Ac-auto tapped trensformer using ac-voltage contoller

Thread Starter


Joined Oct 22, 2007
i have assigment to built matlab model to give that function
"Ac-auto tapped trensformer using ac-voltage contoller"
but i dont how to di it, can anyone help me????


Joined Apr 20, 2004
Is it possible the device is an "autotransformer", also called a variac, and the function is to use it as the AC voltage controller?


Joined Jun 4, 2007
This is called an AVR - Automatic Voltage Regulator, used in many industrial applications. Most of then rely on the buck-boost principle. The UKs mains is a nominal 230V +-10%, so we have to add or subtract a maximum of 23V to/from the incoming mains. So for a 100A supply we need a mains/2 in to 23V, 100A transformer. Now if we have a variac (variable auto transformer) with a fixed tap at its 50% point and we connect the primary of our buck/boost transformer between the tap and the brush, as we rotate the shaft of the variac, we can alter the voltage on the primary of the buck/boost transformer which in turn will add or subtract its secondary voltage to the output mains voltage. So all that is now required is some sort of voltage comparator connected to the the output voltage with its output driving a motor that turns the shaft of the variac. An output accuracy of better then +- .5% is possible, BUT it takes time ~ 1 Sec for the output to stabilise. The buck/boost transformer and variac handles 2.3KW, for a supply rating of 23KW.