UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item A GALLIUM NITRIDE INTEGRATED ONBOARD CHARGER(2020) Zou, Shenli; Khaligh, Alireza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Compared to Silicon metal–oxide–semiconductor field-effect transistors (MOSFETs), Gallium Nitride (GaN) devices have a significant reduction in gate charge, output capacitance, and zero reverse recovery charge, enabling higher switching frequency operation and efficient power conversion. GaN devices are gaining momentum in power electronic systems such as electric vehicle (EV) charging system, due to their promises to significantly enhance the power density and efficiency. In this dissertation, a GaN-based integrated onboard charger (OBC) and auxiliary power module (APM) is proposed for EVs to ensure high efficiency, high frequency, high power density, and capability of bidirectional operation. The high switching frequency operation enabled by the GaN devices and the integration of OBC and APM bring many unique challenges, which are addressed in this dissertation. An important challenge is the optimal design of high-frequency magnetics for a high-frequency GaN-based power electronic interface. Another challenge is to achieve power flow management among three active ports while minimizing the circulating power. Furthermore, the impact of circuit layout parasitics could significantly deteriorate the system interface, due to the sensitivity of GaN device switching characteristics. In this work, the aforementioned challenges have been addressed. First, a comprehensive analysis of the front-end AC-DC power factor correction stage is presented, covering a detailed magnetic modeling technique to address the high-frequency magnetics challenge. Second, the modeling and control of a three-port DC-DC converter, interfacing the AC-DC stage, high-voltage traction battery and low-voltage battery, are discussed to address the power flow challenge. Advanced control methodologies are developed to realize power flow management while maintaining minimum circulating power and soft switching. Furthermore, a new three-winding high-frequency transformer design with improved power density and efficiency is achieved using a genetic-algorithm-based optimization approach. Finally, a GaN-based integrated charger prototype is developed to validate the proposed theoretical hypothesis. The experimental results showed that the GaN-based charging system has the capability of achieving simultaneous charging (G2B) of both HV and LV batteries with a peak efficiency of 95%.Item INTEGRATED INDUCTIVE AND CONDUCTIVE CHARGING SYSTEM FOR ELECTRIC VEHICLES(2019) Uma Sankar, Arun Sankar Uma; Khaligh, Alireza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The global electric vehicle (EV) market acceleration is facilitated by supporting policies deployed by governments and cities to reap multiple benefits in the fields of transport decarbonization, air pollution reduction, energy efficiency, and security. Currently, conductive chargers are a customary method of storing electric energy into the storage elements present onboard of an EV which is inadequate in supporting complete autonomy. The thriving inclination towards the design of autonomous vehicles has shaped wireless charging as an attractive solution in favor of complete autonomy. As long as the wireless charging infrastructure, as well as interoperability standards, are not completely developed, wired and wireless chargers have to co-exist onboard the vehicles for user convenience. Incorporation of an entire parallel wireless charging system on-board an EV, either during manufacturing or after-market increases size, weight, or cost while declining the electric range of the vehicle. The current requisite for multiple on-board charging options motivate the necessity for a solution for efficiently integrating wired and wireless charging systems. In this Ph.D. research, we propose multiple charging architectures capable of integrating inductive and conductive charging systems. The proposed architectures merge the output rectifying stage of an inductive charging system to the existing on-board charger eliminating the additional weight and volume associated with a wireless charger. Since the proposed system involves multiple power conversion stages, a system level study is carried out to select feasible topologies capable of maximizing the efficiency of an integrated system. Additionally, an extended harmonic approximation (EHA) technique is introduced to increase the accuracy of a resonant converter model facilitating the optimized design parameter selection of an inductive charging system. Furthermore, a novel analog synchronous rectification circuit is proposed and designed to enable active rectification maximizing power transfer efficiency. For proof of concept verification, a laboratory prototype of a 3.3kW Silicon Carbide (SiC) based integrated wireless charger is developed that can be interfaced to a variable input voltage (85-265 Vrms) 50/60Hz AC grid. According to the experimental measurements, the charger draws an input current with a total harmonic distortion of 1.3% while achieving an overall efficiency of 92.77% at rated output power.Item APPLYING MARYLAND STATEWIDE ACTIVITY-BASED TRANSPORTATION MODEL TO HIGH-SPEED RAIL AND FUTURE FUEL PRICE SCENARIOS(2018) Asadabadi, Arash; Zhang, Lei; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Maryland Statewide Transportation Model 2.0 (MSTM 2.0) is composed of a Statewide Activity-based Travel Demand Model for Short-distance Travel at its core and two supporting models: An Activity-based Travel Demand Model for Long-distance Travel; and a Tour-based Travel Demand Model for Freight Travel. Therefore, MSTM 2.0 is a microsimulation model system within the activity-based framework for passenger travel, and tour-based framework for freight travel. These capabilities of MSTM 2.0 will enable policy makers to observe effects of their policies on different segments of population (e.g. income groups), which will lead to more equitable policies. In addition, it will help monitoring how travelers’ behavior and their activities change after certain transportation or land use policy is implemented. This thesis aims to demonstrate how MSTM 2.0 can be applied to different future scenarios; First, we test two different future fuel pricing scenarios considering the growth in market penetration of electric vehicles. MSTM 2.0 is revised to reflect how changes in light-duty vehicles fleet will change the auto operation cost and therefore alter the travel patterns for different segments of population in future. Second, the proposed high-speed rail Maglev project is implemented in the model to capture all the possible outcomes of adding a high-speed rail in the Northeast corridor between Washington D.C. and Baltimore. The results of this thesis can support state transportation policymaking by providing a comprehensive estimation of the effects that two likely future scenarios will have on Maryland transportation system.Item Modeling Vehicle Ownership Decisions in Maryland: A Preliminary Stated Preference Survey and Model(2010) Maness, Michael; Cirillo, Cinzia; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In the near future, the culmination of new vehicle technologies, greater competition in the energy markets, and government policies to fight pollution and reduce energy consumption will result in changes in the United States' vehicle marketplace. This project proposes to create a stated preference (SP) survey along with discrete choice models to predict future demand for electric, hybrid, alternative fuel, and gasoline vehicles. The survey is divided into three parts: socioeconomics, revealed preference (RP), and SP sections. The socioeconomics portion asks respondents about themselves and their households. The RP portion asks about household's current vehicles. The SP section presents respondents with various hypothetical scenarios over a future five-year period using one of three game designs. The designs correspond to: changing vehicle technology, fuel pricing and availability, and taxation policy. With these changes to the vehicle marketplace, respondents are asked whether they will keep or replace their current vehicles and if he will purchase a new vehicle and its type. To facilitate the design and administering of the survey, a web survey framework, JULIE, was created specifically for creating stated preference surveys. A preliminary trial of the survey was conducted in September and October 2010 with a sample size of 141 respondents. Using the SP results from this preliminary trial, a multinomial logit model is used to estimate future vehicle ownership by vehicle type. The models show that the survey design allows for estimation of important parameters in vehicle choice.