A Tapped Delta Autotransformer Based 24-Pulse AC-DC Converter for Variable Frequency Induction Motor Drives

This paper deals with the design and analysis of a novel reduced rating autotransformer based twenty-four pulse ac-dc converter for improving power quality at the point of common coupling (PCC) in vector controlled induction motor drives (VCIMD's). The proposed twenty four-pulse ac-dc converter is realized based on a tapped delta autotransformer having different windings at different phase angles. The design of the proposed autotransformer is presented alongwith the necessary modifications required for making it suitable for retrofit applications to replace presently used 6-pulse diode bridge rectifier. The proposed 24-pulse ac-dc converter is found capable of suppressing upto 21st harmonics in the supply current alongwith the power factor improvement close to unity in the wide operating range of the drive. The effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed ac-dc converter. A set of power quality indices on input ac mains and on dc bus for a VCIMD fed from 12-pulse and 24-pulse ac-dc converters are given to compare their performance.