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Title: Research on dimming technology of electronic ballasts for fluorescent lamps
Other Titles: Ying guang deng dian zi zhen liu qi tiao guang ji shu de yan jiu
Authors: Lee, Stephen Tsz Sek (李子碩)
Department: Dept. of Electronic Engineering
Degree: Doctor of Philosophy
Issue Date: 2004
Publisher: City University of Hong Kong
Subjects: Ballasts (Electricity)
Electric lighting -- Control
Fluorescent lamps
Notes: 169 leaves : ill. ; 30 cm.
CityU Call Number: TK4386.L44 2004
Includes bibliographical references (leaves 159-169)
Thesis (Ph.D.)--City University of Hong Kong, 2004
Type: Thesis
Abstract: Unlike incandescent lamps, fluorescent lamps require a device – called “Ballast” to ignite the lamp and stabilize the lamp current. For esthetic and energy saving purposes, dimming of fluorescent lamps are increasingly becoming significant in residential, commercial, and industrial applications. The emphasis of this thesis is on researching the dimming technology for fluorescent lamps. Through thorough investigations into various dimming schemes, some new control concepts were studied. The considerations are not only on the electrical specification of the ballast, such as minimum dimming level, input power factor, input current harmonics, electromagnetic compatibility, etc, but also on the impact on the fluorescent lamp, such as lamp life and visible striation. Fluorescent lamps are different from other electric loads in its nonlinear resistance characteristics. Apart from adjusting the lamp brightness, control of the electrode temperature at the two ends of the lamp tube also gives rise to many design criteria, such as the relationships between the lamp current and the electrode current. It is equally important to understand the physics of the lamp as well as the ballast circuit. Hence, this thesis starts with a comprehensive overview in Chapter one on the operating principle and dimming behavior of the fluorescent lamp, and the ballast design. Dimming criteria requirements of the lamp and electrical specifications of the ballasts will be discussed. Among various dimming concepts, variable frequency and variable voltage controls are the two common ballast design streams. Both of them have their benefits and drawbacks in implementation. A comprehensive evaluation on these two methods will be given in Chapter two. Many existing dimmable ballasts have four input wires, including two for the ac mains power input and two for the dimming level control signal input. The structure is suitable for new sites, but is not suitable for sites that have an existing wiring network. Thus, a favorable dimming control approach for those existing sites would be to allow an ordinary dimmer (that has two wires from the ac mains) to dim a fluorescent lamp. Chapter three proposes a ballast configuration that would have the above capability. In addition to ballasting the lamp, another crucial function of ballasts is to keep the lamp electrodes at a high temperature, so that proper thermionic emission from the emission mix is maintained. These requirements are even more stringent in dimmable ballasts because the lamp current directly influences the electrode power during dimming. Electrode power also significantly affects the lamp life. Chapter four proposes a novel electrode power profiler that can control the electrode power. Among various dimming schemes, controlling the switching frequency of the output inverter is still the most dominant solution in dimmable electronic ballasts. However, the sensitivity of the lamp power to the switching frequency increases as the lamp power decreases. Chapter five proposes a simple solution of using saturable inductor to improve the dimming characteristics. By replacing the resonant inductor with the saturable inductor, the dimming range can be extensively increased without modifying the driving circuit. When the lamp is dimmed, visible striation (appearance of black and white bands along the tube) appears. Striations were found to be eliminated by superimposing a small amount of dc current or low frequency ac current to the electrodes to produce a composite current waveform through the lamp, Chapter six discusses the use of random and chaotic switching techniques to eliminate striation. Finally, Chapter seven will show the final conclusions on the major contributions of the thesis and suggestions for further development.
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