Sensorless speed estimation of induction motor in a direct torque control system

Abstract

Fast and robust torque control in a very wide range of speed is very needed by various industrial AC drive applications. Therefore, since 1986 [1], direct torque control (DTC) has been introduced to satisfy this desire. In order to achieve more economical control, conventional speed sensor has been replacing by sensorless speed estimation. The sensorless schemes are used to improve reliability and decrease maintenance requirements. In this paper, concerned sensorless techniques of induction machine controlled by DTC algorithm are open-loop estimators and MRAS schemes [2], [3]. To demonstrate clearly the advantages and disadvantages between two kinds of sensorless techniques, obtained simulation results are compared. By enhancing speed estimation, the pure integrator is replaced by a low-pass filter to avoid DC drift and saturation problems [2].