The Effects and Mechanisms of Periodic-Carrier-Frequency PWM on Vibrations of Multiphase Permanent Magnet Synchronous Motors

High-frequency vibration and noise induced by pulsewidth modulation (PWM) deteriorate the acoustic performance of permanent magnet synchronous motor (PMSM) drives. Periodic-carrier-frequency PWM (PCFPWM) is an effective method that can disperse the high-frequency harmonics to a wider frequency band, thereby suppressing the peak harmonic. This article presents a detailed study on how exactly PCFPWM affects both the low-frequency and high-frequency vibrations of PMSMs. It is revealed that PCFPWM actually deteriorates low-frequency vibrations of the motor, due to unwanted side effect of additional ac components in d- and q-axis currents and consequent increased torque pulsations. But, this can be remedied by quasi-proportional resonant control of corresponding current harmonics. For high-frequency vibrations, the article thoroughly studies the effects of PCFPWM on current harmonics and the zero-order electromagnetic (EM) force acting on motor stator teeth. Compared with the experimental vibration results, it is found that high-frequency zero-order EM force is the direct and major cause of EM vibrations induced by PCFPWM. This article provides the theoretical basis for future optimization of PCFPWM based on the zero-order EM force as a direct vibration metric.