Control interactions of UPFC multi-control control functions - analysis

Interactions among multiple control functions of a UPFC (unified power flow controller) installed in a power system have been observed in power system simulation and have been reported by the authors previously (Wang, H.F., Int. J. Power and Energy Systems, no.4, p.591-600, 2001; Wang et al., IEEE Power Engineering Lett., vol.20, no.7, 2000). This paper presents new analytical results about these observed interactions and concludes that they are due to the control conflict between the series and shunt parts of the UPFC, which are connected through the internal common capacitor inside the UPFC. In order to predict the possible interactions among the multiple control functions of the UPFC, an interaction indicator is proposed which shows the direction and amount of active power flow through the internal link of the UPFC series and shunt parts at steady-state operation of the power system.