Network Reconfiguration And Partitioning Strategies In Power System Restoration

In recent years,many blackouts occurred at home and abroad,such as 2003 8.14 U.S.blackout,India blackout in 2012,Guangdong Zhanjiang power grid blackout caused by the typhoon,the Turkey"3.31" blackout in 2015.These accidents sounded the alarm for the safe and stable operation of power system.Once a large area blackout occurs,if no prior recovery plan is made,it will cause significant economic losses.Therefore,it is necessary to study the accident treatment of power system and the recovery after full or partial blackout,which is of great theoretical and practical significance to reduce the impact of power failure and power loss,and ensure the safe,rapid and intelligent restoration of power supply after the accident.Power system restoration after blackout can be divided into three stages:black start,network reconfiguration and load recovery.The main task of the network reconfiguration is to transmit power to the missing unit as soon as possible and establish a stable grid structure gradually,which lays a solid foundation for the next stage of full recovery of load.The system recovery strategy in the network reconfiguration phase can be divided into two categories:serial recovery and parallel recovery.Serial recovery strategy in most generators before grid relay recovery plant station;parallel recovery strategy divides the system into several subsystems and recovers them independently.After each subsystem is restored,the system can be restored by grid connection.Given this background,the network reconfiguration strategy based on weighted network node importance and the problem of power system partition restoration are studied in this thesis.Some siginificant research results are obtained as follows:1.The disadvantages of some existing methods such as the betweenness method,the node deletion method,and the node contraction method for evaluating the node importance in weighted networks are first discussed,and a new method based on the node importance evaluation matrix is proposed for this purpose.The proposed method takes the locations of nodes and the contributions of adjacent nodes into consideration.Then,an improved bi-level optimization model is developed based on the node importance evaluation method.In the upper-level,the recovery time of generating units is determined by maximizing the restored generation capacity.While in the lower-level,the restoration path with the maximum average importance is selected to restore the generating unit concerned.Furthermore,an adjustment coefficient is employed to change the proportion of the transmission line capacitance and transmission line operation time so that the recovery of a generation unit will not be delayed by long restoration time of the restoration path.2.A two-step strategy for black-start zoning based on the semi-supervised spectral clustering algorithm is proposed.First,the power flow in a given line and electrical distance between nodes are employed to determine the weight of the line,and then the weighted graph of the power system concerned can be formed.Then,a black-start zoning strategy is presented based on the ratio cut set criterion.The proposed strategy consists of two steps.In the first step,a grouping optimization model of generators to be restored is presented for speeding the power system restoration,with both the maximization of the restored generation quantity and the minimization of the total capacitance of the restored transmission lines included in the objective function of the optimization problem.In the second step,the semi-supervised clustering algorithm is employed to solve the black-start zoning model based on the grouping information attained in the first step.In the semi-supervised spectral clustering algorithm,the k-means++ algorithm is employed to cluster the feature vectors,so as to avoid the drawback of the traditional k-means algorithm that the clustering result is sensitive to the specified initial cluster centers.3.A strategy for black-start zoning based on the current tracing method is proposed.Firstly,the power flow in a given line is employed to determine the weight of the line,and then the weighted graph of the power system concerned can be formed.Then,a black-start zoning strategy is presented based on the mulitiway normalized cut criterion.Then the threep-step method is used to solve the black start partition result.1)a grouping optimization model of generators to be restored is presented for speeding the power system restoration,with the maximization of the restored generation quantity;2)Based on the grouping information attained in the first step,the current trace method is used to calculate the power components of the branch current,based on which the power network diagram is simplified;3)The spectral clustering algorithm is used to solve the black start partition model for the simplified power network graph.Finally,the final black start partition result is obtained in the simplified process.Finally,this thesis summarizes the research which has been done and points out what can be further improved.