An Approach to Embed Power Flow Control Model of UPFC into PSASP Based on User Program Interface Function

The unified power flow controller (UPFC) is one of the most promising flexible AC transmission systems (FACTS) devices for the power flow control. The main objective of power flow control for UPFC is to improve the power flow distribution and increase the transmission capacity over the existing transmission corridor or line. This paper presents a practical engineering methodology of embedding the power flow control model of UPFC into the commercial software -- power system analysis software package (PSASP) based on its user program interface (UPI) function. In the proposed methodology, the interface currents of UPFC series side and UPFC shunt side between the UPFC device and the network are used to control the transmission line power flow and UPFC bus voltage, respectively. In UPFC series side, the current of UPFC series branch is calculated from the target equation of the power flow in the controlled line. In UPFC shunt side, the decoupling control between the active power and reactive power is implemented and the reactive current of UPFC shunt side is used to control the bus voltage. In this study, simulations are performed on a typical two-area power system and a practical 496-bus power system and simulation results show that the proposed methodology can be efficiently applied to the engineering research and analysis of the real power grid with UPFC with good convergence and with only one control parameter needed to be prescribed.