Inertia Emulation in Autonomous DC Microgrids by Attenuation and Low Pass Filtering of Capacitor Current

Abstract

With DC microgrids (DC MG) gaining attention, virtual inertia (VI) schemes for stabilizing the system voltage become increasingly important. With decreased inherent energy storage, conventional droop control causes severe fluctuations in the DC bus voltage. Hence, this paper proposes a VI scheme that emulates inertia by attenuating and low-pass filtering the converter’s capacitor current. Since the capacitor’s current is directly proportional to its rate of change of voltage, attenuating the capacitor current restricts its voltage change which would otherwise occur with higher capacitance. Thus attenuating the capacitor current virtually increases the system capacitance. However, since practical capacitors have some parasitic equivalent series resistance (ESR), attenuation of capacitor current cannot guarantee a distortion-less inertial response when ESR is high. It was found that cascading a low pass filter of time constant governed by the capacitance and ESR can compensate for its impact. Time-domain simulations performed in MATLAB/Simulink and experiments carried out in laboratory-scale setup validate the effectiveness of the proposed VI scheme.