Adaptive State of Charge Control for Droop-Controlled Industrial DC-Microgrids

In order to meet the challenges of upcoming decentralized energy systems, local direct current (DC) microgrids (MG) and energy storage systems (ESS) for industrial production sites have been studied. During charging and discharging processes the state of charge (SoC) of an ESS changes. Microgrid control, often based on droop curves, enables intelligent power distribution as well as voltage restoration in multi-infeed topologies and is necessary for taking care of the occurring SoC deviations. This paper compares different SoC control strategies based on droop control. An adaptive state of charge control has been developed using a proportional controller parameter (PCP) for shifting the droop curve on the current axis. In a case study the adaptive SoC control is validated for a droop-controlled industrial DC-microgrid with an ESS used for peak shaving. The performance of the adaptive SoC control is evaluated using quality criteria, e.g. peak load reduction, cut-off frequency and settling time. It is shown that the state of charge can be successfully kept within the desired range over time.