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| 2. |
- Frost, Anna E., 1988-, et al.
(författare)
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Power flow in the air gap of linear electrical machines by utilization of the Poynting vector : Part 2 - Simulations
- 2022
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Ingår i: The Journal of Engineering. - : Institution of Engineering and Technology. - 2051-3305. ; 2022:9, s. 883-891
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Tidskriftsartikel (refereegranskat)abstract
- Different types of linear generators are simulated and their power flow in the air gap is investigated. The results are compared to the analytical expressions derived in Part 1. The simulations and the analytical expressions in Part 1 show the same general behavior, but the magnitudes are lower for the analytical expressions. One explanation for the difference in magnitude can be that the harmonics of the electric and magnetic fields contribute to the power flow, which is not accounted for in the analytical expressions. Due to results from Part 1, it is investigated if changing the number of poles can decrease the tangential power flow while the normal power flow stays the same. As was suspected, changing the number of poles affected several other factors, which lead to an increase in the normal power flow when increasing the number of poles, even though the electrical power was the same. The tangential power flow also decreased for three out of four generators. Thereby, increasing the number of poles with the same length of the machine, at the cost of reduced pole-pitch, should be done with precaution.
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| 3. |
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| 4. |
- Leijon, Jennifer, et al.
(författare)
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Study of an Altered Magnetic Circuit of a Permanent Magnet Linear Generator for Wave Power
- 2018
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- The wave energy converter (WEC) studied and developed at Uppsala University in Sweden is a point absorbing buoy connected to a linear generator (LG) on the seabed. Previous studies have improved the sustainability of the generator, changing its magnets from Nd2Fe14B-magnets to ferrites. In this paper, the magnetic circuit of the linear generator is further studied. Ferrite magnets of two different types (Y30 and Y40) are studied along with different shapes of pole shoes for the system. The finite element method (FEM) simulations in a program called Ace are performed. The results show that a linear generator including both Y30 and Y40 magnets and shortened T-shaped pole shoes can generate a similar magnetic energy in the airgap as a linear generator only containing Y40 magnets and rectangular pole shoes. This shows that the magnetic circuit can be altered, opening up sizes and strengths of magnets for different retailers, and thereby possibly lowering magnet cost and transportation. This work was previously presented as a conference at the European Wave and Tidal Energy Conference (EWTEC) 2017 in Cork, Ireland; this manuscript has been carefully revised and some discussions, on magnet costs for example, have been added to this paper.
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| 5. |
- 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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| 6. |
- Sjölund, Jonathan, et al.
(författare)
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Effect of Pole Shoe Design on Inclination Angle of Different Magnetic fields in Permanent Magnet Machines
- 2021
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 14:9
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Tidskriftsartikel (refereegranskat)abstract
- Electromagnetic modelling of electrical machines through finite element analysis is an important design tool for detailed studies of high resolution. Through the usage of finite element analysis, one can study the electromagnetic fields for information that is often difficult to acquire in an experimental test bench. The requirement for accurate result is that the magnetic circuit is modelled in a correct way, which may be more difficult to maintain for rare earth free permanent magnets with an operating range that is more likely to be close to non-linear regions for the relation between magnetic flux density and magnetic field strength. In this paper, the inclination angles of the magnetic flux density, magnetic field strength and magnetization are studied and means to reduce the inclination angles are investigated. Both rotating and linear machines are investigated in this paper, with different current densities induced in the stator windings. By proper design of the pole shoes, one can reduce the inclination angles of the fields in the permanent magnet. By controlling the inclination angles, one can both enhance the performance of the magnetic circuit and increase the accuracy of simpler models for permanent magnet modelling.
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| 7. |
- Sjölund, Jonathan, et al.
(författare)
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End Effects and Geometric Compensation in a Linear Permanent Magnet Synchronous Generator with Buried Topology
- 2020
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Ingår i: 2020 International Conference on Electrical Machines (ICEM). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781728199450 ; , s. 455-461
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Konferensbidrag (refereegranskat)abstract
- Electricity production from ocean waves with different design topologies is a topic of big research interest. Many of such topologies are based on submerged linear generators which inherently introduce end forces. In this paper, the detent force is investigated for two different winding patterns using Maxwell stress tensor in a finite element software. Induced voltage is also investigated for active stator area and the unequal contributions due to stator ends. Two ways of overcoming the end forces are further investigated: The first method reduces the magnetic flux difference when the translator is surrounded by stator and air, respectively. The second aims at countering the end forces at both ends for full active stator area. The first investigated end effect compensation decreased the end effects but increased the attraction forces. The second end effect compensation decreased the end forces during full active stator area with little effect on the attraction forces.
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| 8. |
- Sjölund, Jonathan, et al.
(författare)
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End Effects and Geometric Compensation in Linear Permanent Magnet Synchronous Generators with Different Topologies
- 2021
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Ingår i: Designs. - : MDPI AG. - 2411-9660. ; 5:4
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Tidskriftsartikel (refereegranskat)abstract
- Electricity production from ocean waves with different solutions is a topic of major research interest. Many of such designs are based on linear generators that inherently introduce end forces. In this paper, detent force using Maxwell Stress Tensor and induced voltage is initially investigated for two different winding patterns for a generator topology with buried magnets in a finite element software. Two ways of overcoming the end forces are further examined: the first method reduces the magnetic flux variations of the translator between stator and air. The second method aims at countering the end forces at both ends for full active stator area. A comparison is then made between buried and surface-mounted topologies for the second end effect compensation method. Both no-load and load conditions are investigated in the comparison. The end effect compensation shows promising results for both topologies. Some clear similarities of the extended stator used to counter the end forces are also apparent, where the stator extensions completely cover the outer poles of both topologies. The results also indicate a longer full active stator area for the buried topology for the same pole-pitch and stroke length, resulting in a higher average voltage for partial stator overlap
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| 9. |
- Sjölund, Jonathan, et al.
(författare)
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Method for optimizing the magnetic circuit of a linear generator using FEM simulations
- 2020
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226 .- 2158-3226. ; 10:3
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Tidskriftsartikel (refereegranskat)abstract
- Within the area of permanent magnet electrical machines, there is an ongoing focus on replacing the rare earth permanent magnets with alternatives. An option is hard ferrites, commonly used in other applications. The relatively low coercive field strength of the ferrite magnets makes irreversible demagnetization an area that should not be neglected. In this paper, a methodology is proposed for the optimization of a slow-moving linear generator simulated in a finite element environment. The no-load phase voltage is maximized while accounting for iron saturation and permanent magnet irreversible demagnetization. This demagnetization is considered when the translator is alongside either the stator or air. The inclination angle between magnetization and magnetic field strength is accounted for by adjusting the intrinsic coercivity for each element of the permanent magnets. Characteristics for the magnet grades Y30 and Y40 are used in the optimization process. The velocity of the translator is set to resemble a speed common to wave power applications. Commercial finite element software is used together with two optimization algorithms: the genetic algorithm and the particle swarm optimization. The results of these optimization algorithms reach similar optimal solutions for the considered objective function, assuring a result close to a global maximum. The results also show a great difference in the optimal geometry for the two magnet grades and highlight the need to account for irreversible demagnetization when designing generators with ferrite magnets.
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| 10. |
- Sjölund, Jonathan, 1992-
(författare)
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On the System Optimization of Magnetic Circuit with Alternative Permanent Magnets and its Demagnetization
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Permanent magnet (PM) machines are often associated with the usage of rare earth magnets, due to their high energy density. One such rare earth magnet is the neodymium-iron-boron (NdFeB), which is mainly produced in China. Due to the global scarcity of the rare earth magnets, much interest is put into utilizing other permanent magnet materials. Among those materials is the category of ferrite permanent magnets, known for having lower magnetic properties than NdFeB. Ferrites share some of the properties with NdFeB that makes simulations simpler, namely that they have, at least, partly linear behavior in the demagnetization curve. The lower coercive properties of ferrites can, however, force them more easily into the non-linear regions of the demagnetization curves, resulting in a gradual irreversible demagnetization that lowers the performance of the ferrites. In this thesis, the magnetic circuits of electrical machines with ferrites are investigated. The implications of the reduced coercive properties are studied and means to account for the irreversible demagnetization when designing the magnetic circuit. An optimization methodology for the magnetic circuit in a linear generator is developed and presented. It is found that the coercive properties may influence the PM geometry, for the given penalty for demagnetization. By proper pole shoe design, one can reduce the inclination angle of the magnetic fields inside the PMs. The difference in topology between the surface mounted NdFeB and the buried ferrites is studied regarding the inherent longitudinal end forces of linear machines. It is found that the end forces can be reduced under both no-load and load by alterations of the stator ends. Electrical machine simulations in finite element software are often done in a two-dimensional cross section of the machine. The difference between the two-dimensional cross section and the more accurate three-dimensional model is investigated, showing that the magnetic end leakage flux in the end regions can cause a discrepancy between the two models.
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