A Generalized Firing Angle Controller Using Phase-Locked Loop for Thyristor Control

A generalized firing angle controller using a phase-locked loop, for control of thyristors is described. Different types of firing angle variation characteristics are possible because of the generalized phase detector used in the circuit. The controller can operate over a wide range of supply frequencies and is immune to the transients and harmonic distortions in the supply voltage. Also changes in the supply voltage amplitude do not have any effect on the firing angle. The same circuit can be used to provide firing pulses for three- or six-element thyristor configurations. The scheme can be successfully used for thyristor converters and cycloconverters.