Utilization of a Reduced Switch-Count Topology in Regenerative Cascaded H-Bridge (CHB) Medium-Voltage Drives

This article employs a reduced switch-count topology in regenerative cascaded H-bridge (CHB) motor drives. Conventional regenerative CHB drive employs six-switch voltage source converters in the front end of each power cell to capture and utilize the regenerated energy. This solution is accompanied by a high number of switches, gate drives, and control circuits, especially when the number of levels increases. This causes high switching power losses, and increase in the cost, size, and weight of the overall system. This article utilizes a four-switch three-phase inverter active front end to reduce the switch count of the CHB power cell. The utilization of the four-switch inverter creates several challenges in terms of voltage imbalance on the capacitors and harmonics on the grid side. First, these challenges in medium-voltage operation are analyzed and addressed. Then, a new phase alternation connection method and two carrier phase-shifting techniques are proposed in this article to address the input current harmonics and comply with the grid connection standards. The performance of the proposed configuration and control techniques is analyzed theoretically and with simulation studies. The feasibility of the proposed configuration is validated experimentally on a scaled-down seven-level regenerative CHB drive.