A direct digital proportional controller for thyristors

A digital thyristor controller is described which uses an integral pulse-frequency modulator to ensure that the dc voltage appearing across the thyristor load is proportional to the digital control input. By using a microprocessor in an extended form of phase-locked loop around the pulse-frequency modulator, the thyristor(s) and the controller function as a linear gain block unaffected by supply waveform fluctuations, while providing one-cycle response to step disturbances in supply voltage amplitude and frequency.