Battery charger and MPPT controller

Thread Starter

Mckenzieee

Joined Oct 1, 2020
1
I am working on a project where i have to charge a battery from a PV panel source. I have a boost cascaded by a buck converter for my system. The boost converter for P&O MPPT and the buck for the 3 stage battery charging algorithm. So now I am looking to implement the control. So on a theoretical base I understood that load determines the power drawn with the use of the battery charger and that as the load varies on an MPPT the operating point will move away from true maximum power point. With that said, does it mean that the P&O MPPT algorithm can just be implemented independently and will move from true MPPT on its as when connected to a battery charger ? as in will the charging limits set by the battery charger "tell" the MPPT circuit to move further away from true MPPT or is there a combined algorithm for this ? Is there a source code for this that you guys can refer me to?
 

Solar Mike

Joined Apr 26, 2018
24
Having designed numerous MPPT battery chargers, have never had any reason to implement a boost stage prior to the buck circuit; its just inefficient and a waste of power. Unless you are using tiny PV 6v panels (toys) or something very small, I wouldn't recommend it.

For a battery charger the most important measure is charge current and battery voltage; for mppt the requirement is to measure the instantaneous charge current and attempt to maximize it for all levels of PV illumination by varying the buck PWM. At each charge current measure, note the battery end point voltage; when in in Bulk phase and that end point is reached then start a constant voltage timer and keep the voltage constant to allowing the current to taper, then switch to float. These settings being set by the battery chemistry.

I generally stay in MPPT mode as much as possible, but backing off as required depending on the dynamic loads on the battery bank under charge; - talking about large systems here perhaps powering a house etc.

If implementing some sort of pre-boost stage then fix it at times 2 or similar going into your buck stage, do your control in the buck aiming for max current.

Cheers
Mike
 
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