Improvement of power factor and total harmonic distortion of input current for a valley fill electronic ballast

Abstract

The thesis will focus on the power factor correction and harmonic reduction circuit for an electronic ballast of fluorescent lamp. At first different power factor correction techniques are investigated and compared. Among them the valley-fill (VF) passive power factor correction method is used to improve the power factor and THD. The basic VF circuit is studied in detail and it is modified with four different schemes and the effects of different circuit components are analyzed. The VF circuit is used because of its simplicity, high efficiency and less expensive. The modified VF circuit with better performance is proposed in this thesis. It is combined with a current fed resonant inverter as a power circuit, which provides isolation to the driver circuit without the use of any isolation devices. When the inverter is cascaded with the valley fill circuit, the input inductor inherits the boost inductor characteristics and allows the line current to achieve close to sinusoidal shape. As a result the total harmonic distortion reduced. Lastly the modified VF ballast with extended conduction angle is analyzed with three different configurations to have a suitable design which will enhance the performance. In this work, the best result is achieved where the power factor (PF) is 0.995, efficiency is 98.79 % and the THD is 9.83 %. The ORCAD PSPICE simulation results for each configuration are presented in the thesis to highlight the performance of the proposed circuit.