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    MODELING, CONTROL AND ANALYSIS OF DOUBLY FED INDUCTION GENERATOR BASED ON WIND TURBINE SYSTEM
    (2022-06) Abdi Yonis, Samatar
    In the beginning of the 21st century, there was a growing interest in renewable energy sources particularly the wind energy for power generation. The researchers aimed to enhance the development of the design parameters for wind energy generations. However, doubly fed induction generator (DFIG) has been frequently used in wind turbines because of variable speed operations. DFIG has some merits such as, cost effectiveness, higher efficiency and reliability and the fact that it operates in both standalone and when it’s connected to the grid. Complete modeling, control and analysis of DFIG based on wind turbine system has been developed in this thesis. This thesis includes detailed developments of the wind turbine model such as, wind speed, aerodynamic system, drive train and generator model. Moreover, the dynamic model of DFIG in a rotating dq reference frame has been derived. Vector control approach of electrical machines is employed in the whole system. The complete system which consists of models and sub models are integrated and simulated using MATLAB/Simulink environment. Furthermore, to get the maximum output power from the wind turbine model, it’s necessary to design control strategy. This includes rotor side converter (RSC) control, proportional-integral (PI) control, indirect speed control and grid side converter (GSC) control. PI controller has been designed in order the current components follow their references and the current loops has been tuned until the desired value is obtained. The RSC controls torque, flux and active and reactive power. The indirect speed control which is used to drive the torque to follow the maximum power curve is designed at the RSC control. The function of GSC control is to maintain the DC bus voltage constant irrespective of the region of operation and it operates at a unit power factor. Moreover, the steady-state analysis for the most representative magnitudes of DFIG based wind turbine has been investigated in MATLAB. Correspondingly, the steady-state reactive power capability of DFIG is examined. Two case study is considered during steady-state analysis. In case 1, reactive stator power is set at zero which results the value of the maximum stator current to be lowered. In case 2, direct rotor current is set at zero which provides lower stator current, but the reactive power became high. Another objective of the study is to compare the performances of most representative magnitudes of DFIG based wind turbine using PI controller and the proposed method in terms of settling time. The simulated result demonstrates that the performances of the proposed method improves and it has less perturbations compared to the PI controller. Moreover, the proposed method gives strong robustness for controlling the system with variable parameters. The dynamic analysis of current loops behavior in a wind turbine based DFIG has been studied. It is summarized that, to follow properly the dynamic performances of DFIG, it is not required to reach the saturations for the voltage references. Besides, the behavior of the system under different grid fault conditions such as, symmetrical (balanced) and asymmetrical (unbalanced) voltage dips using crowbar protection are analyzed. The simulation result confirms the effectiveness of the proposed system.