Communication-Less Active Damping Method With VSC for Stability Improvement of Grid-Connected DC Microgrid With Selected Frequency Islanding Detection

The islanding detection method (IDM) with current disturbance of selected frequency (CDSF) in dc microgrids is gaining extensive attention thanks to its small nondetection zone and good power quality. However, the CDSF is implemented through a positive feedback loop and thus will lead to instability issues for the dc microgrid even in the grid-connected mode. Conventional stabilization control is generally employed on the distributed generator (DG) side and usually requires an additional uninterrupted communication process, which therefore decreases system reliability. In this article, the impedance model of the dc microgrid is established first to reveal the interaction instability mechanism between the voltage source converter (VSC) and DG equipped with CDSF IDM. On top of that, the notch-filter-based active damping method is proposed on the VSC side to avoid amplitude intersection of impedance near the selected resonant frequency, which effectively mitigates the instability caused by the islanding detection loop without relying on communication. Moreover, the parameter design method is further summarized to provide guidance for the selection of notch bandwidth in the proposed damper. In this manner, the stability of the grid-connected system can be improved while the islanding detecting speed is enhanced. In the end, the effectiveness of the proposed stabilizing method is verified by the experiments.