Re: [TCML] DRSSTC tuning at high power

[Eric Goodchild <ericgoodchild@xxxxxxxxx>]

Oh yeah you definitely need to take advantage of the voltage rating of your
caps and IGBTs. I run a 650VDC to 800VDC bus on my large DRSSTC. The large
sparks don't start to kick in until I get to at least 600VDC or higher.
This is partly because my system is detuned so that it won't start creating
larger sparks until a suitable amount of power is applied.

Eric

On Tue, May 24, 2011 at 8:25 AM, Michael Twieg <mdt24@xxxxxxxx> wrote:

> 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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