Sven,
Do you have a rotoverter? If so you could use with your transverter to
make it for usable AC power instead of only as a battery charger/
inverter source. I think this is what Hector was hinting at as to the
use of the third phase, use the RV with a small VFD to power correct VAR.
If one can use the RV as a synchronous condenser and convert all the
Transverter VAR to watts and save money without big caps! Only need to
voltage limit the windings with GDT's or varistor and zeners.
https://en.wikipedia.org/wiki/Synchronous_condenser