GB883923A - Improvements in control systems for d.c. motors - Google Patents

Abstract

883,923. Automatic speed-control systems. GENERAL ELECTRIC CO. Sept. 18, 1959 [Sept. 22, 1958], No. 31856/59. Class 38 (4). [Also in Group XXXVII] A D.C. motor is supplied from A.C. terminals 6, 14 through a half-wave rectifier 13 and saturable reactor 11 a portion of whose winding 9 is connected across the armature of the motor through rheostat 17. During a negative half-cycle of the applied A.C. when the rectifier 13 blocks the flow of current, the back-electromotive force of the motor develops a magnetomotive force in the core of the reactor which is opposite to that produced by the load current. As a result, the period during which current is delivered to the armature during the subsequent half-cycle of the applied voltage varies inversely with the speed of the motor. In another arrangement, the reactor has a separate control winding connected across the armature of the motor, and the motor field winding is connected across the A.C. terminals in series with a rectifier which is poled to conduct on negative half-cycles. A shunt rectifier permits the flow of current through the field winding during positive halfcycles of the applied voltage, Fig. 2 (not shown). The rectifier in series with the field winding may also be, included in circuit with the control winding of the reactor for limiting the currentflow therethrough during the negative halfcycles and for stopping the current flow during the positive half-cycles. This enables the motor to be operated in the low speed-ranges. The field winding of the motor may be shunted by a tapped resistor from which is derived a voltage which is added to the back-electromotive force of the motor for application to the control winding of the reactor, Figs. 3, 4 (not shown). The reactor may be provided with a reference winding in opposition to the control winding energized in accordance with the armature voltage, and in series with a diode which conducts during negative half-cycles of the applied voltage. A transistor in series with the control winding of the reactor may be controlled in accordance with the armature voltage which is applied between the base and emitter electrodes, Figs. 5, 6 (not shown).