At 11.50 2011.09.17, you wrote:
>Generaly...
>
>If you hava a battery it has an internal resistance. I think you want
>to pull out the maximum power from this power source. In this case
>your external resistor sould be equal with the internal resistance. If
>you increase the value of the external resistance, the current will
>drop on it ( altough the voltage will be higher ). If you decrease the
>value of the external resistance, the voltage will drop on it (
>altough the current will be higher ). So if you multiply the voltage
>with current the result will be the actual power on the external
>component.
>
>For example:
>U battery =3D 600V
>R internal =3D 50 Ohm
>R external =3D 50 Ohm
>
>I =3D U / ( Ri + Re ) =3D 6 Amper
>U ext =3D 300V
>P ext =3D 300V * 6 Amp =3D 1800 Watt
>
>------
>
>U battery =3D 600V
>R internal =3D 50 Ohm
>R external =3D 30 Ohm
>
>I =3D U / ( Ri + Re ) =3D 7.5 Amper
>U ext =3D 600V * 30 / ( 50 + 30 ) =3D 225V
>P ext =3D 225V * 7.5 Amp =3D 1687.5 Watt
>
>------
>
>U battery =3D 600V
>R internal =3D 50 Ohm
>R external =3D 100 Ohm
>
>I =3D U / ( Ri + Re ) =3D 4 Amper
>U ext =3D 600V * 100 / ( 50 + 100 ) =3D 400V
>P ext =3D 400V * 4 Amp =3D 1600 Watt
>
>If you have a solar panel, you can't know the exact value of the
>internal resistance, because sunlight doesn't come countinuesly and
>the clouds disturb the sunlight also. So you have to found the maximum
>point where you can pull the maximum energy from the solar cell or
>other power source because it depends on the illumination.

And how do you do it? So far that's the best approach I thought, but if
someone has a better idea, I'd like to hear it!

In my PIC based SMPS boost circuit, I unload the source (panel in this
case) until the voltage stabilizes, and then save the value into a register=
..
Then I turn on the switch and the inductor starts charging, thus current
increases. When the source voltage becomes half the open voltage I have
previously recorded, that's the optimum current I have to sink from the
source, thus I let e.g. 50mA more for it, then turn off the transistor
switch, until the current decreses to e.g. 50mA less than that optimum
value, then switch the transistor ON, and continue the loop, until the
output capacitors are fully charged, then I stop it. About every second,
I force a return to the outer loop even if the capacitor is not fully
charged, i.e. I measure input voltage at open (not loaded) conditions.
I love to design SMPS using MPU's, never ever used a switching IC in my
life, although of course there are situations (mostly battery-powered
small devices) where it would make perfectly sense to use one.. but for
high power stuff, I prefer to make my own algoritms and use PIC's.

Is there a better way to implement maximum power point tracking?

With kind regards,
Mario



>
>--=20
>~~~~~~~~~~~~~~~~
>http://galzsolt.zzl.org

--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.