This thesis describes a novel approach that utilizes a special property of the Hanning window to accurately detect the fundamental frequency of the data signal in the presence of harmonic and interharmonic interference. After obtaining the fundamental frequency, the same procedure is applied to all possible harmonics to be filtered for further analysis of the interharmonics. The proposed approach is validated using numerical tests. In the literature, different authors have shown the difficulty of extracting a synchronized sampling frequency from the analyzed signal and discussed the effect of deviation of the fundamental in the presence of harmonics. This thesis suggests a new approach to overcome the difficulties, even if the interharmonics present are in frequency bins near the fundamental. In order to perform the interharmonic analysis, the author followed the IEC standard draft signal processing recommendations, with the exception of using a weighted Hanning window instead of a rectangular window in order to minimize the effect of the spectral leakage, and to minimize the effect of interharmonics on the main harmonics.