Optimal Modulation for Suppression of Low-Order Torque Harmonics in Induction Motor Drives

Abstract

This paper proposes an optimal modulation strategy—in the form of optimized pulse patterns (OPPs)— for three-level converters driving medium-voltage induction machines. The proposed method minimizes, and, when physically possible, eliminates the low-order torque harmonics. Different symmetry properties of the pulse patterns are considered, and it is mathematically shown that relaxing the pattern symmetry provides additional degrees of freedom. This enables suppression of the targeted torque harmonics while keeping current harmonics low and close to those of conventional OPPs, used as a baseline. At the same time, the torque ripple produced by the proposed OPPs is comparable to-or, for some modulation indices, even lower than-that of the baseline OPPs. Numerical and experimental results based on a scaled-down, low-voltage drive system demonstrate the effectiveness of the proposed optimal modulation method.