Phase-locked loop effect on non-detection zone of unintentional islanding

The number of small power distributed generators connected to the low voltage distribution networks has increased the possibility of unintentional islanding operations. In this paper, the influence of the Synchronous Reference Frame - Phase Locked Loop (SRF-PLL) for single-phase and three-phase inverter, combined with the wider frequency and voltage protection ranges stated by the Standards, has been considered as causes of increasing possibility of unintentional islanding events. The paper is focused on the enlargement of the protection system Non Detection Zone, due to the single phase PLL on a current- controlled Inverter, as typically used in PhotoVoltaic (PV) or Renewable Energy Source (RES) applications.