Development of EN50438 compliant wavelet-based islanding detection technique for three-phase static distributed generation systems

The increased penetration of photovoltaic (PV) distributed generation (DG) often connected to grid through dc-ac interface has made islanding detection an important and challenging issue for power engineers. Several methods based on passive and active detection schemes have been proposed in the literature. Although passive schemes have a large non-detection zone (NDZ), concern has been raised about active methods because of their degrading effect on power quality. Therefore each grid-connected PV systems needs to be EN50438 compliant to ensure proper interface and power quality standard. This study proposes a db4 wavelet-based passive islanding detection scheme with almost zero NDZ for dc-ac inverter interfaced grid-connected PV DGs. The key idea is to utilise spectral changes in the higher frequency components of voltage at the point of common coupling, which occur after an islanding condition. The effectiveness of the proposed method is tested in simulation of a PV DG system and validated experimentally with an actual 7.5-kW grid-connected inverter system using the dSpace DS1104 DSP. The designed detection algorithm has been computationally less burden on the DSP.