OLTC update

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi All,

To update the IGBT current sharing in the OLTC...

We have say 2000 amps and ten 200 amp IGBTs to switch it.  There is a
problem in how to be sure the IGBTs share that current equally.  If one
IGBT takes like 400 amps, it is a "bad" thing!  The circuit looks like this:

http://hot-streamer-dot-com/temp/OLTC8-10-01.gif

Basically, you slam all those IGBTs on with very low inductance, impedance
balanced "buss work".  Done well, it is simple and easy, once some nasty
details are worked out.  I have put a lot of thought about how I would do
this for the OLTC.  Lots of worry over the 10nH wire bonds inside the IGBTs
and stuff...  However, I guess that was all wasted now since the solution
is...:

http://hot-streamer-dot-com/temp/OLTC8-10-02.gif

Yep!  We have ten independent primary caps too.  If we hook them up like
this, the cap's impedance naturally hard balances the current to the IGBTs.
 It is just a done deal, "painfully" simple... nothing can go wrong.  It's
gotta work.  Even if just one IGBT turns on I "think" it self protects...
If one stays out, it self protects...  (the frequency is wrong, but who
cares...)  

This solution to current sharing of the OLTC's IGBTs is so beautiful, it
makes me wanna cry...

Cheers,

	Terry