Research On Control Strategy And Simulation Of STATCOM System

With the extensive use of the nonlinear power devices, the problems of the reactive power and the harmonic pollution are becoming more serious. The reactive power and the harmonic pollution not only bring to bear on the power-grid system, but also affect the power quality seriously. Therefore, the reactive power compensation and harmonic suppression device came into being. Due to the good dynamic performance, high compensation capability, as well as the control flexibility and diversity, the Static Synchronous Compensator(STATCOM) has attracted more implication and research interests in harmonics governance and reactive power compensation in the power-grid system.We focus on the study of the STATCOM in this dissertation. FirstlyLthe basic structure and working principle are described in detail, followed by the establishment of a mathematical model in the stationary coordinate system. Secondly, the harmonic and reactive currents detection methods of the STATCOM are analyzed. The p-q method and the ip-iq method are introduced based on Instantaneous Reactive Power Theory. The theory analysis indicates that the ip-iq detection method has better performance than the p-q detection method. Then, in the aspect of the current tracking and control of the STATCOM, we analyzed the widely used PWM hysteresis current control and PI control. Research indicates that, although the hysteretic control method is simple with good stability, but its high switching frequency result in switching losses and high mechanical noise. The traditional PI control method can compensate reactive power and suppress harmonics. However, the control effect is not ideal and system power factor is still low. Meanwhile, the grid currents have a certain amount of harmonics. We adopt a recursive integral PI control to cope with these problems, and the parameters of the PI controller are tuned by using the Fuzzy inference theory. In order to overcome the current coupled problem, a d-q coordinate based cross decoupling control method is proposed, and it is applied in the high-voltage STATCOM with large capacity. Finally, the system models in both cases are created under the platform of MATLAB/SIMULINK.The simulation results show that the Fuzzy recursive integral PI control method and nonlinear decoupling control algorithm in d-q coordinate system can effectively track the command current, and realize the reactive power compensation, as well as improving effectively the power system quality. Compared with the conventional PI control, the improved PI control method has the features of faster response and better dynamic performance.