Solar energy is mainly utilized through photovoltaic distributed generation (DG) units which are connected to the distribution network. One of the major concerns brought by DG installation is fast and reliable islanding detection in case of any fault which leads to losing the support of the main utility system. Active islanding detection methods (IDMs) are more reliable than passive ones but they cause power quality issues. Harmonic current injection as an active method has been proposed in many articles which essentially increases the harmonic components in system voltage. In this paper, second harmonic current is injected into the power system in a more wisely manner. In grid-connected mode the second harmonic voltage at point of common coupling (PCC) is reduced and power quality is improved while the harmonic injection causes an exponential rise in second harmonic voltage straight away after islanding occurrence. By monitoring and comparing the second harmonic voltage at PCC with a proper threshold value the islanding occurrence can be detected reliably in a short duration.

Keywords