Research On Cascading Blackouts Based On Complex System Theory

In recent years, a number of large blackouts caused by cascading failures have taken place all over the world. Therefore, it is important to analyze the mechanism of cascading blackouts and propose preventive strategies for large blackouts. However, conventional security analysis strategies for electric power system confront the limitation in studying cascading failures and the mechanisms of large blackouts. And the research on cascading blackouts based on complex system theory has become a hot topic in the power system reliability research.This dissertation focuses on employing complex system theories to analyze cascading blackouts of power system from the aspects of complex network evolution, self-organized criticality and interactions between power grid and communication network, and propose some preventive strategies for large blackouts. This dissertation is organized as follows:The way of power grid topology evolution in slow dynamics of OPA model is improved to investigate the long-term effect of topology characteristics of a power grid on the probability distribution of blackout by adjusting the parameters of the novel model. Simulation results show that the probability of large blackouts in a power grid can be reduced by separately changing any one of these topological parameters. But in most cases, the variation of one topological parameter may cause simultaneous deviations on the others, which might have opposite effects on the distribution of blackout probability. Also in realistic power systems, the topology varies with the construction of transmission lines. From the simulation we found that linking a new substation or power plant to a low-degree bus is a better choice to mitigate large-scale blackouts than linking to a well-connected one.Inspired by the concept of assortativity in complex system theory, a novel index, called line assortativity, is proposed to quantify the distribution characteristic of lines power flows by matching load rate and vulnerability of lines. Line assortativity is used to identify the self-organized criticality of the power system. The simulation results indicate that the index is effective in identifying the self-organized criticality in various power systems operating in some states, by combining it with other indices, such as the average load rate and the power flow entropy. Moreover, the index proposed in this paper is still effective for the power system with a lower load rate, which is an important complement to the existing indices for mitigating large blackouts.Taking the transmission of line-outage-state information as an example, the information network is integrated with the hidden failure model to investigate the impact of node failures in the information network on the cascading failures in power systems. A new index is proposed to identify the key-buses which exert vital influence on blackouts, and it is very effective in power systems operating in various states. Simulation results show that the failures of information network might make the situation even worse and lead to large blackouts. Moreover, the nodes with high-degree or high-betweenness in the information network are not the key information nodes that have important influence in the spread of cascading failures. Rather, compared with the topological characteristics of information nodes in their own network, the vulnerability of the information nodes corresponding transmission lines are better able to characterize the importance of information nodes in the cascading failures of the power system.The model of interaction between a power grid and its communication network in accord with practical power system is proposed. And various route strategies could be generated by adjusting corresponding communication network parameters, by which the impact of transmission characteristics of electrical power communication on cascading blackouts is investigated. Moreover, the inter-similarity between coupled networks is discussed based on complex network theory. And an index is presented to assess the level of inter-similarity between interdependent networks. Simulative results indicate that, with proper routing strategy of communication network, the probability of large blackouts of power system can be reduced and the optimal inter-similarity strategy between coupled networks of different power systems is same, which can be adopted to effectively decrease the probability of large-scale blackout. The inter-similarity index is useful to assess the effect of interdependency between coupled networks on blackouts. And improving the inter-similarity between coupled networks is effective to mitigate large blackouts.