Low voltage area topology identification method and system

Abstract

This scheme relates to a method and system for identifying low-voltage substation topology. The method includes: the substation intelligent fusion terminal periodically sends a topology identification instruction to the low-voltage terminal monitoring unit; the low-voltage terminal monitoring unit triggers the sending of characteristic current according to the topology identification instruction, determines the current characteristic threshold through K‑means++ clustering based on the characteristic current, identifies each characteristic current in the substation, and obtains the identification result according to the current characteristic threshold, and feeds back the identification result to the substation intelligent fusion terminal; the substation intelligent fusion terminal generates substation topology environment information according to the identification result, and sends the identification result and substation topology environment information to the low-voltage power distribution management master station. The current characteristic threshold is determined based on the characteristic current through K‑means++ clustering, so as to identify each characteristic current, no longer use a fixed characteristic current threshold, optimize the characteristic current threshold, reduce the misidentification rate, and improve the topology identification accuracy, thereby further improving the topology identification efficiency.

Description

Technical Field

[0001] The present invention relates to the field of electric power technology, and in particular to a low-voltage station area topology identification method and system. Background Art

[0002] The low-voltage distribution network plays a key role in the power distribution system, mainly involving the monitoring and management of electricity consumption by residents, businesses and major corporate customers. With the rapid popularization of new energy vehicles, charging equipment and grid-connected distributed power generation equipment, these have brought new problems and challenges to the power quality, power supply reliability and economic operation of the low-voltage distribution network. In the low-voltage distribution network system, the organization of topological hierarchical network information is a very important process. Often, inaccurate or misidentified topological network hierarchical information will be detrimental to the monitoring and fault location analysis of key equipment in the distribution network.

[0003] At present, the automatic topology network level identification method commonly used in low-voltage distribution stations is to inject characteristic current into the power line, and realize the combing of each level of topology network by tracking and identifying the characteristic current. Although this method is highly practical, it needs to inject characteristic current into the low-voltage power grid, which leads to high requirements for the identification of this characteristic current. Once the characteristic current is abnormal or the characteristic current threshold is deviated, it will lead to misidentification or abnormal identification. This has high requirements on the environment of the actual low-voltage power network and is not suitable for automatic topology network identification in some special environments.

[0004] Therefore, the traditional automatic topology network level identification method has the problem of low recognition accuracy. Summary of the invention

[0005] Based on this, in order to solve the above technical problems, a low-voltage substation topology recognition method and system are provided, which can improve the recognition accuracy of low-voltage substation topology recognition.

[0006] A method for identifying low voltage area topology, the method comprising:

[0007] The intelligent fusion terminal in the substation periodically sends topology identification instructions to the low-voltage terminal monitoring unit;

[0008] The low-voltage terminal monitoring unit triggers the sending of characteristic current according to the topology identification instruction, and the low-voltage terminal monitoring unit determines the current characteristic threshold value through K-means++ clustering based on the characteristic current;

[0009] The low-voltage terminal monitoring unit identifies each characteristic current in the substation, obtains an identification result according to the current characteristic threshold, and feeds back the identification result to the substation intelligent fusion terminal;

[0010] The substation intelligent fusion terminal generates substation topology environment information according to the identification result, and sends the identification result and the substation topology environment information to the low-voltage power distribution management master station.

[0011] In one embodiment, the low-voltage terminal monitoring unit determines the current characteristic threshold value through K-means++ clustering based on the characteristic current, including:

[0012] The low voltage terminal monitoring unit obtains each characteristic current value corresponding to each characteristic current in the station area, and uses each characteristic current value as a sample data point set;

[0013] The low-voltage terminal monitoring unit selects a data point from the sample data point set as a first characteristic current center point, and calculates an absolute value of a current difference between any data point in the sample data point set and the first characteristic current center point;

[0014] The low voltage terminal monitoring unit continues to select a preset number of characteristic current center points from the sample data point set according to the absolute value of the current difference;

[0015] The low-voltage terminal monitoring unit performs K-means++ clustering on the data points in the sample data point set except the preset number of characteristic current center points and the preset number of characteristic current center points to determine the current characteristic threshold.

[0016] In one embodiment, the low voltage terminal monitoring unit continues to select a preset number of characteristic current center points from the sample data point set according to the absolute value of the current difference, including:

[0017] The low voltage terminal monitoring unit obtains the absolute value of the current difference corresponding to each data point in the sample data point set;

[0018] The low-voltage terminal monitoring unit uses the data point with the largest absolute value of the current difference as the second characteristic current center point, and uses the data point with the second largest absolute value of the current difference as the third characteristic current center point, until a preset number of characteristic current center points are selected.

[0019] In one embodiment, the low voltage terminal monitoring unit identifies each characteristic current in the substation area and obtains an identification result according to the current characteristic threshold, including:

[0020] The low voltage terminal monitoring unit determines in sequence whether each characteristic current in the station area is within the current characteristic threshold;

[0021] The low-voltage terminal monitoring unit marks the recognition result corresponding to the characteristic current within the current characteristic threshold as recognition passed, and marks the recognition result corresponding to the characteristic current not within the current characteristic threshold as recognition failed.

[0022] In one embodiment, the method further comprises:

[0023] The low voltage terminal monitoring unit feeds back the identification result as the characteristic current passed to the substation intelligent fusion terminal.

[0024] In one embodiment, the substation intelligent fusion terminal generates substation topology environment information according to the identification result, including:

[0025] The substation intelligent fusion terminal generates substation topology environment information according to the identified characteristic current.

[0026] In one of the embodiments, the substation intelligent fusion terminal communicates with the low-voltage terminal monitoring unit via a power carrier; the low-voltage power distribution management master station communicates with the substation intelligent fusion terminal via a wireless or wired network.

[0027] A low-voltage area topology identification system, the system comprising: an area intelligent fusion terminal, a low-voltage terminal monitoring unit, and a low-voltage power distribution management master station; wherein:

[0028] The substation intelligent fusion terminal is used to periodically send topology identification instructions to the low-voltage terminal monitoring unit;

[0029] The low-voltage terminal monitoring unit is used to trigger the sending of characteristic current according to the topology identification instruction, and the low-voltage terminal monitoring unit determines the current characteristic threshold value through K-means++ clustering based on the characteristic current;

[0030] The low-voltage terminal monitoring unit is further used to identify each characteristic current in the substation, obtain an identification result according to the current characteristic threshold, and feed back the identification result to the substation intelligent fusion terminal;

[0031] The substation intelligent fusion terminal is also used to generate substation topology environment information according to the identification result, and send the identification result and the substation topology environment information to the low-voltage power distribution management master station.

[0032] The above-mentioned low-voltage substation topology identification method and system periodically sends a topology identification instruction to the low-voltage terminal monitoring unit through the substation intelligent fusion terminal; the low-voltage terminal monitoring unit triggers the sending of characteristic current according to the topology identification instruction, and the low-voltage terminal monitoring unit determines the current characteristic threshold based on the characteristic current through K-means++ clustering; the low-voltage terminal monitoring unit identifies each of the characteristic currents in the substation, and obtains the identification result according to the current characteristic threshold, and feeds the identification result back to the substation intelligent fusion terminal; the substation intelligent fusion terminal generates substation topology environment information according to the identification result, and sends the identification result and the substation topology environment information to the low-voltage power distribution management master station. The current characteristic threshold is determined based on the characteristic current through K-means++ clustering, so as to identify each characteristic current, no longer use a fixed characteristic current threshold, optimize the characteristic current threshold, reduce the misidentification rate, and improve the topology identification accuracy, thereby further improving the topology identification efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A diagram showing an application environment of a low voltage area topology identification method in an embodiment;

[0034] Figure 2 A schematic diagram of a process of identifying a low voltage area topology in one embodiment;

[0035] Figure 3 A schematic diagram of a process of determining a current feature threshold through K-means++ clustering in one embodiment;

[0036] Figure 4 It is a structural block diagram of a low voltage substation topology identification system in one embodiment. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0038] The low voltage area topology identification method provided in the embodiment of the present application can be applied to Figure 1 In the application environment shown. Figure 1As shown, the application environment includes a substation intelligent fusion terminal 100, a low-voltage terminal monitoring unit 200, and a low-voltage power distribution management master station 300; wherein the substation intelligent fusion terminal 100 is connected and communicated with the low-voltage terminal monitoring unit 200 and the low-voltage power distribution management master station 300 respectively. The substation intelligent fusion terminal 100 periodically sends a topology recognition instruction to the low-voltage terminal monitoring unit 200; the low-voltage terminal monitoring unit 200 triggers the sending of characteristic current according to the topology recognition instruction, and the low-voltage terminal monitoring unit 200 determines the current characteristic threshold through K-means++ clustering based on the characteristic current; the low-voltage terminal monitoring unit 200 recognizes each characteristic current in the substation, and obtains the recognition result according to the current characteristic threshold, and feeds the recognition result back to the substation intelligent fusion terminal 100; the substation intelligent fusion terminal 100 generates substation topology environment information according to the recognition result, and sends the recognition result and substation topology environment information to the low-voltage power distribution management master station 300.

[0039] In one embodiment, Figure 2 As shown, a method for identifying a low-voltage area topology is provided, comprising the following steps:

[0040] Step 202: The intelligent fusion terminal of the substation periodically sends a topology identification instruction to the low-voltage terminal monitoring unit.

[0041] The intelligent fusion terminal in the substation area can act as a root node and periodically send topology identification instructions to the low-voltage terminal monitoring unit to perform topology identification.

[0042] Step 204: the low-voltage terminal monitoring unit triggers the sending of characteristic current according to the topology recognition instruction, and the low-voltage terminal monitoring unit determines the current characteristic threshold through K-means++ clustering based on the characteristic current.

[0043] The low-voltage terminal monitoring unit can trigger the characteristic current according to the topology recognition instruction. After the characteristic current is triggered, it can be sent to the substation environment. At this time, the low-voltage terminal monitoring unit can determine the current characteristic threshold based on the characteristic current through K-means++ clustering. Specifically, the low-voltage terminal monitoring unit can adjust the current characteristic threshold according to the characteristic current, and K-means++ clustering can optimize the current characteristic threshold for topology recognition under different current characteristic values.

[0044] Step 206: The low-voltage terminal monitoring unit identifies each characteristic current in the substation, obtains an identification result according to the current characteristic threshold, and feeds back the identification result to the substation intelligent fusion terminal.

[0045] The low-voltage terminal monitoring units at each level identify the characteristic current in the environment. If it is within the current characteristic threshold range, it is judged as normal recognition, otherwise it is judged as unrecognized. Both normal recognition and unrecognized are recognition results. The low-voltage terminal monitoring unit can feed back the recognition results to the intelligent fusion terminal of the substation.

[0046] Step 208: The substation intelligent fusion terminal generates substation topology environment information according to the identification result, and sends the identification result and the substation topology environment information to the low-voltage power distribution management master station.

[0047] The intelligent fusion terminal in the substation area can report topology identification events based on the identification results, and send the identification results and substation topology environment information to the low-voltage power distribution management master station.

[0048] In this embodiment, the substation intelligent fusion terminal periodically sends a topology identification instruction to the low-voltage terminal monitoring unit; the low-voltage terminal monitoring unit triggers the sending of characteristic current according to the topology identification instruction, and the low-voltage terminal monitoring unit determines the current characteristic threshold based on the characteristic current through K-means++ clustering; the low-voltage terminal monitoring unit identifies each characteristic current in the substation, and obtains the identification result according to the current characteristic threshold, and feeds the identification result back to the substation intelligent fusion terminal; the substation intelligent fusion terminal generates the substation topology environment information according to the identification result, and sends the identification result and the substation topology environment information to the low-voltage power distribution management master station. The current characteristic threshold is determined based on the characteristic current through K-means++ clustering, so as to identify each characteristic current, no longer use a fixed characteristic current threshold, optimize the characteristic current threshold, reduce the false recognition rate, and improve the topology recognition accuracy, thereby further improving the topology recognition efficiency.

[0049] In one embodiment, Figure 3 The low voltage area topology identification method provided in the figure may also include a process of determining a current characteristic threshold through K-means++ clustering, and the specific process includes:

[0050] Step 302: The low voltage terminal monitoring unit obtains each characteristic current value corresponding to each characteristic current in the substation, and uses each characteristic current value as a set of sample data points.

[0051] The low voltage terminal monitoring unit can take all characteristic current values ​​in the entire substation environment as a set of sample data points.

[0052] Step 304: the low voltage terminal monitoring unit selects a data point from the sample data point set as the first characteristic current center point, and calculates the absolute value of the current difference between any data point in the sample data point set and the first characteristic current center point.

[0053] The low voltage terminal monitoring unit can select a data point from the sample data point set as the first characteristic current center point, and calculate the absolute value D(n) of the current difference between any data point n in the sample data point set and the first characteristic current center point.

[0054] Step 306: The low voltage terminal monitoring unit continues to select a preset number of characteristic current center points from the sample data point set according to the absolute value of the current difference.

[0055] Among them, the preset number can be represented by k, and the low-voltage terminal monitoring unit can select a new data point from the sample data point set as a new characteristic current center point according to the absolute value of the current difference, and repeat the operation steps 304-306 until k characteristic current center points are selected. Specifically, in one embodiment, the low-voltage terminal monitoring unit obtains the absolute value of the current difference corresponding to each data point in the sample data point set; the low-voltage terminal monitoring unit uses the data point with the largest absolute value of the current difference as the second characteristic current center point, and uses the data point with the second largest absolute value of the current difference as the third characteristic current center point, until the preset number of characteristic current center points are selected. That is, when the low-voltage terminal monitoring unit selects the characteristic current center point, the greater the probability that the data point with a larger absolute value of the current difference D(n) is selected as the new characteristic current center point, the smaller the probability that the data point with a smaller D(n) is selected as the new characteristic current center point.

[0056] Step 308 : The low voltage terminal monitoring unit performs K-means++ clustering on the data points in the sample data point set except for a preset number of characteristic current center points and a preset number of characteristic current center points to determine a current characteristic threshold.

[0057] The low-voltage terminal monitoring unit can calculate the absolute value of the current difference between the remaining data points in the sample data point set and the k characteristic current center points, and divide the remaining data points into clusters with the smallest difference therewith, so as to determine the current characteristic threshold.

[0058] In this embodiment, each characteristic current value corresponding to each characteristic current in the substation is obtained through the low-voltage terminal monitoring unit, and each characteristic current value is used as a set of sample data points; a data point is selected from the sample data point set as the first characteristic current center point, and the absolute value of the current difference between any data point in the sample data point set and the first characteristic current center point is calculated; a preset number of characteristic current center points are further selected from the sample data point set according to the absolute value of the current difference; K-means++ clustering is performed on the data points in the sample data point set except the preset number of characteristic current center points and the preset number of characteristic current center points to determine the current characteristic threshold. Through the K-means++ clustering algorithm, the characteristic current threshold can be optimized and controlled during the topology recognition process, thereby further optimizing the judgment conditions for topology recognition.

[0059] In one embodiment, a low-voltage substation topology identification method is provided that may further include a process for identifying characteristic currents, and the specific process includes: the low-voltage terminal monitoring unit determines in turn whether each characteristic current in the substation is within a current characteristic threshold; the low-voltage terminal monitoring unit marks the identification result corresponding to the characteristic current within the current characteristic threshold as identification passed, and marks the identification result corresponding to the characteristic current not within the current characteristic threshold as identification failed.

[0060] In one embodiment, a low-voltage substation topology identification method provided may further include a process of feeding back characteristic current, and the specific process includes: the low-voltage terminal monitoring unit feeds back the identification result as the characteristic current that has been identified to the substation intelligent fusion terminal.

[0061] In one embodiment, a low-voltage substation topology identification method provided may also include a process of obtaining substation topology environment information, and the specific process includes: the substation intelligent fusion terminal generates the substation topology environment information based on the identified characteristic current.

[0062] In one embodiment, the intelligent fusion terminal of the substation area communicates with the low-voltage terminal monitoring unit via a power carrier; the low-voltage power distribution management master station communicates with the intelligent fusion terminal of the substation area via a wireless or wired network.

[0063] It should be understood that, although the steps in the above-mentioned flowcharts are shown in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps is not strictly limited in order, and these steps can be executed in other orders. Moreover, at least a part of the steps in the above-mentioned flowcharts may include a plurality of sub-steps or a plurality of stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these sub-steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the sub-steps or stages of other steps.

[0064] In one embodiment, Figure 4 As shown, a low-voltage area topology identification system is provided, including: an area intelligent fusion terminal 100, a low-voltage terminal monitoring unit 200, and a low-voltage power distribution management master station 300; wherein:

[0065] The intelligent fusion terminal 100 of the substation is used to periodically send a topology identification instruction to the low-voltage terminal monitoring unit 200;

[0066] The low-voltage terminal monitoring unit 200 is used to trigger the sending of characteristic current according to the topology recognition instruction. The low-voltage terminal monitoring unit 200 determines the current characteristic threshold value through K-means++ clustering based on the characteristic current;

[0067] The low voltage terminal monitoring unit 200 is also used to identify each characteristic current in the substation, obtain the identification result according to the current characteristic threshold, and feed back the identification result to the substation intelligent fusion terminal 100;

[0068] The substation intelligent fusion terminal 100 is also used to generate substation topology environment information according to the identification result, and send the identification result and the substation topology environment information to the low-voltage power distribution management master station 300.

[0069] In one embodiment, the low-voltage terminal monitoring unit 200 is also used to obtain each characteristic current value corresponding to each characteristic current in the substation, and use each characteristic current value as a set of sample data points; select a data point from the sample data point set as the first characteristic current center point, and calculate the absolute value of the current difference between any data point in the sample data point set and the first characteristic current center point; continue to select a preset number of characteristic current center points from the sample data point set according to the absolute value of the current difference; perform K-means++ clustering on the data points in the sample data point set except the preset number of characteristic current center points and the preset number of characteristic current center points to determine the current characteristic threshold.

[0070] In one embodiment, the low-voltage terminal monitoring unit 200 is also used to obtain the absolute value of the current difference corresponding to each data point in the sample data point set; the data point with the largest absolute value of the current difference is used as the second characteristic current center point, and the data point with the second largest absolute value of the current difference is used as the third characteristic current center point, until a preset number of characteristic current center points are selected.

[0071] In one embodiment, the low-voltage terminal monitoring unit 200 is also used to determine in turn whether each characteristic current in the substation is within the current characteristic threshold; mark the identification result corresponding to the characteristic current within the current characteristic threshold as identification passed, and mark the identification result corresponding to the characteristic current not within the current characteristic threshold as identification failed.

[0072] In one embodiment, the low voltage terminal monitoring unit 200 is further used to feed back the identification result of the characteristic current that has been identified to the substation intelligent fusion terminal 100 .

[0073] In one embodiment, the substation intelligent fusion terminal 100 is further used to generate substation topology environment information according to the identified characteristic current.

[0074] The technical features of the above embodiments may be arbitrarily combined. 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.

[0075] The above-mentioned 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 invention patent. 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 patent of the present application shall be subject to the attached claims.

Claims

1. A method for identifying low voltage area topology, characterized in that: The method comprises: The intelligent fusion terminal in the substation periodically sends topology identification instructions to the low-voltage terminal monitoring unit; The low-voltage terminal monitoring unit triggers the sending of characteristic current according to the topology identification instruction, and the low-voltage terminal monitoring unit determines the current characteristic threshold value through K-means++ clustering based on the characteristic current, including: the low-voltage terminal monitoring unit obtains each characteristic current value corresponding to each characteristic current in the substation, and uses each characteristic current value as a set of sample data points; the low-voltage terminal monitoring unit selects a data point from the set of sample data points as the first characteristic current center point, and calculates the absolute value of the current difference between any data point in the set of sample data points and the first characteristic current center point; the low-voltage terminal monitoring unit continues to select a preset number of characteristic current center points from the set of sample data points according to the absolute value of the current difference; the low-voltage terminal monitoring unit performs K-means++ clustering on the data points in the set of sample data points except the preset number of characteristic current center points and the preset number of characteristic current center points to determine the current characteristic threshold value; The low-voltage terminal monitoring unit identifies each characteristic current in the substation and obtains an identification result according to the current characteristic threshold, including: the low-voltage terminal monitoring unit sequentially determines whether each characteristic current in the substation is within the current characteristic threshold; the low-voltage terminal monitoring unit marks the identification result corresponding to the characteristic current within the current characteristic threshold as identification passed, and marks the identification result corresponding to the characteristic current not within the current characteristic threshold as identification failed; and feeds back the identification result to the substation intelligent fusion terminal; The substation intelligent fusion terminal generates substation topology environment information according to the identification result, and sends the identification result and the substation topology environment information to the low-voltage power distribution management master station.

2. The low voltage area topology identification method according to claim 1, characterized in that: The low voltage terminal monitoring unit continues to select a preset number of characteristic current center points from the sample data point set according to the absolute value of the current difference, including: The low voltage terminal monitoring unit obtains the absolute value of the current difference corresponding to each data point in the sample data point set; The low-voltage terminal monitoring unit uses the data point with the largest absolute value of the current difference as the second characteristic current center point, and uses the data point with the second largest absolute value of the current difference as the third characteristic current center point, until a preset number of characteristic current center points are selected.

3. The low voltage area topology identification method according to claim 1, characterized in that: The method further comprises: The low voltage terminal monitoring unit feeds back the identification result as the characteristic current passed to the substation intelligent fusion terminal.

4. The low voltage area topology identification method according to claim 3 is characterized in that: The intelligent fusion terminal of the substation area generates substation area topology environment information according to the identification result, including: The substation intelligent fusion terminal generates substation topology environment information according to the identified characteristic current.

5. The low voltage area topology identification method according to claim 1, characterized in that: The substation intelligent fusion terminal communicates with the low-voltage terminal monitoring unit via a power carrier; the low-voltage power distribution management master station communicates with the substation intelligent fusion terminal via a wireless or wired network.

6. A low voltage area topology identification system, characterized in that: The system includes: an intelligent fusion terminal for the substation area, a low-voltage terminal monitoring unit, and a low-voltage power distribution management master station; wherein: The substation intelligent fusion terminal is used to periodically send topology identification instructions to the low-voltage terminal monitoring unit; The low-voltage terminal monitoring unit is used to trigger the sending of the characteristic current according to the topology identification instruction, and the low-voltage terminal monitoring unit determines the current characteristic threshold value through K-means++ clustering based on the characteristic current, including: the low-voltage terminal monitoring unit obtains each characteristic current value corresponding to each characteristic current in the substation, and uses each characteristic current value as a sample data point set; the low-voltage terminal monitoring unit selects a data point from the sample data point set as the first characteristic current center point, and calculates the absolute value of the current difference between any data point in the sample data point set and the first characteristic current center point; the low-voltage terminal monitoring unit continues to select a preset number of characteristic current center points from the sample data point set according to the absolute value of the current difference; the low-voltage terminal monitoring unit performs K-means++ clustering on the data points in the sample data point set except the preset number of characteristic current center points and the preset number of characteristic current center points to determine the current characteristic threshold value; The low-voltage terminal monitoring unit is also used to identify each of the characteristic currents in the substation area and obtain an identification result according to the current characteristic threshold, including: the low-voltage terminal monitoring unit sequentially determines whether each of the characteristic currents in the substation area is within the current characteristic threshold; the low-voltage terminal monitoring unit marks the identification result corresponding to the characteristic current within the current characteristic threshold as identification passed, and marks the identification result corresponding to the characteristic current not within the current characteristic threshold as identification failed; and feeds back the identification result to the substation area intelligent fusion terminal; The substation intelligent fusion terminal is also used to generate substation topology environment information according to the identification result, and send the identification result and the substation topology environment information to the low-voltage power distribution management master station.

7. The low voltage area topology identification system according to claim 6, characterized in that: The low-voltage terminal monitoring unit is also used to obtain the absolute value of the current difference corresponding to each data point in the sample data point set; the data point with the largest absolute value of the current difference is used as the second characteristic current center point, and the data point with the second largest absolute value of the current difference is used as the third characteristic current center point, until a preset number of characteristic current center points are selected.

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