Fault Tolerant DC–DC Converters at Homes and Offices

The emergence of direct current (DC) microgrids within the context of residential buildings and offices brings in a whole new paradigm in energy distribution. As a result, a set of technical challenges arise, concerning the adoption of efficient, cost-effective, and reliable DC-compatible power conditioning solutions, suitable to interface DC microgrids and energy consuming elements. This thesis encompasses the development of DC–DC power conversion solutions, featuring improved availability and efficiency, suitable to meet the requirements of a comprehensive set of end-uses commonly found in homes and offices. Based on the energy consumption profiles and requirements of the typical elements found at homes and offices, three distinctive groups are established: light-emitting diode (LED) lighting, electric vehicle (EV) charging, and general appliances. For each group, a careful evaluation of the criteria to fulfil is performed, based on which at least one DC–DC power converter is selected and investigated. Totally, a set of five DC–DC converter topologies are addressed in this work, being specific aspects related to fault diagnosis and/or fault tolerance analysed with particular detail in two of them. Firstly, mathematical models are described for LED devices and EV batteries, for the development of a theoretical analysis of the systems’ operation through computational simulations. Based on a compilation of requirements to account for in each end-use (LED lighting, EV charging, and general appliances), brief design considerations are drawn for each converter topology, regarding their architecture and control strategy. Aiming a detailed understanding of the two DC–DC power conversion systems subjected to thorough evaluation in this work – interleaved boost converter and fault-tolerant single-inductor multiple-output (SIMO) converter – under both normal and abnormal conditions, the operation of the systems is evaluated in the presence of open-circuit (OC) faults. Parameters of interest are monitored and evaluated to understand how the failures impact the operation of the entire system. At this stage, valuable information is obtained for the development of fault diagnosis strategies. Taking profit of the data collected in the analysis, a novel fault diagnostic strategy is presented, targeting interleaved DC–DC boost converters for general appliances. Ease of implementation, fast diagnostic and robustness against false alarms distinguish the proposed approach over the state-of-the-art. Its effectiveness is confirmed through a set of operation scenarios, implemented in both simulation environment and experimental context. Finally, an extensive set of reconfiguration strategies is presented and evaluated, aiming to grant fault tolerance capability to the multiple DC–DC converter topologies under analysis. A hybrid reconfiguration approach is developed for the interleaved boost converter. It is demonstrated that the combination of reconfiguration strategies promotes remarkable improvements on the post-fault operation of the converter. In addition, an alternative SIMO converter architecture, featuring inherent tolerance against OC faults, is presented and described. To exploit the OC fault tolerance capability of the fault-tolerant SIMO converter, a converter topology targeted at residential LED lighting systems, two alternative reconfiguration strategies are presented and evaluated in detail. Results obtained from computational simulations and experimental tests confirm the effectiveness of the approaches. To further improve the fault-tolerant SIMO converter with regards to its robustness against sensor faults, while simplifying its hardware architecture, a sensorless current control strategy is presented. The proposed control strategy is evaluated resorting to computational simulations.O surgimento de micro-redes em corrente contínua (CC) em edifícios residenciais e de escritórios estabelece um novo paradigma no domínio da distribuição de energia. Como consequência disso, surge uma panóplia de desafios técnicos ligados à adopção de soluções de conversão de energia, compatíveis com CC, que demonstrem ser eficientes, rentáveis e fiáveis, capazes de estabelecer a interface entre micro-redes em CC e as cargas alimentadas por esse sistema de energia. Até aos dias de hoje, os conversores CC–CC têm vindo a ser maioritariamente utilizados em aplicações de nicho, que geralmente envolvem níveis de potência reduzidos. Porém, as perspectivas futuras apontam para a adopção, em larga escala, destas tecnologias de conversão de energia, também em equipamentos eléctricos residenciais e de escritórios. Tal como qualquer outra tecnologia de conversão electrónica de potência, os conversores CC–CC podem ver o seu funcionamento afectado por falhas que degradam o seu bom funcionamento, sendo que essas falhas acabam por afectar não apenas os conversores em si, mas também as cargas que alimentam, limitando assim o tempo de vida útil do conjunto conversor + carga. Desta forma, é fulcral localizar a origem da falha, para que possam ser adoptadas acções correctivas, capazes de limitar as consequências nefastas associadas à falha. Para responder a este desafio, esta tese contempla o desenvolvimento de soluções de conversão de energia CC–CC altamente eficientes e fiáveis, capazes de responder a requisitos impostos por um conjunto alargado de equipamentos frequentemente encontrados em habitações e escritórios. Com base nos perfis de consumo de energia eléctrica e nos requisitos impostos pelas cargas tipicamente utilizadas em habitações e escritórios, são estabelecidos três grupos distintos: iluminação através de díodos emissores de luz, carregamento de veículo eléctrico (VE) e aparelhos eléctricos em geral. Para cada grupo, é efectuada uma avaliação cuidadosa dos critérios a respeitar, sendo com base nesses critérios que será escolhida e investigada pelo menos uma topologia de conversor CC–CC. No total, são abordadas cinco topologias de conversores CC–CC distintas, sendo que os aspectos ligados ao diagnóstico de avarias e/ou tolerância a falhas são analisados com particular detalhe em duas dessas topologias. Inicialmente, são estabelecidos modelos matemáticos descritivos do comportamento das principais cargas consideradas no estudo – díodos emissores de luz e baterias de VEs – visando a análise teórica do funcionamento dos sistemas em estudo, suportada por simulações computacionais. Com base numa compilação de requisitos a ter em conta em cada aplicação – iluminação através de díodos emissores de luz, carregamento de veículo eléctrico (VE) e aparelhos eléctricos em geral – são estabelecidas considerações ligadas à escolha de cada topologia de conversor não isolado, no que respeita à sua arquitectura e estratégia de controlo. Visando o conhecimento aprofundado das duas topologias de conversor CC–CC alvo de particular enfoque neste trabalho – conversor entrelaçado elevador e conversor de entrada única e múltiplas saídas, tolerante a falhas – quer em funcionamento normal, quer em funcionamento em modo de falha, é avaliado o funcionamento de ambas as topologias na presença de falhas de circuito aberto nos semicondutores activos. Para o efeito, são monitorizados e analisados parâmetros úteis à percepção da forma como os modos de falha avaliados neste trabalho impactam o funcionamento de todo o sistema. Nesta fase, é obtida informação fundamental ao desenvolvimento de estratégias de diagnóstico de avarias, particularmente indicadas para avarias de circuito aberto nos semicondutores activos dos conversores em estudo. Com base na informação recolhida anteriormente, é apresentada uma nova estratégia de diagnóstico de avarias direccionada a conversores CC–CC elevadores entrelaçados utilizados em aparelhos eléctricos, em geral. Facilidade de implementação, rapidez e robustez contra falsos positivos são algumas das características que distinguem a estratégia proposta em relação ao estado da arte. A sua efectividade é confirmada com recurso a uma multiplicidade de cenários de funcionamento, implementados quer em ambiente de simulação, quer em contexto experimental. Por fim, é apresentada e avaliada uma gama alargada de estratégias de reconfiguração, que visam assegurar a tolerância a falhas das diversas topologias de conversores CC–CC em estudo. É desenvolvida uma estratégia de reconfiguração híbrida, direccionada ao conversor entrelaçado elevador, que combina múltiplas medidas de reconfiguração mais simples num único procedimento. Demonstra-se que a combinação de múltiplas estratégias de reconfiguração introduz melhorias substanciais no funcionamento do conversor ao longo do período pós-falha, ao mesmo tempo que assegura a manutenção da qualidade da energia à entrada e saída do conversor reconfigurado. Noutra frente, é apresentada e descrita uma arquitectura alternativa do conversor de entrada única e múltiplas saídas, com tolerância a falhas de circuito aberto. Através da configuração proposta, é possível manter o fornecimento de energia eléctrica a todas as saídas do conversor. Para tirar máximo proveito da tolerância a falhas do conversor de entrada única e múltiplas saídas, uma topologia de conversor indicada para sistemas residenciais de iluminação baseados em díodos emissores de luz, são apresentadas e avaliadas duas estratégias de reconfiguração do conversor, exclusivamente baseadas na adaptação do controlo aplicado ao conversor. Os resultados de simulação computacional e os resultados experimentais obtidos confirmam a efectividade das abordagens adoptadas, através da melhoria da qualidade da energia eléctrica fornecida às diversas saídas do conversor. São assim asseguradas condições essenciais ao funcionamento ininterrupto e estável dos sistemas de iluminação, já que a qualidade da energia eléctrica fornecida aos sistemas de iluminação tem impacto directo na qualidade da luz produzida. Por fim, e para aprimorar o conversor de entrada única e múltiplas saídas tolerante a falhas, no que respeita à sua robustez contra falhas em sensores, é apresentada uma estratégia de controlo de corrente que evita o recurso excessivo a sensores e, ao mesmo tempo, simplifica a estrutura de controlo do conversor. A estratégia apresentada é avaliada através de simulações computacionais. A abordagem apresentada assume vantagens em múltiplos domínios, sendo de destacar vantagens como a melhoria da fiabilidade de todo o sistema de iluminação (conversor + carga), os ganhos atingidos ao nível do rendimento, a redução do custo de implementação da solução, ou a simplificação da estrutura de controlo.This work was supported by the Portuguese Foundation for Science and Technology (FCT) under grant number SFRH/BD/131002/2017, co-funded by the Ministry of Science, Technology and Higher Education (MCTES), by the European Social Fund (FSE) through the ‘Programa Operacional Regional Centro’ (POR-Centro), and by the Human Capital Operational Programme (POCH)

Prognostics and health management of light emitting diodes

Prognostics is an engineering process of diagnosing, predicting the remaining useful life and estimating the reliability of systems and products. Prognostics and Health Management (PHM) has emerged in the last decade as one of the most efficient approaches in failure prevention, reliability estimation and remaining useful life predictions of various engineering systems and products. Light Emitting Diodes (LEDs) are optoelectronic micro-devices that are now replacing traditional incandescent and fluorescent lighting, as they have many advantages including higher reliability, greater energy efficiency, long life time and faster switching speed. Even though LEDs have high reliability and long life time, manufacturers and lighting systems designers still need to assess the reliability of LED lighting systems and the failures in the LED. This research provides both experimental and theoretical results that demonstrate the use of prognostics and health monitoring techniques for high power LEDs subjected to harsh operating conditions. Data driven, model driven and fusion prognostics approaches are developed to monitor and identify LED failures, based on the requirement for the light output power. The approaches adopted in this work are validated and can be used to assess the life of an LED lighting system after their deployment based on the power of the light output emitted. The data driven techniques are only based on monitoring selected operational and performance indicators using sensors whereas the model driven technique is based on sensor data as well as on a developed empirical model. Fusion approach is also developed using the data driven and the model driven approaches to the LED. Real-time implementation of developed approaches are also investigated and discussed

NASA thesaurus. Volume 3: Definitions

Publication of NASA Thesaurus definitions began with Supplement 1 to the 1985 NASA Thesaurus. The definitions given here represent the complete file of over 3,200 definitions, complimented by nearly 1,000 use references. Definitions of more common or general scientific terms are given a NASA slant if one exists. Certain terms are not defined as a matter of policy: common names, chemical elements, specific models of computers, and nontechnical terms. The NASA Thesaurus predates by a number of years the systematic effort to define terms, therefore not all Thesaurus terms have been defined. Nevertheless, definitions of older terms are continually being added. The following data are provided for each entry: term in uppercase/lowercase form, definition, source, and year the term (not the definition) was added to the NASA Thesaurus. The NASA History Office is the authority for capitalization in satellite and spacecraft names. Definitions with no source given were constructed by lexicographers at the NASA Scientific and Technical Information (STI) Facility who rely on the following sources for their information: experts in the field, literature searches from the NASA STI database, and specialized references

Phosphors for solid-state lighting: New systems, deeper understanding

Phosphor materials are a crucial component in energy efficient lighting with the ability to affect overall device performance. The structure and crystal chemistry of these materials greatly dictate the resulting optical properties. Understanding the relationship between structural and optical properties in phosphors allows for insights into the methods for developing materials with targeted properties. Here, we explore the structure-composition-property relationships in phosphor materials using a multitude of structural and optical characterization methods including high resolution synchrotron X-ray and neutron powder diffraction and total scattering, low-temperature heat capacity, temperature- and time-resolved photoluminescence, and density functional theory calculations. We describe the development of several new phosphor compositions and provide an in-depth description of the structural and optical properties. We show structural origins of improved thermal performance of photoluminescence and methods for determining structural rigidity in phosphor hosts that may lead to improved luminescent properties. New white light generation strategies are also explored including quantum dots for improved color rendition and laser-based lighting for efficient and thermally stable high-power lighting.We begin by presenting the development of a green-yellow emitting oxyfluoride solid-solution phosphor Sr2Ba(AlO4F)1-x(SiO5)x:Ce3+. An examination of the host lattice, and the local structure around the Ce3+ activator ions points to how chemical substitutions play a crucial role in tuning the optical properties of the phosphor. The emission wavelength can be tuned from green to yellow by tuning the composition, x. Photoluminescent quantum yield is determined to be 70±5% for some of the examples in the series with excellent thermal properties. Phosphor-converted LED devices are fabricated using an InGaN LED and are shown to exhibit high color rendering white light. Next, we identify two new phosphor solid-solution systems, (Ba1-xSrx)9Sc2Si6O24:Ce3+,Li+ and Ba9(Y1-yScy)2Si6O24:Ce3+. The substitution of Sr for Ba in (Ba1-xSrx)9Sc2Si6O24:Ce3+,Li+results in a decrease of the alkaline earth--oxygen bond distances at all three crystallographic sites, leading to changes in optical properties. The room temperature photoluminescent measurements show the structure has three excitation peaks corresponding to Ce3+ occupying the three independent alkaline earth sites. The emission of (Ba1-xSrx)9Sc2Si6O24:Ce3+,Li+ is red-shifted from the near-UV to blue with compositional changes. The red-shifted photoluminescent quantum yield also increases when Sr is substituted for Ba in these compounds. The end member Ba9Y2Si6O24:Ce3+ was identified as an efficient blue-green phosphor with high thermal stability of the luminescence, viable for near-UV LED excitation. An efficient emission, with a quantum yield of 60%, covers a broad portion of the visible spectrum leading to the observed blue-green color. The emission of this compound can be red-shifted via the solid- Ba9(Y1-yScy)2Si6O24:Ce3+ allowing for tunable color properties when device integration is considered.We then explore the structure--composition relationships and optical properties in newly developed cerium-substituted (Sr,Ba)3(Y,La)(BO3)3 borate phosphors. Examination of the coordination environment of the Ce3+ active site polyhedra coupled with low-temperature photoluminescence reveals three distinct excitation bands corresponding to Ce3+ located on three distinct crystallographic sites. Comparing the position of these excitation bands with crystal field splitting effects due to changes in polyhedral volumes and distortions suggests an assignment of the three excitation bands. These compounds are efficiently excited by UV light with blue emission, the most efficient compound determined to be Sr3La(BO3)3:Ce3+,Na+ with a quantum yield of 50%.A data-driven discovery of energy materials then reveals the efficient BaM2Si3O10:Eu2+ (M = Sc, Lu) phosphors with UV-to-blue and UV-to-blue-green phosphors. Interestingly, substituting Eu2+ in the Lu3+ containing material produces two emission peaks, at low temperature, as allowed by two substitution sites. The photoluminescence of the Sc3+ compound is robust at high temperature, while the Lu-analogue has a large decrease of its room temperature intensity. The decrease in emission intensity is explained as stemming from charge transfer quenching due to the short distances separating the luminescent centers on the Lu3+ substitution site. The correlation between structure and optical response in these two compounds indicates that even though the structures are three-dimensionally connected, high symmetry is required to prevent structural distortions that could impact photoluminescence.Next, the consequences of optimal bond valence on structural rigidity are explored and linked to the improved luminescence properties in SrxBa2-xSiO4:Eu2+ orthosilicate phosphors. We observe that in the intermediate compositions, the two cation sites in the crystal structure are optimally bonded as determined from bond valence sum calculations. Optimal bonding results in a more rigid crystal, as established by the intermediate compositions possessing the highest Debye temperature, determined experimentally from low-temperature heat capacity measurements. Greater rigidity, in turn, results in high luminescence efficiency for intermediate compositions at elevated temperatures.We then conduct an in-depth analysis of the average and local structure, Debye temperature, and structural rigidity in oxide phosphor host materials. The average and local structure of the oxides Ba2SiO4, BaAl2O4, SrAl2O4, and Y2SiO5 are examined in order to evaluate crystal rigidity in light of recent studies suggesting that highly connected and rigid structures yield the best phosphor hosts. Simultaneous momentum-space refinements of synchrotron X-ray and neutron scattering yield accurate average crystal structures, with reliable atomic displacement parameters. The Debye temperature, which has proven to be a useful proxy for structural rigidity, is extracted from the experimental atomic displacement parameters and compared with predictions from density functional theory calculations and experimental low-temperature heat capacity measurements. The role of static disorder on the measured displacement parameters, and the resulting Debye temperatures, are also analyzed using pair distribution function analysis of total neutron scattering, as refined over varying distance ranges of the pair distribution function. The interplay between optimal bonding in the structure, structural rigidity, and correlated motion in these structures is examined, and the different contributions are delineated.Finally, new light generation strategies including quantum dots and laser-based lighting are explored

Literature review - Energy saving potential of user-centered integrated lighting solutions

Measures for the reduction of electric energy loads for lighting have predominantly focussed on increasing the efficiency of lighting systems. This efficiency has now reached levels unthinkable a few decades ago. However, a focus on mere efficiency is physically limiting, and does not necessarily ensure that the anticipated energy savings actually materialize. There are technical and non-technical reasons because of which effective integration of lighting solutions and their controls, and thus a reduction in energy use, does not happen. This literature review aims to assess the energy saving potential of integrated daylight and electric lighting design and controls, especially with respect to user preferences and behaviour. It does so by collecting available scientific knowledge and experience on daylighting, electric lighting, and related control systems, as well as on effective strategies for their integration. Based on this knowledge, the review suggests design processes, innovative design strategies and design solutions which – if implemented appropriately – could improve user comfort, health, well-being and productivity, while saving energy as well as the operation and maintenance of lighting systems. The review highlights also regulatory, technical, and design challenges hindering energy savings. Potential energy savings are reported from the retrieved studies. However, these savings derived from separate studies are dependent on their specific contexts, which lowers the ecological validity of the findings. Studies on strategies based on behavioural interventions, like information, feedback, and social norms, did not report energy saving performance. This is an interesting conclusion, since the papers indicate high potentials that deserve further exploration. Quantifying potential savings is fundamental to fostering large scale adoption of user-driven strategies, since this would allow at least a rough estimation of returns for the investors. However, such quantification requires that studies are designed with an inter-disciplinary approach. The literature also shows that strategies, where there is more communication between façade and lighting designers, are more successful in integrated design, which calls for more communication between stakeholders in future building processes

Emerging and Disruptive Next-Generation Technologies for POC: Sensors, Chemistry and Microfluidics for Diagnostics

Recently, the attention paid to self-care tests and the easy and large screening of a high number of people has dramatically increased. Indeed, easy and affordable tools for the safe management of biological fluids together with self-diagnosis have emerged as compulsory requirements in this time of the COVID-19 pandemic, to lighten the pressure on public healthcare institutions and thus limiting the diffusion of infections. Obviously, other kinds of pathologies (cancer or other degenerative diseases) also continue to require attention, with progressively earlier and more widespread diagnoses. The contribution to the development of this research field comes from the areas of innovative plastic and 3D microfluidics, smart chemistry and the integration of miniaturized sensors, going in the direction of improving the performances of in vitro diagnostic (IVD) devices. In our Special Issue, we include papers describing easy strategies to identify diseases at the point-of-care and near-the-bed levels, but also dealing with innovative biomarkers, sample treatments, and chemistry processes which, in perspective, represent promising tools to be applied in the field

Articles indexats publicats per investigadors del Campus de Terrassa: 2017

Aquest informe recull els 241 treballs publicats per 222 investigadors/es del Campus de Terrassa en revistes indexades al Journal Citation Report durant el 2017Postprint (published version

Marine artificial light at night:An empirical and technical guide

The increasing illumination of our world by artificial light at night (ALAN) has created a new field of global change research with impacts now being demonstrated across taxa, biological ranks and spatial scales. Following advances in terrestrial ecology, marine ALAN has become a rapidly growing research area attracting scientists from across all biomes. Technological limitations, complexities of researching many coastal and marine ecosystems and the interdisciplinary nature of ALAN research present numerous challenges. Drawing on expertise from optical oceanographers, modellers, community ecologists, experimental and molecular biologists, we share practical advice and solutions that have proven useful for marine ALAN research. Discussing lessons learnt early on can help in the effective and efficient development of a field. The guide follows a sensory ecology approach to marine light pollution and consolidates physics, ecology and biology. First, we introduce marine lightscapes highlighting how these differ from terrestrial ones and provide an overview of biological adaptations to them. Second, we discuss study design and technology to best quantify ALAN exposure of and impacts on marine and coastal organisms including molecular tools and approaches to scale-up marine ALAN research. We conclude that the growing field of marine ALAN research presents opportunities not only for improving our understanding of this globally widespread stressor, but also for advancing fundamental marine photobiology, chronobiology and night-time ecology. Interdisciplinary research will be essential to gain insights into natural marine lightscapes shaping the ecology and evolution coastal and marine ecosystems