Author ORCID Identifier:
Date of Graduation
12-2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Engineering (PhD)
Degree Level
Graduate
Department
Electrical Engineering
Advisor/Mentor
Zhao, Yue
Committee Member
Hu, Han
Second Committee Member
McCann, Roy; Song
Third Committee Member
Song, Xiaoqing
Keywords
active neutral point clamped converter; dc ac; High power; Silicon Carbide; Traction
Abstract
The decarbonization of the transportation sector has become an urgent global priority, particularly in heavy-duty domains such as freight rail, mining trucks, and large industrial vehicles. Electrification of these sectors requires traction inverters capable of delivering high efficiency, reliability, and power density under medium-voltage and megawatt-scale conditions. As the critical interface between the electrical source and the traction motor, the inverter governs torque, speed, and energy recovery, and thus directly determines the viability of electrified transport. Among multilevel converter families, the three-level active neutral-point-clamped (ANPC) topology has emerged as a strong candidate due to its improved AC harmonics, reduced voltage stress, and active loss-balancing capability. These features make ANPC inverters attractive for medium-voltage (MV) traction drives, where balanced device utilization and higher switching frequencies are essential for compact, efficient systems. With the recent commercial availability of high-performance silicon carbide (SiC) MOSFETs, the potential of ANPC converters is further enhanced, since SiC devices offer lower switching loss, faster transition speed, and superior thermal capability compared with conventional silicon IGBTs. However, the integration of SiC into high-power MV ANPC converters also introduces new challenges related to parasitic inductance, busbar design, and switching stress. To address these challenges, Chapter 2 presents the design and experimental demonstration of a 500 kVA, 2.6 kV full-SiC ANPC prototype. A novel three-dimensional laminated busbar structure was developed to simultaneously satisfy insulation requirements, high current conduction ability, and reduce commutation-loop inductance. Stray inductance was characterized and validated through simulation, impedance analysis, and double-pulse testing, showing around 50% reduction compared to conventional designs. Converter-level validation through pump-back and three-phase active power tests confirmed the high efficiency (up to 98.7%) and reliable operation of the prototype under MV conditions, thereby demonstrating a practical pathway for full-SiC ANPC traction inverters. While the benefits of SiC are clear, quantitative comparisons against state-of-the-art Si IGBTs remain limited, especially under realistic railway traction conditions. Chapter 3 fills this gap by experimentally evaluating 3.3 kV SiC MOSFET and Si IGBT power modules. Through double-pulse tests across wide current and temperature ranges, SiC MOSFETs were shown to achieve higher dv/dt and di/dt with lower switching losses, while IGBTs exhibited lower voltage overshoot. Continuous three-phase operation demonstrated that SiC-based converters sustain higher switching frequencies (up to 8 kHz) and improved harmonic performance, enabling smaller passive filters, whereas IGBT-based converters remain restricted to lower frequencies due to switching losses and thermal stress. This study provides updated, quantitative evidence to guide device selection in next-generation railway and traction applications. Beyond full-SiC implementations, hybrid ANPC converters that combine Si and SiC devices offer a cost-effective alternative, while maintaining acceptable performance. Within hybrid ANPC systems, the choice of hardware architecture significantly impacts parasitic inductance, dc-link capacitance, and volumetric power density. Chapter 4 therefore compares two 500 kVA hybrid ANPC prototypes: one based on a three-phase integrated power stage (IPS) and the other on modular single-phase power-electronic building blocks (PEBBs). Double-pulse testing showed that the IPS achieves lower commutation-loop inductance and reduced voltage overshoot, validating its parasitic performance advantages. A reactive continuous test further demonstrated the stable operating capability of the IPS under high reactive power. Meanwhile, the PEBB approach, though exhibiting higher stray inductance and smaller dc-link capacitance, achieves higher volumetric power density and superior modularity, making it attractive for scalable and maintainable systems. The comparison highlights complementary advantages: IPS layouts minimize electrical stress and are ideal where reliability is paramount, while PEBB architectures maximize power density and modular flexibility. In conclusion, this dissertation contributes to the advancement of high-power traction inverters in three key ways. First, it demonstrates a validated full-SiC MV ANPC design with a novel low-inductance busbar, offering a practical reference for industrial deployment. Second, it provides an up-to-date, quantitative comparison of Si and SiC devices at the 3.3 kV level, guiding device choice for railway and heavy-duty traction systems. Third, it systematically compares IPS and PEBB architectures for hybrid ANPC converters, clarifying their trade-offs in inductance, capacitance, power density, and modularity. Together, these results offer design methodologies and experimental insights that will support the development of more efficient, reliable, and sustainable traction inverters, thereby enabling the broader electrification of heavy-duty transportation and contributing to global decarbonization goals.
Citation
Ma, Z. (2025). All Silicon Carbide (SiC) and SiC/Si Hybrid Converters for High-Power Traction Applications. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/6042
