Direct Torque Controlled Induction Motor Drive with Reduced Torque Ripple

Direct torque control (DTC) drive allows direct and independent control of flux linkage and electromagnetic torque by the selection of optimum inverter switching modes. But the possibility of generation of only six non-zero voltage vectors results in the production of ripples in the electromagnetic torque and stator flux linkages. In the present paper a new torque ripple reduction strategy applicable for direct torque control is presented. This methodology involves the production of zero vectors along with a non-zero vector during a switching interval determined by the torque and flux errors. As a result 12 combinations of non-zero voltage vectors and 2 zero voltage vectors are possible. The basic DTC and the new method are simulated and the results are compared for their performances. For the same sampling frequency the new method gives much better results.