Charge And Discharge Controller For Photovoltaic MPPT

Let PV charge and discharge controller acquire the function of maximum power point tracking which is one of the effective ways to improve the utilization of PV modules. The topology of charge discharge controller with MPPT function and power consumption of some related devices are studied in this thesis.On the basis of studying the common charging topology and power consumption of related components, an improved dual Buck circuit topology was designed by using of N channel enhanced MOS tube for freewheeling circuit to reduce the loss of circuit. By alternating operation of dual Buck circuit, the heat emitted by the circuit was split in half. Besides, a redundant circuit was formed which increasing the reliability of the system. Proved by MATLAB/Simulink’s simulation, contrasted with the traditional Buck circuit, in this thesis, the dual Buck circuit topology can make photovoltaic charge and discharge controller better play its role, which means the conversion efficiency of the controller is improved.In order to obtain a stable MPPT algorithm, based on the dual buck circuit topology that was used in this thesis, a variable step size perturbation MPPT algorithm was obtained, which could increase the stability of the tracking algorithm near the maximum power point. This algorithm can track the maximum power point and then gradually reduce the step size, finally prevent the emergence of the oscillation phenomenon.The characteristics of lead acid battery were analyzed and a three stage optimal charging method was got, which could ensure that the charging current of the whole charging process will be in the range of the best charging curve of MAS and effectively reduce the damage of the battery in the charging process.Based on the research above, a photovoltaic charge and discharge controller is planned by using ARM as the control core, its prototype and procedures has been completed, in addition, the controller was tested in the laboratory environment. The experimental results show that the charge discharge controller designed in this paper can obtain excellent charging efficiency, which also proves the feasibility and effectiveness of the whole system.