A New Robust Control Strategy for Multistage PV Battery Chargers

This manuscript presents a new overall control strategy for a standalone photovoltaic (PV) battery charging system. The battery can be regarded as an energy storage element in the system for reliable operation, or it can be considered as the load itself while being charged from null to full. The charger consists of a boost converter followed by a buck converter that charges the battery. The two converters are interfaced using a dc link capacitor that can be a super capacitor for increased energy buffer capability and to meet power spikes needed by the load. Traditionally, the boost converter is controlled to achieve maximum power point tracking (MPPT), while the output voltage of the boost converter is regulated by the buck converter, which connects to the battery. In this paper, a coordinated control strategy for the two converters is proposed and implemented to achieve multi-objective performance. When the optimal charging power is less than the offered maximum PV power, a power-matching control mode is initiated to keep the charging process smooth. In this mode of operation, the dc link voltage will be kept constant. When the PV maximum input power is less than the battery optimal charging power, the system shifts into MPPT control. In this paper, the dc link voltage information is used to guide the entire supervisory control system. By offering a range of voltage variation across the de link capacitor, the system can ride through fast shading or partial shading dynamics, which stabilizes the charging process in such normally occurring environmental conditions. Simulation results show the performance of the proposed control strategy.