Study Of Complex Network Theory In The Power Grid

With the rapid development of global economics, large-scaled interconnection of power grids has become an inevitable trend for power systems all over the world. While, the capability of power grid to transfer power over hundreds or thousands of miles also enables the propagation of local failures into global network. Traditional methods have already confronted the limitation in comprehending the mechanism of cascading failure. New solutions are instantly needed to simulate and study the dynamics of complex power system. The theory of complexity and complex network provide an original perspective of global network from the point of view of system level.Based on the summary of complex network theory, including random network, small-world network and scale-free network, the recent blackouts throughout the world and the mechanism of cascading failures draw our attention. Through the statistics and analysis of character variables of domestic power grid accidents with load loss, the power law relationship between the blackout dimension and frequency is discovered, and the theory of Self-Organized Criticality is used to explain such phenomena. Using the method of R/S Analysis, the Hurst exponents of blackout series are respectively calculated, and the fractal characteristic is also explained. With the topology modelling of real-world power grids, the exponentail law of degree distribution, the negative power law and self-similarity of betweenness, the Zipf fractal feature and small-world effect are respectively testified.Based on the strategies of random failure and intentional attack, both the static analysis and dynamic analysis are adopted to study the robustness and vulnerability of networks. The real-world power grids are robust to random failures and are highly vulnerable to intentional attacks on components with high betweenness due to the heterogeneous topology and degree distribution disequilibrium of power grids. The relationship between node degree and average betweenness has the feature of power law, and the phase-transition point of tolerance parameter in the critical behavior of cascading failure is derived theoretically. The computed critical value shows its consistency with the practical dynamic simulation results in east China power grid.With the utilization of global efficiency model, a new efficiency evaluation model with electric distance matrix is proposed, and the efficiency of east and central China power grid is evaluated. Then, a new vulnerability index called weighted line betweenness is proposed to identify the critical lines in the power grid. The simulations on IEEE 39 bus system and central China power grid prove the efficiency of this new vulnerability index.In power grid with exponentail degree distribution, the method of failure propagation probability over entire network is proposd. The macro-control scheme is proposed to adjust the topological parameters in order to optimize the network structure, which could reduce the risk of component failure propagation, especially the risk of cascading failure. And scale-free network with consistent average degree, namely under the economic constraint of fixed cost, is studied. The failure propagation probalility and connectivity analysis under static removal of components are respectively introduced. Through function graphs and the computation of GA algorithm, we can draw a conclusion that, decreasing the power exponent of scale-free network in the interval of (2,3], can not only decrease the risk of failure propagation, but also improve the tolerance and connectivity of scale-free networks. This structure optimization solution can provide an optimal and theoretical reference for engineers and designers.The research on electric power communication physical route network shows that, Zhejiang power communication network is a local-world network and its sub-networks are all scale-free networks, and these nets entirely have the character of small-world effect. The static analysis indicates that, power communication network displays topology robustness against random node and edge failures, but is fragile to intentional attacks of high degree nodes. Under the communication principle of shortest path route, the protection of components with high degree and high betweenness is of great importance.