Cancellation of selected stator harmonics in BLDC by using an adaptive feedforward controller

This paper proposes an adaptive feedforward controller (AFC) for the cancellation of selected low order harmonics from the stator currents of a brushless DC motor (BLDC) with a non-sinusoidal flux distribution. Under proper tuning, the AFC can track selected harmonic orders of the motor back-EMF and counter-modulate the stator voltage to cancel the induced harmonic currents. The proposed AFC is combined with a field-oriented controller (FOC), which regulates the motor speed, in order to provide supplemental modulation action to the stator voltages at the selected harmonic frequencies. Experimental results are presented in the paper, where the AFC was designed to cancel the 5th and 7th harmonics. The results obtained verify the operation of the proposed controller and demonstrate its effectiveness in achieving significant improvement in the stator current waveform.