An enhanced control strategy for an ultra-fast EV charging station in a DC microgrid

Uncoordinated and fast electric-vehicle (EV) charging schemes have significant impacts on the dynamic operation of a microgrid. This paper proposes an enhanced control method for an ultra-fast EV charging station in an islanded dc microgrid (DCMG). Ultra-fast charging stations, which utilize a high dc charging current, create high transients at the common bus voltage. Such transients are higher in islanded microgrids where the dc-bus voltage is more vulnerable due to the absence of the ac grid. Conventionally, the transients are managed by complicating the hardware such as by using a large and costly super-capacitor or superconducting magnetic energy storage. This paper proposes an enhanced software-based solution for EV chargers in a DCMG to significantly reduce the transients of the dc-bus voltage via intelligently controlling the rising time and settling time of the charging current in each sampling time based on the dc-bus voltage variations. Compared with the conventional control methods, the proposed method exhibits higher robustness against system uncertainties and unexpected disturbances, and higher resiliency against out-of-range variations of the charging current. The effectiveness of the proposed control system is validated in MATLAB Simulink, and its stability is verified using both root locus analysis and common quadratic Lyapunov function.