The holy grail of solar charge controllers is the maximum power point tracker (MPPT). How easy would it be to design one that’s both cheap and efficient?
The PWM controller is pretty much finished now, so we’ll use it as a building block and add on MPPT functionality. The sketch shows a few components added to the PWM controller block diagram; a capacitor across the solar panel input, an inductor in line with the battery connection and a Schottky diode to ground.
These additional components would have very little effect at the PWM controller’s switching frequency of around 100Hz, but increase that frequency into the tens of kiloHertz range and the circuit would start to behave as a switched-mode DC-DC buck converter. It should be possible to hold the solar panel input at a different voltage to the battery output.
What about maximum power? How do we measure both the voltage and current from the solar panel. Well, we don’t. We just assume that at maximum solar panel power, we’ll get maximum charge current flowing into the battery. We’ll simply look for maximum battery voltage as we tinker with the PWM duty cycle (otherwise known as peturb and observe).
Just one caveat. I have absolutely no idea if this will work, but I’m keen to give it a try!