Closed-form analytical characterisation of non-linear oscillations in power systems incorporating unified power flow controller

The unified power flow controller (UPFC) is a component that belongs to the flexible AC transmission systems devices family which has been deeply studied under different conditions of operation within the power network. One of its main applications is on damping oscillations in power systems. In this research, the UPFC non-linear interaction with the power system is studied through the use of modal series method, which is a kind of analytical tool that has the ability to characterise the non-linear effects because of small perturbations. The analysis is based on non-linear contribution of UPFC variables when controller parameters are varied; time-domain analysis and non-linear interaction indices are calculated in order to quantify the non-linear effect of UPFC connected to a synchronous machine-infinite busbar test system.