Improved MRAS observer and sensorless control of DFIG during network voltage unbalance

An improved control scheme for sensorless vector control of grid-connected doubly fed induction generators (DFIGs) is presented when the network voltage is unbalanced. The system is based on a rotor current model reference adaptive system (MRAS) in the stator stationary reference frame. The observed rotational speed and rotor position angle are employed for the reference frame transformations of rotor currents and voltages. The modified MRAS scheme is validated with improved control strategy introduced for a DFIG-based wind power generation system during network voltage unbalance. Experimental results obtained from a 1.5-kW DFIG prototype are presented and analyzed.