Active distribution network protection method, system and storage medium based on harmonic injection

Abstract

The protection method, system and storage medium of the active distribution network based on harmonic injection divide the interconnection lines between the grid-connected buses in the distribution network into regions, each region includes two grid-connected distributed power sources; obtain the operating parameters of the region, if the operating parameters of the region meet the harmonic current injection criterion, then determine that a fault occurs in the region, use the two grid-connected distributed power sources in the region as harmonic injection sources, and provide two harmonic currents of different orders respectively; detect the amplitude of each harmonic current at both ends of the interconnection line between the buses in the region; use the difference in the amplitude of any two harmonic currents at both ends of the interconnection line as the protection action amount, when the protection action amount meets the protection setting criterion, then determine that the interconnection line has an in-region fault, trigger the line protection action, when the protection action amount does not meet the protection setting criterion, then determine that the interconnection line has an out-of-region fault, and the line protection does not act. The present invention improves the efficiency of active distribution network protection.

Description

Technical Field

[0001] The present invention belongs to the technical field of active distribution network protection, and in particular relates to a protection method, system and storage medium for an active distribution network based on harmonic injection. Background Art

[0002] With the large-scale integration of renewable energy, the access mode dominated by inverter-type distributed power sources has greatly changed the operating characteristics of the distribution network. In particular, the distribution and fault characteristics of short-circuit current have become more complex, which poses a severe challenge to traditional protection strategies. The rapid development of power electronics technology has provided new ideas for coping with this challenge. Among them, the method of fault detection and location using harmonic signal injection has shown certain potential.

[0003] In the prior art, the current value of the target protection device in the target active distribution network is obtained, and when the current value is greater than the current setting value, the protection action is triggered; wherein, the process of obtaining the current setting value is: according to the provisions of the national standard on the low voltage ride-through process of IIDG, a positive sequence current injection calculation model is created; according to the instantaneous power theory, the positive sequence current injection calculation model is used to determine the negative sequence current injection calculation model; according to the boundary conditions of the target active distribution network failure, the node voltage method is used to determine the voltage equation of each node; according to the positive sequence current injection calculation model, the negative sequence current injection calculation model and the voltage equation, the branch current of each node is calculated by the iteration method; according to the positive sequence current injection calculation model, the negative sequence current injection calculation model and the voltage equation, the current setting value of the target protection device in the target active distribution network is calculated according to the branch current, so as to shorten the protection action response time. The ground fault protection and system used for active distribution network collects the instantaneous value of the three-phase voltage at the busbar on the power supply side of the active distribution network with preset sampling time and sampling frequency, synthesizes the three-phase voltage into the zero-sequence voltage of the active distribution network node, and determines the per-unit value of the zero-sequence voltage. If the per-unit value is greater than the preset threshold value, the zero-sequence voltage is filtered to obtain the instantaneous value matrix of the zero-sequence voltage; based on the instantaneous value matrix, the energy value of the zero-sequence voltage is determined, and based on the energy value, a zero-sequence voltage energy array is generated, and it is determined whether there is a fault potential line or a fault line in the active distribution network according to the zero-sequence voltage energy array; according to the preset criterion, the protection action is executed for the fault potential line or the fault line that is determined to exist, which provides important conditions for the safe and reliable operation of the distribution network. However, the existing technology does not take into account the possible problems that may exist during harmonic injection: first, the power quality problems that may be caused by the comprehensive injection of harmonics, especially in the system with densely connected distributed power sources. The extensive injection of harmonics will significantly affect the power quality of the power grid and is not conducive to the stable operation of the system; second, the protection reliability problem under the partial injection strategy, especially when the harmonic injection point is far away from the fault point, because the harmonic amplitude is small compared to the fundamental wave and the detection device has inherent errors, the harmonic signal may be attenuated or submerged by noise during the transmission process, which will cause the protection device to refuse to operate, that is, it is impossible to identify and isolate the fault in a timely and accurate manner. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the present invention provides a protection method, system and storage medium for an active distribution network based on harmonic injection, so as to further improve the efficiency of active distribution network protection and make the protection have stronger adaptability.

[0005] The present invention adopts the following technical solution.

[0006] The present invention proposes a protection method for an active distribution network based on harmonic injection, wherein the active distribution network includes a plurality of distributed power sources, including:

[0007] The interconnection lines between the grid-connected buses in the distribution network are divided into regions, each region including two grid-connected distributed power sources;

[0008] The operating parameters of the region are obtained, including the fundamental current on the system side and the load side of the region, the rated voltage of the distributed power source and the grid connection point voltage; if the operating parameters of the region meet the harmonic current injection criteria, it is determined that a fault has occurred in the region, and the two grid-connected distributed power sources in the region are used as harmonic injection sources to provide two harmonic currents of different orders respectively;

[0009] The amplitude of each harmonic current at both ends of the tie line between the busbars in the detection area; the difference in the amplitude of any two harmonic currents at both ends of the tie line is taken as the protection action amount. When the protection action amount meets the protection setting criterion, it is determined that the tie line has an in-area fault and the line protection action is triggered. When the protection action amount does not meet the protection setting criterion, it is determined that the tie line has an out-of-area fault and the line protection does not act.

[0010] Preferably, the distributed power source included in each area is an inverter-type distributed power source.

[0011] Preferably, the harmonic current provided by each harmonic injection source satisfies the following constraints:

[0012] 1) The frequency of harmonic current shall not exceed 10 times of the power frequency;

[0013] 2) When the harmonic current is injected every second and lasts for 0.1 second, if the power grid is operating normally, the harmonic current injection will stop; if the power grid is abnormal, the harmonic current injection will continue until the protection device is activated;

[0014] 3) Take 10% of the rated current of the inverter of the harmonic injection source as the amplitude of the harmonic current.

[0015] Preferably, when a harmonic injection source provides Subharmonic currents, another source of harmonic injection provides When subharmonic current occurs, the protection setting criteria are as follows:

[0016] ,

[0017] In the formula, To protect the amount of action; , One end of the line and the other end The amplitude of subharmonic current; , One end of the line and the other end The amplitude of subharmonic current; It is the protection action setting value.

[0018] Preferably, when it is determined that a fault occurs in the interconnection line, the interconnection lines at both ends are Subharmonic current amplitude and The harmonic current amplitudes under subharmonics satisfy the following relationships:

[0019] ,

[0020] When it is determined that a fault occurs in the tie line, the protection action quantity determined based on harmonic injection is Greater than 0.

[0021] Preferably, when it is determined that an out-of-area fault occurs on the tie line, the two ends of the tie line Subharmonic current amplitude and The harmonic current amplitudes under subharmonics satisfy the following relationships:

[0022] ,

[0023] Therefore, when it is determined that an out-of-area fault occurs in the tie line, the operating current determined based on harmonic injection is 0.

[0024] Preferably, the protection action setting value is not less than 10% of the harmonic current amplitude.

[0025] Preferably, within the region, under the same harmonic order, if the difference in the amplitude of the harmonic currents flowing from the two grid-connected buses to the fault point is greater than 0 and it is determined to be an intra-regional fault, then the fault type is determined to be correctly identified;

[0026] In the region, under the same harmonic order, if the difference in the harmonic current amplitudes of the two grid-connected buses flowing to the fault point is 0 and it is determined to be an out-of-region fault, then the fault type is determined to be correctly identified;

[0027] Otherwise, it is determined that the fault type is incorrectly identified and an alarm signal is sent.

[0028] The present invention also provides a protection system for an active distribution network based on harmonic injection, wherein the active distribution network includes a plurality of distributed power sources, including:

[0029] A zone division module is used to divide the interconnection lines between the grid-connected buses in the distribution network into zones, each zone including two grid-connected distributed power sources;

[0030] The harmonic current injection control module is used to obtain the operating parameters of the area, including the fundamental current on the system side and the load side of the area, the rated voltage of the distributed power source and the grid connection point voltage; if the operating parameters of the area meet the harmonic current injection criteria, it is determined that a fault has occurred in the area, and the two grid-connected distributed power sources in the area are used as harmonic injection sources to provide two harmonic currents of different orders respectively;

[0031] The protection action trigger module is used to detect the amplitude of each harmonic current at both ends of the tie line between the busbars in the area; the difference in the amplitude of any two harmonic currents at both ends of the tie line is used as the protection action amount. When the protection action amount meets the protection setting criterion, it is determined that the tie line has an in-area fault and the line protection action is triggered. When the protection action amount does not meet the protection setting criterion, it is determined that the tie line has an out-of-area fault and the line protection does not act.

[0032] Preferably, it also includes: a protection action verification module, which is used for, within the area, under the same harmonic order, if the difference in the harmonic current amplitudes of the two grid-connected busbars flowing to the fault point is greater than 0 and it is determined to be an intra-area fault, then the fault type is determined to be correctly identified; within the area, under the same harmonic order, if the difference in the harmonic current amplitudes of the two grid-connected busbars flowing to the fault point is 0 and it is determined to be an out-of-area fault, then the fault type is determined to be correctly identified; otherwise, it is determined that the fault type is incorrectly identified and an alarm signal is sent.

[0033] A terminal comprises a processor and a storage medium; the storage medium is used to store instructions; the processor is used to operate according to the instructions to execute the steps of the method.

[0034] A computer-readable storage medium stores a computer program, which implements the steps of the method when executed by a processor.

[0035] The beneficial effect of the present invention is that, compared with the prior art, the present invention at least includes: according to the structure of the entire network, the present invention divides the active distribution network into regions, thereby selecting suitable distributed power sources as harmonic injection sources, adjusting the harmonic current injection criteria by the fundamental current and voltage information at both ends of each region, and putting forward requirements for the frequency, amplitude and duration of the injected harmonic current, which not only solves the power quality problems that may be caused by all the injections when there are too many distributed power sources, but also avoids the fault refusal problem caused by the distance between the fault point and the harmonic injection source. The selected harmonic injection source injects harmonics of different frequencies, analyzes the harmonic current amplitude characteristics between each bus, and obtains the setting criteria for line protection, thereby judging whether the line is faulty. Compared with the traditional distribution network protection, the efficiency of active distribution network protection can be further improved, and it has stronger adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a flow chart of the active distribution network protection method based on harmonic injection proposed by the present invention;

[0037] Figure 2 A topological structure and area division diagram of an active power distribution network in an embodiment of the present invention;

[0038] Figure 3An equivalent circuit diagram of a harmonic current provided by a harmonic injection source in an embodiment of the present invention;

[0039] Figure 4 An equivalent circuit diagram under harmonic current provided by another harmonic injection source in an embodiment of the present invention;

[0040] Figure 5 4 is a protection action current diagram of the interconnection line BC in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only embodiments of a part of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0042] The present invention provides a protection method for an active distribution network based on harmonic injection, wherein the active distribution network includes a plurality of distributed power sources, such as Figure 1 As shown, including:

[0043] Step 1, dividing the tie lines between the grid-connected buses in the distribution network into regions, each region including two grid-connected distributed power sources;

[0044] In the embodiment, the structure of the distribution network changes after the distributed power sources are connected to the grid. According to the location of the distributed power sources in the active distribution network, the interconnection lines between the grid-connected busbars in the distribution network are divided into regions according to the principle that every two grid-connected distributed power sources are divided into one region. When a fault is detected in the region, the two grid-connected distributed power sources are used as harmonic injection sources.

[0045] In an embodiment, the distributed power source included in each area is an inverter-type distributed power source.

[0046] Step 2, obtaining the operating parameters of the area, including the fundamental current on the system side and the load side of the area, the rated voltage of the distributed power source and the grid connection point voltage; if the operating parameters of the area meet the harmonic current injection criteria, it is determined that a fault has occurred in the area, and the two grid-connected distributed power sources in the area are used as harmonic injection sources to provide two harmonic currents of different orders respectively.

[0047] Specifically, the harmonic current injection criteria are as follows:

[0048] ,

[0049] In the formula, It is the minimum value of the grid connection point voltage of distributed power sources in a region; is the rated voltage of distributed power sources in a region; For Region The amplitude of the fundamental current on the system side; For Region The amplitude of the fundamental current on the load side; is the number of regions.

[0050] The topology of the active distribution network is as follows: Figure 2 As shown, is the system side power supply, are all locations where the system fails, CB1, CB2, CB3, CB4, CB5, and CB6 are all circuit breakers, Ld represents the load, IIDG1, IIDG2, and IIDG3 are all inverter-type distributed power sources, and A, B, C, and D are all grid-connected buses. For the network structure of the distribution network containing distributed power sources, every two inverter-type distributed power sources are divided into one area. When a fault is detected in the area, the two inverter-type distributed power sources are used as harmonic injection sources. Figure 2 The distribution network model shown in the figure divides the tie lines of bus A and bus B, bus B and bus C between IIDG1 and IIDG2 into area 1, and the tie lines of bus C and bus D between IIDG2 and IIDG3 into area 2. If a short circuit fault occurs in area 1, since the overcurrent amplitude of the inverter-type distributed power source will not exceed 1.2-2.0 times the rated current, which is much smaller than the short-circuit current provided by the system voltage, the ratio of the fundamental current amplitude detected by the protection device at CB1 and the protection device at CB4 will be much greater than 1, while the current amplitude ratio detected by the protection device at CB5 and the protection device at CB6 is close to 1. At this time, IIDG1 and IIDG2 are used as harmonic injection sources.

[0051] In the embodiment, a harmonic injection criterion is constructed according to the sudden changes of fundamental current and voltage of each line to determine whether harmonic injection is required. After the harmonic injection source injects harmonics of different frequencies into the system, a protection criterion is constructed according to the amplitude characteristics of the harmonic current.

[0052] Specifically, the harmonic current provided by each harmonic injection source satisfies the following constraints:

[0053] 1) The frequency of harmonic current shall not exceed 10 times of the power frequency;

[0054] In a network, when the frequency of the current increases, the equivalent reactance in the network will also increase accordingly, which means that if a branch fails, especially a fault characterized by transition resistance, its performance will be more obvious. However, too high a frequency is not without cost, it may shorten the life of power equipment. In addition, in order to ensure that the current is not hindered when passing through the filter of the distributed power source, that is, it does not exceed the highest frequency it is designed to handle, the frequency of the harmonic current is usually controlled to less than 10 times the power frequency to ensure the stable operation of the system.

[0055] 2) When the harmonic current is injected every second and lasts for 0.1 second, if the power grid is operating normally, the harmonic current injection will stop; if the power grid is abnormal, the harmonic current injection will continue until the protection device is activated;

[0056] Injecting harmonic currents into the power grid is essentially a small-scale disturbance test used to evaluate the state of the power grid. Therefore, the duration of this process needs to be carefully designed. If the injection time is too short, it may not fully reflect the problems of the power grid; if the time is too long, it may cause unnecessary interference to the power grid. This can be done according to the following strategy: try to inject a harmonic signal once a second, and if the power grid behaves normally, stop the injection after 0.1 seconds; once an abnormality is detected, continue to inject the harmonic signal until the protection mechanism of the power grid is triggered, so as to respond and solve the problem in time.

[0057] 3) Take 10% of the rated current of the inverter of the harmonic injection source as the amplitude of the harmonic current;

[0058] In order to ensure that the harmonic current can be effectively identified by the protection equipment in the power grid, a sufficiently high amplitude needs to be set. However, too high an amplitude may also have an adverse effect on the power quality of the power grid. Considering that the harmonic current of this method is only injected briefly when an abnormality occurs in the power grid, a relatively safe amplitude can be selected, that is, 10% of the rated current of the inverter of the distributed power source. This setting can ensure that the harmonic current is effectively detected and minimize the impact on the normal operation of the power grid.

[0059] Step 3, detect the amplitude of each harmonic current at both ends of the tie line between the busbars in the area; take the difference between the amplitudes of any two harmonic currents at both ends of the tie line as the protection action amount. When the protection action amount meets the protection setting criterion, it is determined that the tie line has an in-area fault and the line protection action is triggered. When the protection action amount does not meet the protection setting criterion, it is determined that the tie line has an out-of-area fault and the line protection does not act.

[0060] Specifically, when a harmonic injection source provides Subharmonic currents, another source of harmonic injection provides When sub-harmonic current occurs, the protection setting criteria are as follows:

[0061] ,

[0062] In the formula, To protect the amount of action; , One end of the line and the other end The amplitude of subharmonic current; , One end of the line and the other end The amplitude of subharmonic current; It is the protection action setting value.

[0063] When a fault occurs in the interconnection line, Figure 2 In When a fault occurs, IIDG1 injects Subharmonic current, IIDG2 injection Subharmonic current. The equivalent circuit under subharmonic current is as follows Figure 3 As shown, in The equivalent circuit under subharmonic current is as follows Figure 4 As shown. Among them, and They are Subharmonic voltage and Subharmonic voltage; and They are Subharmonics and The equivalent impedance of the system side power supply under subharmonics, and They are Equivalent impedance and sum of inverter-type distributed power supply under subharmonics The equivalent impedance of the inverter-type distributed power source under subharmonics, the equivalent impedance of the inverter-type distributed power source in the embodiment is the same, and They are Subharmonics and The equivalent impedance of the interconnection line between bus A and the fault point under subharmonics is: and They are Subharmonics and The equivalent impedance of the interconnection line between the fault point and busbar B under subharmonics is: and They are Subharmonics and The equivalent impedance of the interconnection line between bus B and bus C under subharmonics is: and They are Subharmonics and The equivalent impedance of the interconnection line between bus C and bus D under subharmonics; is the fault resistance; and The flow from bus A to the fault point is Subharmonic current and Subharmonic current, and The flow from bus B to the fault point is Subharmonic current and Subharmonic current.

[0064] When a fault occurs within the area, bus A flows to the fault point. The subharmonic current satisfies the following relationship:

[0065] ,

[0066] in, .

[0067] ,

[0068] Due to the fault resistance Much smaller than the equivalent impedance and load impedance of the inverter-type distributed power supply, that is, ,get .

[0069] Bus B flows to the fault point The subharmonic current satisfies the following relationship:

[0070] ,

[0071] in, .

[0072] ,

[0073] Due to the fault resistance Much smaller than the equivalent impedance of the inverter-type distributed power source and the equivalent impedance of the system-side power source, we get .

[0074] When an out-of-zone fault occurs, either Subharmonics or Subharmonics, the fault currents at both ends of line AB are approximately equal, that is, .

[0075] Therefore, when a fault is determined, the magnitude relationship of the harmonic current amplitudes flowing from the two grid-connected buses in the area to the fault point is used to verify whether the fault type is correctly identified, including:

[0076] In the region, under the same harmonic order, if the difference in the harmonic current amplitudes of the two grid-connected buses flowing to the fault point is greater than 0 and it is determined to be an internal fault, then the fault type is determined to be correctly identified;

[0077] In the region, under the same harmonic order, if the difference in the harmonic current amplitudes of the two grid-connected buses flowing to the fault point is 0 and it is determined to be an out-of-region fault, then the fault type is determined to be correctly identified;

[0078] Otherwise, it is determined that the fault type is incorrectly identified and an alarm signal is sent.

[0079] The present invention not only proposes a distribution network protection action triggering method based on harmonic injection, but also proposes a protection action triggering verification method based on the characteristics of the harmonic current provided by each bus to the fault point under different types of faults, thereby improving the reliability of the protection action.

[0080] Specifically, when it is determined that a fault occurs in the interconnection line, the Subharmonic current amplitude and The harmonic current amplitudes under subharmonics satisfy the following relationships:

[0081] ,

[0082] Therefore, when it is determined that a fault occurs in the tie line, the protection action quantity determined based on harmonic injection is Greater than 0.

[0083] Specifically, when it is determined that an out-of-area fault occurs on the tie line, the Subharmonic current amplitude and The harmonic current amplitudes under subharmonics satisfy the following relationships:

[0084] ,

[0085] Therefore, when it is determined that an out-of-area fault occurs in the tie line, the operating current determined based on harmonic injection is 0.

[0086] In the embodiment, the protection action setting value is not less than 10% of the harmonic current amplitude.

[0087] The distribution network protection action triggering method based on harmonic injection proposed in the present invention can not only effectively identify the fault type and trigger the protection action in time, but also has a corresponding protection action triggering verification mechanism, which helps to reduce the protection setting value in the dual mode, thereby improving the sensitivity and accuracy of the protection action.

[0088] To verify the effectiveness of the above method, this embodiment establishes a corresponding simulation model in the electromagnetic transient simulation software PSCAD, so as to study various application scenarios of the active distribution network in subsequent experiments. Figure 2 The 20kV distribution network with distributed generation DG is shown in the figure, where the impedance per unit length of the overhead line of the distribution network is 0.1504+j0.3228 . The length of interconnection line AB is 3km, and the lengths of interconnection lines BC and CD are both 6km. The active power of the load is 0.27MW, and its power factor is 0.87. The distributed power source is photovoltaic, and the harmonic frequencies injected by IIDG1~IIDG3 are 400HZ, 300HZ and 400HZ (when a fault is detected, only two IIDGs inject harmonics, as long as the harmonic frequencies injected by the two IIDGs are different). The amplitude of the injected harmonic current is 100A. According to the setting principle, the protection action setting value Take 0.01kA.

[0089] The simulations were performed for different fault locations and fault types, with the fault duration being 1s and the fault resistance being set to 0.1 , the distance from the busbar position is 50%. Figure 5 For When a three-phase short circuit occurs, the protection action value of the interconnection line BC. Figure 5 It is known that When a fault occurs, the protection action value set according to formula (2) can act quickly and reliably when a fault occurs. Table 1 shows the protection action when various short circuit types occur at different fault locations.

[0090] Table 1 Protection action for different fault types

[0091]

[0092] According to the simulation results, no matter which line fails, we can get the same The same conclusion is reached when short circuit occurs. According to the protection criteria proposed by the present invention, normal operation can be achieved.

[0093] Then, taking the interconnection line BC as an example, the different fault resistances under various fault types are simulated, including three-phase short circuit, two-phase grounding and two-phase short circuit. The protection action results are shown in Table 2. It can be seen that when the fault resistance changes, the protection can be reliably operated regardless of the fault type. The action current decreases as the fault resistance increases.

[0094] Table 2 Protection action at different fault impedances

[0095]

[0096] The present invention also provides a protection system for an active distribution network based on harmonic injection, wherein the active distribution network includes a plurality of distributed power sources, including:

[0097] A zone division module is used to divide the tie lines between the grid-connected buses in the distribution network into zones, each zone including two grid-connected distributed power sources;

[0098] The harmonic current injection control module is used to obtain the operating parameters of the area, including the fundamental current on the system side and the load side of the area, the rated voltage of the distributed power source and the grid connection point voltage; if the operating parameters of the area meet the harmonic current injection criteria, it is determined that a fault has occurred in the area, and the two grid-connected distributed power sources in the area are used as harmonic injection sources to provide two harmonic currents of different orders respectively;

[0099] The protection action trigger module is used to detect the amplitude of each harmonic current at both ends of the tie line between the busbars in the area; the difference in the amplitude of any two harmonic currents at both ends of the tie line is used as the protection action amount. When the protection action amount meets the protection setting criterion, it is determined that the tie line has an in-area fault and the line protection action is triggered. When the protection action amount does not meet the protection setting criterion, it is determined that the tie line has an out-of-area fault and the line protection does not act.

[0100] Preferably, it also includes: a protection action verification module, which is used for, within the area, under the same harmonic order, if the difference in the harmonic current amplitudes of the two grid-connected busbars flowing to the fault point is greater than 0 and it is determined to be an intra-area fault, then the fault type is determined to be correctly identified; within the area, under the same harmonic order, if the difference in the harmonic current amplitudes of the two grid-connected busbars flowing to the fault point is 0 and it is determined to be an out-of-area fault, then the fault type is determined to be correctly identified; otherwise, it is determined that the fault type is incorrectly identified and an alarm signal is sent.

[0101] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0102] A computer-readable storage medium may be a tangible device that can hold and store instructions used by an instruction execution device. A computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the above. More specific examples (a non-exhaustive list) of computer-readable storage media include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure in a groove on which instructions are stored, and any suitable combination of the above. The computer-readable storage medium used herein is not to be interpreted as a transient signal itself, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted through a wire.

[0103] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0104] The computer program instructions for performing the operations of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages, such as Smalltalk, C++, etc., and conventional procedural programming languages, such as "C" language or similar programming languages. The computer-readable program instructions may be executed entirely on the user's computer, partially on the user's computer, as a separate software package, partially on the user's computer, partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., using an Internet service provider to connect through the Internet). In some embodiments, by using the state information of the computer-readable program instructions to personalize an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), the electronic circuit may execute the computer-readable program instructions, thereby implementing various aspects of the present disclosure.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A protection method for an active distribution network based on harmonic injection, wherein the active distribution network includes a plurality of distributed power sources, characterized in that: include: The interconnection lines between the grid-connected buses in the distribution network are divided into regions, each region including two grid-connected distributed power sources; Obtain the operating parameters of the region, including the fundamental current on the system side and load side of the region, the rated voltage of the distributed power source and the grid connection point voltage; If the operating parameters of the area meet the harmonic current injection criteria, it is determined that a fault has occurred in the area, and two grid-connected distributed power sources in the area are used as harmonic injection sources to provide two harmonic currents of different orders respectively; The amplitude of each harmonic current at both ends of the tie line between the busbars in the detection area; the difference in the amplitude of any two harmonic currents at both ends of the tie line is taken as the protection action amount. When the protection action amount meets the protection setting criterion, it is determined that the tie line has an in-area fault and the line protection action is triggered. When the protection action amount does not meet the protection setting criterion, it is determined that the tie line has an out-of-area fault and the line protection does not act.

2. The protection method of active distribution network based on harmonic injection according to claim 1, characterized in that: The distributed power sources included in each area are inverter-type distributed power sources.

3. The protection method of active distribution network based on harmonic injection according to claim 1, characterized in that: The harmonic current provided by each harmonic injection source meets the following constraints: 1) The frequency of harmonic current shall not exceed 10 times of the power frequency; 2) When the harmonic current is injected every second and lasts for 0.1 second, if the power grid is operating normally, the harmonic current injection will stop; if the power grid is abnormal, the harmonic current injection will continue until the protection device is activated; 3) Take 10% of the rated current of the inverter of the harmonic injection source as the amplitude of the harmonic current.

4. The protection method of active distribution network based on harmonic injection according to claim 1, characterized in that: When a harmonic injection source provides Subharmonic currents, another source of harmonic injection provides When subharmonic current occurs, the protection setting criteria are as follows: ， In the formula, To protect the amount of action; , One end of the line and the other end The amplitude of subharmonic current; , One end of the line and the other end The amplitude of subharmonic current; It is the protection action setting value.

5. The protection method of active distribution network based on harmonic injection according to claim 4, characterized in that: When determining that a fault occurs in the interconnection line, the Subharmonic current amplitude and The harmonic current amplitudes under subharmonics satisfy the following relationships: ， When it is determined that a fault occurs in the tie line, the protection action quantity determined based on harmonic injection is Greater than 0.

6. The protection method of active distribution network based on harmonic injection according to claim 4, characterized in that: When determining that an out-of-area fault occurs on the tie line, the Subharmonic current amplitude and The harmonic current amplitudes under subharmonics satisfy the following relationships: ， Therefore, when it is determined that an out-of-area fault occurs in the tie line, the operating current determined based on harmonic injection is 0.

7. The protection method of active distribution network based on harmonic injection according to claim 4, characterized in that: The protection action setting value shall not be less than 10% of the harmonic current amplitude.

8. The protection method of active distribution network based on harmonic injection according to claim 1, characterized in that: In the region, under the same harmonic order, if the difference in the harmonic current amplitudes of the two grid-connected buses flowing to the fault point is greater than 0 and it is determined to be an internal fault, then the fault type is determined to be correctly identified; In the region, under the same harmonic order, if the difference in the harmonic current amplitudes of the two grid-connected buses flowing to the fault point is 0 and it is determined to be an out-of-region fault, then the fault type is determined to be correctly identified; Otherwise, it is determined that the fault type is incorrectly identified and an alarm signal is sent.

9. A protection system for an active distribution network based on harmonic injection, the active distribution network comprising a plurality of distributed power sources, characterized in that: include: A zone division module is used to divide the tie lines between the grid-connected buses in the distribution network into zones, each zone including two grid-connected distributed power sources; The harmonic current injection control module is used to obtain the operating parameters of the region, including the fundamental current on the system side and the load side of the region, the rated voltage of the distributed power source and the grid connection point voltage; If the operating parameters of the area meet the harmonic current injection criteria, it is determined that a fault has occurred in the area, and two grid-connected distributed power sources in the area are used as harmonic injection sources to provide two harmonic currents of different orders respectively; The protection action trigger module is used to detect the amplitude of each harmonic current at both ends of the tie line between the busbars in the area; the difference in the amplitude of any two harmonic currents at both ends of the tie line is used as the protection action amount. When the protection action amount meets the protection setting criterion, it is determined that the tie line has an in-area fault and the line protection action is triggered. When the protection action amount does not meet the protection setting criterion, it is determined that the tie line has an out-of-area fault and the line protection does not act.

10. The protection system for active power distribution network based on harmonic injection according to claim 9, characterized in that: Also includes: The protection action verification module is used for within the area. If the difference in the harmonic current amplitudes of the two grid-connected busbars flowing to the fault point under the same harmonic order is greater than 0 and it is determined to be an internal fault, then the fault type is determined to be correctly identified; within the area, if the difference in the harmonic current amplitudes of the two grid-connected busbars flowing to the fault point under the same harmonic order is 0 and it is determined to be an external fault, then the fault type is determined to be correctly identified; otherwise, the fault type is determined to be incorrectly identified and an alarm signal is sent.

11. A terminal comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method according to any one of claims 1 to 8.

12. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 8 are implemented.

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