Improvements in and relating to stageless speed regulation of motors with the aid ofelectric frequency changers

摘要

645,182. Automatic speed-control systems. AKT.-GES. BROWN, BOVERI, & CIE. March 6, 1946, No. 7023. Convention date, March 6, 1945. [Class 38 (iv)] The speed of an electric motor a driving a pump, machine-tool, rolling-mill, &c. is maintained constant over an extensive range of speeds by a frequency changer f supplied with two independent control frequencies, one of which is determined by the angular velocity of the motor while the other, derived from a small generator k or other source, is kept constant, and the sum of the two frequencies derived from the frequency changer f is supplied as a con. trolling frequency to a regulator g associated with an adjustable oscillatory circuit whereby a rolling-sector type regulating resistance x is adjusted to counteract any deviation of the speed of motor a from its required value. The example shows a D.C. motor a connected in a Ward-Leonard system, with its shaft coupled to the rotor of a frequency changer f comprising an asynchronous generator with a 3-phase stator winding energized at a constant frequency, and rotor slip-rings connected to the exciting coils y, z of a Ferraris motor controlling the field rheostat iSP1/SP of the D.C. generator c. The coils z are variably inductive and coils y are capacitative, providing an oscillatory circuit which, at resonance frequency, produces no response in the regulator. The angular velocity N0 of the motor a is then equal to N2 - N1, where N1 is the constant frequency applied to the stator of the frequency changer f by a small synchronous generator k driven by a D.C. motor m. The value of N1 is adjustable by varying the speed of motor m by a field circuit rheostat controlled by a regulator p similar to the regulator g. Alternatively, a less accurate control may be obtained by energizing the stator of the frequency changer directly over lines s connected to the 3-phase supply e for the motor d driving the D.C. generator c. Variation of the speed of the motor a may be effected by adjustment of the choke q. The controlled resonance circuit of the regulator g may comprise grid-controlled discharge tubes, and may be single-phase operated. The Specification as open to inspection under Sect. 91 refers to the use of a stationary frequency changer such as an electronic mixing tube, or modulators, in place of the rotary frequency changer f, and also describes a modification, Fig. 1 (Cancelled), showing the control system applied to the field of a motor which has its armature connected to D.C. supply lines and drives the rotor of a frequency changer, the stator of which is connected to both a synchronous generator and an adjustable oscillatory circuit controlling a Feraris motor for regulating the field rheostat of a D.C. motor driving the synchronous generator. This subject-matter does not appear in the Specification as accepted.