Three Dimensional Switching Table for Reducing Torque Ripple and Switching Frequency in Direct Torque Controlled Induction Motor Drives

To minimize the torque ripples in conventional direct torque controlled (DTC) induction motor drives, intermediate voltage space vectors (virtual voltage vectors) can be applied. These virtual voltage vectors are chosen based on the torque error magnitude within a four-level hysteresis band. Thus, the inverter is switched at most four times within the hysteresis band. This increases the average switching frequency of the drive compared to the conventional DTC scheme. In this paper, certain modifications in the switching of the virtual voltage vector are presented. This modification in switching pattern is based on the sign of the slope of the torque error and a novel three-dimensional switching table is also framed accordingly. The performance of the proposed DTC scheme is numerically investigated in MATLAB simulation environment and results are compared with both conventional DTC scheme.