Off-line supply of solid-state lamps : Lamp modelling, application of the integrated buckflyback converter and proposal of a new optimised scheme

Abstract

Actualmente, los diodos LED se están mostrando la más prometedora fuente de luz debido a sus numerosas ventajas en términos de eficiencia y versatilidad. Un ejemplo de ésta última es su capacidad de regulación de luz, o dimming, que resulta altamente interesante para adecuar los niveles de iluminación a las necesidades precisas, con el consiguiente ahorro energético. Desafortunadamente, la iluminación LED no está exenta de retos. Entre ellos se encuentra la adecuada alimentación de una carga no lineal mediante un convertidor que reúna eficiencia y bajo coste junto con una alta capacidad de regulación de flujo luminoso, entre otros aspectos. Esta tesis doctoral considera las tres principales áreas de interés en iluminación LED. En primer lugar, se estudiará el comportamiento de la lámpara LED como carga de potencia, así como la posibilidad de emplear diferentes configuraciones. En segundo lugar se estudiará la viabilidad e idoneidad del convertidor reductor-retroceso integrado, que ya se desarrolló previamente en otras aplicaciones, para alimentación de lámparas LED. Asimismo, se estudiará la optimización de este convertidor atendiendo a requisitos de rendimiento y vida útil. Finalmente, se explorarán las posibilidades de regulación de flujo luminoso en convertidores integrados, tales como el convertidor reductor-retroceso integrado propuesto.

Abstract: Nowadays, LEDs are rising as the most promising light source due to their several advantages on efficiency and versatility. An example of flexibility is the dimming capability of LEDs, a highly interesting feature nowadays in order to reduce the luminous output of an LED lamp to meet the actual luminance requirements, leading to further energy savings. Unfortunately, LED lighting is not exempt of challenges. Some of these challenges are a proper supply of a non-linear load with a high-efficient, low-cost LED driver, or the implementation of a highly dimmable scheme, among others. This work is focused on the three main areas of research in LED lighting. First, the LED lamp itself is studied regarding its behaviour as a power load, as well as the different lamp configurations that the use of LEDs allows; the LED driver is also a topic of research, where the feasibility and suitability of the Integrated Buck-Flyback Converter, which has already been successfully developed for other applications, is analysed, and the improvement in performance for LED applications is evaluated; and finally, the dimming operation is also covered, exploring the possibilities for dimming integrated single-stage converters such as the Integrated Buck-Flyback Converter proposed in this work. The main objectives of this PhD work are listed below: ‐ Study of the static and dynamic characteristics of commercially-available LED diodes as a function of the junction temperature. For this purpose, both single LEDs and LED lamps with power consumption greater than 25 W, entirely built with single devices, will be considered provided that these lamps are valid for general indoor/outdoor lighting, commercial lighting, street lighting, architectural lighting, etc. ‐ Study on the optimisation of the LED as a power load regarding the different connection strategies possible: single string of series-devices or paralleled strings. ‐ Study on the possibilities that the Integrated Buck-Flyback converter provides for the aforementioned LED lamps supply from the AC mains. Thus, Power Factor Correction will be mandatory in order to comply with IEC 61000-3-2 Class C requirements. ‐ Study of the Integrated Buck-Flyback Converter operation considering two solutions: I)either both inductors in Discontinuous Conduction Mode, or II) with the flyback converter in Continuous Conduction Mode. The advantages of one solution over the other will be evaluated. ‐ Study of the feasibility of the Integrated Buck-Flyback converter life-span enhancement by the substitution of the electrolytic-based bus capacitor with an MKP-based device. ‐ Study and review of the different dimming schemes, either analogue (AM) dimming, Pulse-Width Modulation (PWM) dimming, or other techniques present in scientific literature. ‐ Research and implementation of the PWM dimming technique best suited to the dynamic characteristics of Integrated Single-Stage Converter supplied from the AC mains and featuring Power Factor Correction.