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  • 124101.
    Zhang, Xiaolei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Yang, Weihong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Formation and Characterization of Carbon-Radical Precursors in Char Steam Gasification2010In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 24, p. 6513-6521Article in journal (Refereed)
    Abstract [en]

    Highly reactive radicals play an important role in high-temperature gasification processes. However, the effect of radicals on gasification has not been systematically investigated. In the present study, the formation of carbon-radical precursors using atomic radicals such as OH, O, and H and molecules such as H-2 and O-2 was characterized, and the effect of the precursors on the adsorption step of steam char gasification was studied using quantum chemistry methods. The results revealed that the radicals can be chemisorbed exothermically on char active sites, and the following order of reactivity was observed: O > H-2 > H > OH > O-2. Moreover, hydrogen bonds are formed between steam molecules and carbon-radical complexes. Steam molecule adsorption onto carbon-O and carbon-OH complexes is easier than adsorption onto clean carbon surfaces. Alternatively, adsorption on carbon-O-2, carbon-H-2, and carbon-H complexes is at the same level with that of clean carbon surfaces; thus, OH and O radicals accelerate the physical adsorption of steam onto the char surface, H radical and O-2 and H-2 molecules do not have a significant effect on adsorption.

  • 124102.
    Zhang, Xiaolei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Yang, Weihong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Kinetics of levoglucosan and formaldehyde formation during cellulose pyrolysis process2012In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 96, no 1, p. 383-391Article in journal (Refereed)
    Abstract [en]

    The mechanisms and kinetics studies of the formation of levoglucosan and formaldehyde from anhydroglucose radical have been carried out theoretically in this paper. The geometries and frequencies of all the stationary points are calculated at the B3LYP/6-31+G(D,P) level based on quantum mechanics, Six elementary reactions are found, and three global reactions are involved. The variational transition-state rate constants for the elementary reactions are calculated within 450-1500 K. The global rate constants for every pathway are evaluated from the sum of the individual elementary reaction rate constants. The first-order Arrhenius expressions for these six elementary reactions and the three pathways are suggested. By comparing with the experimental data, computational methods without tunneling correction give good description for Path1 (the formation of levoglucosan); while methods with tunneling correction (zero-curvature tunneling and small-curvature tunneling correction) give good results for Path2 (the first possibility for the formation of formaldehyde), all the test methods give similar results for Path3 (the second possibility for the formation of formaldehyde), all the modeling results for Path3 are in good agreement with the experimental data, verifying that it is the most possible way for the formation of formaldehyde during cellulose pyrolysis.

  • 124103.
    Zhang, Xiaolei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Yang, Weihong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Kinetics study on thermal dissociation of levoglucosan during cellulose pyrolysis2013In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 109, p. 476-483Article in journal (Refereed)
    Abstract [en]

    The mechanisms and kinetics studies of the levoglucosan (LG) primary decomposition during cellulose pyrolysis have been carried out theoretically in this paper. Three decomposition mechanisms (C-O bond scission, C-C bond scission, and LG dehydration) including nine pathways and 16 elementary reactions were studied at the B3LYP/6-31 + G(D, P) level based on quantum mechanics. The variational transition-state rate constants for every elementary reaction and every pathway were calculated within 298-1550 K. The first-order Arrhenius expressions for these 16 elementary reactions and nine pathways were suggested. It was concluded that computational method using transition state theory (TST) without tunneling correction gives good description for LG decomposition by comparing with the experimental result. With the temperature range of 667-1327 K, one dehydration pathway, with one water molecule composed of a hydrogen atom from C3 and a hydroxyl group from C2, is a preferred LG decomposition pathway by fitting well with the experimental results. The calculated Arrhenius plot of C-O bond scission mechanism is better agreed with the experimental Arrhenius plot than that of C-C bond scission. This C-O bond scission mechanism starts with breaking of C1-O5 and C6-O1 bonds with formation of CO molecule (C1-O1) simultaneously. C-C bond scission mechanism is the highest energetic barrier pathway for LG decomposition.

  • 124104.
    Zhang, Xiaolei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Yang, Weihong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Modeling Study of Woody Biomass: Interactions of Cellulose, Hemicellulose, and Lignin2011In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 25, no 10, p. 4786-4795Article in journal (Refereed)
    Abstract [en]

    Lignocellulosic biomass pretreatment and the subsequent thermal conversion processes to produce solid, liquid, and gas biofuels are attractive solutions for today's energy challenges. The structural study of the main components in biomass and their macromolecular complexes is an active and ongoing research topic worldwide. The interactions among the three main components, cellulose, hemicellulose, and lignin, are studied in this paper using electronic structure methods, and the study includes examining the hydrogen bond network of cellulose-hemicellulose systems and the covalent bond linkages of hemicellulose-lignin systems. Several methods (semiempirical, Hartree-Fock, and density functional theory) using different basis sets were evaluated. It was shown that theoretical calculations can be used to simulate small model structures representing wood components. By comparing calculation results with experimental data, it was concluded that B3LYP/6-31G is the most suitable basis set to describe the hydrogen bond system and B3LYP/6-31G(d,p) is the most suitable basis set to describe the covalent system of woody biomass. The choice of unit model has a much larger effect on hydrogen bonding within cellulose-hemicellulose system, whereas the model choice has a minimal effect on the covalent linkage in the hemicellulose-lignin system.

  • 124105.
    Zhang, Xiaolei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Yang, Weihong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Thermal decomposition mechanism of levoglucosan during cellulose pyrolysis2012In: Journal of Analytical and Applied Pyrolysis, ISSN 0165-2370, E-ISSN 1873-250X, Vol. 96, p. 110-119Article in journal (Refereed)
    Abstract [en]

    Levoglucosan (1,6-anhydro-beta-D-glucopyranose) decomposition is an important step during cellulose pyrolysis and for secondary tar reactions. The mechanism of levoglucosan thermal decomposition was studied in this paper using density functional theory methods. The decomposition included direct C-O bond breaking, direct C-C bond breaking, and dehydration. In total, 9 different pathways, including 16 elementary reactions, were studied, in which levoglucosan serves as a reactant. The properties of the reactants, transition states, intermediates, and products for every elementary reaction were obtained. It was found that 1-pentene-3,4-dione, acetaldehyde, 2,3-dihydroxypropanal, and propanedialdehyde can be formed from the C-O bond breaking decomposition reactions. 1,2-Dihydroxyethene and hydroxyacetic acid vinyl ester can be formed from the C C bond breaking decomposition reactions. It was concluded that C-O bond breaking is easier than C-C bond breaking due to a lower activation energy and a higher released energy. During the 6 levoglucosan dehydration pathways, one water molecule which composed of a hydrogen atom from C3 and a hydroxyl group from C2 is the preferred pathway due to a lower activation energy and higher product stability.

  • 124106.
    Zhang, Xiaolei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Yang, Weihong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Dong, Changqing
    Levoglucosan Formation Mechanism during Cellulose PyrolysisArticle in journal (Other academic)
  • 124107.
    Zhang, Xiaolei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Yang, Weihong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Dong, Changqing
    Levoglucosan formation mechanisms during cellulose pyrolysis2013In: Journal of Analytical and Applied Pyrolysis, ISSN 0165-2370, E-ISSN 1873-250X, Vol. 104, p. 19-27Article in journal (Refereed)
    Abstract [en]

    Levoglucosan is one important primary product during cellulose pyrolysis either as an intermediate or as a product. Three available mechanisms for levoglucosan formation have been studied theoretically in this paper, which are free-radical mechanism; glucose intermediate mechanism; and levoglucosan chain-end mechanism. All the elementary reactions included in the pathway of every mechanism were investigated; thermal properties including activation energy. Gibbs free energy, and enthalpy for every pathway were also calculated. It was concluded that free-radical mechanism has the highest energy barrier during the three levoglucosan formation mechanisms, glucose intermediate mechanism has lower energy barrier than free-radical mechanism, and levoglucosan chain-end mechanism is the most reasonable pathway because of the lowest energy barrier. By comparing with the activation energy obtained from the experimental results, it was also concluded that levoglucosan chain-end mechanism fits better with the experimental data for the formation of levoglucosan.

  • 124108.
    Zhang, Xiaoliang
    et al.
    Beihang Univ, Sch Mat Sci & Engn, Beijing 100191, Peoples R China..
    Cappel, Ute B.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Jia, Donglin
    Beihang Univ, Sch Mat Sci & Engn, Beijing 100191, Peoples R China..
    Zhou, Qisen
    Beihang Univ, Sch Mat Sci & Engn, Beijing 100191, Peoples R China..
    Du, Juan
    Beihang Univ, Sch Mat Sci & Engn, Beijing 100191, Peoples R China..
    Sloboda, Tamara
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Svanström, Sebastian
    Uppsala Univ, Dept Phys & Astron, Div Mol & Condensed Matter Phys, Box 516, SE-75120 Uppsala, Sweden..
    Johansson, Fredrik O. L.
    Uppsala Univ, Dept Phys & Astron, Div Mol & Condensed Matter Phys, Box 516, SE-75120 Uppsala, Sweden..
    Lindblad, Andreas
    Uppsala Univ, Dept Phys & Astron, Div Mol & Condensed Matter Phys, Box 516, SE-75120 Uppsala, Sweden..
    Giangrisostomi, Erika
    Helmholtz Zentrum Berlin GmbH, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany..
    Ovsyannikov, Ruslan
    Helmholtz Zentrum Berlin GmbH, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany..
    Liu, Jianhua
    Beihang Univ, Sch Mat Sci & Engn, Beijing 100191, Peoples R China..
    Rensmo, Håkan
    Uppsala Univ, Dept Phys & Astron, Div Mol & Condensed Matter Phys, Box 516, SE-75120 Uppsala, Sweden..
    Gardner, James M.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Johansson, Erik M. J.
    Uppsala Univ, Phys Chem, Dept Chem Angstrom, S-75120 Uppsala, Sweden..
    Probing and Controlling Surface Passivation of PbS Quantum Dot Solid for Improved Performance of Infrared Absorbing Solar Cells2019In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 31, no 11, p. 4081-4091Article in journal (Refereed)
    Abstract [en]

    Surface properties of colloidal quantum dots (CQDs) are critical for the transportation and recombination of the photoinduced charge carrier in CQD solar cells, therefore dominating the photovoltaic performance. Herein, PbS CQD passivated using liquid-state ligand exchange (LSLX) and solid-state ligand exchange (SSLX) strategies are in detail investigated using photoelectron spectroscopy (PES), and solar cell devices are prepared to understand the link between the CQD surface properties and the solar cell function. PES using different energies in the soft and hard Xray regime is applied to study the surface and bulk properties of the CQDs, and the results show more effective surface passivation of the CQDs prepared with the LSLX strategy and less formation of lead-oxide. The CQD solar cells prepared with LSLX strategy show higher performance, and the photoelectric measurements suggest that the recombination of photoinduced charges is reduced for the solar cell prepared with the LSLX approach. Meanwhile, the fabricated solar cells exhibit good stability. This work provides important insights into how to fine-tune the CQD surface properties by improving the CQD passivation, and how this is linked to further improvements of the device photovoltaic performance.

  • 124109. Zhang, Xiaoliang
    et al.
    Zhang, Jindan
    Phuyal, Dibya
    Du, Juan
    Tian, Lei
    Oberg, Viktor A.
    Johansson, Malin B.
    Cappel, Ute B.
    Uppsala University, Sweden.
    Karis, Olof
    Liu, Jianhua
    Rensmo, Hakan
    Boschloo, Gerrit
    Johansson, Erik M. J.
    Inorganic CsPbI3 Perovskite Coating on PbS Quantum Dot for Highly Efficient and Stable Infrared Light Converting Solar Cells2018In: Advanced Energy Materials, ISSN 1614-6832, Vol. 8, no 6, article id 1702049Article in journal (Refereed)
    Abstract [en]

    Solution-processed colloidal quantum dot (CQD) solar cells harvesting the infrared part of the solar spectrum are especially interesting for future use in semitransparent windows or multilayer solar cells. To improve the device power conversion efficiency (PCE) and stability of the solar cells, surface passivation of the quantum dots is vital in the research of CQD solar cells. Herein, inorganic CsPbI3 perovskite (CsPbI3-P) coating on PbS CQDs with a low-temperature, solution-processed approach is reported. The PbS CQD solar cell with CsPbI3-P coating gives a high PCE of 10.5% and exhibits remarkable stability both under long-term constant illumination and storage under ambient conditions. Detailed characterization and analysis reveal improved passivation of the PbS CQDs with the CsPbI3-P coating, and the results suggest that the lattice coherence between CsPbI3-P and PbS results in epitaxial induced growth of the CsPbI3-P coating. The improved passivation significantly diminishes the sub-bandgap trap-state assisted recombination, leading to improved charge collection and therefore higher photovoltaic performance. This work therefore provides important insight to improve the CQD passivation by coating with an inorganic perovskite ligand for photovoltaics or other optoelectronic applications.

  • 124110.
    Zhang, Xiaoxiang
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Numerical Study on Combustion Features of Gasified Biomass Gas2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    There is a great interest to develop biomass combustion systems for industrial and utility applications. Improved biomass energy conversion systems are designed to provide better combustion efficiencies and environmental friendly conditions, as well as the fuel flexibility options in various applications. The gas derived from the gasification process of biomass is considered as one of the potential candidates to substitute traditional fuels in a combustion process. However, the gascomposition from the gasification process may have a wide range of variation depending on the methods and fuel sources. The better understanding of the combustion features for the Gasified Biomass Gas(GBG) is essential for the development of combustion devices to be operated efficiently and safely at the user-end.

    The objective of the current study is therefore aiming to achieve data associated with the combustion features of GBG fuel for improving the efficiency and stability of combustion process. The numerical result is achieved from the kinetic models of premixed combustion with a wide range of operating ranges and variety of gas compositions. The numerical result is compared with experimental data to provide a better understanding of the combustion process for GBG fuel.

    In this thesis the laminar flame speed and ignition delay time of the GBG fuel are analyzed, using 1-D premixed flame model and constant volume model respectively. The result from different kinetics are evaluated and compared with experimental data. The influences of initial temperature, pressure and equivalence ratio are considered, as well as the variation of gas compositions. While the general agreement is reached between the numerical result and experimental data for laminarflame speed prediction, deviations are discovered at fuel-rich region and increased initial temperature. For the ignition delay time, deviations are found in the low-temperature and low pressure regime. The empirical equations considering the influence of initial temperature,pressure and equivalence ratio are developed for laminar flame speed and ignition delay times. The influence of major compositions such as CO, H2 and hydrocarbons are discussed in details in the thesis. Furthermore, a simplified kinetic model is developed and optimized based on the evaluation of existing kinetics for GBG fuel combustion. The simplified kinetic model is expected to be used for simulating the complexc ombustion process of GBG fuel in future studies.

  • 124111.
    Zhang, Xiaoxiang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Jayasuriya, Jeevan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fakhraie, Reza
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Evaluation of reduced kinetics in simulation of gasified biomass gas combustion2013In: ASME Turbo Expo 2013: Turbine Technical Conference and Exposition: Volume 1B: Combustion, Fuels and Emissions, ASME Press, 2013, Vol. 1B, p. V01BT04A045-Conference paper (Refereed)
    Abstract [en]

    It is essentially important to use appropriate chemical kinetic models in the simulation process of gas turbine combustion. To integrate the detailed kinetics into complex combustion simulations has proven to be a computationally expensive task with tens to thousands of elementary reaction steps. It has been suggested that an appropriate simplified kinetics which are computationally efficient could be used instead. Therefore reduced kinetics are often used in CFD simulation of gas turbine combustion. At the same time, simplified kinetics for specific fuels and operation conditions need to be carefully selected to fulfill the accuracy requirements. The applicability of several simplified kinetics for premixed Gasified Biomass Gas (GBG) and air combustion are evaluated in this paper. The current work is motivated by the growing demand of gasified biomass gas (GBG) fueled combustion. Even though simplified kinetic schemes developed for hydrocarbon combustions are published by various researchers, there is little research has been found in literature to evaluate the ability of the simplified chemical kinetics for the GBG combustion. The numerical Simulation tool "CANTERA" is used in the current study for the comparison of both detailed and simplified chemical kinetics. A simulated gas mixture of CO/H2/CH4/CO2/N2 is used for the current evaluation, since the fluctuation of GBG components may have an unpredictable influence on the simulation results. The laminar flame speed has an important influence with flame stability, extinction limits and turbulent flame speed, here it is chosen as an indicator for validation. The simulation results are compared with the experimental data from the previous study [1] which is done by our colleagues. Water vapour which has shown a dilution effect in the experimental study are also put into concern for further validation. As the results indicate, the reduced kinetics which are developed for hydrocarbon or hydrogen combustion need to be highly optimized before using them for GBG combustion. Further optimization of the reduced kinetics is done for GBG and moderate results are achieved using the optimized kinetics compared with the detailed combustion kinetics.

  • 124112.
    Zhang, Xiaoxiang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Jayasuriya, Jeevan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Kinetic Evaluation of the Laminar Flame Speed for Biomass Derived Gas CombustionManuscript (preprint) (Other academic)
    Abstract [en]

    The gas composition derived from gasification of biomass has been used in gasturbine combustion to achieve higher energy efficiency. However, there is an essential requirement to better understand the combustion characteristics of biomass derived gas before it can be used in the existing combustion facilities. A quantified study of the laminar flame speed of biomass derived gas combustionis presented in this paper. The study was carried out based on the kinetic model of the biomass derived gas flame and the results are compared with the experimental data from the our laboratory and various literatures. The laminarflame speed of the biomass derived gas was evaluated through a range of initial temperature (298 K - 398 K) and pressure (1 atm - 10 atm), as well as with various gas compositions. An empirical relationship for estimating the laminarflame speed has been derived for a composition of typical biomass derived gas. Furthermore, the evaluation of laminar flame speeds with various compositions have been carried out through numerical calculations and results were compared with experimental data from previous studies. The hydrogen concentration in gas composition has shown an essential importance for the laminarflame speed variation.

  • 124113.
    Zhang, Xiaoxiang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Jayasuriya, Jeevan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Kinetic Study on Ignition Delay Time of Biomass Derived Gas CombustionManuscript (preprint) (Other academic)
    Abstract [en]

    The ignition delay time is one of the fundamental characteristics of a combustionprocess and has an essential effect on the performance of the combustion process. In the current study, a kinetic study on auto iginition delaytime is carried out for biomass derived gas combustion. A gas mixture of CO/H2/CO2/CH4/N2 is used to represent the typical composition from a biomass gasification process. The gas mixture is mixed with air under a certain range of operating conditions. A pressure range from 1 – 32 atm and an initial temperature range from 900 K to 1250 K were considered in the current study.The correlation between the ignition delay time and the operating conditions (pressures, initial temperatures and equivalence ratio) was derived for the biomass derived gas based on the kinetic calculations and published experimental data. The empirical correlation was obtained for the gas mixture ofCO/H2/CO2/CH4/N2/air and the gas mixture of CO/H2/O2/Ar. The influence of fuel compositions of the ignition delay time has also been discussed within this study. However, the influence of composition variation shown in the current study was not significant and was difficult to be cross-validated by various experimental data.

  • 124114. Zhang, Xiaoyu
    et al.
    Guo, Fuling
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    He, Jinxiang
    Wu, Wenjun
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Hua, Jianli
    Effect of thiophene in bithiazole-bridged sensitizers on the performance of dye-sensitized solar cells2014In: Nano, ISSN 1793-2920, Vol. 9, no 5, p. 1440009-Article in journal (Refereed)
    Abstract [en]

    In this paper, we have designed and synthesized four bithiazole-bridged sensitizers (BT-T2, TBT-T2, BT-T3 and TBT-T3) with triphenylamine and indoline as the donor segment and applied them to dye-sensitized solar cells (DSSCs). For triphenylamine-based sensitizers as BT-T2 and TBT-T2, adding one thiophene unit between triphenylamine donor and bithiazole moiety not only led to bathochromic shift of the maximum absorption and increase of molar extinction coefficient, but also enhanced the photovoltaic conversion efficiency from 7.12% of BT-T2 to 7.51% of TBT-T2. But for indoline-based sensitizers as BT-T3 and TBT-T3, adding one thiophene unit between indoline donor and bithiazole moiety resulted in hypochromatic shift instead of bathochromic shift. We employed the density functional theory (DFT) calculations to further investigate the influence of the thiophene unit on their optical and electronic properties and photovoltaic performance of corresponding DSSC devices. Given the results, a reasonable explanation is the introduction of thiophene unit suppressed the intramolecular charge transfer and charge separation in the conjugation system of indoline-based sensitizer, which led to the hypochromatic shift of the maximum absorption wavelength and finally the low J(sc). Since the J(sc) dropped sharply from 15.26mAcm(-2) to 4.52mAcm(-2), the photovoltaic conversion efficiency decreased dramatically from 7.86% to 1.93%.

  • 124115. Zhang, Xiaoyu
    et al.
    Mao, Jiangyi
    Wang, Dan
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Yang, Jiabao
    Shen, Zhongjin
    Wu, Wenjun
    Li, Jing
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Hua, Jianli
    Comparative Study on Pyrido[3,4-b]pyrazine-Based Sensitizers by Tuning Bulky Donors for Dye-Sensitized Solar Cells2015In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 7, no 4, p. 2760-2771Article in journal (Refereed)
    Abstract [en]

    Dye-sensitized solar cells (DSSCs) with cobalt electrolytes have gained increasing attention. In this Research Article, two new pyrido[3,4-b]pyrazine-based sensitizers with different cores of bulky donors (indoline for DT-1 and triphenylamine for DT-2) were designed and synthesized for a comparative study of their photophysical and electrochemical properties and device performance and were also analyzed through density functional theory calculations. The results of density function theory calculations reveal the limited electronic communication between the biphenyl branch at the cis-position of N-phenylindoline and the indoline core, which could act as an insulating blocking group and inhibit the dye aggregation and charge recombination at the interface of TiO2/dye/electrolyte. As expected, DSSCs based on DT-1 with cobalt redox electrolyte gained a higher photoelectric conversion efficiency of 8.57% under standard AM 1.5 G simulated sunlight, with J(sc) = 16.08 mA cm(-2), V-oc = 802 mV, and FF = 0.66. Both electrochemical impedance spectroscopy (EIS) and intensity-modulated photovoltage spectroscopy (IMVS) suggest that charge recombination in DSSCs based on DT-1 is much less than that in their counterparts of DT-2, owing to the bigger donor size and the insulating blocking branch in the donor of DT-1.

  • 124116.
    Zhang, Xin
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Water, Sewage and Waste technology.
    Application of Partial Nitritation/Anammox Process for Treatment of Wastewater with High Salinity.2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The combination of partial nitritation and anaerobic ammonium oxidation (Anammox) is a composting way to remove the nitrogen in the wastewater. In this article the analysis was made to investigate how the salinity in the wastewater affects the process. Two strategies of salt concentration increase were tested in two reactors. The physical, chemical parameters and the activity of the bacteria in the reactors were monitored. The results of two strategies were compared and the reactor with less salt in each period showed higher bacteria activities and efficiency. Finally the outlook for the future research was made.

  • 124117.
    Zhang, Xin
    et al.
    Guangdong Univ Technol, Coll Art & Design, Guangzhou 510000, Guangdong, Peoples R China..
    Li, Jiehao
    Beijing Inst Technol, Key Lab Intelligent Control & Decis Complex Syst, Beijing 100081, Peoples R China..
    Hu, Zhenhuan
    Guangdong Univ Technol, Coll Art & Design, Guangzhou 510000, Guangdong, Peoples R China..
    Qi, Wen
    Politecn Milan, Dipartimento Elettron Informaz & Bioingn, I-20133 Milan, Italy..
    Zhang, Longbin
    KTH, School of Engineering Sciences (SCI), Centres, BioMEx.
    Hu, Yingbai
    Tech Univ Munich, Dept Informat, D-85748 Munich, Germany..
    Su, Hang
    Guangdong Univ Technol, Coll Art & Design, Guangzhou 510000, Guangdong, Peoples R China.;Politecn Milan, Dipartimento Elettron Informaz & Bioingn, I-20133 Milan, Italy..
    Ferrigno, Giancarlo
    Politecn Milan, Dipartimento Elettron Informaz & Bioingn, I-20133 Milan, Italy..
    De Momi, Elena
    Politecn Milan, Dipartimento Elettron Informaz & Bioingn, I-20133 Milan, Italy..
    Novel Design and Lateral Stability Tracking Control of a Four-Wheeled Rollator2019In: Applied Sciences, E-ISSN 2076-3417, Vol. 9, no 11, article id 2327Article in journal (Refereed)
    Abstract [en]

    Design and control of smart rollators have attracted increasing research interests in the past decades. To meet the requirements of the elderly or disabled users, this paper proposes a novel design and tracking control scheme for empowering and assisting natural human mobility with a four-wheeled rollator. Firstly, by integrating the advantages of Kano Model Analysis and the Theory of Inventive Problem Solving (TRIZ), we introduce a novel Kano-TRIZ industrial design method to design and optimize its mechanical structure. The demand and quality characteristics of the clinical rollator are analyzed according to the Kano model. The Quality Function Deployment (QFD) and TRIZ are adopted to integrate industrial product innovations and optimize the function configuration. Furthermore, a lateral stability controller based on Model Predictive Control (MPC) scheme is introduced to achieve good tracking control performance with the lateral deviation and the heading angle deviation. Finally, the feasibility of the design and control method is verified with a simulation study. The simulation results indicate that the proposed algorithm keeps the lateral position error in a reasonable range. In the co-simulation of ADAMS-MATLAB, the trajectory of the rollator is smooth with constrained position error within 0.1 m, the turning angle and speed can achieve stable tracking control within 5 s and the heading angle is accurate and the speed is stable. A compared experiment with MPC and SMC show that MPC controller has faster response, higher tracking accuracy and smoother trajectory on the novel designed rollator. With the increasing demand for rollators in the global market, the methodology proposed in this paper will attract more research and industry interests.

  • 124118.
    Zhang, Xinhai
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Embedded Control Systems.
    Automated Support for the Architecting of Distributed Embedded Systems: Methods and Analysis for Industrial Adoption2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The architecture design complexity of modern embedded systems, such as in the automotive domain, is growing due to the rapidly evolved functionalities, the increasing amount of interactions between functions and computation nodes, and the stringent extra-functional requirements. Architecture design is crucial since it affects nontrivial system properties such as safety, cost, performance of functionalities and also the development time. An important enabler to deal with this complexity is to provide computer aided architecture design. This thesis focuses on such support for Design Space Exploration (DSE), relying on a model-based design (MBD) environment.

    The goal of this thesis is to improve the industrial adoption of DSE methods to facilitate the architecture design of distributed embedded systems in the automotive industry. The main contributions of this thesis are as follows: (1) Applying architecture recovery in the automotive industry to extract architecture models from legacy ECU source code. The recovered architecture models can be used to facilitate system understanding, to verify the software implementation against its specification and also to enable DSE for architecture design. (2) A systematic gap analysis was conducted between the state-of-the-art DSE methods and the industrial needs, through literature studies and interviews with experienced system architects. Identified gaps are analyzed from the following perspectives: Architecting scenarios, architectural decisions, quality attributes, cost model, procurement strategy, system variability and functional safety. (3) A new problem formulation was proposed to reduce the design space by utilizing the features of evolutionary architecting and the AUTOSAR layered architecture. (4) In order to enhance the flexibility of the DSE methods by enabling the customizability of the architectural constraints, an automatic transformation method is proposed to translate formally described architectural constraints into the corresponding mixed integer linear programming(MILP) constraints, commonly used for DSE. (5) This thesis also investigates the potential impacts of vehicular communication on the future architecture of automotive embedded systems from the timing perspective through a case study to enable a commercial truck with cooperative driving functionalities. The receiving bias problem was identified during the case study and effective architectural solutions were proposed. The case study also showed that the adoption of vehicular communication would not have significant architectural impacts in terms of timing.

  • 124119.
    Zhang, Xinhai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Chen, DeJiu
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Törngren, Martin
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Towards Design Space Exploration through EAST-ADL and AUTOSAR Modeling Frameworks2014Conference paper (Refereed)
  • 124120.
    Zhang, Xinhai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Feng, Lei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Chen, De-Jiu
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Törngren, Martin
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Design-Space Reduction for Architectural Optimization of Automotive Embedded Systems2015In: High Performance Computing and Communications (HPCC), 2015 IEEE 7th International Symposium on Cyberspace Safety and Security (CSS), 2015 IEEE 12th International Conferen on Embedded Software and Systems (ICESS), 2015 IEEE 17th International Conference on, IEEE Computer Society, 2015, , p. 7p. 1103-1109Conference paper (Refereed)
    Abstract [en]

    A key decision for the synthesis of automotiveembedded systems is the allocation of application softwarecomponents to ECUs. Design Space Exploration (DSE) supportsthe decision by automatically characterizing and evaluating alarge number of possible design alternatives, and thereby suggestingthe optimal ones. A primary challenge for applying DSEmethods to support this decision is to reduce the computationtime of the DSE process while maintaining the generality andoptimality. This paper exploits legacy system architectures andthe AUTOSAR standard to preemptively reduce the design space,because both artifacts limit the flexibility of certain designvariables. A new DES formulation incorporating the constraintsof the legacy system architectures and the AUTOSAR standardis proposed in this paper. Computation result shows a largereduction of the computation time comparing to traditionalmodeling and formulations. The scalability of our method is alsoanalyzed by testing it on a set of random problem instances.

  • 124121.
    Zhang, Xinhai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Embedded Control Systems.
    Feng, Lei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Embedded Control Systems.
    Törngren, Martin
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Embedded Control Systems.
    Chen, DeJiu
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Embedded Control Systems.
    Formulating Customized Specifications for Resource Allocation Problem of Distributed Embedded Systems2016In: 2016 IEEE/ACM INTERNATIONAL CONFERENCE ON COMPUTER-AIDED DESIGN (ICCAD), Institute of Electrical and Electronics Engineers (IEEE), 2016Conference paper (Refereed)
    Abstract [en]

    There are plentiful attempts for increasing the efficiency, generality and optimality of the Design Space Exploration (DSE) algorithms for resource allocation problems of distributed embedded systems. Most contemporary approaches formulate DSE as an optimization or SAT problem, based on a set of predefined constraints. In this way, the end users lose the flexibility to guide and customize the exploration based on specifics of their actual problem. Besides, during the design of the DSE algorithms, manual formulation is time consuming and error-prone. To solve these problems, 1) a formal representation is defined for capturing customized architectural constraints based on a combination of propositional logic and Pseudo-Boolean (PB) formulas; 2) A process is designed to automatically translate these architectural constrains into corresponding Integer Linear Programming (ILP) constraints, commonly used for DSE. The translation process is also optimized to create ILP formulation with less introduced variables so as to reduce computation time. The results show that the generated constraints correctly reflect the corresponding specification with decent efficiency.

  • 124122.
    Zhang, Xinhai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Mohan, Naveen
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Törngren, Martin
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Axelsson, J.
    Chen, DeJiu
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Architecture exploration for distributed embedded systems: A gap analysis in automotive domain2017In: 2017 12th IEEE International Symposium on Industrial Embedded Systems, SIES 2017 - Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2017, article id 7993377Conference paper (Refereed)
    Abstract [en]

    A large body of work can be found in literature on Design Space Exploration (DSE) methods for distributed embedded system architecting (DESA). However, almost none of these methods is successfully adopted in automotive industry. To clarify the reasons, this paper 1) analyzes the current state of the art (SOTA) on DSE methods for DESA through a systematic literature study, focusing on the assumed architecting process and concerns; 2) investigates the state of practice (SOP) on DESA in the automotive industry through a literature study and interviews with experienced system architects from five different automotive manufacturers; and 3) analyzes the gap between SOTA and SOP, and thereby discusses potential improvements of DSE methods.

  • 124123.
    Zhang, Xinhai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Persson, Magnus
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Nyberg, Mattias
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Mokhtari, Behrooz
    KTH.
    Einarson, A.
    Linder, H.
    Westman, Jonas
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Embedded Control Systems.
    Chen, DeJiu
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Embedded Control Systems.
    Törngren, Martin
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Experience on applying software architecture recovery to automotive embedded systems2014In: 2014 Software Evolution Week - IEEE Conference on Software Maintenance, Reengineering, and Reverse Engineering, CSMR-WCRE 2014 - Proceedings, IEEE Computer Society, 2014, p. 379-382Conference paper (Refereed)
    Abstract [en]

    The importance and potential advantages with a comprehensive product architecture description are well described in the literature. However, developing such a description takes additional resources, and it is difficult to maintain consistency with evolving implementations. This paper presents an approach and industrial experience which is based on architecture recovery from source code at truck manufacturer Scania CV AB. The extracted representation of the architecture is presented in several views and verified on CAN signal level. Lessons learned are discussed.

  • 124124.
    Zhang, Xinhai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Song, Xinwu
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Feng, Lei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Chen, Lei
    Törngren, Martin
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    A Case Study on Achieving Fair Data Age Distribution in Vehicular Communications2017In: PROCEEDINGS OF THE 23RD IEEE REAL-TIME AND EMBEDDED TECHNOLOGY AND APPLICATIONS SYMPOSIUM (RTAS 2017) / [ed] Parmer, G, IEEE , 2017, p. 307-317Conference paper (Refereed)
    Abstract [en]

    In vehicular communication protocol stacks, received messages may not always be decoded successfully due to the complexity of the decoding functions, the uncertainty of the communication load and the limited computation resources. Even worse, an improper implementation of the protocol stack may cause an unfair data age distribution among all the communicating vehicles (the receiving bias problem). In such cases, some vehicles are almost locked out of the vehicular communication, causing potential safety risk in scenarios such as intersection passing. To our knowledge, this problem has not been systematically studied in the fields of vehicular communication and intelligent transport systems (ITS). This paper analyzes the root of the receiving bias problem and proposes architectural solutions to balance data age distribution. Simulation studies based on commercial devices demonstrate the effectiveness of these solutions. In addition, our system has been successfully applied during the Grand Cooperative Driving Challenge, where complicated scenarios involving platooning maneuvering and intersection coordination were conducted.

  • 124125.
    Zhang, Xinlin
    et al.
    Chalmers, Dept Signals & Syst, S-41296 Gothenburg, Sweden..
    Matthaiou, Michail
    Chalmers, Dept Signals & Syst, S-41296 Gothenburg, Sweden.;Queens Univ Belfast, Sch Elect Elect Engn & Comp Sci, Belfast, Antrim, North Ireland..
    Björnson, Emil
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Coldrey, Mikael
    Ericsson AB, Ericsson Res, Gothenburg, Sweden..
    Debbah, Merouane
    SUPELEC, Alcatel Lucent Chair Flexible Radio, Gif Sur Yvette, France..
    On the MIMO Capacity with Residual Transceiver Hardware Impairments2014In: 2014 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC) / [ed] Jamalipour, A Deng, DJ, IEEE , 2014, p. 5299-5305Conference paper (Refereed)
    Abstract [en]

    Radio-frequency (RF) impairments in the transceiver hardware of communication systems (e.g., phase noise (PN), high power amplifier (HPA) nonlinearities, or in-phase/quadrature-phase (I/Q) imbalance) can severely degrade the performance of traditional multiple-input multiple-output (MIMO) systems. Although calibration algorithms can partially compensate these impairments, the remaining distortion still has substantial impact. Despite this, most prior works have not analyzed this type of distortion. In this paper, we investigate the impact of residual transceiver hardware impairments on the MIMO system performance. In particular, we consider a transceiver impairment model, which has been experimentally validated, and derive analytical ergodic capacity expressions for both exact and high signal-to-noise ratios (SNRs). We demonstrate that the capacity saturates in the high-SNR regime, thereby creating a finite capacity ceiling. We also present a linear approximation for the ergodic capacity in the low-SNR regime, and show that impairments have only a second-order impact on the capacity. Furthermore, we analyze the effect of transceiver impairments on large-scale MIMO systems; interestingly, we prove that if one increases the number of antennas at one side only, the capacity behaves similar to the finite-dimensional case. On the contrary, if the number of antennas on both sides increases with a fixed ratio, the capacity ceiling vanishes; thus, impairments cause only a bounded offset in the capacity compared to the ideal transceiver hardware case.

  • 124126. Zhang, Xinxin
    et al.
    Liu, Junguo
    Tang, Yu
    Zhao, Xu
    Yang, Hong
    Gerbens-Leenes, P. W.
    van Vliet, Michelle T. H.
    Yan, Jinyue
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
    China's coal-fired power plants impose pressure on water resources2017In: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 161, p. 1171-1179Article in journal (Refereed)
    Abstract [en]

    Coal is the dominant fuel for electricity generation around the world. This type of electricity generation uses large amounts of water, increasing pressure on water resources. This calls for an in-depth investigation in the water-energy nexus of coal-fired electricity generation. In China, coal-fired power plants play an important role in the energy supply. Here we assessed water consumption of coal-fired power plants (CPPs) in China using four cooling technologies: closed-cycle cooling, once-through cooling, air cooling, and seawater cooling. The results show that water consumption of CPPs was 3.5 km(3), accounting for 11% of total industrial water consumption in China. Eighty-four percent of this water consumption was from plants with closed-cycle cooling. China's average water intensity of CPPs was 1.15 l/kWh, while the intensity for closed-cycle cooling was 3-10 times higher than that for other cooling technologies. About 75% of water consumption of CPPs was from regions with absolute or chronic water scarcity. The results imply that the development of CPPs needs to explicitly consider their impacts on regional water resources.

  • 124127. Zhang, Xinyu
    et al.
    Qin, Jiaqian
    Liu, Hanyu
    Zhang, Shiliang
    Ma, Mingzhen
    Luo, Wei
    Liu, Riping
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala University, Sweden.
    Pressure-induced zigzag phosphorus chain and superconductivity in boron monophosphide2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 8761Article in journal (Refereed)
    Abstract [en]

    We report on the prediction of the zinc-blende structure BP into a novel C2/m phase from 113 to 208 GPa which possesses zigzag phosphorus chain structure, followed by another P4(2)/mnm structure above 208 GPa above using the particle-swarm search method. Strong electron-phonon coupling lambda in compressed BP is found, in particular for C2/m phase with the zigzag phosphorus chain, which has the highest lambda (0.56-0.61) value among them, leading to its high superconducting critical temperature T-c (9.4 K-11.5 K), which is comparable with the 4.5 Kto 13 Kvalue of black phosphorus phase I (orthorhombic, Cmca). This is the first system in the boron phosphides which shows superconductivity from the present theoretical calculations. Our results show that pressure-induced zigzag phosphorus chain in BP exhibit higher superconducting temperature T-C, opening a new route to search and design new superconductor materials with zigzag phosphorus chains.

  • 124128. Zhang, Xu
    et al.
    Othman, Maisara B
    Pang, Xiaodan
    RISE ACREO AB; Technical University of Denmark.
    Jensen, Jesper B
    Monroy, Idelfonso Tafur
    Bi-directional multi dimension CAP transmission for smart grid communication services2012In: Communications and Photonics Conference (ACP), 2012 Asia, Optical Society of America, 2012, p. 1-3Conference paper (Refereed)
    Abstract [en]

    We experimentally demonstrate bi-directional multi dimension carrierless amplitude and phase (CAP) transmission for smart grid communication services based on optical fiber networks. The proposed system is able to support multi-Gb/s transmission with high spectral efficiency.

  • 124129. Zhang, Xu
    et al.
    Pang, Xiaodan
    Technical University of Denmark, Denmark.
    Deng, Lei
    Zibar, Darko
    Monroy, Idelfonso Tafur
    Younce, Richard
    High phase noise tolerant pilot-tone-aided DP-QPSK optical communication systems2012In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 20, no 18, p. 19990-19995Article in journal (Refereed)
    Abstract [en]

    In this paper we experimentally demonstrate a novel, high phase-noise tolerant, optical dual polarization (DP) quadrature phase-shift keying (QPSK) communication system based on pilot-tone-aided phase noise cancellation (PNC) algorithm. Vertical cavity surface emitting lasers (VCSELs) with approximate 300 MHz linewidth are used as transmitters and local oscillators for coherent detection of optical DP-QPSK signals. The proposed system, with central wavelength at 1540.68 nm, operates at 40 Gb/s over 80 km single mode fiber (SMF) as part of a passive optical network (PON). The deployment of pilot-tone-aided PNC algorithm guarantees a bit error rate (BER) performance below the forward error correction (FEC) threshold. Moreover, we also evaluate a novel digital signal processing (DSP) algorithm for adaptive pilot tone detection.

  • 124130. Zhang, Xu
    et al.
    Pang, Xiaodan
    RISE ACREO AB; Technical University of Denmark.
    Dogadaev, Anton K
    Monroy, Idelfonso Tafur
    Zibar, Darko
    Younce, Richard C
    High spectrum narrowing tolerant 112 Gb/s dual polarization QPSK optical communication systems using digital adaptive channel estimation2012In: 2012 Optical Fiber Communication Conference and Exposition and the National Fiber Optic Engineers Conference, OFC/NFOEC 2012, 2012Conference paper (Refereed)
    Abstract [en]

    We experimentally demonstrate high spectrum narrowing tolerant 112-Gb/s QPSK polarization multiplex system based on digital adaptive channel estimation method. The proposed algorithm is able to detect severe spectrum-narrowed signal even with 20GHz 3dB bandwidth.

  • 124131.
    Zhang, Xu
    et al.
    University of Bedfordshire.
    Zhou, DiBin
    University of Bedfordshire.
    Xiao, Zhu
    University of Bedfordshire.
    Liu, Enjie
    University of Bedfordshire.
    Zhang, Jie
    University of Bedfordshire.
    Alayon Glazunov, Andres
    University of Bedfordshire.
    Dynamic Group PCI Assignment Scheme2011In: The Seventh International Conference on Wireless and Mobile Communications (ICWMC 2011), 2011, p. 101-106Conference paper (Refereed)
    Abstract [en]

    The Physical Cell Identity (PCI) is used to identify femtocell in LTE femtocell as the physical layer identity. Due to the fact that a) the PCIs are normally allocated without planning; and b) the limitation of the number of PCI, the cross-tier PCI confusion problem has arisen. The current solution in 3GPP Release 9 is to use Cell Global Identity (CGI) associated with PCI to solve this problem of confusion. However, using CGI has many serious drawbacks. Especially CGI might cause the inbound-handover is failure. In order to mitigate the CGI problem, this research proposes a dynamic PCI assignment scheme of DG-PCI in the macrocell and femtocell environment. The proposed scheme is tested by using system-level simulation. The simulations showed that the approach offers an optimal PCI distribution between macrocell and femtocell. The test showed that the CGI problem can be solved, and hence increase the successful rate of inbound-handover.

  • 124132. Zhang, Y.
    et al.
    Beskow, Jonas
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH.
    Kjellström, Hedvig
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH.
    Look but Don’t Stare: Mutual Gaze Interaction in Social Robots2017In: 9th International Conference on Social Robotics, ICSR 2017, Springer, 2017, Vol. 10652, p. 556-566Conference paper (Refereed)
    Abstract [en]

    Mutual gaze is a powerful cue for communicating social attention and intention. A plethora of studies have demonstrated the fundamental roles of mutual gaze in establishing communicative links between humans, and enabling non-verbal communication of social attention and intention. The amount of mutual gaze between two partners regulates human-human interaction and is a sign of social engagement. This paper investigates whether implementing mutual gaze in robotic systems can achieve social effects, thus to improve human robot interaction. Based on insights from existing human face-to-face interaction studies, we implemented an interactive mutual gaze model in an embodied agent, the social robot head Furhat. We evaluated the mutual gaze prototype with 24 participants in three applications. Our results show that our mutual gaze model improves social connectedness between robots and users.

  • 124133. Zhang, Y. C.
    et al.
    Lavraud, B.
    Dai, L.
    Wang, C.
    Marchaudon, A.
    Avanov, L.
    Burch, J.
    Chandler, M.
    Dorelli, J.
    Duan, S. P.
    Ergun, R. E.
    Gershman, D. J.
    Giles, B.
    Khotyaintsev, Y. V.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Paterson, W.
    Russell, C. T.
    Schiff, C.
    Tang, B. B.
    Torbert, R.
    Quantitative analysis of a Hall system in the exhaust of asymmetric magnetic reconnection2017In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 5, p. 5277-5289Article in journal (Refereed)
    Abstract [en]

    Taking advantage of high-resolution measurements from the MMS mission, we find evidence for a complete Hall system in the exhaust of asymmetric magnetic reconnection 40 Di downstream of the X line. The investigation of the fine structure of the Hall system reveals that it displays features in the exhaust similar to those reported previously in the ion diffusion region by simulations and observations. This finding confirms the importance of particle-scale processes in the reconnection exhaust as well. On the magnetospheric side of the exhaust, electrons are strongly accelerated by parallel electric fields. This process significantly contributes to feed the Hall current system, resulting in a nonnegligible Hall magnetic field signature on this side despite an otherwise lower density. Calculation of the induced out-of-plane magnetic field by in-plane currents (based on Biot-Savart law) provides direct quantitative evidence for the process of Hall magnetic field generation by the Hall current system. A strong normal Hall electric field is present only on the magnetospheric side of the exhaust region, consistent with previous works. Multipoint data analysis shows that the ion pressure gradient in the ion momentum equation produces this Hall electric field. This global pattern of the Hall system can be explained by kinetic Alfvén wave theory.

  • 124134. Zhang, Y. G.
    et al.
    Somesfalean, Gabriel
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Guo, W.
    Wang, H. S.
    Wu, S. H.
    Qin, Y. K.
    Zhang, Z. G.
    An optical system for measuring nitric oxide using spectral separation techniques2012In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 107, no 2, p. 435-440Article in journal (Refereed)
    Abstract [en]

    An optical sensor based on differential absorption spectroscopy for real-time monitoring of industrial nitric oxide (NO) gas emission is described. The influence of gas absorption interference from sulfur dioxide (SO2) in the environment was considered and a spectral separation technique was developed in order to eliminate this interference effect. The absorption spectrum of SO2 around 226 nm was evaluated by the SO2 concentration obtained using the experimentally recorded absorption spectrum around 300 nm. The absorption spectrum of NO around 226 nm was obtained by subtracting the absorption of SO2 from the integral absorption spectrum of SO2 and NO. The concentration measurements were performed at atmospheric pressure. The technique was found to have a lower detection limit of 0.8 ppm for NO per meter path length (SNR=2) and be immune from the influence from SO2 on the NO measurement. The sensor based on this technique was successfully employed for in situ measurement of SO2 and NO concentrations in the flue gas emitted from an industrial coal-fired boiler.

  • 124135. Zhang, Y.
    et al.
    Hu, L.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Tunable dual-broad-band branch-line coupler utilizing composite right/left-handed transmission lines2005In: JZUS-A - Journal of Zhejiang University. Science, ISSN 1009-3095, Vol. 6 A, no 6, p. 483-486Article in journal (Refereed)
    Abstract [en]

    A tunable dual-broad-band branch-line coupler (BLC) utilizing composite right/left-handed (CRLH) transmission lines is presented. Two λ/4 segments consisting of CRLH transmission lines are added to each port to broaden the dual bands of the branch-line coupler. Numerical simulation and optimal design of the novel coupler are presented. The dual bands of the novel coupler are tunable and broad. The 1-dB bandwidth of each passband is more than 16% of the central frequency.

  • 124136. Zhang, Y.
    et al.
    Jin, Yi
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Xue, W.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Broad-angle polarization beam splitter using an ultra-low permittivity material2009In: 2008 Asia Optical Fiber Communication and Optoelectronic Exposition and Conference, AOE 2008, 2009Conference paper (Refereed)
    Abstract [en]

    We design a broad-angle polarization beam splitter consisting of alternating layers of dielectric and ultra-low permittivity material. Within wide range of incident angles, it shows high transmissivity for one polarization while high reflectivity for another.

  • 124137. Zhang, Y.
    et al.
    Jin, Yi
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Xue, W.
    He, Sailing
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Polarization-independent 2D omni-directional photonic band gaps in a 1D periodic metal-dielectric (anisotropic) structure2009In: Waves in Random and Complex Media, ISSN 1745-5030, E-ISSN 1745-5049, Vol. 19, no 1, p. 39-48Article in journal (Refereed)
    Abstract [en]

    It is shown that there is no polarization-independent two-dimensionally (2D) omni-directional photonic band gap (PBG) for any conventional one-dimensional (1D) metal-dielectric (isotropic) structure. Through the study of band diagrams and some asymptotic analysis, a 1D periodic metal-dielectric (anisotropic) structure is proposed to achieve a polarization-independent 2D omni-directional PBG. Theoretical predictions for both the lossless and lossy cases are verified with finite element method (FEM) simulation of a point source in such a structure.

  • 124138. Zhang, Y. L.
    et al.
    Wang, Y. Z.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics. Department of Mathematics and Physics, Shijiazhuang Tiedao University, China; Institute of Applied Physics, Shijiazhuang Tiedao University, China; China Institute of Atomic Energy, Beijing 102413, China.
    Systematic study of cluster radioactivity of superheavy nuclei2018In: Physical Review C: Covering Nuclear Physics, ISSN 2469-9985, E-ISSN 2469-9993, Vol. 97, no 1, article id 014318Article in journal (Refereed)
    Abstract [en]

    The probable cluster radioactivity (CR) of 118294, 120296, and 122298 is studied by using the unified description (UD) formula, universal (UNIV) curve, Horoi formula, and universal decay law (UDL). The predictions by the former three models suggest that the probable emitted clusters are lighter nuclei, and the calculations within the UDL formula give a different prediction: that both the lighter clusters and heavier ones can be emitted from the parent nuclei. A further study on the competition between α decay and CR of Z=104-124 isotopes is performed. The former three models predict that α decay is the dominant decay mode, but the UDL formula suggests that CR dominates over α decay for Z≥118 nuclei and the isotopes of 118292-296,308-318, 120,284-304,308-324 and 122316-322 are the most likely candidates as the cluster emitters. Because the former three formulas are just preformation models, the lighter cluster emissions can be described. However, the UDL formula can predict the lighter and heavier CR owing to the inclusion of the preformation and fissionlike mechanisms. Finally, it is found that the shortest CR half-lives are always obtained when the daughter nuclei are around the double magic Pb208 within the UDL formula, which indicates that shell effect has an important influence on CR. 

  • 124139. Zhang, Y.
    et al.
    Liu, Sichao
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering. Northwestern Polytechnical University, Shaanxi, China.
    Liu, Y.
    Yang, H.
    Li, M.
    Huisingh, D.
    Wang, Lihui
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    The ‘Internet of Things’ enabled real-time scheduling for remanufacturing of automobile engines2018In: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 185, p. 562-575Article in journal (Refereed)
    Abstract [en]

    Typical challenges that managers of remanufacturing face are composed of the lack of timely, accurate, and consistent information of remanufacturing resources. Therefore, it is difficult to implement real-time production scheduling for the shop floor. To address this problem, the authors applied the concept of the ‘Internet of Things’ to the remanufacturing of automobile engines to form an Internet of Manufacturing Things environment. Under the Internet of Manufacturing Things, an identification technology for disassembled engine parts was designed, and the real-time status of the remanufacturable resources can be monitored. Based on the captured remanufacturing information, a real-time production scheduling method was developed, and a mathematical model was developed to achieve cost reduction, dynamic management of remanufacturable resources, and energy consumption decrease. To obtain an optimal solution, a Pareto-based optimization method was used. Finally, a case study was performed to analyze the effectivity of the proposed method. The results showed that the remanufacturing cost and energy consumption were reduced by 34% and 34% respectively, and the worker load rate was more balanced. These improvements can contribute to more sustainable development and greener production within the remanufacturing industry, especially for remanufacturing of automobile engines.

  • 124140. Zhang, Y.
    et al.
    Muhammed, Mamoun
    KTH, Superseded Departments, Materials Science and Engineering.
    Critical evaluation of thermodynamics of complex formation of metal ions in aqueous solutions VI. Hydrolysis and hydroxo-complexes of Zn2+ at 298.15 K2001In: Hydrometallurgy, ISSN 0304-386X, E-ISSN 1879-1158, Vol. 60, no 3, p. 215-236Article in journal (Refereed)
    Abstract [en]

    The standard thermodynamic properties of Zn2+, its hydrolysis reactions and hydroxo-complex formation are critically evaluated on the basis of published experimental studies and specific interaction theory (SIT) for activity coefficient modelling. A set of thermodynamic data and interaction coefficients are recommended.

  • 124141. Zhang, Y.
    et al.
    Su, Yang
    KTH.
    Zhang, H.
    Zhao, G.
    A comparative study of 10 different methods on numerical solving of point reactor neutron kinetics equations2017In: 2017 25th International Conference on Nuclear Engineering: Nuclear Fuel and Material, Reactor Physics and Transport Theory; Innovative Nuclear Power Plant Design and New Technology Application, ASME Press, 2017Conference paper (Refereed)
    Abstract [en]

    Point reactor neutron kinetics equations describe the time dependent neutron density variation in a nuclear reactor core. These equations are widely applied to nuclear system numerical simulation and nuclear power plant operational control. This paper analyses the characteristics of 10 different basic or normal methods to solve the point reactor neutron kinetics equations. These methods are: explicit and implicit Euler method, explicit and implicit four order Runge-Kutta method, Taylor polynomial method, power series method, decoupling method, end point floating method, Hermite method, Gear method. Three different types of step reactivity values are introduced respectively at initial time when point reactor neutron kinetics equations are calculated using different methods, which are positive reactivity, negative reactivity and higher positive reactivity. The calculation results show that (i) minor relative error can be gain after three types of step reactivity are introduced, when explicit or implicit four order Runge-Kutta method, Taylor polynomial method, power series method, end point floating method or Hermite method is taken. These methods which are mentioned above are appropriate for solving point reactor neutron kinetics equations. (ii) the relative error of decoupling method is large, under the calculation condition of this paper. When a higher reactivity is introduced, the calculation of decoupling method cannot be convergence. (iii) after three types of step reactivity are introduced respectively, the relative error of implicit Euler method is higher than any other method except decoupling method. The third highest is Gear method. (iv) when the higher reactivity is introduced, the relative error of explicit and implicit Euler method are almost coincident, and higher than any other methods obviously. (v) 4 methods are suitable for solution on these given conditions, which are implicit Runge-Kutta method, Taylor polynomial method, power series method and end point floating method, considering both the accuracy and stiffness.

  • 124142. Zhang, Y.
    et al.
    Weber, W. J.
    Jiang, W.
    Hallén, Anders.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Possnert, G.
    Damage evolution and recovery on both Si and C sublattices in Al-implanted 4H-SiC studied by Rutherford backscattering spectroscopy and nuclear reaction analysis2002In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 91, no 10, p. 6388-6395Article in journal (Refereed)
    Abstract [en]

    Damage evolution and subsequent recovery in 4H-SiC epitaxial layers irradiated with 1.1 MeV Al-2(2+) molecular ions at 150 K to ion fluences from 1.5x10(13) to 2.25x10(14) Al cm(-2) were studied by Rutherford backscattering spectroscopy (RBS) and C-12(d,p)C-13 nuclear reaction analysis (NRA) using a 0.94 MeV deuterium (D+) beam in channeling geometry. Disorder on both the Si and C sublattices was measured simultaneously from the RBS scattering and NRA reaction yields. The relative disorder on both sublattices follows a nonlinear dependence on ion fluence that is consistent with a model based on simple defect accumulation and a direct-impact, defect-stimulated process for amorphization. At low ion fluences, the relative disorder on the C sublattice is higher than that on the Si sublattice. Isochronal annealing up to 870 K revealed the existence of three distinct recovery stages at similar to350, 520, and 650 K for low to intermediate damage levels. In highly damaged samples, where a buried amorphous layer is produced, the onset of a fourth recovery stage appears above 800 K. Similar recovery behaviors on both the Si and C sublattices suggests some coupling of recovery processes for Si and C defects.

  • 124143. Zhang, Y.
    et al.
    Weber, W. J.
    Jiang, W. L.
    Hallén, Anders.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Possnert, G.
    Evolution and recrystallization of buried amorphous layers in A1(2)(2+) implanted 4H-SiC2002In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 195, no 04-mar, p. 320-328Article in journal (Refereed)
    Abstract [en]

    Epitaxial 4H-SiC has been irradiated at 150 K with 1.1 MeV Al-2(2+) molecular ions to fluences ranging from 1.5 x 10(13) to 8.00 x 10(14) Al+ cm(-2). The evolution and isochronal recovery of the buried amorphous layers at higher fluences were investigated by in situ Rutherford backscattering spectrometry using a 2.0 MeV He+ beam along the <0001> channeling direction. The damage accumulation at the damage peak in the as-implanted samples indicates a sigmoidal dependence on ion fluence, and a buried amorphous layer is formed at 2.00 x 10(14) Al+ cm(-2). The buried amorphous thickness increased rapidly at 2.00 x 10(14) Al+ cm(-2) and eventually saturated at a thickness of similar to500 nm at the highest fluence. The relative amount of recovery at any depth decreased with increasing ion fluence for temperatures up to 870 K, and once a thick buried amorphous layer is produced, recovery is only observed at the crystalline-amorphous interface. Defect annihilation processes are responsible for the slight recrystallization and sharpening of the damage profiles that are observed at these low annealing temperatures.

  • 124144. Zhang, Y.
    et al.
    Weber, W. J.
    Jiang, W.
    Shutthanandan, V.
    Thevuthasan, S.
    Janson, Martin
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Hallén, Anders
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Annealing behavior of Al-implantation-induced disorder in 4H-SiC2004In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 219, p. 647-651Article in journal (Refereed)
    Abstract [en]

    Single crystal 4H-SiC films were implanted at 150 K with 1.1 MeV Al-2(2+) and subsequently annealed at elevated 2 temperatures. In addition to the damage peak, an enhancement of the backscattering yield between the surface peak and damage peak is observed. Rutherford backscattering spectrometry results indicate that the relative Si disorder at the damage peak recovers significantly as the annealing temperature increases, and the near-surface peak disappears after annealing at 570 K. However, the residual Si disorder is more resistant to high-temperature annealing in the region of the implanted Al. The maximum concentration of Al profile measured by secondary ion mass spectroscopy is a factor of 1000 lower than the level of the residual Si disorder at the same region. Analysis of these results indicates that the excess residual Si disorder around the implanted Al projected range cannot be accounted for by just the Al interstitials; instead, it appears that implanted Al stabilizes or inhibits recovery Si disorder under the current experimental conditions.

  • 124145. Zhang, Y.
    et al.
    Weber, W. J.
    Jiang, W.
    Wang, C. M.
    Hallén, Anders.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Possnert, G.
    Effects of implantation temperature and ion flux on damage accumulation in Al-implanted 4H-SiC2003In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 93, no 4, p. 1954-1960Article in journal (Refereed)
    Abstract [en]

    The effects of implantation temperature and ion flux on damage accumulation on both the Si and C sublattices in 4H-SiC have been investigated under 1.1-MeV Al-2(2+) irradiation at temperatures from 150 to 450 K. The rate of damage accumulation decreases dramatically, and the damage profile sharpens due to significant dynamic recovery at temperatures close to the critical temperature for amorphization. At 450 K, the relative disorder and the density of planar defects increase rapidly with the increasing ion flux, exhibiting saturation at high ion fluxes. Planar defects are generated through the agglomeration of excess Si and C interstitials during irradiation and post-irradiation annealing at 450 K. A volume expansion of similar to8% is estimated for the peak damage region.

  • 124146. Zhang, Y.
    et al.
    Weber, W. J.
    Jiang, W.
    Wang, C. M.
    Shutthanandan, V.
    Hallén, Anders.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Effects of implantation temperature on damage accumulation in Al-implanted 4H-SiC2004In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 95, no 8, p. 4012-4018Article in journal (Refereed)
    Abstract [en]

    Damage accumulation in 4H-SiC under 1.1 MeV Al-2(2+) irradiation is investigated as a function of dose at temperatures from 150 to 450 K. Based on Rutherford backscattering spectroscopy and nuclear reaction analysis channeling spectra, the damage accumulation on both the Si and C sublattices have been determined, and a disorder accumulation model has been fit to the data. The model fits indicate that defect-stimulated amorphization is the primary amorphization mechanism in SiC over the temperature range investigated. The temperature dependence of the cross section for defect-stimulated amorphization and the critical dose for amorphization indicate that two different dynamic recovery processes are present, which are attributed to short-range recombination and long-range migration of point defects below and above room temperature, respectively. As the irradiation temperature approaches the critical temperature for amorphization, cluster formation has an increasing effect on disorder accumulation, and ion flux plays an important role on the nature and evolution of disorder. Dislocation loops, which are mostly formed under high ion flux, act as sinks for point defects, thereby reducing the disorder accumulation rate.

  • 124147. Zhang, Y.
    et al.
    Xiao, S.
    Yu, Y.
    Chen, C.
    Bi, M.
    Liu, L.
    Zhang, Lu
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab). Shanghai Jiao Tong Univ, Peoples R China.
    Hu, W.
    Experimental study of wideband in-band full-duplex communication based on optical self-interference cancellation2016In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 24, no 26, p. 30139-30148Article in journal (Refereed)
    Abstract [en]

    In this paper, we experimentally demonstrate and study a wideband in-band fullduplex (IBFD) wireless communication system based on optical self-interference cancellation (SIC). The optical SIC performances based on antennas for broadband IBFD are firstly evaluated within high frequency bands (&gt; 10GHz). In this system, two electro-absorptionmodulated lasers (EMLs) and a balanced photo-detector (BPD) are employed to remove the wideband self-interference within received wireless signal. By theoretical derivation and experimental verification, the impact factors of SIC are analyzed, especially for non-flatness wireless channel case. Experimental results show more than 30-dB cancellation depth in 100-MHz bandwidth with employment of horn antennas. Besides, IBFD transmission performance based on OFDM signals for different bandwidth with 11.15-GHz center frequency is also demonstrated, and ∼52.2-dB•Hz2/3 spurious-free dynamic range (SFDR) is obtained.

  • 124148.
    Zhang, Yafan
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. RISE Acreo AB.
    Multiphysics Characterization of SiC Power Modules2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis proposes several novel silicon carbide power module design concepts. The goal has been to address the problems with the present designs. The electrical, thermal, and thermomechanical performances of the demonstrators have been evaluated along with presentations of methodologies of experimental and numerical characterizations.

    Compact high-temperature power modules with adequate cooling systems are attractive to automotive applications. Therefore, a novel thermal design of a double-sided liquid/air cooled silicon carbide power module (1200 V, 200 A) has been proposed. The concept integrates a dc-link capacitor, a gate driver board, and finned cooling channels. The cooling concept has been evaluated for three application scenarios based on a validated computational fluid dynamics model. Moreover, a simulation methodology has been developed to quantify the effect of different materials and thicknesses of the cold plates on the temperature of the silicon carbide power dies.

    For medium- and high-power applications, contemporary research concludes that the reliability of the existing packaging technology needs to be improved. Therefore, this work proposes a novel press-pack silicon carbide power module concept. The concept enables bondless package and allows for an order of magnitude higher clamping force on the heatsinks than what can be applied on the dies. First, experimental and numerical methodologies for thermomechanical performance characterization of a press-pack structure have been investigated. By using digital image correlation technique, the deformation of each stacked material layer has been obtained. The developed experiment has led to an analytical estimation of friction coefficients on the contact interfaces. The co-influence of the design parameters on the thermomechanical performance of the press-pack structure has been analyzed through a parametric study based on a finite element model. Second, the novel double press-pack silicon carbide power module concept has been evaluated in a demonstrator in terms of parasitic inductance, thermal resistance, and thermomechanical stress.

    Furthermore, many of the power module designs only stay at the stage of proof-of-concept due to the cost of retooling of the manufacturing facility. Embedded power modules which employ advanced printed circuit board processing and die embedding technologies, enable a solution with possibility of low cost and mass production. Therefore, a novel design concept of a three-phase embedded power module (1200 V, 20 A) has been proposed. Simulation-driven design development has been implemented and lead to a fabricated demonstrator. The electromagnetic, thermal, and thermomechanical performances of the concept have been evaluated by simulations and compared to a commercially available power module.

  • 124149.
    Zhang, Yafan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion. Jönköping University, Sweden.
    Belov, Ilja
    Bakowski, Mietek
    Lim, Jang-Kwon
    Leisner, Peter
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Investigation of a Finned Baseplate Material and Thickness Variation for Thermal Performance of a SiC Power Module2014In: 2014 15th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, EuroSimE 2014, IEEE Computer Society, 2014, article id 6813817Conference paper (Refereed)
    Abstract [en]

    A simplified transient computational fluid dynamics model of an automotive three-phase double-side liquid cooled silicon carbide power inverter, including pin-fin baseplates, has been developed and qualified for parametric studies. Effective heat transfer coefficients have been extracted from the detailed pin-fin baseplate model for two coolant volume flow rates 2 l/min and 6 l/min, at the coolant temperature 105 degrees C. The inverter model includes temperature dependent heat losses of SiC transistors and diodes, calculated for two driving cycles. Baseplate materials such as copper, aluminum-silicon carbide metal matrix composite, aluminium alloy 6061 as well as virtual materials have been evaluated in the parametric studies. Thermal conductivity, specific heat and density have been varied as well as thickness of the finned baseplates (1 to 3 mm). A trade-off between temperature of SiC chips and baseplate weight has been investigated by means of Pareto optimization. The main results of the parametric studies include a weak dependence (1 to 3 degrees C) of the chip temperature on baseplate thickness. Furthermore, switching e.g. between copper and AlSiC results in 5 to 8 degrees C increase of the chip temperature, at 65 to 70 % baseplate weight reduction.

  • 124150.
    Zhang, Yafan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion. Acreo Swedish ICT AB.
    Belov, Ilja
    Jönköpng University.
    Sarius, Niklas G.
    Sp Technical Research Institute of Sweden.
    Bakowski, Mietek
    Acreo Swedish ICT AB.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Leisner, Peter
    Sp Technical Research Institute of Sweden.
    Thermal evaluation of a liquid/air cooled integrated power inverter for hybrid vehicle applications2013In: 2013 14th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, EuroSimE 2013, New York: IEEE , 2013, p. 6529944-Conference paper (Refereed)
    Abstract [en]

    A thermal design of an integrated double-side cooled SiC 50kW-1200V-200A power inverter for hybrid electric vehicle applications has been proposed to enable cooling in two different automotive operating environments: under-hood and controlled temperature environment of passenger compartment. The power inverter is integrated with air/liquid cooled cold plates equipped with finned channels. Concept evaluation and CFD model calibration have been performed on a simplified thermal prototype. Computational experiments on the detailed model of the inverter, including packaging materials, have been performed for automotive industry defined application scenarios, including two extreme and one typical driving cycles. For the studied application scenarios the case temperature of the SiC transistors and diodes have been found to be below 210°C. The maximum steady-state temperature of the DC-link capacitor has been below 127 °C for the worst-case scenario including liquid cooling, and up to 140 °C for the worst-case scenario with air-cooling.

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