An Improved DTC Scheme For The AC Drives Based On Optimal Preview Control Technique

This paper presents an improved direct torque control (DTC) scheme for the induction motor (IM) drives. The proposed method is based on the optimal preview control theory and utilizes a synthesized control model for the IM incorporating the electromagnetic torque as a state variable. The derived optimal preview controller achieves direct control over the machine flux and torque via an optimized stator voltage command which is realized by use of a space vector pulse width modulated (SVPWM) inverter. An error system is constructed to enhance the robustness of the controlled drive against model mismatch and parameter variations. Further, the transient performance is improved by implementing a preview control part for few future values of the desired signal. In comparison with the conventional DTC technique, the presented method provides constant and high inverter switching frequency. This in turn will greatly mitigate the machine flux and torque ripples. Moreover, fast torque response is obtained with reasonable sampling rate and acceptable computation burden. The effectiveness of the proposed technique is verified by simulation studies