Should your voltage degrees are unstable (ie: power stays on, but the particular voltage amount varies lots from your 220V normal), then I think that's the sort of situation in which an AVR is helpful. For big power models, dynamic uninterruptible power supplies (DUPS) are sometimes applied. A synchronous motor/alternator https://kungfu69269.mybuzzblog.com/13509235/uninterruptible-power-supply-system-an-overview