Sensorless control of doubly-fed induction generators in variable-speed wind turbine systems

This paper proposes a sensorless control strategy for doubly-fed induction generators (DFIGs) in variable-speed wind turbine systems (WTS). The proposed scheme uses an extended Kalman filter (EKF) for estimation of rotor speed and rotor position. Moreover, the EKF is used to estimate the mechanical torque of the generator to allow for maximum power point tracking control for wind speeds below the nominal wind speed. For EKF design, the nonlinear state space model of the DFIG is derived. The estimation and control performance of the proposed sensorless control method are illustrated by simulation results at low, high, and close to the synchronous speed. The designed EKF is robust to machine parameter variations within reasonable limits. Finally, the performances of the EKF and a model reference adaptive system (MRAS) observer are compared for time-varying wind speeds.