Improving start-up operation of sensorless DTC of induction machines using simple flux regulation

This paper presents a direct torque control drive system utilizing constant switching frequency controller (CSFC) with EKF based speed estimation. By employing CSFC instead of the conventional hysteresis controller, the torque ripple is reduced and constant switching frequency is achieved, and more importantly, the simple structure of DTC without any modification to the look-up table is maintained. The main contribution to the use of CSFC is on the improvement of speed estimation at start-up and low speed operations. This is accomplished due to the improvement in the stator flux regulation. The experimental results of the proposed system showed a significant improvement in speed and torque estimations at very low and zero speed and are comparable to a more complex implementation of DTC.