Control of torque fluctuations in a PM disc motor

Direct wheel drives in electric vehicles are advantageous because the gearbox, mechanical transmission and differential can be eliminated. Two opportunities then arise: (i) mount the drive motor in the road wheel of the vehicle; or (ii) mount the drive motor inboard on the vehicle chassis. The major drawback associated with (i) is the resultant increase in the unsprung mass of the vehicle, whilst the second option introduces a degree of complexity in the mechanical coupling to the road wheel. However the difficulties associated with (i) can be overcome by using a double-sided axial field machine with a central rotor. The stators of the machine can be attached to the chassis of the car whilst the rotor directly drives the road wheel. Perturbation of the rotor while the vehicle is moving will however cause torque fluctuations in the machine. This paper shows that these torque pulsations can be eliminated by the modulation of the input motor current using a signal obtained from the identification of the flux.