A novel polygon based 15-phase AC-DC converter for vector controlled induction motor drives

In this article, a new approach to improve power quality at AC mains in a vector controlled induction motor drive (VCIMD) is proposed. The novel multi-phase AC-DC converter consisting of a reduced rating autotransformer, leading to savings in weight, size, and cost, results in reduction in harmonic current at AC mains. The resulting supply current is near sinusoidal in shape with low total harmonic distortion (THD) of supply current and a nearly unity power factor The design of the autotransformers is modified for making the proposed AC-DC converter suitable for retrofit applications such as fans in cement industry, pumps in petrochemical industry, steel rolling mills, etc., where presently a six-pulse diode bridge rectifier is used. Moreover the load is varied on VCIMD and its effect on various power quality indices is also presented. To validate the proposed approach, a laboratory prototype of the proposed autotransformer based 15-phase AC-DC converter is designed and developed, and various tests are conducted on it. A set of power quality indices on input AC mains and on DC bus for a VCIMD fed from a 6-pulse AC-DC converter and the proposed 15-phase AC-DC converter are also given to compare their performance.