Analysis of a dq stator flux stabilization method for the doubly-fed induction generator

The doubly-fed induction generator (DFIG) is normally controlled with stator-flux orientation. Stator-voltage orientation can also be adopted. It is a poorly damped system with a natural frequency near the grid frequency. This leads to natural oscillations on the flux and torque and, for stator-flux orientation, in some cases, to instability. An unstable region is verified when fast rotor current controllers are used. Several techniques can be used for the damping and stabilization of this system. This paper presents a study of the DFIG with two active damping and stabilization loops acting at the same time on the rotor d q reference currents. Analytical and simulation results show that this active vector damping method is effective for small perturbations with origin on the stator and large perturbations with origin on the rotor leading to small damping currents. With high gain values on the damping loops, the system is more effective but increases dramatically the damping current. When voltage dips occur, the damping currents should be limited.