GB643771A - Improvements in or relating to control systems for direct current electric motors - Google Patents

Abstract

643,771. Automatic speed control systems. GENERAL ELECTRIC CO., Ltd., and DALE, S. H. Feb. 11, 1948, No. 4044. [Class 38 (iv)] [Also in Group XXXVII] A speed control circuit for a D.C. motor supplied by grid controlled rectifiers, includes a non-linear thermionic amplifier which compensates for the non-linearity of the speed/loadcurrent characteristic of the motor. Transformer 8 and rectifiers 3 and 4, connected for full-wave rectification, supply a shunt or separately excited D.C. motor 1. The D.C. voltage is, controlled by the rectifier grids being connected to a phase shifting network 15 which includes a saturable reactor 16 controlled by a triode 17 directly coupled to a second triode 26. The grid-cathode voltage of this valve is the resultant of the rectifier output voltage, an adjustable reference voltage tapped off a battery 23, and a voltage appearing across resistor 21. This voltage increases non-linearly with increase in motor load current since a voltage proportional to motor current is obtained either from current transformer connected in the anode circuits of the rectifiers, or from a device 30 which comprises a pair of saturable reactors controlling an A.C. supply according to the D.C. load current, and applied in opposition to a reference source 29 to the control grid of a, variable-mu tetrode 28 which is operated over a suitably curved portion of the Ia/Vg characteristic. Thus the rectifier output rises with increase in load current and compensates for the non-linear drooping speed/ load-current characteristic of the motor. Specification 663,772 is referred to.