A buck converter in series with your AC will work
Two (isolated) power sources, one AC, maybe with a transformer and a DC source connected in series.
* the DC source need to be able to source and sink current. (At least sink into a big capacitor)
* and the AC source need to be able withstand DC current...so a standard transformer will be critical.
Thanks for the replies
How can I implement the DC source can be able to source and sink current?