GB859038A - A.c. to d.c. power supply variable as to polarity and magnitude - Google Patents

Abstract

859,038. Control of D.C. motors. BENDIX CORPORATION, [formerly BENDIX AVIATION CORPORATION]. March 23, 1959 [April 14, 1958], No. 9999/59. Class 38 (3). [Also in Group XXXIX] A reversible D.C. motor RM is energized from an A.C. supply 9 through a magnetic amplifier comprising two saturable cores 3, 4 each provided with a power output winding 3g, 4g, a reset winding 3r, 4r and a D.C. control winding 3c, 4c, the power output windings being connected in separate parallel paths which include respective rectifiers 5, 6 and voltage bias means 7, 8. Each rectifier is connected so that its conductive direction is opposed to the associated voltage bias means, and the respective conductive directions in the two paths are related to opposite half-cycles of the A.C. supply. In the absence of a control signal from a source 10, both power output windings are equally conductive and a symmetrical alternating current is applied without effect to the motor. As both reset windings 3r, 4r are connected to the A.C. source, an alternating reset current is established which resets the flux of the saturable core not operative in a given half-cycle and assists the change of flux to saturation in the saturable core operative at that time. When a control signal is applied to the control windings, however, one core is saturated earlier in a respective half-cycle than the other core, and an asymmetric alternating-current output is applied to the motor, the D.C. component of which determines the direction of rotation, according to the control signal polarity. The voltage bias means 7 and 8 are provided to neutralize the effect of the back E.M.F. developed across the motor, since this voltage would otherwise tend to maintain one rectifier conductive during the inoperative half-cycle of its respective parallel path and so adversely effect the flux resetting action. The voltage bias means may be either batteries, Fig. 2 (not shown), or Zener diodes, Fig. 3 (not shown). A modification is described, Fig. 4, in which a further saturable reactor 20 has its power output winding 20a connected between the magnetic amplifier and the motor, and has a control winding 20b connected across the motor terminals. In the absence of a control signal at the magnetic amplifier, the winding 20a presents a high impedance which limits the output of symmetrical alternating current. If, on the other hand, the motor is driven by an asymmetric current, the back E.M.F. across the motor acts through winding 206 and saturates the reactor.