>Can't you add a low pass filter (big inductor) at output?
>It will remove some high-frequency harmonics and make the
>wave more sinusoidal.

One trick to doing this is to use a suitable rated isolating transformer. We 
used to do this for computer installations in industrial areas. In our case 
a 5kVA transformer worked well for a load somewhere between 1/4 and 1/3 of 
the kVA rating.

But as the OP is in a 60Hz area, and wanting to deal with 50Hz, this option 
may not be available. 

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