High resolution spectrum estimation methods for signal analysis in power electronics and systems

Modern frequency power converters generate a wide spectrum of harmonic components. Large converter systems can also generate non-characteristic harmonics and interharmonics. Standard tools of harmonic analysis based on the Fourier transform assume that only harmonics are present and the periodicity intervals are fixed at 20 ms (50 Hz), while periodicity intervals in the presence of interharmonics are variable and very long. A novel approach to harmonic and interharmonic analysis, based on the “subspace” methods, is proposed. The singular value decomposition (SVD) method as applied for signal analysis was also tested for this purpose. Both new high-resolution methods do not show the disadvantages of the traditional tools and allow exact estimation of the interharmonic frequency. To investigate the methods several experiments were performed using simulated signals and the waveforms of a frequency converter current. For comparison, similar experiments were repeated using the FFT with the same number of samples and sampling period. The comparison proved the superiority of the new methods. However, its computation is much more complex than FFT, and requires more extensive mathematical manipulations