Research On Control Strategy Of Power System Low Frequency Oscillation Based On UPFC

As the result of the integration of power electronic technology and automatic control technology, the unified power flow controller is applied more in the power grid, depending on its advanced control characteristics. In this thesis, the mechanism of UPFC for restraining the low frequency oscillation of power system is studied, A UPFC master controller and an additional damping controller are designed to suppress the low frequency oscillation of power system.Firstly, the basic structure and working principle of UPFC is analyzed, the operation mode of UPFC is summarized, the fundamental frequency model and the high frequency mathematical model of UPFC are discussed. Then, based on the fundamental frequency dynamic model and the high frequency mathematical model of UPFC, the UPFC system level controller and the device level controller are designed respectively. System level UPFC controller with nonlinear decoupling control scheme based on two-phase rotating coordinate system, with advantages of fast tracking a given value in the precise control of UPFC,and can realize the independent control of active power and reactive power in the D and Q coordinates.At the same time, this thesis uses the analysis method of UPFC switching function based on SPWM control, analyzes the influence of control parameters and working principle of UPFC. In order to improve low-frequency oscillations in power system,the improved Phillips-Heffron model of power system with UPFC is built,through the analysis of the model, the damping controller which takes the mechanical power generator as the additional signal is built at the same time.Finally, with the help of the MATLAB/Simulink platform, the main circuit simulation model, UPFC controller model and damping controller are build. It can be confirmed through the simulation that the designed UPFC controller as well as the damping controller both has the effect of suppression of low frequency oscillation in power system. The additionaldamping controller can reduce the dynamic response time of the system, and the system can recover the steady state more quickly.