This chapter proposes a novel approach for a generalized unified power flow controller (GUPFC) power flow model. By this modeling approach, an existing power system installed with GUPFCs is transformed to an equivalent augmented network without any GUPFC. It considers five major device limit constraints of the GUPFC, and they are listed as follows: The series-injected voltage magnitude VseLim, The line current through the series converter IseLim, The real power transfer through the dc link PDCLim, The shunt converter current IshLim and The bus voltage on line side of the series converter VmLim. Similar to the interline power flow controller (IPFC), a GUPFC addresses the problem of compensating multiple transmission lines simultaneously. However, a GUPFC incorporates a shunt converter in addition to the two or more series converters employed by an IPFC. The simplest GUPFC configuration possesses five degrees of freedom.