GB684881A - Improvements in or relating to electric motor control systems - Google Patents

Abstract

684,881. Control of two D.C. motors. IGRANIC ELECTRIC CO.. Ltd. Sept. 15, 1950 [Sept. 15, 1949], No. 22731/50. Class 38 (iii) [Also in Group XXXV] A length of material such as a strip of steel passes through mill work rolls 11,12, and is coiled on a reel 13. The rolls 11, 12, are driven by a directcurrent motor 14 which is supplied by generator 17. The wind-up reel is driven by a direct-current motor 19 having a field winding 19a and being supplied from generator 21. An exciter 23 acts as a current regulator for the motor 19 and its output is adapted to vary the excitation of winding 19a by opposing the excitation derived from source 15. A rectifier 24 limits the bucking- action of the exciter 23 which has a reference field winding 27 and an opposing signal field winding 29 which is energised in accordance with the armature current of the motor 19. When the strip is advancing at a steady speed, therefore, the motor 19 is regulated by the exciter 23 to provide constant horsepower output and the strip-tension is kept at a steady value. In order to modify the output of the exciter 23 so as to maintain constant strip-tension during changes of speed of the motor 14, an additional exciter field winding 31 is provided and is energised by machine 32 having field winding 35 connected to the output terminals of an electronic amplifier 45. A direct-current tachometer generator 42 is coupled to the motor 14 and its output is applied through transformer 43 to the input terminals of the electronic amplifier which has thus supplied to it a voltage varying with the rate-of-change of speed of the motor 14. As shown in Fig. 2, the field winding 35 has a centre tapping and is supplied through valves 50, 51, and 52, 53, constituting two full-wave rectifiers. A circuit comprising a saturable reactor 64, transformer winding 56c, transformer 66, and adjustable resistor 65 operates as an adjustable phase-shift network for controlling valves 50, 51, and the other pair of valves are similarly controlled through a network comprising the circuit elements 82, 74c, 84, and 83. The phase-shift networks respectively associated with each set of rectifiers are adjustable by varying the saturation of the reactors 64, 82. The saturating windings of the reactors are connected in a bridge circuit comprising the secondary winding 43b of transformer 43, and a direct reference voltage is injected into the bridge circuit through rectifier 96. When there is no voltage induced in winding 43b the winding 35 is de-energised. During acceleration or deceleration of the motor 14 the winding 43b becomes energised and the balance of the bridge circuit comprising the saturating windings to upset so that one or the other pair of rectifiers 50, 51, or 52, 53, is rendered effective to energise the winding 35 in such a manner that the motor 19 changes its speed to correspond with the speed-change of the other motor. The field winding 35 may be replaced by one not having a centre tap, in which case it is shunted by a pair of ballast resistors having a common junctionpoint, Fig. 5 (not shown).