Optimal Transmission Switching Method For Eliminating Short Circuit Current Overlimit In Multi-infeed System

With the continuous expansion of the scale of the power system,the power grids of different regions in China have a certain degree of short-circuit current overlimit problem,which has seriously threatened the safe and stable operation of the power system.The grid structure has a direct impact on the short-circuit current level of the system.Research on the optimal transmission switching methods for eliminating shortcircuit current overlimit is of great significance for improving the safety and stability margin of power system,reducing the risk of chain failure after the occurrence of accidents and improving the economy of power grid operation.On the other hand,HVDC transmission technology plays an increasingly important role in China’s electric power system by virtue of its advantages of being suitable for long-distance and largecapacity transmission.China has gradually formed a large-scale AC and DC interconnection system.The access of HVDC lines also poses new challenges to the safe and stable operation of the power grid.By analyzing the key safety issues in AC/DC systems,it points out the corresponding relationship between key safety indexes such as short-circuit current level and multi-feed short circuit ratio and node impedance matrix elements.Based on the physical meaning of node impedance matrix elements,a mixed integer linear modeling method of node impedance matrix elements is proposed,and the modeling of key constraints such as short-circuit current and multi-feed short circuit ratio in the optimal transmission switching model is realized.Furthermore,an improved modeling method of multi-feed short circuit ratio constraints is proposed,which can effectively improve the solving efficiency of model.Combined with the branch-adding method,the influence of the system structure change on the short-circuit current level is studied,which provides the relevant theoretical basis for the optimal transmission switching method to limit the shortcircuit current level.Furthermore,a network structure optimization method considering the short-circuit current constraints is proposed to provide optimal transmission switching scheme to eliminate short-circuit current overlimit,and a variety of constraint set reduction strategies are proposed to improve the solving efficiency of the model and enhance the applicability of the model in large-scale systems.The effectiveness of the proposed method is verified with the modified IEEE30 node and IEEE 118 node examples.Considering the situation that multiple DC lines are fed into the same AC network,the multi-feed short circuit ratio of the receiving end AC system should be maintained above a certain level to ensure sufficient commutation voltage for DC lines.This paper first analyzes the relationship between the system structure and the multi-infeed short circuit ratio,and points out the necessity of considering the multi-infeed short circuit ratio in the process of optimal transmission switching.Then,comprehensively considering the N-1 security constraints and various operating constraints,an optimal transmission switching model of AC/DC system for eliminating short-circuit current overlimit that takes into account the safety of the power grid is established,and the corresponding solution strategy is proposed to improve the solution efficiency of the model.The feasibility and effectiveness of the proposed optimization method are verified by the examples of the modified IEEE 30 node system and IEEE 118 node system.