Acoustic Noise of Switched Reluctance and Permanent Magnet Motors: A Comparison in the Context of Electric Brakes

It is held as fact that Permanent Magnet (PM) brushless motors are less noisy than Switched Reluctance (SR) motors, and many methods have been published to reduce the noise of SR drives. This paper provides a systematic experimental comparison of both drives, and of proposed noise- mitigation strategies, in the context of a specific mass-market application: Automotive Electro Mechanical Brakes (EMB). The two motors were designed to fit into the same envelope and to produce similar dynamic performance for the brake system. Sound pressure levels produced by the two motors at key torque-speed points were measured through dynamometer tests under identical conditions. The influence of the hysteresis current and PWM control methods on the acoustic noise was also studied. The acoustic noise was then measured with the EMB systems assembled with the PM and SR motors. Though the measured acoustic noise of the SR motor with dynamometer tests was higher compared to that of the PM motor, the acoustic noise levels of the two EMB systems were found to be similar with only a slight advantage to the PM based system.