Ground fault protection method for flexible DC distribution network based on skewness and integrated energy

Abstract

The invention belongs to the technical field of relay protection of power system distribution network, and provides a flexible DC distribution network grounding fault protection method based on skewness and integrated energy, including fault detection, fault pole selection and fault identification; firstly, a fault detection criterion is constructed according to the amplitude of the pole-to-pole voltage; secondly, a fault pole selection criterion based on zero-mode voltage is constructed, and then it is judged whether a positive pole grounding fault, a negative pole grounding fault or a bipolar grounding fault occurs in the line; then, the skewness sign of the zero-mode current at both ends of the line is used to represent the direction characteristics, and the integral energy difference at both ends of the line is used to represent the amplitude characteristics; the invention uses skewness and integrated energy to construct protection criteria, fully extracts the direction and amplitude change characteristics of the zero-mode current, is conducive to the identification of faults inside and outside the zone, and avoids the problems of difficult threshold setting, poor protection adaptability, small difference inside and outside the zone, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of relay protection of power system distribution network, in particular to a flexible DC distribution network grounding fault protection method based on skewness and integrated energy. Background Art

[0002] The multi-terminal flexible DC distribution network based on modular multi-level converters has many advantages in large-scale distributed renewable energy grid connection and regional grid interconnection. However, if the line fails and is not removed in time, it will damage the power electronic devices and may burn the converter station. At the same time, it is difficult to accurately distinguish between inside and outside the area when a multi-terminal flexible DC distribution network fails, which may lead to large-scale power outages and the risk of electric shock, with extremely serious consequences.

[0003] To this end, those skilled in the art have proposed a flexible DC distribution network grounding fault protection method based on skewness and integrated energy to solve the problems raised by the background technology. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a flexible DC distribution network grounding fault protection method based on skewness and integrated energy to solve the problems in the prior art that it is difficult to accurately distinguish between inside and outside the zone when a fault occurs, it is easy to make misjudgments after high-resistance grounding, the reliability is low, the anti-interference ability is limited, and fault identification is difficult.

[0005] A flexible DC distribution network grounding fault protection method based on skewness and integrated energy includes:

[0006] Step 1. Fault detection: When the inter-electrode voltage amplitude | U pn |Below the set threshold U set When the system starts fault detection;

[0007] Step 2: Fault selection: Compare zero-mode voltage U 0 and threshold δ The size relationship is U 0<- δ When a positive ground fault occurs in the system, δ < U 0< δ When a double-pole grounding fault occurs in the system, U 0> δ When , a negative ground fault occurs in the system;

[0008] Step 3, fault identification: To identify whether the fault occurs inside or outside the zone, based on step 2, the zero-mode current skewness sign is used to characterize the directional characteristics, and the integrated energy difference at both ends of the line is combined to characterize the amplitude characteristics. Through the comprehensive analysis of these two characteristics, the faults inside and outside the zone can be reliably identified.

[0009] Preferably, the inter-electrode voltage amplitude used in step 1 is | U pn |Start fault detection, as shown in the following formula:

[0010]

[0011] In the formula, U pn is the inter-electrode voltage of the system; U set is the set threshold value; U N is the DC rated voltage.

[0012] Secondly, the threshold value in step 1 U set The setting principle is: In order to ensure that there is no false triggering in normal operation and reliable startup in the event of a fault, the threshold value is set to U set =0.9 U N .

[0013] Preferably, the zero mode voltage used in step 2 is U 0 for fault pole selection, as shown in the following formula:

[0014]

[0015] In the formula, U 0 is zero mode voltage; δ is the set threshold;

[0016] Secondly, the threshold in step 2 δ The selection process is as follows: when a positive ground fault occurs, the zero-mode voltage shifts from 0 to - U N ; When a negative ground fault occurs, the zero-mode voltage shifts from 0 to U N To ensure reliability, δ Take 0.2 U N .

[0017] Preferably, step 3 comprises the following specific steps:

[0018] Step 3.1: Calculate the zero-mode current skewness at both ends of the line Sm , S n ; If it is determined in step 2 that a negative ground fault occurs in the system, the negative skewness of the zero-mode current at both ends of the line is calculated; otherwise, the positive skewness of the zero-mode current at both ends of the line is calculated, as shown in the following formula:

[0019]

[0020] In the formula, m and n represent the detection points at both ends of the same line; S m , S n Indicates the zero-mode current deflection at line detection points m and n; x j , y j They represent the zero-mode current at the detection points m and n respectively; N is the number of samples; and is the mean value of zero-mode current;

[0021] Step 3.2: Use the zero-mode current skewness sign at both ends of the line to identify the fault; in fault identification, if sgn( S m )>0 and sgn( S n )>0, it is determined that the line has an internal fault; if the zero-mode current skewness signs at both ends of all lines are positive and negative, that is, , then the fault cannot be identified; otherwise, it is determined to be an out-of-zone fault;

[0022] Step 3.3: In step 3.2, when the zero-mode current skewness sign at both ends of the line cannot be used for fault identification, the zero-mode current integral energy difference represented by the sign function is used To determine the fault area; as shown in the following formula:

[0023]

[0024] In the formula, A m and A n Respectively represent the zero-mode current integrated energy at line detection points m and n; i m ( t j ) indicates that the detection point m is at time t j Zero mode current value; i n ( t j ) indicates that the detection point n is at time tj Zero mode current value; ( t j+1 - t j ) is the time interval between adjacent sampling points, where j =1,2,…, p -1; p is the number of sampling points; The sign indicating the integrated energy difference between the two ends of the line;

[0025] If the sign of the integrated energy difference of a line is If it is opposite to other lines, it is determined that the line has an in-area fault; otherwise, it is determined to be an out-of-area fault.

[0026] The flexible DC distribution network grounding fault protection system based on skewness and integrated energy uses the flexible DC distribution network grounding fault protection method based on skewness and integrated energy, including:

[0027] The fault detection module detects that the voltage amplitude between the poles of the system| U pn |Below the set threshold U set When the fault detection process is started;

[0028] Fault selection module, by comparing the zero-mode voltage U 0 and preset threshold δ The size of the fault is determined by the fault type;

[0029] The fault identification module, based on the fault pole selection module, uses the zero-mode current skewness sign to characterize the directional characteristics, and combines the integrated energy difference at both ends of the line to characterize the amplitude characteristics. By comprehensively analyzing these two characteristics, it is possible to identify whether the fault occurs inside or outside the zone.

[0030] A processor is configured to execute the flexible DC distribution network grounding fault protection method based on skewness and integrated energy.

[0031] A computer-readable storage medium stores a computer program, which implements the above-mentioned flexible DC distribution network grounding fault protection method based on skewness and integrated energy when executed by a processor.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The present invention constructs protection criteria by utilizing skewness and integrated energy, fully extracts the direction and amplitude variation characteristics of zero-mode current, is conducive to the identification of faults inside and outside the zone, and avoids problems such as difficulty in threshold setting, poor protection adaptability, and small difference between inside and outside the zone.

[0034] 2. The present invention has certain adaptability under working conditions such as noise influence, data loss, communication delay, etc. When the grounding resistance is 500Ω and accompanied by 5dB Gaussian white noise, it can effectively identify faults inside and outside the zone without false operation.

[0035] 3. The present invention can not only correctly distinguish internal and external faults in a system where the transmission line distribution of a multi-terminal flexible direct current distribution network is relatively balanced, but also has high applicability when a certain line in the system is extremely long. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a flow chart of the protection method of the present invention;

[0037] Figure 2 It is a skewness characteristic diagram of data distribution in the present invention;

[0038] Figure 3 This is a ±10kV four-terminal DC system diagram in the present invention;

[0039] Figure 4 is the inter-electrode voltage at the measuring point R1 of the present invention;

[0040] Figure 5 is the zero mode current at each measuring point in case A1 of the present invention;

[0041] Figure 6 It is the zero mode current at each measuring point in case B1 of the present invention. DETAILED DESCRIPTION

[0042] The following embodiments of the present invention are described in further detail in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0043] Flexible DC distribution network ground fault protection method based on skewness and integrated energy, such as Figure 1 As shown, including:

[0044] Step 1. Fault detection: When the inter-electrode voltage amplitude | U pn |Below the set threshold U set When the system starts fault detection; the inter-electrode voltage amplitude used in step 1 | U pn |Start fault detection, as shown in the following formula:

[0045]

[0046] In the formula, U pn is the inter-electrode voltage of the system; U setis the set threshold value; U N is the DC rated voltage;

[0047] Secondly, the threshold value in step 1 U set The setting principle is: In order to ensure that there is no false triggering in normal operation and reliable startup in the event of a fault, the threshold value is set to U set =0.9 U N ;

[0048] Step 2: Fault selection: Compare zero-mode voltage U 0 and threshold δ The size relationship is U 0<- δ When a positive ground fault occurs in the system, δ < U 0< δ When a double-pole grounding fault occurs in the system, U 0> δ When a negative ground fault occurs in the system, the zero-mode voltage is used in step 2. U 0 for fault pole selection, as shown in the following formula:

[0049]

[0050] In the formula, U 0 is zero mode voltage; δ is the set threshold;

[0051] Secondly, the threshold in step 2 δ The selection process is as follows: when a positive ground fault occurs, the zero-mode voltage shifts from 0 to - U N ; When a negative ground fault occurs, the zero-mode voltage shifts from 0 to U N To ensure reliability, δ Take 0.2 U N ;

[0052] Step 3, fault identification: In order to identify whether the fault occurs inside or outside the zone, based on step 2, the zero-mode current skewness sign is used to characterize the directional characteristics, and the integrated energy difference at both ends of the line is combined to characterize the amplitude characteristics. Through the comprehensive analysis of these two characteristics, the fault inside and outside the zone can be reliably identified; step 3 includes the following specific steps:

[0053] Step 3.1: Calculate the zero-mode current skewness at both ends of the line S m , Sn If it is determined in step 2 that a negative ground fault occurs in the system, the negative skewness of the zero-mode current at both ends of the line is calculated. Otherwise, the positive skewness of the zero-mode current at both ends of the line is calculated, as shown in the following formula:

[0054]

[0055] In the formula, m and n represent the detection points at both ends of the same line; S m , S n Indicates the zero-mode current deflection at line detection points m and n; x j , y j They represent the zero-mode current at the detection points m and n respectively; N is the number of samples; and is the mean value of zero-mode current;

[0056] Step 3.2: Use the zero-mode current skewness sign at both ends of the line to identify the fault; in fault identification, if sgn( S m )>0 and sgn( S n )>0, it is determined that the line has an internal fault; if the zero-mode current skewness signs at both ends of all lines are positive and negative, that is, , then the fault cannot be identified; otherwise, it is determined to be an out-of-zone fault;

[0057] Step 3.3: In step 3.2, when the zero-mode current skewness sign at both ends of the line cannot be used for fault identification, the zero-mode current integral energy difference represented by the sign function is used To determine the fault area; as shown in the following formula:

[0058]

[0059] In the formula, A m and A n Respectively represent the zero-mode current integrated energy at line detection points m and n; i m ( t j ) indicates that the detection point m is at time t j Zero mode current value; i n ( t j ) indicates that the detection point n is at time t j Zero mode current value; ( tj+1 - t j ) is the time interval between adjacent sampling points, where j =1,2,…, p -1; p is the number of sampling points; The sign indicating the integrated energy difference between the two ends of the line;

[0060] If the sign of the integrated energy difference of a line is If it is opposite to other lines, it is determined that the line has an in-area fault; otherwise, it is determined to be an out-of-area fault.

[0061] Embodiment: The present invention provides a flexible DC distribution network ground fault protection method based on skewness and integrated energy, comprising:

[0062] On the PSCAD / EMTDC simulation platform, Figure 3 The ±10kV four-terminal DC system shown in the figure has four converter stations MMC1, MMC2, MMC3 and MMC4 connected by current limiting reactors. L With line l 12 , l 23 , l 34 and l 41 Connected into a ring grid, each line is equipped with a protection device R on both sides x , x =1~8, T1, T2, T3, T4 are the buses corresponding to the converter station, and the specific parameters are shown in Table 1;

[0063] Table 1 System simulation parameters

[0064]

[0065] Among them, MMC1 adopts constant voltage reactive power control, and MMC2, MMC3, and MMC4 adopt constant active power and constant reactive power control; the sampling frequency of the system is 20kHz, and the data window length is 2ms.

[0066] Simulation Analysis

[0067] Case A1: Line l 12 , l 23 , l 34 , l 41The lengths are 15km, 8km, 10km, and 13km respectively; the system outputs rated power to each converter, the fault occurs at 1s, lasts for 0.1s, the fault type is positive ground fault (PTG), the fault distance to MMC1 station is 0km, and the ground resistance is 1Ω; the inter-pole voltage waveform at the measuring point R1 is shown in Figure 4 ; The zero-mode current at each measuring point is as follows Figure 5 As shown, the skewness values ​​at each measuring point are calculated as shown in Table 2;

[0068] Table 2 Test results of case A1

[0069]

[0070] When a single-pole grounding fault occurs in the line, the inter-pole voltage will shift and the existing fluctuation process will affect the entire system, such as Figure 4 As shown in the figure, the inter-electrode voltage at the measuring point R1 can judge that the system has a ground fault at the second sampling point, which is sensitive and fast; Figure 5 is the zero-mode current at each measuring point. The non-fault pole produces a fluctuation process due to the coupling effect of the line, and the wave head is attenuated during propagation. Therefore, the zero-mode current of the fault line is greater than that of the non-fault line. It can be seen from Table 2 that the skewness can well describe the zero-mode current deviation degree. Among them, sgn( S 1)=sgn(1.48)>0 and sgn( S 2)=sgn(0.97)>0, according to the fault identification criterion, it is concluded that the system has an internal fault, and the fault line is l 12 .

[0071] Case B1: Line l 12 , l 23 , l 34 , l 41 The lengths are 30km, 2km, 2km, and 2km respectively. Except for the line parameters, the other operating conditions are the same as those in Case A1. The zero-mode current at each measuring point is as follows: Figure 6 As shown in Table 3, after the line fails, the entire system is affected and fluctuates. The skewness values ​​are shown in Table 3. The zero-mode current skewness signs on both sides of each line are positive and negative, that is, the line l 12 Skewness sign ,line l 23 Skewness sign ,line l 34 Skewness sign ,linel 41 Skewness sign Fault identification is not possible, and the zero-mode current integral energy difference is used to determine the fault area. Since the zero-mode current of the fault line is large, while that of the non-fault line is relatively small, and when the fault occurs at the edge of the line, the zero-mode current amplitude at one end of the line will be large and the amplitude at the other end will be small; therefore, the line l 12 The integrated energy difference of is the largest and positive in each line, while the other lines are negative, that is, , according to the fault identification criteria, the line l 12 The sign of the integrated energy difference is opposite to that of other lines, so the line is judged l 12 An intra-area fault occurred; it is consistent with the fault setting, so the proposed method can correctly detect the fault area;

[0072] Table 3 Test results of case B1

[0073]

[0074] Working principle:

[0075] 1. Inter-electrode voltage starting

[0076] In order to avoid frequent startup of the proposed method during fault detection, a suitable startup criterion needs to be set; when the system is operating normally, the inter-electrode voltage of the system U pn Stable near the rated voltage value, and when a ground fault occurs, the positive and negative voltages will shift; therefore, when the inter-electrode voltage amplitude | U pn |Below threshold U set When the fault detection criterion is activated, the threshold is set to U set =0.9 U N ,in U N is the DC rated voltage.

[0077] 2. Zero mode voltage determines the fault pole

[0078] The zero-mode voltage of the system can effectively identify the faulty pole. When the system is operating normally or an inter-pole short circuit occurs, the zero-mode voltage will not shift, and the zero-mode component is basically zero. When a positive pole grounding (PTG) fault occurs, the zero-mode voltage shifts from 0 to - U N; When a negative grounding (NTG) fault occurs, the zero-mode voltage shifts from 0 to U N Therefore, the fault pole can be selected by the magnitude of the zero-mode voltage, and the type of fault in the system can be determined accordingly. To ensure reliability, the threshold is set to δ =0.2 U N ,in, U N is the DC rated voltage.

[0079] 3. Skewness

[0080] When a fault occurs in the distribution network, the amplitude of the transient zero-mode current obeys the decaying exponential function, so the skewness feature is used to extract the direction of the zero-mode current at both ends; skewness is a statistical method that can calculate the asymmetry of the probability distribution of the signal relative to the mean. It presents the distribution characteristics of the data and has good detection capabilities for the asymmetric changes of the small current signal caused by the high-resistance fault; since the skewness is essentially the third-order cumulant with zero lag, and the third-order cumulant of any Gaussian process is always zero, the skewness of the noise is theoretically zero; while the skewness of transient components such as the exponential decay DC bias and the oscillation decay component is non-zero; such as Figure 2 As shown in the figure, the distribution is more discrete in the area where the sample data is positive, and more dense in the area where it is negative, and the calculated value of the skewness is positive; otherwise, the calculated value of the skewness is negative; and in mathematics, if the mean line in the window is greater than the median line, the skewness is positive, otherwise it is negative; therefore, in the case of high-resistance faults and strong noise, the skewness characteristics of the zero-mode current can accurately characterize the relationship between the mean line and the median line. If the mean line is greater than the median line, the waveform is positively skewed, otherwise it is negatively skewed, and the direction measurement of the zero-mode current is accurately characterized based on this; the skewness calculation formula is as follows:

[0081]

[0082] In the formula, S k Indicates zero-mode current skewness; x j For the j zero-mode current; N is the total number of samples; is the mean value of the zero mode current.

[0083] 4. Integral Energy

[0084] The integrated energy is used to calculate the transient zero-mode current signal i ( t ) and time t j This method can effectively characterize the accumulation of zero-mode current over time after a fault occurs. The discrete zero-mode current integral energy formula is as follows:

[0085]

[0086] In the formula, A k represents the integrated energy of zero-mode current; i ( t j ) is the time t j Zero mode current; ( t j+1 - t j ) is the time interval between adjacent sampling points, where j =1,2,…, n -1; n is the number of sampling points.

[0087] The flexible DC distribution network grounding fault protection system based on skewness and integrated energy uses the flexible DC distribution network grounding fault protection method based on skewness and integrated energy, including:

[0088] The fault detection module detects that the voltage amplitude between the poles of the system| U pn |Below the set threshold U set When the fault detection process is started;

[0089] Fault selection module, by comparing the zero-mode voltage U 0 and preset threshold δ The size of the fault is determined by the fault type;

[0090] The fault identification module, based on the fault pole selection module, uses the zero-mode current skewness sign to characterize the directional characteristics, and combines the integrated energy difference at both ends of the line to characterize the amplitude characteristics. By comprehensively analyzing these two characteristics, it is possible to identify whether the fault occurs inside or outside the zone.

[0091] The embodiment of the present application provides an electronic device, which is applicable to the above-mentioned flexible DC distribution network grounding fault protection method based on skewness and integrated energy, including:

[0092] Memory, used to protect computer programs and data;

[0093] Processor, used to run system programs.

[0094] The embodiment of the present application provides a computer storage medium, which is applicable to the above-mentioned flexible DC distribution network grounding fault protection method based on skewness and integrated energy.

[0095] Those skilled in the art will appreciate that the embodiments of the present application may be provided as a system or a computer program product. Therefore, the present application may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0096] The present application is described with reference to the flowcharts and / or block diagrams of the devices (systems) and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0097] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0098] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0099] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0100] The memory may include non-permanent memory in a computer-readable medium, random access memory (RAM) and / or non-volatile memory in the form of read-only memory (ROM) or flash RAM. The memory is an example of a computer-readable medium.

[0101] Computer readable media include permanent and non-permanent, removable and non-removable media, and can be implemented by any method or technology to store information. Information can be computer readable instructions, data structures, program modules or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disk read-only memory (CD-ROM), digital versatile disk (DVD) or other optical storage, magnetic cassettes, magnetic disk storage or other magnetic storage devices or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined herein, computer readable media does not include temporary computer readable media (transitory media), such as modulated data signals and carrier waves.

[0102] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, commodity or device including the elements.

[0103] The embodiments of the present invention are provided for the purpose of illustration and description. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations of the present invention. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A flexible DC distribution network grounding fault protection method based on skewness and integrated energy, characterized by: include: Step 1. Fault detection: When the inter-electrode voltage amplitude | U pn |Below the set threshold U set When the system starts fault detection; Step 2: Fault selection: Compare zero-mode voltage U 0 and threshold δ The size relationship is U 0<- δ When a positive ground fault occurs in the system, δ < U 0< δ When a double-pole grounding fault occurs in the system, U 0> δ When , a negative ground fault occurs in the system; Step 3, fault identification: To identify whether the fault occurs inside or outside the zone, based on step 2, the zero-mode current skewness sign is used to characterize the directional characteristics, and the integrated energy difference at both ends of the line is combined to characterize the amplitude characteristics. Through the comprehensive analysis of these two characteristics, the fault inside and outside the zone can be reliably identified; The step 3 comprises the following specific steps: Step 3.1: Calculate the zero-mode current skewness at both ends of the line S m , S n If it is determined in step 2 that a negative ground fault occurs in the system, the negative skewness of the zero-mode current at both ends of the line is calculated. Otherwise, the positive skewness of the zero-mode current at both ends of the line is calculated, as shown in the following formula: ； In the formula, m and n represent the detection points at both ends of the same line; S m , S n They represent the zero-mode current deflection at line detection points m and n respectively; x j 、y j Respectively represent the j-th zero-mode current value at detection points m and n; N is the sample size; and Respectively represent the mean value of zero-mode current at detection points m and n; Step 3.2: Use the zero-mode current skewness sign at both ends of the line to identify the fault; During fault identification, if sgn( S m )>0 and sgn( S n )>0, it is determined that the line has an internal fault; if the zero-mode current skewness signs at both ends of all lines are positive and negative, that is, , then the fault cannot be identified; otherwise, it is determined to be an out-of-zone fault; Step 3.3: In step 3.2, when the zero-mode current skewness sign at both ends of the line cannot be used for fault identification, the zero-mode current integral energy difference represented by the sign function is used To determine the fault area; as shown in the following formula: ； ； ； In the formula, A m and A n Respectively represent the zero-mode current integrated energy at line detection points m and n; i m ( t j ) indicates that the detection point m is at time t j Zero mode current value; i n ( t j ) indicates that the detection point n is at time t j Zero mode current value; ( t j+1 - t j ) is the time interval between adjacent sampling points, where j =1,2,…, p -1; p is the number of sampling points; The sign indicating the integrated energy difference between the two ends of the line; If the sign of the integrated energy difference of a line is If it is opposite to other lines, it is determined that the line has an in-area fault; otherwise, it is determined to be an out-of-area fault.

2. The flexible DC distribution network ground fault protection method based on skewness and integrated energy as claimed in claim 1, characterized in that: The interelectrode voltage amplitude used in step 1 | U pn |Start fault detection, as shown in the following formula: ； In the formula, U pn is the inter-electrode voltage of the system; U set is the set threshold value; U N is the DC rated voltage.

3. A flexible DC distribution network grounding fault protection system based on skewness and integrated energy, characterized by: The flexible DC distribution network ground fault protection method based on skewness and integrated energy according to any one of claims 1-2 comprises: The fault detection module detects that the voltage amplitude between the poles of the system| U pn |Below the set threshold U set When the fault detection process is started; Fault selection module, by comparing the zero-mode voltage U 0 and threshold δ The size of the fault determines the fault type; The fault identification module, based on the fault pole selection module, uses the zero-mode current skewness sign to characterize the directional characteristics, and combines the integrated energy difference at both ends of the line to characterize the amplitude characteristics. By comprehensively analyzing these two characteristics, it is possible to identify whether the fault occurs inside or outside the zone.

4. A processor, characterized in that: The method is configured to execute the flexible DC distribution network ground fault protection method based on skewness and integrated energy according to any one of claims 1 to 2.

5. A computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the computer program is executed by a processor, the flexible DC distribution network grounding fault protection method based on skewness and integrated energy as described in any one of claims 1 to 2 is implemented.

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