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  • 1.
    Acquaviva, Alessandro
    et al.
    Chalmers Univ Technol, Div Elect Power Engn, S-41296 Gothenburg, Sweden..
    Wallmark, Oskar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Grunditz, Emma Arfa
    Chalmers Univ Technol, Div Elect Power Engn, S-41296 Gothenburg, Sweden..
    Lundmark, Sonja Tidblad
    Chalmers Univ Technol, Div Elect Power Engn, S-41296 Gothenburg, Sweden..
    Thiringer, Torbjorn
    Chalmers Univ Technol, Div Elect Power Engn, S-41296 Gothenburg, Sweden..
    Computationally Efficient Modeling of Electrical Machines With Cooling Jacket2019Ingår i: IEEE TRANSACTIONS ON TRANSPORTATION ELECTRIFICATION, ISSN 2332-7782, Vol. 5, nr 3, s. 618-629Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Modeling of electrical machines is a multiphysics problem. Depending on the phenomena of interest and the computational time constraint, this can be done at different levels of detail. In this article, the main approaches to model the thermal behavior of electrical machines with a liquid cooled casing around the stator (often referred to as cooling jacket) are analyzed and a novel approach is presented. The proposed method aims at creating computationally efficient 3-D multiphysics models of electrical machines with liquid cooled jacket. This model is based on the assumption of a fully developed flow in the cooling jacket which allows to scale the computational fluid dynamics (CFD) simulation to 1-D. The slot with a two layer concentrated winding and potting material is modeled using a composite material comprising of both the conductors and slot filler. Similarly, a unified material is used to model the end-windings. Experimental results on a traction machine for vehicle applications are presented showing good agreement with the simulations. Also, a comparison with a 3-D CFD is presented to verify the pressure drop in the pipe bend. Finally, the model is used to simulate a dynamic load cycle, which would be computationally extremely demanding with combined 3-D CFD and thermal FEA of the machine and its cooling.

  • 2.
    Acquaviva,, Alessandro
    et al.
    Chalmers University of Technology, Department of Electrical engineering, Göteborg, Sweden.
    Wallmark, Oskar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Grunditz, Emma
    Chalmers University of Technology, Department of Electrical engineering, Göteborg, Sweden.
    Lundmark, Sonja
    Chalmers University of Technology, Department of Electrical engineering, Göteborg, Sweden.
    Thiringer, Torbjörn
    Computationally efficient modeling of electrical machines with cooling jacketIngår i: Artikel i tidskrift (Refereegranskat)
  • 3.
    Alkeaid, Majed Mohammed G
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik. KTH, Skolan för industriell teknik och management (ITM).
    Study of NEOM city renewable energy mix and balance problem2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Det är viktigt för NEOM projektets ledning att planera och införa projektet med hjälp av förnybara energiresurser på plats. Regionen är rymligt och stort och är en lämplig plats för att kunna generera tillräcklig med energi från sol och vind för energiförsörjning av området. Syftet med studien är att studera en pågående planering och byggnation av en hållbar stad med upp till 10 GW förnybar energi som motsvarar cirka 80 000 fat fossil bränsle. Problem och utmaningar för att försörja en hel stad med förnybara energiresurser kommer att diskuteras. Den förnybara staden förväntas vara ett föredöme för 100% förnybar energi, vilket i kapacitetssammanhang motsvarar 72:4GW, vilket är mer tillräckligt än behovet för NEOM staden. Freiburg och Masdar städer används som fallstudier i examensarbetet. NEOMs kraftproduktionskapacitet kan täcka behovet av hela landet som uppgår till 71GW. Studien visar att den totala kraftproduktionskapaciteten från olika förnybara energiresurser såsom vindkraftparker, tidvattenanläggningar, solcellkraftverk och soltornskraftverk med en kapacitet av 9:1373GW,4:76GW, 57:398GW och 1:11GW respektive kan uppgå till 72:4GW. Saudiarabien har planer på att skaffa 16 kärnkraftverk (17GW vardera) med en total kapacitet på 272GW som kommer att ingå i Saudiarabiens nationella satsningar för framtidens elproduktion och det kan täcka elbehovet om NEOM inte når efterfrågekapaciteten. Utöver ovan har studien föreslagit 6 underjordiska batterier med en kapacitet på 120MW per batteri. Studieresultaten kan användas för kompetensuppbyggnad och vidare forskning om förnybara energiresurser för NEOM Institute of Science and Technology. Resultaten kan också användas för teknikutveckling och forskning inom HVDC- överföringsledningar mellan NEOM, Saudiarabiens huvudnät, Egypten och Jordanien.

  • 4.
    Almas, Muhammad Shoaib
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Vanfretti, Luigi
    Rensselaer Polytech Inst, Elect Comp & Syst Engn, Rensselaer, NY USA..
    Singh, Ravi Shankar
    Tech Univ Eindhoven, Dept Elect Engn, Eindhoven, Netherlands..
    Jonsdottir, Gudrun Margret
    Univ Coll Dublin, Sch Elect & Elect Engn, Dublin, Ireland..
    Vulnerability of Synchrophasor-based WAMPAC Applications' to Time Synchronization Spoofing2018Ingår i: 2018 IEEE POWER & ENERGY SOCIETY GENERAL MEETING (PESGM), IEEE , 2018Konferensbidrag (Refereegranskat)
  • 5.
    Andersson, Kjell
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Hagnestål, Anders
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Sellgren, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Design of a flexible chain for winch based point absorbers2018Ingår i: Proceedings of NordDesign: Design in the Era of Digitalization, NordDesign 2018, 2018Konferensbidrag (Refereegranskat)
  • 6.
    Antonello, Riccardo
    et al.
    University of Padova.
    Peretti, Luca
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Tinazzi, Fabio
    University of Padova.
    Zigliotto, Mauro
    University of Padova, Italy.
    Self-commissioning calculation of dynamic models for synchronous machines with magnetic saturation using flux as state variable2019Ingår i: The Journal of Engineering, ISSN 1872-3284, E-ISSN 2051-3305, nr 17, s. 3609-3613Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper deals with the non-linear modelling of synchronous machines by using the flux linkage as a state variable.The model is inferred from a conventional set of measurements where the relation between the currents and the flux linkages inthe rotating reference frame (also known as dq reference frame) are known by measurements or estimated through finite-element simulations. In particular, the contribution of this paper is twofold: first, it proposes a method to extract the non-linearmodel information which can be easily implemented in electric drives, without the need of offline post-processing of the data.Second, it mathematically demonstrates that the method converges to the final result in a stable way. An example based onexperimental measurements of the current-to-flux look-up tables of an 11-kW synchronous reluctance machine is shown,proving the feasibility of the proposed method.

  • 7.
    Astapov, Victor
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik. Tallinn Univ Technol, Sch Engn, Tallinn, Estonia.
    Divshali, Poria Hasanpor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Söder, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    The Potential of Distribution Grid as an Alternative Source for Reactive Power Control in Transmission Grid2018Ingår i: PROCEEDINGS OF THE 2018 19TH INTERNATIONAL SCIENTIFIC CONFERENCE ON ELECTRIC POWER ENGINEERING (EPE), Institute of Electrical and Electronics Engineers (IEEE), 2018, s. 64-69Konferensbidrag (Refereegranskat)
    Abstract [en]

    Nowadays, the global trend in the energy sector is the spreading use of renewable energy, especially wind generators and solar panels. The high concentration of such sources in distribution grid increases the voltage in case of small load demands and high production which effects the voltage at connection point and, in turn, in transmission grid. To regulate voltage and control reactive power, system operators install costly equipment in transmission grids. This paper considers alternative way of voltage and reactive power managing and discovers possibilities of PV converters in MV and LV grids with different type of control to solve this problem.

  • 8.
    Augustin, Tim
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik. KTH Stockholm.
    Becerra, Marley
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Magnusson, Jesper
    ABB Corporate Research, Västerås.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Parekh, Mrunal
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    System Design of Fast Actuator for Vacuum Interrupter in DC Applications2018Ingår i: 2018 28th International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV), Institute of Electrical and Electronics Engineers (IEEE), 2018, Vol. 2, s. 527-530Konferensbidrag (Refereegranskat)
    Abstract [en]

    One of the major challenges of DC circuit breakers is the required fast mechanical actuator. In this paper, a Thomson coil actuator system for a vacuum interrupter is designed. Active damping is used to decelerate the moving contacts. Challenges are discussed, especially concerning the power supply needed for the Thomson coil actuator. The design philosophy is explained and FEM simulation results are presented. The results indicate that a wide range of combinations of drive circuit capacitance and voltage fulfill the requirements for armature acceleration. However, active damping requires a very careful selection of drive circuit voltage and timing of applied damping.

  • 9.
    Augustin, Tim
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik. KTH Stockholm.
    Becerra, Marley
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Advanced Test Circuit for DC Circuit Breakers2018Ingår i: 20th European Conference on Power Electronics and Applications (EPE'18 ECCE EUROPE), 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    In future HVDC systems, many DC circuit breakers (DCCBs) will be required. In this paper, an advanced test circuit for DCCBs is described. A DC source is combined with a capacitor bank. In contrast to other test circuits, the proposed test circuit allows to replicate constant DC and temporary faults. In addition to conventional faults, this enables testing of auto-reclosing, proactive commutation, and complex test sequences combining all of these modes. The test circuit is easy to setup and also suitable for smaller research facilities. Experimental results from a down-scaled mock-up are included to demonstrate the capabilities of the test circuit.

  • 10.
    Azuatalam, Donald
    et al.
    Univ Sydney, Sch Elect & Informat Engn, Sydney, NSW, Australia..
    Paridari, Kaveh
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Ma, Yiju
    Univ Sydney, Sch Elect & Informat Engn, Sydney, NSW, Australia..
    Foerstl, Markus
    Tech Univ Munich, Inst Elect Energy Storage Technol, Munich, Germany..
    Chapman, Archie C.
    Univ Sydney, Sch Elect & Informat Engn, Sydney, NSW, Australia..
    Verbic, Gregor
    Univ Sydney, Sch Elect & Informat Engn, Sydney, NSW, Australia..
    Energy management of small-scale PV-battery systems: A systematic review considering practical implementation, computational requirements, quality of input data and battery degradation2019Ingår i: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 112, s. 555-570Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    The home energy management problem has many different facets, including economic viability, data uncertainty and quality of strategy employed. The existing literature in this area focuses on individual aspects of this problem without a detailed, holistic analysis of the results with regards to practicality in implementation. In this paper, we fill this gap by performing a comprehensive comparison of seven different energy management strategies, each with different levels of practicality, sophistication and computational requirements. We analyse the results in the context of these three characteristics, and also critique the modelling assumptions made by each strategy. Our analysis finds that using a more sophisticated energy management strategy may not necessarily improve the performance and economic viability of the PV-battery system due to the effects of modelling assumptions, such as the treatment of uncertainties in the input data and battery degradation effects.

  • 11.
    Babazadeh, Davood
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Hohn, Fabian
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Wu, Yimin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Nordström, Lars
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Distributed Two-stage Network Topology Processor for HVDC Grid Operation2017Ingår i: 2017 IEEE POWER & ENERGY SOCIETY GENERAL MEETING, IEEE , 2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents the results of an analysis of distributed two-stage coordination of network topology processor for HVDC grids. In the first stage of the two-stage processor, the substation topology is analyzed locally using an automated graph based algorithm. Thereafter, a distributed algorithm is proposed to used the neighboring information to realize the grid connectivity. For distributed islanding detection, the connectivity problem is formulated as a set of linear equations and solved iteratively using successive-over-relaxation method. The performance of the proposed methods versus conventional one-stage method has been tested in an islandinv, scenario for a 5-terminal HVDC grid.

  • 12.
    Bakas, Panagiotis
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik. ABB Corp Res, Västerås, Sweden..
    Ilves, K.
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik. ABB Corp Res, Västerås, Sweden..
    Norrga, S.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Nee, H.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Hybrid Converter With Alternate Common Arm and Director Thyristors for High-Power Capability2018Ingår i: 2018 20th European Conference on Power Electronics and Applications (EPE’18 ECCE Europe), 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents the basic operating principles of a new hybrid converter that combines thyristors and full-bridge (FB) arms for achieving high active-power capability. This converter consists of a modular multilevel converter (MMC) equipped with additional common arms, which alternate between the upper and lower dc poles. This alternation is achieved by the thyristors that are utilized as director switches and allow the parallel connection of the common arms and the arms of the MMC. The main contributions of this paper are the analysis of the operating principles, the simulation verification of the functionality of the proposed converter, and the comparison of the latter with the full-bridge modular multilevel converter (FB-MMC).

  • 13.
    Baudette, Maxime
    et al.
    KTH.
    Castro, Marcelo
    Univ Fed Juiz de Fora, Juiz de Fora, Brazil..
    Rabuzin, Tin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Lavenius, Jan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Bogodorova, Tetiana
    Ukrainian Catholic Univ, Fac Appl Sci, Lvov, Ukraine..
    Vanfretti, Luigi
    Rensselaer Polytech Inst, Troy, NY 12180 USA..
    OpenIPSL: Open-Instance Power System Library - Update 1.5 to "iTesla Power Systems Library (iPSL): A Modelica library for phasor time-domain simulations"2018Ingår i: Software Quality Professional, ISSN 1522-0540, Vol. 7, s. 34-36Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents the latest improvements implemented in the Open-Instance Power System Library (OpenIPSL). The OpenIPSL is a fork from the original iTesla Power Systems Library (iPSL) by some of the original developers of the iPSL. This fork's motivation comes from the will of the authors to further develop the library with additional features tailored to research and teaching purposes. The enhancements include improvements to existing models, the addition of a new package of three phase models, and the implementation of automated tests through continuous integration.

  • 14.
    Bessegato, Luca
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Modeling of Modular Multilevel Converters for Stability Analysis2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Modulära multinivåomvandlare (MMC) har under senare år utvecklats till den mest relevanta lösningen för olika tillämpningar där kraftelektroniska omriktare är anslutna till växelströmsnät, såsom system för högspänd likströmsöverföring (HVDC) och flexibla system för överföring av växelström (FACTS). Den modulära uppbyggnaden, skalbarhet, låga förluster och låga övertoner är egenskaperna som gör MMC omriktare till en central komponent för framtida hållbara elenergisystem.

     

    Huvudsyftet med denna avhandling är modellering av nätanslutna omvandlare av typ MMC för stabilitetsanalys. Stabiliteten för systemet omvandlare och nät, kan bedömas genom att analysera omvandlarens växelströmssidiga admittans i förhållande till nätimpedansen. En metod har därför utvecklats för att beräkna den modulära multinivåomvandlarens admittans. Metoden tar hänsyn till olinjäriteter i omvandlarens dynamik och kan enkelt anpassas till olika tillämpningar. Därutöver studeras effekterna av hur olika reglersystem påverkar omvandlarens admittans och hur omvandlarens admittans kan omformas. Denna möjlighet är användbar vid utformning av en systemlösning, eftersom reglerparametrarna kan väljas för att undvika oönskade störningar mellan nät och omriktare.

     

    I avhandlingen undersöks även modulära ac/ac-omvandlare för järnvägsbanmatning. Dessa används i länder med lågfrekvensbanmatning så som Tysk-land med 16,7 Hz och Sverige med 16 2/3 Hz. Ett hierarkiskt reglersystem har utvecklats och utvärderats med avseende på järnvägstillämpningens specifika krav och dess driftsförhållanden. Admittansmodeller har utvecklats, för dessa modulära ac/ac-omvandlare, som visar hur det föreslagna hierarkiska reglersystemet påverkar omvandlarens admittans på både trefas- och enfassidan. För att beräkna ac/ac-omvandlarens inkopplingsförhållande appliceras en öppen styrning som estimerar summan av submodulernas kondensatorspänningar. Lyapunovs stabilitetsteori har använts för att bevisa den asymptotiska stabiliteten hos omvandlaren. Den föreslagna öppna styrningen kan också anpassas till en modulär multinivåomvandlare för direkt trefas till trefas omformning.

     

    För att kunna verifiera resultaten experimentellt har en nedskalad prototyp utvecklats. Prototypens märkeffekt är 10 kW och den är uppbyggd av 30 submoduler med helbryggor. Hårdvaran och mjukvaran är utformade så att omvandlaren på ett enkelt sätt kan konfigureras för olika tillämpningar vilket gör den lämplig för olika forskningsprojekt som inkluderar modulära multinivåomriktare. Experiment på den nedskalade MMC:n har genomförts för att validera de resultat och slutsatser som presenteras i avhandlingen.

  • 15.
    Bessegato, Luca
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Harnefors, Lennart
    Ilves, Kalle
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    A Method for the Calculation of the AC-Side Admittance of a Modular Multilevel Converter2018Ingår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Connecting a modular multilevel converter to anac grid may cause stability issues, which can be assessed byanalyzing the converter ac-side admittance in relation to the gridimpedance. This paper presents a method for calculating theac-side admittance of modular multilevel converters, analyzingthe main frequency components of the converter variables individually.Starting from a time-averaged model of the converter,the proposed method performs a linearization in the frequencydomain, which overcomes the inherent nonlinearities of theconverter internal dynamics and the phase-locked loop usedin the control. The ac-side admittance obtained analytically isfirstly validated by simulations against a nonlinear time-averagedmodel of the modular multilevel converter. The tradeoff posedby complexity of the method and the accuracy of the result isdiscussed and the magnitude of the individual frequency componentsis shown. Finally, experiments on a down-scaled prototypeare performed to validate this study and the simplification onwhich it is based.

  • 16.
    Bessegato, Luca
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Ilves, Kalle
    Harnefors, Lennart
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Effects of Control on the AC-Side Admittance of a Modular Multilevel Converter2019Ingår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 34, nr 8, s. 7206-7220, artikel-id 8514034Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The stability of a modular multilevel converter connected to an ac grid can be assessed by analyzing the converter ac-side admittance in relation to the grid impedance. The converter control parameters have a strong impact on the admittance and they can be adjusted for achieving system stability. This paper focuses on the admittance-shaping effect produced by different current-control schemes, either designed on a per-phase basis or in the $dq$ frame using space vectors. A linear analytical model of the converter ac-side admittance is developed, including the different current-control schemes and the phase-locked loop. Different solutions for computing the insertion indices are also analyzed, showing that for a closed-loop scheme a compact expression of the admittance is obtained. The impact of the control parameters on the admittance is discussed and verified experimentally, giving guidelines for designing the system in terms of stability. Moreover, recommendations on whether a simplified admittance expression could be used instead of the detailed model are given. The findings from the admittance-shaping analysis are used to recreate a grid-converter system whose stability is determined by the control parameters. The developed admittance model is then used in this experimental case study, showing that the stability of the interconnected system can be assessed using the Nyquist stability criterion.

  • 17.
    Bessegato, Luca
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Ilves, Kalle
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Harnefors, Lennart
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Östlund, Stefan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Control and Admittance Modeling of an AC/AC Modular Multilevel Converter for Railway Supplies2019Ingår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Modular multilevel converters (MMCs) can be configured to perform ac/ac conversion, which makes them suitable as railway power supplies. In this paper, a hierarchical control scheme for ac/ac MMCs for railway power supplies is devised and evaluated, considering the requirements and the operating conditions specific to this application. Furthermore, admittance models of the ac/ac MMC are developed, showing how the suggested hierarchical control scheme affects the three-phase and the single-phase side admittances of the converter. These models allow for analyzing the stability of the interconnected system using the impedance-based stability criterion and the passivity-based stability assessment. Finally, the findings presented in this paper are validated experimentally, using a down-scaled MMC. 

  • 18.
    Bessegato, Luca
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Modeer, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elektrisk energiomvandling.
    Modeling and control of a tapped-inductor buck converter with pulse frequency modulation2014Ingår i: Energy Conversion Congress and Exposition (ECCE), 2014 IEEE, 2014, s. 3672-3678Konferensbidrag (Refereegranskat)
    Abstract [en]

    The tapped-inductor buck (TI-buck) converter has shown to be a suitable solution for auxiliary power supply for modular multilevel converter submodules. Such application features a large step-down voltage conversion, made at relatively low output power. This converter operates in discontinuous conduction mode with zero voltage switching of the high-voltage valve. This paper treats the dynamic behaviour of the aforementioned converter. First, an average output current model of the converter is developed and a small signal model is obtained. Then, a closed-loop output voltage control, which uses the switching frequency as control variable, is designed and implemented using a microcontroller. Measurements on a down-scaled prototype shows that the control system provides a well-controlled average output voltage, which is stable under significant load variation. Finally, a solution for implementing the start-up of the converter is presented and tested.

  • 19.
    Bessegato, Luca
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Narula, Anant
    Bakas, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Design of a Modular Multilevel Converter Prototype for Research Purposes2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    As modular multilevel converters gradually become the preferred topology for many high-voltage andhigh-power applications, they are widely studied among researchers, who need experimental results tovalidate their studies. This paper discusses the design of a down-scaled modular multilevel converterprototype for research purposes, equipped with 30 full-bridge submodules and 10 kW rating. The designof this prototype is aimed at safety, flexibility, orderliness, and compactness. The challenges posed by theimplementation of the converter prototype are examined, discussing the design of the prototype structure,the communication scheme, the full-bridge submodules, and the control hierarchy. The control systemis based on Xilinx Zynq system-on-chip, which integrates programmable logic and processing system,allowing for extensive computational capability as well as simple reconfiguration. Experimental resultsshowing the prototype in operation at nominal ratings are presented along with the devised graphical userinterface.

  • 20.
    Bessegato, Luca
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Ilves, K.
    Harnefors, Lennart
    Ac-side admittance calculation for modular multilevel converters2017Ingår i: 2017 IEEE 3rd International Future Energy Electronics Conference and ECCE Asia, IFEEC - ECCE Asia 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 308-312Konferensbidrag (Refereegranskat)
    Abstract [en]

    Power electronic converters may interact with the grid, thereby influencing dynamic behavior and resonances. Impedance and passivity based stability criteria are two useful methods that allow for studying the grid-converter system as a feedback system, whose behavior is determined by the ratio of grid and converter impedances. In this paper, the ac-side admittance of the modular multilevel converter is calculated using harmonic linearization and considering five specific frequency components of the converter variables. The proposed model features remarkable accuracy, verified through simulations, and insight into the influence of converter and control parameters on the admittance frequency characteristics, which is useful for understanding grid-converter interaction and designing the system.

  • 21.
    Bessegato, Luca
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Norrga, Staffan
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Ilves, Kalle
    Harnefors, Lennart
    Control of Modular Multilevel Matrix Converters Based on Capacitor Voltage Estimation2016Ingår i: IEEE 8th International Power Electronics and Motion Control Conference (IPEMC-ECCE Asia), 2016, IEEE, 2016, s. 3447-3452, artikel-id 7512848Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, a control method based on capacitor voltage estimation is applied to the modular multilevel matrix converter topology. By using such control method, capacitor voltage measurement is not needed in the high-level control. A state-space model of the converter and the control method is developed. Lyapunov stability theory is used to prove global asymptotic stability of the internal dynamics of the converter. Simulation results showing the behavior of the converter in steady-state and dynamic situations are presented.

  • 22.
    Bessman, Alexander
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemiteknik, Tillämpad elektrokemi.
    Soares, Rúdi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Wallmark, Oskar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Svens, Pontus
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemiteknik, Tillämpad elektrokemi.
    Lindbergh, Göran
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemiteknik, Tillämpad elektrokemi.
    Aging effects of AC harmonics on lithium-ion cells2019Ingår i: Journal of Energy Storage, E-ISSN 2352-152X, Vol. 21, s. 741-749Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    With the vehicle industry poised to take the step into the era of electric vehicles, concerns have been raised that AC harmonics arising from switching of power electronics and harmonics in electric machinery may damage the battery. In light of this, we have studied the effect of several different frequencies on the aging of 28 Ah commercial NMC/graphite prismatic lithium-ion battery cells. The tested frequencies are 1 Hz, 100 Hz, and 1 kHz, all with a peak amplitude of 21 A. Both the effect on cycled cells and calendar aged cells is tested. The cycled cells are cycled at a rate of 1C:1C, i.e., 28 A during both charging and discharging, with the exception of a period of constant voltage at the end of every charge. After running for one year, the cycled cells have completed approximately 2000 cycles. The cells are characterized periodically to follow how their capacities and power capabilities evolve. After completion of the test about 80% of the initial capacity remained and no increase in resistance was observed. No negative effect on either capacity fade or power fade is observed in this study, and no difference in aging mechanism is detected when using non-invasive electrochemical methods of post mortem investigation.

  • 23.
    Bitsi, Konstantina
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Kowal, Damian
    Moghaddam, Reza-Rajabi
    3-D FEM Investigation of Eddy Current Losses in Rotor Lamination Steel Sheets2018Ingår i: 2018 XIII International Conference on Electrical Machines (ICEM), IEEE conference proceedings, 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, a test setup that emulates field conditions equivalent to the ones of the rotor of a Salient Pole Synchronous Machine (SPSM) is presented. A 3-D Finite Element Method (FEM) model of the test setup is used to examine the induced eddy currents and to estimate losses using direct eddy current calculation method. The high mesh resolution of the model enables an accurate calculation and detailed illustration of the induced eddy currents as well as the estimation of related losses via direct computation within the volume of the test samples. A comparison of the estimated eddy current losses is made for different lamination thicknesses and materials of the test object. In the paper it is shown that the approximation that the eddy current losses are directly proportional to the square of the lamination thickness is not valid in the considered cases.

  • 24.
    Björk, Joakim
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Johansson, Karl Henrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Fundamental Performance Limitations in Utilizing HVDC to Damp Interarea Modes2019Ingår i: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 34, nr 2, s. 1095-1104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper considers power oscillation damping (POD) using active power modulation of high-voltage dc transmissions. An analytical study of how the proximity between interarea modal frequencies in two interconnected asynchronous grids puts a fundamental limit to the achievable performance is presented. It is shown that the ratio between the modal frequencies is the sole factor determining the achievable nominal performance. To illustrate the inherent limitations, simulations using a proportional controller tuned to optimize performance in terms of POD are done on a simplified two-machine model. The influence of limited system information and unmodeled dynamics is shown. The analytical result is then further validated on a realistic model with two interconnected 32-bus networks.

  • 25.
    Blom, Evelin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Including Hydropower in Large Scale Power System Models2019Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Hydropower is the most used renewable energy technology with over 4000 TWh electricity generated worldwide in 2017, corresponding to almost 16% of the total electricity generation. In the Nordic countries, hydropower provides an even larger share of the electricity generation with about 50% of the total electricity generation coming from hydro. In other words, hydropower plays a significant role in power systems worldwide in general and in the Nordic power system in particular. Typically the hydropower included in larger power system models are simplified to reduce computation time. These simplifications can be denoted as a hydropower Equivalent which aims to mimic the behaviour of a more detailed description of the hydropower system.

    Here some of the most common power system models of the Nordic system are summarized including a shorter description specifically describing the modelling of hydropower. The models included are Apollo developed by Sweco, Balmorel which is an open-source alternative, EMPS created by Sintef and BID3 developed by Pöyry.

    All four models utilizes so called hydropower Equivalents with one or two stations per geographical area. In BID and EMPS the inflow is divided into regulated and unregulated inflow and only include one hydropower station and associated reservoir per area. Apollo and Balmorel on the other hand include two hydropower stations per area, one regulated, with an associated reservoir, and one unregulated.

  • 26.
    Brauer, Patrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    High-Frequency Voltage Distribution Modelling of a Slotless PMSM from a Machine Design Perspective2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Nästa generations inverterare för styrning av elektriska maskiner, baserade på bredbandgaps komponenter, tillåter högre switchfrekvenser vilket skapar en energieffektivare drivlina. Nackdelen är att snabba spänningsflanker från den höga switchfrekvensen skapar överspänning på stators anslutningar och en ojämn spänningsfördelning i statorlindningen. Det är därför betydelsefullt att förstå hur dessa nya drivlinor påverkar lindningens spänningsfördelning. I denna rapport används en modell kapabel att simulera lindningens spänningsfördelning i det breda frekvensspektrumet 0-10 MHZ. Modellen är framtagen för en faslindning av en PMSM, utan statoröppning, som inkluderar både kapacitiva och induktiva kopplingar samt analytiskt beräknade lindningsförluster. Modellen används för att undersöka spänningsfördelningen i lindningen samt inverkan från designparametrar som isolationsmaterial och lindningsdistribution. Känslighetsanalysen visar att lindingsdistributionen har en signifikant påverkan på både impedansspektrumet och spänningsfördelningen. För den studerade maskintypen är det kapacitansen mellan varv som är dominerande för högfrekventa fenomen. Isolationsmaterial som påverkar denna koppling har en påverkan på impedansspektrumet men är liten för spänningsfördelningen.

  • 27.
    Chaffey, Geraint
    et al.
    ELECTA, KU Leuven, Belgium and EnergyVille, Genk, Belgium.
    Jahn, Ilka
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Loenders, Rick
    ELECTA, KU Leuven, Belgium and EnergyVille, Genk, Belgium.
    Leterme, Willem
    ELECTA, KU Leuven, Belgium and EnergyVille, Genk, Belgium.
    Dejene, Firew Z.
    ELECTA, KU Leuven, Belgium and EnergyVille, Genk, Belgium.
    Wang, Mian
    ELECTA, KU Leuven, Belgium and EnergyVille, Genk, Belgium.
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Van Hertem, Dirk
    ELECTA, KU Leuven, Belgium and EnergyVille, Genk, Belgium.
    Requirements for functional testing of HVDC protection IEDs2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    Development of Intelligent Electronic Devices (IED) for HVDC protection is underway, driven in part by the prospective demands of future multiterminal HVDC systems. There is, however, no consensus on how to test the functionality of an HVDC protection IED. Successful operation of a future multivendor HVDC protection system requires functional specifications and harmonised test procedures for protection system components, including the protection IED. This paper presents an introduction to functional testing methods for HVDC protection IEDs. Evaluating the protection algorithm characteristic using synthetic waveforms is first performed, i.e. ’functional type testing’. Given that test procedures are in part dependent on the protection algorithm, tests are developed and presented for several algorithms. The behaviour of the IED in a power system simulation is then examined during generalised yet representative fault transients, i.e. equivalent to ’dynamic validation type testing’ of AC protection algorithms. The combination of functional and dynamic validation type testing allows the generalised functionality of the IED to be evaluated - testing the algorithm, hardware and software implementation, and overall performance. To provide examples of test procedures, an open-source HVDC IED prototype is tested in a hardware-in-the-loop configuration using a real-time simulator. The operation and accuracy of the protection characteristics are first examined, before the IED performance under representative waveforms is determined. Through tests of several non-unit line protection algorithms, it is shown that, depending on the algorithm applied, the IED is dependable for simulated faults within the protection zone, and secure during external faults. Moreover,the test configurations and procedures required to evaluate the functionality and the criteria for success are developed.

  • 28.
    Chakrabarti, Sambuddha
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Hesamzadeh, Mohammad Reza
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Financial transmission rights: A new proposal2018Ingår i: International Conference on the European Energy Market, EEM, IEEE Computer Society , 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we will consider the problems of Revenue Adequacy (RA) and Hedging to Risk (H2R), faced by the Independent System Operators (ISOs) and holders of Financial Transmission Rights (FTRs) (or, Congestion Revenue Rights, or CRRs as they are variously known), respectively. It is well known, that the main driver for these two problems is the difference in the topology of the network that is used while solving the FTR auction and allocation process, to that used in the Day-Ahead (DA) or Real Time (RT) market dispatch calculations. As we will see in this paper, that the problems of RA and H2 R form a set of conflicting requirements, especially when situations corresponding to changing network topologies are considered. We will, therefore, in the present work, propose a newer type of FTR such that both the above-mentioned problems are averted. We will also present the revised auction mechanism of this new FTR, in order to incentivize both the ISOs and the potential holders to sell and purchase them, respectively.

  • 29.
    Chakrabarti, Sambuddha
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Hesamzadeh, Mohammad Reza
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Financial Transmission Rights: A New Proposal2018Ingår i: 2018 15TH INTERNATIONAL CONFERENCE ON THE EUROPEAN ENERGY MARKET (EEM), IEEE , 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we will consider the problems of Revenue Adequacy (RA) and Hedging to Risk (H2R), faced by the Independent System Operators (ISOs) and holders of Financial Transmission Rights (FTRs) (or, Congestion Revenue Rights, or CRRs as they are variously known), respectively. It is well known, that the main driver for these two problems is the difference in the topology of the network that is used while solving the FTR auction and allocation process, to that used in the Day Ahead (DA) or Real Time (RT) market dispatch calculations. As we will see in this paper, that the problems of RA and H2R form a set of conflicting requirements, especially when situations corresponding to changing network topologies are considered. We will, therefore, in the present work, propose a newer type of FTR such that both the above-mentioned problems are averted. We will also present the revised auction mechanism of this new FTR, in order to incentivize both the ISOs and the potential holders to sell and purchase them, respectively.

  • 30.
    Chamorro Vera, Harold Rene
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Riaño, I.
    Gerndt, R.
    Zelinka, I.
    Gonzalez-Longatt, F.
    Sood, V. K.
    Synthetic inertia control based on fuzzy adaptive differential evolution2019Ingår i: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 105, s. 803-813Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The transformation of the traditional transmission power systems due to the current rise of non-synchronous generation on it presents new engineering challenges. One of the challenges is the degradation of the inertial response due to the large penetration of high power converters used for the interconnection of renewables energy sources. The addition of a supplementary synthetic inertia control loop can contribute to the improvement of the inertial response. This paper proposes the application of a novel Fuzzy Adaptive Differential Evolution (FADE) algorithm for the tuning of a fuzzy controller for the improvement of the synthetic inertia control in power systems. The method is validated with two test power systems: (i) an aggregated power system and its purpose is to understand the controller-system behavior, and (ii) a two-area test power system where one of the synchronous machine has been replaced by a full aggregated model of a Wind Turbine Generator (WTG), whereby different limits in the tuning process can be analyzed. Results demonstrate the evolution of the membership functions and the inertial response enhancement in the respective test cases. Moreover, the appropriate tuning of the controller shows that it is possible to substantially reduce the instantaneous frequency deviation.

  • 31.
    Chamorro Vera, Harold Rene
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Sanchez, A. C.
    Pantoja, A.
    Zelinka, I.
    Gonzalez-Longatt, F.
    Sood, V. K.
    A network control system for hydro plants to counteract the non-synchronous generation integration2019Ingår i: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 105, s. 404-419Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Sweden, a country with abundant hydro power, has expectations to include more wind power into its electrical system. Currently, in order to improve the frequency response requirements of its electrical system, the country is considering upgrading its hydro-governors. This effort is part of maintaining the system frequency and reaction within their limits following any disturbance events. To partially compensate for increased frequency fluctuations due to an increased share of renewables on its system, the frequency response of hydro-governors should be improved. This paper proposes an innovative network control system, through a supplementary control, for the improvement of the hydro-governor's action. This supplementary control allows having more flexibility over the control action and improves the primary frequency control, and thereby the overall system frequency response. The proposed supplementary control, based on an evolutionary game theory strategy, uses remote measurements and a hierarchical dynamic adjustment of the control. Additionally, in order to guarantee an optimal response, a Simulated Annealing Algorithm (SAA) is combined with the supplementary control. This paper illustrates the analysis and design of the proposed methodology, and is tested on two power systems models: (i) an aggregated model that represents the frequency response of Sweden, Norway and Finland, and (ii) The Nordic 32 test system.

  • 32.
    Ciftci, Baris
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Gross, James
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Kildehöj, Lars
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    A Proposal for Wireless Control of Submodules in Modular Multilevel Converters2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    The modular multilevel converter is one of the most preferred converters for high-power conversion applications. Wireless control of the submodules can contribute to its evolution by lowering the material and labor costs of cabling and by increasing the availability of the converter. However, wireless control leads to many challenges for the control and modulation of the converter as well as for proper low-latency high-reliability communication. This paper investigates the tolerable asynchronism between phase-shifted carriers used in modulation from a wireless control point of view and proposes a control method along with communication protocol for wireless control. The functionality of the proposed method is validated by computer simulations in steady state.

  • 33.
    Ciftci, Baris
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Gross, James
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Simple Distributed Control for Modular Multilevel Converters2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    The central control of MMC becomes demanding in computation power and communication bandwidth as the number of submodules increase. Distributed control methods can overcome these bottlenecks. In this paper, a simple distributed control method together with synchronization of modulation carriers in the submodules is presented. The proposal is implemented on a lab-scale MMC with asynchronous-serial communication on a star network between the central and local controllers. It is shown that the proposed control method works satisfactorily in the steady state. The method can be applied as is to MMCs with any number of submodules per arm.

  • 34.
    Crosara, Alessandro
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik. Pöyry.
    Tomasson, Egill
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Söder, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Generation Adequacy in the Nordic and Baltic Region: Case Studies from 2020 to 2050: Flex4RES Project Report2019Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Generation adequacy is a concern in today's electricity market where intermittent renewable energy sources are rapidly becoming a greater share of the generation mix. This study focuses on the Nordic and Baltic power system that is comprised of the system areas of the Nord Pool spot market. Sequential Monte Carlo Simulation is applied to assess the generation adequacy of this multi-area system for several future case studies, based on scenarios defined within the Nordic Flex4RES project. The report gives insights into the characteristics of these adequacy problems that the system could face in a more sustainable future, quantifies their magnitude and presents their characteristics. Finally, a solution based on the demand flexibility of residential electric heating is discussed, as a way to counter capacity deficit problems.

  • 35.
    Dabar, Omar Assowe
    et al.
    CERD, Inst Sci Terre, Route Aeroport,BP 486, Ville, Djibouti..
    Awaleh, Mohamed Osman
    CERD, Inst Sci Terre, Route Aeroport,BP 486, Ville, Djibouti..
    Kirk-Davidoff, Daniel
    Univ Maryland, Dept Atmospher & Ocean Sci, College Pk, MD 20742 USA..
    Olauson, Jon
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Söder, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Awaleh, Said Ismael
    CERD, Inst Sci Terre, Route Aeroport,BP 486, Ville, Djibouti..
    Wind resource assessment and economic analysis for electricity generation in three locations of the Republic of Djibouti2019Ingår i: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 185, s. 884-894Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the Republic of Djibouti, due to increasing electricity demands, the government has planned to increase power supply by using renewable resources such as geothermal, solar and wind energy. This work presents the first wind resource assessment in the Republic of Djibouti using measured wind speed data for the period of three years by meteorological stations at eight locations. The results confirmed that three of the eight locations (i.e. GaliMa-aba, Ghoubbet and Bada Wein) have the best resource, with mean annual wind speeds of more than 6.0 m/s. Wind simulations using NCEP-CFSR and ERA5 models reanalysis shows that the seasonal variations are stable between different years and are broadly consistent with the observed wind speed. The feasibility of three wind farms with total capacity of 275 MW at GaliMa-aba, Ghoubbet and Bada Wein is examined. Using the WindPRO program and two commercial wind turbines in according to IEC 61400-1 design criteria, the electricity generation were technically assessed. These wind farms can produce 1073 GWh of electricity per year, approximately equal to Djibouti's expected average annual electrical demand in 2030. The economic evaluation using the present value cost (PVC) method estimate that the generation cost per kWh at these locations varies from 7.03 US.$ cent/kWh to 9.67 US.$ cent/kWh. Elsevier Ltd. All rights reserved.

  • 36.
    Dimoulkas, Ilias
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Amelin, Mikael
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Use of temperature scenariosl medium and long-term probabilistic heat demand forecasting in district heating2018Ingår i: Euroheat and Power (English Edition), ISSN 1613-0200, Vol. 15, nr 4, s. 10-16Artikel i tidskrift (Refereegranskat)
  • 37.
    Dimoulkas, Ilias
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Herre, Lars
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Khastieva, Dina
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Nycander, Elis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Amelin, Mikael
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Mazidi, P.
    A hybrid model based on symbolic regression and neural networks for electricity load forecasting2018Ingår i: International Conference on the European Energy Market, EEM, IEEE Computer Society, 2018, artikel-id 8469901Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper proposes a hybrid model for electricity load forecasting. Symbolic regression is initially used to automatically create a regression model of the load. Then the explanatory variables and their transformations that have been selected in the model are used as input in an artificial neural network that is trained to predict the electricity load at the output. Therefore symbolic regression operates as a feature selection-creation method and forecasting is done by the artificial neural network. The proposed hybrid model has been successfully used in an electricity load forecasting competition.

  • 38.
    Dimoulkas, Ilias
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Herre, Lars
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Khastieva, Dina
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Nycander, Elis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Amelin, Mikael
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Mazidi, Peyman
    Loyola Andalucia Univ, Loyola Inst Sci & Technol Loyola Tech, Seville, Spain..
    A hybrid model based on symbolic regression and neural networks for electricity load forecasting2018Ingår i: 2018 15TH INTERNATIONAL CONFERENCE ON THE EUROPEAN ENERGY MARKET (EEM), IEEE , 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper proposes a hybrid model for electricity load forecasting. Symbolic regression is initially used to automatically create a regression model of the load. Then the explanatory variables and their transformations that have been selected in the model are used as input in an artificial neural network that is trained to predict the electricity load at the output. Therefore symbolic regression operates as a feature selection creation method and forecasting is done by the artificial neural network. The proposed hybrid model has been successfully used in an electricity load forecasting competition.

  • 39.
    Dimoulkas, Ilias
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Mazidi, Peyman
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik. Loyola.Tech, Loyola Andalucia University, Seville, Spain.
    Herre, Lars
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Neural networks for GEFCom2017 probabilistic load forecasting2019Ingår i: International Journal of Forecasting, ISSN 0169-2070, E-ISSN 1872-8200Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This report describes the forecasting model which was developed by team "4C" for the global energy forecasting competition 2017 (GEFCom2017), with some modifications added afterwards to improve its accuracy. The model is based on neural networks. Temperature scenarios obtained from historical data are used as inputs to the neural networks in order to create load scenarios, and these load scenarios are then transformed into quantiles. By using a feature selection approach that is based on a stepwise regression technique, a neural network based model is developed for each zone. Furthermore, a dynamic choice of the temperature scenarios is suggested. The feature selection and dynamic choice of the temperature scenarios can improve the quantile scores considerably, resulting in very accurate forecasts among the top teams.

  • 40.
    Divshali, Poria Hasanpor
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Söder, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Improving PV Dynamic Hosting Capacity Using Adaptive Controller for STATCOMs2019Ingår i: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 34, nr 1, s. 415-425Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High penetrations of renewable energy sources (RES) in distribution grids lead to new challenges in voltage regulation. These challenges are not just limited to the steady-state voltage rise, but they are extended to rapid voltage changes due to wind speed variations and moving clouds, casting shadows on photovoltaic panels. According to EN50160 in low-voltage (LV) grids, the steady-state voltage should not exceed 1.1 pu (static characteristic), and rapid voltage changes should be kept less than 0.05 pu (dynamic characteristic). These two characteristics may limit the maximum amount of RES that can be installed in LV grids, called, respectively, the static hosting capacity (SHC) and dynamic hosting capacity (DHC). Although existing research just evaluated SHC in distribution grids, high-penetrated RES grids can be faced with such large voltage changes, which cause a smaller DHC than the SHC. This paper studies both SHC and DHC in distribution grids and proposes an adaptive controller for static synchronous compensators to regulate the steady-state and dynamic voltage while avoiding the unnecessary increase in the reactive power. The simulation results in some German distribution grids show considerable effects of the proposed adaptive controller on improving both SHC and DHC.

  • 41.
    Du-Bar, Christian
    et al.
    KTH.
    Mann, A.
    Wallmark, Oskar
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Werke, M.
    Comparison of Performance and Manufacturing Aspects of an Insert Winding and a Hairpin Winding for an Automotive Machine Application2019Ingår i: 2018 8th International Electric Drives Production Conference, EDPC 2018 - Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, two stators with different winding concepts but with the same rotor of an interior permanent magnet synchronous machine (IPMSM) type are presented. Both concepts are investigated based on their performance and their respectively stator cost and stator manufacturing aspects for a yearly production rate of 1 million units.

  • 42.
    Dubar, Christian
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Wallmark, Oskar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Eddy Current Losses in a Hairpin Winding for an Automotive Application2018Ingår i: Proceedings - 2018 23rd International Conference on Electrical Machines, ICEM 2018, Institute of Electrical and Electronics Engineers Inc. , 2018, s. 710-716Konferensbidrag (Refereegranskat)
    Abstract [en]

    It is well known that the effect of eddy current loss increases with a greater cross-sectional area of a wire exposed to a time-varying magnetic field. When using hairpin windings instead of conventional windings, the cross-sectional area of the strands is increased. However, conductors inside a slot are exposed to several simultaneous sources of time-varying magnetic fields that induce eddy currents. The aim of this paper is to study the non-uniform current distributions and the origin of the eddy current losses in such strands, considering typical dimensions and frequencies that are found in an electrical machine for an automotive application.

  • 43.
    Duvnjak Zarkovic, Sanja
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Stankovic, Stefan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Shayesteh, Ebrahim
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Hilber, Patrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Reliability improvement of distribution system through distribution system planning: MILP vs. GA2019Ingår i: 2019 IEEE Milan PowerTech, 2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    Distribution system planning (DSP) is very important because it can result in reliability enhancement and large cost savings for both utilities and consumers. DSP is a complex nonlinear problem, which can be solved with different optimization methods. This paper compares two such optimization methods, conventional (mixed-integer linear programming - MILP) and meta-heuristic (genetic algorithm - GA), applied to the DSP problem: construction of feeders in distribution power system from scratch. The main objective of DSP is to minimize the total cost, where both the investment and operational outage costs are considered, while the reliability of the whole system is maximized. DSP problem is applied to an actual distribution system. Solution methods are outlined, and computational results show that even though GA gives reasonably good results in faster computation time, MILP provides a better optimal solution with simpler implementation.

  • 44.
    Eiriksson, Eysteinn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Distribution grid capacity for reactive power support2017Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Det moderna kraftsystemet förandras snabbara än vad som hade förväntats för 20 årsedan. Fler och fler konventionella kraftverk kommer att stängas till fördel för distributionsgenering.Detta händer nu med trenden att introducera förnybara energikällor tillkraftsystemet.Nätverket utformades för att överföra kraft från generatorer som är anslutna till högspänningsnätetmot konsumenter anslutna till lågspänningsnätet. Med ändrad kraftblandningkommer strömflödena i systemet att förändras vilket resulterar i eventuella nätproblem.Ett av huvudproblemen är att hålla spänningen inom operativa gränser för systemet.När generationen överstiger förbrukningen i ett distributionsnät, kommer strömmen attströmma från lågspänningsnätet till högspänningsnätet vilket kommer att leda till attspänningen stiger i lågspänningsnätet. Reaktivt kraftstöd från distributionsgenering kanvara en värdefull resurs för att mildra problemet. Reaktiv effekt är nödvändig för att drivaelsystemet. Huvudkällan för reaktiv kraft är synkrona generatorer. Om den här källanstängs av måste den reaktiva effekten komma från en annan källa.Denna avhandling undersöker om distributionsgenering skulle kunna användas för attstödja reaktiv kraft till högspänningsöverföringsnätet för att styra spänningen. För dettaändamål studeras ett distributionssystem som ligger nära Worms, Tyskland. Detta distributionssystembestår av två MV-matare med med mycket distributionsgenerering, främstsolceller men även vindturbiner. Förbruknings- och generationsmätningsdata tillhandahöllsav den lokala distributionssystemoperatören. Några reaktiva effektstyrningsmetoderintroduceras och testas på detta system. Av resultaten dras slutsatsen att detär möjligt att tillhandahålla reaktivt kraftstöd från distributionsnät och en spänningsberoendereaktiv effektstyrning kan användas för detta ändamål.

  • 45.
    Estanqueiro, Ana
    et al.
    National Laboratory on Energy and Geology (LNEG).
    Ahlrot, Claes
    E.ON AB.
    Duque, Joaquim
    National Laboratory on Energy and Geology (LNEG).
    Santos, Duarte
    National Laboratory on Energy and Geology (LNEG).
    Gentle, Jake P.
    Idaho National Laboratory (INL).
    Abboud, Alexander W.
    Idaho National Laboratory (INL).
    Morozovska, Kateryna
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Hilber, Patrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Söder, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Kanefendt, Thomas
    Fraunhofer IEE.
    DLR use for optimization of network design withvery large wind (and VRE) penetration2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    Due to the stochastic nature of wind and clouds,the integration of wind and PV generation in the powersystem poses serious challenges to the long-term planning oftransmission systems. Grid reinforcements always involverelevant direct costs while the average load factor of the windand solar PV dedicated transmission lines is usually low.Additionally, in very windy sites, the same high windresource that produces large amounts of wind generation andmay congest the transmission lines transporting it to distantconsumption centres may also have a beneficial effect inincreasing the transmission capacity of those lines. In fact, theoccurrence of wind not only contributes to the loading of theconnecting line, but also increases the line capacity, via theconvective cooling of the cables - one of the main heattransfer mechanisms in conductor heat balance; in otherwords, higher winds speeds contribute to faster cooling ofconductor and therefore higher conductor’s capacitypotential. In this paper the existing methodologies tocharacterize those thermal effects in electrical cables - usuallyreferred as dynamic line rating (DLR) - are applied to severalIEA Task 25 countries case studies to characterize thetechnical value of the dynamic operation of thermallycongested lines, as well as its potential economic benefits.

  • 46.
    Grigoryeva, Anna
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Hesamzadeh, Mohammad Reza
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Tangerås, T.
    Energy system transition in the Nordic market: Challenges for transmission regulation and governance2018Ingår i: Economics of Energy & Environmental Policy, ISSN 2160-5882, E-ISSN 2160-5890, Vol. 7, nr 1, s. 127-146Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The energy system in the Nordic countries faces changes driven by increasing integration with the rest of Europe and changes to the generation mix. These developments pose challenges with respect to future network development and operation. We focus on three major aspects: market integration; generation and network adequacy; the need for more flexibility and frequency control. We describe factors behind these problems and present possible solutions within the Nordic context. One conclusion is that supranational cooperation should be further improved.

  • 47.
    GROULT, Mathieu
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Optimization of Electromechanical Studies for the Connection of Hydro Generation2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Den nuvarande elproduktionsmodellen baseras på kraftverk som är direktkopplade till stamnätet. Stamnätet i sin tur matar distributionsnätet som därefter levererar el till slutkonsumenterna. För att säkerställa stamnätets integritet samt säkerhet och undvika strömavbrott kvantifieras prestandan hos varje generator som är ansluten till det med hjälp av nätkoder. När det gäller det franska stamnätet skrivs prestandakraven i ett dokument som utfärdas av den franska transmissionssystemoperatören (TSO). Olika händelser med olika anslutningskonfigurationer måste simuleras där dess prestanda ska utvärderats. Syftet med dessa simuleringar är att identifiera stabiliteten vid varje elproduktionsenhet med bl. a. dess reaktionstid för den aktiva effekten efter kortslutningar.Med tanke på antalet generatorer som är anslutna till stamnätet framträder ett behov för överföringsoptimering vilket är syftet med detta examensarbete. För att utföra dessa simuleringar på ett effektivt sätt på alla generatorer som ägs av den ledande franska elproducenten, EDF, bidrar denna avhandling med ett verktyg som heter AuDySim kodat i mjukvarorna MATLAB och EUROSTAG. Verktyget gör det möjligt för användaren att konfigurera en elproduktionsenhet innan man utför alla simuleringar som specificeras av TSO:n och samtidigt producerar en rapport som innehåller grafisk- och data resultat. Både simuleringar och rapporten produceras automatiskt för att optimera en bearbetningstid och resursanvändning.För att validera verktygets prestanda utförs två fallstudier på olika typer av kraftverk. De två fallstudierna fokuserar på ett hydraulisk- respektive ett kärnkraftverk. I resultaten utvärderas prestanda för varje typ av kraftverk, med fokus på maskinens rotorvinkelstabilitet och andra viktiga faktorer, såsom spänning och aktiv effekt. Resultat leder till slutsatsen att AuDySim uppfyller sitt uppdrag genom att automatiskt analysera prestanda hos en elektrisk generationsenhet och presentera analysen i en rapport.

  • 48.
    Gómez, Francisco José
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    SEMANTIC INFORMATION AND PHYSICAL MULTI-DOMAIN MODELING AND SIMULATION FOR POWER SYSTEMS2019Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    There are different reasons for combining different modeling languages and simulation

    languages: Exchange of more detailed information about power network components, their

    parameters and, most importantly, mathematical equations describing their behavior and

    the exchange of a mathematical description, using equation-based languages (e.g.:

    Modelica), allows models to be detached from the mathematical solver. This leads to the

    development of new APIs within software tools, which can handle standardized modeling

    language used for model implementation. Furthermore, the mathematical description of

    models and the integration of new simulation standards, such as the FMI, could help

    avoiding ambiguities on how power system models are implemented, by providing

    additional means for the exchange of the complete description of models or parts of a

    model between software tools.

    The aim of this thesis is to provide a new approach for the development of power

    systems modeling and simulation software tools. The thesis is focused on proposing new

    methods, based on available information and simulation standards for the exchange,

    modeling, and simulation of power systems dynamic models; and to show a proof of

    concept of the feasibility of the proposed methods. To this aims, the Common Information

    Model (CIM) for the modeling and exchange of power system information is studied.

    Furthermore, the equation-based language Modelica is described and proposed with the

    aim of complementing the use of the CIM for the modeling and simulation of those

    dynamics models.

    The application of these standards lead to a different view on the modeling and

    simulation of power dynamic network models. The conventional view is that of black box

    modeling. The implementation of network model components is strongly connected to the

    simulation software tool used for steady-state and dynamics calculations. Thus, a modeler

    or test engineer only has access to the parameters of a model and relies on the software

    capabilities to calculate the states and the behavior of that model. This thesis proposes a

    different view per the application of the white box modeling and simulation concept: full

    detail and transparency on the development of a mathematical description of power system

    components and discrete events. Moreover, the combination of information standards with

    equation-based standards to produce network models allows full access and manipulation

    of the complete model details. Finally, transparency regarding the implementation of

    software tools can support either information-based, equations-based languages or

    simulation standards, which are suitable for simulation of dynamic network models.

  • 49.
    Gómez, Francisco José
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Aguilera, Miguel
    Instituto Costaricense de Electricidad (ICE), San José, Costa Rica.
    Vanfretti, Luigi
    Olsen, Svein Harald
    Statnett SF, Oslo, Norway.
    Multi-Domain Semantic Information and Physical Behavior Modeling of Power Systems and Gas Turbines Expanding the Common Information Model2018Ingår i: IEEE Access, E-ISSN 2169-3536Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The rapid increase of Intermittent Energy Resources (IER) there is a need to have dispatchable production available to ensure secure operation and increase opportunity for energy system flexibility. Gas turbine-based power plants offer flexible operation that is being improved with new technology advancements. Those plants provide in general, quick start together with significant ramping capability, which can be exploited to balance IERs. Consequently, to understand this potential source of flexibility, better models for gas turbines are required for power systems studies and analysis. In this work both the required semantic information and physical behavior models of such multi-domain systems are considered. First, UML class diagrams and RDF schemas based on the Common Information Model (CIM) standards are used to describe the semantic information of the electrical power grid. An extension that exploits the ISO 15926 standard is herein proposed to derive the multi-domain semantics required by integrated electrical power grid with detailed gas turbine dynamic models. Second, the Modelica language is employed to create the equation-based models which represent the behavior of a multi-domain physical system. A comparative simulation analysis between the power system domain model and the multi-domain model has been performed. Some differences between the turbine dynamics representation of the commonly used GGOV1 standard model and a more detailed gas turbine model are shown.

  • 50.
    Gómez, Francisco José
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Vanfretti, Luigi
    Electric, Computer and Systems Engineering, Rensselear Polytechnique Institute, Troy, NY, USA.
    Aguilera, Miguel
    Instituto Costaricense de Electricidad (ICE), San José, Costa Rica.
    Olsen, Svein
    Statnett SF, Oslo, Norway.
    CIM-2-mod: A CIM to modelica mapping and model-2-model transformation engine2019Ingår i: SoftwareX, ISSN 2352-7110, Vol. 9, s. 161-167Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    New requirement on power systems analysis tools consider information exchange for both steady-state and system dynamics information. New European regulations on information exchange power system dynamic simulations now require coordinating TSOs operations under different scenarios, some of which require to assess the dynamic behavior of power systems under a vast array of contingencies. As a mean to comply with these regulations and to advance the state-of-the-art, this work describes the software architecture of a Model-To-Model (M2M) transformation tool to create power system dynamic models using Modelica components by linking it to data from the Common Information Model (CIM). This software architecture is conceived to combine the CIM standard language with the Modelica standardized language, and to provide a Free/LibreOpen Source Software (FLOSS) CIM-compliant unambiguous power system modeling solution considering both steady-state and dynamic model representations of the electrical grid.

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