Investigation and Suppression of Harmonics Interaction in High-Power PWM Current-Source Motor Drives

For high-power PWM current-source drive systems, the distortion of dc-link current cannot be ignored due to the low converter switching frequency and the relative small dc choke for reduced cost/weight. The distorted dc-link current may introduce interharmonics in the grid side and the motor side through the rectifier and the inverter, and may give rise to the system resonance at certain motor speeds. When resonance occurs, significant interharmonics are introduced in the drive system, which will degrade the grid-side power quality and produce the excessive torque ripples on the motor side. In this paper, the harmonics interaction in a high-power PWM current-source drive system is investigated, and a method for the system resonance estimation is proposed. Based on the estimation of resonance conditions, a dc-link virtual impedance-based control method is developed to mitigate the resonance resulted from the harmonics interaction. The investigation of harmonics interaction, the proposed resonance estimation method, and the dc-link virtual impedance-based suppression method are verified through both simulations and experiments.