[chbot] Help I don't know enough about SMPS! (And can you help me design one pls)

Robin Gilks robin at gilks.org
Mon Jan 16 02:03:05 GMT 2012


> Yarrr!
>> I have heard good things about LT (Linear Technology). Their reference
>> designs (those in the data sheets and appnotes) are reported to work
>> reliably. They're big in switch mode designs too. Check their range, but
>> I suspect you are pushing the limits (mainly input voltage) with your
>> solar panel. They have a good spice simulator too (LTspice), and are the
>> only company who bothers to mention Linux and say that LTspice works
>> under wine. (There was an article in a recent Elektor about that too).
>> The LT semiconductors should all have spice models for their simulator.
>> I would make extensive use of that in your position.
>   LT Have an amazing array of good stuff, found one that is perfect etc...
> BUT I really want to get to know one topology to do it all, and this is
> not working in an easy way,
>   so does anyone know of a chip/topology etc. that is both easyish (i.e I
> can make it... ) and efficient over these ranges:
>
> So for ~60V -> 27V (~12A) no problem, buck is easy and rel. efficient it
> seems. no kooky magnetics either.
>   BUT 40-60V -> 57V (~6A) is a problem, being buck/boost needing complex
> magnetics etc.... This is the range I am finding difficult, esp as I would
> like minimal (pref. only ref change from micro) modification to change
> Vout.
>     I should qualify this somewhat. COmplex isnt a problem if its going to
> work, its that I am not sure if I could get the magnetics, or make them
> right.
>
> Anyone tried Cuk? Not much out there on it in terms of LT etc.
>
> Hopefully I will be able to make it tonight, and have a chinwag with some
> of you expert types.
>
> TIA
>
> Jasper

Not quite sure why you're trying for boost as well as buck conversion.
Generally, the reason the input volts are so low as to require boost is
because there is not enough sun or not much wind (in the case of a
turbine) so not much power available in the first place - hardly worth the
bother!!

Seems a more effective use of conversion would be to ensure the input
volts are sufficient at the start of power making output (from panels or
turbine) and just use a buck converter.

Solar can learn what to do as it goes along as the panel outputs depends
on many factors - temperature, insolation, angle of incidence to start
with so the controller can play with the loading to do true Max Power
Point Tracking (MPPT).

Wind is easier and more difficult!! Try adjusting the load on the fly and
you could end up with blades spread over a large area!! The usual trick is
to change loading based on the square of generator rpm (even though the
energy follows a cube law with wind speed) - it will be a lot better than
straight linear tracking.

I've not tried MPPT on my turbine yet, mostly for the same reason as you
in that I have yet to research a decent switched mode buck circuit that
can handle up to 100amps at up to 200volts (guessing what my turbine might
produce in a nor'wester).

Not sure if I can make it tonight - will chat if I can :)


-- 
Robin Gilks





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