Pulse-Frequency Modulation Applied to The Digital Control of a Thyristor

An integral pulse-frequency modulator is employed for the direct digital control of a thyristor so that the dc component of the thyristor output is proportional to the numerical output of a digital computer. The modulator reference waveform is proportional to the thyristor anode supply voltage; the modulator output is a train of pulses whose time separation satisfies the condition for linear controller operation. The pulses are counted from the beginning of the positive half-cycle of the reference input; they are gated to the thyristor following detection of coincidence with the number supplied to the digital control input. Sensitivity of the pulse-frequency to disturbances in supply voltage and frequency is reduced by means of phase-lock techniques. The departure from linearity was found experimentally to be less than 1%, and is attributed to the forward saturation voltage drop of the thyristor.