Simulation of open and closed loop controlled UPFC systems

This paper proposes a new real and reactive power coordination controller for a unified power flow controller (UPFC). UPFC has two converters, one is series converter which controls the transmission line real or reactive power flow and other is the shunt converter which controls the bus voltage or shunt reactive power and DC link capacitor voltage. In steady state, the real power demand of the series converter is supplied by the shunt converter of the UPFC. The need for reactive power coordination controller for UPFC arises from the fact that excessive bus voltage (the bus to which the shunt converter is connected) excursions occur during reactive power transfers. A new reactive power coordination controller has been designed to limit excessive voltage excursions during reactive power transfers.