A novel, digitally-controlled, portable photovoltaic power source

Abstract

This paper is to present a novel, digitally-controlled, portable photovoltaic (PV) power source that can be used as a standalone power source in remote missions or made on the jacket to power portable personal electronics. Since the solar cell has a nonlinear voltage-current characteristic, the photovoltaic power system has to track the solar array maximum power point to ensure the efficient operation. The battery is used to store energy when the solar irradiance is sufficient or the load is light and to provide energy to the load in the case of no sunlight or a heavy load. For advanced batteries such as lithium ion cells, the charging current or voltage should be limited in order to protect the battery. The charging and discharging currents are regulated by a charger and a discharger respectively. Since the battery voltage depends on its state-of-charge and the solar array peak-power voltage varies with temperature level, illumination level and age of the solar array, it is essential to cascade a power converter at the system output to obtain bus regulation. To reduce the solar array temperature, a shunt regulator is used to limit the charging current or voltage of the battery by dissipating the excess solar array power. In this paper, an integrated, multi-objective digital power controller for this PV power source is presented, and a state machine based model of the multiobjective controller is described. The large-signal behavior of the system is analyzed. The controller design is then verified by numerical simulation in the virtual test bed (VTB) environment.