Abstract
Due to global energy crisis and severe environmental pollution, the photovoltaic (PV) system has become one of the most important renewable energy sources. Many previous studies on solar charger integrated system only focus on load charge control or switching Maximum Power Point Tracking (MPPT) and charge control modes. This study used two-stage system, which allows the overall portable solar energy charging system to implement MPPT and optimal charge control of Li-ion battery simultaneously. First, this study designs a DC/DC boost converter of solar power generation, which uses variable step size incremental conductance method (VSINC) to enable the solar cell to track the maximum power point at any time. The voltage was exported from the DC/DC boost converter to the DC/DC buck converter, so that the voltage dropped to proper voltage for charging the battery. The charging system uses constant current/constant voltage (CC/CV) method to charge the lithium battery. In order to obtain the optimum PI charge controller parameters, this study used intelligent algorithm to determine the optimum parameters. According to the simulation and experimental results, the control parameters resulted from PSO have better performance than genetic algorithms (GAs).
Highlights
Effective utilization of solar energy is an important research subject of photovoltaic (PV) system at present, and using the electric energy generated by solar cell is the key
This study found that the proposed microcontroller 18F8720 of the portable solar cell charging module can make the firststage DC/DC boost converter track the maximum power point of solar cell and supply electric energy for the secondstage DC/DC buck converter, so as to increase the efficiency of charging module
(1) This study proved that in the first-stage Maximum Power Point Tracking (MPPT), the variable step size incremental conductance method (VSINC) method can track the maximum power point faster than the fixed step size incremental conductance method and can track the maximum power point promptly when the solar irradiance is changed
Summary
Effective utilization of solar energy is an important research subject of photovoltaic (PV) system at present, and using the electric energy generated by solar cell is the key. Many studies of the charger of PV system use single-buck converter to discuss the overall MPPT and charge control system [6]. The defect in using single-buck converter to control the overall system is that one converter only controls one system; in order to achieve the MPPT of solar energy and to control the lithium battery charging, there must be a switching mechanism to identify the control method selected by the system. This single-buck converter system is unable to implement MPPT and charge control simultaneously. The experimental results were compared with simulation result to prove the effect of the proposed control theory
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