Duty-Modulated Direct Torque Control Strategy Based on Efficient Voltage Vector Selection for Induction Motor Drives

The traditional duty-modulated direct torque control (DDTC) suffers from the current distortion and the increased torque ripple due to the improper utilization of zero-voltage vector. To solve the above problems, a novel DDTC strategy based on efficient voltage vector selection is proposed for induction motor (IM). On the basis of analyzing the duty cycle of voltage vector and the droop characteristic of the torque slope, the limited region of the flux droop and the negative influence of zero-voltage vector on the torque ripple are revealed. The proposed strategy redivides the intervals according to the torque increments of voltage vectors and the torque error. The deadbeat response of torque and the variation characteristic of flux are set as the optimization conditions, which generates an efficient selection mechanism for vector combinations. To reduce the current harmonics under the low speed, the proposed strategy retains the candidate vector combinations that can regulate the flux amplitude. At the high speed, the initial torque of voltage vector is ensured to be positive by utilizing the difference between the torque error and torque variation of zero-voltage vector, thereby effectively reducing torque ripple. Finally, the effectiveness of the proposed strategy is verified by experiments on a 2.2 kW IM drive platform.