This paper introduces the mathematical modeling of an advanced member of flexible ac transmission systems (FACTS) controller which is a unified power flow controller (UPFC). This model submitted the implementation of the device in conventional Newton–Raphson (NR) power flow algorithm; it is derived from two-voltage source represented and analyzed in detail. The model takes operational losses of UPFC into account so it represents a more robust and feasible alternative than other methods. Based on the proposed model a program in Matlab language has been written to extend conventional NR algorithm. A computer simulation study performed on IEEE 14-bus test system and IEEE 30-bus test system are presented to test the approach by locating the UPFC anywhere in a power system. The effect of UPFC allocation on power system operation has been investigated in detail and the power losses minimization of the power system with UPFC has been achieved using the proposed method by adjusting the location of UPFC with a proper adjustment of UPFC parameters.