GB1025871A - Improvements relating to the control of electric motors - Google Patents

Abstract

1,025,871. Automatic current control. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd. May 2 1963 [May 23, 1962], No. 19834/62. Heading G3R. [Also in Division H2] In an electric motor control arrangement having a switching circuit, the mean motor current and therefore the torque is held close to a set value despite variations in the motor speed/time characteristic, while the instantaneous line current is prevented from exceeding a set value within the rating of the switching circuit. As shown, a D.C. motor M is connected in parallel with a diode rectifier D and is supplied from a source E via a switching arrangement S which comprises a commutating capacitor 5, a main controlled semi-conductor rectifier 1, an inductance <, a diode rectifier MR and an auxiliary controlled semi-conductor rectifier 6. The instantaneous motor current is sensed by a device 2, e.g. a transductor, chopper amplifier or Hall effect device, the output from which is applied to a comparator 7 which also receives a reference signal from a device 3; the difference signal from the comparator 7 controls a pulse generator 4 having outputs 8 and 9 which are applied respectively to the gates of controlled rectifiers 1 and 6. The arrangement is such that when the controlled rectifier 1 is fired, the supply voltage appears across the diode D and the motor M; when the instantaneous load current reaches a first set level a pulse appears at output 9 of pulse generator 4 and fires the controlled rectifier 6 thus allowing the previously charged capacitor 5 to extinguish the controlled rectifier 1. When the current falls to a second lower level, another pulse appears at output 8 to refire the controlled rectifier 1 to cause the current to build up again. The mean motor current is thus controlled close to a set value determined by the reference device 3; as applied to a battery driven propulsion system for a vehicle, the upper current level may be varied under the control of a foot pedal. The sensing device 2 may be connected to sense the current from the source E rather than the motor current, and the control means for the switch arrangement may comprise a semi-conductor switch device which can be turned ON and OFF by the application of appropriate signals to one or more control electrodes.