Fast Active Islanding Detection Method Based on Second Harmonic Drifting for Inverter-based Distributed Generation

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