HARMONIC-ANALYSIS OF CONVERTER-FED DC SYSTEMS UNDER UNBALANCED AND HARMONIC SUPPLY VOLTAGES

The analysis of converter-fed DC systems under balanced steady-state and transient conditions is well documented in the literature; normal practice is to consider the DC system supplied from a three-phase balanced source at the fundamental frequency, The concept of switching functions has been proposed before to evaluate the harmonic content of a phase-controlled six-pulse three-phase converter under both balanced and unbalanced supply conditions. However, the supply voltages were only at the fundamental frequency. This paper extends the switching function approach to analyze the harmonic content of a phase-controlled DC system when the supply voltages may be unbalanced and contain harmonic components. The input power, harmonic and distortion factors are obtained for different firing angles and compared with those of the ideal balanced case when the DC load consists of a DC motor operating at a constant torque.