Research On Repetitive Control Method Applied To GRID-Connected Inverter

Due to global warming, environmental deterioration, conventional energy shortage and other issues, the development and utilization of new energy sources have been widespread concerned in the world. Solar photovoltaic power generation has been the focus of attention in recent years. And as the interface between photovoltaic power generation and grid, grid-connected inverter has been a hotspot in the field of energy at home and abroad. With grid-connected inverter widely applied, the requirements for the various aspects of the system are increasingly high, especially the quality of grid current waveform. Control system is the core of inverter, and excellent control strategy is the key to improve the quality of grid current. Therefore, this paper focuses on three phase grid-connected inverter based on LCL filter, analyzes it’s topology, mathematical model and filter characteristics, gives the design method of LCL filter parameters, and has the in-depth study of repetitive control strategy. The main work of this paper is as follows:Firstly, the main circuit topology of three phase grid-connected inverter is introduced, it’s mathematical model in the three-phase static symmetry coordinate system, the two-phase static coordinate system and the two-phase rotating coordinate system is established. The characteristic of LCL filter is analyzed, and the constraint and selecting method of it’s parameter design are given. That the factors affecting the inverter waveform distortion are dead time, non-linear loads and grid disturbances is pointed out. Secondly, in order to improve the quality of inverter waveform, repetitive control theory is introduced. The structure and function of each part of the repetitive controller are presented, and the stability, error convergence and harmonic suppression characteristics of the repetitive controller are analyzed in detail. Thirdly, for the shortcoming of repetitive control, the hybrid control strategy combining PI control and repetitive control is adopted. According to different combinations, two different hybrid control strategy are proposed. The design methods and parameter values of PI control, combined control strategy of repetitive control and PI control in series and combined control strategy of repetitive control and PI control in parallel are presented. On this basis, two different combined control strategy of repetitive control and PI control is analyzed respectively from the design method for compensating function, system stability and power frequency harmonic suppression characteristics. And the characteristics of two different combined control strategy are summarized and compared. Finally, MATLAB simulation models of each control strategy are established, Simulation experiments are done and simulation results are analyzed. Simulation results verify the correctness of theoretical analysis.