Thesis (M.S.)--University of Wisconsin--Madison, 1964. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 62-63.

Dissertation (Ph.D. in Philosophy in Electrical Engineering)--Naval Postgraduate School, June 2007. / Dissertation Advisor(s): John McEachen. "June 2007." Includes bibliographical references (p. 197-202). Also available in print.

Thesis (Honors)--College of William and Mary, 2009. / Includes bibliographical references (leaf 43). Also available via the World Wide Web.

M.Tech. (Electrical and Electronic Engineering Technology)

This thesis discusses a principle of continuous speed regulation of AC motors, which is based on frequency conversion, and describes an experimental three-phase converter built for speed test purposes. The converter accepts power from a three-phase 60 cps. source and control signals from an auxiliary three-phase square-wave generator whose fundamental output frequency can be varied between 70 and 570 cps. When the two three-phase inputs are of opposite sequence, fundamental output frequency can be varied between 10 and 510 cps. The converter is of the static switching type. It consists of three identical units, one in each phase. Each unit has four power transistors which are operated in the on-off mode. Control signals are fed to the base-emitter circuits through isolating transformers. A free-running multivibrator in the control unit determines the period of the square-wave signals. The signals are taken from three bistable circuits, triggered in proper sequence through a system of gates. Output voltages from the converter have a relatively high harmonic content. Higher harmonic currents forming zero-sequence systems can be suppressed entirely. Current harmonics of positive and negative sequences must in general be tolerated. A discussion is given on the performance of AC motors when powered by this type of converter. No-load speed tests on small induction motors confirm the, principle on which the experimental work has been based. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

This dissertation makes a study of frequency discriminators and their role in instantaneous frequency measuring (IFM) signal acquisition receivers. Frequency discriminators are the major building blocks of IFM. They are required to measure frequency accurately over very broad bandwidths and to have near unity probabilities of pulse intercept. The major difficulties of the most commonly reported version are identified as a lack of component symmetry and a need to cross over two transmission lines while maintaining isolation. The accuracy due to lack of symmetry shows up analytically. effect on TOUCHSTONE, a micro-computer analysis package, is demonstrated as an excellent analysis tool while alternatives are also suggested. Variations of the standard discriminator are discussed. These are intended to improve performance due to lack of symmetry. None completely solve the cross over problem. A new type of discriminator requiring fewer components is introduced. It requires no cross over and exhibits greater symmetry. Analysis indicates that it performs better than the standard version. Two prototypes show the methods to be reliable and confirm the promise of the new version.

This thesis includes two topics. The first topic is a programmable DLL-based frequency multiplier, which can be a local oscillator in RF applications. The second one is a ROM-less direct digital frequency synthesizer to serve as a good reference clock or to be used in digital modulation and demodulation. A CMOS local oscillator using a programmable DLL-based frequency multiplier is presented. In this work, low-Q on-chip inductors are not needed. The clock of the output frequency is digitally controllable, which is ranged from 7´ to 10´ of an input reference clock. The design is carried out by TSMC 1P5M 0.25 mm CMOS process at 2.5 V power supply. The output frequency range of the physical chips measurement is about 1.0 GHz ~ 1.5 GHz. Maximum power dissipation is 58.2 mW at 1.5 GHz output. A ROM-less direct digital frequency synthesizer (DDFS) employing trigonometric quadruple angle formula is presented. In a system-level simulation, the spurious tones performance is suppressed to be lower than -130 dBc. The resolution is up to 13 bits. The maximum error is also analyzed mathematically to meet the simulation results.

Thesis (M.A.)--University of Wisconsin--Madison, 1966. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

This thesis studies structural dynamic system identification in a frequency-based framework. The basic consideration stems from the fact that frequencies may generally be measured with higher accuracy than other pertinent modal data such as mode shapes; however only a limited number of frequencies may be measured in the conventional context of natural frequencies. Being able to measure extra frequencies is a key to the success of a frequency-based method. The main part of the thesis is therefore organised around the involvement of the so-called artificial boundary condition (ABC) frequencies to augment the frequency dataset for general structural damage identification. In essence, the ABC frequencies correspond to the natural frequencies of the system with additional pin supports, but may be extracted from specially configured incomplete frequency response function matrix of the original structure without the need of physically imposing the additional supports. In the first part of the research, a particular focus is placed on the actual extraction of these ABC frequencies from physical experiments through effective modal testing, data collection, data processing and analysis. The influences of key processes involved in a typical modal experimental procedure, including high-fidelity measurement of the (impact) excitation input, averaging, windowing, and an effective use of post-processing techniques, particularly the Singular Value Decomposition (SVD) technique, are scrutinised in relation to the extraction of the ABC frequencies. With appropriate implementation of testing and data processing procedures, results demonstrate that all one-pin and two-pin ABC frequencies from the first few modes can be extracted with good quality in a laboratory setting, and the accuracy of extracted ABC frequencies is comparable to natural frequencies of corresponding orders. A comprehensive study is then carried out to investigate the sensitivities of ABC frequencies to damages. Two-pin ABC frequency sensitivity is formulated by extending the expression of anti-resonance sensitivity. On this basis, the mode shape contribution is adopted as a criterion for the selection of more sensitive ABC frequencies to be employed in detailed parameter identification or finite element model updating procedures. The soundness of using ABC frequencies in structural parameter identification and the effectiveness of the above ABC frequency selection method are subsequently examined through case studies involving laboratory experiments and the corresponding FE model updating. Furthermore, a preliminary study is carried out to examine the possibility of formulating ABC frequency-based damage indicator, herein with an analogy to the mode shape curvature, for direct damage assessment. As an extended investigation in the general framework of frequency-based dynamic identification, in the last part of the thesis, a complex dynamic system, namely a railway bridge under moving loads & masses, is evaluated with regard to the various frequency characteristics involved. The variation of the natural frequencies of the bridge-moving mass system, as well as the presence of the apparent frequencies from the trainloads, are analysed in detail. Besides simplified theoretical analysis, a computational model is developed to simulate the combined bridge-moving vehicle/train system, where the vehicle mass is coupled with the bridge via surface contact. The model is verified by comparison with field measurement data and theoretical predictions. Parametric studies enable a clear identification of the correlation of the frequency contents between the response and the trainload, and provide new insight into the significance of the so-called driving and dominant frequencies. It is found that much of the dynamic response phenomena, including the resonance effect, may be explained from the view point of the frequency characteristics of the trainload pattern, which is governed primarily by the ratio between the carriage length and the bridge length. Finally, a resonance severity indicator (the Z-factor) is developed for the assessment of the resonance effect in the railway bridge response when the trainload moves at a resonance speed. Numerical results demonstrate that the proposed methods are effective for the determination of the critical speed and the resonance effects, including the situations where a significant carriage mass is incorporated.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 141-143). Also available via the Internet.