Research And Implementation Of MPPT Control Algorithm On Photovoltaic Power System

While enjoying the convenience of modern technology,people are also beginning to pay attention to energy issues,namely the lack of fossil fuels and the environmental pollution caused by the use of traditional fuels,which makes it necessary to develop clean and environmentally friendly green energy.In green energy,solar energy has a unique advantage,and solar power has become one of the effective ways to develop and use solar energy.Among them,photovoltaic cells as an important component of energy conversion,its output characteristics are not only related to the load but also affected by the external environment.In order to improve the photoelectric conversion efficiency,it is necessary to use the maximum power point tracking strategy.Based on the mathematical model of photovoltaic cell,the output characteristics of photovoltaic cell model are studied.Combined with the conductance increment method,a three-stage variable step size conductance incremental MPPT(Maximum Power Point Tracking)strategy is proposed.At the same time,tracking performance of the three-stage variable step size conductance increment method is simulated.Based on the research of self-optimization algorithm,the maximum power point tracking is simulated by using the foraging characteristics of bacterial population.The simulation model is established by Matlab/Simulink simulation platform and the tracking performance of each algorithm is simulated.The main work done is as follows:(1)Based on the research of photovoltaic cells,the structure,classification and power generation principle of photovoltaic cells is studied.The theoretical model of photovoltaic cells is theoretically analyzed.According to the mathematical calculation,the engineering model of photovoltaic cells that is suitable for in different environments is derived,and the output characteristics of photovoltaic cell models are simulated and verified.(2)The principle of maximum power point tracking control is studied.Combined with the simulation of photovoltaic cell model,the output power of constant voltage method,disturbance observation method and conductance increment method under the stable and severe changes of illumination intensity are analyzed.The advantages of the three algorithms are compared.Based on the conductance increment method,an improved variable step size conductance increment method is proposed,which is a three-stage variable step size conductance increment method.The algorithm sets the upper and lower limits for the step size adjustment coefficient compared with the variable step length conductance increment method.The trend of the step adjustment coefficient curve is analyzed,and the tracking effect before and after the algorithm improvement is compared and analyzed.The results show that the three-stage variable step size conductance increment method not only maintains the smalldisturbance of the conductance increment method,but also shortens the tracking time to5~6ms.(3)According to the tracking principle of MPPT,combined with the foraging characteristics of the bacterial population to achieve maximum power point tracking.The chemotaxis operation and migration operation of the traditional bacterial foraging algorithm were optimized,and the calculation of the swimming step size and migration probability with the change of the fitness value of the bacteria was proposed.According to the output characteristics of the photovoltaic cell and the maximum power point tracking mechanism,the fitness function of the bacteria and the initial position of the individual bacteria were established.The results show that the improved algorithm has a significant improvement in tracking speed and accuracy at the maximum power point.(4)Based on TMS320F28335,the experimental platform of photovoltaic power generation system is built.The platform consists of hardware circuit and software module.The hardware circuit includes a main control circuit,a voltage and current signal acquisition circuit,a MOSFET drive circuit,and a Boost circuit;the software module design is mainly composed of an A/D sampling module,an MPPT module,and a PWM generation module.The three-stage variable step size conductance increment method was verified by the established experimental platform.The experimental results show that the average tracking efficiency of the three-stage variable step size conductance increment method can reach97.3%,and the maximum power point tracking is basically realized.