Research On MPPT Control Technology Of Photovoltaic Power Generation

The energy problem has become widely concerned all over the world owing to the ever-increasing depletion of fossil fuels such as oil,coal and natural gas.As an effective means to deal with the energy crisis and environmental protection,the development and application of new energy is the inevitable choice for the sustainable development of all countries.Solar energy is the most ideal renewable energy because of the clean and inexhaustible.In order to improve the conversion efficiency and reduce the cost of power generation,the maximum power point tracking is a key technology in the photovoltaic power generation system.In this thesis,based on the principle and mathematical model of photovoltaic power generation system,the output characteristics and engineering calculation model of photovoltaic cells are analyzed.The type,topology and module of the grid connected PV system are introduced in detail.The two-stage grid connected inverter is selected as the object of study.The simulation model of photovoltaic cells is established in matlab software,and the power output characteristics are analyzed.Through the analysis of the photovoltaic maximum power point tracking principle,respectively several of the most commonly used maximum power point tracking algorithm is studied,including the constant voltage tracking method,short-circuit current method,disturbance observation method and incremental conductance method,optimal gradient method,fuzzy logic control algorithm.Comparing the advantages and disadvantages of each algorithm,based on the incremental conductance method,an improved incremental conductance method is proposed for the two-stage grid connected inverter and the subsequent model predictive control.Aiming at the problem that the traditional PI control system cannot track the maximum power point when the external parameters of the environment intermittently become variable.This research work proposes an MPPT method based on controlled model for predicting future variation.This method is established by designing two-stage grid-connected inverter BOOST circuit which adopts discrete mathematics in definite time to predict future variation and again employ the evaluation function to represent the desired control results.In order to enhance efficiency,the optimal switching state is determined by minimizing the evaluation function of MPPT.Finally,MATLAB/SIMULINK tool is used to simulate the power response characteristics of the PV system.It is observed from simulation and experimental studies that the proposed method is very effective,faster and more accurate than traditional PI control system.