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Subject: Electric power system stability.

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    Damping Interarea Oscillations in Power Systems with DFIG
    (North Dakota State University, 2011) Thapa, Ravi Chandra
    With rapid depletion of fossil fuels and increasing environmental concerns, the trend to capture renewable energy, especially through wind energy resources, is increasing. The doubly fed induction generator (DFIG) is the most widely used generator for wind energy conversion because of its various advantages over other types of generators. In a DFIG, the rotor is fed through back to back converters via slip rings. The converters enable the generation control. This control property can be used to support reliable operation of a grid network system. Interarea oscillation has been a major factor in limiting power transfers in interconnected power systems. Poorly damped modes can trigger oscillatory instability, potentially leading to cascading blackouts in such systems. We consider a two-area system where DFIG based wind generation is integrated with conventional synchronous generators. A simple controller is proposed for the DFIG to improve damping of interarca oscillations. To support the proposition, case studies are conducted in Matlab/Simulink. The effectiveness of the proposed controller is then analyzed by eigenvalue analysis and verified with time domain simulation results. The results show that a properly tuned controller can increase the damping of dominant oscillatory mode by nearly 5% while improving the area transfer by about 200 MW of wind power. The results further show that with the proposed control strategy, damping of dominant oscillatory mode increased by more than 10%.
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    Phasor Measurement Unit Placements for Complete Observability using Linear-Time, Quadratic-Time, and Subquadratic-Time Heuristics
    (North Dakota State University, 2010) Saula, Oluwasijibomi
    A phasor measurement unit (PMU) is considered to have the potential to improve the efficiency of electric power systems by monitoring, control, and protection. Through measurements of all bus voltages, incoming and outgoing currents, and by subsequent calculation of all phase angles, employing PMUs on every substation in a power system will allow complete observation of a power system. However, having a PMU on every substation may not be economically feasible. Therefore, methodologies must be devised that can monitor a system with the minimum possible number of PMUs. In this paper, we propose six graph theoretical PMU placement heuristics. The proposed heuristics overcome the previous approaches in terms of scalability and execution time. The proposed heuristics are thoroughly compared and benchmarked using standard IEEE bus networks ranging from 14 to 300 buses, and a 2,383 bus system.