Research On Maximum Power Tracking Algorithm For Photovoltaic System

With the continuous development of society,the amount of energy consumed by mankind is increasing,and the reserves of conventional energy are depleted,renewable energy began to be widespread concern.Solar energy is widely used because of its abundant reserves,clean and renewable,and low environmental requirements.But at present,the price of photovoltaic panels is relatively high and the conversion efficiency is low.In order to reduce the cost of the system and make use of the solar energy effectively,it is very important to improve its efficiency.On the one hand,the efficiency of photovoltaic cells is affected by the parameters of its internal components,on the other hand,it is affected by the external light intensity,temperature and other factors.In order to improve the efficiency of photovoltaic cells,the maximum power point tracking(Maximum Power Point Tracking,MPPT)control technology should be adopted.In this thesis,the MPPT algorithm is studied.Aiming at the problem that some parameters can not be determined in the mathematical model of the equivalent circuit of the photovoltaic cell,the engineering model of photovoltaic cell is established.The model can be set up according to the actual needs,it has a strong practicality.Due to the sudden increase of the output power of the photovoltaic cell the perturbation observation method uses two points of power to compare the stability is low.In order to solve this problem,a hysteresis comparison method based on three point comparison is used.In order to improve the tracking speed and tracking accuracy of the system,the fixed step size of the hysteresis comparison method is improved to a variable step size.In the far away from the maximum power point,the use of large step to improve the tracking speed,near the maximum power point after the use of small steps to improve the tracking accuracy.Considering the fluctuation caused by the change of the output power of the PV cells at the maximum power point according to the slope,the area difference method is used to determine the step size.In order to verify the validity of the method of area difference hysteresis comparison method,the MPPT model of photovoltaic system is established in Matlab/Simulink,and the simulation experiments are carried out on the area difference hysteresis comparison method,the hysteresis comparison method and the area hysteresis comparison method,and the resultsare analyzed.When the light intensity and temperature are constant,the area difference hysteresis comparison method can track the maximum power point quickly and stably;the area difference step size method has faster tracking speed,but there is a shock in the tracking process;the hysteresis comparison method,although there is no trace in the tracking process,but the tracking speed is slow.When the light intensity and temperature change,the area difference hysteresis comparison method can quickly and stably track the maximum power point;the area difference step size method produces a large oscillation,which may lead to miscarriage of justice;the hysteresis comparison method in tracking the maximum power point,although there is no shock,but the tracking speed is still slower than the area difference hysteresis comparison method.The experimental results show that the area difference hysteresis comparison method both tracking speed and tracking precision in tracking the maximum power point,the external environment changes also can resist the shock system,it has a strong anti-interference ability.