Re: [TCML] DRSSTC CM600 Ringing

[Finn Hammer <f-h@xxxx>]

Tyler,

As others have noted, your waveforms don´t look all that bad. I have
never been able to remove the overshoot on the first transition myself.
My own unlearned explanation to this is, that the phase lead inductor
doesn't work before it has seen a reversal, but that is probably
nonsense.

What are you driving the gates of the bricks with? I ask because if you
whack them open really fast, then it is those rippely waveforms you'd
expect to get.
I have found that if I can open the gates with a nice swoop from the
gatedriver, without any ripple or overshoot on _that_ waveform, then I
also get calmly looking main bridge waveforms.
That's why I use discrete gate drivers with constant current sourcing
capability.
As long as the overshoot remains lower than 1200V you should be allright,
but I never liked any ringing, because i think it looks as if something
is about to break, it's "un beautifull", that's why I built the prediktor
in the first place.

Cheers, Finn Hammer

----- Original meddelelse -----

> Fra: Tyler <tyler.c.c@xxxxxxxxx>
> Til: tesla@xxxxxxxxxx
> Dato: Tor, 12. maj 2011 05:15
> Emne: [TCML] DRSSTC CM600 Ringing
> 
> I just recently finished rebuilding my coil with a new bridge built
> with
> CM600's, and a new controller that is fed by the hammertone prediktor
> phase
> lead.
> 
> It is doing well, and can be adjusted for (almost) no ringing with
> the
> timing adjustments, definitely much less ringing than my previous
> designs.
> The problem is the first few cycles, no matter what I do I can't get
> rid of
> the ringing. No adjustment removes it, and I've never had a design
> that
> lacks this ringing.
> 
> Can be seen in this scope shot (the horizontal line at the top of the
> waveform is the DC bus voltage):
> http://ctyler.scripts.mit.edu/IMG_0027.JPG
> 
> Zoomed in here: http://ctyler.scripts.mit.edu/IMG_0030.JPG
> 
> 
> The only solution I've come up with that helped, but did not
> eliminate the
> problem, was putting in a big 25uF 1kv film capacitor directly across
> the
> rails at the IGBTs, which can be seen in my bridge photo:
> http://ctyler.scripts.mit.edu/IMG_0034.JPG
> 
> Additionally, there seems to be a bit of extra ringing after the
> bridge
> turns off and the energy in the primary is going down, although it's
> possible this will go away when the secondary is in place?
> 
> 
> I've looked around quite a bit and haven't found a reliable solution
> to this
> problem, which is noted in a number of places. Has anyone found
> anything
> that helps out with this?
> 
> Tyler
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