Has anyone done much VFD design? From what I can tell, there are two ways to do it. Either run a H bridge directly from rectified mains (using inductors to filter out the high frequency) or run a H bridge from a buck converter that does the voltage variation so the H bridge merely has to reverse the current every half cycle. The second approach uses one more MOSFET but the 4 MOSFETs in the H bridge do not have to handle high frequency and can therefore be cheaper. It's also easier to design as the high side MOSFET drivers only have to handle low frequency.
Which design is better? Most designs use the H bridge running directly from the B+ supply but I have see one (RV refrigerator) that used a flyback converter for low voltage operation and a buck converter for high voltage operation. I'm not sure if the converters shape the waveform but I assume they do since there's no output inductor.