Present day power systems are very complex and are relied upon to satisfy the developing requests of energy wherever required, with satisfactory quality and expenses. The financial and natural components require the area of generation at remote places. The rebuilding of energy utilities has expanded the vulnerabilities in framework activity. The administrative limitations on the extension of the transmission set-up has brought about diminishment of dependability edges and expanded the dangers of falling blackouts and power outages. This issue can be adequately handled by the presentation of high power electronic controllers for the direction of energy flows and voltages in AC transmission systems. This permits 'adaptable' task of AC transmission frameworks whereby the progressions can be obliged effortlessly without focusing on the framework. Power electronic based frameworks and other static hardware that give controllability of energy flow and voltage are named as FACTS controllers.