Noise reduction for brushless DC motor-sensorless control analysis and back-EMF shape modification

Brushless DC motors are normally built with PM mounted on the rotor, which create the necessary back EMF voltage to produce mechanical power. The shape of this back-EMF voltage is very important in determining the phase voltage supply shape. The new generation of electronic drives uses sinusoidal shape current in order to suppress the harmonic. This paper describes a comparison made on a motor for pump application, with a sine wave back-EMF, and driven with a 120, 125 degree or sine wave control mode. The results show the differences between these modes, when using a sensorless technique to avoid the sensors. In order to complete the analysis, another possibility to decrease the noise is to modify the back-EMF shape. This reduces all the torque harmonics. A method is proposed with only one parameter modification. This method can be applied to a large range of applications.