Converter-fed motor control circuit - uses switching thyristor with two trigger stages for rapid changeover between driving and braking

摘要

The converter has two antiparallel sections connected between a three phase supply and two smoothing chokes with a capacitor between them. It is followed by a switching thyristor in series with an ohmic resistance and in parallel with the capacitor. The thyristor is connected to a pulse emitter, and forms, with the resistance, the input to the conveter section which supplies a number of variable frequency and variable voltage motors. The control system changes the motors from a driving condition to a braking condition, acting as generators. The series resistance and capacitor operate changing from braking to driving occurs only when the voltage in the intermediate rectifying circuit exceeds a given value. The control signal includes two trigger stages. The trigger stage with the smaller reaction amplitude controls the changeover system for the two converter sections and the other controls the switching thyristor.