Master of Science in Engineering (MSEgr), Wright State University, 2009, Electrical Engineering

Doss Jr., Gary Richard. M.S.E., Department of Electrical Engineering, Wright State University, 2009. Novel Intelligent Power Supply Using a Modified Pulse Modulator The objective of this M.S. Thesis was to design, simulate, construct and test a pulse-width-modulated Buck DC-DC Converter and its compensated feedback system. Equations for the design and component selection of a buck converter have been obtained for operating the buck converter in the continuous conduction mode (CCM). A hardware version of the converter design has been implemented to demonstrate the functionality of the designed converter. Also, a digital buck converter control system has been designed and simulated. This digital buck converter led to the development of a proposed control scheme for Switched Mode Power Supplies (SMPS). A novel hybrid feedback control scheme has been proposed, analyzed and simulated. This proposed novel control system implements a proposed novel device that accepts commands from an intelligent source, such as a processor, while allowing the SMPS to apply power to the system under analog control. Once the processor is functioning, it can adjust and tweak characteristics of the power supply to obtain the best power output for the operating environment.

Committee: Marian Kazimierczuk PhD (Advisor); Kuldip Rattan PhD (Committee Member); Xiaodong Zhang PhD (Committee Member) Subjects: Electrical Engineering; Systems Design

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 Electrical Engineering (MSEE), Wright State University, 2016, Electrical Engineering

Radio-frequency power amplifiers are an integral part of today's communication systems. Primary importance is given to improve its efficiency and linearity, which are required for the effective signal transmission. Three main architectures on which, the efficiency of communication systems are based on are: (a) Kahn's technique, (b) Doherty's power amplifiers, and (c) Cheireix out-phasing modulation. Several schemes to implement these techniques exist in literature and their study is very diverse. In this thesis, a detailed literature survey on these techniques is presented, which includes their operation, properties, advantages, disadvantages, and areas of potential applications. This main objective of this thesis is to adopt the Kahn's architecture and implement the various electrical blocks using the latest technology. The main building blocks of the described architecture are: AM/PM signal generator, amplitude detector, dynamic power supply, and a radio-frequency power amplifier. The circuit operation, properties, and circuit-level implementation of all these blocks are presented. The design of a pulse-width modulated buck dc-ac converter used as a dynamic power supply is given. The amplitude-modulated Class-D radio-frequency power amplifier is designed and its performance is evaluated. Each of the circuit-level implementations of the various blocks were designed, built, and simulated on SABER circuit simulator. A test audio signal with frequency 2.5 kHz is generated in the AM/PM signal generator block. A buck dynamic power supply operates at a fixed supply voltage of 25 V with its output voltage varying between 3 V to 23 V. The Class-D radio-frequency power amplifier is designed to generate a carrier frequency of 250 kHz. The efficiency of each stage was determined.

Committee: Marian K. Kazimierczuk Ph.D. (Advisor); Saiyu Ren Ph.D. (Committee Member); Yan Zhuang Ph.D. (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy (PhD), Wright State University, 2013, Engineering PhD

Many integrated circuits are connected to their packaging pins through bondwires. Due to the low cost of bondwires, there is interest in extending operating frequencies or negating their effects in order to keep the price of packaged integrated circuits as low as possible. Bondwires function as lumped circuits consisting of inductors, capacitors, and resistors which can be modeled based on wire geometry. Knowing this, models can be created which approximate the effects of bondwires. With the knowledge of these models, compensation techniques can be implemented which will match the bondwire impedance to the signal line impedance. The effects of these elements on circuit operation is apparent on both signal and power lines to devices. This dissertation is going to present 1. A bondwire model based on physical characteristics of interconnections including neighboring wires. The model is tested against data from fabricated test fixtures, and results compared to those produced by current software. 2. A compensation method for performance degradation caused by bondwires at radio frequencies. Test fixtures implementing these methods are fabricated and checked with results compared to predictions. 3. A method of component stacking which can be used to attach passive components directly to IC die. -Use of above method to improve power distribution network (PDN) performance. Theoretical results are compared to measured test fixture results. -Use of above method to improve performance of off device filters through Q-factor improvement. Improvement verified through test and analysis of a physical test fixture.

Committee: Saiyu Ren Ph.D. (Advisor); Raymond Siferd Ph.D. (Committee Member); Marty Emmert Ph.D. (Committee Member); Marian Kazimierczuk Ph.D. (Committee Member); Ronald Coutu Ph.D. (Committee Member) Subjects: Electrical Engineering; Engineering

Doctor of Philosophy, The Ohio State University, 2004, Electrical Engineering

This PhD research discusses digital control strategies for three-phase Pulse Width Modulated (PWM) voltage inverters used in Uninterruptible Power Supplies (UPS) for single unit and parallel unit systems. For the single inverter system, this research proposes a novel control strategy which utilizes the perfect Robust Servomechanism Problem (RSP) control theory to allow elimination of specified unwanted voltage harmonics from the output voltages under non-linear load conditions and to achieve fast recovery performance on load transient. This technique is combined with a discrete sliding mode current controller that provides fast current limiting capability needed for overload or short circuit conditions. For the parallel inverter system, a combination of two control methods is proposed: average power control method and droop control method. The average power method is used in order to overcome the sensitivity of load sharing to output voltage/current measurement errors and mismatch wiring impedances between units, while the droop method allows the control to still maintain proper load sharing in the event that inter-unit communication is lost. In addition to this, a harmonic droop scheme for sharing of harmonic content of the load currents is introduced based on the proposed single unit control. Control analysis, experimental and simulation studies, using two parallel three-phase PWM inverters, are presented to show the effectiveness of the proposed control strategies, both for single and parallel inverter systems.

Committee: Ali Keyhani (Advisor) Subjects:

Doctor of Business Administration (D.B.A.), Franklin University, 2024, Business Administration

This dissertation examines the impact of inadequate water and electricity supply on Foreign Direct Investment (FDI) in The Gambia. The research highlights how the scarcity and unreliability of these essential utilities significantly deter foreign investment, particularly in key economic sectors such as manufacturing, agriculture, and tourism. In-depth interviews with government officials and foreign direct investors were conducted qualitatively to assess the direct impacts of such utility shortages on businesses' functionality and investment decisions. These findings show that not only does unreliable utility increase operational costs, but it is also positively related to perceived risk and instability by potential investors. It also points to the critical linkage between sustainable infrastructure development and economic growth, necessitating renewable energy solutions that assure utility reliability improvements and further attract environmentally sensitive investors. Additionally, the study contributes to the existing literature by highlighting gaps in previous research, particularly the importance of infrastructure reliability as a critical driver of FDI, alongside traditional factors like political stability and market size. The report further informs policymakers with practical recommendations, including holistic regulatory reforms in technology upgrades and regional cooperation that build better utility infrastructure for the country. Therefore, The Gambia needs to make up for such deficiencies with more amiable environments for FDI if the country is to achieve long-term economic growth and development. This study points out that addressing utility infrastructure challenges is crucial for attracting foreign investment and imperative for achieving sustainable and inclusive economic growth in The Gambia.

Committee: Charles Fenner (Committee Chair); Wendell Seaborne (Committee Member); Rachel Tate (Committee Member) Subjects: Business Administration

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

A new design methodology providing optimal mixed-mode operation for dual-input class-F outphasing Chireix amplifiers is presented. The design starts with single-transistor class-F simulations at the intrinsic I-V reference planes to directly select the optimal peak and backoff resistive loads Rmin and Rmax and input RF gate drives yielding the best combination of efficiencies and output powers without needing to perform a load pull simulation or measurement. New analytic equations expressed only in terms of Rmin and Rmax are given for designing the Chireix combiner at the current source reference planes. Nonlinear embedding is then used to predict the incident power and multi-harmonic source and load impedances required at the package reference planes to physically implement the power amplifier (PA). An analytic formula solely expressed in terms of Rmin and Rmax is reported for the peak and backoff outphasing angles required at the PA input reference planes. A Chireix outphasing PA designed with two 15-W GaN HEMTs exhibits a peak efficiency of 72.58% with peak power of 43.97 dBm and a 8-dB backoff efficiency of 75.22% at 1.9 GHz. Measurements with 10-MHz LTE signals with 9.6-dB PAPR yield 59.4% average drain efficiency at 1.9 GHz while satisfying the 3GPP linearity requirements. A novel frequency-agile PA designed with a modified class-J theory enforcing constant maximum and minimum instantaneous drain voltages for all frequencies is presented. The resulting high efficiency class-J mode which requires a reconfigurable drain supply exhibits clockwise fundamental and second harmonic load impedance trajectories versus frequency facilitating the PA design. This clockwise-loaded class-J (CLCJ) mode enables frequency-agile capability with enhanced efficiency when the proper drain supply voltage co-designed with the clockwise fundamental and harmonic loads is applied. A broadband power amplifier designed with a clockwise-loaded class-J theory is selected for demo (open full item for complete abstract)

Committee: Patrick Roblin (Advisor); Ayman Fayed (Committee Member); Waleed Khalil (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy (PhD), Wright State University, 2020, Electrical Engineering

The pulse-width modulated (PWM) dc-dc converters play a vital role in several industrial applications that include motor drives, electric vehicles, dc distribution systems, and consumer electronics. The switched-mode power converters step the input voltage up or down based on their typology and provide a regulated output voltage. The stability and regulation performance of a power converter can tremendously be improved via a suitable control design. However, due to the nonlinearity of the power converters and the presence of the line and load disturbances, the design of a robust and low-cost control circuit becomes a challenging task. The sliding-mode control of the dc-dc converters has been studied for decades because of its robustness, design simplicity, and suitability for variable structure systems. Despite the merits of the sliding-mode control method, the linear controllers are still dominant and attractive to the commercial applications since they require less design efforts and can be implemented using simple analogue circuits. This research aims to develop simplified sliding-mode control circuits for the classical PWM dc-dc converters in continuous-conduction mode (CCM). The control objectives are to maintain a constant switching frequency, enhance the transient response, provide wide operating range, and track the desired reference voltage under large disturbances. In order to design and test the control circuit, an accurate power converter model should be derived. Hence, large-signal non-ideal averaged models of dc-dc buck and boost converters in CCM are developed. The models are simulated in MATLAB/SIMULINK and compared with the corresponding circuits in SaberRD simulator for validation purpose. Next, PWM-based simplified sliding-mode voltage and current control schemes are designed for the dc-dc buck and boost converters in CCM, respectively. The design procedure and the analogue realization of the control equations are presented, where the control c (open full item for complete abstract)

Committee: Marian K. Kazimierczuk Ph.D. (Advisor); Raúl Ordóñez Ph.D. (Committee Member); Saiyu Ren Ph.D. (Committee Member); Yan Zhuang Ph.D. (Committee Member); Xiaodong Zhang Ph.D. (Committee Member) Subjects: Electrical Engineering

Master of Science in Electrical Engineering (MSEE), Wright State University, 2019, Electrical Engineering

The student's employer is in need of a three phase power supply which can supply a 400Hz signal at +/- 28V at 2A. The input to the power supply is +24VDC at an unspecified current. The student's solution is a configurable frequency and voltage power supply. The student chose to utilize a full bridge DC to DC converter topology. A microcontroller was used for supplying pulse width modulated waveforms, performing analog to digital conversions, and controlling a digital to analog converter. The circuit was modeled using Matlab and tested after being manufactured to confirm proper functionality. The configurable three phase power supply worked as intended. Possible improvements to the design include fixing schematic and printed circuit board errors.

Committee: Marian Kazimierczuk Ph.D. (Advisor); Yan Zhuang Ph.D. (Committee Member); Saiyu Ren Ph.D. (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2016, Business Administration

In the last fifteen years there has been a drastic increase in the outsourcing of manufacturing activities to offshore suppliers, otherwise known as offshore outsourcing. These offshore outsourcing endeavors have often encountered a variety of unanticipated or hidden costs. While these hidden costs can manifest in a variety of forms, two of the main variations are intellectual property risk (i.e., supplier poaching) and quality risk (i.e., supplier shirking). The research in this dissertation utilizes dyadic data from 109 manufacturer-supplier relationships to investigate how the institutional environment of a supplier's location influences the effectiveness of different safeguards and relationship management practices, which can result in increased poaching and shirking. Understanding how to control these hidden costs of outsourcing is what differentiates successful outsourcing relationships and is of critical importance to manufacturers. Manufacturers are often putting their innovations at risk by outsourcing to suppliers in geographical locations that do not protect intellectual property. For that reason, poaching, or supplier's unauthorized use of a buyer's proprietary information, has been considered one of the main hidden costs of outsourcing. The strength of property rights has also been suggested to influence the effectiveness that safeguards have on poaching. Building on these arguments, this dissertation investigates how property rights impact the effectiveness of two safeguards, supplier transaction specific assets and communication, on poaching. Property rights are found to not only have a direct effect on supplier poaching, but they also change the effectiveness of both safeguards. In weak property rights locations, communication is found to be more effective in reducing poaching. Interestingly, in weak property rights locations not only are supplier transaction specific assets less effective in reducing poaching, but increases in these investments (open full item for complete abstract)

Committee: W.C. Benton Jr. (Advisor); Peter Ward (Committee Member); James Hill (Committee Member); Sean Handley (Committee Member) Subjects: Business Administration

Doctor of Philosophy (PhD), Wright State University, 2015, Engineering PhD

Modern energy transmission and signal reproduction techniques rely upon power amplifier (PA) architectures that must operate with high efficiency. Current-source PAs are linear but inherently inefficient; switch-mode PAs are efficient-yet-nonlinear systems, often lacking an efficient means of amplitude modulation (AM) for power transmission. A promising technique for addressing these problems involves replacing the fixed PA supply voltage V_dd with a controlled, variable voltage provided by a dynamic power supply. High-efficiency envelope tracking and amplitude modulation can thereby be provided to both current-source and switch-mode PAs, respectively. This work presents a pulse-width modulated (PWM) dc-dc buck converter for use as the core power stage of a dynamic supply. Although buck converters typically function as fixed-output supplies, this work provides new theoretical dc analysis for operation wherein the output voltage is controlled and variable over a wide, continuous range. A new design procedure for the variable-output PWM dc-dc buck converter is derived. The new dc analysis and design procedure are verified experimentally. Open-loop ac characteristics, such as transient response, frequency response, and dynamic modulation efficiency are assessed via simulation and experimental measurements. The variable-output buck converter is found to operate as designed, with bandwidth dependent upon a sufficiently high PWM switching frequency f_s. Within this bandwidth, minimal modulation distortion is observed, measured efficiency is greater than 90%, and supplied power-on-demand is verified.

Committee: Marian Kazimierczuk Ph.D. (Advisor); Saiyu Ren Ph.D. (Committee Member); Patrick Roblin Ph.D. (Committee Member); Raymond Siferd Ph.D. (Committee Member); LaVern Starman Ph.D. (Committee Member) Subjects: Electrical Engineering

Master of Science in Engineering (MSEgr), Wright State University, 2011, Electrical Engineering

Arc welding machines are typically large, heavy devices that transform an alternating current (AC) input into a low-voltage, direct current (DC) output. Traditionally these high power devices have required steel and copper transformers that account for their bulky size and weight. While the cost of raw materials in electromagnetic components has been increasing the cost of high-power silicon devices has been decreasing. This disparity creates an opportunity for a cost-effective DC-DC switching welder in the consumer market. While DC-DC power electronics are not new to the welding industry, this study, under the commission of a welding equipment manufacturer, aims to develop and prototype a design specifically for an affordable and portable battery-powered welding machine. By eliminating the need for electromagnetic components for isolation and voltage regulation, and focusing on a DC-DC battery-powered device, a unique opportunity exists to create a high-feature product with a minimalist design. The design is implemented with a high-current voltage chopping circuit as well as an assortment of feedback, control, and safety circuitry necessary to complete the machine. By combining simulation, prototype validation and real-world cost limitations, this project outlines the development of a new product for the welding equipment market.

Committee: Marian Kazimierczuk PhD (Advisor); Marian Kazimierczuk PhD (Committee Member); Ronald Riechers PhD (Committee Member); Saiyu Ren PhD (Committee Member) Subjects: Electrical Engineering

PhD, University of Cincinnati, 2006, Business Administration : Quantitative Analysis

Our work, comprising three essays, examines supply chain agent performance in a variety of decentralized systems under both stochastic and deterministic customer demand. In the first two essays, we develop models for both periodic and continuous review inventory policies when the decision-making rights are split between a supplier and a retailer. The second essay also examines a vendor-managed inventory (VMI) agreement. The last essay proposes a novel approach to workload balancing for a company that faces deterministic nonstationary demand and has little, or no, ability to hold inventory. The first two essays seek to answer the following research questions: 1) when does decentralized decision making result in the greatest loss in supply chain performance and 2) what effect does the distribution of channel power have on system and individual agent performance. Channel power here refers to an agent's relative ability to control the decision making process and is modeled using a game-theoretic framework. We characterize optimal policies where possible and we use numerical analysis to generate insights. We find that, from a supply chain perspective, asymmetric power decision structures lead to better performance and customer service. Surprisingly, we identify cases where the lowest costs are incurred at the agent level when the agent is a follower and not a leader in the Stackelberg game. Our analysis also identifies the environmental conditions when the penalty from decentralized decision making is largest and shows that concentrating channel power with one of the agents can represent a viable alternative to coordination mechanisms, when the latter are costly to implement. In the third essay, we use Fourier analysis and Walsh basis functions to decompose an input workload profile into a portfolio of recurrent insourcing and outsourcing contracts to better achieve some desired constant workload level. In addition, we develop mathematical programs based on principles fr (open full item for complete abstract)

Committee: Dr. Michael Fry (Advisor) Subjects:

PhD, University of Cincinnati, 2005, Business Administration : Business Administration

We examine the behavior of a manufacturer and a retailer in decentralized supply chains under price-dependent demand. We investigate the use of several price-commitment policies as coordination mechanisms. The first policy we examine is a retailer's fixed markup (RFM) policy where the retailer commits to a fixed price markup over wholesale price to determine her retail price. The second is a price protection policy where the manufacturer agrees to reimburse the retailer for decreases in the wholesale price. In our first paper we examine the effect of RFM on individual agents' profits and supply chain performance under single period, stochastic demand. Our focus here is on exogenously determined markup values and linear additive demand forms. We prove the existence of optimal pricing and replenishment policies. We also find that RFM can result in significantly greater profit for the supply chain than the price-only contract and leads to Pareto-improving solutions. The second paper extends our analysis by examining the RFM policy under both multiplicative and linear additive demand forms. We obtain closed-form solutions for both RFM and price-only policies and analytically prove that Pareto-improving solutions are not possible under iso-price-elastic, multiplicative demand. We also consider the effect of pricing power in the supply chain by varying who determines the retail price markup. Our results reveal that the effect of retailer ex-ante markup commitment is heavily dependent on both the nature of the demand function and the relative pricing power of different players in the supply chain. The final paper in this dissertation investigates a multi-period, deterministic demand setting. We compare price commitments made by both the retailer and the supplier. RFM represents the retailer's price commitment and price protection is a form of manufacturer price commitment. We prove the existence of unique, optimal pricing and ordering solutions for all policies considered. (open full item for complete abstract)

Committee: Dr. Michael Fry (Advisor) Subjects: Business Administration, Management

Master of Science, The Ohio State University, 2012, Electrical and Computer Engineering

Field-programmable gate arrays (FPGAs) are used in a wide variety of applications and end markets, including digital signal processing, medical imaging, and high-performance computing. This thesis outlines the issues related to powering FPGAs. Supplying and conditioning power are the most fundamental functions of an electrical system. A loading application, be it an FPGA, cannot sustain itself without energy, and cannot fully perform its functions without a stable supply. The fact is transformers, generators, batteries, and other offline supplies incur substantial voltage and current variations across time and over a wide range of operating conditions. They are normally noisy and jittery not only because of their inherent nature but also because high power switching circuits like central processing units (CPUs) and digital signal processing (DSP) circuits usually load it. These rapidly changing loads cause transient excursions in the supposedly noise free supply, the end results of which are undesired voltage droops and frequency spurs where only a dc component should exist. The main component of a power supply is a voltage regulator. The role of the voltage regulator is to convert these unpredictable and noisy supplies to stable, constant, accurate, and load independent voltages, attenuating these ill fated fluctuations to lower and more acceptable levels. Linear or switching regulators based power supplies will be proposed and simulated. Today's FPGAs tend to operate at lower voltages and higher currents than their predecessors. Consequently, power supply requirements may be more demanding, requiring special attention to features deemed less important in past generations. Failure to consider the output voltage, sequencing, power-on, and soft start requirements can result in unreliable power-up or potential damage to FPGAs.

Committee: Joanne Degroat PhD (Committee Chair); Yuan Zheng PhD (Committee Co-Chair) Subjects: Electrical Engineering

Master of Science (MS), Ohio University, 1993, Electrical Engineering & Computer Science (Engineering and Technology)

Computer control of a pulse width modulated AC/DC converter under a variable frequency power supply

Committee: W. Hill (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2013, Business Administration

In recent years, healthcare organizations (HCOs) in the United States and across the globe have come under increasing pressure to reduce cost while maintaining high quality of care. Supplies and equipment contribute significantly to the total healthcare cost as these categories account for approximately 40% of HCO spending. The healthcare supply chain is distinctly different from traditional supply chains, and findings from extant supply chain research may therefore not apply to the healthcare supply chain. The relationship between the supply chain members is a key determinant of supply chain excellence. In this dissertation the role of dependence and inter-organizational power and the effect of supply chain relationships in the healthcare supply chain are investigated. Survey data from 276 procurement professionals from US HCOs are analyzed using factor analysis and structural equation modeling. The relationship between an Original Equipment Manufacturer (OEM) and an HCO is interceded by a middleman, the Group Purchasing Organization (GPO). The analysis offers strong empirical evidence that this interceded relationship is positively affected by an OEM’s non-mediated power and that this relationship positively affects the performance of both the OEM and the HCO. The relationship between the GPO and the HCO is positively affected by the GPO’s non-mediated power, but is surprisingly not affected by the GPO’s mediated power. This GPO-HCO relationship furthermore only affects the GPO’s performance. The results suggest that the performance of an HCO is not affected by a relationship with a GPO. The analysis also indicates that when a buyer uses a procurement service provider, such as a GPO, the buying organization can end up in a dependence trap; An HCO’s dependence on the GPO positively affects the HCO’s dependence on the OEM. Furthermore, an HCO’s dependence on a GPO and on an OEM affects the HCO’s assessment of (open full item for complete abstract)

Committee: W.C. Benton (Advisor); Peter Ward (Committee Member); Gökçe Esenduran (Committee Member) Subjects: Business Administration