Polygon-Connected Autotransformer-Based 24-Pulse AC–DC Converter for Vector-Controlled Induction-Motor Drives

This paper presents a novel autotransformer-based 24-pulse ac–dc converter feeding vector-controlled induction motor drives (VCIMDs) for improving power quality at the point of common coupling. The dc-ripple-reinjection technique is used in achieving the pulse multiplication in a 12-pulse ac–dc converter. The design of the proposed autotransformer is given, and necessary modifications are made in it to provide the same output dc voltage as a 6-pulse diode-bridge ac–dc converter to make it suitable for retrofit applications. The proposed 24-pulse ac–dc converter is found capable of suppressing up to the 21st harmonics in the supply current along with the power-factor improvement close to unity in the wide operating range of the drive. A set of power-quality indexes at input ac mains and on dc bus for a VCIMD fed from various ac–dc converters are also given to compare their performance. A prototype of the proposed autotransformer-based 24-pulse ac–dc converter is developed, and test results are presented to validate the developed design procedure and the simulation models of this ac–dc converter under varying loads.