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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 Jacket2019Inngår i: IEEE TRANSACTIONS ON TRANSPORTATION ELECTRIFICATION, ISSN 2332-7782, Vol. 5, nr 3, s. 618-629Artikkel i tidsskrift (Fagfellevurdert)
    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 jacketInngår i: Artikkel i tidsskrift (Fagfellevurdert)
  • 3.
    Ali, Muhammad Taha
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Ghandhari, Mehrdad
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Optimal tuning and placement of POD for SSCI mitigation in DFIG-based power system2019Inngår i: 2019 IEEE Milan PowerTech, PowerTech 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, artikkel-id 8810891Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The phenomenon of sub-synchronous control interaction (SSCI) in doubly-fed induction generators (DFIGs) is investigated and the optimal tuning and placement of a power oscillation damper (POD) for its mitigation is proposed in this paper. The effect of the POD on the DFIG system is studied by placing it at all the summation junctions of rotor-side converter (RSC) and grid-side converter (GSC) controllers, turn by turn. Five local signals are examined as different input signals to the POD out of which three local signals gave promising results. These signals include the DFIG's active power, the magnitude of the DFIG's apparent power, and the magnitude of the current through the transmission line. Residues are calculated for each POD placement and for each input to the POD. The calculated residues are studied along with the root-locus plots to see the effect of the POD on the mitigation of SSCI and the stability of the DFIG-based system.

  • 4.
    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 problem2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    It is important for NEOM management in the contemporary world to put in place NEOM projects using the available resources. The region in which the NEOM project is spacious and vast with conditions suited to generate energy from solar and wind. The NEOM projectis expected to be set up in the very resourceful state of Saudi Arabia. The purpose of the study is to assist in setting up a sustainable city through the exploitation of solar and wind energy. The aim of the study was to assist in the generation of more than 10 GW renewable energy to replace approximately 80,000 barrels of fossil energy. The problem of coming up with renewable and sustainable energy from the unexploited sources is addressed. The renewable city is expected to be a technological hub based on Green Energy with 100% renewable energy, which is correspond to 72:4GW. Freiburg and Masdar as renewable cities are used as case studies in the research. NEOM power generation capacity is capable to cover Saudi Arabia power generation capacity (approximately 71GW), which is more than enough for a city. The study reveals that the total power generation from wind farms, tidal farms, solar stations, and solar power tower stations are 9:1373GW, 4:76GW, 57:398GW and 1:11GW respectively. Saudi Arabia has plans to set up 16 nuclear plants (17 GW each) for energy purposes (total of 272 GW), which will be part of Saudi Arabia national grid and will be more than enough to cover NEOM electricity demand in case NEOM does not reach demand capacity. In case NEOM energy does not meet the demand, electricity generation from 16 Nuclearpower plants generating 17GW each, and 6 Natural underground batteries with a capacity of 120MW each are recommended. The study results can be applied in NEOM Institute of Science and Technology for further research on renewable energy. The findings can also be used for research extension of HVDC transmission lines between NEOM and Saudi Arabia main grid, Egypt, and Jordan.

  • 5.
    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 Spoofing2018Inngår i: 2018 IEEE POWER & ENERGY SOCIETY GENERAL MEETING (PESGM), IEEE , 2018Konferansepaper (Fagfellevurdert)
  • 6.
    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 absorbers2018Inngår i: Proceedings of NordDesign: Design in the Era of Digitalization, NordDesign 2018, 2018Konferansepaper (Fagfellevurdert)
  • 7.
    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 variable2019Inngår i: The Journal of Engineering, ISSN 1872-3284, E-ISSN 2051-3305, nr 17, s. 3609-3613Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 8.
    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 Grid2018Inngår i: PROCEEDINGS OF THE 2018 19TH INTERNATIONAL SCIENTIFIC CONFERENCE ON ELECTRIC POWER ENGINEERING (EPE), Institute of Electrical and Electronics Engineers (IEEE), 2018, s. 64-69Konferansepaper (Fagfellevurdert)
    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.

  • 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.
    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 Applications2018Inngår i: 2018 28th International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV), Institute of Electrical and Electronics Engineers (IEEE), 2018, Vol. 2, s. 527-530Konferansepaper (Fagfellevurdert)
    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.

  • 10.
    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 Breakers2018Inngår i: 20th European Conference on Power Electronics and Applications (EPE'18 ECCE EUROPE), 2018Konferansepaper (Fagfellevurdert)
    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.

  • 11.
    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 degradation2019Inngår i: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 112, s. 555-570Artikkel, forskningsoversikt (Fagfellevurdert)
    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.

  • 12.
    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 Operation2017Inngår i: 2017 IEEE POWER & ENERGY SOCIETY GENERAL MEETING, IEEE , 2017Konferansepaper (Fagfellevurdert)
    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.

  • 13.
    Bakas, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Hybrid Converters for HVDC Transmission2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The line-commutated converter (LCC) and the voltage-source converter (VSC) are the two main converter technologies utilized in high-voltage direct current (HVDC) transmission applications. Depending on the application requirements, one technology might be more advantageous than the other. On the one hand, the LCC features technological maturity, high efficiency, and high power-transfer capability, but it lacks the ability to independently control active and reactive power and to ride through ac faults. On the other hand, the VSC overcomes the shortcomings of the LCC and offers more functionality, as it features the ability to independently control active and reactive power, ac-fault ride through capability, black-start capability, and superior harmonic performance. Yet, it is less mature, less efficient, and has lower power-transfer capability than the LCC. Thus, the combination of the LCC and the VSC topologies could yield hybrid converters that leverage the complementary characteristics of both technologies and thus are optimized for HVDC applications. Therefore, the main objective of this thesis is to investigate existing and derive new hybrid converters that combine the complementary characteristics of the LCC and VSC technologies.

    The hybrid converters investigated in this thesis are divided in two main categories, namely: (a) current-source; and (b) voltage-source hybrid converters. The former category includes hybrid converters that are based on the LCC structure and utilize a VSC part either for compensating the reactive power consumed by the LCC, or for active filtering of the LCC current harmonics, or for independently controlling active and reactive power, or for achieving a combination of these functionalities. Four different current-source hybrid converters have been investigated and compared in terms of functionality, conduction losses, and semiconductor requirements.

    The second category includes more complex circuits that combine thyristors and modular VSC elements in ways that enable these hybrid converters to operate as VSCs and to achieve high active-power capability. Two new voltage-source hybrid converters are analyzed and compared in terms of active-power capability, semiconductor requirements, and controllability. This study reveals that the hybrid alternate-common-arm converter (HACC) is the most interesting circuit; thus, an in-depth analysis is performed for this converter. The theoretical analysis shows that, under certain operating conditions, the HACC can transfer twice the active power of the full-bridge modular multilevel converter (FB-MMC) with lower semiconductor rating per unit of active power. Yet, if the total commutation time of the thyristors and/or the power angle are increased beyond certain values, the active-power capability of the HACC is reduced. Finally, simulation and experimental results are provided in order to verify the theoretical analysis and prove the feasibility of the HACC.

  • 14.
    Bakas, Panagiotis
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik. ABB Corporate Research, Västerås, Sweden.
    Ilves, K.
    ABB Corporate Research, Västerås, Sweden.
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik. ABB Corporate Research, Västerås, Sweden.
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Hybrid Converter With Alternate Common Arm and Director Thyristors for High-Power Capability2018Inngår i: 2018 20th European Conference on Power Electronics and Applications (EPE’18 ECCE Europe), 2018Konferansepaper (Fagfellevurdert)
    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).

  • 15.
    Bakas, Panagiotis
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Ilves, Kalle
    ABB Corporate Research.
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Hybrid alternate-common-arm converter with director thyristorsImpact of commutation time on the active-power capability: Impact of commutation time on the active-power capability2019Inngår i: Proc. 2019 21st European Conference on Power Electronics and Applications (EPE'19 ECCE Europe), IEEE and EPE Association, Genova, Italy, Sep. 2-6, 2019, Genova, Italy: IEEE and EPE Association , 2019Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    This paper investigates the impact of the thyristor commutation time on the peak currents and the active power capability of the hybrid alternate-common-arm converter (HACC). This converter employs director thyristors for the alternate connection of a common arm in parallel to the main arms. The parallel connection enables current sharing among the arms, which allows the HACC to transfer higher output power without increasing the peak arm current. It is shown that the active-power capability of the HACC is doubled for a certain current-sharing factor, which, however, is altered by the thyristor commutation time. Therefore, the impact of the commutation time on the active-power capability of the HACC is investigated theoretically. Finally, this analysis is verified by simulation results.

  • 16.
    Bakas, Panagiotis
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Ilves, Kalle
    ABB Corporate Research.
    Okazaki, Yuhei
    ABB Corporate Research.
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik. ABB Corporate Research.
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Hybrid alternate-common-arm converter with high power capability: potential and limitationsInngår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    This paper studies a new hybrid converter thatutilizes thyristors and full-bridge (FB) arms for achieving higherpower capability than the full-bridge (FB) modular multilevel converter (MMC) with reduced semiconductor requirements. The study covers the theoretical analysis of the energy balancing,the dimensioning principles, the maximum power capability, and the limitations imposed by the discontinuous operation of theconverter. Based on the analysis of these aspects, the theoretical analysis is concluded by identifying the design constraints that need to be fulfilled for achieving the maximum power capabilityof the converter. It is concluded that the maximum power capability can be achieved for a certain range of modulation indices and is limited by both the commutation time of the thyristors andthe power angle. Finally, simulation and experimental results that confirm the theoretical analysis and the feasibility of the studied converter are presented and discussed.

  • 17.
    Bakas, Panagiotis
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Okazaki, Yuhei
    ABB Corporate Research.
    Ilves, Kalle
    ABB Corporate Research.
    Norrga, Staffan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Harnefors, Lennart
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Design considerations and comparison of hybrid line-commutated and cascaded full-bridge converters with reactive-power compensation and active filtering capabilities2019Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    This paper compares two hybrid topologies that combine the line-commutated converter (LCC) with cascaded full-bridge (FB) converters. The latter are utilized for compensating the reactive power and filtering the current harmonics of the LCC. The method that was developed for dimensioning these hybrid topologies is presented in detail. This method is utilized for calculating the arm voltage and current waveforms, which are used to estimate other important quantities, such as conduction losses and energy variations. Finally, the studied converters are compared in terms of voltage/current ratings, semiconductor requirements, conduction losses, and energy variations.

  • 18.
    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"2018Inngår i: Software Quality Professional, ISSN 1522-0540, Vol. 7, s. 34-36Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 19.
    Bessegato, Luca
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Modeling of Modular Multilevel Converters for Stability Analysis2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Modular multilevel converters (MMCs) have recently become the state-of-the-art solution for various grid-connected applications, such as high-voltage direct current (HVDC) systems and flexible alternating current transmission systems (FACTS). Modularity, scalability, low power losses, and low harmonic distortion are the outstanding properties that make MMCs a key technology for a sustainable future.

     

    The main objective of this thesis is the modeling of grid-connected MMCs for stability analysis. The stability of the interconnected system, formed by the converter and the ac grid, can be assessed by analyzing the converter ac-side admittance in relation to the grid impedance. Therefore, a method for the calculation of the ac-side admittance of MMCs is developed. This method overcomes the nonlinearities of the converter dynamics and it can be easily adapted to different applications. Moreover, the effects of different control schemes on the MMC ac-side admittance are studied, showing how the converter admittance can be reshaped. This is a useful tool for system design, because it shows how control parameters can be selected to avoid undesired grid-converter interactions.

     

    This thesis also studies ac/ac MMCs for railway power supplies, which are used in countries with a low-frequency railway grid, such as Germany (16.7 Hz) and Sweden (16 2/3 Hz). A hierarchical control scheme for these converters 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. For computing the insertion indices, an open-loop scheme with sum capacitor voltage estimation is applied to the ac/ac MMC. Lyapunov stability theory is used to prove the asymptotic stability of the converter operated with the proposed control method. This specific open-loop scheme is also adapted to a modular multilevel matrix converter, which performs three-to-three phase direct conversion.

     

    Finally, this thesis presents the design of a down-scaled MMC prototype for experimental verification, rated at 10 kW with 30 full-bridge submodules. The hardware and the software are designed to be easily reconfigurable, which makes the converter suitable for different research projects focused on MMCs. Experiments on this down-scaled MMC are used to support and validate the key results presented throughout the thesis.

  • 20.
    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 Converter2018Inngår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 21.
    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 Converter2019Inngår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 34, nr 8, s. 7206-7220, artikkel-id 8514034Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 22.
    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 Supplies2019Inngår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Artikkel i tidsskrift (Fagfellevurdert)
    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. 

  • 23.
    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 modulation2014Inngår i: Energy Conversion Congress and Exposition (ECCE), 2014 IEEE, 2014, s. 3672-3678Konferansepaper (Fagfellevurdert)
    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.

  • 24.
    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 Purposes2018Konferansepaper (Fagfellevurdert)
    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.

  • 25.
    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 converters2017Inngår 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. 308-312Konferansepaper (Fagfellevurdert)
    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.

  • 26.
    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 Estimation2016Inngår i: IEEE 8th International Power Electronics and Motion Control Conference (IPEMC-ECCE Asia), 2016, IEEE, 2016, s. 3447-3452, artikkel-id 7512848Konferansepaper (Fagfellevurdert)
    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.

  • 27.
    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 cells2019Inngår i: Journal of Energy Storage, E-ISSN 2352-152X, Vol. 21, s. 741-749Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 28.
    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 Sheets2018Inngår i: 2018 XIII International Conference on Electrical Machines (ICEM), IEEE conference proceedings, 2018Konferansepaper (Fagfellevurdert)
    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.

  • 29.
    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 Modes2019Inngår i: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 34, nr 2, s. 1095-1104Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 30.
    Blom, Evelin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Including Hydropower in Large Scale Power System Models2019Rapport (Annet vitenskapelig)
    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.

  • 31.
    Brauer, Patrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    High-Frequency Voltage Distribution Modelling of a Slotless PMSM from a Machine Design Perspective2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The introduction of inverters utilizing wide band-gap semiconductors allow for higher switching frequency and improved machine drive energy efficiency. However, inverter switching results in fast voltage surges which cause overvoltage at the stator terminals and uneven voltage distribution in the stator winding. Therefore, it is important to understand how next generation machine drives, with higher switching frequency, affect the voltage distribution. For this purpose, a lumped-parameter model capable of simulating winding interturn voltages for the wide frequency range of 0-10 MHz is developed for a slotless PMSM. The model includes both capacitive and inductive couplings, extracted from 2D finite element simulations, as well as analytically estimated resistive winding losses. The developed model of a single phase-winding is used to investigate how machine design aspects such as insulation materials and winding conductor distribution affects both voltage distribution and winding impedance spectrum. Validation measurements demonstrate that the model is accurate for the wide frequency range. The sensitivity analysis suggests that the winding conductor distribution affect both impedance spectrum and voltage distribution. For the slotless machine, capacitance between the winding and the stator is several times smaller than capacitance between turns. Therefore, the high-frequency effects are dominated by the capacitance between turns. Insulation materials that affect this coupling does therefore have an impact on the impedance spectrum but does not have any significant impact on the voltage distribution.

  • 32.
    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 IEDs2019Konferansepaper (Fagfellevurdert)
    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.

  • 33.
    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 proposal2018Inngår i: International Conference on the European Energy Market, EEM, IEEE Computer Society , 2018Konferansepaper (Fagfellevurdert)
    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.

  • 34.
    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 Proposal2018Inngår i: 2018 15TH INTERNATIONAL CONFERENCE ON THE EUROPEAN ENERGY MARKET (EEM), IEEE , 2018Konferansepaper (Fagfellevurdert)
    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.

  • 35.
    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 evolution2019Inngår i: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 105, s. 803-813Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 36.
    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 integration2019Inngår i: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 105, s. 404-419Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 37.
    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 Converters2018Konferansepaper (Fagfellevurdert)
    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.

  • 38.
    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 Converters2019Konferansepaper (Fagfellevurdert)
    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.

  • 39.
    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 (Annet vitenskapelig)
    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.

  • 40.
    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 Djibouti2019Inngår i: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 185, s. 884-894Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 41.
    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 heating2018Inngår i: Euroheat and Power (English Edition), ISSN 1613-0200, Vol. 15, nr 4, s. 10-16Artikkel i tidsskrift (Fagfellevurdert)
  • 42.
    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 forecasting2018Inngår i: International Conference on the European Energy Market, EEM, IEEE Computer Society, 2018, artikkel-id 8469901Konferansepaper (Fagfellevurdert)
    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.

  • 43.
    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 forecasting2018Inngår i: 2018 15TH INTERNATIONAL CONFERENCE ON THE EUROPEAN ENERGY MARKET (EEM), IEEE , 2018Konferansepaper (Fagfellevurdert)
    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.

  • 44.
    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 forecasting2019Inngår i: International Journal of Forecasting, ISSN 0169-2070, E-ISSN 1872-8200Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 45.
    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 STATCOMs2019Inngår i: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 34, nr 1, s. 415-425Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 46.
    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 Application2019Inngår i: 2018 8th International Electric Drives Production Conference, EDPC 2018 - Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2019Konferansepaper (Fagfellevurdert)
    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.

  • 47.
    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 Application2018Inngår i: Proceedings - 2018 23rd International Conference on Electrical Machines, ICEM 2018, Institute of Electrical and Electronics Engineers Inc. , 2018, s. 710-716Konferansepaper (Fagfellevurdert)
    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.

  • 48.
    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. GA2019Inngår i: 2019 IEEE Milan PowerTech, 2019Konferansepaper (Fagfellevurdert)
    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.

  • 49.
    Eiriksson, Eysteinn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Distribution grid capacity for reactive power support2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The modern power system is changing at a rate faster than would have been expected20 years ago. More and more conventional power plants will be shut down in favour ofdistribution generation (DG). This is happening now with the trend of introducing renewableenergy sources (RES) to the power system.The grids were designed to transfer power from generating units connected to the highvoltage grids towards the end consumers connected to the low voltage grids. With changedpower mix, power flows in the system will change resulting in possible grid problems. Oneof the main problems is keeping the voltage within operational limits of the system. Whenthe generation exceeds the consumption in a distribution network, the power will flow fromthe low voltage network towards the high voltage network (reverse power flow) which willcause the voltage to rise in the low voltage network. Reactive power support from DG canbe a valuable resource to mitigate the problem. Reactive power is necessary to operatethe power system. The main source of reactive power is synchronous generators. If thissource is shut down, the reactive power must come from another source.This thesis investigates if DG could be used to support reactive power to the highvoltage transmission network to control the voltage. For this purpose, a distributionsystem located close toWorms, Germany will be studied. This distribution system consistsof two MV feeders with high penetration of DG, mostly photovoltaic (PV) but also windturbines (WT). Consumption and generation measurement data was provided by the localdistribution system operator (DSO). A few reactive power control methods are introducedand tested on this system. From the results, it is concluded that it is possible to providereactive power support from distribution networks and a voltage dependent reactive powercontrol can be used to this purpose.

  • 50.
    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) penetration2018Konferansepaper (Fagfellevurdert)
    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.

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