Re: Pushing the IGBT Envelop

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

Original poster: "Greg Leyh" <lod-at-pacbell-dot-net> 

Interesting website, and coil work!  I'm still unclear on the DRSSTC theory 
of operation, however.  Near as I can figure, the system actually runs as 
an oscillator, but in a quasi-CW mode for relatively short bursts, at an 
unspecified dwell and repetition rate.  Is this roughly correct?

H-bridge drives are great for power converters to 100's of kW, and 
especially when operation from a unipolar DC source is required.
However, an H-Bridge plan wouldn't be cost-effective for the ALF since it 
requires 4X the silicon for the same primary peak current and voltage swing 
-- an important consideration when the material costs for the silicon alone 
is likely to be mid 6-figures.  H-bridges are also susceptable to 
'shoot-through' failure, where timing errors or cosmic-ray induced firing 
of IGBTs can hard-short the DC mains, resulting in catastrophic failure of 
the entire IGBT stack.  For perspective, here's a photo of a catastrophic 
H-bridge drive failure at another lab, believed to have been caused by a 
cosmic ray induced false-triggering one of the IGBTs:
http://www-group.slac.stanford.edu/esd/HBridgeDebris.jpg

The IGBT casings and structures can be seen evenly distributed on the 
floor.  This failure occurred on a system operating at several hundred 
kW... imagine scaling this up to a 5MW system!  It's clear that 
partitioning the primary drive circuitry in order to isolate component 
failures will be essential for a 5MW primary drive system.


>Original poster: "Steve Ward" <steve.ward-at-gmail-dot-com>
>Hi Greg,
>
>Very fascinating stuff going on at SLAC.  I've also read some of your
>papers about IGBT module design (and the downfall in commercial
>modules layouts).
>
>Anyway, DRSSTC is a Dual Resonance Solid State Tesla coil.  We
>basically drive a resonant tank circuit with a solid state driver
>(using IGBTs) and pulse its operation to achieve very high peak
>powers.  Jimmy Hynes was the first person to have a very successful
>coil built under this idea.  I think my coil is currently the largest:
>
>http://hot-streamer-dot-com/srward16/DRSSTC-2.htm
>
>It uses 300A IGBT (dual modules) rated 1200V.  We typically overdrive
>the gates so that we can push greater currents (my system runs at
>about 1200A peak) through smaller IGBTs, mainly since us ametures cant
>afford to buy enough silicon to actually run these things in their
>SOA... and after all, this is tesla coiling!
>
>The DRSSTCs are, as you might expect, slightly more efficient than
>even the best SGTCs.  My coils seem to follow the formula of: spark
>length (inches)=2*sqrt(power).
>
>I was almost hoping that if the advanced lightning facility every
>became reality, that it would be a DRSSTC.  Mainly because you would
>not need extremely high voltage silicon to replace a spark gap.  With
>a DRSSTC, our bang energy is not limited to the storage energy in the
>tank capacitor, it can be much greater (usually its 2X as much).  I
>think the fact that my large DRSSTC can make 11' sparks from just
>600VDC rail voltage and only 4-5kW shows promise for even larger coils
>(silicon permitting).
>
>Steve