Improved speed and current controllers for the Doubly Fed Induction Generator for wind power systems

In this work, improvements to the vector control loops of a double fed induction generator (DFIG) are discussed, the first is the addition of anti-windup algorithms at the speed controller, which allows to limit the torque and its associated currents, without losing controllability of the system while reducing mechanical stress at the shaft when performing speed changes in systems with high moment of inertia. The second improvement intends to mitigate the effects produced by unbalanced grid voltages, where the machine currents and torque are strongly impacted by such unbalance. When analyzed at the synchronous reference frame (dq) the unbalance appears as a ripple with a frequency of 2ωs, such imbalance can be mitigated by adding resonant controllers at the (dq) components of the current control loops of a vector control scheme. The control of the DFIG is realized by connecting a drive to the rotor side, instead of the stator, this work presents the results when these controllers are used in the DFIG. A simplified PI+Resonant control structure is included, as well the tunning methods.