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This paper demonstrates the feasibility of using multiple unified power flow controllers (UPFC) to real-time regulate a desired real and reactive power flow pattern through any two areas in a transmission network, to provide the best voltage profile in the system, and to achieve a quasiminimized total transmission loss. This is accomplished by a centralized optimal control scheme using evolutionary programming algorithms. In this paper the basic operating principles of a UPFC system including its control modes, internal converter structures, and models are briefly reviewed. The unique UPFC power flow control features regarding the real and reactive power control sensitivities and the effects of its locations on the controlled transmission line arc numerically investigated using the concept of P and Q control sensitivity indices. The effectiveness of the proposed control scheme is evaluated by analyzing numerical examples based on IEEE test systems. Simulation results show that the proposed power flow control concept using multiple UPFCs has a great application potential both in real-time power flow control and on the issues concerning power system economical operation and performance enhancement.