Re: Re: [TCML] SSTC full bridge control system question

[Michael Twieg <mdt24@xxxxxxxx>]

All right, I'll try to apply your methodology to our existing
secondary parameters and see if I can get anything promising.  I've
tried already a couple times and can't get it to resonate at the
center frequency; it always goes for the lower frequency.  And to be
honest, that's what I would expect to happen.  There are generally
going to be three frequencies at which the phase of primary is current
is zero (which means zero crossing can work there), but the middle one
is always the largest impedance, and I would expect the other two to
dominate.  As I mentioned before, pulling some of your example numbers
and throwing them into LTspice did result in it resonating at the
center frequency, but I haven't gotten anything else to do that.  Any
idea what causes the controller to select the middle frequency?

-Mike

On Mon, May 3, 2010 at 9:09 PM, Antonio Carlos M. de Queiroz
<acmdq@xxxxxxxxxx> wrote:
> Michael Twieg wrote:
>>
>> That was a fascinating read Antonio.  I was able to replicate your
>> results accurately, even in my zero-crossing control model.  I didn't
>> think that complete beating in the signals was possible with
>> zero-crossing switching, since the beating should require a reversal
>> of phase.  In my previous simulations, the system was always excited
>> to the primary resonant frequencies, and never the "middle" frequency
>> as in you explanation.  Would this be because my own attempts didn't
>> meat your criteria for the spacings/ratios between the resonant and
>> middle frequencies?  I'm still a little cloudy on what you mean by
>> "odd" and "double odd" differences.
>
> For complete beats a set of particular relations among the inductances,
> capacitances, and
> coupling coefficient must exist. Nothing very critical, as the element
> values used in a normal
> SGTC are usually pretty close to the tuning required for an SSTC working in
> "notched" mode,
> in one of the many possible modes (but not identical). I define the "mode"
> by three numbers that
> define the ratio of the two resonance frequencies of the system and the
> excitation frequency (the excitation
> between the resonances). In the best design, the numbers are odd and have
> "double odd" difference,
> as 1:3:5 (difference=2, two times 1, that is odd). Usual systems will be
> around mode 37:39:41,
> as in the example in my page. Irregular modes are also possible, with
> differences between the
> odd numbers being 6 (2x3) or 10 (2x5), but there is no advantage in using
> them.
> Of course, streamer loading affects what is actually obtained, but the
> influence is similar to
> what occurs in a SGTC, that works with similar waveforms (actually, a
> magnifier works with
> more similar waveforms).
> It is really interesting that zero-current switching is natural in SSTCs
> operating in this way.
>
> Antonio Carlos M. de Queiroz
>
>
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