Endeshaw Solomon2026-03-092022-10-23https://etd.hu.edu.et/handle/123456789/1173Low frequency oscillations are an inevitable phenomena of power system. Integration of unified power flow controller (UPFC) and power system stabilizer (PSS) can considerably improve the stability by damping out of low frequency oscillation (LFO). This thesis had presented the damping out of LFO through optimal sizing of PSS and UPFC using an Antlion optimization (ALO) approach to improve the transfer capability of North West region of Ethiopian electric network from Tana Beles to Bahirdar 400kV line. The obtained results (minimal damping ratio, eigenvalues and time domain simulation) of the proposed ALO approach were compared with the results of conventional existing system, teaching learning based optimization (TLBO), particle swarm optimization (PSO) and genetic algorithm (GA) to investigate the efficiency of the proposed approach for various operating conditions of the considered electric network. In this thesis UPFC had been compared and selected from various flexible alternating current transmission system (FACTS) devices and filters to show the robustness of the proposed system. Further, the proposed ALO approach had improved the tuning time to estimate the key parameters of PSS and power oscillation damper (POD). Consequently, the settling time, controller gain and time constants of ALO to attain steady state system is small as compared with teaching learning based optimization, genetic algorithm and particle swarm. The nonlinear equation which describes the system had linearized and then placed in state space form to study and analyze the performance of the system by damping out of LFO problems. System eigenvalues obtained from ALO tuned UPFC-PSS and conventional existing system are compared to study the efficiency of the proposed method for various operating conditions. Besides, time domain simulation comparison proves the superiority of the proposed method over the existing system. Finally using PSS only improves the maximum overshoot by 42.2% and settling time of 63.7% but the proposed optimally sized UPFC-PSS employed with ALO method had improved the maximum overshoot by 56.06% and settling time by 78.7% as compared with conventional existing system (base case). Thus, this thesis addressed the mechanism regarding low frequency oscillation in the electric network by incorporating optimal sizing of PSS equipped with UPFC to the systemenEigenvaluesLFOminimum damping ratioALOPSSUPFCPODThesis