The dissertation presents a generalized average-current-mode control technique (GACMC), which is an extension of the average-current-mode control (ACMC) for single-phase ac-dc boost converters with power factor correction (PFC). Traditional ACMC is generalized in a sense that it offers improved performance in the form of significant reduction of the current control loop bandwidth requirement for a given line frequency in unidirectional and bidirectional boost PFC converters, and additional functionality in the form of reactive power control capability in bidirectional converters. These features allow using a relatively low switching frequency and slow-switching power devices such as insulated-gate bipolar transistors (IGBTs) in boost PFC converters, including those designed for higher ac line frequencies such as in aircraft power systems (360–800 Hz). In bidirectional boost PFC converters, including multilevel topologies, the GACMC offers a capability to supply a prescribed amount of reactive power (with leading or lagging current) independently of the dc load power, which allows the converter to be used as a static reactive power compensator in the power system. A closed-loop dynamic model for the current control loop of the boost PFC converter with the ACMC has been developed. The model explains the structure of the converter input admittance, the current phase lead phenomenon, and lays the groundwork for development of the GACMC. The leading phase admittance cancellation (LPAC) principle has been proposed to completely eliminate the current phase lead phenomenon and, consequently, the zero-crossing distortion in unidirectional converters. The LPAC technique has been adapted for active compensation of the input filter capacitor current in bidirectional boost PFC converters. The dynamic model of the current control loop for bidirectional boost PFC converters was augmented to include a reactive power controller. The proposed control strategy enables the converter to process reactive power and, thus, be used as a reactive power compensator, independently of the converter operation as an ac-dc converter. Multiple realizations of the reactive power controller have been identified and examined in a systematic way, along with their merits and limitations, including susceptibility to the ac line noise. Frequency response characteristics of reactive elements emulated by means of these realizations have been described. Theoretical principles and practical solutions developed in this dissertation have been experimentally verified using unidirectional and bidirectional converter prototypes. Experimental results demonstrated validity of the theory and proposed practical implementations of the GACMC. / Ph. D.

A piezoelectric impedance-based structural health monitoring technique was developed at the Center for Intelligent Material Systems and Structures. It has been successfully implemented on several complex structures to detect incipient-type damage such as small cracks or loose connections. However, there are still some problems to be solved before full scale development and commercialization can take place. These include: i) the damage assessment is influenced by ambient temperature change; ii) the sensing area is small; and iii) the ability to identify the damage location is poor. The objective of this research is to solve these problems in order to apply the impedance-based structural health monitoring technique to real structures. First, an empirical compensation technique to minimize the temperature effect on the damage assessment has been developed. The compensation technique utilizes the fact that the temperature change causes vertical and horizontal shifts of the signature pattern in the impedance versus frequency plot, while damage causes somewhat irregular changes. Second, a new impedance-based technique that uses multiple piezoelectric sensor-actuators has been developed which extends the sensing area. The new technique relies on the measurement of electrical transfer admittance, which gives us mutual information between multiple piezoelectric sensor-actuators. We found that this technique increases the sensing region by at least an order of magnitude. Third, a time domain technique to identify the damage location has been proposed. This technique also uses multiple piezoelectric sensors and actuators. The basic idea utilizes the pulse-echo method often used in ultrasonic testing, together with wavelet decomposition to extract traveling pulses from a noisy signal. The results for a one-dimensional structure show that we can determine the damage location to within a spatial resolution determined by the temporal resolution of the data acquisition. The validity of all these techniques has been verified by proof-of-concept experiments. These techniques help bring conventional impedance-based structural health monitoring closer to full scale development and commercialization. / Master of Science

Les microphones capacitifs sont des transducteurs réciproques dont les qualités (sensibilité, bande passante et tenue dans le temps) en font des instruments de mesure performants. Couramment utilisés jusqu’à présent en récepteurs dans l’air à pression atmosphérique et à température ambiante, dans la gamme de fréquences audibles, ils sont correctement caractérisés dans ce cadre depuis près de trente ans. Mais aujourd’hui, leur miniaturisation (par procédé MEMS) et leur usage nouveau en métrologie fine (en récepteurs comme en émetteurs) - qui exigent une connaissance précise de leur comportement dans des domaines de fréquences élevées (jusqu’à 100 kHz), dans des mélanges gazeux aux propriétés différentes de celles de l’air et dans des conditions de pression et de température beaucoup plus élevées ou beaucoup plus basses que les conditions standards - nécessitent une caractérisation beaucoup plus approfondie, aussi bien en terme de modélisation qu’en terme de résultats expérimentaux. C’est ainsi que ici -i/ les effets des couches limites thermiques (seules les couches limites visqueuses sont habituellement retenues) sont introduits dans le modèle, ce qui amène dans le chapitre premier à une étude analytique de la diffusion thermique en parois minces (dont la portée dépasse le cadre strict du transducteur), -ii/ l’influence des orifices de l’électrode arrière sur la déformée de la membrane est traitée au départ par une méthode analytique originale, qui permet de traduire les conditions en frontière non uniformes sur la surface de l’électrode sous forme de sources locales virtuelles, associées à des conditions de frontière rendues uniformes (chapitre second), -iii/ des solutions analytiques nouvelles, dépendant à la fois des coordonnées radiales et azimutales, sont obtenues pour le champ de déplacement de la membrane et pour les champs de pression dans les cavités du microphone par usage de théories modales compatibles avec les couplages multiples qui y prennent place (troisième chapitre), -iv/ un modèle de « circuit à constantes localisées » (reporté pour l’essentiel en annexe) est proposé, à des degrés divers de précision, qui permet en particulier d’accéder de façon simple à la sensibilité et au bruit thermique du microphone (fin du quatrième chapitre), -v/ une étude au vibromètre laser à balayage a été réalisée (début du quatrième chapitre), qui permet non seulement de mettre en évidence pour la première fois les déformées de membrane complexes qui apparaissent en hautes fréquences, mais encore de les quantifier et par-delà de valider les résultats théoriques obtenus et donc les modèles proposés (même s’ils restent perfectibles comme indiqué dans la conclusion). / Condenser microphones are reciprocal transducers whose properties (sensitivity, bandwidth and reliability) make them powerful measurement tools. So far, they have been commonly used as receivers in the audible frequency range, in air at atmospheric pressure and ambient temperature, they have been appropriately characterised in this context for nearly thirty years. But nowadays, their miniaturisation (using MEMS processes) and their new use for metrological purposes (as receivers as well as transmitters) require much deeper theoretical and experimental characterisations because they require an accurate knowledge of their behaviour in high frequency ranges (up to 100 kHz), in gas mixtures, whose properties differ from those of air, and under pressure and temperature conditions much higher or much lower than standard conditions. Thus, here, -i/ the effects of the thermal boundary layers are introduced in the model (only viscous boundary layers are usually accounted for), leading, in the first chapter, to an analysis of the thermal diffusion of thin bodies (whose scope is beyond the strict frame of capacitive transducers), ii/ the influence of the holes in the backing electrode on the dynamic behaviour of the membrane is initially handled with an original analytical method which allows expressing the non-uniform boundary conditions at the surface of the backing electrode as fictitious localised sources associated to uniform boundary conditions (second chapter), -iii/ new analytical solutions, depending both on the radial and azimuthal coordinates, for the pressure field and for the displacement field inside the cavities behind the membrane are expressed using modal theories in agreement with the strong couplings which occur between the different parts of the transducer (chapter three), -iv/ "lumped element circuits", which are more or less approximated (presented in the Appendix), more particularly result in expressing and assessing the sensitivity and the thermal noise (end of chapter three), -v/ experimental results, obtained from measurements of the displacement field of the membrane using a laser scanning vibrometer, both highlight and quantify for the first time the complex behaviour of the membrane in the highest frequency range, and finally lead to the validation of the theoretical results and therefore, the models presented here (even if the latter may still be improved as outlined in the conclusion).

Les microphones capacitifs sont des transducteurs réciproques dont les qualités (sensibilité, bande passante et tenue dans le temps) en font des instruments de mesure performants. Couramment utilisés jusqu'à présent en récepteurs dans l'air à pression atmosphérique et à température ambiante, dans la gamme de fréquences audibles, ils sont correctement caractérisés dans ce cadre depuis près de trente ans. Mais aujourd'hui, leur miniaturisation (par procédé MEMS) et leur usage nouveau en métrologie fine (en récepteurs comme en émetteurs) - qui exigent une connaissance précise de leur comportement dans des domaines de fréquences élevées (jusqu'à 100 kHz), dans des mélanges gazeux aux propriétés différentes de celles de l'air et dans des conditions de pression et de température beaucoup plus élevées ou beaucoup plus basses que les conditions standards - nécessitent une caractérisation beaucoup plus approfondie, aussi bien en terme de modélisation qu'en terme de résultats expérimentaux. C'est ainsi que ici -i/ les effets des couches limites thermiques (seules les couches limites visqueuses sont habituellement retenues) sont introduits dans le modèle, ce qui amène dans le chapitre premier à une étude analytique de la diffusion thermique en parois minces (dont la portée dépasse le cadre strict du transducteur), -ii/ l'influence des orifices de l'électrode arrière sur la déformée de la membrane est traitée au départ par une méthode analytique originale, qui permet de traduire les conditions en frontière non uniformes sur la surface de l'électrode sous forme de sources locales virtuelles, associées à des conditions de frontière rendues uniformes (chapitre second), -iii/ des solutions analytiques nouvelles, dépendant à la fois des coordonnées radiales et azimutales, sont obtenues pour le champ de déplacement de la membrane et pour les champs de pression dans les cavités du microphone par usage de théories modales compatibles avec les couplages multiples qui y prennent place (troisième chapitre), -iv/ un modèle de " circuit à constantes localisées " (reporté pour l'essentiel en annexe) est proposé, à des degrés divers de précision, qui permet en particulier d'accéder de façon simple à la sensibilité et au bruit thermique du microphone (fin du quatrième chapitre), -v/ une étude au vibromètre laser à balayage a été réalisée (début du quatrième chapitre), qui permet non seulement de mettre en évidence pour la première fois les déformées de membrane complexes qui apparaissent en hautes fréquences, mais encore de les quantifier et par-delà de valider les résultats théoriques obtenus et donc les modèles proposés (même s'ils restent perfectibles comme indiqué dans la conclusion).

Für die Optimierung akustischer Eigenschaften von Räumen ist die Verbesserung deren numerischer Simulationen von entscheidender Bedeutung. Im unteren Frequenzbereich hängt in vielen Fällen die Qualität der Lösungen stark von der Kenntnis akustischer Wandadmittanzen ab. Die vorliegende Arbeit umfasst die Entwicklung und Untersuchung verschiedener auf deterministischen Diskretisierungen des akustischen Randwertproblems basierender Formulierungen zur globalen Bestimmung frequenzabhängiger Admittanzparameter. Mit Admittanzen kann das Reflexions- und Absorptionsverhalten von Wänden quantifiziert werden. Der vorgestellte Ansatz der globalen Admittanzbestimmung in Innenräumen ermöglicht die Berücksichtigung schrägen Schalleinfalls. Die Methode sieht ein Experiment vor, bei dem das Schallfeld mit Mikrofonen abgetastet, alle vorhandenen Schallquellen bestimmt sowie die Geometrie des akustischen Raumes erfasst werden. Mit den in der Arbeit entwickelten Algorithmen wird eine globale Admittanzverteilung für den gesamten Rand aus diesen Daten berechnet. Mit Hilfe erfolgreich identifizierter Admittanzverläufe sollen Simulationen niederfrequenter Wellenausbreitungen in Räumen auch komplizierter Geometrien und Oberflächenbeschaffenheiten durch Hinzunahme von Admittanzrandbedingungen ermöglicht und verbessert werden. Die Bestimmung von Wandadmittanzen aus partiell bekannten Schalldruckwerten wird mathematisch als inverses Problem eingeordnet. Für die inversen Algorithmen werden die Methoden der Randelemente (BE) und der finiten Elemente (FE) zur Diskretisierung des akustischen Randwertproblems verwendet. Aus den Gleichungen der BE-Diskretisierung lässt sich ein schlecht konditioniertes, aber dafür lineares Gleichungssystem für das inverse Problem finden, während die FE-basierte Formulierung ein nichtlineares, aufgrund der Komplexität des Problems meist ebenfalls schlecht konditioniertes Optimierungsproblem darstellt. Ein wesentliches Ergebnis dieser Arbeit ist die Gegenüberstellung der linearen und nichtlinearen Algorithmen des inversen Problems in Hinblick auf deren Herleitungen, die umgesetzten Berechnungsverfahren und der sich stark unterscheidenden Lösungsqualitäten. Untersuchungen der Admittanzrekonstruktion an zwei- und dreidimensionalen theoretischen Modellen verdeutlichen die Einflüsse der Modellgenauigkeit, des Messumfanges und des Messrauschens auf die Ergebnisse der inversen Algorithmen. Anhand der Anwendung auf Messdaten eines bei Brüel & Kjaer durchgeführten Experimentes wird das inverse Verfahren der globalen Admittanzbestimmung einem Praxistest unterzogen. / Reflection and absorption of sound waves on boundaries play a determining role for the optimization of acoustical properties in closed rooms. Above all the geometry and dynamic behavior of the wall structure are responsible for it. These boundary terms are quantifiable within the scope of numerical acoustics by the so-called admittance boundary conditions of the acoustical boundary value problem. Especially at low frequencies the quality of acoustical simulation depends strongly on the recognition of boundary admittances. The present work includes the development of two different inverse algorithms based on deterministic discretization methods for the global determination of frequency-dependent boundary admittance parameters. The approach of global determination of admittances allows to take account for non-perpendicular wave incident. For the method to work an experiment shall be initially conducted. In that process all present sound sources and microphone arrays scanning the sound field must be located and measured and a model of the geometry of the room needs to be created. The developed algorithms calculate then a global admittance distribution based on this data. Using successfully identified admittance characteristics as admittance boundary condition, low frequency simulation in rooms of complex geometry and arbitrary consistency of the surface shall be improved. Identifying boundary admittances out of partially measured sound pressure data is classifiable as inverse acoustic problem. In order to develop inverse formulations the acoustical boundary value problem is discretized by means of the Boundary Element and the Finite Element Method. The inverse formulation of the Boundary Element equations composes an ill-posed but linear system of equations. In contrast, based on Finite Elements only a nonlinear optimization problem can be set up that often features a bad condition due to the complexity of the inverse problem. The comparison of these linear and nonlinear algorithms of the inverse acoustic problem of global determination of boundary admittances in respect of derivation, implemented solution techniques and differing solution qualities states an essential result of this work. The investigation of admittance reconstruction at two and three-dimensional theoretical models reveal the influences of model accuracy, measurement expense and noise on measured data onto the results of both inverse algorithms. Finally, the problem of global admittance determination is subjected to experimentally obtained data (at Brüel & Kjaer) in order to check for practical applicability.

Made available in DSpace on 2016-08-17T14:52:57Z (GMT). No. of bitstreams: 1 Miriam Dora Chavez Lope.pdf: 1604085 bytes, checksum: 7eec68bb32ad68dca944d6146d4e5c5f (MD5) Previous issue date: 2005-03-14 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / In the whole world, the restructuring of the electrical sector promoted by the deregulation of the electric utilities has brought economical benefits for the society; furthermore there has been an increase of the pertinent interest in the subject of power quality. The competitive environment created by the deregulation forces the electric companies of generation and transmission to redefine their objectives in order to reduce their operation costs and to maximize their profits to guarantee their survival. Some of the measures adopted to reach these objectives, such as the postponement of the maintenance and investments for the expansion in the electric network, have as direct consequence the deterioration on the levels of reliability and quality of the supply. In distribution systems, this situation is more critical due to the monopolist nature of the electrical utilities. In other words, the consumers are subjected to the lucrative interests of these companies and, for that reasons, in several countries, the regulatory entities have been establishing goals for the reliability and quality of the supply aiming to punish the distribution utilities that violate these goals. In this new environment the interest of the electric utilities, consumers and regulatory entities for the quality of energy have been increasing due to the economical impact experienced by them. One of the problems of the quality of energy are the voltage sags effects, which has increased in recent years due to the crescent use of new equipments, which are more sensitive to voltage variations. The aim of this work is to develop a probabilistic methodology to analyse voltage sags in distribution networks. With the proposed methodology, power quality índices associated with voltage sags can be estimated in distribution systems, considering the system s topology and failure data. Due to the stochastic nature of the frequency and duration of fault, the proposed methodology is based on probabilistic models that permit to represent the system´s operation under faults. The proposed methodology is based on the combination of the Monte Carlo Method with the Admittance Summation Method. The Monte Carlo Method with sequential simulation is used to sample the failure scenarios and the Admittance Summation Method to evaluate fault currents. These fault currents are evaluated using a phase coordinate model of the distribution system. This model has been used due to the distribution networks unbalance caused by loads and untransposed overhead lines. Furthermore, voltage sags duration has been estimated using the current×time curves of the protection devices (fuses, breakers, reclosers). The proposed methodology has been tested in a feeder belonging to the Maranhão Electric Utility(CEMAR) and the results indicate that the proposed methodology is a good tool for studies of sags in distribution systems because it permits the evaluation of the system s performance against voltage sags, also estimating the compatibility between the system and the customer equipments. The results are shown through probability distributions of the SARFI%V, SARFICBEMA and SARFIITIC índices; cumulative and individual probability distributions, scattering diagrams and coordination charts of the voltage sags. / No mundo todo, a reestruturação do setor de energia promovida pela desregulamentação das empresas elétricas trouxe benefícios econômicos para a sociedade, resultando no aumento do interesse pertinente a questão da qualidade de energia. O ambiente competitivo criado pela desregulamentação obriga às empresas elétricas de geração e transmissão a redefinirem seus objetivos a fim de reduzir seus custos operacionais e maximizar seus lucros para garantir sua sobrevivência. Algumas das medidas adotadas para conseguir estes objetivos, tais como o adiamento da manutenção e investimentos de expansão na rede elétrica têm como conseqüência direta a deterioração dos níveis de qualidade e confiabilidade do fornecimento de energia. Em sistemas de distribuição esta situação é mais crítica devido à natureza monopolista das redes de distribuição. Os consumidores estão sujeitos aos interesses lucrativos destas empresas e, por causa disto, geralmente os órgãos reguladores estabelecem metas de confiabilidade e qualidade do fornecimento de energia elétrica a fim de evitar a deterioração da qualidade de fornecimento de energia e penalizar as empresas que violarem estas metas. Um dos problemas da qualidade de energia que basicamente preocupa são as variações de tensão de curta duração, cujos efeitos aumentaram em anos recentes devido ao crescente uso de equipamentos mais sensíveis à variações de tensão. Este trabalho tem como objetivo desenvolver uma metodologia probabilística para analisar as variações de tensão de curta duração em redes de distribuição. Com a metodologia proposta pode-se estimar índices de qualidade de energia associados as variações de tensão de curta duração em sistemas de distribuição, considerando-se a topologia e dados de falha do sistema. Devido à natureza estocástica da freqüência e duração das faltas, sendo o curto circuito a principal causa das variações de tensão de curta duração, a metodologia proposta se baseia em modelos probabilísticos que permitem representar a operação do sistema frente às faltas. A metodologia proposta se baseia na combinação do Método de Monte Carlo com o Método de Soma de Admitâncias. O Método de Monte Carlo com simulação seqüencial é usado para a amostra de cenários de faltas e o Método de Soma de Admitância para estimar as correntes de faltas. Estas correntes de faltas são estimadas usando-se o modelo de coordenadas de fase do sistema de distribuição. Este modelo é usado devido ao desequilíbrio das redes de distribuição causado pelas cargas e pelas linhas aéreas não transpostas. Além disso, a duração das variações de tensão de curta duração é estimada usando-se as curvas de tempo×corrente dos dispositivos de proteção (fusíveis, disjuntores, religadores). Para comprovar a aplicação prática, a metodologia foi testada em um alimentador da Companhia Energética do Maranhão (CEMAR). Os resultados são apresentados como: distribuições de probabilidade dos índices SARFI%V, SARFICBEMA e SARFIITIC; distribuições de probabilidade individual-cumulativa, diagramas de dispersão e cartas de coordenação das variações de tensão de curta duração. A metodologia proposta é uma ferramenta útil tanto para as empresas elétricas como para consumidores, porque permite avaliar o desempenho do sistema frente às variações de tensão de curta duração e estima a compatibilidade entre o sistema e os equipamentos do consumidor.

Die Anforderungen an schnelle Dioden sind sehr hoch für große Spannungen und große Ströme. Die Beeinflussung des Bauelementverhaltens durch das Design des Dotierprofils mit einem tiefen mehrstufigen Feldstopp aus Selen bildet einen zentralen Punkt der Dissertation. Mit physikalischen Messverfahren werden die in der Literatur nur unzureichend untersuchten Eigenschaften von Selen in Silizium erfasst und als Basis für Bauelementsimulationen verwendet. Für die Untersuchung der Störstelleneigenschaften kommt die klassische aufwändige DLTS zum Einsatz. Des Weiteren werden für diese Untersuchungen die Vorteile der einfacheren frequenzabhängigen Admittanzspektroskopie ausführlich dargelegt. Anhand der Bauelementsimulationen erfolgt ein Vergleich mit Messungen und führt zur Vorstellung und Erläuterung einer verbesserten soften und robusten Diodenstruktur mit tiefen Donatoren aus Selen. / The focus of the following work is the correlation between the field-stop design and the behaviour of high-voltage power diodes. The objective is to present a further improvement of the diode performance using a special field-stop, which optimizes the diode in relation to a soft switching behaviour and an increased robustness. The function of such a field-stop is investigated. Benefits are shown of materials for field-stops with deep impurities in the semiconductor material and of multiple stepped deep field-stop structures. Therefore a central role have silicon diodes with selenium in the field-stop layer. Measurements and simulations with the power device simulator Sentaurus TCAD are done and explain the named correlations. The deep level transient spectroscopy is used as method to analyse the required impurity parameters. Beside this method the evaluation is done by the introduced frequency resolved admittance spectroscopy.

No description available.

This master’s thesis is bent on comparison of four newest method of analog frequency filter design. After the introductory part, a description of properties and internal structure of active elements (Second-Generation Current Conveyor), VG-CCII (Variable Gain Current Conveyor), VCG-CCII (Voltage and current gained second generation current conveyor) a CFTA (Current Follower Transconductance Amplifier) is mentioned. This active elements are used in subsequent design. At the next part, process of frequency filters design by generalized method of filter design flowing from the full admittance network, by extending autonomous circuits, design using the signal flow graphs theory and design with synthetic high-order elements are presented. Thirty nine autonomous circuits are derived from full admittance networks with one and two active elements CFTA. Selected autonomous circuits are used for direct design of frequency filter and for filter design by extending autonomous circuits. Produced structures guarantee the possibility of controlling the quality factor Q0 independently of the characteristic frequency f0. Three frequency filters are designed by method using the signal flow graph theory. Active elements CFTA, VG-CCI and VCG-CCII are used. Full multifunctional frequency filter with conveyors VG-CCII and VCG-CCII guarantee the possibility of controlling the quality factor Q0 and the characteristic frequency f0 independently of the each other. In last part, from 2nd to 5th order low-pass filters by the method using synthetic high-order elements are designed. The behaviour of the selected filters has been verified by simulations in the PSpice program for all of the mentioned methods separately.

Master thesis Testing of Directional Earth Fault Protections Using the Experimentally Obtained Fault Records deals with the protective functions of earth fault protections during earth faults in compensated medium voltage distribution network and their testing options. At the beginning of the thesis we charakterize operation of medium voltage distribution system in general. We begin with definition and characteristics of earth fault and its compartmentalization by the type of the fault, size of the transition resistance and duration. We also mention grounding methods of node winding transformer on medium voltage distribution network and we describe the most common of them in detail, i.e. network grouded through the arc suppression coil and its operation with automatic switching auxiliary resistor. In this part of the thesis we discuss the localization of the earth fault using passive static methods in compensated systems, which include wattmetric, admittance and conductance method. In next section we deal with the fault records stored in COMTRADE file format, its structure and all elements of its configuration and data file. We create and describe an example of converting ADF file format, recorded by Yokogawa oscilloscope fault recorder, into COMTRADE file format using Microsoft Excel program and M-File created in the MATLAB program. In the practical part we introduce workspace devices and software, which includes secondary testing equipment OMICRON CMC 256plus and its software OMICRON Test Universe with Advance Transplay test module, we further describe multifunctional earth fault protection RYo from PROTECTION & CONSULTING, s. r. o. and machine terminal REM 543 from ABB and their protective functions. The last part describes the actual testing of parallel connected earth fault protection with COMTRADE fault records by Advance Transplay test module in the OMICRON Test Universe. In the conclusion we describe evaluation of the suitability of each protective functions of earth fault protection in a variety of sizes the transition resistance at the earth fault location.