2014 Volume 11 Issue 6 Pages 20140143
Islanding phenomenon of Photovoltaic (PV) system should be prevented because it causes a safety problem to utility service personnel and power supply facilities. Until now, various anti-islanding methods have been proposed. However, these are mostly focus on the islanding prevention method for single PV system. Recently, PV system using micro-inverters are widely disseminated in the field. Accordingly, an islanding issue for multiple PV micro-inverter systems has been paid attention due to their interaction not to detect islanding, even though the single micro-inverter unit can prevent islanding when the single unit is only tested. This paper presents an improved active frequency drift (AFD) anti-islanding method for multiple PV micro-inverter systems. The proposed method injects every half-line cycle asymmetrical signals and uses the correlation between the injected asymmetrical signal and the corresponding half line cycle. The proposed method is verified by using PSIM simulation, compared with the conventional AFD method. It shows that the proposed method is highly effective to detect islanding even under multiple micro-inverter system while the conventional one doesn't detect islanding.
