Doctor of Philosophy, University of Akron, 2022, Electrical Engineering

This research proposes a direct voltage control approach for electric motors, including the single-stage converter topology and the control algorithms. The proposed motor drive system achieves smooth output voltage waveforms for phase excitations and utilizes them to extend the drive capability besides improving the torque ripple, noise, and vibration performance. Applicable to various motor types, the direct voltage control (DVC) is mainly investigated for driving switched reluctance motor (SRM) in the scope of this thesis. Different voltage regulation-based control algorithms are studied. Since the capability of shaping the phase voltage precisely allows control of any motor variables, this ability enables regulating the phase currents, flux linkages, and phase voltages to obtain superior performance. A finite element analysis (FEA) is performed to characterize the motor for building a dynamic simulation model for an SRM. The developed DVC and the conventional control are simulated using this machine model in comparison to each other. A new dual polarity power converter (DPC) is modeled, which can buck and boost the DC bus voltage and provides a variable voltage generation (VVG). The DPC can process power in both directions and provide a variable voltage in both positive and negative polarities at the motor windings. Following the DPC design process, power boards and gate driver boards are manufactured and populated as modular systems for individual motor phases. The developed converter model is customized and sized to construct a motor drive for the targeted operating conditions of the investigated SRM. It includes a control board to enable the 3-phase operation and a single DC bus as the power source for all three modular power converters. A resistive load setup is built to test the converter's performance. After verifying the DPC's performance for its designed load conditions and position-dependent dynamics, the motor tests are performed. The motor tests (open full item for complete abstract)

Committee: Yilmaz Sozer (Advisor); Patrick Wilber (Committee Member); Alper Buldum (Committee Member); Igor Tsukerman (Committee Member); J. Alexis De Abreu Garcia (Committee Member) Subjects: Aerospace Engineering; Alternative Energy; Electrical Engineering; Electromagnetics; Electromagnetism; Energy; Engineering; Technology

Doctor of Philosophy, The Ohio State University, 2020, Electrical and Computer Engineering

β-Ga2O3 has recently attracted attention as an ultra-wide bandgap (4.7 eV) semiconductor that can be controllably doped, and grown directly from the melt in single crystal form. The ease of n-type doping with tetravalent cations, a wide variety of bulk single crystal and epitaxial film growth techniques have triggered worldwide interest in β-Ga2O3. The predicted breakdown electric field (6-8 MV/cm) is higher than that of GaN or SiC (~3 MV/cm), which when combined with electron mobility (predicted ~250 cm2/Vs) and electron velocity (1.2×107 cm/s) yields higher figures of merits than SiC and GaN devices. This thesis presents theoretical and experimental investigations of β-Ga2O3 device designs to achieve high-performance RF and power electronics for future applications. The first part of the thesis analyzes the potential device advantages that can be derived from the fundamental β-Ga2O3 material parameters (electron mobility, saturation velocity, and breakdown field). The theoretical β-Ga2O3 device output power density is calculated and compared to GaN HEMTs to find the potential RF applications of β-Ga2O3 devices. The potential of β-Ga2O3 for power devices is also calculated and discussed. Through detailed 2-D device simulation, device design strategies for utilizing the high breakdown field and mitigating low electron mobility effects are proposed. The thesis then focuses on the experimental demonstration and progress on lateral β-Ga2O3 device designs, including (AlGa)2O3/Ga2O3 MODFETs and delta-doped MESFFETs. (AlGa)2O3/Ga2O3 MODFET is one suitable device structure for high-performance β-Ga2O3 electronics because of the 2-D electron gas (2DEG) channel with high electron mobility. The electrical properties of the grown film and the MODFET device characteristics are studied. MBE-grown Ohmic contact is developed for the (AlGa)2O3/Ga2O3 MODFETs to improve their device performance. The high mobility 2DEG channel and low-resistance Ohmic contact enable the direct (open full item for complete abstract)

Committee: Siddharth Rajan (Advisor); Robert Coffie (Committee Member); Steven Ringel (Committee Member); Wu Lu (Committee Member); Xiaoxue Wang (Committee Member) Subjects: Electrical Engineering; Solid State Physics

Doctor of Philosophy, University of Akron, 2018, Mechanical Engineering

Acoustic/Elastic metamaterials have attracted increased attention in recent times. Metamaterials are defined as special materials that exhibit unusual properties not normally found in normal materials. These unusual properties are derived from the specially designed microstructures rather than the chemical composition of the material. Based on the concept of locally resonant metamaterials, these materials are applied in many applications such as impact wave attenuation, blast wave mitigation and wave control and manipulation due to their flexibility and tailoring properties for various needed applications. In this thesis, we present the development of a dissipative elastic metamaterial with multiple Maxwell-type resonators for dynamic load mitigation. Besides the wave attenuation of dynamic loads, we also investigate the asymmetric transmission of elastic waves which has recently been realized by linear structures. We design and propose different diatomic and triatomic elastic metamaterials to obtain large asymmetric elastic wave transmission in multiple low-frequency bands. All these frequency bands can be theoretically predicted to realize one-way wave propagation along different directions of transmission. All proposed models in this research are analytically investigated and numerically verified by both analytical lattice and continuum models. Also, the dynamic responses of the proposed models are explored and analyzed in time and frequency domains. The effect of damping on the proposed models is also investigated for more practical applications. Lastly, experimental verification is further conducted to observe wave asymmetric transmission bands and transient wave responses in time and frequency domains are also explored.

Committee: KWEK-TZE TAN PHD (Advisor); GRAHAM KELLY PHD (Committee Member); GREGORY MORSCHER PHD (Committee Member); PING YI PHD (Committee Member); MALENA ESPANOL PHD (Committee Member) Subjects: Mechanical Engineering

Master of Science, University of Toledo, 2018, Electrical Engineering

The recent development in the wide bandgap (WBG) semiconductor devices such as gallium nitride (GaN) has pushed the limit for the next generation power electronics in terms of high frequency switching applications with high power density. GaN devices have shown promising theoretical advantages such as large bandgap, breakdown field and electron saturation velocity, thereby presenting GaN as an effective alternative for Silicon in high power, temperature and frequency switching applications. Despite having numerous advantages over silicon, GaN technology has suffered with various device level as well as circuit level challenges. Although the very low inherent capacitance of the GaN is one of the most important attributes of the device, it can become disruptive in the presence of significant parasitic circuit inductance. Due to the high sensitivity of these capacitances and their interaction with the parasitic circuit components, undesirable transient events resulting in circuit deterioration can occur. In this thesis work, circuit level reliability issues of GaN due to high VGS stress and high frequency switching has been analyzed with emphasis on external circuit parasitics. The research study targets three important aspects of circuit level reliability issues in a GaN HEMT. It begins with 1. determination of degradation parameters, followed by 2. effect of external gate resistance over degradation parameters and finally 3. analysis of device degradation mechanism with respect to high VGS stress under zero input bias (VDS = 0). A simulation study is also developed to predict the VGS overshoot for a specific gate voltage with respect to parasitic inductance. For this purpose, a 100 V, “EPC-8010” normally o (open full item for complete abstract)

Committee: Raghav Khanna (Committee Chair); Mansoor Alam (Committee Member); Richard Molyet (Committee Member) Subjects: Electrical Engineering