Sensorless torque control of a PM motor using modified HF injection method for audible noise reduction

A random high frequency (HF) injection sensorless vector control is proposed for a low voltage high current permanent magnet (PM) motor. By spreading the frequency of the injected components in a random manor, audible frequencies due to the injection can also be spread over a wide range of frequencies, reducing the perception of the audible noise whilst achieving comparable position estimation to a fixed frequency injection method. Measurements of sound level using a commercial sound meter have been compared for both fixed and random HF injection methods to demonstrate the change in audible noise.