A Rotor-Current-Based Slip Angle Estimator for Grid-Connected Doubly Fed Induction Generator Requiring the Stator Inductance Only

This paper proposes, for variable-speed, gridconnected doubly fed induction generator (DFIG), a slip angle estimator, which is based on rotor current estimation in the synchronous reference frame. This estimator eliminates the need for a speed sensor or a rotor position encoder. The proposed estimator eliminates the need for an integrator to estimate the stator flux and, compared with other model-based estimators, requires the stator inductance only. The stator inductance is the inductance seen from the stator side, and it can be measured which allows using real machine parameter. In addition, this paper investigates the effect of inaccuracy in the stator inductance value on the accuracy of the proposed estimator. Several experiments, such as variable-speed operation, are carried out using a 1.1 kW DFIG to investigate the performance of the proposed estimator.