Paul,
etischer's AC controller MOD thread on DIYElectriCar is a great read
though he has taken an existing VFD and modified it. He covers a lot
of important issues and you will find it interesting.
I have a DC servo driver that might help with your experimenting
that I can send to you. PM your address and I'll send you
a device that includes a Eupec 50a 1200v IGBT module
and some other parts.
IGBT's are good if you are going to run high voltage
but you will want to be sure to saturate the gate
when you drive it, and be sure it is shut off (negative voltage is best)
when the drive pulse is done. They are power monsters
when saturated but they are quite weak in the linear region.
For example, this device will easily handle 25amps
when fully driven into saturation, but will not handle
.5 amp if it is in the half on-half off linear region for very long,
and we're talking ms here.
here is a link to the device and there is a datasheet at this site too.
BSM50GD120DN2-E3226 Eupec/Infineon IGBT Modules
If this link doesn't work, look at Mouser.com and search for
BSM50GD120DN2-E3226
There is a current sensor in it and a pair of current transformers
if you ever want measure the current in a switched section.
Good Luck with your new controller!
Mark