This paper describes the implementation of a new control approach for the Unified Poer Flow Controller (UPFC), which provides active filtering capabilities to this equipment, besides the functions of power flow control and voltage control, as originally proposed by L. Gyugyi [1,2]. The power circuit is made up from two PWM converters which share a common dc link without the need of dc power supplies. An integrated controller attends to both series and shunt converters of the UPFC. It is based on the theory of instantaneous active and reactive power defined in the α-β-0 reference frame [3,4]. A complete model of the new UPFC has been implemented in a digital simulator. Simulation results have confirmed that the new approach has higher performance than those UPFCs which use traditional definitions of powers in the controller.