Re: [TCML] DRSSTC tuning at high power

[Michael Twieg <mdt24@xxxxxxxx>]

I always thought k=0.12 was a bit on the high side already.  It should
nominally take about 8 cycles and 270us before the notch.  And that's what I
see at lower power levels.  Interestingly, I see at higher power levels that
the primary current notches and the secondary current peaks like 40us
sooner.  This seems really weird to me since that time should depend only on
k, which shouldn't change with power level.

We can raise the primary up a few more inches to get a higher k, and yeah we
can raise the voltage quite a bit.  So far we're normally using a bus
voltage around 450V, but the PFC as it is can go up to 600V.  We tried
running it at that level before but it didn't seem to get us much longer
sparks.  Once we get up to tone frequencies above a few hundred Hz the
voltage starts to droop anyways because the PFC starts power limiting (we
were limiting ourselves to 50A off 240V, which is based on the limitation of
our available AC line), so we lowered it down to 450.  If we wanted we could
probably take the voltage as high as 800V (our caps are are rated to 450V x2
in series, and we're using 1200V igbts on a very low inductance laminated
bus).  I think I see what you mean and trying a higher K with a higher bus
voltage might give overall better efficiency.

-Mike

On Tue, May 24, 2011 at 1:43 AM, Steve Ward <steve.ward@xxxxxxxxx> wrote:

> I would try more tuning, ive seen that response before and ive seen it get
> tuned out a lot better than what i see here.  Though at the same time that
> is a lot of cycles and its hard to keep it in tune on that time scale.  Im
> really surprised you need that many cycles of drive even.  From the looks
> of
> it, i'd probably shut off after 5 cycles.  What bus voltage do you run at?
>  Maybe you just need more voltage drive and less cycles.
>
> Steve
>
> On Fri, May 20, 2011 at 10:08 AM, Michael Twieg <mdt24@xxxxxxxx> wrote:
>
> >  found some primary current waveforms I had taken recently.  They're all
> > for
> > the same tuning configuration, but at different repetition rates.
> > At 208Hz:  http://imgur.com/TpjEY
> > at 330Hz:  http://imgur.com/R9ieE
> > at 523Hz:  http://imgur.com/pMq2j
> > Scale is 200A/V or 400A/div
> > You can see how the notch is barely there to begin with at 208Hz, and at
> > the
> > PRF gets higher it disappears and the peak Ip grows greatly.  The first
> > 270us of the waveform is being driven by the H bridge, the rest is just
> > freewheeling.  I can't tell if the power in the secondary is being
> > recovered
> > or not...
> >
> > Do these waveforms look reasonable?
> >
> > -Mike
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