Abstract：The photovoltaic (PV) grid-connected inverter must have the ability of detecting islanding, whose rapidity will directly affect the safe operation of the inverter. For Slide-mode frequency shift (SMS) algorithm, the islanding detection speed reduces rapidly when the load quality factor increases. An improved SMS algorithm is put forward, in which the sine curve used by traditional SMS algorithm is replaced by parabola curve. Since the slope of the selected parabola is infinite at peak, the frequency of the voltage at the point of common coupling rapidly deviates from the grid frequency after islanding and the islanding detection time is substantially shortened. The proposed algorithm is conducted with analysis of the non-detection zone and the parameters of the curve are determined according to the maximum quality factor set by IEEE Std.2000-929. The simulation and experiment results show that the proposed parabolic SMS algorithm has little effect on power quality, and the islanding detection speed using the proposed algorithm is greatly improved.
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2013, Vol. 28 
