Accurate Methods for Signal Processing of Distorted Waveforms in Power Systems

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Research Article Accurate Methods for Signal Processing of Distorted Waveforms in Power Systems A. Bracale,1 G. Carpinelli,1 R. Langella,2 and A. Testa2 1 Dipartimento 2 Dipartimento

di Ingegneria Elettrica, Universit`a degli Studi di Napoli Federico II, Via Claudio 21, 80100 Napoli (NA), Italy di Ingegneria dell’Informazione, Seconda Universit`a degli Studi di Napoli, Via Roma 29, 81031 Aversa (CE), Italy

Received 3 August 2006; Revised 23 December 2006; Accepted 23 December 2006 Recommended by Alexander Mamishev A primary problem in waveform distortion assessment in power systems is to examine ways to reduce the effects of spectral leakage. In the framework of DFT approaches, line frequency synchronization techniques or algorithms to compensate for desynchronization are necessary; alternative approaches such as those based on the Prony and ESPRIT methods are not sensitive to desynchronization, but they often require significant computational burden. In this paper, the signal processing aspects of the problem are considered; different proposals by the same authors regarding DFT-, Prony-, and ESPRIT-based advanced methods are reviewed and compared in terms of their accuracy and computational efforts. The results of several numerical experiments are reported and analysed; some of them are in accordance with IEC Standards, while others use more open scenarios. Copyright © 2007 A. Bracale et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.



The power quality (PQ) in power systems has recently become an important concern for utility, facility, and consulting engineers, since electric disturbances can have significant economic consequences. Several studies have characterized such PQ disturbances. Because of the widespread use of power electronic converters, the interest in waveform distortions has increased, especially because these converters are often the cause of such distortions. Waveform distortions are usually described as a sum of sine waves, each one with a frequency which is an integer (harmonics) or noninteger (interharmonics) multiple of the power supply (fundamental) frequency. As commonly known, the waveform distortion assessment is characterized by analysis and measurement difficulties in the presence of interharmonics. These types of difficulties are due to the change of waveform periodicity and small interharmonic amplitudes, both of which can contribute to high sensitivity to desynchronization problems. A method aimed to standardize the harmonic and interharmonic measurement has been proposed by the IEC [1, 2]. This method utilizes discrete Fourier transform (DFT) performed over a rectangular time window (RW) of exactly ten cycles of fundamental frequency for 50 Hz systems or exactly twelve cycles for 60 Hz systems, corresponding to approxi-

mately 200 milliseconds in both cases. Practically speaking, the pre-determined wi