This paper is intended to study and compare the operation of two methods for estimating the position/ speed of the permanent magnet synchronous motor (PMSM) under sliding mode control. The first method is a model reference adaptive system (MRAS). The second method based on sliding mode observer (SMO). The stability condition of Sliding Mode Observer was verified using the Lyapunov method to make sure that the observer is stable in converging to the sliding mode plane. In this paper the performances of the proposed two algorithms are analyzed using SIMULINK/MATLAB. The simulations results are presented to verify the proposed sensorless control algorithms and can resolve the problem of load disturbance effects by simulations which verify that the two closed-loop control system is robust with respect to torque disturbance rejection. Keyword:Model reference adaptive MRAS PMSM Sensorless speed control Sliding mode control SMC Sliding mode observer SMO Copyright © 2017 Institute of Advanced Engineering and Science.All rights reserved. Corresponding Author:LARBI M'hamed, L2GEGI-Labotatory, University Ibn-Khaldoun of Tiaret, Algeria, 14000. Email: larbi_mh@yahoo.fr INTRODUCTIONThe permanent magnet synchronous motors attract the industrial world attention thanks to their superior advantages, for instance their higher efficiency, low inertia, high torque to current ratio. As an important application of PMSM, the motion control requires not only the accurate knowledge of rotor position for field orientation but also the information of rotor speed for closed-loop control; thus, position transducers such as optical encoders and resolvers are needed to be installed on the shaft [1], [2]. However, these sensors are expensive and very sensitive to environmental constraints such as vibration and temperature [3]. In order to overcome these problems, instead of using position sensors, a sensorless control method has been developed for control of the motor [4]. The basic principle of sensorless control is to deduce the rotor speed and position using various information and means, including direct calculation, parameter identification, condition estimation, indirect measuring and so on. The stator currents and voltages are generally used to calculate the information of speed and rotor position [5].The sliding mode control has been used to improve the robustness of the controller. during the sliding mode, this controller is insensitive to parameter variations and disturbances [6]. Therefore, many approaches for speed estimation have been investigated in the literature [7]-[8].This paper presents two methods for estimating the position and speed of a permanent magnet synchronous motor (PMSM) drive. The first method is Model Reference Adaptive System. It makes use of the redundancy of two machine models of different structures that estimate the same state variable (rotor speed) of different set of input variables [9]. The estimator that does not involve the quantity to be estimated is chosen as the reference model, and the other estima...