Battery Saving Mode in Grid-Forming Battery Storage Systems for Islanded Microgrids

This study presents a novel control strategy for Photovoltaic (PV) power plant controllers, emphasizing their integral role in grid regulations. Modern PV power plants are increasingly required to participate intelligently in grid services during operation. Our proposed PV power plant controller is a smart, sophisticated structure, capable of operating in various modes based on the network status. It monitors the charging level of the connected Battery Energy Storage System (BESS) and the demand load to ensure effective battery management. In islanded microgrids, especially those powered by PV systems, maintaining the health of BESS is crucial. We introduce a grid-forming operation and a battery saving (BS) mode for BESS. The BESS operates in two primary modes: discharging when demand exceeds PV-generated power, and charging when generation surpasses demand. A significant challenge arises as the battery nears its maximum State of Charge (SOC_max), risking overcharging and reduced lifespan. To address this, we propose an algorithm that adjusts the PV system to operate sub-optimally, deviating from the Maximum Power Point Tracking (MPPT) mode. This adjustment prevents engagement of the charging mode at SOC_max. Simulation results show that our algorithm facilitates seamless transitions between battery modes during grid formation, ensuring voltage and frequency stability without compromise.