| 摘要 |
An electrical machine comprises a rotor without windings, a stator having an armature winding 24, 25 and a field winding 10 for generating a magnetomotive force in a direction extending transversely of the magnetomotive force generated by the armature winding. An electronic circuit 40 is provided for controlling the current in the armature winding 24, 25 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. A position sensor is provided for monitoring the rotational position of the rotor and for supplying output signals dependent on the speed of rotation of the rotor. Furthermore a control system 32 supplies control signals to the circuit 40 to control the current in the armature winding 24, 25. In order to enhance the performance at high speed, the control signals are produced in response to sensor output signals which provide an advanced indication of the rotational position of the rotor. Furthermore, in order to prevent oscillation of the rotor on start-up, the control signals supplied to the circuit 40 during an initial start-up period are each produced after a time delay as compared with the production of the control signals over subsequent cycles of rotation during acceleration of the rotor. This can be achieved with simple on/off control of armature and field switching devices, so that the control circuitry can be produced at relatively low cost. |
