Voltage regulation and transient stability enhancement of a radial AC transmission system using UPFC

The unified power flow controller (UPFC) is a typical FACTS (flexible AC transmission systems) device that is capable of the instantaneous control of transmission line parameters. This paper presents the transient model and control system of UPFC. The presented control system enables the UPFC to following the exchanges of line active and reactive power reference values, regulating the DC link voltage and bus voltage. The presented control scheme has the fast dynamic response and therefore, improves the transient behavior of power system after a transient condition. The presented simulation results demonstrate that the presented control system acts properly in the steady and transient states. The presented control system of UPFC was simulated and tested with the PSCAD/EMTDC simulation program.