| 摘要 |
<p>606,820. Automatic control systems for electric motors ; rectifying. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Jan. 10, 1946, No. 939. Convention date, Jan. 10, 1945. [Classes 38 (ii) and 38 (iv)] [Also in Group XXXVII] A control system for a direct-current motor having armature and field circuits energized through rectifier means from an alternating- current source and having an adjustable control circuit for varying the voltage of the rectified current to maintain said motor at a . selected speed, is provided with means for effecting dynamic braking of the motor when the rectifier means are temporarily inoperative, due to rapid adjustment of the control circuit toward a lower value of selected speed. The armature of a direct-current motor M is connected to the secondary winding 6 of a transformer T through two grid-controlled rectifying valves 30 and 31 which may be thyratrons, the motor field winding being constantly excited. An alternating voltage component is applied to the grid circuits of these valves through a transformer 45, the primary winding of which is connected to a phase-shift circuit supplied from a secondary winding of the transformer T. A direct grid voltage component for the valves 30 and 31 is afforded by a circuit comprising a high-vacuum valve 52. The grid circuit of this valve comprises an adjustable negative reference component, a positive component varying with the motor armature voltage, and a negative component proportional to armature current, these components being respectively derived from resistors 60, 68, and 29. The anode current of the valve 52, and the output of the main rectifying valve, are therefore controlled in accordance with motor speed which is kept constant at a value corresponding to the setting of the potentiometer 60. In order quickly to restore the control of the motor when the potentiometer 60 is rapidly adjusted to a lower speed position, thereby discontinuing the operation of the rectifying valves until the motors decelerate to a speed corresponding to the new adjustment, a relay 24 is provided the coil of which is connected in series with the motor armature. The relay 24 drops out at zero current to close a contact 23 and energize a. relay 21 to place a resistor 19 across the motor armature, thereby affording rapid deceleration. This dynamic braking action is also effective when the motor is stopped.</p> |
