A hybrid technique for islanding detection of an inverter based distributed generation

Passive relays may not be able to detect islanding of a distributed generation in a timely manner when the active power mismatch at PCC is low. In this paper a hybrid technique has been implemented for islanding detection of a DG under low active power mismatch condition. The technique combine´s the rate of change of frequency (ROCOF) technique with the method of reactive current injection at inverter terminal. Further a cumulative sum of rate of change of frequency (CSROCOF) index is successfully obtained as an islanding detection parameter for the proposed hybrid islanding detection technique. An adaptive scheme is also implemented which reconfirms the islanding state once the islanding is suspected by CSROCOF value. This avoids the possibility of false tripping. Test system is simulated using MATLAB.