Research On Grid-connected Photovoltaic System Based On Fuzzy And Repetitive-PI

As the increment of energy consuming and deterioration of ecosystem environment, solar energy is concerned by human because it's renewable and free of pollution. Great importance is attached to developing solar photovoltaic (PV) system, and it has become the main form of the solar application. The characteristics of solar cells are affected by the outside environment, and the transfer efficiency is low, leading to the high cost of the PV systerm. To improve the efficiency of the PV system, it's important to research high efficient algorithm to track maximum power points and strategy to control grid connected inverter.First, the paper analysis the principle of solar cells and its work characteristics, and solar cells'electrical circuits and mathematical model are built later. According to the analysis and comparison of the several maximum power points tracking algorithm (MPPT), the adaptive fuzzy PID control strategy is proposed. Analyze the principle of algorithms detailedly, and give the simulation of the system. Comparing with conventional algorithms, the proposed control strategy can effectively improve the system shock phenomena near the maximum power point, lower power loss and enhance robustness of MPPT control system, and thus enhance the efficiency of solar cells.Second, targeting at the inverter control strategy algorithm, based on the classic control strategy, the modified repetitive-PI control strategy is proposed. Study the principle of the proposed control algorithm and analyze the controller design process. The algorithm can improve the steady state performance of system, restrain the disturbance of the grid output current from network side and load side, lower the output current THD value, let the output current in phase with the grid voltage and achieve unity power factor of the system. Finally, based on detailed analysis and summary of single-phase grid system, a laboratory 3KW single-phase grid-connected PV installations is designed, the main circuit choose the former class BOOST voltage match and the later class non-isolated full-bridge inverter as the topology. TMS320LF2812 considers as the control center of grid-connected system to achieve maximum power point tracking, grid connected inverter control, phase locked, communication and display.This article generally involves a detailed theoretical analysis, the main circuit design, software and hardware design, debugging and experimental waveform analysis. Through experimental analysis and simulation, the total current harmonic distortion (THD) of grid-connected inverter output waveform was less than 3%; Power factor was greater than 0.99, and the system efficiency was up to 95%, the desired specifications were achieved. Simulation and experimental results show the effectiveness of the design.