Research On UPFC Control Strategy Of AC Transmission System

At present,my country's electricity demand and energy supply are in a serious reverse distribution situation,and the construction of ultra-high voltage and long distance power grids is imperative.As the main control device in the flexible power transmission system,UPFC is widely used for its good power flow control ability,improved power transmission ability and suppression of power oscillation ability.In order to improve the flexibility and controllability of the AC transmission system,this paper has theoretical significance and application value for the research of power flow control problems and disturbance control problems under the UPFC control strategy of the AC transmission system.In order to solve the problem that the traditional UPFC controller is prone to deteriorate the control performance and the non-linearity of the UPFC device when the operating point changes,the system structure of the unified power flow controller,the working principle of the parallel and series sides of the UPFC,and the power flow control principle are first analyzed;Secondly,for open and closed networks,the power flow distribution characteristics of the AC transmission system are studied.The state feedback accurate linearization theory is used to linearize the UPFC nonlinear form,and the UPFC seventh-order nonlinear system is transformed into a simple,The controllable linear system then carries on the power flow control.Through the simulation of IEEE39 node system,the results show that compared with PI control,the linearized UPFC control strategy has less volatility,fast response speed,and can achieve the goal of optimal regulation.Aiming at the problem of forced oscillation of AC transmission system and UPFC under continuous interference,on the basis of in-depth analysis of the principle of suppressing forced oscillation of unified power flow controller,the UPFC control strategy based on improved repetitive control is given,which combines repetitive control with PI control.Combined to solve the shortcomings that the repeated controller output cannot track the sudden change caused by the sudden change of input and the dynamic response delay of repeated control,the system has good dynamic response performance.The improved repetitive control strategy was simulated and analyzed in a 3-machine 9-node and IEEE39-node system.The simulation verified that the improved repetitive control strategy could well suppress the forced oscillation caused by mechanical power disturbance and excitation disturbance,and also proved that the paper proposed The effectiveness of the control strategy.