Lifting scheme‐based matched wavelet design for effective characterisation of different types of voltage sag

Abstract This study presents a novel scheme for designing biorthogonal wavelets matched to the voltage sag (VS) signals. Instead of using standard wavelets, matched wavelets designed in this study can extract more distinguishing features for better characterisation of sag signals, although this study proposes only the designing process of matched wavelets. The key method used for designing matched wavelets is the lifting scheme, which has never been reported in the literature for constructing matched wavelets for PQ signals. Besides using the lifting scheme, the proposed work preprocesses sag signals to make input signal of lifting scheme rich of sag‐related information. During pre‐processing, 1‐D sag signal is first converted to 2‐D form for capturing information of every small transition (which may be overlooked in 1‐D form) and then made 1‐D by ring projection to implement 1‐D lifting scheme. In this way, biorthogonal wavelets have been well matched to every type of VS signal collected through the experimental setup simulating different line faults, induction motor starting, transformer energisation and heavy load starting. Also, the characteristics of designed wavelets are evaluated in a MATLAB environment using frequency response and pole‐zero mapping in z ‐plane. Higher PSNR values during signal reconstruction proved outperformance of newly designed matched wavelets.