OLTC II- advice on tank cap

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Original poster: "Stephen Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>

Hi folks,

I just received a nice pair of 1200V 600A IGBT bricks today. Thanks Terry! 
It gives me an evil feeling of power just looking at them. Now comes the 
hard part. I need to design a MMC cap that will store at least 2J, 
preferably 5-10J, at 1000V. So we're talking between 2 and 10uF. You might 
think this is easy enough, but it needs to have very low inductance, and 
deliver a peak current that could be more than 10,000A.

Proper film and foil caps seem to be out, because I can't buy them in large 
sizes. It would cost a fortune and be very bulky. So I'm thinking 
metallized polypropylene. 10 to 50 of .22uF 1000V caps in parallel would be 
needed. Can anyone comment on this choice or suggest any particular kinds 
of cap? I used .47uF 500V LCR metallized film caps in my original OLTC with 
no problems. Even though they were only rated 40V/us but I ran them nearer 
200. They got a bit warm though.

Last of all, the construction, how should I arrange the caps for lowest 
inductance and even current sharing? If I had axial caps (leads come out 
the ends) I could drill a grid of holes in two copper-clad PCBs or thin 
copper plates, sandwich the caps between the plates, and solder them in 
place. Would this be a good layout, or would the caps in the middle pass 
less current than the ones at the edges?

Your advice would be much appreciated,

Steve C.