65 research outputs found

    Design and Application of Electrical Machines

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    Electrical machines are one of the most important components of the industrial world. They are at the heart of the new industrial revolution, brought forth by the development of electromobility and renewable energy systems. Electric motors must meet the most stringent requirements of reliability, availability, and high efficiency in order, among other things, to match the useful lifetime of power electronics in complex system applications and compete in the market under ever-increasing pressure to deliver the highest performance criteria. Today, thanks to the application of highly efficient numerical algorithms running on high-performance computers, it is possible to design electric machines and very complex drive systems faster and at a lower cost. At the same time, progress in the field of material science and technology enables the development of increasingly complex motor designs and topologies. The purpose of this Special Issue is to contribute to this development of electric machines. The publication of this collection of scientific articles, dedicated to the topic of electric machine design and application, contributes to the dissemination of the above information among professionals dealing with electrical machines

    Design of a superconducting DC wind generator

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    The trend towards larger power ratings of wind turbines asks for innovations in power generation, which requires lower weight and cost, smaller size, higher efficiency and reliability. Due to high current-carrying capability and no DC losses of superconductors, a superconducting wind generator can have a superior power to weight/volume ratio with high efficiency. The work in the book mainly focuses on the feasibility study and design of a superconducting DC wind generator

    Design of a superconducting DC wind generator

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    Offshore wind energy has received a lot of interest as one important renewable energy source. One promising way to reduce the Levelized Cost of Electricity (LCOE) of offshore wind energy is by developing large wind farms and turbines with large ratings. The average wind turbine size has reached 4.2 MW in 2015 and turbine sizes of 6-8 MW have already been seen in the wind market. Even larger turbine sizes are managing to pave their way from studies to market. The trend towards larger ratings and more offshore installations asks for innovations in power generation, which requires lower weight and cost, smaller size, higher efficiency and reliability. Due to the high current-carrying capability and no DC losses of the superconductors, superior power to weight/volume ratio with high efficiency of a superconducting generator can be achived. Moreover, direct current (DC) transmission has been put forward for the offshore wind farms mainly due to the overall economic benefit, as they are located far away from the land. Hence, this thesis introduces a DC generation and transmission scheme which consists of superconducting DC wind generators and superconducting DC cables as a possible technical solution. This enables a highly efficient and compact generator and in addition a new and also very efficient generator connection scheme at DC. The work presented in the thesis focuses on the feasibility study and design of a superconducting DC wind generator. In part, an optimisation method will be developed by taking superconducting tape length (cost), mass, volume, and efficiency into a simplified objective function. All necessary analytical equations will be derived to connect the electromagnetic design and mechanical design with properties of the superconducting tapes and iron materials. To increase the design accuracy, analytical equations to calculate flux density distribution in the superconducting DC generator will be verified by finite element analysis. Not only the active parts but also inactive structural materials will be included in the mass calculation. Based on the design method, the design of a 10 kW superconducting DC generator demonstrator will be described. The losses of the demonstrator and its commutation, torque and efficiency at different wind speeds will be addressed. As first steps towards the demonstrator, properties of key components, superconducting tapes, iron materials and a superconducting coil, will be tested and characterized. Moreover, a preliminary test of a superconducting coil at 77 K will be completed. In order to identify the potientials that a large scale superconducting DC wind generator could offer, a 10 MW superconducting DC generator will be designed and a comparison with conventional synchronous generators will be made. Additionally, this work will also discuss the savings of HTS tapes by optimizing outer rotor diameter, pole pair number, and superconducting coil height, which contribute to a more competitive alternative to conventional generators

    Magnetic Refrigeration: Design, construction and evaluation of a valve switched rotary prototype. Numerical modeling of a solid state magnetocaloric heat elevator.

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    Este trabajo tiene como objetivo aportar una nueva luz a las posibilidades de que las tecnologías de refrigeración magnética se acerquen al mercado, desplazando de su trono a los sistemas de compresión de vapor.En la introducción a esta tesis, se presenta una breve descripción de los conceptos básicos de esta tecnología y sus "condiciones de frontera", y se incluyen algunas discusiones y reflexiones personales. Se ha diseñado y construido un prototipo rotatorio de refrigeración magnética para probar lo que, en ese momento y según nuestro conocimiento, constituye un nuevo diseño. La singularidad de este prototipo reside en el uso de electroválvulas en conjunto con un sistema de bombeo de fluido continuo. Otro comentario importante sobre este prototipo es que el diseño del imán se realizó mediante un proceso de optimización original. Se llevaron a cabo algunas pruebas con compuestos Gd y GdEr, y se presentan y discuten sus resultados, encontrando también las principales fuentes de pérdidas en el dispositivo. Se desarrolló un modelo de simulación por ordenador para evaluar los tiempos de relajación de temperatura de lechos porosos de esferas de un material magnetocalórico, en función de su diámetro. Esta simulación ayudó a conocer los valores límite y seleccionar el diámetro de las partículas de los materiales magnetocalóricos a utilizar. Finalmente, se realizó un estudio comparativo del uso de sistemas híbridos termoeléctricos-magnetocalóricos. Para ello, se introdujo una ecuación maestra original para el uso de esta tecnología con materiales de transición de primer orden y se programó un modelo informático para realizar simulaciones en diferentes condiciones de trabajo. Con esto, se determinó cómo debían seleccionarse los parámetros de trabajo del sistema para obtener mejoras de rendimiento con respecto a las condiciones de enfriamiento termoeléctrico puro.La tesis se estructura en una introducción general y dos partes separadas, a saber, la construcción de un prototipo rotatorio de refrigeración magnética y el estudio comparativo de sistemas híbridos termoeléctrico-magnetocalóricos. La introducción constituye un solo capítulo y las dos partes separadas comprenden ocho y dos capítulos, respectivamente.La introducción comienza con un análisis de la relevancia de las tecnologías de refrigeración y la importancia de reducir su impacto en el consumo energético mundial, así como su relación con diferentes aspectos estratégicos y ecológicos. A continuación, se aborda la necesidad de encontrar nuevas tecnologías de refrigeración que eviten o minimicen los perjuicios de los sistemas de compresión de vapor. Las tecnologías de enfriamiento magnetocalórico se introducen haciendo un breve resumen histórico y una pequeña revisión sobre los materiales magnetocalóricos relevantes, así como de la termodinámica del efecto magnetocalórico. La introducción finaliza con un análisis de la potencia de refrigeración y las condiciones de salto térmico que deben cubrir los refrigeradores magnetocalóricos, para cumplir con la regulación europea de etiquetadoenergético. Además, se presenta una discusión personal sobre cómo interpretar los gráficos de salto térmico frente a potencia de enfriamiento desde un punto de vista práctico.La Parte I presenta el diseño y construcción de un refrigerador magnético rotatorio. Una descripción completa del proceso de diseño está estructurada en diferentes secciones y subsecciones que comprenden diferentes partes del proceso de diseño. A partir de las especificaciones básicas del capítulo 2, la selección de los materiales magnetocalóricos y su forma se describe en el capítulo 3. Este capítulo incluye un modelo 1D de relajación térmica para un lecho de bolas, que se utilizó para ver las limitaciones del intercambio de calorcon diferentes diámetros de esferas y el fluido que fluye a través del lecho. El capítulo 4 explica el proceso de diseño de la carcasa del bloque de regeneradores, describiendo las principales problemáticas a resolver y las decisiones tomadas al respecto. Este capítulo incluye también una descripción del proceso de fabricación e instalación de termopares, así como una descripción de las herramientas que tuvieron que diseñarse y construirse para obtener mallas conformadas, para separar y retener las partículas esféricas en los regeneradores. En el capítulo 5, se explica detalladamente la optimización del diseño de un imán mediante un proceso original. Se incluye también una comparación del diseño optimizado con las medidas del imán fabricado. En el capítulo 6, se describe el diseño del sistema de distribución de fluidos y se presentan las consideraciones sobre la tubería, la inserción del termopar, el diseño del punto frío y la caracterización del sistema de bombeo. El capítulo 7 describe el sistema de adquisición de datos. Finalmente, el capítulo 8 presenta el proceso de prueba y los resultados obtenidos, para analizar con una discusión sobre las pérdidasy fuentes de ineficiencia observadas. Esta discusión incluye una prueba de relajación térmica realizada, que señala la ubicación de las principales áreas de pérdidas en el dispositivo.La Parte II, aunque más corta, contiene el desarrollo de importantes simulaciones que iluminan la posibilidad de que los sándwiches termoeléctrico-magnetocalórico-termoeléctrico sigan siendo considerados como ladrillos de construcción para equipos de enfriamiento magnético alternativo, aprovechando las mejores características de termoeléctricos y magnetocalóricos. El capítulo 9 es una introducción donde se explica el concepto básico y el capítulo 10 relata la simulación del sistema híbrido. En este último capítulo se describe el modelo del sándwich, incluyendo los parámetros fijos de algunas celdas Peltier comerciales que se utilizan en él, y las particularidades a tener en cuenta a la hora de trabajar con materiales de transición de fase de primer y segundo orden. De especial relevancia es la introducción de una ecuación maestra que permite modelar adecuadamente la transferencia de calor en materiales con transición de primer orden. Se comparan el enfriamiento termoeléctrico puro, el enfriamiento magnetocalórico puro con diodos térmicos pasivos y el enfriamiento magnetocalórico-termoeléctrico híbrido. Finalmente, se comparan también estos resultados con los de otros autores y se da una explicación sobre sus malos resultados.Además de esto, En el Anexo C se proporcionan un conjunto de dibujos con el diseño de diferentes partes del prototipo y utillajes adicionales, desarrollados para la construcción del prototipo.<br /

    Laboratory Directed Research and Development Annual Report - Fiscal Year 2000

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    The integration of input filters in electrical drives

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    PhD ThesisThe integration of passive components such as inductors and capacitors has gained significant popularity in integrated drive research, and future power electronics systems will require more integrated and standardised packages. These give rise to better power density and improved performance. However, packaging techniques and passive components have been considered a technological barrier which is limiting advances in power electronics. The focus on size reduction should be turned towards the passive components, such as converter chokes, DC-link capacitors and electromagnetic interference (EMI) filters, and achieving greater power density depends on innovative integration concepts, flexibility in structures and extended operating temperature ranges while system integration and modularity are not mutually exclusive. This research considers the possibility of integrating input power filter components into electric machines. Particular attention is paid to the integration of electromagnetic line filter inductors to give better utilisation of the motor volume and envelope. This can be achieved by sharing the machine’s magnetic circuit. An LCL line filter has been chosen to be integrated with a gridconnected permanent magnet synchronous machine. Machines have been proposed in this study for low speed (3000 RPM) and high speed (25000 RPM) operation. The two machines have similar dimensions, but the low-speed machine is less challenging in terms of losses and filter integration, so attention is directed more to the high-speed machine. Both are supplied with low- and high-power drives at power ratings of 4.5 kW and 38 kW respectively. Several novel techniques have been investigated to integrate filter inductors into the electrical machines to produce a single mechanically packaged unit without significant increases in size and losses. Different approaches have been simulated using finite element analysis (FEA) to assess the effectiveness of the integration of passives within the machine structure. Each design has been iteratively optimised to determine the best mass of copper and core for the integrated filter inductors, targeting parity in power density when compared to traditional separate packages. The research demonstrates that an approach utilising a double-slot stator machine (named the integrated double slot (IDS) machine) with input filters wound into the outermost slots is the most appropriate choice in terms of achieving higher power density. The integrated filter inductors mimic the electromagnetic behaviour of the discrete industrially packaged inductors but with a volume reduction of 87.6%. A prototype of the IDS machine design of a 38 kW, 25000 RPM, including filter inductors was manufactured and testedthe General Electricity Company of Libya (GECOL), the Engineering and Physical Sciences Research Council (EPSRC), and the Engineering Doctorate scheme at Newcastle University

    Imaging of absolute electrical properties using electroquasistatic and magnetoquasistatic sensor arrays

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2006.Includes bibliographical references (p. 385-390).This research focuses on the enhancement of electroquasistatic and magnetoquasistatic nondestructive evaluation techniques. The terminals of the sensors involved are connected to conductors which are traditionally located on a single plane and have a spatially-periodic structure. The sensor operates as a two-port device with one conductor used to excite the sensor and a second conductor used to sense the response to test materials. Existing measurement capabilities are extended: 1. Multiple sensing elements are incorporated into electroquasistatic and magneto-quasistatic sensors such that the response can be accurately modeled. Single sensing element sensors which remain stationary on a test material's surface cannot provide information about variations in material properties along the surface. Scanning of a single element sensor requires many passes in order to provide high resolution property mapping of the surface. By introducing an array of sensing elements it is possible to provide stationary resolution and increase the rate at which a test material's surface can be mapped. Multiple sensing elements can also provide the ability to independently measure material properties that may otherwise be inseparable.(cont.) The sensors developed allow semi-analytic models to accurately predict their response to layered-media. The sensor is then able to measure absolute material properties using only an air calibration. 2. Existing sensor modeling methods are extended to address new sensor structures. Traditional formulations for models of spatially-periodic sensors were limited to simple conductor patterns on a single plane. These models have been reformulated to address more complex conductor patterns and allow placement on multiple sensor planes. In addition, the models have been used to approximate the sensor response of sensors with aperiodic conductor patterns. 3. Instrumentation for characterizing the terminal response of a many-element sensor is developed. The two-port nature of a single element sensor allows for its characterization by commonly available impedance measurement instruments. The complete realization of the capabilities of a multiple element sensor requires that its terminal response can be rapidly and accurately characterized. An impedance instrument compatible with sensors having up to 39 elements was developed along with methods for accurate calibration.(cont.) 4. A perturbation method is presented for rapidly predicting the response of a magnetoquasistatic sensor to a notch in a conducting material. Since magnetoquasistatic sensors are often used in the detection of cracks, the ability to model the sensor response to a simplified notch representation is desired. Due to the computational efficiency offered by the spatially-periodic layered-media models, a method of utilizing the computed material current density in the absence of the notch is sought. An approximate response is determined by introducing the notch in a way that perturbs the original current distribution. The extended capabilities are demonstrated through measurements on a variety of material configurations. In some cases the measurements can be represented as images of absolute material properties. In addition to the application of this research to quasistatic measurement methods, other disciplines can benefit from this work. Modeling techniques presented are valuable for microstrip and strip-line transmission lines, microcircuits, and can possibly be applied in fields such as geology and geological exploration. Methodologies applied to these sensor arrays may generically be applied to other array types such as: acoustic, optical, thermal, pressure, antenna, and chemical.by Darrell Eugene Schlicker.Ph.D

    DETERMINE: Novel Radar Techniques for Humanitarian Demining

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    Today the plague of landmines represent one of the greatest curses of modern time, killing and maiming innocent people every day. It is not easy to provide a global estimate of the problem dimension, however, reported casualties describe that the majority of the victims are civilians, with almost a half represented by children. Among all the technologies that are currently employed for landmine clearance, Ground Penetrating Radar (GPR) is one of those expected to increase the efficiency of operation, even if its high-resolution imaging capability and the possibility of detecting also non-metallic landmines are unfortunately balanced by the high sensor false alarm rate. Most landmines may be considered as multiple layered dielectric cylinders that interact with each other to produce multiple reflections, which will be not the case for other common clutter objects. Considering that each scattering component has its own angular radiation pattern, the research has evaluated the improvements that multistatic configurations could bring to the collected information content. Employing representative landmine models, a number of experimental campaigns have confirmed that GPR is capable of detecting the internal reflections and that the presence of such scattering components could be highlighted changing the antennas offset. In particular, results show that the information that can be extracted relevantly changes with the antenna separation, demonstrating that this approach can provide better confidence in the discrimination and recognition process. The proposed bistatic approach aims at exploiting possible presence of internal structure beneath the target, which for landmines means the activation or detonation assemblies and possible internal material diversity, maintaining a limited acquisition effort. Such bistatic configurations are then included in a conceptual design of a highly flexible GPR system capable of searching for landmines across a large variety of terrains, at reasonably low cost and targeting operators safety
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