Study On Photovoltaic Charger Based On MPPT Technology

ABSTRACT:Photovoltaic (PV) charger is the connecter of PV cells and battery, which saves power from PV cells to battery. How to improve the charge efficiency is the key technology of photovoltaic power generation, but the traditional charger cannot track the maximum power point of the photovoltaic cells, which reduces the charging efficiency and leads to the loss of energy. A photovoltaic charger is designed through studying the maximum power point tracking (MPPT) technology, which is with practical significance for improving energy efficiency.The thesis analyzes the output characteristics of photovoltaic cells under different environments, and the maximum power point tracking technology including control principle and method are studied. In order to overcome the disadvantage of traditional maximum power point tracking algorithm, an improved perturbation and observation method based on gold segmentation is proposed, which can increase the tracking speed and accuracy. Based on the study of the principle of battery charging and discharging, a feasible scheme is accomplished.The hardware and software arithmetic were achieved. In the hardware, the ATmega48 single chip was chosen as the micro controller, and the flyback converter was designed as the DC/DC transform topological, which was to change the load characters of PV cells in order to track the maximum power point. At the same time, the detection circuit and the charging and discharging circuit were designed. In the software, the maximum power point tracking algorithm was realized, and charging module and discharge module were designed. PWM with adjusting duty cycle was generated to track the maximum power point, and to achieve the phases charging of the battery. In addition, the discharging and the protection from over discharge were designed.Finally, simulation was built to prove the algorithm and circuits. Experimental plat was built and run the program. The results show that the algorithm can track the maximum power point fast and smoothly, and each module work properly, which meet the design requirements.