New Islanding Detection Method for Inverter-Based Distributed Generation Considering Its Switching Frequency

Islanding detection is one of the most important issues for the distributed generation (DG) systems connected to an electric power grid. The conventional passive islanding detection methods inherently have a nondetection zone (NDZ), and active islanding detection methods might cause problems with safety, reliability, stability, and power quality on a power system. This paper proposes a passive islanding detection method with the zero NDZ property by considering the switching frequency from an inverter of the DG system. Moreover, the proposed method does not cause any negative effects in the aforementioned problems because it avoids applying the intended changes such as variations of reactive power and/or harmonics, which are required in the active islanding detection methods. Several case studies are carried out to verify that the proposed method can detect the islanding operation within 20 ms, which is less than 150 ms required in a recloser as the shortest mechanical reclosing (delay) time. Moreover, this value satisfies the requirement of 2 s given in IEEE Std. 1547.