RE: Terry's DRSSTC actually hooked to a coil now >:-))

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Steve,

At 03:40 AM 2/1/2005, you wrote:
> >by following primary current, you just
> >"ride along" with the frequency...
>
> Yup, this is exactly what happens. But you have to be careful because there
> are two possible "rides" the coil can go on. If you design the system to
> give the right voltages and currents on one of these paths, they may be all
> wrong if it switches to the other one.

I guess I am not understanding what the "two paths" are here.  The two coil 
system has primary and secondary resonances which beat against each 
other.  One small and the next larger "notches" due to this beating can be 
seen here:

http://drsstc.com/~terrell/pictures/FullSystem-01.gif

I should have let it go longer and you could see lots of beats.  Between 
the two "notches" you can see where the current (yellow) shifts some.  The 
frequency certainly is not a stable value but bouncing around.  But these 
are perfectly normal for a primary current driven system.  The secondary 
current driven system like Dan's is much different in that the beating is 
in the drive signals where I think it "beats up" the IGBTs more since the 
zero current crossing miss in that case.  The primary current is a powerful 
fourth order system but it seems very "stable" as it beat between the two 
frequencies.  If there is other some weird mode, "I" am not aware of 
it.  Perhaps those that have studied the system's transforms have found 
something there?


> Primary current feedback can't select between the two paths, it will just go
> to the one whose gain is highest.

Yes.  Is that possibly bad?

> If they are about equal, then streamer
> loading may tip the balance and make it switch mid-burst. You can prevent
> that by deliberately mistuning- to ensure lower pole operation, tune the
> primary lower than the secondary, and for upper pole, tune it higher.

Right now primary and secondary are tuned to 85.1kHz and tuned to within 
0.1kHz of each other.  It is trivial to mistune, but I just don't see 
"why"?  If the frequency want's to shift, the driver does not care.  I have 
no local oscillators or anything controlling the H-bridge.  It is totally 
timed from the primary current.  It could go from 1Hz to 100kHz and then to 
200hZ and the driver would not care (1Hz would probably drain the filter 
caps or hit current limits).  Perhaps in the case of an oscillator 
controller like your PLL controller, such shifts are far more of an issue?

If the secondary took a heavy hit, it's oscillations could certainly be 
shifted out of sync with the primary or totally disrupted.  But i would 
think once that load is gone it would all snap right back in place.  But 
the primary would not care much...  I can imagine if the primary were 
driven from a local oscillator, such disruptions could do odd things in 
that six pole feedback system case.


> If you reverse the phase of the primary feedback you get a third possibility
> which is the one described by Antonio de Queiroz and Jimmy Hynes. The system
> oscillates at the "zero" midway between the two "poles". This oscillation is
> not stable in the steady state but it might persist long enough to get
> breakout.

It will just shut off.  The logic will not allow the IGBTs to turn on out 
of phase.  If you reverse the CT, the driver will just counter the start 
pulse current and massively damp the oscillation off.  In the case of a 
secondary current driven coil, you can reverse the CT however.


> It's hard to tell from the trace which mode you're on but I would guess the
> lower pole. The upper pole never shows notches, and the "Antonio" mode won't
> oscillate at all if the feedback phasing is set for driving a single
> resonant circuit.

I "think" it is riding both poles and the resulting primary current 
regardless of frequency or poles and zeros.  The driver just does not care 
what the frequency is or how much it shifts from cycle to cycle.



> "Two modes diverged in a Tesla burst,
> And sorry I could not travel both
> with just one driver, loud I cursed
> And messed around with PSpice first
> To see them pulled by streamer growth"

If you have like a MicroSim model that would help me to understand I would 
love to study it.  I really don't understand the "two modes" thing...

Cheers,

        Terry


> etc
>
>
>
> Steve C.