Patent GB-190701457-A (GB)
Title: Improvements in or relating to the Control of Induction Motors.
Inventor: MILCH MAURICE
Filed: 1907-01-19
Granted: 1908-01-18
Abstract: 1457. Milch, M. Jan. 19. Motors, controlling.-The speed of induction motors is regulated by supplying the rotor with a regulatable current of the same phase and frequency as the currents generated in the rotor itself, the applied current being obtained through the intermediary of a frequency converter, driven by the main current and supplying current for exciting a separately-driven commutator dynamo which produces the current synchronous with the rotor current. This subsidiary current may be obtained from a commutator dynamo, the fields or brushes of which are driven at a speed proportional to the slip of the motor. The transmission lines 1, 2 supply current to the motor to be regulated 12 and, through transformers 19, to a frequency converter 4, which is synchronously coupled to the rotor 13 of the controlled motor. The brushes supply a regulatable exciting-current to the field 22 of a generator which is driven independently, as by an independent motor or by a car axle. Current from the brushes 25 is supplied through switches and resistances to the rotor of the motor 12, such current being of the same phase and frequency as that generated in the rotor itself. An alternative method of producing the regulating-currents consists in the employment of a direct-current dynamo, the brushes or field magnets of which may be revolved. In the arrangement shown in Fig. 2, the armature 17 of such a machine is driven by a synchronous motor 7 and, by means of a differential gear 9, 20. 21, one element 21 of which is driven from the shaft 5 of the motor to be regulated, the field magnets 18 are caused to rotate at a speed proportional to the slip of the regulated motor. The phase of the current generated by the armature 17 may be regulated by shifting the brushes 17', and the value of the current by altering the fields, The above methods are particularly applicable to induction motors which are used in conjunction with fly-wheels to equalize a load. The method may be combined with methods of speed control by concatenation, or by altering the number of the poles. The windings of the apparatus used for producing the required regulating currents in this case are disconnected from the primary source of supply, and are switched on to a source of such variable frequency that the speed of the abovementioned windings corresponding to the new frequency of supply bears the same relation to the synchronous speed of the reconnected induction motor. or group of concatenated motors, as was the case before changing the connexions. Such a source of variable frequency is found in the indued member 28, Fig. 3, of an induction motor of the proper number of poles connected to the mains and synchronously coupled to the regulated motor. When changing the number of poles or concatenating, the taps 29 from the mains to the synchronous motor are broken and the synchronous motor is connected to three points on the rotor of the auxiliary motor. In the case of concatenated control, taps may be taken from the rotor of the last leading motor of the chain. The induced members of the chain of controlled motors may be connected in series, or the delta connected induced members may be connected in star and in series with each other, as shown in Fig. 5, in which a chain of two motors A, 13 has the phases 1, 2, 3 of the two armatures connected in series through switches, and one end of each of the phases 1, 2, 3 connected to a tapping of the closed compensating winding 23 of the generator.