[TCML] solid state varaic

[Scott Bogard <sdbogard@xxxxxxxxx>]

Greetings all,
	So my research into VFDs has indicated that to get the winding to 
believe it is being fed a sine wave of X voltage and Y frequency, they 
use a PWM with a variable duty cycle across the sine wave.  So I'm 
wondering if it would be possible to make a solid state variac in a 
similar manner, the advantage would be light weight and I would assume 
it would be much cheaper when dealing with high powered systems, the 
disadvantage is I don't think it would be possible to get the 140/280V 
output like you can with the real thing.  Basically all one would need 
would be an analog to digital converter being fed by 5VAC off of a 
potentiometer to make it 0-5VAC, this would feed a PWM driven full 
bridge IGBT array, at some point you would need a computer like an 
arduino or some such to logic the digital signal into a duty cycle for 
the bridge.  The intricacies are beyond me, but my research suggests 
this has actually been done in some form (for DRSSTCs anyway) if anybody 
has any experience on how they accomplished this (and if it would work 
with a transformer) please do share.

Scott Bogard.
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