Ibraheem H avatar image
Ibraheem H asked

Bug Report - MPPT algorithm stuck with big power change


Noticed this for a while now and has not been fixed with recent firmware updates.

Using a 100/20 SmartSolar.

When there is a sudden change from high PV power to low PV power for example when a clear sky becomes clouded, I have noticed that the MPPT charge controller moves it's tracked PV voltage very high. For example, if the "normal" PV voltage is 70-80V, the tracked PV voltage is 90V+. It seems like it tries the maximum voltage it can pull from the string. PV power then fluctuates between very low power values because of the low PV power, say 15-16W.

It *looks* to me like the algorithm gets stuck because moving from 15W at 90.1V to 15.01W at 90.2V makes it want to increase the PV voltage. Getting 15.02W from 90.1V makes it want to go slightly lower, and this cycle repeats for around 15 minutes, where it very slowly drifts the PV voltage down until it gets to a voltage that has alot more power, and then gets into a good feedback loop.

It is quite annoying because this can happen during the peak power period of the day.

Turning the charger off, then turning it on again, resets the condition. I kept it in the fault condition today to observe the behaviour so that I can submit this bug report.

My proposal for changes to the algorithm to fix this - every minute or so, see if the current PV voltage is within say 2 standard deviations of the day's PV voltage levels seen after the charger has switched on. If it is outside this range, it is most likely stalled as above. If stalled, manually restart tracking from the mean PV voltage. That should bring the tracker back into a good feedback loop.

MPPT Controllers
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