Research On Coordination And Optimization Strategy Of Flexible AC/DC Hybrid Grid Controller

In recent years,the new flexible AC/DC technology has been widely applied in China's interconnected transmission system,which improves the economy and reliability of the interconnected system to a certain extent.However,the access of flexible AC/DC systems will significantly change the characteristics of the original system,make the interaction mechanism between AC and DC systems more complex,and increase the risk of failure of the original control strategy.In this paper,the transient stability control strategy of flexible AC/DC hybrid system is studied.The main research contents include:(1)For the controllers in the flexible AC/DC transmission system,the model is studied,and the negative damping mechanism caused by the controllers participating in the transient oscillation process of the system is analyzed.Moreover,the influence of the coupling effect between controllers on the stability of the system is discussed emphatically.(2)A multi-objective optimization function considering both stability and robustness is proposed to model the multi-controller coordination optimization problem.That is,the objective function reflecting the global stability of the system is formulated by ITAE criterion,and the robust objective function is formulated by Taguchi method.Moreover,the optimization constraints are simplified by the concept of relevant factors.Based on sensitivity method and principal component analysis theory,a comprehensive evaluation index under various operating conditions is formulated to screen the controller parameters.(3)Based on NSGA-II,the multi-objective optimization function optimization algorithm is constructed to obtain the Pareto optimal solution set,which with both system stability and robustness under multiple operating conditions.In addition,the optimal compromise solution in the solution set can be obtained by constructing the global objective closeness function.(4)Both the improved four-machine two-area system and EPRI36-node system are used as the test system.Then,based on PSASP-MATLAB hybrid simulation technology,the coordinated optimization strategy proposed in this paper is simulated and validated in the test system.The simulation results shows that the parameter optimization of AC/DC controllers can significantly improve the transient stability of the system.