Risk Assessment Of Cascading Failure On Power Grid Based On Complex Network Theory

In recent years, many blackouts caused by cascading failures have taken place in succession all over the world, leading to huge economic losses and social impacts. With the formation of the regional power grid interconnection, links between the various subnets become more close, which means even a partial failure may cause large blackouts in global scope. Therefore, to prevent the occurrence of cascading failures and establish a more safe and reliable power grid, it has great significance in understanding the failure mechanism and process in depth as well as detecting potential failure risks existing in the grid.Firstly, this paper introduces the basic knowledge of complex network theory, the concept of electrical betweenness and the indicators of network transmission efficiency. Taking IEEE118 system for example, statistical analyses are carried on electrical betweenness of both system nodes and lines. The results prove that electrical betweenness can effectively quantify the importance of system nodes and lines in the grid structure. The improved network transmission efficiency index can better fit the actual physical characteristics of power grid as well as effectively evaluate the effect on transmission capacity caused by the change of the power grid structure after cascading failures.Then, aiming at the shortage of the traditional risk assessment in power grid that it only considers operational status instead of grid topology, the new model on risk assessment of cascading failure is established based on the complex network theory. In the new model, the system’s low-voltage severity function and overload severity function are redefined combine with electrical betweenness. Meanwhile, the influence of network structure changes on power transmission capacity is also taken into account. Network transmission efficiency indicators are adopted to define the function on severity of structural changes. Based on the existing research, search method for cascading failure path is proposed according to the pre-k shortest paths and the criterion for dangerous branches is redefined, thus reaching quick and efficient search for the cascading failure path. Based on the improvements above, assessment methods for cascading failures and identification method for lines with vulnerability are given using the risk theory. Taking IEEE39 system for example, the method proposed is analyzed and validated. The results show that the method can effectively make up for the inadequacy of traditional method which only considers the grid operation. And it can also comprehensively identify the existing risks, thus effective reference information would be provided for the safe operation.Finally, by analyzing risk control strategies, the risk control mathematical model for power gird is established and the optimization solution based on simulated annealing particle swarm optimization algorithm is put forward. Furthermore, taking IEEE14 system as an example, by adjusting the output of the generator system, effective risk control is achieved.