So now I have got hold of a big combination woodworking machine, it has 3.8kw motors in so will be looking at 5.5kw VFDs.

One thing I have spotted in the wiring and installation diagrams is that it uses a Neutral to run the contactors (via an isolation transformer I think)

I am assuming this will be an issue with a VFD.

I have a 2.2kw rotary converter on my lathe and this has a neutral provided for exactly this reason.