If your voltage levels are unstable (ie: power stays on, but the particular voltage stage may differ quite a bit in the 220V typical), then I think that's the sort of state of affairs where by an AVR is useful. all lessons and interfaces during the superclass hierarchy (e.g. see https://edwinrsrpo.bloggosite.com/40691772/the-basic-principles-of-ups-uninterrupted-power-supply