Modeling and control of unbalanced and distorted grid voltage of grid‐connected DFIG wind turbine. (10th March 2021) - Abo‐Khalil, Ahmed G.
Summary: This paper presents a mathematical modeling and current control of DFIG wind turbine system in the presence of unbalanced and harmonic distortions in the grid voltage. A proportional resonant (PR) current controller is modeled and implemented to reduce the impacts caused by the presence of double‐frequency, fifth and seventh harmonic components in the generator torque, active and reactive power and the grid active power to which the wind generation system is connected. To reduce the impacts of the presence of the harmonics and unbalanced voltage in the stator and grid active and reactive powers, the dq ‐axis current components of these harmonics are controlled separately in the rotor and grid side converters. The use of PR controllers represents the addition of a specific function that eliminates the negative sequence and harmonic components from the rotor current components which reduce the oscillations of the generator torque and grid active power. The performance of the proposed control algorithm is validated through experiments and evaluated during the grid disturbances. Abstract : This paper presents an improved control strategy for a doubly fed induction generator (DFIG) during unbalanced grid voltage condition. The proposed strategy was applied in both synchronization and grid connected condition. The synchronization process is carried by controlling the extracted positive and negative sequence components of the stator q ‐axis voltage to follow the grid q ‐axis voltage. To do so, the positive and negative sequence components of rotor d ‐axis current are controlled. By incrementing the rotor d ‐axis current, the stator EMF builds up and follows the grid voltage accurately. The stator frequency and the phase difference between the stator and grid voltage are compensated by adjusting the stator d ‐axis positive and negative voltage components to zero. After synchronization, the proposed control strategy focuses on regulating the average stator active power and reactive power control by controlling the positive components of q and d ‐axis currents, respectively. The second target is to minimize the generator torque ripple by controlling the rotor negative sequence components. In the same time, the grid side converter is controlled to minimize the grid power pulsations to reduce the impact of the unbalanced grid voltage. This study focuses in enhancing the dynamics of DFIG during the unbalanced grid voltage by proportional resonant (PR) current controllers. Experiments are carried out to validate the performance improvement by using the proposed method.