Research On Robust Optimization And Control Of Power Grid Cascading Failure Based On Power Flow Model

In today's rapidly developing information age,the role of a power grid is becoming more and more important.With the increasing demand for electricity,the scale of a power grid is becoming larger and larger.How to ensure stable operation of a power grid and prevent large-scale cascading failures becomes an important research topic.Based on the complex network theory,the mechanism of cascading failures and the methods to reduce the scale of cascading failures are studied with a power flow model in this paper.The research conclusions have certain guiding significance for preventing and reducing cascading failures.The specific research contents are as follows:1.Research on robust optimization of a power grid based on the degree-preserving edges crossing reconnection algorithm.From the perspective of network science,using the cascade fault model combined with real electrical characteristics,the network topology is optimized to reduce the scale of cascading failures and improve the robustness.Firstly,the edges are randomly selected by simulated annealing algorithm,and the network degree is preserved and cross-reconnected to obtain the optimal value of the robustness of the power grid.Secondly,the local optimal value of the power grid is obtained by multiple preserved-degree cross-reconnects for the edge that causes the largest failure scale after removal.Finally,the grid robustness is improved by preserved-degree cross-reconnects for the edge that lead to the largest and smallest scale of power grid failure.Comparing the time complexity of the three algorithms,although the effect of the third algorithm on network robustness optimization is not obvious,the optimization is faster.2.Research on cascading failures control based on load shedding.Firstly,the redundancy of nodes is defined according to the redundancy of lines.In the process of load shedding,the amount of load shedding is negatively related to the amount of load redundancy,so the larger the redundancy,the smaller the amount of load shedding.Then,by studying the mechanism of cascading failures propagation with a power flow model,two methods of selecting load nodes shedding are proposed.The first method is to select all load nodes in the neighborhood with the distance of 3 from the initial failure line,and the second is to select all load nodes in the neighborhood with the distance of 3 from the successive failure line.The research results in multiple IEEE test networks show that load shedding in two methods can effectively reduce the scale of cascading failures and improve the robustness of the network.However,due to the difference in the propagation modes of cascading failures in power grids with different topologies,the effect of load shedding using two methods is different.For networks where cascading failures is mainly spread by infection,method 1 is more effective.For networks with cascading failures crossing regional dissemination,method 2 is more effective.3.Research on cascading failures control based on a single load node removal.In the power flow model,the cascading failures occurs in a power grid after the edge is attacked,and the propagation of the cascading failures is suppressed by removing a load node.This paper proposes two methods for removing load nodes,one is global optimization and the other is local optimization.Global optimization means that after an edge in the power grid is attacked,if there are overload nodes or overload lines in the power grid,it will traverse all load nodes in the power grid.When a load node is removed and the cascading failures occurs in the power grid,the load node with the smallest failure scale after removal is found,and the node is regarded as the best removed load node after the line failure.The research shows that if the load node found by global optimization method is removed when the edge is attacked,the scale of cascading failures can be effectively reduced.In order to improve the efficiency and speed of selecting the load nodes that need to be removed,this paper further proposes a local optimization method to find the removed load nodes within the range of 3 from the attacked edge.Through the simulation experiments in IEEE57,IEEE118 and IEEE300 networks,it is found that removing the local optimization load nodes can effectively reduce the scale of cascading failures.Finally,comparing the algorithm complexity of the two methods,the local optimization method can quickly locate the load nodes which need to be removed.Compared with the global optimization method,the effect of control cascading failures is similar.