A unified power flow controller (UPFC) is an advanced member of the group of flexible AC transmission systems (FACTS). This paper is focused on the steady-state modeling of UPFC for the implementation of the device in the conventional Newton-Raphson (NR) power flow algorithm and in a power system analysis software package (PSASP). The model, derived from two-voltage source representation, is presented and analyzed in detail. The model represents a more robust and feasible alternative to others, because it is able to take operational losses of UPFC into account. A program in Fortran-77 language has been written in order to extend the conventional NR algorithm based on the proposed model. The model has also been adapted into PSASP by means of a user-defined modeling technique. Different computer simulation studies performed on IEEE 14-bus and IEEE 30-bus test systems are presented to test and compare the two approaches. A robust and reliable convergence of the power flow studies is guaranteed by implementing the two approaches with high convergence speeds. UPFC can be theoretically located anywhere along a transmission line. In this respect, the effects of UPFC allocation on power system steady-state operation have also been investigated in detail.