Power grid fragile line identification method and system based on power flow betweenness

Abstract

The invention provides a power grid fragile line identification method and system based on power flow betweenness, and relates to the technical field of fragile line identification, and the method comprises the steps: calculating the branch coefficient of a branch of a power grid topological structure; calculating the transmission power of the transmission line and a node branch coefficient according to the branch branch coefficient, and calculating the total injection power of the head end node according to the node branch coefficient; obtaining a power sequence distribution matrix of the topological structure and an inverse matrix of the power sequence distribution matrix according to the transmission power and the total injection power; obtaining a first sub-matrix, a second sub-matrix and a third sub-matrix according to the inverse matrix of the power sequence distribution matrix; and calculating the power flow betweenness of the transmission line according to the transmission power, the total injection power, the first sub-matrix, the second sub-matrix and the third sub-matrix so as to identify the fragile line according to the power flow betweenness. The method does not depend on the result of power grid load flow calculation, when the operation state of the power system changes, repeated iterative load flow calculation does not need to be carried out, and the efficiency of fragile line identification can be improved.

Description

Technical Field

[0001] This application relates to the technical field of fragile line identification, and particularly to a method and system for identifying fragile lines in a power grid based on current flow betweenness. Background Art

[0002] A fragile line refers to a line that can trigger large-scale cascading failures or even system collapse in a power system (power grid) after being disturbed or failing. When identifying fragile lines, the fragile line identification method based on complex network theory analyzes the tendency scale at which the power grid cannot maintain its topological structure integrity and normal operation after the withdrawal or cascading withdrawal of physical units when the power system is disturbed or fails. This identification method is only related to the topological structure of the power system and the impedance parameters of the power system, and cannot reflect the impact of the dynamic change of power flow in the power system on the fragile lines of the power system. Although indicators such as current flow betweenness used for identifying fragile lines in the power system can reflect the state changes of the power system, when calculating the current flow betweenness, power flow calculation needs to be carried out first.

[0003] Power flow calculation must be iterative. Common Newton-Raphson algorithms and Gauss-Seidel iterative methods need to be iterated repeatedly to obtain convergent power flow, and the larger the scale of the power system, the longer the iterative calculation time, resulting in low calculation efficiency of the current flow betweenness. Whether using the method of power flow tracing to calculate power flow or the iterative method to calculate power flow, it requires a long calculation time and cannot meet the requirements of rapid identification of fragile lines, with low identification efficiency. Summary of the Invention

[0004] This application provides a method and system for identifying fragile lines in a power grid based on current flow betweenness to solve the problem of low efficiency in identifying fragile lines.

[0005] The first aspect of this application provides a method for identifying fragile lines in a power grid based on current flow betweenness, including: Calculating the branch coefficient of a branch of the power grid topology; the topology includes a power source node, a load node, a transmission node, and at least one transmission line. The power source node is connected to the load node through the transmission line. The transmission node is a node on the transmission line, and the transmission node includes a head node and a tail node. The branch coefficient of the branch is the power change amount on any transmission line when the power of the transmission node changes; Calculating the transmission power of the transmission line and the node branch coefficient according to the branch coefficient of the branch, so as to calculate the total injection power of the head node according to the node branch coefficient; the node branch coefficient is the power change amount of another transmission node when the power of one transmission node changes; Obtain the power sequence allocation matrix of the topological structure and the inverse matrix of the power sequence allocation matrix according to the transmission power and the total injection power, where the elements in the power sequence allocation matrix are the allocation coefficients of the total injection power on the transmission lines; Obtain a first sub-matrix, a second sub-matrix, and a third sub-matrix according to the inverse matrix of the power sequence allocation matrix; the elements in the first sub-matrix are the power allocation coefficients for the total injection power to be allocated from the power source nodes to the transmission lines, the elements in the second sub-matrix are the power allocation coefficients for the total injection power to be allocated from the transmission lines to the load nodes, and the elements in the third sub-matrix are the power allocation coefficients for the total injection power to be allocated from the power source nodes to the load nodes; Calculate the power flow betweenness of the transmission lines according to the transmission power, the total injection power, the first sub-matrix, the second sub-matrix, and the third sub-matrix, so as to identify vulnerable lines according to the power flow betweenness, and the power flow betweenness is used to evaluate the vulnerability of the transmission lines.

[0006] Optionally, calculating the branch branch coefficient of the power grid topological structure includes: Obtain the node impedance matrix of the topological structure to calculate the branch branch coefficient according to the elements in the node impedance matrix; the value of the element in the node impedance matrix is equal to the voltage value of another transmission node when a unit power is injected at any transmission node.

[0007] Optionally, calculate the branch branch coefficient by the following formula: ; where d is the transmission line, n is the transmission node on any transmission line other than the transmission line d, is the branch branch coefficient of the transmission line d, is the voltage of the head node on the transmission line d when a unit power is injected at the transmission node n, is the voltage of the end node on the transmission line d when a unit power is injected at the transmission node n, and The voltage values of are respectively equal to the values of the elements in the node impedance matrix, is the impedance of the transmission line d.

[0008] Optionally, calculate the transmission power by the following formula: ; where, is the transmission power, is the row vector of the branch branch coefficient, is the power column vector of the power source node, is the power column vector of the load node; Calculate the node branch coefficient by the following formula: ; where is the node branch coefficient of transmission node k when the power of transmission node n changes, C is the set of transmission lines, is the branch coefficient of the c transmission lines connected to transmission node k; Calculate the total injected power by the following formula: ; where is the total injected power, is the row vector of node branch coefficients.

[0009] Optionally, calculate the elements in the power sequence allocation matrix by the following formula: ; where is the element in the power sequence allocation matrix, s is the starting node of the transmission line, t is the ending node of the transmission line, .

[0010] Optionally, the first sub-matrix, the second sub-matrix, and the third sub-matrix are sub-matrices of the inverse matrix of the power sequence allocation matrix.

[0011] Optionally, calculate the power flow betweenness of the transmission line by the following formula: ; where is the power flow betweenness, G is the set of power source nodes, L is the set of load nodes; i is a power source node, j is a load node; is the power capacity of the power source node, is the load capacity of the load node, is the minimum value of the power capacity and the load capacity; is the element in the first sub-matrix at the s-th row and the i-th column, is the element in the second sub-matrix at the s-th row and the j-th column, is the element in the third sub-matrix at the i-th row and the j-th column.

[0012] Optionally, the identifying the vulnerable lines according to the power flow betweenness includes: Normalize the power flow betweenness to obtain normalized data; Sort the normalized data to take the preset number of transmission lines ranked at the front as the vulnerable lines.

[0013] Optionally, normalize the power flow betweenness by the following formula: ; Among them, is the normalized data, is the maximum value of the vulnerability of the transmission line, is the minimum value of the vulnerability of the transmission line.

[0014] The second aspect of this application provides a power grid vulnerable line identification system based on power flow betweenness, which is applied to the power grid vulnerable line identification method provided in the first aspect. The system includes: The first calculation module: used to calculate the branch coefficient of the branches of the power grid topology; the topology includes a power source node, a load node, a transmission node and at least one transmission line. The power source node is connected to the load node through the transmission line. The transmission node is a node on the transmission line. The transmission node includes a head node and a tail node. The branch coefficient of the branch is the power change amount on any transmission line when the power of the transmission node changes; The second calculation module: used to calculate the transmission power of the transmission line and the node branch coefficient according to the branch coefficient of the branch, so as to calculate the total injection power of the head node according to the node branch coefficient; the node branch coefficient is the power change amount of another transmission node when the power of one of the transmission nodes changes; The third calculation module: used to obtain the power sequence distribution matrix of the topology and the inverse matrix of the power sequence distribution matrix according to the transmission power and the total injection power. The elements in the power sequence distribution matrix are the distribution coefficients of the total injection power on the transmission line; The fourth calculation module: used to obtain the first sub-matrix, the second sub-matrix and the third sub-matrix according to the inverse matrix of the power sequence distribution matrix; the elements in the first sub-matrix are the power distribution coefficients of the total injection power allocated from the power source node to the transmission line, the elements in the second sub-matrix are the power distribution coefficients of the total injection power allocated from the transmission line to the load node, and the elements in the third sub-matrix are the power distribution coefficients of the total injection power allocated from the power source node to the load node; The identification calculation module: used to calculate the power flow betweenness of the transmission line according to the transmission power, the total injection power, the first sub-matrix, the second sub-matrix and the third sub-matrix, so as to identify the vulnerable line according to the power flow betweenness. The power flow betweenness is used to evaluate the vulnerability of the transmission line.

[0015] The present application provides a method and system for identifying vulnerable lines in a power grid based on current transfer betweenness. The method includes: calculating the branch coefficient of each branch in the power grid topology; calculating the transmission power of the transmission line and the node branch coefficient according to the branch coefficient, and calculating the total injection power of the head node according to the node branch coefficient; obtaining the power sequence distribution matrix of the topology and the inverse matrix of the power sequence distribution matrix according to the transmission power and the total injection power; obtaining the first sub-matrix, the second sub-matrix and the third sub-matrix according to the inverse matrix of the power sequence distribution matrix; calculating the current transfer betweenness of the transmission line according to the transmission power, the total injection power, the first sub-matrix, the second sub-matrix and the third sub-matrix, and identifying the vulnerable line according to the current transfer betweenness. The method does not depend on the result of power flow calculation in the power grid. When the operating state of the power system changes, only the power of the power supply node and the power of the load node need to be updated, and there is no need to perform iterative power flow calculation, which can improve the efficiency of identifying vulnerable lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the present application, the drawings required for the embodiments will be briefly introduced below. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0017] Figure 1 It is a schematic diagram showing an example of nodes and transmission lines in the power grid topology provided by an embodiment of the present application; Figure 2 It is a flowchart of a method for identifying vulnerable lines in a power grid based on current transfer betweenness provided by an embodiment of the present application; Figure 3 It is a schematic diagram of a 5-node power grid topology provided by an embodiment of the present application; Figure 4 It is a schematic diagram of the structure of a system for identifying vulnerable lines in a power grid based on current transfer betweenness provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] The embodiments will be described in detail below, and the examples are shown in the drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following examples do not represent all embodiments consistent with the present application. They are only examples of systems and methods consistent with some aspects of the present application described in detail in the claims.

[0019] Indices such as current transfer entropy can reflect the changes in the state of the power system and are commonly used for identifying vulnerable lines in the power system. However, when calculating the current transfer entropy, power flow calculation needs to be carried out first. Power flow calculation requires iteration. Both the common Newton-Raphson algorithm and Gauss-Seidel iteration method need to be iterated repeatedly to obtain a convergent power flow. Moreover, the larger the scale of the power system, the longer the iteration calculation time, resulting in low calculation efficiency of the current transfer entropy. Whether using the method of power flow tracing or the iterative method to calculate the power flow, it takes a long calculation time and cannot meet the requirements of rapid identification of vulnerable lines, with low identification efficiency.

[0020] To solve the problem of low efficiency in identifying vulnerable lines, some embodiments of this application provide a method for identifying vulnerable lines in the power grid based on current transfer entropy. Before explaining the identification method of this application, a brief explanation of the current transfer entropy is given first. In the power system, when the power source node transmits power flow (i.e., power, and the power grid power flow is active power) to the load node, it needs to pass through some transmission lines in the power grid. When the proportion of the power flow transmitted by any one transmission line in the total transmitted power flow is larger, it is more important in the power flow transmission and is also more vulnerable in the power system. By accumulating the importance of all transmission lines transmitting power flow between all power source-load node pairs in the power grid, the vulnerability index of the transmission line in the whole network of lines, that is, the current transfer entropy, can be obtained.

[0021] The power grid topology structure includes power source nodes, load nodes, transmission nodes, and at least one transmission line. The power source nodes are connected to the load nodes through the transmission lines. It can be understood that the transmission nodes are the nodes on the transmission lines, and the transmission nodes include the head nodes and the end nodes. Refer to Figure 1 , Figure 1 In, G5 and G6 are power source nodes, L5 and L6 are load nodes, p7, p8, and p9 are transmission nodes, and lx and ly are transmission lines. Taking the transmission line lx in Figure 1 as an example, p7 is the head node of the transmission line lx, p8 is the end node of the transmission line lx, and for the transmission line ly, p8 is the head node of the transmission line ly, p9 is the end node of the transmission line ly. For the combined transmission line of lx and ly, p7 is the head node, p9 is the end node, and p8 is the transmission node on the transmission line. Assuming the transmission line is s-t, s is the head node of the transmission line, and t is the end node of the transmission line, then the current transfer entropy of the transmission line s-t can be expressed as: ; (1) Among them, is the current transfer entropy, G is the set of power source nodes, L is the set of load nodes, i is the power source node, j is the load node, is the power capacity of the power source node, is the load capacity of the load node, is the minimum value of the power supply capacity and the load capacity, is the tidal flow (power) transmitted from the power supply node to the load node, is the component of the power flow transmitted between the source-load node pairs on the transmission line s-t, and the source-load node pairs are power supply-load node pairs (i, j). Among them, the values of i and j can be 1, 2, 3…, N.

[0022] According to the definition of the power flow betweenness, it is necessary to first perform a power flow calculation. According to the method of power flow tracing, the component of the power flow transmitted between the source-load node pairs on the transmission line s-t can be calculated by the following formula : ; (2) Among them, is the power allocated from the power supply node i to the transmission line, is the power allocated from the load node j to the transmission line, is the transmission power of any transmission line s-t. In formula (2), the power allocated from the power supply node i to the transmission line and the power allocated from the load node j to the transmission line can be calculated by the following formulas respectively: ; (3) Among them, is the power of the power supply node, is the power of the load node, is the total injection power of the head node s, is the first sub-matrix, is the element in the s-th row and i-th column of the first sub-matrix; is the second sub-matrix, is the element in the s-th row and j-th column of the second sub-matrix.

[0023] The power transmitted from the power supply node to the load node can be calculated by the following formula : ; (4) Among them, is the third sub-matrix, is the element in the i-th row and j-th column of the third sub-matrix. In the above formulas (3)-(4), A is the power sequence allocation matrix. The power sequence allocation matrix A is used to reflect the allocation relationship of the total injection power of the head node s on each transmission line, that is, the proportion of the transmission power on the transmission line s-t in the total injection power of the head node s. Therefore, it can be understood that the elements in the power sequence allocation matrix A are the allocation coefficients of the total injection power on the transmission line, and the power sequence allocation matrix A is an N×N matrix, where N is the total number of nodes in the power grid.

[0024] , , are sub - matrices of the inverse matrix A of the power sequence distribution matrix A -1 . Then the third sub - matrix is an M×N - order matrix, where M is the total number of power source nodes, the elements in only include the columns corresponding to the power source nodes in the inverse matrix A -1 . The first sub - matrix is a D×M - order matrix, where D is the number of head nodes of the transmission line s - t, the elements in only include the rows corresponding to the head node s and the columns corresponding to the power source node i in the inverse matrix A -1 . The second sub - matrix is a D×N - order matrix, the elements in only include the columns corresponding to the head node s in the inverse matrix A -1 . The elements in are the power distribution coefficients for the power to be distributed from the power source nodes to the transmission lines, the elements in are the power distribution coefficients for the power to be distributed from the transmission lines to the load nodes, the elements in are the power distribution coefficients for the power to be distributed from the power source nodes to the load nodes.

[0025] The elements in the power sequence distribution matrix A can be calculated by the following formula: ; (5) where, , is an element in the power sequence distribution matrix A.

[0026] According to formulas (1) - (5), the current - injection - based betweenness can be expressed as: ; (6) Simplifying formula (6), the simplified expression of the current - injection - based betweenness can be obtained: ; (7) When using the current - injection - based method to calculate and , , and A -1 will change with the operating state of the power system, that is, the power of the power source nodes and the power of the load nodes change. If the current - injection - based betweenness is calculated according to formula (7), every time the operating state of the power system changes, new , and A -1, and then substitute it into formula (7) to update the power flow betweenness. The iterative power flow calculation and complex power flow tracing calculation will limit the efficiency of power flow betweenness calculation. To improve the calculation efficiency of power flow betweenness, refer to Figure 2 , the identification method provided by some embodiments of the present application includes: S100: Calculate the branch coefficient of the power grid topology.

[0027] The branch coefficient is the power change amount on any transmission line s-t when the power of the transmission node changes. Calculating the branch coefficient of the power grid topology includes: obtaining the node impedance matrix of the topology structure to calculate the branch coefficient according to the elements in the node impedance matrix. Embodiments of the present application start from the physical meaning of the node impedance matrix of the power system, define the correlation matrix of the transmission node power and the transmission line power, so as to improve the power flow betweenness without using complex power flow tracing calculation, thereby improving the calculation efficiency of the power flow betweenness.

[0028] The value of the element in the node impedance matrix is equal to the voltage value of another transmission node when a unit power is injected at any transmission node. Among them, the node impedance matrix can be obtained through the inverse matrix of the node admittance matrix, which is a prior art and will not be specifically described in the present application. The reactance of the transmission line in the power grid is much greater than the resistance. When the resistance of the transmission line is ignored (this assumption is a commonly recognized assumption in the power system), assuming that any transmission node n is the transmission node on the transmission line s-t, then when a unit power is injected at the transmission node n, the voltage difference between the head and end of any transmission line s-t is , where is the voltage of the head node on the transmission line, is the voltage of the end node on the transmission line, then and The voltage values are equal to the values of the elements in the node impedance matrix.

[0029] The impedance of the transmission line s-t is When, the current flowing through the transmission line s-t is . Assuming that the voltages of all nodes in the power grid system are near the rated value (this assumption is a commonly recognized assumption in the power system), then the current on the transmission line s-t is proportional to the transmission power of the transmission line s-t, that is, when the power of the transmission node n changes by a unit power, the power change amount on the transmission line s-t is . Accordingly, define the first correlation matrix of the transmission node power and the transmission line power, and the element in the d-th row and n-th column of the first correlation matrix is , Defines the power change amount on the d-th transmission line when the power of the transmission node n changes, that is, the branch coefficient. In some embodiments, the branch coefficient can be calculated by the following formula: ; (8) where d is the transmission line, n is the transmission node on any transmission line other than the transmission line d, is the branch coefficient of the transmission line d, is the voltage of the head node on the transmission line d when a unit power is injected at the transmission node n, is the voltage of the end node on the transmission line d when a unit power is injected at the transmission node n, is the impedance of the transmission line d. The first incidence matrix can reflect the influence of the power change of the transmission node in the power grid on the power change of the transmission line. The first incidence matrix is an N×N matrix.

[0030] S200: Calculate the transmission power of the transmission line and the node branch coefficient according to the branch coefficient, so as to calculate the total injection power of the head node according to the node branch coefficient.

[0031] The node branch coefficient is the power change amount of another transmission node when the power of one transmission node changes. When only considering the influence of the power change of the power source node i and the load node j, by superimposing the influence of the power change of the power source node i and the load node j, the transmission power of the transmission line s-t can be obtained as: ; (9) Define and as the power column vector of the power source node and the power column vector of the load node respectively. It can be understood that and are both N-dimensional column vectors. The non-power source node elements in are 0, and the power source node elements are the power of the power source node. The elements of each node in are the power of the load node. By superimposing the influence of the power change of the power source node and the load node on the power change of the transmission line s-t, the transmission power of the transmission line s-t under the influence of the change of the power source node and the load node can be obtained. The transmission power can be expressed as: ; (10) where is the row vector of the branch coefficient, and is also the element of the d-th row in the first incidence matrix , corresponding to the d-th transmission line s-t; is the power column vector of the power source node, is the power column vector of the load node. ​​

[0032] For the convenience of calculation, a second incidence matrix Q is defined based on the first incidence matrix to represent the power change degree of c transmission lines connected to the transmission node k when the power of the transmission node n changes. The element Q(k, n) in the second incidence matrix Q is used to represent the power change degree of the transmission node k when the power of the transmission node n changes, that is, the node branch coefficient. According to Kirchhoff's law, the power of the transmission node k is the sum of the powers of c transmission lines connected to the transmission node k. In some embodiments, the node branch coefficient can be calculated by the following formula: ; (11) where is the node branch coefficient of the transmission node k when the power of the transmission node n changes, C is the set of transmission lines, is the branch coefficient of the c transmission lines connected to the transmission node k, and the matrix composed of the elements is a sub-matrix of the first incidence matrix T, which is a c×1 matrix, and the second incidence matrix Q is a D×N matrix.

[0033] When the power of the power supply and the power of the load are known, when it is the s-th row of the second incidence matrix Q, is the power injected into the first node s of the transmission line. Therefore, the total injected power (the sum of the power injected into the transmission line and the power of the power supply) of the first node s can be expressed as: ; (12) where is the total injected power, is the row vector of the node branch coefficient.

[0034] S300: Obtain the power sequence allocation matrix of the topological structure and the inverse matrix of the power sequence allocation matrix according to the transmission power and the total injected power.

[0035] According to the above formula (10), formula (12), and formula (5), the redefined power sequence allocation matrix A can be obtained. The element in the power sequence allocation matrix A can be expressed as: ; (13) where . According to the elements in the redefined power sequence allocation matrix A in formula (13), the inverse matrix of the power sequence allocation matrix A can be calculated. This calculation process is a process that can be obtained through the prior art and is not specifically described in this application.

[0036] S400: Obtain the first sub-matrix, the second sub-matrix, and the third sub-matrix according to the inverse matrix of the power sequence allocation matrix.

[0037] As can be seen from the above embodiments, the elements in the first sub-matrix are the power distribution coefficients for the total injection power to be distributed from the power source nodes to the transmission lines, the elements in the second sub-matrix are the power distribution coefficients for the total injection power to be distributed from the transmission lines to the load nodes, and the elements in the third sub-matrix are the power distribution coefficients for the total injection power to be distributed from the power source nodes to the load nodes. The first sub-matrix, the second sub-matrix, and the third sub-matrix obtained according to the inverse matrix of the power sequence distribution matrix are respectively , , , where is a matrix of order D×M, is a matrix of order D×N, is a matrix of order M×N. The elements in the first sub-matrix, the second sub-matrix, and the third sub-matrix have been described in the above embodiments and will not be elaborated in this step.

[0038] S500: Calculate the power flow betweenness of the transmission lines based on the transmission power, the total injection power, the first sub-matrix, the second sub-matrix, and the third sub-matrix, so as to identify the vulnerable lines according to the power flow betweenness. The power flow betweenness is used to evaluate the vulnerability of the transmission lines.

[0039] Substitute Equation (10), Equation (12), and Equation (13) into Equation (7), and the improved form of the power flow betweenness can be obtained. The expression of the improved power flow betweenness is:[[]] ; (14)[[]] where is the element in the s-th row and the i-th column of the first sub-matrix, is the element in the s-th row and the j-th column of the second sub-matrix, is the element in the i-th row and the j-th column of the third sub-matrix.

[0040] In the expression of the improved power flow betweenness in Equation (14), only the power of the power source nodes and in the column vectors and the power of the load nodes are variables, and the rest of the parameters are constants. When and change, they can be directly substituted into Equation (14) for calculation. Moreover, the power of the power source nodes and the power of the load nodes do not require power flow calculation. The identification method provided in the embodiments of the present application overcomes the weakness of the existing methods for identifying vulnerable lines based on power flow betweenness and other methods that rely on the results of power grid power flow calculations. When the operating state of the power system changes, only the power of the power source nodes and the power , without the need for iterative power flow calculations, the efficiency of identifying vulnerable lines can be improved.

[0041] To improve the stability and interpretability of the evaluation results, the power flow betweenness can also be normalized. In some embodiments, identifying vulnerable lines based on the power flow betweenness includes: Normalize the power flow betweenness to obtain normalized data; sort the normalized data to take the preset number of transmission lines with the top rankings as vulnerable lines.

[0042] The power flow betweenness can be normalized by the following formula: ; where is the normalized data, is the maximum value of the transmission line vulnerability, is the minimum value of the transmission line vulnerability.

[0043] See Figure 3 , Figure 3 in which, l1 - l6 are transmission lines, p1 - p5 are transmission nodes, and G1 - G4 are power supply nodes. Taking the power grid system in Figure 3 as an example, the identification method of the present application is used to identify vulnerable lines. The parameters of the power grid system are shown in Tables 1 - 2: Table 1: Transmission Line Parameters of 5 - Node Power Grid System

[0044] Table 2: Transmission Node Parameters of 5 - Node Power Grid System

[0045] Table 3: Transmission Line Vulnerabilities of 5 - Node Power Grid System

[0046] The vulnerabilities of the transmission lines identified according to the identification method of the present application are shown in Table 3. According to the vulnerability ranking in Table 3, the transmission line l5 is a vulnerable line.

[0047] Based on the above method, some embodiments of the present application also provide a power grid vulnerable line identification system based on power flow betweenness, which is applied to the method provided in the above embodiments. See Figure 4 , the system includes: The first calculation module: used to calculate the branch - branch coefficient of the power grid topology.

[0048] The topological structure includes a power source node, a load node, a transmission node, and at least one transmission line. The power source node is connected to the load node through the transmission line. The transmission node is a node on the transmission line. The transmission node includes a head node and a tail node. The branch coefficient of a branch is the amount of power change on any transmission line when the power of the transmission node changes.

[0049] The second calculation module: is used to calculate the transmission power of the transmission line and the branch coefficient of the node according to the branch coefficient of the branch, so as to calculate the total injection power of the head node according to the branch coefficient of the node.

[0050] Wherein, the branch coefficient of the node is the amount of power change of another transmission node when the power of one of the transmission nodes changes.

[0051] The third calculation module: is used to obtain the power sequence distribution matrix of the topological structure and the inverse matrix of the power sequence distribution matrix according to the transmission power and the total injection power.

[0052] Wherein, the element in the power sequence distribution matrix is the distribution coefficient of the total injection power on the transmission line.

[0053] The fourth calculation module: is used to obtain the first sub-matrix, the second sub-matrix, and the third sub-matrix according to the inverse matrix of the power sequence distribution matrix.

[0054] Wherein, the element in the first sub-matrix is the power distribution coefficient for the total injection power to be distributed from the power source node to the transmission line. The element in the second sub-matrix is the power distribution coefficient for the total injection power to be distributed from the transmission line to the load node. The element in the third sub-matrix is the power distribution coefficient for the total injection power to be distributed from the power source node to the load node.

[0055] The identification calculation module: is used to calculate the power flow betweenness of the transmission line according to the transmission power, the total injection power, the first sub-matrix, the second sub-matrix, and the third sub-matrix, so as to identify the vulnerable line according to the power flow betweenness. The power flow betweenness is used to evaluate the vulnerability of the transmission line.

[0056] As can be seen from the above technical solutions, the embodiments of the present application provide a method and system for identifying vulnerable lines in a power grid based on power flow betweenness. The method includes: calculating the branch coefficient of each branch of the power grid topology; calculating the transmission power of the transmission line and the node branch coefficient according to the branch coefficient, so as to calculate the total injection power of the head node according to the node branch coefficient; obtaining the power sequence distribution matrix of the topology and the inverse matrix of the power sequence distribution matrix according to the transmission power and the total injection power; obtaining the first sub-matrix, the second sub-matrix and the third sub-matrix according to the inverse matrix of the power sequence distribution matrix; calculating the power flow betweenness of the transmission line according to the transmission power, the total injection power, the first sub-matrix, the second sub-matrix and the third sub-matrix, so as to identify the vulnerable lines according to the power flow betweenness. The method does not depend on the results of power flow calculation of the power grid. When the operating state of the power system changes, only the power of the power source node and the power of the load node need to be updated, and there is no need to perform iterative power flow calculations, which can improve the efficiency of identifying vulnerable lines.

[0057] For the similarities between the embodiments provided in the present application, reference can be made to each other. The specific embodiments provided above are only several examples under the general concept of the present application, and do not constitute a limitation on the protection scope of the present application. For those skilled in the art, any other implementation manners extended based on the solution of the present application without creative efforts belong to the protection scope of the present application.

Claims

1. A method for identifying vulnerable lines in a power grid based on power flow betweenness, characterized in that: include: Calculate the branch coefficient of the power grid topology; The topological structure includes a power node, a load node, a transmission node and at least one transmission line, the power node is connected to the load node through the transmission line, the transmission node is a node on the transmission line, the transmission node includes a head node and a terminal node, and the branch coefficient is the power change amount on any of the transmission lines when the power of the transmission node changes; Calculating the transmission power of the transmission line and the node branching coefficient according to the branch branching coefficient, so as to calculate the total injection power of the head-end node according to the node branching coefficient; The node branch coefficient is the power change amount of another transmission node when the power of one of the transmission nodes changes; Acquire a power order allocation matrix of the topology structure and an inverse matrix of the power order allocation matrix according to the transmission power and the total injection power, wherein the elements in the power order allocation matrix are allocation coefficients of the total injection power on the transmission line; The first submatrix, the second submatrix and the third submatrix are obtained according to the inverse matrix of the power sequence allocation matrix; the elements in the first submatrix are the power allocation coefficients of the total injected power allocated from the power source node to the transmission line, the elements in the second submatrix are the power allocation coefficients of the total injected power allocated from the transmission line to the load node, and the elements in the third submatrix are the power allocation coefficients of the total injected power allocated from the power source node to the load node; The power flow betweenness of the transmission line is calculated according to the transmission power, the total injection power, the first sub-matrix, the second sub-matrix and the third sub-matrix to identify the vulnerable line according to the power flow betweenness, and the power flow betweenness is used to evaluate the vulnerability of the transmission line.

2. The method for identifying vulnerable lines in a power grid based on power flow betweenness according to claim 1, characterized in that: The calculation of the branch coefficient of the power grid topology structure includes: A node impedance matrix of the topological structure is obtained to calculate the branch branching coefficient according to elements in the node impedance matrix; the value of the element in the node impedance matrix is ​​equal to the voltage value of another transmission node when unit power is injected into any transmission node.

3. The method for identifying vulnerable lines in a power grid based on power flow betweenness according to claim 2 is characterized in that: The branch coefficient is calculated by the following formula: ； Where d is the transmission line, n is the transmission node on any transmission line except transmission line d, is the branch coefficient of the transmission line d, is the voltage of the first-end node on the transmission line d when unit power is injected into the transmission node n, is the voltage at the end node on the transmission line d when unit power is injected into the transmission node n, and The voltage values ​​are equal to the values ​​of the elements in the node impedance matrix. is the impedance of the transmission line d.

4. The method for identifying vulnerable lines in a power grid based on power flow betweenness according to claim 3 is characterized in that: The transmission power is calculated by the following formula: ； in, is the transmission power, is the row vector of branch coefficients, is the power column vector of the power node, is the load node power column vector; The node branching coefficient is calculated by the following formula: ； in, is the node branching coefficient of transmission node k when the power of transmission node n changes, C is the set of transmission lines, is the branch coefficient of the c transmission lines connected to the transmission node k; The total injected power is calculated by the following formula: ； in, is the total injected power, is the row vector of node branching coefficients.

5. The method for identifying vulnerable lines in a power grid based on power flow betweenness according to claim 4 is characterized in that: The elements in the power order allocation matrix are calculated by the following formula: ； in, is the element in the power order allocation matrix, s is the head node of the transmission line, t is the end node of the transmission line, .

6. The method for identifying vulnerable lines in a power grid based on power flow betweenness according to claim 1, characterized in that: The first sub-matrix, the second sub-matrix and the third sub-matrix are sub-matrices of the inverse matrix of the power order allocation matrix.

7. The method for identifying vulnerable lines in a power grid based on power flow betweenness according to claim 4, characterized in that: The power flow betweenness of the transmission line is calculated by the following formula: ； in, is the power flow betweenness, G is the set of power nodes, L is the set of load nodes; i is the power node, j is the load node; is the power capacity of the power node, is the load capacity of the load node, is the minimum value of power supply capacity and load capacity; is the element in the sth row and ith column of the first submatrix, is the element in the sth row and jth column of the second submatrix, is the element in the i-th row and j-th column of the third submatrix.

8. The method for identifying vulnerable lines in a power grid based on power flow betweenness according to claim 1, characterized in that: The identifying of the vulnerable line according to the power flow betweenness includes: Normalizing the power flow betweenness to obtain normalized data; The normalized data is sorted so as to select a preset number of transmission lines that are ranked first as vulnerable lines.

9. The method for identifying vulnerable lines in a power grid based on power flow betweenness according to claim 8, characterized in that: The power flow betweenness is normalized by the following formula: ； in, To normalize the data, is the maximum value of the transmission line vulnerability, is the minimum value of the transmission line vulnerability.

10. A power grid vulnerable line identification system based on power flow betweenness, characterized in that: The method for identifying vulnerable lines in a power grid based on power flow betweenness as described in any one of claims 1 to 9, the system comprising: The first calculation module is used to calculate the branch branching coefficient of the power grid topology structure; the topology structure includes a power node, a load node, a transmission node and at least one transmission line, the power node is connected to the load node through the transmission line, the transmission node is a node on the transmission line, the transmission node includes a head node and a terminal node, and the branch branching coefficient is the power change amount on any of the transmission lines when the power of the transmission node changes; The second calculation module is used to calculate the transmission power and node branching coefficient of the transmission line according to the branch branching coefficient, so as to calculate the total injection power of the head-end node according to the node branching coefficient; the node branching coefficient is the power change amount of another transmission node when the power of one of the transmission nodes changes; A third calculation module: used for obtaining a power order allocation matrix of the topology structure and an inverse matrix of the power order allocation matrix according to the transmission power and the total injection power, wherein the elements in the power order allocation matrix are allocation coefficients of the total injection power on the transmission line; The fourth calculation module is used to obtain the first sub-matrix, the second sub-matrix and the third sub-matrix according to the inverse matrix of the power sequence allocation matrix; the elements in the first sub-matrix are the power allocation coefficients of the total injected power allocated from the power supply node to the transmission line, the elements in the second sub-matrix are the power allocation coefficients of the total injected power allocated from the transmission line to the load node, and the elements in the third sub-matrix are the power allocation coefficients of the total injected power allocated from the power supply node to the load node; An identification and calculation module is used to calculate the power flow betweenness of the transmission line according to the transmission power, the total injection power, the first sub-matrix, the second sub-matrix and the third sub-matrix, so as to identify the vulnerable line according to the power flow betweenness, and the power flow betweenness is used to evaluate the vulnerability of the transmission line.

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