Island division method and system considering load importance degree and power failure user number

Abstract

The invention discloses an island division method and system considering load importance degree and power failure user number, and the method comprises the steps: building a power distribution network node network diagram, and dividing a first-stage load, a second-stage load and a third-stage load according to the load importance degree; based on the power distribution network node network diagram, determining an island boundary by taking a distributed power supply access point as an island center starting point; searching and determining a primary load in the island boundary by adopting a distributed power supply power circle method; and after the first-level load is searched, if the distributed power supply has residual capacity, considering the second-level load, the third-level load and the number of users contained in load nodes, establishing a multi-target optimization model by taking the maximum equivalent load and the maximum number of users in the load nodes as targets, and carrying out island division based on the multi-target optimization model. Island division is carried out under the condition of considering the load importance degree and the number of power failure users, and the overall power supply reliability and stability of the power grid can be remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power system automation, and in particular to an island division method and system taking into account load importance and the number of power outage users. Background Art

[0002] With the continuous development of power systems, the interconnection of power grids is becoming more and more common, which leads to the increasing scale of power grids. Although large-scale power grids have certain economic benefits, they increase the probability of failure of power components in the system to a certain extent, thus posing a threat to power supply reliability.

[0003] The grid structure of traditional distribution networks is basically one-way radial type, that is, with a substation as the center, power is supplied to power users in a certain area. The radial power grid has the advantages of simple structure and fixed flow direction, but it also has some inherent shortcomings. For example, if a fault occurs near the root node, all downstream users will not be able to use electricity normally, and the reliability of power supply will be greatly reduced. With more and more distributed generation (DG) connected to the distribution network, the original single-power radial distribution structure has been changed. This means that even if a power failure occurs upstream, downstream power users can continue to supply power through the distributed generation to form an island, greatly reducing the scope of power outages.

[0004] An island refers to a local independently operated power subsystem formed when a distributed generation system continues to supply power to an independent distribution network that is separated from the main grid when the grid is out of power due to a fault, maintenance or other reasons. Island operation is a special type of operation mode for interconnected power grids and distributed generation and distribution systems. Unintentionally formed islands may cause harm to the system, user equipment, maintenance personnel, etc., and may also cause an imbalance in power supply and demand, which in turn reduces the reliability of power supply in the distribution network. At the same time, if the power network containing DG is prepared to deal with the formation of islands, and the areas where islands may form are actively divided into islands, a flexible and optimized island operation mode can be generated when the system fails, which can improve the reliability of power supply in the distribution system and give full play to the potential of distributed energy.

[0005] The island partitioning method taking into account the number of power outage users gives priority to reducing the number of power outage users during the island partitioning process. By rationally planning and adjusting the grid structure, more users can still maintain power supply in the event of grid failure or network outage. This method significantly improves the overall power supply reliability and stability of the grid. The island partitioning method taking into account the number of power outage users benefits more users by rationally allocating power resources within the island. When distributed power sources are limited, electricity can be preferentially allocated to a wider range of users to avoid resource waste or uneven power supply. Therefore, it is necessary to provide an island partitioning modeling method that takes into account the importance of the load and the number of power outage users. Summary of the invention

[0006] The present invention aims to solve the technical problems in the related art at least to a certain extent. To this end, the first object of the present invention is to provide an island division method taking into account the importance of loads and the number of power outage users, which realizes island division taking into account the importance of loads and the number of power outage users, and can significantly improve the overall power supply reliability and stability of the power grid.

[0007] The second object of the present invention is to provide an island partitioning system that takes into account the importance of loads and the number of users experiencing power outages.

[0008] To achieve the above object, the present invention is implemented through the following technical solutions:

[0009] An island division method considering load importance and the number of power outage users includes:

[0010] Establish a distribution network node network diagram and divide the load into primary, secondary and tertiary loads according to their importance;

[0011] Based on the distribution network node network diagram, the distributed power access point is taken as the island center starting point to determine the island boundary;

[0012] The distributed generation power circle method is used to search and determine the primary load within the island boundary;

[0013] After searching the primary load, if there is residual capacity in the distributed generation, the secondary and tertiary loads and the number of users contained in the load nodes are considered, and a multi-objective optimization model is established with the maximum equivalent load and the maximum number of load node users as the goal, and island division is performed based on the multi-objective optimization model.

[0014] Preferably, starting from the distributed power access point as the center starting point of the island, the shortest path algorithm is used to expand the search for all boundary points of the island to determine the island boundary, and the shortest path algorithm is the Dykstra minimum path method.

[0015] Preferably, the distributed power source power circle method is to use the distributed power source access point as the center of the circle and the distributed power source capacity as the search radius, and search and determine the primary load along the topological direction of the distribution network node network.

[0016] Preferably, the island division is performed based on a multi-objective optimization model, including:

[0017] The weighted combination method is adopted to combine the multi-objective functions in the multi-objective optimization model into a unified objective function in a linear combination manner, and based on the unified objective function, the equivalent load and the number of users of all branch lines containing secondary loads and tertiary loads are weightedly calculated and prioritized so as to divide the branch line with the largest weighted value into the island.

[0018] Preferably, the method further comprises: when the capacity of the distributed power source is unbalanced with the load power, using a method of adding an equivalent load to balance the capacity of the distributed power source with the load power.

[0019] To achieve the above object, the second aspect of the present invention provides an island division system that takes into account the importance of loads and the number of power outage users, including:

[0020] The first building module is used to establish a distribution network node network diagram and divide the load into primary load, secondary load and tertiary load according to the load importance;

[0021] The first determination module is used to determine the island boundary based on the distribution network node network diagram and taking the distributed power source access point as the island center starting point;

[0022] The second determination module is used to search and determine the primary load within the island boundary by using the distributed power generation power circle method;

[0023] The second building module is used to establish a multi-objective optimization model with the maximum equivalent load and the maximum number of load node users as the goal, considering the secondary load and the tertiary load and the number of users contained in the load node after searching the primary load if the distributed power source has residual capacity;

[0024] The solution module is used to solve the multi-objective optimization model and realize island partitioning.

[0025] Preferably, the first determination module is specifically used to start from the distributed power access point as the island center starting point, and use the shortest path algorithm to expand the search for all boundary points of the island to determine the island boundary, and the shortest path algorithm is the Dykstra minimum path method.

[0026] Preferably, the second determination module is specifically used to search and determine the primary load along the topological direction of the distribution network node network with the distributed power source access point as the center and the distributed power source capacity as the search radius.

[0027] Preferably, the solution module is specifically used to use a weighted combination method to combine the multi-objective functions in the multi-objective optimization model into a unified objective function in a linear combination manner, and based on the unified objective function, perform weighted calculations on the equivalent loads and the number of users of all branch lines containing secondary loads and tertiary loads, and perform priority sorting to divide the branch lines with the largest weighted values ​​into the island.

[0028] Preferably, the system further comprises a load power balancing module for balancing the capacity of the distributed power source with the load power by adding an equivalent load when the capacity of the distributed power source and the load power are unbalanced.

[0029] The present invention has at least the following technical effects:

[0030] The present invention considers the number of load users in the process of island division, which can ensure that the power supply area in each island covers as many users as possible, maximize the number of power users, and reduce the losses and impacts caused by power outages on users. Secondly, it can avoid the situation where the load is concentrated in some areas and the power supply is insufficient in other areas during island division. This user number balancing strategy balances the number of users and the load, which can optimize resource allocation and avoid resource waste or overinvestment caused by insufficient load or overload in the island, thereby not only helping to reduce the operating costs in the island, but also improving the overall economy of the island. Finally, the island is divided reasonably to ensure that each island covers as many users as possible, which helps to reduce the impact of large-scale power outages on society, especially in places where continuous power supply is required, such as important infrastructure areas. This method helps to maintain public safety and the normal operation of economic activities. In short, the island division strategy considering the number of load users has significant advantages in optimizing power supply coverage, improving system reliability, reducing social impact and reducing island operation costs, making the power system more flexible, efficient and fair in dealing with faults and distributed power generation.

[0031] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The flowchart of the island division method considering the load importance and the number of power outage users according to an embodiment of the present invention.

[0033] Figure 2 This is a structural block diagram of an island partitioning system that takes into account load importance and the number of power outage users according to an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The present embodiment is described in detail below, and examples of the embodiment are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0035] In order to solve the technical problems in the background technology, the present invention proposes an island division scheme that takes into account the importance of loads and the number of power outage users. The island division should consider that the power load in the island should not exceed the maximum power that the DG can supply. The DG capacity and the power load in the island should be able to match each other, so that the island can both exert the power supply capacity of the DG and not overload the DG; the island should contain as many important loads as possible, and the division of the island should ensure that the higher-level power loads are included in the island as much as possible. Therefore, under the premise of ensuring the power supply of important loads, a multi-objective optimization model with the maximum equivalent load and the maximum number of users at the load point as the goal is established, and the equivalent loads and the number of users are weighted. The calculation and priority sorting are performed to determine the island with the maximum number of users.

[0036] The following describes the island division method and system of this embodiment taking into account the importance of loads and the number of power outage users with reference to the accompanying drawings.

[0037] Figure 1 Flow chart of the island division method considering the load importance and the number of power outage users in an embodiment of the present invention. Figure 1 As shown, the method includes:

[0038] Step S101: Establish a distribution network node network diagram, and divide the loads into primary loads, secondary loads, and tertiary loads according to their importance.

[0039] Specifically, the data of distribution lines and components can be imported, a network diagram of distribution network nodes can be established, and load levels can be divided according to the importance of the loads. The loads in the power system are divided into three levels according to the different requirements for power supply reliability. The first-level load requires uninterrupted power supply, and the second-level load also requires uninterrupted power supply if possible. Therefore, the loads can be divided into first-level loads, second-level loads, and third-level loads.

[0040] Step S102: Based on the distribution network node network diagram, the island boundary is determined with the distributed power access point as the island center starting point.

[0041] In this embodiment, the distributed power access point can be used as the center starting point of the island, and the shortest path algorithm is used to expand the search for all boundary points of the island to determine the island boundary. The shortest path algorithm is the Dykstra minimum path method.

[0042] Specifically, the boundary can be determined using the Dykstra minimum path method. Assume that the distribution network node network graph G = (V, E), the node set V and the edge set E, and that the starting node is s, and the shortest path length to any node v is d(s, v). Initially, d(s, v) of each node v is set to be infinite, and the starting point d(s, s) = 0, that is:

[0043]

[0044] Furthermore, for each edge (u,v) from node u to node v, if the distance from u to v is shorter than the previously recorded d(s,v), then update d(s,v) with the following update formula:

[0045] d(s,v)=min(d(s,v),d(s,u)+ω(u,v)) (2)

[0046] Where d(s,u) represents the path length from node s to node u, and the non-negative weight ω(u,v) represents the weight of the edge from node u to node v.

[0047] From all the nodes that have not been visited yet, select the node u with the smallest current path length to expand, that is:

[0048] u=mind(s,v),v∈Q (3)

[0049] Where Q is the set of all unvisited nodes.

[0050] Thus, the search can be extended to obtain all boundary points of the isolated island, so that the boundary of the isolated island can be determined.

[0051] Step S103: using the distributed generation power circle method to search and determine the primary load within the island boundary.

[0052] In this embodiment, the number of users is not considered, and a distributed power source power circle method is adopted, with the distributed power source access point as the center of the circle and the distributed power source capacity as the search radius, and only the primary load is searched along the topological direction of the network.

[0053] The power circle of DG is determined by active power, as shown in formula (4):

[0054]

[0055] Where P DG is the active capacity of DG, is the active load of the i-th primary load node; n is the total number of primary load nodes in the power circle. According to the active capacity of DG, the range of the power circle is preliminarily determined, and the search is performed from the starting point of the power circle to the root node. Only the active load of the primary load is calculated, and the primary load in the island is first determined to ensure the importance of the primary load.

[0056] When determining the power circle of the distribution network system, if there is a load node n+1, the power in the power circle satisfies the following conditions at the same time:

[0057]

[0058] Then the n+1th load node is excluded.

[0059] Step S104: After searching the primary load, if there is residual capacity in the distributed power source, the secondary load, the tertiary load and the number of users contained in the load node are considered, and a multi-objective optimization model is established with the maximum equivalent load and the maximum number of load node users as the goal, and island division is performed based on the multi-objective optimization model.

[0060] In this embodiment, island division is performed based on a multi-objective optimization model, including: using a weighted combination method to combine the multi-objective functions in the multi-objective optimization model into a unified objective function in a linear combination manner, and based on the unified objective function, weighted calculation of the equivalent load and the number of users of all branch lines containing secondary loads and tertiary loads is performed, and priority sorting is performed to divide the branch line with the largest weighted value into the island.

[0061] After searching the primary load, if the DG still has remaining capacity, the secondary and tertiary loads are considered. At this time, the number of users contained in the load node must also be considered. Then, a multi-objective optimization model with the maximum equivalent load and the maximum number of users at the load node as the goal is established, that is, the multi-objective function of island partitioning:

[0062]

[0063] Where, L i is the load power at each load point, W i is the load weight of each load node, N i is the maximum number of users in each load node, m is the total number of loads of the secondary load nodes and the tertiary load nodes, and:

[0064]

[0065] The DG power constraint is:

[0066]

[0067] In the formula, ΔS dg is the maximum power of the DG margin.

[0068] In order to coordinate the optimal values ​​of each objective and obtain the optimal solution that is better for each sub-objective, the weighted combination method is used to combine the multi-objective functions into a unified objective function in the form of linear combination, and then sort them by priority, and divide the branch route with the largest weighted value into the island.

[0069] Considering that the units and properties of different objective functions may not be uniform, such as formula (6) is the maximum equivalent load, and formula (7) is the maximum number of users, it is necessary to convert the values ​​of each objective function into a normalized target between 0 and 1, and then combine them into a unified objective function using weighting factors according to the importance of each target. The mathematical method for converting each objective function into a value between 0 and 1 is as follows:

[0070] Assume that each objective function f h (X) The upper limit b of the function value change h and the lower limit a h for:

[0071] a h ≤f h (X)≤b h (10)

[0072] Corresponding to f h (X) The independent variable value x of the conversion function h for:

[0073]

[0074] The objective function f(X) after weighted combination is transformed into:

[0075] f(X)=∑w h f h '(x') (12)

[0076] In the formula, w h It represents the weight of each objective in the optimization design, which is obtained based on experimental results or empirical values. h '(x') represents the normalized objective function after transformation. At this time, the weighting factor in the formula adopts the normalized weighting method, that is:

[0077] ∑w h =1 (13)

[0078] Similarly, if there is a node M+1, the power circle satisfies:

[0079]

[0080] Where M represents the total number of load nodes in the power circle, P i is the active load of the ith load node. When the situation in formula (14) occurs, the M+1th load node can be excluded from the power circle, and an equivalent load can be added to the load node that is in the branch that cuts the power circle and is inside the power circle. The load node connected to the branch where power flows into the power circle is defined as the root node in the power circle, and the rest are general load nodes. If the load node to which the equivalent load is added is a general load node, the additional equivalent load can be calculated using the following formula:

[0081] ΔS=∑(P r +jQ r ) (15)

[0082] Where r is the subsequent load node of other branches connected to this load node, ΔS is the additional equivalent load, and P r , Q r are the active power and reactive power of load node r respectively.

[0083] If the load node to which the equivalent load is added is the root node, the equivalent load added is:

[0084] ΔS=(P DG +jQ DG )-∑(P k +jQ k ) (16)

[0085] In the formula, Q DG is the reactive capacity of the distributed generation, k is the load node in the power circle, P k , Q k are the active power and reactive power of the k load node respectively.

[0086] At this time, the capacity of DG in the power circle after adding the equivalent load is balanced with the load power.

[0087] This method divides the islands with the goal of maximizing the equivalent load and the number of users at the load nodes. First, the loads are divided according to their importance and weights are established according to the specific situation. The maximum boundary of the island is determined using the Dykstra minimum path method, which is helpful for searching the primary load. Then, the primary load within the boundary is given priority, and the influence of the number of users is not considered. The DG minimum power circle method is used to search only for the primary load to ensure that the important load is included in the island. Finally, if the DG has a surplus, a multi-objective optimization model with the maximum equivalent load and the maximum number of users at the load nodes is established. The weighted combination method is used to weight the equivalent load and the number of users of the section, and the priority is sorted. Then the branch line section with the largest weighted value is divided into the island.

[0088] Figure 2 FIG. 1 is a structural block diagram of an island partitioning system considering the load importance and the number of power outage users according to an embodiment of the present invention. Figure 2 As shown, the island division system 100 considering the load importance and the number of power outage users includes a first building module 10, a first determining module 20, a second determining module 30, a second building module 40 and a solving module 50 which are connected in sequence.

[0089] Among them, the first construction module 10 is used to establish a distribution network node network diagram, and divide the primary load, secondary load and tertiary load according to the importance of the load; the first determination module 20 is used to determine the island boundary based on the distribution network node network diagram, with the distributed power access point as the island center starting point; the second determination module 30 is used to search and determine the primary load within the island boundary using the distributed power circle method; the second construction module 40 is used to consider the secondary load and the tertiary load and the number of users contained in the load node after searching for the primary load, if there is residual capacity in the distributed power source, and establish a multi-objective optimization model with the maximum equivalent load and the maximum number of load node users as the goal; the solution module 50 is used to solve the multi-objective optimization model to achieve island division.

[0090] In one embodiment of the present invention, the first determination module 20 is specifically used to start from the distributed power access point as the center starting point of the island, and use the shortest path algorithm to expand the search for all boundary points of the island to determine the island boundary, and the shortest path algorithm is the Dykstra minimum path method.

[0091] In one embodiment of the present invention, the second determination module 30 is specifically used to search and determine the primary load along the topological direction of the distribution network node network with the distributed power source access point as the center and the distributed power source capacity as the search radius.

[0092] In one embodiment of the present invention, the solution module 50 is specifically used to use a weighted combination method to combine the multi-objective functions in the multi-objective optimization model into a unified objective function in a linear combination manner, and based on the unified objective function, perform weighted calculations on the equivalent loads and the number of users of all branch lines containing secondary loads and tertiary loads, and perform priority sorting to divide the branch line with the largest weighted value into the island.

[0093] In one embodiment of the present invention, the system further comprises a load power balancing module for balancing the capacity of the distributed power source with the load power by adding an equivalent load when the capacity of the distributed power source is unbalanced with the load power.

[0094] It should be noted that the specific implementation of the island division system considering the load importance and the number of power outage users in this embodiment can refer to the specific implementation of the island division method considering the load importance and the number of power outage users mentioned above. To avoid redundancy, it will not be repeated here.

[0095] In summary, the present invention considers the number of load users in the process of island division, which can ensure that the power supply area in each island covers as many users as possible, maximize the number of power users, and reduce the losses and impacts caused by power outages on users. Secondly, it can avoid the situation where the load is concentrated in some areas and the power supply is insufficient in other areas during island division. This user number balancing strategy balances the number of users and the load, which can optimize resource allocation and avoid resource waste or over-investment caused by insufficient load or overload in the island, thereby not only helping to reduce the operating costs in the island, but also improving the overall economy of the island. Finally, the island is divided reasonably to ensure that each island covers as many users as possible, which helps to reduce the impact of large-scale power outages on society, especially in places where continuous power supply is required, such as important infrastructure areas. This method helps to maintain public safety and the normal operation of economic activities. In short, the island division strategy considering the number of load users has significant advantages in optimizing power supply coverage, improving system reliability, reducing social impact and reducing island operation costs, making the power system more flexible, efficient and fair in dealing with faults and distributed generation.

[0096] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0097] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A method for dividing isolated islands taking into account the importance of loads and the number of users experiencing power outages, characterized in that: include: Establish a distribution network node network diagram and divide the load into primary, secondary and tertiary loads according to their importance; Based on the distribution network node network diagram, the distributed power access point is taken as the island center starting point to determine the island boundary; The distributed generation power circle method is used to search and determine the primary load within the island boundary; After searching the primary load, if there is residual capacity in the distributed generation, the secondary and tertiary loads and the number of users contained in the load nodes are considered, and a multi-objective optimization model is established with the maximum equivalent load and the maximum number of load node users as the goal, and island division is performed based on the multi-objective optimization model.

2. The island division method considering the load importance and the number of power outage users as claimed in claim 1 is characterized in that: Starting from the distributed power access point as the center starting point of the island, the shortest path algorithm is used to expand the search for all boundary points of the island to determine the island boundary. The shortest path algorithm is the Dykstra minimum path method.

3. The island division method considering the load importance and the number of power outage users as claimed in claim 1, characterized in that: The distributed power circle method uses the distributed power access point as the center of the circle and the distributed power capacity as the search radius, and searches along the topological direction of the distribution network node network to determine the primary load.

4. The island division method considering the importance of load and the number of power outage users as claimed in claim 1, characterized in that: Island division is performed based on a multi-objective optimization model, including: The weighted combination method is adopted to combine the multi-objective functions in the multi-objective optimization model into a unified objective function in a linear combination manner, and based on the unified objective function, the equivalent load and the number of users of all branch lines containing secondary loads and tertiary loads are weightedly calculated and prioritized so as to divide the branch line with the largest weighted value into the island.

5. The island division method considering the importance of load and the number of power outage users as claimed in claim 1, characterized in that: The method further comprises: When the capacity of distributed generation and load power are unbalanced, the method of adding equivalent load is used to balance the capacity of distributed generation and load power.

6. An island division system considering the importance of load and the number of power outage users, characterized in that: include: The first building module is used to establish a distribution network node network diagram and divide the load into primary load, secondary load and tertiary load according to the load importance; The first determination module is used to determine the island boundary based on the distribution network node network diagram and taking the distributed power source access point as the island center starting point; The second determination module is used to search and determine the primary load within the island boundary by using the distributed power generation power circle method; The second building module is used to establish a multi-objective optimization model with the maximum equivalent load and the maximum number of load node users as the goal, after searching for the primary load, if there is residual capacity of the distributed power source, considering the secondary load and the tertiary load and the number of users contained in the load node; The solution module is used to solve the multi-objective optimization model and realize island partitioning.

7. The island division system considering the importance of load and the number of power outage users as claimed in claim 6, characterized in that: The first determination module is specifically used to start from the distributed power access point as the island center starting point, and use the shortest path algorithm to expand the search for all boundary points of the island to determine the island boundary, and the shortest path algorithm is the Dykstra minimum path method.

8. The island division system considering the importance of load and the number of power outage users as claimed in claim 6, characterized in that: The second determination module is specifically used to search and determine the primary load along the topological direction of the distribution network node network with the distributed power source access point as the center and the distributed power source capacity as the search radius.

9. The island division system considering the load importance and the number of power outage users as claimed in claim 6, characterized in that: The solution module is specifically used to use a weighted combination method to combine the multi-objective functions in the multi-objective optimization model into a unified objective function in a linear combination manner, and based on the unified objective function, perform weighted calculations on the equivalent loads and the number of users of all branch lines containing secondary loads and tertiary loads, and perform priority sorting to divide the branch line with the largest weighted value into the island.

10. The island division system considering the importance of load and the number of power outage users as claimed in claim 6, characterized in that: It also includes a load power balancing module, which is used to balance the distributed power capacity and load power by adding equivalent load when the distributed power capacity and load power are unbalanced.

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