Sevcon Limited

Technical Operations, Incorporated

Caterpillar Tractor Co.

Sevcon Engineering Limited

Albert E Sloan

David Gurwicz

Arthur Wild

Barry Moss

William R Ord

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.

Fail-safe system for pulse-controlled three-terminal d.c. motor

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.

Field weakening system for pulse-controlled three-terminal d.c. motor

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.

Regenerative braking system for three-terminal d.c. motor

A control circuit for controlling the current supplied from a d.c. source such as a battery to the actuating coil of an electromagnetically operated contactor, comprising switching means such as a transistor operable repetitively to connect the coil to and disconnect the coil from the source, and control circuit means for varying the mark-to-space ratio of the switching thereby to vary the mean voltage applied to the coil. The mean voltage can be controlled so that the mean current through the coil when the contactor is closed remains substantially constant irrespective of the voltage of the battery, so that the same contactor and control circuit can be used with a number of batteries of different voltages.

Control circuit for electromagnetically operated contactor

A thyristor pulse control circuit has a main thyristor, a commutation circuit including a commutating capacitor, and a bypass contactor connected across the main thyristor, and is provided with apparatus for applying a gating signal to the main thyristor immediately before the contacts of the bypass contactor close and also immediately before the contacts of the bypass contactor close to prevent arcing at the contacts. The application of the gating signal is inhibited if a comparison of the voltage across the commutating capacitor with the load current flowing immediately before the bypass contactor closes indicates that the load current is too great to be safely commutated by the commutating capacitor at the measured voltage.

Thyristor pulse control circuits

A pulse controller for controlling the current supply to a plurality of d.c. loads through a respective main thyristor for each load is provided with digital circuitry operable to maintain the mark-space ratios of voltage applied to the loads in a relationship to one another which is set by a differential control circuit while the mark-space ratios are simultaneously varied in response to a drive control circuit. The controller may be used to control two d.c. motors respectively driving right-hand and left-hand traction wheels of a battery-electric vehicle, to provide differential drive when the vehicle negotiates a curve.

Thyristor pulse controller for plural loads

A pulse controller for a reversible d.c. series motor is provided, in place of the conventional freewheel diode across the armature and field and plugging diode across the armature, with a unidirectional current path connected across the armature and field and containing sufficient impedance to prevent build-up of motor current in interpulse periods when the motor is in a plugging mode, and switch means for shorting out the impedance during normal motoring.

Pulse controllers

A thyristor pulse controller in which current supply to each of a plurality of d.c. loads is controlled by respective main thyristors and a single commutating capacitor common to all the main thyristors is provided, the capacitor being connected across the main thyristors to commutate them one at a time at intervals not less than the time required to forward charge the commutating capacitor from the d.c. source and to reverse the charge on the capacitor.

A thyristor pulse controller having an electromagnetically actuated shorting contactor comprising an actuating coil and an armature which moves on energization of the actuating coil to close the contactor tips and which moves on de-energization of the coil to open the contactor tips and to create an air-gap in the magnetic circuit of the coil, is provided with an interlock circuit comprising a voltage sensing circuit connected in parallel with the contactor actuating coil, the voltage sensing circuit being adapted to provide an output signal when the modulus of the voltage across the actuating coil exceeds a predetermined value which is lower than the modulus of the voltage across the coil at the instant when the contactor tips open. A unidirectional current path, which may be provided by the interlock circuit itself, is connected across the actuating coil to discipate inductive energy in the coil when the contactor opens.

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Gateshead, United Kingdom

Albert E Sloan