Research On Maximum Power Point Tracking And Grid-connected Control Strategy Of Photovoltaic Power Generation System

Energy is the material basis and power source of the development of human society.Since the industrial revolution,human activities have caused a lot of serious environmental problems with the massive use of traditional resources.With the rapid development of the world transforming from industrial society to a low carbon society,green energy development has become a major issue.Solar photovoltaic power generation is developing as an important part of the composition of the world green energy,owing to its renewable capacity,cleanness and infinity and so on.Under this background,in this paper,the research object is the photovoltaic grid-connected generation system,and its research involves the maximum power point tracking(MPPT)control technology and grid-connected control strategy.Firstly,this paper has a deep study on photovoltaic cells.Through analyzing the operational principle and the character of photovoltaic cells,a mathematical model in the general environment is established.Then several simulation models of photovoltaic cells are built by matlab.Through the simulation of photovoltaic cells which are partly covered by shadow,this paper analyzes the change rules of the photovoltaic cells output character.And the variation is the basis of MPPT algorithm which is adapt to photovoltaic cells that work in non-uniform illumination.As for the maximum power point tracking,the tracking performance of the perturb & observe algorithm and the incremental conductance algorithm are compared and analyzed on the simulation platform.And a control strategy of variable step size is proposed to improve the tracking speed of the incremental conductance algorithm.To solve the problem of the maximum power point tracking of photovoltaic array which works under local shading condition,a maximum power point tracking algorithm with global searching capability is designed.It scans and compares the voltage values of all sampling points to determine the voltage near the maximum power point,and takes the voltage value as the initial point of the perturb & observe algorithm to search,and finally determines the position of the maximum power point.The simulation results show that the proposed algorithm can avoid the tracking of the maximum power point going into local extremum,and can reduce the power loss of the system.Compared with other kinds of algorithms,the proposed algorithm has many advantages,such as simple design ideas and fast searching speed,and quick to adapt to the environment changes,etc.This paper also has a research on the control strategy of three-phase grid-connected inverter,and designs a inverter control system with unity power factor based on the control strategy of grid voltage orientation.In the system,to realize the decoupling control of the current,the transformation of inverter current is from the three phase stationary coordinate system to the synchronous rotating coordinate system.And a DC voltage outer loop and current inner loop are designed to realize voltage and current dual loop control.The combined with Photovoltaic array module and MPPT module,the control chart of the three phase Photovoltaic grid-connected inverter system is finished.The simulation results show that the three-phase grid-connected inverter can achieve grid-connected operation with unity power factor.