Research On Grid-connected Control Strategy For Photovoltaic Power Generation System

In the 21 st century, the world faced with the increasingly serious energy crisis and environmental pollution, to seek alternative new energy become the highest priority of sustainable development, solar power as a mainstream direction of the solar energy application has received the widespread attention around the world for its non-polluting and renewable. In this thesis, the PV grid-connected inverter as the research foundation, the purpose is to improve the efficiency of grid-connected system and the power quality of power grid, the research content includes the Maximum Power Point Tracking(MPPT) control, grid-connection control and harmonic management of grid-connected system.Firstly, the structure of the PV power generation systems are introduced,based on analysis of the grid-connected inverter topology and control methods,select two-stage non-isolated topology structure as the research object of this article. On the basis of a mathematical mode of the equivalent of PV cells, the simulation output of PV cells under different conditions. For nonlinear output characteristic of PV cells, by analyzing of the working principle and the advantages and disadvantages of usual MPPT control methods, a kind of fuzzy PID control based on the fuzzy control is put forward and applied to the MPPT control.The simulation results show that the control effect of this method is more accurate and stable.Secondly, aiming at the voltage disturbance problem of single-phase PV grid-connected power generation, the double closed loop PI control based on grid voltage feed-forward was used to the realize the goal of transmission high quality to the grid; On this basis, it analyzes the main circuit of three-phase PV grid-connected power generation system and modeling, based on double closed loop PI control of the synchronous rotating coordinates and QPR control of two-phase stationary coordinates are put forward and used to achieve interconnection purposes; Mainly studies the implementation of the Space Vector Pulse Width Modulation(SVPWM) modulation in the three-phase PV grid-connected power generation, and the simulation analysis was carried out on the above control strategy.Finally, by comparing the working principle of the PV grid-connected power generation system and active power filter(APF), combined with the advantages and disadvantages of the both, the APF is applied to the PV grid-connected power generation system, the research mainly focuses on harmonic management methodand the instruction of synthesis methods about the new system, the final simulation results show that the new system can output active power to the grid,and can also be used as APF to harmonic management, it can prove it were feasible and correct about the structure of system, the design of parameter and control strategy.