| 摘要 |
719,652. Control of A.C. and D.C. motors. GENERAL ELECTRIC CO., Ltd., and FRIEDLANDER, E. S. April 9, 1953 [April 9. 1952], No. 9093/52. Class 38(3) [Also in Group XXXV] A traction system comprises an alternating- current motor 15, which may be of the synchronous type, mechanically coupled to a direct-current generator 16 arranged to supply a direct-current motor 20 which, in turn drives a frequency converter 21. Traction motors 25 are supplied from the frequency converter and the torque of these motors is controlled by regulating the magnitude of the current fed to the machine 20 from the machine 16. The machine 15 also acts as a phase converter since it is energized from a single-phase source and provides the machine 21 with threephase current. A shunt field winding 57 of the generator 16 is connected to a boosting or bucking exciter 50 which has a field winding 52 carrying the armature current of the machine 20. A control field winding 56 of the exciter 50 opposes the winding 52 and is energized from a constant voltage source through a double reversing potentiometer 30, 31, and a permanent magnet generator 62 which is driven by a synchronous motor 63 fed from the output slip-rings of the frequency converter 21 so that the excitation of the generator 16 is modified in dependence upon the frequency of the current fed to the traction motors. Thus, when the output frequency of the machine 21 is low the excitation of the direct-current generator is arranged to be greater than when the output frequency is higher and this provides desirable control characteristics. In an alternative arrangement the machine 62 is driven by the traction motors. In a modified system (Fig. 2), the excitation of the generator 16 is controled in dependence upon the degree of slip in the motors 25. An auxiliary frequency converter machine 70 is mechanically coupled to the shaft of one of the traction motors and has its stator windings fed from the supply to the traction motors. The frequency of the output of the machine 70 is thus dependent upon the slip, and this output is applied to a hysteresis motor 71 normally acting as a synchronous motor to drive a direct-current tachometer generator 72. The field winding 52 of the exciter 50 is supplied from the generator 72 so as to tend to reduce the excitation of the generator 16 when the slip is too great. In order to prevent excessive speed of the tachometer generator 72 during starting or other transient conditions a centrifugal brake 74 is provided, the motor 71 stopping with a constant but limited torque when over-loaded. |
