Research On The Low-Power Single-Phase PV Grid-Connected System And Control Strategy

With the rapid development of global economy, traditional energy sources are consumed a lot, and it triggers many problems including energy crisis, environment pollution and so on. In order to solve these problems, more and more attention is paid to the development and utilization of new energy. With abundant energy storage, solar energy has the great potential to become the major energy resource in the future. Undoubtedly, Photovoltaic (PV) grid-connected generation is an important approach for the solar energy utilization. In order to maximize the use of solar energy, a deep research on maximum power point tracking (MPPT) methods and control strategies of grid-connected inverter is made, and simulation verifications are performed. Meanwhile, the topological structure of grid system and the parameter selection are designed in this thesis.Firstly, in this thesis, the background of photovoltaic generation and its development status both at home and abroad are introduced, and the composition of photovoltaic generation system is studied and analyzed in detail. Considering the characteristics of this system, a structure of the double-stages photovoltaic grid-connected generation with easy to control BOOST circuit and the single-phase full-bridge inverter circuit is adopted in this thesis. Through the theoretical analysis and calculation, the parameters of components in the circuit are calculated and selected. Simultaneously the hardware circuit also has been designed using PROTEL software.Secondly, the simulation model of solar battery is established and the photovoltaic cells output characteristics are analyzed by using MATLAB/Simulink simulation software. Also, the influence of output characteristics of PV cell when changing ambient temperature and light intensity condition is analyzed. Several common maximum power points tracking algorithms are introduced. Then, the center differential increment algorithm for MPPT is proposed. It contributes to the improvement of tracking precision and response speed.Thirdly, combined with the feed-forward control of grid voltage, the dual closed-loop tracking control method is adopted in this thesis, which achieves the grid current and voltage synchronization. In order to weaken the influence, which engenders from the periodic disturbance signal in the city power grid on the inverter output current, repetitive control method is applied to the current loop control. The control method is demonstrated effectively by the simulation results.Furthermore, the simulation model of solar battery, MPPT control and grid-connected inverter control are built on the platform of MATLAB/Simulink. The advantage, feasibility and correctness of the control strategies proposed in this thesis are confirmed.