Conceptually, is a MPPT controller for charging (simple) batteries with energy from solar panels basically a buck converter whose feedback loop (which influences the PWM duty cycle) is geared toward maintaining the maximum power point rather than a stable voltage?

Can it be only a buck converter or does it need to be a buck/boost one?

  • \$\begingroup\$ (a) yes (b) that depends on the solar panel and battery voltages. \$\endgroup\$ – Brian Drummond May 27 '18 at 20:14

Yup, it's a buck converter (or boost) ...

...but with a supervisory control computer which is frequently testing slightly higher and lower current draws, and using that data to optimize for V*A. This is no small thing.

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  • \$\begingroup\$ Doesn't that happen as a consequence of perturbing the PWM duty cycle and observing results? \$\endgroup\$ – Ivan Voras May 27 '18 at 20:47
  • \$\begingroup\$ when the software decides to change current, presumably a PWM change would be the method for doing that, yes. I would expect the software to decide to, say, decrease current to 5400ma, then tell the PWM subsystem to generate whatever duty cycle has that effect, with feedback applied to that too. \$\endgroup\$ – Harper - Reinstate Monica May 27 '18 at 21:12
  • \$\begingroup\$ I guess it can be dumber than that. Like "try a little smaller/bigger duty cycle, see what happens, set new baseline accordingly, rinse and repeat". \$\endgroup\$ – Dampmaskin May 27 '18 at 22:04
  • \$\begingroup\$ @Dampmaskin perhaps that sort of dead reckoning would work and save a step; however it still needs to focus on current, since it's maxing for V*A, not V*PWM%. And solar panels are highly non-linear,so changing PWM could have unexpected results. \$\endgroup\$ – Harper - Reinstate Monica May 27 '18 at 22:57
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    \$\begingroup\$ Yes, it would need to measure the current as well as the voltage, and multiply them together. But I don't think it needs to know anything beyond "more power is better than less power" in order to oscillate closely around the maximum power point. \$\endgroup\$ – Dampmaskin May 28 '18 at 9:40

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