On Tuesday, July 5, 2011 2:55:30 PM UTC-7, Jon Elson wrote:
On 07/05/2011 01:45 PM, Spehro Pefhany wrote:
On Tue, 05 Jul 2011 10:52:22 -0700, Jim
wrote:

Spehro Pefhany wrote:

Will any commonly available 240V VFDs go up to 400Hz? Need around
7.5HP.

A VFD does NOT produce 240 V sine waves. It produces 400 V square waves
that are the equivalent to a MOTOR, ONLY! it will definitely fry
any electronics you connect to it!

So, feed threephase motor 1 from the VFD, feed two of the phase wires
to motor 2, which is shaft-coupled to motor 1. The third phase wire
on motor 2 is a sinewave output at 400 Hz. This is kinda like a rotary
converter, except it's the AC waveform smoothing you're really after.