The closed loop control is a human twisting a knob until watts are max, by reading a watt meter. Repeat as necessary.
What I learned is that I thought I had a 2 way DC to DC converter, but this one is one way - a step-up converter. It is a boost converter and I needed a buck converter, and the type I was thinking is a combined buck boost.
I found a bunch of cheap ones but they are only 3 amps. I need to find one that is say 15 amps (10 minimum), that takes 16.5v as it's input, up to 23V (my Voc) and will put out say an adjustable 10.5-15.0 or more volts. Ideally it is modifiable to adjust the input voltage as well as the output voltage since stock the usually only let you control the output set point.
Meanwhile the up-voltage converter has a lot of cool uses as a constant voltage charger which is quite efficient. You can set it to a float voltage. You can set it to a charge or equalize voltage. I just used it to top charge one battery from another with no solar needed, and much less loss than say using an inverter with an AC charger.
Jim
