A polycrystalline diamond was tested as a bearing material for a tilting pad thrust bearing to be used in an electric submersible pump, which elevates process fluids from the bottom of well bores. The goal of this study was to compare the PCD to a current best of technology, which is stainless steel with an engineering polymer.This study found that PCD can handle larger loads than current technology but is limited in size due to diamond sintering and manufacturing constraints. The maximum size is Ø75mm.

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The development of high power density three-phase ac converter has been a hot topic in power electronics area due to the increasing needs in applications like electric vehicle, aircraft and aerospace, where light weight and/or low volume is usually a must. Many challenges exist due to the complicated correlations in a three-phase power converter system. In addition, with the emerging SiC device technology the operating frequency of the converter can be potentially pushed to the range from tens of kHz to hundreds of kHz at higher voltage and higher power conditions. The extended frequency range brings opportunities to further improve the power density of the converter. Technologies based on existing devices need to be revisited. In this dissertation, a systematic methodology to analyze and design the high power density three-phase ac converter is developed. All the key factors of the converter design are explored from the high density standpoint. Firstly, the criteria for the passive filter selection are derived and the relationship between the switching frequency and the size of the EMI filter is investigated. A function integration concept as well as the physical design approach is proposed. Secondly, a topology evaluation method is presented, which provides the insight into the relationships between the system constraints, operating conditions and design variables. Four topologies are then compared with the proposed approach culminating with a favored topology under the given conditions. Thirdly, a novel average model is developed for the selected topology, and used for devising a carrier-based control approach with simple calculation and good regulation performance. Fourthly, the converter failure mode operation and corresponding protection approaches are discussed and developed. Finally, a 10 kW three-phase ac/ac converter is built with the SiC devices. All the key concepts and ideas developed in this work are implemented in this hardware system and then verified by the experimental results. / Ph. D.

The emergence of wide-bandgap-based (WBG) devices, such as silicon carbide (SiC) and gallium nitride (GaN), have unveiled unprecedented opportunities, enabling the realization of superior power conversion systems. Among the potential areas of advancement are medium-voltage (MV) and high-voltage (HV) applications, due to the growing demand for high-power-density and high-efficiency power electronics converters. These advancements have propelled a wide adoption of electric vehicles (EV), which in the future will require great improvements in the charging time of these vehicles. Thereby, this thesis attempts to address such a challenge and bring about technological improvements, enabling faster, more efficient, and more effective ways of charging an electric vehicle through the application of MV 3.3 kV SiC MOSFETs. The current fast-charging solution involves heavy and bulky MV-LV transformers, which add installation complexity for EV charging stations. However, this thesis presents an alternative power-delivery solution utilizing an MV dual-active-bridge (DAB) converter. The proposed architecture is designed to directly interface with the MV grid for high-power, fast-charging capabilities while eliminating the need for an installation of the MV-LV transformer. The MV DAB converter utilizes 3.3 kV SiC MOSFETs to realize the next 800 V EV charging system, along with an extended zero-voltage-switching (ZVS) scheme, in order to provide an efficient charging strategy across a wide range of battery voltage levels. Lastly, a detailed design comparison analysis of an MV Flyback converter, targeted for the auxiliary power supply for the proposed MV EV charging architecture, is presented. / The field of power electronics, which controls and manages the conversion of electrical energy, is an important topic of discussion, as new technologies like electric vehicles (EV) are quickly emerging and disrupting the current status-quo of vehicle-choice. In order to promote timely and extensive adoption of such an enabling EV technology, it is critical to understand the current challenges involving EV charging stations and seek out opportunities to engender future innovations. Indeed, wide-bandgap (WBG) devices, such as silicon carbide (SiC) and gallium nitride (GaN), have unveiled unprecedented opportunities in enabling the realization of superior power conversion systems. Thus, utilizing these WGB devices in EV charging applications can bring about improved design and development of EV fast chargers that are faster-charging, more efficient, and more effective. Hence, this thesis presents an opportunity in EV charging station applications with the utilization of medium-voltage SiC MOSFETs. Because the current fast-charging solution involves a heavy and bulky transformer, it adds installation complexity for EV charging stations. However, this thesis presents an alternative power-delivery solution that could potentially provide an efficient and fast-charging mechanism of EVs while reducing the size of EV chargers. All things considered, this thesis provides in-depth evaluation-studies of medium-voltage 3.3 kV SiC MOSFET-based power converters, targeted for future fast EV charging applications. The development and design of the hardware prototype is presented in this thesis, along with testing and verification of experimental results.

The demand for high-power converters are surging due to applications like renewable energy, motor drives and grid-interface applications. Typically, these converters’ power ranges from tens of kilowatts (kW) to several megawatts (MW). To reach such high power levels the converter voltage ratings must increase, as the current ratings cannot be reached by the available devices or because the system losses become excessive. To address this, two strategies can be utilized: multilevel topologies (e.g. Multilevel Modular Converter or Flying Capacitor Multilevel Converter) and high voltage switches. For medium voltage applications, the most commonly employed switches are the IGBT and the IGCT. Both are silicon-based technology and are limited to a rated voltage of 6.5 kV and 4.5 kV, respectively. Often, these devices switching frequency are limited to less than 1 kHz. To expand the frontiers of medium voltage converters and to demonstrate the capabilities of wide band gap devices in medium voltage, a 7-level 13.8 kV AC 22 kV DC 1.1 MW flying capacitor multilevel converter based on 10 kV SiC MOSFET with 2.5 kHz switching frequency was designed and constructed. Given the complexity of a multilevel topology, the high voltage levels, and the critical nature of the loads, a failure in a high-power converter can incur significant costs, long service downtime, and safety risks to personnel. Hence, understanding the failure modes of these converters is essential for designing protections and mitigation strategies to prevent or reduce the risks of failures. Furthermore, the adoption of 10 kV SiC MOSFET introduces additional challenges in terms of protection. Despite their well-known benefits, these devices exhibit shorter energy withstanding time compared with their silicon counterpart, and increased insulation stress resulting from the high dv/dt imposed by the fast-switching transient at higher voltages. In this context, a failure mode analysis was conducted for the converter aforementioned. The analysis examined the fault dynamics and evaluated the protections schemes at the converter level. The study identified a failure mechanism between cells, so called Cell Short- Circuit Fault (CSCF), capable of damaging the entire phase-leg. In response, a protection scheme based on TVS (Transient Voltage Suppression) diodes was designed to prevent extremely imbalanced cell voltages and failure propagation. Because of the high electric field intensity environment of the converter, an FEA (Finite Element Analyses) simulation is performed to verify and control the electric field (E-field) intensity within the protection module itself and in the converter assembly. Next, the protection module insulation design was successfully verified in a Partial Discharge (PD) experiment. In sequence, an experimental verification utilizing an equivalent circuit based on the fault model demonstrated the efficacy of the protection module. Waveforms extracted while the converter was operating showing the protection module acting during a fault are presented and analyzed. Finally, the influence of the protection module in the switching of the 10 kV SiC MOSFET was evaluated via a double pulse test (DPT), revealing negligible effects on the converter performance. / Center of Power Electronics Systems (CPES) Department of Energy (DoE) / Master of Science / Due to governmental policies and market opportunities renewable energy (e.g. solar and wind energy) is increase its share in the electricity generation in the US and around the world. This scenario poses challenges regarding the stability of the grid and variation in the generation along the day. One of the alternatives to alleviate the problem is to use highpower converters that provides a interface between grid and manufacturing plants. This type of converter have bidirectional capabilities and can store the energy generated by solar farms during the day and return it to the grid at night for example. Moreover, it can provide grid support capabilities in terms of variation of frequency and voltage. To expand on the grid interface converters application concept, a medium voltage power converter in 22 kV DC and 13.8 kV AC is designed utilizing novel techniques and the latest technologies in semiconductors, 10 kV SiC MOSFETs. The benefits of this design are a small form factor, high efficiency, immunity to electromagnetic interference and power quality. This work presents a failure mode analysis of the power converter aforementioned, the analysis examined the fault dynamics and an evaluation of the protections schemes at the converter level. The failure analysis revealed the need of a protection scheme extremely imbalanced cell voltages and failure propagation. Hence, a protection module based on TVS (Transient Voltage Suppression) diodes was successfully designed and tested. Due to the high voltages present in this equipment, an FEA (Finite Element Analyses) simulation is performed to verify and control the electric field (E-field) intensity within the protection module itself and in the converter assembly. Experimental results are provided for insulation design integrity (partial discharge test), for the efficacy of the protection module against the fault, and for the impact of the protection module on the operation performance.

Dans le domaine de l’électronique de puissance, les dispositifs en carbure de silicium (SiC) sont bien adaptés pour fonctionner dans des environnements à haute température, haute puissance, haute tension et haute radiation. Le carbure de silicium (SiC) est un matériau semi-conducteur à large bande d’énergie interdite. Ce matériau possède des caractéristiques en température et une tenue aux champs électriques bien supérieure à celles de silicium. Ces caractéristiques permettent des améliorations significatives dans une grande variété d’applications et de systèmes. Parmi les interrupteurs existants, le JFET en SiC est l’interrupteur le plus avancé dans son développement technologique, et il est au stade de la pré-commercialisation. Le travail réalisé au cours de cette thèse consiste à caractériser électriquement des JFET- SiC de SiCED en fonction de la température (25°C-300°C). Des mesures ont été réalisé en statique (courant-tension), en dynamique (capacité-tension) et en commutation sur charge R-L (résistive-inductives) et dans un bras d’onduleur. Un modèle multi-physique du transistor VJFET de SiCED à un canal latéral a été présenté. Le modèle a été développé en langage MAST et validé aussi bien en mode de fonctionnement statique que dynamique en utilisant le simulateur SABER. Ce modèle inclut une représentation asymétrique du canal latéral et les capacités de jonction de la structure. La validation du modèle montre une bonne concordance entre les mesures et la simulation. / In the field of power of electronics, silicon carbide (SiC) devices are well suited to operate in environments at high temperature, high power, high voltage and high radiation. The silicon carbide belongs to the class of wide band gap semiconductor material. Indeed, this material has higher values than the silicon ones for the temperature breakdown and a high electric field breakdown. These characteristics enable significant improvements in wide varieties of applications and systems. Among the existing switches, SiC JFET is the most advanced one in its technological development because it is at the stage of pre-marketing. The study realized during this thesis was to electrically characterize SiC JFETs from SiCED versus the temperature (25°C-300°C). The characteristic are based on static measurements (currentvoltage), capacitive measurements (capacitive-voltage) and switching measurements in an R-L (resistor-inductor) load circuit and an inverter leg. A multi-physical model of the VJFET with a lateral channel is presented. The model was developed and validated in MAST language both in static and dynamic modes using the SABER simulator. The model includes an asymmetric representation of the lateral channel and the junction capacitances of the structure. The validation of the model shows a good agreement between measurements and simulation.