Wide area voltage sag control in transmission lines using modified UPFC

A modified conceptual structure of MUPFC for controlling the voltage sags in interconnected power systems is presented in this paper. For this purpose, the conventional UPFC is distributed through several series and one shunt converters. By this way, the higher frequency components are removed which only the 3th-order is remained. Also, by using single-phase series converters, better dynamic performances with proper reliability are provided. So, there are more redundancy possibilities through different operating conditions. The proposed single-phase series converters are floated from the ground which there is not required high-voltage protections equipment through transmission lines resulted in lower initial and operational costs compared to conventional UPFCs. Real-time ability of the proposed scheme is investigated through a 3-phase transmission line stressed by fault events in which by distributing the series converters through the line, the ability of MUPFC through time domain simulations is evaluated. Results present proper performances of the proposed controller scheme for voltage sags fast restoration with high damping ratio.