Method and system for identifying vulnerable part of power system under extreme event

Abstract

The invention provides a method and a system for identifying a vulnerable part of a power system under an extreme event, and the method comprises the steps: determining an equivalent degree index according to the degree of a node in a power grid and the influence on the network connection level; determining a connectivity influence index according to the influence on the network connectivity after the channel is lost; identifying nodes with structural vulnerability and power transmission channels according to the equivalent degrees and connectivity influence indexes; determining a node equivalent power flow betweenness index according to the load carried by the node and the load for supplying power to the interconnected node; determining an equivalent power flow betweenness index of the power transmission channel according to the transmission power of the channel and the proportion of power vacancy caused by loss in the total load capacity of the receiving end system; identifying functional vulnerability nodes and power transmission channels according to the equivalent power flow betweenness indexes of the nodes and the power transmission channels; and determining the nodes and the power transmission channels which present the structure and function vulnerabilities at the same time as comprehensive vulnerable nodes or channels, thereby realizing quantitative identification of the vulnerability degrees of the power grid nodes and the power transmission channels under the extreme event.

Description

Technical Field

[0001] The present invention relates to the field of power system vulnerability assessment and analysis, and in particular to a method and system for identifying vulnerable parts of a power system under extreme events. Background Art

[0002] The vulnerability of the power system can be considered as the characteristics of the overall structure or function of the power system itself being affected when the components or systems are disturbed. From the perspective of the operation of the power system, the topological structure of the power grid provides a basic carrier for the realization of the system's functions, but if the participation of the system's operating state is not considered, the structural vulnerability assessment will be meaningless; at the same time, the physical characteristics and operating characteristics of the system rely on its own topological structure. Therefore, structural vulnerability and state vulnerability are interdependent, and the two together characterize the strength of the system's safety performance. The difference is that structural vulnerability is more about exploring the vulnerable parts of the system from the perspective of topological structure, while state vulnerability is a comprehensive consideration of the integrity of the system's topological structure, the rigor of physical laws, and the rationality of operating parameters, and has a comprehensive feature. Among them, the structural vulnerability assessment is mainly based on complex network theory, selecting statistical feature quantities (such as degree, betweenness, etc.), integrating the system's physical characteristics according to the topological structure of the power grid, and constructing vulnerability assessment indicators; the state vulnerability assessment is mainly based on the system's operating state, including steady state and transient state, to capture physical feature quantities. The existing relevant theoretical system can be divided into deterministic methods and probabilistic methods from a mathematical perspective. In general, current research mainly focuses on the vulnerability assessment of power system under normal operation and conventional faults, and there is little research on the identification of vulnerable parts of power systems under extreme damage scenarios such as severe natural disasters and intentional attacks. Therefore, it is urgent to combine the main characteristics of vulnerable parts of power systems under extreme events, and conduct research on the identification of vulnerable parts of power systems under extreme damage scenarios, so as to lay an important foundation for targeted defense deployment. Summary of the invention

[0003] In view of the above technical problems, the present invention provides a method for identifying vulnerable parts of a power system under extreme events, comprising:

[0004] Determine the equivalent degree index of the node according to the degree of the node itself and the influence of the node on the network connection level in the power system network; determine the connectivity impact index of the channel according to the influence of the channel loss on the network connectivity; identify the nodes and transmission channels of the structural vulnerability of the power system by the node equivalent degree index and the channel connectivity impact index;

[0005] Determine the node equivalent power flow intermediate index according to the load carried by the node itself and the load supplied by the node to the interconnected node; determine the equivalent power flow intermediate index of the transmission channel according to the proportion of the channel's own transmission power and the power shortage caused by the loss of the channel in the total load of the receiving system; identify the nodes and transmission channels with power system functional vulnerability by the equivalent power flow intermediate index of the node and the equivalent power flow intermediate index of the transmission channel;

[0006] Based on the nodes and transmission channels with structural vulnerabilities, and the nodes and transmission channels with functional vulnerabilities, nodes and transmission channels that exhibit both structural and functional vulnerabilities are screened and identified as comprehensive vulnerable points or channels.

[0007] Furthermore, according to the node's own degree in the power system network and the node's influence on the network connection level, the equivalent degree index of the node is determined, including:

[0008] After the node is disconnected from the grid, when the grid is disconnected;

[0009] The smaller the node's own degree value is, the smaller its impact on the network connectivity is, the more complete the largest connected subgraph in the remaining network is, the higher the network connectivity is, and the smaller the node's equivalent degree value is, which means the node is less important.

[0010] The higher the node's own degree value is, the greater its impact on the network connectivity is, and the smaller the number of nodes in the maximum connected subgraph of the remaining network is, the larger the node's equivalent degree value is, which means the node is more important.

[0011] According to the node's own degree in the power system network and the node's influence on the network connection level, the equivalent degree index of the node is specifically:

[0012]

[0013] In the formula, D(node i ) is the equivalent degree of node i, k i is the degree of node i, N is the total number of initial network nodes, N sub is the number of nodes in the maximum connected subgraph of the remaining network after node i is lost.

[0014] Furthermore, according to the impact of channel loss on network connectivity, the connectivity impact index of the channel is determined, including:

[0015] After the channel is disconnected from the grid, the grid interconnection decreases or even decouples;

[0016] When the channel is disconnected from the power grid, the more complete the largest connected subgraph in the remaining network is, the smaller the impact of the channel disconnection on the network connectivity is, and the smaller the connectivity impact index is, which means the channel is less important;

[0017] On the contrary, the greater the impact of channel disconnection on network connectivity, the greater the connectivity impact index, which means the higher the importance of the channel;

[0018] According to the impact of channel loss on network connectivity, the connectivity impact index of the channel is as follows:

[0019]

[0020] Where N is the total number of initial network nodes, N sub is the number of nodes in the maximum connected subgraph of the remaining network after the channel is lost.

[0021] Furthermore, identifying nodes and transmission channels of structural vulnerability of the power system by using the node equivalent degree index and the channel connectivity impact index includes:

[0022] The higher the node's own degree value is, the greater its impact on the network connectivity is, and the smaller the number of nodes in the maximum connected subgraph of the remaining network is, the greater the node's equivalent degree value is, the higher the importance of the node is, and the node is a structurally fragile node;

[0023] The smaller the number of nodes in the maximum connected subgraph of the remaining network after the channel is lost, the greater the impact of channel disconnection on the network connectivity; the larger the connectivity impact index, the higher the importance of the channel, and the channel is a structurally fragile channel.

[0024] Furthermore, according to the load carried by the node itself and the load supplied by the node and the interconnected nodes, the node equivalent power flow betweenness index is determined, including:

[0025] The greater the load carried by the node itself and the greater the load that the node supplies to the interconnected nodes, the greater the value of the node equivalent power flow betweenness index;

[0026] According to the load carried by the node itself and the load supplied by the node to the interconnected nodes, the equivalent power flow betweenness index of the node is specifically:

[0027]

[0028] In the formula, J(node i ) is the equivalent power flow betweenness of node i, P ij is the active power flow of the line between node i and node j, n is the outgoing degree of node i, P i is the load carried by node i, P j is the load carried by node j.

[0029] Furthermore, according to the proportion of the channel's own transmission power and the power shortage caused by the loss of the channel in the total load of the receiving system, the equivalent power flow betweenness index of the transmission channel is determined, including:

[0030] The greater the channel's own transmission power value, the greater the channel's impact on the power balance of the sending and receiving end systems;

[0031] The greater the proportion of power shortage caused by channel loss in the total load of the receiving system, the more serious the impact on the receiving system;

[0032] According to the proportion of the channel's own transmission power and the power shortage caused by the loss of the channel in the total load of the receiving system, the equivalent power flow betweenness index of the channel is as follows:

[0033] Internal transmission channel of synchronous power grid: Transmission channels between asynchronous power grids:

[0034] Where RE is the receiving power grid, P i is the active power flow through line i, n is the number of transmission channels fed into the receiving grid r (i=1,2,……,n), ΔP j is the power transferred through the remaining channels j after the channel r feeding into the receiving grid is lost, m is the number of remaining channels (j = 1, 2, ..., m), ΔP jmax is the power margin of channel j, P r is the total load of the receiving grid r (r∈RE).

[0035] Furthermore, according to the fact that there is no power transfer after the DC channel between the asynchronous interconnected power grids is lost, the transmission channels are divided into transmission channels within the synchronous power grid and transmission channels between asynchronous power grids.

[0036] Furthermore, identifying nodes and transmission channels with power system functional vulnerability using the node equivalent power flow betweenness index and the equivalent power flow betweenness index of the transmission channel includes:

[0037] The greater the load carried by the node itself, the greater the load that the node supplies to the interconnected nodes, the greater the value of the node equivalent power flow betweenness index, and the more important the power supply performance of the node, the node is a functionally vulnerable node;

[0038] The greater the active power transmitted by the internal channel of the synchronous power grid, the higher the proportion of the power shortage in the total load at the receiving end, the greater the value of the channel equivalent power flow intermediate index, the more important the power supply performance of the channel, and the channel is a functionally fragile channel;

[0039] The greater the active power value transmitted by the transmission channel between asynchronous power grids, the greater the proportion of the transmitted power in the total load of the receiving system, the greater the value of the channel equivalent power flow intermediate index, the more important the power supply performance of the channel is, and the channel is a functionally fragile channel.

[0040] The present invention also provides a system for identifying vulnerable parts of a power system under extreme events, comprising:

[0041] The structural vulnerability identification module is used to determine the equivalent degree index of the node according to the node's own degree in the power system network and the node's influence on the network connection level; determine the channel connectivity impact index according to the influence of the channel loss on the network connectivity; identify the nodes and transmission channels of the structural vulnerability of the power system by the node equivalent degree index and the channel connectivity impact index;

[0042] The functional vulnerability identification module is used to determine the node equivalent power flow betweenness index according to the load carried by the node itself and the load supplied by the node to the interconnected node; determine the equivalent power flow betweenness index of the transmission channel according to the proportion of the channel's own transmission power and the power shortage caused by the loss of the channel in the total load of the receiving end system; identify the nodes and transmission channels with functional vulnerability of the power system by the equivalent power flow betweenness index of the node and the equivalent power flow betweenness index of the transmission channel;

[0043] The comprehensive identification module is used to screen nodes and transmission channels that present both structural and functional vulnerabilities based on the nodes and transmission channels with structural vulnerabilities and the nodes and transmission channels with functional vulnerabilities, and identify them as comprehensive vulnerable points or channels. The remaining nodes or channels that only present a single aspect of vulnerability are vulnerable nodes or channels in the corresponding aspect.

[0044] The present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program implements the steps of any one of the methods in the above claims when executed by a processor.

[0045] The present invention provides a method and system for identifying vulnerable parts of an electric power system under extreme events. The method and system start from the two perspectives of structural vulnerability and functional vulnerability for power grid nodes and transmission channels, draw on concepts such as degree and betweenness in complex network theory, integrate system topological characteristics, physical characteristics and operating characteristics, construct vulnerable part identification indicators, and realize quantitative identification of the vulnerability of power grid nodes and transmission channels under extreme events. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a flow chart of a method for identifying vulnerable parts of a power system under extreme events provided by an embodiment of the present invention;

[0047] Figure 2 is a process diagram of identifying vulnerable parts of a power system under extreme events involved in an embodiment of the present invention;

[0048] Figure 3 It is a 500kV power grid geographical wiring diagram involved in an embodiment of the present invention;

[0049] Figure 4 is a system bus voltage curve before and after load shedding under a full-stop fault at different nodes involved in an embodiment of the present invention;

[0050] Figure 5 is a schematic diagram of an inter-provincial power transmission channel involved in an embodiment of the present invention;

[0051] Figure 6 is a system operation curve after the W-S channel is disconnected according to an embodiment of the present invention;

[0052] Figure 7 is a system operation curve after the W-Z channel is disconnected according to an embodiment of the present invention;

[0053] Figure 8 is a system bus frequency curve after the AQ-XC channel is disconnected according to an embodiment of the present invention;

[0054] Fig. 9 is a system bus frequency curve after the XC-GD channel is disconnected according to an embodiment of the present invention;

[0055] Fig.10 The embodiment of the present invention relates to a system bus frequency curve after the FFJS channel is disconnected;

[0056] Fig.11 It is a schematic diagram of the system structure for identifying vulnerable parts of a power system under extreme events provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0057] Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present invention, so the present invention is not limited to the specific implementation disclosed below.

[0058] Example 1

[0059] Figure 1 A flow chart of a method for identifying vulnerable parts of a power system under extreme events is shown, the method comprising the following steps:

[0060] Step S101, determining the equivalent degree index of the node according to the node's own degree in the power system network and the node's influence on the network connection level; determining the connectivity impact index of the channel according to the influence of the channel loss on the network connectivity; identifying the nodes and transmission channels of the structural vulnerability of the power system by the node equivalent degree index and the channel connectivity impact index.

[0061] Structural vulnerability identification, first of all, in terms of nodes, when a node is disconnected from the power grid, the power grid may be decoupled; the smaller the node's own degree value is, and the smaller the impact on the network connectivity is, the more complete the largest connected subgraph in the remaining network is, and the higher the network connectivity is, the smaller the node's equivalent degree value is, which means the importance of the node is lower; the higher the node's own degree value is, and the greater the impact on the network connectivity is, the smaller the number of nodes in the largest connected subgraph of the remaining network is, the larger the node's equivalent degree value is, which means the importance of the node is higher. According to the node's own degree in the power system network and the node's impact on the network connection level, the equivalent degree index of the node is specifically:

[0062]

[0063] In the formula, D(node i ) is the equivalent degree of node i, k i is the degree of node i, N is the total number of initial network nodes, N sub is the number of nodes in the maximum connected subgraph of the remaining network after node i is lost.

[0064] Secondly, in terms of transmission channels, after the channel is disconnected from the power grid, the interconnection of the power grid decreases or even decouples; the more complete the largest connected subgraph in the remaining network is, the smaller the impact of channel disconnection on network connectivity, the smaller the connectivity impact index is, and the lower the structural importance of the channel is; conversely, the greater the impact of channel disconnection on network connectivity, the greater the connectivity impact index is, and the higher the importance of the channel is. According to the impact of channel loss on network connectivity, the connectivity impact index of the channel is specifically:

[0065]

[0066] Where N is the total number of initial network nodes, N sub is the number of nodes in the maximum connected subgraph of the remaining network after the channel is lost.

[0067] Step S102, determining a node equivalent power flow betweenness index according to the load carried by the node itself and the load supplied by the node to the interconnected node; determining an equivalent power flow betweenness index of the transmission channel according to the proportion of the channel's own transmission power and the power shortage caused by the loss of the channel in the total load of the receiving system; identifying nodes and transmission channels with functional vulnerability of the power system by the node equivalent power flow betweenness index and the equivalent power flow betweenness index of the transmission channel.

[0068] Functional vulnerability identification, first of all, in terms of nodes, the greater the load carried by the node itself and the greater the load that the node supplies to the interconnected nodes, the greater the value of the node equivalent power flow betweenness index; according to the load carried by the node itself and the load that the node supplies to the interconnected nodes, the node equivalent power flow betweenness index is determined, specifically:

[0069]

[0070] In the formula, J(node i ) is the equivalent power flow betweenness of node i, P ij is the active power flow of the line between node i and node j, n is the outgoing degree of node i, P i is the load carried by node i, P j is the load carried by node j.

[0071] Secondly, in terms of transmission channels, the greater the transmission power value of the channel itself, the greater the impact of the channel on the power balance of the sending and receiving systems; the greater the proportion of the power shortage caused by the loss of the channel in the total load of the receiving system, the more serious the impact on the receiving system; according to the proportion of the transmission power of the channel itself and the power shortage caused by the loss of the channel in the total load of the receiving system, the equivalent power flow intermediate index of the channel is determined. Considering that there is no power transfer after the DC channel between asynchronous interconnected power grids is lost, the transmission channels are divided into transmission channels within the synchronous power grid and transmission channels between asynchronous power grids. The equivalent power flow intermediate index of the channel is specifically: Internal transmission channel of synchronous power grid: Transmission channels between asynchronous power grids:

[0072] Where RE is the receiving power grid, P i is the active power flow through line i, n is the number of transmission channels fed into the receiving grid r (i=1,2,……,n), ΔP j is the power transferred through the remaining channels j after the channel r feeding into the receiving grid is lost, m is the number of remaining channels (j = 1, 2, ..., m), ΔP jmax is the power margin of channel j, P r is the total load of the receiving grid r (r∈RE).

[0073] The greater the active power transmitted by the internal channel of the synchronous power grid, the higher the proportion of the power shortage in the total load at the receiving end, the greater the value of the channel equivalent power flow intermediate index, the more important the power supply performance of the channel, and the channel is a functionally fragile channel;

[0074] The greater the active power value transmitted by the transmission channel between asynchronous power grids, the greater the proportion of the transmitted power in the total load of the receiving system, the greater the value of the channel equivalent power flow intermediate index, the more important the power supply performance of the channel is, and the channel is a functionally fragile channel.

[0075] Step S103: Based on the nodes and transmission channels with structural vulnerabilities and the nodes and transmission channels with functional vulnerabilities, the nodes and transmission channels that present both structural and functional vulnerabilities are screened and determined as comprehensive vulnerable points or channels. The remaining nodes or channels that present only a single aspect of vulnerability are the vulnerable nodes or channels of the corresponding aspect.

[0076] Example 2

[0077] The process of identifying vulnerable parts of the power system under extreme events is shown in the attached figure. Figure 2 As shown. The first is structural vulnerability identification. Starting from the structural performance, the node equivalent degree index and channel connectivity impact index are defined, and the equivalent degree index of the nodes in the whole network and the connectivity impact index of the transmission channel are calculated. The nodes and channels with the highest order are structurally vulnerable nodes and channels. According to the number of screening requirements, the set of structurally vulnerable nodes and channels is determined, and the degree of damage to the integrity of the system grid after the nodes and transmission channels are damaged is evaluated. Then, functional vulnerability identification is carried out. From the perspective of power supply function, the equivalent power flow betweenness index of nodes and transmission channels is defined, and the equivalent power flow betweenness index of nodes and transmission channels in the whole network is calculated. Similarly, the nodes and channels with the highest order are functionally vulnerable nodes and channels. According to the number of screening requirements, the set of functionally vulnerable nodes and channels is determined, and the impact assessment of the loss of power after the loss of nodes and transmission channels is realized. The last step is comprehensive vulnerability identification. Nodes or channels that appear in both the structural vulnerable set and the functional vulnerable set are screened. If the node or channel shows strong vulnerability in both aspects, it is determined to be a comprehensive vulnerable node or channel. The remaining nodes or channels that only appear in a single set are vulnerable nodes or channels in the corresponding aspects.

[0078] (1) Structural vulnerability identification

[0079] 1) In terms of nodes, from the perspective of local and global characteristics, the structural performance of a node is reflected locally as the degree of the node itself, and globally as the impact of the node on the connectivity level of the entire network. Based on this, the degree index in complex networks is improved, and the equivalent degree index of the node is defined as follows:

[0080]

[0081] In the formula, D(node i ) is the equivalent degree of node i, k i is the degree of node i, N is the total number of initial network nodes, N sub is the number of nodes in the maximum connected subgraph of the remaining network after node i is lost.

[0082] From formula (1), it can be seen that when the attacked node is disconnected from the power grid, it may cause the power grid to be disconnected. The smaller the value of the node's own degree is, the smaller the impact on the network connectivity is, the more complete the maximum connected subgraph in the remaining network is, the higher the network connectivity is, the smaller the value of the node equivalence is, and the lower the structural importance of the node is; conversely, the higher the value of the node's own degree is, the greater the impact on the network connectivity is, the smaller the number of nodes in the maximum connected subgraph of the remaining network is, the larger the value of the node equivalence is, and the higher the structural importance of the node is.

[0083] 2) In terms of transmission channels, transmission channels interconnect nodes to form a power grid. When the channel is damaged, the interconnection of the power grid decreases or even decouples. Therefore, considering the impact of channel loss on network connectivity, the connectivity impact indicators of the channel are defined as follows:

[0084]

[0085] Where N is the total number of initial network nodes, N sub is the number of nodes in the maximum connected subgraph of the remaining network after the channel is lost.

[0086] From formula (2), we can see that when the attacked channel is disconnected from the power grid, the larger the maximum connected subgraph in the remaining network remains, that is, N sub The larger the value, the smaller the impact of channel disconnection on network connectivity, the smaller the connectivity impact index, and the lower the structural importance of the channel; conversely, N sub The smaller it is, the greater the impact of channel disconnection on network connectivity, the larger the connectivity impact index is, the higher the structural importance of the channel is, and it is a structurally vulnerable link.

[0087] (2) Functional vulnerability identification

[0088] 1) In terms of nodes, from the perspective of power supply function, the load impact after the node loss mainly includes two parts: one is the load carried by the node itself, and the other is the load supplied to other interconnected nodes (according to the most serious situation, the transfer of power is not considered for the time being). The traditional power flow betweenness index is improved, and the node equivalent power flow betweenness index is defined as follows:

[0089]

[0090] In the formula, J(node i ) is the equivalent power flow betweenness of node i, P ij is the active power flow of the line between node i and node j, n is the outgoing degree of node i, that is, the line power flow P ij The number of positive branches (j = 1, 2, ..., n) (the outflow direction is defined as positive), P i is the load carried by node i, P j is the load carried by node j.

[0091] From formula (3), it can be seen that the node equivalent power flow betweenness index not only takes into account the node's own load, but also considers the power supply capacity and importance of the connected nodes. The node out-degree represents the number of branches that the node supplies power to other nodes. The larger the out-degree, the larger the power supply range; the proportion of the power flow of the connected line in the connected node load represents the importance of the power supply to the connected node. The higher the proportion, the greater the line flow, indicating that the equivalent power supply capacity for the connected node is stronger; the node's own load P i The larger it is, the larger the value of the node equivalent power flow betweenness index is when combined with the aforementioned positive correlation index, which means that the power supply performance of the node is more important.

[0092] 2) In terms of transmission channels, as the power transmission link connecting the sending and receiving systems, the importance of the function of the transmission channel is mainly reflected in two aspects: one is the size of its own transmission power. The larger the transmission power value, the greater the impact on the power balance of the sending and receiving systems after being damaged; the second is the proportion of the power shortage caused by the loss of the channel in the total load of the receiving system. The larger the proportion of the shortage power, the more serious the impact on the receiving system after being damaged. Considering the power transfer of the power transmission channel of the power grid, if the ability of the remaining channels to accept power transfer is very strong, the impact of the loss of the channel can be weakened to a certain extent. Due to the different power transfer situations of AC and DC transmission channels, there is no power transfer channel after the DC channel between asynchronous interconnected power grids is lost (the impact of parallel DC power increase is not considered for the time being). Therefore, it is considered to divide the transmission channel into two categories: transmission channels within synchronous power grids and transmission channels between asynchronous power grids. Based on the above factors, the equivalent power flow intermediate index of the transmission channel is defined as follows:

[0093] Internal transmission channel of synchronous power grid: Transmission channels between asynchronous power grids:

[0094] In formula (4), RE is the receiving-end power grid set, P i is the active power flow through line i, n is the number of transmission channels fed into the receiving grid r (i=1,2,……,n), ΔP jis the power transferred through the remaining channels j after the channel r feeding into the receiving grid is lost, m is the number of remaining channels (j = 1, 2, ..., m), ΔP xjam is the power margin of channel j, that is, the difference between the transmission power limit of channel j and the current power, P r is the total load of the receiving grid r (r∈RE).

[0095] In formula (5), RE is the receiving-end power grid set, P i is the active power flow through line i, n is the number of transmission channel lines (i = 1, 2, ..., n), P r is the total load of the receiving grid r (r∈RE).

[0096] From formula (4), it can be seen that the equivalent power flow betweenness index of the transmission channel inside the synchronous power grid takes into account both the absolute value of the channel transmission power and the proportion of the possible power shortage in the total load of the receiving system, taking into account the characteristics of the channel itself and its impact on the power supply of the receiving system. Represents the active power delivered by the channel, ΔP jmax Represents the limited channel power margin during power transfer, i.e., power transfer capability, ΔP j -ΔP jmax It can represent the power shortage caused by channel loss. The value should be greater than or equal to 0, that is:

[0097]

[0098] The greater the active power transmitted by the channel, the higher the proportion of the power shortage caused in the total load at the receiving end, and the larger the value of the channel equivalent power flow intermediate index, which means that the power supply performance of the channel is more important, and the greater the impact on the system after being damaged, which is a functionally vulnerable link.

[0099] From formula (5), we can see that the equivalent power flow between asynchronous power grid transmission channels considers both the absolute value of the channel transmission power and the relative value of the total load of the receiving system, and also takes into account the characteristics of the channel itself and its impact on the power supply of the receiving system. represents the active power delivered by the channel, It represents the proportion of channel power in the total load of the receiving system. The greater the transmitted active power value and the higher the proportion, the greater the value of the channel equivalent power flow intermediate index, which means that the power supply performance of the channel is more important, and the impact on the system after being damaged is greater, which is a functionally vulnerable link.

[0100] (3) Comprehensive vulnerability identification

[0101] Based on the calculation results of the structural vulnerability and functional vulnerability indicators of the nodes and transmission channels of the entire network, the nodes or channels that appear in both the structural vulnerability set and the functional vulnerability set are screened. If the node or channel shows strong vulnerability in both aspects, it is determined to be a comprehensive vulnerable node or channel; the remaining nodes or channels that only appear in a single set are vulnerable nodes or channels in the corresponding aspects.

[0102] Example 3

[0103] (1) Node vulnerability assessment

[0104] Taking a provincial power grid as an example, the vulnerable nodes within the power grid are mined and identified. Based on the power grid's abundant data, the power grid load is about 33,400MW. Vulnerability screening is performed on the 500kV level nodes of the power grid. The 500kV power grid geographical wiring diagram is as follows: Figure 3 shown.

[0105] Firstly, the structural vulnerability is analyzed, and the degree statistics of 500kV nodes are shown in Table 1.

[0106] Table 1 500kV node degree statistics

[0107]

[0108] When counting the number of network nodes, the number of nodes connected to the first-level section of the node outgoing line is taken into account. After calculation and analysis, the equivalent degree indicators of the above nodes are arranged in descending order as shown in Table 2.

[0109] Table 2 500kV node equivalent degree index calculation table

[0110] Serial number Node Name degree N <![CDATA[N sub ]]> Equivalence 1 FS 11 26 24 11.92 2 SY 10 26 24 10.83 3 AD 9 26 23 10.17 4 CP 9 26 24 9.75 5 MTG 8 26 24 8.67 6 TZ 7 26 25 7.28 7 XHC 7 26 25 7.28 8 TB 6 26 24 6.50 9 KXC 4 26 25 4.16 10 YZ 4 26 25 4.16 11 R 2 26 25 2.08 12 HD 2 26 25 2.08 13 CB 2 26 25 2.08 14 GM 2 26 25 2.08 15 CY 2 26 25 2.08 16 XD 2 26 25 2.08 17 LZ 2 26 25 2.08

[0111] As shown in Table 2, from the perspective of structural performance, the top vulnerable nodes are FS station, SY station and AD station, and the equivalent degree indexes of the above nodes are all above 10. Since the 500kV power grid is a ring network structure, the number of nodes N in the maximum connected subgraph of the remaining network after different nodes are lost is sub The difference is not obvious, that is, the impact on network connectivity is small. Overall, the size of the equivalent degree is positively correlated with the degree.

[0112] Then, the vulnerability of the node power supply function is analyzed, and the node equivalent power flow betweenness index is arranged in descending order as shown in Table 3.

[0113] Table 3 Calculation table of equivalent power flow index of 500kV node

[0114] Serial number Node Name Equivalent power flow betweenness 1 SY 6353.1 2 FS 5905.9 3 AD 5864.7 4 CP 5229.1 5 XHC 4321.7 6 TZ 4157.6 7 TB 2888.9 8 CB 2424.3 9 HD 2160.6 10 XD 2085.5 11 MTG 2025.1 12 R 2015.2 13 GM 1683.2 14 YZ 1598.0 15 LZ 1484.8 16 KXC 1294.6 17 CY 1215.2

[0115] As can be seen from Table 3, from the perspective of power supply function, the top vulnerable nodes are SY station, FS station and AD station. These nodes carry a large load and have a strong power support function for the connected branches. The above node set is the same as the top three structural vulnerable node sets, with only a slight difference in order. Therefore, the above three nodes can be considered as comprehensive vulnerable nodes, which are vulnerable links in both structure and function.

[0116] Furthermore, a comparative analysis is conducted on the impact of different node failures on the safe and stable operation of the system. Taking the node full stop failure as an example, the system load loss after the full stop of different nodes is compared. The top-ranked comprehensive vulnerable nodes SY station, FS station and AD station are selected for comparison with the randomly selected TB station, HD station and LZ station. Consider taking low-voltage load reduction measures when the node bus voltage is lower than 0.8pu, and the load removal ratio is configured according to the constant impedance type. The statistics of the system load removal after the full stop failure are shown in Table 4, and the system bus voltage curve before and after load removal is shown in Table 4. Figure 4 shown.

[0117] Table 4 Statistics of system load shedding after all nodes fail

[0118] Serial number Node Name Load removal (MW) Removal load ratio 1 SY 14580 43.7％ 2 AD 18000 53.9％ 3 FS 9100 27.2％ 4 TB 80 0.2％ 5 HD 330 1.0％ 6 LZ — —

[0119] Depend on Figure 4 It can be seen that the failure of SY, AD and FS stations caused the voltage collapse of the local power grid, and the node bus voltage dropped to around 0.6pu. After a large number of load shedding measures were taken, the system voltage recovered to the rated value, and the loss load accounted for 43.7%, 53.9% and 27.2% of the total load of Beijing network respectively; after the HD and TB stations were completely shut down, the voltage of some buses was slightly lower than 0.8pu, and only a small amount of load needed to be cut off. After the LZ station was completely shut down, no load needed to be cut off. It can be seen that the severity of the impact of the vulnerable node fault screened by the proposed identification method on the system operation is significantly higher than that of other nodes, which proves the effectiveness and accuracy of the proposed method.

[0120] (2) Transmission channel vulnerability assessment

[0121] Taking a regional power grid as an example, the vulnerability analysis of the transmission channel is carried out. Considering the different characteristics of AC channels and DC channels, and the fact that the power grid has multiple inter-provincial AC interconnection channels and multiple DC feed-in channels, it is necessary to conduct a comparative vulnerability analysis of the AC and DC channels respectively.

[0122] (1) Transmission channels within the synchronous grid

[0123] Based on the current grid flood high mode data, the total load of the regional grid is 230,000MW, and the rotating reserve capacity is 18,500MW. The inter-provincial communication channels within the grid are selected, and the W-S transmission channel and W-Z transmission channel are used as examples for vulnerability comparison. The transmission channel composition is as follows: Figure 5 As shown in the figure, since the impact of disconnection of the transmission channel on the connectivity of the power grid is basically the same, the following mainly analyzes the impact on the function.

[0124] Under the W power transmission mode, the initial power flow distribution of the channel is shown in Table 5.

[0125] Table 5 Initial channel flow statistics

[0126]

[0127] According to statistics, the load of JS power grid under this mode is 103910MW, and the load of ZJ power grid is 54090MW. Considering that after the transmission channel is lost, the sending and receiving ends are still in a synchronous power grid, the power is transferred in the internal channel of the power grid. For example, after the W-S channel is lost, the AH sending end and the JS receiving end are still synchronous interconnected power grids, and the surplus power of the sending end will be transferred from the W-Z channel and then transmitted through the ZJ, SH and JS interconnection channels. The power transfer after the W-S channel and the W-Z channel are disconnected is shown in Table 6, where the maximum power transfer that can be tolerated is calculated according to the difference between the channel thermal stability limit and the initial power.

[0128] Table 6 Power transfer and shortage calculation table after channel disconnection

[0129]

[0130] According to the calculation results in Table 6, the equivalent power flow intermediate numbers of the W-S channel and the W-Z channel are calculated as follows:

[0131]

[0132] By comparison, the equivalent power flow intermediate value of the W-Z channel is higher, indicating that the damage to the channel will have a greater impact on the system. Furthermore, in order to verify the effectiveness of the proposed method, the impact of different transmission channel faults on the safe and stable operation of the system is simulated and analyzed through BPA.

[0133] According to the simulation results, after all W-S channels are disconnected, the power flow transfer causes the GD-PY single-circuit line to trip due to overload, and the system can maintain stable operation. The system bus voltage and frequency curves are as follows: Figure 6 shown.

[0134] After all W-Z channels are disconnected, the flow transfer causes the EX-HF double-circuit line and DT-TM double-circuit line to trip due to overload, and the HN-WH UHV double-circuit line oscillates and decouples, eventually leading to system instability. The system bus voltage and frequency curves are shown in Figure 1. Figure 7 shown.

[0135] The simulation results show that the impact of W-Z channel failure on the system is more serious under this method, which is consistent with the indicator calculation conclusion of the proposed method.

[0136] (2) Transmission channels between asynchronous power grids

[0137] Based on the current grid flood and low mode data, the total load of the entire network is 140,000MW, and the rotating reserve capacity is 18,500MW. The large-capacity DC transmission channels fed into the power grid are selected, and the AQ-XC channel, XC-GD channel and FFJS channel (HB section) are used as examples for vulnerability comparison. The above channels all concentrate several DC transmission lines, as shown in Table 7. Due to the short channel gap distance, there is a risk of all transmission channels being disconnected under unconventional conditions.

[0138] Table 7 Transmission channel statistics

[0139] Serial number Channel Name Transmission projects included in the channel Total channel capacity (MW) 1 AQ—XC Channel LS+JS+FF+GN+LF 21800 2 XC-GD channel JS+FF+GN+LF 17800 3 FFJS Channel FF+JS 13600

[0140] According to Table 7, the equivalent power flow intermediate index of different transmission channels can be calculated as shown in Table 8.

[0141] Table 8 Calculation table of equivalent power flow betweenness index of transmission channel

[0142]

[0143] It can be seen from Table 8 that the equivalent power flow betweenness value of the AQ-XC channel is the largest, and the corresponding vulnerability level is the highest; the equivalent power flow betweenness value of the FFJS channel is the smallest, and the corresponding vulnerability level is the lowest.

[0144] Furthermore, a comparative analysis is conducted on the impact of different transmission channel failures on the safe and stable operation of the system. Taking the failure of all transmission channels being disconnected as an example, the system load loss after different channels are disconnected is compared. The grid low-frequency load reduction scheme is shown in Table 9, the load reduction statistics after the channel is disconnected are shown in Table 10, and the system bus frequency curve after the fault is shown in Table 11. Figure 8 to Figure 10 16.

[0145] Table 9 Power grid low frequency load reduction configuration scheme

[0146]

[0147] Table 10 Statistics of system load removal after channel disconnection

[0148] Serial number Channel Name Load removal (MW) Removal load ratio Minimum frequency (Hz) 1 AQ—XC Channel 22480 16.06％ 48.5 2 XC-GD channel 12850 9.18％ 48.7 3 FFJS Channel 9828 7.02％ 48.76

[0149] From Table 10, Figure 8 to Figure 10 It can be seen that after the AQ-XC channel, XC-GD channel and JS channel were disconnected, a large amount of power shortage occurred in the power grid, and the system bus frequency dropped to 48.5Hz, 48.7Hz and 48.76Hz respectively, triggering the system low-frequency load reduction action. After the load was removed, the system frequency recovered to near the rated value. The proportion of removed load to the total network load was as high as 16.06%, 9.18% and 7.02% respectively. The AQ-XC channel has the highest degree of vulnerability, and its impact on the safe and stable operation of the system after its disconnection is significantly more serious than the other two channels.

[0150] In summary, the proposed method can effectively identify the vulnerability degree of the transmission channel and provide a reference for the quantitative comparative analysis of the vulnerability of the transmission channel.

[0151] Example 4

[0152] Based on the same inventive concept, the present invention also provides a system for identifying vulnerable parts of a power system under extreme events, such as Fig.11 As shown, including:

[0153] The structural vulnerability identification module 110 is used to determine the equivalent degree index of the node according to the node's own degree in the power system network and the node's influence on the network connection level; determine the connectivity impact index of the channel according to the influence of the channel loss on the network connectivity; identify the nodes and transmission channels of the structural vulnerability of the power system by the node equivalent degree index and the channel connectivity impact index;

[0154] The functional vulnerability identification module 120 is used to determine the node equivalent power flow betweenness index according to the load carried by the node itself and the load supplied by the node to the interconnected node; determine the equivalent power flow betweenness index of the transmission channel according to the proportion of the channel's own transmission power and the power shortage caused by the loss of the channel in the total load of the receiving end system; identify the nodes and transmission channels with functional vulnerability of the power system by the equivalent power flow betweenness index of the node and the equivalent power flow betweenness index of the transmission channel;

[0155] The comprehensive identification module 130 is used to screen nodes and transmission channels that present both structural and functional vulnerabilities based on the nodes and transmission channels with structural vulnerabilities and the nodes and transmission channels with functional vulnerabilities, and determine them as comprehensive vulnerable points or channels. The remaining nodes or channels that only present a single aspect of vulnerability are vulnerable nodes or channels in the corresponding aspect.

[0156] The present invention provides a method and system for identifying vulnerable parts of an electric power system under extreme events. The method and system start from the two perspectives of structural vulnerability and functional vulnerability for power grid nodes and transmission channels, draw on concepts such as degree and betweenness in complex network theory, integrate system topological characteristics, physical characteristics and operating characteristics, construct vulnerable part identification indicators, and realize quantitative identification of the vulnerability of power grid nodes and transmission channels under extreme events.

[0157] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, 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 disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0158] 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 flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, 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 flowchart and / or block diagram. 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.

[0159] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate 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 A function specified in one or more boxes.

[0160] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0161] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalents that do not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for identifying vulnerable parts of a power system under extreme events, characterized in that: include: Determine the equivalent degree index of the node according to the degree of the node itself and the influence of the node on the network connection level in the power system network; determine the connectivity impact index of the channel according to the influence of the channel loss on the network connectivity; identify the nodes and transmission channels of the structural vulnerability of the power system by the node equivalent degree index and the channel connectivity impact index; Determine the node equivalent power flow betweenness index according to the load carried by the node itself and the load supplied by the node to the interconnected nodes; Determine the equivalent power flow betweenness index of the transmission channel according to the proportion of the channel's own transmission power and the power shortage caused by the loss of the channel in the total load of the receiving system; identify the nodes and transmission channels with functional vulnerability of the power system according to the equivalent power flow betweenness index of the node and the equivalent power flow betweenness index of the transmission channel; Based on the nodes and transmission channels with structural vulnerabilities, and the nodes and transmission channels with functional vulnerabilities, nodes and transmission channels that exhibit both structural and functional vulnerabilities are screened and identified as comprehensive vulnerable points or channels.

2. The method according to claim 1, characterized in that According to the node's own degree in the power system network and the node's influence on the network connection level, the equivalent degree index of the node is determined, including: After the node is disconnected from the grid, when the grid is disconnected; The smaller the node's own degree value is, the smaller its impact on the network connectivity is, the more complete the largest connected subgraph in the remaining network is, the higher the network connectivity is, and the smaller the node's equivalent degree value is, which means the node is less important. The higher the node's own degree value is, the greater its impact on the network connectivity is, and the smaller the number of nodes in the maximum connected subgraph of the remaining network is, the larger the node's equivalent degree value is, which means the node is more important. According to the node's own degree in the power system network and the node's influence on the network connection level, the equivalent degree index of the node is specifically: In the formula, D(node i ) is the equivalent degree of node i, k i is the degree of node i, N is the total number of initial network nodes, N sub is the number of nodes in the maximum connected subgraph of the remaining network after node i is lost.

3. The method according to claim 1, characterized in that According to the impact of channel loss on network connectivity, the channel connectivity impact indicators are determined, including: After the channel is disconnected from the grid, the grid interconnection decreases or even decouples; When the channel is disconnected from the power grid, the more complete the largest connected subgraph in the remaining network is, the smaller the impact of the channel disconnection on the network connectivity is, and the smaller the connectivity impact index is, which means the channel is less important; On the contrary, the greater the impact of channel disconnection on network connectivity, the greater the connectivity impact index, which means the higher the importance of the channel; According to the impact of channel loss on network connectivity, the connectivity impact index of the channel is as follows: Where N is the total number of initial network nodes, N sub is the number of nodes in the maximum connected subgraph of the remaining network after the channel is lost.

4. The method according to claim 1, characterized in that The nodes and transmission channels of the structural vulnerability of the power system are identified by the node equivalent degree index and the channel connectivity impact index, including: The higher the node's own degree value is, the greater its impact on the network connectivity is, and the smaller the number of nodes in the maximum connected subgraph of the remaining network is, the greater the node's equivalent degree value is, the higher the importance of the node is, and the node is a structurally fragile node; The smaller the number of nodes in the maximum connected subgraph of the remaining network after the channel is lost, the greater the impact of channel disconnection on the network connectivity; the larger the connectivity impact index, the higher the importance of the channel, and the channel is a structurally fragile channel.

5. The method according to claim 1, characterized in that According to the load carried by the node itself and the load supplied by the node and the interconnected nodes, the node equivalent power flow betweenness index is determined, including: The greater the load carried by the node itself and the greater the load that the node supplies to the interconnected nodes, the greater the value of the node equivalent power flow betweenness index; According to the load carried by the node itself and the load supplied by the node to the interconnected nodes, the equivalent power flow betweenness index of the node is specifically: In the formula, J(node i ) is the equivalent power flow betweenness of node i, P ij is the active power flow of the line between node i and node j, n is the outgoing degree of node i, P i is the load carried by node i, P j is the load carried by node j.

6. The method according to claim 1, characterized in that According to the proportion of the channel's own transmission power and the power shortage caused by the loss of the channel in the total load of the receiving system, the equivalent power flow betweenness index of the transmission channel is determined, including: The greater the channel's own transmission power value, the greater the channel's impact on the power balance of the sending and receiving end systems; The greater the proportion of power shortage caused by channel loss in the total load of the receiving system, the more serious the impact on the receiving system; According to the proportion of the channel's own transmission power and the power shortage caused by the loss of the channel in the total load of the receiving system, the equivalent power flow betweenness index of the channel is as follows: Internal transmission channel of synchronous power grid: Transmission channels between asynchronous power grids: Where RE is the receiving-end power grid, P i is the active power flow through line i, n is the number of transmission channels fed into the receiving grid r (i=1,2,……,n), ΔP j is the power transferred through the remaining channels j after the channel r feeding into the receiving grid is lost, m is the number of remaining channels (j = 1, 2, ..., m), ΔP xjam is the power margin of channel j, P r is the total load of the receiving grid r (r∈RE).

7. The method according to claim 6, characterized in that Since there is no power transfer after the DC channel between asynchronous interconnected power grids is lost, the transmission channels are divided into transmission channels within the synchronous power grid and transmission channels between asynchronous power grids.

8. The method according to claim 1, characterized in that Identifying nodes and transmission channels with functional vulnerability of the power system by using the equivalent power flow betweenness index of the node and the equivalent power flow betweenness index of the transmission channel includes: The greater the load carried by the node itself, the greater the load that the node supplies to the interconnected nodes, the greater the value of the node equivalent power flow betweenness index, and the more important the power supply performance of the node, the node is a functionally vulnerable node; The greater the active power transmitted by the internal channel of the synchronous power grid, the higher the proportion of the power shortage in the total load at the receiving end, the greater the value of the channel equivalent power flow intermediate index, the more important the power supply performance of the channel, and the channel is a functionally fragile channel; The greater the active power value transmitted by the transmission channel between asynchronous power grids, the greater the proportion of the transmitted power in the total load of the receiving system, the greater the value of the channel equivalent power flow intermediate index, the more important the power supply performance of the channel is, and the channel is a functionally fragile channel.

9. A system for identifying vulnerable parts of a power system under extreme events, characterized in that: include: The structural vulnerability identification module is used to determine the equivalent degree index of the node according to the node's own degree in the power system network and the node's influence on the network connection level; determine the channel connectivity impact index according to the influence of the channel loss on the network connectivity; identify the nodes and transmission channels of the structural vulnerability of the power system by the node equivalent degree index and the channel connectivity impact index; The functional vulnerability identification module is used to determine the node equivalent power flow betweenness index according to the load carried by the node itself and the load supplied by the node to the interconnected node; determine the equivalent power flow betweenness index of the transmission channel according to the proportion of the channel's own transmission power and the power shortage caused by the loss of the channel in the total load of the receiving end system; identify the nodes and transmission channels with functional vulnerability of the power system by the equivalent power flow betweenness index of the node and the equivalent power flow betweenness index of the transmission channel; The comprehensive identification module is used to screen nodes and transmission channels that present both structural and functional vulnerabilities based on the nodes and transmission channels with structural vulnerabilities and the nodes and transmission channels with functional vulnerabilities, and identify them as comprehensive vulnerable points or channels. The remaining nodes or channels that only present a single aspect of vulnerability are vulnerable nodes or channels in the corresponding aspect.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 8 are implemented.

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