Identification method for affected part in case of microgrid line fault

Abstract

The invention relates to a method for identifying affected parts during microgrid line faults, belongs to the technical field of microgrid short-circuit faults, and solves the problem of how to determine the affected parts of a microgrid in an extremely short time so as to enable the affected parts to exit from operation and be protected when various scales of microgrids have short-circuit faults in the prior art. Obtaining a micro-grid topological structure, a short-circuit fault occurrence position and a connection state of each line; establishing an affected part identification model according to the limiting condition of the topological structure; and inputting the micro-grid topological structure, the short-circuit fault occurrence position and the connection state of each line in the micro-grid into the affected part identification model so as to obtain affected parts in the micro-grid. The method achieves the determination of the affected states of the part based on the position of the short-circuit fault and other parts, achieves the effective and rapid recognition, and improves the safety and recovery efficiency of the microgrid.

Description

Technical Field

[0001] The present invention relates to the technical field of microgrid short-circuit faults, and in particular to a method for identifying affected components when a microgrid line fails. Background Art

[0002] Microgrid is a small power generation, distribution and consumption system composed of distributed power sources, energy storage systems, energy conversion devices, monitoring and protection devices, loads, etc. Microgrid technology provides a flexible and orderly feasible technical approach for distributed grid-connected power generation and large-scale consumption and utilization of new energy and renewable energy. After effectively integrating various distributed intermittent new energy power generation, microgrid can be connected to the active distribution network as an intelligent subsystem, enhancing the interactivity, controllability and reliability of the active distribution network, thereby improving the overall energy efficiency of the power system.

[0003] Microgrids can flexibly control the characteristics of distributed power sources, providing an effective way to develop and utilize my country's abundant and considerable renewable energy resources, which is conducive to promoting energy conservation and emission reduction, improving the low-carbonization of power structure, and promoting the development of intelligent green electricity. In order to accelerate the engineering practice of microgrids, power workers have conducted extensive research in its analysis and modeling, operation optimization, control strategy, energy storage technology and devices, and protection technology. The components and equipment types in microgrids are complex and have different operating characteristics, which brings difficulties to system modeling, coordinated control, and comprehensive protection. After a microgrid fails, accurately finding the line and taking it out of operation has also become a current problem. Summary of the invention

[0004] In view of the above analysis, an embodiment of the present invention aims to provide a method for identifying affected components when a microgrid line fails, so as to solve the problem of how to determine the affected components of a microgrid in a very short time when a short circuit failure occurs in microgrids of various sizes, so as to make them exit operation.

[0005] The embodiment of the present invention provides a method for identifying affected components when a microgrid line fails, specifically comprising:

[0006] Obtain the microgrid topology, the location of the short-circuit fault, and the connection status of each line in the microgrid;

[0007] Establishing an affected component identification model based on the limiting conditions of the topological structure;

[0008] The microgrid topology, the location of the short-circuit fault, and the connection status of each line in the microgrid are input into the affected component identification model to obtain the affected components in the microgrid.

[0009] Optionally, the connection status includes closed, open, closed and short-circuited.

[0010] Optionally, the limiting conditions include:

[0011] 1) When the line is closed and short-circuited, the points on both sides are affected by the short-circuit fault;

[0012] 2) The points on both sides of the closed line are affected by the short-circuit fault in the same way, while the points on both sides of the open line are affected by the short-circuit fault in independent ways;

[0013] 3) The difference between the injected virtual flow and the absorbed virtual flow at a certain point is equal to the difference between the outflow virtual flow and the inflow virtual flow;

[0014] 4) Only closed circuits are allowed to flow through the virtual flow;

[0015] 5) A point can inject a virtual flow into the virtual network only if there is a closed and short-circuited line among the lines directly connected to the point.

[0016] Optionally, the step of inputting the microgrid topology, the location of the short circuit fault, and the connection status of each line in the microgrid into an affected component identification model to obtain the affected components in the microgrid includes: determining the components directly affected by the fault according to the limiting condition 1).

[0017] Optionally, the step of inputting the microgrid topology, the location where the short circuit fault occurs, and the connection status of each line in the microgrid into an affected component identification model to thereby obtain the affected components in the microgrid further includes: determining the impact of the fault on components directly or indirectly connected to the components directly affected by the fault according to limited conditions 1) and 2).

[0018] Optionally, the method of inputting the microgrid topology structure, the location where the short circuit fault occurs, and the connection status of each line in the microgrid into the affected component identification model to obtain the affected components in the microgrid also includes: determining the impact of the fault on components that have no direct or indirect connection with the components directly affected by the fault according to 3)-5).

[0019] Optionally, the determining, according to 3) to 5), the impact of the fault on the components that are not directly or indirectly connected to the components directly affected by the fault includes:

[0020] 5) Determine the point in the topology structure where the virtual flow can be injected into the virtual network according to the location and conditions of the short circuit fault;

[0021] According to the connection status of each line in the microgrid and condition 4), determine the lines in the topology structure through which the virtual flow can flow;

[0022] According to the injection of virtual flows at each point in the topology and the flow of virtual flows through the lines, the impact of the fault on components that have no direct or indirect connection with the components directly affected by the fault is obtained based on condition 3).

[0023] Optionally, the limiting condition 1) is implemented by the following formula:

[0024]

[0025]

[0026] Among them, μ m is a 0-1 variable, indicating whether point m is affected by a short circuit fault. If so, μ m =1, otherwise μ m =0; is a 0-1 variable indicating whether the line (m,n) is closed and short-circuited. If so, otherwise E is the set of lines in the microgrid topology.

[0027] Optionally, the limiting condition 2) is implemented by the following formula:

[0028]

[0029] Among them, l m,n is a 0-1 variable indicating whether the line (m,n) is closed. If so, l m,n =1, otherwise l m,n =0.

[0030] Optionally, the limiting conditions 3)-5) are implemented by the following formula:

[0031]

[0032]

[0033]

[0034] Where V is the set of midpoints in the microgrid topology; Ω 子 (m) represents the sub-point set of point m; Ω 母 (m) represents the set of generatrix points of point m; ε m is a non-negative continuous variable, indicating the size of the virtual flow injected at point m; θ m,n is a continuous variable, indicating the size of the virtual flow on the line (m,n); M is a maximum positive constant.

[0035] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0036] 1. Based on the microgrid topology, the location of the short-circuit fault, and the connection status of each line in the microgrid, determine the components directly affected by the short-circuit fault and the status of other components affected, and effectively identify them quickly, thereby improving the safety and recovery efficiency of the microgrid.

[0037] 2. Starting from the original topology, the connection relationship of the microgrid is expressed in a concise way, which is more conducive to modeling and analysis, and is conducive to the identification of affected components when a short circuit fault occurs in the microgrid, and then it is conducive to optimizing the planning of renewable energy combinations, promoting the rapid development of power technology, establishing a system analysis model, determining the appropriate operation mode and switching method, reasonably formulating operation and scheduling strategies, studying new equipment and comprehensive control methods for various equipment, and developing protection technologies that are compatible with the characteristics of microgrids.

[0038] In the present invention, the above model can be expanded to assist in microgrid optimization decisions in more scenarios. Other features and advantages of the present invention will be described in the subsequent description, and some advantages may become apparent from the description or be understood by implementing the present invention. The objects and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0040] Figure 1 This is a schematic diagram of the identification principle of the affected components of the microgrid in an embodiment of the present invention;

[0041] Figure 2 It is a typical DC microgrid structure;

[0042] Figure 3 The topological diagram of the microgrid topology mapping point corresponding to the typical DC microgrid structure.

[0043] Reference numerals:

[0044] 101-111 represent different affected parts respectively;

[0045] 1- mapping point of the first connection point of the DC bus; 2- mapping point of the connected DC / DC first converter; 3- mapping point of the DC energy storage; 4- mapping point of the second connection point of the DC bus; 5- mapping point of the connected AC / DC converter; 6- mapping point of the transformer; 7- mapping point of the power transmission part on the left side of the transformer in the AC grid frame; 8- mapping point of the third connection point of the DC bus; 9- mapping point of the connected DC / AC second converter; 10- mapping point of the AC energy storage; 11- mapping point of the fourth connection point of the DC bus ; 12-the mapping point of the connected DC / AC third converter; 13-the mapping point of the photovoltaic generator; 14-the mapping point of the fifth connection point of the DC bus; 15-the mapping point of the connected DC / AC fourth converter; 16-the mapping point of the AC load; 17-the mapping point of the sixth connection point of the DC bus; 18-the mapping point of the connected DC / AC fourth converter; 19-the mapping point of the wind turbine; 20-the mapping point of the seventh connection point of the DC bus; 21-the mapping point of the connected DC / DC fifth converter; 22-the DC load mapping point. DETAILED DESCRIPTION

[0046] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0047] A specific embodiment of the present invention discloses a method for identifying affected components when a microgrid line fails, such as Figure 1 As shown, specifically including: obtaining the microgrid topology, the location of the short circuit fault, and the connection status of each line in the microgrid;

[0048] An affected component identification model is established according to the limiting conditions of the topological structure; the microgrid topological structure, the location of the short-circuit fault and the connection status of each line in the microgrid are input into the affected component identification model to obtain the affected components in the microgrid.

[0049] The connection states include closed, open, and closed and short.

[0050] The limiting conditions include:

[0051] 1) When the line is closed and short-circuited, the points on both sides are affected by the short-circuit fault;

[0052] 2) The points on both sides of the closed line are affected by the short-circuit fault in the same way, while the points on both sides of the open line are affected by the short-circuit fault in independent ways;

[0053] 3) The difference between the injected virtual flow and the absorbed virtual flow at a certain point is equal to the difference between the outflow virtual flow and the inflow virtual flow;

[0054] 4) Only closed circuits are allowed to flow through the virtual flow;

[0055] 5) A point can inject a virtual flow into the virtual network only if there is a closed and short-circuited line among the lines directly connected to the point.

[0056] Specifically, the constraints of the affected component identification model when the microgrid line fails can be expressed as:

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066] Where E is the set of midlines in the microgrid topology; V is the set of midpoints in the microgrid topology; Ω 子 (m) represents the sub-point set of point m; Ω 母 (m) represents the set of generatrix points of point m; μ m is a 0-1 variable, indicating whether point m is affected by a short circuit fault. If so, μ m =1, otherwise μ m =0; is a 0-1 variable indicating whether the line (m,n) is closed and short-circuited. If so, otherwise l m,n is a 0-1 variable indicating whether the line (m,n) is closed. If so, l m,n =1, otherwise l m,n =0;ψ m,n is a 0-1 variable indicating whether the line (m,n) is short-circuited. If so, ψ m,n =1, otherwise ψ m,n =0;ε m is a non-negative continuous variable, indicating the size of the virtual flow injected at point m; θ m,n is a continuous variable, indicating the size of the virtual flow on the line (m,n); M is a maximum positive constant.

[0067] It can be understood that the child point set of point m represents the set of subordinate points of the virtual flow direction at point m along the virtual flow direction; the parent point set of point m represents the set of superior points flowing toward point m along the virtual flow direction.

[0068] Among them, formula 1 and formula 2 mean that if any line (m,n) is closed and short-circuited, that is, Then the points on both sides are affected by the short circuit fault, that is, μ m =1, μ n =1; Formula 3 will l m,n and ψ m,n is connected, indicating that if and only if the line (m,n) is closed, that is, l m,n =1, and the line (m,n) is short-circuited, that is, ψ m,n =1, Formula 4, Formula 5 and Formula 6 are linearizations of Formula 3; Formula 7 indicates that the points on both sides of the closed line are in the same state as to whether they are affected by the short-circuit fault, and the points on both sides of the open line are not restricted as to whether they are affected by the short-circuit fault. That is, when l m,n = 1, there must be μ m =μ n Formulas 1 to 7 constrain the points on both sides of the short circuit and the closed line and the points that are directly or indirectly connected to the points on both sides. However, Formulas 1 to 7 alone cannot fully determine the points that are not directly or indirectly connected to the points directly affected by the fault. For example, Formulas 1 to 7 cannot determine the points in the "island" without short circuit (such as Figure 1 The three isolated points on the right side of the figure are affected by the fault (μ m )". Therefore, Formula 8, Formula 9 and Formula 10 are proposed. Formula 8, Formula 9 and Formula 10 establish a virtual network: the points on both sides of the closed and short-circuited line inject virtual flow into the virtual network, and the points affected by the short-circuit fault absorb the virtual flow from the virtual network, thereby constraining the state of the points not directly connected to the closed and short-circuited line affected by the short-circuit fault. Among them, Formula 8 is the virtual flow balance constraint, which means that point m injects virtual flow ε m With the absorption of virtual flow μ m (If point m is affected by a fault, that is, μ m = 1, it absorbs unit virtual flow, otherwise it does not absorb virtual flow) the difference is equal to its outflow virtual flow With the incoming virtual stream The difference; Formula 9 defines the flow of the virtual flow, which means only closed lines, i.e. l m,n =1, the virtual flow is allowed to flow; Formula 10 means that if and only if there is a closed and short-circuited line among the lines directly connected to point m, that is, Click m to inject virtual flows into the virtual network.

[0069] When a microgrid line fault occurs, an affected component identification model is established, wherein the objective function of the affected component identification model when a microgrid line fault occurs can be expressed as:

[0070] mint(Formula 11)

[0071] Here, t is an arbitrary constant.

[0072] Since any feasible solution in the feasible domain space limited by the constraints is the result of identifying the affected components, the objective function of the model with a constant t can meet the model requirements. There is no need to include variables in the objective function, which reduces the complexity of the model and improves the speed of model solution.

[0073] The affected component identification model when the microgrid line fails can be expressed as:

[0074] mint

[0075] st(Formula 1),(Formula 2),

[0076] (Formula 4)-(Formula 10)

[0077] Finally, the microgrid topology, short-circuit fault location, and connection status of each line in the microgrid are input into the established microgrid line fault affected component identification model to determine the affected components of the microgrid.

[0078] Specifically, the microgrid topology structure, the short circuit fault location and the connection status of each line in the microgrid are input into the affected component identification model to obtain the affected components in the microgrid, including: determining the components directly affected by the fault according to the limited condition 1).

[0079] Determine the impact of the fault on components directly or indirectly connected to the component directly affected by the fault based on the limiting conditions 1) and 2).

[0080] According to 3)-5), determine the impact of the fault on components that are not directly or indirectly connected to the components directly affected by the fault.

[0081] Among them, the impact of the fault on the components that are not directly or indirectly connected to the components directly affected by the fault is determined according to 3)-5), including:

[0082] 5) Determine the point in the topology structure where the virtual flow can be injected into the virtual network according to the location and conditions of the short circuit fault;

[0083] According to the connection status of each line in the microgrid and condition 4), determine the lines in the topology structure through which the virtual flow can flow;

[0084] According to the injection of virtual flows at each point in the topology and the flow of virtual flows through the lines, the impact of the fault on components that have no direct or indirect connection with the components directly affected by the fault is obtained based on condition 3). The limiting condition 1) is implemented by the following formula:

[0085]

[0086]

[0087] Among them, μ m is a 0-1 variable, indicating whether point m is affected by a short circuit fault. If so, μ m =1, otherwise μ m =0; is a 0-1 variable indicating whether the line (m,n) is closed and short-circuited. If so, otherwise E is the set of lines in the microgrid topology.

[0088] The limiting condition 2) is achieved by the following formula:

[0089]

[0090] Among them, l m,n is a 0-1 variable indicating whether the line (m,n) is closed. If so, l m,n =1, otherwise l m,n =0.

[0091] The limiting conditions 3)-5) are achieved by the following formula:

[0092]

[0093]

[0094]

[0095] Where V is the set of midpoints in the microgrid topology; Ω 子 (m) represents the sub-point set of point m; Ω 母 (m) represents the set of generatrix points of point m; ε m is a non-negative continuous variable, indicating the size of the virtual flow injected at point m; θ m,n is a continuous variable, indicating the size of the virtual flow on the line (m,n); M is a maximum positive constant.

[0096] Based on the microgrid topology, the present invention provides a specific embodiment, mapping the actual microgrid components as points in the topology, and mapping the microgrid wires and cables as lines in the topology. Figure 2-Figure 3As shown, the DC energy storage is mapped as point 3, the connected DC / DC first converter is mapped as point 2, and the first connection point with the DC bus is mapped as point 1; the power transmission part on the left side of the transformer in the AC power grid frame is mapped as point 7, the transformer is mapped as point 6, the connected AC / DC converter is mapped as point 5, and the second connection point with the DC bus is mapped as point 4; the AC energy storage is mapped as point 10, the connected DC / AC second converter is mapped as point 9, and the third connection point with the DC bus is mapped as point 8; the photovoltaic generator is mapped as point 13, the connected DC / The AC third converter is mapped to point 12, and the fourth connection point with the DC bus is mapped to point 11; the AC load is mapped to point 16, the connected DC / AC fourth converter is mapped to point 15, and the fifth connection point with the DC bus is mapped to point 14; the wind turbine is mapped to point 19, the connected DC / AC fourth converter is mapped to point 18, and the sixth connection point with the DC bus is mapped to point 17; the DC load is mapped to point 22, the connected DC / DC fifth converter is mapped to point 21, and the seventh connection point with the DC bus is mapped to point 20.

[0097] Those skilled in the art will appreciate that all or part of the processes of the above-mentioned embodiments can be implemented by instructing related hardware through a computer program, and the program can be stored in a computer-readable storage medium, wherein the computer-readable storage medium is a disk, an optical disk, a read-only storage memory, or a random access memory, etc.

[0098] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for identifying affected components when a microgrid line fails, characterized in that: Specifically include: Obtain the microgrid topology, the location of the short-circuit fault, and the connection status of each line in the microgrid; Establishing an affected component identification model based on the limiting conditions of the topological structure; The microgrid topology, the location of the short-circuit fault, and the connection status of each line in the microgrid are input into the affected component identification model to obtain the affected components in the microgrid.

2. The method for identifying affected components when a microgrid line fails according to claim 1, characterized in that: The connection states include closed, open, and closed and short.

3. The method for identifying affected components when a microgrid line fails according to claim 1, characterized in that: The limiting conditions include: 1) When the line is closed and short-circuited, the points on both sides are affected by the short-circuit fault; 2) The points on both sides of the closed line are affected by the short-circuit fault in the same way, while the points on both sides of the open line are affected by the short-circuit fault in independent ways; 3) The difference between the injected virtual flow and the absorbed virtual flow at a certain point is equal to the difference between the outflow virtual flow and the inflow virtual flow; 4) Only closed circuits are allowed to flow through the virtual flow; 5) A point can inject a virtual flow into the virtual network only if there is a closed and short-circuited line among the lines directly connected to the point.

4. The method for identifying affected components when a microgrid line fails according to claim 3, characterized in that: The method of inputting the microgrid topology, the location of the short circuit fault, and the connection status of each line in the microgrid into the affected component identification model to obtain the affected components in the microgrid includes: determining the components directly affected by the fault according to the limiting condition 1).

5. The method for identifying affected components when a microgrid line fails according to claim 3, characterized in that: The method of inputting the microgrid topology, the location where the short circuit fault occurs, and the connection status of each line in the microgrid into the affected component identification model to obtain the affected components in the microgrid also includes: determining the impact of the fault on the components directly or indirectly connected to the components directly affected by the fault according to the limiting conditions 1) and 2).

6. The method for identifying affected components when a microgrid line fails according to claim 3, characterized in that: The method of inputting the microgrid topology structure, the location where the short circuit fault occurs, and the connection status of each line in the microgrid into the affected component identification model to obtain the affected components in the microgrid also includes: determining the impact of the fault on components that have no direct or indirect connection relationship with the components directly affected by the fault according to 3)-5).

7. The method for identifying affected components when a microgrid line fails according to claim 3, characterized in that: The determination of the impact of the fault on the components that are not directly or indirectly connected to the components directly affected by the fault according to 3) to 5) includes: 5) Determine the point in the topology structure where the virtual flow can be injected into the virtual network according to the location and conditions of the short circuit fault; According to the connection status of each line in the microgrid and condition 4), determine the lines in the topology structure through which the virtual flow can flow; According to the injection of virtual flows at each point in the topology and the flow of virtual flows through the lines, the impact of the fault on components that have no direct or indirect connection with the components directly affected by the fault is obtained based on condition 3).

8. The method for identifying affected components when a microgrid line fails according to any one of claims 3 or 4, characterized in that: The limiting condition 1) is achieved by the following formula: Among them, μ m is a 0-1 variable, indicating whether point m is affected by a short circuit fault. If so, μ m =1, otherwise μ m =0; is a 0-1 variable indicating whether the line (m,n) is closed and short-circuited. If so, otherwise E is the set of lines in the microgrid topology.

9. The method for identifying affected components when a microgrid line fails according to claim 8, characterized in that: The limiting condition 2) is achieved by the following formula: Among them, l m,n is a 0-1 variable indicating whether the line (m,n) is closed. If so, l m,n =1, otherwise l m,n =0.

10. The method for identifying affected components when a microgrid line fails according to claim 9, characterized in that: The limiting conditions 3)-5) are achieved by the following formula: Where V is the set of midpoints in the microgrid topology; Ω 子 (m) represents the sub-point set of point m; Ω 母 (m) represents the set of generatrix points of point m; ε m is a non-negative continuous variable, indicating the size of the virtual flow injected at point m; θ m,n is a continuous variable, indicating the size of the virtual flow on the line (m,n); M is a maximum positive constant.

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