Control of a center-node unified power flow controller in transmission line applications

The modeling, analysis and linearizing control of a new device, the center-node unified power flow controller (C-UPFC), fitted at the midpoint of a transmission line is the theme of this paper. C-UPFC consists of a rectifier connected through an excitation transformer to the midpoint of the line and two inverters whose outputs are connected through series transformers with the transmission line. The output of the rectifier through a coupling DC capacitor sources the inverters. With six independent control variables, it is shown that both the source and load real and reactive powers can be controlled in addition to maintaining the transmission line midpoint and DC capacitor voltages at specified voltage magnitudes, ensuring complete system controllability and maximum power transfer. Performance curves and dynamic simulation results are given which show the control possibilities and the usefulness of the linearizing control scheme