Flexible AC Transmission Systems FACTS include unified power flow controllers (UPFC). Incorporation of a UPFC by a comprehensive Newton-Raphson power flow model into an existing MATLAB NewtonRaphson power flow algorithm is the subject of this paper. Unlike existing UPFC models available in open literature, this UPFC power flow model is modified to set control of active and reactive powers and voltage magnitude in any combination or to not control all of them. A set of analytical equations has been derived to provide better UPFC initial conditions. Their solution algorithm exhibits quadratic or near quadratic convergence characteristics. Based on this model, it is possible to estimate the UPFC control variables and the UPFC converters ratings. Also the effects of the UPFC coupling transformers impedances on the UPFC control variables and converters ratings are clarified and highlighted.