In principle it's easy, the isolation circuit is just a transformer. If you want to regulate the output voltage there may need to be a feed back path through another either transformer or through an opto-isolator.
Actually designing and building it is rather more difficult, I'm assuming that if you're using PWM you are probably using frequencies higher than 50 Hz, and you need to understand how this affects the design of the transformer.
I suggest you look in the university library for anything you can find on switch mode power supply design, you may well find information there on just this type of circuit. Also have a look at the e-books on this website.
Andy Millar CEng MIET CMgr MCMIhttp://www.linkedin.com/in/millarandy
"The aim of argument, or of discussion, should not be victory, but progress." Joseph Joubert