Droop-Based State-of-Charge Balancing Approach for Energy Storage Units in Autonomous Microgrids

The proper operation of microgrids relies on the efficient functioning of all converters within the system. If a converter fails for any reason, the microgrid may not meet operational requirements. One common cause of converter failure is when battery energy storage units (BESUs) are charged or discharged beyond their permissible limits, leading to their state-of-charge (SoC) exceeding maximum or minimum thresholds. This paper proposes a droop-based control approach, in which each converter injects or absorbs active power based on the SoC of its BESU. This method balances the SoC of all BESUs gradually and prevents overcharging or over-discharging in any unit. The effectiveness of the proposed method is validated through simulations in MATLAB/Simulink for an AC microgrid with three parallel converters. Although this paper focuses on an AC microgrid, the proposed method could easily be applied to DC microgrids.