Cascading Failure Modeling Of Electrical Cyber-physical System And Its Application

With the promotion of strategies of smart grid and energy internet,power system has developed into a typical cyber-physical system(CPS)composed of power network containing a large number of power equipment and information network for status monitoring of power equipment.The deep coupling with information system improves the intelligence and efficiency of power system,but it also brings a variety of cyber-security issues.The introduction of information and communication technology makes the system vulnerable to data transmission congestion and information network attack.In addition,the variable demand of users and the large-scale grid connection of distributed energy have increased the uncertainty of power grid operation.The research on cascading failure modeling of electrical CPS under the influence of various realistic factors is of great value to identify the failure evolution mechanism and enhance the robustness of the system.Some elegant mathematical frameworks based on percolation theory and network models integrating the basic physical characteristics of the system are proposed to describe the cascading failure of electrical CPS,which provides a practical idea to describe the failure evolution process and system robustness of complex electrical CPS.However,the current research on electrical CPS usually cannot fully consider the inherent physical properties and dynamic operating characteristics of the system,and often ignores the influence of some realistic factors in the system.Based on this,considering the actual physical functions and operation dynamics of the electrical CPS,we analyze the cascading failure propagation mechanism of coupled system,study the robustness of the system against cascading failure,and explore the influence mechanism of some realistic factors such as grid uncertain factors,information network virus propagation and routing strategy.The research results of this paper are summarized as follows:Considering the functional differences of network elements,interdependence between networks and specific dynamic operating characteristics,a stochastic cascading failure model for studying the cascading failure propagation of electrical CPS is proposed.The model takes into account the influence of grid uncertain factors,and makes up for the deficiency of previous work in describing the spatio-temporal characteristics of failure propagation.Considering the failure attributes of network elements,the failures of network elements are divided into deterministic topology connection failure,communication operation failure and stochastic grid operation failure.The probabilistic power flow is incorporated with a stochastic model based on extended Gillespie method to determine the failure power element and failure occurrence time,which provides a practical method for introducing uncertainty in cascading failure analysis.In addition,the effects of load uncertainty and heavy load demand on the system cascading failure are also studied.The research results reveal the internal mechanism of cascading failure propagation in electrical CPS,and demonstrate the effectiveness and applicability of the proposed model.Considering the essential differences between information network and power network in terms of network structure,physical operation and dynamic behavior,we study the robustness of electrical CPS considering the influence of system operation parameters and dynamic behavior.Based on the thermal stability model of power line,a stochastic line trip mechanism considering the thermal effect of power line is derived,which lays a foundation for characterizing the time-domain characteristics of failure propagation.The DC optimal power flow model is used to simulate the actual monitoring and control functions of information network to the power network,which overcomes the deficiency that the topological interaction cannot describe the wide area control function of information network.The robustness index considering the time-domain characteristics of failure propagation is defined,which solves the problem that the previous index cannot describe the failure propagation rate.Moreover,the effects of information network connection strength under different operating parameters and network coupling mode under different attack modes on the robustness of electrical CPS are analyzed.The research results reveal the internal relationship between the network structure and operating parameters of electrical CPS and its robustness.Considering the community structure of coupled system and the transmission delay of information network,we study the impact of wind power uncertainty on the cascading failure of electrical CPS.Based on the dependence between networks and the functional characteristics of network elements,a modular network model of electrical CPS is constructed,which lays a foundation for analyzing the influence of community structure on the cascading failure.The probability theory is introduced into power flow calculation to simulate the power grid dynamics under the influence of wind power uncertainty,which successfully introduces the wind power uncertainty into the cascading failure analysis of coupled system.The discrete packet transmission model and stochastic line trip mechanism are combined to analyze the impact of communication delay on the grid cascading failure,which provides a method to introduce communication delay into cyber-physical interaction.In addition,the relationship between community structure as well as transmission performance of information network and the robustness of modular coupled system is also explored.The research results reveal the influence mechanism of wind power uncertainty and penetration level on the cascading failure of electrical CPS,and describe the influence law of community structure and data transmission performance of information network on the robustness of modular coupled system.Based on the biological virus propagation model,the influence of computer virus propagation in the information network on the cascading failure of electrical CPS is studied,which provides theoretical guidance for analyzing the influence of information virus propagation on the power system operation.Considering the community structure and functional characteristics of the electrical CPS,we create a network model.The impacts of virus infection in the information network and power flow overload on the cascading failure propagation of coupled system are described.The virus infection state of information nodes is used to describe the effectiveness of monitoring power nodes,and the DC optimal power flow model is used to describe the control strategy of information network to the power grid,which reflects the actual monitoring and control functions of information network in the operation of power grid.In addition,the effects of virus propagation parameters,immune mode and community structure strength on the cascading failure of coupled system are analyzed.The research results describe the influence of virus propagation on the cascading failure of electrical CPS,and reveal the influence mechanism of immune strategy and community structure strength of information network on the virus propagation and the cascading failure of coupled system.A cascading failure model of electrical CPS considering the routing protocol of information network and the static power frequency characteristics of power grid is proposed,and the influence of communication routing strategy on the cascading failure of electrical CPS is studied.The discrete packet transmission model following specific routing strategy is used to describe the dynamic data transmission of information network,and a data transmission failure model of information network is established based on the average packet transmission time,which provides a method to describe the failures related to packet transmission.The dynamic power flow model considering the static power frequency characteristics of load and generator is used to describe the power flow dynamics of power network,which makes up for the shortcomings of previous work in describing the influence of grid frequency response and voltage violation.In addition,the relationship between topology characteristics of information network and routing transmission efficiency as well as cascading failure propagation of coupled system is also studied.The research results demonstrate the universality of the proposed model and reveal the influence of routing strategy on the cascading failure of electrical CPS.