Adaptive Automotive Lighting Systems

Over the past few years, the use of LEDs within the automotive and avionic industries has increased due to their high efficiency, durability and wide range of light brightness. As the use of LEDs within these industries grows, a need for reliable, high performance drivers becomes more relevant. Companies are implementing LEDs for applications involving adaptive lighting or simple dimming features. This thesis shows implementation of various non-isolated analog converters integrated with digital dimmers to achieve these adaptive lighting systems. Adaptive lighting systems involve reading an input from an external source (brake pedal or steering wheel) and changing the brightness and/or pattern of the brake/headlights to convey more information to the driver and their surroundings. The analog converters will implement Linear Technology’s LED driver IC’s, while the digital dimmers comprise of microcontrollers and discrete components. The design, simulation, and hardware verification will showcase the abilities of these analog converters. Results will demonstrate the proposed applications for both adaptive front and brake lighting

An Off-line Single-Inductor Multiple-Output LED Driver With High Dimming Precision and Full Dimming Range

This paper presents a single-inductor multiple-output (SIMO) LED driver with precise dimming and full dimming range. Based on the coordination of a string-level scheme and a system-level dimming scheme, the proposed SIMO LED driver can overcome practical constraints of existing SIMO LED drivers such as limited dimming range and needs for high-current switches. The proposal can achieve dimming precision up to an accuracy of 0.8% and also full dimming range. It has the flexibility of using either phase-shift or synchronous pulsewidth-modulated (PWM) switching for dimming control. The proposed circuit and control operations have been practically verified with a 25-W off-line SIMO-driven LED system. Practical evaluations of its power quality and energy efficiency are also provided

A review and classification of LED ballasts

This paper presents a review on existing ballasts for light-emitting diodes (LED) with considerations to their compliance to regulations, technological challenges, and on meeting various application requirements. All existing LED ballasts, including those proposed in recent literature, have been appropriately classified and systematically organized for the discussion. The dissemination of this information and its understanding is helpful for future R&D pursuits in this area. © 2013 IEEE.published_or_final_versio

Simplified Daylight Spectrum Approximation by Blending Two Light Emitting Diode Sources

Energy-conscious facility designs strive to include natural daylight in workspaces. To improve the efficiency of illumination, significant efforts are underway to adopt more efficient light emitting diode (LED) lamps and to effectively integrate daylight with active dimming of electric lighting. However, the correlated color temperature (CCT) and spectral content of daylight varies throughout the day while existing electric light sources produce light with a fixed CCT, resulting in mixed-illumination environments. The color rendering requirements for a lamp that permits the selection of color temperature across a significant portion of the daylight locus is explored. The analysis indicates that it is possible to form a lamp having only two independently controllable groups of narrowband emitters that is capable of producing light that achieves a nearly colorimetric match to daylight from 4000-10,000K. A prototype LED lamp, with a simple control and novel drive scheme, which produces white light over a range of CCTs by blending light from a pair of sources, each with numerous, tuned LED emitters, is demonstrated. The prototype validates the lamp concept -- producing light over a broad range of CCT values (4000-8000K) while maintaining a stable color quality rendering score without requiring computations for spectral approximation once employed

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)

Design and Test of Wide Input and Output Constant Current LED Driver

This senior project aims to provide design and test the performance of a DC-DC constant current LED driver for use in a larger DC smart building infrastructure. In this instance, a SEPIC topology is chosen to provide high efficiency output current at output voltages that can be above or below the input voltage. This is challenging since the same design must operate at similar efficiency for vastly different environmental conditions. As a part of a larger system, the design must be able to perform the given task consistently regardless of changes to the source and load power. The design uses the LT3795 LED controller to operate power switches and inductors to transform the input power into usable output power for a string of LEDs. The controller is paired with an onboard microcontroller to provide error reporting and supplement the PWM dimming control features of the IC. Simulations were done to ensure the efficiency of the design remained above 93% within the full range of input and output voltages, along with a range of PWM frequencies and duty cycles. After manufacturing and assembly, the board was found to be under specification regarding the input and output voltage ranges, as well as below the efficiency target. This was largely due to issues regarding the layout assembly of the finished product

Design Techniques of Highly Integrated Hybrid-Switched-Capacitor-Resonant Power Converters for LED Lighting Applications

The Light-emitting diodes (LEDs) are rapidly emerging as the dominant light source given their high luminous efficacy, long lift span, and thanks to the newly enacted efficiency standards in favor of the more environmentally-friendly LED technology. The LED lighting market is expected to reach USD 105.66 billion by 2025. As such, the lighting industry requires LED drivers, which essentially are power converters, with high efficiency, wide input/output range, low cost, small form factor, and great performance in power factor, and luminance flicker. These requirements raise new challenges beyond the traditional power converter topologies. On the other hand, the development and improvement of new device technologies such as printed thin-film capacitors and integrated high voltage/power devices opens up many new opportunities for mitigating such challenges using innovative circuit design techniques and solutions. Almost all electric products needs certain power delivery, regulation or conversion circuits to meet the optimized operation conditions. Designing a high performance power converter is a real challenge given the market’s increasing requirements on energy efficiency, size, cost, form factor, EMI performance, human health impact, and so on. The design of a LED driver system covers from high voltage AC/DC and DC/DC power converters, to high frequency low voltage digital controllers, to power factor correction (PFC) and EMI filtering techniques, and to safety solutions such as galvanic isolation. In this thesis, we study design challenges and present corresponding solutions to realize highly integrated and high performance LED drivers combining switched-capacitor and resonant converters, applying re-configurable multi-level circuit topology, utilizing sigma delta modulation, and exploring capacitive galvanic isolation. A hybrid switched-capacitor-resonant (HSCR) LED driver based on a stackable switched-capacitor (SC) converter IC rated for 15 to 20 W applications. Bulky transformers have been replaced with a SC ladder to perform high-efficiency voltage step-down conversion; an L-C resonant output network provides almost lossless current regulation and demonstrates the potential of capacitive galvanic isolation. The integrated SC modules can be stacked in the voltage domain to handle a large range of input voltage ranges that largely exceed the voltage limitation of the medium-voltage-rated 120 V silicon technology. The LED driver demonstrates > 91% efficiency over a rectified input DC voltage range from 160 VDC to 180 VDC with two stacked ICs; using a stack of four ICs > 89.6% efficiency is demonstrated over an input range from 320 VDC to 360 VDC . The LED driver can dim its output power to around 10% of the rated power while maintaining >70% efficiency with a PWM controlled clock gating circuit. Next, the design of AC main rectifier and inverter front end with sigma delta modulation is described. The proposed circuits features a pair of sigma delta controlled multilevel converters. The first is a multilevel rectifier responsible for PFC and dimming. The second is a bidirectional multilevel inverter used to cancel AC power ripple from the DC bus. The system also contains an output stage that powers the LEDs with DC and provides for galvanic isolation. Its functional performance indicates that integrated multilevel converters are a viable topology for lighting and other similar applications