Extraction of harmonics using composite observers

Online extraction of individual harmonics from repetitive signals using a composite asymptotic observer is presented in this paper. The settling period and the bandwidth of the observer depend on how far the observer poles have been placed from the origin of the s-plane or the z-plane. The errors in the magnitude and phase of the extracted components, due to the deviation of the signal from the central frequency of the observer, are made very small by providing an integrated phase-locking arrangement. Further improvement in the accuracy, particularly in the extracted higher harmonics, is due to the introduction of multirate sampling. © 2007 IEEE.