Perhaps you might try explaining exactly what you're trying to do?, I don't know about anyone else, but I'm pretty confused!.
I suspect you're confusing yourself (and us) with what you mean by PWM?.
Very basically there are two types:
1) Speed control - you have a pot controlling either frequency or duty, this adjusts the amount of power to the motor, and thus the speed.
2) Power supply - there is feedback from the output that regulates the PWM (again either frequency or duty), to maintain a constant output.