Stator flux active damping by optimal rotor current injection for grid tied doubly-fed induction generator

Doubly-fed induction generator (DFIG) tied with grid and controlled in the stator flux oriented reference frame is known to have poor damping due to the large time constant of the stator circuit. Therefore, the stator flux exhibits sustained oscillation subjected to any disturbances. In this paper, we propose a state feedback control method to actively damp the oscillation by injecting optimal amount of rotor current. The controller is further modified to simplify the implementation of the control and to minimize the effect of current injection on the power converter rating. The modified controller can be termed as a suboptimal controller. The performance of the designed controllers are verified through simulation of the simplified model of DFIG with an arbitrary initial stator flux perturbation. The required rotor current injections are observed in each of the cases of design. Effect of current injection by different controller on the converter rating is also explained. The suboptimal control is implemented to damp the stator flux oscillation in a DFIG, used in wave energy conversion system (WECS). In WECS, the stator flux oscillation appears due to the phase sequence switching of the DFIG. Simulation results show that the active damping control improves the damping of the system.