Abstract: A pulse control circuit for a d.c. series motor having an armature and two oppositely-wound field windings, comprises a contactor in series with the motor, two main thyristors each connected in series with the armature and a respective one of the field windings, means for controlling the mark-to-space ratio of conduction of each thyristor, one or other of the main thyristors being brought into operation in dependence upon the desired direction of drive of the armature, means for sensing failure of commutation of the main thyristor, and means for causing opening of the contactor in response to such sensing. The control circuit includes means for firing the other main thyristor immediately commutation failure is sensed, thereby to limit the net field flux and motor torque in the period during which the contactor is opening.

Abstract: A pulse control circuit for a d.c. series motor having an armature and two oppositely-wound field windings, comprises two semiconductor static switching devices, such as thyristors, each connected in series with the armature and a respective one of the field windings, control means for varying the mark-to-space ratio of conduction of each switching device thereby to vary the mean voltage applied to the motor, one or other of the switching devices being brought into operation to energize the associated field winding in dependence on the desired direction of drive of the armature. The control means is adapted, when the mark-to-space ratio of one of the static switching devices has been brought to a predetermined maximum value, to cause simultaneous operation of the other static switching device at a lower mark-to-space ratio thereby to energize the associated field winding so as to reduce the net flux in the motor and further increase the motor speed.

Abstract: A pulse control circuit for a three-terminal d.c. series motor having an armature and two oppositely-wound field windings comprises a respective main thyristor in series with each field winding, one or other of the main thyristors being operated at a variable mark-to-space ratio to energize the field winding appropriate to drive the motor in a selected direction. The circuit includes switch means operable to connect the motor in a regenerative braking mode in which the armature and each field winding are connected to the battery in series with a freewheel diode and with a diode across the motor so that charging current can flow from the motor to the battery during regenerative braking. Circuit means are provided to effect initial energization of at least one field winding when the circuit is first switched to the regenerative braking mode.