Research On MPPT Algorithm Charging Controller For PV Systems

Photovoltaic charger is the connecter of PV cell and battery, which saves power from PV cell to battery. How to improve the charge efficiency is the key technology of photovoltaic power generation, but the traditional charger cannon track the maximum power point of the photovoltaic cell, which reduces the charging efficiency and lead to the loss of energy. A photovoltaic charger is designed through studying the maximum power point tracking technology, which is improving energy efficiency.The thesis is analyzed the output characteristics of photovoltaic cell and studied the maximum power point tracking technology. Through the ideal condition of the PV cell output characteristics analysis and simulation to overcome the traditional MPPT speed slow, low accuracy, poor anti-interference ability and low output efficiency and to find a suitable MPPT control strategy for small PV system. In order to reduce the vibration output of PV system, the artificial immune theory is applied to the fuzzy MPPT algorithm formed the immune fuzzy MPPT algorithm. At the same time, combined with the analysis of three phase dynamic model of lead-acid battery, the charging algorithm conducted in-depth research and exploration, using reasonable control strategy made full use of the PV cell output energy and consistent with the ideal charging curve of the lead-acid battery.The hardware and software arithmetic are achieved. In the hardware, the STM8S single chip is chosen as the micro controller and the Buck main circuit topology is designed as the DC/DC transform topological, which is to change the load characters of PV cell in order to track the maximum power point. At the same time, the detection circuit and the charging circuit are designed. In the software, using C language to write the corresponding control procedures and algorithms, and charging module and protection module are designed. PWM with adjusting duty cycle is generated to track the maximum power point and to achieve the phases charging of the battery.Finally, simulation and circuit are built to prove the algorithms and circuits. Experimental plat is built and run the program. The results show that the algorithms can track the maximum power point fast and smoothly. According to the voltage state of the lead-acid battery changing controller corresponding charging ways, when the MPPT stage can quickly track changes according to the external environment, improve the dynamic characteristics of the PV system output and the output efficiency of the system, response speed and robustness, and reduce the effects of harmonics on the load. And each module work properly, which meet the design requirements.