A battery/supercapacitor hybrid energy storage system for DC microgrids

This paper explores the frequency coordinating virtual impedance concept and proposes a control strategy for the co-ordination control of a hybrid energy storage system in DC microgrids. It investigates power decoupling methods to better attenuate the ripple power by filtration. Lead-acid battery and supercapacitor are used to form a hybrid energy storage system and are connected to a common DC grid through bi-directional DC-DC converters. Battery converter can absorb low frequency power variations while the high frequency power variations can be absorbed by supercapacitor converter. Battery supplies the long term power demand and supercapacitor responds to the short term power fluctuations during transient process in this proposed method. For the reduction of ripple power in the battery, this paper discusses the insertion of high order low/high pass filters for battery and supercapacitor converters instead of lower order low/high pass filters. The effectiveness of the proposed concept is shown through simulation and experimental results.