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Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 253-261). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

In this dissertation, we present the theory and application of polyspectral signal analysis techniques for interharmonics in shipboard power systems. Interharmonics are generated from various kinds of adjustable speed drives (ASD) in such power systems. ASDs are highly nonlinear devices due to the use of rectifiers and inverters. Since interharmonics can seriously hamper the normal operation of electric ships in many different ways (e.g., excitation of undesirable electrical and/or mechanical resonances, misoperation of control devices, and light flicker), the detection and analysis of interharmonic-related events is a critical issue in assessing power quality in an all-electric ship. Standard signal analysis techniques for regular harmonics are not immediately applicable to interharmonics due to their small amplitude and uncertain frequency of occurrence. Hence, we propose the use of alternative polyspectral analysis techniques such as higher-order spectra (the cross bispectrum/bicoherence) for the detection and analysis of the ASD-generated interharmonics. First, we develop the interharmonic application specific definitions of the cross bispectrum and the cross bicoherence. The statistical characteristics and frequency domain symmetries are also investigated. We apply the modified cross bispectrum to interharmonic detection problems. Due to their small amplitudes, the detection of interharmonics is sensitive to many undesirable factors such as spectral leakage and measurement error. Our analysis results demonstrate that the detection performance of the conventional DFT-based method is seriously degraded in the presence of noise. Hence, we develop a constant false alarm rate (CFAR) interharmonic detector based on the modified cross bispectrum. Our analysis and experimental results show that our method can provide more robust detection performance than conventional methods in the presence of noise. We also develop an ASD condition monitoring method based on the cross bicoherence. The key idea is to diagnose the status of the load side of an ASD from observations made at the source side. In this dissertation, we apply our method to detection and analysis of phase imbalance at the load side of the ASD. Our experimental results demonstrate that the proposed method provides a unique interharmonic signature for detection and classification of asymmetric impedance associated with the phase imbalance. Furthermore, the proposed method shows a more sensitive detection performance compared to the conventional imbalance measurement method, which enables prognosis of potential faults. A novel quadratic phase coupling detector for a single data record with coherent interharmonics is developed. The traditional bicoherence definition fails when its ’phase randomization’ assumption is not satisfied. This assumption is not appropriate for certain applications such as continuous monitoring of rotating machines. Therefore, we propose a novel quadratic phase coupling detector and compare it with previous techniques. It is shown that our detector is superior to previous detectors at high SNRs, and can also address partially coherent cases which previous approaches could not properly address. Flicker issues related to interharmonics are also discussed. We present a newly found limitation of the current IEC flickermeter regarding detecting flicker caused by low frequency interharmonics. We also present observation results of flicker responses of various lamps including light-emitting-diode (LED) lamps. Our observation results confirm that compact fluorescent and LED lamps are sensitive to high frequency interharmonics, although the IEC flickmeter can not detect flicker caused by such interharmonics. Hence, we develop an alternative flicker detection method based on down-up sampling. Our experiment results show that our method can detect flicker regardless of the value of the interharmonic frequencies. Independent of interharmonic topics, we also present our additional achievement involving application of wavelet denoising techniques to network congestion monitoring problems. This was a collaboration with researchers at the Department of Computer Sciences in the University of Texas at Austin, and mainly completed before becoming engaged in the electric ship project. By applying wavelet techniques, we could drastically enhance shared congestion detection performance over previously proposed methods. / text

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M. Tech. Electrical Engineering. / Discusses the placement of windings in the slots of high phase order induction machines (HPOIMs) leads to a stepped-like waveform of stator (rotor) MMFs which exhibit space harmonics as well as the fundamental wave. The interaction of air-gap field components, which have the same pole number but rotate at different speeds, produce the torque ripple whose magnitude depends on the product of the magnitude of the two interacting fields. The frequency of the torque ripples also depends on the difference between the speeds of these two fields. A winding configuration or a combination of different configurations that reduces some air-gap components has the edge in terms of mitigating the ripple torque contents.

Fast algorithms for potential evaluation in N-body problems often tend to be extremely abstract and complex. This thesis presents a simple, hierarchical approach to solving the potential evaluation problem in O(n) time. The approach is developed in the field of electrostatics and can be extended to N-body problems in general. Herein, the potential vector is expressed as a product of the potential matrix and the charge vector. The potential matrix itself is a product of component matrices. The potential function satisfies the Laplace equation and is hence expressed as a linear combination of spherical harmonics, which form the general solutions of the Laplace equation. The orthogonality of the spherical harmonics is exploited to reduce execution time. The duality of the various lists in the algorithm is used to reduce storage and computational complexity. A smart tree-construction strategy leads to efficient parallelism at computation intensive stages of the algorithm. The computational complexity of the algorithm is better than that of the Fast Multipole Algorithm, which is one of the fastest contemporary algorithms to solve the potential evaluation problem. Experimental results show that accuracy of the algorithm is comparable to that of the Fast Multipole Algorithm. However, this approach uses some implementation principles from the Fast Multipole Algorithm. Parallel efficiency and scalability of the algorithms are studied by the experiments on IBM p690 multiprocessors.

Darbe analizuojamos dažnio keitiklio į tinklą generuojamos aukštesniosios eilės harmonikos. Atlikti nagrinėjamo dažnio keitiklio tuščiosios veikos ir apkrovos bandymai, bei išmatuotos generuojamos į tinklą aukštesniosios eilės srovės harmonikos. Nustatyta netiesinių iškreipių faktoriaus priklausomybė nuo maitinimo įtampos dažnio ir apkrovos. Taip pat atliktas vieno iš tinklo taršos slopinimo įrenginių – linijinio droselio bandymas. Nustatyta, kad netiesinių iškreipių faktorius, priklausomai nuo apkrovos kito nuo 30 % iki 80 %, dirbant 50 Hz dažniu. Didinant maitinimo įtampos dažnį, netiesinių iškreipių faktorius kito nuo 43,3 % iki 79,5 %, esant nurodytąjai variklio apkrovai. Naudojant linijinį droselį, santykinis netiesinių iškreipių faktorius sumažinamas 5,8 %, dirbant 25 Hz, ir 9 %, dirbant 50 Hz maitinimo įtampos dažniu. Nustatyta, kad dažnio keitiklio į tinklą generuojamos aukštesniosios eilės srovės harmonikos gerokai viršino leistinąsias ribines vertes, atitinkamai 5-oji – 3,3 karto, 7-oji – 4,7 karto, 11-oji – 5,9 karto, 13-oji – 8,5 karto ir 15-oji – 1,8 karto. Taigi naudoti harmonikų filtrus rekomenduotina, norint užtikrinti sistemos patikimumą ir ilgesnį eksploatacijos laiką, taip pat filtrų pagalba galima apsaugoti tinklo iškraipymams jautrią įrangą. / The work analyses the higher order harmonics into power system generated by the frequency inverter. Perform issue frequency inverter non load and load test and established generates into network higher order harmonics. Established total harmonic distortion dependence of the mains frequency ant the load. Also was made research of one network pollution reduction equipment – line choke. It was found that harmonic distortion, depending on the load was varied from 30 % to 80 %, at 50 Hz operating frequency. Increasing mains voltage frequency, harmonic ranged changed from 43,3 % to 79,5 %, at full asynchronous motor load. Using line choke total demand distortion is reduced from 5,8 % at 25 Hz, to 9 % at 50 Hz mains frequency. Established that frequency inverter pollution of higher current harmonics significatly higher than allowable, accordingly, the 5 th – 3,3 time, the 7 th – 4,7 times, the 11 th – 5,9 times and the 15 th – 1,8 times. Thus, the use of harmonic filter ir recomended to ensure system reliability and longer service life, as well filter heps to protect for current distortion sensitive equipment.

Tone pairs constructed with the frequencies of the overtones moving in opposition to the missing fundamental frequencies they imply, produce expertise differences in the tracking of pitch direction. One interpretation of this result is that it arises as a function of rudimentary differences in the perceptual systems of musicians and non-musicians. Several experiments suggest instead a more embodied source of expertise to be found in vocal mediation such that the effect of musical experience in these tasks is the result of the most salient action of musicians: making sound. / x, 87 leaves : ill. ; 29 cm

Harmonic distortion in a power system can excite non-characteristic harmonics from converter interfaced loads and generators which can then propagate back into the system, exciting other harmonics in the system. In this thesis, a harmonic analysis tool is presented that is designed to perform high accuracy, computationally efficient, steady-state harmonic analysis of distribution systems when multiple converter interfaced loads and generators exist in the system. The harmonic analysis tool requires less detail and engineering time than PSCAD/EMTDC while offering reliable assessment of harmonic coupling problems that are not captured by existing frequency-domain harmonic analysis tools. To do this, 5 harmonic models of common power electronic converter topologies were developed and implemented into this tool. The harmonic models are shown to be highly accurate; when tested in an unbalanced system with even and odd harmonic distortion, the harmonic models showed a maximum error of less than 0.4% when compared to PSCAD/EMTDC.