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  • 1.
    Grop, Henrik
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Krings, Andreas
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Persson, Holger
    Semi-analytical modeling of the end-winding self-inductance in large AC machines2012In: Proceedings of the 15th International Conference on Electrical Machines and Systems (ICEMS), Institution of Electrical Engineers of Japan (IEEJ), 2012, p. 6401782-Conference paper (Refereed)
    Abstract [en]

    A semi-analytical model for calculation of self-inductance of complex coil geometries having a rectangular cross-section (form-wound coils) is proposed and evaluated. A step-by-step validation is carried on using both 2D-FEM simulations and measurements on a coil placed in air. A second version of the model is developed, to speed up the computation time through removing the possibility to analyze the contribution of the internal flux in the conductor. The predicted value of the self-inductance of a diamond-shaped coil placed in air is within 5% of the measured value.

  • 2.
    Krings, Andreas
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Iron Losses in Electrical Machines - Influence of Material Properties, Manufacturing Processes, and Inverter Operation2014Doctoral thesis, monograph (Other academic)
    Abstract [en]

    As the major electricity consumer, electrical machines play a key role for global energy savings. Machine manufacturers put considerable efforts into the development of more efficient electrical machines for loss reduction and higher power density achievements. A consolidated knowledge of the occurring losses in electrical machines is a basic requirement for efficiency improvements.

    This thesis deals with iron losses in electrical machines. The major focus is on the influences of the stator core magnetic material due to the machine manufacturing process, temperature influences, and the impact of inverter operation.

    The first part of the thesis gives an overview of typical losses in electrical machines, with focus put on iron losses. Typical models for predicting iron losses in magnetic materials are presented in a comprehensive literature study. A broad comparison of magnetic materials and the introduction of a new material selection tool conclude this part.

    Next to the typically used silicon-iron lamination alloys for electrical machines, this thesis investigates also cobalt-iron and nickel-iron lamination sheets. These materials have superior magnetic properties in terms of saturation magnetization and hysteresis losses compared to silicon-iron alloys.

    The second and major part of the thesis introduces the developed measurement system of this project and presents experimental iron loss investigations. Influences due to machine manufacturing changes are studied, including punching, stacking and welding effects. Furthermore, the effect of pulse-width modulation schemes on the iron losses and machine performance is examined experimentally and with finite-element method simulations.

    For nickel-iron lamination sheets, a special focus is put on the temperature dependency, since the magnetic characteristics and iron losses change considerably with increasing temperature. Furthermore, thermal stress-relief processes (annealing) are examined for cobalt-iron and nickel-iron alloys by magnetic measurements and microscopic analysis.

    A thermal method for local iron loss measurements is presented in the last part of the thesis, together with experimental validation on an outer-rotor permanent magnet synchronous machine.

  • 3.
    Krings, Andreas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Cossale, Marco
    Politecnico di Torino.
    Tenconi, Alberto
    Politecnico di Torino.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Magnetic Materials for Electrical Machines: a Selection Guide from the Engineering Application Point of View2014Conference paper (Refereed)
  • 4.
    Krings, Andreas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Mousavi, Seyedali
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Temperature Influence of NiFe Steel Laminations on the Characteristics of Small Slotless Permanent Magnet Machines2013In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 49, no 7, p. 4064-4067Article in journal (Refereed)
    Abstract [en]

    High performance electrical machines can operate at temperatures of 100 degrees C and beyond in rotor and stator cores. However, magnetic properties are generally measured at room temperatures around 23 degrees C to 25 degrees C according to the standards, even if it is known that the magnetization of some materials is substantially influenced by increasing temperatures. This paper investigates the thermal influence on the magnetic properties and iron losses in the stator cores of small slotless permanent magnet synchronous machines (PMSMs). The stator stack is made of thin nickel iron (NiFe) lamination sheets. Magnetic measurements of the stator core are conducted for different frequencies and flux densities at several temperatures between 25 degrees C and 105 degrees C. The obtained measurement data is afterwards used in finite element method (FEM) simulations to investigate the influence of the magnetic property change on the machine performance. For the PMSM in consideration, the FEM simulations show that an increased stator core temperature reduces the electromagnetic torque considerably; approximately 1/3 of the torque reduction due to increased rotor magnet and stator core temperatures (from 25 degrees C to 100 degrees C) can be attributed to the increased stator core temperature.

  • 5.
    Krings, Andreas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nategh, Shafigh
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Stening, Alexander
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Grop, Henrik
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Measurement and Modeling of Iron Losses in Electrical Machines (Invited Paper)2012In: Proceedings of the 5th International Conference Magnetism and Metallurgy WMM'12, Gent, Belgium: Gent University , 2012, p. 101-119Conference paper (Other academic)
    Abstract [en]

    This paper gives an overview of nowadays used simulation models and measurement methods in order to determine iron losses in electrical machinery. The paper provides machine designers and system engineers with an overview of suitable iron loss models applicable for the machine design process and simulations. Furthermore, possible methods for iron loss measurements in electrical machines are presented from ongoing research projects. Besides standard electrical power measurements, iron losses are determined by thermal and magnetic property measurements, taking into account different IEC and IEEE standards.The goal is to emphasize the different possibilities of iron loss measurement methods and possible application areas for electrical machinery.

  • 6.
    Krings, Andreas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nategh, Shafigh
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Influence of the Welding Process on the Magnetic Properties of a Slot-less Permanent Magnet Synchronous Machine Stator Core2012In: Proceedings of the 2012 XXth International Conference on Electrical Machines, IEEE conference proceedings, 2012, p. 1331-1336Conference paper (Refereed)
    Abstract [en]

    In this paper, the influence of the welding processduring the manufacturing of small, slot-less permanent magnetsynchronous machines (PMSMs) is studied. The focus lies onthe change of the magnetic properties and the iron losses inthin, high quality Si-alloyed electrical steel sheets (NO 20). It isshown that the welding process changes the magnetic materialproperties significantly and increases the specific iron losses.Experimental results are provided for magnetic flux densitiesup to 1.3 T and frequencies in the range of 0.1Hz to 200Hz.

  • 7.
    Krings, Andreas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nategh, Shafigh
    SmartMotor AS, Rolls-Royce Group, Norway .
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Influence of the Welding Process on the Performance of Slotless PM Motors With SiFe and NiFe Stator Laminations2014In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 50, no 1, p. 296-306Article in journal (Refereed)
    Abstract [en]

    The influence of the welding process during the manufacturing of small slotless permanent-magnet synchronous machines (PMSMs) is studied in this paper. The focus lies on the change of the magnetic properties in high-quality silicon-iron (SiFe) and nickel-iron (NiFe) electrical steel sheets with thicknesses of 0.1 and 0.2 mm. It is shown that the welding process changes the magnetic material properties significantly and increases the specific iron losses. Experimental results are provided for magnetic flux densities up to 1.5 T and frequencies from quasi-static to 200 Hz. The obtained measurement data is afterward used in finite-element method (FEM) simulations to investigate the influence of the magnetic property changes on the motor performance, particularly with regard to stator core losses.

  • 8.
    Krings, Andreas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nategh, Shafigh
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Local Iron Loss Identification by Thermal Measurements on an Outer-Rotor Permanent Magnet Synchronous Machine2012In: Proceedings of the 15th International Conference on Electrical Machines and Systems (ICEMS 2012), Sapporo: Institution of Electrical Engineers of Japan (IEEJ), 2012, p. 6401970-Conference paper (Refereed)
    Abstract [en]

    This paper presents the experimental determination of iron losses in an outer-rotor permanent magnet synchronous machine (PMSM) by using an inverse thermal model (ITM) in connection with transient thermal measurements. First, the theory and assumptions lying behind the method are presented. Afterwards, 3D finite element method (FEM) based simulations are used to determine the flux density distribution and iron losses in the magnetic steel parts of the investigated machine. Thermal measurements are conducted to determine local iron losses in the stator tooth tips using the ITM. Finally, measurement and FEM simulation results are compared.

  • 9.
    Krings, Andreas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Overview and Comparison of Iron Loss Models for Electrical Machines2010In: Journal of Electrical Engineering, ISSN 1582-4594, Vol. 10, no 3, p. 162-169Article in journal (Refereed)
    Abstract [en]

    One important factor in the design process and optimization of electrical machines and drives are iron losses in the core. By using new composite materials and low-loss electrical Silicon-Iron (SiFe) steels, the losses in the magnetic flux conducting parts of the machine can be reduced significantly. However, it is necessary to have accurate but also easy implementable iron loss models to take the loss effects into account, preferable already during the first design steps and simulations of new electrical machines.

    The goal of this paper is to give an overview of available iron loss models and to summarize and compare certain models for analytical and numerical machine design methods.

  • 10.
    Krings, Andreas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Overview and Comparison of Iron Loss Models for Electrical Machines2010Conference paper (Refereed)
    Abstract [en]

    One important factor in the design process and optimization of electrical machines and drives are iron losses in the core. By using new composite materials and low-loss electrical SiFe steels, the losses in the magnetic flux conducting parts of the machine can be reduced significantly. However, it is necessary to have accurate but also easy implementable iron loss models to take the loss effects into account, preferable already during the first design steps and simulations of new electrical machines.

    The goal of this paper is to give an overview of available iron loss models and to summarize and compare certain models for analytical and numerical machine design methods.

  • 11.
    Krings, Andreas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Influence of PWM Switching Frequency and Modulation Index on the Iron Losses and Performance of Slot-less Permanent Magnet Motors2013In: Proceedings of the 16th International Conference on Electrical Machines and Systems, Busan: KIEE - The Korean Institute of Electrical Engineering , 2013, p. 474-479Conference paper (Refereed)
    Abstract [en]

    This paper investigates the influence of switching frequency and modulation index on the iron losses in thin silicon-iron (SiFe) lamination sheets of a small slot-less permanent magnet synchronous machine (PMSM). First, measurements are conducted on one welded and one non-welded stator core for switching frequencies between 1 kHz and 20 kHz and modulation indices of 0.4, 0.7, and 0.9, keeping constant fundamental flux density peak values. The obtained measurement data is afterwards used in finite element method (FEM) simulations to investigate the switching frequency influenceon the performance of the PMSM.

  • 12.
    Krings, Andreas
    et al.
    ABB AB Corporate Research, Sweden .
    Soulard, Juliette
    ABB AB Corporate Research, Sweden .
    Wallmark, Oskar
    ABB AB Corporate Research, Sweden .
    PWM Influence on the Iron Losses and Characteristics of a Slot-less Permanent Magnet Motor with SiFe and NiFe Stator Cores2015In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 51, no 2, article id 6891228Article in journal (Refereed)
    Abstract [en]

    This paper investigates the influence of switching frequency and modulation index combined with welding on the iron losses in thin silicon-iron and nickel-iron lamination sheets of a small slot-less permanent magnet synchronous machine. First, measurements are conducted on welded and non-welded stator ring cores for switching frequencies between 1 kHz and 20 kHz and modulation indices of 0.4, 0.7, and 0.9, keeping constant fundamental flux density peak values. This is possible by changing the DC link voltage of the inverter. The obtained measurement data is afterwards used in finite element method (FEM) simulations to investigate the inverter influence on the performance of the permanent magnet synchronous machine.

  • 13.
    Nategh, Shafigh
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Huang, Zhe
    Lunds tekniska högskola.
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Leksell, Mats
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Krings, Andreas
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Thermal Modeling of Directry Cooled Electric Machenes Using Lumped Parameter and Limited CFD AnalysisArticle in journal (Other academic)
  • 14.
    Nategh, Shafigh
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Krings, Andreas
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Huang, Zhe
    Lunds tekniska högskola.
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Leksell, Mats
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Lindenmo, Magnus
    Evaluation of stator and rotor lamination materials for thermal management of a PMaSRM2012In: Proceedings of the 20th International Conference on Electrical Machines, ICEM 2012, 2012, p. 1309-1314Conference paper (Refereed)
    Abstract [en]

    In this paper, the thermal impact of using different steel laminations in the stator and the rotor of a permanentmagnet assisted synchronous reluctance machine designed for an automotive application is studied. In this regard, two main parameters of the steel lamination materials, thickness and amount of alloy content in weight percent, are studied. Frequency characteristics of the iron losses of the studied materials are used to estimate iron losses in the stator and rotor laminations. An accurate lumped parameter model including a housing water jacket cooling system is used to model thermal effects and estimate the temperature distribution in critical parts of the machine. The predicted temperature distributions in the machines show that using lamination materials with different amounts of alloy content leads to 2%-10% variation in the temperatures of rotor and winding. However, using materials with different thicknesses results in substantial temperature changes in critical parts of the machine (up to 75%).

  • 15.
    Nategh, Shafigh
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Krings, Andreas
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Leksell, Mats
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Evaluation of Impregnation Materials for Thermal Management of Liquid-Cooled Electric Machines2014In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 61, no 11, p. 5956-5965Article in journal (Refereed)
    Abstract [en]

    In this paper, the thermal impact of using different impregnation materials on high-performance liquid-cooled electric machines is studied. In this regard, varnish, Epoxylite, and a silicone-based thermally conductive material are considered. To study thermal effects of using different impregnation materials in theory, an advanced lumped-parameter thermal model of the studied electric machines is developed. In addition to the simulation studies, three identical induction machines using the aforementioned materials are manufactured and evaluated. Experimental tests are carried out at a wide range of current magnitudes and cooling conditions. A good agreement between the temperature measurements and corresponding simulation results is observed. It is demonstrated that using innovative thermally conductive materials in the stator slots and the end winding bodies of liquid-cooled electric machines results in a significant reduction in the winding hot spot temperature. Additionally, the influence of the critical parameters on the impregnation material performance, e. g., impregnation goodness and slot fill factor, is studied.

  • 16.
    Schoenen, Timo
    et al.
    RWTH Aachen University.
    Krings, Andreas
    RWTH Aachen University.
    van Treek, Daniel
    RWTH Aachen University.
    De Doncker, Rik W.
    RWTH Aachen University.
    Maximum DC-link voltage utilization for optimal operation of IPMSM2009In: 2009 IEEE INTERNATIONAL ELECTRIC MACHINES & DRIVES CONFERENCE, VOLS 1-3, IEEE, 2009, p. 1541-1544Conference paper (Refereed)
    Abstract [en]

    In hybrid and electrical vehicles the electric components have to be optimized to their limits. The voltage which is delivered by a high-voltage battery should be used fully by the machine. This paper describes the influence of the dc-link voltage on the efficiency and the operating limits of the electric system. For the optimal usage of the dc-link voltage, the converter control has to be extended to the six-step mode. This paper starts with a short introduction describing the electrical components of the developed hybrid vehicle. Afterwards the restrictions due to the voltage limit of the high voltage battery are analyzed. A field oriented control (FOC) is chosen to achieve a high performance control system. However, the field oriented control is not capable to fully utilize the available dc-link voltage. As will be shown it is possible to improve the control strategy of the electrical machine. Especially in applications with limited dc-link voltage and high power density, the new control strategy leads to a better utilization and a higher efficiency of the electrical system.

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