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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
61

A novel method for major harmonic sources identification in high voltage transmission systems

Liang, Shun. January 2009 (has links)
Thesis (Ph.D.)--University of Texas at Arlington, 2009.
62

Extreme ultraviolet polarimetry with laser-generated high-order harmonics /

Brimhall, Nicole, January 2007 (has links) (PDF)
Thesis (M.S.)--Brigham Young University. Dept. of Physics and Astronomy, 2007. / Includes bibliographical references (p. 50-54) and index.
63

Nonlinear ultrasonics signal processing considerations and a nonlinear parameter for rayleigh waves /

Mueller, Thorsten Oliver. January 2005 (has links)
Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2006. / Kim, Jin-Yeon, Committee Member ; Qu, Jianmin, Committee Member ; Jacobs, Laurence, Committee Chair. Includes bibliographical references.
64

The double spherical harmonics approximation for cylindrical and spherical geometries

Wang, Chi-chung, January 1967 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1967. / Typescript. Vita. Description based on print version record. Includes bibliographical references.
65

Phase-matching optimization of laser high-order harmonics generated in a gas cell /

Sutherland, Julia Robin Miller, January 2005 (has links) (PDF)
Thesis (M.S.)--Brigham Young University. Dept. of Physics and Astronomy, 2005. / Includes bibliographical references (leaves 48-52).
66

Ισχύς σε τριφασικά κυκλώματα παρουσία αρμονικών

Καραγιώργος, Βασίλειος 03 October 2011 (has links)
Κατά την μελέτη ηλεκτρικών μεγεθών υπό μη-ημιτονοειδείς συνθήκες ιδιαίτερο αντικείμενο αποτελούν τα φαινόμενα που σχετίζονται με την ισχύ. Οι γνωστές προσεγγίσεις για την ισχύ σε ημιτονοειδή κατάσταση δεν επαρκούν και είναι εσφαλμένες. Η παρουσία ανώτερων αρμονικών καθώς και η ασυμμετρία τάσεων και ρευμάτων μας αναγκάζει σε μια διαφορετική προσέγγιση της ηλεκτρικής ισχύος. Έτσι γίνεται εύκολα κατανοητό γιατί έχει ενταθεί η ανάγκη να ορισθούν ορθώς οι συνιστώσες ισχύος ώστε  να περιγράψουμε τα φυσικά φαινόμενα ισχύος και τις ιδιότητες των κυκλωμάτων παρουσία αρμονικών  να αντισταθμίσουμε κάποιες συνιστώσες ώστε να επιτύχουμε διόρθωση του συντελεστή ισχύος  να μετρηθούν κάποιες ποσότητες για την διαμόρφωση κατάλληλου τιμολογίου ηλεκτρικής ενέργειας  να χρησιμοποιηθούν για τον καθορισμό της ονομαστικής ισχύος των συνιστούντων στοιχείων του εξοπλισμού (π.χ. καλώδια , μετασχηματιστές, γεννήτριες κ.τ.λ.)  να καθορισθούν δείκτες για την επίπτωση των αρμονικών στον εξοπλισμό. Η παρούσα διπλωματική εργασία ασχολείται με κάποια από τα παραπάνω ζητήματα και περιλαμβάνει τα κάτωθι κεφάλαια: Το Κεφάλαιο 1 αποτελεί μια γενική εισαγωγή του θέματος της παρούσας διπλωματικής εργασίας. Στο Κεφάλαιο 2 ορίζονται τα αρμονικά προβλήματα. Στο Κεφάλαιο 3 παρουσιάζονται οι κυριότερες θεωρίες ισχύος για μονοφασικά κυκλώματα παρουσία αρμονικών. Το Κεφάλαιο 4 αναφέρεται στην ισχύ σε τριφασικά συστήματα με τάσεις και εντάσεις ημιτονοειδείς. Το Κεφάλαιο 5 αναφέρεται στην στιγμιαία ισχύ σε μη-συμμετρικά ή/και μη-ημιτονοειδή τριφασικά συστήματα. Το Κεφάλαιο 6 αναφέρεται στην φαινόμενη ισχύ σε μη-συμμετρικά ή/και μη-ημιτονοειδή τριφασικά συστήματα. Το Κεφάλαιο 7 αναφέρεται στην ενεργό ισχύ σε μη-συμμετρικά ή/και μη-ημιτονοειδή τριφασικά συστήματα. Το Κεφάλαιο 8 αναφέρεται στην μη-ενεργό ισχύ σε μη-συμμετρικά ή/και μη-ημιτονοειδή τριφασικά συστήματα. Στο Κεφάλαιο 9 παρουσιάζονται τα συμπεράσματα που προκύπτουν από την παρούσα διπλωματική εργασία. / -
67

SUPPRESSION OF HARMONIC TORQUE AND HARMONIC CURRENT IN PERMANENT MAGNET SYNCHRONOUS MOTOR

Abou Qamar, Nezar Yehya 01 May 2018 (has links)
In this dissertation harmonic current, harmonic torque originated at the load and harmonic torque originated at the motor, where modeled and treated via closed loop control. The dissertation propose a remedy for cancelling harmonic current by placing the proposed adaptive feedforward controller (AFC) in parallel with the FOC current control. Similarly, harmonic torque load was cancelled by proposing an AFC in parallel with the speed control loop. Harmonic torque originated in the motor mainly due to harmonic flux where cancelled through the estimation of harmonic flux, which was achieved by a novel Minimal Parameter Harmonic Flux Estimator (MPHFE). The latter is formulated such that the inductance, resistance, and stator current and its derivative are not necessary for the estimation of the harmonic eflux. This was achieved by forcing the harmonic current induced by the harmonic flux component to zero through the combined action of a Field-Oriented Controller (FOC) and a feed-forward controller. Subsequently, the harmonic flux can be obtained directly from the estimated harmonic back-EMF without the involvement of other motor parameters. Finally, the estimated flux is used in conjunction with a comprehensive analysis of the motor harmonic torque to determine the stator current compensation to eliminate the torque harmonic. A systematic approach to assign the parameter of the AFC controller were developed in this dissertation. Furthermore, multiple experiments were conducted to demonstrate the efficacy of the proposed control schemes harmonics.
68

Analysis for electrical energy and overall efficiency in distribution networks with harmonic distortion

Negumbo, Rosalia January 2009 (has links)
Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2009 / Traditionally, harmonics are ignored in overall efficiency and energy usage studies. However, in the modern era, power systems contain levels of harmonics which can no longer be ignored by engineers, planners, energy conservationists and economists. The directions of power flows have to be considered when harmonics are present in the power network. A methodology and new formulae for individual and overall efficiency and energy usage is developed at each frequency (f1, h and H) and forms the main contribution to research in this field. Two case studies were conducted; a measurement based laboratory experiment set-up and a simulated case study. In the set-up, measurements of current, voltage and power at different points in the network for the 1st, 5th and 7th frequencies were taken. Current and voltage results were used for hand calculations to prove the measured power flows and directions. The measurements were taken with a Fluke 345 three-phase harmonic power quality analyzer. For the simulated case study, a network was investigated using the DIgSILENT and SuperHarm software packages. Their results were compared and it was found that DIgSILENT is the preferred package for power results. It was found that the total harmonic distortion limit for voltage in the simulated network exceeded an acceptable level. The harmonic mitigation solution chosen was to design a passive filter to decrease the distortion by shifting the resonance point of the network. The method to design the passive filter and its impact on efficiency and energy usage is included in the thesis. Unique power flow direction diagrams are developed as part of the methodology and form an essential step in the derivation of the new formulae. Efficiencies, power losses and energy usage at individual and combined frequencies were determined. Results showed the negative effects of harmonics on overall efficiency, energy usage and power losses of the system. The methodology and new formulae developed was found to be effective and their application is recommended for use by industry.
69

Effects of overvoltage on power consumption

Dimitriadis, Panagiotis January 2015 (has links)
In the recent years there is an increasing need of electrical and electronic units for household, commercial and industrial use. These loads require a proper electrical power supply to convey optimal energy, i.e. kinetic, mechanical, heat, or electrical with different form. As it is known, any electrical or electronic unit in order to operate safely and satisfactory, requires that the nominal voltages provided to the power supply are kept within strict boundary values defined by the electrical standards and certainly there is no unit that can be supplied with voltage values above or below these specifications; consequently, for their correct and safe operation, priority has been given to the appropriate electrical power supply. Moreover, modern electrical and electronic equipment, in order to satisfy these demands in efficiency, reliability, with high speed and accuracy in operation, employ modern semiconductor devices in their circuitries or items. Nevertheless, these modern semiconductor devices or items appear non-linear transfer characteristics in switching mode, which create harmonic currents and finally distort the sinusoidal ac wave shape of the current and voltage supply. This dissertation proposes an analysis and synthesis of a framework specifically on what happens on power consumption in different types of loads or equipment when the nominal voltage supply increases over the permissibly limits of operation. A variety of loads have been selected from those used in everyday life, for household needs, office needs, as well as trade and industry. They were classified in two main categories, the passive loads and the non-linear loads. The classification was made on the event that the passive loads do not create harmonic currents but the non-linear loads create harmonic currents. For the above purpose was made practical experimental testings on several loads – equipment of both the categories in the laboratories, summarising the effects of the supplying voltages in power consumption at higher values1 gradually, from the nominal values up to the overvoltages. Also in some cases, for more accurate observation, was used the PSpice simulating program. 1 For a better understanding of the events, some experimental testings was made at lower supplying voltages – undervoltages across the loads. Finally, the results from the experimental testings confirmed that the effects of the overvoltages are: the increased consumption of power,  the decrease of the lifespan of electronic components due to overheating,  they are different with respect to the nature of the loads,  the increased amplitude of the current harmonics in the non-linear loads. For harmonic current reduction, an easy to use Pulse Width Modulation (PWM) method is proposed through booster topology, using a minimum number of components. This electronic circuit (harmonic current reducer) is cheap and easy to use, and can be easily connected between the mains supply and the non-linear load. It reduces, or keeps in low level the amplitudes of the current harmonics of the supplying current (distorted) of a non-linear load, in order to offer an extra protection or relief to the load when the supplying voltage or mains increases from its nominal value to undesired overvoltage values. Also, in order to avoid the undesirable effects on power consumption, due to overvoltages, design of a prototyping electronic circuit is proposed. This circuit (stabiliser), like the above harmonic current reducer, can be easily connected between the mains supply and a load or equipment; despite the mains supply variations, it keeps constant the desired or nominal voltage supply (voltage amplitude, Vpeak to peak) across the load or equipment.
70

Generation of microwave harmonics of millimetric wavelength

Knight, D. J. E. January 1965 (has links)
No description available.

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