In this paper a novel hybrid method for islanding detection of inverter- based distributed generation is proposed. This algorithm which is a combination of Slip mode frequencyshift (SMS) and reactive power versus frequency (Q−f) as active methods detects the islanding phenomena by forcing the DG lose its stable operation and drift the frequency out of the allowed normal range of the frequency relays. A simple passive islanding detection scheme that relies on frequency relays such as under/over frequency protection (UFP/OFP) would be sufficient to detect the moment of islanding. For demonstrating the performance of the proposed method, it is evaluated under the IEEE 1547, UL 1741 anti-islanding test configuration and multiple-DG operation. The studies reported in this paper are based on time-domain simulations in the MATLAB/Simulink. The proposed hybrid method detects islanding more efficiently for loads with high quality factor (Qf); also it operates accurately in condition of load switching and does not interfere with the power system operation during normal conditions. Simulation results prove that the proposed method decreases the time of islanding detection and has less Non Detection Zone in comparison to previous methods. In addition, the technique represents to be robust under multiple-DG operations.
