Optimized destabilizing islanding protection scheme for grid-tied inverters insensitive to short term network disturbances

When interconnecting inverter based distributed generation (DG) systems to the distribution grid, an islanding detection is essential to avoid substantial safety and performance implications. Many anti- islanding methods currently used for grid connected inverters have weaknesses as high sensitivity resulting in spurious tripping or distortion of the output currents, particularly in multi-inverter installations. The main objective of the work presented here is to develop a new destabilising anti- islanding detection scheme, which combines an active frequency shift technique using positive feedback with a Rate of Change of Frequency (RoCoF) detector and an innovative control algorithm. It enables to discriminate between short term frequency disturbances on the network and transition to or operation of an undesirable island. The optimized approach presented here reliably avoids unintentional islanding and furthermore exhibits optimal performance during frequency fluctuations in the network. It will be demonstrated that the new scheme has better performance than existing ones by using a SIMULINK model.