Power distribution network single-phase earth fault phase selection method for asymmetric current active compensation

Abstract

The invention provides a power distribution network single-phase earth fault phase selection method for asymmetric current active compensation, and the method comprises the steps: controlling a flexible grounding protection device to adjust the output when a power distribution network is in normal operation and has no earth fault, enabling the zero-sequence voltage of a power distribution system to approach zero, and enabling the zero-sequence voltage to approach zero; measuring a three-phase grounding parameter asymmetric current flowing through the flexible grounding protection device at the moment as a reference current; then, the flexible grounding protection device is controlled to continuously inject compensation current which is equal to the reference current in amplitude and opposite to the reference current in direction into the power distribution system so as to suppress zero-sequence voltage caused by asymmetry of three-phase grounding parameters; when a single-phase earth fault occurs in the power distribution network, detecting and acquiring the zero-sequence voltage and the phase voltage of each phase of the current system; and determining a reference phase based on the phase of the zero sequence voltage, calculating the absolute value of the phase difference between the phase of each phase voltage and the reference phase, and determining the phase with the minimum absolute value of the phase difference as a grounding fault phase.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power distribution network electric parameter measurement and single-phase grounding fault detection, and particularly relates to a single-phase grounding fault phase selection method for power distribution network with asymmetric current active compensation. BACKGROUND

[0002] As a main component of power distribution network faults, single-phase grounding faults account for more than 80% of the total number of faults, and are prone to cause electrical fires, equipment breakdowns, and electric shock accidents, posing a serious threat to the safe and reliable operation of power distribution networks. The prerequisite for reliable suppression of single-phase grounding faults in power distribution networks is the identification of the grounding fault phase.

[0003] Single-phase grounding fault phase selection methods for power distribution networks can be mainly divided into passive signal methods and active signal injection methods. Traditional phase selection methods use passive signal methods, which utilize signals generated by grounding faults for phase selection. However, this method is difficult to capture the moment when the fault signal is generated, and it is difficult to obtain transient signals. In addition, high-resistance grounding faults are easily affected by three-phase ground parameter asymmetry. Active signal injection methods, on the other hand, use injected signals for fault phase identification, which is easy to control and has distinct characteristics. The invention with the publication number CN112881858A, "Single-phase grounding fault phase selection method for parameter asymmetric power distribution network", proposes injecting current with different amplitudes into the power distribution network twice to identify the fault phase. However, this method requires two adjustments of the injected current value after a grounding fault, resulting in slow response speed. The document "Active phase selection method for high-resistance grounding faults in power distribution networks based on characteristic phase difference" (《Electric Power Systems and Automation Conference》, April 2025) proposes controlling the zero-sequence voltage to be a three-phase asymmetric voltage after a grounding fault, and then comparing the phase of the injected current and the fault phase voltage to identify the fault phase. This method takes into account the influence of three-phase ground parameter asymmetry, but if a low-resistance grounding fault occurs, the zero-sequence voltage is close to the fault phase supply voltage. If the control is a three-phase asymmetric voltage, the signal injection device will have an overcurrent, which can easily cause the injection equipment to burn out. SUMMARY

[0004] In view of the defects and deficiencies of the prior art, the present application provides a power distribution network single-phase grounding fault phase selection method and system based on asymmetric current flexible compensation. The method aims to solve the problems of slow response speed of the existing active injection signal method, overcurrent risk of low resistance grounding fault, and insufficient phase selection accuracy of passive signal method. The core technical solution includes two parts: when the power distribution network is normally operated and there is no grounding fault, the flexible grounding protection device is controlled to adjust the output, so that the zero sequence voltage of the power distribution system tends to be zero, and the three-phase ground parameter asymmetric current flowing through the device at this time is measured as a reference current. The compensation current with equal amplitude and opposite direction of the reference current is continuously injected into the system to suppress the zero sequence voltage disturbance caused by the three-phase ground parameter asymmetry, creating ideal conditions for subsequent phase selection; when the power distribution network occurs single-phase grounding fault, the zero sequence voltage and each phase voltage of the system are detected in real time, and the phase phase of the zero sequence voltage phase offset by 90 degrees is used as the reference phase. The phase difference absolute value between each phase voltage phase and the reference phase is calculated, and the phase with the smallest phase difference absolute value is determined as the grounding fault phase.

[0005] The flexible grounding protection device used in the present application is composed of a phase separation switch, a power electronic converter and a control system. The phase separation switch and the power electronic converter are connected in series between the phase line and the ground of the power distribution system. The power electronic converter can adapt to single-phase H-bridge, single-phase half-bridge or single-phase output circuit formed by three-phase converter topology reconstruction, ensuring accurate injection and flexible regulation of compensation current. Compared with the prior art, the present application eliminates the parameter asymmetry interference by active flexible compensation before fault, and quickly selects the phase without the need for secondary adjustment of the injected signal after fault. Not only does it significantly improve the phase selection accuracy and anti-interference ability in different grounding fault scenarios such as low resistance and high resistance, but also avoids the overcurrent risk in low resistance fault in principle, effectively improving the reliability and safety of power distribution network grounding fault handling. It has important significance for reducing power distribution network downtime and ensuring power supply stability.

[0006] The technical solution specifically adopted by the present application to solve its technical problems is:

[0007] A single-phase grounding fault phase selection method for power distribution network based on asymmetric current active compensation, comprising:

[0008] When the power distribution network is normally operated and there is no grounding fault, the flexible grounding protection device is controlled to adjust the output, so that the zero sequence voltage of the power distribution system tends to be zero, and the three-phase ground parameter asymmetric current flowing through the flexible grounding protection device at this time is measured as a reference current; then, the flexible grounding protection device is controlled to continuously inject a compensation current with equal amplitude and opposite direction of the reference current into the power distribution system to suppress the zero sequence voltage caused by the three-phase ground parameter asymmetry;

[0009] When a single-phase grounding fault occurs in the power distribution network, the zero-sequence voltage and the phase voltages of each phase of the current system are detected and obtained; based on the phase of the zero-sequence voltage, a reference phase is determined, the phase difference absolute value between the phase of each phase voltage and the reference phase is calculated, and the phase with the minimum phase difference absolute value is determined as the grounding fault phase.

[0010] Further, the specific way of adjusting the output of the flexible grounding protection device to make the zero-sequence voltage of the power distribution system approach zero is as follows: taking the zero-sequence voltage of the power distribution system as the control target, adopting a closed-loop control algorithm with zero-sequence voltage deviation as the feedback quantity, collecting the zero-sequence voltage signal in real time and calculating the deviation from zero, adjusting the output parameters of the flexible grounding protection device until the amplitude of the zero-sequence voltage is less than a preset threshold.

[0011] Further, the specific method for determining the reference phase is as follows: obtaining the phase of the zero-sequence voltage of the current system, and obtaining the reference phase by subtracting 90° from the phase.

[0012] Further, the flexible grounding protection device comprises a phase separation switch, a power electronic converter, and a control system electrically connected to the power electronic converter; the phase separation switch is connected in series with the power electronic converter, and the path after the series connection is connected between the phase line and the ground of the power distribution system.

[0013] The power electronic converter is a single-phase H-bridge converter, a single-phase half-bridge converter, or a single-phase output circuit formed by topology reconstruction of a three-phase converter.

[0014] Further, the specific control method for controlling the flexible grounding protection device to continuously inject a compensation current with an amplitude equal to that of the three-phase ground parameter asymmetric current and an opposite direction into the power distribution system is as follows: after measuring the three-phase ground parameter asymmetric current, the compensation current is continuously injected; during the injection process, the zero-sequence voltage of the power distribution system is monitored in real time, and if the amplitude of the zero-sequence voltage exceeds a preset threshold, the amplitude or phase of the compensation current is adjusted to make the zero-sequence voltage return to within the threshold.

[0015] Further, the amplitude and direction of the compensation current are determined based on the measured three-phase ground parameter asymmetric current.

[0016] Further, when a high-resistance grounding fault occurs in the power distribution network, the accuracy of the phase difference absolute value calculation is ensured by the following method: when detecting the zero-sequence voltage and the phase voltages of each phase, a filtering algorithm is used to eliminate voltage signal interference, and then a phase-locked loop is used to extract the voltage phase.

[0017] Further, the specific way of measuring the three-phase ground parameter asymmetric current flowing through the flexible grounding protection device is as follows: the zero-sequence current signal of the ground path is collected by a current sensor built in the flexible grounding protection device, and the zero-sequence current signal corresponds to the three-phase ground parameter asymmetric current.

[0018] And, an asymmetric current active compensation power distribution network single-phase grounding fault phase selection system, comprising:

[0019] A flexible grounding protection device, comprising a phase separation switch, a power electronic converter and a control system, the phase separation switch and the power electronic converter are connected in series between the phase line and the ground of the power distribution system;

[0020] A parameter measurement module is configured to adjust the output of the flexible grounding protection device in cooperation with the flexible grounding protection device when the power distribution network is in normal operation and no grounding fault occurs, so that the zero sequence voltage of the power distribution system approaches zero, and the three-phase ground parameter asymmetric current flowing through the flexible grounding protection device is measured at this time;

[0021] A compensation control module is configured to control the flexible grounding protection device to continuously inject a compensation current equal in magnitude and opposite in direction to the three-phase ground parameter asymmetric current into the power distribution system to suppress the zero sequence voltage caused by the three-phase ground parameter asymmetry;

[0022] A fault phase selection module is configured to detect and obtain the zero sequence voltage and the phase voltage of each phase of the current system when a single-phase grounding fault occurs in the power distribution network, determine a reference phase based on the phase of the zero sequence voltage, calculate the phase difference absolute value between the phase of each phase voltage and the reference phase, and determine the phase with the smallest phase difference absolute value as the grounding fault phase.

[0023] And a computer device, comprising a memory, a processor and a computer program stored on the memory, the processor executes the computer program to realize the method as described above.

[0024] A non-transitory computer readable storage medium having a computer program stored thereon, the computer program being executed by a processor to realize the method as described above.

[0025] Compared with the prior art, the present application and its preferred schemes at least include the following beneficial effects:

[0026] The present application effectively overcomes the interference of three-phase ground parameter asymmetry on the accuracy of single-phase grounding fault phase selection, creates ideal system conditions for fault phase selection through the design of actively injecting precise compensation current before the fault, significantly improves the reliability and anti-interference ability of the phase selection result, and avoids the defects of traditional passive signal method affected by transient signal capture difficulty and parameter asymmetry.

[0027] The response speed is more advantageous, without the need for adjustment or secondary injection of signals after the fault occurs, the fault phase can be quickly identified based on the preset phase criterion, solving the problem of response lag of some active injection signal methods, and helping to shorten the fault handling time.

[0028] The safety is obviously improved, the asymmetric parameter compensation mode based on current suppression is adopted, the risk of overcurrent generated by the signal injection device in the low resistance grounding fault scene is avoided in principle, the safety hidden danger such as equipment burning is avoided, compared with the phase selection scheme depending on voltage control, and the engineering practicability is higher.

[0029] The adaptability is wider, whether it is high resistance or low resistance grounding fault scene, the fault phase recognition can be stably realized, and the flexible grounding protection device adopted can adapt to various types of power electronic converters, so that the actual distribution system demand can be flexibly configured, and the safe and reliable operation of the distribution network is provided, which has a positive significance for reducing power loss and improving power supply stability. BRIEF DESCRIPTION OF DRAWINGS

[0030] The application will be further described in detail below in combination with the drawings and specific embodiments:

[0031] Figure 1 The flexible grounding distribution system fault phase selection algorithm and the corresponding circuit structure diagram of the embodiment of the application;

[0032] Figure 2 The equivalent circuit diagram of the distribution network zero sequence of the embodiment of the application;

[0033] Figure 3 The fault phase selection method simulation model schematic diagram based on asymmetric current flexible compensation of the simulation example of the embodiment of the application;

[0034] Figure 4 The simulation waveform diagram when the A phase of the simulation example of the embodiment of the application is grounded through low resistance 50 ohm and high resistance 5000 ohm resistor;

[0035] Figure 5 The simulation waveform diagram when the B phase of the simulation example of the embodiment of the application is grounded through low resistance 50 ohm and high resistance 5000 ohm resistor;

[0036] Figure 6 The simulation waveform diagram when the C phase of the simulation example of the embodiment of the application is grounded through low resistance 50 ohm and high resistance 5000 ohm resistor. DETAILED DESCRIPTION

[0037] In order to make the features and advantages of the application more obvious and easy to understand, the following examples are described in detail as follows:

[0038] It should be pointed out that the following detailed description is exemplary, and is intended to provide further description of the present application. Unless otherwise specified, all technical and scientific terms used in the specification have the same meaning as generally understood by those skilled in the art to which the present application belongs.

[0039] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0040] The existing fault phase selection method based on active injection signal has problems of insufficient response speed and overcurrent risk. The application provides a single-phase grounding fault phase selection method based on asymmetric current flexible compensation for a power distribution network. First, when the power grid is in normal operation, the system zero sequence voltage is controlled at a target value by a flexible grounding protection device, and the three-phase ground parameter asymmetric current I bd of the system is accurately measured. Then, a compensation current equivalent to and opposite to the current is actively injected into the system to eliminate the influence of parameter asymmetry and create ideal conditions for subsequent phase selection. When a single-phase grounding fault occurs, the phase with the smallest difference between the phase voltage phase and the reference phase (ΨU0-90°) is determined as the fault phase. The application can immediately identify the fault phase after the grounding fault occurs, and has fast response speed. In addition, the injection of asymmetric current can inhibit three-phase asymmetry, and there is no risk of overcurrent in low resistance grounding fault, which is safe. Through active flexible compensation, the disturbance of system asymmetry to the accuracy of phase selection is overcome, the problems of slow response speed and overcurrent risk in the existing single-phase grounding fault phase selection method for the power distribution network are solved, the reliability and safety of the grounding fault phase selection are significantly improved, and the application plays an important role in reducing power outages of the power distribution network.

[0041] As shown in Figure 1 , the embodiment provides a specific implementation process of the flexible grounding power distribution system fault phase selection algorithm, including the following steps:

[0042] S1, asymmetric current measurement and parameter asymmetry suppression: when the power distribution network is in normal operation and no grounding fault occurs, the flexible grounding protection device is controlled to act to maintain the zero sequence voltage of the power distribution system at a first target value, and the three-phase ground parameter asymmetric current I bd flowing through the flexible grounding protection device is measured. Then, the flexible grounding protection device is controlled to continuously inject a compensation current with the same amplitude and opposite direction as I bd into the power distribution system to suppress the zero sequence voltage caused by three-phase ground parameter asymmetry.

[0043] S2, grounding fault identification and phase selection: when a single-phase grounding fault occurs in the power distribution network, the current system zero sequence voltage U0 and each phase voltage are detected and obtained; based on the phase relationship between the phase of the zero sequence voltage U0 and the phase of each phase voltage, the phase of the grounding fault is identified and determined.

[0044] As a preferred embodiment, the method of controlling the operation of the flexible grounding protection device to maintain the zero-sequence voltage of the power distribution system at the first target value is as follows: taking the zero-sequence voltage of the power distribution system as the control target, using a closed-loop control algorithm, adjusting the output of the flexible grounding protection device to make the zero-sequence voltage approach zero.

[0045] The first target value is zero, which means controlling the zero-sequence voltage U0=0.

[0046] As a preferred embodiment, the method for identifying and determining the phase in which a ground fault has occurred based on the phase relationship between the phase of the zero-sequence voltage U0 and the phases of each phase voltage is specifically as follows: the flexible grounding protection device injects I into the system. bd Furthermore, after a ground fault occurs, calculate the phase ΨU of each phase voltage. A ΨU B ΨU C The absolute value of the phase difference between the phase and a reference phase (ΨU0-90°) is used, where ΨU0 is the phase of the current system zero-sequence voltage U0. The phase with the smallest absolute value of the phase difference is determined to be the phase with the ground fault.

[0047] The flexible grounding protection device proposed in this embodiment includes a phase-separation switch and a power electronic converter, as well as a control system connected thereto. The phase-separation switch and the power electronic converter are connected in series between each phase line of the power distribution system and the ground.

[0048] The power electronic converter mentioned in this embodiment is a single-phase H-bridge converter, a single-phase half-bridge converter, or a single-phase output circuit composed of a three-phase converter.

[0049] This invention proposes a method for suppressing three-phase ground parameter asymmetry based on flexible compensation of asymmetrical current. Firstly, the zero-sequence voltage is used as the control target. A flexible grounding protection device is used to control the zero-sequence voltage to zero, and the current I flowing through the flexible grounding protection device at this time is... bd Save. Then, using zero-sequence current as the control target, inject current I into the system using a flexible grounding protection device. bd The principle for suppressing three-phase ground parameter asymmetry current is as follows:

[0050] The three-phase-to-ground parameters of power distribution lines inherently exhibit asymmetry. The asymmetry of overhead lines is typically 0.5% to 1.5%, with a theoretical limit of 3.5%, while the asymmetry of cable lines is much smaller than that of overhead lines. Assuming the three-phase-to-ground asymmetry voltage is represented by U... bd This indicates that when the system is running normally, according to Figure 2 Based on the zero-sequence equivalent circuit of the distribution network shown and Kirchhoff's current law, we can obtain:

[0051] (1)

[0052] where Y A , Y B and Y C are the system A, B, C phase-to-ground admittance respectively. If the system zero sequence voltage is zero, the injected current is:

[0053] (2)

[0054] Substitute equation (2) into equation (1), if the injected current I Z is shown in equation (2), the system zero sequence voltage will also be zero.

[0055] If the three-phase-to-ground parameter asymmetry suppression adopts the voltage suppression method, that is, the zero sequence voltage is controlled to be zero, and the flexible grounding protection device is delayed to be put into operation after the ground fault occurs, the injected current I ZU of the flexible grounding protection device and the fault point current I f are respectively:

[0056] (3)

[0057] If the ground fault resistance R f is small, the fault point current and the injected current of the flexible grounding protection device are both large, which may cause overcurrent.

[0058] If the three-phase-to-ground parameter asymmetry suppression adopts the current suppression method, that is, the zero sequence asymmetric current I bd is injected into the power distribution network, and the flexible grounding protection device is delayed to be put into operation after the ground fault occurs, the injected current I ZI of the flexible grounding protection device is:

[0059] (4)

[0060] At this time, if it is a low-resistance ground fault, the zero sequence voltage U0 is close to the negative value of the fault phase power supply voltage, that is, -E A , but the total ground admittance Y0 of the power distribution system is much smaller than 1 / R f , so the fault point current and the injected current of the flexible grounding protection device are both small, and overcurrent will not be generated.

[0061] The application also provides a single-phase ground fault selection method for a power distribution network based on asymmetric current flexible compensation, specifically, the flexible grounding protection device injects I bd into the system, after the ground fault occurs, the phase difference of A, B, C phase voltages ΨU A , ΨU B , ΨU C and the phase (ΨU0-90°) is compared, wherein the phase with the smallest difference is the fault phase, and ΨU0 is the phase of the system zero sequence voltage, and the principle is specifically as follows:

[0062] By Figure 2 and Kirchhoff's current law, after grounding fault:

[0063] (5)

[0064] Where Y0 is the total ground admittance of the system, R f is the grounding fault transition resistance, U f is the ground voltage of the fault phase. Substituting equation (2) into equation (5), after arranging, we get:

[0065] (6)

[0066] Where R f is the resistance, Y0=1 / r0+jωC0, and 1 / r0 is much smaller than ωC0, so Y0 is mainly capacitive, that is, the admittance is the main component. Therefore, after the grounding fault flexible grounding protection device injects I bd into the system, the fault phase voltage U f phase ΨU f and (ΨU0-90°) are in phase, and accordingly the grounding fault phase can be identified. Specifically:

[0067] By measuring the three-phase voltage phase and the zero-sequence voltage phase, and according to the equation ΨU f = (ΨU0-90°), the fault phase voltage phase can be calculated, and the value is independent of the size of the grounding fault resistance. Finally, the calculated ΨU f phase and the measured three-phase voltage phase ΨU A , ΨU B , ΨU C are subtracted and the absolute value is taken, that is:

[0068] (7)

[0069] The phase with the smallest difference value is the fault phase, and the criteria for the fault phase being A phase, B phase and C phase are respectively:

[0070] (8)

[0071] In order for those skilled in the art to better understand the technical solutions of the present application, the present application will be further introduced in combination with a simulation example.

[0072] A power distribution network simulation model containing 6 feeder lines as shown in Figure 3 is built by using PSCAD / EMTDC software. The power distribution line adopts Bergeron model. Among them, feeder 6 is a three-phase ground parameter asymmetric line, so that the system asymmetry degree is about 4.0%.

[0073] right Figure 3 The flexible grounding distribution network shown has a fault point at fault point 12. Three-phase ground parameter asymmetry is set from 0.03s, and from 0.1s to 0.2s, the voltage method is used to suppress the three-phase ground parameter asymmetry, controlling the zero-sequence voltage to zero. The output current of the flexible grounding protection device during this period is measured as the asymmetric current. From 0.2s to 0.4s, the current method is used to suppress the three-phase ground parameter asymmetry. From 0.3s to 0.4s, a ground fault occurs, and three-phase ground parameter asymmetry current compensation is performed, along with ground fault phase selection. From 0.4s to 0.5s, the voltage method is used to suppress the ground fault. Simulation results for low-resistance 50 ohms and high-resistance 5000 ohms ground faults in phases A, B, and C are as follows. Figures 4-6 As shown in the figure. The simulation results show that the proposed method can select the ground fault phase regardless of whether the resistance is high or low.

[0074] In this embodiment, during normal grid operation, the system's zero-sequence voltage is controlled to the target value through a flexible grounding protection device, and the asymmetrical current I of the system's three-phase ground parameters is accurately measured. bd Subsequently, a compensation current of equal and opposite magnitude is actively injected into the system to eliminate the influence of parameter asymmetry and create ideal conditions for subsequent phase selection. When a single-phase ground fault occurs, the phase with the smallest difference between the voltage phase of each phase and the reference phase (ΨU0-90°) is determined as the faulty phase by calculating the difference between the phase of each phase voltage and the reference phase. This embodiment overcomes the interference of system asymmetry on the accuracy of phase selection through active flexible compensation, solves the problems of slow response speed and overcurrent risk in the single-phase ground fault phase selection method of distribution network, and significantly improves the reliability and safety of ground fault phase selection.

[0075] Compared with the prior art, the present invention has the following beneficial effects:

[0076] 1. This invention takes into account the influence of three-phase ground parameter asymmetry, and compared with traditional ground fault phase selection methods, it has higher phase selection accuracy and stronger anti-interference capability. This invention injects a signal before the ground fault and performs ground fault phase selection immediately after the ground fault. Compared with methods that inject signals twice after the ground fault for ground fault phase selection, this invention has the advantage of faster response speed.

[0077] 2. This invention injects a three-phase ground parameter asymmetrical current into the distribution network before a ground fault, and selects the ground fault phase based on the zero-sequence voltage and the three-phase voltage phase. Compared to controlling the zero-sequence voltage, this invention eliminates the risk of overcurrent and offers higher safety.

[0078] Based on the same inventive concept, the present application further provides a computer device, comprising: one or more processors, and a memory for storing one or more computer programs; the program comprises program instructions, and the processor is configured to execute the program instructions stored in the memory. The processor can be a central processing unit (CPU), and can also be other general-purpose processors, digital signal processors (DSP), application specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc., which are the computing core and control core of the terminal, and are configured to implement one or more instructions, and are specifically configured to load and execute one or more instructions in the computer storage medium to implement the above method.

[0079] It needs to be further explained that, based on the same inventive concept, the present application further provides a computer storage medium, which stores a computer program, and the computer program is executed by the processor to perform the above method. The storage medium can adopt any combination of one or more computer readable media. The computer readable medium can be a computer readable signal medium or a computer readable storage medium. The computer readable storage medium may, for example, be but is not limited to an electrical, magnetic, optical, infrared, or semiconductor system, device or apparatus, or any combination of the above. More specific examples (non-exhaustive list) of the computer readable storage medium include: an electrical connection with one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. In the present application, the computer readable storage medium can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, device or apparatus.

[0080] It should be noted that, unless otherwise defined, technical terms or scientific terms used in the present application shall have the common meaning understood by one of ordinary skill in the art to which the present application pertains. The terms "first", "second", and similar terms used in the present application do not denote any order, quantity, or importance, but are used to distinguish different components. The terms "comprise", "comprising", and similar terms mean that the elements or objects before the term encompass the elements or objects listed after the term and their equivalents, and do not exclude other elements or objects. The terms "connected" or "connected" and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The terms "upper", "lower", "left", "right", and the like are used only to represent relative positional relationships, and when the absolute positions of the described objects are changed, the relative positional relationships can also be changed accordingly.

[0081] The above description is only the preferred embodiments of the present application, and is not intended to limit the present application in other forms. Any person skilled in the art can modify or change the above-mentioned disclosed technology into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change, and modification of the above-mentioned embodiments made without departing from the technical solution of the present application, and in accordance with the technical essence of the present application, shall still fall within the protection scope of the present application.

[0082] The present application is not limited to the above-mentioned preferred embodiments, and anyone can derive other various forms of a single-phase grounding fault phase selection method for an asymmetric current active compensation power distribution network under the inspiration of the present application. Any equivalent change and modification made in accordance with the scope of the present application shall fall within the scope of the present application.

Claims

1. A method for single-phase earth fault phase selection of an electric power distribution network with asymmetric current active compensation, characterized in that, The method comprises the following steps: When the power distribution network is in normal operation and no ground fault occurs, the flexible grounding protection device is controlled to adjust the output so that the zero sequence voltage of the power distribution system tends to be zero, and the three-phase-to-ground parameter asymmetric current flowing through the flexible grounding protection device is measured as a reference current; Subsequently, the flexible grounding protection device is controlled to continuously inject a compensation current into the power distribution system, the compensation current having an equal magnitude and opposite direction to the reference current, so as to suppress the zero sequence voltage caused by the three-phase-to-ground parameter asymmetry; When a single-phase ground fault occurs in the power distribution network, the zero sequence voltage and the phase voltage of each phase of the current system are detected and obtained, a reference phase is determined based on the phase of the zero sequence voltage, the phase difference absolute value between the phase of each phase voltage and the phase of the reference phase is calculated, and the phase with the minimum phase difference absolute value is determined as the ground fault phase; The specific method for determining the reference phase is to obtain the phase of the zero sequence voltage of the current system, and to obtain the reference phase by subtracting 90° from the phase.

2. The single-phase-to-ground fault phase selection method of the power distribution network with asymmetric current active compensation according to claim 1, characterized in that: The specific way of controlling the flexible grounding protection device to adjust the output so that the zero sequence voltage of the power distribution system tends to be zero is to take the zero sequence voltage of the power distribution system as a control target, to adopt a closed-loop control algorithm with zero sequence voltage deviation as a feedback quantity, to collect the zero sequence voltage signal in real time and to calculate the deviation from zero, to adjust the output parameters of the flexible grounding protection device, and to continue until the magnitude of the zero sequence voltage is less than a preset threshold.

3. The single-phase ground fault selection method of the power distribution network with asymmetric current active compensation according to claim 1, characterized in that: The flexible grounding protection device comprises a split-phase switch, a power electronic converter, and a control system electrically connected to the power electronic converter; the split-phase switch and the power electronic converter are connected in series, and the series connection is connected between the phase line and the ground of the power distribution system; The power electronic converter is a single-phase H-bridge converter, a single-phase half-bridge converter, or a single-phase output circuit formed by topology reconstruction of a three-phase converter.

4. The single-phase-to-ground fault phase selection method of the power distribution network with asymmetric current active compensation according to claim 1, characterized in that: The specific control method of controlling the flexible grounding protection device to continuously inject a compensation current into the power distribution system, the compensation current having an equal magnitude and opposite direction to the three-phase-to-ground parameter asymmetric current, is to continuously inject the compensation current after measuring the three-phase-to-ground parameter asymmetric current; during the injection process, the zero sequence voltage of the power distribution system is monitored in real time, and if the magnitude of the zero sequence voltage exceeds a preset threshold, the magnitude or phase of the compensation current is adjusted so that the zero sequence voltage returns to the threshold.

5. The single-phase-to-ground fault phase selection method of an unbalanced current active compensation power distribution network according to claim 1, characterized in that: The magnitude and direction of the compensation current are determined based on the measured three-phase-to-ground parameter asymmetric current.

6. The single-phase-to-ground fault phase selection method of an unbalanced current actively compensated distribution network according to claim 1, characterized in that: When a high-resistance ground fault occurs in the power distribution network, the accuracy of the phase difference absolute value calculation is ensured by the following method: when detecting the zero sequence voltage and the phase voltage of each phase, a filtering algorithm is used to eliminate the interference of the voltage signal, and then the phase of the voltage is extracted through a phase-locked loop.

7. The single-phase-to-ground fault phase selection method of an unbalanced current actively compensated distribution network according to claim 1, characterized in that: The specific way of measuring the three-phase-to-ground parameter asymmetric current flowing through the flexible grounding protection device is to collect the zero sequence current signal of the ground path through the current sensor built in the flexible grounding protection device, the zero sequence current signal corresponding to the three-phase-to-ground parameter asymmetric current.

8. An asymmetrical current active compensation power distribution network single-phase ground fault phase selection system, characterized in that, The method comprises the following steps: The flexible grounding protection device comprises a phase separation switch, a power electronic converter and a control system, the phase separation switch and the power electronic converter are connected in series between a phase line and ground of a power distribution system; a parameter measurement module, configured to adjust the output of the flexible grounding protection device in cooperation with the flexible grounding protection device when the power distribution network is in normal operation and no grounding fault occurs, so that the zero sequence voltage of the power distribution system tends to be zero, and to measure the three-phase parameter asymmetric current flowing through the flexible grounding protection device at this time; a compensation control module, configured to control the flexible grounding protection device to continuously inject a compensation current into the power distribution system, the compensation current having an equal magnitude and opposite direction to the three-phase parameter asymmetric current, so as to suppress the zero sequence voltage caused by the three-phase parameter asymmetry; a fault phase selection module, configured to detect and obtain the zero sequence voltage and the phase voltage of each phase of the current system when a single-phase grounding fault occurs in the power distribution network, determine a reference phase based on the phase of the zero sequence voltage, calculate the phase difference absolute value between the phase of each phase voltage and the reference phase, and determine the phase with the minimum phase difference absolute value as the grounding fault phase. 9.A non-transitory computer-readable storage medium having stored thereon a computer program. The computer program is executed by a processor to implement the method of any one of claims 1-7.

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