This is the conceptual block diagram of the solar mppt implemented without an mcu.
We start with a dc-dc converter, with voltage feedback taken from the input.
This will hold the panels at a fixed voltage.
There is a schematic of this implemented with an MC34063 earlier in this thread.
Functionally, the mppt uses the Perturb & Observe (P & O) hill climbing algorithm.
Starting with the square wave oscillator, through R4, to the voltage feedback node.
This is the perturb signal. This causes the pwm to increase & decrease slightly at a half second rate.
As the pwm goes up & down slightly, we measure the current going to the battery.
This is differentiated, to give us a signal which tells us if the current is increasing or decreasing.
We then compare this signal to our square wave signal, using an Xor gate.
There are 2 possible states.
1: Increasing and decreasing the pwm causes an increase & decrease in the output current (in phase)
2: Increasing and decreasing the pwm causes a decrease & increase in the output current (out of phase)
The output of the Xor gate is integrated, and used as the average control signal to the pwm.
So, when it's in phase, it drives the average control signal higher.
When it's out of phase, it drives the average control signal lower.
The outcome is that it hunts back & forth across the maximum power point.
In a practical implementation, to reduce component count, the differentiator & integrator are a dual op-amp (LM358)
and the square wave oscillator & Xor gate is a CD4046 phase locked loop.
Without this block diagram & explanation, the real circuit diagram wouldn't make a whole lot of sense.
Needless to say, the real circuit diagram will follow in due course.
Amanda
