Some of the fancier UPSs can change the frequency. You need a unit where the load is always powered by the inverter. I have a Liebert UPStation GXT that has a feature like that in the manual, but I've never tried it. You'd still need a transformer or autotransformer to step the output up to 220V.
An even more devious way is to take an audio oscillator set to 50 Hz and feed it into an audio amp that's rated at 100W or more (since your load will be about 90W). Then add a transformer to take the output from the amp and boost it to 220 V. For example, a transformer that's designed to take 220V to 24V would be about right. Obviously, the transformer would also have to be rated at 100W or better.
Ed