Date of Award

May 2020

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Electrical Engineering and Computer Science


Sara Eftekharnejad

Second Advisor

Prasanta K. Ghosh


Power Systems, Steady-State Stability, Uncertainty Modeling of Wind Power, Voltage Stability Index, Wind Power Generation, Wind Power Integration

Subject Categories



To reduce greenhouse gas emissions, higher penetration levels of renewable energy resources are added to existing power grids. Among them, wind energy resources are becoming a major source of electricity generation. However, wind energy production has a critical downside: intermittency. The intermittent nature of wind energy in combination with the load demand uncertainties, make it difficult to maintain power system stability and reliability. In addition, the uncertainty and variability of wind power generation (WPG) forces power utilities to retain higher levels of spinning reserves (SRs) to maintain power balance in the system. While necessary to ensure grid reliability, the utilization of those reserves often leads to an increase in operating costs of the power system.

To ensure the continuous operation of reliable and economically efficient power systems, system operators and planners need to study the impact of WPGs on bulk power systems and determine the best ways to manage their variability. Such studies require efficient and effective probabilistic models characterizing the variable nature of wind power. Therefore, this dissertation develops new methodologies for modeling the uncertainty and variability of WPG. The developed methods are combined with stability indices to form analytical tools for analyzing the impact of increased penetration of wind energy on power system steady-state stability. The case study results show that the developed methods simulate real-world wind power scenarios, which lead to an accurate assessment of the impact of wind generation uncertainty on power systems.

With large-scale adoption of renewable energy, a significant amount of conventional generation units could be replaced with wind energy resources. The best way to use the variable WPG and the remaining conventional generation resources, for continuous balance between load and generation, remains to be determined. Within this context, this dissertation investigates the problem of optimal substitution of conventional generation units by wind-powered generators, while considering the variability of WPG and the uncertainties of energy demand. The goal is to ensure that during unplanned wind power unavailability, the system has the ability to meet the load demand, and maintain steady acceptable voltage levels in the grid. A two-stage solution methodology is proposed to the problem in consideration. The first stage determines the best candidates, among conventional generator (CG) resources, for retirement and replacement by WPG resources. The best candidates for wind replacement are selected such that the adverse impacts of wind power intermittency on system stability and reliability are minimized. In the second stage, the expected amount of wind generation to be added at each retired CG bus is determined. The simulation results show that the developed method facilitates the integration of high wind energy with a reduced need for additional spinning reserves in the system.


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