Research On The Power Syetem Controlled Islanding Boundary Searching Problem And Islanding Timing Optimization Strategy

With the primary goal of interconnection between China's power grids gradually being implemented,the electrical connection between regional power grids becomes tighter and tighter.Under these circumstances,it becomes more and more complicated for a power system to operate in a stable state.Therefore,if the power system suffers from severe faults,how to take the safety and stability control is a great challenge to grid operators.The traditional splitting devices are based on the local electrical information,which lacks of inter-system coordination.There is a certain degree of incompatibility between the increasingly complicated grid operating conditions and traditional way of splitting.However,the extensive configuration of PMU in power grid and the continuous development of WAMS technology makes information technology widely applied in power system,which gives the foundation to do research on the active unified,centralized and coordinated controlled islanding strategies.The thesis made the summarization and literature review of islanding strategies based on the works of major projects of state grid corporation.This paper researched controlled islanding strategies of interconnected power grids after suffering the disturbance of serious faults.The specific contents are the "Where to split" and "how to split" problem,that is,the power system optimal controlled islanding boundaries searching problem and the active operating location and timing optimization of fault isolation.The main contents and achievements of this thesis are as follows:(1)The general graph model of the controlled islanding problem is established.Firstly,the interconnection grid is equivalent to the graph model according to the basic knowledge of the graph theory.Besides,the constraints and the objective function of controlled islanding problem are set up combined with the basic rules of islanding process.(2)A three-stage tabu search algorithm is proposed to solve the problem of controlled islanding under the prerequisite of guaranteeing electrical stability and safety and stability constraints.The three-stage tabu search algorithm mainly consist of initial construction,boundary movement as well as stability verification.The minimum power imbalance among the isolated power islands is used as the objective function.The feasibility and validity of the algorithm are verified by 15 simulation examples carried out in 5 different standard power systems.(3)The electrical distance variation between the isolated islands are proposed to solve the problem of voltage safety and power angle stability,which is caused by the dislocation operation of the partitioned grid.The damage degree of the grid structure is analyzed simultaneously.Considering the influence of the voltage and the power angle stability on the post-partitioned grid,this thesis puts forward the optimal selection principle of islanding boundaries.It takes power imbalance of isolated islands as well as the impact of the power grid and the structure into consideration as much as possible.(4)To prevent the risk of traditional partitioning power system measures based on local devices,active optimizations of operating location and timing of fault isolation are proposed.The contents of principle include:in the case of ideal two-generator out-of-step oscillation mode,the reliability of the splitting device needs to be increased;for a certain instability mode,when the two groups of generators in a number of cross-cutting set,the possible oscillation center migration needs to be considered,and more anti-out centers are configured to prevent the out-of-step oscillation center from falling on the preset single boundary,which can increase the reliability of the control strategies to deal with the oscillation center migration.