Research On Safety Evaluation And Optimization Strategy Of Multi-DC System Participating In Network Reconfiguration

With the development of DC transmission and power electronics technology,the economic and operational reliability of DC transmission projects have been greatly improved.Due to its advantages in long-distance,large-capacity transmission and regional interconnection,it has developed rapidly around the world in recent years.However,the connection of DC transmission and other new power components has made the power system withstand greater safety risks.In recent years,the resulting safety accidents are not uncommon,and even caused major power outages.Therefore,the safe operation of the power system and the safe and rapid recovery after a major power outage are still important content of the power system analysis.Based on China's multi-DC infeed grid scenario,this paper analyzes the security issues of multi-DC systems participating in the grid reconstruction process,and constructs a recovery active power static security region with the thermal stability of the branch as the main research object during recovery.The fast calculation method of safety margin and the optimization strategies suitable for power system recovery scenarios are also studied in this paper,aiming at guiding the grid operators to retore and dispatch for improving the safety during grid restoration.The main contributions and innovations are described as following:1)A restoration active power static security region model suitable for multi-DC systems participating in the grid reconstruction process is established.By analyzing the main security constraints and node power injecting characteristics during grid reconstruction,taking the thermal stability of branch circuits as the main research object,this paper studied the safety of power grid in recovery time.Based on traditional safety region research,a multi-feed system restoring active power static safety region is constructed as the basis for evaluating the safety of the power system restoration process.2)A fast calculation method of safety margin corresponding to the restoring static security region is proposed.By screening redundant boundary surfaces and slack optimization objective functions,a fast safety margin calculation method that can give static safety distance is obtained.Based on the geometric characteristics of the safety region,a fast safety margin estimation method is proposed using hyperplane equations.Based on the idea of first estimating the safety margin and then quickly calculating safety distance for the unsatisfactory scenes,a safety margin calculation method adapted to the recovery scenario is formed to realize the safety assessment of the power grid during recovery.3)An optimization strategy to improve the safety margin of lines under heavy load or overload during grid reconstruction is proposed.From the analysis of the optimization of the operating state and the optimization of the boundary to the security region,the optimization strategies of the security margin for different scenarios are proposed.The optimization strategy in the operating state includes the optimization of the balanced load recovery within the time step and the DC power adjustment and corrective control method improving the current operating state.The impact of restoration path,line loop closure,and TCSC parameter adjustment on the boundary of the safety domain are studied,and use it as an auxiliary optimization measure to improve the safety margin of the system together with the operation state optimization strategy to ensure the safety of restoration.