Abstract：When the power generated by the distributed power generation system matches with the demand power of the local load, and the angle of the load equals that of the current disturbance, even if the islanding occurs, the voltage at the point of the common coupling (PCC) is always within the range of non-detecting zone (NDZ), therefore, it is difficult for the active frequency drift (AFD) method to detect the islanding effect. As for the problem, a novel current-disturbing method in the 2Nth period is proposed in this paper. That is, the same current is controlled as AFD method in the (2N) th voltage period, and in the (2N+1)th voltage period the current does not be distorted, but it is in phase with the voltage. The islanding can be identified by judging whether the error of the voltage frequencies at PCC between the (2N) th and (2N+1)th periods changes alternately in the form of the positive and negative signs. The simulation and experimental results verify that this method can resolve the problem of NDZ effectively and is also applied to the grid-connected operation for many inverters.
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2009, Vol. 24 
