Series Connection of IGBT / MOSFET Switches - SSSG

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Original poster: "David Sharpe by way of Terry Fritz <twftesla-at-qwest-dot-net>" <sccr4us-at-erols-dot-com>

Terry, All

As a sidebar from the Chicago Power Electronics Conference,
I found this URL for an App. Note from IXYS concerning
applying IGBT's or MOSFET's in series for capacitive discharge
(OLTC) applications.

  http://www.ixys-dot-com/t080698a.pdf

I guess the scaling is limited to your pocketbook or intestinal
fortitude.  Getting supply voltages to each level of series switch
requires ingenuity.  One method commonly used is a high current
current loop using a half bridge converter feeding a CT backward
like a pistol soldering gun.  This current loop feeds a CT/PT on
each level of switch with local HFAC to DC conversion.
High frequency (20-100Khz) at 20-30A will allow up to 2-3A
drive capable power to be available at each level of series switch.

Triggering is performed fiberoptically, only way to guarantee
synchronous triggering, and HV isolation.  I would also add a
TVSS as Terry as done for each level in parallel with R and C,
and this design feature is also included in gigawatt level switches
previously mentioned.  If discrete IGBT's are used, costs could
be kept fairly reasonable (maybe <$50 per switch level).  Modules
are at least 5X more expensive per delivered load kVA, only
real advantage is isolated mounting to a grounded heatsink.

So it looks like we are right on the cusp of a practical, high power
solid state spark gap system that is within reasonable cost for an
advanced experimenter.

Regards
Dave Sharpe TCBOR
Chesterfield, VA USA