DC distribution network backup protection method and system based on current time domain integral

Abstract

The present invention discloses a DC distribution network backup protection method and system based on current time-domain integral, belonging to the field of power systems and automation technology. The present invention comprises: obtaining historical fault data of a medium-voltage flexible DC distribution protection system; determining the time-domain characteristics of the fault current based on the fault data; and constructing a current time-domain integral based on the fault current time-domain characteristics; constructing a differential protection criterion based on the current time-domain integral; obtaining fault data of the medium-voltage flexible DC distribution protection system; judging the fault data based on the differential protection criterion; and executing a protection action based on the judgment result. The present invention has a low computational complexity, low sampling frequency requirements, and is easy to implement.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems and automation thereof, and more particularly to a backup protection method and system for a DC distribution network based on current time-domain integral. Background Art

[0002] With the development of energy storage and distributed generation technologies and the widespread application of DC loads, flexible DC distribution networks are adapting to the needs of smart distribution networks and the energy internet. However, unlike DC transmission systems, flexible DC distribution systems have variable operating modes and complex fault characteristics. After a DC short-circuit fault, transient current changes extremely rapidly and has a large peak value. If the fault is not isolated in time, it will cause significant impact and damage to system components. Due to the short DC line sections of DC distribution networks, the characteristics of faults at the end of the line and those outside the area are similar. Especially when the line shorts through a transition resistor, the fault characteristics are difficult to capture. Therefore, existing AC system protection and flexible DC transmission protection are difficult to directly apply to DC distribution networks.

[0003] Existing flexible DC system protection methods can be categorized as single-terminal and multi-terminal protection, depending on the local fault information utilized. Single-terminal electrical quantity protection relies on time delays to ensure protection selectivity, eliminating the need for communication. However, this approach suffers from poor responsiveness. Furthermore, single-terminal electrical quantity protection, such as overcurrent protection, is susceptible to the effects of transition resistance and system operation. Multi-terminal protection research primarily focuses on dual-terminal protection. While communication-based dual-terminal protection offers high selectivity, it lacks sensitivity for high-resistance faults. Summary of the Invention

[0004] In response to the above problems, the present invention proposes a DC distribution network backup protection method based on current time domain integral, comprising:

[0005] Acquire historical fault data of a medium voltage flexible direct current distribution protection system, determine a time domain characteristic of a fault current based on the fault data, and construct a time domain integral of a current based on the time domain characteristic of the fault current;

[0006] constructing a differential protection criterion based on the current time-domain integral;

[0007] Fault data of the medium voltage flexible direct current distribution protection system is acquired, the fault data is judged based on the differential protection criterion, and a protection action is executed based on the judgment result.

[0008] Optional, fault current time domain characteristics, including:

[0009] When a fault occurs in a line area of ​​the medium voltage flexible DC power distribution protection system, the fault component currents on the M side and the N side of the line area both flow toward the fault point, and the current fault component on the M side of the line and the current fault component on the N side of the line are both positive;

[0010] If a fault occurs at point F1 outside the rectifier area within the line area, the current mutation at the head end of the line will be negative, and the current mutation at the end end will be positive;

[0011] If a fault occurs at point F5 outside the inverter side area within the line area, the current mutation amount at the head end of the line is positive, and the current mutation amount at the end end is negative.

[0012] Optionally, the expression for the current time domain integral is as follows:

[0013]

[0014]

[0015] Where: Δi M (k), Δi N (k) is the current sudden change on the M and N sides of the line at time k, T w is the data window length, i DCM (t) is the time domain integral of the current on the M side of the line at time t, i DCN (t) is the time domain integral of the current on the N side of the line at time t.

[0016] Optional, the expression of differential protection criterion is as follows:

[0017] i h +i l >|ki h -i l |+i set

[0018] Among them, i h is the larger of the time domain integrals of the current on the M and N sides of the line, i l is the smaller of the time domain integrals of the current on the M and N sides of the line, i set is the fixed threshold value and k is the scaling factor.

[0019] Optionally, protection actions are performed based on the judgment result, including:

[0020] when i h +i l >|ki h -i l |+i set When it is determined to be an internal fault, the protection is activated;

[0021] when i h +i l <|ki h -i l |+i set When the fault occurs, it is judged as an out-of-zone fault and the protection does not operate.

[0022] In another aspect, the present invention further proposes a DC distribution network backup protection system based on current time domain integral, comprising:

[0023] An initialization module is configured to obtain historical fault data of a medium voltage flexible DC power distribution protection system, determine a time domain characteristic of a fault current based on the fault data, and construct a time domain integral of a current based on the time domain characteristic of the fault current;

[0024] A criterion module, configured to construct a differential protection criterion based on the current time-domain integral;

[0025] The action execution module is used to obtain fault data of the medium voltage flexible DC distribution protection system, judge the fault data based on the differential protection criterion, and execute a protection action based on the judgment result.

[0026] Optional, fault current time domain characteristics, including:

[0027] When a fault occurs in a line area of ​​the medium voltage flexible DC power distribution protection system, the fault component currents on the M side and the N side of the line area both flow toward the fault point, and the current fault component on the M side of the line and the current fault component on the N side of the line are both positive;

[0028] If a fault occurs at point F1 outside the rectifier area within the line area, the current mutation at the head end of the line will be negative, and the current mutation at the end end will be positive;

[0029] If a fault occurs at point F5 outside the inverter side area within the line area, the current mutation amount at the head end of the line is positive, and the current mutation amount at the end end is negative.

[0030] Optionally, the expression for the current time domain integral is as follows:

[0031]

[0032]

[0033] Where: Δi M (k), Δi N (k) is the current sudden change on the M and N sides of the line at time k, T w is the data window length, i DCM (t) is the time domain integral of the current on the M side of the line at time t, i DCN (t) is the time domain integral of the current on the N side of the line at time t.

[0034] Optional, the expression of differential protection criterion is as follows:

[0035] i h +i l >|ki h -i l |+i set

[0036] Among them, i h is the larger of the time domain integrals of the current on the M and N sides of the line, i l is the smaller of the time domain integrals of the current on the M and N sides of the line, i set is the fixed threshold value and k is the scaling factor.

[0037] Optionally, protection actions are performed based on the judgment result, including:

[0038] when i h +i l >|ki h -i l |+i set When it is determined to be an internal fault, the protection is activated;

[0039] when i h +i l <|ki h -i l |+i set When the fault occurs, it is judged as an out-of-zone fault and the protection does not operate.

[0040] In yet another aspect, the present invention further provides a computing device comprising: one or more processors;

[0041] a processor for executing one or more programs;

[0042] When the one or more programs are executed by the one or more processors, the above-described method is implemented.

[0043] In another aspect, the present invention further provides a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed, the method described above is implemented.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The present invention provides a DC distribution network backup protection method based on current time-domain integrals, comprising: obtaining historical fault data from a medium-voltage flexible DC distribution protection system; determining the time-domain characteristics of the fault current based on the fault data; and constructing a current time-domain integral based on the fault current time-domain characteristics; constructing a differential protection criterion based on the current time-domain integral; obtaining fault data from the medium-voltage flexible DC distribution protection system; judging the fault data based on the differential protection criterion; and executing a protection action based on the judgment result. The present invention requires little computation, has low sampling frequency requirements, and is easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a flow chart of the method of the present invention;

[0047] Figure 2 A schematic diagram of a DC line fault in a flexible DC distribution network according to an embodiment of the method of the present invention;

[0048] Figure 3 Schematic diagram of the correct action of the fault protection in the forward zone according to the embodiment of the method of the present invention;

[0049] Figure 4 Schematic diagram of the correct operation of the reverse out-of-zone fault protection in an embodiment of the method of the present invention;

[0050] Figure 5 This is a schematic diagram of the correct operation of the forward out-of-zone fault protection according to an embodiment of the method of the present invention;

[0051] Figure 6 It is a structural diagram of the system of the present invention. DETAILED DESCRIPTION

[0052] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to provide a thorough and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments shown in the accompanying drawings is not intended to limit the present invention. In the accompanying drawings, identical elements are denoted by the same reference numerals.

[0053] Unless otherwise specified, the terms used herein (including technical terms) have the meanings commonly understood by those skilled in the art. In addition, it is understood that terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0054] Example 1:

[0055] The present invention proposes a backup protection method for DC distribution network based on current time domain integral. Figure 1 Shown, including:

[0056] Step 1: Acquire historical fault data of a medium voltage flexible DC power distribution protection system, determine a time domain characteristic of a fault current based on the fault data, and construct a time domain integral of a current based on the time domain characteristic of the fault current;

[0057] Step 2: constructing a differential protection criterion based on the current time domain integral;

[0058] Step 3: Acquire fault data of the medium voltage flexible DC distribution protection system, judge the fault data based on the differential protection criterion, and execute a protection action based on the judgment result.

[0059] Among them, the time domain characteristics of the fault current include:

[0060] When a fault occurs in a line area of ​​the medium voltage flexible DC power distribution protection system, the fault component currents on the M side and the N side of the line area both flow toward the fault point, and the current fault component on the M side of the line and the current fault component on the N side of the line are both positive;

[0061] If a fault occurs at point F1 outside the rectifier area within the line area, the current mutation at the head end of the line will be negative, and the current mutation at the end end will be positive;

[0062] If a fault occurs at point F5 outside the inverter side area within the line area, the current mutation amount at the head end of the line is positive, and the current mutation amount at the end end is negative.

[0063] Among them, the expression of the current time domain integral is as follows:

[0064]

[0065]

[0066] Where: Δi M (k), Δi N (k) is the current sudden change on the M and N sides of the line at time k, T w is the data window length, i DCM (t) is the time domain integral of the current on the M side of the line at time t, i DCN (t) is the time domain integral of the current on the N side of the line at time t.

[0067] Among them, the expression of the differential protection criterion is as follows:

[0068] i h +i l >|ki h -i l |+i set

[0069] Among them, i h is the larger of the time domain integrals of the current on the M and N sides of the line, i l is the smaller of the time domain integrals of the current on the M and N sides of the line, i set is the fixed threshold value and k is the scaling factor.

[0070] The protection action is executed based on the judgment result, including:

[0071] when i h +i l >|ki h -i l |+i set When it is determined to be an internal fault, the protection is activated;

[0072] when i h +i l <|ki h -i l |+i set When the fault occurs, it is judged as an out-of-zone fault and the protection does not operate.

[0073] The present invention will be further described below with reference to specific cases of the present invention:

[0074] The specific implementation steps are as follows:

[0075] 1. Determine the time domain characteristics of the fault current:

[0076] According to the provisions on the positive direction of current in relay protection, the positive direction of current on each side is from the busbar to the line. Figure 2 As shown in the figure, when a fault occurs, due to the characteristic of the capacitive current discharging toward the fault point, the fault component currents on both sides flow toward the fault point, so the fault component of the current on the M side and the fault component of the current on the N side of the line are both positive, that is, △i M >0,△i N >0. When the fault occurs at point F1 outside the rectifier area, the current at the head end of the line will suddenly change to negative △i M <0, and the terminal current mutation is positive △i N >0. When F5 fault occurs outside the inverter side of the line, the sudden change of the current at the head end of the line is positive △i M >0, and the terminal current mutation is negative △i N <0. According to the transient characteristics of this fault, a new principle of longitudinal protection based on transient current mutation can be constructed.

[0077] 2. Construct the current time domain integral:

[0078] As the fault progresses, the current mutation gradually increases. In order to further highlight the characteristics of the post-fault current mutation, the fault component current calculated value at a single sampling moment is amplified, and the current mutation calculated value within a time window is integrated to extract the fault characteristics. The current time domain integral is constructed, and the expression is as follows:

[0079]

[0080]

[0081] Where: Δi M (k), Δi N (k) is the sudden change in the current on the M and N sides at time k, which is defined as the current at time k minus the load current at a certain moment before the fault; T w is the data window length; i DCM (t) is the time domain integral of the current on the M side at time t; iDCN (t) is the time domain integral of the N-side current at time t, which is the current time and the time T before w The sum of all calculated values ​​of the fault component current on this side within the time is accumulated.

[0082] When there is an internal fault in the line, the time domain integrals of the currents on both sides are positive; when there is an external fault in the line, the signs of the time domain integrals of the currents on both sides are opposite.

[0083] 3. Structural protection criteria:

[0084] According to the magnitude of the time domain integral of the current on the M side and the N side, i is defined as h is the larger of the time domain integrals of the currents on both sides, i l For the smaller one.

[0085]

[0086]

[0087] Using the characteristics of the time domain integral of the current at both ends of the line when there is a fault inside or outside the line area, the differential protection criterion is constructed as follows:

[0088] i h +i l >|ki h -i l |+i set (5)

[0089] Where i set is a fixed threshold value, and k is a proportional coefficient.

[0090] i h +i l is the operating current, |ki h -i l | is the braking current, |k h -i l |+i set is the action threshold value, comparing the size of the action amount and the braking amount. When i h +i l >|ki h -i l |+i set When i h +i l <|ki h -i l |+i set When it is judged as an out-of-zone fault, the protection does not operate. Its specific actions are as follows: Figure 3-5 As shown, Figure 3As shown in the figure, the protection for the fault in the forward zone is correctly operated. When a metallic bipolar short circuit fault occurs at the midpoint F3 of the DC line, the fault in the zone is determined to have occurred 0.4ms after the protection is started, and the circuit breaker operates to isolate the fault. Figure 4 As shown in the figure, the protection for faults outside the reverse zone is correctly operated. When a metallic bipolar short circuit fault occurs at the outlet F1 of converter 1, the protection is reliable and does not operate. Figure 5 As shown in FIG. 1 , the protection for the fault outside the forward zone operates correctly. When a metallic bipolar short circuit fault occurs at the outlet F5 of converter 3, the protection does not operate reliably.

[0091] This invention, targeting medium-voltage flexible DC power distribution systems, utilizes the difference in the time-domain integral of fault currents within and outside the zone to construct a fault identification criterion. This solution can reliably identify metallic faults within the zone within 0.4ms and short-circuit faults across a 20Ω transition resistor within the zone within 1.3ms.

[0092] Compared with the existing solutions, the solution of the present invention has the following advantages:

[0093] (1) Using two-terminal electrical quantities to form protection, and using the accumulated fault characteristics within a short time window, it can quickly identify metallic and high-resistance faults in the area.

[0094] (2) The protection is constructed by using fault current calculation, which has small calculation amount, low sampling frequency requirement and is easy to implement.

[0095] Example 2:

[0096] The present invention also proposes a DC distribution network backup protection system 200 based on current time domain integral quantity, such as Figure 6 Shown, including:

[0097] Initial module 201 is used to obtain historical fault data of the medium voltage flexible DC power distribution protection system, determine the time domain characteristics of the fault current based on the fault data, and construct the current time domain integral based on the time domain characteristics of the fault current;

[0098] A criterion module 202 is configured to construct a differential protection criterion based on the current time domain integral;

[0099] The action execution module 203 is configured to obtain fault data of the medium voltage flexible DC power distribution protection system, judge the fault data based on the differential protection criterion, and execute a protection action based on the judgment result.

[0100] Among them, the time domain characteristics of the fault current include:

[0101] When a fault occurs in a line area of ​​the medium voltage flexible DC power distribution protection system, the fault component currents on the M side and the N side of the line area both flow toward the fault point, and the current fault component on the M side of the line and the current fault component on the N side of the line are both positive;

[0102] If a fault occurs at point F1 outside the rectifier area within the line area, the current mutation at the head end of the line will be negative, and the current mutation at the end end will be positive;

[0103] If a fault occurs at point F5 outside the inverter side area within the line area, the current mutation amount at the head end of the line is positive, and the current mutation amount at the end end is negative.

[0104] Among them, the expression of the current time domain integral is as follows:

[0105]

[0106]

[0107] Where: Δi M (k), Δi N (k) is the current sudden change on the M and N sides of the line at time k, T w is the data window length, i DCM (t) is the time domain integral of the current on the M side of the line at time t, i DCN (t) is the time domain integral of the current on the N side of the line at time t.

[0108] Among them, the expression of the differential protection criterion is as follows:

[0109] i h +i l >|ki h -i l |+i set

[0110] Among them, i h is the larger of the time domain integrals of the current on the M and N sides of the line, i l is the smaller of the time domain integrals of the current on the M and N sides of the line, i set is the fixed threshold value and k is the scaling factor.

[0111] The protection action is executed based on the judgment result, including:

[0112] when i h +i l >|ki h -i l |+i set When it is determined to be an internal fault, the protection is activated;

[0113] when i h +i l <|ki h -i l |+i set When the fault occurs, it is judged as an out-of-zone fault and the protection does not operate.

[0114] The present invention has small calculation amount, low sampling frequency requirement and is easy to implement.

[0115] Example 3:

[0116] Based on the same inventive concept, the present invention also provides a computer device, which includes a processor and a memory, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or may 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 gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding function, so as to implement the steps of the method in the above embodiment.

[0117] Example 4:

[0118] Based on the same inventive concept, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It can be understood that the computer-readable storage medium here can include both built-in storage media in the computer device and, of course, extended storage media supported by the computer device. The computer-readable storage medium provides a storage space that stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space. These instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the steps of the method in the above embodiment.

[0119] It will be understood by those skilled in the art that the embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention 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 code. The solutions in the embodiments of the present invention may be implemented in various computer languages, for example, the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0120] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, 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 produce 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 flowcharts and / or block diagrams. 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.

[0121] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work 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 The function specified in one or more boxes.

[0122] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0123] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0124] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A DC distribution network backup protection method based on current time domain integral, characterized in that: The DC distribution network backup protection method comprises: Acquire historical fault data of a medium voltage flexible direct current distribution protection system, determine a time domain characteristic of a fault current based on the fault data, and construct a time domain integral of a current based on the time domain characteristic of the fault current; constructing a differential protection criterion based on the current time-domain integral; Acquire fault data of the medium voltage flexible DC distribution protection system, judge the fault data based on the differential protection criterion, and execute a protection action based on the judgment result; The expression of the current time domain integral is as follows: Where: Δi M (k), Δi N (k) is the current sudden change on the M and N sides of the line at time k, T w is the data window length, i DCM (t) is the time domain integral of the current on the M side of the line at time t, i DCN (t) is the time domain integral of the current on the N side of the line at time t; The expression of the differential protection criterion is as follows: in h +i l >|to h -i l |+i set Among them, i h is the larger of the time domain integrals of the current on the M and N sides of the line, i l is the smaller of the time domain integrals of the current on the M and N sides of the line, i set is the fixed threshold value and k is the scaling factor.

2. The DC distribution network backup protection method according to claim 1, characterized in that: The time domain characteristics of the fault current include: When a fault occurs in a line area of ​​the medium voltage flexible DC power distribution protection system, the fault component currents on the M side and the N side of the line area both flow toward the fault point, and the current fault component on the M side of the line and the current fault component on the N side of the line are both positive; If a fault occurs at point F1 outside the rectifier area within the line area, the current mutation at the head end of the line will be negative, and the current mutation at the end end will be positive; If a fault occurs at point F5 outside the inverter side area within the line area, the current mutation amount at the head end of the line is positive, and the current mutation amount at the end end is negative.

3. The DC distribution network backup protection method according to claim 1, characterized in that: The performing of the protection action based on the judgment result includes: when i h +i l >|ki h -i l |+i set When it is determined to be an internal fault, the protection is activated; when i h +i l <|ki h -i l |+i set When the fault occurs, it is judged as an out-of-zone fault and the protection does not operate.

4. A DC distribution network backup protection system based on current time domain integral, characterized in that: The DC distribution network backup protection system includes: An initialization module is configured to obtain historical fault data of a medium voltage flexible DC power distribution protection system, determine a time domain characteristic of a fault current based on the fault data, and construct a time domain integral of a current based on the time domain characteristic of the fault current; A criterion module, configured to construct a differential protection criterion based on the current time-domain integral; an action execution module, configured to obtain fault data of the medium voltage flexible DC distribution protection system, judge the fault data based on the differential protection criterion, and execute a protection action based on the judgment result; The expression of the current time domain integral is as follows: Where: Δi M (k), Δi N (k) is the current sudden change on the M and N sides of the line at time k, T w is the data window length, i DCM (t) is the time domain integral of the current on the M side of the line at time t, i DCN (t) is the time domain integral of the current on the N side of the line at time t; The expression of the differential protection criterion is as follows: in h +i l >|to h -i l |+i set Among them, i h is the larger of the time domain integrals of the current on the M and N sides of the line, i l is the smaller of the time domain integrals of the current on the M and N sides of the line, i set is the fixed threshold value and k is the scaling factor.

5. The DC distribution network backup protection system according to claim 4, characterized in that: The time domain characteristics of the fault current include: When a fault occurs in a line area of ​​the medium voltage flexible DC power distribution protection system, the fault component currents on the M side and the N side of the line area both flow toward the fault point, and the current fault component on the M side of the line and the current fault component on the N side of the line are both positive; If a fault occurs at point F1 outside the rectifier area within the line area, the current mutation at the head end of the line will be negative, and the current mutation at the end end will be positive; If a fault occurs at point F5 outside the inverter side area within the line area, the current mutation amount at the head end of the line is positive, and the current mutation amount at the end end is negative.

6. The DC distribution network backup protection system according to claim 4, characterized in that: The performing of the protection action based on the judgment result includes: when i h +i l >|ki h -i l |+i set When it is determined to be an internal fault, the protection is activated; when i h +i l <|ki h -i l |+i set When the fault occurs, it is judged as an out-of-zone fault and the protection does not operate.

7. A computer device, characterized in that: include: one or more processors; a processor for executing one or more programs; When the one or more programs are executed by the one or more processors, the method according to any one of claims 1 to 3 is implemented.

8. A computer-readable storage medium, characterized in that A computer program is stored thereon, and when the computer program is executed, the method according to any one of claims 1 to 3 is implemented.

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