Modelling and Controlling of UPFC for Power System Transient Studies

The unified power flow controller (UPFC) is a typical FACTS (Flexible AC Transmission Systems) device that is capable of 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 and bus voltage. The presented control scheme has the fast dynamic response and hence is adequate for improving transient behaviour of power system after transient conditions. The presented simulation results demonstrate that the presented control system acts properly in the steady and transient states. It is shown that by adding a supplementary control system to the shunt inverter control system, it is possible to balance line current too. The presented control and power system of UPFC was simulated and tested with the PSCAD/EMTDC simulation program.