[TCML] SSTC full bridge control system question

[Michael Twieg <mdt24@xxxxxxxx>]

Hello, this is my first post, please be kind,
I'm working with a team of engineers to build a large solid state musical
tesla coil, and my task in to project is to build control and telemetry
hardware.  We've chosen a full bridge design, a two coil configuration (flat
spiral primary), and we're using an interrupter based loosely on steve
ward's design to control its switching.  Like his, it senses primary current
and switches on zero crossing.  I've built the hardware and verified that it
works in small scale testing.

When simulating the two-coil system, I'm observing the peak splitting in
resonance, and noticing that of the two peaks, one gives a higher gain in
voltage on the secondary (the resonance of the secondary coil), while the
other gives a low primary impedance and thus a high primary current (this is
the resonance of the primary coil).  It seems that it would be preferable to
operate at the secondary resonance, since it gives higher voltages with less
primary current.  However, I've found that in simulation, it is impossible
to get the interrupter controller to operate at the desired secondary
resonance, and it instead operates at the primary resonance.  This results
in excessive currents in our full bridge (much more than our IGBTs will
like) for modest secondary voltages (we're aiming for between one and two
MV).  I'm unable to find any combination of coil parameters which allows the
controller to operate at the secondary resonance.

So my question is, is there any way to get a controller to operate at the
secondary resonant frequency while switching at zero current on the
primary?  If not, then how are people like Steve able to attain high
secondary voltages without requiring enormous (like several KA) peak primary
currents?  Is there something wrong with the way I'm characterizing the coil
system or the controller?

Thanks in advance,
-Mike
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