A Downsizing Strategy for Combinatorial PMSG Based Wind Turbine and Micro-SMES System Applied in Standalone DC Microgrid

This paper presents a combinatorial standalone permanent magnet synchronous generator (PMSG) based variable speed wind turbine (VSWT) and small-size superconducting magnetic energy storage (SMES) system into the DC microgrid system. The principal purpose of SMES system is to preserve power balance by absorbing power during peak wind generation and to release it during low power generation. This work accomplished by describing the optimized design of the SMES solenoid coil, ensuring the desired energy storage capacity based on the simulated annealing (SA) algorithm. More importantly, the new control technique is developed for bi-directional DC-DC converter to level output power of the wind turbine depending on the demand thereby reducing the capacity of the DC-DC converter system. Detailed simulation studies implemented in PSCAD/EMTDC corroborate the superior robustness and balancing performance of the proposed micro-SMES controller with an optimal coil size under various situations including variable wind speed. This combination will result in “scaling-factors” knowledge through downsizing strategy which will lead to the most efficient system from cost cutting, energy savings, and downsizing viewpoints

Analysis and Modeling of Advanced Power Control and Protection Requirements for Integrating Renewable Energy Sources in Smart Grid,

Attempts to reduce greenhouse gas emissions are promising with the recent dramatic increase of installed renewable energy sources (RES) capacity. Integration of large intermittent renewable resources affects smart grid systems in several significant ways, such as transient and voltage stability, existing protection scheme, and power leveling and energy balancing. To protect the grid from threats related to these issues, utilities impose rigorous technical requirements, more importantly, focusing on fault ride through requirements and active/reactive power responses following disturbances. This dissertation is aimed at developing and verifying the advanced and algorithmic methods for specification of protection schemes, reactive power capability and power control requirements for interconnection of the RESs to the smart grid systems. The first findings of this dissertation verified that the integration of large RESs become more promising from the energy-saving, and downsizing perspective by introducing a resistive superconducting fault current limiter (SFCL) as a self-healing equipment. The proposed SFCL decreased the activation of the conventional control scheme for the wind power plant (WPP), such as dc braking chopper and fast pitch angle control systems, thereby increased the reliability of the system. A static synchronous compensator (STATCOM) has been proposed to assist with the uninterrupted operation of the doubly-fed induction generators (DFIGs)-based WTs during grid disturbances. The key motivation of this study was to design a new computational intelligence technique based on a multi-objective optimization problem (MOP), for the online coordinated reactive power control between the DFIG and the STATCOM in order to improve the low voltage ride-through (LVRT) capability of the WT during the fault, and to smooth low-frequency oscillations of the active power during the recovery. Furthermore, the application of a three-phase single-stage module-integrated converter (MIC) incorporated into a grid-tied photovoltaic (PV) system was investigated in this dissertation. A new current control scheme based on multivariable PI controller, with a faster dynamic and superior axis decoupling capability compared with the conventional PI control method, was developed and experimentally evaluated for three-phase PV MIC system. Finally, a study was conducted based on the framework of stochastic game theory to enable a power system to dynamically survive concurrent severe multi-failure events, before such failures turn into a full blown cascading failure. This effort provides reliable strategies in the form of insightful guidelines on how to deploy limited budgets for protecting critical components of the smart grid systems

The Extraction and Use of Image Planes for Three-dimensional Metric Reconstruction

The three-dimensional (3D) metric reconstruction of a scene from two-dimensional images is a fundamental problem in Computer Vision. The major bottleneck in the process of retrieving such structure lies in the task of recovering the camera parameters. These parameters can be calculated either through a pattern-based calibration procedure, which requires an accurate knowledge of the scene, or using a more flexible approach, known as camera autocalibration, which exploits point correspondences across images. While pattern-based calibration requires the presence of a calibration object, autocalibration constraints are often cast into nonlinear optimization problems which are often sensitive to both image noise and initialization. In addition, autocalibration fails for some particular motions of the camera. To overcome these problems, we propose to combine scene and autocalibration constraints and address in this thesis (a) the problem of extracting geometric information of the scene from uncalibrated images, (b) the problem of obtaining a robust estimate of the affine calibration of the camera, and (c) the problem of upgrading and refining the affine calibration into a metric one. In particular, we propose a method for identifying the major planar structures in a scene from images and another method to recognize parallel pairs of planes whenever these are available. The identified parallel planes are then used to obtain a robust estimate of both the affine and metric 3D structure of the scene without resorting to the traditional error prone calculation of vanishing points. We also propose a refinement method which, unlike existing ones, is capable of simultaneously incorporating plane parallelism and perpendicularity constraints in the autocalibration process. Our experiments demonstrate that the proposed methods are robust to image noise and provide satisfactory results

Effect of injection strategies on a single-fuel RCCI combustion fueled with isobutanol/isobutanol + DTBP blends

© 2020 Elsevier Ltd. All rights reserved. This manuscript is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence (http://creativecommons.org/licenses/by-nc-nd/4.0/).In recent years, improved combustion controllability through in-cylinder reactivity stratification by using two different fuels have led to introduction of dual-fuel reactivity controlled compression ignition (RCCI) strategy. In conventional RCCI, gasoline or natural gas can be used as the low-reactivity fuel, and diesel or biodiesel can be used as the high-reactivity fuel. This strategy has the potential to operate with a single low-reactivity fuel and direct injection (DI) of the same fuel blended with a small amount of cetane improver. In the present study, numerical simulations have been carried out to study injection strategy in a single-fuel RCCI engine fueled with isobutanol – isobutanol + 20% di-tert-butyl peroxide (DTBP). Firstly, the effects of start of injection (SOI) timing, injection pressure (pinj), spray cone angle (SCA), and DI fuel ratio were explored. Then, the effect of DI fuel ratio was discussed in each best case in order to decrease the high DI requirement. The results indicate that SOI = −88° ATDC, pinj = 1400 bar, and SCA = 45° can improve the single-fuel RCCI engine performance and emissions compared to the baseline case (SOI = −58° ATDC, pinj = 600 bar, SCA = 72.5°). Moreover, it is shown that by advancing the SOI timing to −88° ATDC, a 20% reduction in DI ratio, 3.3% increase in gross indicated efficiency (GIE) together with reductions in CO, and NOx emissions by 3.56 g/kW-h and 0.254 g/kW-h, could be achieved, respectively.Peer reviewedFinal Accepted Versio

Impact of Al2O3Al_2O_3 Passivation on the Photovoltaic Performance of Vertical WSe2WSe_2 Schottky Junction Solar Cells

Transition metal dichalcogenide (TMD) materials have emerged as promising candidates for thin film solar cells due to their wide bandgap range across the visible wavelengths, high absorption coefficient and ease of integration with both arbitrary substrates as well as conventional semiconductor technologies. However, reported TMD-based solar cells suffer from relatively low external quantum efficiencies (EQE) and low open circuit voltage due to unoptimized design and device fabrication. This paper studies $Pt/WSe_2$ vertical Schottky junction solar cells with various $WSe_2$ thicknesses in order to find the optimum absorber thickness.Also, we show that the photovoltaic performance can be improved via $Al_2O_3$ passivation which increases the EQE by up to 29.5% at 410 nm wavelength incident light. The overall resulting short circuit current improves through antireflection coating, surface doping, and surface trap passivation effects. Thanks to the ${Al_2O_3}$ coating, this work demonstrates a device with open circuit voltage ($V_{OC}$) of 380 mV and short circuit current density ($J_{SC}$) of 10.7 $mA/cm^2$. Finally, the impact of Schottky barrier height inhomogeneity at the $Pt/WSe_2$ contact is investigated as a source of open circuit voltage lowering in these device

The Association of Balance, Fear of Falling, and Daily Activities With Drug Phases and Severity of Disease in Patients With Parkinson

Introduction: In the elderly, functional balance, fear of falling, and independence in daily living activities are interrelated; however, this relationship may change under the influence of drug phase and the severity of disease in individuals with idiopathic Parkinson disease. This study aimed to investigate the association of functional balance, fear of falling, and independence in the Activities of Daily Living (ADL) with the drug on- and drug off-phases. Methods: A total of 140 patients with Parkinson disease (age: Mean±SD; 60.51±12.32 y) were evaluated in terms of their functional balance, fear of falling, and independence in their daily activities by the Berg Balance Scale (BBS), Fall Efficacy Scale-International (FES-I), and Unified Parkinson Disease Rating Scale-ADL (UPDRS-ADL), respectively, in drug on- and drug off-phases. The Hoehn and Yahr scale recorded global disease rating. The Spearman coefficient, Kruskal-Wallis, and Mann-Whitney tests were used to find out whether the distribution of scale scores differs with regard to functional balance or disease severity. Results: A strong correlation was found between the functional balance, fear of falling, and independence in ADL with both drug phases. The results also showed the significant difference in the distribution of the FES-I and UPDRS-ADL scores with regard to functional balance (except independence in ADL in drug off-phase). Also, the distribution of the scores of BBS, FES-I, and UPDRS-ADL showed significant differences with regard to disease severity. Conclusion: The study showed a strong correlation between functional balance, fear of falling, and independence in ADL that can be affected by the drug phase and severity of the disease. However, more studies are needed to understand this relationship precisely.This work was supported by the Student Research Committee in Iran University of Medical Sciences, Tehran, Iran.S

Serially connected monolayer MoS FETs with channel patterned by a 7.5 nm resolution directed self-assembly lithography

We demonstrate sub-10 nm transistor channel lengths by directed self-assembly patterning of monolayer MoS[subscript 2] in a periodic chain of homojunction semiconducting-(2H) and metallic-phase (1T') MoS[subscript 2] regions with half-pitch of 7.5 nm. The MoS[subscript 2] composite transistor possesses an off-state current of 100 pA/μm and an I[subscript on]/I[subscript off] ratio in excess of 10[subscript 5]. Modeling of the resulting current-voltage characteristics reveals that the 2H/1T' MoS[subscript 2] homojunction has a resistance of 75 Ω.μm while the 2H-MoS[subscript 2] exhibits low-field mobility of ~8 cm[superscript 2]/V.s and carrier injection velocity of ~10[superscript 6] cm/s.United States. Office of Naval Research. Presidential Early Career Award for Scientists and EngineersNational Science Foundation (U.S.). Nano-Engineered Electronic Device Simulatio

Graphene Functionalization: a Route towards the Use of Graphene for Microelectronic Applications

Graphene is a gapless semiconductor with a high charge carrier mobility. In an attempt to apply this promising material for electrical and optical applications, functionalization of graphene is a prerequisite to introduce a bandgap.In this thesis, we present our findings on two major graphene functionalization methods: covalent and non-covalent functionalization of graphene in order to apply it for electronic and optical applications.Regarding the covalent functionalization, using oxygen plasma treatment we observed the occurrence of the metal-to-semiconductor transition in single layer graphene (SLG). Careful control of the plasma treatment allows reproducible production of semiconducting graphene. Semiconductivity is demonstrated by electrical and photoluminescence (PL) measurements. Opening of the bandgap as a result of the plasma treatment is explained in terms of graphene surface functionalization with chemisorbed oxygen atoms. Using ab initio calculations, we then present more details about the oxygen - graphene interaction and its effect on the graphene optoelectronic properties. A bandgap is indeed predicted by the calculation, when graphene is decorated with oxygen atoms in a specific chemisorption configuration. We then demonstrate Schottky rectifying junctions between semiconducting, modified SLG and a metal. The occurrence of a Schottky barrier between semiconducting graphene and metals with different work functions is investigated by electrically characterizing the as-fabricated junctions. We also compare the effects of the oxygen treatment on the structural, optical, and electrical properties of single-layer and bilayer graphene (BLG). We observe only photoluminescence in SLG, whereas the BLG remain optically unchanged. DFT calculations are carried on representative oxidized SLG and BLG models to predict electronic density of states and band structures. Sufficiently oxidized SLG shows a bandgap and thus loss of semimetallic behavior, while single-side oxidized BLG maintains its semimetallic behavior even at high oxygen density in agreement with the results of the PL experiments. DFT calculations confirm that the Fermi velocity in single-side oxidized BLG is remarkably comparable with that of pristine SLG, pointing to a similarity of electronic band structure. Regarding the non-covalent functionalization, we first investigated the effects of thermal annealing on SLG samples deposited on SiO2 supports. We found that heating SLG samples in inert atmosphere induces permanent changes in their electrical/optical properties, without affecting their structural properties. We believe that charge transfer from the SiO2 support is responsible for the occurrence of hole doping in our SLG samples. The Raman spectra measured on annealed SLG samples contain signatures of excess positive charge accumulated in graphene. The findings are further confirmed by electrical characterization performed on SLG-FETs. In a different approach, we show a procedure to reversibly tune the excess charge concentration in SLG, from p- to n-type, up to 1.2×10E13/cm2. The tuning is achieved by engineering the interaction between graphene and the underlying substrate with an amino group-terminated self-assembled monolayer, and subsequent rinsing in aqueous solutions at controlled pH. Raman spectroscopy and electrical measurements on treated graphene devices confirm the occurrence of doping. We found the field-effect mobility not to be significantly affected by the procedure.In last part of this thesis we demonstrate a technique to improve the Ion/I off ratio in bilayer graphene FET by asymmetrical doping of layers. Doping is achieved by n-doping the bottom layer by depositing bilayer graphene flakes on NH2-SAM and hole doping the top layer via coating the device with a film of F4TCNQ-containing polymer. Asymmetric surface doping of bilayer graphene can induce an electric field between both layers which results in opening of an electronic bandgap due to symmetry breaking. DFT modeling shows an effective electric field between the layers and field effect measurements show an increase of Ion/I off ratio in bilayer FET up to ~100 due to opening of the bandgap. The demonstrated Ion/I off ratio is the highest to date reported value for graphene based devices.status: publishe