This paper presents the design, analysis and development of a novel tapped star connected 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 (VCIMDs). A star connected autotransformer with four windings per phase at different phase angles is used to realize the proposed twenty-four-pulse ac-dc converter. The basic design equations are derived to calculate the number of turns in different windings for achieving the harmonic reduction in the proposed autotransformer. The design of autotransformer is further modified for making it suitable for retrofit applications to replace presently used 6-pulse diode bridge rectifier. The proposed 24-pulse ac-dc converter is able to eliminate up to 21st harmonics in the supply current along with 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. Different power quality indices on input ac mains and on dc bus for a VCIMD fed from a 12-pulse and a 24-pulse ac-dc converters are also given to compare their performance. Various tests are conducted on the developed prototype of proposed autotransformer based 24-pulse ac-dc converter. Different power quality indices are measured on developed 24-pulse ac-dc converter to validate the design and simulation model.
