Fault restoration method for power distribution network considering interconnection of uninterruptible power supply and dc line

Abstract

The application discloses a power distribution network fault recovery method considering uninterrupted power supply and DC line interconnection, solves an island grading division model of the power distribution network considering the uninterrupted power supply to obtain an island division scheme, and optimizes and solves a power mutual aid model during the power distribution network fault recovery considering the DC line interconnection based on the island division result, so that the power distribution network fault recovery method considering the uninterrupted power supply is obtained, which can reduce the number of single power supply islands, effectively prolongs the power supply time of the recovered load, improves the recovery rate of important load and the utilization rate of power generation resources in the power distribution network fault recovery stage after the fault occurs.

Description

TECHNICAL FIELD

[0001] The embodiment of the present application relates to the technical field of power distribution network fault recovery, and in particular to a power distribution network fault recovery method considering the interconnection of uninterrupted power supply and DC lines. BACKGROUND

[0002] With the increasing frequency of extreme weather, the frequent occurrence of faults also poses greater and greater challenges to the power grid. The power distribution network can quickly restore power supply after a fault occurs, which is of great significance to the normal production and life of society and the promotion of social development. With the increasing penetration of distributed power sources in the power distribution network, distributed power sources can be used to quickly restore power supply in the outage area by dividing islands after a fault occurs, thereby improving system power supply reliability.

[0003] The existing power distribution network containing distributed power sources reduces the outage range and restores the power supply of important loads by island division and network reconstruction after a fault occurs, and prolongs the power supply time of the load by uninterrupted power supply (UPS), thereby improving the resilience of the power distribution system. It is particularly important to improve the ability of the power distribution system to withstand power failure and to quickly restore to normal state after a fault. However, the current multi-island strategy rarely considers the role of various types of power sources in the recovery process and the connection between islands, resulting in a complex network topology after a fault, a short power supply time of the load, and ineffective use of distributed power sources. SUMMARY

[0004] To this end, the embodiment of the present application provides a power distribution network fault recovery method considering the interconnection of uninterrupted power supply and DC lines, to solve the technical problem that the existing multi-island strategy rarely considers the role of various types of power sources in the recovery process and the connection between islands, resulting in a complex network topology after a fault, a short power supply time of the load, and ineffective use of distributed power sources. By reducing the number of islands during island division, establishing a connection between islands during the recovery phase after a fault, and considering the synergistic effect of various types of power sources, the power supply time of the recovered load is effectively increased, the recovery time after a fault is shortened, the recovery rate of the load is improved, and the utilization rate of power generation resources is improved.

[0005] In order to achieve the above-mentioned purpose, the embodiment of the present application provides the following technical scheme:

[0006] According to the first aspect of the embodiment of the present application, the embodiment of the present application provides a power distribution network fault recovery method considering the interconnection of uninterrupted power supply and DC lines, the method comprising:

[0007] An island hierarchical partitioning model of a power distribution network considering UPS is established, and constraint conditions including power balance constraint in an island, UPS operation constraint and island operation constraint are considered, the island hierarchical partitioning model includes a primary island partitioning model and an island optimization model, the primary island partitioning model takes the maximum important load restoration amount as an objective, a primary island partitioning result satisfying the constraint is obtained by solving the primary island partitioning model, and the island optimization model takes the minimum number of branch breakages as an objective, and an optimal island partitioning result is obtained by optimizing the primary island partitioning result to reduce the number of single-DG power supply islands.

[0008] An AC line is changed into a DC line, a power mutual aid model during fault restoration of a power distribution network considering DC line interconnection is established, constraint conditions including operation constraint of the power distribution network, topology constraint of the power distribution network, system power flow constraint and system safety constraint are considered, and an optimal island joint result is obtained by solving the power mutual aid model based on the optimal island partitioning result, so that a power mutual aid power distribution network fault restoration strategy is obtained.

[0009] Further, the island hierarchical partitioning model of the power distribution network considering the UPS is established, and specifically further includes:

[0010] An uninterruptible power supply model is established.

[0011]

[0012] In the formula, UPS capacity upper limit at node j is represented; Backup capacity of an external battery at node j is represented; Maximum load at node j is represented; θ jf η j Power factor and inverter conversion efficiency of the UPS at node j are represented respectively; P sb N and n represent capacity of each battery group, number of battery groups and number of batteries in each battery group respectively.

[0013] Further, the objective function of the primary island partitioning model is the maximum important load restoration amount, that is:

[0014]

[0015] In the formula, f1 represents a value function of restored load; n represents a set of nodes; K represents a set of islands; T represents a set of discrete fault restoration time intervals; Δt represents interval length of discrete fault time intervals; ω i Load weight coefficient of node i is represented; Active power of restored load of node i is represented; λ i,g is an integer variable, λ i= 1 means that the outage load i is restored in the island g, otherwise i,g = 0.

[0016] The objective function of the island optimization model is to minimize the number of branch breakages, that is:

[0017]

[0018] In the formula, b is a branch set of the distribution network; k ij is the switch state of the branch ij, k ij = 1 means that the branch is closed, otherwise k ij = 0.

[0019] Further, considering the constraint conditions including island power balance constraints, UPS operation constraints and island operation constraints, specifically including:

[0020] The island power balance constraint is:

[0021]

[0022] In the formula, K represents a set of islands; T represents a set of discrete fault recovery time intervals; λ i,g is an integer variable, λ i,g = 1 means that the outage load i is restored in the island g, otherwise λ i,g = 0. represents the active power generated by the distributed power supply at node i at time t; represents the active power absorbed by the load at node i at time t; is the discharge power of the UPS at node i at time t;

[0023] The UPS operation constraint is:

[0024]

[0025] In the formula, represents the operation loss of the UPS at node j at time t; is the loss coefficient of the UPS at node j; is the discharge power of the UPS at node j at time t; are the maximum and minimum discharge power of the UPS at node j at time t, respectively; are the upper and lower limits of the UPS capacity at node j, respectively;

[0026] The island operation constraint is:

[0027]

[0028] In the formula, b represents a branch set of the distribution network; denotes the power flowing through line l from the first node i to the last node j in the island; ij denotes the maximum power transmission that line l ij can bear; denotes the square of the node voltage value of node i at time t; and are the upper and lower limits of the voltage of node i, respectively; denotes the square of the branch current value of branch ij at time t; is the upper limit of the current of branch ij.

[0029] Further, the solving process of the island classification and division model of the distribution network includes:

[0030] First, the breadth-first search algorithm is used to solve the primary island division model to obtain the maximum power supply area that satisfies the power constraint in the island, and then the hybrid particle swarm algorithm is used to optimize and solve the objective function of the island classification model. When the maximum number of iterations is reached or the program search termination condition is met, the optimal value matrix of each control variable in the distribution network is output, and the final island division scheme is obtained by operating each tie switch according to the optimized value matrix.

[0031] Further, a power mutual aid model during the fault recovery of the distribution network considering the interconnection of DC lines is established, which specifically includes:

[0032] The power mutual aid model during the fault recovery of the distribution network ensures that the load recovery power supply range is large enough. The objective function of the power mutual aid model during the fault recovery of the distribution network is:

[0033]

[0034] In the formula, denotes the active power of load i in island g, Δt denotes the time length used in each stage during the distribution recovery process, and T' denotes the set of all stages; is a 0-1 integer variable, represents that load i has been restored to power supply in island g, otherwise not represents the network loss of the entire system;

[0035] The power mutual aid constraint is:

[0036] ΔG gij = |G gi -G gj |, i, j ∈ g, G gi ≥ 0 ∪ G gj ≥ 0

[0037] ​

[0038] Pgi represents the active power of the distributed generator in island g; Pgi represents the active power of the distributed generator in island g; Pgi represents the active power of the distributed generator in island g; Pgi represents the active power of the distributed generator in island g; Pgi represents the active power of the distributed generator in island g; Pgi represents the active power of the distributed generator in island g;

[0039] Further, a power mutual aid model during the fault recovery of the distribution network considering the interconnection of DC lines is established, and specifically further includes:

[0040] The un-recovered or not fully recovered loads in the island are selectively recovered to obtain different power mutual aid island combinations to select the optimal island combination meeting the power mutual aid objective function;

[0041] The load regulation model is:

[0042]

[0043] Pgi represents the active power of the distributed generator in island g; L,i Pgi represents the active power of the distributed generator in island g; Pgi represents the active power of the distributed generator in island g; Pgi represents the active power of the distributed generator in island g;

[0044] The load regulation constraint is:

[0045]

[0046] The above formula represents the adjustable range of all un-recovered or not fully recovered loads, wherein n2 represents the set of un-recovered or not fully recovered loads; and N represents that all the loads in n2 are fully connected.

[0047] Further, the constraint conditions including the operation constraint of the distribution network, the topology constraint of the distribution network, the system power flow constraint, and the system security constraint are considered, and specifically include:

[0048] The operation constraint of the distribution network includes the distributed generator output constraint and the UPS operation constraint;

[0049] The distributed generator output constraint is:

[0050]

[0051] Pgi represents the active power of the distributed generator in island g; Pj(t) and Qj(t) are the active and reactive power output of the source at node j in time period t, respectively; Pj(t) and Qj(t) are the active and reactive power output of the source at node j in time period t, respectively; Cj is the capacity of the source connected to node j; Cj is the capacity of the source connected to node j; Cj is the capacity of the source connected to node j;

[0052] Distribution network topology constraints are:

[0053]

[0054] wherein, is a 0-1 integer variable, indicating the state of the line between node i and node j in island k, indicates that the line (i, j) is connected, otherwise indicates that the line is disconnected; β ij,k and β ji,k are also 0-1 integer variables, respectively indicating the relationship between node i and node j in island k; b indicates the set of lines; Ω(i) indicates all nodes connected to node i; L m indicates the set of nodes not containing the balance node; m indicates the source node as the balance node in island k;

[0055] System flow constraints are:

[0056] When the distribution network fails, the network topology changes, the traditional Distflow flow model is improved, the line opening variable is introduced to relax the flow equation, and the Distflow flow operation constraint suitable for distribution network fault restoration is obtained, including:

[0057]

[0058] wherein, K indicates the set of islands; T indicates the interval set of discrete fault restoration time periods; L indicates the set of lines; G indicates the set of nodes; the active and reactive power of the distributed power source at node j in island k is and Pij(t) and Qij(t) are the active and reactive power flowing from node i to node j on line (i, j); and Pj(t) and Qj(t) are the active and reactive power output of the source at node j in time period t, respectively; r ij and x ij are the resistance and reactance of line (i, j); is the square of the amplitude of the current on line (i, j); is the line opening variable, the line (i, j) is closed, and the variable value is 1, otherwise it is 0; M is a constant, the value of M is 0 when the line (i, j) in island k is normally connected, otherwise it is infinite; and Pij and Qij are the active power and reactive power consumed by the load at node j, respectively; and Pjh and Qjh are the active power and reactive power flowing from node j to node h, respectively; and Vil and Vui are the upper and lower limits of the voltage at node i, respectively; and Pgi and Qgi are the upper limits of the active power and reactive power supplied by the distributed synchronous generator, respectively, and the reactive power of the power supply is freely adjusted within the range; Iij is the maximum current allowed to pass through the line (i, j);

[0059] The capacity constraint is:

[0060]

[0061] The above formula indicates that the remaining capacity of the power supply side needs to meet the power supply demand of the restored load in the restoration process, where n represents a set of nodes; K represents a set of islands; T represents a set of interval sets of discrete fault restoration time periods; Δt represents the interval length of the discrete fault period; ω i wi represents the load weight coefficient of node i; Pi represents the active power of the restored load of node i; λ i,g is an integer variable, λ i = 1 indicates that the power failure load i is restored to power supply within the island g, and vice versa λ i,g = 0; Rgi represents the remaining capacity of the distributed synchronous generator and the uninterruptible power supply within the island g.

[0062] Further, the solving process of the power mutual aid model during the fault restoration of the power distribution network considering the interconnection of DC lines specifically includes:

[0063] The power mutual aid model during the fault restoration of the power distribution network contains integer variables and nonlinear constraints, and the relaxation of the nonlinear constraints is converted into convex constraints through relaxation, the entire model is converted into a mixed integer second-order cone programming model, which belongs to a convex optimization model, the solving method of the convex optimization model adopts YAMIP programming, and CPLEX and MOSEK software are used to solve the mixed integer second-order cone programming model to obtain the restoration strategy of the power distribution network considering the interconnection of DC lines.

[0064] According to a second aspect of the embodiments of the present application, the embodiments of the present application provide a power distribution network fault restoration system considering the interconnection of uninterruptible power supplies and DC lines, the system comprising:

[0065] The island hierarchical division module is configured to establish an island hierarchical division model of the power distribution network considering the UPS, and the constraint conditions include power balance constraints in the island, operation constraints of the UPS and operation constraints in the island, the island hierarchical division model includes a primary island division model and an island optimization model, the primary island division model aims to maximize the amount of important load recovery, and the primary island division result satisfying the constraints is obtained by solving the primary island division model, and the island optimization model aims to minimize the number of branch breakages, and the optimal island division result is obtained by optimizing the primary island division result to reduce the number of single-DG-powered islands.

[0066] The island inter-power mutual aid module is configured to transform the AC line into a DC line, establish a power mutual aid model during the power distribution network fault recovery considering the DC line interconnection, consider constraint conditions including operation constraints of the power distribution network, topological constraints of the power distribution network, system power flow constraints and system safety constraints, solve the power mutual aid model based on the optimal island division result to obtain an optimal island joint result, and thus obtain a power distribution network fault recovery strategy of island inter-power mutual aid.

[0067] According to a third aspect of the embodiments of the present application, the embodiments of the present application provide an electronic device, the device comprising: a processor and a memory;

[0068] The memory is configured to store one or more program instructions;

[0069] The processor is configured to run the one or more program instructions to perform the steps of the power distribution network fault recovery method considering the UPS and the DC line interconnection.

[0070] According to a fourth aspect of the embodiments of the present application, the embodiments of the present application provide a computer readable storage medium, and the computer readable storage medium stores a computer program, and the computer program is executed by a processor to implement the steps of the power distribution network fault recovery method considering the UPS and the DC line interconnection.

[0071] Compared with the prior art, the power distribution network fault recovery method considering the UPS and the DC line interconnection has the following beneficial effects:

[0072] 1. The present application is based on the power distribution network scenario considering the UPS, and the number of switch breakages is considered in the island division model, which reduces the number of formed islands, restores the power supply of important loads, increases the equivalent value of recovered islands, expands the power supply range, and improves the reliability of power supply.

[0073] 2. The present application further reduces the number of islands by transforming the AC line, so that the independently operated islands are connected through the tie line.

[0074] 3. Considering the adjustment of the non-recovered or not fully recovered load, the range of island fusion can be effectively expanded, compared with the division of the entire fault power distribution system into a large island and multiple single-source small islands, the recovery strategy considering power interconnection between islands has flexibility, various forms of contact, and reasonable combination can effectively improve the utilization of power generation resources and the effect of load recovery;

[0075] 4. Based on the island division strategy considering the number of switch openings, the connection between islands is considered during the fault recovery stage, and a power distribution network fault recovery strategy that can improve the load recovery amount, shorten the fault recovery time, increase the power supply time of the recovered load, and improve the flexibility of the power distribution network is obtained;

[0076] 5. Considering the synergistic effect of distributed power supply and uninterrupted power supply and the regulation of load, the possible forms of island combination are increased, and in the presence of distributed power supply downtime, the normal power supply of the load in the island fusion area can be maintained, the advantages of coordinated multi-source power supply are exerted, the resistance of the system after partial distributed power supply downtime is enhanced, and the flexibility of the power distribution system is improved. BRIEF DESCRIPTION OF DRAWINGS

[0077] The drawings accompanying the specification of this application form a part thereof, serve to provide further understanding of the application, and together with the description of the exemplary embodiments of the application and explanations thereof serve to explain the application, and do not constitute an improper limitation of the application. In the drawings:

[0078] Figure 1 A flowchart of a power distribution network fault recovery method considering the interconnection of uninterrupted power supply and DC lines provided for an embodiment of the application;

[0079] Figure 2 A specific implementation flowchart of a power distribution network fault recovery method considering the interconnection of uninterrupted power supply and DC lines provided for an embodiment of the application;

[0080] Figure 3 An improved PG&E 33 node power distribution system schematic diagram in a power distribution network fault recovery method considering the interconnection of uninterrupted power supply and DC lines provided for an embodiment of the application;

[0081] Figure 4 A power distribution network fault condition schematic diagram in a power distribution network fault recovery method considering the interconnection of uninterrupted power supply and DC lines provided for an embodiment of the application;

[0082] Figure 5 A different power distribution network fault recovery strategy schematic diagram in a power distribution network fault recovery method considering the interconnection of uninterrupted power supply and DC lines provided for an embodiment of the application;

[0083] Figure 6A comparison chart of power supply time length and load recovery rate of each strategy in a power distribution network fault recovery method considering the interconnection of uninterrupted power supply and DC line provided by the embodiment of the present application is provided.

[0084] Figure 7 An AC line modification schematic diagram of the power distribution network fault recovery method considering the interconnection of uninterrupted power supply and DC line provided by the embodiment of the present application is provided.

[0085] Figure 8 A structure schematic diagram of the power distribution network fault recovery system considering the interconnection of uninterrupted power supply and DC line provided by the embodiment of the present application is provided. DETAILED DESCRIPTION

[0086] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0087] The following detailed description is exemplary description, which aims to provide further detailed description of the present application. Unless otherwise specified, all technical terms used in the present application have the same meaning as that generally understood by the general technical personnel in the field to which the present application belongs. The terms used in the present application are only for the purpose of describing the specific embodiments, and are not intended to limit the exemplary embodiments according to the present application.

[0088] The first embodiment of the present application provides a power distribution network fault recovery method considering the interconnection of uninterrupted power supply and DC line. In the power distribution network scenario considering uninterrupted power supply (UPS), the purpose of combining hierarchical division of island and power mutual aid considering the interconnection of DC line in the fault recovery stage is to reduce the number of single power supply small islands, to improve the utilization rate of power generation resources, the recovery effect of important loads and the flexibility of power distribution system by considering the connection between islands. The following will be described in conjunction with Figure 1 and Figure 2 The first embodiment of the present application provides a power distribution network fault recovery method considering the interconnection of uninterrupted power supply and DC line.

[0089] As Figure 1 shown, in step S100, a power distribution network island hierarchical division model considering UPS is established, considering the constraint conditions including island power balance constraint, UPS operation constraint and island operation constraint, the island hierarchical division model includes a primary island division model and an island optimization model, the primary island division model takes the maximum important load recovery amount as the target, and the primary island division model is solved to obtain the primary island division result satisfying the constraint, the island optimization model takes the minimum branch opening number as the target, and the primary island division result is optimized to reduce the number of single DG power supply islands to obtain the optimal island division result.

[0090] The power distribution network island grading model considering the uninterruptible power supply includes primary island division and island optimization.

[0091] First, an uninterruptible power supply model is established, that is:

[0092] The UPS capacity is set according to the maximum load delay demand of the UPS electrical equipment, and the delay time is set to 2 hours in this embodiment.

[0093]

[0094] In formulas (1), (2), (3), represents the upper limit of the UPS capacity at node j; represents the backup capacity of the external battery of the UPS at node j; represents the maximum load at node j; θ jf , η j respectively represent the power factor and the inverter conversion efficiency of the UPS at node j; P sb , N, n respectively represent the capacity of each battery group, the number of battery groups, and the number of batteries in each battery group.

[0095] The primary island division model has a target function of maximum important load recovery, that is:

[0096]

[0097] In formula (4), f1 represents the value function of the recovered load; n represents the set of nodes; K represents the set of islands; T represents the interval set of discrete fault recovery time periods; Δt represents the interval length of discrete fault periods; ω i represents the load weight coefficient of node i; represents the active power of the recovered load of node i. λ i,g is an integer variable, λ i =1 indicates that the power loss load i is restored to power supply within the island g, and vice versa λ i,g =0.

[0098] The island optimization model has a target function of minimum number of branch breakages, that is:

[0099]

[0100] In formula (5), f2 represents the number of closed branches, maxf2 represents the target of maximizing the number of closed branches, and b is the branch set; k ij is the switch state of the branch ij, k ij =1 indicates that the branch is closed, and vice versa k ij =0.

[0101] where the power balance constraint in island g is:

[0102]

[0103] In equation (6), K represents the set of islands; T represents the set of intervals of discrete fault recovery periods; λ i,g is an integer variable, λ i,g = 1 indicates that the outage load i is restored in island g, otherwise λ i,g = 0. represents the active power generated by the distributed generator at node i at time period t; represents the active power absorbed by the load at node i at time period t; is the discharge power of the UPS at node i at time period t.

[0104] The UPS operation constraint is:

[0105]

[0106] In the equation: represents the operation loss of the UPS at node j at time t; is the loss coefficient of the UPS at node j; is the discharge power of the UPS at node j at time t; are the maximum and minimum discharge power of the UPS at node j at time t, respectively; are the upper and lower limits of the UPS capacity at node j, respectively.

[0107] The island operation constraint is:

[0108]

[0109]

[0110] In equations (7), (8), and (9), b represents the set of distribution network branches; represents the power flowing through the line l ij from the first end node i to the end node j in the island; represents the maximum power transmission that the line l ij can withstand; represents the square of the node voltage value of node i at time t; and are the upper and lower limits of the voltage of node i, respectively; represents the square of the branch current value of branch ij at time t; is the upper limit of the current of branch ij.

[0111] First, a breadth-first search algorithm is used to solve the primary islanding model, obtaining the maximum power supply area that satisfies the energy constraints within the islands. Then, a hybrid particle swarm optimization algorithm is used to optimize the objective function of the islanding hierarchy model. When the set maximum number of iterations is reached or the program search cutoff condition is met, the optimal value matrix of each control variable in the distribution network is output. Based on the optimized value matrix, each tie switch is operated to obtain the final islanding scheme. The final islanding scheme reduces the number of islands formed while restoring power supply to important loads, increasing the equivalent value of island restoration, expanding the power supply range, and improving power supply reliability.

[0112] like Figure 1 As shown, in step S200, the AC line is converted into a DC line, and a power mutual assistance model is established during the fault recovery of the distribution network considering the interconnection of DC lines. The model considers the constraints including the operation constraints of the distribution network, the topology constraints of the distribution network, the power flow constraints of the system, and the system security constraints. Based on the optimal islanding result, the power mutual assistance model is solved to obtain the optimal islanding joint result, thereby obtaining the distribution network fault recovery strategy with power mutual assistance between islands.

[0113] During distribution network fault recovery, the power mutual assistance model considering DC line interconnection ensures a sufficiently large load restoration range, freeing it from the voltage and frequency constraints of closed AC lines. This allows for more possible combinations of power mutual assistance, facilitating renewable energy absorption and load restoration. The objective function of the power mutual assistance model during distribution network fault recovery is:

[0114]

[0115] In equation (10), f3 represents the load recovery amount minus the network loss, and maxf3 represents the objective of maximizing the load recovery amount while minimizing the network loss. Let represent the active power of load i within island g, Δt represent the duration of each stage during the recovery process, and T′ represent the set of all stages. For 0-1 integer variables, This means that load i has been restored to power within island g, and vice versa. This represents the network loss of the entire system.

[0116] Critical loads are mainly concentrated in urban areas, while distributed energy resources are located at the suburban edges. Modifying existing closed-loop power lines and intermediate lines, converting AC lines into branch lines, relaxes the power exchange constraints of isolated transformer substations. By breaking free from the closed-loop constraints of AC lines, more combinations of power exchange are possible, facilitating renewable energy integration and load restoration. For example... Figure 7 .

[0117] The power mutual assistance constraint is:

[0118] ΔG gij =|G gi -G gj |,i,j∈g,G gi ≥0∪G gj ≥0 (11)

[0119]

[0120] In equations (11) and (12), G gi G is the power margin for redundancy within the island i. gj ΔG represents the power margin for redundancy within the isolated island j. gij This represents the difference in power margin between island i and island j, indicating the redundancy of power supply. This represents the sum of active power that distributed power sources within island g can generate; This represents the sum of the uninterruptible power discharge power within the isolated island g; This represents the sum of active power absorbed by the loads within the isolated island g; It represents the total active power that can be generated by all distributed power sources in the distribution network; It represents the sum of the charging and discharging power of all uninterruptible power sources in the distribution network, with charging power being positive and discharging power being negative; this formula represents the power supply margin of power redundancy in the islanded network.

[0121] Consider selectively restoring unrestored or incompletely restored loads to obtain different power balance combinations, and select the optimal combination that satisfies the power balance objective function.

[0122] Based on formulas (13), (14), and (15) mentioned below, selective restoration is performed on loads that have not been restored and controllable loads that have not been fully restored. Specifically:

[0123] After two isolated islands perform power exchange and merge into one region, the distributed power sources that originally belonged to these two islands can simultaneously supply power to the loads within the region. This scheme uses power redundancy differences for exchange, meaning that one island has redundant power supply. After merging, more loads can be supplied, allowing for selective restoration of controllable loads that haven't fully recovered or haven't been restored, based on the constraints mentioned earlier. While there may be many island combinations capable of power exchange, this scheme ultimately selects the combination that maximizes the objective function f3 value—that is, the combination with the most load restoration and the lowest network loss. This process is also selective.

[0124] The load control model is as follows:

[0125]

[0126] In equations (13) and (14), P L,i Let P' be the total active power of the load at node i. L,i Let be the active power of the uncontrollable load at node i; Let be the active power of the controllable load at node i; Let be the maximum active power of the controllable load at node i.

[0127] Load control constraints are:

[0128]

[0129] Equation (15) represents the range of adjustments that can be made for all unrestored or incompletely restored loads, where λ i Indicates whether the load at node i is connected to the island and power is restored, λ i =1 indicates access, λ i =0 indicates that the load has not been restored; n' and n2 represent the sets of loads that have not been restored or have not been fully restored; n represents the set of nodes in the distribution network; N indicates that all loads within n2 are connected.

[0130] Establishing operational constraints for the distribution network includes distributed generation output constraints and uninterruptible power supply (UPS) operational constraints.

[0131] Establish distribution network topology constraints, system power flow constraints, operating voltage constraints, and branch capacity constraints.

[0132] The output constraints of distributed power sources are:

[0133]

[0134]

[0135] In equations (16), (17), and (18), These represent the active power and reactive power generated by the power source at node j during time period t, respectively. The upper and lower limits of the active power output of the power source at node j within the time period t; The capacity of the power supply connected to node j; The minimum operating power factor of the power supply at node j;

[0136] The capacity constraint is:

[0137]

[0138] Equation (19) indicates that the remaining capacity on the power supply side must meet the power supply demand of the restored load during the restoration process. Where n represents the set of nodes; K represents the set of islands; T represents the set of discrete fault restoration intervals; Δt represents the interval length of the discrete fault restoration period; ω i This represents the load weighting coefficient for node i. λ represents the active power of the restored load at node i. i,g For integer variables, γ i =1 indicates that the power-loss load i has its power restored within the island g, and vice versa. i,g =0; This represents the remaining capacity of distributed synchronous generators and uninterruptible power supplies within island g.

[0139] The distribution network topology constraints are:

[0140]

[0141] In equations (20), (21), and (22), This is a 0-1 integer variable representing the network connection status between node i and node j within island k. This indicates that lines (i,j) are connected; otherwise, it indicates that the line is disconnected. β ij,k and β ji,k Also 0-1 integer variables, representing the relationship between node i and node j within island k respectively; b represents the set of paths; Ω(i) represents all nodes connected to node i; L m represents the set of nodes that do not contain balancing nodes; m represents the power nodes within island k that act as balancing nodes.

[0142] Equation (20) represents the relationship between the line status and the first and last nodes. Equation (21) represents that node i, excluding the balancing node, can only have one parent node. Equation (22) represents that the balancing node has no parent node.

[0143] The system power flow constraints are:

[0144] When a fault occurs in the distribution network, the network topology changes. Therefore, the traditional Distflow power flow model is improved by introducing the line interruption variable γ. t,ij Relaxing the power flow equations yields Distflow operation constraints applicable to distribution network fault recovery, including:

[0145]

[0146] In equations (23), (24), (25), (26), (27), (28), and (29), K represents the set of islands; T represents the set of discrete fault recovery time intervals; L represents the set of lines; G represents the set of nodes; and the island k represents the set of nodes. and These represent the active power and reactive power flowing from node i to node j on line (i,j), respectively. and The distributed power source at node j generates active and reactive power; r ij and x ij Let (i,j) be the resistance and reactance of the line. It is the square of the magnitude of the current on line (i,j); The variable represents the opening and closing of the line. Its value is 1 when the line (i,j) is closed, and 0 otherwise. M is an infinite constant, which means that its value is 0 when the line (i,j) in island k is normally connected, and infinite otherwise. and These represent the active power and reactive power consumed by the load at node j, respectively. and These are the active power and reactive power flowing from node j to node h, respectively. and These represent the upper and lower limits of the voltage at node i, respectively, and are set to 0.95 times and 1.05 times. and These are the upper limits for the active and reactive power output of the distributed synchronous generator, respectively, and the reactive power output of the generator can be freely adjusted within these limits. This represents the maximum current allowed to pass through line (i,j).

[0147] Equation (23) is the power balance equation of node j; Equations (24), (25), and (26) are convex relaxation treatments of equation (23) to relax the operation constraints and topology constraints of the distribution network by introducing inequality constraints, so that the active power, reactive power and line current of the disconnected branch are zero, and there are no constraints on the closed branch; Equation (25) is a variant of the power definition of the flow from node i to node j; Equations (26)-(29) are the safety constraints of the system operation.

[0148] The power mutual assistance model during distribution network fault recovery contains integer variables and nonlinear constraints. Relaxing the nonlinear constraints transforms them into convex constraints, and the entire model is transformed into a mixed-integer second-order cone programming model, which belongs to the convex optimization model. The solution method for the convex optimization model uses YAMIP programming, CPLEX, and MOSEK to solve the mixed-integer second-order cone programming model, yielding a distribution network recovery strategy considering DC line interconnections.

[0149] This invention first solves the islanding hierarchy model of a distribution network considering uninterruptible power supplies (UPS) to obtain an islanding scheme. Based on the islanding results, it optimizes the power balance model of the distribution system considering DC line interconnection, which contains integer variables and nonlinear constraints. This yields a distribution network fault recovery method that can establish connections between islands, effectively extend the power supply time of restored loads, improve load recovery rate, and increase the utilization rate of power generation resources during the recovery phase after a fault. This flexible distribution network recovery method, through the establishment of the islanding hierarchy model considering UPS, reduces the number of generated islands while rapidly restoring important loads. During the recovery phase, based on the aforementioned islanding results, it considers DC line interconnection and load regulation constraints, and obtains a power balance model during distribution network fault recovery under constraints such as distributed generation output, UPS operation, and distribution network topology. The distribution system recovery power balance model contains integer variables and nonlinear constraints. Relaxing the nonlinear constraints transforms them into convex constraints, and the entire model is transformed into a mixed-integer second-order cone programming model, belonging to the convex optimization model. The constructed non-convex nonlinear model is transformed into a mixed-integer second-order cone programming model using the second-order cone relaxation method and then solved. By solving the distribution network islanding hierarchical partitioning model considering uninterruptible power sources and the power mutual assistance model during distribution network fault recovery considering DC line interconnection, a distribution network fault recovery method is obtained that can reduce the number of single-source small islands, consider the interconnection between islands to improve the utilization rate of power generation resources, the load recovery effect, and the resilience of the distribution system.

[0150] To verify the effectiveness of the distribution network fault recovery method considering uninterruptible power supplies and DC line interconnections provided by this invention, this example provides a specific instance: the improved PG&E33 node distribution system is shown in the attached figure. Figure 3 As shown in Table 1, the distribution network parameters are shown in Table 2, and the node load weight levels and weight coefficients are shown in Table 3. The weights for level 1, level 2, and level 3 loads are 100, 10, and 1, respectively. The distributed generation parameters are shown in Table 3.

[0151] Table 1 Parameters of the 33-node power distribution system

[0152]

[0153]

[0154] Table 2 Node Load Weight Levels and Weight Coefficients

[0155] Load level Load node number Load weight Primary load 3，6，13，19，23，30 100 Secondary load 2，5，7，8，12，15，16，20，22，26，27，28，29，31 10 Tertiary load Remaining load 1

[0156] Table 3 Distributed power generation parameters

[0157]

[0158] The following is an overview of the fault conditions in the improved IEEE 33-node point matching system. Figure 4 As shown, if there are six faults in the line and the faults cannot be repaired in a short time, it is considered a broken line.

[0159] The strategy of this invention is as follows: Using the distribution network fault recovery method that takes into account uninterruptible power supply and DC line interconnection proposed in this invention, the number of switch disconnections is considered in the islanding model to form fewer single-source power supply islands. Then, based on the islanding already divided by the aforementioned islanding model, the AC line is modified and power mutual assistance is performed in the fault recovery stage to obtain the final recovery strategy.

[0160] Comparison Strategy 1: Optimize the islanding by using the islanding hierarchy proposed in this invention, but do not consider power mutual assistance between islands during the fault recovery phase.

[0161] Comparison Strategy 2: This invention uses the power mutual assistance between islands in the fault recovery phase, but does not consider the hierarchical islanding in the islanding phase, and only solves the primary islanding model.

[0162] Comparison Strategy 3: The proposed distribution network fault recovery method is not used. In the islanding stage, only the primary islanding model is solved, and the power mutual assistance between islands is not considered in the fault recovery stage.

[0163] The fault recovery scenario obtained using the distribution network fault recovery method proposed in this invention, which considers uninterruptible power supplies and DC line interconnections, is shown in the appendix. Figure 5 As shown in Figure a; the fault recovery scenario obtained by comparing strategy 1 is shown in the appendix. Figure 5 As shown in b; the fault recovery scenario obtained by comparing strategy 2 is attached. Figure 5 As shown in c; the fault recovery scenario obtained by comparing strategy 3 is attached. Figure 5 As shown in d.

[0164] The power distribution network fault recovery scheme proposed in this invention, such as Figure 5 As shown in Figure a, while ensuring the normal power supply to important loads, the power supply range of a single island is expanded by adjusting the access of controllable loads 33 and 18 and closing the tie lines (9, 15) and (18, 33), thereby reducing the number of islands powered by a single power source, and the load is restored on this basis.

[0165] The diagrams illustrating the load restoration amount and power supply duration for each strategy are as follows: Figure 6 Based on the aforementioned schematic diagrams of fault recovery scenarios for each strategy, it can be seen that by using the islanded mutual assistance scheme proposed in this paper, the number of single-power islands is reduced, and the synergistic effect of distributed power sources, uninterruptible power sources, and controllable loads within the islands can increase the power supply duration of the loads and increase the load recovery capacity.

[0166] The network losses for each strategy are shown in Table 5. Due to the consideration of power sharing between islands and the closing of the tie switch, which changes the network topology, the network loss of the recovery strategy of this invention is higher than that of the comparative strategy 3. However, due to the coordinated cooperation of distributed power supply and uninterruptible power supply, the network loss does not increase significantly.

[0167] Table 5 Network Loss and Load Recovery for Each Strategy

[0168]

[0169] The above analysis leads to the following conclusions: (1) Considering the number of switches disconnected in the islanding model reduces the number of islands formed while restoring power to important loads, increasing the equivalent value of island restoration, expanding the power supply range, and improving power supply reliability. (2) Considering the adjustment of unrestored or incompletely restored loads can effectively expand the scope of island integration. Compared with dividing the entire faulted power distribution system into one large island and multiple single-power-source small islands, the restoration strategy considering power mutual assistance between islands is more flexible, has diverse connection forms, and reasonable combination can effectively improve the utilization rate of power generation resources and the load restoration effect. (3) Based on the islanding strategy considering the number of switches disconnected, considering power mutual assistance between islands during the fault restoration stage yields a restoration strategy that can increase the load restoration amount, shorten the fault restoration time, increase the power supply time of restored loads, and improve the elasticity of the distribution network.

[0170] Corresponding to the distribution network fault recovery method considering uninterruptible power supplies and DC line interconnection disclosed in the above embodiments, this invention also discloses a distribution network fault recovery system considering uninterruptible power supplies and DC line interconnection, such as... Figure 8 As shown, it specifically includes:

[0171] The islanding classification module is used to establish a distribution network islanding classification model that considers UPS. It considers constraints including power balance constraints within the island, UPS operation constraints, and island operation constraints. The islanding classification model includes a primary islanding model and an islanding optimization model. The primary islanding model aims to maximize the recovery of important loads. The primary islanding model is solved to obtain a primary islanding classification result that meets the constraints. The islanding optimization model aims to minimize the number of branch disconnections. The primary islanding classification result is optimized to reduce the number of islands powered by a single DG to obtain the optimal islanding classification result.

[0172] The inter-island power mutual assistance module is used to convert AC lines into DC lines, establish a power mutual assistance model during the fault recovery of the distribution network considering the interconnection of DC lines, and consider the constraints including the operation constraints of the distribution network, the topology constraints of the distribution network, the system power flow constraints, and the system security constraints. Based on the optimal island partitioning result, the power mutual assistance model is solved to obtain the optimal island joint result, thereby obtaining the distribution network fault recovery strategy of inter-island power mutual assistance.

[0173] It should be noted that for a detailed description of a distribution network fault recovery system considering uninterruptible power supply and DC line interconnection provided in the embodiments of the present invention, please refer to the relevant description of a distribution network fault recovery method considering uninterruptible power supply and DC line interconnection provided in the embodiments of the present invention, which will not be repeated here.

[0174] In addition, embodiments of the present invention also provide an electronic device, the device comprising: a processor and a memory; the memory for storing one or more program instructions; the processor for executing one or more program instructions to perform the steps of a distribution network fault recovery method considering uninterruptible power supply and DC line interconnection as described in any of the preceding embodiments.

[0175] It should be noted that for a detailed description of an electronic device provided in the embodiments of the present invention, please refer to the relevant description of a power distribution network fault recovery method considering uninterruptible power supply and DC line interconnection provided in the embodiments of this application, which will not be repeated here.

[0176] In addition, embodiments of the present invention also provide a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of a distribution network fault recovery method considering uninterruptible power supply and DC line interconnection as described in any of the preceding claims.

[0177] It should be noted that for a detailed description of a computer-readable storage medium provided in the embodiments of the present invention, please refer to the relevant description of a power distribution network fault recovery method considering uninterruptible power supply and DC line interconnection provided in the embodiments of this application, which will not be repeated here.

[0178] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not the only ones. All modifications within the scope of this invention or its equivalents are included in this invention.

[0179] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0180] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0181] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0182] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0183] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for fault recovery in a distribution network considering the interconnection of uninterruptible power supplies and DC lines, characterized in that, The method includes: A hierarchical islanding model for distribution networks considering UPS is established, taking into account constraints including power balance constraints within the island, UPS operation constraints, and island operation constraints. The hierarchical islanding model includes a primary islanding model and an islanding optimization model. The primary islanding model aims to maximize the recovery of critical loads, and the primary islanding model is solved to obtain a primary islanding result that satisfies the constraints. The islanding optimization model aims to minimize the number of branch disconnections, and the primary islanding result is optimized to reduce the number of islands powered by a single DG to obtain the optimal islanding result. The AC lines are converted into DC lines, and a power mutual assistance model is established during the fault recovery of the distribution network considering the interconnection of DC lines. The model takes into account the constraints including the operation constraints of the distribution network, the topology constraints of the distribution network, the power flow constraints of the system, and the security constraints of the system. Based on the optimal islanding results, the power mutual assistance model is solved to obtain the optimal islanding joint results, thereby obtaining the distribution network fault recovery strategy of power mutual assistance between islands. Establish a hierarchical islanding model for distribution networks that takes UPS into account, which specifically includes: Establish an uninterruptible power supply model: In the formula, Represents a node The maximum capacity of the UPS at that location; Represents a node The backup capacity of the UPS external battery; Represents a node Maximum load at the location; , Representing nodes respectively The power factor and inverter conversion efficiency of the UPS at the location; , , These represent the capacity of each battery group, the number of battery groups, and the number of batteries in each battery group, respectively. The objective function of the primary islanding model is to maximize the recovery of critical loads. The objective function of the primary island partitioning model is: In the formula, A function representing the value of restoring the load; Represents a set of nodes; T represents the set of isolated islands; T represents the set of discrete fault recovery time intervals. The interval length represents the discrete fault period; Represents a node The load weighting coefficient; Represents a node The active power of the restored load; For integer variables, Indicates power loss load On the deserted island Power is restored internally, and vice versa. ; The objective function of the island optimization model is to minimize the number of branch breaks, i.e.: In the formula, f2 represents the number of closed branches, and maxf2 represents the objective of maximizing the number of closed branches. For distribution network branch collection; branch road The on / off state, Indicates a closed branch, otherwise ; Establish a power mutual assistance model during distribution network fault recovery considering DC line interconnections, specifically including: The power reciprocity model during distribution network fault recovery ensures a sufficiently large load restoration range. The objective function of the power reciprocity model during distribution network fault recovery is: In the formula, f3 represents the load recovery amount minus the network loss, and maxf3 indicates that the objective is to maximize the load recovery amount while minimizing the network loss. Indicates being on an isolated island Internal load active power, This indicates the time taken for each stage in the power distribution restoration process; Represents the set of all stages; For 0-1 integer variables, Representative load On the deserted island Power has been restored in some areas, while it has not been restored in others. ; Represents the network loss of the entire system; The power mutual assistance constraint is: In the formula, G gi G is the power margin for redundancy within the island i. gj ∆G represents the power margin for redundancy within the isolated island j. gij This represents the difference in power margin between island i and island j, indicating the redundancy of power supply. Indicates an isolated island The sum of active power that can be generated by distributed power sources within the area; Indicates an isolated island The sum of the discharge power of the uninterruptible power supply within; Indicates being designated as an isolated island The sum of active power absorbed by the load within the area; It represents the total active power that can be generated by all distributed power sources in the distribution network; It represents the sum of the charging and discharging power of all uninterruptible power sources in the distribution network, with charging power being positive and discharging power being negative.

2. The method for fault recovery in a distribution network considering uninterruptible power supply and DC line interconnection as described in claim 1, characterized in that, Consider the constraints, including islanded power balance constraints, UPS operation constraints, and islanded operation constraints, specifically including: The power balance constraint within the island is: In the formula, T represents the set of isolated islands; T represents the set of discrete fault recovery time intervals. For integer variables, Indicates power loss load Restore power within the isolated island, or vice versa. ; Represents a node Distributed power sources The active power generated during a given time period; Represents a node Load at The active power absorbed during a given time period; For nodes During UPS time period The discharge power; The UPS operating constraints are as follows: In the formula, Represents a node UPS at the time Operating losses; For nodes The loss factor of the UPS; For nodes At UPS time The discharge power; , They are nodes At UPS time Maximum and minimum discharge power; , They are nodes The upper and lower limits of UPS capacity; The constraints for operation within the isolated island are: In the formula, Represents the set of branches in a distribution network; This indicates that the flow passes through the first node within the island. End node is The route The power; Indicates the line The maximum power transmission capacity; Represents a node The square of the node voltage at time t; and They are nodes Upper and lower limits of voltage; Indicates a branch The square of the branch current at time t; branch road The upper limit of the current.

3. The method for fault recovery in a distribution network considering uninterruptible power supply and DC line interconnection as described in claim 1, characterized in that, The solution process for the hierarchical partitioning model of distribution network islands includes: First, a breadth-first search algorithm is used to solve the primary islanding model to obtain the maximum power supply area that satisfies the power constraints within the island. Then, a hybrid particle swarm optimization algorithm is used to optimize the objective function of the islanding hierarchical model. When the set maximum number of iterations is reached or the program search cutoff condition is met, the optimal value matrix of each control variable in the distribution network is output. Based on the optimized value matrix, each tie switch is operated to obtain the final islanding scheme.

4. The method for fault recovery in a distribution network considering the interconnection of uninterruptible power supplies and DC lines according to claim 1, characterized in that, Establishing a power mutual assistance model during distribution network fault recovery considering DC line interconnections, specifically including: Selectively restore unrestored or incompletely restored loads within the island to obtain different power-matching island combinations, and select the optimal island combination that satisfies the power-matching objective function; The load control model is as follows: In the formula, P L,i Let λ be the total active power of the load at node i. i Indicates whether the load at node i is connected to the island and power is restored, λ i =1 indicates access, λ i =0 indicates that it was not recovered. For nodes The active power of uncontrollable loads; For nodes The active power of the controllable load; For nodes The maximum active power of the controllable load; Load control constraints are: The above formula represents the adjustable range of all unrestored or incompletely restored loads, where n', This represents a set of loads that have not been restored or have not been fully restored. Indicates all All loads within the area are connected.

5. A method for fault recovery in a distribution network considering uninterruptible power supplies and DC line interconnection as described in claim 1, characterized in that, Consider the constraints, including distribution network operation constraints, distribution network topology constraints, system power flow constraints, and system security constraints, specifically including: The operational constraints of the power distribution network include distributed generation output constraints and UPS operational constraints. The output constraint of the distributed power source is: In the formula, , Time periods Inside The active and reactive power generated by the power source at the node; , Time period Inside The upper and lower limits of the active power output of the power source at the node; for The capacity of the power supply connected to the node; For nodes Minimum operating power factor of the power supply at the location; The distribution network topology constraints are: In the formula, This is a 0-1 integer variable representing the network connection status between node i and node j within island k. This indicates that lines (i,j) are connected; otherwise, it indicates that the lines are disconnected. and Also 0-1 integer variables, representing the relationship between node i and node j within island k respectively; b represents the set of routes; This represents all nodes connected to node i; This represents the set of nodes that do not contain balancing nodes; m represents the power nodes within island k that act as balancing nodes. The system power flow constraints are: When a fault occurs in the distribution network, the network topology changes. The traditional Distflow power flow model is improved by introducing line interruption variables to relax the power flow equations, resulting in Distflow power flow operation constraints suitable for distribution network fault recovery, including: In the formula, T represents the set of isolated islands; L represents the set of discrete fault recovery time intervals; G represents the set of lines; and G represents the set of nodes. Within island k... and These represent the active power and reactive power flowing from node i to node j on line (i,j), respectively. and It generates active and reactive power for the distributed power sources on node j; and Let (i,j) be the resistance and reactance of the line. It is the square of the magnitude of the current on line (i,j); The variable is the line opening / closing variable. The value of the variable is 1 when the line (i,j) is closed, and 0 otherwise. M is a constant. The value of M is 0 when the line (i,j) in island k is normally connected, and infinity otherwise. and They are nodes The active and reactive power consumed by the load; and They are nodes Flow to Node Active power and reactive power; and These represent the upper and lower limits of the voltage at node i, respectively. and These are the upper limits for the active and reactive power outputs of the distributed synchronous generator, respectively, and the reactive power output of the power source can be freely adjusted within these limits. This represents the maximum current allowed to pass through line (i,j); The capacity constraint is: The above formula indicates that the remaining capacity on the power supply side must meet the power supply needs of the restored load during the recovery process, where, Represents a set of nodes; T represents the set of isolated islands; T represents the set of discrete fault recovery time intervals. The interval length represents the discrete fault period; Represents a node The load weighting coefficient; Represents a node The active power of the restored load; For integer variables, Indicates power loss load On the deserted island Power is restored internally, and vice versa. ; Indicates an isolated island The remaining capacity of internal distributed synchronous generators and uninterruptible power supplies.

6. A method for fault recovery in a distribution network considering uninterruptible power supplies and DC line interconnection as described in claim 5, characterized in that, The solution process for the power mutual assistance model during fault recovery in distribution networks considering DC line interconnections specifically includes: The power mutual assistance model during distribution network fault recovery contains integer variables and nonlinear constraints. Relaxing the nonlinear constraints transforms them into convex constraints, and the entire model is transformed into a mixed integer second-order cone programming model, which belongs to the convex optimization model. The solution method for the convex optimization model is to use YAMIP programming and CPLEX and MOSEK software to solve the mixed integer second-order cone programming model to obtain the distribution network recovery strategy considering DC line interconnection.

7. A power distribution network fault recovery system considering uninterruptible power supply and DC line interconnection, characterized in that, The system includes: The islanding classification module is used to establish a distribution network islanding classification model that considers UPS. It considers constraints including power balance constraints within the island, UPS operation constraints, and island operation constraints. The islanding classification model includes a primary islanding model and an islanding optimization model. The primary islanding model aims to maximize the recovery of important loads. The primary islanding model is solved to obtain a primary islanding classification result that meets the constraints. The islanding optimization model aims to minimize the number of branch disconnections. The primary islanding classification result is optimized to reduce the number of islands powered by a single DG to obtain the optimal islanding classification result. The inter-island power mutual assistance module is used to transform AC lines into DC lines, establish a power mutual assistance model during the fault recovery of the distribution network considering the interconnection of DC lines, and consider the constraints including the operation constraints of the distribution network, the topology constraints of the distribution network, the system power flow constraints, and the system security constraints. Based on the optimal island partitioning result, the power mutual assistance model is solved to obtain the optimal island joint result, thereby obtaining the distribution network fault recovery strategy of inter-island power mutual assistance. Establish a hierarchical islanding model for distribution networks that takes UPS into account, which specifically includes: Establish an uninterruptible power supply model: In the formula, Represents a node The maximum capacity of the UPS at that location; Represents a node The backup capacity of the UPS external battery; Represents a node Maximum load at the location; , Representing nodes respectively The power factor and inverter conversion efficiency of the UPS at the location; , , These represent the capacity of each battery group, the number of battery groups, and the number of batteries in each battery group, respectively. The objective function of the primary islanding model is to maximize the recovery of critical loads. The objective function of the primary island partitioning model is: In the formula, A function representing the value of restoring the load; Represents a set of nodes; T represents the set of isolated islands; T represents the set of discrete fault recovery time intervals. The interval length represents the discrete fault period; Represents a node The load weighting coefficient; Represents a node The active power of the restored load; For integer variables, Indicates power loss load On the deserted island Power is restored internally, and vice versa. ; The objective function of the island optimization model is to minimize the number of branch breaks, i.e.: In the formula, f2 represents the number of closed branches, and maxf2 represents the objective of maximizing the number of closed branches. For distribution network branch collection; branch road The on / off state, Indicates a closed branch, otherwise ; Establish a power mutual assistance model during distribution network fault recovery considering DC line interconnections, specifically including: The power reciprocity model during distribution network fault recovery ensures a sufficiently large load restoration range. The objective function of the power reciprocity model during distribution network fault recovery is: In the formula, f3 represents the load recovery amount minus the network loss, and maxf3 indicates that the objective is to maximize the load recovery amount while minimizing the network loss. Indicates being on an isolated island Internal load active power, This indicates the time taken for each stage in the power distribution restoration process; Represents the set of all stages; For 0-1 integer variables, Representative load On the deserted island Power has been restored in some areas, while it has not been restored in others. ; Represents the network loss of the entire system; The power mutual assistance constraint is: In the formula, G gi G is the power margin for redundancy within the island i. gj ∆G represents the power margin for redundancy within the isolated island j. gij This represents the difference in power margin between island i and island j, indicating the redundancy of power supply. Indicates an isolated island The sum of active power that can be generated by distributed power sources within the area; Indicates an isolated island The sum of the discharge power of the uninterruptible power supply within; Indicates being designated as an isolated island The sum of active power absorbed by the load within the area; It represents the total active power that can be generated by all distributed power sources in the distribution network; It represents the sum of the charging and discharging power of all uninterruptible power sources in the distribution network, with charging power being positive and discharging power being negative.

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