• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 6045
  • 1235
  • 1235
  • 1235
  • 1235
  • 1235
  • 1232
  • 786
  • 309
  • 296
  • 283
  • 181
  • 76
  • 54
  • 35
  • Tagged with
  • 12779
  • 8320
  • 8182
  • 1706
  • 1595
  • 1218
  • 1083
  • 1010
  • 790
  • 783
  • 658
  • 500
  • 466
  • 399
  • 385
  • 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.
11

'n Saamgestelde drywingselektroniese tussenkringmutator as deurloopspanningsbron

Badenhorst, Maré 08 May 2014 (has links)
M.Ing. (Electrical and Electronic Engineering) / The South African Railways covers a total distance of some 24 000 km, making use of a signalling network of 1000 interlocking systems. This comprises of the order of 1000 signalling houses each with its own unlnterruptible power supply system of which a DC·AC converter Is one of the components. Due to the requirements by Spoomet, high frequency (ultrasonic) chopper technology had to be used. This treatise describes the design and development of a 3 kVA composite DC·AC converter with an ultrasonic AC link for this application. In the primary converter (centre tapped topology) ZVS Is achieved by good circuit layout and controlled transformer capacitance. As a result the performance of the converter was improved with regard to efficiency and switching transients compared to the conventional hard switched converter. The four pulse topology with an output LC·filter was used for the secondary converter. Due to the modulation technique being used, the load perceived the switching frequency as 20kHz while the actual switching frequency was only 10kHz. In this way switching losses were kept within reasonable limns as well as satisfying the low audible noise requirement. The stability of the LC·filter was achieved with a current feedback loop. The literature describes the capacitor current being used in the feedback loop. In this case the Inductor current was used with the advantage of output short circuit protection without an additional current measurement. Apart from the advantages of small weight and volume from a maintenance point of view, the composite DC·AC converter also achieved high efficiency (> 85%) over a wide load range (10%-100% of full load).
12

Structural Identification and Parametric Estimation of Multivariable Systems

Kwong, York-Hon 02 1900 (has links)
<p>The identification of discrete linear time-invariant multivariable systems has been investigated. This thesis consists of three interrelated parts. In the first part, linear systems have been described in canonical forms which are mostly suitable for system identification. Inter-relationships between the input-output difference canonical form due to Bonivento, Guidorzi and Marro (1973) and the state-space canonical form due to Luenberger (1967) have been studied. In the second part structures of linear multivariable systems have been studied. An efficient algorithm has been developed to identify a set of structural indices directly from the input-output data of a system. The order of the system is, then, determined in terms of these structural indices. In the last part, estimation of system parameters from the input-output data has been studied. Recursive algorithms have been developed for estimating the system parameters sequentially from noise-free and noise-corrupted data. Digital computer simulations with noise-free as well as noise-corrupted data have been utilized to illustrate the usefulness of the proposed procedures.</p> / Master of Engineering (ME)
13

Decoupling Orbital and Attitude Control of Communications Technology Satellite

Yau, Yiu Joe 04 1900 (has links)
<p>Based on Altman's model, a state model and a measurement model are obtained. Both models are linearized and the linear state variable feedback method is then applied to decouple the linearized system.</p> <p>Computer programmes for decoupling are written and the results are then discussed.</p> <p>Suggestions for future work are proposed.</p> / Master of Engineering (ME)
14

On-Line System Identification in Real Time Using Minicomputer

Tang, M. 04 1900 (has links)
<p>By making use of measurements of the input and output of an unknown system, the characterizing parameters are found by using matrix pseudoinverse method. For noise-corrupted measurement, least squares estimation of the parameters are obtained.</p> <p>Stochastic approximation is employed to improve the estimation.</p> <p>Both methods are tested on-line in real time using the PDP-11/45 minicomputer while the system is simulated on the TR-20 analog computer.</p> / Master of Engineering (ME)
15

Design and Synthesis of a VHF Surface Acoustic Wave Oscillator

Seiler, Dieter G. 12 1900 (has links)
<p>This thesis covers the design and fabrication of a Surface Acoustic Wave (SAW) oscillator. The oscillator was designed to operate at 124 MHz in the fundamental mode and was constructed on an ST-X quartz substrate. The type of SAW oscillator incorporated was of the delay line type where a SAW delay line is inserted in the feedback loop of an amplifier with excess gain. The delay line exhibited a bandpass characteristic with an insertion loss of 32 dB. The oscillator has a short-term stability of 2.0 parts in 10⁷over 1 second and a medium-term stability of less than 8 ppm over 12 hours. The oscillator had an effective loaded Q of 628 and power output was -10 dBm into 50 Ω with the second harmonic down 22 dB, and the third down 33 dB. The theory of operation of the SAW delay line oscillator is covered along with fabrication procedures and experimental results.</p> / Master of Engineering (ME)
16

A Walsh Vocoder

Milunovic, Stephen January 1975 (has links)
<p>The concepts of the analogue channel vocoder and digital FFT vocoder are utilized in the analysis of a Walsh vocoder. The FFT and Walsh vocoders are simulated in Fortran on a CDC6400 computer. The simulations contain a simplified cepstrum pitch detector to simulate a hardware pitch detector. The Walsh vocoder simulation is identical to the FFT vocoder simulation with the Fast Walsh Transform operation replacing the Fast Fourier Transform operations (FWT and FFT respectively) in the channel signal calculations and transforms into the time domain.</p> <p>Sentences of different lengths and speakers are processed by the simulated vocoders and the resultant synthesized speech is analyzed for comparative quality and intelligibility.</p> <p>An unsuccessful attempt is made to effect a vocoder which does not require a pitch detector with the calculation of the time invariant sequency power spectrum replacing the channel signal calculations in the vocoder simulations. Long term frequency and sequency enveloped are used to shape the frequency and sequency power spectra derived from the transmitted time invariant sequency power spectrum in the FFT and Walsh vocoder simulations respectively.</p> / Master of Engineering (ME)
17

A Model For Magnetic Bubbles in Ion Implanted Type of Channels

Mikhail, Hakim Sami 12 1900 (has links)
<p>The purpose of this thesis is to present a model for magnetic domains wholly situated inside an ion implanted channel. In this model, ion implantation is assumed to change the saturation magnetization, the wall energy density, and the in-plane susceptibility. As a result the channel and the domain induce magnetic pole distributions on the channel walls which interact with the bubble domain, altering its geometry and energy. An analysis for a circular domain with variable penetration and location in the channel, as well as a variational formulation for a generally deformable domain of fixed penetration in the implanted channel, are presented. The latter case has been programmed and the results obtained are discussed. The case of a domain penetrating into the unimplanted region outside the channel is also considered.</p> / Master of Engineering (ME)
18

Computer Simulation of Ion Implantation

El-Agizi, George Nabil 12 1900 (has links)
<p>In this work, a computer simulation for ion implantation has been carried out based on a simplified random model. This simulation has been used to obtain range profiles and deposited damaging energy distributions, for any system and for a wide energy range. The obtained distributions show good agreement with the third order Edgeworth expansion approximation of the standard transport theory solution (the WSS theory). By taking into account the motion of the first knock on atoms, as well as the incident ion itself, a good agreement between the simulation and the WSS theory is found for the damage distribution. A random model for dealing with poly-atomic targets is presented. Results obtained show good agreement with the available experimental results for range profiles. The simulation includes obtaining a complete picture of the collision cascade (in space and time). The complete picture of the collision is discussed in relation to the recently observed "molecular effect" and explains some available experimental results. The examination of typical cascades suggests that high energy density regions are responsible primarily for the obtained departures from "Linear Cascade Theory".</p> / Master of Engineering (ME)
19

Adaptive State Estimation for Systems with White and Coloured Noise

Tom, Alvan F.W. 07 1900 (has links)
<p>The problem of adaptive state estimation which involves the identification of the Kalman gain matrix without a priori information on the noise statistics is presented. A scheme incorporating an identification algorithm and a tracking algorithm is proposed. This scheme provides a powerful approach for adaptive state estimation.</p> <p>An ARMA model for system description is derived for preliminary analysis of the noise transition matrix when the observation noise is sequentially correlated.</p> <p>The innovations process for systems with coloured observation noise is shown to be white for optimum filtering.</p> <p>Simulations are performed on an inertial navigation system for both white and coloured observation noise. Numerical results indicate the superiority of the filter with tracking over one without. Performance of the filter for coloured observation noise confirms the theoretical derivation of the ARMA model.</p> / Master of Engineering (ME)
20

Analysis of Damping and Synchronizing Torques in Power System Stability Studies

Shaltout, Abdel-Maksoud Adel 07 1900 (has links)
<p>Recently the problem of dynamic instability has been increased due to the recent trends in synchronous machine design and the growth in the relative size of the power stations. In this thesis such a problem has been examined by analysing the damping and synchronizing torque coefficients. Different methods for calculating those torque coefficients have been reviewed, and a new method based on a more accurate representation for the machine has been developed. Because of the more detailed representation the new resultant torque coefficients permit the investigation of additional properties of those coefficients, as well as more precise analysis of the properties previously studied. The problem of weak or negative damping associated with the use of high gain and quick response static exciters has been given special attention. Different schemes for producing a stabilizing signal have been discussed. A design procedure for a stabilizer which assures successful operation over the whole generation range has been outlined.</p> / Master of Engineering (ME)

Page generated in 0.0666 seconds