Power Quality Improvement in a Speed Sensorless Stand-alone DFIG Feeding General Unbalanced Non-linear Loads

This paper reports the performance of a speed sensorless stand-alone Variable Speed Constant Frequency (VSCF) Doubly Fed Induction Generator (DFIG) capable of supplying all types of loads. The proposed method maintains the Total Harmonic Distortion (THD) of the machine current and the load voltage within acceptable limits. In contrast to previously proposed methods, in this paper, the stator side converter supplies the unbalanced and harmonic component of the load current to eliminate the machine torque pulsation. The zero sequence component of the load current is compensated using a delta connected winding in a three winding transformer. A reactive power based model reference adaptive system (Q-MRAS) is used for the slip speed estimation and hence elimination of the speed sensor. The effectiveness of the proposed control scheme is verified by a real time digital simulator.