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Subject: Electric motors, Induction.

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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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    A Precision Slip Frequency Detector
    (North Dakota State University, 1957) Horvik, Eivind
    The problem of measuring low values of slip of induction machines is present in most Electrical Engineering laboratories. A rather high accuracy of the determination is necessary for theoretical calculations of motor loading, using equivalent circuit techniques. Conventional methods of determining slip fail to give high accuracy at low values of slip. This thesis presents a solution to this problem by describing the design and construction of a precision slip frequency detector of nominal cost. The principle employed is that of beat frequency comparison of the rotor shaft speed against line frequency. The output of the beat frequency detector actuates a multivibrator-differentiating circuit, the output of which triggers an electro-mechanical counter. A photoelectric pickup device for determining shaft speed is also discussed.