Study Of UPFC For Suppressing Forced Oscillation In Power Grid

In recent years,the interconnection and intercommunication between major power grid regions across the country has been continuously enhanced.In such a complex system,the probability of continuous periodic disturbances,especially disturbance near the natural frequency of the system is greatly increased.And it is easy to cause large-scale forced power oscillation in the power system.The paper focuses on the targeted suppression methods of forced power oscillations in power systems,and has carried out the following related research:1)The mechanism,oscillation characteristics and influencing factors of forced oscillation are studied,and the suppression ideas and methods are proposed for its oscillation characteristics.Firstly,the forced oscillation differential model in the single-machine infinity system and multi-machine interconnection system is established.The generation mechanism,propagation mechanism,oscillation characteristics and the influencing factors of the forced oscillation amplitude are analyzed.And the proposed method and method for suppressing forced oscillation are proposed according to the law.It means important reference value in-depth study of inhibition measures.2)A unified power flow controller(UPFC)control strategy with auxiliary controller is proposed to suppress forced oscillation of the power system.Firstly,the control principle of UPFC is studied and its equivalent power injection model is built.Secondly,based on the forced oscillation characteristics,the linearized state space method is used to analyze the mechanism of UPFC to improve the damping of the system.On this basis,the auxiliary controller is used to further enhance the control effect of UPFC on system damping,and a controller parameter tuning method for forced oscillation suppression is proposed.Finally,the effectiveness of the proposed method is verified in a four-machine two-zone system.3)A forced oscillation method for the UPFC suppression system using the repetitive control technique is proposed.Firstly,the feasibility of applying ideal repetitive control technology to forced oscillation suppression is studied and demonstrated.Based on this,a plug-in modified repetitive control(PMRC)with higher stability and suitable for suppressing forced oscillation is designed,which proves that it has excellent tracking performance for the system steady-state reference value.Further,a method of combining UPFC with the PMRC and outputting the suppression power according to the PMRC tracking requirement is proposed.The simulation results in the equivalent two-machine system and the actual power grid of Nanjing Xihuan Network show that the proposed method can effectively suppress the forced power oscillation of the system.