Acoustic noise and vibration of direct-torque-controlled permanent magnet brushless DC drives

A systematic approach to identify the vibration and acoustic noise sources in a direct-torque-controlled (DTC) PM BLDC drive is presented and compared with that in BLAC DTC drive. Experimental results show that the acoustic noise may be radiated by the radial vibration of the stator and the vibration of connected mechanical parts due to torque pulsation and stator torsional vibration. In the BLDC DTC prototype drive, the interaction between the field harmonics and PWM switching current harmonics appears to be the dominant source of radial vibration and acoustic noise. If the acoustic noise in both BLDC DTC and BLAC DTC is mainly caused by the interactions between the armature reaction field harmonics themselves, and between the armature reaction field harmonics and PM field harmonics, the BLDC DTC drive is expected to produce higher acoustic noise because the phase current and hence the armature reaction field of BLDC DTC drive is rich of non-triplen odd harmonics. However, if the acoustic noise radiated from BLDC DTC and BLAC DTC drives is largely attributed to PWM switching current harmonic induced vibrations, as found in this paper, the sound pressure level in a BLDC DTC drive may be lower than its BLAC counterpart.