The FACTSs (Flexible AC Transmission Systems) devices have all the capabilities to provide fast control of active and reactive power through a transmission line. The UPFC (Unified PowerFlow Controller) is a member of the FACTS family with very unique features. UPFC can control active and/or reactive power simultaneously or independently. This paper establishes the improved performance of ZSI (Z-Source Inverter) based UPFC over VSI (Voltage Source Inverter) based UPFC for power flow improvement. The simulation models developed in Matlab/Simulink have been used to show the improvement in active and reactive power flows in an interconnected network.