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Neuromuscular electrical stimulation and the central nervous systemLagerquist, Olle. January 2009 (has links)
Thesis (Ph.D.)--University of Alberta, 2009. / A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Faculty of Physical Education and Recreation, Center for Neuroscience. Title from pdf file main screen (viewed on September 17, 2009). Includes bibliographical references.
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Development of a soft-core based power electronic conversion controllerNsumbu, Cassandra Daviane January 2014 (has links)
Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2014. / The application of digital control techniques has become dominant in power electronics
owing to several advantages they present, when compared to analogue solutions. Their
development is based on the use of microprocessors and microcontrollers, such as
Application Specific Integrated Circuit (ASIC), Digital signal processors (DSP), Field
Programmable Gate Arrays (FPGA), or a combination of these devices.
This thesis presents an investigation of a soft-core based FPGA control system as a solution
for power electronic applications. The aim was the development and implementation of a
conversion controller, which purpose is to supply control inputs in the form of digital Pulse
Width Modulation (PWM) signals, to a number of power electronic applications, such as
single half and full bridge DC-DC converters, three phase and multicell inverters. The PWM
control technique is achieved via their power semiconductor switching devices. These PWM
control signals are necessary for the high frequency conversion of an analog input voltage
(AC, DC or unregulated) to an analog output voltage of another level (AC or DC). This was
intended to be achieved by exploiting and combining the advantages that FPGA and
embedded processors provide such as high reconfigurability and multipurpose ability. This
controller’s digital outputs, namely PWM switching signals, can be directly delivered to an
analog signal amplification circuit to create an adequate voltage level before being processed
by the converters’ switches.
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Development of an original 10 kHz Ti : Sa regenerative cavity allowing 17 fs CEP stable 1 kHz TW-class amplification or wavelength tunability / Développement d’une nouvelle configuration de cavité régénérative à 10 kHz, permettant l’amplification à1 kHz d’impulsions de durée 17 fs, stabilisées en CEP dans la classe TW ou accordables en longueur d’onde à10 ou 1 kHzGolinelli, Anna 21 January 2019 (has links)
Au cours de dix dernières années la science aux attoseconde ou Physique au champ-fort a été l’objet d’un fort développement. La production d’impulsions laser énergétiques de courte durée à haute cadence et stabilisées en CEP constitue la première étape pour accéder aux dynamiques ultra-rapides caractérisant l’interaction de la matière avec une source de lumière cohérente, intense et ultra-rapide. Le travail de cette thèse consiste à améliorer globalement les performances d’un système laser Ti:Sa à haute cadence optimisé pour la génération des impulsions attoseconde. Nous avons développé une nouvelle configuration de cavité régénérative fonctionnant à 10 kHz qui permet une meilleure gestion des effets thermiques dans le cristal. En sortie de l’amplificateur les impulsions atteignent des valeurs de puissance de 5 W en bande étroite (35 fs), ou 2.7 W en bande spectrale large permettant une compression des impulsions proche de 17 fs. La CEP des impulsions en sortie d’amplificateur a été stabilisée ; le bruit résiduel mesuré tir-à-tir est de 210 mrad pendant trois heures.L’amplificateur peut supporter également le fonctionnement en mode accordable, en sélectionnant des spectres de 30 à 40 nm de largeur à mi-hauteur et en accordant leur longueur d’onde centrale dans une gamme de 80 nm autour de 800 nm. Nous avons conçu et mis en fonctionnement un amplificateur multi-passages non-cryogéné à imagerie par lentille thermique pour accroître la puissance des impulsions jusqu’à 10 W à une cadence de 1 kHz. Le régime de forte saturation d’amplificateur garantit une variation négligeable (±3% pic à pic) de la puissance des impulsions en sortie du module, face à une variation importante de la puissance en entrée (±25% pic à pic) sur la bande spectrale accordable. L’amplification peut encore être plus importante grâce à une ligne d’amplification à refroidissement cryogénique, qui permet d’atteindre des puissances au niveau TW, à la cadence de 1 kHz, tout en maintenant un régime de courte durée (17.5 fs) et stabilité en CEP (350 mrad de bruit résiduel tir-à-tir). Nous proposons aussi une étude des sources de bruit de CEP dans les modules hautement dispersifs: nous avons conçu une nouvelle approche numérique sur la base d’un logiciel de tracé de rayon commercial (Zemax) pour évaluer les variations de CEP dans les modules contenant réseaux de diffraction. / The last decade has seen a lot of progress in attosecond science or in strong field physics. Generating energetic, few-cycle laser pulses with stabilized Carrier-Envelope Phase at high repetition rate constitutes the first step to access the ultra-fast dynamics underlying the interaction of matter with intense, ultrashort coherent light source. The work of this thesis consists in globally improving the performances of a high repetition rate Ti:Sa laser system optimized for attosecond science. We present an original 10 kHz Ti:Sa CPA laser based on an newlydesigneddouble-crystal cavity for thermal lensing management. The amplifier delivers up to 5 W in narrow band mode (35 fs pulses), or 2.7 W in broad band mode, supporting 17 fs pulses after temporal compression. We demonstrate shot-to-shot CEP stabilization with a remaining noise of 210 mrad over three hours at the front-end output. In parallel to the short pulse duration operation mode, it is possible to use the front end in a wavelength tunability mode within a 80 nm range around 800 nm, with a resolution of 1 nm and 30 to 40 nm of bandwidth. We designed and demonstrated a complete water-cooled lens-less multipass amplifier using thermal lensing for modeadaptation boosting the pulse energy up to 10mJ at 1 kHz repetition rate (up to 10 W). The saturation regime of the amplifier ensures negligible variation (±3% peak to peak) of the output power for significant variation of the input power (±25% peak to peak) over the tunability range. The energy scalability of the front-end is demonstrated by coupling its output to cryogenically cooled amplifier, delivering 1 kHz, TW-class pulses at 17.5 fs and CEP stabilized with a residual noise of 350 mrad. A study of CEP noise sources in high dispersive module is also addressed, proposing a numerical approach based on a commercial ray-tracing software (Zemax) for predicting CEP fluctuation in grating based modules.
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Discrete-time crossing-point estimation for switching power convertersSmecher, Graeme. January 2008 (has links)
No description available.
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Evaluation of the Response of Perpetual Pavement at Accelerated Pavement Loading Facility: Finite Element Analysis and Experimental InvestigationHernandez, Jaime A. 22 September 2010 (has links)
No description available.
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Variable speed constant frequency power conversion with permanent magnet synchronous and switched reluctance generatorsRim, Geun-hie 20 October 2005 (has links)
Power electronics is inevitably concerned with the processing of variable speed power generations such as in wind turbines, aircraft systems and naval on-board ship systems. The nature of these types of energy is distinct in that their frequency and power vary depending on the speed of the prime-mover. To make use of the variable speed energy, a power processing scheme which transforms the variable speed energy into a constant frequency power is required. There are measures such as mechanical and electrical links for such purposes. Electrical link systems are chosen in this study due to their fast responses and high reliabilities. The power conversion stage may be a dc link with a line-commutated converter, a dc link with a self-commutated inverter, or a cycloconverter. The line-commutated converter and cycloconverter power stages require a fixed frequency supply for operation whereas the self-commutated inverter is capable of stand-alone operation, thus making it attractive.
Two cases of variable speed power generation using a permanent magnet synchronous machine (hereafter referred to as PMSM) and a switched reluctance machine (hereafter referred to as SRM) were studied in this dissertation. The possible use of PMSMs has been proved by the good correlation between the experimental results and the theoretically predicted results. Three different control strategies have been proposed, implemented in hardware, and experimentally verified. The efficiency of the VSCF power conversion with a self commutated converter were comparable to the one using a line-commutated converter.
A novel converter topology with no dc link capacitor has been proposed for the application of SRMs to the VSCF power conversion. The proposed topology directly links the constant frequency ac source to the SRM. This feature enhances the reliability of the power conversion scheme and reduces the weight and volume of the system. The correlation between the theoretical and experimental results of some key issues showed the feasibility of the proposed VSCF power conversion scheme.
In the course of the study, one stage ac to dc power conversion with a compact transformer was required for dc loads. However, phase-controlled ac to dc conversion has the disadvantages of low power factor and harmonic pollution on the utility side, particularly in the case where dc voltage regulation is required. Therefore, a novel single phase rectifier for dc load which provides ohmic isolation with a high frequency transformer is extensively investigated. The proposed scheme had a wide output variation on dc output while maintaining unity power factor and sinusoidal current in the ac input side. Three control strategies for the operation of the converter were proposed and verified experimentally. The harmonic spectra on ac and dc sides are analytically derived and experimentally proved under some load conditions. / Ph. D.
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Experimental study and numerical simulations of the spectral properties of XUV lasers pumped by collisional excitation / Etude expérimentale et simulations numériques des propriétés spectrales de lasers X pompés par excitation collisionnelleMeng, Limin 20 December 2012 (has links)
La caractérisation spectrale détaillée des lasers XUV générés dans des plasmas est un enjeu important des projets actuels de développement qui visent à augmenter la puissance crête de ces sources. En effet les propriétés spectrales de ces lasers conditionnent d'autres propriétés importantes, telle que la durée minimum accessible (limite de Fourier). La plus courte durée actuellement démontrée expérimentalement est de 1 picoseconde. La technique d'injection d'un plasma de laser XUV avec une impulsion femtoseconde de rayonnement harmonique d'ordre élevé offre des perspectives très prometteuses pour réduire la durée d'impulsion jusqu'à quelques 100 femtosecondes, pourvu que l'on sache maintenir une bande spectrale de gain suffisamment large.Les lasers XUV pompés par excitation collisionnelle dans des ions néonoïdes et nickeloïdes ont été développés dans des plasmas chauds créés aussi bien par décharge électrique rapide que par différents types de lasers de puissance. On a ainsi accès à une large variété de sources lasers XUV, qui diffèrent par les caractéristiques du faisceau émis, mais aussi par les paramètres du plasma (densité, température) dans la zone de gain. On peut donc s'attendre à des propriétés spectrales différentes. Le but du travail que nous présentons est d'étudier les propriétés spectrales des différents types de lasers XUV collisionnels existants, et d'évaluer leur capacité à amplifier des impulsions de durée inférieure à 1 picoseconde, dans un mode injecté.La caractérisation spectrale des lasers XUV est expérimentalement difficile parce que la résolution spectrale nécessaire (∆λ/λ ~10-5) n'est pas accessible avec les meilleurs spectromètres actuels. Dans notre étude, nous avons atteint cette résolution en mesurant la cohérence temporelle de la source à l'aide d'un interféromètre à division de front d'onde, spécifiquement conçu pour ces mesures, à partir desquelles largeur spectrale peut être déduite.Nous avons caractérisé trois types de lasers XUV collisionnels, développés dans trois laboratoires différents: pompage transitoire dans le molybdène nickeloïde, pompage par décharge électrique dans l'argon néonoïde et pompage quasi-stationnaire dans le zinc néonoïde. Dans chaque cas la cohérence temporelle a été mesurée précisément. De plus nous avons étudié l'effet de la saturation de l'amplification et (pour le Ni-like Mo) l'influence du mode injecté. Nous avons également étudié le comportement temporel du laser transitoire Ni-like Mo à l'aide d'une caméra streak X ultra-rapide. Nos mesures spectrales sont comparées à des résultats de simulations numériques prenant en compte les différents mécanismes d'élargissement ainsi que les effets de transfert radiatif. Nous avons étudié l'évolution du profil spectral avec l'amplification et la saturation, et nous avons évalué les limites de Fourier correspondantes.Le temps de cohérence le plus court (ie la largeur spectrale la plus grande) est mesuré pour le laser XUV quasi-stationnaire, qui correspond au plasma qui a la plus forte densité et la plus forte température ionique. / Improving the knowledge of the spectral and temporal properties of plasma-based XUV lasers is an important issue for the ongoing development of these sources towards significantly higher peak power. The spectral properties of the XUV laser line actually control several physical quantities that are important for applications, such as the minimum duration that can be achieved (Fourier-transform limit). The shortest duration experimentally achieved to-date is ~1 picosecond. The demonstrated technique of seeding XUV laser plasmas with a coherent femtosecond pulse of high-order harmonic radiation opens new and promising prospects to reduce the duration to a few 100 fs, provided that the gain bandwidth can be kept large enough.XUV lasers pumped by collisional excitation of Ni-like and Ne-like ions have been developed worldwide in hot plasmas created either by fast electrical discharge, or by various types of high-power lasers. This leads to a variety of XUV laser sources with distinct output properties, but also markedly different plasma parameters (density, temperature) in the amplification zone. Hence different spectral properties are expected. The purpose of our work was then to investigate the spectral behaviour of the different types of existing collisional excitation XUV lasers, and to evaluate their potential to support amplification of pulses with duration below 1 ps in a seeded mode.The spectral characterization of plasma-based XUV lasers is challenging because the extremely narrow bandwidth (typically ∆λ/λ ~10-5) lies beyond the resolution limit of existing spectrometers in this spectral range. In our work the narrow linewidth was resolved using a wavefront-division interferometer specifically designed to measure temporal coherence, from which the spectral linewidth is inferred. We have characterized three types of collisional XUV lasers, developed in three different laboratories: transient pumping in Ni-like Mo, capillary discharge pumping in Ne-like Ar and quasi-steady state pumping in Ne-like Zn. Besides the accurate measurement of the temporal coherence of the laser in each case, we have studied the spectral behaviour when the laser is operated in the saturation regime and (in Ni-like Mo) when it is seeded with high-order harmonic radiation. We have also investigated the temporal behaviour of the Ni-like Mo transient XUV laser, using an ultrafast X-ray streak camera. Our linewidth measurements are compared with detailed numerical calculations including relevant broadening mechanisms as well as radiative transfer effects. The evolution of the spectral profile with amplification and saturation was studied for different plasma parameters, and corresponding Fourier-transform limit duration were evaluated.The shortest temporal coherence (ie the largest bandwidth) is measured for the quasi-steady state pumping XUV laser, which operates at the highest density and ionic temperature.
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A generalized 3D pulse width modulator for multi-level voltage source inverters in three-phase four-wire power systemsDai, Ning Yi January 2007 (has links)
University of Macau / Faculty of Science and Technology / Department of Electrical and Electronics Engineering
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Modeling and control of fuel cell based distributed generation systemsJung, Jin Woo, January 2005 (has links)
Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xvi, 209 p.; also includes graphics. Includes bibliographical references (p. 202-209). Available online via OhioLINK's ETD Center
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A comparative analysis of proportional-integral compensated shunt active power filtersGray, Matthew Alan. January 2004 (has links)
Thesis (M.S.) -- Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.
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