Re: Slope Compensation and Vodka

From: Genome (genome_at_nothere.com)
Date: 08/11/04 

Date: Wed, 11 Aug 2004 03:29:54 GMT

"terry" <the_domes@xtra.co.nz> wrote in message
news:4ReSc.11758$N77.520748@news.xtra.co.nz...
| "Genome" <genome@nothere.com> wrote in message
| news:HhfSc.620$Qs4.75@newsfe5-gui.ntli.net...
| >
| > "colin" <no.spam.for.me@ntlworld.com> wrote in message
| > news:mBeSc.2139$K84.1781@newsfe3-gui.ntli.net...
| > |
| > | "Genome" <genome@nothere.com> wrote in message
| > | news:PieSc.594$Qs4.137@newsfe5-gui.ntli.net...
| > | > I'm trying to gain a bit of insight into things to do with slope
| > | > compensation in peak current mode control.
| > | >
| > | > I model it, I sit and look at it.... I drink Vodka, actually I
mix
| > the
| > | > Vodka with Cider.
| > | >
| > | > I wonder.
| > | >
| > | > Now, I've seen various explanations about the whys and
wherefores
| > and I
| > | > don't understand them. However, as part of my website I need to
| > explain
| > | > it to others.
| > | >
| > | > Is there a simpler way?
| > | >
| > | > What I see is that when subharmonic oscillation occurs there are
| > | > multiple solutions to the sum that's being solved by the system.
| > | >
| > | > With slope compensation those sums are reduced to one unique
| > solution.
| > | >
| > | > That's my take on things.... is there a way of proving it
| > | > mathematically?
| > | >
| > | > DNA
|
| IIRC its associated with the sampled-data nature of the overall
control
| loop, which the standard linear analysis conveniently ignores. Ray
Ridley
| did his PhD thesis on basically including the effects of
discretisation in
| the analysis. Others have approached the subject from slightly
different
| avenues, but when you include this sampled-data behaviour the
duty-cycle
| dependant subharmonic oscillation pops out the wash. And (kinda
obviously)
| it doesnt miraculously disappear when D = 0.4999999, rather the
effects
| gradually reduce, disappearing at around D=35%. Normally the
explanation is
| a nice hand-wavey description of what takes place DURING this
oscillation,
| and how to fix it, rather than saying WHY it takes place.
|
| I went to one of his seminars once, and found it to be, overall, not
much
| practical use - it seemed to be mostly a pitch for his FRA's. The
maths was
| interesting, but like everyone else he didnt give usd all the
equations we
| need to close the loop on the half-dozen or so different converters
that
| people in practice build. A shame really, cos it probably all fits
onto a
| single page....
|
| Cheers
| Terry
|
|

That's a bum. I can't say why it takes place but I can believe why it
happens.

I don't believe in an analysis that talks about 'stability'..... or dare
I say sampled data behaviour.

I do believe in multiple solutions without slope compensation that get
reduced to a unique solution with slope compensation. Its just the
method required to prove it.

But I wouldn't tout that one around.

Smidley's in it for the bucks, has to roll his shirt sleeve up to take a
*** and someone else washes his trousers for him.

DNA