If your voltage levels are unstable (ie: power stays on, but the particular voltage level may differ a whole lot from your 220V typical), then I believe that's the sort of circumstance where an AVR is useful. This three-stage method lowers AC-aspect sound considerably,⁵ so it can be done there https://graphic-design94714.blogadvize.com/41249967/a-secret-weapon-for-uninterruptible-power-supply-symbol