Flexible Power Control of Distributed Grid-Connected Series-Photovoltaic-Battery Systems

To enhance the power quality and stability of photovoltaic (PV) systems, energy storage elements such as batteries can be included. Among various structures of PV-battery-hybrid (PVBH) systems, the series configuration attracts much popularity. However, certain operating conditions have not previously been considered for the series PVBH system. For instance, when the electrical grid is overloaded, the power generation of the PVBH system should be regulated below a certain constraint. Moreover, when the battery state-of-charge (SoC) reaches an upper or lower limit, the battery converter may lose its capability in power buffering. To address these issues, a flexible power control approach for the grid-connected series PVBH system is proposed in this paper. With the proposed control method, the PV power variations can be compensated by the battery operation following a desired ramp-rate, and the total power can be limited to a certain level in order to avoid potential overloading. When the PV power is higher than the grid demand, the surplus PV power can either be absorbed by the battery or discarded depending on the battery SoC. Experimental results from hardware prototype have validated the effectiveness of the proposed solution.