Low Pass Filter Design
It would appear that you need to put a series capacitor at the wire labeled AC PWM to block the DC power supply voltage from reaching the PWM pin on the MCV.  The size of the capacitor is determined by the frequency spectrum of your PWM signal since any size capacitor will block the DC.  You will also need an inductor at your power supply.  The inductor will allow the DC current to reach your circuit but will prevent the PWM signal from being shorted by the low impedance of your DC power supply.  The size of the inductor is determined again by the frequency spectrum of your PWM signal.  Its current carrying capacity, however, is determined by how much DC current your circuit is drawing.  You can recover your PCM signal at the load side of the inductor.