Control and analysis of a unified power flow controller

This paper presents a control scheme and comprehensive analysis for a UPFC (unified power flow controller), on the basis of theory, computer simulation and experiment. This developed theoretical analysis reveals that a conventional power-feedback control scheme makes the UPFC induce power swings in transient states. The conventional control scheme has no capability of damping power swings, so the time constant of damping is independent of active and reactive power feedback gains integrated in its control circuit. This paper proposes a generalized control scheme which is characterized by successfully damping power swings in transient states. Experimental results obtained from a 10 kVA laboratory setup agree well with both analytical and simulated results. Moreover, it is shown that the proposed control scheme is viable and effective in damping of power swings in transient states