الفهرس 
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Abstract
Voltage stability is a long-standing and critical issue in power systems. It can be defined as ‘‘the ability of a power system to maintain steady voltages at all buses in the system after being subjected to a disturbance from a given initial operating condition’’. This thesis aims to address the voltage stability studies from different points of view. The voltage stability can be analyzed by many methodologies which may fundamentally be classified as dynamic analysis and static analysis.
from the dynamic analysis point of view, the voltage of a conventional generator and a renewable energy resource is regulated using the PID controller. A comparison between different optimization techniques to tune the controller gains has been studied to find out which is the best technique. The objective of these optimization techniques is to minimize the generator’s output voltage error and to improve the dynamic performance. These optimization techniques are Flower pollination algorithm (FPA), Teaching–learning based optimization (TLBO) algorithm, Harmony Search optimization algorithm (HS), and Local Unimodal Sampling (LUS). The result of the comparison shows that TLBO is the most suitable technique for this study.
from the static analysis point of view, the voltage of a 69-bus radial distribution system is regulated by allocating DGs at the system’s busses. DGs are small scale generating units which can exist at the distribution systems. They are most probably renewable energy resources. They are also the reason for the emergence of the concept of microgrids that make up the main electrical network. An optimization technique is used to select the optimal size and location of the DG at the system under study to improve its voltage profile. Various cases have been studied by changing the constraints for the optimization technique. These constraints are related to the maximum size of the DGs and their number. It has been found that the size of the added DGs is more effective than their number for this system.
So the thesis consists of six chapters: Introduction, which gives an overview about voltage stability in Microgrids and how it is studied in this thesis, Literature Survey, which is about voltage stability in power system, reasons for the global trend towards renewable energy and its benefits to the world, explanation of the meaning of the DGs, the appearance of the word microgrid and its definition, Voltage Regulation For Classic Generation, at which the PID controller used for minimizing the steady state error of the conventional generator’s output voltage is studied and a comparison between the chosen optimization techniques is made, Voltage Regulation For Renewable Energy Resources, at which the PID controller used for minimizing the steady state error of the PV system’s output voltage is studied, Optimal Allocation For Distributed Generation, at which the 69-bus, 12.66 kV radial distribution system is studied and how to improve its voltage profile by connecting DGs to its busses, and Conclusion, which gives a summary of extracted conclusions and the future work.