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. / Thesis / Master of Applied Science (MASc)

High power converters are widely used in many industries. At power levels in the range of Mega Watt (MW), power conversion at medium voltage (MV) is preferred due to better efficiency and lower cost. For medium voltages applications, multilevel converters are widely adopted due to the features they offer with respect to two-level converters. Cascaded H-bridge topology is a widely adopted multilevel topology because of its modularity, scalability, and reliability. The conventional cascaded H-bridge topology allows two-quadrant operation. In order to allow fourquadrant operation, an active front end version of the cascaded H-bridge topology has been proposed in literature and recently commercialized. In the field, power converters operates under harsh loading and environmental conditions. The resulting stresses imposed on converter components cause their gradual degradation. In cascaded H-bridge converters, typically power cell components such as power modules, DC-bus capacitors, and control PCBs are v highly stressed. Under these stresses power cell components degrade and require replacement in the field, otherwise unexpected failures may occur. The thesis aim is to address power cell components reliability through proposing novel regenerative cascaded H-bridge converter control schemes to reduce components stresses and failure probability without increasing size, cost, or complexity. First, a novel PWM active front end control scheme has been proposed to reduce the inherent ripple current stresses on the DC-bus capacitors. Second, the thesis proposes a novel grid or near grid switching frequency front end control scheme to reduce stresses on power modules and the power cell cooling requirements. Third, novel cascaded H-bridge front end control schemes are proposed to reduce the sensor count, thereby decreasing failure rate and cutting down cost. The proposed work has been thoroughly validated through detailed 9- cell regenerative cascaded H-bridge system simulation and experimentation. / Thesis / Doctor of Philosophy (PhD)