Driving an N-Channel MOSFET H-Bridge from a voltage doubler
If you need to raise the voltage for your signal to trigger an N-channel MOSFET on the high-side of your bridge, you can use any isolating DC-DC converter to output 12VDC(isolated) &amp; tie the converter's output "GND" to the +240V of the line you're wanting to switch.

This places the +12V output 12V above the "virtual ground"of your +240VDC line, thus providing your 252V voltage for driving the N-MOSFET(s).