AC drives (inverters) are dead simple to design and exctremely difficult to make work. You have all kinds of "special concerns" such as RPM gaps, power vs speed in combination with max power at various RPMs and loads.

I would say that you have 3 options
1) get it designed by someone that has designed a few already
2) buy it (they are cheap, check e.g. ABB)
3) burn some motors.

re 1) you will need to make an awful lot of units to compete with theose already out there.
re 2) if you try to build an even marginalaly fumctional inverter as a one/ten off the components will cost you more than an ABB inverter.
re 3) even with "big brand" inverters some brands (at that time) ocasionally burned a motor.

Just an example: each and every calculation will show that for 400V a 1400V IGBT is more than sufficient. That has proven false, using 1600V units is required or one of 25 units per year will blow.

Erik