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  • 1.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Kjellqvist, Tommy
    Elekt Konsult AB, Kraftelektronik, Sweden.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    High-voltage DC-feeder solution for electric railways2012In: IET Power Electronics, ISSN 1755-4535, E-ISSN 1755-4543, Vol. 5, no 9, 1776-1784 p.Article in journal (Refereed)
    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.

  • 2.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Kjellqvist, Tommy
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    HVDC Feeder Solution for Electric Railways2012In: IET Power Electronics, ISSN 1755-4535, E-ISSN 1755-4543Article in journal (Refereed)
    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.

  • 3.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Schütte, Thorsten
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Use of converters for feeding of AC railways for all frequencies2012In: Energy for Sustainable Development, ISSN 0973-0826, Vol. 16, no 3, 368-378 p.Article in journal (Refereed)
    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.

  • 4.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Skogberg, Ronny
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Lagos, Mario
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Identifying electrically infeasible traffic scenarios on the iron ore line: Applied on the present-day system, converter station outages, and optimal locomotive reactive power strategies2015In: PROCEEDINGS OF THE ASME JOINT RAIL CONFERENCE, 2015, AMER SOC MECHANICAL ENGINEERS , 2015Conference paper (Refereed)
    Abstract [en]

    This paper presents the main findings of a Master's Thesis project carried out in cooperation between Transrail and Royal Institute of Technology (KTH). The main objective was to create a plugin for checking the electric power system feasibility of a train traffic plan with an associated driving strategy created by TRAINS a Transrail software product. Secondary aims with the project was to study power system feasibilities during converter station outages, and to which extent optimal operation of the locomotive converters' reactive power assure power system feasibilities. In the developed optimal reactive power strategies, the main priority was to fulfill the desired traffic plans, whereas the secondary priority was to minimize railway power system power consumption. The case studies are applied on representative traffic scenarios and power system models representing the northern part of the Iron Ore line in Northern Sweden. The focus of the study is set on the IORE locomotives and the iron ore trains they haul. The optimized locomotive reactive power regards IORE, so also the investigated power system feasibilities of the traffic plans.

  • 5.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Optimizing the power flows in a railway power supply system FED by rotary converters2015In: PROCEEDINGS OF THE ASME JOINT RAIL CONFERENCE, 2015, AMER SOC MECHANICAL ENGINEERS , 2015Conference paper (Refereed)
    Abstract [en]

    This study focuses on optimizing the operation of rotary railway-feeding converters. Since a large share of rotary converters can be expected to be in operation for decades to come in the railway power supply systems (RPSSs), it is important to make their operation as efficient as possible. The existing rotary converters may have unused capabilities particularly in load sharing, but also to some extent in reactive power compensation. Load-sharing improvement can be done in two steps; (1) coarsely by unit commitment within a converter station, (2) fine-tuned by controlling the terminal voltage of the converter station on the railway-side. The proposed optimization models minimize RPSS losses, including losses in the converters. The models are implemented and solved in the GAMS environment. The case studies are applied on Sweden-inspired RPSS designs and configurations, and the train load situations are varied. Ideas and experiences regarding improved computational efficiency for solving the problems are discussed.

  • 6.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Schütte, Thorsten
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    An electromechanical moving load fixed node position and fixed node number railway power supply systems optimization model2013In: Transportation Research Part C: Emerging Technologies, ISSN 0968-090X, E-ISSN 1879-2359, Vol. 30, 23-40 p.Article in journal (Refereed)
    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.

  • 7.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    HVDC feeding with OPF and unit commitment for electric railways2012In: Electrical Systems for Aircraft, Railway and Ship Propulsion (ESARS), 2012, IEEE , 2012, 6387481- p.Conference paper (Refereed)
    Abstract [en]

    In this paper a railway power system design based on an HVDC feeder is suggested. 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. The ratings of the catenary-connected ones can be lower than substation transformers or rotary converters, since the power conversion can be fully controlled. Simulations of the proposed solution show clear advantages regarding transmission losses and voltages compared to conventional systems, especially for cases with long catenary sections, and when there are substantial shares of regeneration from the trains.

  • 8.
    Abrahamsson, Lars
    et al.
    KTH, Superseded Departments, Electric Power Systems.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    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 lineManuscript (preprint) (Other academic)
    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.

  • 9.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    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 line2012Article in journal (Refereed)
    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.

  • 10.
    Arshad, Waqas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Chin, Yung-kang Robert
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Bäckström, Thomas
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    On finding compact motor solutions for transient applications2001In: Proceedings of the IEEE International Electric Machines Conference, 2001, 743-747 p.Conference paper (Refereed)
  • 11. Berg, Niklas
    et al.
    Erikssson, Sture
    Sadarangani, Chandur
    Bäckström, Thomas
    Östlund, Stefan
    KTH, Superseded Departments, Electrical Systems.
    Malmqvist, Anders
    Hybriddrivanordning samt hjulfordon försett med en hybriddrivanordning1998Patent (Other (popular science, discussion, etc.))
  • 12.
    Bessegato, Luca
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Harnefors, Lennart
    Ilves, Kalle
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Control of Direct AC/AC Modular Multilevel Converters Using Capacitor Voltage Estimation2016In: 2016 18TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'16 ECCE EUROPE), IEEE, 2016Conference paper (Refereed)
    Abstract [en]

    This paper applies a control method based on current control and sum-capacitor-voltage estimation to the direct ac/ac modular multilevel converter. As capacitor voltages are estimated, their measurements are not needed in the high-level control, which simplifies the communication between the main controller and the submodules of the converter. The stability of the internal dynamics of the converter, using the aforementioned control method, is studied using Lyapunov stability theory, proving that the system is globally asymptotically stable. The behavior of the converter is simulated focusing on three-phase 50 Hz to single-phase 16 (2)/(3) Hz conversion, which is typical for railway power supply systems of some European countries. Simulation results are in agreement with the expected behavior of the converter, both in steady-state and dynamic situations.

  • 13. Brokemper, Michael
    et al.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Initial Rotor Position Detection for an Integrated PM Synchronous Motor Drive1995In: Conference Record of the 1995 IEEE Industry Applications Society 30th Annual Meeting, 1995, 741-747 p.Conference paper (Refereed)
  • 14.
    Bäckström, Thomas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Engströmer, Henrik
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Control of the Integrated Energy Transducer Drive for Hybrid Electric Vehicles1997Conference paper (Refereed)
  • 15. Bäckström, Thomas
    et al.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Integrated Energy Transducer Drive for Hybrid Electric Vehicles1997In: Proceedings of the 7th European Conference on Power Electronics and Applications, EPE'97, 1997, 4.721-4.726 p.Conference paper (Refereed)
  • 16.
    Bäckström, Thomas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Integrated Energy Transducer for Hybrid Electric Vehicles1997In: Proceesdings of the IEE 8th International conference on Electrical Machines and Drives, EMD'97, 1997, 239-243 p.Conference paper (Refereed)
  • 17.
    Cosic, Alija
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Design of an Electromechanical Actuator for Active Lateral Suspension2008Report (Other academic)
  • 18.
    Hu, Yifei
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Cosic, A.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Zhang, Hui
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Design and optimization procedure of a single-sided linear induction motor applied to an Articulated funiculator2016In: 2016 IEEE 8th International Power Electronics and Motion Control Conference, IPEMC-ECCE Asia 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, 3096-3102 p., 7512790Conference paper (Refereed)
    Abstract [en]

    The paper describes the design of a single-sided linear induction motor (SLIM) intended for an Articulated Funiculator (AF). A procedure is proposed where first an analytical design is carried out to obtain a preliminary geometry. The analytical design is based on approximate equivalent circuits under constrained conditions. In the second step a two-dimensional finite element method (2D-FEM) analysis is performed to validate the accuracy of the analytical models. The modification and optimization are conducted to acquire the best design.

  • 19. Kjaer, Philip C.
    et al.
    Norrga, Staffan
    KTH, Superseded Departments, Electrical Systems.
    Östlund, Stefan
    KTH, Superseded Departments, Electrical Systems.
    A primary-switched line-side converter using zero-voltage switching2001In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 37, no 6, 1824-1831 p.Article in journal (Refereed)
    Abstract [en]

    A new primary-switched ac/dc converter and its modulation are presented. It employs a single- or three-phase transformer, with a matrix converter (primary) and a conventional two-level converter (secondary). This allows galvanic isolation at medium-frequency zero-voltage primary commutation and five line-side voltage levels. Two distinct modulation methods are explained in detail, and it is shown how a combination of these allows optimal operation in terms of efficiency and voltage harmonics. Measured waveforms on a 30-kW prototype confirm the expected performance.

  • 20.
    Kjaer, Philip
    et al.
    ABB Corporate Research.
    Norrga, Staffan
    ABB Corporate Research.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    A primary-switched converter using zero-voltage switching2000In: Proccedings of the IEEE Industry Applications Society Annual Meeting 2000, 2000Conference paper (Refereed)
  • 21.
    Kjellqvist, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Design of a Permanent Magnet Synchronous Machine for an Electromechanical Active Suspension2001Conference paper (Refereed)
  • 22.
    Kjellqvist, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Carlsson, Fredrik
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Control and design requirements of an electromechanical actuator for active suspension of rail vehicles1999Conference paper (Refereed)
  • 23.
    Kjellqvist, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Carlsson, Fredrik
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Electromechanical actuator for active suspension in rail vehicles1999Conference paper (Refereed)
  • 24.
    Kjellqvist, Tommy
    et al.
    KTH, Superseded Departments, Electrical Systems. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Norrga, Staffan
    KTH, Superseded Departments, Electrical Systems.
    Östlund, Stefan
    KTH, Superseded Departments, Electrical Systems. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Design Considerations for a Medium Frequency Transformer in a Line Side Power Conversion System2004In: Proceedings of the 35th Annual IEEE Power Electronics Specialist Conference, PESC 2004, IEEE , 2004, 704-710 p.Conference paper (Refereed)
    Abstract [en]

    Design considerations are presented for a medium frequency transformer in a line side power conversion system for electric railway traction. The system employs soft commutation in order to reduce switching losses and allow for high operating frequency of the transformer. Two different designs are evaluated; The first one is dry insulated and the second one is liquid-immersed. Calculations indicate that a 1 MVA transformer operating at 4 kHz could be realized with an active weight of below 150 kg for both dry and liquid-immersed transformer concepts. The transformers are modeled magnetically, electrically and thermally, and a geometric optimization procedure based on a cost function is applied to achieve an optimum design.

  • 25.
    Kjellqvist, Tommy
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930). KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Switching Frequency Limit for Soft-Switching MF Transformer System for AC-fed Traction2005In: Proceesings of the 36th Annual IEEE Power Electronics Specialist Conference, PESC 2005, IEEE , 2005, 1678-1684 p.Conference paper (Refereed)
    Abstract [en]

    The migration to line side power conversion topologies comprising a medium frequency transformer in AC-fed propulsion systems may reduce size and weight of the conversion system. The switching frequency is a crucial factor affecting the viability of such a conversion system. An increased switching frequency of a mutually commutated conversion system comprising a medium frequency transformer employing soft switching is verified by single pulse measurements. A test bench to characterize standard IGBT modules under soft switching has been build and loss measurements on a 3.3 kV IGBT module are presented for hard and soft switching. A loss model of the investigated topology is developed and the maximum switching frequency for a converter equipped with the investigated module is estimated for hard and soft switching.

  • 26.
    Kjellqvist, Tommy
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930). KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Norrga, Staffan
    ABB AB, Sweden .
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Ilves, Kalle
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Thermal Evaluation of a Medium Frequency Transformer in a Line Sider Conversion System2009In: Proceedings of the 13th International European Electronics Conference and Exhibition, EPE '09, IEEE , 2009, 2517-2526 p.Conference paper (Refereed)
    Abstract [en]

    A central part of a medium frequency conversion system is the transformer. A medium frequency transformer for railway propulsion may be stressed beyond 30kV with voltage slopes around 50kV/mu s depending on topology while the geometric dimensions are small. A 170kVA transformer prototype operated at 4 kHz has been developed and tested.

    A transient thermal model of the transformer is developed and verified experimentally. The transient thermal behavior is important in propulsion applications where the conversion system is often heavily overloaded. Simulations indicate that the overloading capability of the transformer is comparable to a conventional traction transformer. Experimental results are in good agreement with the model.

  • 27.
    Kjellqvist, Tommy
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930). KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Active Snubber Circuit for Source Commutated Converters Utilizing the IGBT in the Linear Region2008In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 23, no 5, 2595-2601 p.Article in journal (Refereed)
    Abstract [en]

    This paper describes a gate control method where an IGBT is controlled in its linear region by means of closed loop control in order to regulate the voltage slope during turn-on and to clamp the voltage of an anti-parallel diode in a source commutated converter. Controlling the voltage slope may be necessary in a high voltage converter to avoid emission of EMI or to avoid triggering oscillations which may cause insulation failure. Controlling the switching trajectory without influence from the device characteristics is important where series-connection is necessary to increase the overall blocking voltage. The control method has been verified by means of a prototype.

  • 28.
    Larsson, Tomas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Active DC Link Filter for AC-AC Converters1995Conference paper (Refereed)
  • 29.
    Larsson, Tomas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    An active DC link filter for two frequency electric locomotives1994Conference paper (Refereed)
  • 30. Laury, John
    et al.
    Abrahamsson, Lars
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    OPF for an HVDC Feeder Solution for Railway Power Supply Systems2012Conference paper (Refereed)
  • 31.
    Laury, John
    et al.
    KTH, School of Electrical Engineering (EES).
    Abrahamsson, Lars
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    OPF for an HVDC feeder solution for railway power supply systems2014In: WIT Transactions on the Built Environment, ISSN 1746-4498, E-ISSN 1743-3509, Vol. 135, 803-812 p.Article in journal (Refereed)
    Abstract [en]

    With increasing railway traffic, the demand for electrical power increases. However, railway power systems are often weak causing high transmission losses and large voltage drops. One possible method for strengthening the railway power supply system is to implement a High Voltage Direct Current (HVDC) feeder in parallel to the Overhead Contact Line (OCL). The HVDC feeder is connected to the OCL by converters. This paper describes different properties and characteristics of such an HVDC feeder solution. An AC/DC unified Optimal Power Flow (OPF) model and unit commitment is used to obtain proper control of the converters. The non-linear load flow and converter loss equations, and the binary variables for the unit commitment, lead to an optimization problem of Mixed Integer Non- Linear Programming (MINLP) type. The optimization problem is formulated in the software GAMS, and is solved by the solver BONMIN. In each case, the objective has been to minimize the total active power losses.

  • 32. López-López, ÁJ.
    et al.
    Abrahamsson, Lars
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Pecharromán, R. R.
    Fernández-Cardador, A.
    Cucala, P.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    A variable no-load voltage scheme for improving energy efficiency in DC-electrified mass transit systems2014In: 2014 Joint Rail Conference, JRC 2014, 2014Conference paper (Refereed)
    Abstract [en]

    Railway mass transit systems like subways play a fundamental role in the concept of sustainable cities. In these systems, the amount of passengers strongly fluctuates along the day. Hence, in order to provide a proper service without incurring disproportionate energy consumption, operation at different traffic densities is required. The majority of underground systems are DC-electrified. Standard DC voltages in railway systems are low for historical and safety reasons. In the rush hours, the large number of trains demanding power of the system may lead to overloaded substations and voltage dips. This problem is partially mitigated by means of substation-transformer tap regulation, which allows operators to increase the no-load voltage. High no-load voltage has a beneficial effect at all trafficdensity scenarios in terms of transmission losses. However, at the same time it effectively reduces the system's capacity to absorb regenerated energy, which may lead to inefficient energy consumption figures during off-peak hours. In this paper, the sensitivity of system energy consumption to no-load voltage has been analyzed. Several traffic-density scenarios in a case-study system are explored. As a result, a scheduled no-load voltage scheme is proposed for the operation of the system. This operation strategy improves energy efficiency without incurring a high investment cost. The only costs related to this proposed method are the costs of wear-andtear in tap-changers. In case there are devices such as energy storage systems installed in the system, there would be additional operation costs related to a simultaneous update of the voltage limits for their operation.

  • 33.
    Norrga, Staffan
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Meier, Stephan
    KTH, Superseded Departments, Electrical Systems.
    Östlund, Stefan
    KTH, Superseded Departments, Electrical Systems.
    A three-phase soft-switched isolated AC/DC converter without auxiliary circuit2004In: IEEE IND APPLICAT SOC ANN M, 2004, 1768-1775 p.Conference paper (Refereed)
    Abstract [en]

    An ac/dc converter topology comprises a voltage source converter (VSC) with capacitive snubbers and a 2-phase by 3-phase cycloconverter, connected by an MF transformer. By alternately commutating the two converters it is possible to achieve soft switching conditions for all of the semiconductor elements. Furthermore, it is shown that resonant commutation of the voltage source converter is possible by utilizing the cycloconverter in order to momentarily short-circuit the transformer terminals. This allows for soft commutation of the VSC down to zero load. Furthermore, the design and operation of a 40 kVA prototype converter system based on the studied concept is described.

  • 34.
    Norrga, Staffan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Meier, Stephan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    A three-phase soft-switched isolated AC/DC converter without auxiliary circuit2008In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 44, no 3, 836-844 p.Article in journal (Refereed)
    Abstract [en]

    This paper describes an ac/dc converter system consisting of a voltage-source converter (VSC) with purely capacitive snubbers and a two-phase by three-phase cycloconverter, connected via a medium-frequency (MF) transformer. By alternately commutating the two converters, it is possible to achieve beneficial switching conditions for all semiconductor devices. A commutation and modulation algorithm is described, which allows for pulsewidth-modulation control of the output voltage while maintaining soft switching. Low-load operation of the converter is a potential difficulty because the load current may be insufficient for recharging the snubber capacitors of the VSC. However, if the cycloconverter is used to momentarily short circuit the transformer, a quasi-resonant commutation mode of the VSC can be achieved, making a fast and soft commutation of the VSC down to zero load possible, without an auxiliary circuit. Furthermore, the design and operation of a 40-kVA prototype converter system are described. The experimental results from the prototype clearly show the practical feasibility of the studied concept.

  • 35.
    Sadarangani, Chandur
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Arshad, Waqas
    KTH, Superseded Departments, Electrical Systems.
    Bäckström, Thomas
    Östlund, Stefan
    KTH, Superseded Departments, Electrical Systems.
    Arrangement Related to Seatbelts2001Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    The invention includes an arrangement related to seatbelts (1) adapted to a vehicle, having at all events two securing points (2a, 2b), intended for the belt, which points are related to a chassis (3a) belonging to the vehicle, at all events one of the securing points (2b) belonging to the belt consisting of a reel (40), drivable by an electric motor (4), in order to be able to reel belt sections or parts near the securing points (2d) thereon with an intention of being able to hold belt stretchings (2e, 2f) stretched against a person's chest and/or trunk portion or vice versa. One or more sensors are adapted to, at a value occurring above a selected limit value, let said electric motor (4) be activated to drive the reel (40) in a direction in order to increase the stretching force in said belt, and said electric motor consists of a polyphase motor. Said polyphase motor (4) is designed to present a low electric inductance and/or a high torque density, in order to thereby be able to provide a relatively high starting torque, high torque and endure high overload during intermittent operation conditions.

  • 36.
    Sadarangani, Chandur
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Östlund, Stefan
    KTH, Superseded Departments, Electrical Systems.
    Bäckström, Thomas
    Hybriddrivsystem: [Hybrid drive system)1995Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A hybrid drive system includes an internal combustion engine with an output shaft. An energy converter is connected to the output shaft via a coupling. The energy converter has first and second rotors which are rotatable at different speeds in relation to each other. At least one of the rotors is provided with one or more windings which are supplied with current from a current converter. The current converter is supplied with direct current from a direct current source. A transmission with variable gear ratio is coupled to one of the rotors. The transmission and the current converter cooperate via a control arrangement. The control arrangement comprises a control unit for controlling rotational speed and torque of the internal combustion engine and the energy converter.

  • 37. Skoglund, M.
    et al.
    Bark, P.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Dual mode locomotives systems study of new freight locomotives for Sweden2008Conference paper (Refereed)
    Abstract [en]

    A conceptual study for a Swedish dual-mode locomotive is presented. The primary energy sources are AC electricity from an overhead catenary system or a diesel-electric generator system. The study focuses on analysing how freight operations and locomotive utilisation can be improved and how it can affect environmental aspects of freight operations. Based on project experiences and operative demands, a system proposal has been presented. The rated power output is considerably higher in electric mode compared to diesel mode. The reason for this being higher power demand on electrified main lines compared to branch lines and yards lacking overhead catenary where the power need is lower. The starting tractive effort will however be the same regardless of electric mode or diesel mode, making it possible to haul the same train weight in both propulsion modes. The study has shown that dual-mode locomotives for Swedish freight operations are most interesting in order to improve operations, degree of utilisation and environmental performance.

  • 38.
    Skoglund, Mattias
    et al.
    TFK - Transport Research Institute.
    Bark, Peter
    TFK - Transport Research Institute.
    Östlund, Stefan
    KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group. KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Dual mode locomotives - System studies of new freight locomotives for Sweden2008In: Proceedings of IEEE/ASME Joint Railroad Conference, 2008, 263-268 p.Conference paper (Refereed)
    Abstract [en]

    A conceptual study for a Swedish dual-mode locomotive is presented. The primary energy sources are AC electricity from an overhead catenary system or a diesel-electric generator system. The study focuses on analysing how freight operations and locomotive utilisation can be improved and how it can affect environmental aspects of freight operations. Based on project experiences and operative demands, a system proposal has been presented. The rated power output is considerably higher in electric mode compared to diesel mode. The reason for this being higher power demand on electrified main lines compared to branch lines and yards lacking overhead catenary where the power need is lower. The starting tractive effort will however be the same regardless of electric mode or diesel mode, making it possible to haul the same train weight in both propulsion modes. The study has shown that dual-mode locomotives for Swedish freight operations are most interesting in order to improve operations, degree of utilisation and environmental performance.

  • 39. Skoglund, Mattias
    et al.
    Bark, Peter
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    The Swedish T43H Hybrid Locomotive2009In: 16th ITS World Congress, 2009Conference paper (Refereed)
    Abstract [en]

    Experiences from the Swedish hybrid locomotive (T43H) are presented. The locomotive has a series hybrid propulsion system with a comparatively small diesel engine and a large battery pack. Original layout was a traditional diesel-electric power train. Indications from switch operations show fuel savings of 37 to 50 % with the hybrid locomotive. The Swedish experiences are thus in parity with North American experiences showing savings between 30 and 80 %. The evaluation showed that hybrid locomotives in switch duty have significant advantages compared to conventional diesel locomotives in terms of reducing fuel consumption and improving environmental performance.

  • 40.
    Troche, Gerhard
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Traffic and Logistics (closed 20110301). KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Östlund, Stefan
    Skoglund, Mattias
    Pre-study for conversion of dieselelectric freight locomotive class TMz into a dual-power locomotive2009Report (Other academic)
  • 41.
    Zhang, Hongyang
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Benchmark of high-power STATCOM topologies for flicker compensation2016In: 2016 18TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'16 ECCE EUROPE), IEEE, 2016Conference paper (Refereed)
    Abstract [en]

    The current from an electrical arc furnace (EAF) in a steel plant is highly unsymmetrical, i.e. it comprises a large amount of negative sequence. This causes problems with the voltage stability in the capacitor submodules for a static synchronous compensator (STATCOM), when implemented using the modular multilevel converter (M2C) concept. In order to counteract the uncontrollability of the capacitor voltage, a common practice is to circulate a zero-sequence fundamental current or a direct current. The method brings the benefit of re-balancing the active power among the individual phases while it requires over-rating of the valve current or dc voltage of the STATCOM. This would in practice give a more expensive design. This paper presents a benchmark of various M2C-based STATCOM designs considering the valve overrating. The STATCOM topologies will be benchmarked with the EAF modeled for all possible combinations of positive-and negative-sequence current. The rating comparison considering the dc capacitor ripple and zero-sequence harmonic injection are discussed.

  • 42.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    A primary switched converter system for traction applications1992Doctoral thesis, monograph (Other academic)
  • 43.
    Östlund, Stefan
    KTH, Superseded Departments, Electrical Systems.
    Dual system locomotives for future rail freight operation2002Conference paper (Other academic)
  • 44.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Dual system locomotives for future rail freight operation: Concept and preliminary ratings2005Report (Other academic)
  • 45.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Electric Railway Traction2012 (ed. 10)Book (Other academic)
  • 46.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Influence of the control principle on a high-voltage inverter system for reduction of traction transformer weight1990In: Elektrische Bahnen, Vol. 88, no 3, 110-115 p.Article in journal (Refereed)
  • 47.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Influence of the control principle on a high-voltage inverter system for reduction of traction transformer weight1987Conference paper (Refereed)
  • 48.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Performance of future regional high speed trains1998In: Proceedings of the 1998 ASME/IEEE Joint Railroad Conference, 1998, 21-28 p.Conference paper (Refereed)
  • 49.
    Östlund, Stefan
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Rail Power Supplies Going More Power Electronic [Technology Leaders]2014In: IEEE Electrification Magazine, ISSN 2325-5897, Vol. 2, no 3, 6912057Article in journal (Refereed)
    Abstract [en]

    In recent years, interest has risen in using electrified rail operations as an environmentally friendly and efficient way of producing passenger and freight services. New high-speed lines are being designed and built throughout Europe and China, and there is also an increasing interest in high speed rail services in southeast Asia and the United States. To meet this demand, the electrification of railways has rendered increased interest both for new lines and for upgrading existing systems to higher power capacity. Historically, the first rail electrifications were designed as low-voltage dc systems, where the dc voltage was typically generated by dc generators. The limitations in the voltage capability of dc machines and related equipment limited the voltage considerably. More than 100 years later, we still have dc traction systems generated by rectifiers connected to the three-phase grid with voltages in the range of 650 or 750 V up to 3 kV. Because of large voltage drops and excessive losses, it is required that the connecting points to the threephase system are located with a relatively short mutual distance.

  • 50.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Reduction of traction transformer weight by using a naturally commutated high-voltage inverter with increased frequency1988Licentiate thesis, monograph (Other academic)
12 1 - 50 of 62
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