The objective of this project is to design robust speed control of Permanent Magnet Synchronous Motor (PMSM). The mathematical model of PMSM is highly non-linear with uncertainties and disturbances. The most obvious method is to estimate these disturbances and design robust controller to attenuate the effect of disturbances from output. In this project, the load torque which typically occurs as disturbance in servo system is estimated using Disturbance Observer (DO). Non-linear model of PMSM is linearized using Jacobean linearization around an operating point and state feedback controller with integral term is designed at this operating point. Novelty of the proposed method lies in the way DO is used to update this operating point, which is similar to gain scheduling approach. To extend this method for sensorless operation, sliding mode observer (SMO) is used with DO in cascade. The proposed scheme is validated using simulations on MATLAB/SIMULINK and experimental setup using TMS320F28027. The results show improved performance as compared to traditional methods over a wide range of speed.