| Due to gradual depletion of fossil fuels, the continuous increase in energy demand associated with growing environmental protection awareness, alternative or renewable energy sources have drawn great attention worldwide. Considering environmental factors and development potential, solar energy is one of the most prospected renewable energy sources, because of its inexhaustible and clean. The mainstream among ways of using solar energy is photovoltaic (PV) technology, which has gained considerable important in recent years. This thesis has studied a three-phase grid-connected PV system, focusing on the control strategy of DC/DC and DC/AC; moreover, detailed analysis and simulation have done from the system topology, the maximum power tracking, parameters selection and inverter control.This thesis has done the research in PV system components, main circuit topology, filter circuit, system classification and inverter control, selected two-stage three-phase three-level system and filter circuit as the main circuit. Analyzing different maximum power point tracking (MPPT) algorithm, the traditional disturbance observer method was chosen as basis for the research. In this thesis, a variable step disturbance observer method based on Newton observations is proposed, on the basis of the general principles of law on traditional disturbance observer, the simulation results show that the improved control algorithm correctness and effectiveness.Finally, a detailed study and analysis of grid inverter control strategy has done in the thesis, choosing the voltage and current double closed-loop control strategy. In this system, parameters design and system model has been done based on the control strategy, and the Matlab/Simulink software was used to for system model and simulation, verifying the correctness of the system model.As a conclusion, simulation and actual test research have been done in this thesis, the simulation results demonstrate the effectiveness of the proposed method. |
