Current Search: Powers (x)
Pages
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Title
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Power Effects on Consumer Well-Being: Two Essays on The Power Effects on Donation and Material/Experiential Consumption.
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Creator
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Liu, Yue, He, Xin, Tafaghodijami, Ata, Massiah, Carolyn, Yang, Xiaojing, Mao, Huifang, University of Central Florida
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Abstract / Description
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Power is a fundamental concept in social science (Russell 1938), which has gained much academic attention in various disciplines. Two essays of this dissertation examine the theoretical and practical implications of power effects on donation decisions and material/experiential consumption.The first essay demonstrates power's moderating effect on the relationship between publicity and donation. Specifically, it is proposed that powerful people tend to donate more in public (vs. private)...
Show morePower is a fundamental concept in social science (Russell 1938), which has gained much academic attention in various disciplines. Two essays of this dissertation examine the theoretical and practical implications of power effects on donation decisions and material/experiential consumption.The first essay demonstrates power's moderating effect on the relationship between publicity and donation. Specifically, it is proposed that powerful people tend to donate more in public (vs. private) situation, whereas powerless people do not show such a difference. This effect is driven by people's concern about self-presentation in a donation scenario. Additionally, this effect only holds when people strongly believe that high donation enhances others' positive impression of them, but dilutes when such belief is not held. The theorizing is supported across four studies.The second essay focuses on how power influences consumers' preferences for material and experiential products. It is predicted that those who feel powerless tend to spend more of their discretionary money on material products than experiential products. This effect occurs through feelings of resourcefulness caused by possessing material or experiential goods. In addition, this effect is further moderated by implicit theory, such that the impact of power on material versus experience product choice persists for incremental theorists but dissipates for entity theorists. Three experiments provide support to this proposition.Overall, by investigating how power influences people's donation behavior and choice of material/experiential products, this dissertation strengthens the understanding of power's effectson consumer behavior and provides practical implications on how power status can influence consumers' well-being.
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Date Issued
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2017
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Identifier
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CFE0006894, ucf:51710
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0006894
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Title
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A New Six Sigma Implementation Approach For Power Generation Gas Turbines Repair Process Development.
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Creator
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Ghunakikar, Somesh, Elshennawy, Ahmad, Rabelo, Luis, Thompson, William, Furterer, Sandra, University of Central Florida
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Abstract / Description
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Power Generation gas turbines used for heavy duty application mainly constitutes three modules; compressor, combustion and turbine. Typically, all these parts are designed by OEM companies for specific number of hours and cycles (also known as starts) before they become dysfunctional. In addition, Gas Turbine (GT) also have intended repair interval depending upon the type of part application and anticipated damages during service operation. Thus, GT parts need inspections and repair (overhaul...
Show morePower Generation gas turbines used for heavy duty application mainly constitutes three modules; compressor, combustion and turbine. Typically, all these parts are designed by OEM companies for specific number of hours and cycles (also known as starts) before they become dysfunctional. In addition, Gas Turbine (GT) also have intended repair interval depending upon the type of part application and anticipated damages during service operation. Thus, GT parts need inspections and repair (overhaul) after certain operating hours in order to recondition them so that they can be fit for reoperation to produce power. In this dissertation, a unique six sigma DFSS approach for development of GT parts overhaul is presented for total quality improvement. In this dissertation report, a unique six sigma DFSS approach is presented applicable to the development of repair processes for GT parts that can be used during overhauling of the parts. All six sigma phases of the proposed DFSS approach along with repair product development cycle are discussed. Various six sigma tools which yield significant benefits for the process users are also discussed. Importantly, a statistical probabilistic life analysis approach is proposed in order to verify the structural integrity of a repaired GT part. Finally a case study of GT axial compressor diaphragms (stators) to illustrate various phases and six sigma tools usage during each phase of the DFSS approach is discussed. The overall significant benefit of the proposed DFSS approach was to achieve total quality improvement to deliver final GT repair process, faster repair development cycle and end customer satisfaction.
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Date Issued
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2016
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Identifier
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CFE0006105, ucf:51199
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0006105
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Title
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Impact of wireless channel uncertainty upon M-ary distributed detection systems.
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Creator
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Hajibabaei Najafabadi, Zahra, Vosoughi, Azadeh, Rahnavard, Nazanin, Atia, George, University of Central Florida
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Abstract / Description
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We consider a wireless sensor network (WSN), consisting of several sensors and a fusion center (FC), which is tasked with solving an $M$-ary hypothesis testing problem. Sensors make $M$-ary decisions and transmit their digitally modulated decisions over orthogonal channels, which are subject to Rayleigh fading and noise, to the FC. Adopting Bayesian optimality criterion, we consider training and non-training based distributed detection systems and investigate the effect of imperfect channel...
Show moreWe consider a wireless sensor network (WSN), consisting of several sensors and a fusion center (FC), which is tasked with solving an $M$-ary hypothesis testing problem. Sensors make $M$-ary decisions and transmit their digitally modulated decisions over orthogonal channels, which are subject to Rayleigh fading and noise, to the FC. Adopting Bayesian optimality criterion, we consider training and non-training based distributed detection systems and investigate the effect of imperfect channel state information (CSI) on the optimal maximum a posteriori probability (MAP) fusion rules and detection performance, when the sum of training and data symbol transmit powers is fixed. Our results show that for Rayleigh fading channel, when sensors employ $M$-FSK or binary FSK (BFSK) modulation, the error probability is minimized when training symbol transmit power is zero (regardless of the reception mode at the FC). However, for coherent reception, $M$-PSK and binary PSK (BPSK) modulation the error probability is minimized when half of transmit power is allocated for training symbol. If the channel is Rician fading, regardless of the modulation, the error probability is minimized when training transmit power is zero.
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Date Issued
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2016
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Identifier
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CFE0006111, ucf:51209
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0006111
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Title
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MODELING AND ANALYSIS OF POWER MOSFETS FOR HIGH FREQUENCY DC-DC CONVERTERS.
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Creator
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Xiong, Yali, Shen, John, University of Central Florida
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Abstract / Description
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Evolutions in integrated circuit technology require the use of a high-frequency synchronous buck converter in order to achieve low cost, low profile, fast transient response and high power density. However, high frequency operation leads to increased power MOSFET switching losses. Optimization of the MOSFETs plays an important role in improving converter performance. This dissertation focuses on revealing the power loss mechanism of power MOSFETs and the relationship between power MOSFET...
Show moreEvolutions in integrated circuit technology require the use of a high-frequency synchronous buck converter in order to achieve low cost, low profile, fast transient response and high power density. However, high frequency operation leads to increased power MOSFET switching losses. Optimization of the MOSFETs plays an important role in improving converter performance. This dissertation focuses on revealing the power loss mechanism of power MOSFETs and the relationship between power MOSFET structure and its power loss. The analytical device model, combined with circuit modeling, cannot reveal the relationship between device structure and its power loss due to the highly non-linear characteristics of power MOSFETs. A physically-based mixed device/circuit modeling approach is used to investigate the power losses of the MOSFETs under different operating conditions. The physically based device model, combined with SPICE-like circuit simulation, provides an expeditious and inexpensive way of evaluating and optimizing circuit and device concepts. Unlike analytical or other SPICE models of power MOSFETs, the numerical device model, relying little on approximations or simplifications, faithfully represents the behavior of realistic power MOSFETs. The impact of power MOSFET parameters on efficiency of synchronous buck converters, such as gate charge, on resistance, reverse recovery, is studied in detail in this thesis. The results provide a good indication on how to optimize power MOSFETs used in VRMs. The synchronous rectifier plays an important role in determining the performance of the synchronous buck converter. The reverse recovery of its body diode and the Cdv/dt induced false trigger-on are two major mechanisms that impact SyncFET's performance. This thesis gives a detailed analysis of the SyncFET operation mechanism and provides several techniques to reduce its body-diode influence and suppress its false Cdv/dt trigger-n. This thesis also investigates the influence of several circuit level parameters on the efficiency of the synchronous buck converter, such as input voltage, circuit parasitic inductance, and gate resistance to provide further optimization of synchronous buck converter design.
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Date Issued
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2008
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Identifier
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CFE0002278, ucf:47858
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0002278
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Title
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Dynamic modeling of pwm and single-switch single-stage power factor correction converters.
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Creator
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Zhu, Guangyong, Batarseh, Issa E., Engineering
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Abstract / Description
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University of Central Florida College of Engineering Thesis; The concept of averaging has been used extensively in the modeling of power electronic circuits to overcome their inherent time-variant nature. Among various methods, the PWM switch modeling approach is most widely accepted in the study of closed-loop stability and transient response because of its accuracy and simplicity. However, a non-ideal PWM switch model considering conduction losses is not available except for converters...
Show moreUniversity of Central Florida College of Engineering Thesis; The concept of averaging has been used extensively in the modeling of power electronic circuits to overcome their inherent time-variant nature. Among various methods, the PWM switch modeling approach is most widely accepted in the study of closed-loop stability and transient response because of its accuracy and simplicity. However, a non-ideal PWM switch model considering conduction losses is not available except for converters operating in continuous conduction mode (CCM) and under small ripple conditions. Modeling of conductor losses under large ripple conditions has not been reported in the open literature, especially when the converter operates in discontinuous conduction mode (DCM). In this dissertation, new models are developed to include conduction losses in the non-ideal PWM switch model under CCM and DCM conditions. The developed model is verified through two converter examples and the effect of conduction losses on the steady state and dynamic responses of the converter is also studied. Another major constraint of the PWM switch modeling approach is that it heavily relies on finding the three-terminal PWM switch. This requirement severely limits its application in modeling single-switch single-stage power factor correction (PFC) converters, where more complex topological structures and switching actions are often encountered. In this work, we developed a new modeling approach which extends the PWM switch concept by identifying the charging and discharging voltages applied to the inductors. The new method can be easily applied to derive large-signal models for a large group of PFC converters and the procedure is elaborated through a specific example. Finally, analytical results regarding harmonic contents and power factors of various PWM converters in PFC applications are also presented here.
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Date Issued
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1999
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Identifier
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CFR0001716, ucf:52925
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFR0001716
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Title
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The effects of dynamic versus isometric postactivation potentiation on collegiate female rowers.
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Creator
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Harat, Idan, Fukuda, David, Stout, Jeffrey, Wells, Adam, University of Central Florida
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Abstract / Description
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Post-activation potentiation (PAP) has been shown to improve acute power-based performance, and the potential to enhance rowing performance. To examine PAP effects with rowing performance, 40 collegiate female rowers performed isometric potentiating (ISO), dynamic potentiating (DYN) and typical control (CON) warm-up protocols, after which they completed a three-minute all-out test (3MT) to evaluate their total distance, peak power, mean power, critical power, anaerobic working capacity (W')...
Show morePost-activation potentiation (PAP) has been shown to improve acute power-based performance, and the potential to enhance rowing performance. To examine PAP effects with rowing performance, 40 collegiate female rowers performed isometric potentiating (ISO), dynamic potentiating (DYN) and typical control (CON) warm-up protocols, after which they completed a three-minute all-out test (3MT) to evaluate their total distance, peak power, mean power, critical power, anaerobic working capacity (W') and stroke rate. Fifteen-second splits for distance and mean power were also analyzed. The PAP protocols were performed on a rowing ergometer, in a movement pattern that simulated rowing. ISO consisted of 5 (&)#215; 5-second static muscle actions with the ergometer handle rendered immovable with a nylon boat-strap, while DYN consisted of 2 (&)#215; 10-second all-out rowing bouts, separated by a 2-minute rest interval. A two-way (condition by experience level) interaction was found for distance, mean power and W' with significant differences (DYN (>) CON; 5.6 m, 5.9W and 1561.6 J) for more experienced rowers ((>)3.75 years; n=19) and no differences for less experienced rowers (n=18). A main effect for stroke rate was found with DYN(>)CON (1 s/min). Split analysis of mean power output revealed a two-way (condition by 15s split) interaction independent from experience level. Mean power in DYN was significantly greater than CON and ISO in the 15-30, 30-45, 45-60 and 60-75 second intervals. These results suggest that dynamic PAP may be beneficial for experienced rowers and that these strategies might benefit a greater power output over shorter distances regardless of experience. Future studies should investigate potential benefits of this protocol over a full race distance and identify the difference between experienced and less experienced rowers.
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Date Issued
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2019
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Identifier
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CFE0007465, ucf:52665
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0007465
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Title
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HIGHLY INTEGRATED DC-DC CONVERTERS.
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Creator
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Jia, Hongwei, Shen, Zhen, University of Central Florida
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Abstract / Description
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A monolithically integrated smart rectifier has been presented first in this work. The smart rectifier, which integrates a power MOSFET, gate driver and control circuitry, operates in a self-synchronized fashion based on its drain-source voltage, and does not need external control input. The analysis, simulation, and design considerations are described in detail. A 5V, 5-μm CMOS process was used to fabricate the prototype. Experimental results show that the proposed rectifier functions...
Show moreA monolithically integrated smart rectifier has been presented first in this work. The smart rectifier, which integrates a power MOSFET, gate driver and control circuitry, operates in a self-synchronized fashion based on its drain-source voltage, and does not need external control input. The analysis, simulation, and design considerations are described in detail. A 5V, 5-μm CMOS process was used to fabricate the prototype. Experimental results show that the proposed rectifier functions as expected in the design. Since no dead-time control needs to be used to switch the sync-FET and ctrl-FET, it is expected that the body diode losses can be reduced substantially, compared to the conventional synchronous rectifier. The proposed self-synchronized rectifier (SSR) can be operated at high frequencies and maintains high efficiency over a wide load range. As an example of the smart rectifierÃÂÃÂÃÂÃÂ's application in isolated DC-DC converter, a synchronous flyback converter with SSR is analyzed, designed and tested. Experimental results show that the operating frequency could be as high as 4MHz and the efficiency could be improved by more than 10% compared to that when a hyper fast diode rectifier is used. Based on a new current-source gate driver scheme, an integrated gate driver for buck converter is also developed in this work by using a 0.35μm CMOS process with optional high voltage (50V) power MOSFET. The integrated gate driver consists both the current-source driver for high-side power MOSFET and low-power driver for low-side power iv MOSFET. Compared with the conventional gate driver circuit, the current-source gate driver can recovery some gate charging energy and reduce switching loss. So the current-source driver (CSD) can be used to improve the efficiency performance in high frequency power converters. This work also presents a new implementation of a power supply in package (PSiP) 5MHz buck converter, which is different from all the prior-of-art PSiP solutions by using a high-Q bondwire inductor. The high-Q bondwire inductor can be manufactured by applying ferrite epoxy to the common bondwire during standard IC packaging process, so the new implementation of PSiP is expected to be a cost-effective way of power supply integration.
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Date Issued
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2010
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Identifier
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CFE0003040, ucf:48354
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0003040
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Title
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Mission Analysis for Pico-Scale Satellite Based Dust Detection in Low Earth Orbits.
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Creator
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Belli, Jacob, Xu, Yunjun, Lin, Kuo-Chi, Bradley, Eric, University of Central Florida
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Abstract / Description
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A conceptual dust detection mission, KnightSat III, using pico-scale satellites is analyzed. The purpose of the proposed KnightSat III mission is to aid in the determination of the size, mass, distribution, and number of dust particles in low earth orbits through a low cost and flexible satellite or a formation of satellites equipped with a new dust detector. The analysis of a single satellite mission with an on-board dust detector is described; though this analysis can easily be extended to...
Show moreA conceptual dust detection mission, KnightSat III, using pico-scale satellites is analyzed. The purpose of the proposed KnightSat III mission is to aid in the determination of the size, mass, distribution, and number of dust particles in low earth orbits through a low cost and flexible satellite or a formation of satellites equipped with a new dust detector. The analysis of a single satellite mission with an on-board dust detector is described; though this analysis can easily be extended to a formation of pico-scale satellites. Many design aspects of the mission are discussed, including orbit analysis, power management, attitude determination and control, and mass and power budgets. Two of them are emphasized. The first is a new attitude guidance and control method, and the second is the online optimal power scheduling. It is expected that the measurements obtained from this possible future mission will provide insight into the dynamical processes of inner solar system dust, as well as aid in designing proper micro-meteoroid impact mitigation strategies for future man-made spacecraft.
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Date Issued
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2013
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Identifier
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CFE0004813, ucf:49728
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0004813
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Title
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MAXIMUM ENERGY HARVESTING CONTROL FOROSCILLATING ENERGY HARVESTING SYSTEMS.
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Creator
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Elmes, John, Batarseh, Issa, University of Central Florida
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Abstract / Description
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This thesis presents an optimal method of designing and controlling an oscillating energy harvesting system. Many new and emerging energy harvesting systems, such as the energy harvesting backpack and ocean wave energy harvesting, capture energy normally expelled through mechanical interactions. Often the nature of the system indicates slow system time constants and unsteady AC voltages. This paper reveals a method for achieving maximum energy harvesting from such sources with fast...
Show moreThis thesis presents an optimal method of designing and controlling an oscillating energy harvesting system. Many new and emerging energy harvesting systems, such as the energy harvesting backpack and ocean wave energy harvesting, capture energy normally expelled through mechanical interactions. Often the nature of the system indicates slow system time constants and unsteady AC voltages. This paper reveals a method for achieving maximum energy harvesting from such sources with fast determination of the optimal operating condition. An energy harvesting backpack, which captures energy from the interaction between the user and the spring decoupled load, is presented in this paper. The new control strategy, maximum energy harvesting control (MEHC), is developed and applied to the energy harvesting backpack system to evaluate the improvement of the MEHC over the basic maximum power point tracking algorithm.
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Date Issued
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2007
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Identifier
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CFE0001822, ucf:47345
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0001822
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Title
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CONTROL STRATEGY FOR MAXIMIZING POWER CONVERSION EFFICIENCY AND EFFECTIVENESS OF THREE PORT SOLAR CHARGING STATION FOR ELECTRIC VEHICLES.
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Creator
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Hamilton, Christopher, Batarseh, Issa, University of Central Florida
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Abstract / Description
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Recent trends in the energy sector have provided opportunities in the research of alternative energy sources and optimization of systems that harness these energy sources. With the rising cost of fossil fuel and rising concern about detrimental effects that fossil fuel consumption has on the environment, electric vehicles are becoming more prevalent. A study put out in 2009 gives a prediction that in the year 2025, 20% of new vehicles will be PHEVs. As energy providers become more concerned...
Show moreRecent trends in the energy sector have provided opportunities in the research of alternative energy sources and optimization of systems that harness these energy sources. With the rising cost of fossil fuel and rising concern about detrimental effects that fossil fuel consumption has on the environment, electric vehicles are becoming more prevalent. A study put out in 2009 gives a prediction that in the year 2025, 20% of new vehicles will be PHEVs. As energy providers become more concerned about a growing population and diminishing energy source, they are looking into alternative energy sources such as wind and solar power. Much of this is done on a large scale with vast amounts of land used for solar or wind farms to provide energy to the grid. However, as population grows, requirements of the physical components of a power transmission system will become more demanding and the need for remote micro-grids will become more prevalent. Micro-grids are essentially smaller subsystems of a distribution system that provide power to a confined group of loads, or households. Using the idea of micro grid technology, a solar charging station can be used as a source to provide energy for the immediate surroundings, or also to electric vehicles that are demanding energy from the panels. Solar charging stations are becoming very popular, however the need for improvement and optimization of these systems is needed. This thesis will present a method for redesigning the overall architecture of the controls and power electronics of typical carports so that efficiency, reliability and modularity are achieved. Specifically, a typical carport, as seen commonly today, has been built on the University of Central Florida campus in Orlando. This carport was designed in such a way that shifting from conventional charging methods is made easy while preserving the fundamental requirements of a practical solar carport.
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Date Issued
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2010
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Identifier
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CFE0003490, ucf:48954
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0003490
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Title
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Wireless Power Transfer for Space Applications: System Design and Electromagnetic Compatibility Compliance of Radiated Emissions.
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Creator
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Vazquez Ramos, Gabriel, Yuan, Jiann-Shiun, Sundaram, Kalpathy, Wu, Xinzhang, Soto Toro, Felix, University of Central Florida
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Abstract / Description
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This dissertation evaluates the possibility of wireless power transfer (WPT) systems for space applications, with an emphasis in launch vehicles (rockets). After performing literature review for WPT systems, it was identified that magnetic resonance provides the more suited set of characteristics for this application. Advanced analysis, simulation and testing were performed to magnetic resonance WPT systems to acquire system performance insight. This was accomplished by evaluating/varying...
Show moreThis dissertation evaluates the possibility of wireless power transfer (WPT) systems for space applications, with an emphasis in launch vehicles (rockets). After performing literature review for WPT systems, it was identified that magnetic resonance provides the more suited set of characteristics for this application. Advanced analysis, simulation and testing were performed to magnetic resonance WPT systems to acquire system performance insight. This was accomplished by evaluating/varying coupling configuration, load effects and magnetic element physical characteristics (i.e. wire material, loop radius, etc.). It was identified by analysis, circuit simulation and testing that the best coupling configuration for this application was series-series and series-shunt with Litz wire loop inductors. The main concern identified for the implementation of these systems for space applications was radiated emissions that could potentially generate electromagnetic interference (EMI). To address this EMI concern, we developed the Electromagnetic Compatibility Radiated Emissions Compliance Design Evaluation Approach for WPT Space Systems. This approach systematically allocates key analyses, simulations and tests procedures to predict WPT EMC compliance to NASA's EMC standard Mil-Std-461E/F. Three prototype/magnetic elements were successfully assessed by implementing the WPT EMC design approach. The electric fields intensity generated by the WPT prototypes/magnetic elements tested were: 30.02 dBuV/m, 28.90 dBuV/m and 82.13 dBuV/m (requirement limit: 140 dBuV/m). All three prototypes successfully transferred power wirelessly and successfully met the NASA EMC requirements.
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Date Issued
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2012
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Identifier
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CFE0004448, ucf:49344
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0004448
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Title
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THE EFFECTS OF POWER DISTANCE, AND GENDER ON THE USE OF NONVERBAL IMMEDIACY BEHAVIORS IN SYMMETRICAL AND ASYMMETRICAL POWER CONDITIONS: A CROSS-CULTURAL STUDY.
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Creator
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Santilli, Vincent, Miller, Ann, University of Central Florida
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Abstract / Description
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Previous cross-cultural research in nonverbal immediacy indicates that nonverbal immediacy behavior varies across cultures, and some researchers have suggested that power distance might serve as a moderating variable, however no research has systematically set out to determine whether that is the case. This study assessed the perceived use of nonverbal immediacy under symmetric and asymmetric power conditions, as well as gender, in three cultures: Brazil, Kenya, and the United States....
Show morePrevious cross-cultural research in nonverbal immediacy indicates that nonverbal immediacy behavior varies across cultures, and some researchers have suggested that power distance might serve as a moderating variable, however no research has systematically set out to determine whether that is the case. This study assessed the perceived use of nonverbal immediacy under symmetric and asymmetric power conditions, as well as gender, in three cultures: Brazil, Kenya, and the United States. Quantitative data was collected from 527 participants who completed a nonverbal immediacy measure and an individual power distance measure under either a symmetric or an asymmetric power condition. Results related to power distance partially supported the idea that cultural power distance may act as a moderating variable with regard to the use of nonverbal immediacy behaviors. Related to gender, results revealed that: (a) female participants perceived more nonverbal immediacy behaviors than males, (b) under symmetric power conditions females were perceived to use more nonverbal immediacy than males, and (c) under asymmetric power conditions there was no statistically significant difference between use of nonverbal immediacy behaviors between females and males. Implications of results, limitations, and suggestions for future research are presented.
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Date Issued
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2010
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Identifier
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CFE0003043, ucf:48368
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0003043
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Title
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ANALYSIS AND DESIGN OF A MODULAR SOLAR-FED FAULT-TOLERANT POWER SYSTEM WITH MAXIMUM POWER POINT TRACKING.
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Creator
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Al-Atrash, Hussam, Batarseh, Issa, University of Central Florida
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Abstract / Description
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Solar power is becoming ever more popular in a variety of applications. It is particularly attractive because of its abundance, renewability, and environment friendliness. Solar powered spacecraft systems have ever-expanding loads with stringent power regulation specifications. Moreover, they require a light and compact design of their power system. These constraints make the optimization of power harvest from solar arrays a critical task. Florida Power Electronics Center (FPEC) at UCF set to...
Show moreSolar power is becoming ever more popular in a variety of applications. It is particularly attractive because of its abundance, renewability, and environment friendliness. Solar powered spacecraft systems have ever-expanding loads with stringent power regulation specifications. Moreover, they require a light and compact design of their power system. These constraints make the optimization of power harvest from solar arrays a critical task. Florida Power Electronics Center (FPEC) at UCF set to develop a modular fault-tolerant power system architecture for space applications. This architecture provides a number of very attractive features including Maximum Power Point Tracking (MPPT) and uniform power stress distribution across the system. MPPT is a control technique that leads the system to operate its solar sources at the point where they provide maximum power. This point constantly moves following changes in ambient operating conditions. A digital controller is setup to locate it in real time while optimizing other operating parameters. This control scheme can increase the energy yield of the system by up to 45%, and thus significantly reduces the size and weight of the designed system. The modularity of the system makes it easy to prototype and expand. It boosts its reliability and allows on-line reconfiguration and maintenance, thus reducing down-time upon faults. This thesis targets the analysis and optimization of this architecture. A new modeling technique is introduced for MPPT in practical environments, and a novel digital power stress distribution scheme is proposed in order to properly distribute peak and thermal stress and improve reliability. A 2kW four-channel prototype of the system was built and tested. Experimental results confirm the theoretical improvements, and promise great success in the field.
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Date Issued
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2005
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Identifier
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CFE0000469, ucf:46357
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0000469
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Title
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MODELING,DESIGN,AND CHARACTERIZATION OF MONOLITHIC BI-DIRECTIONAL POWER SEMICONDUCTOR SWITCH.
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Creator
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Fu, Yue, Shen, Z.John, University of Central Florida
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Abstract / Description
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Bidirectional power switching devices are needed in many power management applications, particularly in lithium-ion battery protection circuitry. A monolithic bidirectional power switch fabricated with a simplified CMOS technology is introduced in this dissertation. Throughout the design process, ISE TCAD tool plays an important role. Design variables are carefully analyzed to improve the device performance or yield the best trade off. Optimization is done with the help of TCAD simulation and...
Show moreBidirectional power switching devices are needed in many power management applications, particularly in lithium-ion battery protection circuitry. A monolithic bidirectional power switch fabricated with a simplified CMOS technology is introduced in this dissertation. Throughout the design process, ISE TCAD tool plays an important role. Design variables are carefully analyzed to improve the device performance or yield the best trade off. Optimization is done with the help of TCAD simulation and theoretical calculations. The device has been successfully fabricated using simplified 0.5 micron CMOS process. The experimental result shows a breakdown voltage of 25V. Due to the interdigitated source to source design, the inter-terminal current flowing path is effectively reduced to a few microns. The experimental result shows an ultra low specific on resistance. In comparison with other bi-directional power semiconductor switches by some major semiconductor manufacturers, the proposed BDS device has less than one half of the specific on resistance, thus substantially lower on state power loss of the switch. The proposed BDS device has a unique NPNPN structure, in comparison with NPNP structure, which is the analytical structure for CMOS latch-up, the proposed device inherently exhibits a better latch up immunity than CMOS inverter, thanks to the negative feed back mechanism of the extra NPN parasitic BJT transistor. In order to implement the device into simulators like PSPICE or Cadence IC Design, a compact model named variable resistance model has been built. This simple analytical model fits quite well with experimental data, and can be easily implemented by Verilog-A or other hardware description languages. Also, macro modeling is possible provided that the model parameters can be extracted from experimental curves. Several advanced types of BDS devices have been proposed, they exceed the basic BDS design in terms of breakdown voltage and /or on resistance. These advanced structures may be prominent for further improvement of the basic BDS device to a higher extend. Some cell phone providers such as Nokia is already asking for higher breakdown voltage of BDS device, due to the possibility of incidentally insert the battery pack into the cell phone with wrong pin polarity. Hopefully, the basic BDS design or one of these advanced types may eventually be implemented into the leading brand cell phone battery packs.
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Date Issued
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2007
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Identifier
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CFE0001605, ucf:47168
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0001605
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Title
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DESIGN, MODELING, AND CONTROL OF THREE-PORT CONVERTERS FOR SOLAR POWER APPLICATIONS.
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Creator
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Reese, Justin, Batarseh, Issa, University of Central Florida
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Abstract / Description
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This paper describes the results of research into multi-port converter design and control, specifically a pair of three-port topologies based on the half-bridge and full-bridge topologies. These converters are capable of simultaneous and independent regulation of two out of their three ports, while the third port provides the power balance in the system. A dynamic model was developed for each topology to aid in testing and for designing the control loops. The models were then used to design...
Show moreThis paper describes the results of research into multi-port converter design and control, specifically a pair of three-port topologies based on the half-bridge and full-bridge topologies. These converters are capable of simultaneous and independent regulation of two out of their three ports, while the third port provides the power balance in the system. A dynamic model was developed for each topology to aid in testing and for designing the control loops. The models were then used to design the control structures, and the results were tested in Simulink. In addition, a basic outline of a system level architecture to control multiple converters working in parallel is presented. To improve the reliability of this system, output current sharing controls were also developed. Finally, one of the topologies is analyzed in detail in order to obtain a set of design equations that can be used to improve the efficiency, weight, and cost of the converter for a specific application.
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Date Issued
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2007
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Identifier
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CFE0001921, ucf:47487
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0001921
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Title
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TRANSIENT RESPONSE IMPROVEMENT FOR MULTI-PHASE VOLTAGE REGULATORS.
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Creator
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Xiao, Shangyang, Batarseh, Issa, University of Central Florida
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Abstract / Description
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Next generation microprocessor (Vcore) requirements for high current slew rates and fast transient response together with low output voltage have posed great challenges on voltage regulator (VR) design . Since the debut of Intel 80X86 series, CPUs have greatly improved in performance with a dramatic increase on power consumption. According to the latest Intel VR11 design guidelines , the operational current may ramp up to 140A with typical voltages in the 1.1V to 1.4V range, while the slew...
Show moreNext generation microprocessor (Vcore) requirements for high current slew rates and fast transient response together with low output voltage have posed great challenges on voltage regulator (VR) design . Since the debut of Intel 80X86 series, CPUs have greatly improved in performance with a dramatic increase on power consumption. According to the latest Intel VR11 design guidelines , the operational current may ramp up to 140A with typical voltages in the 1.1V to 1.4V range, while the slew rate of the transient current can be as high as 1.9A/ns [1, 2]. Meanwhile, the transient-response requirements are becoming stringer and stringer. This dissertation presents several topics on how to improve transient response for multi-phase voltage regulators. The Adaptive Modulation Control (AMC) is a type of non-linear control method which has proven to be effective in achieving high bandwidth designs as well as stabilizing the control loop during large load transients. It adaptively adjusts control bandwidth by changing the modulation gain, depending on different load conditions. With the AMC, a multiphase voltage regulator can be designed with an aggressively high bandwidth. When in heavy load transients where the loop could be potentially unstable, the bandwidth is lowered. Therefore, the AMC provides an optimal means for robust high-bandwidth design with excellent transient performance. The Error Amplifier Voltage Positioning (EAVP) is proposed to improve transient response by removing undesired spikes and dips after initial transient response. The EAVP works only in a short period of time during transient events without modifying the power stage and changing the control loop gain. It facilitates the error amplifier voltage recovering during transient events, achieving a fast settling time without impact on the whole control loop. Coupled inductors are an emerging topology for computing power supplies as VRs with coupled inductors show dynamic and steady-state advantages over traditional VRs. This dissertation first covers the coupling mechanism in terms of both electrical and reluctance modeling. Since the magnetizing inductance plays an important role in the coupled-inductor operation, a unified State-Space Averaging model is then built for a two-phase coupled-inductor voltage regulator. The DC solutions of the phase currents are derived in order to show the impact of the magnetizing inductance on phase current balancing. A small signal model is obtained based on the state-space-averaging model. The effects of magnetizing inductance on dynamic performance are presented. The limitations of conventional DCR current-sensing for coupled inductors are addressed. Traditional inductor DCR current sensing topology and prior arts fail to extract phase currents for coupled inductors. Two new DCR current sensing topologies for coupled inductors are presented in this dissertation. By implementation of simple RC networks, the proposed topologies can preserve the coupling effect between phases. As a result, accurate phase inductor currents and total current can be sensed, resulting in excellent current and voltage regulation. While coupled-inductor topologies are showing advantages in transient response and are becoming industry practices, they are suffering from low steady-state operating efficiency. Motivated by the challenging transient and efficiency requirements, this dissertation proposes a Full Bridge Coupled Inductor (FBCI) scheme which is able to improve transient response as well as savor high efficiency at (a) steady state. The FBCI can change the circuit configuration under different operational conditions. Its "flexible" topology is able to optimize both transient response and steady-state efficiency. The flexible core configuration makes implementation easy and clear of IP issues. A novel design methodology for planar magnetics based on numerical analysis of electromagnetic fields is offered and successfully applied to the design of low-voltage high power density dc-dc converters. The design methodology features intense use of FEM simulation. The design issues of planar magnetics, including loss mechanism in copper and core, winding design on PCB, core selections, winding arrangements and so on are first reviewed. After that, FEM simulators are introduced to numerically compute the core loss and winding loss. Consequently, a software platform for magnetics design is established, and optimized magnetics can then be achieved. Dynamic voltage scaling (DVS) technology is a common industry practice in optimizing power consumption of microprocessors by dynamically altering the supply voltage under different operational modes, while maintaining the performance requirements. During DVS operation, it is desirable to position the output voltage to a new level commanded by the microprocessor (CPU) with minimum delay. However, voltage deviation and slow settling time usually exist due to large output capacitance and compensation delay in voltage regulators. Although optimal DVS can be achieved by modifying the output capacitance and compensation, this method is limited by constraints from stringent static and dynamic requirements. In this dissertation, the effects of output capacitance and compensation network on DVS operation are discussed in detail. An active compensator scheme is then proposed to ensure smooth transition of the output voltage without change of power stage and compensation during DVS. Simulation and experimental results are included to demonstrate the effectiveness of the proposed scheme.
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Date Issued
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2008
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Identifier
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CFE0002397, ucf:47738
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0002397
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Title
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FPGA-BASED DESIGN OF A MAXIMUM-POWER-POINT TRACKING SYSTEM FOR SPACE APPLICATIONS.
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Creator
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Persen, Todd, Ejnioui, Abdel, University of Central Florida
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Abstract / Description
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Satellites need a source of power throughout their missions to help them remain operational for several years. The power supplies of these satellites, provided primarily by solar arrays, must have high efficiencies and low weights in order to meet stringent design constraints. Power conversion from these arrays is required to provide robust and reliable conversion which performs optimally in varying conditions of peak power, solar flux, and occlusion conditions. Since the role of these arrays...
Show moreSatellites need a source of power throughout their missions to help them remain operational for several years. The power supplies of these satellites, provided primarily by solar arrays, must have high efficiencies and low weights in order to meet stringent design constraints. Power conversion from these arrays is required to provide robust and reliable conversion which performs optimally in varying conditions of peak power, solar flux, and occlusion conditions. Since the role of these arrays is to deliver power, one of the principle factors in achieving maximum power output from an array is tracking and holding its maximum-power point. This point, which varies with temperature, insolation, and loading conditions, must be continuously monitored in order to react to rapid changes. Until recently, the control of maximum power point tracking (MPPT) has been implemented in microcontrollers and digital signal processors (DSPs). While DSPs can provide a reasonable performance, they do not provide the advantages that field-programmable gate arrays (FPGA) chips can potentially offer to the implementation of MPPT control. In comparison to DSP implementations, FPGAs offer lower cost implementations since the functions of various components can be integrated onto the same FPGA chip as opposed to DSPs which can perform only DSP-related computations. In addition, FPGAs can provide equivalent or higher performance with the customization potential of an ASIC. Because FPGAs can be reprogrammed at any time, repairs can be performed in-situ while the system is running thus providing a high degree of robustness. Beside robustness, this reprogrammability can provide a high level of (i) flexibility that can make upgrading an MPPT control system easy by merely updating or modifying the MPPT algorithm running on the FPGA chip, and (ii) expandability that makes expanding an FPGA-based MPPT control system to handle multi-channel control. In addition, this reprogrammability provides a level of testability that DSPs cannot match by allowing the emulation of the entire MPPT control system onto the FPGA chip. This thesis proposes an FPGA-based implementation of an MPPT control system suitable for space applications. At the core of this system, the Perturb-and-observe algorithm is used to track the maximum power point. The algorithm runs on an Alera FLEX 10K FPGA chip. Additional functional blocks, such as the ADC interface, FIR filter, dither generator, and DAC interface, needed to support the MPPT control system are integrated within the same FPGA device thus streamlining the part composition of the physical prototype used to build this control system.
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Date Issued
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2004
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Identifier
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CFE0000287, ucf:46232
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0000287
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Title
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SMALL-SCALE HYBRID ALTERNATIVE ENERGY MAXIMIZER FOR WIND TURBINES AND PHOTOVOLTAIC PANELS.
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Creator
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Kerley, Ross, Batarseh, Issa, University of Central Florida
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Abstract / Description
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This thesis describes the creation of a small-scale Hybrid Power System (HPS) that maximizes energy from a wind turbine and photovoltaic array. Small-scale HPS are becoming an increasingly viable energy solution as fossil fuel prices rise and more electricity is needed in remote areas. Modern HPS typically employ wind speed sensors and three power stages to extract maximum power. Modern systems also use passive rectifiers to convert AC from the wind turbine to DC that is usable by power...
Show moreThis thesis describes the creation of a small-scale Hybrid Power System (HPS) that maximizes energy from a wind turbine and photovoltaic array. Small-scale HPS are becoming an increasingly viable energy solution as fossil fuel prices rise and more electricity is needed in remote areas. Modern HPS typically employ wind speed sensors and three power stages to extract maximum power. Modern systems also use passive rectifiers to convert AC from the wind turbine to DC that is usable by power electronics. This passive system inefficiently wastes power and introduces damaging harmonic noise to the wind turbine. The HPS described in this thesis does not require external wind speed sensors, and has independent wind and solar Maximum Power Point Tracking (MPPT). It converts AC from the wind turbine to DC with a Vienna rectifier that can be controlled to improve efficiency, allow MPPT, and allow Power Factor Correction (PFC). PFC all but eliminates the harmonic noise that can damage the wind turbine. A prototype HPS was built and evaluated that combines the two renewable sources in such a way that only two power stages are necessary, the Vienna rectifier and a step-down converter. This thesis describes the prototype and reports the results obtained.
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Date Issued
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2011
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Identifier
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CFH0004087, ucf:44799
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFH0004087
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Title
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CHARACTERIZATION OF AN INLINE ROW IMPINGEMENT CHANNEL FOR TURBINE BLADE COOLING APPLICATIONS.
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Creator
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Ricklick, Mark, Kapat, Jayanta, University of Central Florida
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Abstract / Description
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Gas turbines have become an intricate part of today's society. Besides powering practically all 200,000+ passenger aircraft in use today, they are also a predominate form of power generation when coupled with a generator. The fact that they are highly efficient, and capable of large power to weight ratios, makes gas turbines an ideal solution for many power requirement issues faced today. Designers have even been able to develop small, micro-turbines capable of producing efficient...
Show moreGas turbines have become an intricate part of today's society. Besides powering practically all 200,000+ passenger aircraft in use today, they are also a predominate form of power generation when coupled with a generator. The fact that they are highly efficient, and capable of large power to weight ratios, makes gas turbines an ideal solution for many power requirement issues faced today. Designers have even been able to develop small, micro-turbines capable of producing efficient portable power. Part of the turbine's success is the fact that their efficiency levels have continuously risen since their introduction in the early 1800's. Along with improvements in our understanding and designs of the aerodynamic components of the turbine, as well as improvements in the areas of material design and combustion control, advances in component cooling techniques have predominantly contributed to this success. This is the result of a simple thermodynamic concept; as the turbine inlet temperature is increased, the overall efficiency of the machine increases as well. Designers have exploited this fact to the extent that modern gas turbines produce rotor inlet temperatures beyond the melting point of the sophisticated materials used within them. This has only been possible through the use of sophisticated cooling techniques, particularly in the 1st stage vanes and blades. Some of the cooling techniques employed today have been internal cooling channels enhanced with various features, film and showerhead cooling, as well as internal impingement cooling scenarios. Impingement cooling has proven to be one of the most capable heat removal processes, and the combination of this cooling feature with that of channel flow, as is done in impingement channel cooling, creates a scenario that has understandably received a great deal of attention in recent years. This study has investigated several of the unpublished characteristics of these impingement channels, including the channel height effects on the performance of the channel side walls, effects of bulk temperature increase on heat transfer coefficients, circumferential heat variation effects, and effects on the uniformity of the heat transfer distribution. The main objectives of this dissertation are to explore the various previously unstudied characteristics of impingement channels, in order to sufficiently predict their performance in a wide range of applications. The potential exists, therefore, for a designer to develop a blade with cooling characteristics specifically tailored to the expected component thermal loads. Temperature sensitive paint (TSP) is one of several non-intrusive optical temperature measurements techniques that have gained a significant amount of popularity in the last decade. By employing the use of TSP, we have the ability to provide very accurate (less than 1 degree Celsius uncertainty), high resolution full-field temperature measurements. This has allowed us to investigate the local heat transfer characteristics of the various channel surfaces under a variety of steady state testing conditions. The comparison of thermal performance and uniformity for each impingement channel configuration then highlights the benefits and disadvantages of various configurations. Through these investigations, it has been shown that the channel side walls provide heat transfer coefficients comparable to those found on the target surface, especially at small impingement heights. Although the side walls suffer from highly non-uniform performance near the start of the channel, the profiles become very uniform as the cross flow develops and becomes a dominating contributor to the heat transfer coefficient. Increases in channel height result in increased non-uniformity in the streamwise direction and decreased heat transfer levels. Bulk temperature increases have also been shown to be an important consideration when investigating surfaces dominated by cross flow heat transfer effects, as enhancements up to 80% in some areas may be computed. Considerations of these bulk temperature changes also allow the determination of the point at which the flow transitions from an impingement dominated regime to one that is dominated by cross flow effects. Finally, circumferential heat variations have proven to have negligible effects on the calculated heat transfer coefficient, with the observed differences in heat transfer coefficient being contributed to the unaccounted variations in channel bulk temperature.
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Date Issued
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2009
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Identifier
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CFE0002955, ucf:47948
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0002955
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Title
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UNIFIED LARGE AND SMALL SIGNAL STATE-SPACE BASED MODELING AND SYMBOLIC SIMULATION FOR PWM CONVERTERS.
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Creator
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Shoubaki, Ehab, Batarseh, Issa, University of Central Florida
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Abstract / Description
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In this Dissertation, which concentrates on discrete modeling for control purposes of DC/DC converters and simulation through symbolic techniques. A Unified Discrete State-Space Model for power converters in CCM is presented. Two main approaches to arriving at the discrete model are used. The first approach involves an impulse function approximation of the duty cycle modulation of the converter switches, and this approach results in a small signal discrete model. The Second approach is direct...
Show moreIn this Dissertation, which concentrates on discrete modeling for control purposes of DC/DC converters and simulation through symbolic techniques. A Unified Discrete State-Space Model for power converters in CCM is presented. Two main approaches to arriving at the discrete model are used. The first approach involves an impulse function approximation of the duty cycle modulation of the converter switches, and this approach results in a small signal discrete model. The Second approach is direct and does not involve any approximation of the modulation, this approach yields both a large signal nonlinear discrete model and a linear small signal model. Harmonic analysis of the converter's states at steady-state is done for steady-state waveform acquisition, which increases the accuracy of the model especially for finding the control to inductor current frequency response. Also the harmonic Analysis technique is used to both obtain the response of the converter to a load transient and to finding the optimal duty cycle response that minimizes the disturbance. Finally the Discrete model is verified for the Half-Bridge DC/DC topology for its three main control schemes (Asymmetric, Symmetric, DCS). A GUI platform in MATLAB is presented as a wrapper that utilizes the models and analysis presented in this thesis. Symbolic simulation techniques are developed in general manner for linear piecewise circuits and then through State-Space formalism specialized for DC/DC converters. A general symbolic solver programmed in JAVA that implements said techniques is presented.
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Date Issued
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2009
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Identifier
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CFE0002836, ucf:48061
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0002836
Pages