Research On Photovoltaic Global Maximum Power Point Tracking And Grid-connected Control Method

As coal and other energy sources become less and less,while environmental pollution is serious,clean energy is becoming more and more important,especially photovoltaic power generation.Photovoltaic Maximum Power Point Tracking(MPPT)and grid-connected control are the most core of PV generation technology,but PV generation efficiency is not high,the external environment has a great influence on generation efficiency,at the same time,considering the effect of the MPPT directly affected by control of grid-connected inverter,so,based on PV grid-connected generation system as the research object,in this thesis,the key research is the MPPT technology considering the impact of grid-connected inverter,and the main work is as follows:Firstly,by analyzing the principle and mathematical model of PV cells,the PV cells simulation model is built by MATLAB/SIMULINK,and its characteristic curve is analyzed.Considering building,cloudy,trees,etc,would cause the existence of partial shadow environment,hot spot effect caused by partial shadow environment is analyzed,and the principle of solving hot spot effect by using the bypass diode and multiple peak problem caused by that are analyzed.With four PV cells in series as the research object,the existence of multiple peak problem caused by partial shadow environment is verified by simulation.According to single peak MPPT algorithms in uniform illumination environment,compared analyzing in the advantages and disadvantages of the commonly used algorithms is done,and then puts forward a single peak variable step perturbation and observation method and variable step conductance increment method suitable for different system requirements,precision and convergence speed are improved effectively.Compared analyzing in the advantages and disadvantages of the commonly used Global Maximum Power Point Tracking(GMPPT)algorithms is done,considering the Particle Swarm algorithm(PSO)is relatively simple,and can effectively achieves the global extremum search,while single peak variable step MPPT algorithm can quickly find the Maximum Power Point,and operates stably after searching the optimum extremum,GMPPT algorithm is proposed by combining PSO algorithm with variable step method,thus not only ensuring the precision but faster tracking speed.Finally,the proposed single peak MPPT algorithm and GMPPT algorithm are verified by simulation.Considering the stability of busbar voltage directly affect the accuracy of the MPPT algorithm in the input side of the grid inverter,determine the single phase two levels PV grid-connected inverter as the research object,and analyzing in the three kinds inverter control methods and three kinds control strategy of PV piconets are done,and finally selecte the droop control strategy of the peer control mode as the focus of this thesis research,an improved droop control algorithm based on PV grid inverter is proposed,for PV generation system not only to ensure the maximum power into the grid,at the same time to satisfy the interconnection requirements.Finally,the simulation model of PV system is built,and the improved control strategy is verified by simulation.