Dynamic Control of a DFIG Wind Power Generation System to Mitigate Unbalanced Grid Voltage

Abstract

This paper presents an improved control strategy for a doubly-fed induction generator (DFIG) during unbalanced grid voltage conditions. The proposed strategy was applied in both synchronization and grid-connected conditions. 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. This strategy can be accomplished by controlling the positive and negative sequence components of the rotor d-axis current. By perturbing 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 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. At 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 on enhancing the dynamics of DFIG during the unbalanced grid voltage by using Multivariable State Feedback (MSF) current controllers. Experiments are carried out to validate the performance improvement by using the proposed method. The simulation and experimental results showed superior performance of the proposed control strategy.

Wind Turbine Simulation and Control Using Squirrel-Cage Induction Generator for Dfig Wind Energy Conversion Systems

“…In this way, the structural design of the tower and wind turbine structures requires a smaller mechanical structure, and this results in the reduction of its total weight. In addition, the control of the pitch angle has the advantage, in the case of an emergency stop of the turbine, smoother response when compared to stopping the turbine using the brake torque [34][35][36][37]. This control is also used for the simple start of a wind turbine.…”

Modeling and control of unbalanced and distorted grid voltage of grid‐connected DFIG wind turbine

“…To minimize the effect of unbalanced grid voltage on the DFIG, different control techniques are discussed in several studies. The most discussed method is to use two sets of PI controllers to regulate the positive and negative components of the rotor currents 25,26 . A good performance in the steady‐state condition is achieved when PI controllers are used.…”

Reactive Current Constraints and Coordinated Control of DFIG’s RSC and GSC During Asymmetric Grid Condition

“…However, the DFIG-based wind turbine has been found to be quite sensitive to grid disturbance due to the direct connection between the stator windings and the weak power grid [5]. For instance, when an asymmetric grid dip occurs, the DFIG rotor current will get seriously distorted with associated pulsations emerging in the stator active and reactive powers, and the electromagnetic power as well [6]- [9], which may lead to the disconnection of the wind turbines from the faulty grid.…”

“…Aiming to enhance the uninterrupted operation ability of the DFIG-based wind turbines, various control methods have been proposed. In [9], a coordinated control of the rotor-and grid-side converters (RSC and GSC, respectively) during voltage unbalance is proposed, where the RSC is controlled to eliminate the torque pulsation at double supply frequency and the GSC is controlled to compensate the oscillation of the stator output active power. In [10]- [12], it had been found that adopting collaborative control of the RSC and GSC, multiple control targets can be achieved simultaneously.…”

“…In [10]- [12], it had been found that adopting collaborative control of the RSC and GSC, multiple control targets can be achieved simultaneously. It is noteworthy that in [9]- [12] the harmful torque pulsation is generally recognized to be a big concern in the control improvement of the DFIG system.…”