GB1097212A - Current control systems including controllable semiconductor rectifiers - Google Patents

Abstract

1,097,212. Automatic voltage control. SIEMENS-SCHUCKERTWERKE A. G. March 2, 1965, No. 8958/65. Heading G3R. The field circuit of a generator 17 is controlled in dependence upon output voltage variations by a thyristor 5 in series with the field winding 6. The trigger circuit for the thyristor includes transistors 8, 9 and a capacitor 7 which charges up over a resistor 10 when the generator is started up. When the potential on the capacitor reaches a certain value thyristor 5 is triggered on by way of transistors 8 and 9; capacitor 15 then charges up to switch off transistors 8 and 9, but the thyristor 5 remains conductive until the next zero current point in the voltage supply to the field winding. If the output voltage exceeds a desired value, a transistor 11 is rendered conductive by a sensing circuit constituted by a voltage divider 2, 3 and a reference Zener diode 12, whereby the capacitor 7 discharges through the transistor 11. The time taken for the capacitor 7 to recharge through resistor 10 is thus varied by the action of transistor 11, so that the instant in the halfcycle at which thyristor 5 is triggered varies in a manner to keep the average excitation current at a value sufficient to maintain a constant output voltage. The control system may also be applied to rectifiers and inverters.