A question about MPPT regulators for the elctronic whizs

William_H

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I understand the concept of MPPT and I have built a switch mode voltage reducer to produce 14v for battery charging from a (40v max) solar panel.
The nature of the switch mode converter is that as it sucks power from the solar panel it reduces the solar panel voltage so increasing the current needed to produce the required voltage. This increased current pulls down the solar panel voltage further so that on a small panel it almost imediately takes the panel away from its max power point until it produces nothing.
Now I figure I can detect the panel voltage say about 30v and if that falls lower, throttle back the converter (using a spare built in comparator) . Hardly proper tracking of max power point but better than nothing.
My question is how do MPPT controllers actual determine and control the voltage/current to kep it at Max Power Point?
 

grumpy_o_g

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Lon nan Gruagach

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I would design the controller to draw a requested current, measure the voltage, calculate power and then change the requested current, re-calculate and decide which comes out best .

"perturb and observe" as per the wiki link from grumpy_o_g

you can make it bright enough to reduce the oscillation that is mentioned in the article.
 

William_H

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Thank you all. Some food for thought, learnt a bit, but all a bit humbling. It seesm ity is not as easy as I thought. olewill
 

Beyondhelp

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Yep they work by trial and error. Kind of like what you are doing, they keep adjusting the switching point until p = max, then they will alter ++ -- slightly to see how it improves it or not. Quite simple really but will need a micro behind it to make it sensible. Resistance changes within the panels depending on exposure to UV and temperature, so P-Max also moves about. Also remember, you may not want 14v on your output as your target, as if the battery is low that will never happen until its on float.

FWIW I realised in about an hour of messing about that it was far easier to buy a MPPT charger, one of these infact: http://www.ebay.co.uk/itm/MPPT-20A-...381?pt=LH_DefaultDomain_3&hash=item20e0d6ce55

I assume you are using 24v panels? with Pmax of around 30v? If so this will do the job, as that is exactly what I have done It will drop my pair of 12Vnom panels in series to 12v battery charge. It works very well, and does a load of other stuff as well.
 

William_H

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Thanks Beyond help. Yes I am getting the idea that it is all abit difficult without a microprocessor and good soft ware. The wikipedia link helped a little. That controller in your link looks good. (won't post to Oz however) I have real suspicions about some of the Chines ones on ebay. It seems some don't really track at all. Just transform the voltage down. Which is what i intend to do when I get the panel. (at least for a try) olewill
 
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