This paper presents a new reducer-order observer for sensorless control of doubly fed induction generators (DFIGs), based on the Luenberger algorithm. Stable operation of the suggested observer is also considered in the design guidelines. Stator flux is selected as the state variable for the observer and its estimation error is used to correct the observer operation. The gain matrix of the proposed observer is calculated on the basis of flux error dynamics. The adaptation mechanism of the proposed observer is selected based on an estimation of rotor currents. A proportional integrator (PI) block is used in the structure of the adaptation mechanism for the transformation of its output signal. Furthermore, a fuzzy PI is designed to be applied to the observer structure, and a generalized study is carried out on the parameter estimation for the proposed observer. Simulation and practical results show the appropriate operation and speed tracking capability of the observer.