Line Harmonics of Converters with DC-Motor Loads

The line current and voltage harmonics generated by thyristor dc-motor drives, in particular with 3-phase 6-pulse dc converters, are analyzed. As industry continues to raise the power level of the converters, it is becoming more and more important to find techniques for calculating the current and voltage harmonics that avoid making the often unrealistic assumptions of the procedures used in the past. Yet these techniques must maintain, in as simple a form as possible, all the necessary curves and expressions for predicting them under the required conditions. A more accurate model of the line- current waveform is analyzed allowing for both the overlap angle and dc-current ripple, and the results are presented as a convenient set of graphs and also as a set of mathematical expressions for use on a programmable calculator. The calculated current harmonics are then used to derive the corresponding voltage harmonics toegther with their phase relationship. These voltage harmonics are then reconstructed into the relevant voltage waveform on a plotter.