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In this paper, comparative study between wavelet transform (WT) and -transform (ST) based on extracted features for detection of islanding and power quality (PQ) disturbances in hybrid distributed generation (DG) system is presented. The hybrid system consists of DG resources like photovoltaic, fuel cell, and wind energy systems connected to grid. The negative sequence component of the voltage signal is used in islanding detection of these resources from the grid. Voltage signal extracted directly at the point of common coupling is considered for detection of PQ disturbances. Further, the effect of variation of grid impedances on islanding and PQ disturbances and effect of islanding on the coherency between the energy resources is also presented in this paper. The study for different scenarios of DG system is presented in the form of time-frequency analysis. The energy content and standard deviation of ST contour and WT signal is also reported in order to validate the graphical results. The results demonstrate the advantages of -transform over WT in detection of islanding and different disturbances under noise-free as well as noisy scenarios.Index Terms-Distributed generation (DG), hybrid system (HS), islanding, power quality disturbance, -transform (ST), wavelet transform (WT).

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Dynamic variation in power system frequency is required to be estimated in order to implement correcting measures. This study presents power system frequency estimation by using a leaky least mean-square algorithm. The proposed approach uses a variable leak adjustment technique to avoid drifting of the weights involved in the estimation mechanism. A variable adaptation step size is also incorporated in the algorithm to attain faster convergence. The performance of the proposed algorithm is studied through simulations for several critical cases that often arise in a power system. These studies show that the present algorithm is superior over the existing ones in estimating power system frequency. Studies made on experimental data also support the superiority.

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