Nondetection Zone Elimination and Detection Speed Improvement for DC Microgrids Islanding Detection With Adaptive Resonant Frequency

Islanding detection based on current disturbance of selected frequency (CDSF) is gaining widespread acceptance in dc microgrids due to its high detecting accuracy and good power quality. However, the selected static disturbance frequency at a specific operating state causes the expansion of the nondetection zone (NDZ) and the decrease of the detection speed under different system power conditions. In this article, the sensitivity model of current perturbation is developed to intuitively reveal the mechanism of oscillation frequency shift and the occurrence of the NDZ. Then, the theoretical resonant frequency is derived to analyze the frequency shift range with the consideration of system power changing, which provides the NDZ boundaries accurately. Moreover, an islanding detection method (IDM) with the adaptive resonant frequency is proposed to provide zero NDZ and fast detection speed by dynamically selecting the most sensitive frequency in different power operating cases. Thus, the conflict between the NDZ and detection speed is effectively addressed. Finally, the effectiveness of the proposed IDM is validated by both the simulations and experimental results.