A New Switch-Count Reduction Configuration and New Control Strategies for Regenerative Cascaded H-Bridge Medium Voltage Motor Drives

Abstract

Cascaded H-bridge (CHB) multilevel inverters have significant popularity with motor drives applications due to their modularity, scalability, and reliability. Typical CHB inverters employ diode rectifiers that allow unidirectional power flow from the grid to the load. To capture and utilize the regenerated energy in regenerative applications, regenerative CHB drives were introduced with two-level voltage source converters in the front end to allow bidirectional energy flow. This solution is accompanied by challenges of high number of switches and control circuits, high switching power losses, and massive dimensions. Recently, developing more economic versions of regenerative cascaded H-bridge drives has become one of the hottest topics in power electronics research. In this thesis work, two solutions are proposed for more energy efficient and economic regenerative CHB drives. The first solution is a proposed power cell configuration that reduces the number of switches per cell by two. Additionally, phase alternation connection method and carrier phase-shifting techniques are introduced to address the challenges of the presented configuration. The switch-count reduction reduces the system’s complexity, switches’ cost, and footprint. The second proposed solution is a new controller to operate the front-end converters as fundamental frequency ends (FFEs). The proposed controller is employed in both the conventional regenerative cascaded H-bridge and the proposed reduced switch-count configuration. This solution minimizes the switching power losses, and results in more compact and economic design, with higher DC-link utilization. Theoretical analysis and simulation studies of both proposed solutions show promising performance and capability to be applied as energy-efficient and cost effective regenerative CHB motor drives. Experimental validation of the proposed reduced switch-count configuration is presented for STATCOM operation of a scaled-down 7-Level regenerative CHB drive system. The future work of this thesis includes experimental validation of the proposed FFE controller, and operation of the system with regenerative motor load.