Parameter Boundary Characterization for DC Microgrid Islanding Detection Based on Time-Domain Voltage Oscillation Trajectory Analysis

Unintentional islanding events cause potential threats to the safety of dc microgrids. Selected frequency islanding detection is considered a promising technology thanks to its good power quality and high detection accuracy. However, the conventional frequency-domain-based islanding detection parameter boundary cannot consider the impact of detection time, which causes a quite slow detection speed and thus leads to detection failure. To overcome this obstacle, a linear model of the islanding dc system is developed first to analyze the steady-state response of the voltage at the point of common coupling (PCC). On top of that, the components of the islanding system characteristic equation are analyzed based on modal analysis, which lays a good foundation for simplifying the time-domain response model of the PCC voltage. Then, the oscillation trajectory of the PCC voltage triggered by the islanding event is characterized in the time domain, which facilitates the analysis and calculation of islanding detection time. Furthermore, the boundary of the islanding detection parameters considering the detection time effect is accurately depicted to guide the resonator design. In this manner, the effect of resonant parameters on the detection time can be evaluated visually while the fast detection speed is also ensured. Finally, the proposed method is validated in simulations and hardware-in-loop experiments.