This paper proposes a simple but effective method to reduce the torque ripple for direct torque control (DTC) of induction motor drives. The proposed DTC provides a global minimum torque ripple, which satisfies the root-mean-square (rms) criteria of torque ripple. Such a global minimum torque ripple DTC has not been derived before. The proposed global minimum torque ripple DTC is a two-step design. The first step drives the torque error to zero at the end of the control period. Then, the second step reduces the torque bias and rms ripple by modifying the asymmetry switching patterns of the applied voltage vectors of the first step into symmetry ones. Theoretical analysis is provided to show that the torque ripple of the proposed DTC is a global minimum rms ripple. Furthermore, to verify the effectiveness of this study, a DSP-based experimental induction motor DTC drive system is built. Simulation and experimental results verify that the torque ripple performance has been improved.
