A hybrid time-frequency approach based fuzzy logic system for power island detection in grid connected distributed generation

A new time-frequency approach for power island detection in distributed generation systems is presented in this paper, using a hybrid fast variant of the S-Transform (ST) algorithm and a fuzzy expert system. The fast S-Transform algorithm with different types of frequency scaling, band pass filtering and interpolation techniques, results in significantly reduced computational cost, than the conventional S-Transform approach. The relevant spectral features of negative sequence voltage and current signals obtained from the distributed generation (DG) system terminals are extracted from the time-frequency matrix, obtained through fast ST. These features are used as inputs to a fuzzy expert system (FES), to distinguish between an islanding or non-islanding event, over a variety of operating conditions of the DGs including the change of system configurations, power imbalance, etc. The accuracy and response time of this new approach is compared with several well-known techniques (including time-frequency transform based methods), by applying it on both standard and existing distribution networks. (C) 2012 Elsevier Ltd. All rights reserved.