Distribution line current differential protection method based on DTW algorithm

Abstract

The invention discloses a DTW algorithm-based distribution line current differential protection method, relates to the technical field of power distribution network relay protection, and aims to solve the problems that the III-section type overcurrent protection performance is reduced and the optical fiber communication cost is high after a distributed power supply is connected. According to the method, a 5G communication technology, a five-point numerical differential algorithm, amplitude limiting average filtering and a DTW similarity distance algorithm are fused, and current differential protection is achieved; the method comprises the steps of collecting three-phase current on two sides of a line in real time, starting a criterion through a fault current change rate, suppressing noise through amplitude-limiting average filtering, and normalizing data; the core is that the current sequence similarity is calculated by using a DTW algorithm, and a fault is accurately judged; according to the method, the influence of 5G communication time delay is eliminated, and the reliability of distribution network protection and control is improved; meanwhile, optical fibers are replaced by 5G, so that the cost is greatly reduced, the economical efficiency of distribution network protection is improved, and popularization and application are facilitated; the innovative technology provides powerful support for intelligent upgrading and sustainable development of a power distribution network.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution network relay protection, and in particular to a distribution line current differential protection method based on a DTW algorithm. Background Art

[0002] With the transformation of the global energy structure and the in-depth implementation of the new power system development strategy, the penetration rate of distributed power sources (such as solar photovoltaic, wind power generation, etc.) in the distribution network continues to increase. This change has greatly enriched the types of power sources in the distribution network, but it has also posed severe challenges to the traditional distribution network protection technology. Most of my country's traditional distribution networks use III-stage overcurrent protection schemes such as current quick break. This protection scheme can better ensure the rapid identification and isolation of faults when the distribution network topology is relatively simple and the power supply form is single. However, with the widespread access of distributed power sources, the topology and form of the distribution network have changed significantly, and the action performance of the traditional III-stage overcurrent protection has begun to deteriorate, which is specifically manifested in problems such as protection refusal to operate, false operation, and excessive action time, which seriously affects the safety and reliability of the distribution system.

[0003] In order to solve the above problems, some regional distribution networks with high requirements for power supply reliability have gradually adopted current differential protection schemes. Current differential protection is based on Kirchhoff's current law. It determines whether a fault has occurred by comparing the difference in current on both sides of the line. It has the advantages of strong adaptability to network structure, fast action speed, and good selectivity. However, current differential protection requires high-precision current synchronous sampling and high-speed communication transmission. Traditionally, optical fiber communication is used to achieve this requirement. However, due to the characteristics of the distribution network with many points and wide coverage, if optical fiber communication is used for data transmission, it will greatly increase the construction and maintenance costs, limiting the large-scale application of current differential protection in the distribution network.

[0004] In recent years, with the rapid development of 5G communication technology, its high bandwidth and ultra-low latency characteristics have provided a new solution for current differential protection of distribution networks. Using 5G communication technology to realize differential protection data transmission channels can significantly reduce communication costs and improve economic benefits. However, in practical applications, 5G communication still has uncertainty problems in data transmission delay and delay jitter, which may have an adverse effect on the calculation accuracy of protection action criteria, and thus affect the reliability and selectivity of protection actions.

[0005] In summary, although the existing technology has solved some of the problems faced by the distribution network protection after the access of distributed power sources to a certain extent, there are still many shortcomings, such as the deterioration of the performance of the III-stage overcurrent protection, the high cost of the current differential protection, and the uncertainty of the 5G (5th Generation Mobile Communication Technology) communication data transmission delay and delay jitter. Therefore, it is particularly important to develop a new distribution line current differential protection method that can overcome the above defects and has good economy and reliability.

[0006] Based on the above background, the present invention proposes a distribution line current differential protection method based on the DTW (Dynamic Time Warping) algorithm. The method comprehensively utilizes the advantages of low-latency 5G communication technology, five-point numerical differential algorithm protection start-up criterion, limited average filtering and DTW similarity distance algorithm, aiming to improve the reliability of distribution network protection and control, and reduce communication costs, providing a new solution for distribution network protection after distributed power sources are connected. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a distribution line current differential protection method based on the DTW algorithm to solve the problem that after the distribution network is connected to the distributed power source, the traditional three-stage current protection is difficult to ensure the reliability and selectivity of the operation.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a distribution line current differential protection method based on DTW algorithm, comprising the following steps: Step 1: Use the intelligent electronic protection device IED to sample the three-phase current on both sides of the line in real time to form a real-time sampling array with a sampling frequency of 10kHz and a data storage length of 400. Data transmission is achieved through 5G wireless communication technology. Step 2: Use the five-point numerical differentiation algorithm of the first-order derivative to calculate the fault current change rate, and set the protection start criterion based on the change rate. Substitute the sample array data obtained in Step 1 into the start criterion. If the fault current change rate is greater than the set protection start threshold, the current differential protection is started. Step 3: When the current differential protection start-up conditions are met, the current sampling arrays on both sides of the line are subjected to limited average filtering to determine the maximum deviation allowed between two adjacent sampling data. The filtered current sampling array is obtained by comparison and arithmetic averaging. Step 4: Perform current normalization processing on the filter array after the limiting average filtering in Step 3, extract the maximum and minimum values ​​in the current sequence, and perform amplitude compression on each sampling value in the current sequence so that it falls within the normalization interval; Step 5: Use the DTW algorithm to calculate the similarity distance between the current sequences obtained after current normalization in Step 4, and determine the threshold value of differential protection action. Based on the rapid increase of the DTW similarity distance, construct the current differential protection criterion based on the DTW algorithm; Step 6: Compare the DTW similarity distance value calculated in Step 5 with the differential protection action setting threshold. If the DTW similarity distance is greater than the setting threshold, it is determined that a fault has occurred on the line and the current differential protection action is executed.

[0009] In a preferred solution, the real-time sampling of the three-phase current data on both sides of the line in Step 1 specifically includes using an intelligent electronic protection device IED to sample the three-phase current on both sides of the line in real time to form a sampling array , The length of the sampling array is 400, which corresponds to twice the number of sampling points of 200 per power frequency cycle of 20ms. That is, the value of k is twice the number of samples per cycle, which corresponds to 400. m and n refer to the two sides of the line respectively. They represent the a, b and c phases of the system respectively.

[0010] In the preferred solution, the current differential protection start criterion constructed in Step 2 is to calculate the fault current change rate by a five-point numerical differentiation algorithm of the first-order derivative: , its setting expression is: (1) in, is the time interval of data collection points; , , , and is the sampling array and Any five consecutive sampling point data; To protect the startup threshold; It is the maximum sampling value of the three-phase current in each cycle when the line is operating normally; is the setting coefficient, the value range is 0.02~0.03; Fault current change rate The calculated value is greater than the set protection start threshold , then the new algorithm of current differential protection is started.

[0011] In a preferred solution, the specific steps of performing amplitude limiting average filtering on the current sampling arrays obtained by sampling on both sides of the line in Step 3 include: Step 3.1: Determine the maximum deviation allowed between two adjacent sampling data , value , the current sampling array The value sampled last The value sampled last time For comparison: (2) If the above formula holds, then the value sampled next is considered Valid, need to be retained; if the above formula does not hold, then the value sampled next time is considered The current value is invalid because it is abnormal data. The current value needs to be abandoned and replaced with the value sampled last time. Processing to obtain a new array after limiting processing ; Step 3.2: From the new array after clipping N sampling values ​​are taken continuously and used as a queue. The length of the queue is fixed to N. According to the first-in-first-out principle, a data at the head of the original queue is discarded each time, and the new data obtained by each sampling is put at the end of the queue to form a new queue. The arithmetic average operation is performed on the N data in the newly formed queue, so that the filter array processed by the limited average filter algorithm can be obtained. Similarly, the above filtering process is performed on the current array on the other side of the line to obtain the filtered array ; Where N is a positive integer, the value is , recommended 8.

[0012] In a preferred solution, the specific steps of performing current normalization processing on the filter array after the amplitude limiting average filtering processing in Step 4 include: Extracting current sequence The maximum value in and minimum value , for the current sequence Each data in the current sampling is compressed so that each current sampling value falls within Thus, a normalized current sampling sequence is obtained. Similarly, the normalized current sampling sequence can be obtained , the amplitude compression method is as follows: (3) in, is the sequence number of each current sampling point in the current sequence; is the current value of the nth current sampling point; is the normalized value of the current at the nth current sampling point.

[0013] In the preferred solution, in step 5, the current differential protection criterion based on the DTW algorithm is constructed by calculating the current sequence obtained after the current normalization processing according to the DTW algorithm. and , The negative sign indicates that the data Take the opposite similarity distance to determine the differential protection action threshold , taking advantage of the fact that the DTW similarity distance increases rapidly after a fault occurs in the area, a current differential protection criterion based on the DTW algorithm is constructed. The specific steps include: Step 5.1: Calculate the two current sequences in Step 4 and The Euclidean distance matrix M between them, assuming that their lengths are x and y respectively, calculate the Euclidean distance between the elements of the two current sequences, obtain the elements of the distance matrix M, and then form a The distance matrix M, the matrix elements The calculation formula is: (4) in, The current sequence The i-th data in and current sequence The jth data The Euclidean distance between them, the smaller the distance value, the higher the similarity; Step 5.2: Find a path from the upper left corner to the lower right corner of the distance matrix M , so that the sum of the elements on the path is minimized, the shortest path The current sequence and The similarity distance , the path selection needs to meet the following three constraints: boundary condition, the selected path must start from the upper left corner of the distance matrix M and end at the lower right corner; continuity, the selected path can only continue backward along its adjacent element points; minimum value, in the selected path, the distance value of the path must be the smallest; The recursive calculation formula is as follows: (5) in, From the upper left corner of the matrix To any point The shortest path; Step 5.3: Determine the differential protection action threshold , add up the first column elements of the distance matrix M in Step 5.1 to get , the first row elements of the distance matrix M are accumulated to obtain , differential protection action threshold The setting calculation formula is as follows: (6).

[0014] In a preferred solution, the specific step of determining that a fault has occurred on the line and executing the current differential protection action in Step 6 includes: Differential protection action setting threshold For comparison: (7) If the DTW similarity distance is greater than the setting threshold, it is determined that a fault has occurred on the line and the current differential protection is executed; otherwise, the current differential protection does not operate.

[0015] The present invention provides a distribution line current differential protection method based on the DTW algorithm, which has the following beneficial effects: 1. The present invention solves the problem that after the distribution network is connected to the distributed power source, the traditional three-stage current protection is difficult to ensure the reliability and selectivity of the action, and when the differential protection data transmission channel is realized using 5G communication technology, the uncertainty of data transmission delay and delay jitter has an adverse effect on the accuracy of the protection action criterion calculation; 2. The present invention introduces the DTW algorithm and calculates the similarity distance between current sequences, effectively overcoming the problem that traditional current differential protection methods are often difficult to handle due to data asynchrony caused by communication delay and delay jitter, thereby improving the accuracy and reliability of current differential protection and enabling rapid and accurate fault identification; 3. The present invention applies the DTW algorithm to the current differential protection of the distribution line for the first time, and performs fault judgment by calculating the DTW similarity distance of the current sequence. This method can more accurately identify the similarity of the current waveform and improve the accuracy and reliability of fault judgment; 4. The present invention utilizes the high bandwidth and ultra-low latency characteristics of 5G communication technology to solve the problems of high cost and complex construction and maintenance of traditional optical fiber communication methods, realizes real-time transmission of differential protection data, and reduces the impact of data transmission delay and delay jitter on the accuracy of protection action; 5. The present invention introduces the DTW algorithm into the field of current differential protection and judges faults by calculating the DTW similarity distance of the current sequence. The innovative application of this algorithm provides new ideas and methods for current differential protection and improves the accuracy and sensitivity of fault detection. 6. The present invention combines the limiting average filtering algorithm to process the current sampling data. By setting the maximum deviation value between adjacent sampling data and taking N sampling values ​​continuously for arithmetic averaging, the noise and abnormal data are effectively filtered out, thereby improving the accuracy and reliability of the current data. 7. The present invention adopts a five-point numerical differential algorithm to calculate the fault current change rate and sets a protection start threshold. The differential protection algorithm is started only when the fault current change rate is greater than the threshold. This setting of the start criterion can effectively reduce the occurrence of false operations. 8. The present invention organically integrates multiple technologies such as low-latency 5G communication technology, five-point numerical differential algorithm, limited average filtering algorithm and DTW algorithm to form a complete current differential protection system, which realizes comprehensive monitoring and protection of distribution line current; 9. The present invention comprehensively utilizes the advantages of low-latency 5G communication technology, five-point numerical differential algorithm protection start-up criterion, limited average filtering and DTW similarity distance algorithm, which can effectively overcome the influence of data transmission delay and delay jitter on the accuracy of protection action, and does not require expensive optical fiber as a communication medium, thereby improving economic benefits and protection performance; 10. The present invention uses a variety of technical means to effectively overcome the problems of poor performance and high cost in traditional current protection methods, improve the reliability and economy of protection actions, and provide a strong guarantee for the safe and stable operation of the distribution network; 11. The method of the present invention has strong adaptability to network structure and can be widely used in distribution networks of different scales and structures, especially after the distributed power source is connected, it can better ensure the reliability and selectivity of protection; 12. The proposal and application of the present invention are helpful to improve the stability and reliability of the distribution network after the access of distributed power sources, and ensure the safe and stable operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described below in conjunction with the accompanying drawings and implementation examples: Figure 1 is a flow chart of the protection method of the present invention; Figure 2 A simulation model diagram of Example 2 of the present invention built on the PSCAD simulation platform; Figure 3 This is a schematic diagram of determining whether to start according to the fault current change rate according to the start criterion of embodiment 2 of the present invention; Figure 4 This is a comparison diagram of single-phase current waveforms before and after limiting average filtering in Example 2 of the present invention; Figure 5 This is an example diagram of the DTW similarity distance algorithm according to Embodiment 2 of the present invention. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments: Example 1 like Figure 1 As shown, a distribution line current differential protection method based on DTW algorithm includes the following steps: Step 1: Use the intelligent electronic protection device IED to sample the three-phase current on both sides of the line in real time to form a real-time sampling array with a sampling frequency of 10kHz and a data storage length of 400. Data transmission is achieved through 5G wireless communication technology. Step 2: Use the five-point numerical differentiation algorithm of the first-order derivative to calculate the fault current change rate, and set the protection start criterion based on the change rate. Substitute the sample array data obtained in Step 1 into the start criterion. If the fault current change rate is greater than the set protection start threshold, the current differential protection is started. Step 3: When the current differential protection start-up conditions are met, the current sampling arrays on both sides of the line are subjected to limited average filtering to determine the maximum deviation allowed between two adjacent sampling data. The filtered current sampling array is obtained by comparison and arithmetic averaging. Step 4: Perform current normalization processing on the filter array after the limiting average filtering in Step 3, extract the maximum and minimum values ​​in the current sequence, and perform amplitude compression on each sampling value in the current sequence so that it falls within the normalization interval; Step 5: Use the DTW algorithm to calculate the similarity distance between the current sequences obtained after current normalization in Step 4, and determine the threshold value of differential protection action. Based on the rapid increase of the DTW similarity distance, construct the current differential protection criterion based on the DTW algorithm; Step 6: Compare the DTW similarity distance value calculated in Step 5 with the differential protection action setting threshold. If the DTW similarity distance is greater than the setting threshold, it is determined that a fault has occurred on the line and the current differential protection action is executed.

[0018] In this embodiment, the real-time sampling of the three-phase current data on both sides of the line in Step 1 specifically includes using an intelligent electronic protection device IED to sample the three-phase current on both sides of the line in real time to form a sampling array , The length of the sampling array is 400, which corresponds to twice the number of sampling points of 200 per power frequency cycle of 20ms. That is, the value of k is twice the number of samples per cycle, which corresponds to 400. m and n refer to the two sides of the line respectively. They represent the a, b and c phases of the system respectively.

[0019] Furthermore, the current differential protection start-up criterion constructed in Step 2 is to calculate the fault current change rate by a five-point numerical differentiation algorithm of the first-order derivative: , its setting expression is: (1) in, is the time interval of data collection points; , , , and is the sampling array and Any five consecutive sampling point data; To protect the startup threshold; It is the maximum sampling value of the three-phase current in each cycle when the line is operating normally; is the setting coefficient, the value range is 0.02~0.03; Fault current change rate The calculated value is greater than the set protection start threshold , then the new algorithm of current differential protection is started.

[0020] Furthermore, the specific steps of performing the limiting average filtering process on the current sampling arrays on both sides of the line obtained by sampling in Step 3 include: Step 3.1: Determine the maximum deviation allowed between two adjacent sampling data , value , the current sampling array The value sampled last The value sampled last time For comparison: (2) If the above formula holds, then the value sampled next is considered Valid, need to be retained; if the above formula does not hold, then the value sampled next time is considered The current value is invalid because it is abnormal data. The current value needs to be abandoned and replaced with the value sampled last time. Processing to obtain a new array after limiting processing ; Step 3.2: From the new array after clipping N sampling values ​​are taken continuously and used as a queue. The length of the queue is fixed to N. According to the first-in-first-out principle, a data at the head of the original queue is discarded each time, and the new data obtained by each sampling is put at the end of the queue to form a new queue. The arithmetic average operation is performed on the N data in the newly formed queue, so that the filter array processed by the limited average filter algorithm can be obtained. Similarly, the above filtering process is performed on the current array on the other side of the line to obtain the filtered array ; Where N is a positive integer, the value is , recommended 8.

[0021] Furthermore, the specific steps of performing current normalization processing on the filter array after the amplitude limiting average filtering processing in Step 4 include: Extracting current sequence The maximum value in and minimum value , for the current sequence Each data in the current sampling is compressed so that each current sampling value falls within Thus, a normalized current sampling sequence is obtained. Similarly, the normalized current sampling sequence can be obtained , the amplitude compression method is as follows: (3) in, is the sequence number of each current sampling point in the current sequence; is the current value of the nth current sampling point; is the normalized value of the current at the nth current sampling point.

[0022] Furthermore, in step 5, a current differential protection criterion based on the DTW algorithm is constructed, which is a current sequence obtained after current normalization processing according to the DTW algorithm. and , The negative sign indicates that the data Take the opposite similarity distance to determine the differential protection action threshold , taking advantage of the fact that the DTW similarity distance increases rapidly after a fault occurs in the area, a current differential protection criterion based on the DTW algorithm is constructed. The specific steps include: Step 5.1: Calculate the two current sequences in Step 4 and The Euclidean distance matrix M between them, assuming that their lengths are x and y respectively, calculate the Euclidean distance between the elements of the two current sequences, obtain the elements of the distance matrix M, and then form a The distance matrix M, the matrix elements The calculation formula is: (4) in, The current sequence The i-th data in and current sequence The jth data The Euclidean distance between them, the smaller the distance value, the higher the similarity; Step 5.2: Find a path from the upper left corner to the lower right corner of the distance matrix M , so that the sum of the elements on the path is minimized, the shortest path The current sequence and The similarity distance , the path selection needs to meet the following three constraints: boundary condition, the selected path must start from the upper left corner of the distance matrix M and end at the lower right corner; continuity, the selected path can only continue backward along its adjacent element points; minimum value, in the selected path, the distance value of the path must be the smallest; The recursive calculation formula is as follows: (5) in, From the upper left corner of the matrix To any point The shortest path; Step 5.3: Determine the differential protection action threshold , add up the first column elements of the distance matrix M in Step 5.1 to get , the first row elements of the distance matrix M are accumulated to obtain , differential protection action threshold The setting calculation formula is as follows: (6).

[0023] Furthermore, the specific steps of determining that a fault occurs on the line and executing the current differential protection action in Step 6 include: Differential protection action setting threshold For comparison: (7) If the DTW similarity distance is greater than the setting threshold, it is determined that a fault has occurred on the line and the current differential protection is executed; otherwise, the current differential protection does not operate.

[0024] Example 2 In another preferred embodiment, based on the above embodiment 1, in order to verify the effectiveness of the present invention, we built a distribution network simulation model containing distributed photovoltaic power sources on the PSCAD simulation platform, such as Figure 2 shown.

[0025] 1. System model and parameter setting The system power supply is connected to the distribution network through a transformer with a transformation ratio of 35KV / 10KV. The photovoltaic DG (Distributed Photovoltaic) equivalent source is connected to the distribution network in two connection forms: 10KV·T connected to the public grid bus and 10KV·T connected to the public grid line. The distribution network contains two types of energy storage: electrochemical energy storage and capacitive energy storage. The rated operating frequency of the distribution network is 50Hz. The parameters of each line are as follows: Line L1 is 5 km long; Line L2 is 6 km long; Line L3 is 3 km long; Line L4 is 9 km long; Line L5 is 2KM long; Line L6 is 4KM long; Positive sequence line parameters: r 1=3.38×10 -4 Ω / m, xl 1=2.6×10 -4 Ω / m, xc 1=384.3MΩ·m; zero-sequence line parameters r 0=1.027×10 -3 Ω / m, xl 0=8.25×10 -4 Ω / m, xc 0=1143.8MΩ·m.

[0026] 2. Fault scenarios and data sampling Assume that at 0.6s, a single-phase metallic ground short circuit fault occurs at 60% (i.e., 3KM) of line L1. Intelligent electronic protection equipment (IED) is used to sample the a, b, and c three-phase currents on both sides of the line (side m and side n) in real time. The sampling frequency is 10kHz, that is, the number of sampling points in each power frequency cycle (20ms) is 200. The sampling array stores data with a length of 2 cycles, i.e., 400 sampling points, forming a sampling array. , .

[0027] 3. Protection start criteria First, calculate the protection start threshold: (8) Next, the five-point numerical differentiation algorithm of the first-order derivative is used to calculate the fault current change rate. If the change rate is greater than the set protection start threshold, the current differential protection is started; the protection start criterion and its setting expression are: (9) The calculated value of the fault current change rate is greater than the set protection start threshold, and the current differential protection algorithm is started. Figure 3It is a schematic diagram of calculation results of Example 2 for judging whether the new current differential protection algorithm is started according to the starting criterion.

[0028] 4. Limiting average filtering When the protection start condition is met, the current sampling array on both sides of the line , Perform limiting average filtering to sample the current array Take this as an example, the specific steps are as follows: (1) Limiting processing: Determine the maximum deviation allowed between two adjacent sampling data , the next sampling value The previous sampling value For comparison: (2) If the deviation value is exceeded, it is considered as abnormal data and replaced by the previous value; (2) Average filtering: Take N (8 in this example) sample values ​​from the filtered array to form a queue. According to the first-in-first-out principle, discard a data at the head of the original queue each time and sample a new data to form a new queue at the end of the queue. Perform arithmetic average calculation on the 8 data in the original queue and each newly formed queue in turn to obtain the filtered array processed by the limited average filtering algorithm. ; Similarly, the filter array can be obtained ; Figure 4 3 is a comparison diagram of the three-phase current waveforms before and after limiting and averaging filtering in the embodiment.

[0029] 5. Current normalization The filter array processed by the limiting average filter algorithm and Perform current normalization and convert the current sequence The maximum and minimum values ​​in the current series are extracted, which are 896.7A and -895.9A respectively. The amplitude compression formula is used to calculate the current series. Perform amplitude compression so that each current sampling value falls within Take compressing a data point as an example: (10) Amplitude compression is performed on all data points to obtain a normalized current sampling sequence. Similarly, the normalized current sampling sequence can be obtained .

[0030] 6. DTW similarity distance calculation and fault judgment (1) Calculate the distance matrix M: Calculate two normalized current sequences and , whose lengths are 400 and 400 respectively, calculate the Euclidean distance between the elements of the two current sequences, and obtain 160,000 elements of the distance matrix M, which then forms a The distance matrix M is Matrix Elements The calculation process is as follows: (11) An example of the DTW similarity distance algorithm is shown below: Figure 5 As shown in the figure, an example of the DTW algorithm is shown, taking the two sequences J and K as examples. , ; (2) Find the shortest path: Use the DTW algorithm to find the path from the upper left corner to the lower right corner of the distance matrix M. , so that the sum of elements on the path is minimized, which is the similarity distance: (12) To obtain, ; (3) Determine the differential protection action threshold :Accumulate the elements of the first column of the distance matrix M to obtain , the first row elements of the distance matrix M are accumulated to obtain , calculate the differential protection action threshold value, that is, the differential protection action setting threshold value: (13); (4) Fault diagnosis: The calculated The value of and the differential protection action setting threshold Compare and judge the fault condition of this line: (14) The above formula is established, indicating that the DTW similarity distance of the sampled current sequence is greater than the differential protection action setting threshold , it is determined that a fault has occurred in the area, and the current differential protection based on the DTW algorithm is activated.

[0031] In summary, an innovative distribution line current differential protection method based on the DTW algorithm is proposed. This method comprehensively optimizes the shortcomings of the traditional three-stage current protection in terms of action reliability and selectivity after the distribution network is connected to the distributed power source, as well as the adverse effects of data transmission delay and delay jitter on the accuracy of protection action criterion calculation when differential protection data transmission is realized using 5G communication technology. The core of this method is to introduce the DTW algorithm, which effectively solves the problem of data asynchrony caused by communication delay and delay jitter that is difficult to handle in traditional current differential protection by calculating the similarity distance between current sequences. The application of the DTW algorithm not only improves the accuracy and reliability of current differential protection, but also enables faults to be identified quickly and accurately, providing a new idea and method for current differential protection. In addition, the present invention also integrates low-latency 5G communication technology. A complete current differential protection system is formed by combining various technical means such as the five-point numerical differential algorithm, the limited average filtering algorithm, etc.; the system realizes comprehensive monitoring and protection of the distribution line current. By comprehensively using a variety of technical means, it effectively overcomes the problems of deteriorated action performance and high cost in traditional current protection methods, improves the reliability and economy of protection action, and provides a strong guarantee for the safe and stable operation of the distribution network; this method not only has significant advantages in network structure adaptability, but can also be widely used in distribution networks of different sizes and structures, especially after the access of distributed power sources, it can better ensure the reliability and selectivity of protection; this method is an innovative and efficient protection means, which provides solid technical support for the safe and stable operation of the distribution network, promotes the development of smart grids, and contributes to the sustainable development of the power industry.

Claims

1. A distribution line current differential protection method based on DTW algorithm, characterized in that: The method comprises the following steps: Step 1: Use the intelligent electronic protection device IED to sample the three-phase current on both sides of the line in real time to form a real-time sampling array with a sampling frequency of 10kHz and a data storage length of 400. Data transmission is achieved through 5G wireless communication technology. Step 2: Use the five-point numerical differentiation algorithm of the first-order derivative to calculate the fault current change rate, and set the protection start criterion based on the change rate. Substitute the sample array data obtained in Step 1 into the start criterion. If the fault current change rate is greater than the set protection start threshold, the current differential protection is started. Step 3: When the current differential protection start-up conditions are met, the current sampling arrays on both sides of the line are subjected to limited average filtering to determine the maximum deviation allowed between two adjacent sampling data. The filtered current sampling array is obtained by comparison and arithmetic averaging. Step 4: Perform current normalization processing on the filter array after the limiting average filtering in Step 3, extract the maximum and minimum values ​​in the current sequence, and perform amplitude compression on each sampling value in the current sequence so that it falls within the normalization interval; Step 5: Use the DTW algorithm to calculate the similarity distance between the current sequences obtained after current normalization in Step 4, and determine the threshold value of differential protection action. Based on the rapid increase of the DTW similarity distance, construct the current differential protection criterion based on the DTW algorithm; Step 6: Compare the DTW similarity distance value calculated in Step 5 with the differential protection action setting threshold. If the DTW similarity distance is greater than the setting threshold, it is determined that a fault has occurred on the line and the current differential protection action is executed.

2. The current differential protection method based on DTW algorithm according to claim 1, characterized in that: The real-time sampling of the three-phase current data on both sides of the line in Step 1 specifically includes using an intelligent electronic protection device IED to sample the three-phase current on both sides of the line in real time to form a sampling array , , the length of the sampling array is 400, which corresponds to twice the number of sampling points 200 per 20ms power frequency cycle, that is, k The value is twice the number of samples per cycle, corresponding to 400. m and n refer to the two sides of the line respectively. They represent the a, b and c phases of the system respectively.

3. The current differential protection method based on DTW algorithm according to claim 1, characterized in that: The starting criterion of the current differential protection constructed in Step 2 is to calculate the fault current change rate by the five-point numerical differentiation algorithm of the first-order derivative. , its setting expression is: （1）； in, is the time interval of data collection points; , , , and is the sampling array and Any five consecutive sampling point data; To protect the startup threshold; It is the maximum sampling value of the three-phase current in each cycle when the line is operating normally; is the setting coefficient, the value range is 0.02~0.03; Fault current change rate The calculated value is greater than the set protection start threshold , then the new algorithm of current differential protection is started.

4. The current differential protection method based on DTW algorithm according to claim 1, characterized in that: The specific steps of performing the limiting average filtering process on the current sampling arrays on both sides of the line obtained by sampling in Step 3 include: Step 3.1: Determine the maximum deviation allowed between two adjacent sampling data , value , the current sampling array The value sampled last The value sampled last time For comparison: （2）； If the above formula holds, then the value sampled next is considered Valid, need to be retained; if the above formula does not hold, then the value sampled next time is considered The current value is invalid because it is abnormal data. The current value needs to be abandoned and replaced with the value sampled last time. Processing to obtain a new array after limiting processing ; Step 3.2: From the new array after clipping N sampling values ​​are taken continuously and used as a queue. The length of the queue is fixed to N. According to the first-in-first-out principle, a data at the head of the original queue is discarded each time, and the new data obtained by each sampling is put at the end of the queue to form a new queue. The arithmetic average operation is performed on the N data in the newly formed queue, so that the filter array processed by the limited average filter algorithm can be obtained. Similarly, the above filtering process is performed on the current array on the other side of the line to obtain the filtered array ; Where N is a positive integer, the value is , recommendation 8.

5. The current differential protection method based on DTW algorithm according to claim 1, characterized in that: The specific steps of performing current normalization processing on the filter array after the amplitude limiting average filtering processing in Step 4 include: Extracting current sequence The maximum value in and minimum value , for the current sequence Each data in the current sampling is compressed so that each current sampling value falls within Thus, a normalized current sampling sequence is obtained. Similarly, the normalized current sampling sequence can be obtained , the amplitude compression method is as follows: （3）； in, is the sequence number of each current sampling point in the current sequence; is the current value of the nth current sampling point; is the normalized value of the current at the nth current sampling point.

6. The current differential protection method based on DTW algorithm according to claim 1, characterized in that: In step 5, the current differential protection criterion based on the DTW algorithm is constructed, which is the current sequence obtained after the current normalization processing calculated by the DTW algorithm. and , The negative sign indicates that the data Take the opposite similarity distance to determine the differential protection action threshold , taking advantage of the fact that the DTW similarity distance increases rapidly after a fault occurs in the area, a current differential protection criterion based on the DTW algorithm is constructed. The specific steps include: Step 5.1: Calculate the two current sequences in Step 4 and The Euclidean distance matrix M between them, assuming that their lengths are x and y respectively, calculate the Euclidean distance between the elements of the two current sequences, obtain the elements of the distance matrix M, and then form a The distance matrix M, the matrix elements The calculation formula is: （4）； in, The current sequence The i-th data in and current sequence The jth data The Euclidean distance between them, the smaller the distance value, the higher the similarity; Step 5.2: Find a path from the upper left corner to the lower right corner of the distance matrix M , so that the sum of the elements on the path is minimized, the shortest path The current sequence and The similarity distance , the path selection needs to meet the following three constraints: boundary condition, the selected path must start from the upper left corner of the distance matrix M and end at the lower right corner; continuity, the selected path can only continue backward along its adjacent element points; minimum value, in the selected path, the distance value of the path must be the smallest; The recursive calculation formula is as follows: （5）； in, From the upper left corner of the matrix To any point The shortest path; Step 5.3: Determine the differential protection action threshold , add up the first column elements of the distance matrix M in Step 5.1 to get , the first row elements of the distance matrix M are accumulated to obtain , differential protection action threshold The setting calculation formula is as follows: （6）。 7. The current differential protection method based on DTW algorithm according to claim 1, characterized in that: The specific steps of determining that a fault occurs on the line and executing the current differential protection action in Step 6 include: Differential protection action setting threshold For comparison: （7）； If the DTW similarity distance is greater than the setting threshold, it is determined that a fault has occurred on the line and the current differential protection is executed; otherwise, the current differential protection does not operate.

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