Aportaciones al modelado de lámparas fluorescentes para aplicaciones en alta frecuencia con regulación del flujo luminoso

Abstract

ABSTRACT: Despite the strong market penetration of LED based lighting systems, fluorescent fixtures still capitalize most of the existing indoor lighting installations nowadays. The current trend shows an increasing need of more efficient, flexible and controllable ballasts. In the near future, high efficiency lighting systems based on fluorescent lamps are likely to become a dominant solution due to its cost effectiveness. Therefore, there is a clear chance to develop new designs and control techniques in this field. Unfortunately, the flexibility required in current lighting systems is not feasible using traditional electromagnetic ballasts, thus the use of electronic ballasts will presumably become intensive. However, if lamp electrodes are not treated conveniently, the use of electronic ballasts does not ensure a longer lamp life. This fact implies not only the need to conveniently preheat the electrodes prior ignition, but also to maintain proper operating conditions during steady state, especially when lamp operates below its rated power level. The present doctoral work aims to make some contributions to the modeling of fluorescent lamps for high frequency dimming applications. It pursues to obtain new models that provide more accurate description of lamp behavior, also taking into account the power level and ambient temperature. Based on these premises, present document starts with a description of the basic characteristics of the most commonly used light sources, their physical implementation and their operational principles. Besides, in Chapter 1, the electrical characteristics of different lamps are described focusing in the most critical aspects for the design of the supply system. In Chapter 2, a deep revision is made regarding the state of the art in fluorescent lamp modelling. This chapter is divided in two different blocks: discharge models and electrode models. In first block, existing static models are revised, followed by the great and small signal dynamic models. The second block is focused on electrode behavior, analyzing the different working stages that take place between ignition and steady state operation. In this block, the existing regulations are also introduced. These regulations describe the optimum conditions to operate in dimming mode and define the best way to include the electrodes in the lamp equivalent circuit. Finally, the procedure to calculate the SoS limits is introduced. Chapter 3 describes the small signal characterization of fluorescent lamps with output power control. The two different circuit configurations that were used are described in detail. In first place, the circuit used to avoid the partial compensation of lamp’s negative impedance that occurs due to the series resistance of the electrodes is described. The second circuit used was designed to include and measure the effect of the electrodes together with the arc dynamic impedance. This chapter describes the hardware and the control program of both characterization circuits. In Chapter 4, a general review of the tests that were carried out is performed, highlighting the type of lamp, electrode heating procedure and the environmental conditions in which they were developed. The following sections of the chapter are dedicated to expose the contributions of this Thesis regarding the small signal modeling of fluorescent lamps. Chapter 5 describes the applications that were developed. Chapter starts explaining some general design considerations for high frequency resonant ballasts with output power control followed by a detailed description of the generalized averaging procedure used to analyze the dynamic characteristics of resonant inverters. This chapter continues with the completion of an application example of small-signal characterization of fluorescent lamps for different power levels, followed by a stability analysis using the small-signal double-pole double-zero model in a resonant ballast with regulated output power. Chapter 5 concludes with an explanation of the effect of ambient temperature on the stability range.