Phase-Locked Loop for Improvement of Power-Factor of AC/DC Converters

Abstract

The present paper reports about the design and working of the firing scheme of pulse-width modulated single-phase bridge rectifier using a PLL system. Equidistant positioning of output voltage pulses of rectifier permits control upto the maximum value and requires gating of some thyristors periodically at a frequency, 'which is a multiple of the converter's source frequency. A PLL system along with a frequency divider generates such a harmonic signal and the inherent phase shift between the input and the output is suitably compensated. Different gate signals of different thyristors are generated from the basic synchronized and modulated high-frequency signal by means of suitable TTL circuits in IC chips. Oscillographic records of some variables of the firing circuit and the power circuit are presented and discussed.