Photovoltaic Charge And Discharge Controller And Its Application

ABSTRACT:A photovoltaic charge and discharge controller combined with maximum power point tracking (MPPT) can effectively reduce the cost of solar energy applications. In this thesis, the structure of photovoltaic controller and MPPT are studied in depth.Firstly, the basic working principles of solar cells and lead-acid batteries have been researched. Through the simulation model of the solar cell and the lead-acid battery, the solar cells’ output performance has been shown, and the main influence factors that shorten the life of the lead-acid batteries during the charging process have been analyzed. All the work mentioned above laid a solid foundation of the follow-up research and design for the photovoltaic charge and discharge controller.Secondly, several common charging methods have been researched. Combined the input and output property of the battery with the uniqueness of photovoltaic system, a three-stage charging method with MPPT has been designed. Then the study of the Maximum Power Point Tracking has been undertaken in-depth. Based on the buck circuit designed in this thesis, the simulation model of MPPT has been established. Then, the simulation is conducted and the results demonstrate the feasibility of the MPPT control scheme, and the suitable tracking algorithm is selected through the simulation analysis.Thirdly, this system uses AVR microcontroller as the main controller. The voltage of the solar cells and batteries are constantly detected. The full charge, the constant-voltage charge and the float charge are respectively achieved, which based on adjusting the duty ratio of the switch through the feedback of charging current or the charging voltage. This thesis has completed the hardware design of the photovoltaic charge and discharge controller and accomplished the relevant algorithm and program.Finally, the photovoltaic charge and discharge controller is applied to the solar garden lamp system. Experimental results demonstrate that this controller implements the charge and discharge control function effectively in the solar garden lamp system. The expectant result has been verified in actual application.