A Sinusoidal Pulsewidth Modulated Three-Phase AC to DC Converter-Fed DC Motor Drive

The external performances such as power factor, displacement factor, harmonic factor, and ripple factor of a three-phase ac to dc converter-fed separately excited dc motor drive employing sinusoidal pulsewidth modulation (SPWM) control technique are obtained for different speeds and modulation indexes. Since separately excited dc motors with armature voltage control provide constant torque operation, the external performance is also determined for the drive motor operating at different values of constant load torque. Motoring and regenerating operations of the dc drive machine are considered. The three-phase PWM converter-motor drive system is analyzed, taking commutation effects into account in motoring and regenerating operations. The analysis has revealed 27 common modes in one repetitive period of the output voltage. The sequence of modes for all pulses in one period of the output voltage is established. Experimental oscillograms of typical waveforms from a laboratory-sized dc motor are illustrated to verify the basic principles of operation. Although the converter circuit requires some additional components in comparison with the commonly used phase-controlled converter, the improved performance characteristics make it attractive for industrial applications involving large power ratings.