Basic control of unified power flow controller

A unified power flow controller (UPFC) is a typical FACTS device capable of instantaneous control of three power system parameters. This paper presents a basic control system which enables the UPFC to follow the changes in reference values of the active and reactive power supplied from the outer system controller. The analysis is based on the transformation of the three-phase power system to the rotating reference frame. As a step closer to a practical application of the UPFC, a modified control structure with a predictive control loop and precontrol signal for a DC-voltage control was designed. The new control system offers better stability and transient performance in comparison with the classical decoupled strategy, especially considering the harmonic distortion of the current being controlled. The derived basic control of the UPFC was tested with the NETOMAC program system.