Hybrid islanding detection method by virtual synchronous generator in micro-grids with flexible DG

Islanding detection (ID) is one of the important tasks in protection systems of micro-grid with flexible DG (FDG). In many years lots of methods for ID is proposed. Any of these methods have some advantages and disadvantages for instance active methods have a small non detection zone (NDZ) despite of distortion in power quality and passive methods maintain the power quality but they can´t detect all conditions since they have remarkable NDZ. In this paper a modified control structure for an inverter that emulates the synchronous generator proposed which the ID control loop is modeled by virtual rotor damper windings. For implementation of this ID method according to features of rotor damper windings, discrete wavelet transform (DWT) is applied to exploit the signal transient specification in order to activate the virtual rotor damper windings. The disturbances that inject to the system in sever transient mode is maintain the power quality in desired level, furthermore it could detect islanding in proper time. The efficiency of this new hybrid ID method simulated in MATLAB software and it has shown the high accuracy with low parameters deviation and smooth transition between grid-connected mode and islanding.