An adaptive droop control method for balancing the SoC of distributed batteries in AC microgrids

This paper proposes a new multi-segment adaptive droop control method, applied in islanded AC microgrids with distributed energy storage systems (DESSs) and hybrid PV/Battery units, for balancing their state of charge (SoC). The power/frequency characteristic curves are adjusted locally in real-time, based on the SoC level of the respective battery. Aim of the control is to maintain a comparable number of charging/discharging cycles among the batteries, while preserving the power balance in the islanded microgrid. The control strategies are implemented in each battery without relying on communications or a central management algorithm. The microgrid frequency is used as communication parameter in order to adjust the charging/discharging rate of each storage system. Detailed simulation results verify the effectiveness of this method in an islanded microgrid consisting of several loads, powered by PVs, hybrid PV/Battery units and DESSs.