Variable structure control of a disc motor with lateral rotor movement

This paper investigates the effect of lateral movement of the rotor of an axial field permanent magnet disc motor when the drive shaft is perturbed by the load. This movement results in significant torque pulsations. It is shown that the torque pulsations can be eliminated using a variable structure control strategy. To implement a variable structure control, instantaneous torque feedback is necessary, this signal is obtained from a state space observer. The speed range of the machine is increased by flux weakening. This is implemented using a lookup table. One of the many possible applications of a disc motor with lateral movement is in an electric vehicle where the shaft directly drives the road wheel whilst the stators are connected to the chassis of the vehicle. This will result in vertical rotor movement while the vehicle is moving. Similarly this type of drive could be used to drive an electric motorbike, or could be used in any application where the rotor is moving out of alignment.