Voltage drifting islanding detection methods (IDMs) force the voltage 1 at point of common 2 coupling (PCC) to move outside the appropriate limits, so that under/over voltage protection 3 disconnects distributed generation (DG) units. This kind of IDMs does not possess the advantage of 4 keeping micro-grid energized after islanding occurrence. There are active IDMs without forcing the 5 islanded micro-grid to lose its stable operation but they degrade the power quality because of 6 perturbation injection. In this study, an active IDM is proposed which makes the second harmonic 7 of PCC voltage drift suddenly after islanding occurrence and pass a predefined threshold value 8 without affecting the fundamental component. When islanding is detected the method is deactivated 9 and the voltage and frequency remain in expected limits in the conditions of power balance. Another 10 advantage of the proposed method is that it decreases the second harmonic of PCC voltage in grid11 connected mode and improves the power quality of system unlike other active IDMs. Regression 12 analysis is utilized to distinguish islanding event from non-islanding ones that increase the second 13 harmonic of PCC voltage. The UL 1741 test results for two connected DG units show that the 14 proposed method detects islanding occurrence in a multi-inverter system in less than 100ms. Also, 15 the correct performance of the proposed method has been shown for non-islanding conditions. The 16 paper simulations are performed using PSCAD/EMTDC software.

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