Application of UPFC to Enhance Transient Stability Limit

It has been reported that the simplest and most practical mode of operation of a unified power flow controller (UPFC) is the perpendicular voltage control mode. This paper investigates the improvement of transient stability limit of a simple power system with the help of a UPFC operated in perpendicular voltage control mode. All the equations required for this purpose are systematically derived. The same equations can also be used to represent a static synchronous compensator (STATCOM) or a static synchronous series compensator (SSSC) by setting some of the control parameters of the UPFC to zero. A combination of full and continuous controls is then used to maximize the first swing stability limit of a system in the presence of a UPFC, STATCOM and SSSC. The effectiveness of the above technique of improving the stability limit is then tested on a single- machine infinite bus system and the results found for various operations of the UPFC are also compared.