CN115801546B - Power distribution network information physical system reliability assessment method considering information disturbance - Google Patents
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Abstract
The invention discloses a reliability evaluation method of a power distribution network information physical system considering information disturbance, which comprises the following steps: s1, establishing a CPS reliability model of a power distribution network; s2, solving a corresponding incidence matrix in the reliability model; s3, solving a minimum cut set of the information physical system of the power distribution network by the incidence matrix: s4, calculating the reliability index of the information physical system of the power distribution network. The invention considers the complexity of the CPS of the distribution network in structure and characteristics, and performs reliability modeling on the system by adopting a mode of combining a fault tree and a Petri network when a reliability model is established, thereby realizing the unification of a physical system and an information system during modeling; the modeling advantages of the fault tree can be fully exerted by combining two modes with modeling, the solving efficiency and accuracy of the system reliability are greatly improved, and the reliability index calculation can be carried out on the system with the changed topological structure only by partially modifying the incidence matrix of the Petri network diagram. Therefore, the method is suitable for popularization and application.
Description
Technical Field
The invention belongs to the technical field of reliability evaluation of power distribution networks, and particularly relates to a reliability evaluation method of a power distribution network information physical system considering information disturbance.
Background
With the wide application of information technology, traditional distribution networks are gradually developed into information physical systems with highly integrated information physical systems. The physical system provides energy support for the information system, and the information system provides 3C (Communication, control) technical support for the physical system, so that cooperative interaction between information flow and energy flow is realized. However, the highly information system-dependent nature of the physical systems in the CPS of a power distribution network, compared to conventional reliability evaluations of the power distribution network, poses a number of new challenges in reliability evaluation of the system. On one hand, the interaction mechanism of information physics is more fuzzy, the complexity of CPS analysis of the power distribution network is obviously increased, on the other hand, the information physics infrastructure is highly dependent, and information attack and the failure of the information system can bring potential negative influence to the reliability of CPS operation of the power distribution network. In recent years, malicious network attack events occur continuously, and the running state of the system is influenced, so that the urban economy and the stable social development are influenced. The reason for the significant loss is that the system state change is not judged in time and reasonable measures are taken. The external security threat of the network system is mainly network attack, and the internal threat is mainly network element failure. Therefore, analysis of the influence of various information disturbances such as external threats and internal threats on the CPS reliability of the power distribution network is urgently needed. Because the reliability research of the power distribution network is mature, the focus of the CPS reliability analysis of the power distribution network is to define the coupling mechanism of a physical system and an information system, consider how to evaluate the reliability of the system after the influence of information disturbance on the state of the system, and update the related evaluation method and reliability index.
Although related researches considering information disturbance are gradually in depth at present, most of the conventional power distribution network reliability evaluation methods are still used, and the influence of the information disturbance on the system reliability is not reflected on indexes. The indexes adopted for evaluating the reliability of the CPS of the power distribution network also mostly keep using the reliability indexes of the traditional power distribution network, so the related research has the following defects: on one hand, as the research on the physical interaction of the information is continuously in depth, the results generated by the information faults are refined, so that the influence of the information disturbance on the system state is required to be reflected in the index, and the influence on the system reliability is reflected, and therefore, the evaluation range of the original index is required to be properly expanded; on the other hand, from the point of information physical fusion, the reliability index capable of comprehensively and quantitatively evaluating the reliability of an information physical system is lacking, and the influence of information disturbance on the system cannot be scientifically measured. From the point of information physical fusion, the limitation of the reliability evaluation index of the traditional power distribution network is broken through.
Meanwhile, in the aspect of reliability modeling, as the system scale is continuously expanded, a method for modeling by singly adopting a fault tree is adopted, analysis is more complicated during modeling, the problem of state combination space explosion easily occurs in solving, and calculation is too complicated when a minimum cut set is directly solved by the fault tree; in the aspect of reliability evaluation, when an analog method is adopted to evaluate the reliability of the model, the reliability is closely related to the number of samples selected during sampling, the simulation time is too long, and the requirement of online evaluation is difficult to meet; in the aspect of reliability evaluation indexes, most of the existing indexes are difficult to meet the reliability evaluation requirements of an information physical system by using the reliability evaluation indexes of the traditional power distribution network, and the influence of information disturbance on the system reliability is not reflected on the indexes. The reliability index capable of carrying out comprehensive quantitative evaluation on the reliability of the information physical system is lacking.
Disclosure of Invention
The invention aims to provide a reliability evaluation method of a power distribution network information physical system considering information disturbance, aiming at the influence of various information disturbance on the system state and the reliability, a generalized power distribution network CPS reliability evaluation index considering the information disturbance is defined, and the system reliability under the influence of the information disturbance can be accurately evaluated.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
a reliability evaluation method of a power distribution network information physical system considering information disturbance comprises the following steps:
s1, establishing a CPS reliability model of a power distribution network:
s1.1, determining a fault top event according to the topological structure and the coupling relation of the information physical system of the power distribution network;
s1.2, analyzing a load fault reason, establishing a load fault tree model and simplifying the model;
s1.3, carrying out qualitative analysis on the load fault tree model, and converting the load fault tree model into a corresponding Petri net model;
s2, solving a corresponding incidence matrix in the reliability model:
s2.1, obtaining an input matrix and an output matrix of a Petri network model according to a Petri network structure;
s2.2, solving an incidence matrix according to the input matrix and the output matrix;
s3, solving a minimum cut set of the information physical system of the power distribution network by the incidence matrix:
s3.1, searching an event top library and an input event;
s3.2, judging whether the event is an intermediate warehouse, if not, the warehouse is a bottom warehouse, and if so, returning to the step S3.1;
s3.3, expanding all the bottom libraries to obtain a cut set and simplifying the cut set into a minimum cut set;
s4, calculating the reliability index of the information physical system of the power distribution network:
s4.1, solving the occurrence probability of the fault roof event according to the minimum cut set;
s4.2, solving the probability that each load point is in a network attack state;
s4.3, calculating the annual failure rate and annual average power failure time of each load point, and obtaining each reliability index based on the annual failure rate and annual average power failure time;
and S4.4, calculating each reliability index of the generalized power distribution network information physical system considering information disturbance, and evaluating the reliability of the system.
Further, in step S2.2, a four-tuple matrix is defined based on the Petri net model:
wherein ,
for the collection of the library, +.>
Representing faults of lines, transformers, switching elements, servers, switches and IEDs in the fault tree;
For the set of transitions, +.>
Representing a fault transfer process in the fault tree;
The directional arc is a set of an input function and an output function and represents the transmission direction of a fault;
An initial token for the system;
representing the Petri net model as onenRow of linesmColumn matrix:
A=
wherein ,
in the formula ,
is an element of the output matrix of the Petri net, < >>
Is an element of an input matrix of a Petri net, the matrixANamely quaternary matrix->
Is used for the correlation matrix of the (a).
Further, in step S4.1, the probability of occurrence of the fault roof event is determined by using the probability of occurrence of the minimum cut set, and the mathematical expression is:
in the formula ,P(T) For fault top eventsTThe probability of the occurrence of this is,
for the smallest cutset, +.>
、
Is->
、f、eProbability of occurrence of individual cutsets;mis the maximum value of the minimum cutset number.
Further, in step S4.2, the calculation method of the probability that the load point is in the network attack state is as follows:
assuming a certain load pointlThe minimal cut of faults has the numbers of switches, IED devices and servers respectivelya、bAndcthe load point is in the network attack state probabilityp l The method comprises the following steps:
P l =1-
wherein: the probability of the load point in the normal operation state is (1-p l ) 。
Further, in step S4.3, each reliability index obtained includes:
1) Average power failure frequency index of generalized system
: reflecting the frequency of load shedding due to control failure caused directly by physical element failure or by information disturbance, the index is defined as:
in the formula ：
representing the number of load points;
Indicate->
The number of users at each load point;
Representing the number of load point cuts directly caused by physical element faults;
Indicating the number of load point reduction times caused by control failure due to the failure of the information element;
Representing the number of load point cuts due to control failure caused by network attack IED;
2) Average power outage duration index for generalized system
: an annual average duration reflecting load shedding of the system due to control failure caused directly by physical component failure or by information disturbance, the index being defined as:
in the formula ：
the annual power failure time of a load point caused by the fault of a physical element is represented;
The annual power failure time of the load point caused by the control failure due to the failure of the information element is represented;
Representing the annual blackout time of a load point caused by control failure due to network attack of the IED;
3) Generalized power shortage expectancy
Reflecting the expected power shortage amount of the system caused by the control failure caused by the physical element failure or caused by the information disturbance, wherein the index is defined as;
in the formula ：
representing the expected value of the defective power supply amount directly caused by the physical element failure;
Representing a desired value of the defective power supply amount caused by the control failure due to the failure of the information element itself;
Representing a desired value of a shortage of power due to a control failure caused by a network attack IED;
4) Generalized power availability index
Reflecting the ratio of the number of uninterrupted power supply hours of the user to the total power supply time required by the user in the system, and determining the indexThe meaning is as follows:
compared with the prior art, the invention has the following beneficial effects:
(1) The invention considers the complexity of the CPS of the distribution network in structure and characteristics, and performs reliability modeling on the system by adopting a mode of combining a fault tree and a Petri network when a reliability model is established, thereby realizing the unification of a physical system and an information system during modeling; the modeling advantages of the fault tree can be fully exerted by combining two modes with modeling, the solving efficiency and accuracy of the system reliability are greatly improved, and the time is saved; using the reachability of the Petri net, it can be determined whether the system is likely to be running to a specified state in a given initial state; the reliability index calculation can be carried out on the system with the changed topological structure only by partially modifying the incidence matrix of the Petri network diagram. The reliability evaluation index of the generalized power distribution network information physical system considering information interference is defined, and the system reliability can be more accurately described.
(2) Aiming at the influence of various information disturbance on the system state and reliability, the invention defines the CPS reliability evaluation index of the generalized distribution network considering the information disturbance, and can accurately evaluate the system reliability under the influence of the information disturbance.
(3) The reliability of the system is evaluated by adopting an analytic method, the correlation matrix of the system is written according to the reliability model of the system, the minimum cut set is obtained by the correlation matrix, and the reliability index of the system is obtained according to the minimum cut set, so that the accurate calculation of the reliability index is realized.
Drawings
Fig. 1 is a schematic diagram of a conventional CPS structure of a power distribution network.
Fig. 2 is a schematic diagram of an IED model of an information-physical interface in the prior art.
FIG. 3 is a block diagram of a reliability evaluation method according to the present invention.
FIG. 4 is a schematic diagram of a fault tree analysis step in the present invention.
Fig. 5 is a schematic diagram of an exemplary power distribution system according to the present invention.
FIG. 6 is a fault tree of load point B in an embodiment of the present invention.
FIG. 7 is a Petri net representation of a logical AND, OR, NOT in an embodiment of the present invention, where (a) logical AND (b) logical OR (c) logical NOT.
Fig. 8 is a diagram of a load point B fault Petri net in an embodiment of the present invention.
FIG. 9 is the initial values assigned to the L2 library in the present invention-embodiment.
Fig. 10 is a graph showing the operation result of the fault of L2 in the embodiment of the present invention.
Fig. 11 is a schematic structural diagram of a CPS system for power distribution network in an embodiment of the invention.
Fig. 12 is a topology of an information system in an embodiment of the present invention.
FIG. 13 is a graph showing the variation trend of average outage frequency of the system at different failure rates according to the embodiment of the present invention.
Fig. 14 shows reliability indexes under different attack targets in the embodiment of the present invention.
FIG. 15 illustrates an attack on an IED pair in an embodiment of the inventionG SAIDI Is used to influence the histogram.
FIG. 16 illustrates an attack on an IED pair in an embodiment of the inventionG EENS Is used to influence the histogram.
FIG. 17 is a diagram of an attack on two IED pairs in an embodiment of the inventionG SAIDI Is used to influence the histogram.
FIG. 18 illustrates an attack on two IED pairs in an embodiment of the inventionG EENS Is used to influence the histogram.
Fig. 19 is a schematic view of an access network structure in an embodiment of the present invention.
Fig. 20 is a graph of reliability index for different access network structures in accordance with an embodiment of the present invention.
Fig. 21 is a fault tree model of load point 1 in the present embodiment.
FIG. 22 is a diagram of a Petri net model of load point 1 failure in an embodiment of the present invention.
Detailed Description
The invention will be further illustrated by the following description and examples, which include but are not limited to the following examples.
The invention discloses a reliability evaluation method of a power distribution network information physical system considering information disturbance, which is mainly used for breaking through the limitation of the reliability evaluation index of the traditional power distribution network from the angle of information physical fusion. In a CPS of a power distribution network, a physical system mainly comprises traditional elements such as overhead lines, isolating switches, transformers and the like, and provides energy support for an information system; the information system mainly comprises a server, a switch, intelligent terminal equipment (Intelligent Electronic Device, IED) and other elements, and monitors, controls and protects the physical system. The structure of the power distribution network CPS is shown in FIG. 1. An information physical system is a combination of a physical layer, a communication layer, and a decision layer. The physical layer is composed of conventional power system equipment required for power generation, transmission and distribution. While the introduction of sensors and communication networks further increases the possibilities for reliable and efficient operation of the power system, the communication layer enables real-time decisions to be made using real-time data from the physical layer.
The schematic diagram of the IED model is shown in fig. 2, where the IED is an interface device for connecting an information system and a physical system, and is composed of a fault monitoring unit, a relay protection unit, and a control unit. The function of the IED is to monitor and collect the real-time state of the power grid and transmit the real-time state to the total station server through the communication network, the total station server performs decision scheduling according to the collected data, processes various accidents and sends control signals to the IED equipment, and at the moment, the IED transmits instructions to the primary equipment through various interactions, so that the power distribution network physical system and the information system are effectively coupled.
The CPS reliability evaluation method of the power distribution network is shown in figure 3. Modeling by adopting a mode of combining a fault tree and a Petri network in modeling; the influence of information disturbance on the system state is considered, and a reliability index is defined; and in the reliability evaluation, evaluating by adopting a mode of solving a minimum cut set in an analytic method.
In the aspect of CPS reliability modeling of a power distribution network, as the causal relationship of a fault tree model is clear and vivid, comprehensive and concise description can be made on various reasons and logic relationships causing accidents, so that the reasons of load faults in a system can be clearly and accurately analyzed, but for a complex system, the steps of compiling the fault tree are more, the compiled fault tree is also more huge, in addition, the calculation is more complex, and the qualitative and quantitative analysis is difficult; and, the fault tree model is a static analysis model, and the dynamic process of the reliability of the inspected system cannot be researched. The Petri network has the main advantages of being capable of processing the practical phenomena which are difficult to solve by common methods, such as concurrency, synchronization, asynchronization, parallelism, nondeterminacy and the like. It has a simple, well-defined syntax and semantics that enable the description of different levels of abstraction of a system. Using the reachability of the Petri net, it can be determined whether the system is likely to be running to a specified state in a given initial state, and the fault tree can be conveniently represented by the Petri net. Therefore, the invention adopts a mode of combining fault trees and Petri networks to model the system when the reliability of the system is modeled.
The fault tree is a logic diagram that describes event causal relationships by event symbols, transition symbols, and logic gate symbols. The fault tree analysis mainly analyzes the reasons of faults of all elements in the CPS of the power distribution network, so that all combination modes of the reasons of the faults and an analysis method of occurrence probability are determined. The steps of the fault tree analysis are shown in fig. 4.
The invention constructs fault tree as follows: firstly, determining a fault roof event, namely the least hope of the system; analyzing all possible reasons for the fault roof event, analyzing the logic relation among the reasons and connecting the reasons by using a logic gate; then analyzing whether the input event directly connected with the fault top event can be further decomposed, if so, decomposing the input event as the input event of the next stage event until all the input events can not be further decomposed, and the event which can not be decomposed any more is the bottom event.
A typical distribution system is shown in fig. 5, and is a typical radial distribution system, and is composed of two feeder lines, three main lines L1, L2 and L3, and three branch lines L4, L5 and L6. The trunk lines are separated by isolating switches, and T is a tie switch.
If the fault roof event is a load point B fault, possible reasons for the fault roof event are as follows: the main line L2 fails, the branch line L5 fails, and the disconnector is opened. Since the failure of the main line L1 and the main line L3 is a cause of the disconnection of the disconnector, and only one of all possible causes occurs, the load point B must be faulty. The load point B fault tree is shown in fig. 6 without regard to breaker and tie switch input failure.
L2 and L5 in the figure represent the failure of the trunk line L2 and the branch line L5, respectively; l1 and L3 represent the opening of the disconnector due to the main lines L1 and L3, respectively. Fig. 6 clearly shows all possible causes of the load B failure in the exemplary radial power distribution system of fig. 4. The Petri net model of the system can be obtained through analysis of the fault tree, and a series of reliability indexes can be solved.
While the network structure of the Petri network is static, the Petri network is dynamically executable in that a Token (Token) therein can flow in the network according to defined occurrence rules, and thus modeling of an information physical system having event-driven characteristics with the Petri network is possible.
The CPS reliability modeling of the power distribution network is carried out by adopting a mode of combining a fault tree and a Petri network, the fault tree model is converted into the Petri network model, and a four-element matrix is defined based on the Petri network model:
wherein ,
for the collection of the library, +.>
Representing faults of lines, transformers, switching elements, servers, switches and IEDs in the fault tree;
For the set of transitions, +.>
Representing a fault transfer process in the fault tree;
The directional arc is a set of an input function and an output function and represents the transmission direction of a fault;
Is the system initial token.
The fault tree is a logical relationship of fault propagation in the system and can be conveniently converted into a Petri net representation. The logical and, or, not representation of the Petri net when converted from the fault tree to the Petri net is shown in fig. 7. The transformation of the fault tree model of load B of fig. 6 into a Petri net model is shown in fig. 8 according to the logical transformation rules.
The advantages of the combination of the two modeling modes of the fault tree and the Petri net are as follows:
(1) The model is comprehensive and accurate
The modeling advantage of the fault tree can be fully exerted by combining two modes with modeling. The cause and effect relationship of the fault tree is clear and vivid, and various reasons and logic relationships causing faults can be comprehensively and simply described. Can carry out qualitative analysis, quantitative analysis and system evaluation. By using the fault analysis thought, various reasons causing faults can be comprehensively and accurately described when the reliability modeling is carried out on the CPS of the power distribution network.
(2) High solving efficiency
For an example with 5 layers and 7 bottom events, 8 steps are needed to solve the minimum cut set through the fault tree, and only 3 steps are needed to solve the minimum cut set by using the Petri network. Therefore, the method of firstly modeling by using the fault tree and converting the fault tree into the Petri net so as to solve the minimum cut set can effectively improve the solving efficiency of the system. And an information system is added to the CPS of the power distribution network on the basis of the traditional power distribution network to monitor and control the physical system, so that the system structure is more complex, and the minimum cut set calculation is very complex and consumes a great amount of time if the fault tree model is only adopted to calculate the minimum cut set of the system. Therefore, the two modes are combined, the solving efficiency and accuracy of the system reliability can be greatly improved, and the time is saved.
(3) Failure transfer process image
Using the reachability of the Petri net, it can be determined whether the system is likely to be running to a specified state at a given initial state. By utilizing the characteristic of the Petri network, the Petri network can be used for assigning an initial identifier to any library in the graph when an initial state is defined in PIPE software, and the Petri network is operated, so that the transmission process of the Token, namely the transmission process of the fault, can be clearly seen, and meanwhile, the finally arrived library, namely the result caused by the fault, can be obtained immediately, thereby providing convenience for system fault analysis and reliability calculation. The initial identifier assigned to the L2 library in the Petri network shown in FIG. 8 is shown in FIG. 9, which shows that the L2 fails at this time, the program is run at this time, the running result shown in FIG. 10 is obtained, and the failure of the load point B is displayed.
The structure of the Petri net can be represented by a matrix, so that the property of the Petri net can be analyzed by a linear algebra method. Representing the Petri net model as oneuRow of linesvColumn matrix:
A=
wherein ,
in the formula ,
for an element in the output matrix of the Petri net, < ->
For elements in the input matrix of the Petri net, the matrixANamely four-element->
Is used for the correlation matrix of the (a). The output matrix of the Petri net shown in FIG. 8 +.>
And input matrix->
The method comprises the following steps of:
according to the output matrix
And input matrix->
The association matrix corresponding to the Petri network can be obtained as follows:
in the system shown in fig. 5, the disconnecting switch DS2 is turned on (e.g., L3 fails) due to a fault, etc., the main line L3 and the load thereof are powered by the feeder line 2, when the reliability of the system is evaluated, if only the fault tree modeling is adopted, the system structure needs to be re-analyzed, and a fault tree model is built, but if the fault tree modeling is combined with the Petri network, only the output matrix and the input matrix need to be changed into:
and then solving the minimum cut set, the method can greatly save modeling time, thereby improving modeling efficiency. Particularly for a CPS of a power distribution network, the information system is added to enable the system structure to be more complex, interaction among all parts is more frequent, modeling is carried out in a mode of combining a fault tree and a Petri network, and modeling efficiency can be greatly improved, so that modeling is more accurate.
The minimum cut set analysis method mainly aims at solving a minimum cut set of load points in a network, calculates to obtain a reliability index, can reflect the minimum fault composition mode of system faults, is a necessary condition of the system faults, and can conveniently analyze the reliability of the system based on the minimum cut set. Because the Petri network has the characteristics of accessibility, bouncy and the like, various common phenomena in a complex system can be well described, and a very rich analysis method exists. The incidence matrix analysis method is suitable for a large-scale Petri network model with higher complexity. The method comprises the steps of calculating a topological relation embodied in a Petri network model based on the Petri network model, converting the topological relation into a form of an associated matrix, solving a minimum cut set by the associated matrix, and finally solving the occurrence probability of a fault top event according to the fault rate of each element in the minimum cut set, so as to solve the reliability index of the system.
The external security threat in information perturbation is mainly a network attack, which generally exploits security vulnerabilities of elements, by injecting dummy data to tamper with the original data. The internal threat is mainly the failure of the component itself. Because the failure rate of the information element is the inherent property of the element and can not be changed along with the change of external factors, the invention uses the failure rate of the information element
To indicate the success rate of the network attack of the information elementP atk To represent. Because the network attack aiming at the IED equipment has the greatest influence on the system, the invention takes the IED network attack as an example to carry out analysis and calculationOther information element network attacks compute the same IED network attacks. According to the characteristics and influences of two security threats, the system state is divided into a normal operation state and a network attack state, and the information element faults can occur at any time in both states.
Specifically, the occurrence probability of the fault roof event is determined by adopting the occurrence probability of the minimum cut set, and the mathematical expression is as follows:
in the formula ,P(T) For fault top eventsTThe probability of the occurrence of this is,
for the smallest cutset, +.>
、
Is->
、f、eProbability of occurrence of individual cutsets;mis the maximum value of the minimum cutset number.
In step S4.2, the calculation method of the probability that the load point is in the network attack state is as follows:
assuming a certain load pointlThe minimal cut of faults has the numbers of switches, IED devices and servers respectivelya、bAndcthe load point is in the network attack state probabilityp l The method comprises the following steps:
p l =1-
in the formula ：
for the probability of success of a network attack on an IED device, the negativeThe probability of the loading point in the normal operation state is (1-p l ) 。
Number of load outages caused by failure of information element
Power failure time->
And the amount of load loss->
The method comprises the following steps of:
in the formula ：
representing component failure rates of the IED device, the switch, and the server, respectively;
the annual failure time of a single IED device, a switch and a server is respectively represented;
Indicating load pointlIs a load average of (3).
Load outage times caused by network attacks
Power failure time->
And the amount of load loss->
The method comprises the following steps of: />
in the formula ：
representing the number of IED devices in the minimal cut set that are subject to network attacks.
In order to account for the influence of information disturbance on the reliability of a system, the invention takes load reduction caused by information element faults and network attacks into account on the basis of a traditional power distribution network reliability evaluation index system, defines a generalized power distribution network CPS reliability evaluation index considering information disturbance, and characterizes the change of the system reliability caused by control failure due to physical element faults and information disturbance. Average power failure frequency in load point year
(times-a) Average annual power failure time->
The obtained reliability indexes are based on indexes, and each reliability index comprises:
1) Average power failure frequency index of generalized system
: reflecting the frequency of load shedding due to control failure caused directly by physical element failure or by information disturbance, the index is defined as:
in the formula ：
representing the number of load points;
Indicate->
The number of users at each load point;
Representing the number of load point cuts directly caused by physical element faults;
Indicating the number of load point reduction times caused by control failure due to the failure of the information element;
Representing the number of load point cuts due to control failure caused by network attack IED;
2) Average power outage duration index for generalized system
: an annual average duration reflecting load shedding of the system due to control failure caused directly by physical component failure or by information disturbance, the index being defined as:
in the formula ：
the annual power failure time of a load point caused by the fault of a physical element is represented;
The annual power failure time of the load point caused by the control failure due to the failure of the information element is represented;
Representing the annual blackout time of a load point caused by control failure due to network attack of the IED;
3) Generalized power shortage expectancy
Reflecting the expected power shortage amount of the system caused by the control failure caused by the physical element failure or caused by the information disturbance, wherein the index is defined as;
in the formula ：
representing the expected value of the defective power supply amount directly caused by the physical element failure;
Representing a desired value of the defective power supply amount caused by the control failure due to the failure of the information element itself;
Representing a desired value of a shortage of power due to a control failure caused by a network attack IED;
4) Generalized power availability index
Reflecting the ratio of the number of uninterrupted power supply hours of a user to the total power supply time required by the user in the system, the index is defined as:
thus, the reliability evaluation flow proposed in the present invention can be summarized in the following four phases:
s1, establishing a CPS reliability model of a power distribution network:
s1.1, determining a fault top event according to the topological structure and the coupling relation of the information physical system of the power distribution network;
s1.2, analyzing a load fault reason, establishing a load fault tree model and simplifying the model;
s1.3, carrying out qualitative analysis on the load fault tree model, and converting the load fault tree model into a corresponding Petri net model;
s2, solving a corresponding incidence matrix in the reliability model:
s2.1, obtaining an input matrix and an output matrix of a Petri network model according to a Petri network structure;
s2.2, solving an incidence matrix according to the input matrix and the output matrix;
s3, solving a minimum cut set of the information physical system of the power distribution network by the incidence matrix:
s3.1, searching an event top library and an input event;
s3.2, judging whether the event is an intermediate warehouse, if not, the warehouse is a bottom warehouse, and if so, returning to the step S3.1;
s3.3, expanding all the bottom libraries to obtain a cut set and simplifying the cut set into a minimum cut set;
s4, calculating the reliability index of the information physical system of the power distribution network:
s4.1, solving the occurrence probability of the fault roof event according to the minimum cut set;
s4.2, solving the probability that each load point is in a network attack state;
s4.3, calculating the failure rate and the annual average power failure time of each load point, and calculating each reliability index based on the failure rate and the annual average power failure time;
and S4.4, calculating each reliability index of the generalized power distribution network information physical system considering information disturbance, and evaluating the reliability of the system.
Specifically, the present embodiment adopts the modified IEEE RBTS BUS2 system to verify the above method, as shown in fig. 11. The system is an improved CPS of the power distribution network, which is formed by configuring a corresponding information system based on an IEEE RBTS BUS2 system. The information system in this embodiment adopts a star topology, data is communicated by EPON, and an optical fiber, a control center server, a plurality of switches and IEDs for controlling each switching element are laid along a primary network frame of the power distribution network, as shown in fig. 12. The reliability parameters of the physical system are shown in tables 1-3, and the failure rate and repair time of each element in the information system are shown in table 4.
Watch (watch)
Element reliability raw data
wherein ：λ P is a permanent failure rate;rmean time to fail-over;r P for a standby replacement time;sis the switch switching time.
TABLE 2 feeder type and Length Table for RBTS-BUS2
TABLE 3 load Point user types and peak loads
TABLE 4 failure rates and repair times for elements of information systems
In order to simplify the calculation, the embodiment makes some general assumptions, and in the research, other two important systems of the power system, namely the power generation system and the power transmission system, and an initial power supply are considered to be reliable; each element is independent, and only the steady-state influence of faults is considered; the influence of other factors such as weather and the like is not considered, and only the power failure caused by equipment failure is considered; the load of the intact section can be fully transferred after the fault of the tie switch.
Taking the load point LP1 fault as an example, a fault tree as shown in fig. 21 may be established. The fault tree model shown in fig. 21 is converted into the Petri net model shown in fig. 22 according to the conversion rule between the fault tree and the Petri net model. The minimum cut set for each load point is calculated as shown in table 5.
TABLE 5 minimum cut-set for each load point
scene 1: information system effects are considered.
Scene 2: information systems are considered to be entirely reliable.
The reliability index of the two scenes is calculated separately and the result of scene 2 is compared with the result of the prior art, the calculation results are shown in table 6.
TABLE 6 reliability index result comparison
As can be seen from the calculation results of the method of the present invention of table 6,G SAIFI the deviation of (2) was 0.09%,G SAIDI the deviation of (2) was 0.07%,G EENS the deviation of (2) is 0.05%,G ASAI the deviation of (2) is 0. The calculation results are highly consistent, which proves that the method provided by the invention is reasonable and effective.
As can be seen from the results of Table 6, the system reliability index is calculated in consideration of the influence of the information systemG SAIFI 、G SAIDI 、G EENS Compared with the scene 1, the power failure frequency and the power failure time of the system and the power failure requirement of the system are increased to a certain extent after the influence of the information system is considered. The reason for this is that the uncertainty of the system increases considering the information system effect, and the information system failure also affects the reliability of the system, resulting in a decrease in the system reliability. Thus, while the information system helps to improve the efficiency of the fault management process, the resulting reliability impact should not be neglected, particularly in the case of increasingly deep coupling between future information and physical systems, which also represents a significant concern for the information system to evaluate the reliability of the distribution network.
The impact of the failure rate of the information element on the CPS reliability of the distribution network is analyzed as follows:
in order to study the degree of influence of various information elements on the reliability of the system under different failure rates, the degree of influence of single failure of an information element on the reliability of the CPS of the power distribution network is considered herein (one element is selected as an unreliable element, and other elements are considered to be completely reliable). The failure rate of each type of information element is gradually increased or decreased by a certain proportion, the failure rate of other equipment is kept unchanged, and the average value of the multiple calculation results is calculated. The system reliability index of various information elements under different failure rates can be obtained through the index changeG SAIDI As shown in fig. 13.
It can be seen that the failure rate variation of different devices has a difference in the impact on the CPS reliability of the distribution network. The magnitude of the impact of a single information element failure on CPS reliability is ordered as: IED device > switch > server. Wherein server failure changes have less impact on reliability than IEDs and switches. The main reason is that the server has enough protection measures at the present stage, so that the failure rate of the server is greatly reduced, and the reliability influence of the server interruption on the CPS of the power distribution network is not great. The main functions of the IED device are data acquisition and instruction execution, whether the IED fails or not affects the transmission performance of an information system, and the failure of the IED device directly leads to the failure of the action of elements in a physical system connected with the IED device. Therefore, reducing the failure rate of the IED has an important meaning for improving the power supply reliability, and provides a reference for system investment.
The impact of network attacks on the CPS reliability of the distribution network is analyzed as follows:
in a distribution network CPS, the potential main points of attack are servers of the control center and intelligent electronic devices connected through switches. The network attack conditions are as follows:
power distribution network normal operation, network attacker attacks IED equipment
(1) If the IED fails, network attack does not affect the reliability of the system;
(2) if an IED is attacked during normal operation, the consequences are related to the number and location of the attacked IEDs.
Power distribution network normal operation, network attacker attacks master station server
(1) If the information system is completely invalid, the master station server cannot be attacked;
(2) if a portion of the information system fails, an attacker can use the master station to control the IED;
(3) if the information system is normal, the attacked master station may cause the whole system to be paralyzed.
To analyze the impact of different network attack objects on the reliability of the system, the following three scenarios can be classified for research, and the results are shown in fig. 14.
Scene 3: the attack target is the master server.
Scene 4: the attack target is one IED.
Scene 5: the attack target is two IEDs.
As can be seen from fig. 14, the influence of the network attack object on the reliability of the system is that one IED > two IEDs > the distribution master station in order from large to small, which indicates that for the information system, a method with a higher success rate is selected to perform the network attack, which causes a larger economic loss to the system. In order to study the impact of a specific IED attack on the reliability of the system, various schemes for one IED and two IEDs to be under network attack are calculated based on the condition that the physical system is operating normally. The scheme types are shown in Table 7, and the results are shown in FIGS. 15-18.
TABLE 7 scheme partitioning of network attack IEDs
As can be seen from fig. 15 and fig. 16, the reliability index of the system rises to a different extent when an IED is attacked, compared with the reliability index under the condition that no network attack is considered, which means that the reliability of the system is reduced when an IED is attacked, and under the condition that a physical system operates normally, the fewer the number of switches on a bus where the IED control switches are located, the fewer the number of connected IEDs, and the less the influence of the IED control switches on the reliability of the system.
As can be seen from fig. 17 and 18, the reliability index of the system rises to a different extent when both IEDs are attacked than when the network attack is not considered, which means that attacking both IEDs reduces the reliability of the system, and for network attacks the longer the distance between the two IEDs in the attacked IED combination, the greater the impact on the reliability. Accordingly, a reference can be provided for defending resource investment.
The influence of the access network structure on the CPS reliability of the power distribution network is analyzed as follows:
the topology of the information system network is also an important factor affecting the reliability of the CPS of the distribution network. Therefore, the influence of various access network structures such as bus type, star type, tree type, net type and the like on the CPS reliability of the power distribution network is studied. A schematic diagram of the access network structure is shown in fig. 19. The result of the impact of different access network structures on the system reliability index is shown in fig. 20.
As can be seen from the results of FIG. 20, the net structureG SAIDI AndG EENS The index is minimum, and the reliability of the system is highest, because the system has more redundant communication lines as standby, and the reliability of the system is improved. Second, the star-shaped structureG SAIDI AndG EENS The index is slightly higher than that of the net-shaped structure, but the reliability index change amplitude is smaller compared with other structures. Therefore, a suitable access network structure needs to be selected according to the reliability requirements.
When the reliability index calculation is carried out on different access network structures, the superiority of the method for combining the fault tree and the Petri network is also reflected, the calculation can be continued only by changing the incidence matrix of the Petri network, and the reliability evaluation efficiency is greatly improved.
The above embodiment is only one of the preferred embodiments of the present invention, and should not be used to limit the scope of the present invention, but all the insubstantial modifications or color changes made in the main design concept and spirit of the present invention are still consistent with the present invention, and all the technical problems to be solved are included in the scope of the present invention.
Claims (5)
1. The reliability evaluation method of the information physical system of the power distribution network taking information disturbance into consideration is characterized by comprising the following steps of:
s1, establishing a CPS reliability model of a power distribution network:
s1.1, determining a fault top event according to the topological structure and the coupling relation of the information physical system of the power distribution network;
s1.2, analyzing a load fault reason, establishing a load fault tree model and simplifying the model;
s1.3, carrying out qualitative analysis on the load fault tree model, and converting the load fault tree model into a corresponding Petri net model;
s2, solving a corresponding incidence matrix in the reliability model:
s2.1, obtaining an input matrix and an output matrix of a Petri network model according to a Petri network structure;
s2.2, solving an incidence matrix according to the input matrix and the output matrix;
s3, solving a minimum cut set of the information physical system of the power distribution network by the incidence matrix:
s3.1, searching an event top library and an input event;
s3.2, judging whether the event is an intermediate warehouse, if not, the warehouse is a bottom warehouse, and if so, returning to the step S3.1;
s3.3, expanding all the bottom libraries to obtain a cut set and simplifying the cut set into a minimum cut set;
s4, calculating the reliability index of the information physical system of the power distribution network:
s4.1, solving the occurrence probability of the fault roof event according to the minimum cut set;
s4.2, solving the probability that each load point is in a network attack state;
s4.3, calculating the annual failure rate and annual average power failure time of each load point, and obtaining each reliability index based on the annual failure rate and annual average power failure time; wherein the reliability index comprises a generalized system average power failure frequency index reflecting the frequency of load shedding caused by control failure directly caused by physical element failure or caused by information disturbance
The method comprises the steps of carrying out a first treatment on the surface of the Reflecting that the system is caused directly by or through failure of a physical elementGeneralized system average outage duration index +_for average duration of load shedding due to control failure caused by information disturbance>
The method comprises the steps of carrying out a first treatment on the surface of the Generalized power shortage amount expectancy reflecting expected power shortage amount caused by control failure of system due to physical element failure or caused by information disturbance>
The method comprises the steps of carrying out a first treatment on the surface of the Generalized power supply availability index reflecting ratio of number of uninterrupted power supply hours of user to total power supply time required by user in system>
；
And S4.4, calculating each reliability index of the generalized power distribution network information physical system considering information disturbance, and evaluating the reliability of the system.
2. The method for evaluating reliability of a physical system of information of a power distribution network in consideration of information disturbance according to claim 1, wherein in step S2.2, a four-tuple matrix is defined based on the Petri network model:
wherein ,
for the collection of the library, +.>
Representing faults of lines, transformers, switching elements, servers, switches and IEDs in the fault tree;
For the set of transitions, +.>
Representing a fault transfer process in the fault tree;
The directional arc is a set of an input function and an output function and represents the transmission direction of a fault;
An initial token for the system;
representing the Petri net model as oneuRow of linesvColumn matrix:
A=
wherein ,
in the formula ,
for an element in the output matrix of the Petri net, < ->
For elements in the input matrix of the Petri net, the matrixANamely quaternary matrix->
Is used for the correlation matrix of the (a).
3. The method for evaluating reliability of a power distribution network information physical system considering information disturbance according to claim 2, wherein in step S4.1, the probability of occurrence of a fault top event is determined by using the probability of occurrence of a minimum cut set, and the mathematical expression is:
P(T)=P（K 1 
K 2 
K m 
=
+
+…+
in the formula ,P(T) For fault top eventsTProbability of occurrence, ++>
、
Is->
、f、eProbability of occurrence of individual cutsets;mis the maximum value of the minimum cutset number.
4. The method for evaluating reliability of a power distribution network information physical system considering information disturbance according to claim 3, wherein in step S4.2, the calculation mode of the probability that the load point is in the network attack state is as follows:
assuming a certain load pointlThe minimal cut of faults has the numbers of switches, IED devices and servers respectivelya、bAndcthe load point is in the network attack state probabilityp l The method comprises the following steps:
p l =1-
in the formula ：
for the probability of success of network attack on IED equipment, the probability of the load point in a normal operation state is (1-p l )；
Wherein the number of load outages caused by the failure of the information element
Power failure time->
And the amount of load loss->
The method comprises the following steps of:
in the formula ：
representing component failure rates of the IED device, the switch, and the server, respectively;
the annual failure time of a single IED device, a switch and a server is respectively represented;
Indicating load pointlAverage load of (2);
load outage times caused by network attacks
Power failure time->
And the amount of load loss->
The method comprises the following steps of: />
+(
in the formula ：
representing the number of IED devices in the minimal cut set that are subject to network attacks.
5. The method for evaluating the reliability of an information physical system of a power distribution network in consideration of information disturbance according to claim 4, wherein in step S4.3, each reliability index obtained includes:
1) Average power failure frequency index of generalized system
: reflecting the frequency of load shedding due to control failure caused directly by physical element failure or by information disturbance, the index is defined as:
in the formula ：
representing the number of load points;
Indicating load pointlThe number of users of (a);
Representing the number of load point cuts directly caused by physical element faults;
Indicating the number of load point reduction times caused by control failure due to the failure of the information element;
Representing the number of load point cuts due to control failure caused by network attack IED;
2) Average power outage duration index for generalized system
: reflecting the system's failure directly due to physical elementAn annual average duration of load shedding resulting in or through control failure caused by information disturbance, the index being defined as:
in the formula ：
the annual power failure time of a load point caused by the fault of a physical element is represented;
The annual power failure time of the load point caused by the control failure due to the failure of the information element is represented;
Representing the annual blackout time of a load point caused by control failure due to network attack of the IED;
3) Generalized power shortage expectancy
Reflecting the expected power shortage amount of the system caused by the control failure caused by the physical element fault or caused by the information disturbance, the index is defined as:
in the formula ：
representing the expected value of the defective power supply amount directly caused by the physical element failure;
Representing a desired value of the defective power supply amount caused by the control failure due to the failure of the information element itself;
Representing a desired value of a shortage of power due to a control failure caused by a network attack IED;
4) Generalized power availability index
Reflecting the ratio of the number of uninterrupted power supply hours of a user to the total power supply time required by the user in the system, the index is defined as:
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