Research On Two-stage Single-Phase Grid-Connected Photovoltaic System

With global energy demand growing, energy crisis and environmental polution problem caused by traditional energy serious consumption could not be ignored any more. So much attention has been paid on the development and utilization of renewable energy. Among them, solar energy is getting more and more praise as a sort of resourse-rich, renewable and nuisanceless natural energy. In recent years, the rapid development of power electronic technology makes photovoltaic power plants gradually with the value of large-scale promotional. Undoubtedly Photovoltaic (PV) grid generation will become an important approach for the solar energy utilization. Therefore, the research and design on the grid-connected photovoltaic system has practical significance.Single-phase grid system is the main research object in this paper, the analysis and research of this system is carried out detailedly from following aspects:the topology of grid system, the parameter selection, the maximum power point tracking, and the control strategy of the combination of the single-phase grid inverter and the active filter.Firstly, the photovoltaic cell simulation model is seted up by using Simulink; To demonstrate feasibility of the maximum power point tracking (MPPT), the influence of output characteristics of PV cell when changing ambient temperature and light intensity condition is analyzed; On the basis above, several commonly used maximum power points tracking method is researched, and through the comparison of these methods, the traditional tracking method has been improved, the probability of a mistake of judgment in the optimization process has been reduced.Secondly, considering the characteristics of low power single-phase gird-connected system, a kind of small size, low cost, easy to control DC-DC circuit and a bridge type DC-AC inverter circuit is adopted in this paper. In order to obtain the accurate main circuit components, the parameters in main circuit are calculated and the hardware circuit also has been designed.Furthermore, combined with the feed-forward control scheme of grid voltage, SPWM dual closed-loop tracking control method is adopted in this paper, which achieved the grid current and voltage synchronization and ensured the stability of the bus voltage. Because traditional PI regulator can not achieve the zero steady-state error tracking, the ZRP (quasi-the proportion of resonant regulator controller) is utilized to improve the system. The control strategy is demonstrated effectively by the simulation results.