Cascading Failure Prevention And Control Strategies Based On Complex Network Theory

So far, the frequent blackout accidents have caused people’s attention. Many researchers analyzed power system network structure characteristics according to the theory of complex network and the results showed that most of the electric power network at home and abroad had small-world and scale-free properties.This type of network has a relatively close structure, and high transmission efficiency, but also the inherent fragility, which means when a cascade failure is triggered, the failure will spread through the network in the form of overload and achieve widespread dissemination via long-range connections in the network in a fast speed and a large scope. Therefore, the research on the strategy of the inhibition of cascade failure in view of the small world grid structure vulnerability was very urgent. This thesis is based on the theory of complex network, and a dynamic evolution model of cascading failure was set up to research on the strategy of the inhibition of cascading failure. Main contents include:the orouagation characteristics analysis of cascading failure in electric power network, the strategy of the inhibition of cascading failure, and the optimization matching model of transmission capacity, etc.The thesis builds up a static model of the electric power network based on complex network theory, counts the network topological structure characteristics parameters and analyzes the network structure characteristics. The thesis also simulates the fault spread characteristic according to the dynamic model of cascading failure, reveals the fault propagation characteristics in eletric power network with different structure, and pointed out that high clustering grids have large amounts of redundant connection structure. In the process of fault propagation these redundant connection structure can lead to repeated infection and accumulation in the local area, which is the main factor for the fault size is not sensitive to changes of tolerate coefficient(that is, redundant transmission capacity). The thesis also observes the evolution process of load factor in the failure propagation process and illustrates why cascading failure continues to spread in power network. At last the thesis combined with the results of analysis in two aspects and explains the cause of the power network vulnerability from the mechanism.According to above analysis results, an improved capital match model is proposed. Through the reasonable matching of redundancy in the system transmission capacity, it can achieve the optimal state of the distribution of load factor and prevent blackout accidents. First, a new evaluation index is put forward based on entropy theory to quantify the importance of the branch for failure propagation. Then a transmission capacity matching model with control parameters is proposed to adjust the transmission capacity of each line. Finally, based on the risk assessment theory, a accessor method of control parameters is given, which is, when the tolerance coefficient(that is, the redundant transmission capacity) is known, the value of control parameters can be set to optimize the system state and to reduce the risk of cascading failure happens.As a kind of real network, electric power network face the danger of potential disturbance at any time, and optimal power grid planning cannot completely avoid the happening of blackout accidents, so the thesis also studies the strategy of the inhibition of cascading failure. Based on the fault propagation characteristics of small world grid, combined with the local control of fault propagation, a local control strategy of cascading failure for small world grid is proposed. The strategy considers both the overall network situation at faults occurring time and the details of the initial failure to determine the initial failure propagation range. By cutting off notes with higher generated load by failure propagation and lower structure load to change the local fault structure features and the spread of fault in local network, so as to achieve the aim of inhibition of cascading failure.The thesis summarize the research results at last and point out the next research direction.