Online identification and compensation of torque disturbances in permanent magnet AC motors

Permanent magnet AC motors generate parasitic torque pulsations, owing to several electromagnetic phenomena, such as imperfections in the motor and in the associated power inverter. Excitation of the mechanical resonances on the load side is generally the worst consequence of such disturbances: speed oscillations arise which may dramatically limit the performances in high precision applications. A compact model of the pulsating torque in sinusoidal permanent magnet motors is discussed in this paper. Static experimental validation and online identification algorithms are presented as well. A compensation, applied as a modification of the output of the position controller, is finally proposed. Experiments carried out on a laboratory equipment demonstrate the effectiveness of the control scheme in suppressing oscillations