Reliability Assessment Of Distribution Cyber Physical System

Smart grid is the core of the third industrial revolution,in which information and communication technologies will be highly integrated through the power generation,transmission,distribution and utilization of electricity to achieve the bidirectional flow of power and information.The smart grid has become a typical cyber physical system(CPS)due to the deep integration of physical system and cyber system from the sensor of the bottom layer and intelligent agent(such as relay protection,DER)to the entire system.And the false information is more likely to affect the physical system and increase the risk of the operation of power grid because of the integrated cyber-physical system.How to guarantee a safe and reliable operation of power grid under the background of the integration has become a critical challenge.Therefore,the main focus in the thesis is to make a scientific and effective reliability assessment of the distribution network CPS by comprehensively considering cyber system reliability and interaction between cyber and physical system,on the basis of the traditional power grid reliability evaluation.A reliability assessment method considering fault management schemes is proposed for distribution network CPS.Firstly,a fault tree model is established for fault location,fault isolation,and service restoration,considering the dynamic support function of cyber system in the three fault management states.Then,an event tree model is established according to the sequential process of fault management,and the impact of cyber system failure on fault management consequences is quantificationally described.Finally,the operation states of cyber physical system and the dynamic process of fault management are simulated by means of sequential Monte Carlo method,and system reliability is assessed.The results of case studies on RBTS Bus6 F1 and RBTS Bus6 F2 systems show that fault location failure,due to cyber system failure,may expand the power supply interrupted districts,and fault isolation as well as service restoration failure causes the increase of load-point outage duration.Then,fault management consequences are changed.With massive distributed generation(DG)connected to power grid and the implement of demand response,fault management processes also include the coordination control of grid-connected and islanding operations of microgrid and demand response,which are all deeply dependent on reliable cyber systems.A reliability assessment method considering DG and demand response is proposed for distribution network CPS.A fault tree model is established for off-grid failure considering the influence of cyber system on the operation from the grid-connected mode to the islanded mode.A load shedding strategy considering demand response and cyber system failure is proposed.The impact of cyber system on failure effects is studied for centralized and hybrid fault management modes respectively,and an event tree model is used to analyze failure effects.The results of case studies on RBTS Bus6 F4 system show that cyber system failure has a significant impact on the coordination control of demand response and DG,and that system reliability could be improved by changing fault management mode because the hybrid mode has much higher reliability than the centralized.