Reliability Assessment Of Cyber-Physical Power System Based On Stochastic Flow Network

Since the smart grid was proposed,with the gradual penetration of advanced monitoring,sensing,control,computing and communication technologies,modern power system has gradually become a Cyber-physical Power System(CPPS)in which bidirectional flow of information and energy dominated by information systems.The power information system under CPPS framework provides a strong backing for the safe operation of power system.However,at the same time,phenomena such as the congestion,delay,and packet loss of communication network also bring new potential risks to CPPS.It is difficult to quantify the impact of information system on physical system in CPPS by traditional power system reliability theory.If it is directly used to evaluate CPPS reliability,the result will be either too optimistic or too pessimistic.Therefore,exploring the interaction between information system and physical system in CPPS and building an information-physical integrated CPPS reliability model are of great significance to the construction and planning of future smart grids.This thesis focuses on the reliability assessment of CPPS under the dominance of information systems,and is committed to the integration of stochastic flow network theory and power system reliability theory to form an information-physical integrated reliability assessment method.Firstly,the classical stochastic flow network is applied to the information side of the generation and transmission CPS.Based on the idea of information flow,the capacity multi-state Markov model of information components was established,and a stochastic flow network model for information systems was formed.Then,considering the problem that the control center may not be able to obtain the global data under the constraint of the information equipment capacity,the stochastic flow network model on the information side and the reliability model on the physical side are bridged by using the receiving rate of the information sink node under the stochastic flow network model as the index to quantify the observability of the physical system.In this thesis,the reliability assessment scheme of generation and transmission CPS with information equipment capacity as the main constraint is constructed,and the influence of network traffic fluctuation and information equipment capacity on generation and transmission CPS is discussed.Secondly,aiming at the transmission characteristics in the communication process of power information system,an improved stochastic flow network is proposed,which extends the single attribute finite discrete state of nodes in the network to the multi-attribute infinite continuous state.That makes it more suitable for the modeling of packet loss,delay and error characteristics in the process of data transmission.In addition,the transmission characteristic matrix is used to describe the improved stochastic flow network,and the path search method of the stochastic flow network based on the transmission characteristic matrix is given,and the communication availability between nodes is proposed as an index to measure the reliability of the improved stochastic flow network.Therefore,it provides a reliability modeling idea covering the communication transmission characteristics for the information side of CPPS,and also provides a quantitative index for the transmission failure of the information side of CPPS.Finally,considering the role of distribution automation system in the process of power distribution CPS fault handling,an improved stochastic flow network model of information side of distribution CPS is established.Then,in the fault handling process,starting from the control logic of the intelligent terminal,the state change process of the physical system of the distribution CPS under the fault of the information system is analyzed.Based on this,the stochastic flow network model of the information system is embedded into the reliability model of distribution network with the coupling point of the communication availability between the intelligent terminal and the control center.In this way,a distribution CPS reliability assessment scheme combining the analytic method and the simulation method is formed.Combined with an example,this thesis analyzes the reliability change of distribution CPS in the presence of information system failure and the improvement effect of two remote terminals and three remote terminals on the reliability of distribution network,and verifies the feasibility of the model and the necessity of considering the role of information system in the reliability assessment of CPPS.