Multi-stage recovery method and system for recovering power supply for important load based on micro-grid

Abstract

The invention discloses a multi-stage recovery method and system for recovering power supply for an important load based on a micro-grid, and relates to the field of power distribution network control of a power system, and the method comprises the steps: recognizing all recovery paths between the micro-grid and the important load under a steady state condition, removing the paths which do not meet a constraint condition, and after a fault occurs and a power failure occurs, carrying out the recovery of all recovery paths. Identifying and storing the recovery paths which are not influenced by the fault in the residual paths in a candidate recovery path table; identifying an available micro-grid, and deleting a path starting from a non-available micro-grid in the candidate recovery path table; based on the candidate recovery path table and the constraint condition, constructing a recovery scheme, and evaluating a target function value of the recovery scheme; selecting an optimal recovery scheme by adopting a multi-stage recovery method according to the target function value of the recovery scheme; according to the invention, the power supply time of the important load is longer; the uncertainty of power grid energy is considered, and a recovery scheme is flexibly determined according to the available condition of the micro-grid after the fault.

Description

Technical Field

[0001] The present invention relates to the field of power distribution network control of an electric power system, and in particular to a multi-stage restoration method and system for restoring power supply to important loads based on a microgrid. Background Art

[0002] The resilience of the power grid to extreme natural disasters such as earthquakes, storms, and floods is one of the most important issues for smart networks. Resilience is the ability of the power grid to prepare and adapt to changes in conditions, and to handle and self-recover them. Grid recovery improvements are one solution to improve the resilience of the distribution network in emergency situations. After an extreme natural disaster, the distribution network may face severe damage. If a natural disaster destroys the main grid or makes the distribution network trolled from the main grid, the distribution network will face power outages. In this case, the power of the main grid is not available, and the remaining distributed generation units and microgrids can only serve as power sources for the outage loads. These units have limited power output and electrical energy, and cannot restore all the outage loads. Therefore, the loads must be restored according to their importance. Some loads are more important in the distribution network, such as hospitals, water supply stations, street lights, communication stations, etc. These loads are called important loads. Therefore, in the critical situation of power outages in the network, restoring important loads becomes a central issue for network operators.

[0003] Existing solutions consider introducing energy storage systems, distributed power sources, and remote control switches to help important loads restore power supply, and some researchers have proposed microgrid formation strategies to handle the restoration process. The disadvantages of these solutions are that they do not take into account the priority of important load restoration, and they only consider one restoration plan during the power outage, which cannot guarantee that the plan is optimal during the entire outage period. Summary of the invention

[0004] In view of the above-mentioned problems, the present invention is proposed.

[0005] Therefore, the technical problem solved by the present invention is: how to provide an optimal recovery strategy that can consider the priority of important loads and effectively restore power supply to important loads when a power outage occurs in the distribution network?

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] In a first aspect, an embodiment of the present invention provides a multi-stage restoration method for restoring power supply to important loads based on a microgrid, comprising:

[0008] Identify all restoration paths between the microgrid and important loads under steady-state conditions, eliminate paths that do not meet constraints, and store the remaining paths;

[0009] After a fault occurs and a power outage occurs, identifying and storing in a candidate restoration path table a restoration path that is not affected by the fault among the stored remaining paths;

[0010] Identify available microgrids, and remove paths starting from non-available microgrids from the candidate restoration path table;

[0011] Based on the candidate recovery path table and constraints, a recovery plan is constructed and the objective function value of the recovery plan is evaluated;

[0012] According to the objective function value of the recovery plan, a multi-stage recovery method is used to select the best recovery plan.

[0013] As a preferred solution of a multi-stage restoration method for restoring power to important loads based on microgrids, wherein:

[0014] The constraints include:

[0015] The bus voltage and line current constraints are expressed as:

[0016]

[0017] Among them, v i 、V min 、V max are the voltage amplitude of bus i, the lower limit and upper limit of voltage amplitude respectively; I j and I max j are the current and upper limit of line j respectively, N b and N l are the collections of buses and lines respectively;

[0018]

[0019] Where P j and Q j are the active power and reactive power passing through line j respectively; P di and Q di are the active power and reactive power of load i respectively; R j and X j are the resistance and reactance of line j respectively;

[0020] The distributed generation output active and reactive power constraints are expressed as:

[0021]

[0022] Where P DG,i and Q DG,i DG i Output active and reactive power, P max DG,i and Qmax DG,i DG i Output active power upper limit and reactive power upper limit;

[0023] Feeder capacity constraint, expressed as:

[0024]

[0025] Where S maxF k is the maximum allowed capacity of feeder k, and F is the set of feeders.

[0026] As a preferred solution of a multi-stage restoration method for restoring power to important loads based on microgrids, wherein:

[0027] The constraints also include:

[0028] The radial constraints of the power grid topology are as follows:

[0029] Define four matrices A, B, C and D obtained from the power grid diagram; where matrix A represents the number of branches connected to each node, matrix B represents directly connected nodes, matrix C describes the generation source of the power grid, and matrix D is equal to Bn*C, where n is the number of nodes;

[0030] If the following rules are followed, the new grid configuration will be radial and all loads will work normally: all elements of matrix A are not zero; a=2(n-1); all elements of matrix D are not zero, where a is the sum of the elements of matrix a.

[0031] As a preferred solution of a multi-stage restoration method for restoring power to important loads based on microgrids, wherein:

[0032] The available microgrid is not affected by the fault and satisfies the following constraints:

[0033]

[0034] Among them, E m (t+1) is the power of the microgrid at time t+1, is the amount of electricity required to supply the local load of microgrid m in the time interval (t, t+1), is the reserve power of microgrid m at time t+1; M is the set of microgrids; the microgrid that does not meet the conditions of available microgrid is a non-available microgrid.

[0035] As a preferred solution of a multi-stage restoration method for restoring power to important loads based on microgrids, wherein:

[0036] The objective function includes:

[0037] The first objective function is the weighted recovery power of important loads, expressed as:

[0038]

[0039] Among them, E Lj，(t,t+1) is the power restored by load j during the time period t~t+1, w j is the weight of load j, indicating the priority of load j; (t, t+1) is the set of restored loads in time period t to t+1; where T S is the start time of the recovery cycle, T E The end time of the recovery cycle;

[0040] The second objective function is the number of switching operations, expressed as:

[0041] f 2 =N sw (t,t+1),t∈(T S ,T E )

[0042] Where N sw (t, t+1) is the number of switching operations required to complete the recovery plan within the time period t to t+1.

[0043] As a preferred solution of a multi-stage restoration method for restoring power to important loads based on microgrids, wherein:

[0044] The evaluation of the objective function value of the recovery scheme includes:

[0045]

[0046] Where m is the set of recovery solutions, f ij is the value of criterion i for the jth option, i.e., f ij is the value of the objective function i of the jth solution; f * i and f - i are the best and worst values ​​of all criterion functions for all alternatives, respectively.

[0047] As a preferred solution of a multi-stage restoration method for restoring power to important loads based on microgrids, wherein:

[0048] The multi-stage recovery method includes:

[0049] Determine the best and worst values ​​of the weighted restored power and the number of switching operations for all schemes; for the weighted restored power, the best value is the maximum value and the worst value is the minimum value; for the number of switching operations, the best value is the minimum value and the worst value is the maximum value;

[0050] Calculate the utility measure and regret measure, expressed as:

[0051]

[0052] Among them, S j and R j They represent the utility measure and regret measure respectively; n is the number of objective functions, w i is the weight of objective function i;

[0053] Calculate the multi-stage recovery index of the j-th alternative, expressed as:

[0054]

[0055] Among them, Q j It means calculating the multi-stage recovery index of the j-th alternative, and the value of v is set to 0.5;

[0056] The recovery schemes are ranked according to the multi-stage recovery index, where the recovery scheme with the smallest multi-stage recovery index is represented as the best value.

[0057] In a second aspect, an embodiment of the present invention provides a multi-stage restoration system for restoring power to important loads based on a microgrid, including:

[0058] A restoration path collection module is used to identify all restoration paths between the microgrid and important loads under steady-state conditions, eliminate paths that do not meet the constraints, and store the remaining paths;

[0059] A candidate path determination module, used for identifying and storing in a candidate recovery path table a recovery path that is not affected by the failure among the stored remaining paths after a failure occurs and a power outage occurs;

[0060] an identification module, used for identifying available microgrids, and deleting paths starting from non-available microgrids in a candidate restoration path table;

[0061] An evaluation module is used to construct a recovery plan based on the candidate recovery path table and constraint conditions, and evaluate the objective function value of the recovery plan;

[0062] The selection module is used to select the best recovery scheme using a multi-stage recovery method according to the objective function value of the recovery scheme.

[0063] In a third aspect, an embodiment of the present invention provides a computing device, including:

[0064] Memory and processor;

[0065] The memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions. When the one or more programs are executed by the one or more processors, the one or more processors implement the multi-stage recovery method for restoring power supply to important loads based on a microgrid as described in any embodiment of the present invention.

[0066] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the multi-stage recovery method for restoring power supply to important loads based on a microgrid.

[0067] Beneficial effects of the present invention: The present invention proposes a multi-stage recovery strategy. Based on the objective function under consideration, the multi-stage recovery method is used to solve the fault recovery problem hour by hour, and the optimal recovery plan for each hour of the fault is given to quickly solve the power outage problem of the power grid; the priority of important loads is taken into account in the recovery process to ensure that the loads with high priority are restored to power first, thereby making the power supply time of important loads longer; considering the uncertainty of power grid energy, the recovery plan is flexibly determined according to the availability of the microgrid after the fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0069] Figure 1 It is an overall flow chart of a multi-stage restoration method for restoring power supply to important loads based on a microgrid according to the first embodiment of the present invention;

[0070] Figure 2 It is a schematic diagram of network performance after an extreme event occurs in the multi-stage restoration method for restoring power supply to important loads based on a microgrid according to the first embodiment of the present invention;

[0071] Figure 3 It is a single-line diagram of a 123 bus distribution network in a simulation example of a multi-stage restoration method for restoring power supply to important loads based on a microgrid according to a second embodiment of the present invention;

[0072] Figure 4 It is a microgrid topology diagram in a simulation example of a multi-stage restoration method for restoring power supply to important loads based on a microgrid as described in the second embodiment of the present invention. DETAILED DESCRIPTION

[0073] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0074] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0075] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0076] Example 1

[0077] Reference Figure 1-Figure 2 , which is the first embodiment of the present invention, provides a multi-stage restoration method for restoring power supply to important loads based on a microgrid, comprising:

[0078] S1: Identify all restoration paths between the microgrid and important loads under steady-state conditions, eliminate paths that do not meet the constraints, and store the remaining paths;

[0079] Specifically, all restoration paths between the microgrid and important loads can be identified through the Bellman-Ford algorithm under steady-state conditions.

[0080] In the embodiment of the present application, the constraints include:

[0081] The bus voltage and line current constraints are expressed as:

[0082]

[0083] Among them, v i 、V min 、V max are the voltage amplitude of bus i, the lower limit and upper limit of voltage amplitude respectively; I j and I max j are the current and upper limit of line j respectively, N b and N l are the collections of buses and lines respectively;

[0084]

[0085] Where P j and Q j are the active power and reactive power passing through line j respectively; P di and Q di are the active power and reactive power of load i respectively; R j and X j are the resistance and reactance of line j respectively;

[0086] The distributed generation output active and reactive power constraints are expressed as:

[0087]

[0088] Where P DG,i and Q DG,i DG i Output active and reactive power, P max DG,i and Q max DG,i DG i Output active power upper limit and reactive power upper limit;

[0089] Feeder capacity constraint, expressed as:

[0090]

[0091] Where S maxF k is the maximum allowed capacity of feeder k, and F is the set of feeders.

[0092] The radial constraints of the power grid topology are as follows:

[0093] Define four matrices A, B, C and D obtained from the power grid diagram; where matrix A represents the number of branches connected to each node, matrix B represents directly connected nodes, matrix C describes the generation source of the power grid, and matrix D is equal to Bn*C, where n is the number of nodes;

[0094] If the following rules are followed, the new grid configuration will be radial and all loads will work normally: all elements of matrix A are not zero; a=2(n-1); all elements of matrix D are not zero, where a is the sum of the elements of matrix a.

[0095] It should be noted that this step is performed under steady-state conditions, that is, the network is working in a normal state and there are no faults in the network. Afterwards, the paths that do not meet the constraints are eliminated and the remaining paths are stored. This step takes a long time and is performed under normal circumstances, so it does not affect the solution of the recovery problem in an emergency.

[0096] S2: After a fault occurs and a power outage occurs, identifying and storing a restoration path that is not affected by the fault in the stored remaining paths in a candidate restoration path table;

[0097] S3: Identify available microgrids and delete the paths starting from non-available microgrids in the candidate restoration path table;

[0098] In the embodiment of the present application, the available microgrid is not affected by the fault and satisfies the following constraints:

[0099]

[0100] Among them, E m (t+1) is the power of the microgrid at time t+1, is the amount of electricity required to supply the local load of microgrid m in the time interval (t, t+1), is the reserve power of microgrid m at time t+1; M is the set of microgrids; the microgrid that does not meet the conditions of available microgrid is a non-available microgrid.

[0101] S4: Based on the candidate recovery path table and constraints, a recovery plan is constructed and the objective function value of the recovery plan is evaluated;

[0102] In the embodiment of the present application, the objective function includes:

[0103] The first objective function is the weighted recovery power of important loads, expressed as:

[0104]

[0105] Among them, E Lj，(t,t+1) is the power restored by load j during the time period t~t+1, w j is the weight of load j, indicating the priority of load j; (t, t+1) is the set of restored loads in time period t to t+1; where T S is the start time of the recovery cycle, T E The end time of the recovery cycle;

[0106] The second objective function is the number of switching operations, expressed as:

[0107] f 2 =N sw (t,t+1),t∈(T S ,T E )

[0108] Where N sw (t, t+1) is the number of switching operations required to complete the recovery plan within the time period t to t+1.

[0109] The evaluation of the objective function value of the recovery scheme includes:

[0110]

[0111] Where m is the set of recovery solutions, f ij is the value of criterion i for the jth option, i.e., f ij is the value of the objective function i of the jth solution; f * i and f - i are the best and worst values ​​of all criterion functions for all alternatives, respectively.

[0112] S5: According to the objective function value of the recovery plan, a multi-stage recovery method is used to select the best recovery plan.

[0113] In an embodiment of the present application, the multi-stage recovery method includes:

[0114] Determine the best and worst values ​​of the weighted restored power and the number of switching operations for all schemes; for the weighted restored power, the best value is the maximum value and the worst value is the minimum value; for the number of switching operations, the best value is the minimum value and the worst value is the maximum value;

[0115] Calculate the utility measure and regret measure, expressed as:

[0116]

[0117] Among them, S j and R j They represent the utility measure and regret measure respectively; n is the number of objective functions, w i is the weight of objective function i;

[0118] Calculate the multi-stage recovery index of the j-th alternative, expressed as:

[0119]

[0120] Among them, Q j It means calculating the multi-stage recovery index of the j-th alternative, and the value of v is set to 0.5;

[0121] The recovery schemes are ranked according to the multi-stage recovery index, where the recovery scheme with the smallest multi-stage recovery index is represented as the best value.

[0122] It should be noted that the network performance after extreme events is Figure 2 As shown, the network performance is divided into failure stage, recovery stage and normal recovery stage;

[0123] Assume that the fault occurs at time t eoccurs in time period t e to pe was isolated;

[0124] In time period t pe to r In the preparation of the recovery plan, at time point t r Execute the recovery plan, in time period t r to pr In the time period t, the switching operation related to the recovery scheme is completed. pr to ir , restoring the load according to the restoration plan;

[0125] In time period t ir to pir In the process, the faulty components are repaired or replaced to restore the system to its pre-fault state; at time point t pir After that, the network is in normal status.

[0126] Steps S3-S5 were all performed every hour.

[0127] It should also be stated that the multi-stage recovery method is an efficient and straightforward multi-criteria decision making method (MCDM). This method helps to solve problems where the decision makers cannot accurately determine their preferences and the criteria are different. The multi-stage recovery method ranks the alternatives according to the criteria considered. To do this, the multi-stage recovery method ranks the alternatives according to their "closeness" to the "ideal" solution.

[0128] The above is a schematic scheme of the multi-stage restoration method for restoring power to important loads based on microgrids in this embodiment. It should be noted that the technical scheme of the multi-stage restoration system for restoring power to important loads based on microgrids and the technical scheme of the multi-stage restoration method for restoring power to important loads based on microgrids above belong to the same concept. For details not described in detail in the technical scheme of the multi-stage restoration system for restoring power to important loads based on microgrids in this embodiment, please refer to the description of the technical scheme of the multi-stage restoration method for restoring power to important loads based on microgrids above.

[0129] In this embodiment, a multi-stage restoration system for restoring power to important loads based on a microgrid includes:

[0130] A restoration path collection module is used to identify all restoration paths between the microgrid and important loads under steady-state conditions, eliminate paths that do not meet the constraints, and store the remaining paths;

[0131] A candidate path determination module, used for identifying and storing in a candidate recovery path table a recovery path that is not affected by the failure among the stored remaining paths after a failure occurs and a power outage occurs;

[0132] an identification module, used for identifying available microgrids, and deleting paths starting from non-available microgrids in a candidate restoration path table;

[0133] An evaluation module is used to construct a recovery plan based on the candidate recovery path table and constraint conditions, and evaluate the objective function value of the recovery plan;

[0134] The selection module is used to select the best recovery scheme using a multi-stage recovery method according to the objective function value of the recovery scheme.

[0135] This embodiment further provides a computing device, which is applicable to a multi-stage restoration method for restoring power supply to important loads based on a microgrid, including:

[0136] Memory and processor; the memory is used to store computer executable instructions, and the processor is used to execute computer executable instructions to implement the multi-stage restoration method for restoring power supply to important loads based on microgrid as proposed in the above embodiment.

[0137] This embodiment also provides a storage medium having a computer program stored thereon, which, when executed by a processor, implements a multi-stage restoration method for restoring power supply to important loads based on a microgrid as proposed in the above embodiment.

[0138] The storage medium proposed in this embodiment and the multi-stage recovery method for restoring power supply to important loads based on a microgrid proposed in the above embodiment belong to the same inventive concept. The technical details not described in detail in this embodiment can be referred to the above embodiment, and this embodiment has the same beneficial effects as the above embodiment.

[0139] Example 2

[0140] Reference Figure 3-Figure 4 Tables 1 to 3 are an embodiment of the present invention, which provides a multi-stage restoration method for restoring power supply to important loads based on a microgrid. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through simulation experiments.

[0141] The simulation experiment was carried out on the 123 bus distribution network. The single-line diagram of the network is shown in Figure 3 As shown in Figure 1, there are 5 CLs (Critical Loads) at nodes 41, 50, 99, 101, and 114; in addition, 3 microgrids are connected to nodes 54, 62, and 72. The topology and detailed information of the microgrid generation units are shown in Figure 1. Figure 4 and as shown in Table 1. The software environment is implemented. The assumptions considered are as follows:

[0142] - During the restoration process, non-critical loads can be isolated from the main power supply path by opening the remote control switch;

[0143] - After the fault occurs, the main grid loses power, and the only power generation device is the microgrid in the distribution network that has not failed (this situation is prone to extreme events);

[0144] ——The power outage time is 20 hours;

[0145] Each microgrid needs 20% reserve capacity.

[0146] The simulation results are as follows:

[0147] Assuming that the fault occurs on line 57–58, the fault is isolated by opening the switches on both sides of the fault line. In addition, assuming that all microgrids are available, the weight factors of important and non-important loads are 1 and 0.01, respectively.

[0148] Table 1 Detailed information of microgrid

[0149] Device Name parameter DG1(Master) SN=500kV A, V=1.0pu, f=60HZ, EM=6MWh BT1,2 SN=100kV A, P=20kW, Q=10kV ar, EM=3MWh WT1,2 PN=100kW, p=40 / 50kW, Pf=0.95 L1,2,3,4 p=50 / 25 / 36 / 20kW, Q=20 / 5 / 11 / 15kV ar(MGLD1,2,3,4) MGPCCTr SN=500kV A, V=4.16kV / 0.48kV, r=0.1%)

[0150] Table 2 Number of available paths for providing important loads for the fault on line 57-58

[0151]

[0152] Table 3 Simulation results

[0153]

[0154] For the fault on line 57-58, Table 2 gives the number of possible restoration paths for providing critical loads through the microgrid. For example, microgrid-54 has 157 possible restoration paths to provide 3 different critical loads. According to Table 2, there are 742 possible restoration paths that need to be evaluated to select the best restoration scheme for each time interval. At this stage, the multi-stage restoration method must select the best restoration scheme based on the values ​​of different objective functions associated with each restoration path. Table 3 shows the simulation results in this case.

[0155] Table 3 shows that within the first 10 hours of the blackout, MG-54 restored CL-41 and CL-50 through 6 switching operations, MG-62 restored CL-99 and CL-101 through 5 switching operations, and MG-72 restored CL-114 through 8 switching operations. The “number of switching operations” includes switching operations to isolate the restoration path from the rest of the network and switching operations to close the normally open switches. That is, these switching operations are performed to remove branches from the main restoration path. For example, in order to supply power to CL-114 from MG-72 within the first 10 hours of the blackout, the switches on lines 66-63, 73-78, 73-74, 103-104, 109-110, 113-116, and 114-115 must be opened, and the normally open switch on line 66-67 must also be closed (8 switching operations). During the next 10 hours of outage, MG-72 was unable to participate in the restoration process because its power was consumed in the first 10 hours to supply CL-114. During the 10-12 interval, MG-72 was unavailable and MG-54 restored CL-114. During this period, MG-62 continued to supply CL-99 and 101. During the 12-13 interval, in addition to CL-99 and 101, MG-62 also supplied CL-114, and MG-54 also restored CL-41 and 50.

[0156] After the first 13 hours of the outage, the available power of MG-54 is exhausted and the only available MG in the network is MG-62. According to the network topology after the failure and the radial constraints, MG-62 is able to participate in the restoration of CL-99, CL-101, and CL-114, only because the only possible restoration path for MG-62 to CL-41 and CL-50 goes through node 54 connected to MG-54. Therefore, according to the radial constraints, MG-62 cannot restore CL-41 and CL-50. Therefore, CL-41 and CL-50 are no longer restored, and in the time interval 13-17, MG-62 restores CL-99, CL-101, and CL-114. In general, in this case, the power supply time of CL-41 and 50 is 13 hours, and the power supply time of CL-99, 101, and 114 is 17 hours.

[0157] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A multi-stage restoration method for restoring power to important loads based on a microgrid, characterized in that: include: Identify all restoration paths between the microgrid and important loads under steady-state conditions, eliminate paths that do not meet constraints, and store the remaining paths; After a fault occurs and a power outage occurs, identifying and storing in a candidate restoration path table a restoration path that is not affected by the fault among the stored remaining paths; Identify available microgrids, and remove paths starting from non-available microgrids from the candidate restoration path table; Based on the candidate recovery path table and constraints, a recovery plan is constructed and the objective function value of the recovery plan is evaluated; According to the objective function value of the recovery plan, a multi-stage recovery method is used to select the best recovery plan.

2. The multi-stage restoration method for restoring power supply to important loads based on a microgrid as claimed in claim 1, characterized in that: The constraints include: The bus voltage and line current constraints are expressed as: Among them, v i 、V min 、V max are the voltage amplitude of bus i, the lower limit and upper limit of voltage amplitude respectively; I j and are the current and upper limit of line j respectively, N b and N l are the collections of buses and lines respectively; Where P j and Q j are the active power and reactive power passing through line j respectively; P di and Q di are the active power and reactive power of load i respectively; R j and X j are the resistance and reactance of line j respectively; The distributed generation output active and reactive power constraints are expressed as: Where P DG,i and Q DG,i DG i Output active and reactive power, and DG i Output active power upper limit and reactive power upper limit; Feeder capacity constraint, expressed as: in is the maximum allowed capacity of feeder k, and F is the set of feeders.

3. The multi-stage restoration method for restoring power supply to important loads based on a microgrid as claimed in claim 2, characterized in that: The constraints also include: The radial constraints of the power grid topology are as follows: Define four matrices A, B, C and D obtained from the power grid diagram; where matrix A represents the number of branches connected to each node, matrix B represents directly connected nodes, matrix C describes the generation source of the power grid, and matrix D is equal to Bn*C, where n is the number of nodes; If the following rules are followed, the new grid configuration will be radial and all loads will work normally: all elements of matrix A are not zero; a=2(n-1); all elements of matrix D are not zero, where a is the sum of the elements of matrix a.

4. The multi-stage restoration method for restoring power supply to important loads based on a microgrid as claimed in claim 3, characterized in that: include: The available microgrid is not affected by the fault and satisfies the following constraints: Among them, E m (t+1) is the power of the microgrid at time t+1, is the amount of electricity required to supply the local load of microgrid m in the time interval (t, t+1), is the reserve power of microgrid m at time t+1; M is the set of microgrids; the microgrid that does not meet the conditions of available microgrid is a non-available microgrid.

5. The multi-stage restoration method for restoring power supply to important loads based on a microgrid as claimed in claim 4, characterized in that: The objective function includes: The first objective function is the weighted recovery power of important loads, expressed as: Among them, E Lj，(t,t+1) is the power restored by load j during the time period t~t+1, w j is the weight of load j, indicating the priority of load j; (t, t+1) is the set of restored loads in time period t to t+1; where T S is the start time of the recovery cycle, T E The end time of the recovery cycle; The second objective function is the number of switching operations, expressed as: f2=N sw (t,t+1),t∈(T S ,T E ) Where N sw (t, t+1) is the number of switching operations required to complete the recovery plan within the time period t to t+1.

6. The multi-stage restoration method for restoring power supply to important loads based on a microgrid as claimed in claim 5, characterized in that: The evaluation of the objective function value of the recovery scheme includes: Where m is the set of recovery solutions, f ij is the value of criterion i for the jth option, i.e., f ij is the value of the objective function i of the jth solution; and are the best and worst values ​​of all criterion functions for all alternatives, respectively.

7. The multi-stage restoration method for restoring power supply to important loads based on a microgrid as claimed in claim 6, characterized in that: The multi-stage recovery method includes: Determine the best and worst values ​​of the weighted restored power and the number of switching operations for all schemes; for the weighted restored power, the best value is the maximum value and the worst value is the minimum value; for the number of switching operations, the best value is the minimum value and the worst value is the maximum value; Calculate the utility measure and regret measure, expressed as: Among them, S j and R j They represent the utility measure and regret measure respectively; n is the number of objective functions, w i is the weight of objective function i; Calculate the multi-stage recovery index of the j-th alternative, expressed as: Among them, Q j It means calculating the multi-stage recovery index of the j-th alternative, and the value of v is set to 0.5; The recovery schemes are ranked according to the multi-stage recovery index, where the recovery scheme with the smallest multi-stage recovery index is represented as the best value.

8. A system using a multi-stage restoration method for restoring power to important loads based on a microgrid as described in any one of claims 1 to 7, characterized in that: include: A restoration path collection module is used to identify all restoration paths between the microgrid and important loads under steady-state conditions, eliminate paths that do not meet the constraints, and store the remaining paths; A candidate path determination module, used for identifying and storing in a candidate recovery path table a recovery path that is not affected by the failure among the stored remaining paths after a failure occurs and a power outage occurs; an identification module, used for identifying available microgrids, and deleting paths starting from non-available microgrids in a candidate restoration path table; An evaluation module is used to construct a recovery plan based on the candidate recovery path table and constraint conditions, and evaluate the objective function value of the recovery plan; The selection module is used to select the best recovery scheme using a multi-stage recovery method according to the objective function value of the recovery scheme.

9. A computing device comprising: Memory and processor; The memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions. When the computer-executable instructions are executed by the processor, the steps of the multi-stage restoration method for restoring power supply to important loads based on a microgrid are implemented as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the steps of the multi-stage restoration method for restoring power supply to important loads based on a microgrid as described in any one of claims 1 to 7.

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