A Digital Pulsewidth Modulator Employing Advanced Modulation Techniques

Advanced pulsewidth modulation (PWM) techniques for inverters allow the use of high-efficiency ac drives with low torque and speed pulsations and with reduced losses. A digital control scheme for a thyristor inverter is presented, where firing patterns satisfying given requirements like harmonic elimination or loss minimization have been calculated and stored in programmable read-only memory (PROM). Moreover, such a tontrol permits a continuous variation of output voltage over the modulation range for full inverter utilization. Evaluation using a 22-kW induction motor drive verified that the control provides a clean frequency spectrum over the operating range of the drive (0-100 Hz).