| 1. |
- Antonopoulos, Antonios, et al.
(författare)
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Experimental evaluation of the impact of harmonics on induction motors fed by modular multilevel converters
- 2014
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Ingår i: Proceedings - 2014 International Conference on Electrical Machines, ICEM 2014. - 9781479943890 ; , s. 768-775
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Konferensbidrag (refereegranskat)abstract
- Inverter-based electrical-machine drives suffer from significantly higher losses compared to sinusoidal-supply-based alternatives, fed directly from the grid. Using multilevel inverters it becomes possible to partially mitigate the effects of the switched supply waveform, while keeping the advantages of variable-speed operation. This paper aims to evaluate the increase of the losses occurring in an induction motor (IM) fed by a modular multilevel converter (M2C), when compared to grid-connected operation, in order to evaluate the impact of the inverter-generated harmonics in the machine. It is confirmed that the losses created in the motor due to the harmonic content of the inverter-generated waveforms are very low, and almost equivalent to a purely sinusoidal supply. The investigation includes an analysis of the harmonic content from experimental waveforms obtained by an 11-kW IM laboratory setup, and it is further supported by measurements of the temperature rise in the IM-stator windings. It is concluded that the M2C could create the conditions even for high-power motors to be operated without any derating.
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| 2. |
- Kontos, Sofia, et al.
(författare)
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An Overview of MnAl Permanent Magnets with a Study on Their Potential in Electrical Machines
- 2020
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 13:21
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, hard magnetic materials for future use in electrical machines are discussed. Commercialized permanent magnets used today are presented and new magnets are reviewed shortly. Specifically, the magnetic MnAl compound is investigated as a potential material for future generator designs. Experimental results of synthesized MnAl, carbon-doped MnAl and calculated values for MnAl are compared regarding their energy products. The results show that the experimental energy products are far from the theoretically calculated values with ideal conditions due to microstructure-related reasons. The performance of MnAl in a future permanent magnet (PM) generator is investigated with COMSOL, assuming ideal conditions. Simplifications, such as using an ideal hysteresis loop based on measured and calculated saturation magnetization values were done for the COMSOL simulation. The results are compared to those for a ferrite magnet and an NdFeB magnet. For an ideal MnAl hysteresis loop, it would be possible to replace ferrite with MnAl, with a reduced weight compared to ferrite. In conclusion, future work for simulations with assumptions and results closer to reality is suggested.
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| 3. |
- Mörée, Gustav, et al.
(författare)
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A Review of Permanent Magnet Models Used for Designing Electrical Machines
- 2022
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Ingår i: IEEE Transactions on Magnetics. - : IEEE. - 0018-9464 .- 1941-0069. ; 58:11
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Forskningsöversikt (refereegranskat)abstract
- This article serves as an overview of existing models of permanent magnets (PMs) for electrical machines. The review study starts with the linear recoil model, which is commonly used to describe the reversible part of the demagnetizing curve. It is a simple model, especially useful for representing materials with high anisotropy, such as ferrite, NdFeB, and SmCo. The model is harder to apply for nonlinear materials, such as Alnico, but still possible since their recoil curves are linear. The study shows how the linear recoil model could be extended to include irreversible demagnetization, temperature dependence, and angular dependence. All such models have their advantages and disadvantages, which will be discussed further. Both the magnetization and the risk of demagnetization are temperature-dependent. It could be noted that NdFeB has an increased risk of demagnetization at high temperatures, while ferrite has it at very low temperatures. The temperature dependence is described and compared for several materials, also including simplifying models. There are different methods to include the inclination angle of an applied magnetic field when studying the demagnetization of PMs. Several models describe different phenomena associated with the underlying dynamics of magnetism. Such models could then consider coercivity mechanisms and coherent rotation of magnetization, both with the Stoner-Wohlfarth model and models of domain wall motions.
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| 4. |
- Mörée, Gustav, et al.
(författare)
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Comparison of Poynting's vector and the power flow used in electrical engineering
- 2022
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Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 12:8
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Tidskriftsartikel (refereegranskat)abstract
- This paper will analyze how the energy flux of Poynting's vector is compared to the power flow in electrical engineering, where the power, instead, is defined by voltages and currents. There are alternatives to Poynting's energy flux vector that agree more with circuit theory methods such that the energy flow is in the current conductor and not in the insulation surrounding it. One such basic formulation would only consist of the total current density and the voltage potential, but it would need an alternative theorem for energy transfer. Another formulation proposed by Slepian would instead still agree with Poynting's energy transfer theorem, but it needs to add the power of alternating magnetic vector potential. The alternatives to Poynting's vector may better illustrate the energy flow in electrical engineering, but two things could be considered in their generality. First, since they are expressed by potentials, they are gauge invariant and depend on the definition of the potentials. Second, Poynting's vector is used to formulate the electromagnetic momentum, and any alternative energy flow vectors would not. These two notes are of minor importance in electrical engineering, and the alternatives could be used as good alternatives for describing power flow. The main purpose of this paper is to bridge the differences between the physical theory of energy flux and the methods in electrical power engineering. This could simplify the use of energy flux and Poynting's vector in engineering problems.
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| 5. |
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| 6. |
- Mörée, Gustav
(författare)
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Models of magnetism in electrical machines
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The magnetic field is a fundamental part of an electrical machine, for establishing the torque and inducing voltages and currents. Then acting as the link between mechanical power and electrical power. This thesis will give a comprehensive study of how magnetism could be modeled. Covering how the magnetic field relates to energy transfer, power flow, and the forces of electrical machines.An electromagnetic energy transfer is usually described by Poynting’s vector, which has a different formulation than the power flow of electrical engineering. The main difference is that Poynting’s vector localizes the energy flux in the surrounding electromagnetic fields of a current-carrying conductor, instead of inside the conductor itself.The forces in a machine can be modeled by the field lines of the magnetic flux density. The force density consists of two vector components: the magnetic tension force and the magnetic pressure gradient force. The magnetic tension force acts to straighten curved field lines, based on the curvature of the flux density. The magnetic pressure gradient force acts from areas of high flux to areas of low flux. The force density could describe the forces in a synchronous machine, both for the torque of the load and for the machine’s radial forces between the rotor and the stator.The force density could also be used to improve the understanding of Maxwell stress tensor,as they are easier to illustrate as vectors, compared to the matrix form within the Maxwell stresstensor. It also expresses the location of the force density, which can improve the use of enclosedvolumes when calculating forces based on the divergence theorem with Maxwell stress tensor.
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| 7. |
- Mörée, Gustav, et al.
(författare)
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Overview of Hybrid Excitation in Electrical Machines
- 2022
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 15:19
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid excitation is a technology that combines the advantages of field windings and permanent magnets for inducing magnetic flux. This article studies the benefits of hybrid excitation and provides an outlook on their possible applications, such as wind power generators and electric vehicle motors. Compared to permanent magnet-based machines, hybrid excitation gives a variable flux while still using the advantage of the permanent magnets for a portion of the flux. This article also looks into some different categories of machines developed for hybrid excitation. The categories are based on the reluctance circuit, the relative geometrical location of the field windings relative to the permanent magnets, or the placement of the excitation system.
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| 8. |
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| 9. |
- Mörée, Gustav, et al.
(författare)
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Review of Hysteresis Models for Magnetic Materials
- 2023
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 16:9
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Forskningsöversikt (refereegranskat)abstract
- There are several models for magnetic hysteresis. Their key purposes are to model magnetization curves with a history dependence to achieve hysteresis cycles without a frequency dependence. There are different approaches to handling history dependence. The two main categories are Duhem-type models and Preisach-type models. Duhem models handle it via a simple directional dependence on the flux rate, without a proper memory. While the Preisach type model handles it via memory of the point where the direction of the flux rate is changed. The most common Duhem model is the phenomenological Jiles–Atherton model, with examples of other models including the Coleman–Hodgdon model and the Tellinen model. Examples of Preisach type models are the classical Preisach model and the Prandtl–Ishlinskii model, although there are also many other models with adoptions of a similar history dependence. Hysteresis is by definition rate-independent, and thereby not dependent on the speed of the alternating flux density. An additional rate dependence is still important and often included in many dynamic hysteresis models. The Chua model is common for modeling non-linear dynamic magnetization curves; however, it does not define classical hysteresis. Other similar adoptions also exist that combine hysteresis modeling with eddy current modeling, similar to how frequency dependence is included in core loss modeling. Most models are made for scalar values of alternating fields, but there are also several models with vector generalizations that also consider three-dimensional directions.
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| 10. |
- Mörée, Gustav, et al.
(författare)
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Review of Play and Preisach models for hysteresis in magnetic materials
- 2023
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Ingår i: Materials. - : MDPI. - 1996-1944. ; 16:6
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Tidskriftsartikel (refereegranskat)abstract
- This paper studies the properties of the Preisach model and the play model, and compare their similarities. Both are history-dependent hysteresis models that are used to model magnetic hysteresis. They are described as discrete sums of simple hysteresis operators but can easily be reformulated as integral equations of continuous distribution functions using either a Preisach weight distribution function or a play distribution function. The models are mostly seen as phenomenological or mathematical tools but can also be related to friction-like pinning of domain-wall motions, where Rayleigh’s law of magnetic hysteresis can be seen as the simplest case on either the play model or the Preisach model. They are poor at modeling other domain behavior, such as nucleation-driven hysteresis. Yet another hysteresis model is the stop model, which can be seen as the inverted version of the play model. This type of model has advantages for expressions linked to energy and can be related to Steinmetz equation of hysteresis losses. The models share several mathematical properties, such as the congruency property and wiping-out property, and both models have a history of dependence that can be described by the series of past reversal points. More generally, it is shown that the many models can be expressed as Preisach models, showing that they can be treated as subcategories of the Preisach type models. These include the play model, the stop model and also the alternative KP-hysteron model.
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