Comparative investigation of PWM techniques for general motors´ new drive for electric vehicles

Results of a comparative investigation of deterministic and random PWM techniques to be employed in a new AC drive system for electric vehicles, currently under development at General Motors Company, are presented. The study, employing the advanced simulation package SABER from Avant! Corp., was focused on the reduction of electromagnetic interference (EMI) when a deterministic PWM strategy is replaced with a random PWM (RPWM) method. To assess the impact of the PWM technique on the drive performance, the drive efficiency, torque ripple, and dynamic response of the current control system were also investigated. Two RPWM techniques with randomly varied switching frequency of the inverter were considered: one with the sampling frequency of the modulator varying in step with the switching frequency, and one with a fixed sampling frequency equal to the average switching frequency. The study has demonstrated good potentials of RPWM techniques, whose use results in EMI reduction by 10 dB and more, while the drive performance is barely affected.