What are the techniques in voltage stability?

This question may be answered in so many ways beacaause the question seems to be broad. hoever we can start this way; If you wantr o stabilise ac voltage then use a automatic volatge regulator. there are so many cicuits yu chose from elctronics books if you want to stabilise direct current, there are circuits avilable. if you undertstand electronics and have basic knowledge building/assembling simple circuits, you can make your own voltage regulator to whatever voltage level you want.there are semi integrated circuits (ic) that are designed to regulate a specific voltage level or adjustable voltage regulators you can buy.