Date of Award
Spring 2019
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Electrical and Computer Engineering
First Advisor
Weise, Nathan
Second Advisor
EL-Refaie, Ayman
Third Advisor
Bowman, Anthony
Abstract
The number of safety-critical loads in electric power areas have been increasing drastically in the last two decades. These loads include the emerging more-electric aircraft (MEA), uninterruptible power supplies (UPS), high-power medical instruments, electric and hybrid electric vehicles (EV/HEV) and ships for military use, electric space rovers for space exploration and the like. This dissertation introduces two novel fault-tolerant three-level power converter topologies, named advanced three-level active neutral point clamped converter (A3L-ANPC) and advanced three-level active T-Type (A3L-ATT) converter. The goal of these converters is to increase the reliability of multilevel power converters used in safety-critical applications.These new fault-tolerant multilevel power converters are derived from the conventional ANPC and T-Type converter topologies. The topologies has significantly improved the fault-tolerant capability under any open circuit or certain short-circuit faults in the power semiconductor devices. In addition, under healthy conditions, the redundant phase leg can be utilized to share overload current with other main legs, which enhances the overload capability of the converter. The conduction losses in the power devices can be reduced by sharing the load current with the redundant leg. Moreover, unlike other existing fault-tolerant power converters in the literature, full output voltages can be always obtained during fault-tolerant operation. Experimental prototypes of both the A3L-ANPC and A3L-ATT converters were built based on Silicon Carbide (SiC) MOSFETs. Experimental results confirmed the anticipated performance of the novel three-level converter topologies.SiC MOSFET technology is at the forefront of significant advances in electric power conversion. SiC MOSFETs switch significantly faster than the conventional Silicon counterparts resulting in power converters with higher efficiency and increased switching frequencies. Low switching losses are one of the key characteristics of SiC technology. In this dissertation, hard and soft switching losses of a high power SiC MOSFET module are measured and characterized at different voltage and current operating points to determine the maximum operating frequency of the module. The purpose of characterizing the SiC MOSFET module is to determine the feasibility of very high frequency (200kHz-1MHz) power conversion which may not be possible to be implemented in the conventional Silicon based high power conversion. The results show that higher switching frequencies are achievable with soft switching techniques in high power converters.