Re: DRSSTC Primary Circuit Feedback Control

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Jimmy Hynes <jphynes@xxxxxxxxx>

Hi,




> > > The models (not real confident in the numbers..) say the IGBTs will do
> > > about 40 watts of heat as is.  But with "perfect" zero cross switching,
> > > that goes down to 1.2 watts!!
> >
> >Huh? What frequency and switching times? My simulations showed about a
> >factor of 2 increase in loss when hard switching about 80% of peak
> >current. A factor of 30 is hard to believe.
>
> Looses at "zero current" are real low.  Just the primary RMS current
> then...  But not sure I trust then numbers.  IGBTs are not really linear so
> switching losses get pretty high if the current is high.  That mJ loss
> stuff on the data sheets adds up...  Also worrisome having 20,000 volts
> behind it!!!

Oh, that's where you got the switching loss numbers. I wouldn't trust
those too much either. What I did is use Pspice to simulate the
circuit, and integrate the instantaneous product of voltage across the
IGBT and the current through it. I'm not sure how accurate the models
are when it's way out of spec, but I'd trust this way a little more