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Grid impedance estimation based adaptive controller design for back-to-back wind turbine power converters for stable operation in distorted and weak grid

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2019
Temiz, Hakan
This thesis involves grid impedance estimation based adaptive controller design for back-to-back wind turbine power converters for stable operation in distorted and weak grid. The study focuses on the low frequency harmonic elimination of injected current to the grid under distorted grid conditions and maintaining system stability under wide range of grid impedance values for Voltage Source Inverters (VSIs) connected to the grid via LCL filter. To eliminate 5th and 7th harmonics of the injected current, a current controller with harmonic compensator is developed on the grid side controller. The system stability is evaluated by means of several control methods and ensured by adjusting the parameters of Phase Locked Loop (PLL) based on real-time estimated grid impedance. The control design is analyzed by detailed computer simulations. Obtained results are verified by laboratory experiments with a 300 kW wind turbine system which consists of squirrel cage induction generator, IGBT based back-to-back converter and LCL filter. Different operating conditions are considered to provide a through performance evaluation of the designed system.