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  • 1.
    A. M. Naiini, Maziar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Horizontal Slot Waveguides for Silicon Photonics Back-End Integration2014Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis presents the development of integrated silicon photonic devices. These devices are compatible with the present and near future CMOS technology. High-khorizontal grating couplers and waveguides are proposed. This work consists of simulations and device design, as well as the layout for the fabrication process, device fabrication, process development, characterization instrument development and electro-optical characterizations.

    The work demonstrates an alternative solution to costly silicon-on-insulator photonics. The proposed solution uses bulk silicon wafers and thin film deposited waveguides. Back-end deposited horizontal slot grating couplers and waveguides are realized by multi-layers of amorphous silicon and high-k materials.

    The achievements of this work include: A theoretical study of fully etched slot grating couplers with Al2O3, HfO2 and AIN, an optical study of the high-k films with spectroscopic ellipsometry, an experimental demonstration of fully etched SiO2 single slot grating couplers and double slot Al2O3 grating couplers, a practical demonstration of horizontal double slot high-k waveguides, partially etched Al2O3 single slot grating couplers, a study of a scheme for integration of the double slot Al2O3  waveguides with selectively grown germanium PIN photodetectors, realization of test chips for the integrated germanium photodetectors, and study of integration with graphene photodetectors through embedding the graphene into a high-k slot layer.

    From an application point of view, these high-k slot waveguides add more functionality to the current silicon photonics. The presented devices can be used for low cost photonics applications. Also alternative optical materials can be used in the context of this photonics platform.

    With the robust design, the grating couplers result in improved yield and a more cost effective solution is realized for integration of the waveguides with the germanium and graphene photodetectors.

     

     

     

     

    Fulltekst (pdf)
    Thesis
  • 2. Abasahl, B.
    et al.
    Zand, I.
    Lerma Arce, C.
    Kumar, S.
    Quack, N.
    Jezzini, M. A.
    Hwang, H. Y.
    Gylfason, Kristinn B.
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Porcel, M. A. G.
    Bogaerts, W.
    Towards Low-Power Reconfigurable Photonic ICs Based on MEMS Technology2018Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    With the progress and industrialization of photonic integrated circuits (PIC) in the past few decades, there is a strong urge towards design and prototyping in a fast, low-cost and reliable manner. In electronics, this demand is met through field programmable gate arrays (FPGA). In the Horizon 2020 MORPHIC (MEMS-based zerO-power Reconfigurable Photonic ICs) project, we are developing a reconfigurable PIC platform to address this demand in the field of photonics and to facilitate the path from idea towards realization for PIC designers and manufacturers.

  • 3.
    Abbas, Khizra
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Autonomous Gate Drivers Tailored for Triangular Current Mode-Based Zero-Voltage Switching Two-Level Three-Phase Inverters for Electric Vehicle Drive Systems2024Inngår i: Energies, E-ISSN 1996-1073, Vol. 17, nr 5, artikkel-id 1060Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The demand for highly efficient and dynamic electric vehicles (EVs) has increased dramatically. The traction inverter, a pivotal component in an EV powertrain, plays a crucial role. This study is dedicated to designing a traction inverter with focus on achieving high efficiency and elevated power density and mitigating electromagnetic interference (EMI) issues. To realize these objectives, autonomous gate drivers (AGDs) are proposed and designed using LTspice simulation software. The aim is to achieve zero voltage switching (ZVS) at both turn-on and turn-off through the utilization of triangular current mode (TCM) control on the gate driver. The AGDs implement a current modulation scheme by sensing the current and voltage and generating gate-source voltage signals with minimal delays. The implemented current modulation scheme by the AGDs results in an efficiency exceeding 99% for a 10 kW power rating. The sinusoidal output waveforms not only contribute to extending the motor lifespan by mitigating sharp-edge voltages but also bring advantages such as reduced switch stress, decreased EMI, and simplified thermal management.

  • 4.
    Abbas, Khizra
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Kostov, Konstantin
    RISE Research Institutes of Sweden, Department Smart Hardware, Stockholm, Sweden.
    Comprehensive Insight into the Operational Dynamics of TCM-Based Zero-Voltage Switching (ZVS) Two-Level Three-Phase Inverters for Electric Vehicle (EV) Motor-Drive Applications2024Inngår i: 2024 IEEE Texas Power and Energy Conference, TPEC 2024, Institute of Electrical and Electronics Engineers (IEEE) , 2024Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper introduces a novel triangular-current mode (TCM), zero-voltage switching (ZVS) two-level three-phase inverter, specifically designed to enhance the performance of the electric vehicle (EV) drive system. The primary objective is to enhance the inverter efficiency by minimizing turn-on and turn-off switching losses while mitigating electromagnetic interference (EMI) by generating sinusoidal output waveforms. The distinctive feature of this inverter lies in its gate driver, which executes the current modulation scheme. Achieving ZVS during turn-on involves the gate driver sensing the switch voltage and turning it on at zero voltage, utilizing TCM. For turn-off ZVS, the gate driver monitors the switch current, turning it off when it exceeds a predefined reference value. With a carefully placed snubber capacitor, turn-off ZVS is achieved. The implemented current modulation scheme yields an efficiency exceeding 99% for a 10 kW power rating. The sinusoidal output waveforms not only enhance motor lifespan by safeguarding against sharp-edge voltages but also offer benefits like reduced switch stress and simplified thermal management.

  • 5.
    ABBASI, MUHAMMAD MOHSIN
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Solving Sudoku by Sparse Signal Processing2015Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Sudoku is a discrete constraints satisfaction problem which is modeled as an underdetermined linear

    system. This report focuses on applying some new signal processing approaches to solve sudoku and

    comparisons to some of the existing approaches are implemented. As our goal is not meant for

    sudoku only in the long term, we applied approximate solvers using optimization theory methods. A

    Semi Definite Relaxation (SDR) convex optimization approach was developed for solving sudoku. The

    idea of Iterative Adaptive Algorithm for Amplitude and Phase Estimation (IAA-APES) from array

    processing is also being used for sudoku to utilize the sparsity of the sudoku solution as is the case in

    sensing applications. LIKES and SPICE were also tested on sudoku and their results are compared with

    l1-norm minimization, weighted l1-norm, and sinkhorn balancing. SPICE and l1-norm are equivalent

    in terms of accuracy, while SPICE is slower than l1-norm. LIKES and weighted l1-norm are equivalent

    and better than SPICE and l1-norm in accuracy. SDR proved to be best when the sudoku solutions are

    unique; however the computational complexity is worst for SDR. The accuracy for IAA-APES is

    somewhere between SPICE and LIKES and its computation speed is faster than both.

    Fulltekst (pdf)
    fulltext
  • 6. Abd Elghany, M. A.
    et al.
    El-Moursy, M. A.
    Korzec, D.
    Ismail, Mohammed
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar. Ohio State University, United States .
    High throughput architecture for OCTAGON network on chip2009Inngår i: 2009 16th IEEE International Conference on Electronics, Circuits and Systems, ICECS 2009, IEEE , 2009, s. 101-104Konferansepaper (Fagfellevurdert)
    Abstract [en]

    High Throughput Octagon architecture to achieve high performance Networks on Chip (NoC) is proposed. The architecture increase. The throughput oy the network by 17% while preservin. The average latency. The area of High Throughput OCTAGON switch is decreased by 18% as compared to OCTAGON switch. The total metal resources required to implement High Throughput OCTAGON design is increased by 8% as compared to the total metal resources required to implement OCTAGON design. The extra power consumption required to achiev. The proposed architecture is 2% oy the total power consumption oy the OCTAGON architecture.

  • 7.
    Abdalmoaty, Mohamed
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Learning Stochastic Nonlinear Dynamical Systems Using Non-stationary Linear Predictors2017Licentiatavhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    The estimation problem of stochastic nonlinear parametric models is recognized to be very challenging due to the intractability of the likelihood function. Recently, several methods have been developed to approximate the maximum likelihood estimator and the optimal mean-square error predictor using Monte Carlo methods. Albeit asymptotically optimal, these methods come with several computational challenges and fundamental limitations.

    The contributions of this thesis can be divided into two main parts. In the first part, approximate solutions to the maximum likelihood problem are explored. Both analytical and numerical approaches, based on the expectation-maximization algorithm and the quasi-Newton algorithm, are considered. While analytic approximations are difficult to analyze, asymptotic guarantees can be established for methods based on Monte Carlo approximations. Yet, Monte Carlo methods come with their own computational difficulties; sampling in high-dimensional spaces requires an efficient proposal distribution to reduce the number of required samples to a reasonable value.

    In the second part, relatively simple prediction error method estimators are proposed. They are based on non-stationary one-step ahead predictors which are linear in the observed outputs, but are nonlinear in the (assumed known) input. These predictors rely only on the first two moments of the model and the computation of the likelihood function is not required. Consequently, the resulting estimators are defined via analytically tractable objective functions in several relevant cases. It is shown that, under mild assumptions, the estimators are consistent and asymptotically normal. In cases where the first two moments are analytically intractable due to the complexity of the model, it is possible to resort to vanilla Monte Carlo approximations. Several numerical examples demonstrate a good performance of the suggested estimators in several cases that are usually considered challenging.

    Fulltekst (pdf)
    fulltext
  • 8. Abdelhakim, A.
    et al.
    Blaabjerg, F.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Single-Stage Boost Modular Multilevel Converter (BMMC) for Energy Storage Interface2020Inngår i: 2020 22nd European Conference on Power Electronics and Applications, EPE 2020 ECCE Europe, Institute of Electrical and Electronics Engineers (IEEE) , 2020, artikkel-id 9215788Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Single-stage DC-AC power converters are gaining higher attention due to their simpler structure compared to the two-stage equivalent solution. In this paper, a single-stage DC-AC converter solution is proposed for interfacing a low voltage (LV) DC source with a higher voltage AC load or grid, where this converter has a modular structure with multilevel operation. The proposed converter, which is called boost modular multilevel converter (BMMC), comprises the boosting capability within the inversion operation, and it is mainly dedicated for interfacing LV energy storage systems, such as fuel cells and batteries, and it allows the use of LV MOSFETs (« 300 V), in order to utilize their low ON-state resistance, along with LV electrolytic capacitors. This converter is introduced and analysed in this paper, where simulation results using PLECS, considering a 10 kW three-phase BMMC, are presented in order to verify its functionality.

  • 9.
    Abdi Kelishami, Alireza
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsnät.
    Secure Privacy-Friendly Instant Messaging (IM) for Guidepal2015Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    It is fascinating, and yet often neglected, that a user’s privacy can be invaded notonly by the absence of security measures and mechanisms, but also by improperor inadequate usage of security services and mechanisms. When designingsecure systems, we must consider what services are needed and what is not.The work in this thesis revolves around privacy-friendly instant messaging (IM)systems. In such a system, an inadequate usage of security measures leads tohaving IM servers being able to intercept or gather users’ private conversations.An improper usage of security measures could bring about non-repudiationwhich is desirable when signing contracts, but unwelcome in IM and privateconversations.We will look into requirements of the desired IM system, study the currentstate-of-the-art solutions, deploy an IM server, and briefly extend an existingmodern privacy-friendly IM protocol and an open source mobile application tomeet our security and privacy requirements. This extended IM application iscalled Guidepal-IM and is available as open source1The thesis work is introduced and carried out at Guidepal, a startup companyin Stockholm. It is therefore supervised partly at Guidepal and partly at KTH.Since Guidepal is also looking into possibilities of integrating an IM featureto its current social media apps, our contribution would also briefly extend tostudying the limitations and recommendations for Guidepal’s social media appto help user privacy preservation.

    Fulltekst (pdf)
    fulltext
  • 10.
    Abedi, Amin
    et al.
    UNIGE, Inst Environm Sci, Geneva, Switzerland.;UNIGE, Comp Sci Dept, Geneva, Switzerland..
    Hesamzadeh, Mohammad Reza
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Romerio, Franco
    UNIGE, Inst Environm Sci, Geneva, Switzerland.;UNIGE, Geneva Sch Econ & Management, Geneva, Switzerland..
    Adaptive robust vulnerability analysis of power systems under uncertainty: A multilevel OPF-based optimization approach2022Inngår i: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 134, artikkel-id 107432Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    With the growing level of uncertainties in today's power systems, the vulnerability analysis of a power system with uncertain parameters becomes a must. This paper proposes a two-stage adaptive robust optimization (ARO) model for the vulnerability analysis of power systems. The main goal is to immunize the solutions against all possible realizations of the modeled uncertainty. In doing so, the uncertainties are defined by some predetermined intervals defined around the expected values of uncertain parameters. In our model, there are a set of first-stage decisions made before the uncertainty is revealed (attacker decision) and a set of second-stage decisions made after the realization of uncertainties (defender decision). This setup is formulated as a mixedinteger trilevel nonlinear program (MITNLP). Then, we recast the proposed trilevel program to a single-level mixed-integer linear program (MILP), applying the strong duality theorem (SDT) and appropriate linearization approaches. The efficient off-the-shelf solvers can guarantee the global optimum of our final MILP model. We also prove a lemma which makes our model much easier to solve. The results carried out on the IEEE RTS and modified Iran's power system show the performance of our model to assess the power system vulnerability under uncertainty.

  • 11.
    Abedi, Amin
    et al.
    Institute for Environmental Sciences, University of Geneva, Switzerland.
    Hesamzadeh, Mohammad Reza
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Romerio, Franco
    Institute for Environmental Sciences, University of Geneva, Switzerland.
    An ACOPF-based bilevel optimization approach for vulnerability assessment of a power system2021Inngår i: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 125, artikkel-id 106455Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper examines the effects of reactive power dispatch, losses, and voltage profile on the results of the interdiction model to analyze the vulnerability of the power system. First, an attacker-defender Stackelberg game is introduced. The introduced game is modeled as a bilevel optimization problem where the attacker is modeled in the upper level and the defender is modeled in the lower level. The AC optimal power flow (ACOPF) is proposed as the defender's tool in the lower-level problem to mitigate the attack consequences. Our proposed ACOPF-based mathematical framework is inherently a mixed-integer bilevel nonlinear program (MIBNLP) that is NP-hard and computationally challenging. This paper linearizes and then transforms it into a one-level mixed-integer linear program (MILP) using the duality theory and some proposed linearization techniques. The proposed MILP model can be solved to the global optimum using state-of-the-art solvers such as Cplex. Numerical results on two IEEE systems and Iran's 400-kV transmission network demonstrate the performance of the proposed MILP for vulnerability assessment. We have also compared our MILP model with the DCOPF-based approach proposed in the relevant literature. The comparative results show that the reported damage measured in terms of load shedding for the DCOPF-based approach is always lower than or equal to that for the ACOPF-based approach and these models report a different set of critical lines, especially in more stressed and larger power systems. Also, the effectiveness and feasibility of the proposed MILP model for power-system vulnerability analysis are discussed and highlighted. 

  • 12.
    Abedin, Ahmad
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektronik och inbyggda system.
    Germanium layer transfer and device fabrication for monolithic 3D integration2021Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Monolithic three-dimensional (M3D) integration, it has been proposed,can overcome the limitations of further circuits’ performance improvementand functionality expansion. The emergence of the internet of things (IoT) isdriving the semiconductor industry toward the fabrication of higher-performancecircuits with diverse functionality. On the one hand, the scaling of devices isreaching critical dimensions, which makes their further downscaling techno-logically difficult and economically challenging, whereas, on the other hand,the field of electronics is no longer limited only to developing circuits thatare meant for data processing. Sensors, processors, actuators, memories, andeven power storage units need to be efficiently integrated into a single chip tomake IoT work. M3D integration through stacking different layers of deviceson each other can potentially improve circuits’ performance by shorteningthe wiring length and reducing the interconnect delay. Using multiple tiersfor device fabrication makes it possible to integrate different materials withsuperior physical properties. It offers the advantage of fabricating higher-performance devices with multiple functionalities on a single chip. However,high-quality layer transfer and processing temperature budget are the majorchallenges in M3D integration. This thesis involves an in-depth explorationof the application of germanium (Ge) in monolithic 3D integration.Ge has been recognized as one of the most promising materials that canreplace silicon (Si) as the channel material for p-type field-effect transistors(pFETs) because of its high hole mobility. Ge pFETs can be fabricated atsubstantially lower temperatures compared to Si devices which makes theformer a good candidate for M3D integration. However, the fabrication ofhigh-quality Ge-on-insulator (GOI) layers with superior thickness homogene-ity, low residual doping, and a sufficiently good interface with buried oxide(BOX) has been challenging.This thesis used low-temperature wafer bonding and etch-back techniquesto fabricate the GOI substrate for M3D applications. For this purpose, aunique stack of epitaxial layers was designed and fabricated. The layer stackcontains a Ge strain relaxed buffer (SRB) layer, a SiGe layer to be used asan etch stop, and a top Ge layer to be transferred to the handling wafer.The wafers were bonded at room temperature, and the sacrificial wafer wasremoved through multiple etching steps leaving 20 nm Ge on the insulatorwith excellent thickness homogeneity over the wafer. Ge pFET devices werefabricated on the GOI substrates and electrically characterized to evaluatethe layer quality. Finally, the epitaxial growth of the highly doped SiGeand sub-nm Si cap layers have been investigated as alternatives for improvedperformance Ge pFETs.The Ge buffer layer was developed through the two-step deposition tech-nique resulting in defect density of107cm−3and surface roughness of 0.5 nm.The fully strainedSi0.5Ge0.5film with high crystal quality was epitaxiallygrown at temperatures below 450°C. The layer was sandwiched between theGe buffer and the top 20 nm Ge layer to be used as an etch-stop in the etch- back process. A highly selective etching method was developed to remove the3μm Ge buffer and 10nm SiGe film without damaging the 20 nm transferringGe layer.The Ge pFETs were fabricated at temperatures below 600°C so that theycould be compatible with the M3D integration. The back interface of thedevices depleted atVBG= 0V, which confirmed the small density of fixedcharges at the Ge/BOX interface along with a low level of residual doping inthe Ge channel. The Ge pFETs with 70 % yield over the whole wafer showed60 % higher carrier mobility than Si reference devices.Low-temperature epitaxial growth of Si passivation layer on Ge was de-veloped in this thesis. For electrical evaluation of the passivation layer,metal-oxide-semiconductor (MOS) capacitors were fabricated and character-ized. The capacitors showed an interface trap density of3×1011eV−1cm−2,and hysteresis as low as 3 mV at Eox of 4MV/cm corresponding to oxide trapdensity of1.5×1010cm−2. The results indicate that this Si passivation layersubstantially improves the gate dielectric by reducing the subthreshold slopeof Ge devices while increasing their reliability. The in-situ doped SiGe layerwith a dopant concentration of2.5×1019cm−3and resistivity of 3.5 mΩcmwas selectively grown on Ge to improve the junction formation.The methods developed in this thesis are suitable for large-scale M3Dintegration of Ge pFET devices on the Si platform. The unique Ge layertransfer and etch-back techniques resulted in the fabrication of GOI substrateswith high thickness homogeneity, low residual doping, and sufficiently goodGe/BOX interface. The process temperatures for Ge transfer and pFETsfabrication are kept within the range of the M3D budget. Integration of theSi cap for gate dielectric formation and SiGe layers in the source/drain regionmay increase device performance and reliability

    Fulltekst (pdf)
    fulltext
  • 13.
    Abedin, Ahmad
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektronik och inbyggda system, Integrerade komponenter och kretsar.
    Zurauskaite, Laura
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektronik och inbyggda system, Integrerade komponenter och kretsar.
    Asadollahi, Ali
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektronik och inbyggda system, Integrerade komponenter och kretsar. KTH.
    GOI fabrication for Monolithic 3D integrationInngår i: Artikkel i tidsskrift (Annet vitenskapelig)
  • 14.
    Abeywickrama, K. G. Nilanga B.
    et al.
    Chalmers, Div High Voltage Engn, Dept Mfg & Mat Technol, SE-41296 Gothenburg, Sweden..
    Daszczynski, Tadeusz
    Warsaw Univ Technol, PL-00611 Warsaw, Poland..
    Serdyuk, Yuriy V.
    Chalmers, Div High Voltage Engn, Dept Mfg & Mat Technol, SE-41296 Gothenburg, Sweden.;Natl Acad Sci Ukraine, Inst Electrodynam, Kiev, Ukraine.;ABB High Voltage Technol Ltd, R&D HV Lab, Zurich, Switzerland..
    Gubanski, Stanislaw M.
    KTH.
    Determination of complex permeability of silicon steel for use in high-frequency modeling of power transformers2008Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 44, nr 4, s. 438-444Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Information about frequency dependence of complex permeability of silicon steel is a vital input parameter in calculations of transformer winding inductance used for modeling. high-frequency behavior (100 Hz-1 MHz). We present two ways of determining small signal complex permeability spectra in frequency domain and compare and discuss the results. The first method is based on an optimization procedure, in which inductance of a winding is measured and calculated by analytical formulas and finite-element modeling. The second method makes use of a single sheet tester. We show that the magnitude of effective permeability of the silicon steel laminations remains significant up to about 100 kHz. We also report on the effect of magnetic viscosity on complex permeability.

  • 15.
    Abrahamson, Lars
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Fast calculation of the dimensioning factors of the railway power supply system2007Inngår i: Computational Methods and Experimental Measurements XIII, WIT Press, 2007, Vol. 46, s. 85-95Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Because of environmental and economical reasons, in Sweden and the rest of Europe, both personal and goods transports on railway are increasing. Therefore great railway infrastructure investments are expected to come. An important part of this infrastructure is the railway power supply system. Exactly how much, when and where the traffic will increase is not known for sure. This means investment planning for an uncertain future. The more uncertain parameters, such as traffic density and weight of trains, and the further future considered, the greater the inevitable amount of cases that have to be considered. When doing simulations concerning a tremendous amount of cases, each part of the simulation model has to be computationally fast - in real life this means approximations. The two most important issues to estimate given a certain power system configuration, when planning for an electric traction system, are the energy consumption of the and and the train delays that a too weak system would cause. In this paper, some modeling suggestions of the energy consumption and the maximal train velocities are presented. Two linear, and one nonlinear model are presented and compared. The comparisons regard both computer speed and representability. The independent variables of these models are a selection of parameters describing the power system, i.e.: power system technology used on each section, and traffic intensity.

    Fulltekst (pdf)
    fulltext
  • 16.
    Abrahamsson, Lars
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Optimal Railroad Power Supply System Operation and Design: Detailed system studies, and aggregated investment models2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Railway power supply systems (RPSSs) differ mainly from public power systems from that the loads are moving. These moving loads are motoring trains. Trains can also be regenerating when braking and are then power sources. These loads consume comparatively much power, causing substantial voltage drops, not rarely so big that the loads are reduced. By practical reasons most RPSSs are single-phase AC or DC. Three-phase public grid power is either converted into single-phase for feeding the railway or the RPSS is compartmentalized into separate sections fed individually from alternating phase-pairs of the public grid. The latter is done in order not to overload any public grid phase unnecessarily much.

    This thesis summarizes various ways of optimally operating or designing the railway power supply system. The thesis focuses on converter-fed railways for the reasons that they are more controllable, and also has a higher potential for the future. This is also motivated in a literature-reviewing based paper arguing for the converter usage potential. Moreover, converters of some kind have to be used when the RPSS uses DC or different AC frequency than the public grid.

    The optimal operation part of this thesis is mainly about the optimal power flow controls and unit commitments of railway converter stations in HVDC-fed RPSSs. The models are easily generalized to different feeding, and they cope with regenerative braking. This part considers MINLP (mixed integer nonlinear programming) problems, and the main part of the problem is non-convex nonlinear. The concept is presented in one paper. The subject of how to model the problem formulations have been treated fully in one paper.

    The thesis also includes a conference article and a manuscript for an idea including the entire electric train driving strategy in an optimization problem considering power system and mechanical couplings over time. The latter concept is a generalized TPSS (Train Power Systems Simulator), aiming for more detailed studies, whereas TPSS is mainly for dimensioning studies. The above optimal power flow models may be implemented in the entire electric train driving strategy model.

    The optimal design part of this thesis includes two aggregation models for describing reduction in train traffic performance. The first one presented in a journal, and the second one, adapted more useful with different simulation results was presented at a conference. It also includes an early model for optimal railway power converter placements.

    The conclusions to be made are that the potential for energy savings by better operation of the railway power system is great. Another conclusion is that investment planning models for railway power systems have a high development potential. RPSS planning models are computationally more attractive, when aggregating power system and train traffic details.

    Fulltekst (pdf)
    fulltext
  • 17.
    Abrahamsson, Lars
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Railway Power Supply Models and Methods for Long-term Investment Analysis2008Licentiatavhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    The aim of the project is to suggest an investment planning programwhere the welfare of the society is to be maximized. In order to beable to decide on a wise investment plan, one needs to know theconsequences of different choices of power system configurations.Therefore the impacts of different future traffic demands are ofinterest for a railway power system owner.Since investments are supposed to last a long time, their futureusage has to be considered. Moreover, the lead times of investmentscan be of considerable duration lengths. Because of the uncertaintyof the future, deterministic case studies might not be suitable andthen a large number of outcomes are to be studied, probable outcomesas well as outcomes with a high level of impact.In order to be able to make a valid long-term investment analysis ofthe railway power supply system, one needs to use proper railwaypower supply models and methods. The aim of this thesis is topresent a stable modeling and methodological basis for the cominginvestment planning phase of this PhD research project. The focus isset on studying the consequences of a railway power supply systemwhich is too weak.The thesis contains an overview of models of some electrical andmechanical relations important for electric traction systems. Someof these models are further developed, and some are modified forimproved computational properties. A flexible electric tractionsystem simulator based on the above mentioned models has beendeveloped and the applied methods and resulting abilities arepresented.The main scientific contribution of this thesis is that a fast andapproximative neural network model, which calculates some importantaggregated results of the interaction between the railway powersystem and the train traffic, has been developed. This approximativemodel was developed in order to reduce computation times. Reductionof computation times is very important when a huge number ofoutcomes are studied. A complete simulation of a train power systemin operation takes a long time, often not less than about a tenth ofthe simulated traffic time. The neural network is trained with someselected aggregated results extracted from a wide set of railwayoperation simulation cases. The choices of network inputs andoutputs are motivated in the thesis. The performance of thesimulator as well as the approximator are visualized in casestudies.

    Fulltekst (pdf)
    FULLTEXT02
  • 18.
    Abrahamsson, Lars
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Kjellqvist, Tommy
    Elekt Konsult AB, Kraftelektronik, Sweden.
    Östlund, Stefan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    High-voltage DC-feeder solution for electric railways2012Inngår i: IET Power Electronics, ISSN 1755-4535, E-ISSN 1755-4543, Vol. 5, nr 9, s. 1776-1784Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    For AC railway power supply systems with a different frequency than the public grid, high-voltage AC transmission lines are common, connected to the catenary by transformers. This study suggests an alternative design based on an high-voltage DC (HVDC)-feeder, which is connected to the catenary by converters. Such an HVDC line would also be appropriate for DC-fed railways and AC-fed railways working at a public-grid frequency. The converter stations between the public grid and the HVDCfeeder can be sparsely distributed, not denser than on 100 km distances, whereas the converters connecting the HVDC-feeder to the catenary are distributed denser. Their ratings can be lower than present-day substation transformers or converters, since the power flows can be fully controlled. Despite a relatively low-power rating, the proposed converters can be highly efficient because of the use of medium frequency technology. The proposed feeding system results in lower material usage, lower losses and higher controllability compared with the present solutions. Simulations of the proposed solution show clear advantages regarding transmission losses and voltages compared with conventional systems, especially for cases with weak feeding, and when there are substantial amounts of regeneration from the trains.

    Fulltekst (pdf)
    fulltext
  • 19.
    Abrahamsson, Lars
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Kjellqvist, Tommy
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Östlund, Stefan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    HVDC Feeder Solution for Electric Railways2012Inngår i: IET Power Electronics, ISSN 1755-4535, E-ISSN 1755-4543Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The railway power supply systems in many sparsely populated countries are relatively weak. Weak railway power supply systems causes problems with power quality, voltage drops, and high transmission losses.

    For AC railway power supply systems with a different frequency than the public grid, high-voltage AC (HVAC) transmission lines are common, connected to the catenary by transformers.

    In this paper an alternative design based on an HVDC feeder is suggested. The HVDC feeder is connected to the catenary by converters. Such an HVDC line would also be appropriate for DC-fed railways and AC-fed railways working at public frequency. The converter stations between the public grid and the HVDC feeder can be sparsely distributed, in the range of 100 km or more, whereas the converters connecting the HVDC feeder to the catenary are distributed with a much closer spacing. Their ratings can be lower than substation transformers or electro-mechanical converters, since the power flow can be fully controlled.

    Despite a relatively low power rating, the proposed converters can be highly efficient due to the use of medium frequency technology. The HVDC-based feeding system results in lower material usage, lower losses and higher controllability compared to present solutions.

    Simulations of the proposed solution show clear advantages regarding transmission losses and voltages compared to conventional systems, especially for cases with long distances between feeding points to the catenary, and when there are substantial amounts of regeneration from the trains.

    Fulltekst (pdf)
    fulltext
  • 20.
    Abrahamsson, Lars
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Schütte, Thorsten
    Östlund, Stefan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Use of converters for feeding of AC railways for all frequencies2012Inngår i: Energy for Sustainable Development, ISSN 0973-0826, E-ISSN 2352-4669, Vol. 16, nr 3, s. 368-378Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Railways are the most energy-efficient land-based mode of transport, and electrification is the most energy-efficient way to power the trains. There are many existing solutions to supply the trains with electricity. Regardless of which particular technology is chosen, it is beneficial to interconnect the public power grids to grids supplying power to the railways. This paper shows that the most efficient, flexible, and gentle-for-the-public-grid way of doing that is through power electronic-based power converters. Converters offer great benefits regardless of whether the overhead contact lines are of DC-type or AC type, and regardless of the AC grid frequency. This paper presents neither new theory nor new experimental results. Based on already available information, this paper presents logical arguments leading to this conclusion from collected facts. Over time what used to be advanced and high-cost equipment earlier can nowadays be purchased at reasonable cost. It is obvious that for most electrically-fed railways, the use of modern power converters is attractive. Where the individual trains are high consumers of energy, the railway gradients are substantial, and the public grids feeding the railway are weak, the use of converters would be technically desirable, if not necessary for electrification.It is expected that more high-speed railways will be built, and more existing railways will be electrified in the foreseeable future. This paper could provide some insights to infrastructure owners and decision makers in railway administrations about value additions that converter-fed electric railways would provide.

    Fulltekst (pdf)
    fulltext
  • 21.
    Abrahamsson, Lars
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    An SOS2-based moving trains,fixed nodes, railway power system simulator2012Inngår i: WIT Transactions on the Built Environment, WIT Press, 2012, s. 813-823Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents and proposes an optimization model for railway power supply system simulations. It includes detailed power systems modeling train movements in discretized time considering running resistance and other mechanical constraints, and the voltage-drop-induced reduction of possible train tractive forces. The model has a xed number of stationary power system nodes. The proposed model uses SOS2 (special ordered sets of type 2) variables to distribute the train loads to the two most adjacent power system nodes available. The impact of the number of power system nodes along the contact line and the discretized time step length impacts on model accuracy and computation times are investigated. The program is implemented in GAMS (General Algebraic Modeling System). Experiences from various solver choices are also presented. The train traveling times are minimized in the example. Other studies could, e.g. consider energy consumption minimization. The numerical example is representative for a Swedish non-centralized, rotary-converter fed railway power supply system. The proposed concept is however generalizable and could be applied for all kinds of moving load power system studies.

    Fulltekst (pdf)
    fulltext
  • 22.
    Abrahamsson, Lars
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Basic modeling for electric traction systems under uncertainty2006Inngår i: PROCEEDINGS OF THE 41ST INTERNATIONAL UNIVERSITIES POWER ENGINEERING CONFERENCE, VOLS 1 AND 2, NEW YORK: IEEE , 2006, s. 252-256Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The objective of this paper is initially to present a basic modeling of the railway traction system. This model includes the basic technologies used today. The voltage dependencies of the maximal possible power consumption as well as the maximal velocity of the common Re-locomotives are included. The latter is very crucial for the studies of time table sensitivity, which is of our immediate interest. Moreover, a method is presented, that estimates the expected train delay time for a given feeding technology. The reference timetable assumes the same train and surrounding conditions, but no voltage drops. In the numerical example where the developed model is applied to a realistic test system, a set of possible amounts of railway traffic are treated as uncertainties. Mainly, the contributions of this paper are three: compiling and connecting already accepted models, the development of a method for numerical calculations using this model compilation, and an example to apply this model on.

    Fulltekst (pdf)
    fulltext
  • 23.
    Abrahamsson, Lars
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Fast calculation of some important dimensioning factors of the railway power supply system2007Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Because of environmental and economical reasons, in Sweden and the rest of Europe, both personal and goods transports on railway are increasing. Therefore great railway infrastructure investments are expected to come. An important part of this infrastructure is the railway power supply system. Exactly how much, when and where the traffic will increase is not known for sure. This means investment planning for an uncertain future. The more uncertain parameters, such as traffic density and weight of trains, and the further future considered, the greater the inevitable amount of cases that have to be considered. When doing simulations concerning a tremendous amount of cases, each part of the simulation model has to be computationally fast – in real life this means approximations. The two most important issues to estimate given a certain power system configuration, when planning for an electric traction system, are the energy consumption of the grid and the train delays that a too weak system would cause. In this paper, some modeling suggestions of the energy consumption and the maximal train velocities are presented. Two linear models, and one nonlinear model are presented and compared. The comparisons regard both computer speed and representability. The independent variables of these models are a selection of parameters describing the power system, i.e.: power system technology used on each section, and traffic intensity.

    Fulltekst (pdf)
    fulltext
  • 24.
    Abrahamsson, Lars
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Fast Estimation of Relations Between Aggregated Train Power System Data and Traffic Performance2011Inngår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 60, nr 1, s. 16-29Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Transports via rail are increasing, and major railway infrastructure investments are expected. An important part of this infrastructure is the railway power supply system (RPSS). Future railway power demands are not known. The more distant the uncertain future, the greater the number of scenarios that have to be considered. Large numbers of scenarios make time-demanding (some minutes, each) full simulations of electric railway power systems less attractive and simplifications more so. The aim, and main contribution, of this paper is to propose a fast approximator that uses aggregated traction system information as inputs and outputs. This approximator can be used as an investment planning constraint in the optimization. It considers that there is a limit on the intensity of the train traffic, depending on the strength of the power system. This approximator approach has not previously been encountered in the literature. In the numerical example of this paper, the approximator inputs are the power system configuration; the distance between a connection from contact line to the public grid, to another connection, or to the end of the contact line; the average values and the standard deviations of the inclinations of the railway; the average number of trains; and their average velocity for that distance. The output is the maximal attainable average velocity of an added train for the described railway power system section. The approximator facilitates studies of many future railway power system loading scenarios, combined with different power system configurations, for investment planning analysis. The approximator is based on neural networks. An additional value of the approximator is that it provides an understanding of the relations between power system configuration and train traffic performance.

    Fulltekst (pdf)
    fulltext
  • 25.
    Abrahamsson, Lars
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Fast estimation of the relation between aggregated train power system information and the power and energy converted2008Inngår i: 2008 Australasian Universities Power Engineering Conference, AUPEC 2008, IEEE conference proceedings, 2008, s. 1-6Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Transports on rail are increasing and major investments in the railway infrastructure, including the Railway Power Supply System (RPSS), are expected. The future railway power demands are naturally not known for certain. The more remote the uncertain future, the greater the number of scenarios that have to be considered. Large numbers of scenarios make time demanding simulations unattractive. The aim of this paper is to present a fast approximator that uses aggregated RPSS information. Since the electrical and mechanical relations governing an RPSS are quite intricate, an approximator based on Neural Networks (NN), is applied. This paper presents a design suggestion for an NN estimating the power and energy flows through each converter station, given RPSS data and levels of train traffic. Even if the future usage of the NN is investment planning, the modeling of such an approximator has a value in itself concerning the understanding of the relations between RPSS and train traffic.

    Fulltekst (pdf)
    fulltext
  • 26.
    Abrahamsson, Lars
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Fast estimation of the relation between aggregated train power system information and the power and energy converted2009Inngår i: Australian Journal of Electrical and Electronic Engineering, ISSN 1448-837X, Vol. 6, nr 3, s. 311-318Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Transports on rail are increasing and major investments in the railway infrastructure, including the railway power supply system (RPSS), are expected. The future railway power demands are naturally not known for certain. The more remote the uncertain future, the greater the number of scenarios that have to be considered. Large numbers of scenarios make time-demanding simulations unattractive. The aim of this paper is to present a fast approximator that uses aggregated RPSS information. Since the electrical and mechanical relations governing an RPSS are quite intricate, an approximator based on neural networks (NN) is applied. This paper presents a design suggestion for an NN estimating the power and energy flows through each converter station, given RPSS data and levels of train traffic. Even if the future usage of the NN is investment planning, the modelling of such an approximator has a value in itself concerning the understanding of the relations between RPSS and train traffic.

    Fulltekst (pdf)
    fulltext
  • 27.
    Abrahamsson, Lars
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Operation simulation of traction systems2008Inngår i: COMPUTERS IN RAILWAYS XI, 2008, Vol. 103, s. 283-292Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The objective of this paper is initially to present a basic modeling of the railway traction system. This model includes the basic technologies used today. The voltage dependencies of the maximal possible power consumption as well as the maximal velocity of the common Rc-locomotives are included. The latter is very crucial for the studies of time table sensitivity, which is of our immediate interest. Moreover, a method is presented that estimates the expected train delay time for a given feeding technology. The reference timetable assumes the same train and surrounding conditions, but no voltage drops. In the numerical example where the developed model is applied to a realistic test system, a set of possible amounts of railway traffic are treated as uncertainties. Mainly, the contributions of this paper are three: compiling and connecting already accepted models, the development of a method for numerical calculations using this model compilation, and an example to apply this model on.

    Fulltekst (pdf)
    fulltext
  • 28.
    Abrahamsson, Lars
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Railway power supply investment decisions considering the voltage drops: Assuming the future traffic to be known2009Inngår i: 2009 15th International Conference on Intelligent System Applications to Power Systems, ISAP '09, 2009Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Transports on rail are increasing and major railway infrastructure investments are expected. An important part of this infrastructure is the railway power supply system. The future railway power demands are naturally not known for certain. The more distant the uncertain future is, the greater the number of scenarios that have to be considered. Large numbers of scenarios make time demanding simulations unattractive. Therefore a fast approximator that uses aggregated railway power supply system information has been developed. In particular the approximator studies the impacts of voltage drops on the traffic flow. The weaker the power system and the heavier the traffic, the greater the voltage drops. And the greater the voltage drops, the more limited the maximal attainable tractive force on the locomotives. That approximator is in this paper used as a constraint in the embryo of a railway power supply system investment planning program, where investment decisions are assumed to be realized immediately, and there is no preexisting power supply system to consider. The traffic forecasts are in this first approach assumed to be perfect. This stepwise creation of the planning program makes evaluating it easier. The basic investment planning model presented here constitutes the foundation for further improvements.

  • 29.
    Abrahamsson, Lars
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Traction Power System Capacity Limitations at Various Traffic Levels2011Inngår i: WCRR, World Congress on Railway Research, 2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The aim, and main contribution, of this paper is to propose a fine-tuned fast approximator, based on neural networks, that uses aggregated traction system information as inputs and outputs. This approximator can be used as an investment planning constraint in the optimization. It considers that there is a limit on the intensity of the train traffic, depending on the strength of the power system. In the numerical examples of this paper, the approximator inputs are the power system configuration, the distance between a connection from contact line to the public grid to another connection, and the average number of trains for that distance. The output is the maximal attainable average velocity of trains of a specific kind for the by the inputs described railway power system section. An alternative output – the traveling time is also presented. The main emphasis of this paper is on the example section, since the contribution of this paper is mainly to show on the improved simplicity and reality compliance. The applicative contribution is twofold, an improved TPSA as a planning/decision making program constraint, whereas it also can be used as a scientifically developed rule of thumb for a planner active in the field. The aim is not primarily to show that the idea works, or to motivate the principal idea, since that is done earlier. The approximator facilitates studies of many railway power system loading scenarios, combined with different power system configurations, for investment planning analysis. The approximator is based on neural networks. An additional value of the approximator is that it provides an understanding of the relations between power system configuration and train traffic performance.

    Fulltekst (pdf)
    fulltext
  • 30.
    Abrahamsson, Lars
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Östlund, Stefan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Schütte, Thorsten
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    An electromechanical moving load fixed node position and fixed node number railway power supply systems optimization model2013Inngår i: Transportation Research Part C: Emerging Technologies, ISSN 0968-090X, E-ISSN 1879-2359, Vol. 30, s. 23-40Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents an optimization model for simulations of railway power supply systems. It includes detailed power systems modeling, train movements in discretized time considering running resistance and other mechanical constraints, and the voltage-drop-induced reduction of possible train tractive forces. The model has a fixed number of stationary power system nodes, which alleviates optimized operation overtime. The proposed model uses SOS2 (Special Ordered Sets of type 2) variables to distribute the train loads to the two most adjacent power system nodes available. The impacts of the number of power system nodes along the contact line and the discretized time step length on model accuracy and computation times are investigated. The program is implemented in GAMS. Experiences from various solver choices are also discussed. The train traveling times are minimized in the example. Other studies could e.g. consider energy consumption minimization. The numerical example is representative for a Swedish decentralized, rotary-converter fed railway power supply system. The proposed concept is however generalizable and could be applied for all kinds of moving load power system studies.

    Fulltekst (pdf)
    fulltext
  • 31.
    Abrahamsson, Lars
    et al.
    KTH, Tidigare Institutioner (före 2005), Elkraftteknik.
    Östlund, Stefan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Optimal PowerFlow (OPF) Model with Unified AC-DC Load Flow and Optimal Commitmentfor an AC-catenary Railway Power Supply System (RPSS) fed by aHigh Voltage DC (HVDC) transmission lineManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    In this paper an alternative railway power systems design based on an HVDC feeder is studied. The HVDC feeder is connected to the catenary by converters. Such an HVDC line is also appropriate for DC-fed railways and AC-fed railways working at public frequency.

    A unit commitment optimal power flow model has been developed and is applied on a test system. In this paper, the model is presented in detail. The model, in the form of an MINLP program, uses unified AC-DC power flow to minimize the entire railway power system losses.

    Simulations of the proposed solution show clear advantages regarding transmission losses and voltages compared to conventional systems, especially for cases with long distances between feeding points to the catenary, and when there are substantial amounts of regeneration from the trains.

  • 32.
    Abrahamsson, Lars
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Östlund, Stefan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Optimal PowerFlow (OPF) Model with Unified AC-DC Load Flow and Optimal Commitmentfor an AC-catenary Railway Power Supply System (RPSS) fed by aHigh Voltage DC (HVDC) transmission line2012Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper an alternative railway power systems design based on an HVDC feeder is studied. The HVDC feeder is connected to the catenary by converters. Such an HVDC line is also appropriate for DC-fed railways and AC-fed railways working at public frequency. A unit commitment optimal power flow model has been developed and is applied on a test system. In this paper, the model is presented in detail. The model, in the form of an MINLP program, uses unified AC-DC power flow to minimize the entire railway power system losses. Simulations of the proposed solution show clear advantages regarding transmission losses and voltages compared to conventional systems, especially for cases with long distances between feeding points to the catenary, and when there are substantial amounts of regeneration from the trains.

    Fulltekst (pdf)
    fulltext
  • 33. Accoto, Nadia
    et al.
    Rydén, Tobias
    Lund University.
    Secchi, Paolo
    Bayesian Hidden Markov Models for Performance-Based Regulation of Continuity of Electricity Supply2010Inngår i: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 25, nr 3, s. 1236-1249Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A fundamental aspect in the regulation of the continuity of electricity supply is the identification of faults that could be caused by an exceptional event and, therefore, that are outside the utility control and responsibility. Different methods have been proposed during the years: the interpretation of the observed faults as a signal of an underlying system naturally leads to the analysis of the problem by means of a hidden Markov model. Thesemodels, in fact, are widely used for introducing dependence in data and/or for modeling observed phenomena depending on hidden processes. The application of this method shows that the model is able to identify exceptional events; moreover, the study of the estimated model parameters gives rise to reality-linked considerations.

  • 34.
    Ackermann, Thomas
    KTH. Energynautics GmbH, Germany; Technical University in Darmstadt (TUD), Germany..
    Introduction2012Inngår i: Wind Power in Power Systems, Second Edition, Wiley , 2012, s. 1-5Kapittel i bok, del av antologi (Fagfellevurdert)
  • 35.
    Ackermann, Thomas
    KTH. Energynautics GmbH, Langen, Germany.
    Stability augmentation of a grid-connected wind farm2009Annet (Fagfellevurdert)
  • 36.
    Ackermann, Thomas
    et al.
    KTH, Tidigare Institutioner (före 2005).
    Andersson, G.
    Söder, Lennart
    KTH, Tidigare Institutioner (före 2005).
    Distributed generation: a definition2001Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 57, nr 3, s. 195-204Artikkel i tidsskrift (Fagfellevurdert)
  • 37.
    Ackermann, Thomas
    et al.
    KTH, Tidigare Institutioner (före 2005).
    Andersson, G.
    Söder, Lennart
    KTH, Tidigare Institutioner (före 2005).
    Overview of government and market driven programs for the promotion of renewable power generation2001Inngår i: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 22, nr 1-3, s. 197-204Artikkel i tidsskrift (Fagfellevurdert)
  • 38.
    Ackermann, Thomas
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Andersson, Göran
    Söder, Lennart
    KTH, Tidigare Institutioner (före 2005).
    Electricity market regulations and their impact on distributed generation2000Inngår i: Electric Utility Deregulation and Restructuring and Power Technologies, 2000. Proceedings. DRPT 2000. International Conference on, 2000, s. 608-613Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Distributed generation (DG) has attracted a lot of attention recently and might become more important in future power generation systems. As different definitions are used worldwide, the paper briefly discusses the definition of DG. The future development of DG, however, will, to a not insignificant part, depend on the legal framework. As the legal framework can vary significantly for different competitive electricity markets, this paper briefly identifies and analyses some variations in the regulatory approaches, e.g. for power exchanges, balance services and ancillary services, in different countries. It also illustrates the influence of market regulations on the development of distributed power generation. Based on this analysis, it can be concluded that regulatory aspects might decisively influence the development of distributed power generation

  • 39.
    Ackermann, Thomas
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Centeno-Lopez, Eva
    Söder, Lennart
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Grid Issues for Electricity Production Based on Renewable Energy Sources in Spain, Portugal, Germany, and United Kingdom2008Bok (Annet vitenskapelig)
    Fulltekst (pdf)
    fulltext
  • 40.
    Ackermann, Thomas
    et al.
    KTH, Tidigare Institutioner (före 2005).
    Söder, Lennart
    KTH, Tidigare Institutioner (före 2005).
    An overview of wind energy-status 20022002Inngår i: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 6, nr 1-2, s. 67-128Artikkel, forskningsoversikt (Fagfellevurdert)
  • 41.
    Ackermann, Thomas
    et al.
    KTH, Tidigare Institutioner (före 2005).
    Söder, Lennart
    KTH, Tidigare Institutioner (före 2005).
    Wind energy technology and current status: a review2000Inngår i: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 4, nr 4, s. 315-374Artikkel, forskningsoversikt (Fagfellevurdert)
  • 42.
    Acosta, Martha N.
    et al.
    School of Mechanical and Electrical Engineering, Universidad Autónoma de Nuevo León, San Nicolás de los Garza 66455, NL, Mexico.
    Gonzalez-Longatt, Francisco
    Department of Electrical Engineering, Information Technology and Cybernetics, University of South-Eastern Norway, 3918 Porsgrunn, Norway.
    Andrade, Manuel A.
    School of Mechanical and Electrical Engineering, Universidad Autónoma de Nuevo León, San Nicolás de los Garza 66455, NL, Mexico.
    Rueda Torres, Jose Luis
    Electrical Sustainable Energy Group, Department of Electrical Sustainable Energy, Faculty of Electrical Engineering, Mathematics and Computer Science, Delft University of Technology, 2628 Delft, CD, The Netherlands.
    Chamorro Vera, Harold Rene
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik.
    Assessment of Daily Cost of Reactive Power Procurement by Smart Inverters2021Inngår i: Energies, E-ISSN 1996-1073, Vol. 14, nr 16, artikkel-id 4834Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The reactive power control mechanisms at the smart inverters will affect the voltage profile, active power losses and the cost of reactive power procurement in a different way. Therefore, this paper presents an assessment of the cost–benefit relationship obtained by enabling nine different reactive power control mechanisms at the smart inverters. The first eight reactive power control mechanisms are available in the literature and include the IEEE 1547−2018 standard requirements. The ninth control mechanism is an optimum reactive power control proposed in this paper. It is formulated to minimise the active power losses of the network and ensure the bus voltages and the reactive power of the smart inverter are within their allowable limits. The Vestfold and Telemark distribution network was implemented in DIgSILENT PowerFactory and used to evaluate the reactive power control mechanisms. The reactive power prices were taken from the default payment rate document of the National Grid. Simulation results demonstrate that the optimal reactive power control mechanism provides the best cost–benefit for the daily steady-state operation of the network.

  • 43. Adams, Sophie
    et al.
    Kuch, Declan
    Diamond, Lisa
    Fröhlich, Peter
    Henriksen, Ida-Marie
    Katzeff, Cecilia
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik, Strategiska hållbarhetsstudier.
    Ryghaug, Marianne
    Yilmaz, Selin
    Social license to automate: A critical review of emerging approaches to electricity demand management2021Inngår i: Energy Research & Social Science, ISSN 2214-6296, E-ISSN 2214-6326, Vol. 80, nr October, s. 102210-12, artikkel-id https://doi.org/10.1016/j.erss.20102210Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

     Electricity demand-side management (DSM) programs are becoming increasingly important to energy system managers in advanced industrialized countries, especially those with high renewable energy penetration. As energy user participation is paramount for their success but has proven to be difficult to obtain, we explore the usefulness of the ‘social license’ concept, originally developed in the mining sector, to refer to the process of creating acceptance in DSM programs aimed at managing or controlling household energy resources such EVs, batteries, and heating and cooling devices. We argue that analyzing the attainment or lack of ‘social license’ may be useful to energy policy-makers and researchers for understanding public concerns with not only supply-side energy resources, but also DSM. We do so by (1) drawing attention to potential frictions between demands for flexibility on the one hand and social practices and habits on the other; (2) attending to the ways that users’ engagement in DSM programs is influenced by their sense of control and agency, and their trust in program providers; and (3) exploring the ways that users may understand their stake in the energy system and may participate in programs as collectives rather than simply as individuals. We argue that a ‘social license to automate’ could not only describe a set of tools to manage participation in DSM projects, but rather assess the ways users effectively feel part of new energy systems designed to serve them. 

  • 44.
    Adler, Mark
    et al.
    Brandeis Univ, Dept Math, Waltham, MA 02254 USA..
    Johansson, Kurt
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.).
    van Moerbeke, Pierre
    UCLouvain, Dept Math, Louvain, Belgium.;Brandeis Univ, Waltham, MA 02254 USA..
    A SINGULAR TOEPLITZ DETERMINANT AND THE DISCRETE TACNODE KERNEL FOR SKEW-AZTEC RECTANGLES2022Inngår i: The Annals of Applied Probability, ISSN 1050-5164, E-ISSN 2168-8737, Vol. 32, nr 2, s. 1234-1294Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Random tilings of geometrical shapes with dominos or lozenges have been a rich source of universal statistical distributions. This paper deals with domino tilings of checker board rectangular shapes such that the top two and bottom two adjacent squares have the same orientation and the two most left and two most right ones as well. It forces these so-called "skew-Aztec rectangles" to have cuts on either side. For large sizes of the domain and upon an appropriate scaling of the location of the cuts, one finds split tacnodes between liquid regions with two distinct adjacent frozen phases descending into the tacnode. Zooming about such split tacnodes, filaments appear between the liquid patches evolving in a bricklike sea of dimers of another type. This work shows that the random fluctuations in a neighborhood of the split tacnode are governed asymptotically by the discrete tacnode kernel, providing strong evidence that this kernel is a universal discrete-continuous limiting kernel occurring naturally whenever we have doubly interlacing patterns. The analysis involves the inversion of a singular Toeplitz matrix which leads to considerable difficulties.

  • 45.
    Adolfsson, Tobias
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Hälsoinformatik och logistik.
    Dellenby, Axel
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Hälsoinformatik och logistik.
    Pre-study of optical LED units for shunting signals2021Independent thesis Basic level (university diploma), 10 poäng / 15 hpOppgave
    Abstract [en]

    Alstom wanted to investigate the possibility of adapting its light emitting diode (LED) technology for shunting signals in train traffic. The LED technology uses 50V, but Alstom wants to adapt it for 12V. The LED technology is energy efficient but needs to be adapted for existing signal interlocking by drawing a higher current. This meant that the possibility of reactive power compensation was investigated to obtain lower thermal dissipation in dwarf signal. The essay presents a couple of possible solutions. One of the solutions is to raise the voltage by using a booster converter to use the existing 50V LED unit. Capacitors were reviewed to be used in reactive power compensation to increase current supply. One of the solutions then became a capacitor bank. Simulations indicated that a booster converter and a capacitor bank can be used to adapt the circuit. However, some modifications must be made.

    Fulltekst (pdf)
    fulltext
  • 46. Agustsson, J. S.
    et al.
    Agustsson, B. V.
    Eriksson, A. K.
    Gylfason, Kristinn B.
    KTH, Skolan för elektro- och systemteknik (EES), Mikrosystemteknik.
    Olafsson, S.
    Johnsen, K.
    Gudmundsson, J. T.
    Hydrogen uptake in MgO thin films grown by reactive magnetron sputtering2006Konferansepaper (Annet vitenskapelig)
    Abstract
  • 47. Agustsson, J. S.
    et al.
    Arnalds, U. B.
    Ingason, A. S.
    Gylfason, Kristinn B.
    KTH, Skolan för elektro- och systemteknik (EES), Mikrosystemteknik.
    Johnsen, K.
    Olafsson, S.
    Gudmundsson, Jon Tomas
    University of Iceland, Iceland.
    Electrical resistivity and morphology of ultra thin Pt films grown by dc magnetron sputtering on SiO(2)2008Inngår i: Journal of Physics Conference Series, IOP Science , 2008, Vol. 100Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Ultra thin platinum films were grown by dc magnetron sputtering on thermally oxidized Si (100) substrates. The electrical resistance of the films was monitored in-situ during growth. The coalescence thickness was determined for various growth temperatures and found to increase from 1.3 nm for films grown at room temperature to 1.8 nm for films grown at 250 degrees C, while a continuous film was formed at a thickness of 3.9 nm at room temperature and 3.5 nm at 250 degrees C. The electrical resistivity increases with increased growth temperature, as well as the morphological grain size, and the surface roughness, measured with a scanning tunneling microscope (STM).

    Fulltekst (pdf)
    fulltext
  • 48. Agustsson, Jon S.
    et al.
    Gylfason, Kristinn B.
    KTH, Skolan för elektro- och systemteknik (EES), Mikrosystemteknik.
    Olafsson, Sveinn
    Johnsen, Kristinn
    Gudmundsson, Jon T
    Electrical properties of thin MgO films2005Konferansepaper (Annet vitenskapelig)
  • 49.
    Ahmad, Ashfaq
    et al.
    Univ Engn & Technol, ACTSENA Res Grp, Taxila 47050, Pakistan..
    Arshad, Farzana
    Univ Engn & Technol, ACTSENA Res Grp, Taxila 47050, Pakistan..
    Naqvi, Syeda Iffat
    Univ Engn & Technol, ACTSENA Res Grp, Taxila 47050, Pakistan..
    Amin, Yasar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK.
    Tenhunen, Hannu
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK. TUCS, University of Turku, Turku, 20520, Finland.
    Loo, Jonathan
    Middlesex Univ, Sch Engn & Informat Sci, Dept Comp Sci, London, England..
    Flexible and Compact Spiral-Shaped Frequency Reconfigurable Antenna for Wireless Applications2020Inngår i: IETE Journal of Research, ISSN 0377-2063, E-ISSN 0974-780X, Vol. 66, nr 1, s. 22-29Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A flexible, spiral-shaped frequency reconfigurable antenna with a compact size (20 x 24 mm(2)) is presented. The proposed antenna has a low-profile planar structure and is able to operate at five different frequency bands, i.e., 4.19-4.48, 5.98-6.4, 3.42-4.0, 5.4-5.68, and 6.8-7.0 GHz. The multiband operation enables the antenna to cover aeronautical radio navigation, fixed satellite communication, WLAN, and WiMAX standards. A radiating element is backed by Rogers (R) 5880 substrate with a thickness of 0.508 mm and dielectric constant of 2.2. The spiral shape is achieved by introducing different strips. Frequency reconfiguration is achieved by the incorporation of a lumped element in a strip, so that the antenna can switch between different resonances. To validate the performance of the antenna, the prototype of the design was fabricated and tested. Good acquiescent is seen between simulated and measured results. The proposed antenna operates efficiently with appreciable return loss, directivity, bandwidth, and peak gain.

  • 50.
    Ahmad, Sarosh
    et al.
    Govt Coll Univ Faisalabad GCUF, Dept Elect Engn & Technol, Faisalabad 38000, Pakistan.;Univ Carlos III Madrid, Dept Signal Theory & Commun, Madrid 28911, Spain..
    Khan, Shahid
    COMSATS Univ Islamabad, Dept Elect & Comp Engn, Abbottabad Campus, Abbottabad 22060, Pakistan.;Univ Lorraine, Inst Super Elect & Automat, F-57070 Lorraine, France..
    Manzoor, Bilal
    Univ Engn & Technol UET, Dept Telecom Engn, Taxila 47050, Pakistan..
    Soruri, Mohammad
    Univ Birjand, Tech Fac Ferdows, Birjand 9717434765, Iran..
    Alibakhshikenari, Mohammad
    Univ Carlos III Madrid, Dept Signal Theory & Commun, Madrid 28911, Spain..
    Dalarsson, Mariana
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik.
    Falcone, Francisco
    Univ Publ Navarra, Elect Elect & Commun Engn Dept, Pamplona 31006, Spain.;Univ Publ Navarra, Inst Smart Cities, Pamplona 31006, Spain..
    A Compact CPW-Fed Ultra-Wideband Multi-Input-Multi-Output (MIMO) Antenna for Wireless Communication Networks2022Inngår i: IEEE Access, E-ISSN 2169-3536, Vol. 10, s. 25278-25289Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this article, a compact coplanar waveguide (CPW) technique based ultra-wideband multiple-input-multiple-output (MIMO) antenna is proposed. The design is characterized by a broad impedance bandwidth starting from 3 GHz to 11 GHz. The overall size of the MIMO design is 60 x 60 mm(2) (1.24 x 1.24 lambda(2)(g) @ 3 GHz) with a thickness of 1.6 mm. To make the design ultra-wideband, the proposed MIMO antenna design has four jug-shaped radiating elements. The design is printed on a FR-4 substrate (relative permittivity of epsilon(r) = 4.4 and loss tangent of tan delta = 0.025). The polarization diversity phenomenon is realized by placing four antenna elements orthogonally. This arrangement increases the isolation among the MIMO antenna elements. The simulated results of the ultra-wideband MIMO antenna are verified by measured results. The proposed MIMO antenna has a measured diversity gain greater than 9.98, envelope correlation coefficient (ECC) less than 0.02, and good MIMO performance where the isolation is more than -20dB between the elements. The group delay, channel capacity loss (CCL), and the total active reflection coefficient (TARC) multiplexing efficiency and mean effective gain results are also analyzed. The group delay is found to be less than 1.2ns, CCL values calculated to be less than 0.4 bits/sec/Hz, while the TARC is below -10dB for the whole operating spectrum. The proposed design is a perfect candidate for ultra-wideband wireless communication systems and portable devices.

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