CN109936133A - A Vulnerability Analysis Method of Power System Considering Cyber-Physical Joint Attack - Google Patents

Abstract

The present disclosure provides a power system vulnerability analysis method considering cyber-physical joint attacks. When the primary equipment (generators, transformers, transmission lines, etc.) of a power grid in a certain area is physically damaged and then withdraws from operation, it causes changes in the topology of the power grid, which may Problems such as power flow transfer, branch power limit and power imbalance will occur in the power system. If the information system is attacked by information at this time, it is considered that the power dispatching center has lost the ability to optimize and adjust, and the power grid adopts the method of proportionally adjusting the generated power to ensure power balance. The over-limit branch will be cut off by the relay protection device. After the equipment is not attacked and the damaged equipment is out of service, the power dispatching center will optimize the load loss with the goal of minimizing the load loss, and coordinate the adjustment and control from the power supply side and the load side to ensure the power balance of the power grid and eliminate the branch power exceeding the limit.

Description

A Vulnerability Analysis Method of Power System Considering Cyber-Physical Joint Attack

technical field

The present disclosure relates to a power system vulnerability analysis method considering cyber-physical joint attack.

Background technique

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

Smart grid is a composite system composed of information virtual network and physical entity network, which is characterized by the close coordination of information system and physical system. With the continuous development of the smart grid, the automation of the power system has been continuously improved, the number of various measurement and calculation, decision-making and control units in the power grid has greatly increased, and the scale of the power information network has become larger and larger. The power system has developed into a complex system with deep integration of information and physics, and its stable operation is inseparable from the real-time scheduling of its information system. The information system collects the operation data of the power system and sends it to the power dispatching center for analysis and processing. The dispatching center makes real-time decisions and adjusts and controls the power system to ensure the safe and stable operation of the power system. At present, unstable factors such as terrorist threats and military conflicts appear frequently in the world. As a hub for the mutual conversion of various energy sources, the power system is the country's key infrastructure and has a huge impact on national security, economic development, and social stability. One of the key targets of terrorist attacks.

Under the above background, it is particularly important to study the vulnerability analysis and calculation methods of power-cyber-physical fusion systems. At present, there are two main ways of attacking the power system: the first is to directly physically damage the primary equipment of the power system, mainly targeting power plants, substations, transmission lines, bus nodes and even some important loads. , this attack method will cause one or more power equipment to fail and go out of operation, thereby changing the topology of the power network, seriously affecting the normal power transmission and distribution functions, and may even cause a series of cascading failures, causing the grid to de-load , causing large-scale power outages; another attack method is that terrorists use advanced network technology to invade the power information network and destroy the function of the information system. Since the control and mutual coordination of the physical equipment in the power system depend to a large extent on the information system, attacks on the information system may lead to complex physical interaction processes in the power system, and ultimately threaten the security of the entire system. Compared with physical attacks, information attacks have the characteristics of low cost and strong concealment, and the damage to the power system may be more serious. The information system and the physical system are interactive. Because of the close coupling between the two, a problem in any link may lead to serious accident consequences. At present, most of the literatures consider the impact of a single attack on the power system, and do not study and analyze the information attack and physical attack together.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present disclosure proposes a power system vulnerability analysis method considering cyber-physical joint attack. The present disclosure focuses on the functions of the power dispatching control center in view of the highly integrated cyber-physical characteristics of the current power system, and integrates the power information system Integrated modeling with power physics systems. Quantitative analysis method is used to simulate the dynamic evolution process of the power system after being attacked, and the loss of load is used as the evaluation index of the accident consequences to analyze the vulnerability of the power system. It is possible to identify the vulnerable elements of the power grid, so as to take targeted protective measures to reduce the losses of the power system after an attack.

In order to achieve the above object, the present disclosure adopts the following technical solutions:

A power system vulnerability analysis method considering cyber-physical joint attack, including the following steps:

(1) Set the state of each power grid element that is out of operation after being destroyed;

(2) Carry out topology analysis to obtain the number of disconnected power islands after the power grid is attacked, as well as the power supply, network and load conditions of each power island;

(3) Elimination of branch overload for each power island containing both generator and power load;

(4) Continue to analyze the topology to obtain the number of new power islands that are not connected to each other due to cascading failures, and repeat steps (3) for the power supply, network and load conditions of each new power island. ) until no cascading failure occurs;

(5) Judging whether each new power island that includes both the generator set and the power load has been calculated, if so, count the load loss, otherwise return to (4) to analyze and calculate the remaining new power island;

(6) Taking the loss of load in the case of load loss as the evaluation index of the accident consequences after the power system is attacked by cyber-physical joint attacks, the component that causes the most loss of load after being attacked is the vulnerable component of the power grid.

As a further limitation, in the step (1), taking the function of the power dispatching center as the starting point, the information system and the physical system are integrated into modeling and analysis.

As a further limitation, in the step (3), it specifically includes: simulating the power flow distribution of the system, specifically, for an island where the power generation is greater than the power consumption, the respective outputs are proportionally reduced according to the output of each unit; If the output of each unit is larger than the island of power generation, the output of each unit will be increased proportionally according to the spinning reserve of each unit. If the spinning reserve is insufficient, on the basis of full power generation of all units, the load level of each power consumption will be proportionally reduced. If the branch circuit is overloaded, the cascading fault will be judged.

As a further limitation, in the step (3), the specific process of judging the cascading failure includes that if the dispatch center is attacked by the network, loses the ability to sense and control the operating state, and cannot handle the overload of the branch, then all the overloaded branches are tripped, and the Carry out system topology analysis; if the dispatch center has not been attacked by the network, has the ability to sense and control the operating state, and handle branch overload, the dispatch center will re-dispatch power generation and take corresponding load reduction measures according to the strategy that minimizes the load loss of the island. Eliminate branch overload.

As a further limitation, in the step (3), in the system topology analysis, it is obtained through the topology analysis that the power island is further delisted into a number of new disconnected power islands due to cascading failures, and the number of each power island Power, network and load profiles for new power islands.

As a further limitation, in the step (3), the primary equipment in the power system is taken as the destruction target, the decision variables are the output and load levels of the generator sets of each node under the control of the dispatch center, and the objective function is to make the total loss of the system. minimum load.

As a further limitation, in the step (3), the constraints of the objective function include: when the following conditions occur, the power line 1 will be unavailable: each generator set, transmission line, node, substation in the power system The vector of the functional state is 0-1, wherein the vector of the functional state of 1 corresponds to the power element being hit and the function fails, and the vector of the functional state of 0 corresponds to the normal function of the power element without being hit.

As a further limitation, in the step (3), the constraints of the objective function include: the power line 1 is hit and the function fails, the head/end node of the power line 1 is hit and the function fails, and the power line 1 fails. When the connected substation is hit and the function fails, and a fault in the multi-circuit line on the same pole, the power line l on the same pole also fails.

As a further limitation, in the step (3), the constraints of the objective function include: when the following conditions occur, the generator set j will be unavailable: the generator set j is hit and the function fails or the generator set j is connected The incoming node is hit and the function fails.

As a further limitation, in the step (3), the constraints of the objective function also include DC power flow equation constraints, branch power flow equation constraints, and power balance constraints; inequality constraints: branch power flow safety constraints, generator sets Output constraint and load active power variation constraint.

A power system vulnerability analysis system considering cyber-physical joint attacks, running on a processor or memory, configured to execute the following instructions:

(1) Set the state of each power grid element that is out of operation after being destroyed;

(2) Carry out topology analysis to obtain the number of disconnected power islands after the power grid is attacked, as well as the power supply, network and load conditions of each power island;

(3) Elimination of branch overload for each power island containing both generator and power load;

(4) Continue to analyze the topology to obtain the number of new power islands that are not connected to each other due to cascading failures, and repeat steps (3) for the power supply, network and load conditions of each new power island. ) until no cascading failure occurs;

(5) Judging whether each new power island that includes both the generator set and the power load has been calculated, if so, count the load loss, otherwise return to (4) to analyze and calculate the remaining new power island;

(6) Taking the loss of load in the case of load loss as the evaluation index of the accident consequences after the power system is attacked by cyber-physical joint attacks, the component that causes the most loss of load after being attacked is the vulnerable component of the power grid.

Compared with the prior art, the beneficial effects of the present disclosure are:

Aiming at the high integration of information and physics in the current power system, the present disclosure focuses on the functions of the power dispatching control center, and integrates the power information system and the power physics system into modeling. Quantitative analysis method is used to simulate the dynamic evolution process of the power system after being attacked, and the loss of load is used as the evaluation index of the accident consequences to analyze the vulnerability of the power system. Ability to identify vulnerable elements of the power grid, so that targeted protection measures can be taken to reduce losses after an attack on the power system;

The present disclosure adopts the vulnerability analysis method based on the DC power flow, and the calculation speed is fast, and the problem of iterative non-convergence in the AC power flow calculation process is avoided.

The present disclosure considers the influence of the actual topology structure of the power system, is more in line with the operating conditions of the system, has more accurate calculation results and better practicability.

Description of drawings

The accompanying drawings that form a part of the present application are used to provide further understanding of the present application, and the schematic embodiments and descriptions of the present application are used to explain the present application and do not constitute improper limitations on the present application.

Figure 1 is the flow chart of vulnerability analysis;

Figure 2 is a diagram of the IEEE RTS-24 node test system.

Detailed ways:

The present disclosure will be further described below with reference to the accompanying drawings and embodiments.

It should be noted that the following detailed description is exemplary and intended to provide further explanation of the application. Unless otherwise specified, all technical and scientific terms used in the examples have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It should be noted that the terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural as well, furthermore, it is to be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates that There are features, steps, operations, devices, components and/or combinations thereof.

In this disclosure, terms such as "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", "side", "bottom", etc. The orientation or positional relationship is based on the orientation or positional relationship shown in the drawings, and is only a relational word determined for the convenience of describing the structural relationship of each component or element of the present disclosure, and does not specifically refer to any component or element in the present disclosure, and should not be construed as a reference to the present disclosure. public restrictions.

In the present disclosure, terms such as "fixed connection", "connected", "connected", etc. should be understood in a broad sense, indicating that it may be a fixed connection, an integral connection or a detachable connection; it may be directly connected, or through an intermediate connection. media are indirectly connected. For the relevant scientific research or technical personnel in the field, the specific meanings of the above terms in the present disclosure can be determined according to specific situations, and should not be construed as limitations on the present disclosure.

The present disclosure is based on the conventional DC power flow model, and after taking into account the constraints of the topology structure of the actual power system, an improved power system vulnerability analysis and calculation method is formed.

After the power system is attacked, if the short-term transient process is ignored, and only the operation situation of the power system re-entering the steady state after the accident is concerned, the steady-state method of the power system can be used for analysis. The dynamic evolution process of the power system after the cyber-physical attack can be described as follows: when the primary equipment (generators, transformers and transmission lines, etc.) of the power grid in a certain area is physically damaged and then withdraws from operation, causing changes in the topology of the power grid, there may be power Problems such as power flow transfer, branch power limit and power imbalance of the system. If the information system suffers an information attack at this time, it is considered that the power dispatching center has lost the ability to optimize and adjust, and the power grid adopts the method of proportionally adjusting the generated power to ensure power balance. The topology will change again, and even a series of cascading failures will occur. If the information system is not attacked, after the damaged equipment is out of service, the power dispatching center will optimize the load loss with the goal of minimizing the load loss, and coordinate the adjustment and control from the power supply side and the load side to ensure the power balance of the power grid and eliminate the branch power exceeding the limit. , so as to avoid cascading failures. In the whole process, the topology analysis algorithm is used to obtain the disassembly of the power grid, and the calculation of each power grid area is carried out. For the above dynamic evolution process, the steps in Figure 1 are used to simulate.

The process of Figure 1 is described as follows:

(1) Set the component running state. Set grid elements such as generators, substations and transmission lines that are out of service after being destroyed;

(2) System topology analysis. Through topology analysis, we can get the number of disconnected power islands (subsystems) after the power grid is attacked, and the power supply, network and load of each power island;

(3) Perform the following analysis on each power island (subsystem) that contains both generators and power loads:

(3.1) Simulation system power flow distribution. First of all, in order to ensure the power balance in the area, for the island with more power generation than electricity consumption, the output of each unit is reduced proportionally according to the output size of each unit; for the island with power consumption greater than power generation, it is increased proportionally according to the rotating reserve of each unit If the output of each unit is insufficient, it is necessary to reduce the load level of each power consumption proportionally on the basis of full power of all units. Carry out power flow calculation according to the adjusted power generation and load, and judge whether there is branch overload, then there is no entry (4), if there is branch overload, enter (3.2);

(3.2) Cascading failure judgment. If the dispatch center is attacked by the network, loses the ability to sense and control the operating state, and cannot handle the overload of the branch, all overloaded branches will trip and enter (3.3). If the dispatch center is not attacked by the network, it has the ability to sense and control the operating state If the branch overload can be handled, the dispatching center will re-dispatch the power generation according to the strategy to minimize the load loss of the island and take corresponding load reduction measures to eliminate the branch overload, and then enter (4);

(3.3) System topology analysis. Through topology analysis, it is obtained that the power island is further delisted into several new disconnected power islands (subsystems) due to cascading failures, as well as the power supply, network and load conditions of each new power island;

(4) Determine whether each power island (subsystem) that includes both the generator set and the power load has been calculated, and if so, enter (5), otherwise return to (3), and analyze and calculate the remaining power island;

(5) Simulate the steps of system power flow distribution, cascading failure judgment, and system topology analysis for each new power island (subsystem) that includes both generator sets and power loads, until no cascading failure occurs (no new power island);

(6) Judging whether each new power island (subsystem) containing both the generator set and the power load has been calculated, if so, enter (7), otherwise return to (5), and analyze and calculate the remaining new power island;

(7) Statistical load loss.

According to this method, the load loss of each power island can be obtained, and the sum of the load loss of each electrical island is the damage effect under this attack mode, and the total load loss is used as the power system vulnerability assessment index.

The present disclosure considers the mutual influence of the information system and the physical system, takes the function of the power dispatch center as the starting point, and conducts an integrated modeling analysis of the information system and the physical system. Consider the cyber-physical joint attack launched by terrorists on the power system: the power system has suffered a physical attack, that is, some primary equipment of the power system is physically damaged and out of operation. At the same time, the power dispatching center may have suffered an information attack. If it is attacked by information, the function of the dispatching center will fail, and it cannot optimize the adjustment and control of the generator output and load of each node of the power grid; if it is not attacked by information, the dispatching center can work normally. , the power grid can be optimized and adjusted by starting the standby unit, rescheduling the power of the generator, and reducing the load of the non-important load. The goal is to minimize the loss of load in the entire network. On the basis of the topology analysis algorithm, a vulnerability analysis method based on DC power flow is proposed, and the dynamic process of power system accident evolution is quantitatively simulated and analyzed. , the components that cause the most load loss after being attacked are the vulnerable components of the power grid, which need to be protected. The present disclosure finds out the vulnerable components of the power grid by establishing an analysis model of the vulnerability of the power grid, so as to take effective protection measures to reduce the loss of the power system from being attacked. The model constructed is a mixed integer nonlinear programming problem. The IEEE RTS-24 node test system is used to verify the proposed algorithm. The example analysis shows the feasibility and effectiveness of the proposed problem and its model.

The purpose of the present disclosure is to construct an integrated model of a power cyber-physical system, and based on the DC power flow equation, taking into account the constraints of the actual power system topology, improve and form a vulnerability analysis method oriented to the power system transmission network.

The purpose of this disclosure is achieved by the following technical solutions:

Availability of power dispatch control center

First define the availability variable of the power dispatch center:

In formula (1), η represents the availability of the dispatch control center, which is a 0-1 variable. A value of 1 means that the dispatch center is working normally, and a value of 0 means that the dispatch center is out of function.

objective function

The planning problem takes primary equipment such as generator sets, power lines, nodes and substations in the power system as the destruction targets, and the decision variables are the output and load levels of the generator sets at each node under the control of the dispatch center (if the node is controllable), The objective function is to minimize the total loss of load in the system:

In formula (2): P _G , P _L are the system decision variables controlled by the system operator, which are the vector expressions of the active power output of the node generator and the node load level respectively, and their dimension is equal to the total number of nodes in the power grid. ΔP _Li is the amount of active power loss of load i.

Restrictions

After the power grid components are physically damaged, considering that the action of the relay protection equipment makes the damaged components out of operation, the constraints on the change of the power system network topology are as follows:

In formula (3), δ ^Gen , δ ^Line , δ ^Bus , and δ ^Sub are the vector expressions representing the functional states of each generator set, transmission line, node, and substation in the power system, respectively. The vector dimension is related to the generator set, The number of transmission lines, nodes and substations is the same, and its elements are 0 or 1. 1 corresponds to the power element being hit and the function fails, and 0 corresponds to the power element that is not hit and functions normally. is the jth element in the vector δ ^Gen , that is, the functional state of the generator set j, which is a 0-1 variable; is the l-th element in the vector δ ^Line , that is, the functional state of the transmission line l, and is a 0-1 variable; is the nth element in the vector δ ^Bus , that is, the functional state of node n, which is a 0-1 variable; is the s-th element in the vector δ ^Sub , that is, the functional state of the substation s, which is a 0-1 variable.

In formulas (4) and (5), Y and H are respectively the vector expression forms that characterize whether the power lines and generator sets are available under the influence of the topological structure of the power system. The vector dimension is the same as the number of power lines and generator sets. 1 or 0, 0 corresponds to the power element unavailable, and 1 corresponds to the power element available. The meaning of formula (4) is that the power line l will be unavailable when the following conditions occur: that is, the power line l is hit and the function fails, the first/end node of the power line l is hit and the function fails, and the power line l is connected to the power line l. The substation is hit and the function fails, and if the power line l is one of the multi-circuit lines on the same pole, for physical damage, the multi-circuit lines on the same pole will generally be out of operation at the same time. For program analysis, that is If one circuit l' of the multi-circuit lines on the same pole fails, the power line l on the same pole also fails. Y _l is the available state of power line l, and are the functional states of the first and last nodes connected by the power line l, both are 0-1 variables; is the set of all power lines connected to substation s, means all substations s connected to power line l; is a set composed of other power lines running in parallel with the power line l on the same pole, For all power lines l' running in parallel with the same pole of the power line. The meaning of formula (5) is that the generator set j will be unavailable when the following conditions occur: that is, the generator set j is hit and the function fails, or the node connected to the generator set j is hit and the function fails, where H _j is the availability status of genset j, is the functional state of the node connected to the generator set j, both are 0-1 variables.

In addition to the above topology constraints, the constraints also include equation constraints: DC power flow equation constraints, branch power flow equation constraints, power balance constraints; inequality constraints: branch power flow safety constraints, generator output constraints and load active power changes constraint.

P _G -P _L =Bθ (6)

Equation (6) is the DC power flow equation, where _PG is the active power vector injected by the generator at each node, _PL is the active power vector of each node load, B is the DC power flow susceptance matrix, and θ is the node phase angle vector.

Equation (7) is the equation constraint of the active power flow of the transmission branch, where P _l is the active power flow of the transmission branch l, x _l is the reactance of the transmission branch l, A _ln is the element in the line-node correlation matrix, θ _n is the phase angle of node n, N is the set of system nodes, and D is the set of power lines.

Equation (8) is the power balance equation, where P _Gj is the active power output of generator j, ΔP _Gj is the active power regulation amount of generator j under the control of the dispatch center, and G _n is the set of all generators on node n in the system ; P _Li is the active power of load i, ΔP _Li is the active power loss of load i, and L _n is the set of all loads on node n in the system.

Equation (9) is the upper and lower limit constraints of the transmission branch l power, is the upper limit of the active power transmission value of the transmission branch l.

Equation (10) is the upper and lower limit constraints of the active power output of generator j, are the upper and lower limits of the active power output of generator j, respectively.

Equation (11) is the active power loss constraint of load i, and L is the set of all loads in the system.

Specifically, the calculation example of IEEE RTS-24 node system

Figure 2 shows the IEEE RTS-24 node test system, which includes 10 nodes with generator sets (32 generators); 17 nodes with loads; 38 branches; branches 3-24 are substations The tie transformers and branches 9-11, 9-12, 10-11 and 10-12 of Substation 1 are the tie transformers of Substation 2.

Table 1 presents the IEEE RTS-24 node system generator set data.

Table 1 IEEE RTS-24 node system generator set data

Table 2 gives the data of the branch reactance and transmission power limit of the IEEE RTS-24 node system.

Table 2 IEEE RTS-24 node system branch reactance and transmission power limits

Table 3 presents the IEEE RTS-24 node system load data.

Table 3 IEEE RTS-24 node system load data

According to the above given parameters, the algorithm proposed in this embodiment is used to calculate the IEEE RTS-24 test system.

Table 4 shows the load loss of the power grid under each damage scheme and the proportion of the total load (the total load is 2850MW).

Table 4 Calculation results of vulnerability of IEEE RTS-24 node system to cyber-physical joint attack

Table 4 shows that when the power grid loss ratio reaches more than 70%, nodes 13, 15 and 18 all appear as attack targets and are vulnerable nodes of the power grid; lines 12-23 and double-circuit lines 20-23 on the same pole almost appear in Among all the destruction schemes, lines 7-8 and 16-17 also appeared more frequently, which are vulnerable branches of the power grid. No matter which attack scheme is aimed at, the vulnerable nodes and branches of the power grid are basically unchanged. Through the above analysis, the security protection of these nodes and branches should be strengthened to reduce the loss when the power grid is attacked.

Table 5 shows the comparison results of the load loss of the power grid under only physical attack and simultaneous cyber-physical attack. If the power grid is only physically attacked, the dispatch center functions normally and can optimally control the power grid with the least amount of lost load. Select attack plan 2 and attack plan 5 in Table 1, and compare the load loss when the dispatch center is available and the dispatch center is unavailable.

Table 5 Comparison of the load loss of only physical attack and simultaneous cyber-physical attack

Table 5 shows that for the same attack scheme, the load loss of the power grid is significantly reduced under the optimal regulation of the dispatching center, so the dispatching control center is also a target that needs to be protected. In the process of power supply recovery, the dispatch center should be guaranteed to resume normal work first, in order to minimize losses.

To sum up, based on the background of the current high integration of cyber-physics in the current power system, on the basis of the conventional DC power flow model, and taking into account the constraints of the actual topology structure of the power system, the present invention proposes a vulnerability analysis model for the power system to be attacked by cyber-physical joint attacks. This kind of attack problem is described as a mixed integer nonlinear programming problem, and the loss of load is used as the evaluation index of the accident consequences to analyze the vulnerability of the power system. By applying the model of the invention, analyzing and comparing different attack schemes, the vulnerable nodes and branches in the power system can be effectively excavated, so as to take corresponding protective measures, reduce the risk and loss of the power system being attacked, and improve the operation security of the power system . Since the influence of the actual topology structure of the power system is considered, the algorithm is more in line with the operating conditions of the system, the calculation results are more accurate, and the practicability is better. Through the example analysis of the IEEERTS-24 node test system, it is shown that the algorithm is practical and effective for the vulnerability analysis and calculation of the power system transmission network.

The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the protection scope of this application.

Although the specific embodiments of the present disclosure have been described above in conjunction with the accompanying drawings, they do not limit the protection scope of the present disclosure. Those skilled in the art should understand that on the basis of the technical solutions of the present disclosure, those skilled in the art do not need to pay creative efforts. Various modifications or variations that can be made are still within the protection scope of the present disclosure.

Claims (10)

1. A power system vulnerability analysis method considering cyber-physical joint attack is characterized in that: comprise the following steps: (1) Set the state of each power grid element that is out of operation after being destroyed; (2) Carry out topology analysis to obtain the number of disconnected power islands after the power grid is attacked, as well as the power supply, network and load conditions of each power island; (3) Elimination of branch overload for each power island containing both generator and power load; (4) Continue to analyze the topology to obtain the number of new power islands that are not connected to each other due to cascading failures, and repeat steps (3) for the power supply, network and load conditions of each new power island. ) until no cascading failure occurs; (5) Judging whether each new power island that includes both the generator set and the power load has been calculated, if so, count the load loss, otherwise return to (4) to analyze and calculate the remaining new power island; (6) Taking the loss of load in the case of load loss as the evaluation index of the accident consequences after the power system is attacked by cyber-physical joint attacks, the component that causes the most loss of load after being attacked is the vulnerable component of the power grid. 2. A power system vulnerability analysis method considering cyber-physical joint attack as claimed in claim 1, characterized in that: in the step (1), taking the function of the power dispatch center as the entry point, the information system and the Integrated modeling and analysis of physical systems. 3. A power system vulnerability analysis method considering cyber-physical joint attack as claimed in claim 1, characterized in that: in the step (3), it specifically comprises: simulating the power flow distribution of the system, specifically, for power generation For islands that are larger than electricity consumption, the output of each unit will be reduced proportionally according to the output of each unit; for islands that consume more electricity than power generation, the output of each unit will be increased proportionally according to the spinning reserve of each unit. If the spinning reserve is insufficient, Then, on the basis of full power generation of all units, the load level of each power consumption will be proportionally reduced accordingly, and if there is branch overload, cascading failure will be judged. 4. a kind of power system vulnerability analysis method considering cyber-physical joint attack as claimed in claim 3, is characterized in that: in described step (3), the concrete process of cascading failure judgment comprises if dispatch center is attacked by network, If the operation status perception and control ability is lost, and the branch overload cannot be handled, all overloaded branches will be tripped, and the system topology analysis will be carried out; The center conducts power generation rescheduling and corresponding load shedding measures to eliminate branch overload according to the strategy to minimize the load loss of the island. 5. a kind of power system vulnerability analysis method considering cyber-physical joint attack as claimed in claim 4 is characterized in that: in described step (3), in system topology analysis, through topology analysis, it is concluded that this power island is due to chain-linking The fault is further declassified into the number of new disconnected power islands, and the power, network and load conditions of each new power island. 6. A power system vulnerability analysis method considering cyber-physical joint attack as claimed in claim 5, characterized in that: in the step (3), a primary device in the power system is used as the destruction target, and the decision variable is The output and load level of the generator sets at each node under the control of the dispatch center, and the objective function is to minimize the total loss of load in the system. 7. A power system vulnerability analysis method considering cyber-physical joint attack as claimed in claim 1, characterized in that: in the step (3), the constraints of the objective function include: when the following conditions occur, all It will cause the power line l to be unavailable: the vector of the functional state of each generator set, transmission line, node, and substation in the power system is 0-1. Among them, the vector of the functional state is 1, which corresponds to the power element being hit and the function fails. The vector of the functional state is 0, which corresponds to the normal function of the power element without being hit. 8. A power system vulnerability analysis method considering cyber-physical joint attack as claimed in claim 7, characterized in that: in the step (3), the constraints of the objective function include: power line 1 is hit The function failure, the first/end node of the power line 1 is hit and the function fails, the substation connected to the power line 1 is hit and the function fails, and a fault in the multi-circuit line on the same pole Line l is also faulty; Or, in the step (3), the constraints of the objective function include: when the following conditions occur, the generator set j will be unavailable: the generator set j is hit and the function fails or the node connected to the generator set j is affected. The function fails due to the blow. 9. A power system vulnerability analysis method considering cyber-physical joint attack as claimed in claim 8, characterized in that: in the step (3), the constraint condition of the objective function further comprises a DC power flow equation constraint, Branch power flow equation constraints, power balance constraints; inequality constraints: branch power flow safety constraints, generator output constraints and load active power change constraints. 10. A power system vulnerability analysis system considering cyber-physical joint attacks, characterized in that it runs on a processor or a memory and is configured to execute the following instructions: (1) Set the state of each power grid element that is out of operation after being destroyed; (2) Carry out topology analysis to obtain the number of disconnected power islands after the power grid is attacked, as well as the power supply, network and load conditions of each power island; (3) Elimination of branch overload for each power island containing both generator and power load; (4) Continue to analyze the topology to obtain the number of new power islands that are not connected to each other due to cascading failures, and repeat steps (3) for the power supply, network and load conditions of each new power island. ) until no cascading failure occurs; (5) Judging whether each new power island that includes both the generator set and the power load has been calculated, if so, count the load loss, otherwise return to (4) to analyze and calculate the remaining new power island; (6) Taking the loss of load in the case of load loss as the evaluation index of the accident consequences after the power system is attacked by cyber-physical joint attacks, the component that causes the most loss of load after being attacked is the vulnerable component of the power grid.