The Study Of Controlled Splitting Strategy And Vulnerability Of Power System

With the expansion of power system, the structure is increasingly complex.Unpredictable hazards that may be caused by vulnerable lines become more damaging.These hazards may cause out of step oscillation and cascading failures, and thensystem crash, and eventually may bring about large area blackout. Controlled splitting,as an emergency measure against hazards, is to split interconnected grid into two ormore stable power islands to prevent the spread of the faults. And it is a last barrier ofdefense to ensure the power system security. Vulnerable lines analysis, as an effectivemethod of detecting and preventing potential danger of power system, can reduce thepossibility of cascading failures, as well as the possibility of system splitting. Theresearch of controlled splitting and vulnerable lines has attracted widespread attention,and is important to prevent hazards even great significance and to build flexible andstrong smart grid. Based on this, the main work of this thesis is as follows:Firstly, a new alternate optimization method based on master-slave problem tosearch for optimal splitting strategy is proposed. The strategy divides the completemodel into a master problem and a slave problem. The master problem is graphpartitioning problem and the slave problem is optimal power flow problem, and theyare coupled by node loads. The graph partitioning problem can be solved by CGKP(Connected Graph Constrained Knapsack Problem) algorithm. Optimal power flowhas two models, one is complete AC model, and the other is simplified DC model.Both models are studied and compared. The examples show that the alternativemethod can reduce the load shed, and the alternative method based on DC-OPF canobtain a better splitting strategy with less load shed in short time.Secondly, optimizing strategy is used to identify the vulnerable lines of thesystem. The appraisal index of vulnerable lines is that the removal of a small group oflines causes a severe blackout. A bilevel optimization problem is form based on theappraisal index. The outer problem is a combination of on-off state of lines, and theinner problem is an optimal power flow problem. The bilevel optimization model isconverted into a single level optimization problem by replacing the inner problem byits KKT conditions. Based on analysis of the KKT multiplier, the original system is divided into a generation-rich area and a load-rich area. And then the approximatevulnerable lines are obtained based on the network inhibition problem.Finally, a coordinated splitting analysis software is developed. The man-machineinterface is developed in the Windows environment, and service programs includingpower flow program, splitting program and optimal power flow program aredeveloped in Linux environment. And the interactive function between client andserver is achieved.