To reduce current requires impedance.
Linear regulator drops voltage and burns watts.
Switching regulator has an inductor; current ramps up over time, so switching on an off limits current (and relates to voltage conversion.)
PWM can't do either. So I don't believe it regulates current.
Max 45A array, it said.
Yes, it could measure current and PWM a calculated amount. But using temperature would be free, if it had temperature protection.
Most MPPT could take any size array. Even a battery (thousands of amps on tap.)
A PWM regulator works just like PWM-controlling motors or other types of loads. It slices up the incoming voltage really fast, and together with an output filter capacitor the practical result is a lower voltage on the output. For a given output load, different duty cycles result in different output voltages. To regulate output current, all the regulator has to do is set the output voltage to whatever results in the target current. This is done automatically through a feedback loop.