Answer / ashraf majid

Thyristor convertor type AVR(Automatic Voltage Regulator)
is made of Thyristors(Silicon Controlled Rectifiers,SCRs).
We know that output DC voltage from an SCR will not only
depend upon the r.m.s. value of Input voltage applied, but
also at the angle at which the input AC cycle is fired
(using gate signal). If the firing angle is zero(in a
simple circuit), then maximum DC output voltage will be
obtained.If the firing angle is changed from 0 to 180,then
maximum to minimum voltage is obtained. This property could
be used to build an AVR. The firing angle proportional to
Output voltage could be used to trigger the thyristor,in a
closed loop manner and a nearly constant DC voltage(Average
Value) can be obtained.An invertor circuitory could be
utilised to get a regulated AC supply.
Many other configurations can be build from thyristors to
get a regulated AC supply.

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