Cancellation of harmonic torque disturbance in permanent magnet synchronous motor drives by using an adaptive feedforward controller

The effects of disruptive harmonic torque disturbances on permanent magnet synchronous motor drives originating at the mechanical load or from cogging can be mitigated by producing a counteracting electric torque. The study proposes using an adaptive feedforward controller (AFC) for this purpose. The AFC is designed to operate as an auxiliary loop in parallel with a field-oriented controller, which provides speed control. The AFC input is the motor speed control error. The loop is tuned at the frequency of the harmonic torque and its output is added to the q -axis current reference as a variation current of the same frequency. The main advantage of the proposed method is that it does not require an estimation of the disturbance torque. The theoretical analysis of the scheme is presented in the study. Experimental results are also presented in the study from a motor drive system where the mechanical load produces harmonic torques. The results demonstrate the effectiveness of the AFC in significantly reducing speed oscillations by cancelling the effect of the torque harmonic disturbance.