Research on operating and integrating inductive elements in dimmable electronic ballasts

Abstract

Dimmable electronic ballasts for fluorescent lamps have been increasingly accepted in residential, commercial, and industrial lighting applications. Important factors in the design of electronic ballasts are high power factor, low total harmonic distortion, low electromagnetic interference, low lamp current crest factor, and low flickering. In order to comply with international standard such as IEC 1000-3-2 Class C appliances, many existing electronic ballasts consist of an input power factor correction stage cascaded with a second stage high-frequency ballast inverter stage. The two stages are inter-linked by a dc voltage. This research focuses on investigating the intrinsic and extrinsic operating characteristics of the ballast-lamp system. Original lamp power control technique and component integration method will be proposed. In Chapter 1, the basics of the fluorescent lamps and ballasts will be introduced. Modeling of the lamp-ballast system will be discussed. An overview of different dimming technologies will be given. In Chapter 2, a comparative study on the performance characteristics between the variable switching frequency and variable dc link voltage control schemes for the dimming operation of electronic ballasts using a half-bridge series-resonant parallel-loaded inverter will be discussed. An approximated fundamental-frequency model that includes the characteristics of the nonlinear lamp resistance will be derived. In Chapter 3, a low-cost solution of converting the popularly adopted non-dimmable electronic ballast circuit for fluorescent lamps with self-oscillating series resonant inverter into a dimmable one will be discussed. Dimming function is achieved by increasing the switching frequency of the inverter from the natural frequency of the resonant tank, so that less energy is coupled to the lamp. Control of the switching frequency is based on deriving an adjustable dc current source from the resonant inductor in the resonant tank to control the operating point of the saturable transformers for driving the switches in the inverter. The overall implementation does not require any integrated circuit. In Chapter 4, a hybrid lamp power control scheme for dimmable electronic ballast will be discussed. Apart from adjusting the lamp brightness, the proposed method also minimizes the ambient temperature effect on affecting the light output. Instead of regulating the lamp current, the proposed method is based on regulating the lamp power. First dimming is achieved by regulating the dc voltage at the ballast inverter input. Second variation of the lamp power (due to the temperature effect) is regulated by sensing the inverter average input current for adjusting the switching frequency of the inverter. In Chapter 5, an integrated inductor structure for a typical configuration of dimmable electronic ballasts is proposed. Based on the z-parameter gyrator-capacitor model, the modeling, design and analysis of the ballast operation will be presented. A comparative study of the two-inductor and the integrated-inductor design will be carried out. Simplified design procedures will be given. In Chapter 6, an overall conclusion of the above research topics will be given. In addition, some suggestions for further development will be concluded.

Date of Award	3 Oct 2005
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	S.Y. Hui (Co-supervisor) & Shu Hung Henry CHUNG (Supervisor)