Speed estimation methods for sensorless induction motor drives can be divided into two types. The
first is based on acquiring data about fundamental components of stator currents and voltages. The
second is based on the injection of high-frequency signals carried on stator voltages or currents.The
latter type allows stable operation around zero frequency,and low speeds, However, besides its
complexity, it increases the losses and torque ripple. The former type is difficult to operate at low
speeds. In this paper, a modified speed estimation method of the first type is proposed to improve the
performance of a sensorless vector controller. The proposed method is based on model reference
adaptive control (MRAC) that uses the stator current and rotor flux as state variables for estimating the
speed. In this method, the stator current error is represented as a function of first degree of the
estimated speed error. Therefore, the proposed method beside offering a four quadrant operation,
produces fast speed estimation and is robust to parameter variations. The superiority of the proposed
method is verified by simulation