Browsing by Author "FSAHA MEBRAHTU"

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    ENHANCING LOW VOLTAGE RIDE THROUGH CAPABILITY OF DFIG BASED WIND TURBINE: A CASE STUDY OF ADAMA-II WIND TURBINE
    (Hawassa University, 2019-08-18) FSAHA MEBRAHTU
    Doubly fed induction generators (DFIG) based wind turbines (WT) are major sources of energy generation around the world. One of such energy source is wind generation, which is very much popular now days. It utilizes doubly fed induction generator (DFIG) to generate electricity in generation mode. But sometimes wind turbines are disconnected from the power system in the event of grid faults. To avoid grid instability as well as to ensure the secure and reliable operation of the power systems, all wind turbines must stay connected with the grid during faults and capable to ensure the operation of the utility grid side during voltage sags in the event of a fault that is performed by analyzing the low voltage ride through (LVRT) capability of DFIG based wind turbines.. DFIG is very sensitive to any grid disturbances, if a severe voltage dip occurred due to grid fault, high currents will pass through stator and rotor windings and also a very high DC voltage would be induced in converter circuit, which may lead to damage the converter circuit and the DFIG windings. A crowbar protections system is essential to avoid the disconnection of the doubly fed induction wind generators from the network during faults and to protect the DFIG from the dangerous effects of the electrical fault. Accordingly, Ethiopia have been started to expand its energy generation by installing renewable energy source like wind farm. Presently, Ethiopia has installed wind farms like Ashegoda, Adama-I and Adama-II. The Adama-II wind farm project has 153 MW with 102 units, each of with generation capacity of 1.5 MW. This work focused on the improvement of low voltage ride through capability (LVRT) of Adama-II wind turbines. In this thesis a crowbar protection system is used to improve the power system fault ride through capability of DFIG of Adama-II. During the symmetrical fault using crowbar protection the value of crowbar current at time three 3 seconds is overshoot to 3000 A and it will reduce to the original condition after 100 ms. Also the value of stator voltage, stator flux during faulty and symmetrical conditions before the fault and after are the same, but during the voltage dip the stator flux is decreased and the stator voltage is also reduced. The dynamic behavior of DFIG under normal and various grid fault conditions are simulated and analyzed to provide the recommendations. MATLAB/Simulink software is utilized for the development of proposed system