A Twelve-Phase AC-DC Converter for Power Quality Improvement in Direct Torque Controlled Induction Motor Drives

This paper presents the design and analysis of a star connected autotransformer based twelve-phase ac-dc converter for improving power quality at the point of common coupling (PCC) in direct torque controlled induction motor drives (DTCIMD's). A star connected autotransformer with five windings per phase is used to realize the twelve-phase ac-dc converter. The basic design equations are derived to calculate the number of turns in different windings for achieving harmonic reduction in the proposed autotransformer based ac-dc converter. The designed twelve-phase 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 DTCIMD is also studied to demonstrate the effectiveness of the proposed ac-dc converter.