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Re: [TCML] First notch quenching?

Hi everyone

This touches on some issues that I was intending to raise on 4hv.org if I
could manage to complete registration, but as it has come up here ...

Why would one want a DRSSTC to 'quench' after the first 'notch'?  (By which
I assume that what is meant is adjusting the interrupter's pulse width so
that the burst ends at the next primary zero current crossing after the
first 'notch' would otherwise occur.  At which point, the half- or full-
bridge IGBTs are not driven so that the excess energy in the primary
capacitor promptly feeds back into the DC storage capacitor via the
freewheeling diodes anti-parallel to the IGBTs.)

The arguments against that occur to me are:

1.  A DRSSTC is not like a SGTC (where all the energy must be injected into
the primary capacitor before the spark strikes) in that not 'quenching'
allows one to continue to pump energy into the primary tank circuit.
2.  Because of the freewheeling diodes anti-parallel to the IGBTs, leaving
the IGBTs undriven might not isolate the energy in the secondary -
presumably, after the end of a burst, the mutual inductance of the primary
and secondary still allows energy to be transferred to the primary and then
to the DC storage capacitor.
3.  According to Dan McCauley in the miniBrute reference design book, his
idea is to detune the primary tank circuit so that notching does not occur.
(I assume until streamer loading on the secondary circuit reduces its
resonant frequency.)

An argument in favour that occurs to me is that, if (contrary to 3 above)
notching occurs, the energy transfer back to the primary from the secondary
may well cause the primary current limit to be exceeded thus causing the
burst to be terminated before any additional benefit is achieved from
sustaining the burst. 

This is my first post, I'm relatively new to DRSSTCs and not an EE.
Therefore I will apologise in advance for whatever misconceptions are buried
in the above.

Michael Barr-David

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Scott Bogard
Sent: Tuesday, 25 February 2014 11:14 AM
To: Tesla Coil Mailing List
Subject: [TCML] First notch quenching?

Greetings folks,
     A bit of a theoretical question, I'm a bit rusty so thanks for your
patience, is it still impossible to quench on first notch?  I was trying to
explain the whole "notching" concept to someone and it occurred to me, if an
IGBT or other switch was inserted to bypass the tank capacitor enitrely and
physically disconnect the primary immediately after first notch, it would
greatly impede the tendency to transfer energy back into the primary, as it
would no longer be at the same resonate frequency.  I feel like I might be
missing something, or maybe not, or perhaps even it doesn't matter as such a
feat is impossible with current semiconductor technology.  At any rate just
felt like putting this out there, help me to remember if you could folks.

Scott Bogard.

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