Can any body has details available for various design technique of MV drives? can it be shared?

I know people that use a step down transformer to a 480 VAC VFD then step back up to motor. Vector drives still seem to perform well through the transformer. They say it saves money and the maintenance people like working with the low voltage. Probably would be limited to 600 hp/450 kW.

Dear Rohit,
There are various ways of MV Drive design.
Supply:
An extremely common version is the use of a suitable step down transformer ( MV or HV / 1.6KV 3 winding transformer) which feeds a 12 pulse diode bridge generating a DC Voltage of 4kV thereby making it possible to generate 3.3kV output to the motor. Same for 6.6kV.
A recent trend is to have direct 3.3kV fed to the drive eliminating the need for a input transformer.

Rectifier Section:
A second design is the type of front end. You can use multiwinding transformer and multi pulse diode network to reduce harmonics or use an Active Front End technique to facilitate regeneration and low harmonics.

Inverter Section:
This has remained almost constant with changes being mainly in software and method of control. Each company has stuck to their control method ( 3 Level, 5 Level, Multi Bridge etc) and their device ( IGCT, IGBT, HV-IGBT etc)

For small powers, a Step Down - 690VAC VFD - Step up solution is still offered, though I see this trend fading off.

Shibu