Patent GB-629390-A (GB)
Title: Improvements in and relating to electric motor control systems
IPC: H02P5/74
Filed: 1947-08-01
Abstract: 629,390. Multi-current machines. ELECTROLUX CORPORATION. Aug. 1, 1947, Nos. 21117 and 21118. Convention dates, Jan. 24, 1942, and Jan. 15, 1943. [Class 35] [Also in Group XXXVII] A control system for simultaneous operation of a plurality of electric motors includes connection means arranged and operable to supply operating current to at least the stator structures of all of said motors simultaneously to cause rotation of the rotor structures thereof, and connection means arranged and operable when the supply of operating current causing rotation of said rotors is cut off, either before starting or to effect stoppage of the motors, to directly supply an external current to the rotor windings in order to move the rotor into a predetermined position relative to the poles of the fixed stator field and hence relative to the stator. A plurality of direct-current motors 10 have their field windings 16 and 18 supplied in series from a source 20. The armature of the motors comprise windings 22 connected by taps to commutators 26 associated with brushes 28 and 30, the pairs of brushes of the several motors being connected in parallel. Each armature has slip-rings 56, 58, and 60, connected therewith. Associated with the slip-rings are interconnected brushes 68, 70, and 72. The motors may be aligned before starting by exciting the field windings and moving a switch 36 to the left-hand position to pass current through the armatures by taps 66 and brushes 28. The magnetic field so produced in each armature interacts with the main field due to the coils 16 and 18 and the armature is rotated until a balanced condition is obtained wherein it is magnetically locked in a set position. Similar operation obtains in all the motors so that the shafts are brought into angular alignment. The motors are started by moving the switch 36 to the right to energize the brushes 28 and 30, synchronism being maintained due to the interchange of three-phase alternating-currents between the several armatures through the connections 74, 76, and 78. If the switch 36 is again moved to the left-hand position energizing potential is removed from the brushes 28 and 30 and the motors decelerate. Direct-current is applied to the armatures through taps 66 and brushes 28, and the magnetic field in the rotating armatures caused thereby induces alternating-currents in the main field windings which are fed back to the source 20, thereby providing dynamic braking. Alternating- currents are also produced in the armatures due to rotation in the main field. These currents are fed back to the machine supplying the armatures. When stopping, the armatures are aligned in a manner similar to that described initially. The motors are held in synchronism during deceleration due to the alternating- currents induced in the inter-connected main field windings, as referred to above. In Fig. 2 (not shown) the means for aligning the armatures prior to or following operation of the motors is independent of the connections to the brushes 28, a double-pole, double-throw switch being provided alternatively to energize said alignment means or to energize the motors for running. A resistor 82 which prevents possible short-circuiting is not required in this arrangement. The field coils of each motor may be connected in series or parallel with one another, and the field windings of the several motors may be likewise connected. Fig. 4 (not shown) illustrates a system comprising press-buttons and time-delay relays for automatically effecting the connections for aligning and synchronizing the motors. In Fig. 5 (not shown) the application to the control of a number of threephase synchronous motors is illustrated. The stator windings are excited with direct-current, and the rotor windings are supplied with alternating-current for running and, in a like manner to that described, with direct-current for aligning the rotors. In Fig. 6 each motor is provided with a main armature winding 303, an auxiliary winding 304, and a field winding 305. The commutator (not shown) is associated with brushes 306 and 307<1> which are connected in parallel with those of other motors through a switch 319 to a direct-current source 314. The armature windings are tapped through sliprings and a switch 313 to the supply. Reversing switches 320 and 321, a short-circuiting switch 323, and a main switch 322 are provided. Closure of the main switch and the switch 313 supplies current to the armatures through taps 307 and 308. The auxiliary windings produce fluxes the axes of which are coincident with those of the main windings: The resultant armature fields are aligned with the main fields due to coils 305. The switch 313 is opened and switch 319 is closed for starting the motor. The interconnection of taps 307 and 308 provide for the interchange of synchronizing currents between the armatures during running. Increased dynamic braking is provided by short-circuiting the brushes 306 and 307<1> by switch 323. Switches 320 and 321 enable one motor to be driven reversely with regard to the other. Figs. 7, 8, and 9 (not shown) illustrate other methods of connecting the main and auxiliary armature windings. The Specification as open to inspection under Sect. 91 comprises also a reference to the control of a single induction motor both the stator and rotor windings of which are supplied with direct-current for alignment purposes. This subject-matter does not appear in the Specification as accepted.