It can in theory be added to just about any type of battery controller, but with the proviso that any negative feedback around a control loop must be slow enough to be made stable.
A typical battery charger controller has two separate feedback loops.
The first control loop reduces the output power when the output current exceeds some set maximum (current limit). When in current limit, the output current will be fixed at maximum, and the output voltage will not be controlled, but will be somewhere below maximum.
The second control loop reduces the output power when the output voltage has reached some maximum (voltage regulation). The output voltage will be fixed at maximum, and the output current is not controlled, but will be somewhere below current limit.
Both the above control loops use output voltage and output current sensing to limit the respective values.
All this is pretty obvious and well known by all of us. Nothing new there....
For MPPT control, we need to add a third control loop. This control loop works in the same way as the others to reduce the output power of the controller, but by sensing the INPUT voltage to the controller, which is assumed to be the solar panel voltage.
The way this works, output power of the controller is reduced when the solar panel voltage tries to fall below the maximum MPPT solar voltage. Its actually trying to regulate the voltage coming out of the solar panels so that the panels can never be loaded down below the maximum power panel voltage.
You will find at sunrise the solar panel voltage will rapidly spring up to the maximum power voltage and sit at that voltage all day, or until the battery is fully charged. Only when the battery is fully charged can the solar panel voltage increase upward towards the full open circuit voltage.
What actually happens is the controller pulls as much power from the solar panels as is available, and no more.
On a cloudy day it may only be only a few watts, in full sun it could be hundreds of watts. It puts all of the available solar power into the battery until the battery is fully charged without overloading the panel.