ABSTRACT:This paper presents a new direct torque control (DTC) strategy for BLDC motor based on speed behaviour of PI and SMC based DTC of BLDC motor. In conventional direct torque controlled BLDC motor drive, there is usually undesired torque and flux ripple. So tuning PI parameters(Kp, Ki) are essential to DTC system to improve the performance of the system. PI controller is widely used in motor control system due to the simple control structure. In conventional PI controller, the performance of the motor may cause unexpected torque disturbances. To overcome the problems with PI controllers, in this paper, sliding mode controller is proposed to resolve the speed tracking problem for DTC of BLDC motor drive. The simulation results of DTC of BLDC motor drive with PI & SMC controllers are compared in the MATLAB/simulink environment.KEYWORDS:PI and SMC controllers,BLDC motor, DTC, MATLAB/simulink. I.INTRODUCTIONBLDC motors have many advantages over brushed DC motors and induction motors. A few of those have better speed versus torque characteristics, high dynamic response, high efficiency, long operating life, noiseless operation. The permanent magnet brushless dc motor is gaining popularity because of its usage in computers, aerospace, military and robots. The BLDC motor is inherently electronically controlled and requires rotor position informationfor proper communications of the current. The only drawback of conventional dc motors is that they need a commutator and brushes which are subjected to wear& tear and require regular maintenance. In BLDC motors the functions of brushes and commutator were implemented by position sensor and inverter. There are several methods to vary the speed of the BLDC motor over a wide range. The most modern technique is direct torque control method (DTC).The DTC offers many advantages like fast torque response, no need of coordinate transformation and less dependence on the rotor parameters. The conventional PI (Proportional, Integral) control method is widely used in motor control system due to the simple control structure and easiness of design. However tuning the parameters of PI controller is a difficult task. In conventional PI controller, the performance of the motor may cause unexpected torque disturbances. In order to resolves the speed tracking problem for DTC of BLDC motor drive various approaches have been suggested such as sliding mode controller (SMC) and Fuzzy controller, ANFIS controllers etc The proposed sliding mode controller(SMC) is one of the modern controller used to solve speed tracking problemsfor DTC of BLDC motor drive.This controller works irrespective of the parameter variations and load torque disturbances. The SMC method is an excellent control technique and a promising approach for solving the conventional PI controller parameters problem. Purpose of the present work:The objective of the present work is to provide an alternative approach to solve speed tracking problems for DTC of BLDC motor drive.This method uses the principle of Direct Torque Control...