A dual five-level inverter-fed induction motor drive with common-mode voltage elimination and dc-link capacitor voltage balancing using only the switching-state redundancy - Part II

The open-loop control scheme presented in part I of this paper for a dual five-level-inverter-fed induction motor (IM) drive with two dc power supplies maintains dc-link capacitor voltage balancing and common-mode voltage (CMV) elimination throughout the operating range of the drive. The operating limitation of the proposed open-loop control scheme to take corrective action toward the existing unbalance in the dc-link-capacitor voltages is also pointed out in part I of this. paper. As a solution to this, a simple closed-loop control scheme, which is based only on the switching-state redundancy, is proposed in this part of the paper. The proposed closed-loop control scheme not only prevents further unbalancing of capacitor voltages but also takes corrective actions to bring back the capacitor voltages in the balanced state. The proposed closed-loop scheme achieves dc-link capacitor voltage balancing and elimination of CMV together in the complete modulation range, including overmodulation of up to the 24-step operation. The proposed control scheme does not affect the output fundamental voltage generated by the inverter, as it effectively utilizes only the availability of redundant switching states of the inverter, and does not call for additional power circuit hardware. The scheme is presented with the simulation studies and experimentally verified with a 1.5-kW open-end winding IM drive.