الفهرس 
Chapter One: IntroductionOnly 14 pages are availabe for public view
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Abstract
Voltage stability is a power system’s ability to maintain consistently acceptable voltages at all system buses under normal operating conditions and after being disturbed. Voltage instability arises primarily due to an imbalance in reactive capacity. The load ability of a bus in the power system depends on the system’s reactive power support A power system reaches voltage instability when there is a gradual and uncontrollable decrease in voltage due to an interruption, increased load demand or changed system condition. In this case, only by reducing the demand for reactive power or adding additional reactive power can the system be saved from voltage failure. In practice reactive power is compensated at the weakest bus. It can be improved by power reactive compensator which is called FACTS devices. FACTS devices have power flow management capabilities, reducing transmission losses, meeting voltage security constraints, and increasing system efficiency and safety. These are also very helpful in enhancing network reliability and the system’s complex behavior. All of these benefits of FACTS systems are primarily due to their rapid response to immediate disruptions and versatility under normal operating conditions.
In This Thesis, two controllers (PI and Fuzzy Logic Controllers) have been applied on two types of FACTS devices (STATCOM and UPFC) to control the quality of line power flow and improve the voltage profile at all buses of the network. The proposed controller controls the switching signal of STATCOM and UPFC converters to control the line power flow and improve the power quality of the grid. Harmony search (HS) algorithm optimization control technique has been used to optimize the parameters of the proposed controller which give the best results and achieve the stability under different operating conditions or during any disturbance in the system. A comparison between PI controller and FLC at STATCOM and UPFC are investigated over a vast running case with multiple disturbances and under different operating conditions. Also the effect of adding photovoltaic system to the network will be studied. MATLAB/Simulink and computer simulations are utilized to perform all the investigation studies with the proposed controllers. All the comparative analyses are displayed as a family of curves.