A method and system for identifying key branches of a power grid based on overload cascading failures

Abstract

The present invention belongs to the field of power grid security analysis and provides a method and system for identifying key branches of a power grid based on overload-type cascading failures. The method comprises establishing an improved DC current taking into account voltage and reactive power, and quickly estimating the voltage and reactive power of the system while ensuring the convergence of the regional current; establishing an overload-type cascading failure evolution model taking into account the effects of the system automatic control device and the system's rough correction control measures; based on the overload-type cascading failure evolution model, performing a large-scale cascading failure simulation on the system to obtain the accident chain, load loss rate and branch loss rate corresponding to each cascading failure; calculating the importance index of each branch based on the probability of each branch appearing in the accident chain and the loss caused to the system, thereby screening out the key branches; the method provides an importance evaluation index of the current-carrying branch of the power grid, and effectively identifies the key branches of the power grid by calculating the importance index of each current-carrying branch through large-scale cascading failure simulation.

Description

Technical Field

[0001] The present invention belongs to the technical field of power grid security analysis, and in particular relates to a method and system for identifying key branches of a power grid based on overload-type cascading failures. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Many major power outages that have occurred at home and abroad have shown that the failure of key branches of the power grid has played an important role in promoting the development of chain failures in major power outages, seriously threatening the safe and stable operation of the power grid.

[0004] When a current-carrying branch in a power grid fails, it disrupts the system's original topology and may even cause the grid to disconnect. It also disrupts the system's power balance and causes large-scale power flow shifts. In highly interconnected power grids, large-scale power flow shifts can easily cause adjacent equipment to exceed their current limits, leading to the shutdown of their relay protection devices and subsequent failures. Cascading power failures can significantly damage the system's functionality and structure, ultimately causing a major power outage. Furthermore, during power flow shifts, the system's automatic safety devices adjust promptly to maintain power balance and voltage stability. Current-carrying equipment typically tolerates a certain period of sustained overload, providing an opportunity for corrective control in emergency operation. Rapid adjustments and control measures can quickly eliminate the overload, preventing subsequent branch disconnection and cascading failures. This demonstrates that cascading power system failures are a continuous, complex, and dynamic process.

[0005] The existing overload cascading failure models and key branch identification methods for power grids have certain drawbacks:

[0006] (1) Although the power system cascading failure simulation model based on AC power flow or AC / DC power flow can more comprehensively reflect the changes in the system's operating status, the treatment of power flow non-convergence is too subjective, and the calculation is complex and inefficient.

[0007] (2) The critical branch identification method based on self-organized criticality theory often ignores the role of the system's automatic control devices and the system's corrective control measures, and is unable to accurately assess the impact of cascading failures on the system, which in turn leads to deviations in the screening of critical branches. Summary of the Invention

[0008] In order to solve the above problems, the present invention proposes a method and system for identifying critical branches of a power grid based on overload-type cascading failures. The present invention considers the impact of overload-type cascading failures on the safety of the power grid, establishes an overload-type cascading failure evolution model based on a DC power flow algorithm taking into account voltage and reactive power, obtains an importance evaluation index for current-carrying branches, and identifies critical current-carrying branches.

[0009] According to some embodiments, a first solution of the present invention provides a method for identifying critical branches of a power grid based on overload-type cascading failures, which adopts the following technical solutions:

[0010] A method for identifying key branches of a power grid based on overload cascading failures, comprising:

[0011] Establish an improved DC power flow that takes voltage and reactive power into account, and quickly estimate the system voltage and reactive power while ensuring the convergence of regional power flows;

[0012] Based on the estimated system voltage and reactive power, taking into account the role of the system automatic control device and the system's corrective control measures, an overload cascading fault evolution model is established;

[0013] Based on the overload cascading failure evolution model, a large-scale cascading failure simulation is carried out on the system to obtain the accident chain, load loss rate and branch loss rate corresponding to each cascading failure. According to the probability of each branch appearing in the accident chain and the loss caused to the system, the importance index of each branch is calculated to screen out the critical branches.

[0014] Furthermore, the improved DC power flow taking into account voltage and reactive power is established to quickly estimate the voltage and reactive power of the system while ensuring the convergence of the regional power flow;

[0015] The voltage phase angle of each node in the system is obtained based on the traditional DC power flow;

[0016] According to the vector calculation method, the node injection power equation is used to derive the linear expression of the node voltage amplitude, and then the estimated value of the node voltage is obtained;

[0017] The system reactive power distribution is estimated based on the voltage phase angle and amplitude.

[0018] Furthermore, the overload cascading failure evolution model is established based on the estimated system voltage and reactive power, taking into account the effects of the system automatic control device and the system's corrective control measures, including:

[0019] (1) For a normally operating system network, set the current-carrying branch to stop operating due to a fault to simulate the source-type fault of the system;

[0020] (2) Perform network topology analysis and update information such as power supply, grid structure, and load of each subnet;

[0021] (3) Calculate each regional subnet one by one. For subnets that have both loads and power sources, go to (4). For subnets that do not contain both loads and power sources, go to (6).

[0022] (4) Power balancing adjustment for subnets with both loads and power sources:

[0023] (5) For subnet areas where no cascading failures occur, in order to ensure the safe and stable operation of the system, the correction control strategy given with the goal of minimizing power outage losses is adjusted:

[0024] (6) Store subnet power supply, grid structure and load information;

[0025] (7) Determine whether all subnets have been calculated. If not, go to (3); otherwise, go to (8).

[0026] (8) Output the power supply, grid structure and load information of each subnet after the cascading failure of the system, as well as the cascading failure accident chain. The accident chain is the chain of failed branches during the cascading failure process.

[0027] Furthermore, with respect to (4), the power balancing adjustment for the subnet having both load and power supply is specifically as follows:

[0028] (4.1) Perform power balance adjustment, simulate the system power balance device, and adjust the system power. For node-type subnets, after power balance adjustment, there is no need to perform power flow calculation and correction control, so go to (6); for regional subnets, go to (4.2).

[0029] (4.2) Perform improved DC power flow calculation on the subnet to obtain the system node voltage amplitude and branch power;

[0030] (4.3) Determine whether the node voltage is too low. For nodes with lower voltage, simulate the system voltage stabilization device and reduce the load of the low-voltage node by a certain proportion, then go to (4.1), otherwise go to (4.4).

[0031] (4.4) Determine whether the branch exceeds the stability limit. For the transmission branch that exceeds its stability limit, simulate the action of the system relay protection device, cut off the overloaded branch, and then go to (2); if there is no overloaded branch, go to (5).

[0032] Furthermore, before performing large-scale cascading failure simulation on the system based on the overload-type cascading failure evolution model, a current-carrying branch importance evaluation index is established, and the current-carrying branch importance evaluation index includes an index that characterizes the importance of the branch to the system function and an index that characterizes the importance of the branch to the system structure.

[0033] Furthermore, the index characterizing the importance of the branch to the system function is defined as follows:

[0034]

[0035] Where m1 is the set of fault chains obtained by large-scale cascading failure simulation, m2 is the set of fault chains including branch l, and n m1 and n m2 are the number of accident chains corresponding to sets m1 and m2 respectively, and PLR∈m2 is the load loss rate corresponding to the accident chain in set m2;

[0036] The index characterizing the importance of the branch to the system structure is defined as follows:

[0037]

[0038] Where LLR∈m2 is the branch loss rate corresponding to the fault chain in set m2.

[0039] Furthermore, the load loss rate is the ratio of the load active power removal amount to the original total active power of the system after the cascading failure;

[0040] The branch loss rate is the ratio of the number of failed branches during the development of cascading failures to the total number of original branches in the system.

[0041] According to some embodiments, a second solution of the present invention provides a critical branch identification system for a power grid based on overload cascading failures, which adopts the following technical solutions:

[0042] A power grid critical branch identification system based on overload cascading failures, comprising:

[0043] The voltage and reactive power estimation module is configured to establish an improved DC power flow that takes voltage and reactive power into account, and to quickly estimate the voltage and reactive power of the system while ensuring the convergence of the regional power flow;

[0044] an overload type cascading failure evolution model building module configured to build an overload type cascading failure evolution model based on estimated system voltage and reactive power, taking into account the effects of system automatic control devices and system corrective control measures;

[0045] The critical branch screening module of the power grid is configured to perform large-scale cascading failure simulations on the system based on the overload-type cascading failure evolution model, obtain the accident chain, load loss rate and branch loss rate corresponding to each cascading failure, and calculate the importance index of each branch based on the probability of each branch appearing in the accident chain and the loss caused to the system, thereby screening out critical branches.

[0046] According to some embodiments, a third aspect of the present invention provides a computer-readable storage medium.

[0047] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the method for identifying key branches of a power grid based on overload-type cascading failures as described in the first aspect above.

[0048] According to some embodiments, a fourth aspect of the present invention provides a computer device.

[0049] A computer device comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the steps of the method for identifying critical branches of a power grid based on overload-type cascading failures as described in the first aspect above are implemented.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] The present invention constructs a dynamic evolution model of overload-type cascading failures with the help of an improved DC power flow algorithm that takes voltage and reactive power into account. The model takes into account the system power balance and the regulatory role of the voltage stabilization device during the cascading failure process, as well as the system's corrective control measures. It can more accurately simulate the dynamic evolution process of the system cascading failure after branch failure and calculate the impact of the cascading failure on the system function and structure. On this basis, an importance evaluation index for the current-carrying branches of the power grid is given. The importance index of each current-carrying branch is calculated through large-scale cascading failure simulation, thereby realizing the effective identification of key branches of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0053] Figure 1 This is a flow chart of a method for identifying key branches of a power grid based on overload-type cascading failures according to an embodiment of the present invention;

[0054] Figure 2 is a flow chart of the dynamic evolution process of overload cascading failures according to an embodiment of the present invention;

[0055] Figure 3 Schematic diagram of the power balancing process during a fault process according to an embodiment of the present invention. DETAILED DESCRIPTION

[0056] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0057] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0058] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0059] In the absence of conflict, the embodiments of the present invention and the features thereof may be combined with each other.

[0060] Example 1

[0061] like Figure 1 As shown, this embodiment provides a method for identifying key branches of a power grid based on overload-type cascading failures, the method comprising the following steps:

[0062] The voltage and reactive power estimation module is configured to establish an improved DC power flow that takes voltage and reactive power into account, and to quickly estimate the voltage and reactive power of the system while ensuring the convergence of the regional power flow;

[0063] an overload type cascading failure evolution model building module configured to build an overload type cascading failure evolution model based on estimated system voltage and reactive power, taking into account the effects of system automatic control devices and system corrective control measures;

[0064] The critical branch screening module of the power grid is configured to perform large-scale cascading failure simulations on the system based on the overload-type cascading failure evolution model, obtain the accident chain, load loss rate and branch loss rate corresponding to each cascading failure, and calculate the importance index of each branch based on the probability of each branch appearing in the accident chain and the loss caused to the system, thereby screening out critical branches.

[0065] Specifically, if Figure 1 As shown, the specific process of this method includes:

[0066] 1. Establish an improved DC power flow that takes voltage and reactive power into account, enabling rapid estimation of system voltage and reactive power:

[0067] The improved DC power flow that takes voltage and reactive power into account first obtains the voltage phase angle of each node in the system based on the traditional DC power flow. Then, the node injection power equation is used to derive the linear expression of the node voltage amplitude, and then the estimated value of the node voltage is obtained. Finally, the system reactive power distribution is estimated based on the voltage phase angle and amplitude. The specific calculation process is as follows:

[0068] Cascading failures in power systems usually occur in high-voltage ring networks. The network's smaller impedance ratio ensures the accuracy of DC power flow calculations. The traditional DC power flow equation is expressed as follows:

[0069] P=Bθ (1)

[0070] Where: P is the column vector of active injected power at the node, B is the node admittance matrix ignoring branch resistance, and θ is the column vector of the system node voltage phase angle.

[0071] For PQ node i, its complex power can be expressed as:

[0072]

[0073] Where: is the injected complex power of node i, is the voltage vector of node i, is the conjugate of the current vector injected into node i. Based on the vector calculation rule and the node injection current equation, the following derivation can be made:

[0074]

[0075] Where: n b is the number of nodes in the system, Y ik is the node admittance matrix element. Depending on whether the node voltage amplitude is known, the nodes can be divided into PQ nodes and non-PQ nodes, where non-PQ nodes include PV nodes and balance nodes, and the above formula can be expressed as:

[0076]

[0077] Where: Ω PQ and Ω else and represent the node sets consisting of PQ nodes and non-PQ nodes respectively. Further transformation of the above formula yields:

[0078]

[0079] set up:

[0080]

[0081] It can be expressed as:

[0082]

[0083] Where: Y PQ is the node admittance matrix formed by PQ nodes, is the column vector of the voltage vector of the PQ node, U PQ is the column vector of the voltage amplitude of the PQ node, c=(c i ), d=(d i ), ⊙ is the vector dot division operator, that is, vector c and vector U PQ Divide the corresponding elements.

[0084] For a normally operating network, assuming that the voltage amplitude of the PQ node is 1 p.u., then:

[0085]

[0086] U available PQ The approximate solution is:

[0087]

[0088] Therefore, the improved DC power flow taking into account voltage and reactive power is obtained through the above formula (9), and the estimated value of the node voltage is obtained; finally, the system reactive power distribution is estimated based on the voltage phase angle and amplitude.

[0089] 2. Establish an overload cascading failure evolution model, such as Figure 2 As shown, specifically including:

[0090] (1) For a normally operating system network, set the current-carrying branch to stop operating due to a fault to simulate the source-type fault of the system.

[0091] (2) Perform network topology analysis and update information such as power supply, grid structure and load of each subnet.

[0092] (3) Calculate each regional subnet one by one. For subnets that have both loads and power sources, proceed to (4). For subnets that do not contain both loads and power sources, proceed to (6).

[0093] (4) Power balancing and adjustment for subnets with both loads and power sources, including:

[0094] (4.1) Perform power balance adjustment, simulate the system power balance device, and adjust the system power. It should be noted that for node-type subnetworks (networks containing only one node bus), after power balance adjustment, power flow calculation and correction control are not required. Go to (6); for regional subnetworks (networks containing multiple node buses), go to (4.2).

[0095] (4.2) According to 1, the improved DC power flow calculation is performed on the subnet to obtain the system node voltage amplitude and branch power.

[0096] (4.3) Determine whether the node voltage is too low. For nodes with lower voltage, simulate the system voltage stabilization device and reduce the load of the low-voltage node by a certain proportion, then go to (4.1), otherwise go to (4.4).

[0097] (4.4) Determine whether the branch exceeds the stability limit. For the transmission branch that exceeds its stability limit, simulate the action of the system relay protection device, cut off the overloaded branch, and then go to (2); if there is no overloaded branch, go to (5).

[0098] (5) For subnet areas where no cascading failures occur, in order to ensure the safe and stable operation of the system, the correction control strategy given with the goal of minimizing power outage losses is adjusted.

[0099] (6) Store information such as subnet power supply, grid structure and load.

[0100] (7) Determine whether all subnets have been calculated. If not, go to (3); otherwise, go to (8).

[0101] (8) Output the power supply, grid structure and load information of each subnet after the cascading failure of the system, as well as the cascading failure accident chain. The accident chain is the chain of failed branches during the cascading failure process.

[0102] The evolution of power balance during the fault process, e.g. Figure 3 As shown, specifically including:

[0103] When the power generation of the regional subgrid is greater than the load, each generator reduces its output according to its participation factor to maintain the power balance of the system; when the power generation is less than the load but the sum of the current power generation and the unit's hot standby is greater than the load, the generator set increases its output according to the "hot standby margin". This adjustment strategy can ensure that the generator set output does not exceed the upper limit during the adjustment process; if the sum of the current power generation and the unit's hot standby is still less than the load, the generator is first set to put all the hot standby into use to meet the load demand as much as possible, and then the load is proportionally cut to maintain the power balance of the system.

[0104] Specifically, the correction control evolution process during the fault process

[0105] By combining the power outage loss with the optimization problem of grid correction control, a correction control model is proposed to minimize the power outage loss within the system security constraints. Its objective function is:

[0106]

[0107] Where n b represents the number of nodes in the system, α i 、F iThey represent the power outage ratio and power outage loss function of node i respectively. i It can be expressed as α i The quadratic function F i =(k1α 2i +k2α i )P Li , where k1 and k2 are both constants, and the function should be an increasing concave function crossing zero; P Li is the active load on node i.

[0108] Constraints include equality constraints, i.e., the balance equations of active and reactive power; and inequality constraints, i.e., upper and lower limits on the active and reactive output of generators, upper and lower limits on the node load shedding ratio, upper and lower limits on the node voltage, and upper and lower limits on the apparent power of branches:

[0109]

[0110] Where, P Gi and Q Gi is the active and reactive output power of the generator at node i, P Li and Q Li is the active and reactive power of the load on node i. The load on the node adopts a constant power model, and the load power factor is kept unchanged during the shedding process.

[0111]

[0112]

[0113]

[0114]

[0115] Where: and are the upper and lower limits of the active output of the generator at node i, and are the upper and lower limits of reactive power output of the generator at node i, and are the upper and lower limits of the node load shedding ratio, usually and They are the upper and lower limits of the voltage amplitude on node i, usually set P l and Q l are the active power and reactive power transmitted by branch l, is the upper limit of the transmission capacity of branch l, n bra Indicates the number of branches in the system.

[0116] 3. Identification of key current-carrying branches

[0117] In order to better evaluate the impact of cascading failures caused by current-carrying branch failures on the system, two indicators, load loss rate and branch loss rate, are defined to quantify the losses caused by cascading failures to the system from the aspects of system function and structure, respectively.

[0118] The load loss rate is the ratio of the load active power removal after a cascading fault to the original total active power of the system:

[0119]

[0120] Where: It is the active power of the load cut off at each node during the cascading failure process.

[0121] The branch loss rate is the ratio of the number of failed branches to the total number of original branches in the system during the development of cascading failures:

[0122]

[0123] Where: It is the number of branches that fail during a cascading fault, including branches that fail as the source, branches that are cut off by relay protection devices during a cascading fault, and branches that fail indirectly due to busbar faults.

[0124] Based on this, the indicator that characterizes the importance of branch l to the system function is:

[0125]

[0126] Where m1 is the set of fault chains obtained by large-scale cascading failure simulation, m2 is the set of fault chains including branch l, and n m1 and n m2 are the number of accident chains corresponding to sets m1 and m2 respectively, and PLR∈m2 is the load loss rate corresponding to the accident chain in set m2.

[0127] The index that characterizes the importance of branch l to the system structure is:

[0128]

[0129] Where LLR∈m2 is the branch loss rate corresponding to the fault chain in set m2.

[0130] According to Section 2 of the technical solution, a large-scale cascading failure simulation is conducted on the system to obtain the accident chain, load loss rate, and branch loss rate corresponding to each cascading failure. Based on the probability of each branch appearing in the accident chain and the loss caused to the system, the importance index of each branch is calculated to screen out the key branches.

[0131] Example 2

[0132] This embodiment provides a power grid critical branch identification system based on overload cascading failures, including:

[0133] The voltage and reactive power estimation module is configured to establish an improved DC power flow that takes voltage and reactive power into account, and to quickly estimate the voltage and reactive power of the system while ensuring the convergence of the regional power flow;

[0134] an overload type cascading failure evolution model building module configured to build an overload type cascading failure evolution model based on estimated system voltage and reactive power, taking into account the effects of system automatic control devices and system corrective control measures;

[0135] The critical branch screening module of the power grid is configured to perform large-scale cascading failure simulations on the system based on the overload-type cascading failure evolution model, obtain the accident chain, load loss rate and branch loss rate corresponding to each cascading failure, and calculate the importance index of each branch based on the probability of each branch appearing in the accident chain and the loss caused to the system, thereby screening out critical branches.

[0136] The examples and application scenarios implemented by the above modules and corresponding steps are the same, but are not limited to the contents disclosed in the above embodiment 1. It should be noted that the above modules as part of the system can be executed in a computer system such as a set of computer executable instructions.

[0137] The descriptions of the various embodiments in the above embodiments have different focuses. For parts not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0138] The proposed system can be implemented in other ways. For example, the system embodiment described above is merely illustrative. For example, the above module division is only a logical function division. In actual implementation, other division methods may be used. For example, multiple modules can be combined or integrated into another system, or some features can be ignored or not implemented.

[0139] Example 3

[0140] This embodiment provides a computer-readable storage medium having a computer program stored thereon. When the program is executed by a processor, the steps of the method for identifying critical branches of a power grid based on overload cascading failures as described in the first embodiment above are implemented.

[0141] Example 4

[0142] This embodiment provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the steps of the method for identifying critical branches of a power grid based on overload-type cascading failures as described in the first embodiment above are implemented.

[0143] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of hardware embodiments, software embodiments, or embodiments combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage and optical storage, etc.) containing computer-usable program code.

[0144] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0145] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0146] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0147] Those skilled in the art will appreciate that all or part of the processes in the above-described method embodiments can be implemented by instructing related hardware through a computer program. The program can be stored in a computer-readable storage medium, and when executed, the program can include the processes in the above-described method embodiments. The storage medium can be a magnetic disk, an optical disk, a read-only memory (ROM), or a random access memory (RAM).

[0148] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. A method for identifying key branches of a power grid based on overload cascading failures, characterized in that: include: Establish an improved DC power flow that takes voltage and reactive power into account, and quickly estimate the system voltage and reactive power while ensuring the convergence of regional power flows; Based on the estimated system voltage and reactive power, taking into account the role of the system automatic control device and the system's corrective control measures, an overload cascading fault evolution model is established, including: (1) For a normally operating system network, set the current-carrying branch to stop operating due to a fault to simulate the source-type fault of the system; (2) Perform network topology analysis and update the power supply, grid structure, and load of each subnet; (3) Calculate each regional subnet one by one. For subnets that have both loads and power sources, go to (4). For subnets that do not contain both loads and power sources, go to (6). (4) Power balancing adjustment for subnets with both loads and power sources: (5) For subnet areas where no cascading failures occur, in order to ensure the safe and stable operation of the system, the correction control strategy given with the goal of minimizing power outage losses is adjusted: (6) Store subnet power supply, grid structure and load information; (7) Determine whether all subnets have been calculated. If not, go to (3); otherwise, go to (8); (8) Output the power supply, grid structure, and load information of each subnet after the cascading failure of the system, as well as the cascading failure accident chain. The accident chain is the chain of failed branches during the cascading failure process; Based on the overload cascading failure evolution model, a large-scale cascading failure simulation is carried out on the system to obtain the accident chain, load loss rate and branch loss rate corresponding to each cascading failure. According to the probability of each branch appearing in the accident chain and the loss caused to the system, the importance index of each branch is calculated to screen out the critical branches.

2. A method for identifying key branches of a power grid based on overload cascading failures according to claim 1, characterized in that: The improved DC power flow taking into account voltage and reactive power is established to quickly estimate the voltage and reactive power of the system while ensuring the convergence of regional power flow: The voltage phase angle of each node in the system is obtained based on the traditional DC power flow; According to the vector calculation method, the node injection power equation is used to derive the linear expression of the node voltage amplitude, and then the estimated value of the node voltage is obtained; The system reactive power distribution is estimated based on the voltage phase angle and amplitude.

3. A method for identifying key branches of a power grid based on overload cascading failures according to claim 1, characterized in that: Regarding (4), the power balancing adjustment for the subnet with both load and power supply is specifically as follows: (4.1) Perform power balance adjustment, simulate the system power balance device, and adjust the system power. For node-type subnets, after power balance adjustment, there is no need to perform power flow calculation and correction control, so go to (6); for regional subnets, go to (4.2). (4.2) Perform improved DC power flow calculation on the subnet to obtain the system node voltage amplitude and branch power; (4.3) Determine whether the node voltage is too low. For low-voltage nodes, simulate the system voltage stabilization device and reduce the load of the low-voltage node by a certain proportion, then go to (4.1), otherwise go to (4.4). (4.4) Determine whether the branch exceeds the stability limit. For the transmission branch that exceeds its stability limit, simulate the action of the system relay protection device, cut off the overloaded branch, and then go to (2); if there is no overloaded branch, go to (5).

4. A method for identifying key branches of a power grid based on overload cascading failures according to claim 1, characterized in that: Before performing large-scale cascading failure simulation on the system based on the overload-type cascading failure evolution model, a current-carrying branch importance evaluation index is established. The current-carrying branch importance evaluation index includes an index characterizing the importance of the branch to the system function and an index characterizing the importance of the branch to the system structure.

5. A method for identifying key branches of a power grid based on overload cascading failures according to claim 4, characterized in that: The index characterizing the importance of the branch to the system function is defined as follows: Where m1 is the set of fault chains obtained by large-scale cascading failure simulation, m2 is the set of fault chains including branch l, and n m1 and n m2 are the number of accident chains corresponding to sets m1 and m2 respectively, and PLR∈m2 is the load loss rate corresponding to the accident chain in set m2; The index characterizing the importance of the branch to the system structure is defined as follows: Where LLR∈m2 is the branch loss rate corresponding to the fault chain in set m2.

6. A method for identifying key branches of a power grid based on overload cascading failures according to claim 5, characterized in that: The load loss rate is the ratio of the load active power removal amount to the original total active power of the system after the cascading failure; The branch loss rate is the ratio of the number of failed branches during the development of cascading failures to the total number of original branches in the system.

7. A power grid critical branch identification system based on overload cascading failures, characterized by: include: The voltage and reactive power estimation module is configured to establish an improved DC power flow that takes voltage and reactive power into account, and to quickly estimate the voltage and reactive power of the system while ensuring the convergence of the regional power flow; The overload cascading failure evolution model building module is configured to build an overload cascading failure evolution model based on the estimated system voltage and reactive power, taking into account the effects of the system automatic control devices and the system's corrective control measures, including: (1) For a normally operating system network, set the current-carrying branch to stop operating due to a fault to simulate the source-type fault of the system; (2) Perform network topology analysis and update the power supply, grid structure, and load of each subnet; (3) Calculate each regional subnet one by one. For subnets that have both loads and power sources, go to (4). For subnets that do not contain both loads and power sources, go to (6). (4) Power balancing adjustment for subnets with both loads and power sources: (5) For subnet areas where no cascading failures occur, in order to ensure the safe and stable operation of the system, the correction control strategy given with the goal of minimizing power outage losses is adjusted: (6) Store subnet power supply, grid structure and load information; (7) Determine whether all subnets have been calculated. If not, go to (3); otherwise, go to (8); (8) Output the power supply, grid structure, and load information of each subnet after the cascading failure of the system, as well as the cascading failure accident chain. The accident chain is the chain of failed branches during the cascading failure process; The critical branch screening module of the power grid is configured to perform large-scale cascading failure simulations on the system based on the overload-type cascading failure evolution model, obtain the accident chain, load loss rate and branch loss rate corresponding to each cascading failure, and calculate the importance index of each branch based on the probability of each branch appearing in the accident chain and the loss caused to the system, thereby screening out critical branches.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method for identifying key branches of a power grid based on overload cascading failures according to any one of claims 1 to 6 are implemented.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the steps of the method for identifying key branches of a power grid based on overload cascading failures according to any one of claims 1 to 6 are implemented.

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