An Effective Control Algorithm For Hybrid Superconducting Magnetic/battery Energy Storage Systems Employed In Dc Microgids

DC microgrids are exposed to diverse disturbances that can cause DC bus voltage instability and power quality issues. Renewable volatility and fault occurrence on the power lines are considered as high-impact variations, which jeopardize the resilience of the microgrid. Therefore, employment of a battery energy storage system is a prominent solution to improve the stability and ensure the safe operation for end-users. However, short-term cyclic activity and abrupt power variations have adverse effects on battery lifespan. This study proposes an effective control strategy for a hybrid superconducting magnetic energy storage (SMES)/battery system to protect the battery from rapid lifetime fading and to improve DC bus voltage stability. Under the proposed strategy, SMES is the prior-responsive device, while battery mode of operation (i.e., idling, charging or discharging) depends on SMES current value. Specifically, battery is kept in idle mode as long as SMES current is within a user-defined dead band and is triggered as soon as SMES current deviates from that. In such cases, battery enters smoothly either the discharging or the charging mode following a different droop curve for each mode of operation. To verify the effectiveness of the proposed system over a battery-only system, a comparative analysis between them under two different scenarios is presented, namely PV fluctuation and DC fault.