Abstract
The increasing number of power electronic systems used in automotive applications has made electromagnetic interference (EMI) a serious issue in today's automobiles. This EMI problem has to be overcome at lower cost. A spread spectrum clock generator (SSCG) is a well-known method for effectively broadening the spectrum and lowering peak EMI emitted from a high-speed CPU without using additional filters and shields. We applied this technique to a pulse-width-modulated (PWM) motor-inverter system by varying the carrier frequency with time. It was found that this method reduced EMI from a prototype system by 3-5 dB in the frequency range from 500 kHz to 2 MHz. As a repercussion of varying the carrier frequency, current and torque ripples increased and motor controllability decreased. Test data indicating that the ripples can be reduced by synchronizing the current sensing timing with the control timing are presented. This paper also proposes a feed-forward control methodology that takes into account the ratio between the constant dead time of the inverter and the variation in the carrier period time. The proposed method can further reduce the ripples and improve the controllability of the PWM motor-inverter system.
Keywords: PWM, Motor, Inverter, Control, EMI, Carrier frequency, SSCG