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New approach based on structured singular value ([mu]-synthesis) was proposed for the robust decentralized unified power flow controller (UPFC) design. To achieve decentralization, using the Schauder fixed point theorem the synthesis and analysis of multi-input multi-output (MIMO) control system translated into a set of equivalent multi-input single-output (MISO) control system. Power systems similar to other industrial plants contain different kinds of uncertainties which should be considered in controller design procedure. For this reason, the idea of [mu]-synthesis technique being used for designing of UPFC controllers. The proposed [mu]-based controller had a decentralized scheme and advantage of a decentralized controller design reduction in the controller complexity and suitability for practical implementation. The effectiveness of the proposed control strategy evaluated under operating conditions on damping of low frequency oscillations in comparison with the classical controller to demonstrate its robust performance through nonlinear time simulation and some performance indices. Key words: Unified power flow controller, decentralized control, [mu]-synthesis, Flexible Ac Transmission Systems (FACTS), robust control, structured singular value, INTRODUCTION In recent years, the fast progress in the field of power electronics has opened new opportunities for the power industry via utilization of the controllable FACTS devices such as [...]

An industrial plant, such a power system, always contains parametric uncertainties. In the design of a controller the uncertainties have to be considered. Otherwise, if the real plant differs from the assumed plant model, a controller, designed based on classical controller design approaches, may not ensure the stability of the overall system. In this paper design of robust control for the UPFC controllers including power-flow and DC voltage regulator, using a [H.sub.[infinity]] loop-shaping design via a normalized coprime factorization approach, where loop-shape refers to magnitude of the loop transfer function L = GK as function of frequency is presented. As an example, we have designed a case for the system to compare the proposed method with a conventional method (classical P-I controller). AS the results of the linear and nonlinear simulations, the validity of the proposed method has been confirmed. Keywords: Unified Power Flow Controller (UPFC); Flexible AC Transmission Systems (FACTS); power system oscillation; [H.sub.[infinity]] loop-shaping, INTRODUCTION The Flexible AC Transmission Systems (FACTS) based on power electronics offer an opportunity to enhance controllability, stability, and power transfer capability of AC transmission systems . The Unified Power [...]