Flexible AC transmission systems: technology for the future

A novel concept of power systems design and operation has been developed: flexible AC transmission systems (FACTS). FACTS technology can increase the loading on existing systems and assist in directing power flow in an interconnected network. The concept is based on the following view: systems are mechanically controlled for the most part, and the speed of response is slow. If control could be achieved at electronic speed with smart power electronic devices, great strides could be made in increasing loading of existing transmission systems and providing more flexible systems in the future where power flows could be controlled to facilitate business transactions among utilities. The first element in this work is to develop large semiconductors capable of handling power-class voltages and currents. A second area of research is now producing the smart devices. Controllers can be built to use the characteristics of these smart power electronic devices to perform functions such as controlling voltage, impedance, and phase angle