A hybrid approach in study of UPFC effects on the transient stability of

A hybrid approach in study of UPFC effects on the transient stability of multi machine power systems

Abstract
In this paper, a hybrid method on investigation of UPFC effects on transient stability of multi machine power system has been introduced. Based on the combination of output results of time domain simulation (TDS) and transient energy function (TEF) analysis, study of power system transient stability is converted to the study of transient stability of only one machine, so called critical machine. The effects of UPFC in three basic control mode namely in-phase voltage control (ivc), quadrature voltage control (qvc) and shunt compensation control (sh.c) on the transient stability margin and for various fault clearing times, has been studied. Based on acquired results, it can be seen that in-phase and quadrature voltage control have the most effects on the improvement of transient stability margin. Also, ivc is more robust than other control modes against increase of fault clearing time. The proposed method determines the critical machine based on the swing curves result from TDS, and then provides SM of the critical machine with trivial computation by use of machine speeds and inertia Constants. The method doesn’t need to include of UPFC description equation in to the transient energy function. The proposed method was successfully demonstrated on the 7-machine CIGRE test system

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