solid state 3-phase converter?

[KD4CPL]

Has anyone actually tried a Variable Frequency Drive as a way of obtaining 3-phase for vintage high power transmitters?
VFD's are solid state devices that are normally used as motor controllers, and they are available as 220v 1-phase to 3-phase converters. BUT (big BUT) all the ones I have seen say DO NOT switch the load (which is exactly what you need to do in a transmitter). I'm also wary about xfmr heating from harmonics from these switching gadgets.

Any direct experience with transmitter applications - or a pointer to some gadget I've missed that woud be happy in the application - is greatly appreciated.

So far the only solution I have seen is a rotary converter (motor-generator) for 1-phase to 3-phase conversion.
cheers,
Nick K4NYW

[kb3ouk]

With a little creativeness, you could get one of those to work on a transmitter. The trick would be to switch from transmit to receive without removing the B+ from the finals. It can be done, the best way to go would be to cathode key the finals. If you've ever looked at the K1JJ 813sx813s schematic on AMWindow, that's what Tom did, by putting a relay in the center tap of the filament transformer. On receive the center tap is grounded through a 50k resistor, then on transmit it is shorted out by the relay.

[W2VW]

Like you say, switch the load = kaboom. Open the mains feed first then switch the load off. Maybe the DC bus capacitance within the VFD could be reduced.