A robust control method to improve the performance of a unified power flowcontroller

The unified power flow controller (UPFC) modeled in synchronous reference f rame is investigated for the control of power flow in a transmission system . An ac voltage vector generated by a GTO-based inverter is injected in ser ies with the phase voltage in the transmission line to control real and rea ctive power flow. A robust H-infinity controller is proposed to regulate li ne currents in both the shunt and series inverters of the UPFC. The control ler ensures robust performance and internal stability of the UPFC against p ower system disturbances and unstructured parameter variations. Conventiona l PI control system performance is compared with that based on the proposed scheme to highlight excellent robustness features in the new scheme. (C) 2 000 Elsevier Science S.A. All rights reserved.