Variable Switching Sequence PWM Strategy of Dual Three-Phase Machine Drive for High-Frequency Current Harmonic Suppression

The circulating current harmonics are inherent disadvantages of dual three-phase machines, resulting in additional copper losses, severe current distortions, and high switching ripples. Traditional strategies offer many methods to suppress low-order current harmonics but pay little attention to the high-frequency harmonics and the performance improvement over one pulsewidth-modulation (PWM) cycle. Because of the ability of model predictive PWM (MPP) technique to predict real-time current ripples, this article proposes a variable switching sequence PWM (VSSPWM) strategy to optimize the current harmonic in a PWM period. The proposed method derives current ripples to predict real-time trajectories and root-mean-square (rms) values of current harmonics. By this means, VSSPWM can be implemented based on the enumeration and evaluation of all admissible switching sequence patterns. The cost function is designed to evaluate the rms current and select the optimal switching sequence. Simulation and experimental results have verified the effectiveness of the proposed strategy that VSSPWM can provide good high-frequency current harmonics suppression performance.