A flexible AC transmission system (FACTS) provides a structured method to augment the transmission capabilities of conventional electrical energy systems. It is intended to enhance controllability, reliability and transfer capability using power electronic equipment and control techniques. HVDC are high voltage direct current systems. Both systems complement each other, they each have their specific area of application, and they can work together, in a coordinated fashion, for example, to accommodate growing shares of renewable energy such as wind power, which needs to be transferred over long distances from generation sites to demand centres.