This paper proposes a passive islanding detection method based on computing a set of frequency dependent reference impedance magnitudes and comparing them with the measured impedance magnitudes at the point of common coupling (PCC). The reference impedance may be identified online over a selected frequency band from the measured voltage and current at PCC. Islanding is detected when the magnitude differences between reference impedance and measured impedance over the chosen frequency band are smaller than a preset threshold.
Robustness of the proposed method is verified in a distribution network, the method avoids misdiagnosing islanding condition as normal condition. Performance analyses are discussed from two perspectives of non-detection zone (NDZ) and fault detection zone (FDZ). By combining the under voltage/over voltage (UV/OV) and under frequency/over frequency (UF/OF) methods with the proposed method, the NDZs of UV/OV and UF/OF methods can be reduced.