Design and analysis of a low THD Electronic ballast with improved input power factor

Abstract

This thesis proposes a two-stage high-power factor and low THD electronics ballast for a 40W commercial fluorescent tube lamp. The proposed ballast uses a Ĉuk Buck-Boost ac-dc converter in continuous conduction mode (CCM) as a power factor and input current shaper/pre-regulator. The dc-dc Ĉuk converter between ac-dc diode rectifier and the resonant inverter of the ballast makes the input current high frequency switched. As a result of in phase high frequency switching, the input current can be easily filtered with small sized filter to obtain low THD input current and also to maintain high input power factor. In the proposed electronic ballast topology, a self oscillating half bridge series resonant parallel loaded inverter (SRPLI) is used for the conversion of dc supply obtained by bridge rectifier to high frequency ac supply. Use of high frequency ac for fluorescent lights allows better conversion of energy to light than in the utility supply low frequency ac supply. Also, the ignition cum voltage balancing inductors used in these lamps are reduced in size providing further increase of efficiency by reducing copper loss in the inherent resistance in inductors. The design, modeling and simulation of the proposed topology is carried out in Orcad environment for a 40W, 220V, 50Hz fluorescent lamp. The design is implemented practically. The zero voltage switching (ZVS) is achieved which reduces the switching losses. The power quality indices like total harmonic distortion of ac mains current (THDi), power factor (PF) and energy conversion efficiency are evaluated to demonstrate the behavior of proposed electronic ballast.