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Articles 25081 - 25110 of 34635

Full-Text Articles in Engineering

Relative Intensity Noise Study In The Injection-Locked Integrated Electroabsorption Modulator-Lasers, Xiaomin Jin, Bennet Yun Tarng, Shun-Lien Chuang Jan 2009

Relative Intensity Noise Study In The Injection-Locked Integrated Electroabsorption Modulator-Lasers, Xiaomin Jin, Bennet Yun Tarng, Shun-Lien Chuang

Electrical Engineering

We present a comprehensive analytical theoretical model for the relative intensity noise (RIN) spectrum of integrated semiconductor quantum-well (QW) lasers under injection-locking. We use a novel setup by employing an integrated electroabsorption modulator-laser (EML) to measure the RIN of the injection-locked distributed feedback (DFB) laser, where the modulator section is used as a photodetector. The EML has an anti-reflection coating on the laser side, so that an injection light from an external master laser can be coupled effectively into the laser section. This scheme simplifies the setup and reduces the alignment loss between discrete optical components. Experimental data indicates that …

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Performance Study Of Series Loaded Resonant Converter Using Super Barrier Rectifiers, Taufik, Michael Mccarthy, Scott Watkins, Makbul Anwari Jan 2009

Performance Study Of Series Loaded Resonant Converter Using Super Barrier Rectifiers, Taufik, Michael Mccarthy, Scott Watkins, Makbul Anwari

Electrical Engineering

In power electronics efficiency improvement is constantly being sought out through venues such as improved topologies or improved devices. Series loaded resonant (SLR) DC-DC converter is a type of soft-switching topology widely known for providing improved efficiency. This paper investigates the efficiency and transient performance of SLR when a new type of diode called Super Barrier RectifierTM is being used. The design of SLR, results from computer simulations, and hardware measurements will be discussed. The efficiency measurements from all conduction modes in SLR using three types of diodes (pn, schottky, and SBR) will be presented along with transient study of …

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A Multicultural Comparison Of Engineering Students: Implications To Teaching And Learning, Zaki Shkair Seddigi, Luiz Fernando Capretz, David House Jan 2009

A Multicultural Comparison Of Engineering Students: Implications To Teaching And Learning, Zaki Shkair Seddigi, Luiz Fernando Capretz, David House

Electrical and Computer Engineering Publications

Problem statement: Personality considerations have become increasingly important in recent years, but studies involving the personality characteristics of engineers have been scarcely reported. Engineers today are expected to have a broader range of skills than in the recent past because users are now equally concerned with the technical as well as the personal services provided by engineers. Approach: A multicultural personality profile of engineering students had been presented in this study. The MBTI was used as an instrument to sort personality types of engineering students at both King Fahd University of Petroleum and Minerals in Saudi Arabia and University of …

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Achievable Rates And Resource Allocation Strategies For Imperfectly Known Fading Relay Channels, Junwei Zhang, M. Cenk Gursoy Jan 2009

Achievable Rates And Resource Allocation Strategies For Imperfectly Known Fading Relay Channels, Junwei Zhang, M. Cenk Gursoy

Department of Electrical and Computer Engineering: Faculty Publications

Achievable rates and resource allocation strategies for imperfectly known fading relay channels are studied. It is assumed that communication starts with the network training phase in which the receivers estimate the fading coefficients. Achievable rate expressions for amplify-and-forward and decode-and-forward relaying schemes with different degrees of cooperation are obtained. We identify efficient strategies in three resource allocation problems: (1) power allocation between data and training symbols, (2) time/bandwidth allocation to the relay, and (3) power allocation between the source and relay in the presence of total power constraints. It is noted that unless the source-relay channel quality is high, cooperation …

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Ground-Plane Quasicloaking For Free Space, Efthymios Kallos, Christos Argyropoulos, Yang Hao Jan 2009

Ground-Plane Quasicloaking For Free Space, Efthymios Kallos, Christos Argyropoulos, Yang Hao

Department of Electrical and Computer Engineering: Faculty Publications

Ground-plane cloak designs are presented, which minimize scattering of electromagnetic radiation from metallic objects in the visible spectrum. It is showed that simplified ground-plane cloaks made from only a few blocks of all-dielectric isotropic materials, either embedded in a background medium or in free space, can provide considerable cloaking performance while maintaining their broadband nature. A design which operates isolated in free space that cloaks radiation originating from a specified direction is also analyzed. These schemes should be much easier to be demonstrated experimentally compared to full designs.

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Sequencing, Analysis, And Annotation Of Expressed Sequence Tags For Camelus Dromedarius, Abdulaziz M. Al-Swailem, Maher M. Shehata, Faisel M. Abu-Duhier, Essam J. Al-Yamani, Khalid A. Al-Busadah, Mohammed S. Al-Arawi, Ali Y. Al-Khider, Abdullah N. Al-Muhaimeed, Fahad H. Al-Qahtani, Manee M. Manee, Badr M. Al-Shomrani, Saad M. Al-Qhtani, Amer S. Al-Harthi, Kadir C. Akdemir, Mehmet S. Inan, Hasan H. Otu Jan 2009

Sequencing, Analysis, And Annotation Of Expressed Sequence Tags For Camelus Dromedarius, Abdulaziz M. Al-Swailem, Maher M. Shehata, Faisel M. Abu-Duhier, Essam J. Al-Yamani, Khalid A. Al-Busadah, Mohammed S. Al-Arawi, Ali Y. Al-Khider, Abdullah N. Al-Muhaimeed, Fahad H. Al-Qahtani, Manee M. Manee, Badr M. Al-Shomrani, Saad M. Al-Qhtani, Amer S. Al-Harthi, Kadir C. Akdemir, Mehmet S. Inan, Hasan H. Otu

Department of Electrical and Computer Engineering: Faculty Publications

Despite its economical, cultural, and biological importance, there has not been a large scale sequencing project to date for Camelus dromedarius. With the goal of sequencing complete DNA of the organism, we first established and sequenced camel EST libraries, generating 70,272 reads. Following trimming, chimera check, repeat masking, cluster and assembly, we obtained 23,602 putative gene sequences, out of which over 4,500 potentially novel or fast evolving gene sequences do not carry any homology to other available genomes. Functional annotation of sequences with similarities in nucleotide and protein databases has been obtained using Gene Ontology classification. Comparison to available …

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Genes Differentially Expressed By Cumulus Cells And Assays Using Same To Identify Pregnancy Competent Oocytes, Jose B. Cibelli, Amy E. Iager, Hasan H. Otu Jan 2009

Genes Differentially Expressed By Cumulus Cells And Assays Using Same To Identify Pregnancy Competent Oocytes, Jose B. Cibelli, Amy E. Iager, Hasan H. Otu

Department of Electrical and Computer Engineering: Faculty Publications

A genetic means of identifying "pregnancy competent" oocytes is provided. The means comprises detecting the level of expression of one or more genes that are expressed at characteristic levels (upregulated or downregulated) in cumulus cells derived from pregnancy competent oocytes. This characteristic gene expression level, or pattern referred to herein as the "pregnancy signature", also can be used to identify subjects with underlying conditions that impair or prevent the development of a viable pregnancy, e.g., pre-menopausal condition, other hormonal dysfunction, ovarian dysfunction, ovarian cyst, cancer or other cell proliferation disorder, autoimmune disease and the like. In preferred embodiments the …

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Samplemaskinginellipsometerand The Like Systems Including Detection Of Substrate Backside Reflections, Martin M. Liphardt, James D. Welch, Corey L. Bungay, John A. Woollam Jan 2009

Samplemaskinginellipsometerand The Like Systems Including Detection Of Substrate Backside Reflections, Martin M. Liphardt, James D. Welch, Corey L. Bungay, John A. Woollam

Department of Electrical and Computer Engineering: Faculty Publications

A system and method of preventing substrate backside reflected components in a beam of electromagnetic radiation caused to reflect from the surface of a sample in an ellipsometer or polarimeter system, involving placing a mask adjacent to the surface of the sample which allows electromagnetic radiation to access the sample over only a limited area, wherein to access the sample over only a limited area, wherein the mask can include detector elements for collecting electromagnetic radiation reflected from the sample backside.

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Sample Investigating System, Martin M. Liphardt, Thomas E. Tiwald, Blaine D. Johs, Jeffery S. Hale, Craig M. Herzinger, Steven E. Green, Ping He, Ronald A. Synowicki, John A. Woollam Jan 2009

Sample Investigating System, Martin M. Liphardt, Thomas E. Tiwald, Blaine D. Johs, Jeffery S. Hale, Craig M. Herzinger, Steven E. Green, Ping He, Ronald A. Synowicki, John A. Woollam

Department of Electrical and Computer Engineering: Faculty Publications

A spectroscopic system for adjusting spacing between an adjacent source/detector as a unit, and a sample, and a reflecting means for directing an incident beam which refelcts from said sample back onto said sample and then into the detector along a locus which is in a plance of incidence that is offset from that of the incident beam, or directly from the reflecting means into the detecor, including means for reducing reflections of a beam fo electromagnetic from the back of a sample, including methodology of use.

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Simulation Of Coherent Radar Imaging Using Continuous Wave Noise Radar, Jing Xu, Michael Hoffman, B.L. Cheong, R.D. Palmer Jan 2009

Simulation Of Coherent Radar Imaging Using Continuous Wave Noise Radar, Jing Xu, Michael Hoffman, B.L. Cheong, R.D. Palmer

Department of Electrical and Computer Engineering: Faculty Publications

A computationally simple cross-correlation model for multiple backscattering from a continuous wave (CW) noise radar is developed and verified with theoretical analysis and brute-force time-domain simulations. Based on this cross-correlation model, a modification of an existing numerical method originally developed by Holdsworth and Reid for spaced antenna (SA) pulsed radar is used to simulate the estimated cross correlation corresponding to atmospheric backscattering using a coherent CW noise radar. Subse- quently, coherent radar imaging (CRI) processing comparisons between the CW noise radar and a con- ventional pulsed radar are presented that verify the potential of CW noise radar for atmospheric imaging.

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Thin Films Formed By Selenization Of CuinXB1−X Precursors In Se Vapor, C. A. Kamler, Rodney J. Soukup, Natale J. Ianno, J. L. Huguenin-Love, J. Olejníček, S. A. Darveau, C. L. Exstrom Jan 2009

Thin Films Formed By Selenization Of CuinXB1−X Precursors In Se Vapor, C. A. Kamler, Rodney J. Soukup, Natale J. Ianno, J. L. Huguenin-Love, J. Olejníček, S. A. Darveau, C. L. Exstrom

Department of Electrical and Computer Engineering: Faculty Publications

Previous attempts in producing light absorbing materials with bandgaps near the 1.37 eV efficiency optimum have included the partial substitution of gallium or aluminum for indium in the CIS system. The most efficient of these solar cells to date have had absorber layers with bandgaps < 1.2 eV. It is logical that an even smaller substitutional atom, boron, should lead to a wider bandgap with a smaller degree of atomic substitution. In this study, copper–indium–boron precursor films are sputtered onto molybdenum coated glass substrates and post-selenized. In the selenized films, although X-ray diffraction (XRD) measurements confirm that a CIS phase is present, Auger electron spectroscopy (AES) results indicate that boron is no longer homogeneously dispersed throughout the film as it was in the case of the unselenized precursor.

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Controlled Growth Of Carbon Nanotubes On Electrodes Under Different Bias Polarity, Yi Gao, Yunshen Zhou, W. Xiong, M. Mahjouri-Samani, M. Mitchell, Yongfeng Lu Jan 2009

Controlled Growth Of Carbon Nanotubes On Electrodes Under Different Bias Polarity, Yi Gao, Yunshen Zhou, W. Xiong, M. Mahjouri-Samani, M. Mitchell, Yongfeng Lu

Department of Electrical and Computer Engineering: Faculty Publications

Carbon nanotubes (CNTs) of different alignments, such as surface-bounded and vertically aligned arrays, enable applications in different fields. In this study, controlled growth of CNTs with different alignments was achieved by electrically biasing catalyzed electrodes with different polarities in a laser-assisted chemical vapor deposition process. CNT growth was suggested to be guided by the movement of electrically charged catalyst-nanoparticles under the influence of an external electric field. This discovery provides a convenient approach to control the alignment of CNT arrays for different applications.

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Energy Efficiency Of Fixed-Rate Wireless Transmissions Under Queueing Constraints And Channel Uncertainty, Deli Qiao, M. Cenk Gursoy, Senem Velipasalar Jan 2009

Energy Efficiency Of Fixed-Rate Wireless Transmissions Under Queueing Constraints And Channel Uncertainty, Deli Qiao, M. Cenk Gursoy, Senem Velipasalar

Department of Electrical and Computer Engineering: Faculty Publications

Energy efficiency of fixed-rate transmissions is studied in the presence of queueing constraints and channel uncertainty. It is assumed that neither the transmitter nor the receiver has channel side information prior to transmission. The channel coefficients are estimated at the receiver via minimum mean-square-error (MMSE) estimation with the aid of training symbols. It is further assumed that the system operates under statistical queueing constraints in the form of limitations on buffer violation probabilities. The optimal fraction of power allocated to training is identified. Spectral efficiency–bit energy tradeoff is analyzed in the low-power and wideband regimes by employing the effective capacity …

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Energy Efficiency Of Fixed-Rate Wireless Transmissions Under Qos Constraints, Deli Qiao, M. Cenk Gursoy, Senem Velipasalar Jan 2009

Energy Efficiency Of Fixed-Rate Wireless Transmissions Under Qos Constraints, Deli Qiao, M. Cenk Gursoy, Senem Velipasalar

Department of Electrical and Computer Engineering: Faculty Publications

Transmission over wireless fading channels under quality of service (QoS) constraints is studied when only the receiver has perfect channel side information. Being unaware of the channel conditions, transmitter is assumed to send the information at a fixed rate. Under these assumptions, a two-state (ON-OFF) transmission model is adopted, where information is transmitted reliably at a fixed rate in the ON state while no reliable transmission occurs in the OFF state. QoS limitations are imposed as constraints on buffer violation probabilities, and effective capacity formulation is used to identify the maximum arrival rate that a wireless channel can sustain while …

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Analysis Of Energy Efficiency In Fading Channels Under Qos Constraints, Deli Qiao, M. Cenk Gursoy, Senem Velipasalar Jan 2009

Analysis Of Energy Efficiency In Fading Channels Under Qos Constraints, Deli Qiao, M. Cenk Gursoy, Senem Velipasalar

Department of Electrical and Computer Engineering: Faculty Publications

Energy efficiency in fading channels in the presence of Quality of Service (QoS) constraints is studied. Effective capacity, which provides the maximum arrival rate that a wireless channel can sustain while satisfying statistical QoS constraints, is considered. Spectral efficiency–bit energy tradeoff is analyzed in the low-power and wideband regimes by employing the effective capacity formulation, rather than the Shannon capacity. Through this analysis, energy requirements under QoS constraints are identified. The analysis is conducted under two assumptions: perfect channel side information (CSI) available only at the receiver and perfect CSI available at both the receiver and transmitter. In particular, it …

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The Impact Of Qos Constraints On The Energy Efficiency Of Fixed-Rate Wireless Transmissions, Deli Qiao, M. Cenk Gursoy, Senem Velipasalar Jan 2009

The Impact Of Qos Constraints On The Energy Efficiency Of Fixed-Rate Wireless Transmissions, Deli Qiao, M. Cenk Gursoy, Senem Velipasalar

Department of Electrical and Computer Engineering: Faculty Publications

Transmission over wireless fading channels under quality of service (QoS) constraints is studied when only the receiver has channel side information. Being unaware of the channel conditions, transmitter is assumed to send the information at a fixed rate. Under these assumptions, a two-state (ON-OFF) transmission model is adopted, where information is transmitted reliably at a fixed rate in the ON state while no reliable transmission occurs in the OFF state. QoS limitations are imposed as constraints on buffer violation probabilities, and effective capacity formulation is used to identify the maximum throughput that a wireless channel can sustain while satisfying statistical …

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Output Maximization Control For Dfig Wind Turbines Without Using Wind And Shaft Speed Measurements, Wei Qiao, Xiang Gong, Liyan Qu Jan 2009

Output Maximization Control For Dfig Wind Turbines Without Using Wind And Shaft Speed Measurements, Wei Qiao, Xiang Gong, Liyan Qu

Department of Electrical and Computer Engineering: Faculty Publications

Wind turbine generators (WTGs) are usually equipped with mechanical sensors to measure wind speed and turbine shaft rotating speed for system monitoring, control, and protection. The use of these sensors increases the cost and hardware complexity and reduces the reliability of the WTG system. This paper proposes a novel real-time speed estimation algorithm for wind turbines equipped with doubly-fed induction generators (DFIGs). In the proposed algorithm, both the wind and turbine shaft speeds are estimated from the measured DFIG output electrical power. The estimated speeds are then used to determine the maximum power point of the DFIG wind turbine. A …

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Coordinated Reactive Power Control Of A Large Wind Farm And A Statcom Using Heuristic Dynamic Programming, Wei Qiao, Ronald D. Harley, Ganesh Kumar Venayagamoorthy Jan 2009

Coordinated Reactive Power Control Of A Large Wind Farm And A Statcom Using Heuristic Dynamic Programming, Wei Qiao, Ronald D. Harley, Ganesh Kumar Venayagamoorthy

Department of Electrical and Computer Engineering: Faculty Publications

A novel interface neurocontroller (INC) is proposed for the coordinated reactive power control between a large wind farm equipped with doubly fed induction generators (DFIGs) and a static synchronous compensator (STATCOM). The heuristic dynamic programming (HDP) technique and radial basis function neural networks (RBFNNs) are used to design this INC. It effectively reduces the level of voltage sags as well as the over-currents in the DFIG rotor circuit during grid faults, and therefore, significantly enhances the fault ride-through capability of the wind farm. The INC also acts as a coordinated external damping controller for the wind farm and the STATCOM, …

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Control Of Ipm Synchronous Generator For Maximum Wind Power Generation Considering Magnetic Saturation, Wei Qiao, Qu, Richard G. Harley Jan 2009

Control Of Ipm Synchronous Generator For Maximum Wind Power Generation Considering Magnetic Saturation, Wei Qiao, Qu, Richard G. Harley

Department of Electrical and Computer Engineering: Faculty Publications

Permanent-magnet synchronous generators (PMSGs) are commonly used for small variable-speed wind turbines to produce high-efficiency, high-reliability, and low-cost wind power generation. This paper proposes a novel control scheme for an interior PMSG (IPMSG) driven by a wind turbine, in which the d-axis and q-axis stator-current components are optimally controlled to achieve the maximum wind power generation and loss minimization of the IPMSG. The effect of magnetic saturation, which causes the highly nonlinear characteristics of the IPMSG, is considered in the control-scheme design. The optimal d-axis stator-current command is obtained as a function of the IPMSG rotor speed by solving a …

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Real-Time Implementation Of A Statcom On A Wind Farm Equipped With Doubly Fed Induction Generators, Wei Qiao, Ganesh Kumar Venayagamoorthy, Ronald G. Harley Jan 2009

Real-Time Implementation Of A Statcom On A Wind Farm Equipped With Doubly Fed Induction Generators, Wei Qiao, Ganesh Kumar Venayagamoorthy, Ronald G. Harley

Department of Electrical and Computer Engineering: Faculty Publications

Voltage stability is a key issue to achieve the uninterrupted operation of wind farms equipped with doubly fed induction generators (DFIGs) during grid faults. This paper investigates the application of a static synchronous compensator (STATCOM) to assist with the uninterrupted operation of a wind turbine driving a DFIG, which is connected to a power network, during grid faults. The control schemes of the DFIG rotor- and grid-side converters and the STATCOM are suitably designed and coordinated. The system is implemented in real-time on a Real Time Digital Simulator. Results show that the STATCOM improves the transient voltage stability and therefore …

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Missing-Sensor-Fault-Tolerant Control For Sssc Facts Device With Real-Time Implementation, Wei Qiao, Ganesh Kumar Venayagamoorthy, Ronald G. Harley Jan 2009

Missing-Sensor-Fault-Tolerant Control For Sssc Facts Device With Real-Time Implementation, Wei Qiao, Ganesh Kumar Venayagamoorthy, Ronald G. Harley

Department of Electrical and Computer Engineering: Faculty Publications

Control of power systems relies on the availability and quality of sensor measurements. However, measurements are inevitably subjected to faults caused by sensor failure, broken or bad connections, bad communication, or malfunction of some hardware or software. These faults, in turn, may cause the failure of power system controllers and consequently, severe contingencies in the power system. To avoid such contingencies, this paper presents a sensor evaluation and (missing sensor) restoration scheme (SERS) by using auto-associative neural networks (auto encoders) and particle swarm optimization. Based on the SERS, a missing-sensor-fault-tolerant control is developed for controlling a static synchronous series compensator …

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Echo-State-Network-Based Real-Time Wind Speed Estimation For Wind Power Generation, Wei Qiao Jan 2009

Echo-State-Network-Based Real-Time Wind Speed Estimation For Wind Power Generation, Wei Qiao

Department of Electrical and Computer Engineering: Faculty Publications

Wind turbine generators (WTGs) are usually equipped with one or more well-calibrated nemometers to measure wind speed for system monitoring, control, and protection. The use of these mechanical sensors increases the cost and hardware complexity and reduces the reliability of the WTG system. This paper proposes an echo-state-network (ESN)-based real-time wind speed estimation algorithm for WTG systems. The ESN is designed to provide a nonlinear inverse model of the WTG dynamics, which is used to estimate the wind speed in real time from the measured WTG output electrical power and shaft speed at any turbine blade pitch angle. The estimated …

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Voltage Analysis Of Distribution Systems With Dfig Wind Turbines, Baohua Dong, Sohrab Asgarpoor, Wei Qiao Jan 2009

Voltage Analysis Of Distribution Systems With Dfig Wind Turbines, Baohua Dong, Sohrab Asgarpoor, Wei Qiao

Department of Electrical and Computer Engineering: Faculty Publications

Wind energy is becoming the most viable renewable energy source mainly because of the growing concerns over carbon emissions and uncertainties in fossil fuel supplies and the government policy impetus. The increasing penetration of wind power in distribution systems may significantly affect voltage stability of the systems, particularly during wind turbine cut-in and cut-off disturbances. Currently, doubly fed induction generator wind turbine (DFIG-WT) is the most popular wind turbine. This paper investigates the issues of voltage stability improvement and grid-loss reduction of distribution systems which include DFIG-WTs under unbalanced heavy loading conditions. Simulation studies are carried out in IEEE 34-bus …

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Coordinated Reactive Power Control Of A Large Wind Farm And A Statcom Using Heuristic Dynamic Programming, Wei Qiao, Ronald G. Harley, Ganesh Venayagamoorthy Jan 2009

Coordinated Reactive Power Control Of A Large Wind Farm And A Statcom Using Heuristic Dynamic Programming, Wei Qiao, Ronald G. Harley, Ganesh Venayagamoorthy

Department of Electrical and Computer Engineering: Faculty Publications

A novel interface neurocontroller (INC) is proposed for the coordinated reactive power control between a large wind farmequippedwith doubly fed induction generators (DFIGs) and a static synchronous compensator (STATCOM). The heuristic dynamic programming (HDP) technique and radial basis function neural networks (RBFNNs) are used to design this INC. It effectively reduces the level of voltage sags as well as the over-currents in the DFIG rotor circuit during grid faults, and therefore, significantly enhances the fault ride-through capability of thewind farm. The INCalso acts as a coordinated external damping controller for the wind farm and the STATCOM, and therefore, improves power …

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Missing-Sensor-Fault-Tolerant Control For Sssc Facts Device With Real-Time Implementation, Wei Qiao, Ganesh Venayagamoorthy, Ronald G. Harley Jan 2009

Missing-Sensor-Fault-Tolerant Control For Sssc Facts Device With Real-Time Implementation, Wei Qiao, Ganesh Venayagamoorthy, Ronald G. Harley

Department of Electrical and Computer Engineering: Faculty Publications

Control of power systems relies on the availability and quality of sensor measurements. However, measurements are inevitably subjected to faults caused by sensor failure, broken or bad connections, bad communication, or malfunction of some hardware or software. These faults in turn may cause the failure of power system controllers and consequently severe contingencies in the power system. To avoid such contingencies, this paper resents a sensor evaluation and (missing sensor) restoration scheme (SERS) by using auto-associative neural networks (auto-encoders) and particle swarm optimization (PSO). Based on the SERS, a missing-sensor-fault-tolerant control (MSFTC) is developed for controlling a static synchronous series …

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Dynamic Modeling And Control Of Doubly Fed Induction Generators Driven By Wind Turbines, Wei Qiao Jan 2009

Dynamic Modeling And Control Of Doubly Fed Induction Generators Driven By Wind Turbines, Wei Qiao

Department of Electrical and Computer Engineering: Faculty Publications

Two different models are presented and developed in PSCAD/EMTDC to represent a variable-speed wind turbine equipped with a doubly fed induction generator (DFIG). One is the most detailed switching-level (SL) model. The other is a simplified fundamental-frequency (FF) model. The effect of different shaft system representations on the dynamic behavior of the wind turbine generator (WTG) system and the issue of damping low-frequency torsional oscillations are investigated. Dynamic and transient simulation studies are carried out to compare two models with different shaft system representations. Results show that the FF model is sufficient while the lumpedmass shaft model is insufficient to …

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Enhanced Chemical Vapor Deposition Of Diamond By Wavelength-Matched Vibrational Excitations Of Ethylene Molecules Using Tunable Co2 Laser Irradiation, Hao Ling, Q. Xie, T. Gebre, X. K. Shen, Yongfeng Lu Jan 2009

Enhanced Chemical Vapor Deposition Of Diamond By Wavelength-Matched Vibrational Excitations Of Ethylene Molecules Using Tunable Co2 Laser Irradiation, Hao Ling, Q. Xie, T. Gebre, X. K. Shen, Yongfeng Lu

Department of Electrical and Computer Engineering: Faculty Publications

Wavelength-matched vibrational excitations of ethylene (C2H4 molecules using a tunable carbon dioxide (CO2) laser were employed to significantly enhance the chemical vapor deposition (CVD) of diamond in open air using a precursor gas mixture of C2H4, acetylene (C2H2), and oxygen (O2). The CH2-wag vibration mode (v7) of the C2H4 molecules was selected to achieve the resonant excitation in the CVD process. Both laser wavelengths of 10.591 and 10.532 μm were applied to the CVD processes to compare …

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Laser-Induced Resonant Excitation Of Ethylene Molecules In C2H4/C2H2/O2 Reactions To Enhance Diamond Deposition, Hao Ling, Jian Sun, X. Han, T. Gebre, Z. Q. Xie, M. Zhao, Yongfeng Lu Jan 2009

Laser-Induced Resonant Excitation Of Ethylene Molecules In C2H4/C2H2/O2 Reactions To Enhance Diamond Deposition, Hao Ling, Jian Sun, X. Han, T. Gebre, Z. Q. Xie, M. Zhao, Yongfeng Lu

Department of Electrical and Computer Engineering: Faculty Publications

Vibrational resonant excitation of ethylene (C2H4) molecules using a carbon dioxide laser was employed to promote reactions in precursors of ethylene, acetylene (C2H2), and oxygen to enhance diamond deposition. One of the vibrational modes (CH2 wag mode, v7) of the C2H4 molecules was selected to achieve the resonant excitation in the reactions. Optical emission spectroscopy was used to study the effects of laser resonant excitation on the reactions for diamond deposition. The optical emissions of CH and C2 species were enhanced with the laser excitation, …

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Micro-Fabricated Hydrogen Sensors Operating At Elevated Temperatures, Chi Lu Jan 2009

Micro-Fabricated Hydrogen Sensors Operating At Elevated Temperatures, Chi Lu

University of Kentucky Doctoral Dissertations

In this dissertation, three types of microfabricated solid-state sensors had been designed and developed on silicon wafers, aiming to detect hydrogen gas at elevated temperatures. Based on the material properties and sensing mechanisms, they were operated at 140°C, 500°C, and 300°C. The MOS-capacitor device working at 140°C utilized nickel instead of the widely-used expensive palladium, and the performance remained excellent. For very-high temperature sensing (500°C), the conductivity of the thermally oxidized TiO2 thin film based on the anodic aluminum oxide (AAO) substrate changed 25 times in response to 5 ppm H2 and the response transient times were just …

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Maxwell Garnett Rule For Dielectric Mixtures With Statistically Distributed Orientations Of Inclusions, Marina Koledintseva, Richard E. Dubroff, Robert W. Schwartz Jan 2009

Maxwell Garnett Rule For Dielectric Mixtures With Statistically Distributed Orientations Of Inclusions, Marina Koledintseva, Richard E. Dubroff, Robert W. Schwartz

Electrical and Computer Engineering Faculty Research & Creative Works

An analytical model of an effective permittivity of a composite taking into account statistically distributed orientations of inclusions in the form of prolate spheroids will be presented. In particular, this paper considers the normal Gaussian distribution for either zenith angle, or azimuth angle, or for both angles describing the orientation of inclusions. The model is an extension of the Maxwell Garnett (MG) mixing rule for multiphase mixtures. The resulting complex permittivity is a tensor in the general case. The formulation presented shows that the parameters of the distribution law for orientation of inclusions affect the frequency characteristics of the composites, …

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