Design and comparison of active frequency drifting islanding detection methods for DG system with different interface controls

The active islanding detection methods (IDMs) can effectively mitigate the islanding non-detection zones (NDZs) compared with passive IDMs in the inverter based DG systems but the improvement depends highly on the interface control schemes. In this paper, different reactive power variation based IDMs, including Active Frequency Drift method (AFD), Slip Mode Frequency Shift Method (SMS) and Sandia Frequency Shift Method (SFS), are implemented on the DG system with different interface controls. The performance of each IDM is further compared and the influence of the interface control schemes is also analyzed. Combined with current control, AFD can reduce the NDZs if the load is capacitive. SMS and SFS provide small NDZs because of the positive feedback especially for the load with small quality factor. In the power controlled DG system, the active frequency drifting is restrained by the outer power loop which functions as a high-pass filter, thus extending the NDZs. In the DG system equipped with the voltage control scheme, the outer voltage loop provides positive effects on the active frequency drifting IDMs so that the overall NDZs reduce. All the analysis is verified with MATLAB/ SIMULINK simulations.