Polygon connected autotransformer based 24-pulse AC-DC converter for power quality improvement

This paper deals with a polygon connected autotransformer based 24-pulse AC-DC converter for power quality improvement in vector controlled induction motor drives (VCIMD´s). A polygon connected autotransformer with multi windings per phase at different phase angles is used to realize the proposed 24-pulse AC-DC converter. The design of proposed autotransformer is presented along with the necessary modifications required for making it suitable for retrofit applications, where presently a 6-pulse diode bridge rectifier is used. The proposed 24-pulse AC-DC converter is able to eliminate upto 21^st 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. A set of power quality indices on input ac mains and on DC bus for a VCIMD fed from six-pulse and proposed AC-DC converter are presented to compare their performance.