Elastic power distribution network power supply recovery method considering micro-grid interconnection

Abstract

The invention relates to the technical field of power distribution networks, and discloses an elastic power distribution network power supply recovery method considering micro-grid interconnection, and the key points of the technical scheme are as follows: constructing a target function with the maximum weighted load capacity as the core; the method comprises the following steps: establishing a father node model of nodes, establishing a line interconnection time sequence model, establishing a line power supply state decision variable model, verifying the feasibility of a power supply recovery scheme through a dynamic frequency simulation model, and determining an interconnectable micro-grid boundary based on boundary search after a disaster; then auxiliary variables are introduced to establish an elastic power distribution network sequence recovery model considering micro-grid interconnection, and finally, a mode of verifying scheme feasibility through dynamic frequency simulation analysis is combined with a node father node model, a line interconnection time sequence model and a line power supply state decision variable model; the purposes of improving the overall inertia and frequency supporting capacity of the system, improving the post-disaster power grid recovery efficiency and guaranteeing the safety of the recovery scheme are achieved.

Description

Technical Field

[0001] This invention relates to the field of power distribution network technology, and more specifically, to a method for restoring power supply to a resilient power distribution network that takes into account microgrid interconnection. Background Technology

[0002] Currently, with the widespread integration of distributed power sources and energy storage devices into distribution networks, islanded microgrid structures with local autonomy capabilities are gradually taking shape. When extreme weather disasters or sudden faults cause power outages in the main grid, islanded microgrids can quickly restore local power supply with the help of black-start power sources, energy storage devices, and distributed power sources, becoming an important means to improve the resilience of distribution networks.

[0003] However, traditional power restoration methods have significant limitations. They typically assume that multiple isolated microgrids operate independently, neglecting the synergistic effects of inter-microgrid interconnection. While microgrid interconnection can create larger-scale regional power supply units and significantly improve the overall system inertia and frequency support capabilities to mitigate frequency drops during concentrated load commissioning during phased post-disaster recovery, the establishment of microgrid interconnections is constrained by various factors, including the recovery progress of microgrid boundary nodes, line connectivity status, interconnection timing optimization and coordination, and verification of system frequency stability and power supply security after interconnection. Furthermore, existing research largely focuses on the recovery optimization of single microgrids or the route scheduling of repair teams, paying insufficient attention to the timing decisions, boundary identification, and post-interconnection frequency security analysis of inter-microgrid interconnections, lacking a comprehensive method that can directly guide post-disaster power restoration decisions.

[0004] Therefore, the present invention provides a method for restoring power supply to a flexible distribution network that takes into account microgrid interconnection, thereby improving the above-mentioned technical problems. Summary of the Invention

[0005] This disclosure aims to address the shortcomings of existing technologies by providing a method for restoring power supply to a resilient distribution network that considers microgrid interconnection. The invention employs a post-disaster approach: first, determining the boundaries of interconnectable microgrids based on boundary search; then, introducing auxiliary variables to establish a sequential restoration model for the resilient distribution network that considers microgrid interconnection; and finally, verifying the feasibility of the scheme through dynamic frequency simulation analysis. Simultaneously, it combines node parent node models, line interconnection timing models, and line power supply status decision variable models to achieve the goals of improving the overall system inertia and frequency support capabilities, enhancing post-disaster power grid restoration efficiency, and ensuring the safety of the restoration scheme.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a method for restoring power supply to a flexible distribution network considering microgrid interconnection, comprising the following steps:

[0007] Step 1: With the goal of improving the power supply recovery capability of the resilient distribution network, construct an objective function with the maximum weighted load as the core.

[0008] Step 2: Establish the parent node model of the nodes and determine the parent node of each non-black start power source;

[0009] Step 3: Establish a line interconnection timing model, determine the connection lines and interconnection timing between the two microgrids, and screen the potential nodes and timing for establishing a connection between the two independently operating microgrids;

[0010] Step 4: Establish a decision variable model for line power supply status to meet the requirements for determining the line power supply status within and between microgrids.

[0011] Step 5: Verify the feasibility of the power supply restoration scheme using a dynamic frequency simulation model.

[0012] As a preferred embodiment of the present invention, the objective function expression constructed in step 1 is:

[0013] Where T is the set of power restoration time steps; N is the set of load nodes; ω i Load weighting; This represents the amount of active power recovery at node i at time t.

[0014] As a preferred embodiment of the present invention, step 2, establishing the parent node model of the node, includes: constructing the microgrid interconnection model and solving for the parent node, wherein the microgrid interconnection model introduces 0-1 variables. Whether node i can be powered by the microgrid composed of the k-th distributed power source at time t is determined by the black-start power source node. The decision is based on three conditions: the value of the node, the connection relationship between the upstream node and the black-start power supply, and the state of power restoration of the line. And through the formula and It means; where h = θ k (i) represents the parent node of node i corresponding to the black-starting power source in microgrid k, c hi / ih.t It represents the power supply status of the line.

[0015] As a preferred embodiment of the present invention, the parent node solution includes the following steps:

[0016] Input the graph G, which represents the topological relationship of the system, and the matrix element takes the value 1 to indicate that there is an edge between the nodes and the value 0 to indicate that there is no edge.

[0017] Set the black start power point as the root node and start traversing the graph from that node.

[0018] If there are untraversed nodes, recursively search the adjacent nodes of the current node;

[0019] If there are untraversed adjacent nodes, traverse all adjacent nodes and record the parent node; otherwise, find the next untraversed node.

[0020] The solution ends after all nodes have been traversed and the parent node information has been recorded.

[0021] As a preferred technical solution of the present invention, when establishing the line interconnection timing model in step 3, the connection line for microgrid interconnection is determined by two conditions: 1) the two nodes involved in the interconnection are recovered nodes and both are outer nodes of the microgrid; 2) there is a connecting path between the two nodes in the topology, and a 0-1 variable b is introduced. i Indicator node i is the outermost node of the microgrid, and 0-1 variable m ij To determine whether line ij is a microgrid interconnection line, use formula b. i and m ij calculate:

[0022]

[0023] in, This represents the system's correlation matrix, used to represent the connection relationships between nodes in the topology.

[0024] As a preferred technical solution of the present invention, the line power supply state model established in step 4 is constructed by the following formula:

[0025]

[0026] Where ψ ij The minimum total number of steps required to restore power to nodes i and j, T max For the maximum power supply recovery time step, s i.t and s j.t Let i and j represent the recovery states of nodes i and j at time t, respectively. The time steps required for synchronous power supply after the two microgrids are interconnected, c ij.t Let be a 0-1 variable representing the power supply state of line ij at time t.

[0027] As a preferred embodiment of the present invention, in step 5, when verifying the feasibility of the power supply restoration scheme through a dynamic frequency simulation model, a frequency swing equation is used. Describe the system's frequency dynamic characteristics;

[0028] Where M is the system's equivalent inertia, Δf is the system's frequency deviation, D is the system's damping coefficient, and ΔP G For the change in power supply, ΔP L This refers to changes in load power.

[0029] As a preferred embodiment of the present invention, the parameter values ​​in the dynamic frequency simulation model are set as follows: RG =0.25, K E =20, K=20, T1=0.01s, T2=0.02s, T3=0.2s, T4=0.25s, T5=0.009s, T6=0.0384s, T d =0.024s, T E =0.02s, where R G K is the governor droop coefficient. E Where K is the excitation system gain, T1 to T6 are controller gains, and T1 is the excitation system gain. d T E These are the time constants for the corresponding stages.

[0030] As a preferred technical solution of the present invention, the elastic distribution network sequential recovery model considering microgrid interconnection established in step 3 is linearized, and the model is solved quickly using a solution tool to obtain the optimal power supply recovery decision result.

[0031] As a preferred technical solution of the present invention, the above method is applicable to the scenario of multi-microgrid collaborative power supply restoration and frequency security analysis after a distribution network failure caused by extreme disasters.

[0032] In summary, the present invention has the following beneficial effects:

[0033] Firstly, by interconnecting multiple isolated microgrids during the power restoration process, the equivalent inertia of the system is significantly improved, enabling stronger frequency support during the concentrated load commissioning phase, reducing the risk of frequency drops, and effectively improving the stability of system operation.

[0034] Secondly, by introducing a microgrid boundary search mechanism and a line interconnection timing model, it is possible to dynamically identify interconnectable microgrid boundary nodes and achieve interconnection at the appropriate time, thereby promoting the coordinated recovery of multiple isolated microgrids, forming a large-scale regional power supply unit, and thus improving the overall recovery efficiency of the power grid after a disaster.

[0035] Third, after optimizing the decision model, the power supply restoration scheme is verified by combining it with the dynamic frequency simulation model. This can effectively verify the frequency changes and system inertial response characteristics during the restoration process, ensuring the safety and feasibility of the restoration scheme.

[0036] Fourth, the sequential recovery path is modeled in detail and a sequential recovery path table is introduced, so that the decision results can be detailed to each time step and the presentation is more vivid and intuitive.

[0037] Fifth, the proposed line power supply status decision variable model can uniformly describe the power supply status of lines within a microgrid and the power supply status of interconnected lines between microgrids, overcoming the limitation of traditional models that are only applicable to single microgrid recovery. Attached Figure Description

[0038] Figure 1 A flowchart of a method for restoring power supply to a flexible distribution network considering microgrid interconnection, provided as an embodiment of the present invention;

[0039] Figure 2 This is a flowchart of the parent node solving process provided in an embodiment of the present invention;

[0040] Figure 3 This is a schematic diagram of the microgrid dynamic frequency model provided in an embodiment of the present invention;

[0041] Figure 4 These are two sets of comparative calculation examples provided in the embodiments of the present invention. Detailed Implementation

[0042] The present application will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application. These all fall within the protection scope of the present application.

[0043] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0044] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.

[0045] Furthermore, the technical features involved in the various embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0046] This invention aims to address the problems of traditional power restoration methods that involve multiple isolated microgrids operating independently without considering interconnection and synergy effects. Furthermore, existing research lacks sufficient attention to the timing decisions, boundary identification, and frequency security analysis following microgrid interconnection, resulting in a lack of comprehensive methods to directly guide post-disaster power restoration decisions. Additionally, the power restoration scheme suffers from high system implementation complexity and difficulty in ensuring frequency security. Therefore, this invention proposes a flexible distribution network power restoration method considering microgrid interconnection for collaborative power restoration and frequency security analysis of multiple microgrids after distribution network failures caused by extreme disasters. This method determines the boundaries of interconnectable microgrids through boundary search, introduces auxiliary variables to establish a sequential restoration model considering microgrid interconnection, and combines a node parent node model, a line interconnection timing model, a line power supply status decision variable model, and a dynamic frequency simulation model. The objective function is the maximum load restoration amount, and the model is linearized. A configurable model and differentiated verification mechanism are used to adapt to the complex power restoration requirements in microgrid interconnection scenarios. This achieves the goals of improving overall system inertia and frequency support capabilities, increasing the overall post-disaster power grid restoration efficiency, ensuring the safety and feasibility of restoration schemes, and reducing system implementation complexity.

[0047] Please refer to Figure 1 , Figure 1 A flowchart illustrating a resilient distribution network power restoration method considering microgrid interconnection, as described in an embodiment of this disclosure, is shown. The overall process mainly includes the following five steps:

[0048] Step 1: With the goal of improving the power supply recovery capability of the flexible distribution network, construct an objective function with the maximum weighted load as the core.

[0049] The objective function expression is:

[0050]

[0051] Where T is the set of power restoration time steps; N is the set of load nodes; ω i Load weighting; This represents the amount of active power recovery at node i at time t.

[0052] Step 2: Establish the parent node model of the node and determine the parent node of each non-black start power supply.

[0053] Step 2-1: Establishing the parent node model of the node includes:

[0054] The model introduces 0-1 variables This characterizes whether node i can be powered by the microgrid formed by the k-th distributed power source at time t, i.e., it determines whether a restored power supply path exists between node i and the black-start power source k. The following three conditions can be used to determine this.

[0055] 1) The node where the black start power supply is located Must be 1;

[0056] 2) The upstream node h of node i is directly or indirectly connected to the black-start power supply k;

[0057] 3) Power supply to line (h,i) has been restored.

[0058] The above three conditions can be expressed by formulas (2)-(3):

[0059]

[0060] Where h = θ k (i) indicates that for a black-start power source in microgrid k, node h is the parent node of node i. Equation (2) indicates that a node connected to the black-start power source is powered by the black-start voltage; Equation (3) indicates that when node h is powered by microgrid k and line (h,i) is energized, then node i is also powered by microgrid k.

[0061] Step 2-2, Solving for the parent node:

[0062] As can be seen from formula (2), it is necessary to determine the parent node of each non-black start power node, and the determination of the parent node is related to the selection of the topology root node.

[0063] Taking graph G as an example, the process of finding the parent node of a node is as follows: Figure 2 As shown, it can be mainly divided into the following steps:

[0064] 1) Input the incidence matrix of graph G, which represents the topological relationship of the system; for an undirected graph, each element in the matrix indicates whether there is an edge between nodes, with a value of 1 indicating an edge and 0 indicating no edge;

[0065] 2) Set the black start power point as the root node, and start the graph traversal from this node;

[0066] 3) If there are untraversed nodes, recursively search the adjacent nodes of the current node;

[0067] 4) If there are untraversed adjacent nodes, traverse all adjacent nodes and record the parent node of each node; if there are no untraversed nodes, find the next untraversed node.

[0068] 5) The solution ends after all nodes have been traversed and their parent node information has been recorded. At this point, the parent node of each node in the graph has been determined.

[0069] Step 3: Establish a line interconnection timing model, determine the connection lines and interconnection timing between the two microgrids, and screen potential nodes and opportunities for the two independently operating microgrids to establish a connection.

[0070] During the microgrid interconnection process, it is necessary to determine the connection lines between the two microgrids, that is, to identify the potential nodes where the two independently operating microgrids can establish a connection. The boundaries of microgrids MG1 and MG2 continuously expand during the power restoration process. When the boundary nodes of both microgrids are restored and there are connecting lines, the two independently operating islanded microgrids can be interconnected into a larger microgrid.

[0071] The established sequential recovery model of the resilient distribution network considering microgrid interconnection is linearized, and the model is solved quickly using the solver tool (CPLEX) to obtain the optimal power supply recovery decision result.

[0072] Therefore, the interconnection path of a microgrid can be determined by the following two conditions: 1) Both nodes participating in the microgrid interconnection must be restored nodes and both must be outer nodes of the microgrid; 2) Nodes belonging to the two microgrids must have a topologically connected path. A 0-1 variable b is also introduced. i Indicator node i is the outermost node of the microgrid, and 0-1 variable m ij To determine whether line ij is a microgrid interconnection line, calculate using formulas (3) and (4):

[0073]

[0074] in, b is the system's incidence matrix, used to represent the connection relationships between nodes in the topology; i This is a 0-1 variable, indicating whether node i is the outermost node of the microgrid; if so, then b i =1, otherwise b i =0;m ij The variable is 0-1, used to determine whether the line ij between node i and node j is a microgrid interconnection line. Equation (3) is used to solve whether node i is an outer node of the microgrid; Equation (4) determines whether line ij is a microgrid connection line.

[0075] Step 4: Establish a decision variable model for line power supply status to meet the requirements for determining the line power supply status within and between microgrids.

[0076] The established line power supply state model is constructed using formulas (5)-(7):

[0077]

[0078] Where, ψ ij The minimum total number of steps required to restore power to nodes i and j; c is the time step required for synchronous power supply after the microgrids of node i and node j are interconnected. ij.tThe variable is 0-1, representing the power supply state of line ij at time t. Equations (5) and (6) determine the time when lines ij are interconnected; Equation (7) shows that the power supply state remains unchanged after the line is restored to power.

[0079] Step 5: Verify the feasibility of the power supply restoration scheme using a dynamic frequency simulation model.

[0080] Step 5-1 Feasibility verification of power restoration plan:

[0081] During the power restoration process, each load commissioning will cause a change in the system frequency. The frequency swing equation (8) is used to describe the dynamic characteristics of the system frequency:

[0082]

[0083] In the formula, M is the equivalent inertia of the system; Δf is the frequency deviation of the system; D is the damping coefficient of the system; ΔP G For the change in power supply; ΔP L Equation 8) shows the change in system frequency when the load of the power system changes. The system frequency is affected by multiple factors, including generator power output, load changes, system inertia, and damping effects.

[0084] like Figure 3 As shown, in this model, the parameter values ​​in the dynamic frequency simulation model are set as follows: R G =0.25, K E =20, K=20, T1=0.01s, T2=0.02s, T3=0.2s, T4=0.25s, T5=0.009s, T6=0.0384s, T d =0.024s, T E =0.02s, where R G K is the governor droop coefficient. E Where K is the excitation system gain, T1 to T6 are controller gains, and T1 is the excitation system gain. d T E These are the time constants for the corresponding stages.

[0085] As a specific example, the invention is further illustrated in one embodiment.

[0086] In this embodiment, the IEEE-33 node distribution network simulation system is used to verify the effectiveness of the proposed approach. It is assumed that the main grid is affected by an extreme natural disaster and cannot be restored to power in a short period, meaning that all nodes in the distribution network are in a state of complete power loss during the initial recovery phase.

[0087] like Figure 4As shown, this section verifies the advantages of considering microgrid interconnection during power restoration through two sets of comparative examples. Example 1 uses the power restoration method considering microgrid interconnection proposed in this chapter; Example 2 uses the traditional method without considering microgrid interconnection.

[0088] As shown in Figure 4, compared with the traditional power restoration method that does not consider microgrid interconnection, the optimization method proposed in this chapter achieves an improvement of 3.9% and 20.5% in terms of load restoration amount and weighted load restoration amount, respectively.

[0089] 1) The weighted load recovery of the IEEE 33-node system considering microgrid interconnection is improved by 20.5%. This result shows that the method in this chapter can significantly improve the system inertia in power restoration, enhance the system's ability to cope with disturbances, and has obvious advantages in terms of load recovery amount and load recovery speed.

[0090] 2) After microgrids are interconnected, power can be shared and mutual assistance can be achieved between microgrids, thus improving power utilization and increasing the utilization rate of flexible resources under extreme disasters.

[0091] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for restoring power supply to a flexible distribution network considering microgrid interconnection, characterized in that, The method includes the following steps: Step 1: With the goal of improving the power supply recovery capability of the resilient distribution network, construct an objective function with the maximum weighted load as the core. Step 2: Establish the parent node model of the nodes and determine the parent node of each non-black start power source; Step 3: Establish a line interconnection timing model, determine the connection lines and interconnection timing between the two microgrids, and screen the potential nodes and timing for establishing a connection between the two independently operating microgrids; Step 4: Establish a decision variable model for line power supply status to meet the requirements for determining the line power supply status within and between microgrids. Step 5: Verify the feasibility of the power supply restoration scheme using a dynamic frequency simulation model.

2. The method for restoring power supply to a flexible distribution network considering microgrid interconnection as described in claim 1, characterized in that, The objective function expression constructed in step 1 is: Where T is the set of power restoration time steps; N is the set of load nodes; ω i Load weighting; This represents the amount of active power recovery at node i at time t.

3. The method for restoring power supply to a flexible distribution network considering microgrid interconnection as described in claim 1, characterized in that, Step 2, establishing the parent node model of the nodes, includes: constructing the microgrid interconnection model and solving for the parent node. The microgrid interconnection model introduces 0-1 variables. Whether node i can be powered by the microgrid composed of the k-th distributed power source at time t is determined by the black-start power source node. The decision is based on three conditions: the value of the node, the connection relationship between the upstream node and the black-start power supply, and the state of power restoration of the line. And through the formula and It means; where h = θ k (i) represents the parent node of node i corresponding to the black-starting power source in microgrid k, c hi / ih.t It represents the power supply status of the line.

4. The method for restoring power supply to a flexible distribution network considering microgrid interconnection as described in claim 3, characterized in that, Finding the parent node involves the following steps: Input the graph G, which represents the topological relationship of the system, and the matrix element takes the value 1 to indicate that there is an edge between the nodes and the value 0 to indicate that there is no edge. Set the black start power point as the root node and start traversing the graph from that node. If there are untraversed nodes, recursively search the adjacent nodes of the current node; If there are untraversed adjacent nodes, traverse all adjacent nodes and record the parent node; otherwise, find the next untraversed node. The solution ends after all nodes have been traversed and the parent node information has been recorded.

5. A method for restoring power supply to a flexible distribution network considering microgrid interconnection as described in claim 1, characterized in that, In step 3, when establishing the timing model for the interconnection of microgrids, the interconnection lines are determined by two conditions: 1) the two nodes involved in the interconnection are recovered nodes and both are outer nodes of the microgrid; 2) there is a connecting path between the two nodes in the topology, and a 0-1 variable b is introduced. i Indicator node i is the outermost node of the microgrid, and 0-1 variable m ij To determine whether line ij is a microgrid interconnection line, use formula b. i and m ij calculate: in, This represents the system's correlation matrix, used to represent the connection relationships between nodes in the topology.

6. The method for restoring power supply to a flexible distribution network considering microgrid interconnection as described in claim 1, characterized in that, The line power supply state model established in step 4 is constructed using the following formula: Where ψ ij The minimum total number of steps required to restore power to nodes i and j, T max For the maximum power supply recovery time step, s i.t and s j.t Let i and j represent the recovery states of nodes i and j at time t, respectively. The time steps required for synchronous power supply after the two microgrids are interconnected, c ij.t Let be a 0-1 variable representing the power supply state of line ij at time t.

7. A method for restoring power supply to a flexible distribution network considering microgrid interconnection as described in claim 1, characterized in that, In step 5, when verifying the feasibility of the power supply restoration scheme using a dynamic frequency simulation model, the frequency swing equation is adopted. Describe the system's frequency dynamic characteristics; Where M is the system's equivalent inertia, Δf is the system's frequency deviation, D is the system's damping coefficient, and ΔP G For the change in power supply, ΔP L This refers to changes in load power.

8. A method for restoring power supply to a flexible distribution network considering microgrid interconnection as described in claim 7, characterized in that, The parameter values ​​in the dynamic frequency simulation model are set as follows: R G =0.25, K E =20, K=20, T1=0.01s, T2=0.02s, T3=0.2s, T4=0.25s, T5=0.009s, T6=0.0384s, T d =0.024s, T E =0.02s, where R G K is the governor droop coefficient. E Where K is the excitation system gain, T1 to T6 are controller gains, and T1 is the excitation system gain. d T E These are the time constants for the corresponding stages.

9. A method for restoring power supply to a flexible distribution network considering microgrid interconnection as described in claim 1, characterized in that, The sequential recovery model of the resilient distribution network considering microgrid interconnection established in step 3 is linearized, and the model is solved quickly using a solution tool to obtain the optimal power supply recovery decision result.

10. The method for restoring power supply to a flexible distribution network considering microgrid interconnection according to any one of claims 1 to 9, characterized in that, It is applicable to scenarios involving coordinated power supply restoration and frequency security analysis of multiple microgrids after distribution network failures caused by extreme disasters.

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