Adaptive droop control for balancing SOC of distributed batteries in DC microgrids

Abstract

To guarantee efficient and stable operation of a microgrid, overcharging and unbalanced state of charge (SOC) of batteries have to be mitigated. An adaptive droop control scheme is proposed in this study to provide energy management between distributed batteries having unbalanced SOC and different capacities. The proposed approach suggests using a droop factor proportional to the nth order of SOC in the charging mode and inversely proportional to the nth order of SOC in the discharging mode. Moreover, a modification is proposed to adapt the performance taking into account the battery relative capacity. The relative capacity of an individual battery is defined as the ratio between the maximum capacity of all batteries and the battery capacity. The proposed adaptive droop control scheme is investigated and analysed based on an accurate model of dc microgrid incorporating lithium-ion battery, photovoltaic, permanent-magnet synchronous generator-based wind energy system and constant power loads. Several operating conditions were considered to validate the proposed control approach. The proposed control scheme has been succeeded in keeping the dc bus voltage within limits and equalising SOC of batteries, either having similar or having different capacities.