| Energy and environmental issues continue to plague human development. At present, most energy is supplied in the form of electric power, so PV which has features of clean, sustainable and security, is gradually given more and more approval. The key to control the power from the photovoltaic panels reasonable connect to grid is synchronization control method, and control performance, efficiency and availability of the whole photovoltaic power generation system are the influence of it. Further research and exploration to improve the synchronization control method is of great significance to improve the control effect, so the research of grid connected control method is carried on in this paper. The contents are as follows:First, the grid connected PV system about back flow system and forward flow system, current type and voltage type inverter and other inverter topology, unipolar carrier phase frequency modulation method and the traditional SPWM method are researched in this paper. Then the overall structure of the single phase photovoltaic grid connected power generation synchronous control system is determined.Second, the characteristics of PID control, repetitive control, PR control, fuzzy control are analyzed and studied in this paper, and the necessity and advantages of composite control is pointed out. Third, composite grid connected current control method is put forward in this paper. T he quasi PR controller is used to replace the PI controller t o avoid the principle of steady state error. The fuzzy control is used to adaptive adjust three coefficients of PR controller, so longitudinal changes are made in the amplitude of grid connected current gain to improve the dynamic response capability, and lateral changes of bandwidth are made to deal with the fluctuation of grid frequency. Quasi PR controller for harmonic filtering is used in order to reduce the total harmonic distortion of the grid current, which makes the nonlinear system of photovoltaic power generation can be deal with the grid connected current control module. The repetitive control method is introduced to further reduce the steady state error and THD. The method of power grid frequency detection is also studied in this paper.Fourth, The SIMULINK platform is used to build simulation model of single-phase grid connected control system in this paper, then repetitive and PI control method, quasi PR method, fuzzy quasi PR method, fuzzy quasi PR and harmonic filtering method, fuzzy quasi PR and harmonic filtering and repetitive control method are compared in the simulation platform. The THD, tracking error of reference current and actual current and other aspects are compared and analyzed. Then a small power experiment is made.A ccording to the simulation experiment results, because of the grid connected current composite control method studied in this paper, the control effect is improved, THD and the current error of grid connected current are reduced. Quick control, well grid connected current waveform and the ability to deal with the fluctuation of grid frequency are the features of the method. It has good application value to the synchronization control. |
