That amount of energy implyes in a non elementar design.
I developed a 3KVA UPS and a lot of parameters must be monitored ( IacIN / IacOUT / Ibat / VacIN / VacOUT ).
The easiest, quickest and cheapest solution is to use a motor coupled to a generator such that you have 220v AC 50HZ driving the motor and both 220v AC 60 Hz or 110v AC 60 Hz coming out of the generator - some makers even incorporate spped control into these to keep the o/p freq more constant under load changes...
Regards, Orson Cart.