13-11-2014, 04:15 PM
Abstracts: Multipulse converters are converters providing more than six pulses of DC voltage per cycle or the converter having more steps in AC input current than that of six pulse rectifier supply current. The converters which are also known as rectifiers are generally fed from three phase ac supply have problems of power quality in terms of harmonics injected into the supply which cause poor power factor, ac voltage distortion and rippled dc outputs. Because of these problems in ac-dc conversion, several standards and guidelines are specified. So to overcome these problems it is preferred to modify the converter structure at design stage using active or passive wave shaping of input currents. In this project, a 12-pulse rectifier has been designed for high voltage applications. Four 3-phase systems are obtained from a single 3-phase source using zig-zag interconnection of conventional single-phase transformers. From two 30º displaced (star-delta connection) 3-phase systems feeding two 6-pulse rectifiers that are series/parallel connected, a 12-pulse rectifier topology is obtained. Thus, from the four 3-phase systems that are displaced by 10º, (obtained using zigzag connections) three 12-pulse rectifiers are obtained that are cascaded to realize a 36-pulse rectifier. Phase shifts of 10º and 30º are made using star, delta and zigzag connections and thus, finally the addition of relevant line voltages.