12-sector methodology of torque ripple reduction in a direct torque controlled induction motor drive

A Direct Torque Control (DTC) drive allows direct and independent control of flux linkage and electromagnetic torque by the selection of optimum inverter switching modes. Also transformation of coordinates and voltage decoupling are not required. However, the possible discrete inverter switching vectors cannot always generate exact stator voltage required, to obtain the demanded electromagnetic torque and stator flux linkages. This results in the production of ripples in the torque as well as flux waveforms. In the present paper a torque ripple reduction methodology is proposed. In this method the circular locus of flux phasor is divided into 12 sectors as compared to six sector divisions in conventional DTC method. The new method thus provides a total of 14 voltage vectors. For the same sampling interval 12 sector method gives improved results. The basic DTC scheme and the 12 sector method are simulated and compared for their performances.