Analysis of the Voltage Dip withstand of a Wind Turbine System connected to the Grid by Advanced Techniques

In the context of seeking new and alternative energy sources, wind energy is of significant importance due to its renewable and clean nature. However, the wind turbines based on DFIG are highly sensitive to grid disturbances, which negatively affect both the DFIG and its associated electronic control circuits. Therefore, this thesis presents an analysis based on voltage dips for a grid-connected wind turbine system. Initially, we studied the mathematical models of DFIG and its vector control using PI controller, and the wind turbine with its control using MPPT. Research has indicated that while PI controller is effective for linear systems with a consistent nature, it lacks robustness and efficiency in nonlinear systems characterized by variability and disturbances. To address this challenge, the Backstepping control approach has been suggested. This approach is particularly suitable for nonlinear systems due to its recursive structure. It employs a virtual control element based on the Lyapunov function to streamline the complexities of nonlinear control problems. Afterwards, we examined fuzzy control, which provides an approximate solution for nonlinear systems and reduces the noise generated by the system, in addition to enhancing robustness and stability. Despite the advantages offered by BSC and FLC, a hybrid control technology called FBSC has been proposed to combine them. This technique synthesizes the strengths of both BSC and FLC, aimed at providing an approximate solution for complex and uncertain nonlinear systems using a virtual fuzzy control element, guided by the Lyapunov function to simplify fuzzy parameters. This technique was applied to enhance the control of DFIG’s rotor. The enhancement lies in achieving lower ripples of stator active and reactive powers, reduced total harmonic distortion (THD) of the stator currents, and robustness against parameter variations. Subsequently, the DFIG was subjected to both symmetrical and asymmetrical voltage dips, which led to stator and rotor overcurrents. However, it has been shown that asymmetrical dips are more harmful than symmetrical dips due to the oscillations carried on the rotor currents, which correspond to a significant increase in THD, and high ripples of the stator active and reactive powers. To address this problem, a Dynamic Voltage Restorer (DVR) was proposed to restore the grid voltage, which provides results almost as good as before the dips occurred. In essence, the combination of optimized DFIG control and DVR provides a reliable and robust solution for maintaining energy quality and stability within power systems.