Patent ID: 6646406
Filing Date: 2003-11-11
Classification: H02P

Abstract:
An electrical machine comprising a rotor without windings, a stator having an armature winding and field magnet means for generating a magnetomotive force in a direction extending transversely of the magnetomotive force generated by the armature winding, circuit means for controlling the current in the armature winding such that periods in which a magnetomotive force in one direction is associated with a first current pulse alternate with periods in which a magnetomotive force in the opposite direction is associated with a second current pulse, and position sensing means for monitoring the rotational position of the rotor and for supplying output signals at a rate dependent on the speed of rotation of the rotor, characterised by control means for supplying control signals to the circuit means to control the current in the armature winding in response to said output signals, the control means being arranged to produce a control signal of extended duration at the beginning of the first current pulse on start-up of the rotor from rest as compared with the duration of the control signals produced over the remainder of the first current pulse.