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  • 1.
    Abrahamson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Fast calculation of the dimensioning factors of the railway power supply system2007In: Computational Methods and Experimental Measurements XIII, WIT Press, 2007, Vol. 46, 85-95 p.Conference paper (Refereed)
    Abstract [en]

    Because of environmental and economical reasons, in Sweden and the rest of Europe, both personal and goods transports on railway are increasing. Therefore great railway infrastructure investments are expected to come. An important part of this infrastructure is the railway power supply system. Exactly how much, when and where the traffic will increase is not known for sure. This means investment planning for an uncertain future. The more uncertain parameters, such as traffic density and weight of trains, and the further future considered, the greater the inevitable amount of cases that have to be considered. When doing simulations concerning a tremendous amount of cases, each part of the simulation model has to be computationally fast - in real life this means approximations. The two most important issues to estimate given a certain power system configuration, when planning for an electric traction system, are the energy consumption of the and and the train delays that a too weak system would cause. In this paper, some modeling suggestions of the energy consumption and the maximal train velocities are presented. Two linear, and one nonlinear model are presented and compared. The comparisons regard both computer speed and representability. The independent variables of these models are a selection of parameters describing the power system, i.e.: power system technology used on each section, and traffic intensity.

  • 2.
    Abrahamsson, Lars
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Railway Power Supply Models and Methods for Long-term Investment Analysis2008Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    The aim of the project is to suggest an investment planning programwhere the welfare of the society is to be maximized. In order to beable to decide on a wise investment plan, one needs to know theconsequences of different choices of power system configurations.Therefore the impacts of different future traffic demands are ofinterest for a railway power system owner.Since investments are supposed to last a long time, their futureusage has to be considered. Moreover, the lead times of investmentscan be of considerable duration lengths. Because of the uncertaintyof the future, deterministic case studies might not be suitable andthen a large number of outcomes are to be studied, probable outcomesas well as outcomes with a high level of impact.In order to be able to make a valid long-term investment analysis ofthe railway power supply system, one needs to use proper railwaypower supply models and methods. The aim of this thesis is topresent a stable modeling and methodological basis for the cominginvestment planning phase of this PhD research project. The focus isset on studying the consequences of a railway power supply systemwhich is too weak.The thesis contains an overview of models of some electrical andmechanical relations important for electric traction systems. Someof these models are further developed, and some are modified forimproved computational properties. A flexible electric tractionsystem simulator based on the above mentioned models has beendeveloped and the applied methods and resulting abilities arepresented.The main scientific contribution of this thesis is that a fast andapproximative neural network model, which calculates some importantaggregated results of the interaction between the railway powersystem and the train traffic, has been developed. This approximativemodel was developed in order to reduce computation times. Reductionof computation times is very important when a huge number ofoutcomes are studied. A complete simulation of a train power systemin operation takes a long time, often not less than about a tenth ofthe simulated traffic time. The neural network is trained with someselected aggregated results extracted from a wide set of railwayoperation simulation cases. The choices of network inputs andoutputs are motivated in the thesis. The performance of thesimulator as well as the approximator are visualized in casestudies.

  • 3.
    Abrahamsson, Lars
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Optimal Railroad Power Supply System Operation and Design: Detailed system studies, and aggregated investment models2012Doctoral 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.

  • 4.
    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 1755-4543Article 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.

  • 5.
    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 1755-4543, 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.

  • 6.
    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.

  • 7.
    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.

  • 8.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Fast Estimation of Relations Between Aggregated Train Power System Data and Traffic Performance2011In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 60, no 1, 16-29 p.Article in journal (Refereed)
    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.

  • 9.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Basic modeling for electric traction systems under uncertainty2006In: PROCEEDINGS OF THE 41ST INTERNATIONAL UNIVERSITIES POWER ENGINEERING CONFERENCE, VOLS 1 AND 2, NEW YORK: IEEE , 2006, 252-256 p.Conference paper (Refereed)
    Abstract [en]

    The objective of this paper is initially to present a basic modeling of the railway traction system. This model includes the basic technologies used today. The voltage dependencies of the maximal possible power consumption as well as the maximal velocity of the common Re-locomotives are included. The latter is very crucial for the studies of time table sensitivity, which is of our immediate interest. Moreover, a method is presented, that estimates the expected train delay time for a given feeding technology. The reference timetable assumes the same train and surrounding conditions, but no voltage drops. In the numerical example where the developed model is applied to a realistic test system, a set of possible amounts of railway traffic are treated as uncertainties. Mainly, the contributions of this paper are three: compiling and connecting already accepted models, the development of a method for numerical calculations using this model compilation, and an example to apply this model on.

  • 10.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Fast estimation of the relation between aggregated train power system information and the power and energy converted2009In: Australian Journal of Electrical and Electronic Engineering, ISSN 1448-837X, Vol. 6, no 3, 311-318 p.Article in journal (Refereed)
    Abstract [en]

    Transports on rail are increasing and major investments in the railway infrastructure, including the railway power supply system (RPSS), are expected. The future railway power demands are naturally not known for certain. The more remote the uncertain future, the greater the number of scenarios that have to be considered. Large numbers of scenarios make time-demanding simulations unattractive. The aim of this paper is to present a fast approximator that uses aggregated RPSS information. Since the electrical and mechanical relations governing an RPSS are quite intricate, an approximator based on neural networks (NN) is applied. This paper presents a design suggestion for an NN estimating the power and energy flows through each converter station, given RPSS data and levels of train traffic. Even if the future usage of the NN is investment planning, the modelling of such an approximator has a value in itself concerning the understanding of the relations between RPSS and train traffic.

  • 11.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Operation simulation of traction systems2008In: COMPUTERS IN RAILWAYS XI, 2008, Vol. 103, 283-292 p.Conference paper (Refereed)
    Abstract [en]

    The objective of this paper is initially to present a basic modeling of the railway traction system. This model includes the basic technologies used today. The voltage dependencies of the maximal possible power consumption as well as the maximal velocity of the common Rc-locomotives are included. The latter is very crucial for the studies of time table sensitivity, which is of our immediate interest. Moreover, a method is presented that estimates the expected train delay time for a given feeding technology. The reference timetable assumes the same train and surrounding conditions, but no voltage drops. In the numerical example where the developed model is applied to a realistic test system, a set of possible amounts of railway traffic are treated as uncertainties. Mainly, the contributions of this paper are three: compiling and connecting already accepted models, the development of a method for numerical calculations using this model compilation, and an example to apply this model on.

  • 12.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Fast calculation of some important dimensioning factors of the railway power supply system2007Conference paper (Refereed)
    Abstract [en]

    Because of environmental and economical reasons, in Sweden and the rest of Europe, both personal and goods transports on railway are increasing. Therefore great railway infrastructure investments are expected to come. An important part of this infrastructure is the railway power supply system. Exactly how much, when and where the traffic will increase is not known for sure. This means investment planning for an uncertain future. The more uncertain parameters, such as traffic density and weight of trains, and the further future considered, the greater the inevitable amount of cases that have to be considered. When doing simulations concerning a tremendous amount of cases, each part of the simulation model has to be computationally fast – in real life this means approximations. The two most important issues to estimate given a certain power system configuration, when planning for an electric traction system, are the energy consumption of the grid and the train delays that a too weak system would cause. In this paper, some modeling suggestions of the energy consumption and the maximal train velocities are presented. Two linear models, and one nonlinear model are presented and compared. The comparisons regard both computer speed and representability. The independent variables of these models are a selection of parameters describing the power system, i.e.: power system technology used on each section, and traffic intensity.

  • 13.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Traction Power System Capacity Limitations at Various Traffic Levels2011In: WCRR, World Congress on Railway Research, 2011Conference 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.

  • 14.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Fast estimation of the relation between aggregated train power system information and the power and energy converted2008In: 2008 Australasian Universities Power Engineering Conference, AUPEC 2008, IEEE conference proceedings, 2008, 1-6 p.Conference paper (Refereed)
    Abstract [en]

    Transports on rail are increasing and major investments in the railway infrastructure, including the Railway Power Supply System (RPSS), are expected. The future railway power demands are naturally not known for certain. The more remote the uncertain future, the greater the number of scenarios that have to be considered. Large numbers of scenarios make time demanding simulations unattractive. The aim of this paper is to present a fast approximator that uses aggregated RPSS information. Since the electrical and mechanical relations governing an RPSS are quite intricate, an approximator based on Neural Networks (NN), is applied. This paper presents a design suggestion for an NN estimating the power and energy flows through each converter station, given RPSS data and levels of train traffic. Even if the future usage of the NN is investment planning, the modeling of such an approximator has a value in itself concerning the understanding of the relations between RPSS and train traffic.

  • 15.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    Fast estimation of aggregated results of many load flow solutions in electric traction systems2008In: COMPUTERS IN RAILWAYS XI, WIT Press, 2008, Vol. 103, 411-423 p.Conference 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. This means investment planning for an uncertain future. The more remote the uncertain future, the greater the amount of scenarios that have to be considered. Large numbers of scenarios make time demanding (some tens of minutes, each) simulations less attractive and simplifications more so. The aim of this paper is to present a fast approximator that uses aggregated traction system information as inputs and outputs. This facilitates studies of many future railway power system loading scenarios, combined with different power system configurations, for investment planning analysis. Since the electrical and mechanical relations governing an electric traction system are quite intricate, an approximator based on neural networks (NN), is applied. This paper presents a design suggestion for a NN estimating power system caused limits on active and reactive power load, i.e., limits on the levels of train traffic.

  • 16.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Railway power supply investment decisions considering the voltage drops: Assuming the future traffic to be known2009In: 2009 15th International Conference on Intelligent System Applications to Power Systems, ISAP '09, 2009Conference 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.

  • 17.
    Abrahamsson, Lars
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    An SOS2-based moving trains,fixed nodes, railway power system simulator2012In: WIT Transactions on the Built Environment, WIT Press, 2012, 813-823 p.Conference 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.

  • 18.
    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.

  • 19.
    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, 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.

  • 20.
    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.

  • 21.
    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.

  • 22.
    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.

  • 23.
    Ackermann, Thomas
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Wind Power in Power Systems2005Book (Other academic)
    Abstract [en]

    As environmental concerns have focussed attention on the generation of electricity from clean and renewable sources, wind energy has become the world's fastest growing energy source. The authors draw on substantial practical experience to address the technical, economic and safety issues inherent in the exploitation of wind power in a competitive electricity market. Presenting the reader with all the relevant background information key to understanding the integration of wind power into the power systems, this leading edge text: Presents an international perspective on integrating a high penetration of wind power into the power system Offers broad coverage ranging from basic network interconnection issues to industry deregulation and future concepts for wind turbines and power systems Discusses wind turbine technology, industry standards and regulations along with power quality issues Considers future concepts to increase the penetration of wind power in power systems Presents models for simulating wind turbines in power systems Outlines current research activities Essential reading for power engineers, wind turbine designers, wind project development and wind energy consultants dealing with the integration of wind power systems into distribution and transmission networks, this text would also be of interest to network engineers working for power utility companies dealing with interconnection issues and graduate students and researchers in the field of wind power and power systems.

  • 24.
    Ackermann, Thomas
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Historical Development and Current Status of Wind Power2012In: Wind Power in Power Systems, Second Edition, John Wiley & Sons, 2012, 21-24 p.Chapter in book (Refereed)
    Abstract [en]

    The chapter provides an overview of the historical development (mechanical and electrical power generation) of wind power. It also present the current status of wind power world-wide (capacity installed) together with a discussion of the main drivers for the wind power development, e.g. feed-in tariffs, green certificates etc. Furthermore, the chapter briefly discuss the current trends in wind turbine technology, e.g. larger turbines, and projects development, e.g. offshore wind power.

  • 25.
    Ackermann, Thomas
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Distributed resources and re-regulated electricity markets2007In: Electric power systems research, ISSN 0378-7796, Vol. 77, no 9, 1148-1159 p.Article in journal (Refereed)
  • 26.
    Ackermann, Thomas
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Transmission Systems for Offshore Wind Farms2005In: Wind Power in Power Systems, John Wiley & Sons, 2005, 479-503 p.Chapter in book (Other academic)
  • 27.
    Ackermann, Thomas
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Historical Development and Current Status of Wind Power2005In: Wind Power in Power Systems, John Wiley & Sons, 2005, 1, 5-24 p.Chapter in book (Other academic)
  • 28.
    Ackermann, Thomas
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Andersson, Göran
    Söder, Lennart
    KTH, Superseded Departments.
    Electricity market regulations and their impact on distributed generation2000In: Electric Utility Deregulation and Restructuring and Power Technologies, 2000. Proceedings. DRPT 2000. International Conference on, 2000, 608-613 p.Conference paper (Refereed)
    Abstract [en]

    Distributed generation (DG) has attracted a lot of attention recently and might become more important in future power generation systems. As different definitions are used worldwide, the paper briefly discusses the definition of DG. The future development of DG, however, will, to a not insignificant part, depend on the legal framework. As the legal framework can vary significantly for different competitive electricity markets, this paper briefly identifies and analyses some variations in the regulatory approaches, e.g. for power exchanges, balance services and ancillary services, in different countries. It also illustrates the influence of market regulations on the development of distributed power generation. Based on this analysis, it can be concluded that regulatory aspects might decisively influence the development of distributed power generation

  • 29.
    Ackermann, Thomas
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Centeno-Lopez, Eva
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Grid Issues for Electricity Production Based on Renewable Energy Sources in Spain, Portugal, Germany, and United Kingdom2008Book (Other academic)
  • 30.
    Ackermann, Thomas
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Holttinen, H.
    Overview of Integration Studies - Methodologies and Results2012In: Wind Power in Power Systems, Second Edition, John Wiley & Sons, 2012, 2, 361-386 p.Chapter in book (Refereed)
  • 31.
    Ackermann, Thomas
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Energynautics GmbH, Germany; Technical University in Darmstadt (TUD), Germany.
    Morthorst, P. E.
    Economic Aspects of Wind Power in Power Systems2005In: Wind Power in Power Systems, John Wiley & Sons, 2005, 383-410 p.Chapter in book (Other academic)
  • 32.
    Ackermann, Thomas
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Orths, A.
    Rudion, K.
    Transmission Systems for Offshore Wind Power Plants and Operation Planning Strategies for Offshore Power Systems2012In: Wind Power in Power Systems, John Wiley & Sons, 2012, 2, 293-327 p.Chapter in book (Refereed)
    Abstract [en]

    The electric system within an offshore wind power plant and its connection to the main power system pose new challenges to the experts. The best way of interconnecting the wind turbines inside a wind farm has to be found, fulfilling both, redundancy requirements without compromising economic feasibility. The best choice between technologies (HVAC, HVDC - VSC or LCC) for connecting windfarms to shore has to be made, depending on several criteria. The risk of losing this connection versus redundancy has to be economically evaluated. By combining interconnectors and offshore windfarm connections in a modular way, a DC offshore grid can be developed. Anyhow, already during the planning phase the secure operation should be considered thoroughly, because the optimal architecture has to be found, minimizing the necessary assets ensuring secure operation and facilitating later expansion options. The interaction with the onshore grid has to be investigated as well. To enable investigations covering these issues a benchmark offshore test system has been developed which is described in this chapter.

  • 33.
    Ackermann, Thomas
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    The Value of Wind Power2012In: Wind Power in Power Systems, John Wiley & Sons, 2012, 2, 131-155 p.Chapter in book (Refereed)
    Abstract [en]

    The aim of the power plants in a power system is to supply the load in an economical, reliable and environmentally acceptable way. Different power plants can fulfil these requirements in different ways. In order to select the right sources it is important to compare the value of the different sources using an objective approach. The aim of this chapter is describe the different needs of a power system and how these needs can be met with wind power, that is, the value of wind power in a certain system. The values are operating cost value, capacity value, control value, grid loss reduction value and grid investment value. The values can be calculated for different types of power plants, they can be both positive and negative, and they can be calculated both as a physical cost value and a market value.

  • 34.
    Ackermann, Thomas
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Tröster, E.
    New Control Concept for Offshore Wind Power Plants: Constant-Speed Turbines on a Grid with Variable Frequency2012In: Wind Power in Power Systems, John Wiley & Sons, 2012, 2, 345-359 p.Chapter in book (Refereed)
    Abstract [en]

    By using a permanent magnet induction machine as wind generator, the gearbox and converter can be omitted, and the total number of parts reduced leading to a low maintenance and reliable turbine for offshore application. The rotation speed of the turbine however cannot be matched to the wind speed, reducing the energy yield at part load. To overcome this drawback, a central converter can be used, which adjusts the frequency of the local grid in the wind park; this is the so-called park-variable concept. This concept has been compared with respect to energy yield with constant speed and variable speed turbines. Overall, the differences in energy yield of the investigated concepts are so small that other criteria, such as reliability or cost, may be relevant for the selection of one or the other approach. Above all, the park-variable concept represents an interesting alternative to today's common concepts.

  • 35.
    Adib Murad, Ahsan
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Gómez, Francisco José
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Equation-Based Modeling of FACTS using Modelica2015Conference paper (Refereed)
    Abstract [en]

    This paper reports results of extending the iTesla Modelica Power System Library with the implementation of new Modelica models for power electronic-based FACTS (Flexible AC Transmission System) to be used in phasor time-domain simulations. To show the applicability of Modelica for modeling FACTS devices and power system simulation, a software-to-software validation is performed against the Power System Analysis Toolbox (PSAT), which is used as the reference software for validation. A quantitative and qualitative assessment of the validation results between PSAT and Modelica is given.

  • 36.
    Adib Murad, Ahsan
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Gómez, Francisco José
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Statnett SF, Oslo.
    Equation-Based Modeling of Three-Winding and Regulating Transformers using Modelica2015Conference paper (Refereed)
    Abstract [en]

    The simulation of power transformer models is important when analyzing the dynamic behavior of power systems, in particular, when considering voltage magnitude or phase regulation controls. This paper reports results of extending the library of transformers in the iTesla Modelica Power Systems Library. Three transformer models have been implemented: a three-winding transformer, an under-load tap changing transformer (ULTC) and a phase shifting transformer (PST). An IEEE 14-Bus, power system test model was also implemented, both in Modelica and PSAT, to assess the performance of the models. Software-to-software validation is carried out against PSAT, a quantitative and qualitative assessment of the validation results between PSAT and Modelica is given.

  • 37.
    Ahlberg, Jesper
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modelling of Ice Storms and their Impact on a part of the Swedish Transmission Network2006Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this master thesis a weather model to simulate an ice storm is developed. Precipitation, wind and movement are modelled by mathematical functions to create a realistic model.

    The weather model is used to calculate wind and ice loads on power lines. Two dierent models for the ice accretion on the power lines are used and compared. Data from two storms in Sweden in 1995 and 1999 are studied. In the simulations, the precipitation is assumed to fall as freezing rain instead of snow. The ice and wind loads are calculated in detail for two power lines in southern Sweden. The calculated loads are compared to what is assumed to be the critical loads for the poles, and the risks of power outages in connection with these storms are discussed.

  • 38.
    Ahmed, Noman
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Haider, Arif
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Van Hertem, Dirk
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Zhang, Lidong
    ABB Power Systems, Ludvika.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Prospects and challenges of future HVDC SuperGrids with modular multilevel converters2011In: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011) / [ed] EPE Association, 2011Conference paper (Refereed)
    Abstract [en]

    In order to transmit massive amounts of power generated by remotely located power plants, especially offshore wind farms, and to balance the intermittent nature of renewable energy sources, the need for a stronger high voltage transmission grid is anticipated. Due to limitations in AC power transmission the most likable choice for such a grid is a high voltage DC (HVDC) grid. However, the concept of the HVDC grid is still under active development as different technical challenges exist, and it is not yet possible to construct such a DC grid. This paper deals with prospects and technical challenges for the future HVDC SuperGrids. Different topologies for a SuperGrid and the possibility to use modular multilevel converters (M2Cs) are presented. A comprehensive overview of different sub-module implementations of M2C is given. An overview of short circuit behaviour of the M2C is also given, as well as a discussion on the choice between cables or overhead lines and DC-side resonance issues.

  • 39.
    Ahnlund, Joakim
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Short-circuit Contributions from Fully-rated Converter Wind Turbines: Modeling and simulation of steady-state short-circuit contributions from FRC wind turbines in offshore wind power plants2014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In recent years there has been an increase in wind power plants installed out at sea. The generated power of wind turbine generators (WTGs) are collected through numerous subsea cables into a single hub, the offshore platform. Subsequently, this platform is interconnected with the onshore main grid through a further stretch of cable. In the event of a fault, a sudden increase in current, so called short-circuit current, will occur somewhere in the system. The short-circuit current will, depending on the duration and location of the fault, potentially harm the power system. In order to accurately determine the dimensions and rating of the equipment installed in the offshore wind power plant (OWPP), the magnitude of this current needs to be studied. Furthermore, depending on the country in which the OWPP is installed, the transmission system operator (TSO) might pose different low-voltage-ride-through (LVRT) requirements on the system. One such requirement is that the installed turbines should provide voltage regulation through injection of reactive current. A type of generator able to achieve this is a so-called fully-rated converter windturbine generator (FRC WTG). Through a power electronic interface, the reactive and active current components of the generator can be freely controlled. With a high level of reactive current injected during a fault in the OWPP, the short-circuit contribution from these FRC WTGs needs to be evaluated. In this master’s thesis, a method has been developed in order to determine the steady-state short-circuit contribution from multiple FRC WTGs. This methodology is based on an iterative algorithm, and has been implemented in the simulation tool PowerFactory. To evaluate the performance of the method, two case studies were performed. In order to improve simulation times, an already existing WTG aggregation model has been implemented to reduce the number of turbines in the test system. From the results, it is concluded that the method obtains the expected FRC WTG short-circuit currents with sufficient accuracy. Furthermore, the deviation from the expected results are evaluated using a numerical tool. This project was initiated and conducted at ABB in Västerås, Sweden.

  • 40. Al-Hammouri, A.T.
    et al.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Chenine, Moustafa
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Honeth, Nicholas
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Leelaruji, Rujiroj
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Virtualization of synchronized phasor measurement units within real-time simulators for smart grid applications2012In: Power and Energy Society General Meeting, 2012 IEEE, IEEE , 2012, 6344949- p.Conference paper (Refereed)
    Abstract [en]

    Synchronized phasor measurement units (PMUs) provide GPS-time tagged high-sampling rate positive-sequence voltage and current phasors. When placed in high-voltage substations in power networks, PMUs can provide real-time information that is necessary for the development of Smart Transmission Grid software applications for improving power system monitoring, control and protection. The development of these applications, particularly for use within control centers for on-line purposes, is limited by the availability of and access to real-time PMU data and other information. One attractive approach for application development is the use of real-time simulators to which PMUs can be interfaced as hardware-in-the-loop (HIL) devices to harvest PMU data. However, this approach has technical and economical limitations, which can be tackled by the virtualization of PMU devices. This article describes the development of an entirely software-based synchronized phasor measurement unit for use within real-time simulators that will allow the emulation of a large number of real-life PMUs, which in turn can be used for creating new phasor-based applications.

  • 41. Ali, Muhammad
    et al.
    Matevosyan, Julija
    Milanovic, J. V.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Effect of wake consideration on estimated costs of wind energy curtailments2009In: 8th International Workshop on Large Scale Integration of Wind Power into Power Systems as well as on Transmission Networks of Offshore Wind Farms, 14-15 Oct. 2009 Bremen, 2009Conference paper (Refereed)
    Abstract [en]

    Measures such as energy curtailment or gridreinforcement are required to integrate the upcoming windgeneration in parts of the power system with existing transmissionbottlenecks. In order to choose between these two measurespotential wind energy curtailments and its costs need to becarefully evaluated. The paper analyzes the effect of wakeconsideration on the overall energy curtailment cost. For thispurpose detailed wake model was used taking into account partialand multiple shading of wind turbines. It is shown that not onlywind speed but also wind direction of the incoming wind affects theamount of energy produced by a wind farm. A comparison ofcurtailment cost with cost for grid reinforcement in areas withlimited transmission capacity was carried out with and withoutconsideration of wake effect. The effect on curtailment cost due toavailability of wind turbines is also investigated both with andwithout wake effect consideration. The results have proven thatwith consideration of wake effect and availability potential windenergy curtailments are reduced and hence curtailment costs arelowered, making curtailment a cheaper option than gridreinforcement. The method illustrated in the paper can be used inpre-feasibility study to compare the costs of wind curtailment withthe costs of grid reinforcement in order to make sound economicdecision. The method can also be applied in wind farm energy yield estimation.

  • 42.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Baudette, Maxime
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Løvlund, S
    Gjerde, J.O
    Synchrophasor Network, Laboratory and Software Applications Developed in the STRONg2rid Project2014In: PES General Meeting Conference & Exposition, 2014 IEEE, IEEE conference proceedings, 2014, 1-5 p.Conference paper (Refereed)
    Abstract [en]

    This paper presents the activities carried out in one of the work packages of the Nordic Energy Research funded project Smart Transmission Grid Operation and Control (STRONg2rid). The main objective of the work package is to deploy a state-of-the-art software and hardware for developing power system operation, protection, control and automation applications. Several PMUs have been deployed at partner universities and a network of synchrophasors has been set up. In addition the Smart Transmission System Laboratory (SmarTS-Lab) has been established. This laboratory serves as a test-bench to develop and verify smart transmission grid technologies. A software development kit (S3DK) was developed within the project. The S3DK has been used to implement PMU-based applications and deploy them in different targets, including smart phones and tablets. Several tools and software applications which utilize synchrophasor measurements (from the laboratory or the deployed university PMU network) to perform power system monitoring, sub-synchronous power oscillation detection, etc., have been developed and are presented herein.  

  • 43.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Kilter, Jako
    Tallinn University of Technology-Estonia.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Experiences with Steady-State PMU Compliance Testing using Standard Relay Testing Equipment2014In: Electric Power Quality and Supply Reliability Conference (PQ), 2014, IEEE conference proceedings, 2014, -110 p.Conference paper (Refereed)
    Abstract [en]

    This paper presents the results of steady state compliance testing of phasor measurement units (PMUs) from three different vendors in a laboratory environment. Testing is performed by providing three phase voltage and current injections to the VT and CT inputs of the PMUs through Freja-300 stand-alone protection relay test set. Testing is performed according to the standard “IEEE C37.242-2013 - IEEE Guide for Synchronization, Calibration, Testing, and Installation of Phasor Measurement Units (PMUs) for Power System Protection and Control”. The paper discusses the test setup, testing process and overall test results of this project. The limitations of stand-alone testing equipment and recommendations for utilizing real-time hardware-in-the-loop simulation for thorough testing of PMUs are also presented. 

  • 44.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Leelaruji, Rujiroj
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Over-current relay model implementation for real time simulation & Hardware-in-the-Loop (HIL) validation2012In: IECON 2012 - 38th Annual Conference on IEEE Industrial Electronics Society, Montreal, QC: IEEE conference proceedings, 2012, 4789-4896 p.Conference paper (Refereed)
    Abstract [en]

    Digital microprocessor based relays are currently being utilized for safe, reliable and efficient operation of power systems. The overcurrent protection relay is the most extensively used component to safeguard power systems from the detrimental effects of faults. Wrong settings in overcurrent relay parameters can lead to false tripping or even bypassing fault conditions which can lead to a catastrophe. Therefore it is important to validate the settings of power protection equipment and to confirm its performance when subject to different fault conditions. This paper presents the modeling of an overcurrent relay in SimPowerSystems (\textsc {matlab}/Simulink). The overcurrent relay has the features of instantaneous, time definite and inverse  definite minimum time (IDMT) characteristics. A power system is modeled in SimPowerSystems and this overcurrent relay model is incorporated in the test case. The overall model is then simulated in real-time using Opal-RT's eMEGAsim real-time simulator to analyze the relay's performance when subjected to faults and with different characteristic settings in the relay model. Finally Hardware-in-the-Loop validation of the model is done by using the overcurrent protection feature in Schweitzer Engineering Laboratories Relay SEL-487E. The event reports generated by the SEL relays during Hardware-in-the-Loop testing are compared with the results obtained from the standalone testing and software model to validate the model.

  • 45.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    PERFORMANCE EVALUATION OF PROTECTION FUNCTIONS FOr IEC 61850-9-2 PROCESS BUS USING REAL-TIME HARDWARE-IN-THE-loop simulation approach2013Conference paper (Refereed)
    Abstract [en]

    With the evolution of Process Bus (IEC 61850-9-2), there is a need to assess the performance of protection schemes using process bus against those where traditional copper wires are implemented. Differential protection is the fundamental and most commonly used protection for transformers, motors and generators. In this paper a power system is modelled in SimPowerSystems and is executed in real-time using Opal-RT’s eMEGAsim real-time simulator. Hardware-in-the loop validation of a process bus implementation for differential protection for a two winding transformer is done by using the differential protection feature in ABB’s RED-670 relay. The event reports generated by the ABB relay during Hardware-in-the-Loop testing are compared for three different scenarios i.e. complete process bus, hybrid process bus and complete traditional topology.   

  • 46.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Methodologies for Power Protection Relay Testing: From Conventional to Real-Time Hardware-in-the-Loop (HIL) Simulation Approaches2013In: 10th International Conference on Power System Transients, 2013Conference paper (Refereed)
    Abstract [en]

    Performance testing of the protection relays ensures that a particular protection scheme will operate reliably and fast enough to disconnect a faulty zone from the rest of the network, thus mitigating the effect of fault on the power system. It is therefore important to validate the settings of power protection equipment and to confirm its performance when subject to different fault conditions. Traditionally, commissioning engineers make use of standalone protection relay test sets for analyzing the performance of relays when subjected to different voltage and current injections. With the advent of digital simulators the model of the power system can be executed in real-time and protection relays can be interfaced as hardware-in-the-loop to evaluate their performance when subjected to different faults in the simulated power system. This gives an added value of analyzing the overall behavior of the power system coupled with the relay performance under faulty conditions. In addition, the utilization of GOOSE messages for status, control and protection purposes puts an extra requirement to completely test the IEC 61850 capabilities of the protection relays.

    This article illustrates two different techniques namely standalone testing and real-time hardware-in-the-loop testing used for protection relays performance verification. Both techniques are evaluated for hardwired and IEC 61850-8-1 (GOOSE) signals. The instantaneous overcurrent protection feature of Schweitzer Engineering Laboratories Relay SEL-421 is used for complete standalone and RT-HIL testing. For RT-HIL testing, the test case is modeled in MATLAB/Simulink and executed in real-time using Opal-RT's eMEGAsim real-time simulator. The event reports generated by standalone and RT-HIL testing for both hardwired and GOOSE signals is used to verify the tripping times achieved. Finally the performance of hardwired and GOOSE tripping times are compared and the overall standalone and RT-HIL techniques are evaluated.

  • 47.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Implementation of Conventional and Phasor Based Power System Stabilizing Controls for Real-Time Simulation2014In: Industrial Electronics Society, IECON 2014 - 40th Annual Conference of the IEEE, IEEE conference proceedings, 2014, 3770-3776 p.Conference paper (Refereed)
    Abstract [en]

    This paper presents the implementation of three different types of Power System Stabilizers (PSS) and a Static Var Compensator with a supplementary Phasor Power Oscillation Damper (POD) control for real-time simulation. The Klein-Rogers-Kundur model is used as test case and the PSS and Phasor-POD’s performance is evaluated for both large and small disturbances.  Modeling is performed in the MATLAB/Simulink environment and is executed in real-time using Opal-RT’s eMEGAsim Real-Time Simulator. The simulation results and the developed model will be used to deploy hardware prototype based on embedded controllers to provide power oscillation damping. Real-time software in the loop (SIL) approach is used for validating developed models as a first logical step towards development of a prototype hardware controller.

  • 48.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    Statnett SF, Oslo, Norway.
    Experimental Performance Assessment of a Generator's Excitation Control System using Real-Time Hardware-in-the-Loop Simulation2014In: Industrial Electronics Society, IECON 2014 - 40th Annual Conference of the IEEE, IEEE conference proceedings, 2014, 3756-3762 p.Conference paper (Refereed)
    Abstract [en]

    This paper presents methods and results for experimental performance assessment using Real-Time Hardware-in-the-Loop (RT-HIL) simulation of an Excitation Control System (ECS) for both terminal voltage regulation and power oscillation damping. The ECS configured for this study is Unitrol 1020 from ABB and its performance is assessed for both Automatic Voltage Regulator (Auto) and Field Current Regulator (Manual) modes. RT-HIL simulation is performed by using Opal-RT’s eMEGAsim RT Simulator using a power system model including a synchronous generator. Finally, the Power System Stabilizing feature of Unitrol 1020 is calibrated and assessed.  

  • 49.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Statnett, Oslo.
    RT-HIL Testing of an Excitation Control System for Oscillation Damping using External Stabilizing Signals2015Conference paper (Refereed)
    Abstract [en]

    A feature of an Excitation Control System (ECS) for synchronous generators is to enable power system stabilization by providing an additional input to the Automatic Voltage Regulator (AVR) for external stabilization signals. This paper explores this feature by externally generating stabilization signals which are fed as an analog input to a commercial ECS. This allows bypassing the built-in PSS function in the ECS and gives more freedom to the end-user to utilize custom stabilizer models. ABB’s Unitrol 1020 Excitation Control System is coupled with Opal-RT’s eMEGAsim Real-Time simulator to perform Hardware-in-the-Loop simulation of the ECS. The output of several stabilizer models is fed to the ABB’s Unitrol 1020 ECS as external power system stabilization signals to analyze their performance for small signal stability enhancement.  

  • 50.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Løvlund, Stig
    Gjerde, J.O
    Open Source SCADA Implementation and PMU Integration for Power System Monitoring and Control Applications2014In: PES General Meeting | Conference & Exposition, 2014 IEEE, IEEE conference proceedings, 2014, -5 p.Conference paper (Refereed)
    Abstract [en]

    This paper presents the implementation of an Open Source SCADA system in a laboratory and discusses methods for PMU data integration into SCADA. SCADA BR is a web-browser based SCADA that enables the user to access monitoring, control and automation equipment over multiple protocols. For implementation, protection relays from SEL are configured as DNP3 outstations to act as slaves and SCADA BR which is installed in one of the workstations in the laboratory acts as master. The evaluation of SCADA BR has been performed by executing a power system model in a real-time simulator and coupling its analog outputs with the protection relays. The integration of PMU measurements in the SCADA system and their use for monitoring is discussed. The limitations of the SCADA systems to fully utilize PMU data are also presented.

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