mppt vs pwm

BFL13 wrote:

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That is what I was asking earlier with questioning the panel voltage once no longer at Vmp. Answer was panel voltage goes up higher than Vmp so input and output power is less and so output amps is lower at that Vbatt. But if there is a load greater than battery charging, panel voltage goes down (back up the knee on the IV curve) allowing output amps to go up. (I never quite understood how that panel voltage change happens)
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Wikipedia "Maximum Power point tracking" wrote:
When the batteries in an off-grid system are fully charged and PV production exceeds local loads, an MPPT can no longer operate the panel at its maximum power point as the excess power has no load to absorb it. The MPPT must then shift the PV panel operating point away from the peak power point until production exactly matches demand.

I also get the impression from Wikipedia that the Buck converter accomplishes this and MPPT by controlling the ratio of input and output impedences (by changing its duty cycle).

Wikipedia "Buck Converter" wrote:
A buck converter can be used to maximize the power transfer through the use of impedance matching. An application of this is in a "maximum power point tracker" commonly used in photovoltaic systems.

The Wikipedia article provides a formula for this. By setting the impedance ratio via the Buck converters duty cycle, the controller can pick the MPP input impedence giving the max panel power.

I presume the output impedence will vary depending upon the batteries SOC and other loads on the system so the duty cycle will have to change to maintain the proper input impedence for MPP operation.

Anyway, more food for thought. Most of this is way over my head ...