الفهرس 
Introduction
Flexible AC Transmission SystemOnly 14 pages are availabe for public view
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Abstract
In recent years, power demand has increased substantially while the expansion of power generation and transmission has been severely limited due to limited resources and environmental restrictions. As consequences, some transmission lines are heavily loaded and the system stability becomes a power transfer limiting factor. The power quality issue, especially voltage problem, is a vital concern in power system today. Voltage sag and voltage swell are considered as the most common type of power quality problems. Transmission networks of modern power systems are becoming increasingly stressed because of growing demand and restrictions on building new lines. One of the consequences of such stressed system is the threat of losing stability following a disturbance. Flexible Alternating Current Transmission Systems (FACTS) technology opens up new opportunities for controlling power and enhancing the usable capacity of present as well as new and upgraded lines. The Unified Power Flow Controller (UPFC) is a FACTS device which traditionally uses power electronics to enhance power flow, improve voltage sag and swell and improve transient stability. The UPFC can control active and reactive power flow in transmission line by means of injection controllable series voltage to the transmission line. The UPFC mitigates voltage problems at its terminal by controlling the amount of reactive power injected into or absorbed from power system. When system voltage is low, UPFC generates reactive power and when system voltage is high it absorbs reactive power. This thesis introduces a new vision of using UPFC that enhances and widens the range of controlling both active and reactive power flow, mitigates the voltage sag and swell and improves transient stability in a transmission grid while minimizing the harmonics and keeping the voltage in the specified limit. It also presents different UPFC controllers i.e. PI based UPFC and ANFIS based UPFC. A model of 110Mvar GTO based UPFC on a 500KV transmission system is simulated and its response is analyzed using MATLAB simulink toolbar as well as the fuzzy logic toolbar.