Line pilot protection method for AC / DC hybrid distribution network based on 5G communication

Abstract

The present invention discloses a longitudinal protection method for AC / DC hybrid distribution network lines based on 5G communication. The present invention is aimed at line faults in AC / DC hybrid distribution networks, transmits signals and data based on 5G communication, uses the current data detected at the protection installation to calculate the current characteristic coefficient to determine the occurrence of the fault, and then starts the subsequent fault identification process. The present invention uses the speed and reliability of 5G communication in signal transmission to transmit the start signal and current data between the protection at both ends of the line. The current data on both sides are used to calculate the action parameters reflecting the current correlation and construct a fault selection criterion, and the fault type is judged according to the calculation results of the action parameters. The present invention uses 5G fast communication in the AC / DC hybrid distribution network to realize the effective identification and positioning of AC / DC hybrid distribution network line faults, which has practical significance for the safe and stable operation of the AC / DC hybrid distribution network.

Description

Technical Field

[0001] The present invention belongs to the field of relay protection of AC / DC hybrid distribution networks in power systems, and in particular relates to a line longitudinal protection method for AC / DC hybrid distribution networks based on 5G communication. Background Art

[0002] As distributed power sources (DGs) continue to grow in the electric energy sector, the number of DC loads, such as electric vehicles, connecting to the power grid is increasing. Traditional AC distribution networks face challenges such as low operational efficiency and insufficient flexibility. AC / DC hybrid distribution networks, however, offer advantages such as high transmission efficiency, ease of access to DGs, and minimal line losses, making them a key research area for future distribution networks. As low-inertia systems, AC / DC hybrid distribution networks experience rapid increases in short-circuit current when a fault occurs, necessitating rapid and reliable fault identification and interruption.

[0003] Currently, line protection in AC / DC hybrid distribution networks can be categorized into single-ended protection (based on local measurements) and dual-ended protection (based on communications). Dual-ended protection requires information exchange between both sides of the line. Currently, a common method for this exchange is to lay optical fiber along the line. However, laying optical fiber is difficult and requires high investment, resulting in high construction and maintenance costs. Furthermore, some areas are not suitable for laying optical fiber due to geographical factors.

[0004] The rapid development of 5G technology, with its high reliability and low latency, has provided a new means of data communication for power systems. By slicing 5G networks, the responsiveness required for distribution network protection can be effectively met. Furthermore, 5G communication requires only the installation of equipment at the receiving and transmitting points, with information transmitted via 5G base stations. This avoids the high costs associated with laying fiber optic cables along the lines and can serve as an effective method for exchanging data between two terminals for protection. Summary of the Invention

[0005] In order to overcome the defects of the above-mentioned prior art, the present invention provides a method for longitudinal protection of AC / DC hybrid distribution network lines based on 5G communication. The method transmits signals and data based on 5G communication, calculates the current characteristic coefficient using the current data detected at the protection installation to determine the occurrence of a fault, and then initiates the subsequent fault identification process. The present invention utilizes the speed and reliability of 5G communication in signal transmission to transmit the start signal and current data between the protection at both ends of the line. The current data on both sides is used to calculate the action parameters and construct the fault selection criterion, and the fault type is determined based on the calculation results of the action parameters.

[0006] In order to solve the above technical problems, the technical methods adopted by the present invention are as follows:

[0007] A 5G communication-based AC / DC hybrid distribution network line pilot protection method includes the following steps:

[0008] S1. Collect current data of the positive and negative lines on this side at a preset sampling rate;

[0009] S2. Extract the current characteristic coefficient based on the current data of the positive and negative lines on this side. When the current characteristic coefficient on this side is greater than the start criterion threshold, it is determined that the start criterion is met, and a start signal is sent to the protection on the opposite side of the line using 5G communication;

[0010] When the local side meets the start criterion or receives the start signal sent by the protection on the opposite side of the line, it enters step S3 to start fault detection;

[0011] S3: Use 5G communication to transmit the current data of the positive and negative lines on the local side to the protection on the opposite side, and simultaneously receive the current data of the positive and negative lines on the opposite side;

[0012] S4. Calculate the operating parameters based on the current data of the positive and negative lines on this side and the current data of the positive and negative lines on the opposite side. If the calculated operating parameters meet the fault criterion within the area, the fault is determined to have occurred on the current line, and the process proceeds to step S5. Otherwise, the fault is determined to have occurred on another line, the protection is reset, the process is exited, and the fault detection process ends.

[0013] S5. Determine a comparison coefficient for reflecting the difference between the positive and negative poles based on the calculation result of the action parameters, select a fault type using the comparison coefficient, and quickly trip the DC circuit breaker of the faulty line to isolate the fault based on the fault type selection result.

[0014] Furthermore, the line opposite side protection in step S2 specifically includes:

[0015] In a DC distribution line, DC circuit breakers are installed at both ends of each line and are configured with the same protection strategy. The protections installed on both sides of the same line are called opposite-side protection.

[0016] Furthermore, the specific process of calculating the current characteristic coefficient in step S2 includes:

[0017] The low-frequency feature extraction formula is used to extract the sampled data I0 twice, where:

[0018] The first low-frequency feature extraction obtains vector I1, the formula is:

[0019]

[0020] The second low-frequency feature extraction obtains vector I2, the formula is:

[0021]

[0022] Among them, R0 is the low-frequency decomposition function, I 0,mis the mth value of vector I0, I 1,k is the kth value of vector I1; I 1,m is the mth value of vector I1, I 2,k is the kth value of vector I2; M0 is the total number of elements contained in vector I0; M1 is the total number of elements contained in vector I1; m∈N*, k∈N*;

[0023] The high-frequency feature extraction formula is used to extract the high-frequency features of vector I2 to obtain the feature vector D2. The high-frequency feature extraction formula is as follows:

[0024]

[0025] Among them, W0 is the high frequency decomposition function, D 2,k is the kth value of the eigenvector D2 finally obtained, I 2,m is the mth value of vector I2; M2 is the total number of elements contained in vector I2;

[0026] According to the characteristic vector D2, the current characteristic coefficient is obtained using the coefficient calculation formula. The coefficient calculation formula is as follows:

[0027]

[0028] Among them, A is the current characteristic coefficient finally obtained; K is the vector D 2,k The total number of elements contained;

[0029] According to the above process, the positive line current data and the negative line current data are extracted respectively to obtain the positive current characteristic coefficient A + and negative electrode current characteristic coefficient A - .

[0030] Furthermore, in step S2, when the current characteristic coefficient of this side is greater than the starting criterion threshold, it is determined that the starting criterion is met. Specifically, when at least one of the positive current characteristic coefficient and the negative current characteristic coefficient is greater than the starting criterion threshold, it is determined that the starting criterion is met.

[0031] Furthermore, in step S4, based on the current data of the positive and negative lines on the local side and the current data of the positive and negative lines on the opposite side, the fault detection start time is taken as the starting point t0, and the positive current data and the negative current data within the preset data window length are selected.

[0032] Furthermore, the action parameter calculation method described in step S4 is:

[0033]

[0034] Among them, S + 、S -They are positive action parameters and negative action parameters respectively; is the positive current data on this side, is the contralateral positive electrode current data; is the negative electrode current data on this side, is the contralateral negative electrode current data; is the i-th value of the positive electrode current data on this side; is the average value of the positive electrode current data on this side; is the i-th value of the contralateral positive electrode current data; is the average value of the contralateral positive electrode current data; is the i-th value of the negative electrode current data on this side; is the average value of the negative electrode current data on this side; is the i-th value of the negative electrode current data on the opposite side; is the average value of the negative electrode current data on the opposite side; n is the number of sampling points within the preset data window length;

[0035] The calculated result of the action parameter is within the interval [-1, 1], which can correctly reflect the correlation between the currents at both ends.

[0036] Furthermore, the intra-zone fault judgment criterion in step S4 is specifically: at least one of the positive pole action parameter and the negative pole action parameter is a positive number.

[0037] Furthermore, the comparison coefficient for reflecting the difference between the positive and negative electrodes is determined according to the calculation result of the action parameters in step S5, specifically:

[0038]

[0039] Wherein, ρ is the contrast coefficient, S + 、S - They are the positive action parameters and the negative action parameters respectively.

[0040] Furthermore, the specific implementation of the fault type selection in step S5 includes:

[0041] When ρ>K1, it is determined that a positive ground fault has occurred;

[0042] When K2<ρ≤K1, it is determined that an inter-pole short circuit fault occurs;

[0043] When ρ≤K2, it is determined that a negative grounding fault has occurred;

[0044] Among them, K1 is the first threshold for fault selection, and K2 is the second threshold for fault selection.

[0045] The present invention has the following beneficial effects: Based on 5G technology, the present invention improves the traditional two-terminal protection of DC lines: first, a feature extraction algorithm based on wavelet decomposition is used to process current data, and a startup criterion is constructed based on the extracted current characteristic coefficients. Compared with the traditional startup criterion, it can better reflect the current fault characteristics and ensure the reliable startup of the protection on both sides. Secondly, the present invention achieves stable interaction of signals at both ends of the line by leveraging the high reliability and low latency characteristics of 5G communication. On this basis, the current data on both sides of the line are used to calculate the action parameters that can reflect the correlation between the currents on both sides. In this way, the fault discrimination and fault selection criteria within the line area are constructed. The constructed criteria are simple and reliable, can effectively characterize the difference between positive and negative poles, do not require a complex threshold setting process, and are not affected by transition resistance. The present invention only requires the use of 5G signal transmission / reception devices at the protection installation site, and does not require the laying of optical fiber along the line, effectively improving the economic efficiency of the AC / DC hybrid distribution network. At the same time, the proposed protection method is not affected by the parameters and operating conditions of other power electronic equipment in the AC / DC hybrid distribution network, can adapt to AC / DC hybrid distribution networks of different structures, and has good engineering practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0047] Figure 1 1 is a schematic diagram of a line pilot protection method for an AC / DC hybrid distribution network based on 5G communication according to an embodiment of the present invention;

[0048] Figure 2 This is a simulation model diagram of an AC / DC hybrid distribution network according to an embodiment of the present invention;

[0049] Figure 3 This is a waveform diagram of the positive and negative currents at protection 41 according to an embodiment of the present invention;

[0050] Figure 4 This is a graph showing changes in the positive and negative current characteristic coefficients at the protection 41 according to an embodiment of the present invention;

[0051] Figure 5 This is the current data waveform collected at protection 41 in an embodiment of the present invention;

[0052] Figure 6 41 is the current data waveform received by the protection 41 in the embodiment of the present invention;

[0053] Figure 7This is a flow chart of a method for longitudinal protection of AC / DC hybrid distribution network lines according to an embodiment of the present invention. DETAILED DESCRIPTION

[0054] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0055] Book Figure 1 FIG2 is a schematic diagram of a method for pilot protection of AC / DC hybrid distribution network lines based on 5G communication according to an embodiment of the present invention, comprising the following steps:

[0056] S1. Collect the current data of the positive and negative lines on this side at a preset sampling rate.

[0057] S2. Extract the current characteristic coefficient based on the current data of the positive and negative lines on this side. When the current characteristic coefficient on this side is greater than the start criterion threshold, it is determined that the start criterion is met, and a start signal is sent to the protection on the opposite side of the line using 5G communication;

[0058] When the local side meets the start criterion or receives the start signal sent by the protection on the opposite side of the line, it enters step S3 to start fault detection.

[0059] S3. Use 5G communication to transmit the current data of the positive and negative lines on this side to the protection on the opposite side, and at the same time receive the current data of the positive and negative lines on the opposite side.

[0060] S4. Calculate the action parameters based on the current data of the positive and negative lines on this side and the current data of the positive and negative lines on the opposite side. If the calculated action parameters meet the fault judgment criteria within the area, it is determined that the fault occurred on this section of the line, and the process proceeds to step S5; otherwise, it is determined that the fault occurred on other lines, the protection is reset, the process is exited, and the fault detection process ends.

[0061] S5. Determine a comparison coefficient for reflecting the difference between the positive and negative poles based on the calculation result of the action parameters, select a fault type using the comparison coefficient, and quickly trip the DC circuit breaker of the faulty line to isolate the fault based on the fault type selection result.

[0062] This invention utilizes the high-speed and low-latency characteristics of 5G technology, and realizes the signal transmission and data transmission process required for dual-end protection of AC / DC hybrid distribution networks based on 5G communication, ensuring the reliability and speed of data transmission, and meeting the requirements of DC distribution networks for protection speed, selectivity and reliability.

[0063] Based on the above embodiments, the present invention can also be improved as follows.

[0064] In a preferred embodiment, the contralateral protection in step S2 is specifically explained as follows:

[0065] In a DC distribution line, DC circuit breakers are installed at both ends of each line, configured with the same protection strategy. The protections installed at both ends of the same line are called opposite-side protection.

[0066] In a preferred embodiment, the specific process of obtaining the current characteristic coefficient in step S2 includes:

[0067] The low-frequency feature extraction formula is used to extract the sampled data I0 twice, where:

[0068] The first low-frequency feature extraction obtains vector I1, the formula is:

[0069]

[0070] The second low-frequency feature extraction obtains vector I2, the formula is:

[0071]

[0072] Among them, R0 is the low-frequency decomposition function, I 0,m is the mth value of vector I0, I 1,k is the kth value of vector I1; I 1,m is the mth value of vector I1, I 2,k is the kth value of vector I2; M0 is the total number of elements contained in vector I0; M1 is the total number of elements contained in vector I1; m∈N*, k∈N*.

[0073] The high-frequency feature extraction formula is used to extract the high-frequency features of vector I2 to obtain the feature vector D2. The high-frequency feature extraction formula is as follows:

[0074]

[0075] Among them, W0 is the high frequency decomposition function, D 2,k is the kth value of the eigenvector D2 finally obtained, I 2,m is the mth value of vector I2; M2 is the total number of elements contained in vector I2.

[0076] According to the characteristic vector D2, the current characteristic coefficient is obtained using the coefficient calculation formula. The coefficient calculation formula is as follows:

[0077]

[0078] Among them, A is the current characteristic coefficient finally obtained; K is the vector D 2,k The total number of elements contained.

[0079] The above process is used to extract the features of the positive current data and the negative current data respectively, and the positive current characteristic coefficient A is obtained. + and negative electrode current characteristic coefficient A- .

[0080] In a preferred embodiment, when the current characteristic coefficient on this side is greater than the starting criterion threshold, it is determined that the starting criterion is met. Specifically, when at least one of the positive current characteristic coefficient and the negative current characteristic coefficient is greater than the starting criterion threshold, it is determined that the starting criterion is met. When there is no fault in the DC line, the line current fluctuates slightly; when a fault occurs in the line, the line current fluctuates greatly due to the presence of the fault current. When a fault occurs in the positive line, the current characteristic coefficient calculated from the positive current data is greater than the starting criterion threshold; and when a fault occurs in the negative line, the current characteristic coefficient calculated from the negative current data is greater than the starting criterion threshold; therefore, the specific starting criteria are set as follows:

[0081] A + >A set ∪A - >A set

[0082] Among them, A set is the starting criterion threshold.

[0083] Because current waveforms fluctuate significantly during faults, low- and high-frequency feature extraction of current data effectively distinguishes currents during fault and non-fault conditions, ensuring reliable fault detection. This also avoids the need to constantly operate communication equipment and protection processing units during non-fault conditions, extending equipment life.

[0084] In a preferred embodiment, the step S4 is based on the current data of the positive and negative lines on this side and the current data of the positive and negative lines on the opposite side, specifically taking the moment of starting fault detection as the starting point t0, selecting the positive current data and the negative current data within the preset data window length, and finally obtaining the same number of current data collected at the positive pole and the current data collected at the negative pole.

[0085] In a preferred embodiment, the action parameter calculation method in step S4 is:

[0086]

[0087] Among them, S + 、S - They are positive action parameters and negative action parameters respectively; is the positive current data on this side, is the contralateral positive electrode current data; is the negative electrode current data on this side, is the contralateral negative electrode current data; is the i-th value of the positive electrode current data on this side; is the average value of the positive electrode current data on this side; is the i-th value of the contralateral positive electrode current data; is the average value of the contralateral positive electrode current data; is the i-th value of the negative electrode current data on this side; is the average value of the negative electrode current data on this side; is the i-th value of the negative electrode current data on the opposite side; is the average value of the negative electrode current data on the opposite side; n is the number of sampling points within the preset data window length;

[0088] The calculation results of the action parameters are within the interval [-1,1]. The action parameter calculation method adopted can effectively reflect the relevant characteristics of the current at both ends of the line when a fault occurs.

[0089] In a preferred embodiment, the intra-zone fault criterion in step S4 is specifically: at least one of the positive pole action parameter and the negative pole action parameter is a positive number. That is:

[0090] When a fault occurs outside the line area, both the positive and negative pole action parameters are negative.

[0091] When a fault occurs in the line area, S + >0∪S - > 0. This strategy only needs to judge the positive or negative result of the action parameter calculation, without considering complex threshold setting and protection coordination. It is easy to implement and has high sensitivity.

[0092] In a preferred embodiment, the specific implementation of the contrast coefficient in step S5 includes:

[0093]

[0094] Wherein, ρ is the contrast coefficient, S + 、S - They are the positive action parameters and the negative action parameters respectively.

[0095] In a preferred embodiment, the specific implementation of the fault type selection in step S5 includes:

[0096] When ρ>K1, it is determined that a positive ground fault has occurred;

[0097] When K2<ρ≤K1, it is determined that an inter-pole short circuit fault occurs;

[0098] When ρ≤K2, it is determined that a negative grounding fault has occurred;

[0099] Among them, K1 is the first threshold for fault selection; K2 is the second threshold for fault selection.

[0100] Only the above-mentioned action parameter calculation results are used to construct the fault selection criterion, without the need for a complex parameter calculation process, thus avoiding the erroneous action of the DC circuit breaker and being able to take into account both the speed and reliability of protection.

[0101] The following combination Figure 2 The figure shows a schematic diagram of the simulation model of the AC / DC hybrid distribution network built on the PSCAD simulation platform, which specifically introduces the grounding protection method of the present invention. The AC grid voltage is 35kV, the transformer ratio is 35kV / 10kV, and Δ / Y connection is adopted. The rated capacity of the converter station is 10MVA. The AC / DC hybrid distribution network has a ring structure with a total of four DC feeders, and DC circuit breakers are installed at both ends of each feeder. The DC line voltage level is ±10kV, the unit length resistance value of the DC line is 0.078Ω / km, the unit length inductance value is 0.48mH / km, and the length of the four feeders is 20km. During normal operation, the photovoltaic output power is 1MW, and the energy storage charging and discharging power is 0.5MW.

[0102] S21. Collect current data of the positive and negative lines on this side at a preset sampling rate. In this embodiment, the sampling rate is determined to be 10 kHz.

[0103] S22. Extract the current characteristic coefficient based on the current data of the positive and negative lines on this side. When the current characteristic coefficient on this side exceeds the start criterion threshold, it is determined that the start criterion is met, and a start signal is sent to the protection on the opposite side of the line using 5G communication. When calculating the current characteristic coefficient, the data window length is determined to be 0.5ms.

[0104] Each protection installation is equipped with a 5G signal transmitter / receiver. Figure 7 The flowchart shown focuses on the DC line protection 41 on line 4. A metallic positive ground fault F is set 5 km away from the installation of protection 41. g , fault time 2s. Protection 41 positive and negative current waveforms are as follows Figure 3 As shown in the figure, it can be seen that the positive current fluctuates greatly at 2s. According to the fluctuation of the current under normal operation, the start criterion threshold A is preset artificially. set The positive and negative electrode currents are used to calculate the positive electrode current characteristic coefficient and the negative electrode current characteristic coefficient, respectively, as shown in the following example: Figure 4 As shown. When the positive line fails, the current characteristic coefficient calculated from the positive current data increases significantly. It can be seen that the positive current characteristic coefficient is much larger than A after 2s. set Therefore, the start criterion is established at 2s. Immediately use 5G communication to quickly transmit the start signal to the protection 42 on the opposite side of the line, such as Figure 2 As shown by the light dashed line in . At the same time, fault detection begins.

[0105] S23. Use 5G communication to transmit the positive and negative line current data on this side to the opposite side protection, and at the same time receive the positive and negative line current data at the opposite side protection transmitted from the opposite side.

[0106] S24, calculate the action parameters based on the current data of the positive and negative lines on this side and the current data of the positive and negative lines on the opposite side. Take the time when the fault detection starts as the starting point t0, select the positive current data and negative current data within the preset data window length. In this embodiment, the preset data window is set to 1ms, according to Figure 4 It can be seen that the starting time is 2s, and the positive and negative current data for the final action parameter calculation contain 10 data points. Therefore, the positive and negative current data within the time window [2s, 2.001s] of the protection 41 are collected, such as Figure 5 And use 5G communication to transmit to protection 42. At the same time, wait for the positive and negative current data collected and transmitted from the opposite side protection 42. The transmission process is as follows Figure 2 The dark dotted line in the figure shows the positive and negative current data collected at protection 42. Figure 6 As shown. Then, the fault judgment inside and outside the line area begins immediately. If the action parameter calculation result meets the fault judgment criteria inside the area, it is determined that the fault occurs on the current line, and the process goes to step S25 for fault identification; otherwise, it is determined that the fault occurs on other lines, the protection is restored, the process is exited, and the fault detection process ends;

[0107] Specifically, the calculation formula of the action parameters is:

[0108]

[0109] Among them, S + 、S - They are positive action parameters and negative action parameters respectively; is the positive current data on this side, is the contralateral positive electrode current data; is the negative electrode current data on this side, is the contralateral negative electrode current data; is the i-th value of the positive electrode current data on this side; is the average value of the positive electrode current data on this side; is the i-th value of the contralateral positive electrode current data; is the average value of the contralateral positive electrode current data; is the i-th value of the negative electrode current data on this side; is the average value of the negative electrode current data on this side; is the i-th value of the negative electrode current data on the opposite side; is the average value of the negative electrode current data on the opposite side. + =0.8141, S -=-0.2029.

[0110] Determine whether it is an internal fault based on the calculation results and the internal fault judgment criteria. The internal fault judgment criteria are as follows:

[0111] S + >0∪S - >0

[0112] Based on this, it is determined that the fault is an internal fault and the protection is not reset. The process proceeds to step S25 to start fault type selection.

[0113] S25. Determine a comparison coefficient for reflecting the difference between the positive and negative poles based on the calculation result of the action parameters, select a fault type using the comparison coefficient, and quickly trip the DC circuit breaker of the faulty line based on the fault type selection result to isolate the fault.

[0114] Specifically, the specific calculation method of the contrast coefficient is:

[0115]

[0116] Wherein, ρ is the comparison coefficient. The specific implementation of fault type selection includes:

[0117] When ρ>K1, it is determined that a positive ground fault has occurred;

[0118] When K2<ρ≤K1, it is determined that an inter-pole short circuit fault occurs;

[0119] When ρ≤K2, it is determined that a negative grounding fault has occurred;

[0120] Among them, K1 is the first threshold for fault selection, and its value is determined to be 1.5 based on a large number of simulation test results. K2 is the second threshold for fault selection, and its value is determined to be 0.5 based on a large number of simulation test results. According to step S3, the positive and negative pole action parameters are calculated, and ρ is calculated to be 4.012. Therefore, ρ>K1, the fault type is determined to be a positive pole grounding fault, and the positive pole DC circuit breaker at the DC line protection 41 trips, thereby achieving the DC grounding fault F g Reliable isolation.

[0121] In summary, this embodiment verifies the correctness and feasibility of the AC / DC hybrid distribution network line longitudinal protection method based on 5G communication proposed in the present invention.

[0122] The embodiments of the present application are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only intended to help understand the method and core ideas of the present application. At the same time, changes or modifications made by those skilled in the art based on the ideas of the present application, the specific implementation methods, and the scope of application of the present application, all fall within the scope of protection of the present application. In summary, the contents of this specification should not be construed as limiting the present application.

Claims

1. A method for pilot protection of AC / DC hybrid distribution network lines based on 5G communication, characterized in that: The following steps are involved: S1. Collect current data of the positive and negative lines on this side at a preset sampling rate; S2. Extract the current characteristic coefficient based on the current data of the positive and negative lines on this side. When the current characteristic coefficient on this side is greater than the start criterion threshold, it is determined that the start criterion is met, and a start signal is sent to the protection on the opposite side of the line using 5G communication; When the local side meets the start criterion or receives the start signal sent by the protection on the opposite side of the line, it enters step S3 to start fault detection; S3: Use 5G communication to transmit the current data of the positive and negative lines on the local side to the protection on the opposite side, and simultaneously receive the current data of the positive and negative lines on the opposite side; S4. Calculate the action parameters based on the current data of the positive and negative lines on the local side and the current data of the positive and negative lines on the opposite side. If the calculated action parameters meet the fault criterion within the area, it is determined that the fault occurs on the current line, and the process proceeds to step S5. Otherwise, the fault is determined to have occurred in other lines, the protection is restored, the process is exited, and the fault detection process ends; S5. Determine a comparison coefficient for reflecting the difference between the positive and negative poles based on the calculation result of the action parameters, select a fault type using the comparison coefficient, and quickly trip the DC circuit breaker of the faulty line to isolate the fault based on the fault type selection result; The specific process of calculating the current characteristic coefficient includes: The sampling data I0 is subjected to two low-frequency feature extraction formulas. Frequency feature extraction, where: The first low-frequency feature extraction obtains vector I1, the formula is: The second low-frequency feature extraction obtains vector I2, the formula is: Among them, R0 is the low-frequency decomposition function, I 0,m is the mth value of vector I0, I 1,k is the kth value of vector I1; I 1,m is the mth value of vector I1, I 2,k is the kth value of vector I2; M0 is the total number of elements contained in vector I0; M1 is the total number of elements contained in vector I1; m∈N*, k∈N*; The high-frequency feature extraction formula is used to extract the high-frequency features of vector I2 to obtain the feature vector D2. The high-frequency feature extraction formula is as follows: Among them, W0 is the high frequency decomposition function, D 2,k is the kth value of the eigenvector D2 finally obtained, I 2,m is the mth value of vector I2; M2 is the total number of elements contained in vector I2; According to the characteristic vector D2, the current characteristic coefficient is obtained using the coefficient calculation formula. The coefficient calculation formula is as follows: Among them, A is the current characteristic coefficient finally obtained; K is the vector D 2,k The total number of elements contained; According to the above process, the positive line current data and the negative line current data are extracted respectively to obtain the positive current characteristic coefficient A + and negative electrode current characteristic coefficient A - ; The action parameter calculation method is: Among them, S + 、S - They are positive action parameters and negative action parameters respectively; is the positive current data on this side, is the contralateral positive electrode current data; I s - is the negative electrode current data on this side, is the contralateral negative electrode current data; is the i-th value of the positive electrode current data on this side; is the average value of the positive electrode current data on this side; is the i-th value of the contralateral positive electrode current data; is the average value of the contralateral positive electrode current data; is the i-th value of the negative electrode current data on this side; is the average value of the negative electrode current data on this side; is the i-th value of the negative electrode current data on the opposite side; is the average value of the negative electrode current data on the opposite side; n is the number of sampling points within the preset data window length; The calculated result of the action parameter is within the interval [-1, 1], which can correctly reflect the correlation between the currents at both ends.

2. The AC / DC hybrid distribution network line pilot protection method based on 5G communication according to claim 1, characterized in that: The line opposite side protection in step S2 specifically includes: In a DC distribution line, DC circuit breakers are installed at both ends of each line and are configured with the same protection strategy. The protections installed on both sides of the same line are called opposite-side protection.

3. The AC / DC hybrid distribution network line pilot protection method based on 5G communication according to claim 1, characterized in that: When the current characteristic coefficient of the local side is greater than the starting criterion threshold value described in step S2, it is determined that the starting criterion is met. Specifically, when at least one of the positive current characteristic coefficient and the negative current characteristic coefficient is greater than the starting criterion threshold value, it is determined that the starting criterion is met.

4. The AC / DC hybrid distribution network line pilot protection method based on 5G communication according to claim 1, characterized in that: In step S4, based on the current data of the positive and negative lines on the local side and the current data of the positive and negative lines on the opposite side, the fault detection time is taken as the starting point t0, and the positive current data and the negative current data within the preset data window length are selected.

5. The AC / DC hybrid distribution network line pilot protection method based on 5G communication according to claim 1, characterized in that: The intra-zone fault judgment criterion in step S4 is specifically: at least one of the positive pole action parameter and the negative pole action parameter is a positive number.

6. The AC / DC hybrid distribution network line pilot protection method based on 5G communication according to claim 1, characterized in that: The comparison coefficient for reflecting the difference between the positive and negative electrodes is determined according to the calculation result of the action parameters in step S5, specifically: Wherein, ρ is the contrast coefficient, S + 、S - They are the positive action parameters and the negative action parameters respectively.

7. The AC / DC hybrid distribution network line pilot protection method based on 5G communication according to claim 1, characterized in that: The specific implementation of the fault type selection in step S5 includes: When ρ>K1, it is determined that a positive ground fault has occurred; When K2<ρ≤K1, it is determined that an inter-pole short circuit fault occurs; When ρ≤K2, it is determined that a negative grounding fault has occurred; Wherein, ρ is the contrast coefficient, K1 is the first threshold for fault selection, and K2 is the second threshold for fault selection.

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