Transient response of the modified variable-phase-shift automatic voltage regulator

In the variable-phase-shift automatic voltage regulator, the output is sampled at half-cycle intervals, and compared to a reference. The error is applied to a phase control circuit and filter, whose output is a sinusoid of constant amplitude, at mains frequency, but variable phase. This is amplified by a class B power amplifier, and added to the mains line voltage in such a sense as to correct it. Theoretical, simulation and experimental results are given to demonstrate the high accuracy (of the order of 0.2%), very fast response (between one half and one cycle) and low distortion of the device.