Improved sensorless EKF-based direct torque control at low speed with constant switching frequency controller

A sensorless extended Kalman filter (EKF) based direct torque control (DTC) with a constant switching frequency control (CSFC) of induction motor is proposed in this research work. By replacing the conventional 3-level hysteresis controller with a CSFC, the weakening of the stator flux at low speed is avoided and the flux regulation is improved; consequently the estimated speed at low speed is also improved. In this paper, the performance comparison between the conventional hysteresis comparator-based DTC drive (DTC-Hys) and a CSFC-based DTC (DTC-CSFC) is performed experimentally. It is shown that significant improvement in the estimated speed and drive performance at low speed is achieved with the DTC-CSFC.