A reference current perturbation method for islanding detection of a multi-inverter system

An active islanding detection method without destabilizing the system gives the advantage of accurate decision and the capability to keep the micro-grid energized while islanding occurs. Harmonic and perturbation current injection are such active methods, but none in the literature has discussed about islanding detection in multi-inverter systems. This paper proposes an active islanding detection method for multi-inverter systems which works based on perturbation of direct (d-) and quadrature (q-) axis reference currents of inverters. The perturbations are synchronized according to voltage phase at point of common coupling (PCC) to avoid interaction. The q-axis voltage at PCC is considered as the output of system and the frequency response (FR) of system is obtained analytically for normal and island modes. The results show that the FR of system especially its phase has a noticeable difference in normal and island modes, which islanding can be detected by comparing the phase of system FR with a proper threshold. At the end, the analytical results are confirmed by some simulations using the software PSCAD/EMTDC.