A Power Management Strategy for PV/Battery Hybrid Systems in Islanded Microgrids

In this paper, a power management strategy for PV/battery hybrid systems in islanded microgrids is proposed. The control strategy enables the photovoltaic (PV)/battery unit to operate as a voltage source that employs an adaptive droop control to share the load with other sources while charging the battery. Also, the PV/battery unit can track and supply the maximum PV power to the microgrid as long as there is sufficient load. Otherwise, the hybrid unit will autonomously follow the changing load while storing the excess energy in the battery. The control strategy is designed to modify the PV operating point to match the load autonomously whenever the available PV power is higher than the load and the battery is fully charged. In addition, the battery can provide the operational functions that a separate storage unit may provide in an islanded microgrid, such as regulating voltage and frequency, and supplying deficit power in the microgrid. This is achieved by utilizing multi-loop control and multi-segment adaptive droop control without relying on communications or a state machine. Small-signal models of the proposed control loops are developed to investigate system stability. The system performance is validated using experimental results from a 3-KVA prototype microgrid.