Development of islanding detection device for PV inverters by harmonic impedance detection and performance verification using resonant circuit

When distributed generators (DGs) such as photovoltaic (PV) systems are widely employed in distribution systems, it is important to quickly prevent the islanding operation caused by a power system fault to ensure electrical safety. So, we propose a novel islanding detection method by harmonic injection synchronized with the exciting current harmonics of the pole transformer. We have developed the prototype inverters that apply the proposed method and carried out an experimental study with a resonant circuit having a quality factor ranging from 0.5 to 3.0. We were able to show the feasibility of detecting the islanding operation quickly and reliably, even if the islanding state is in the nondetection zone. According to the experimental results, it was demonstrated that mutual interference does not occur owing to the synchronous state between the active signals, and it was also shown that the proposed method is applicable to the islanding detection system under clustered installation of PV systems. © 2013 The Institute of Electrical Engineers of Japan.