24-pulse ac-dc converter for harmonic mitigation

A new harmonic mitigator based on 24-pulse ac-dc conversion is proposed to feed voltage source inverter supplying squirrel-cage induction motor drive. The proposed converter consists of a newly designed hexagon-connected autotransformer with reduced magnetics rating and having simplicity in design and manufacturing. The proposed 24-pulse ac-dc converter is found capable of suppressing less than 23rd harmonic in the supply current. The power factor is also improved to near unity in the wide operating range of the vector-controlled induction motor drive (VCIMD). Moreover, the design of the autotransformer is modified to make it suitable for applications, where presently a 6-pulse diode bridge rectifier is used. A laboratory prototype of the proposed autotransformer-based 24-pulse ac-dc converter feeding a VCIMD 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.