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Förslaget inkom 2011-07-01

Controlled HVDC feeder in railway power supply systems

OBS! ANSÖKNINGSTIDEN FÖR DETTA EXJOBB HAR LÖPT UT.
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A cooperation between the Department of Electric Power Systems; and the Department of Electrical Machines and Power Electronics

Controlled HVDC feeder in railway power supply systems

Aim:
The objective with this Master’s thesis work is to study the technical benefits of introducing HVDC (High Voltage Direct Current) transmission lines into the RPSS (Railway Power Supply System). Models for studying a typical Swedish RPSS are available at the department of Electric Power Systems, whereas models for the HVDC line – and most important, its power converters exist at the Department of Electrical Machines and Power Electronics. These models should be merged and used to study the performance of the RPSS for various loadings and with different control strategies of the HVDC converter stations.

Comparisons should be performed between a RPSS with HVDC feeder and one using existing RPSS technology. Comparisons should preferably be of mainly technical, but also of economical nature. The latter, because it is not only of interest showing that something is better, the price for an improvement is also an important issue – especially for a public good as the railway infrastructure.

Background:
Rail bound traffic driven by environmentally friendly electricity is a necessity for a global world with a fairly intact climate. In Sweden, but also in the rest of the world, great investments are done on the expansion of infrastructure for rail-bound traffic.
Moreover, today, with cheaper and more powerful semiconductors, controllable power converters become more available. With such equipment, it is possible to convert AC power to DC power, to a great extent of controllability of active and reactive power flows and AC voltages at the connection points between the DC line and adjacent AC lines. This makes DC transmission more attractive. Advantages with DC transmission are lower losses, and that the cables can be buried alongside the railway track. . Today, controllable power systems are often called Smart Grids because of their increased functionality. .

The PhD project “Future Feeding Systems for Railways” at KTH is about planning for future expansion of the railway power grid. Within this PhD project, a train power system simulator (TPSS) has been developed. The simulator is a Matlab program that for the solving of some equations calls upon GAMS (www.gams.com). In the Master Thesis project, “Direct generation of low frequency single phase AC for the Railway in Norway and Sweden”, a separate GAMS program was used for RPSS calculations. Depending of the details of the studies being made, either of them can be used, or something else, if the student comes up with good a suggestion.

The Master’s thesis student is through this work given an insight into how electrically driven railway systems work, in particular how to control power flows. The particular cased studies will be made for the low frequency (16.7 Hz) RPSS types of northern Europe (Sweden, Norway, Germany, Austria, Switzerland). In addition, the student will obtain experience in Matlab, and some understanding in how the GAMS-software works.

Examples of cases that could be studied:
• What happens if (all) the converters are set to mimic rotary converters, as is the case of today’s static converter stations?
• How redundant is the system if a main converter station falls out? Are there risks for overloading the distributed converter stations? If that happens, can that be avoided with a more sophisticated control of the distributed converter stations?
• How much energy is saved by controlling the converters such that losses are minimized?
• How much could traffic be increased without endangering set voltage level limits by actively controlling reactive power levels in asynchronous-motor-driven trains and in converter stations?
• Are the control strategies realistic? E.g.; is it possible to close to minimize losses in the RPSS by not knowing it all (as in the ideal case), but by just knowing, say, voltage levels and power flows at the converter stations?
• Are these improvements worth the price?
• Etc.

Location:
The Master’s thesis work will be carried out at KTH. There is also a possibility to be stationed at the Swedish Transport Administration in Borlänge or Sundbyberg if it shows up to be of relevance and interest.

Suitable background:
A suitable background is a Master of Engineering in Electrical Engineering or Engineering Physics, An interest in Matlab programming, railways and optimization is a plus

Literature:
If you have any explicit questions, contact us!

Examiner:
Stefan Östlund, KTH, stefan.ostlund@ee.kth.se

Make a contact:
Are you interested in this Master’s thesis work? Then, please contact Lars Abrahamsson, lars.abrahamsson@ee.kth.se, phone: +46 8-790 70 58 or cell phone +46 70 256 22 82.



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