Fuzzy Logic Control of the Ultracapacitor Interface for Enhanced Transient Response and Voltage Stability of a DC Microgrid

This paper proposes a novel fuzzy logic-based scheme to control the power flow from an ultracapacitor (UC) in a battery-UC hybrid energy storage system of a dc microgrid. The fuzzy logic controller determines the current reference for the UC converter to regulate the dc bus voltage tightly. Low-bandwidth controllers are designed for battery interfacing converter, which in combination with the proposed fuzzy controller, improve the quality of the current drawn from the battery. The fuzzy controller is simple to design and does not require the knowledge of the mathematical model of the system. It is a single input single output controller, which incurs low implementation complexity. It does not have “wind-up” issues as in the traditional proportional integral controller (PI)/PID controllers, which makes the controller relatively faster. In addition, the control strategy does not demand load current sensing. Low pass filter high pass filter (HPF) filters are also not used in this strategy, which eliminates the nonoptimal power-sharing problem associated with the frequency-based control strategies. The presented simulation results show the superiority of the proposed strategy over the conventional frequency-based control strategy. The hardware results validate the practical feasibility of the proposed scheme.