When your voltage ranges are unstable (ie: power stays on, but the actual voltage level varies lots from your 220V typical), then I feel that's the sort of circumstance exactly where an AVR is helpful. For large power models, dynamic uninterruptible power supplies (DUPS) are sometimes employed. A synchronous motor/alternator https://johnny03pr9.blogripley.com/34478645/new-step-by-step-map-for-uninterruptible-power-supply-definition