A novel pulse firing scheme for constant angle triggering of 3-phi thyristor converters

The details of a novel and simple triggering circuit for the firing angle control of 3-phi thyristor converters operating under variable frequency supply is explained. The firing angle remains almost constant for a given control voltage and for a wide range of supply frequency variations. The circuit uses only 1-phi sensing, to generate the triggering pulses necessary for 3-phi converters working under variable frequency supply and the firing pulses are spaced equidistantly. The circuit is inherently immune to noise and transients, due to the use of CMOS integrated circuits and optocouplers. The circuit can be used for applications such as rotor control of slip-ring induction motors. The experimental results obtained for the triggering circuit are presented.