting actuator between line 1 and line 2, L T'120 is the inductance of the current limiting actuator between Line 1 and Line 2 in zero mode.

8. A fault identification device for a multi-DC system, characterized in that: include: a first fault category acquisition module, configured to acquire an estimated first fault category when a fault occurs in a target multi-DC system, and determine, based on the first fault category, a target calculation formula matching the first fault category from among mode voltage calculation formulas corresponding to a plurality of preset fault categories; a second fault category determination module, configured to calculate, based on the target calculation formula, a line mode voltage and a zero mode voltage corresponding to a current limiting actuator on a fault-occurring line in the target multi-DC system, and determine a target coordinate point according to the line mode voltage and the zero mode voltage, and determine a second fault category corresponding to the target multi-DC system according to a position of the target coordinate point in a preset four-quadrant modal voltage interval, wherein the preset four-quadrant modal voltage interval includes a plurality of sub-intervals, and each sub-interval indicates a fault category; A target fault category determination module is used to determine a target fault category corresponding to the target multi-DC system according to the first fault category and the second fault category.

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

10. A computer device comprising a storage medium, a processor, and a computer program stored in the storage medium and executable on the processor, characterized in that: When the processor executes the computer program, the method according to any one of claims 1 to 7 is implemented.

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