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  • 401. Laverty, D. M.
    et al.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Al Khatib, Iyad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Applegreen, Viktor K.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Best, R. J.
    Morrow, D. J.
    The OpenPMU Project: Challenges and perspectives2013In: 2013 IEEE Power and Energy Society General Meeting (PES), IEEE , 2013Conference paper (Refereed)
    Abstract [en]

    The OpenPMU project is a platform for the development of Synchrophasor measurement technology, Phasor Measurement Units (PMU), in an open source manner. The project has now been operating for a number of years and has seen increased adoption at Universities and interest from electrical utilities. The OpenPMU device has recently been tested against the IEEE C37.118 standard and shown to operate within the specification. This paper discusses the OpenPMU project from the perspective of the past two years of experience and evaluates successes and opportunities for improvements in both the OpenPMU device and the philosophy of the design.

  • 402. Laverty, David M.
    et al.
    Best, Robert J.
    Brogan, Paul
    Al Khatib, Iyad
    KTH.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Morrow, D. John
    The OpenPMU Platform for Open-Source Phasor Measurements2013In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 62, no 4, p. 701-709Article in journal (Refereed)
    Abstract [en]

    OpenPMU is an open platform for the development of phasor measurement unit (PMU) technology. A need has been identified for an open-source alternative to commercial PMU devices tailored to the needs of the university researcher and for enabling the development of new synchrophasor instruments from this foundation. OpenPMU achieves this through open-source hardware design specifications and software source code, allowing duplicates of the OpenPMU to be fabricated under open-source licenses. This paper presents the OpenPMU device based on the Labview development environment. The device is performance tested according to the IEEE C37.118.1 standard. Compatibility with the IEEE C37.118.2 messaging format is achieved through middleware which is readily adaptable to other PMU projects or applications. Improvements have been made to the original design to increase its flexibility. A new modularized architecture for the OpenPMU is presented using an open messaging format which the authors propose is adopted as a platform for PMU research.

  • 403. Laverty, David M.
    et al.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Best, Robert J.
    Morrow, D. John
    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.
    OpenPMU technology platform for Synchrophasor research applications2012In: Power and Energy Society General Meeting, 2012 IEEE, IEEE conference proceedings, 2012, p. 6345398-Conference paper (Refereed)
    Abstract [en]

    OpenPMU, the Open Source Phasor Measurement Unit, is a platform for the development of Synchrophasor measurement technology in an open source manner. The OpenPMU design modularizes the key components of a Phasor Measurement Unit (PMU) into three subsystems; measurement, phase estimation and telecoms. The advantage to the researcher is that the interfaces between each subsystem are open and human readable, allowing for rapid integration of new work into an existing framework. This allows for new work to be prototyped rapidly and tested in an online environment.

    This paper introduces the OpenPMU technology platform. The subsystem modules and the methods of exchanging data are described. Present work on the platform is discussed and an open invitation to join the development process is extended to all.

  • 404.
    Lazaridis, Lazaros
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Economic Comparison of HVAC and HVDCSolutions for Large Offshore Wind Farms underSpecial Consideration of Reliability2005Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    An economic comparison of several HVAC-HVDC transmission systems from large offshore windfarms is presented. The power output from the offshore windfarm is modeled by an aggregated power curve. The transmission cost for several transmission systems is calculated for a wide range of windfarm�s rated powers, transmission distances and average wind speeds. Energy losses, energy availability and investment costs constitute the input parameters to the study. For the calculation of the energy availability an algorithm that takes in account the aggregated model of the windfarm and the probability distribution of the wind speed is introduced. The availability study is based on statistical data concerning the reliability of the components of HVAC-HVDC transmission systems.

  • 405.
    Leelaruji, Rujiroj
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Availability Assessment of HVDC Converter Transformers Using Markov Modeling2008Conference paper (Other academic)
  • 406.
    Leelaruji, Rujiroj
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Coordination of protection system and VSC-HVDC to mitigate cascading failures2010Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The rapid development of the global economics has made power systems allover the world become large-scale interconnected grids. This increases the capabilityof power grids to transfer power over the long distance to serve the desiredpower demand with the minimum cost of operation. Unfortunately, it alsoenables the propagation of local failures into global networks. In other words,if a blackout happens in a power system, the size and the damage may significantlyincrease.

    One of the main ways in which blackouts become widespread is cascadingfailures. This type of failure originates after a critical component of the systemhas been removed fromthe service by protective relaying. As a consequence, theload handled by the failed component needs to be redistributed which mightcause an overloading on other components in the system.

    On the other hand, the high power electronics controllable devices suchas Voltage Source Converters-based High Voltage Direct Current (VSC-HVDC)transmission are recently developed. These electronics devices have the potentialadvantages such as the ability to independently control active and reactivepower, and maintain voltage to be at acceptable level. Therefore, they are consideredto be the promising devices that with an appropriately designed controlstrategy, they can substantially improve the performance and reliability of thepower system.

    This thesis presents the possibility to consider protection system status inthe control of VSC-HVDC link. A great deal of this research is development ofcoordination between this power electronic device and protection system which normally are considered separately. The derivation of protection system has been selected to determine the operation of VSC-HVDC. The methodology isbased on utilizing the signal created from a logical evaluation of relay and simplificationsof certain parameters. By introducing information from the relays tothe VSC-HVDC link via Central Control Unit (CCU), the modulation of transmitted power is devised in order to reduce the risk of system-wide failures. In turn,this means an avoided blackout.Furthermore, this thesis also includes the preliminary suggestion to selectthe location of VSC-HVDC. The methodology is based on predicting voltage instabilityusing voltage stability indices and related parameterswhich are derivedby using Singular ValueDecomposition method. The solutions indicate an effectivelocation for applying corrective action such as load shedding. This optimallocation is selected to reinforce the control strategy of VSC-HVDC in order toprevent cascading failures in the more encompassing systems.

  • 407.
    Leelaruji, Rujiroj
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Methods for Synchrophasor-Based Power SystemInstability Detection and HVDC Control2012Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The recent availability Phasor Measurement Unit (PMU) functionalities in relay technology has opened up new opportunities for power system protection, allowing this microprocessor-based technology to be used beyond traditional protection purposes. This technology now also considers the computation and communication mechanisms that allow the transmission of synchronized phasor measurements. This makes possible the use of these features in protection applications. As a result, Wide-Area Monitoring, Protection and Control (WAMPAC) systems can expand by using protective relays built with synchrophasor capabilities which may facilitate many applications such as the synchronization distributed generation to large power grids or for the integration of renewable sources of energy.

    This thesis rationalizes the need of coordination between protective relays with synchrophasor capabilities and High Voltage Direct Current (HVDC) controls to steer power systems away from instability conditions. The concept of coordination involves the use of feasible communication mechanisms which can be exploited by protection systems to send out synchornized voltage and current phasors to a mechanism which determines preventive, corrective, and protective actions particularly by taking advantage of the availability of HVDCs. Coordination refers to the ability of the protective systems and HVDCs to cooperate and to harmonize their actions so that voltage instability can be avoided. Synchrophasor processing capabilities allow for the exploitation of phasor measurements while satisfying protective relaying requirements.

    The author addresses the challenge of mitigation of voltage instability through two sequential approaches. First, voltage sensitivities computed from synchrophasor data can be used for voltage stability monitoring and can be exploited for delivering wide-area early action signals. These signals can be used for activating controllable devices such as HVDCs which may also exploit phasor measurements for control. In order to provide reliable information, synchrophasor data must be pre-processed to extract only the useful features embedded in the measurements and to correct for errors. The methodology is derived by considering both positive-sequence simulations for methodology development purposes, and real phasor measurement data from a real-time (RT) hardware-in-the-loop (HIL) laboratory. The use of the RT-HIL laboratory allows to test the robustness of the developed approach in a more realistic environment, this will guarantee its performance for use in control rooms. The methodology has also been tested with real PMU data obtained from the Norwegian transmission system showing the validity and applicability of the method.

    The wide-area early action signals derived from the method are then used for voltage stability mitigation through HVDC control. The signals are used to trigger the operation of HVDCs or to change their control modes before they reach stringent operating conditions. In addition, synchrophasors are also exploited as feedback signals feeding supplementary stability controls. The proper selection of signals and activation of these special HVDC control is investigated.

    The second approach is used to ensure that HVDCs will operate securely when their transfer is pushed towards the maximum transferable power level. It is shown that Classical HVDCs are prone to voltage instability when operating on weak AC grids. To cope with this delicate operation scenarios, the Automatic Voltage Stabilizer (AVS) and Automatic Power Order Reduction (APOR) controls are implemented for HVDC control to cope with these undesired conditions. The implementation is carried out both in off-line and real-time simulation environments.

  • 408.
    Leelaruji, Rujiroj
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Knazkins, Valerijs
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modeling Adequacy for Cascading Failure Analysis2008Conference paper (Refereed)
    Abstract [en]

    This paper describes the mechanisms of cascading failure as the cause of severe blackouts. The severe blackouts that occurred in 2003 affecting large metropolitan areas around the globe are first reviewed. Then the probable root cause of each blackout events is identified in order to seek effective corrective preventive solutions. Several of the well-known techniques for cascading failure analysis and correction are discussed and characterized based on their fundamental features. Thereupon a new model power system component is proposed for simulating cascading failure in actual networks.

  • 409.
    Leelaruji, Rujiroj
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Knazkins, Valerijs
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    The use of voltage stability indices and proposed instability prediction to coordinate with protection systems2009In: World Academy of Science, Engineering and Technology 53 2009, 2009Conference paper (Other academic)
    Abstract [en]

    This paper proposes a methodology for mitigating the occurrence of cascading failure in stressed power systems. The methodology is essentially based on predicting voltage instability in the power system using a voltage stability index and then devising a corrective action in order to increase the voltage stability margin. The paper starts with a brief desccription of the cascading failure mechanism which is probable root cause of severe blackouts. Then, the voltage instability indices are introduced in order to evaluate stability limit. The aim of the analysis is to assure that the coordination of protection, by adopting load shedding scheme, capable of enhancing performance of the system after the major location of instability is determined. Finally, the proposed method to generate instability prediction is introduced.

  • 410.
    Leelaruji, Rujiroj
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Setréus, Johan
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Olguin, Gabriel
    Bertling, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Availability Assessment of the HVDC Converter Transformer System2008In: Proceedings of the 10th International Conference on Probabilistic Methods Applied to Power Systems, PMAPS 2008, New York: IEEE , 2008, p. 575-582Conference paper (Refereed)
    Abstract [en]

    This paper presents a reliability assessment of the HVDC converter transformer system (CTS) comparing different component models and configurations. The CTS model is based on the Markov modelling approach, which is shown to be well suited for these relatively small systems. The failure rate data in the models is based on statistical surveys by CIGRE. A number of scenarios are calculated in order to evaluate the impact of the availability of the CTS given different conditions. The result shows on the benefit in availability using a spare transformer, particularly at a close location of the HVDC station.

  • 411.
    Leelaruji, Rujiroj
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    A Synopsis on Synchrophasor Standards and Guides: Measurements, Data Transfer, Concentration, Testing and Implementation RequirementsArticle, review/survey (Refereed)
    Abstract [en]

    In 2009 the US Department of Energy announced the award of $3.4 Billion under the Smart Grid Investment Grant Program. As a result, many operators in North America were awarded grants to deploy a great number PMUs across their service area, with its related communications and IT infrastructure. Outside North America the deployment of new PMUs and related infrastructure also continues to increase.The availability of this new infrastructure will enable the development and implementation of new applications that utilize time-synchronized dynamic measurements. The recently developed synchrophasor standards PC37.118.1 and PC37.118.2, and guides PC37.242, and PC37.244, are relevant for the development of synchrophasor applications by providing a framework to support interoperability and reliability.This section provides a synopsis of the recently developed standards on synchrophasor measurement requirements and data transfer, as well as guides for requirements on phasor data concentration, and synchronization, calibration, testing, and installation of PMUs.

  • 412.
    Leelaruji, Rujiroj
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    "All-in-one" test system modelling and simulation for multiple instability scenarios2011Report (Other academic)
  • 413.
    Leelaruji, Rujiroj
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Detailed modelling, implementation and simulation of an "all-in-one" stability test system including power system protective devices2012In: Simulation (San Diego, Calif.), ISSN 1569-190X, E-ISSN 1878-1462, Vol. 23, p. 36-59Article in journal (Refereed)
    Abstract [en]

    This paper presents modelling and simulation results for multiple instability scenarios of the "all-in-one" test system. The test system is an alteration of the Bonneville Power Administration test system constructed to capture transient (angle), frequency and voltage instability phenomena, resulting in system collapse, within one system. The paper describes general overview of the test system and its associated individual devices modelling. These modelling are both customized and adapted from the built-in model developed by PowerFactory simulation software. The paper also provides a description of different instabilities that can be reproduced by this self-contained system. One of the case study is demonstrated in detail with the necessary initialization settings for reproducing instability scenario.

  • 414.
    Leelaruji, Rujiroj
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Power System Protective Relaying: basic concepts, industrial-grade devices, and communication mechanisms2011Report (Other academic)
  • 415.
    Leelaruji, Rujiroj
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Power System Protective Relaying: basic concepts, industrial-grade devices, and communication mechanisms2012In: Standard Handbook for Electrical Engineers / [ed] W. Beaty, McGraw-Hill, 2012, 16Chapter in book (Other academic)
    Abstract [en]

    This chapter provides a survey of protective relaying technology and its associated communications technology used in today’s power transmission systems. A review and comparison between different vendors of protective relays is provided to highlight the industrial state-of-the art implementation of protective functions currently available. The bulk of this chapter is concerned mainly with power system relaying communication. The various protocols and network topologies used for protective relaying purposes are explained. Associated communication standards are outlined. The aim of this part is to provide an introduction and sufficient background on the communication technologies used by protection systems.

  • 416.
    Leelaruji, Rujiroj
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    State-of-the-art in the industrial implementation of protective relay functions, communication mechanism and synchronized phasor capabilities for electric power systems protection2012In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 16, no 7, p. 4385-4395Article, review/survey (Refereed)
    Abstract [en]

    Protective systems in electricity delivery networks have a major role to play in the increasing of renewable energy systems, and a broad understanding of their current a future application can aid into better taking them into account for achieving future energy networks that adapt for the incorporation of renewable energy generation sources. This paper provides a survey in the state of the art of protective relaying technology and its associated communications technology used in todays power transmission systems. The paper also provides the fundamental knowledge concerned with power system relaying communications. The unifying theme of this paper is to highlight that the future potential of these devices lies in realizing the possibility of going beyond their traditional application as stand-alone equipments with the single role of acting the last line of defense so that they can be handled with the increment of renewable energy power delivery systems in near future.

  • 417.
    Leelaruji, Rujiroj
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Utilizing synchrophasor-based protection systems with VSC-HVDC controls to mitigate voltage instability2012In: 2012 IEEE International Conference on Power System Technology (POWERCON), New York: IEEE , 2012Conference paper (Refereed)
    Abstract [en]

    This article rationalizes the need of coordination between protective systems and VSC-HVDC controls to steer power systems away from voltage instability conditions. The concept of coordination involves the use of feasible communication mechanisms which can be exploited by protection systems to send out a 'protective information set' to an algorithm which will determine preventive, corrective, and protective actions particularly by taking advantage of the availability of VSC-HVDC. This 'protective information set' considers synchrophasor vector processing capabilities which allows for the exploitation of phasor measurements while satisfying protective relaying data transmission and processing requirements. Coordination refers to the ability of the protective systems and VSC-HVDCs to cooperate and to synchronize their actions so that voltage instability can be avoided.

  • 418.
    Leelaruji, Rujiroj
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Almas, Muhammad Shoaib
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Voltage Stability Monitoring using Sensitivities Computed from Synchronized Phasor Measurement Data2012In: Power and Energy Society General Meeting, 2012 IEEE, IEEE , 2012, p. 6344838-Conference paper (Refereed)
    Abstract [en]

    Wide-area early warning systems are dependent on synchrophasor data-based applications for providing timely information to operators so that preventive actions can be taken. This article proposes the use of voltage sensitivities computed from syncrhophasor data for voltage stability monitoring, and a visualization approach that can be implemented in wide-area early warning systems. In order to provide reliable information, synchrophasor data must be pre-processed to extract only the useful features embedded in measurements and correct for errors. Hence, this article also addresses the issue of data filtering and correction, and proposes a filtering methodology for robust voltage sensitivity computation. The methodology is developed considering both positive-sequence simulations for methodology development purposes, and real phasor measurement data from a real-time (RT) hardware-in-the-loop (HIL) laboratory for testing the robustness of the developed approach for use in the control room. The results from both approaches are contrasted against each other, the limitations of the positive-sequence simulation ap- proach for developing PMU-data applications are highlighted and the challenges of working with the RT HIL lab are recognized. 

  • 419.
    Leelaruji, Rujiroj
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Coordination of protection and VSC-HVDC systems for mitigating cascading failures2010In: 2010 International Conference on Power System Technology: Technological Innovations Making Power Grid Smarter, POWERCON2010, VDE Verlag GmbH, 2010, p. 5666604-Conference paper (Refereed)
    Abstract [en]

    This paper proposes a methodology to coordinate protection relays with a VSC-HVDC link for mitigating the occurrence of cascading failures in stressed power systems. The methodology uses a signal created from an evaluation of the relay's status and simplifications of certain system parameters. This signal is sent to a Central Control Unit (CCU) which determines corrective action in order to reduce the risk of cascading failures.

  • 420.
    Leelaruji, Rujiroj
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Gjerde, J. O.
    Lovlund, S.
    PMU-based voltage instability detection through linear regression2013In: 2013 IEEE PES Asia-Pacific Power and Energy Engineering Conference (APPEEC), IEEE Computer Society, 2013, p. 6837108-Conference paper (Refereed)
    Abstract [en]

    This paper proposes a linear regression method using synchrophasor measurement for voltage stability monitoring. The method preprocesses synchrophasor measurements in order to eliminate inconsistencies and errors that embedded in them. This data is then used in the computation of sensitivities suitable for voltage stability monitoring. Some important electrical components such as Over Excitation limiter and OnLoad Tap Changer which create discrete changes affecting in voltage instability have been included to assess the method's performance. Moreover, both process and measurement noises, obtained from real-time hardware-in-the-loop simulation and real PMU measurements from the Norwegian network, respectively, have been applied to validate robustness of the proposed methodology.

  • 421.
    Leelaruji, Rujiroj
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Uhlen, Kjetil
    Gjerde, Jan Ove
    Computing Sensitivities from Synchrophasor Data for Voltage Stability Monitoring and Visualization2015In: International Transactions on Electrical Energy Systems, E-ISSN 2050-7038, Vol. 6, p. 933-947Article in journal (Refereed)
    Abstract [en]

    Wide-area early warning systems are dependent on synchrophasor data-based applications for providing timely information to operators so that preventive actions can be taken. This article proposes the use of voltage sensitivities computed from synchrophasor data for voltage stability monitoring, and a visualization approach that can be implemented in widearea early warning systems. In order to provide reliable information, this article addresses the issue of data filtering and correction, and proposes a filtering methodology for robust voltage sensitivity computation. The methodology is developed considering both positive-sequence simulations for methodology development purposes, and real phasor measurement data from a real-time (RT) hardware-in-the-loop (HIL) laboratory for testing the robustness of the developed approach under more realistic conditions. The limitations of the positive-sequence simulation approach for developing PMU-data applications are highlighted, and the challenges of working with the RT HIL lab are recognized. The proposed sensitivity computation approach have also been applied to a real PMU-data obtained from the Nordic transmission system where results are sustained.

  • 422.
    Li, Jialin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modal Analysis of Power Systems with Doubly Fed Induction Generators2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    To ensure the reliable operation of the power system, stability analysis considering the interaction between wind power and power system must be understood. In this thesis, the impact of wind power on the stability of Nordic32A power system is of interest.

    Many wind farms nowadays employ doubly fed induction generator (DFIG) variable speed wind turbines. In this thesis, a third order DFIG model and its control circuits are employed. The particle swarm optimization algorithm is developed to tune the power system stabilizer, which can greatly increase the computational efficiency and improve the damping of the power system.

    Modal analysis is conducted to investigate the behavior of a wind power plant in a conventional power system. The interaction between generators is investigated when we add wind power plants in different locations. In some cases, some unstable oscillation modes may be observed due to the inter-area and local oscillations among different synchronous generator groups in the system.

  • 423.
    Li, Wei
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    A PMU-based state estimator considering classic HVDC links under different control modes2015In: Sustainable Energy, Grids and Networks, ISSN 2352-4677, Vol. 2, p. 69-82Article in journal (Refereed)
    Abstract [en]

    This paper aims to develop a PMU-based state estimation algorithm that considers the presence of classic HVDC links operating under different control modes. Thus, hybrid AC/DC grid state estimation becomes feasible. In this algorithm we assume that DC link measurements can be sampled and reported at the same rate as PMU measurements, so that both AC and DC states can be estimated simultaneously in real-time. The estimation algorithm uses synchrophasors in polar coordinates, which allows angle bias detection and correction. In addition, some practical issues for the proposed state estimator are discussed, including observability and measurement redundancy, measurement noise and weightings, and angle bias correction. Finally, study cases using different power system models are carried out to show the state estimator’s performances during both steady conditions and dynamic changes. Relatively small residuals during steady conditions validate accuracy; results during dynamic changes verify the estimator’s reliability.

  • 424.
    Li, Wei
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Statnett SF, Research and Development, Oslo, Norway.
    A PMU-Based State Estimator For Networks Containing VSC-HVDC links2015In: 2015 IEEE POWER & ENERGY SOCIETY GENERAL MEETING, IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    This paper presents a PMU-based state estimation algorithm that considers the presence of voltage source converter-based high voltage direct current (VSC-HVDC) links. The network model of a VSC-HVDC link with its control modes is developed and then combined with an AC model to accomplish a hybrid AC/DC network model. The measurement model in this algorithm considers the properties of PMU measurements, thus separating the network model with measurements. Additionally, DC link measurements are assumed to be sampled synchronously, time-stamped and reported at the same rate as PMU measurements. Then, by applying the nonlinear weighted least squares (WLS) algorithm, a PMU-based state estimator can solve for both AC and DC states simultaneously. To validate the algorithm, a simulation study for a 6-bus hybrid AC/DC test system is shown in this paper.

  • 425.
    Li, Wei
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Inclusion of Classic HVDC links in a PMU-based state estimator2014In: PES General Meeting | Conference & Exposition, 2014 IEEE, IEEE conference proceedings, 2014, p. 1-5Conference paper (Refereed)
    Abstract [en]

    This article presents a PMU-based state estimator algorithm that considers the presence of classic HVDC links. A hybrid AC/DC network model is developed to combine the AC network and DC links. The algorithm assumes that DC link measurements can be sampled synchronously, are time-stamped and reported at the same rate as PMU measurements. Then, by applying the weighted least squares algorithm, a linear state estimator can solve for both AC and DC states simultaneously. To validate the algorithm, a state estimation model is built for a 9-bus and the KTH-Nordic 32 systems, for both AC-only and hybrid AC/DC networks. In addition, the influence of losing DC measurements and effects of measurement noise on the state estimator are briefly discussed.

  • 426.
    Li, Wei
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Chompoobutrgool, Yuwa
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Development and implementation of hydro turbine and governor models in a free and open source software package2012In: Simulation (San Diego, Calif.), ISSN 1569-190X, E-ISSN 1878-1462, Vol. 24, p. 84-102Article in journal (Refereed)
    Abstract [en]

    This article studies accurate and detailed hydro turbine and governor models, and implements these models in Power System Analysis Toolbox (PSAT)-a free and open source software. The implementation of these models in PSAT is approached using a general methodology, which is described in detail. To evaluate the performances of the developed hydro turbine and governor models, simulation studies are carried out on test systems of different scales, from a single-machine infinite-bus (SMIB) system to a larger system which includes 20 generators. Further more, transient stability analysis and small signal stability analysis are carried out to assess the performance of the implemented models.

  • 427.
    Li, Wei
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Farrokhabadi, Mostafa
    Modeling of Custom Hydro Turbine and Governor Models for Real-Time Simulation2012In: 2012 IEEE COMPENG 2012: Workshop on Complexity in Engineering, IEEE conference proceedings, 2012, p. 83-88Conference paper (Refereed)
    Abstract [en]

    This article develops three different hydro turbineand governor (HTG) models to fulfill adequate modeling requirements for the representation of hydro power generation inthe Nordic grid. To validate the performance of the developed models, both off-line and real-time simulation studies on a single machine infinite-bus (SMIB) system are carried out. Apart from SMIB system, real-time simulations are also executed for alarger scale power system—the IEEE Reliability Test System1996 (IEEE RTS 96) in this article to determine the models’dynamic performance in larger and more complex networks. Inaddition, how to properly transfer an off-line models developedin SimPowerSystems (SPS) for real-time simulation in RT-LAB is addressed; including valuable experiences obtained from these simulation exercises.

  • 428.
    Li, Ying
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modelling of the Flexibility of the Swedish Power System2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis studies the flexibility of Swedish power system. Because of the increase of

    fuel price and the environmental issues, renewable energy plays an increasingly important

    role. Sweden parliament has a planning frame of 30 TWh wind power energy per year in

    2020. Wind power generation is largely dependent of wind speed. Since wind speed varies

    all the time and is hard to be predicted, the introduction of wind power will cause variation

    of power generation which needs to be balanced. Therefore, it is very important to study the

    regulation capacity of the power system in order to balance wind power. In Sweden, it is

    hydropower and thermal power that plays the role as balancing power. In earlier studies at

    Department of Electric Power Systems KTH, a model has been built to examine the flexibility

    of Swedish hydropower system. The aim of this thesis is to further develop this original

    model. In the improved model, the flexibility of thermal power in Sweden is included.

    Moreover, the improved model further considers the future value of stored water and the

    impact of delayed running water released from the upstream power plants at the end of

    simulated week.

    The whole model is a large short-time planning problem and the objective of this model is to

    maximize the profits. In this thesis, the profit is expressed as the future value of hydropower

    minus the generation cost of thermal unit. Besides, the profit also includes the income and

    the cost for the trading energy. The improved model is built as an optimization problem in

    GAMS. The time step is one hour and the time span of each simulation is one week. The load

    consumption and wind power production in each area are given as time series. The

    constraints considered in this model include the generation limitations, operational

    constraints of thermal power plants, hydrological coupling of hydropower plants, load

    balance in each bidding area and transmission capacity. Several case studies are performed

    in this thesis. Two models, both original model and improved model, will be tested. To find

    out how large the regulation capacity the Swedish power system has, four different

    expansion levels of wind power: 0 MW, 4000 MW, 8000 MW and 12000 MW are introduced.

    The information regarding hydropower is obtained from statistic data in 2009 and the wind

    power data for each week is coming from scaling the data in earlier studies. The operational

    constraints of thermal power plants are based on the statistics data from 2008 to 2012. The

    main finding from these case studies is that spillage will not increase when more wind power

    is introduced to the system but only increase when the export capacity is reached and the

    surplus power cannot be exported to other countries. Therefore, it can be concluded that

    the Swedish power system has good possibilities to balance large amounts of wind power.

    However, some simplifications and assumptions are made when the model is built, which

    will give rise to some inaccuracy to the result. Therefore, in the end of this thesis, some

    future studies are suggested to further improve this model.

  • 429. Liljegren, C.
    et al.
    Ackermann, Thomas
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Wind Power on the Swedish Island of Gotland2005In: Wind Power in Power Systems, John Wiley & Sons, 2005, p. 283-297Chapter in book (Other academic)
  • 430.
    Lilliecrona, Johan
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    The impact of grid connnection of large-scale wind farms on the transmission grid in the south of Sweden2005Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this report, the static and dynamic impact on the transmission grid in the south of Sweden has been studied when connecting two large wind farms. The two wind farms are Lillgrund, 150 MW, and Krieger’s Flak, 640 MW. The study has been performed using the software Power System Simulator for Engineers, PSS/E. The static study shows no problem with voltage level or losses. However, during low load situations, the 135 kV lines between Trelleborg and Sege risk becoming overloaded. This problem must be addressed before both wind farms are allowed to be connected to the system.Dynamically, the implementation of a dynamic model for Baltic Cable is vital for the study. The cable has dynamic effects, like commutation failure in the converter station in Kruseberg, that need to be modelled. The simulations show a need to install an SVC if wind turbines equipped with ordinary fixed speed induction generators are used. Simulations with General Electric’s dynamic model for its 3.6 MW wind turbine show that there is no need to install an SVC in order for the voltage to re-establish. However, no comparison with actual data has been made so the correctness of the model can not be checked. The simulations also show a low impact on the system when disconnecting both wind farms simultaneously. Finally, no problems with rotor angle stability have been found.

  • 431. Lin, J.
    et al.
    Hesamzadeh, Mohammad Reza
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Galland, O.
    Application of null space method in computing electricity prices with voltage-stability constraints2014In: 2014 North American Power Symposium, NAPS 2014, 2014Conference paper (Refereed)
    Abstract [en]

    Nodal pricing is used in electricity markets around the world to facilitate the electricity trading among market participants. The nodal prices are computed by finding the shadow prices of the energy balance and branch constraints in the optimization problem at each node for each market period. The conventional approach to compute the nodal prices is by formulating a security-constrained economic dispatch using DC power flow equations, which ignore the voltage constraints. However, voltage-demand dependence at each electrical node is well studied in the area of voltage stability. In this paper, we first model the voltage constraints using the null space methodology. Then, we derive the voltage-price relationship at each node by deriving two different curves - voltage-demand curve, and price-demand curve - for each node of the system. This information on voltage-price relationship can be useful for better understanding of the economics of voltage support and also for pricing voltage regulation as a novel ancillary service.

  • 432.
    Lindgren, Elin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Minimizing Regulation Costs in Multi-Area Systems with Uncertain Wind Power Forecasts2006Conference paper (Refereed)
  • 433.
    Lindgren, Elin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Minimizing regulation costs in multi-area systems with uncertain wind power forecasts2008In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 11, no 1, p. 97-108Article in journal (Refereed)
    Abstract [en]

    In a power system where there are many fast and/or large changes in generation or consumption, e.g. in a system with large amounts of wind power, it is more complicated to handle the frequency control efficiently. Minimizing regulation costs for the system operator in such a system requires the possibility to simulate the frequency control in the time range from minutes to a few hours. In this paper, it is shown how the frequency control during normal operation can be optimized using a multi-area model, without exceeding frequency limits or transmission capacity. The model has also been expanded to include uncertainties in wind power forecasts, which may lead to an increase of the regulating costs. The optimization model is applied to numerical examples to show the impact of wind power on costs for regulating power and to show the value of better wind speed forecasts. No load forecast errors are taken into account.

  • 434.
    Lindgren, Elin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Power system modeling for multi-area regulating market simulation2005In: 2005 IEEE Russia Power Tech, PowerTech, St. Petersburg, 2005Conference paper (Refereed)
    Abstract [en]

    In a power system with many fast and/or large changes in the generation or the consumption, for example in a system with large amounts of wind power, the frequency control is more complicated to handle efficiently. Minimizing regulation costs for the system operator in such a system requires the possibility to simulate the frequency control, but the existing methods for calculations are neither efficient enough with respect to computation time nor accurate enough. This paper shows how the frequency control can be optimized, thereby reducing the regulation costs, using a multi-area model combined with a DC load flow. The multi-area modeling is described and the optimization is applied to a numerical example.

  • 435.
    Lindgren, Elin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Wind Power Impact on Costs for Regulating Power in Multi-Area Markets2005In: Fifth International Workshop on Large-Scale Integration of Wind Power and Transmission Networks for Offshore Wind Farms, Glasgow, Scotland, 2005Conference paper (Refereed)
  • 436.
    Linnanheimo, Krister
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Analys av elkvalitetsproblemlokalt nät Forsbacka2008Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [sv]

    I Forsbacka har det uppstått klagomål angående elkvalitén. Elkvalitetsproblemet är aven typ som kallas flicker eller flimmer på svenska. Ljusutbytet från glödlampor ärspeciellt känsliga för vissa spänningsvariationer som får ljuset att uppfattas somflimrande. Ett sådant ljus kan vara mycket störande och påverkakoncentrationsförmågan hos människor som vistas i ljuset och kan även undermedvetetpåverka individer som inte är medvetna om problemet.Forsbacka är ett mindre samhälle med ca 1800 inv. och har en elintensiv stålindustri.Tidigare mätningar visar på stort flicker i området och tyder på att störningarna kankomma från subtransmissionsnätet som Forsbacka är inkopplat till. I Stackbo söder omGävle är subtransmissionsnätet till Forsbacka inkopplat till det nationella stamnätet.Transmissionsledningen mellan Stackbo och Forsbacka är kort ca 5 km. Om störningenskapas på subtransmissionsnätet nedströms om Forsbacka och redan är stor i Forsbackahur stor är då störningen längre ut på transmissionsnätet? Skulle då inte problemenlängre ut på transmissionsnätet vara så stora att de vore åtgärdade pga. klagomål?Nedströms om Forsbacka på subtransmissionsnätet finns kända flickerkällor somljusbågsugnar. Den mest vedertagna standarden för flickermätning ger ett mått påstörningen i en mätpunkt men erbjuder ingen möjlighet att mäta i riktning tillflickerkällor eller hur mycket flicker en källa producerar. Det utgör ett hinder för attpeka ut vilka förbrukare som försämrar elkvalitén på nätet och framförallt hur mycket.Uppstår flickret lokalt i Forsbacka eller levereras flickret till Forsbacka från detovanförliggande subtransmissionsnätet? Om flickret inte genereras i Forsbacka kan detdå finnas någon lösning för att dämpa problemet till rimliga nivåer lokalt i Forsbacka?Levereras problemet till Forsbacka via subtransmissionsnätet så att det enda rimligaalternativet för förbättrad elkvalitet i Forsbacka är att begära bättre elkvalitet påsubtransmissionsnätet som förser Forsbacka med el?För undersöka de olika frågeställningarna analyseras flickret i Forsbacka teoretiskt medmodeller av elsystemet kring Forsbacka.Under examensarbetets gång har det framkommit att problemet med flicker är starktkopplat till glödlampor och ljusutbytet från dessa. Genom att välja alternativa ljuskällorsom energilampor eller lysrör kan problemet kraftigt minskas.Det har också framkommit att problemet troligen inte skapas i Forsbacka samt att desstekniska karaktär är så svår att det inte finns någon lösning till rimlig kostnad för attdämpa problemet endast lokalt i Forsbacka.Med en ny storhet som kallas Flicker Power som Peter Axelberg beskriver i sinavhandling [1] kan dock riktningen till en flickerkälla mätas samt dess bidrag till flickerpå nätet. Med sådana mätningar skulle kanske i framtiden krav kunna ställas påförbrukare som genererar flicker, så att det dämpas redan vid källan.

  • 437.
    Lundgren, Andreas
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hjälpkraftsystem med två lågspänningsnivåer2008Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Because of increasing demand of power on Malmbanan the capacity of the existing wires which supply the trains must be increased. This increases the stress on the existing poles and for this reason the system for supplying the loads along the railway is to be removed from the poles and be replaced by some other system. This thesis is a study on a two-level low voltage (1 kV and 0.4 kV) electrical system with the aim to investigate if it can be an alternative to the system used today taking into account the voltages, fault currents and costs.

    In this thesis the following tasks have been performed:

    � Gathering of data

    � Description of basic theory

    � Loadow and fault current calculations of the system with MATLAB

    � Life Cycle Cost estimate of the system

    � Analysis and conclusions from the results

    The results show that the new system can be an alternative to replace today's system. The simulations and calculations show that the voltage drop is at an acceptable level and that the fault currents are large enough to supply a safe disconnection if a fault occurs at the far end of the system.

  • 438.
    Lyden Johansson, Pär
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Svensson, Stefan
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Analys av systemfaktorers påverkan på tillförlitligheten i distributionsnät2005Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this master thesis outage statistics covering tree years from two distribution grids are analyzed with the purpose to deduce which factors yield outages. The statistics are extensive therefore allowing in-depth analysis of both customer and system related factors. From this starting point and as a model of explanation energy not supplied is studied as the consequence and the measurement of the inconvenience caused by outages. Different methods for calculating energy not supplied are developed and studied and put in comparison to the method used in Network Performance Assessment Model, which is the Swedish frame work for regulating electricity distribution.

    Analysis of the outage statistics show a relation between the type category of customer and outages that can be deduced to the variance and the density associated with that customer category. Prioritization of different customer categories is elevated also in this aspect. The variation in outage frequency between the different categories and parts of the grid is to be proven significant in relation to the energy not supplied, which has impact of the assessment of the Customer Reliability Value in the Network Performance Assessment Model. The calculation of the amount of redundancy performed in the Network Performance Assessment Model is also influenced by the method of calculation for energy not supplied. Finally suggestions of alternatives for diversifying this calculation are made.

  • 439. López-López, ÁJ.
    et al.
    Abrahamsson, Lars
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Pecharromán, R. R.
    Fernández-Cardador, A.
    Cucala, P.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    A variable no-load voltage scheme for improving energy efficiency in DC-electrified mass transit systems2014In: 2014 Joint Rail Conference, JRC 2014, 2014Conference paper (Refereed)
    Abstract [en]

    Railway mass transit systems like subways play a fundamental role in the concept of sustainable cities. In these systems, the amount of passengers strongly fluctuates along the day. Hence, in order to provide a proper service without incurring disproportionate energy consumption, operation at different traffic densities is required. The majority of underground systems are DC-electrified. Standard DC voltages in railway systems are low for historical and safety reasons. In the rush hours, the large number of trains demanding power of the system may lead to overloaded substations and voltage dips. This problem is partially mitigated by means of substation-transformer tap regulation, which allows operators to increase the no-load voltage. High no-load voltage has a beneficial effect at all trafficdensity scenarios in terms of transmission losses. However, at the same time it effectively reduces the system's capacity to absorb regenerated energy, which may lead to inefficient energy consumption figures during off-peak hours. In this paper, the sensitivity of system energy consumption to no-load voltage has been analyzed. Several traffic-density scenarios in a case-study system are explored. As a result, a scheduled no-load voltage scheme is proposed for the operation of the system. This operation strategy improves energy efficiency without incurring a high investment cost. The only costs related to this proposed method are the costs of wear-andtear in tap-changers. In case there are devices such as energy storage systems installed in the system, there would be additional operation costs related to a simultaneous update of the voltage limits for their operation.

  • 440.
    Mahmood, Farhan
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Improving the Photovoltaic Modelin PowerFactory2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 441.
    Mahmood, Farhan
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hooshyar, Hossein
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Statnett SF, Norway.
    A method for extracting steady state components from syncrophasor data using Kalman filters2015In: 2015 IEEE 15th International Conference on Environment and Electrical Engineering, EEEIC 2015 - Conference Proceedings, IEEE , 2015, p. 1498-1503Conference paper (Refereed)
    Abstract [en]

    Data from Phasor Measurement Units (PMUs) may be exploited to provide steady state information to the applications which require it. Raw PMU data is polluted with noise and cannot be directly fed to applications without adequate processing. This paper presents a method to extract steady state components from Syncrophasor data using Kalman Filters (KF). This method is capable of reducing the noise, to compensate for missing data and filtering of outliers in signals. The Residue in each KF iteration is computed. The measurement noise covariance matrix R is calculated by computing the variance of residue using rolling windows. The performance of presented method is evaluated by using PMU data generated from a Hardware-In-the-Loop (HIL) experimental setup.

  • 442.
    Mahmood, Farhan
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Hooshyar, Hossein
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Implementation of an architecture for steady state model synthesis of active distribution networks using syncrophasors2016Other (Refereed)
  • 443.
    Mahmood, Farhan
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Hooshyar, Hossein
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Sensitivity Analysis of a PMU-Fed Steady State Model Synthesis Method for Active Distribution Networks2017In: 2017 IEEE POWER & ENERGY SOCIETY GENERAL MEETING, IEEE, 2017Conference paper (Refereed)
    Abstract [en]

    The purpose of this paper is to carry outsensitivityanalysisofa method that performssteady state model synthesis(SSMS)of active distribution networksusing SyncrophasorMeasurements.An extended version of the Total Vector Error (TVE) is used as a metric to evaluate how sensitive the output of the SSMS method is to the changesinthe inputsto the method.Location of PMUs in the system,system operating point,and occurrence of different disturbancesareconsideredas the input tothe SSMS method. The sensitivity analysis is performed through several case studieseach containing changesin one of the inputs.

  • 444.
    Mahmood, Farhan
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hooshyar, Hossein
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modeling of a detailed photovoltaic generation system for EMT-type simulation2014In: ENERGYCON 2014 - IEEE International Energy Conference, IEEE Computer Society, 2014, p. 916-921Conference paper (Refereed)
    Abstract [en]

    This article presents a detailed three-phase grid connected PV model which includes important control systems required for EMT-type simulation. A one diode model for the PV array is used to simulate environmental constraints such as solar irradiation. A detailed control system including dc voltage control, inner current control, MPPT and PWM control are implemented in order to simulate the model during steady state and dynamic conditions. The PV model is merged with a simple distribution network to investigate the PV's interaction with the AC grid. Several simulation scenarios are presented in order to validate the performance of the model.

  • 445.
    Manshaei, Leila
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modelling of Photovoltaic power plantsin SIMPOW2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis project represents an improved model of a grid connected three phase, singlestage PV system implemented in SIMPOW program. The proposal model consists of a PVgenerator employing a PWM converter in order to interface the AC network. The main objectiveof the project is to introduce the main components of the represented model as well as therequired controller schemes. In order to achieve the accurate performance of the PV system withrespect to the integration grid, both AC and DC side network are equipped with controllerfacilities, optimizing the system operation. The control facilities, implemented on the DC side,are mainly focusing on regulation of the output DC voltage of the generator depending on therequirements of the system. The newly proposal MPPT model represents an improvedoptimization strategy for the DC voltage extraction corresponding to various environmentalconditions. The AC side controllers are designed considering the PV system dynamiccontribution on the grid as well as its participation in reactive power provision to the network. Tostudy the accuracy of the dynamic operation of the system, several case studies have beenperformed on AC and DC side. The results of those studies have been discussed considering theirsimulation diagrams.

  • 446.
    Maritaud, Benoit
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Voltage Stability: update of LTCblocking parameters and valorisation ofcapacitors investments2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Modern society is largely dependent on electricity supply and Transmission System Operators (TSOs)have to ensure the reliability of supply in situations that are increasingly difficult to manage due tohigher consumption levels and variability of new intermittent energy sources. In order to ensure thesystem’s safety, voltage stability is a matter of prime importance and is dealt with for different timeframes.Ahead, new reactive power compensation means are installed to prevent voltage collapse. Then, if avoltage collapse gets under way, ultimate mitigation measures have to be taken: Load Tap Changershave to be blocked because of their negative action in critical situations.The first objective of this Master’s Thesis consists on the development of a method to optimize theLTC blocking parameters through dynamic simulation. Then, this method has been applied in fourregions of the French grid and the results have been implemented in the end of the year 2012.The second objective of this Master’s Thesis consists of the development of a method to assess theeconomic gain thanks to the investment in reactive power compensation means for the French TSO.

  • 447.
    Marko, Vistica
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Value of Stochasticity in Hydropower Planning Optimization2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    With respect to market liberalization, efficient use of resources is becoming more important for players in the market. In order to achieve that different optimization techniques were developed which enable better operational efficiency. These techniques can be segmented into two different categories, depending on their time horizon:

    • Yearly time horizon – mid-term hydropower scheduling

    • Daily time horizon – short-term hydropower scheduling

    These two time horizons account for two case studies presented in this thesis.

    In the first case study (mid-term planning), the focus is on determining power plant’s optimal operating strategy, while taking into account the uncertainty in inflows and prices. Stochastic dynamic programming has been chosen as mid-term optimization technique. Since stochastic dynamic programming calls for a discretization of control and state variables, it may fall under the curse of dimensionality and therefore, the modeling of stochastic variables is important.

    By implementing a randomized search heuristic, a genetic algorithm, into the existing stochastic dynamic programming schema, the optimal way of using the stochasticity tries to be found. Two price models are compared based on the economic quality of the result.

    The results give support to the idea of using search heuristics to determine the optimal stochasticity setup, however, some deviations from the expected results occur.

    Second case study deals with short-term hydropower planning, with a focus on satisfying the predefined demand schedule while obtaining maximum profit. With short-term hydropower planning being a nonlinear and nonconvex problem, the main focus is on the linearization of unit performance curves, as well as satisfying technical constraints from the power plant perspective. This optimization techniques also includes the water value in the solution. The problem has been solved by means of mixed integer linear programming.

    The results from the second case study are fully in line with the expectations and it is shown that mixed integer linear programming approach gives good results with good computational time.

    Suggested improvements to the model and potential for future work can be found in the final chapter of this thesis.

  • 448. Martin, F.
    et al.
    Sanchez-Miralles, A.
    Villar, J.
    Calvillo, Christian Francisco
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Optimal Planning and Operation of Distributed Energy Resources Considering Uncertainty on EVs2015In: 2015 IEEE FIRST INTERNATIONAL SMART CITIES CONFERENCE (ISC2), 2015Conference paper (Refereed)
    Abstract [en]

    Operation of distributed energy resources is taking importance nowadays. This paper proposes an optimal planning and operation model of distributed energy resources in a district taking into account the mobility of consumers using conventional fuel vehicles (EV) or electric vehicles (EV). The stochastic model considers the uncertainty of the type of vehicle, availability and distance traveled, and then it manages the available resources to obtain the maximum benefit from the grid. Results show that the EVs assist to achieve greater benefits of the distributed resources. Moreover, the costs per driven km are mainly independent of the type of vehicle considered.

  • 449. Martinez, E. M.
    et al.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Segundo Sevilla, Felix Rafael
    KTH, School of Electrical Engineering (EES).
    Automatic triggering of the interconnection between Mexico and central America using discrete control schemes2013In: 2013 4th IEEE/PES Innovative Smart Grid Technologies Europe, ISGT Europe 2013, IEEE , 2013, p. 6695333-Conference paper (Refereed)
    Abstract [en]

    In the current energy exchange market it is essential to guarantee continuity and quality of supply both in steady state and during contingencies that might occur in any subsystem of interconnected systems. In this work it is shown how the geographical and topological characteristics of the subnetworks directly affect the quality and reliability in the energy exchange, especially when subsystems are interconnected without asynchronous ties that prevent power, frequency or voltage oscillations. This paper describes the problems faced by the interconnection between Mexico and the countries that define the Interconnected Electric System of the Central American Countries (SIEPAC). Different oscillations that have occurred are analyzed. Discrete control schemes to automatically trigger the 400 KV circuit that interconnects the systems of Mexico and Guatemala are proposed.

  • 450. Matevosyan, J.
    et al.
    Bolik, S. M.
    Ackermann, Thomas
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Technical Regulations for the Interconnection of Wind Power Plants to the Power System2012In: Wind Power in Power Systems, John Wiley & Sons, 2012, 2, p. 209-240Chapter in book (Refereed)
    Abstract [en]

    This chapter provides a brief discussion and analysis of the current status of interconnection regulations for wind turbines and wind turbines in Europe. The chapter starts with a short overview of the relevant technical regulation issues, which includes a brief description of the relevant interconnection regulations considered in this chapter. This is followed by a detailed comparison of the different interconnection regulations. The discussion also includes the capabilities of wind turbines to comply with these requirements. Finally, issues related to international interconnection practice are briefly discussed.

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