Research And Design Of Single-phase Grid-connected Photovoltaic Inverter System

In front of the severe energy crisis and the urgent environmental problems, solar energy is highly valued and widely used because of its abundant, clean and pollution-free etc. Grid-connected photovoltaic(PV) is the main trend of utilization for solar energy. Among all the PV grid-connected system, single-phase non-isolated low power inverter grid system with its advantages of light weight, easy installation and high efficiency etc are welcomed. Therefore, this paper aims to make research and design on single-phase grid-connected PV system.This thesis adopts Boost pre-stage booster circuit plus single-phase bridge inverter circuit as the main circuit. Firstly,through the analysis of photovoltaic effect theory, the equivalent circuit and mathematical model of PV cells are obtain. Then based on the analysis to characteristis of its power-voltage(P-U) output characteristic curve, this paper has made comparison of several common MPPT(Maximum Power Point Tracking) contorl methods, and an improved variable step duty cycle perturbation and observation method is proposed in order to achieve the MPPT control of PV cells. The inverting control of grid-connected current is the other central technology that is studied in this system. The voltage and current double closed loop PI control with grid voltage feed-forward control as control strategy of PV grid inverter is determined. And derivation of the mathematical model and parameters design process of its control system are also given in this paper.With adoption of MATLAB / Simulink simulation software, the paper has made simulation experiment on single-phase PV grid-connected system control strategy,also, finishing the digital control System design based on TMS320F2812 DSP controller in CCS3.3 programming environment, a combination of hardware circuit to complete some experiment. The result from the simulation and experiment shows single-phase photovoltaic inverter system can quickly trace the maximum power point of photovoltaic cells during the conditions of change environment, also,grid-connected current can precisely follow with grid voltage and realize grid friendly,and the THD(Total Hormonic Distorion) is 2.63%, reaching the requirement of grid Connection.