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This paper deals with a reduced rating delta-polygon autotransformer based twenty-four-pulse AC-DC converter feeding variable frequency induction motor drives (VFIMD's) for improving power quality at the point of common coupling (PCC). The proposed twenty four-pulse ac-dc converter is realized on the principle of dc ripple re-injection technique for harmonic mitigation. The design of the proposed autotransformer is developed along with the necessary modifications required for making it suitable for retrofit applications, where presently a 6-pulse diode bridge rectifier is used. The effect of load variation on VFIMD is also studied to demonstrate the effectiveness of the proposed ac-dc converter. The extensive tests are conducted on the developed prototype autotransformer based ac-dc converters. Different power quality indices of 6-pulse, 12-pulse and proposed 24-pulse ac-dc converters are obtained from simulation and verified from experimental results.