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HVDC Feeder Solution for Electric Railways
KTH, School of Electrical Engineering (EES), Electric Power Systems.ORCID iD: 0000-0003-2109-060X
KTH, School of Electrical Engineering (EES), Electric Power Systems.
KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.ORCID iD: 0000-0001-7330-146X
2012 (English)In: IET Power Electronics, 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.

Place, publisher, year, edition, pages
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
URN: urn:nbn:se:kth:diva-101752OAI: diva2:549010

QS 2012

Available from: 2012-12-04 Created: 2012-09-03 Last updated: 2013-02-22Bibliographically approved
In thesis
1. Optimal Railroad Power Supply System Operation and Design: Detailed system studies, and aggregated investment models
Open this publication in new window or tab >>Optimal Railroad Power Supply System Operation and Design: Detailed system studies, and aggregated investment models
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.
Trita-EE, ISSN 1653-5146 ; 2012:062
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
urn:nbn:se:kth:diva-107037 (URN)978-91-7501-584-2 (ISBN)
Public defence
2012-12-17, sal Q2, Osquldasväg 10, KTH, Stockholm, 10:00 (English)

QC 20121206

Available from: 2012-12-06 Created: 2012-12-05 Last updated: 2013-02-25Bibliographically approved

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