Power flow control and voltage stability limit: regulating transformer versus UPFC

Power flow through an AC transmission line can be controlled by injecting an adjustable compensating voltage in series with the line. This paper evaluates and compares the power flow control ranges of a simple system obtained by injecting an adjustable series compensating voltage produced by a regulating transformer and unified power flow controller. The static voltage stability limits of the system with a regulating transformer and unified power flow controller are also determined and compared. In evaluating the power flow control ranges and voltage stability limits, the transmission line of the system is modelled in four different ways. The results obtained for various line models are also compared.