ABSTRACT
The input voltage and output current of AC voltage controllers pass through the value zero in every cycle. This simplifies the modeling of a thyristor. A thyristor can be turned on by applying a pulse of short duration, and it is turned off by natural commutation due to the characteristics of the input voltage and the current. Pulse-width modulation techniques can be applied to AC voltage controllers with bidirectional switches in order to improve the input power factor of the converters. The load current of AC voltage controllers is AC, and the current of a thyristor always passes through zero. When the converter switches are turned on, the input voltage is connected to the load. The AC voltage controllers provide a variable output voltage but the frequency of the output voltage is fixed and in addition the harmonic content is high, especially at a low output voltage range.
