A modified Active Frequency Drift method for anti-islanding of grid-connected PV systems

Anti-islanding is an indispensable protecting function in grid-connected photovoltaic (PV) systems. As one of islanding detection methods, active frequency drift with positive feedback (AFDPF) methods are widely used currently. Such methods, however, increase the grid current harmonics to a large extent. This paper proposes a modified AFDPF method which can effectively detect the islanding in due course through calculating the cross-correlation index to change the rate of frequency deviation whilst keeping the increment of total harmonic distortion (THD) of the grid current small enough during normal operating situation. The corresponding numerical simulation and experiment based on the anti- islanding test standard from IEEE Std. 929-2000 demonstrate that the proposed method has better performances than the conventional detection methods.