Research On Variable Step-size Dichotomy Algorithm For Stand-alone Photovoltaic System

With the development of science and technology and the advancement ofindustrial civilization, the demands for fossil fuels are growing. The excessiveexploitation and usage of coal and oil have been having a huge impact for the globalclimate, and polluting the environment. Pollution and energy shortage forced humanbeings to search for a clean and environmentally-friendly energy replacing the fossilfuel. As a clean and renewable energy, solar power has got more and more attentionand has been developed rapidly in recent years. Because of the relatively lowphotoelectric conversion efficiency of photovoltaic solar cell and its operatingcharacteristics is affected greatly by environmental factors, maximum power pointtracking for photovoltaic cells is becoming a more and more important research topic.In this paper, photovoltaic system is designed achieving the maximum power pointtracking for solar cells.In this paper, the working principles and output characteristics are researchedand analyzed, and the simulation model of photovoltaic cell is built inMATLAB/Simulink. Then the principles and relevant knowledge of commonly usedmaximum power point tracking method and DC/DC converter circuits are studied.The variable step size dichotomy method was further improved and chosen to be theMPPT method in this paper. PIC16F877A microcontroller was chosen to be the coreof the control circuit chip of photovoltaic system, based on the working principles ofstand-alone photovoltaic system. PIC16F877A microcontroller has a low energyconsumption with high stability and built-in integrated multi-function. The variablestep size dichotomy method are programmed in MPLAB IDE in C language, andburned into the PIC16F877A microcontroller with PIC-kit2tool.The maximum power point can be rapidly found with the improved dichotomymethod with small oscillation near the MPP. The output voltage and output current ofthe solar cell are collected by the PIC16F877A microcontroller,which is featured withthe variable step size dichotomy method, controlling the duty cycle of MOSFET ofDC/DC converter and realizing maximum power tracking.