Supercapacitor-based Active Stabilization Method for DC Microgrid with Constant Power Load Causing Instantaneous Instability

In this paper, an active stabilization method using supercapacitor for a DC microgrid with a constant power load (CPL) causing instantaneous instability is proposed. DC microgrid has several advantages over its counterpart AC microgrid, such as high reliability, efficiency, and power quality with straightforward control. The share of tightly regulated loads, called CPL, is gradually increasing. These loads impose instantaneous instability problems in the DC bus as a major concern. As most of the transient components' frequencies are less than the switching frequency, and the magnitude is smaller than the DC link voltage, average model of the converters is sufficient to analyze the stability of the DC microgrid. Thus, in this paper, an average model is used. Lithium-Ion battery is used for energy time-shift to deal with the intermittent nature of renewables. A combined control strategy is developed for the battery and supercapacitor to facilitate active stabilization to reduce oscillation in DC bus voltage caused by CPL. Transient and high-frequency component of the reference current is assigned to the supercapacitor, whereas DC and low-frequency component reference current are assigned to the battery. Solar photovoltaic generation is considered, which interfaces to the DC bus via a practical DC-DC boost converter. This makes the stability analysis more generous. Simulation work is performed in MATLAB Simulink environment, and the results are verified with Hardware In Loop (HIL) OPAL-RT (RT-4510) simulator.