An Improved Power-Quality 30-Pulse AC–DC for Varying Loads

This paper presents the design and analysis of a novel 30-pulse ac-dc converter for harmonic mitigation under varying loads. The proposed 30-pulse ac-dc converter is based on a polygon-connected autotransformer with reduced magnetics. The proposed ac-dc converter is able to eliminate lower than 29th order harmonics in the ac supply current. The resulting supply current is near sinusoidal in shape with low total harmonic distortion and a nearly unity power factor. Moreover, the design of an autotransformer is modified to make it suitable for retrofit applications, where presently a 6-pulse diode bridge rectifier is used. To validate the proposed approach, various power-quality indices are presented under varying loads. The proposed ac-dc converter is found to be suitable for retrofit applications with a large load variation and where harmonic reduction is more stringent. The laboratory prototype of the proposed autotransformer-based 30-pulse ac-dc converter is developed and test results are presented which validate the developed design procedure and the simulation models of this ac-dc converter