(Later ammendment: A rewound or low voltage AC Induction motor actually gets the most power with a controller that is about 6 times more powerful than the orginal motor.)
I have been scanning eBay for Variable Speed Drives for the past 3 months, and contacting many vendors for new prices. The new prices range from $3800 to nearly $8000 (AU$). Second hand drives were generally around AU$2000. On very rare occasions they have been snapped up at < $1000. I had pretty much decided to wait for a little while and purchase a Chinese VSD from INVT (I still might later on) when a Lenze brand drive came up on eBay. I had checked out TECO, Danfoss, Allen Bradley, Yaskawa, Siemens, Hitachi, Vacon, Durpulse, WEG and many more but had never heard of Lenze. BTW What I found out was provided a VSD had a 'DC bus' and was NOT an HVAC unit (Heating Lighting and Air Conditioning) then it was suitable. Size and weight start to become important factors. I did some quick research and discovered that, while this one was underrated for my purposes, it would "do for now". Lenze tended to do 'Servo' drives but this was a general purpose inverter. It's a Lenze 9327 rated at 16kW with capability of a further 160% for 60 seconds. That translates to 30 Amps continuous with peaks of 48 Amps for 60 seconds. This is about half what I want long term. What clinched the purchase was that the 16kW, 22kW and 30kW all came in the same enclosure size. There may be some avenue for upgrading it to 30kW. Anyway, it arrived yesterday. It's a little smashed around either from heavy handed shipping and not-quite perfect packaging, or just being cut out of a production line and thrown on the floor. I'm not too surprised - it was cheap.
I thought I'd better have a good look before 'firing' it up - it was rattling as well.
Here is the partially disassembled unit.
The clamps and rope are holding the plastic case together after super gluing. Regular plastic glue had no effect at all. I will reinforce the repaired parts of the case carefully with hot glue once I determine if it will stick.
This is the important part that was broken. The big electrolytic capacitors are not fastened down all that well and had caused the orange plastic internal mounting frame to break. The frame was warped out of shape and putting pressure on connectors that were not going to hold up for long.
You can see damage here to the side of the case. More than just cosmetic as it has to ensure no-one can be zapped.