Optimization of Current Dynamic Performance and Torque Harmonic for Induction Motor Field-Weakening Control Under Hexagon Voltage Extension

The hexagon voltage extension can increase the maximum output torque of the induction motor in the field-weakening region. However, nonlinearity voltage and insufficient voltage margin under hexagon voltage operation can lead to torque harmonics and current dynamic performance degradation, respectively. Focusing on these two problems, this article has quantitatively analyzed the transient voltage vector and the voltage margin requirements when the current changes dynamically. The relation between the torque harmonic and the fundamental output torque is derived in multiple reference frames. Based on the analysis, both the dynamic problem and the harmonic problem under hexagon voltage extension are attributed to the nonadjustable voltage control issue. To solve both problems simultaneously, this article proposes the optimization structure for multistate voltage control. The current, speed, and voltage amplitude are used for distinguishing the motor operation states. In different states, the linear voltage, the hexagon voltage, and the adaptive voltage are employed for harmonic suppression, maximum torque improvement, and dynamic optimization, respectively. Finally, the comparative experimental results show that the proposed method is superior to the conventional method in terms of the current dynamic performance improvement and the torque harmonic suppression.