Study On The Method Of Searching The Islanding Boundary For The Interconnected Power Grid And The Stability Of Isolated Islands After Splitting

With the increasing interconnection of regional power grids and the increasing scale of power grids,at the same time,the continuous integration of new energy into the power grid makes the operation mode of the power grid increasingly complex,which leads to the increasingly prominent problem of the security and stability of the power system in China.As a last line of defense after the great disturbance of power system,splitting is effective in avoiding fault diffusion and preventing large area blackouts.Therefore,the analysis and selection of a reasonable optimal search method for separation surfaces and the study of the stability of isolated islands after splitting have important theoretical and practical values for ensuring the safe,stable and reliable operation of the power grid.This paper is mainly based on the national Power Grid Corp science and technology project.Based on a large number of literatures,this paper studies the search method of separation surfaces and the transient stability and static stability of isolated island.The main works and achievements of the paper are as follows:(1)The basic theory of graph theory and the theory of transient stability and static stability of power system are summarized.A detailed analysis of the solutions to the related problems of the graph theory and their solutions,such as clustering analysis,minimization of the maximum flow,selection of optimal paths,and traversal of graphs,etc.;Based on graph theory and related concepts of power system,the power grid is abstracted as a non-direct point weight/edge graph that meets certain conditions.The transient stability and static stability of the power system are summarized,and the theory of extended equal area rule is used to analyze the stability control of the island.It provides a theoretical basis for the follow-up study of the paper.(2)The method of searching the separation surfaces of interconnected power grids is studied.Firstly,aiming at how to choose a reasonable separation surfaces for the out-of-step splitting,an optimization method for split parcels with the goal of minimizing the damage of the sub-regional power grid structure is proposed,which takes the minimum damage of the zoned grid structure as the target.The extent of the change of the electrical distance between the end of the terminal substation is used to characterize the damage degree of the disassembly to the grid structure of the grid;Secondly,for the problem of controlled separation surfaces searching of optimal sections,this paper proposes a two-stage optimal parsing section search method of "partition + search".The method chooses the voltage amplitude and phase angle of each node before and after the disturbance as feature values.The fuzzy C-means clustering algorithm is used to divide the grid structure into stable?disturbed.and disentangled regions.Then,the minimum power flow impact is used as the objective function in the disaggregated region.Finally,the paper finally solved the controlled islanding boundary searching problem through the Edmonds-Karp and Dijkstra algorithm.This method can obtain accurate delisting strategies.(3)Aiming at the islanding transient and static problems after the splitting,a stability control strategy for the islanded system after splitting is proposed.First,based on the extended equal area method,the generator in the isolated island of two groups is polymerized,and the analytical formula of the center power and power angle of the Isle is constructed.The stability margin of the island is calculated by the static extended equal area rule,and the cutting load is determined;Then,the DC power flow algorithm is used to calculate the sensitivity of the split section branch to the generator and load,and the emergency control object is determined;In order to ensure the stable operation of islands after emergency control measures are taken,the DC power flow algorithm is used to calculate the maximum transmission capacity of the line and the voltage limit of the line after assuming measures before emergency control,and the control object is adjusted according to the over-limit condition;Finally,based on the operating point of the island system after the emergency control,a second-order state matrix of the system is constructed,and the characteristic root is determined to determine whether there is a static working point in the island system.Simulation results verify the effectiveness and practicability of this strategy.