Master of Science, The Ohio State University, 1986, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 2006, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 2008, Graduate School

Committee: Not Provided (Other) Subjects:

Doctor of Philosophy, The Ohio State University, 2024, Welding Engineering

Welding low alloy steels can result in formation of undesirable properties in the heat affected zone with high hardness and low toughness caused by martensite formation. Such issues often require tempering procedures to improve properties and reduce cracking susceptibility. The temper bead welding technique has been applied by the power generation industry to produce tempered heat affected zones without post-weld heat treatment. The development of good temper bead procedures can be cumbersome which served as motivation for a portion of the work in this study. This research contained four elements focused on performance of low alloy steel heat affected zones after temper bead welding. These included development of an experimental and computational approach to evaluate tempering response and tempering efficiency, application of the developed methodologies using a finite element model-based design of experiment approach, characterization of the effect of short-term tempering reheats on impact properties, and evaluation of the precipitation kinetics during short-term tempering reheats. The tempering response quantification method was developed to quantify the tempering effect of the multiple non-isothermal cycles during multi-pass welding processes. A novel computational framework was developed to evaluate and quantify the tempering response and tempering efficiency in the heat affected zone in temper bead welding. This involved integrating finite element models with the tempering response methodology to allow distribution analysis of hardness, microstructure, corresponding surface areas, and other tempering response indicators. These methodologies were demonstrated and validated in temper bead weld overlays on Grade 22 steel. Efforts to facilitate temper bead procedure optimization motivated development of a computational finite element model-based design of experiment framework to evaluate a range of weld process parameters and tailor procedures to optimize perfor (open full item for complete abstract)

Committee: Boian Alexandrov PhD (Advisor); Avraham Benatar PhD (Committee Member); Carolin Fink PhD (Committee Member) Subjects: Materials Science

Master of Science in Electrical Engineering, University of Dayton, 2024, Electrical and Computer Engineering

Hybrid/Full electric aircraft (HEA/FEA) represents an attractive concept due to its potential to reduce CO2 emissions, decrease fossil-fuel consumption, enhance overall aircraft efficiency, and lower operational costs. As technology progresses towards hybrid/full electric aircraft, the development of high-performance motor drive systems becomes imperative. This necessity introduces new constraints, particularly in low-pressure environments. Designing for high-altitude applications requires careful consideration to prevent issues like partial discharge and power system failures in the air. Converters must exhibit ultra-high efficiency, high power density, and exceptional reliability. While wide band-gap devices, such as Silicon-carbide based Metal Oxide Silicon Field Effect Transistors (SiC-MOSFETs), offer improved switching and high-temperature performance over silicon counterparts, their integration into HEA/FEA applications remains challenging. The high switching speed of SiC-MOSFETs reduces switching losses and facilitates the design of high-density inverters. However, selecting suitable devices is critical for designing high-power-rated inverters. Moreover, the risk of partial discharge increases at high voltages in conditions of low air pressure, posing a threat to inverter longevity by compromising system insulation. This thesis evaluates three distinct inverter/converter topologies comprehensively to determine the optimal circuit topology for HEA/FEA applications. The study explores design strategies to ensure busbar integrity, preventing partial discharge without compromising parasitic control. Throughout the thesis, a three-phase megawatt-scale inverter and a 3.3 kV, 288 A power module are designed, fabricated, and tested to validate the proposed design strategies.

Committee: Cao Dong (Committee Chair); Kumar Jitendra (Committee Member); Ratliff Bradley (Committee Member) Subjects: Electrical Engineering; Engineering

Master of Science, Miami University, 2024, Electrical and Computer Engineering

Silicon Carbide (SiC) MOSFETs are seeing a higher demand with the increased electrified automobiles and aircraft. Manufacturers produce SiC MOSFETs in many different packages, from bare dies to discrete packages to integrated power modules. The transportation sector requires higher current power conversion, and in some applications, it is unclear whether to use parallel power devices or a power module. This research compares the abilities of commercial off-the-shelf (COTS) power module packages and parallel discrete devices in TO-247 packages for higher current applications. Power modules from Wolfspeed and GE Aerospace are compared with each other and TO-247-4 packaged discrete devices from Microchip Technology and Qorvo. The following thesis contains the motivations behind this research, a literature review about SiC MOSFET packages and current sharing between parallel MOSFETs, the procedure and current progress of this research, printed circuit board (PCB) layouts for the devices, and experimental results using a double pulse test and an efficiency test utilizing a boost converter configuration. Finally, a conclusion with future work is presented.

Committee: Mark Scott (Advisor); Dmitriy Garmatyuk (Committee Member); Dave Hartup (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy (Ph.D.), University of Dayton, 2024, Materials Engineering

Ceramic matrix composites (CMC) are candidate high-temperature materials for gas turbine engines. GTE components that could utilize CMCs include exhaust diffusers, combustor shrouds, and turbine blades and vanes (1, 2). However, current gas path temperatures are high enough that superalloy metals and even CMCs require cooling air drawn from the compressor for turbomachinery that is immediately downstream of the combustor. This cooling air will subject those blade and vane interior cooling passages and cooling holes to intermediate temperature air at a water vapor partial pressure near 1 atm. Specimens from a Hi-Nicalon Type S/BN/SiC (MI) composite with multiple machined holes were subjected to a furnace dwell and then tensile tested at room temperature. The furnace temperature range was 500°C-1100°C and the atmosphere was pure steam. Pure steam at 1 atmosphere approximated the sea level partial pressure of water vapor in the cooling air going through turbomachinery cooling holes. Exposure of control specimens was done in laboratory air at the same temperatures as the steam furnace specimens. Data included tensile results along with digital image correlation, computed tomography, microscopy, and spectroscopy results. The hole array was analytically modeled to predict its resulting stress concentration factor; test results showed that the hole array caused a lower stress concentration factor than analytical modeling predicted. There was significant strength degradation in some conditions due primarily to oxidation of the boron nitride fiber coating, with coating volatilization at lower temperatures and probable fiber to matrix bonding and imposed fiber stresses at higher temperatures. The greatest strength degradation occurred in the 500°C-600°C steam range. The fiber coating oxidation/volatilization was especially evident near the holes and was exacerbated in the lower temperature tests by porosity networks from composite processing that were open (open full item for complete abstract)

Committee: Ronald Kerans (Committee Chair); Charles Browning (Committee Member); Craig Przybyla (Committee Member); Li Cao (Committee Member); George Jefferson (Committee Member); James Larsen (Committee Member) Subjects: Materials Science

Doctor of Philosophy (PhD), Ohio University, 2023, Chemical Engineering (Engineering and Technology)

Internal corrosion of transmission tubulars is a huge concern in the oil and gas industry. Corrosion inhibitors (CIs) are often considered the first step in mitigating internal corrosion due to their high efficiency and cost-effectiveness. Yet, predicting the efficiency of corrosion inhibitors, developed and tested in a laboratory environment, in operating field conditions is very challenging. In addition, the presence of corrosion residues or corrosion products on the internal surface of tubular steels can significantly affect the inhibition performance of organic corrosion inhibitors. This aspect is only rarely considered when characterizing the performance of corrosion inhibitors. Therefore, understanding their effects on corrosion inhibition is of great benefit in applying corrosion inhibitors to tackle internal corrosion issues, particularly in aging pipelines. This work mainly focuses on evaluating the corrosion inhibition and revealing the inhibition mechanisms in the absence and presence of various corrosion residues or products, commonly found in oil and gas production. The first half of this work (Chapter 5 and 6) presents a methodology for the characterization of corrosion inhibitors and proposes several innovations to an inhibition prediction model, originally based on the work of Dominguez, et al.. An inhibitor model compound, i.e., tetradecyl phosphate ester (PE-C14), was synthesized in-house and characterized to obtain necessary parameter values required as inputs for the inhibition model. The updated inhibition model could predict steady state and transient corrosion inhibition behaviors with good accuracy. The second half of the presented work (Chapter 7, 8, and 9) focuses on the effects of corrosion residue (Fe3C) and products (FeCO3 and FeS) on corrosion inhibition and advances the understanding of the associated inhibition mechanisms. The galvanic effect caused by residual Fe3C on corrosion rate and inhibition efficiency was quantitatively (open full item for complete abstract)

Committee: Marc Singer (Advisor); Srdjan Nesic (Committee Member); David Young (Committee Member); Sumit Sharma (Committee Member); Katherine Cimatu (Committee Member); Katherine Fornash (Committee Member) Subjects: Chemical Engineering; Engineering; Materials Science

Doctor of Philosophy, The Ohio State University, 2023, Electrical and Computer Engineering

The aviation industry faces a growing imperative to decrease greenhouse gas emissions and transition towards more electric aircraft (MEA) and all-electric aircraft (AEA). One key requirement for a successful transition is increasing the power density and efficiency of onboard power converters. Wide-bandgap (WBG) power switching devices, such as silicon carbide (SiC), present a promising solution due to their high voltage capability and rapid switching speed. However, these devices also pose a challenge as their fast switching speed can adversely affect insulation systems. This dissertation aims to investigate and offer a deeper understanding of, as well as solutions to, the challenges related to partial discharge (PD) in aircraft power wiring under high dv/dt voltage pulses generated by SiC devices. The dissertation begins with an overview of the significant technical challenges related to PD that arise from using SiC device-based variable speed drives (VSD). It then discusses existing studies addressing these challenges and the failure of insulation systems due to PD. The literature review highlights disagreements in current research and the absence of comprehensive investigations into PD behavior caused by high dv/dt square-wave voltage pulses and their impact on the premature failure of insulation systems. Subsequently, the dissertation delves into the challenges associated with the PD phenomenon in aviation wires, explaining the factors that influence PD behavior, accurate PD detection methods, and the extraction of meaningful features to quantify PD intensity. This is followed by an experimental study of PD-induced aging under various conditions to explore the effects of different variables on PD behavior and the failure mechanism of aviation wires. The experimental conditions are chosen to examine voltage rise time, voltage amplitude, ambient pressure, ambient temperature, and the dielectric material of aviation wires. The experimental results reveal (open full item for complete abstract)

Committee: Jin Wang (Advisor); Julia Zhang (Committee Member); Anant Agarwal (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2022, Electrical and Computer Engineering

Silicon carbide (SiC) power devices have been emerging as next-generation semiconductors for power electronics with their superior material properties compared to silicon counterparts as well as other wide band gap devices. Among the power devices, metal-oxide-semiconductor field-effect transistors (MOSFETs) are the most desirable semiconductor devices in power switching applications due to their ease of gate drive. As demands for power MOSFETs increase in the industries such as automotive, aerospace, and defense where stringent reliability standards are required, reliability concerns in SiC devices become more pronounced. Reliability concerns in SiC MOSFETs can be divided into two groups: defect-related issues in Metal-Oxide-Semiconductor structure and design trade-off-related issues. Although it is beneficial for SiC to have SiO2 as a native oxide in terms of using advanced silicon process technology, thermally grown SiO2 on SiC contains a large number of interface defects that are introduced by residual carbon. Interface defects and near interface oxide traps are the main cause of low effective inversion layer mobility of SiC MOSFETs and unstable threshold voltage at high temperatures. Moreover, defects in the bulk oxide are also responsible for mobility degradation by Coulomb scattering as well as bias-stress-dependent threshold voltage instability. Commercially available 1.2 kV SiC MOSFETs are evaluated to study the interface traps and near interface oxide traps. It is especially important to examine the trap-induced threshold voltage instability in commercial devices to determine their robustness for automotive applications. Design trade-offs that give rise to the other reliability concerns are also related to the low inversion layer mobility. Short channel length and thin gate oxide adopted to counteract the high on-resistance from the low inversion layer mobility result in low short-circuit time and low screening efficiency of the extrinsic defects in th (open full item for complete abstract)

Committee: Agarwal Anant (Advisor); Julia Zhang (Committee Chair); Paul Berger (Committee Chair); Marvin White (Committee Chair) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2022, Electrical and Computer Engineering

Modular multilevel converters (MMCs) are currently widely used in medium and high voltage applications. In recent years, with the rapid development of silicon carbide (SiC) devices, growing attention has been placed on adopting SiC devices in MMCs. Thanks to the device's superior electrical and thermal characteristics, the SiC devices, especially the emerging medium voltage ones, are promising to benefit MMC based systems in numerous specifications, such as improved power density, reduced thermal stress, and higher efficiency. However, medium voltage systems can also experience challenges brought about by devices' fast switching speed, including worse electromagnetic interference (EMI), reflected wave phenomenon, and partial discharge. To better utilize the SiC devices in MMCs, this dissertation seeks to evaluate the effects of applying SiC power modules in MMCs. The analysis and discussions include the influential factors of the dv/dt seen at the load terminal, the dv/dt reduction methods, and the effect of high dv/dt on EMI noise and the system insulation design. The analysis is based on a 1 MVA MMC built with the 1.7 kV rated SiC power modules. The influential factors are discussed in three aspects: the source of high dv/dt, the propagation loop, and the control methods. The effects of the three aspects are discussed and evaluated with mathematical models, spice simulations, and hardware tests. It is straightforward that the load terminal dv/dt would change along with the device terminal dv/dt, which is the source of the high switching speed noise. Moreover, the design of passive components in a MMC system also affects the dv/dt by introducing the filtering effect. That is, the parasitic components and the arm inductors would form R-L-C networks between the power modules and the load, and the high order networks would bring down the dv/dt along the propagation loop of the switching transients. Last but not least, the control methods also affect the dv/dts at th (open full item for complete abstract)

Committee: Jin Wang (Advisor); Anant Agarwal (Committee Member); Mahesh Illindala (Committee Member); Longya Xu (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2022, Electrical and Computer Engineering

Partial discharge (PD) is a localized dielectric breakdown of a solid or fluid dielectric under high voltage (HV) stress. It may eventually lead to total breakdown and affect the reliability of electrical systems. With the increasing switching speed of wide bandgap (WBG) devices, PD is more likely to happen in the power converter system. On the other hand, the PD is hard to detect because of the large interference caused by fast switching events. The unprecedented challenges call for the PD characteristic and recognition studies related to WBG devices. Compared to silicon (Si) devices, the switching speed of silicon carbide (SiC) devices can reach 100 kV/µs. The literature review of existing PD studies on SiC devices is conducted. Based on the literature review, several challenges can be seen from the ultra-fast switching speed of SiC devices. They are shortness of ultra-fast dv/dt pulse generators challenges, PD detection challenges, unknown PD mechanism challenges, and limited artificial intelligence (AI) implementation related to SiC devices challenges. To address these issues, two sets of ultra-fast dv/dt pulse generators are designed and manufactured based on SiC devices. They are a 1.7 kV pulse generator and a 10 kV pulse generator with 250 kV/µs and 100 kV/µs output abilities, respectively. A three-step PD study method is proposed to systematically investigate the PD mechanism with different voltage excitations. The three-step PD study includes the PD tests under single pulses, repetitive pulses, and sinusoidal pulse width modulation (SPWM) pulses. AI technique is implied to study PD detection from noise, PD severity diagnosis, and PD location recognition for the SiC converter system. The generic AI implementation flowchart for the PD study is provided. The AI flowchart involves a PD collection module, a PD features extraction module, and an AI analysis module. For the PD features extraction module, traditional PD feature extraction methods are discussed. (open full item for complete abstract)

Committee: Wang Jin (Advisor); Ahmet Selamet (Committee Member); Abhishek Gupta (Committee Member); Anant K. Agarwal (Committee Member) Subjects: Electrical Engineering

Master of Science in Materials Science and Engineering (MSMSE), Wright State University, 2021, Materials Science and Engineering

A metallic network has been embedded in a silicon carbide fiber– silicon carbide (SiC) matrix ceramic composite (CMC) in order to combine the functional properties of the metal and the structural properties of the CMC. The processing of the composite involves iterative pre-ceramic polymer infiltration and heating to temperatures at 1100°C. The metallic structure embedded in the CMC must retain its unique properties during processing and cannot convert to a silicide or carbide resulting from diffusion of Si and C species from the SiC matrix. To gain an understanding of the diffusion process, a fully processed CMC with tungsten, tantalum, and molybdenum wires will be heated at various temperatures for the same duration. The diffusion zone will be measured and then kinetics equations will be applied to determine the failure kinetics. Understanding the diffusion kinetics and phases formed at higher temperature can provide a processing path which avoids metal degradation.

Committee: Hong Huang Ph.D. (Advisor); Joy Gockel Ph.D. (Committee Member); Zlatomir Apostolov Ph.D. (Committee Member) Subjects: Materials Science

Master of Science, The Ohio State University, 2021, Electrical and Computer Engineering

Power electronic devices represent one of the commonly used devices in a wide range of applications. With the increasing demand for electrical power, applying voltage on the electronic devices goes up drastically, which means that the new generation of power device requires good performance under high voltages. Nowadays, silicon carbide (SiC), and gallium nitride (GaN) are two of the commonly used materials for power electronic devices because of their wide bandgap, high breakdown field, and high mobility properties. For future high voltage applications, many researchers focus on the beta phase gallium oxide (β-Ga2O3) which has a much wider bandgap and much higher breakdown field comparing with SiC and GaN. However, one of the main obstacles is that β-Ga2O3 has low thermal conductivity, which means that the device temperature will result in degradation of output performance in high voltage applications. In this thesis, I have studied three parameters that are temperature-dependent and designed an Sn-doped β-Ga2O3 MOSFET using β-Ga2O3, sapphire, 4H-SiC, and diamond as the substrate. By analyzing the thermal performance and output performance of the device with different substrates, I found that if only consider the device temperature reduction in low drain bias, using the sapphire substrate, 4H-SiC substrate, and diamond substrate could reduce the increasing lattice temperature by 14% to 67%. At the same time, the peak drain current could increase 7.5% to 22%. Because of the temperature decrease, the degradation of output characteristics is not severe under higher voltages. In this thesis, the device structure is simpler as compared with the commercialized product, but the result of the thesis could provide an approach to solve the self-heating effect for β-Ga2O3 power devices.

Committee: Hongping Zhao (Advisor); Wu Lu (Committee Member) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 2021, Nuclear Engineering

Additive manufacturing (AM) facilitates rapid prototyping, development of novel designs and replacement of older fabrication techniques. This technique, while still expanding, is being researched to replace current electronic and sensor fabrication methods. AM offers many advantages including fast production times, on hand production capabilities, and customizability. The nuclear industry has begun exploring the possibility of using additive manufacturing for future and current reactor designs and construction. Sensor development is one area within the nuclear realm, where AM could make tremendous improvements. Rapid prototyping of future instrumentation would allow for a faster and better design process where ideas can be tested and modified easily. This paper details the development of an additive manufactured sensor for radiation detection purposes for the nuclear industry. Instrumentation serves many purposes in the nuclear industry from sensors to monitor power that must withstand a harsh reactor environment to precise energy spectroscopy of samples for isotope identification and quantification. Some devices, such as those used in alpha spectroscopy like solid-state semiconductor detectors, require a cleanroom and many different tools and procedures to fabricate completely. AM offers a unique opportunity to fabricate these devices while minimizing the required cleanroom work and equipment and replacing it with fast and easy to use AM machines. Aerosol inkjet deposition is a type of 3D printing that enables the deposition of functional material onto a substrate. This technique can be used for metals, biological material, and dielectrics. Fabrication of radiation and temperature sensors can be achieved rapidly and easily through the deposition of metal nanoparticle inks onto a semiconductor wafer. These devices offer a simple, yet effective device configuration capable of high energy resolution alpha and gamma spectroscopy depending on the semiconductor material. (open full item for complete abstract)

Committee: Raymond Cao (Advisor); Thomas Blue (Committee Member); Anant Agarwal (Committee Member); Pooran Joshi (Committee Member) Subjects: Nuclear Engineering

Master of Science, The Ohio State University, 2021, Electrical and Computer Engineering

Advancements in semiconductor technology present new challenges in electric machine construction, operation, and control. Silicon carbide (SiC)-based power electronics are becoming the new standard for high-power consumer and commercial devices, and are implemented in technologies such as power inverters, converters and rectifiers. This paper focuses on the effects of inverter drives for traction motors in electric vehicles with high dV/dt rates on bar-wound machine windings, including the expected impacts on insulation materials under prolonged periods of high voltage stress. Partial discharge inception voltage testing was performed to evaluate the voltage bus level at which breakdown will start to occur. A simulation model was constructed using finite element analysis, the results of which were validated with experimental results using a commercially available SiC inverter and traction motor. Correlation has been established between the preliminary simulation results and experimental data. It is proven that as DC bus voltages increase with the capabilities of SiC devices, the voltage stresses inside the stator windings approach levels which could cause partial discharge and premature insulation degradation in existing stator designs.

Committee: Julia Zhang (Advisor); Jin Wang (Committee Member) Subjects: Alternative Energy; Design; Electrical Engineering; Electromagnetics; Electromagnetism; Energy; Engineering; Solid State Physics; Sustainability; Transportation

Master of Science, Miami University, 2020, Mechanical and Manufacturing Engineering

Titanium alloy is a useful and widely used material, but it is particularly difficult to machine. Conventional flood cooling methods used to remove heat from and reduce friction in the work zone have many disadvantages. Minimum quantity lubrication (MQL) provides a quality alternative, but highly effective lubricants are needed for this method to be successfully used on titanium alloy. The two-dimensional material graphene has been proposed for use in nanolubricants. This study aims to investigate the tribological behaviors of graphene nanofluids and find the optimal concentration/base combination for MQL milling of titanium alloy.

Committee: Zhijiang Ye (Advisor); Mark Sidebottom (Committee Member); Muhammad Jahan (Committee Member) Subjects: Engineering; Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2020, EECS - Electrical Engineering

Radiation is of great importance in both fundamental science (e.g., understanding black holes, exploring the time evolution and the origin of the universe) and technological applications (e.g., diagnosing and treating diseases in medicine, and producing electricity at nuclear plant). Among all the radiation studies, radiation in semiconductor materials attracts the most attention in the information era with numerous semiconductor devices operating in space and on earth. Although silicon (Si) still dominates the semiconductor industry, a number of wide bandgap (WBG) semiconductors have demonstrated advantages in harsh environment applications. Among them, silicon carbide (SiC), with a family of polytypes and excellent properties such as wide bandgap (2.3-3.2 eV), high displacement energies (20-35 eV), excellent elastic modulus (~200-700 GPa) and outstanding thermal conductivity (~500 W m-1K-1), has shown great potential for high temperature, high power, and radiation resistant applications. A quite large body of work has been performed during recent decades to understand the radiation effects in the SiC electronic devices, such as field effect transistors (FETs), bipolar junction transistors (BJTs), and diodes. Meantime, while micro/nano- electromechanical systems (M/NEMS) have gained tremendous advancements and made great impact on many important applications including inertial sensing (e.g., gyroscopes, accelerators), radio-frequency (RF) signal processing and communication, radiation study in M/NEMS has been quite limited, especially for those based on beyond-Si materials. This dissertation makes an initial thrust toward investigating radiation effects in SiC M/NEMS. First, we develop an innovative 3D integrated MEMS platform, by exploiting a scheme consisting of an array of vertically stacked SiC thin diaphragms (and Si ones for comparison). This integrated design and configuration not only scientifically enables probing different radiation effects (wi (open full item for complete abstract)

Committee: Philip Feng (Committee Chair); Christian Zorman (Committee Member); Chung-Chiun Liu (Committee Member); Xiong (Bill) Yu (Committee Member); Hossein Lavasani (Committee Member) Subjects: Aerospace Engineering; Electrical Engineering; Mechanical Engineering; Physics

Doctor of Philosophy, The Ohio State University, 2019, Electrical and Computer Engineering

After 60 years' development, Silicon (Si) devices are approaching their performance limitations set by their own material properties. They have difficulties meeting requirements of future medium and high-voltage applications. Medium-voltage Silicon Carbide (SiC) devices break the constraints of Si devices and are projected to be their successors. However, the research of medium-voltage SiC devices is still at an early stage. Technical challenges hinder their applications. This dissertation aims to study and/or provide solutions to key challenges of applying medium-voltage SiC devices. This work first summarizes the major technical challenges and associated research efforts of applying medium-voltage SiC devices. The summary is based on a survey of recent developments of medium-voltage SiC devices and evaluation results of three device examples. Then this dissertation addresses four technical challenges: gate drive design for medium-voltage SiC devices, auxiliary power supply design for gate drives, partial discharges in motor windings, and reflected waves in motor drives. Designs of gate drives and its auxiliary power supplies are challenging. It is because of the fast switching speed of medium-voltage SiC devices and high insulation requirements in high-voltage systems. This work presents a gate drive and its auxiliary power supply targeting 10 kV SiC MOSFETs. The gate drive features a common-mode transient immunity (CMTI) over 200 kV/µs and an overcurrent protection time within 700 ns. Its power supply has an input voltage of 7 kV and an insulation capability over 10 kV. The gate drive and auxiliary power supply further enable the development of a self-sustained circuit building block, which can serve as one of the sub-modules in high-voltage multilevel converters. The high voltage rating and fast switching speed of medium-voltage SiC devices cause concerns of partial discharges. This work studies the partial discharge in a medium-voltage motor winding. A test (open full item for complete abstract)

Committee: Wang Jin (Advisor); Agarwal Anant (Committee Member); Zhang Julia (Committee Member) Subjects: Electrical Engineering

Master of Science in Engineering, Youngstown State University, 2019, Rayen School of Engineering

Molybdenum (Mo) is one of the metals categorized as refractory metal due to its thermal properties. For that reason, it is very attractive for high-temperature applications. This thesis covers the investigation of silicon carbide (SiC) Schottky diodes fabricated using Mo as the Schottky contact. The Mo Schottky contacts were deposited using magnetron sputtering on the n-type 4H-SiC. The temperature of the SiC substrates was varied from 25 °C to 900 °C. The electrical properties of the diodes were determined by current-voltage, capacitance-voltage and current-voltage-temperature measurements. Structural properties of Schottky contacts deposited at different temperatures were also characterized using x-ray diffraction spectroscopy. The results obtained reveal that the as-deposited diodes had energy barrier heights that ranged from 1.02 to 1.67 eV and ideality factors varying from 1.04 to 1.23. Contacts deposited at 600 °C produced the optimum property consisting of a barrier height of 1.34 eV and ideality factor of 1.05. The diodes were further thermally processed by keeping them exposed to 500 °C for 24 hours diodes in vacuum. From these, the barrier height ranging from 1.00 eV to 1.70 eV was obtained. The variation in electrical properties is explained as due to changes in crystal quality. Current-voltage temperature measurements to further characterize the electrical properties of diodes at different temperatures were performed. Contacts deposited at 500°C produced the largest Richardson's constant (A**) of 3.74 A/K-cm2 and a barrier height of 1.32 eV. Changes in ideality factors and barrier heights are observed due to the formation of interfacial silicide layers. X-ray diffraction results show the formation of MoSi2 and Mo5Si2

Committee: Tom Nelson Oder PhD (Advisor); Jalal Jalali PhD (Committee Member); Faramarz Mossayebi PhD (Committee Member) Subjects: Electrical Engineering; Physics