| This thesis describes the results of a comparative investigation of deterministic and random pulse width modulation (PWM) techniques to be employed in a new ac drive system for electric vehicles, currently under development at the General Motors Advanced Technology Vehicles division. 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 an impact of the PWM technique on the drive performance, the drive efficiency, torque ripple, and dynamic response of the current control system were investigated as well. 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 results demonstrated good potentials of RPWM techniques, resulting in EMI reduction by 10 dB and more, while barely affecting the drive performance. |
