Phase-locked loop control of thyristor convertors

The paper describes a controlled rectifier with firing pulses supplied from a separate oscillator lockedto the convertor a.c. supply. The phase difference between the pulse oscillator and the a.c. supply can be controlled from 5° to 175°, giving a full control range for the thyristor convertor. A multiplexer, supplied with the convertor input voltage and gated with signals from the firing pulse oscillator, gives an output waveform identical to the thyristor convertor and is used as a phase detector for the feedback signal to the pulse oscillator. The circuit is insensitive to distortion on the supply net.