Distributed fault self-healing method and system for active distribution network, and device and medium

Abstract

The present disclosure relates to the technical field of power systems. Disclosed are a distributed fault self-healing method and system for an active distribution network, and a device and a medium. In the present disclosure, using a two-terminal waveform difference as a faulty section locating principle is applicable to an active distribution network, which contains various types of DGs and different DG permeabilities. The present disclosure has a relatively low requirement for data computation and storage regarding an STU, and topology identification and update can be automatically completed during operation by simply configuring basic static network topology information for the STU, thereby adapting to a change in the operation mode of the network. By means of the present disclosure, a rational fault recovery rule is set, and important load nodes can be recovered as much as possible while meeting a network power constraint. In a recovery solution, the presence of distributed generation is taken into consideration, and different processing methods are designed according to whether the distributed generation can operate in an island manner for a long period of time.

Description

A distributed fault self-healing method, system, device and medium for active distribution network

[0001] The present disclosure claims priority from a patent document filed on November 23, 2023, with application number 202311571411.1 and titled “A method, system, device and medium for distributed fault self-healing in an active distribution network”. The entire contents of the document are incorporated by reference into the present disclosure. Technical Field

[0002] The present disclosure relates to the technical field of power systems, and in particular to a distributed fault self-healing method, system, device, and medium for an active power distribution network. Background Art

[0003] The widespread access of distributed generation (DG) has transformed traditional distribution networks into active distribution networks (ANDs), but it has also brought new problems to the self-healing control of distribution networks. The self-healing control of distribution networks mainly includes fault section location, isolation, and fault recovery.

[0004] For fault location, the main methods include matrix methods, longitudinal methods, and intelligent algorithms. The matrix method defines a correlation matrix based on the actual distribution network structure. It is intuitive and has a clear principle. However, this method uses matrix operations to determine the fault location. When the network structure is complex, it places high demands on data storage and computation at the distribution master station. The longitudinal method, modeled after the transmission network, has the advantages of clear principles and accurate location. However, this method requires large-scale and costly modifications to distribution network equipment and places high demands on the distribution network's communication system. Intelligent algorithms primarily utilize optimization algorithms to refine the optimization objective and use the optimization results to locate the fault section of the distribution network. They are suitable for locating multiple faults in large, complex distribution networks. However, intelligent algorithms are complex, their principles are less intuitive, and they place high demands on the computing platform. The speed of fault location is closely related to the optimization speed, resulting in a long overall fault location time.

[0005] In terms of fault recovery, there are currently three methods: relying solely on DG islanding; a step-by-step approach that first uses the main distribution network to restore power, then uses DG; a step-by-step approach that first uses DG to restore power, then uses the main distribution network to restore power; and a synchronized approach that integrates DG with the main network. The DG islanding approach is suitable for situations where the main power source cannot be used for fault recovery. While the step-by-step recovery strategy maximizes DG capacity, it does not guarantee the lowest power outage losses. Synchronous recovery solutions, on the other hand, can maximize the restoration of power to the lost loads.

[0006] In terms of self-healing control models, with the advancement of fiber-optic communication and intelligent terminal technologies in distribution networks, distributed, intelligent control models that are independent of master stations will become the future trend in smart distribution networks. Distributed control models are further categorized into hierarchical coordinated control and peer-to-peer coordinated control. The hierarchical control model divides distribution network terminals into multiple tiers based on their functions, achieving fault recovery through interaction between these tiers. In the peer-to-peer coordinated control model, each agent terminal is equal, enabling independent fault recovery operations through information sharing and collaboration. Compared to centralized control models, the greatest advantage of distributed control models is their high processing speed and reduced requirements for data storage and computing power on the terminal units. However, this model also makes it difficult to implement complex fault recovery strategies, often failing to execute optimal fault recovery plans.

[0007] Summary of the Invention

[0008] The present disclosure provides a distributed fault self-healing method, system, device and medium for an active power distribution network, which solves the technical problem that it is difficult to implement complex fault recovery strategies in the existing distributed control mode and that the optimal fault recovery solution is often not executed.

[0009] A first aspect of the present disclosure provides a distributed fault self-healing method for an active distribution network, which is applied to the active distribution network. The active distribution network includes intelligent terminal units installed at each distribution node and a common coupling point of a distributed power source. The intelligent terminal units divide the active distribution network based on their own configured local topology information and distributely store static network topology information. When the network operation mode of the active distribution network changes, the static network topology information is adaptively updated to generate dynamic network topology information. The method includes:

[0010] S1. In response to receiving a fault self-healing request, determining the active distribution network corresponding to the fault self-healing request and obtaining fault current data corresponding to each intelligent terminal unit;

[0011] S2. Based on the fault current data, the Fréchet section location principle is used to locate and isolate the fault section;

[0012] S3. Based on the dynamic network topology information, distributed power supply restoration is performed on the non-fault sections.

[0013] Optionally, step S1 includes:

[0014] S11, responding to receiving a fault self-healing request, wherein the fault self-healing request is a self-healing request issued when a current mutation starting element detects a current mutation;

[0015] S12. Determine the active distribution network corresponding to the fault self-healing request, and obtain fault current data corresponding to each intelligent terminal unit.

[0016] Optionally, step S2 includes:

[0017] S21. Based on the sliding interface, calculate the Fréchet distance value of each phase line using the fault current data, wherein the Fréchet distance value is generated by a preset state transition equation;

[0018] S22, when the number of times that the Fréchet distance value is greater than the setting value is greater than a preset number threshold, determining that the section associated with the Fréchet distance value is a faulty section, wherein the setting value is generated by a preset setting value function;

[0019] S23. Control the circuit breaker associated with the fault section to trip.

[0020] Optionally, step S3 includes:

[0021] S31. When the common coupling point of the distributed generation is a type A DG node, based on the dynamic network topology information, the distributed power supply restoration strategy for the non-fault section is adopted to restore the non-fault section power supply.

[0022] S32. When the common coupling point of the distributed power generation is a type B DG node, a reclosing strategy is used to restore distributed power supply to the non-fault section based on the dynamic network topology information.

[0023] Optionally, step S31 includes:

[0024] S311. When the common coupling point of the distributed generation is a type A DG node, the intelligent terminal units of the fault nodes associated with both ends of the fault section update the adjacency relationship with the opposite end, and forward the fault information to each adjacent distribution node respectively until the distribution node where the tie switch is located or there is no adjacent distribution node;

[0025] S312. When each distributed power generation common coupling point receives fault information, it sends an island operation status instruction to each distribution node in the island area associated with each distributed power generation common coupling point, and the distribution nodes near the area boundary in the island area disconnect the corresponding load switches;

[0026] S313. When the distribution nodes where the tie switches located upstream of the fault section are located receive fault information sent by the upstream fault node, they send unavailable information to the distribution nodes that can be restored by themselves.

[0027] S314. When the distribution nodes where the tie switches located downstream of the fault section are located receive fault information sent by the downstream fault node, tie switches other than the distribution nodes where the tie switches associated with the downstream fault node are located are used to restore power to the power-lost section.

[0028] S315. Taking the receipt of the fault information sent by the downstream fault node as the timing starting point, when the power supply restoration time for the power-off area reaches the preset restoration time threshold, query the recovery status of the distribution node downstream of the downstream fault node and outside the island area, the recovery status of the adjacent distribution node, and the number of the contact switch for power restoration, and complete the corresponding switching action.

[0029] Optionally, step S314 includes:

[0030] S3141. When the distribution nodes where the tie switches downstream of the fault section are located receive fault information sent by the downstream fault node, determine whether any tie switches other than the distribution node where the tie switch associated with the downstream fault node is located have lost power. If so, read the available margin of the current tie switch and execute step S3142. If not, send the corresponding available margin to the adjacent distribution nodes and execute step S3142.

[0031] S3142: If the load associated with the distribution node receiving the available margin is less than the available margin, the distribution node is restored, the available margin is updated, and the information is forwarded to the adjacent distribution node. If the load associated with the distribution node outside the island area is greater than the updated available margin, step S3143 is executed. If the load associated with the distribution node within the island area is greater than the updated available margin, step S31410 is executed.

[0032] S3143: The distribution node outside the island area is regarded as a branch node. If there is a pure load branch in the branch where the branch node is located and the branch node can be restored by other tie switches, then step S3144 is executed; if not, then step S3145 is executed;

[0033] S3144: Determine whether the available capacity of the tie switch associated with the branch node can restore the pure load branch. If so, mark all distribution nodes in the pure load branch as recoverable nodes and restore them. Update the available capacity and forward it to the adjacent distribution nodes. Return to step S3142.

[0034] If not, the branch node is marked as a pause-restore node, the current remaining available capacity is recorded, and pause-restore information is sent to the associated tie switches. It is determined whether the other tie switches have pause-restore information. If not, step S3149 is executed for the branch node and downstream loads. If so, step S3149 is executed only for the pure load branch.

[0035] S3145: Determine whether the branch node is a pause-resume node. If so, execute step S3146; otherwise, execute step S3147.

[0036] S3146. Compare the available capacity of the tie switch associated with the current branch node with the available capacity of another tie switch recorded by the branch node, select the tie switch with the maximum available capacity for restoration, and determine whether the pure load branch can be restored. If so, mark all distribution nodes of the pure load branch as nodes that can be restored by the current tie switch. If not, execute step S3149 only for the pure load branch and traverse downstream.

[0037] S3147: Determine whether the current branch node can be restored by other tie switches of other paths. If so, execute step S3148; if not, execute step S3149.

[0038] S3148: Determine whether the current branch node has tie switch margin for other paths. If not, record the available capacity of the tie switch associated with the current branch node. When a tie switch stops recovering, execute step S3143. If it does, select the tie switch with the maximum available capacity for recovery. If recovery is possible, update the available capacity and execute step S3142. If recovery is not possible, send an available capacity shortage message to the associated tie switch.

[0039] S3149: The current distribution node is used as the root branch node. When the pause and resume node receives the information request command, it stops forwarding and sends a stop request message to the upstream root branch node. If the upstream root branch node can restore all downstream loads after traversing all downstream loads, it sends a pending restoration instruction to the distribution nodes associated with all downstream loads. If there is a pause and resume node among the distribution nodes associated with all downstream loads, the remaining capacity after restoration is sent to the pause and resume node, and step S3146 is executed.

[0040] When the power distribution node in the island area receives the information request command, step S31411 is executed;

[0041] S31410: If a distribution node in the island area receives available margin forwarded by an adjacent distribution node outside the island area, the node determines the number of adjacent distribution nodes. If the number of adjacent distribution nodes is less than a preset threshold, the node does not take any action. If the number of adjacent distribution nodes is equal to the preset threshold, the node returns to step S3142. If the number of adjacent distribution nodes is greater than the preset threshold, the node returns to step S3143.

[0042] S31411. If a distribution node in the island area receives an information request command forwarded by an adjacent distribution node outside the island area, it determines the number of adjacent distribution nodes. If the number of adjacent distribution nodes is less than the preset number threshold, it sends a stop request message to the root branch node. If the number of adjacent distribution nodes is equal to the preset number threshold, the distributed power supply common coupling point forwards the information request command to the adjacent distribution node. If the number of adjacent distribution nodes is greater than the preset number threshold, it sends downstream branch point information to the root branch node and sends an information request command to the adjacent distribution node.

[0043] Optionally, step S315 includes:

[0044] S3151. Taking the receipt of fault information sent by the downstream fault node as the timing starting point, when the power supply restoration time for the power outage area reaches a preset restoration time threshold, query the restoration status of the distribution node downstream of the downstream fault node and outside the island area, the restoration status of the adjacent distribution node, and the number of the tie switch performing power restoration;

[0045] S3152: Disconnect the load switch associated with the distribution node whose recovery state is not restored;

[0046] S3153. Disconnect the load switches between two adjacent distribution nodes whose recovery status is restored but which are restored by different tie switches.

[0047] Optionally, step S32 includes:

[0048] S321. When the common coupling point of the distributed generation is a type B DG node, a voltage check is performed on the upstream feeder of the fault section. If no voltage exists, a reclosing command is issued.

[0049] S322. If the reclosing instruction is to reclose to a permanent fault, and the upstream intelligent terminal unit of the fault section detects a secondary overcurrent, the associated circuit breaker is disconnected and a closing instruction is sent to the intelligent terminal unit at the tie switch until the intelligent terminal unit at the tie switch meets the closing conditions and then closes the circuit breaker;

[0050] S323. If the reclosing instruction is for a transient fault, the upstream intelligent terminal unit of the fault section sends a reclosing success message to the downstream intelligent terminal unit of the fault section;

[0051] S324. When the downstream intelligent terminal unit of the fault section receives the reclosing success information, a voltage-free operation is performed on the downstream feeder of the fault section. If the distributed power source common coupling point associated with the downstream intelligent terminal unit is in an out-of-operation state, a reclosing instruction is generated.

[0052] S325. If there is voltage on the downstream feeder, perform synchronization check on the downstream intelligent terminal unit and close the circuit breaker after the grid connection conditions are met.

[0053] A second aspect of the present disclosure provides an active distribution network distributed fault self-healing system, which is applied to the active distribution network. The active distribution network includes intelligent terminal units installed at each distribution node and the common coupling point of the distributed power source. The intelligent terminal units divide the active distribution network based on their own configured local topology information and distributely store static network topology information. When the network operation mode of the active distribution network changes, the static network topology information is adaptively updated to generate dynamic network topology information. The system includes:

[0054] a response module configured to, in response to receiving a fault self-healing request, determine an active power distribution network corresponding to the fault self-healing request and obtain fault current data corresponding to each intelligent terminal unit;

[0055] The positioning and isolation module is configured to locate and isolate the fault section based on the fault current data using the Fréchet section positioning principle;

[0056] The power supply restoration module is configured to perform distributed power supply restoration on non-fault sections based on dynamic network topology information.

[0057] A third aspect of the present disclosure provides an electronic device, comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the active distribution network distributed fault self-healing method as described in any one of the above items.

[0058] A fourth aspect of the present disclosure provides a computer-readable storage medium having a computer program stored thereon, which, when executed, implements the distributed fault self-healing method for an active power distribution network as described in any one of the above items.

[0059] It can be seen from the above technical solutions that the present disclosure has the following advantages:

[0060] 1. The present disclosure uses the difference in two-terminal waveforms as the fault section location principle, which can be adapted to active distribution networks containing multiple DG types and different DG penetration rates.

[0061] 2. The present disclosure has low requirements for STU data calculation and storage. It only needs to configure basic static network topology information for STU, and topology identification and update can be automatically completed during operation to adapt to changes in the distribution network operation mode.

[0062] 3. This disclosure sets reasonable fault recovery rules to restore as many important load nodes as possible while meeting the power constraints of the distribution network. The recovery plan takes into account the existence of distributed power generation and designs different treatment methods based on whether they can operate in isolated islands for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the related technologies known to the inventors, the following briefly introduces the drawings required for use in the embodiments or the related technical descriptions known to the inventors. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0064] FIG1 is a flowchart of a method for self-healing a distributed fault in an active power distribution network provided in a first embodiment of the present disclosure;

[0065] FIG2 is a schematic diagram of an active distribution network including an STU according to a second embodiment of the present disclosure;

[0066] FIG3 is a schematic diagram of an equivalent circuit of a motor-type DG provided in the second embodiment of the present disclosure;

[0067] FIG4 is a schematic diagram of an equivalent circuit of an inverter-type DG provided in the second embodiment of the present disclosure;

[0068] FIG5 is a schematic diagram of an active distribution network provided in the second embodiment of the present disclosure;

[0069] FIG6 is a schematic diagram of the Fréchet principle provided in the second embodiment of the present disclosure;

[0070] FIG7 is a flowchart of the Fréchet distance protection provided in the second embodiment of the present disclosure;

[0071] FIG8 is a schematic diagram of a local distribution network provided in the second embodiment of the present disclosure;

[0072] FIG9 is a schematic diagram of a switch status query instruction transmission sequence provided in the second embodiment of the present disclosure;

[0073] FIG10 is a schematic diagram of a local distribution network including a type A DG provided in the second embodiment of the present disclosure;

[0074] FIG11 is a target network diagram provided by Example 2 of the present disclosure;

[0075] FIG12 is a structural block diagram of an active distribution network distributed fault self-healing system provided in the third embodiment of the present disclosure. DETAILED DESCRIPTION

[0076] The embodiments of the present disclosure provide a distributed fault self-healing method, system, device and medium for an active distribution network, which are used to solve the technical problems that it is difficult to implement complex fault recovery strategies in the existing distributed control mode and the optimal fault recovery solution is often not executed.

[0077] In order to make the purpose, features, and advantages of the invention disclosed herein more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0078] The present disclosure provides a distributed fault self-healing method for an active power distribution network, and formulates corresponding fault section location, isolation and fault recovery methods;

[0079] 1. Analyze the fault current characteristics of the active distribution network and propose the Fréchet section location principle based on the comparison of the waveform differences of two-terminal quantities according to the fault characteristics;

[0080] 2. Based on the Fréchet section location principle, a fault section location and isolation solution is constructed using a distributed control model;

[0081] 3. Construct reclosing strategy and power supply restoration strategy for non-fault sections based on restoration objectives, constraints, restoration ideas, and distributed power supply processing methods.

[0082] Please refer to FIG1 , which is a flowchart of the steps of a distributed fault self-healing method for an active power distribution network provided in a first embodiment of the present disclosure.

[0083] The present disclosure provides a distributed fault self-healing method for an active distribution network, which is applied to the active distribution network. The active distribution network includes intelligent terminal units installed at each distribution node and the common coupling point of distributed power sources. The intelligent terminal units divide the active distribution network based on their own configured local topology information and distributely store static network topology information. When the network operation mode of the active distribution network changes, the static network topology information is adaptively updated to generate dynamic network topology information. The method includes:

[0084] S1. In response to receiving a fault self-healing request, determining an active power distribution network corresponding to the fault self-healing request and obtaining fault current data corresponding to each intelligent terminal unit.

[0085] The fault self-healing request refers to the self-healing request issued by the current sudden change starting element when it detects a current sudden change in the active distribution network.

[0086] In an embodiment of the present disclosure, in response to receiving a self-healing request issued by a current mutation starting element when detecting a current mutation in an active distribution network, the corresponding active distribution network is determined according to the current mutation starting element that issues the fault self-healing request, and the fault current data corresponding to each intelligent terminal unit in the active distribution network is obtained.

[0087] S2. Based on the fault current data, the Fréchet section location principle is used to locate and isolate the fault section.

[0088] In the disclosed embodiment, the acquired fault current data is used to calculate the Fréchet value of each phase through the Fréchet section location principle, the corresponding fault section is located according to the Fréchet value, and the fault section is isolated by tripping the associated circuit breaker.

[0089] S3. Based on the dynamic network topology information, distributed power supply restoration is performed on the non-fault sections.

[0090] In the embodiment of the present disclosure, after the fault section is located and isolated, distributed power supply restoration is performed on the non-fault section based on the dynamic network topology information of the active power distribution network.

[0091] In this disclosure, in response to receiving a fault self-healing request, the active distribution network corresponding to the fault self-healing request is determined, and fault current data corresponding to each intelligent terminal unit is obtained. Based on the fault current data, the Fréchet segment location principle is used to locate and isolate the faulty segment. Distributed power supply restoration is then performed to non-faulty segments based on dynamic network topology information. This addresses the technical issues of existing distributed control modes, which make it difficult to implement complex fault recovery strategies and often fail to execute optimal fault recovery plans. By utilizing fault current waveform differences as a fault segment location principle, this disclosure is adaptable to active distribution networks with multiple DG types and varying DG penetration rates. When all load switches are circuit breakers, this disclosure can rapidly locate and isolate the faulty segment, and restore power to non-faulty segments. This disclosure fully considers coordination with DG anti-islanding protection and low voltage ride-through. Each STU is equipped with automatic network topology recognition, enabling it to adapt control strategies based on real-time changes in the network topology.

[0092] A second embodiment of the present disclosure provides a distributed fault self-healing method for an active distribution network, which is applied to an active distribution network. The active distribution network includes intelligent terminal units installed at each distribution node and a common coupling point of a distributed power source. The intelligent terminal units divide the active distribution network based on their own configured local topology information and distributely store static network topology information. When the network operation mode of the active distribution network changes, the static network topology information is adaptively updated to generate dynamic network topology information. The method includes:

[0093] S1. In response to receiving a fault self-healing request, determining an active power distribution network corresponding to the fault self-healing request and obtaining fault current data corresponding to each intelligent terminal unit.

[0094] A Smart Terminal Unit (STU) is a protection unit with independent data processing capabilities and the ability to autonomously control switching operations. These units are capable of peer-to-peer communication based on various communication networks. Distributed fault self-healing involves fault location, isolation, and recovery in a distributed control mode independent of a master station. This distributed fault self-healing solution offers flexible operation, with each protection device utilizing only local information from the entire network to function. STUs with peer-to-peer communication capabilities can also identify local or global network topologies, adapting their operating modes and fault self-healing strategies in real time based on varying network status.

[0095] It's important to note that distributed control relies on smart terminal units (STUs) installed at various distribution nodes and distributed power generation points of common coupling (PCCs). STUs are protection units with independent data processing capabilities and the ability to autonomously control switch actions. They can communicate peer-to-peer over various communication networks. As shown in Figure 2, STUs are installed in various ring main units in the distribution network and can control the opening and closing of local switches. The color of the switch in the figure represents the switch's opening and closing status: black represents closed, and white represents open.

[0096] The active distribution network consists of multiple sections, each of which is composed of adjacent STUs. For example, in Figure 2, STU4 and STU5 form a section, designated as Section 1; STU5 and STU6 form a section, designated as Section 2. If a fault occurs in Section 1, it is considered an internal fault for STU4 and STU5, and an external fault for STU5 and STU6. The terms "internal" and "external" refer to the protected section formed by adjacent STUs.

[0097] The prerequisites for implementing this solution are summarized as follows:

[0098] 1) In order to minimize the scope of power outage and avoid the distributed power supply from continuously injecting short-circuit current into the fault section after a fault, switches are installed at both ends of each section, and all switches are circuit breakers.

[0099] 2) Each STU can independently control the opening and closing of local circuit breakers.

[0100] 3) Each STU has strong current and voltage data acquisition, storage and calculation capabilities.

[0101] 4) Each STU can be interconnected through the communication network.

[0102] Furthermore, step S1 includes:

[0103] S11, responding to receiving a fault self-healing request, wherein the fault self-healing request is a self-healing request issued when a current mutation starting element detects a current mutation;

[0104] S12. Determine the active distribution network corresponding to the fault self-healing request, and obtain fault current data corresponding to each intelligent terminal unit.

[0105] In an embodiment of the present disclosure, in response to receiving a fault self-healing request, wherein the fault self-healing request is a self-healing request issued when a current mutation starting element detects a current mutation, the active distribution network corresponding to the fault self-healing request is determined, and the fault current data corresponding to each intelligent terminal unit is obtained.

[0106] S2. Based on the fault current data, the Fréchet section location principle is used to locate and isolate the fault section.

[0107] It should be noted that in order to design the section location method, it is necessary to analyze the fault current characteristics of the active distribution network. There are two main types of power sources in the active distribution network: motor-type DG and inverter-type DG.

[0108] Generally speaking, the motor-type DG can be equivalent to a power supply with a large internal resistance, and its equivalent circuit is shown in Figure 3. is the electromotive force of the motor type DG, and its phase is not much different before and after the fault; Z dg The impedance of the motor type DG is generally 4-5 times that of the system power supply; is the fault current output by the motor type DG. The voltage phase at the motor type DG access point is also basically unchanged, so the voltage phases at points M and N are still not much different after the fault. Then, the short-circuit current provided by the main power supply and the motor type DG is and The angle that lags behind the voltage at the power access point is the impedance angle of the line. and The phase difference is not large, and the amplitude is related to the internal resistance of the power supply and the distance between the power supply and the fault point.

[0109] The characteristics of the fault current output by the inverter type DG after a fault are relatively complex, mainly related to the control characteristics of the inverter. Generally, the fault current amplitude is between 1 and 1.2 times the rated current. The equivalent circuit of the inverter type DG is shown in Figure 4. In Figure 4, It is the inverter type DG short-circuit current that is not limited by amplitude; Z dg It is the equivalent impedance of DG, which is used to limit the maximum short-circuit current; It is the short-circuit current limited by amplitude. For the short-circuit current of inverter type DG The reactive current Iq and active current I d They are:

[0110] Where, I q is the reactive current amplitude, u1 is the per-unit value of the positive sequence voltage amplitude at the DG grid connection point, I N is the amplitude of the DG output rated current; I d is the active current amplitude, P N is the rated active power of DG, u is the positive sequence voltage of DG grid connection point, I max is the amplitude of the maximum output current of DG, which can be 1.2 times I N .

[0111] Then, the short-circuit current of the inverter DG is The amplitude I m and phase They are:

[0112] According to the above formula, the magnitude of the fault current output by an inverter-type DG must not exceed 1.2 times the rated current, and its magnitude is related to the voltage drop at the grid connection point. The fault current phase lags behind the voltage phase at the grid connection point, and the degree of lag is also related to the voltage drop.

[0113] For fault section location, the fault current characteristics of the active distribution network are analyzed. According to the fault characteristics, a section location method based on the comparison of the difference between the two-terminal waveforms is proposed as follows: As shown in Figure 5, Figure 5 is a schematic diagram of the active distribution network. Under normal conditions and out-of-zone fault conditions, the current flowing through the line is a through-type current. and Approximately equal; when a fault occurs in the area, Provided by the main power supply, its value is very large, generally much larger than the load current. When the DG is an inverter type distributed power source, the fault current provided by the DG The amplitude is often small and the phase angle is controlled; when the DG is a motor-type distributed power source, the short-circuit current output by the DG is large and the phase angle is subject to certain fluctuations. and There will be huge differences in amplitude and phase angle. Therefore, a comprehensive comparison can be made using an algorithm. and The protection principle is constructed based on the amplitude and phase difference. The present disclosure adopts the Fréchet distance metric and The amplitude and phase difference of

[0114] The protection principle based on fault current waveform differences is simple and reliable. However, its introduction into distribution networks requires addressing two major challenges: data synchronization and communication channels. With the ongoing development of distribution automation, distribution communication networks have begun to take shape, addressing the communication channel issue. When a fault occurs at a point in a line, a protection device at one end detects the sudden change in current and immediately requests data from the other end to determine the waveform difference. Synchronization only requires considering communication delay, which is negligible given the short length of distribution lines. The Fréchet distance algorithm employed is also less affected by communication delay, thus addressing synchronization issues. The Fréchet segment location principle is illustrated in Figure 6. It uses a metric to determine an optimal distance value, which represents the degree of difference between two trajectories. Assume that two points v and m depart along their respective trajectories V and M at velocities α(t) and β(t), respectively. The infimum of the maximum distance between them is the Fréchet distance, t∈[0,1]. Its mathematical definition is as follows.

[0115] Where: V is the trajectory of point v; M is the trajectory of point m; V(α(t)) represents the position of point v at time t; M(β(t)) represents the position of point m at time t; d represents the distance between the two points under a certain measurement method; inf is the infimum.

[0116] At a certain moment t0, time window T w Take two sets of sinusoidal AC signals A and B with different amplitudes and phase angles as an example to explain specifically. A and B can be expressed as follows:

[0117] Where: M represents the amplitude; w is the signal frequency; is the initial phase angle.

[0118] Consider A and B as two trajectories in space. If the sampling is synchronous and the signal is continuous, it can be considered that there are two points on the trajectory moving from the initial position at the same speed w along their respective trajectories for a time window length. The Fréchet distance between A and B is as follows:

[0119] Considering the selection of the time window, the following final expression can be obtained:

[0120] Fréchet distance directly measures the morphological characteristics of the waveform. From the above formula, we know that when T w When the frequency is greater than or equal to half a cycle, It only takes half a cycle time window to converge stably to

[0121] When the waveforms A and B are exactly the same, ΔM 12=0, The Fréchet distance is 0. When the amplitude difference between A and B is fixed, for example, ΔM 12 = 0, Fréchet distance and Similarly, when the phase angle difference between A and B is fixed, for example Fréchet distance is positively correlated with amplitude difference. When the amplitude difference and phase angle difference of waveforms A and B increase, ΔM 12 and Will increase simultaneously As it increases, the Fréchet distance increases. It's worth noting that differential protection requires currents on both sides. The trajectory of point v (A) and the trajectory of point m (B) represent the waveforms of the currents on both sides, respectively. Therefore, the Fréchet distance comprehensively measures the differences in signal amplitude and phase angle, and can more sensitively reflect changes in waveforms.

[0122] a i and b j are the original currents in the fault current data and The elements in the discrete time domain sampling sequence are n, the sequence length is n, the sampling frequency is 4kHz, and the time window is 10ms. In the specific implementation, the Fréchet distance can be solved by the following preset state transfer equation:

[0123] Where: E(i,j) represents The first i points and The shortest path between the first j points in the time domain sampling sequence.

[0124] First, generate a two-dimensional matrix E, calculate the initial condition E(1,1), calculate E(i,1) and E(1,j) based on E(1,1), and then calculate the remaining elements E(i,j) in the matrix. Finally, and The Fréchet distance between them is E(n,n), which is the lower right corner element of the two-dimensional matrix E, as shown below: Where, represents the Fréchet distance value, E(n,n) represents the value of the lower right corner element of the two-dimensional matrix;

[0125] The specific calculation process is to input the preset state transfer equation according to the fault current data and solve it. Finally, the element value of the lower right corner element of the matrix E is taken. This element value is the Fréchet distance value.

[0126] The protection principle action criteria are as follows: Where, F setis the set value.

[0127] The protection setting value comprehensively considers the influence of line unbalanced capacitance current, communication delay, mutual inductor error, and noise. The preset setting value function is specifically expressed as follows: Where: I cmax is the per-unit value of the peak capacitance current; U N is the rated line voltage of the transmission line; X c is the capacitive reactance of the transmission line; I N Indicates the rated current of the transmission line; K rel is the reliability coefficient, which can be 1.2-1.5; F n Under normal circumstances Taking into account the influence of communication delay, mutual inductor error and noise, the redundancy factor β can be set to 0.3.

[0128] The specific implementation of the above protection scheme is shown in Figure 7. Currents on both sides of the line are collected in real time, and a current mutation trigger element is used to determine the triggering criteria. If the triggering criteria are met, the current values ​​on both sides of the line for each phase are first extracted within a 10ms data window before the triggering moment. A sliding window calculation is initiated, and each sampling point within the data window is updated. Filtering and synchronous correction are then performed. The Fréchet distance of each phase is then calculated. If a phase meets the protection criteria for more than three consecutive times, it is considered an internal fault. Otherwise, it is an external fault, and the protection does not operate.

[0129] Furthermore, step S2 includes:

[0130] S21. Based on the sliding interface, calculate the Fréchet distance value of each phase line using the fault current data, wherein the Fréchet distance value is generated by a preset state transition equation;

[0131] S22, when the number of times that the Fréchet distance value is greater than the setting value is greater than a preset number threshold, determining that the section associated with the Fréchet distance value is a faulty section, wherein the setting value is generated by a preset setting value function;

[0132] S23. Control the circuit breaker associated with the fault section to trip.

[0133] In the disclosed embodiment, referring to FIG. 7 , a current mutation is detected by the activation element based on the current mutation amount. If a current mutation is detected, the fault current data of each phase of the line is extracted, and the Fréchet distance value of each phase is calculated using a sliding window. In this embodiment, the setting value can be determined based on the above-mentioned protection setting value by comprehensively considering the influence of the line unbalanced capacitance current, communication delay, mutual inductor error, and noise. When the Fréchet distance value of each phase is greater than the setting value for more than three consecutive times, it is determined to be an internal fault, and a trip signal is generated. If the number of times is less than or equal to three, it is determined to be an external fault, and the protection is restored.

[0134] In a specific implementation, steps S1 and S2 are as follows: 1) After a certain STU detects a sudden change in current and starts up, it requests fault current data from all adjacent STUs and calculates the fault current data flowing through each of its controlled switches within one cycle after the fault. The fault current data includes the real and imaginary parts of the fault current, as well as the fault current amplitude. 2) The STU that receives the fault current data request command first determines the location of the data requesting STU. Since there is a unique power distribution section between the data requesting STU and the local STU, the local STU should find the local controlled switches located in that section and then send the fault current data flowing through that switch to the data requesting STU. 3) Generally speaking, except for the beginning and end of the section, the local STU can receive fault current data sent by two or even more adjacent STUs, and the local STU can calculate multiple fault current data flowing through the local switch. The fault current data at both ends of the section should be selected for calculation to determine the faulty section. Therefore, after receiving fault current data from an adjacent STU, the local STU should select a local switch located in the section defined by the adjacent STU and itself, based on the adjacent STU's location. The fault current flowing through this switch and the fault current sent by the adjacent STU are then used to perform calculations. 4) The STU compiles the fault current data at both ends of the section and, based on the fault current sampling data on both sides, locates the section using the Fréchet section location principle proposed above in this disclosure. If the fault is within the section, the corresponding circuit breaker is tripped; otherwise, the STU is reset after a certain delay to prepare for the next possible fault. 5) If a weak feed occurs—that is, an STU downstream of the faulty section is not activated but receives a data request from an upstream STU—then the STU will send all-zero data to the other end. Regardless of the protection principle employed, the upstream STU of the faulty section will reliably determine that the fault is within the section. Furthermore, if the upstream STU detects all-zero fault current data from the downstream STU, it will send a remote trip command to the downstream STU on the weak feed side, tripping the corresponding circuit breaker to completely isolate the faulty section.

[0135] It is worth mentioning that in the judgment of the fault section, this application proposes a new Fréchet section location principle for the judgment of the fault section. The essence of the Fréchet section location principle is to compare the amplitude and phase differences of the fault current waveforms on both sides. It can be combined with current differential. As an alternative solution, the traditional current differential judgment and fault current amplitude comparison method can also be used to achieve the judgment of the fault section.

[0136] For ease of understanding, the present disclosure provides a specific application example, as shown below:

[0137] The above process is illustrated using the fault at point f1 shown in Figure 2 as an example. After the fault occurs at point f1, since power sources are present both upstream and downstream of the fault point, STUs 4 and 5 each start up and request fault current data from their adjacent STUs. Since STU4 is the feeder-end STU and its only adjacent STU is STU5, upon startup, in addition to calculating the fault current data flowing through switch K42, it only sends a fault current data request command to STU5. After receiving the data request command from STU4, STU5 determines that local switch K51 is located in the section between STU5 and STU4 and sends the fault current data flowing through switch K51 to STU4. STU4 receives the current data from STU5 and selects the fault current data flowing through switch K42 for calculation, thereby determining that the fault is located within the section and controlling circuit breaker K42 to open, isolating the faulty section. Similarly, STU5 sends fault current data requests to STU4 and STU6, respectively. It then receives the fault current data for switches K42 and K61, and uses these data in conjunction with the fault current data for switches K51 and K52 for calculations. STU5 determines that the fault is located in the section between STU4 and STU5, and trips circuit breaker K51 to isolate the fault.

[0138] STU6 detects the flow of fault current and sends a request for fault current data to neighboring STU5 and STU3. After receiving the current data flowing through switches K52 and K32, it selects the data flowing through local switches K61 and K62 for calculation. For section K52-K61, the fault current is a through-current, allowing STU6 to reliably determine that the fault is located outside the section. For section K62-K32, no short-circuit current flows, failing to reach the threshold for the proposed section location principle, thus determining that the fault is not located within that section.

[0139] It is worth mentioning that since the fault occurs in the protection section formed by STU4 and STU5, the fault is considered an internal fault for the protection section formed by STU4 and STU5; for the protection section formed by STU5 and STU6, it is considered an external fault.

[0140] It should be noted that the active distribution network includes intelligent terminal units installed at each distribution node and distributed power common coupling point. The intelligent terminal units divide the active distribution network based on their own configured local topology information and store static network topology information in a distributed manner. When the network operation mode of the active distribution network changes, the static network topology information is adaptively updated to generate dynamic network topology information.

[0141] The implementation of the disclosed fault recovery solution requires the use of network topology information. In a distributed control mode, due to the limited data storage capabilities of the STUs, it is generally impossible to configure complete global network topology information for each STU. Even if this could be configured, changes to the distribution network's grid structure would require modifying the pre-configured information in all STUs, resulting in a significant maintenance workload. Furthermore, different operating modes of the distribution network correspond to different network topologies. Therefore, the STUs must be able to acquire network topology information.

[0142] Before introducing a specific distributed fault recovery solution, the present disclosure first formulates a distributed topology information identification and storage solution. This information is formulated to meet the needs of distributed fault recovery.

[0143] 1) Static network topology information

[0144] Static network topology information is the topology information within the local range of the current STU. This information needs to be manually configured and is generally not changed. After the grid structure changes, it needs to be manually modified by the staff. Since the topology information configured in the STU is only local information, the maintenance workload is very small. During the initial configuration, the static network topology information stored in each STU is shown in Table 1. For type A DG, the node where the DG is located and the boundary node within the island should also store the topology information shown in Table 2. For the STU at the interconnecting switch, different available margin information from two power sources is generally stored. The static network topology information of this STU is shown in Table 3. The adjacency relationship in Table 1 refers to the adjacent relationship between two nodes, which can be obtained by the process of obtaining the upstream and downstream relationships between STUs in the identification and storage of dynamic network topology information.

[0145] Table 1. Static network topology information table of STU

[0146] Table 2. Information stored in the STU at the node where the A-type DG is located

[0147] Table 3. Information stored in the STU at the tie switch

[0148] 2) Identification and storage of dynamic network topology information

[0149] While the grid structure is fixed, different network operation modes correspond to different topologies, and the corresponding topology information should be updated as the topology changes. This information can be obtained during the initial operation of the STU. During subsequent operations, it should be updated periodically or after switch positions are changed to automatically adapt to changes in network operation status. Different STUs should store different types of dynamic network topology information. Generally speaking, the main types of topology information are shown in Tables 4 through 7.

[0150] Table 4 shows the upstream and downstream relationship information of adjacent STUs. Since the operation mode of the distribution network will change in real time, the upstream and downstream relationship of adjacent nodes will also change. Therefore, this information belongs to dynamic network topology information. In order for the STU to obtain the upstream and downstream relationship information, the following identification and storage scheme should be adopted: the power supply side STU first sends a switch status query instruction to its adjacent STU. After the adjacent STU receives the instruction, it marks the STU that sends the instruction to itself as the upstream STU, and the remaining adjacent STUs as downstream STUs; accordingly, for the switches controlled by the STU, if the adjacent STU of the section where a switch is located is the upstream STU, then the switch is the upstream switch, and the remaining switches are downstream switches. If all the feeder switches controlled by the STU itself are in the closed state, the switch status query instruction will continue to be forwarded to the downstream STU until the STU at the interconnecting switch is in the disconnected position or there is no adjacent STU. In the local distribution network shown in Figure 8, switch K32 is a normally open interconnecting switch, and feeder K53 is a normally open interconnecting switch. K71 is a branch feeder, and K63 is a switch at the PCC of DG1. Figure 8 illustrates the process of acquiring information about the upstream and downstream relationships of adjacent STUs in the distribution network. STU1 is the STU on the system power supply side. It sends a switch status query command to STU2. Upon receiving the query command, STU2 marks STU1 as its upstream STU and STU3 as its downstream STU. Since the adjacent STU in the section where switch K21 is located is STU1, K21 is the upstream switch and K22 is the downstream switch. Since the feeder switches K21 and K22 controlled by STU2 are both closed, STU2 forwards the query command to STU3. Since K32 is a tie switch in the open position, STU3 stops forwarding the message. Similarly, STU4 also forwards the switch status query command downstream step by step. After receiving the query command, STU5 forwards it to its adjacent STU6 and STU7, respectively. The node where STU7 is located is the end and has no other adjacent STUs, so the forwarding process stops. STU6 will continue to forward the message until STU3. The information transmission sequence of the switch status query instruction is shown in Figure 9.

[0151] Table 4. STU upstream and downstream relationship information

[0152] Table 5 shows the information about tie switches that can recover themselves. The acquisition process is as follows: Under normal operation, the STU at the tie switch sends its own number and communication address information to the STU at the adjacent node. Upon receiving this message, the adjacent STU forwards it to its adjacent STU until there are no adjacent nodes or the adjacent node is a tie switch node or power supply node. During this process, each branch node that receives this forwarded information records the tie switch information in Table 3-5. The tie switch information in this table is categorized by source. If a branch node receives tie switch information transmitted via adjacent node x, it indicates that the tie switch will also recover itself through adjacent node x. Because the available capacity of the tie switch changes dynamically during the recovery process, the table also includes the current recovery status of the tie switch.

[0153] Table 5. Information table of tie switches that can restore themselves (branch nodes)

[0154] Table 6 shows the self-recoverable tie switch information table. Its acquisition process is as follows: Under normal operation, the STU at the tie switch sends its own number and communication address to the adjacent STU. Upon receiving this message, the adjacent STU continues to forward the message to its adjacent STU until there are no adjacent nodes or the adjacent node is a tie switch node or a power supply node. During the information forwarding process, if a boundary node within a planned island receives tie switch-related information from a node outside the island, the boundary node within the island should incorporate the node number of the sender into the tie switch information and send it to the STU at the DG node. The DG node that receives the message should record which adjacent node outside the planned island forwarded the tie switch information, and record the relevant information in Table 6. It is important to note that after receiving the tie switch message, the boundary node within the planned island, in addition to sending the information to the DG central node, continues to forward the information according to the "forward to its adjacent STU" rule.

[0155] Table 6. Information table of tie switches that can restore themselves (Type A DG node)

[0156] The above topology identification process is illustrated using the local distribution network containing a Type A DG, as shown in Figure 10. The dashed box in the figure represents the planned islanded operating range of the DG connected to Node 1. Tie switches are located at Nodes 8 and 11, and STUx is installed at Node x. Under normal operation, STU8 first sends its own number and communication address information to STU7. STU7 then forwards this information to STU6. Upon receiving this message, STU6, as a boundary node within the planned island, incorporates the node number 7 of the sender, STU7, into the tie switch information and sends it to STU1, the node where the DG is located. Upon receiving the message, STU1 records the relevant information about tie switch 8 and notes that it was forwarded from the adjacent node 7 outside the island. Similarly, STU1 will also receive and record the relevant information about tie switch 11. To enable the tie switch to notify all recoverable branch nodes or Type A DG nodes of its own status, this disclosure provides a table of downstream nodes recoverable by the tie switch, as shown in Table 7. This table is stored in the STU at the tie switch. The information acquisition process is as follows: After receiving information about the tie switch that can restore itself, a branch node not only records the tie switch information in Table 5 but also sends its own node number and communication address to the tie switch based on the communication address. Similarly, a Type A DG node should also send its own node number and communication address to the tie switch STU after receiving the tie switch information. The tie switch STU, having received the numbers and communication addresses of each branch node and Type A DG node, stores this information in Table 7.

[0157] Table 7. Information of downstream nodes that can be restored by tie switches

[0158] Table 8. Load information

[0159] Table 9. Available margin of tie switch in initial state

[0160] S3. Based on the dynamic network topology information, distributed power supply restoration is performed on the non-fault sections.

[0161] Furthermore, step S3 includes:

[0162] During the recovery process, insufficient available capacity of the tie switch and the suspended recovery state are both considered "stop recovery" states. The specific distributed fault recovery process is as follows:

[0163] S31. When the common coupling point of the distributed generation is a type A DG node, based on the dynamic network topology information, the distributed power supply restoration strategy for the non-fault section is adopted to restore the non-fault section power supply.

[0164] S32. When the common coupling point of the distributed power generation is a type B DG node, a reclosing strategy is used to restore distributed power supply to the non-fault section based on the dynamic network topology information.

[0165] It should be noted that for DGs that can operate in an islanded state for a long time (this type of DG is defined as "Type A DG"), they should try to switch to an islanded operation state after losing contact with the main power supply to maintain uninterrupted power supply to the local load.

[0166] For DG units that cannot operate in an islanded state for extended periods, if they possess low voltage ride-through capability (defined as "Type B DG"), they should first undergo the low voltage ride-through process after a fault. If the DG remains connected to the main power source after a successful ride-through, the area has recovered successfully and remains connected to the grid. If the ride-through fails during the process, or if it remains in islanded operation after a successful ride-through, the unit should be decommissioned. For DG units that cannot operate in an islanded state and lack low voltage ride-through capability (defined as "Type C DG"), they should be quickly decommissioned after a fault.

[0167] In the embodiment of the present disclosure, different power restoration strategies are selected to perform power restoration according to the type of the distributed power generation common coupling point of the active power distribution network.

[0168] Furthermore, step S31 includes:

[0169] S311. When the common coupling point of the distributed generation is a type A DG node, the intelligent terminal units of the fault nodes associated with both ends of the fault section update the adjacency relationship with the opposite end, and forward the fault information to each adjacent distribution node respectively until the distribution node where the tie switch is located or there is no adjacent distribution node;

[0170] S312. When each distributed power generation common coupling point receives fault information, it sends an island operation status instruction to each distribution node in the island area associated with each distributed power generation common coupling point, and the distribution nodes near the area boundary in the island area disconnect the corresponding load switches;

[0171] S313. When the distribution nodes where the tie switches located upstream of the fault section are located receive fault information sent by the upstream fault node, they send unavailable information to the distribution nodes that can be restored by themselves.

[0172] S314. When the distribution nodes where the tie switches located downstream of the fault section are located receive fault information sent by the downstream fault node, tie switches other than the distribution nodes where the tie switches associated with the downstream fault node are located are used to restore power to the power-lost section.

[0173] S315. Taking the receipt of the fault information sent by the downstream fault node as the timing starting point, when the power supply restoration time for the power-off area reaches the preset restoration time threshold, query the recovery status of the distribution node downstream of the downstream fault node and outside the island area, the recovery status of the adjacent distribution node, and the number of the contact switch for power restoration, and complete the corresponding switching action.

[0174] In the disclosed embodiment, for ease of understanding, the specific logic of S311-S315 is as follows: 1) After a section of the active distribution network is disconnected due to a fault and reclosing fails, the STUs at the downstream and upstream nodes of the faulty section update their adjacency with the other end and send a message about the upstream / downstream fault to the downstream / upstream nodes, respectively. After receiving the message, a node forwards it to its respective adjacent nodes until it reaches the node where the tie switch is located or there are no adjacent nodes. 2) After each Type A DG node receives the fault message forwarded by the downstream STU of the faulty section, it quickly sends an instruction to enter the island operation state to the nodes within the planned island. All nodes within the island record that they have entered the island operation state. After receiving the instruction, the boundary nodes within the island disconnect the corresponding switches (without updating the adjacency relationship between nodes). Each Type B DG node begins the low voltage ride-through process or directly exits operation according to the aforementioned rules. After each tie switch receives the fault message forwarded by the upstream STU of the faulty section, it sends a message stating that it is unavailable to all nodes that can be recovered by it. 3) The STU at the interconnecting switch stores the two margin information in Table 3. After receiving the fault message forwarded by the downstream STU of the fault section, the interconnecting switch STU first determines which adjacent node on the trunk feeder line the fault message originated from and selects another interconnecting switch to supply the power-off zone with the available margin. 4) With the receipt of the upstream fault message as the starting point, after the maximum recovery time limit of the above recovery process is reached, the terminal downstream of the fault point and outside the island range queries the recovery status of the local node, the recovery status of the adjacent node, and the number of the interconnecting switch that restored it, and completes the switching operation process (updating the connection relationship between adjacent nodes after the switch status is updated). The logic is as follows: Logic ①: The unrecovered node disconnects the load switch of the local node. Logic ②: If the local node has been restored and the adjacent node has also been restored, but the two nodes were restored by different interconnecting switches, the switch between the two nodes is disconnected and the adjacency relationship between the nodes is updated.

[0175] Furthermore, step S314 includes:

[0176] S3141. When the distribution nodes where the tie switches downstream of the fault section are located receive fault information sent by the downstream fault node, determine whether any tie switches other than the distribution node where the tie switch associated with the downstream fault node is located have lost power. If so, read the available margin of the current tie switch and execute step S3142. If not, send the corresponding available margin to the adjacent distribution nodes and execute step S3142.

[0177] S3142: If the load associated with the distribution node receiving the available margin is less than the available margin, the distribution node is restored, the available margin is updated, and the information is forwarded to the adjacent distribution node. If the load associated with the distribution node outside the island area is greater than the updated available margin, step S3143 is executed. If the load associated with the distribution node within the island area is greater than the updated available margin, step S31410 is executed.

[0178] S3143: The distribution node outside the island area is regarded as a branch node. If there is a pure load branch in the branch where the branch node is located and the branch node can be restored by other tie switches, then step S3144 is executed; if not, then step S3145 is executed;

[0179] S3144: Determine whether the available capacity of the tie switch associated with the branch node can restore the pure load branch. If so, mark all distribution nodes in the pure load branch as recoverable nodes and restore them. Update the available capacity and forward it to the adjacent distribution nodes. Return to step S3142.

[0180] If not, the branch node is marked as a pause-restore node, the current remaining available capacity is recorded, and pause-restore information is sent to the associated tie switches. It is determined whether the other tie switches have pause-restore information. If not, step S3149 is executed for the branch node and downstream loads. If so, step S3149 is executed only for the pure load branch.

[0181] S3145: Determine whether the branch node is a pause-resume node. If so, execute step S3146; otherwise, execute step S3147.

[0182] S3146. Compare the available capacity of the tie switch associated with the current branch node with the available capacity of another tie switch recorded by the branch node, select the tie switch with the maximum available capacity for restoration, and determine whether the pure load branch can be restored. If so, mark all distribution nodes of the pure load branch as nodes that can be restored by the current tie switch. If not, execute step S3149 only for the pure load branch and traverse downstream.

[0183] S3147: Determine whether the current branch node can be restored by other tie switches of other paths. If so, execute step S3148; if not, execute step S3149.

[0184] S3148: Determine whether the current branch node has tie switch margin for other paths. If not, record the available capacity of the tie switch associated with the current branch node. When a tie switch stops recovering, execute step S3143. If it does, select the tie switch with the maximum available capacity for recovery. If recovery is possible, update the available capacity and execute step S3142. If recovery is not possible, send an available capacity shortage message to the associated tie switch.

[0185] S3149: The current distribution node is used as the root branch node. When the pause and resume node receives the information request command, it stops forwarding and sends a stop request message to the upstream root branch node. If the upstream root branch node can restore all downstream loads after traversing all downstream loads, it sends a pending restoration instruction to the distribution nodes associated with all downstream loads. If there is a pause and resume node among the distribution nodes associated with all downstream loads, the remaining capacity after restoration is sent to the pause and resume node, and step S3146 is executed.

[0186] When the power distribution node in the island area receives the information request command, step S31411 is executed;

[0187] S31410: If a distribution node in the island area receives available margin forwarded by an adjacent distribution node outside the island area, the node determines the number of adjacent distribution nodes. If the number of adjacent distribution nodes is less than a preset threshold, the node does not take any action. If the number of adjacent distribution nodes is equal to the preset threshold, the node returns to step S3142. If the number of adjacent distribution nodes is greater than the preset threshold, the node returns to step S3143.

[0188] S31411. If a distribution node in the island area receives an information request command forwarded by an adjacent distribution node outside the island area, it determines the number of adjacent distribution nodes. If the number of adjacent distribution nodes is less than the preset number threshold, it sends a stop request message to the root branch node. If the number of adjacent distribution nodes is equal to the preset number threshold, the distributed power supply common coupling point forwards the information request command to the adjacent distribution node. If the number of adjacent distribution nodes is greater than the preset number threshold, it sends downstream branch point information to the root branch node and sends an information request command to the adjacent distribution node.

[0189] In the disclosed embodiment, for ease of understanding, the specific logic of S3141-S31411 is as follows: After the STU at the tie switch receives a fault message forwarded by the downstream STU of the fault section, it first determines which adjacent node on the trunk feeder line the fault information originated from and selects another tie switch to supply the power-off zone with the available margin. The STU then determines whether the node where the tie switch is located has lost power. If so, the STU reads the available margin of the tie switch power supply and proceeds to step 1. If not, the STU sends the available margin of the tie switch to the adjacent node (the available margin information sent always includes the node number and communication address of the tie switch, which will not be repeated below), and proceeds to step 1.

[0190] Step ①: After the node receives or reads the available margin of the power supply of the tie switch, if the available margin is greater than the load of the node, the node can be restored by the corresponding tie switch. After confirming the recovery, the node updates the available margin of the tie switch and forwards it to the adjacent and adjacent nodes, and so on, until a node has been restored or has not lost power. If a node receives the available capacity of the tie switch and finds that the capacity is insufficient to restore itself, the node sends a message of insufficient available capacity to the corresponding tie switch (the sending process of the STU at the tie switch after receiving the message must always be carried out and will not be repeated below). If the node within the operating range of the type A DG island receives the tie switch margin information, it transfers to step ⑨; if the branch node receives the tie switch margin information, it transfers to step ②.

[0191] Step ②: If there is a pure load branch in the branch connected to the branch node itself and the branch node can be restored by the available tie switch of other paths, go to step ③; otherwise, go to step ④.

[0192] Step 3: The branch node determines whether the available capacity of the current tie switch can restore the load of the pure load branch. If so, all nodes in the branch are marked as recoverable by the current tie switch. After recovery, the node updates the tie switch's available margin and forwards the information to adjacent and neighboring nodes, proceeding to step 1. Otherwise, the branch node is marked as a suspended recovery node, the remaining available capacity of the current tie switch is recorded, and a suspension recovery message is sent to the current tie switch. If the suspended recovery node determines that the tie switches of all other paths have stopped recovery, the following operations are performed: If no tie switch suspension recovery message exists, proceed to step 8 and restore the branch node and downstream load. If so, to avoid disordered recovery, proceed to step 8 only for the pure load branch and traverse downstream.

[0193] Step ④: Determine whether the branch node is a branch node for pause recovery. If so, proceed to step ⑤; otherwise, proceed to step ⑥.

[0194] Step 5: Compare the available capacity of the current tie breaker with the available capacity of the other tie breaker recorded at the node. A message indicating insufficient available capacity is sent to the tie breaker with the smaller capacity. The larger value is selected to restore the node and its downstream branch load. If the load-only branch can be restored, all nodes in that branch are marked as recoverable by the current tie breaker. Otherwise, the branch node proceeds to step 8 for only the load-only branch, traversing downstream.

[0195] Step 6: Determine whether the branch node can be restored by the other tie switches from the other two paths. If so, proceed to step 7; otherwise, proceed to step 8.

[0196] Step 7: Determine whether tie-switch capacity from other paths already exists. If no tie-switch capacity currently exists, the current tie-switch capacity is recorded and the node enters a waiting state. If, during the waiting process, the branch node determines that a tie-switch on a particular path has stopped recovering, the branch becomes a purely load-bearing branch and proceeds to step 2. If a tie-switch capacity already exists, the two capacities are compared, and a message indicating insufficient available capacity is sent to the smaller tie-switch. The tie-switch with the largest available capacity is then selected to power the branch node. If recovery is possible, the remaining capacity of the restored tie-switch is updated and forwarded to adjacent nodes, proceeding to step 1. If recovery is not possible, a message indicating insufficient available capacity is sent to the corresponding tie-switch.

[0197] Step ⑧: Set this node as the root branch node and formulate a recovery strategy based on the method for solving the 0-1 knapsack problem. During the above search process, if a node that has paused recovery receives an information request command, it stops forwarding the information request command and similarly sends a message to the upstream root branch node, indicating that it has stopped forwarding the information request. It also sends a message indicating the presence of the paused recovery node, including the communication address of the paused recovery node. After traversing all downstream loads, if the upstream root branch node determines that all downstream loads cannot be restored, it sends a message to the corresponding tie switch indicating insufficient available capacity. Simultaneously, it obtains the optimal recovery strategy based on the aforementioned method and sends a message indicating that the node to be restored can be restored by the current tie switch. If the upstream root branch node determines that all downstream loads can be restored, it sends a message indicating that the node to be restored can be restored by the current tie switch. If there are any downstream nodes that have paused recovery, the remaining capacity after restoration must be sent to the paused recovery node. After the paused recovery node receives the available capacity from the tie switch, it proceeds to step ⑤. If a node within the operating range of a Type A DG island receives an information request command, it proceeds to step ⑩.

[0198] Step 9: If a node within the island receives the tie switch available margin forwarded from an adjacent node outside the island, and the node has not been restored, the node will incorporate the adjacent node number outside the island into the tie switch margin information (so that the DG node knows which adjacent node outside the island sent the tie switch available margin to itself) and notify the DG node of the tie switch available margin. After receiving the tie switch available capacity, the DG node notifies all nodes within the island that the corresponding tie switch has been restored and performs the following operations: If the DG island area has only one external adjacent node, no operation is performed; if there are two external adjacent nodes, the DG island area is treated as a normal node that has been restored, and the tie switch remaining capacity is forwarded to the outer boundary node of the island, and the process proceeds to step 1; if there are more than two external adjacent nodes, the DG island area can be treated as a generalized branch node with a load capacity of 0. The functions originally required by the branch node should be assumed by the DG node. The tie switches that can be connected to the island area are all tie switches that can restore the generalized branch node, and then the process proceeds to step 2.

[0199] Step ⑩: If a node within the island receives a load information request command forwarded by an adjacent node outside the island, and the node has not been restored, the node will incorporate the number of the adjacent node outside the island into the load information request command (so that the DG node knows which adjacent node outside the island sent the load information request command to itself) and notify the DG node of the load information request command. After receiving the load information request command, the DG node notifies all nodes within the island that the corresponding tie switch has been restored, and performs the following operations (if the DG island as a whole is a suspended recovery node, the above-mentioned processing method is used): If there is only one external adjacent node in the DG island area, a message of information request stop is sent to the root branch node; if there are two external adjacent nodes, the DG node forwards the information request command to the remaining adjacent nodes outside the island range; if there are more than two external adjacent nodes, a downstream branch point information is sent to the root branch point, and a load information request command is sent to the remaining adjacent nodes outside the island.

[0200] Furthermore, step S315 includes:

[0201] S3151. Taking the receipt of fault information sent by the downstream fault node as the timing starting point, when the power supply restoration time for the power outage area reaches a preset restoration time threshold, query the restoration status of the distribution node downstream of the downstream fault node and outside the island area, the restoration status of the adjacent distribution node, and the number of the tie switch performing power restoration;

[0202] S3152: Disconnect the load switch associated with the distribution node whose recovery state is not restored;

[0203] S3153. Disconnect the load switches between two adjacent distribution nodes whose recovery status is restored but which are restored by different tie switches.

[0204] In the embodiment of the present disclosure, for ease of understanding, the specific logic of S3151-S3153 is as follows:

[0205] Starting from the receipt of upstream fault information, after the maximum recovery time limit of the above recovery process is reached, the terminal downstream of the fault point and outside the island range queries the recovery status of its own node, the recovery status of the adjacent node, and the number of the tie switch that restored it, and completes the switching operation process (after the switch status is updated, the connection relationship between adjacent nodes is updated). The logic is as follows:

[0206] Logic ①: The unrecovered node disconnects the load switch of this node.

[0207] Logic ②: If the current node has been restored and the adjacent node has also been restored, but the two nodes are restored by different connecting switches, then disconnect the switch between the two nodes and update the adjacency relationship between the nodes.

[0208] After reaching the predetermined upper limits of the fault recovery time and switch operation time, each tie switch closes, and the STU at the tie switch transmits this closing information to its downstream adjacent STU. Upon receiving this message, a Type B DG during the low voltage ride-through process detects that it has been reconnected to the grid. Upon receiving this message, an STU at a boundary node within the isolated area of ​​a Type A DG can check whether both itself and the adjacent load nodes have been restored by the same tie switch. If so, it closes the internode switch; otherwise, the switch remains open.

[0209] For ease of understanding, the embodiment of the present disclosure provides a specific application example, as shown below: Taking Figure 11 as an example for analysis, Figure 11 is a multi-connection and multi-branch active distribution network, which includes 42 nodes, 4 tie switches, and 2 Type A DGs. The initial planned island range of the DG is shown in the dotted box in the figure. The relevant information of the load nodes in the figure and the available capacity of the tie switches are shown in Tables 8 and 9; all Type A in Figure 11 means that all DGs in the figure have island operation capabilities.

[0210] Assume that the local loads at nodes 17, 21, 24, and 32, where the tie switches are located, are all powered by other power sources. Because tie switch 17 has sufficient available capacity to restore power to node 8, for simplicity, the load information for nodes 8-16 and 37 is not included in the table.

[0211] Assuming a permanent fault occurs at point f in the diagram, the specific recovery process will now be described based on the aforementioned recovery scheme: After a permanent fault occurs at point f in Figure 11, the STUs at nodes 1 and 2 relay the fault information to all upstream and downstream STUs. Upon receiving the fault message, tie switch 21 determines that it is upstream of the faulted section and sends a message stating that it is unavailable to all branch nodes and type A DG nodes that can be recovered. Upon receiving the message, the relevant nodes update their tie switch information to be able to recover. Upon receiving the fault message, DG1 and DG2 determine that the fault is not within their planned island area and that they are downstream of the faulted section. They notify the planned island boundary switches 27-28, 30-31, 38-39, 9-10, and 13-14 to disconnect, quickly returning to island operation. Tie switches 24, 32, and 17 receive the fault message and determine that they are downstream of the faulted section, independently initiating the power restoration process. For different tie switches, since their respective recovery processes are independent, the time at which each node receives various messages varies, making the recovery process dynamic. The following describes the case where the tie switch recovery speed is 32 > 24 > 17. Tie switch 32 first recovers node 31. When recovering node 30, since node 30 is a boundary node of a DG island, it sends 2MVA of available remaining capacity to node 41, where the DG is located. Because the DG island area has more than two nodes connected to external nodes, the entire DG island area is considered a branch node with a load capacity of 0. Since the island area is connected to tie switches 24, 32, and 17, node 41 has not yet received any information about insufficient available margin on the tie switches. Therefore, the island can still be recovered by the other tie switches, and there is a pure load branch downstream, which meets the situation in step 3 above. Node 41 determines that tie switch 32's available capacity is sufficient to restore the pure load branch downstream of the island (nodes 39 and 40, totaling 2 MVA). Therefore, it restores the island and the downstream load. After restoration, all nodes within the island record that they have been restored by tie switch 32. Node 41 calculates that the tie switch's available capacity after restoration is 0 and sends the tie switch's available capacity to adjacent node 27 outside the island. Since node 27 cannot be restored, it notifies tie switch 32, instructing it to send a capacity shortage message to all downstream branch nodes and type A DG nodes. After tie switch 24 restores nodes 22, 23, 2, 3, and 4 (totaling 22 MVA), it encounters branch node 5, leaving 18 MVA of tie switch available capacity. At this point, node 5 has received the insufficient available capacity message from tie switch 32 but has not received the relevant message from tie switch 17, matching the situation described in step 3 above. Node 5 first determines whether the pure load branch (nodes 5, 25, 26, and 27, totaling 15 MVA) can be restored. Since the tie switch capacity is sufficient to restore the downstream pure load branch, the above nodes are notified that the tie switch 24 has been restored, and the updated tie switch margin of 3 MVA is forwarded to node 6.After receiving the message, node 6, because the tie switch capacity was insufficient to restore itself, notified tie switch 24, instructing it to send a capacity shortage message to all downstream branch nodes and DG nodes. Tie switch 17 still had 17 MVA of remaining capacity after restoring node 8. By the time it restored node 7, it had already received capacity shortage messages from tie switches 32 and 24. Therefore, using node 7 as the root branch node, it sent a load information request command to its neighboring nodes. After receiving branch restoration stop messages from nodes 5 and 36 and not receiving any downstream branch point information, node 7 concluded that the downstream traversal had concluded. Since the total unrestored load downstream was 25 MVA (nodes 6, 7, 33-36), it was impossible to restore all of it. Therefore, node 7 notified tie switch 17 to send a capacity shortage message to all downstream branch nodes and DG nodes. A dynamic programming algorithm calculated that restoring load nodes 6, 7, 33, and 36 would optimize the restoration process. Therefore, node 7 notified these nodes that tie switch 17 was available for restoration. After the restoration process was complete, nodes 34 and 35 could not be restored. After reaching the upper limit of the recovery process, terminals downstream of the fault point and outside the island range query the recovery status of their own and adjacent nodes, as well as the numbers of the tie switches that restored them. Subsequently, the switches on branch 6-7 are disconnected, and the load switches at nodes 34 and 35 are disconnected. After reaching the upper limit of the recovery process and the upper limit of the switch operation time, each tie switch is closed, and the tie switch closing information is relayed. After receiving the tie switch closing information, node 38 discovers that both it and adjacent node 39 have been restored by tie switch 32. Therefore, switches 38-39 are closed, while switches 27-28 remain open. Similarly, switches 9-10 and 13-14 are closed.

[0212] Furthermore, step S32 includes:

[0213] S321. When the common coupling point of the distributed generation is a type B DG node, a voltage check is performed on the upstream feeder of the fault section. If no voltage exists, a reclosing command is issued.

[0214] S322. If the reclosing instruction is to reclose to a permanent fault, and the upstream intelligent terminal unit of the fault section detects a secondary overcurrent, the associated circuit breaker is disconnected and a closing instruction is sent to the intelligent terminal unit at the tie switch until the intelligent terminal unit at the tie switch meets the closing conditions and then closes the circuit breaker;

[0215] S323. If the reclosing instruction is for a transient fault, the upstream intelligent terminal unit of the fault section sends a reclosing success message to the downstream intelligent terminal unit of the fault section;

[0216] S324. When the downstream intelligent terminal unit of the fault section receives the reclosing success information, a voltage-free operation is performed on the downstream feeder of the fault section. If the distributed power source common coupling point associated with the downstream intelligent terminal unit is in an out-of-operation state, a reclosing instruction is generated.

[0217] S325. If there is voltage on the downstream feeder, perform synchronization check on the downstream intelligent terminal unit and close the circuit breaker after the grid connection conditions are met.

[0218] In the embodiment of the present disclosure, the fault section can be accurately identified and the fault can be cleared without delay, so the existing distribution network reclosing strategy is no longer applicable. Therefore, a new reclosing strategy needs to be designed for the present disclosure.

[0219] When the common coupling point of the distributed power source is a type B DG node, a new reclosing strategy is used to restore the distributed power supply. After the fault section is removed, the upstream STU of the section starts the reclosing operation after a delay. First, it checks for no voltage to ensure that the downstream circuit breaker is open. If there is no voltage on the line, a reclosing command is issued. If a permanent fault is reclosed, the upstream STU detects a secondary overcurrent and trips the circuit breaker on this side. If it is a transient fault, the upstream STU sends a message of successful reclosing to the downstream STU. After receiving the message, the downstream STU first checks for no voltage. If the downstream DG has exited operation, the STU can directly issue a closing command to complete the entire reclosing process. If there is still voltage in the downstream feeder, it means that the downstream DG is in a networked state. In order to prevent a large inrush current when connected to the grid, the downstream STU must also perform a synchronization check and close the circuit breaker after meeting the grid connection conditions.

[0220] After the upstream STU recloses to a permanent fault, in addition to issuing a trip command, it also sends a closing command to the STU at the tie switch. The STU at the tie switch will close when closing conditions (voltage and synchronization checks) are met, restoring power to the non-faulty section. It's worth noting that these closing conditions refer to voltage and synchronization checks. If there's no DG downstream of the tie switch STU, closing is done with a voltage check; if there is a DG, synchronization checks are performed. The grid connection condition refers to closing upon detecting voltage synchronization between the DG and the grid connection point.

[0221] It should be noted that power restoration to non-faulty sections primarily relies on reclosing the circuit breaker at the tie switch. For example, in the case of fault F1, the section is first located. If the fault is located in the section between STU4 and STU5, the fault is isolated and reclosed after isolation. If the reclosing is due to a permanent short-circuit, the section must be isolated again. At this point, the section formed by STU5 and STU6 is considered non-faulty, and power restoration to the non-faulty section is required. This means that the K32 circuit breaker at tie switch STU3 must be reclosed to ensure system power can reach the non-faulty section. The entire reclosing process is as described above.

[0222] In this disclosure, in response to receiving a fault self-healing request, the active distribution network corresponding to the fault self-healing request is determined, and fault current data corresponding to each intelligent terminal unit is obtained. Based on the fault current data, the Fréchet segment location principle is used to locate and isolate the faulty segment. Distributed power supply restoration is then performed to non-faulty segments based on dynamic network topology information. This addresses the existing technical issues of difficulty implementing complex fault recovery strategies under distributed control modes, often failing to implement optimal fault recovery solutions. This disclosure utilizes fault current waveform differences as a fault segment location principle, making it adaptable to active distribution networks with multiple DG types and varying DG penetration rates. When all load switches are circuit breakers, this disclosure can rapidly locate and isolate the faulty segment, and restore power to non-faulty segments. This disclosure fully considers coordination with DG anti-islanding protection and low voltage ride-through. Each STU has automatic network topology recognition capabilities, enabling it to adapt relevant control strategies based on real-time changes in the network topology.

[0223] Please refer to FIG12 , which is a structural block diagram of an active power distribution network distributed fault self-healing system provided in the third embodiment of the present disclosure.

[0224] The present disclosure provides an active distribution network distributed fault self-healing system, which is applied to the active distribution network. The active distribution network includes intelligent terminal units installed at each distribution node and the common coupling point of the distributed power source. The intelligent terminal units divide the active distribution network based on their own configured local topology information and distribute the static network topology information. When the network operation mode of the active distribution network changes, the static network topology information is adaptively updated to generate dynamic network topology information. The system includes:

[0225] The response module 201 is configured to, in response to receiving a fault self-healing request, determine the active power distribution network corresponding to the fault self-healing request and obtain fault current data corresponding to each intelligent terminal unit;

[0226] The positioning and isolation module 202 is configured to locate and isolate the fault section based on the fault current data using the Fréchet section positioning principle;

[0227] The power supply restoration module 203 is configured to perform distributed power supply restoration on non-fault sections based on dynamic network topology information.

[0228] Furthermore, the response module 201 includes:

[0229] a fault self-healing request submodule, configured to respond to a received fault self-healing request, wherein the fault self-healing request is a self-healing request issued when the current mutation starting element detects a current mutation;

[0230] The fault current data submodule is configured to determine the active power distribution network corresponding to the fault self-healing request and obtain the fault current data corresponding to each intelligent terminal unit.

[0231] Furthermore, the positioning isolation module 202 includes:

[0232] The Fréchet distance value submodule is configured to calculate the Fréchet distance value of each phase line based on the sliding interface using the fault current data, wherein the Fréchet distance value is generated by a preset state transition equation;

[0233] a determination submodule configured to determine that a section associated with the Fréchet distance value is a faulty section when the number of times the Fréchet distance value is greater than a set value is greater than a preset number threshold, wherein the set value is generated by a preset set value function;

[0234] The tripping submodule is configured to control the tripping of the circuit breaker associated with the fault section.

[0235] Furthermore, the power restoration module 203 includes:

[0236] The non-fault section power supply restoration strategy submodule is configured to restore distributed power supply to the non-fault section using the non-fault section power supply restoration strategy based on dynamic network topology information when the distributed generation common coupling point is a type A DG node;

[0237] The reclosing strategy submodule is configured to use the reclosing strategy to restore distributed power supply to the non-fault section based on the dynamic network topology information when the common coupling point of the distributed power generation is a type B DG node.

[0238] Furthermore, the non-fault section power supply restoration strategy submodule includes:

[0239] The A-type DG node unit is configured to, when the common coupling point of the distributed power generation is a type A DG node, update the adjacency relationship with the opposite end through the intelligent terminal units of the fault nodes associated with both ends of the fault section, and forward the fault information to each adjacent distribution node respectively until the distribution node where the tie switch is located or there is no adjacent distribution node;

[0240] The island operation state instruction unit is configured to send an island operation state instruction to each distribution node in the island area associated with each distributed power source common coupling point when the distributed power source common coupling point receives fault information, so that the distribution nodes near the area boundary in the island area disconnect the corresponding load switches;

[0241] The information sending unit is configured to send unavailable information to the distribution node that can be restored by itself when the distribution node where each tie switch located upstream of the fault section receives the fault information sent by the upstream fault node;

[0242] The power supply restoration unit is configured to, when the distribution nodes where the tie switches located downstream of the fault section are located receive fault information sent by the downstream fault node, use tie switches other than the distribution nodes where the tie switches associated with the downstream fault node are located to restore power to the power-lost section;

[0243] The switch action unit is configured to use the fault information sent by the downstream fault node as the timing starting point. When the power supply restoration time for the power-loss area reaches a preset restoration time threshold, it queries the recovery status of the distribution node downstream of the downstream fault node and outside the island area, the recovery status of the adjacent distribution node, and the number of the interconnecting switch for power restoration, and completes the corresponding switch action.

[0244] Furthermore, the power restoration unit includes:

[0245] The power failure judgment subunit is configured to, when the distribution node where each tie switch located downstream of the fault section is located receives fault information sent by the downstream fault node, determine whether there is a power failure in any tie switch other than the distribution node where the tie switch associated with the downstream fault node is located; if there is a power failure, read the available margin of the current tie switch and jump to the distribution node subunit for restoration; if there is no power failure, send the corresponding available margin to the adjacent distribution node and jump to the distribution node subunit for restoration;

[0246] The distribution node recovery sub-unit is configured to, if the load associated with the distribution node receiving the available margin is less than the available margin, restore the distribution node, update the available margin and forward it to the adjacent distribution node; if the load associated with the distribution node outside the island area is greater than the updated available margin, jump to the branch node sub-unit; if the load associated with the distribution node within the island area is greater than the updated available margin, jump to the available margin sub-unit;

[0247] The branch node sub-unit is configured to use the distribution node outside the island area as a branch node. When there is a pure load branch in the branch where the branch node is located and the branch node can be restored by other tie switches, the node is jumped to the recoverable node sub-unit. If not, the node is jumped to the suspended recovery node sub-unit.

[0248] The recoverable node subunit is configured to determine whether the available capacity of the tie switch associated with the branch node can restore the pure load branch. If so, all distribution nodes in the pure load branch are marked as recoverable nodes and restored, and the available capacity is updated and forwarded to the adjacent distribution nodes, returning to the jump recovery distribution node subunit.

[0249] If not, the branch node is marked as a pause-recovery node, the current remaining available capacity is recorded, and the pause-recovery information is sent to the associated tie switches. It is determined whether the other tie switches have the pause-recovery information. If not, the branch node and the downstream load are jumped to the root branch node subunit. If so, only the pure load branch is jumped to the root branch node subunit.

[0250] The pause recovery node sub-unit is configured to determine whether the branch node is a pause recovery node, and if so, jump to the available capacity sub-unit, and if not, jump to the switch recovery sub-unit;

[0251] The available capacity sub-unit is configured to compare the available capacity of the tie switch associated with the current branch node with the available capacity of another tie switch recorded by the branch node, select the tie switch with the maximum available capacity for restoration, and determine whether the pure load branch can be restored. If so, all distribution nodes of the pure load branch are marked as nodes that can be restored by the current tie switch. If not, only the pure load branch is jumped to the root branch node sub-unit and traversed downstream;

[0252] The switch recovery sub-unit is configured to determine whether the current branch node can be recovered by the remaining tie switches of the remaining paths, and if so, jump to the switch remainder sub-unit; if not, jump to the root branch node sub-unit;

[0253] The switch remainder subunit is configured to determine whether the current branch node has tie switch remainder for other paths. If not, it records the available capacity of the tie switch associated with the current branch node. When a tie switch stops recovering, it jumps to the branch node subunit. If it exists, it selects the tie switch with the maximum available capacity for recovery. If it can be recovered, it updates the available capacity and jumps to the recovery distribution node subunit. If it cannot be recovered, it sends an available capacity shortage message to the associated tie switch.

[0254] The root branch node sub-unit is configured to use the current distribution node as the root branch node. When the pause and resume node receives the information request command, it stops forwarding and sends a stop request message to the upstream root branch node. If the upstream root branch node can restore all downstream loads after traversing all downstream loads, it sends a pending restoration instruction to the distribution nodes associated with all downstream loads. If there is a pause and resume node among the distribution nodes associated with all downstream loads, the remaining capacity after restoration is sent to the pause and resume node, and the available capacity sub-unit is jumped.

[0255] When the power distribution node in the island area receives the information request command, it jumps to the information request command subunit;

[0256] The available remainder subunit is configured to, if a distribution node in the island area receives available remainder forwarded by an adjacent distribution node outside the island area, determine the number of adjacent distribution nodes, and if the number of adjacent distribution nodes is less than a preset number threshold, take no action; if the number of adjacent distribution nodes is equal to the preset number threshold, return to jump to the recovery distribution node subunit; if the number of adjacent distribution nodes is greater than the preset number threshold, return to jump to the branch node subunit;

[0257] The information request command subunit is configured to determine the number of adjacent distribution nodes if a distribution node in the island area receives an information request command forwarded by an adjacent distribution node outside the island area. If the number of adjacent distribution nodes is less than a preset number threshold, a stop request message is sent to the root branch node. If the number of adjacent distribution nodes is equal to the preset number threshold, the distributed power supply common coupling point forwards the information request command to the adjacent distribution node. If the number of adjacent distribution nodes is greater than the preset number threshold, downstream branch point information is sent to the root branch node, and an information request command is sent to the adjacent distribution node.

[0258] Furthermore, the switch action unit includes:

[0259] The power supply restoration time subunit is configured to use the receipt of fault information sent by the downstream fault node as the timing starting point. When the power supply restoration time for the power outage area reaches a preset restoration time threshold, it queries the restoration status of the distribution node downstream of the downstream fault node and outside the island area, the restoration status of the adjacent distribution node, and the number of the tie switch for power restoration;

[0260] A first load switch disconnecting subunit is configured to disconnect a load switch associated with a distribution node whose recovery state is unrecovered;

[0261] The second load switch disconnecting subunit is configured to disconnect the load switch between two adjacent distribution nodes whose recovery status is restored but which are restored by different tie switches.

[0262] Furthermore, the reclosing strategy submodule includes:

[0263] The B-type DG node unit is configured to perform a voltage check on the upstream feeder of the fault section when the common coupling point of the distributed generation is a B-type DG node, and issue a reclosing command if no voltage exists;

[0264] The permanent fault unit is configured to, if the reclosing instruction is to reclose to a permanent fault and the upstream intelligent terminal unit of the fault section detects a secondary overcurrent, disconnect the associated circuit breaker and send a closing instruction to the intelligent terminal unit at the tie switch until the intelligent terminal unit at the tie switch meets the closing conditions and then closes the circuit breaker;

[0265] The instantaneous fault unit is configured such that if the reclosing instruction is a transient fault, the upstream intelligent terminal unit of the fault section sends a reclosing success message to the downstream intelligent terminal unit of the fault section;

[0266] The reclosing command unit is configured to perform a voltage-free operation on the downstream feeder of the fault section when the downstream intelligent terminal unit of the fault section receives the reclosing success information, and generate a reclosing command if the distributed power source common coupling point associated with the downstream intelligent terminal unit is in an out-of-operation state;

[0267] The synchronization check unit is configured to perform synchronization check operation on the downstream intelligent terminal unit if there is voltage on the downstream feeder, and close the circuit breaker after the grid connection conditions are met.

[0268] In this disclosure, in response to receiving a fault self-healing request, the active distribution network corresponding to the fault self-healing request is determined, and fault current data corresponding to each intelligent terminal unit is obtained. Based on the fault current data, the Fréchet segment location principle is used to locate and isolate the faulty segment. Distributed power supply restoration is then performed to non-faulty segments based on dynamic network topology information. This addresses the existing technical issues of difficulty implementing complex fault recovery strategies under distributed control modes, often failing to implement optimal fault recovery solutions. This disclosure utilizes fault current waveform differences as a fault segment location principle, making it adaptable to active distribution networks with multiple DG types and varying DG penetration rates. When all load switches are circuit breakers, this disclosure can rapidly locate and isolate the faulty segment, and restore power to non-faulty segments. This disclosure fully considers coordination with DG anti-islanding protection and low voltage ride-through. Each STU has automatic network topology recognition capabilities, enabling it to adapt relevant control strategies based on real-time changes in the network topology.

[0269] An electronic device according to an embodiment of the present disclosure includes: a memory and a processor, wherein a computer program is stored in the memory; when the computer program is executed by the processor, the processor executes the active power distribution network distributed fault self-healing method according to any of the above embodiments.

[0270] The memory can be an electronic memory such as a flash memory, an EEPROM (Electrically Erasable Programmable Read-Only Memory), an EPROM, a hard disk, or a ROM. The memory has a storage space for program codes configured to execute any of the method steps in the above method. For example, the storage space configured as program code can include individual program codes configured to implement the various steps in the above method. These program codes can be read from or written to one or more computer program products. These computer program products include program code carriers such as a hard disk, a compact disc (CD), a memory card, or a floppy disk. The program code can be compressed, for example, in an appropriate form. When these codes are run by a computing processing device, the computing processing device performs the various steps in the above-described method.

[0271] An embodiment of the present disclosure provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed, a distributed fault self-healing method for an active power distribution network according to any embodiment of the present disclosure is implemented.

[0272] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0273] In the several embodiments provided in this application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the above units is only a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0274] The units described above as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0275] In addition, the functional units in the various embodiments of the present disclosure may be integrated into a single processing unit, or each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0276] If the above-mentioned integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present disclosure is essentially or the part that contributes to the relevant technology understood by the inventor or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the above-mentioned methods of each embodiment of the present disclosure. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk and other media that can store program code.

[0277] As described above, the above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than to limit the same. Although the present disclosure has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. A distributed fault self-healing method for an active distribution network, wherein: Applied to an active distribution network, the active distribution network includes intelligent terminal units installed at each distribution node and a common coupling point of a distributed power source. The intelligent terminal units divide the active distribution network based on the local topology information configured by themselves and store static network topology information in a distributed manner. When the network operation mode of the active distribution network changes, the static network topology information is adaptively updated to generate dynamic network topology information. The method includes: S1. In response to receiving a fault self-healing request, determining an active distribution network corresponding to the fault self-healing request and obtaining fault current data corresponding to each intelligent terminal unit; S2. Based on the fault current data, the Fréchet section location principle is used to locate and isolate the fault section; S3. Based on the dynamic network topology information, distributed power supply restoration is performed on non-faulty sections.

2. The distributed fault self-healing method for active power distribution network according to claim 1, wherein: Step S1 includes: S11, responding to receiving a fault self-healing request, wherein the fault self-healing request is a self-healing request issued when a current mutation starting element detects a current mutation; S12. Determine the active distribution network corresponding to the fault self-healing request, and obtain the fault current data corresponding to each intelligent terminal unit.

3. The distributed fault self-healing method for active power distribution network according to claim 1, wherein: Step S2 includes: S21, based on the sliding interface, using the fault current data to calculate the Fréchet distance value of each phase line, wherein the Fréchet distance value is generated by a preset state transfer equation; S22, when the number of times that the Fréchet distance value is greater than the setting value is greater than a preset number threshold, the section associated with the Fréchet distance value is determined to be a faulty section, wherein the setting value is generated by a preset setting value function; S23. Control the circuit breaker associated with the faulty section to trip.

4. The distributed fault self-healing method for active power distribution network according to claim 1, wherein: Step S3 includes: S31. When the common coupling point of the distributed power generation is a type A DG node, based on the dynamic network topology information, the non-fault section power supply restoration strategy is adopted to restore the distributed power supply to the non-fault section; S32. When the common coupling point of the distributed power source is a type B DG node, a reclosing strategy is used to restore distributed power supply to the non-fault section based on the dynamic network topology information.

5. The distributed fault self-healing method for active power distribution network according to claim 4, wherein: Step S31 includes: S311, when the common coupling point of the distributed generation is a type A DG node, the intelligent terminal units of the faulty nodes associated with both ends of the faulty section update the adjacency relationship with the opposite end, and forward the fault information to each adjacent distribution node respectively until the distribution node where the tie switch is located or there is no adjacent distribution node; S312, when each distributed power source common coupling point receives fault information, it sends an island operation status instruction to each distribution node in the island area associated with each distributed power source common coupling point, and the distribution node close to the area boundary in the island area disconnects the corresponding load switch; S313, when the distribution nodes where the tie switches located upstream of the fault section are located receive the fault information sent by the upstream fault node, they send unavailable information to the distribution nodes that can be restored by themselves; S314, when the distribution nodes where the tie switches located downstream of the fault section are located receive the fault information sent by the downstream fault node, the tie switches other than the distribution nodes where the tie switches associated with the downstream fault node are located are used to restore power supply to the power-lost area; S315. Taking the receipt of the fault information sent by the downstream fault node as the timing starting point, when the power supply restoration time for the power-off area reaches the preset restoration time threshold, query the recovery status of the distribution node downstream of the downstream fault node and outside the island area, the recovery status of the adjacent distribution node, and the contact switch number for power supply restoration, and complete the corresponding switch action.

6. The distributed fault self-healing method for active power distribution network according to claim 5, wherein: Step S314 includes: S3141. When the distribution nodes where the tie switches located downstream of the fault section are located receive the fault information sent by the downstream fault node, it is determined whether there is a power failure in the tie switches other than the distribution node where the tie switch associated with the downstream fault node is located. If there is a power failure, the available margin of the current tie switch is read and step S3142 is executed. If there is no power failure, the corresponding available margin is sent to the adjacent distribution node and step S3142 is executed. S3142: If the load associated with the distribution node receiving the available margin is less than the available margin, the distribution node is restored, the available margin is updated and forwarded to the adjacent distribution node; if the load associated with the distribution node outside the isolated island area is greater than the updated available margin, step S3143 is executed; if the load associated with the distribution node in the isolated island area is greater than the updated available margin, step S31410 is executed; S3143, taking the distribution node outside the island area as a branch node, if there is a pure load branch in the branch where the branch node is located and the branch node can be restored by other tie switches, then execute step S3144, if not, then execute step S3145; S3144, determine whether the available capacity of the tie switch associated with the branch node can restore the pure load branch. If so, mark all the distribution nodes in the pure load branch as recoverable nodes and restore them, update the available capacity and forward it to the adjacent distribution nodes, and return to step S3142. If not, the branch node is marked as a pause-restore node, the current remaining available capacity is recorded, and the pause-restore information is sent to the associated tie switch, and it is determined whether the other tie switches have the pause-restore information. If not, step S3149 is executed for the branch node and the downstream load. If so, step S3149 is executed only for the pure load branch. S3145, determine whether the branch node is a pause recovery node, if so, execute step S3146, if not, execute step S3147; S3146. Compare the available capacity of the tie switch associated with the current branch node with the available capacity of another tie switch recorded in the branch node, select the tie switch with the maximum available capacity for restoration, and determine whether the pure load branch can be restored. If so, mark all distribution nodes of the pure load branch as nodes that can be restored by the current tie switch. If not, execute step S3149 only for the pure load branch and traverse downstream. S3147, determine whether the current branch node can be restored by other tie switches of other paths, if yes, execute step S3148, if no, execute step S3149; S3148, determine whether the current branch node has tie switch margins for other paths, if not, record the available capacity of the tie switch associated with the current branch node, and when the tie switch stops recovering, execute step S3143, if it exists, select the tie switch with the maximum available capacity for recovery, if it can be recovered, update the available capacity and execute step S3142, if it cannot be recovered, send available capacity shortage information to the associated tie switch; S3149, taking the current distribution node as the root branch node, when the pause and resume node receives the information request command, it stops forwarding and sends the stop request information to the upstream root branch node. If the upstream root branch node can restore all downstream loads after traversing all downstream loads, it sends a pending restoration instruction to the distribution nodes associated with all downstream loads. If there is a pause and resume node among the distribution nodes associated with all downstream loads, the remaining capacity after restoration is sent to the pause and resume node, and step S3146 is executed. When the power distribution node in the isolated island area receives the information request command, step S31411 is executed; S31410, if the distribution node in the isolated island area receives the available margin forwarded by the adjacent distribution node outside the isolated island area, the number of adjacent distribution nodes is determined, if the number of adjacent distribution nodes is less than the preset number threshold, no action is taken, if the number of adjacent distribution nodes is equal to the preset number threshold, return to execute step S3142, if the number of adjacent distribution nodes is greater than the preset number threshold, return to execute step S3143; S31411. If a distribution node in the island area receives an information request command forwarded by an adjacent distribution node outside the island area, the number of adjacent distribution nodes is determined. If the number of adjacent distribution nodes is less than a preset number threshold, a stop request message is sent to the root branch node. If the number of adjacent distribution nodes is equal to the preset number threshold, the distributed power source common coupling point forwards the information request command to the adjacent distribution node. If the number of adjacent distribution nodes is greater than the preset number threshold, downstream branch point information is sent to the root branch node, and an information request command is sent to the adjacent distribution nodes.

7. The distributed fault self-healing method for active power distribution network according to claim 5, wherein: Step S315 includes: S3151, taking the receipt of the fault information sent by the downstream fault node as the timing starting point, when the power supply restoration time for the power failure area reaches the preset restoration time threshold, querying the restoration status of the distribution node downstream of the downstream fault node and outside the island area, the restoration status of the adjacent distribution node, and the number of the contact switch for power restoration; S3152, disconnecting the load switch associated with the distribution node whose recovery state is not restored; S3153. Disconnect the load switch between two adjacent distribution nodes whose recovery status is restored but which are restored by different contact switches.

8. The distributed fault self-healing method for active power distribution network according to claim 4, wherein: Step S32 includes: S321. When the common coupling point of the distributed generation is a type B DG node, a voltage-free operation is performed on the upstream feeder of the fault section. If no voltage exists, a reclosing command is issued; S322, if the reclosing instruction is to reclose to a permanent fault, and the upstream intelligent terminal unit of the fault section detects a secondary overcurrent, the associated circuit breaker is disconnected and a closing instruction is sent to the intelligent terminal unit at the tie switch until the intelligent terminal unit at the tie switch meets the closing conditions and then closes the circuit; S323. If the reclosing instruction is a transient fault, the upstream intelligent terminal unit of the fault section sends a reclosing success message to the downstream intelligent terminal unit of the fault section; S324, when the downstream intelligent terminal unit of the fault section receives the reclosing success information, a voltage-free operation is performed on the downstream feeder of the fault section, and if the distributed power source common coupling point associated with the downstream intelligent terminal unit is in the exit operation state, a reclosing instruction is generated; S325. If there is voltage on the downstream feeder, perform synchronization check on the downstream intelligent terminal unit and close the circuit breaker after the grid-connected conditions are met.

9. An active power distribution network distributed fault self-healing system, wherein: Applied to active distribution network, the active distribution network includes intelligent terminal units installed at each distribution node and distributed power source common coupling point. The intelligent terminal unit divides the active distribution network based on the local topology information configured by itself and stores static network topology information in a distributed manner. When the network operation mode of the active distribution network changes, the static network topology information is adaptively updated to generate dynamic network topology information. The system includes: A response module is configured to, in response to receiving a fault self-healing request, determine an active power distribution network corresponding to the fault self-healing request and obtain fault current data corresponding to each intelligent terminal unit; A positioning and isolation module is configured to locate and isolate the fault section based on the fault current data using the Fréchet section positioning principle; The power supply restoration module is configured to perform distributed power supply restoration on non-fault sections based on dynamic network topology information.

10. An electronic device, wherein: It comprises a memory and a processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the processor executes the steps of the active power distribution network distributed fault self-healing method according to any one of claims 1 to 8.

11. A computer-readable storage medium having a computer program stored thereon, wherein: When the computer program is executed, the distributed fault self-healing method for an active power distribution network as described in any one of claims 1 to 8 is implemented.

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