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Optimal Railroad Power Supply System Operation and Design: Detailed system studies, and aggregated investment models
KTH, School of Electrical Engineering (EES), Electric Power Systems.ORCID iD: 0000-0003-2109-060X
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , xii, 77 p.
Series
Trita-EE, ISSN 1653-5146 ; 2012:062
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-107037ISBN: 978-91-7501-584-2 (print)OAI: oai:DiVA.org:kth-107037DiVA: diva2:574526
Public defence
2012-12-17, sal Q2, Osquldasväg 10, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20121206

Available from: 2012-12-06 Created: 2012-12-05 Last updated: 2013-02-25Bibliographically approved
List of papers
1. Use of converters for feeding of AC railways for all frequencies
Open this publication in new window or tab >>Use of converters for feeding of AC railways for all frequencies
2012 (English)In: Energy for Sustainable Development, ISSN 0973-0826, Vol. 16, no 3, 368-378 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2012
Keyword
Railway power supply systems, Converters
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-96797 (URN)10.1016/j.esd.2012.05.003 (DOI)000308522500014 ()2-s2.0-84865444200 (Scopus ID)
Note

QC 20120926

Available from: 2012-06-12 Created: 2012-06-12 Last updated: 2017-12-07Bibliographically approved
2. HVDC Feeder Solution for Electric Railways
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
3. 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 line
Open this publication in new window or tab >>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 line
2012 (English)Article in journal (Refereed) Submitted
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.

Place, publisher, year, edition, pages
IEEE Press, 2012
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-107031 (URN)
Note

QS 2012

Available from: 2012-12-06 Created: 2012-12-05 Last updated: 2013-02-22Bibliographically approved
4. An SOS2-based moving trains,fixed nodes, railway power system simulator
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, 813-823 p.Conference 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
Keyword
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
5. An electromechanical moving load fixed node position and fixed node number railway power supply systems optimization model
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, 23-40 p.Article 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.

Keyword
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
6. Fast Estimation of Relations Between Aggregated Train Power System Data and Traffic Performance
Open this publication in new window or tab >>Fast Estimation of Relations Between Aggregated Train Power System Data and Traffic Performance
2011 (English)In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 60, no 1, 16-29 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2011
Keyword
Load flow, neural networks, railway
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-30549 (URN)10.1109/TVT.2010.2091293 (DOI)000286385700003 ()2-s2.0-78751660527 (Scopus ID)
Note
© 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20110303Available from: 2012-01-17 Created: 2011-02-28 Last updated: 2017-12-11Bibliographically approved
7. Traction Power System Capacity Limitations at Various Traffic Levels
Open this publication in new window or tab >>Traction Power System Capacity Limitations at Various Traffic Levels
2011 (English)In: WCRR, World Congress on Railway Research, 2011Conference paper, Published paper (Refereed)
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.

Keyword
railway power systems, neural networks, load flow, simulation, approximation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-52665 (URN)
Conference
9th world congress on railway research, May 22-26 2011
Note
QC 20111222Available from: 2012-01-17 Created: 2011-12-19 Last updated: 2012-12-06Bibliographically approved
8. Railway power supply investment decisions considering the voltage drops: Assuming the future traffic to be known
Open this publication in new window or tab >>Railway power supply investment decisions considering the voltage drops: Assuming the future traffic to be known
2009 (English)In: 2009 15th International Conference on Intelligent System Applications to Power Systems, ISAP '09, 2009Conference paper, Published paper (Other academic)
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.

Keyword
Decision making, Mathematical modeling, Neural networks, Planning, Railway power supply, Approximators, Investment decisions, Investment planning, Power demands, Power supply, Power supply system, Power systems, Railway infrastructure, Tractive force, Traffic flow, Traffic forecasts, Voltage drop, Electric load forecasting, Electric power systems, Engines, Intelligent systems, Motor transportation, Railroad transportation, Railroads, Rails, Traffic surveys, Voltage control, Investments
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-36374 (URN)10.1109/ISAP.2009.5352887 (DOI)2-s2.0-76549104711 (Scopus ID)9781424450985 (ISBN)
Note
QC 20110712Available from: 2012-01-17 Created: 2011-07-12 Last updated: 2012-12-06Bibliographically approved

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Citation style
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  • ieee
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