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Publications (10 of 27) Show all publications
Abrahamsson, L., Skogberg, R., Östlund, S., Lagos, M. & Söder, L. (2015). Identifying electrically infeasible traffic scenarios on the iron ore line: Applied on the present-day system, converter station outages, and optimal locomotive reactive power strategies. In: PROCEEDINGS OF THE ASME JOINT RAIL CONFERENCE, 2015: . Paper presented at ASME/ASCE/IEEE 2015 Joint Rail Conference, JRC 2015; San Jose; United States; 23 March 2015 through 26 March 2015. AMER SOC MECHANICAL ENGINEERS
Open this publication in new window or tab >>Identifying electrically infeasible traffic scenarios on the iron ore line: Applied on the present-day system, converter station outages, and optimal locomotive reactive power strategies
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2015 (English)In: PROCEEDINGS OF THE ASME JOINT RAIL CONFERENCE, 2015, AMER SOC MECHANICAL ENGINEERS , 2015Conference paper, Published 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.

Place, publisher, year, edition, pages
AMER SOC MECHANICAL ENGINEERS, 2015
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-174004 (URN)10.1115/JRC2015-5799 (DOI)000360510000106 ()2-s2.0-84936803806 (Scopus ID)978-0-7918-5645-1 (ISBN)
Conference
ASME/ASCE/IEEE 2015 Joint Rail Conference, JRC 2015; San Jose; United States; 23 March 2015 through 26 March 2015
Note

QC 20150930

Available from: 2015-09-30 Created: 2015-09-24 Last updated: 2015-09-30Bibliographically approved
Abrahamsson, L. & Östlund, S. (2015). Optimizing the power flows in a railway power supply system FED by rotary converters. In: PROCEEDINGS OF THE ASME JOINT RAIL CONFERENCE, 2015: . Paper presented at ASME/ASCE/IEEE 2015 Joint Rail Conference, JRC 2015; San Jose; United States; 23 March 2015 through 26 March 2015. AMER SOC MECHANICAL ENGINEERS
Open this publication in new window or tab >>Optimizing the power flows in a railway power supply system FED by rotary converters
2015 (English)In: PROCEEDINGS OF THE ASME JOINT RAIL CONFERENCE, 2015, AMER SOC MECHANICAL ENGINEERS , 2015Conference paper, Published 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.

Place, publisher, year, edition, pages
AMER SOC MECHANICAL ENGINEERS, 2015
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-174003 (URN)10.1115/JRC2015-5798 (DOI)000360510000105 ()2-s2.0-84936818158 (Scopus ID)978-0-7918-5645-1 (ISBN)
Conference
ASME/ASCE/IEEE 2015 Joint Rail Conference, JRC 2015; San Jose; United States; 23 March 2015 through 26 March 2015
Note

QC 20150930

Available from: 2015-09-30 Created: 2015-09-24 Last updated: 2015-09-30Bibliographically approved
López-López, Á., Abrahamsson, L., Pecharromán, R. R., Fernández-Cardador, A., Cucala, P., Östlund, S. & Söder, L. (2014). A variable no-load voltage scheme for improving energy efficiency in DC-electrified mass transit systems. In: 2014 Joint Rail Conference, JRC 2014: . Paper presented at 2014 Joint Rail Conference, JRC 2014, 2 April 2014 through 4 April 2014, Colorado Springs, CO.
Open this publication in new window or tab >>A variable no-load voltage scheme for improving energy efficiency in DC-electrified mass transit systems
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2014 (English)In: 2014 Joint Rail Conference, JRC 2014, 2014Conference paper, Published 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.

Keywords
Costs, Energy efficiency, Energy utilization, Investments, Mass transportation, Railroad transportation, Beneficial effects, Energy storage systems, Mass transit systems, Operation strategy, Sustainable cities, System energy consumption, Traffic densities, Underground systems, Light rail transit
National Category
Transport Systems and Logistics Energy Engineering
Identifiers
urn:nbn:se:kth:diva-167534 (URN)10.1115/JRC2014-3818 (DOI)000359389500089 ()2-s2.0-84902816964 (Scopus ID)9780791845356 (ISBN)
Conference
2014 Joint Rail Conference, JRC 2014, 2 April 2014 through 4 April 2014, Colorado Springs, CO
Note

QC 20150610

Available from: 2015-06-10 Created: 2015-05-22 Last updated: 2015-09-18Bibliographically approved
Laury, J., Abrahamsson, L. & Östlund, S. (2014). OPF for an HVDC feeder solution for railway power supply systems. Paper presented at Conference of 14th International Conference on Railway Engineering Design and Optimization, COMPRAIL 2014. WIT Transactions on the Built Environment, 135, 803-812
Open this publication in new window or tab >>OPF for an HVDC feeder solution for railway power supply systems
2014 (English)In: WIT Transactions on the Built Environment, ISSN 1746-4498, E-ISSN 1743-3509, Vol. 135, p. 803-812Article in journal (Refereed) Published
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.

Keywords
Electric power systems, Feeding, Integer programming
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-168678 (URN)10.2495/CR140671 (DOI)2-s2.0-84903688956 (Scopus ID)
Conference
Conference of 14th International Conference on Railway Engineering Design and Optimization, COMPRAIL 2014
Note

QC 20150608

Available from: 2015-06-08 Created: 2015-06-08 Last updated: 2017-12-04Bibliographically approved
Abrahamsson, L., Östlund, S., Schütte, T. & Söder, L. (2013). An electromechanical moving load fixed node position and fixed node number railway power supply systems optimization model. Transportation Research Part C: Emerging Technologies, 30, 23-40
Open this publication in new window or tab >>An electromechanical moving load fixed node position and fixed node number railway power supply systems optimization model
2013 (English)In: Transportation Research Part C: Emerging Technologies, ISSN 0968-090X, E-ISSN 1879-2359, Vol. 30, p. 23-40Article in journal (Refereed) Published
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.

Keywords
Optimization, Railway, Power systems, Special ordered sets of type 2 (SOS2), MINLP, Moving loads
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-107033 (URN)10.1016/j.trc.2013.01.009 (DOI)000318387500002 ()2-s2.0-84875241859 (Scopus ID)
Note

QC 20130610. Updated from submitted to published.

Available from: 2012-12-06 Created: 2012-12-05 Last updated: 2017-12-07Bibliographically approved
Pilo, E., Rouco, L., Fernandez, A. & Abrahamsson, L. (2012). A Monovoltage Equivalent Model of Bi-Voltage Autotransformer-Based Electrical Systems in Railways. IEEE Transactions on Power Delivery, 27(2), 699-708
Open this publication in new window or tab >>A Monovoltage Equivalent Model of Bi-Voltage Autotransformer-Based Electrical Systems in Railways
2012 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 27, no 2, p. 699-708Article in journal (Refereed) Published
Abstract [en]

This paper presents an equivalent model that allows representing bi-voltage autotransformer- based systems (such as 2 x 25 kV ac, 2 x 15 kV ac) as if they were monovoltage systems. This model can be used for symmetrical (such as 2 x25-kV 50-Hz systems) and unsymmetrical (such as 12/24-kV 25-Hz systems) configurations. It is based on two simplifying hypotheses that establish relationships between currents and voltages in the positive and negative phases. These hypotheses are discussed and the accuracy of the model is evaluated by comparing the results with a detailed conventional model of power-supply systems.

Keywords
Power system modeling, rail transportation power system
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-95114 (URN)10.1109/TPWRD.2011.2179814 (DOI)000302503900031 ()2-s2.0-84859759310 (Scopus ID)
Note
QC 20120515Available from: 2012-05-15 Created: 2012-05-14 Last updated: 2017-12-07Bibliographically approved
Abrahamsson, L. & Söder, L. (2012). An SOS2-based moving trains,fixed nodes, railway power system simulator. In: WIT Transactions on the Built Environment: . Paper presented at Comprail 2012, 13th International Conference on Design and Operation in Railway Engineering 2012,11 - 13 September 2012,New Forest, UK (pp. 813-823). WIT Press
Open this publication in new window or tab >>An SOS2-based moving trains,fixed nodes, railway power system simulator
2012 (English)In: WIT Transactions on the Built Environment, WIT Press, 2012, p. 813-823Conference paper, Published paper (Refereed)
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.

Place, publisher, year, edition, pages
WIT Press, 2012
Keywords
Optimization, railway, power systems, load flow, special ordered, sets of type 2, MINLP, moving loads, simulation, driving strategies
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-107032 (URN)10.2495/CR140681 (DOI)2-s2.0-84903746589 (Scopus ID)9781845647667 (ISBN)
Conference
Comprail 2012, 13th International Conference on Design and Operation in Railway Engineering 2012,11 - 13 September 2012,New Forest, UK
Funder
StandUp
Note

QC20130724

Available from: 2012-12-06 Created: 2012-12-05 Last updated: 2015-11-30Bibliographically approved
Abrahamsson, L., Kjellqvist, T. & Östlund, S. (2012). High-voltage DC-feeder solution for electric railways. IET Power Electronics, 5(9), 1776-1784
Open this publication in new window or tab >>High-voltage DC-feeder solution for electric railways
2012 (English)In: IET Power Electronics, ISSN 1755-4535, E-ISSN 1755-4543, Vol. 5, no 9, p. 1776-1784Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Institution of Engineering and Technology, 2012
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-124636 (URN)10.1049/iet-pel.2011.0219 (DOI)000317655400018 ()2-s2.0-84880017472 (Scopus ID)
Note

QC 20130813

Available from: 2013-07-23 Created: 2013-07-23 Last updated: 2017-12-06Bibliographically approved
Abrahamsson, L., Kjellqvist, T. & Östlund, S. (2012). HVDC Feeder Solution for Electric Railways. IET Power Electronics
Open this publication in new window or tab >>HVDC Feeder Solution for Electric Railways
2012 (English)In: IET Power Electronics, ISSN 1755-4535, E-ISSN 1755-4543Article in journal (Refereed) In press
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.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-101752 (URN)
Note

QS 2012

Available from: 2012-12-04 Created: 2012-09-03 Last updated: 2017-12-07Bibliographically approved
Abrahamsson, L., Östlund, S. & Söder, L. (2012). HVDC feeding with OPF and unit commitment for electric railways. In: Electrical Systems for Aircraft, Railway and Ship Propulsion (ESARS), 2012. Paper presented at 2012 Electrical Systems for Aircraft, Railway and Ship Propulsion, ESARS 2012, 16 October 2012 through 18 October 2012, Bologna (pp. 6387481). IEEE
Open this publication in new window or tab >>HVDC feeding with OPF and unit commitment for electric railways
2012 (English)In: Electrical Systems for Aircraft, Railway and Ship Propulsion (ESARS), 2012, IEEE , 2012, p. 6387481-Conference paper, Published 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.

Place, publisher, year, edition, pages
IEEE, 2012
Series
Electrical Systems for Aircraft, Railway and Ship Propulsion, ESARS, ISSN 2165-9400
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-118378 (URN)10.1109/ESARS.2012.6387481 (DOI)2-s2.0-84873427392 (Scopus ID)978-146731370-4 (ISBN)
Conference
2012 Electrical Systems for Aircraft, Railway and Ship Propulsion, ESARS 2012, 16 October 2012 through 18 October 2012, Bologna
Note

QC 20130218

Available from: 2013-02-18 Created: 2013-02-18 Last updated: 2013-02-18Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-2109-060X

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