GB1158783A - Electric Motor Control System - Google Patents

Abstract

1,158,783. Automatic control for compressors. ENGLISH ELECTRIC CO. Ltd. Sept. 5, 1966 [June 4, 1965], No.23879/65. Heading G3R. A gas compressor 5, whose load torque varies considerably during each revolution of its shaft, is driven by a D.C. motor 6 which is energized through mercury arc converter 8. A fast-acting controller 9 for the converter compares a reference signal on line 10 with a signal representing the motor current whereby the difference between the two signals is reduced towards zero. The desired mean speed of the compressor is set by a reference signal, on line 22, which is compared in controller 20 with a signal from tachometer generator 15, the difference-signal being averaged over a period by delay unit 24 to adjust the mean level of the current reference signal on line 10 to a new value whereby the signal on line 25 is reduced towards zero. Cyclical variations in the tachometer signal are detected by differentiating unit 17 for passing signals to the reference unit 19 further to modify the reference signal on line 10 which is inverted with regard to the signal on line 18. The armature current thus varies substantially in correspondence with the cyclic variations in torque, enabling the inertia of the compressor and motor to be reduced without excessive speed variation, or to maintain the inertia at the same value whilst reducing the speed variation. The differentiating unit 17 may be omitted, the reference unit 19 being controlled only by the signal on line 25.