Stability enhancement of DFIG-based wind turbine system through linear quadratic regulator

This study proposes an optimal control scheme based on linear quadratic regulator (LQR) to control of the oscillatory behaviour of the doubly-fed induction generator (DFIG) connected to the grid and improve the stability. The control approach integrates a non-linear dynamic state estimation by means of unscented Kalman filter to estimate the unobservable internal states, to be used by the LQR. The only measurements required to achieve the control objective are terminal voltage and stator current of the DFIG which may have measurement-noise to some extent. The detailed model of the DFIG-based wind turbine with two-mass drive-train model has been described first and then its linearised state model has been obtained to identify the oscillatory modes, which have further been used to decide the weight matrices for LQR. The performance of the proposed LQR-based damping controller has been compared with the power system stabiliser incorporated with the DFIG. The efficacy of the proposed scheme of the DFIG has also been tested in WSCC 3-machine 9-bus power system by integrating the DFIG in it.