Frequency Disturbance Triggered D-Axis Current Injection Scheme for Islanding Detection

An islanding detection technique, based on monitoring of impedance based parameter at the terminal of distributed generators (DG) through the low frequency current injection is proposed in this paper. To reduce the power quality issues, current injection is initiated only during the grid disturbances. The disturbances are identified by comparing the frequency data of the DG bus with respect to reference substation bus. After the disturbance identification, a low frequency current is injected through the inverter d-axis current controller. An impedance based parameter is formulated to check the status of operation of microgrid. The islanding detection parameter is a function of Thevenins impedance seen at the inverter DG terminals. The main advantage of the proposed method is that, the power quality degradation associated with current injection methods is considerably minimized. Further, the considered islanding detection parameter is independent of the operating condition of inverter based DG. Various islanding and non-islanding cases are simulated to study the selectivity of the proposed technique. The simulation and control hardware in the loop test results show the effectiveness of the proposed technique in identifying islanding in less than 170ms.