| 1. |
- Potapenko, Tatiana
(författare)
-
Wave energy converter: hydrodynamics and control
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Waves, just like wind and solar radiation, is a widely available renewable energy source. Waves are created when winds move across the sea surface. The estimated potential of wave energy is abundant, but the commercial harvesting technologies are still in their infancy. There are different wave energy converter designs, one of which is developed at Uppsala University and is based on a permanent magnet linear generator. A semi-submerged buoy on the water surface absorbs the energy of the wave and converts the mechanical energy into electricity with a direct drive linear generator.One of the main goals in wave energy research is to enhance the absorbed power for a single device and multiple devices in wave energy parks. The energy harvest can be increased in different ways: by optimizing the buoy, the generator, and/or by implementing control strategies. To assess the best optimization strategies numerical modeling is an inexpensive tool, aimed to predict the complex behavior of the system. This licentiate thesis focuses on the study of wave energy converters in irregular waves for testing sites, such as in Lysekil (Sweden) and Wave Hub (UK). The numerical model is used to analyze the wave energy conversion power performance. The hydrodynamic model involves radiation force approximation for a state-space model. It has been shown that a higher order of approximation can be achieved by vector fitting than by the transfer function fitting in the frequency domain, especially for the interaction of several bodies with the incident wave. Wave energy converter concepts are evaluated in terms of absorbed power for the resistive load connection, representing the passive control of the currents in the generator windings. Additionally, RC-load intends to model a grid-connected generator with active rectification, such that phase angle is compensated. Finally, a power-hardware-in-the-loop study of a grid-connected wave energy converter is presented. The current and voltage profiles of a grid-connected wave energy converter are shown with a suggestion on the implementation of RLC filter for power smoothing.
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| 2. |
- Adjei, Evans, et al.
(författare)
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Regional labour market effects of immigration on low-skilled workers: the case of Sweden 1990–2003
- 2021
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Ingår i: International Journal of Social Economics. - : Emerald Group Publishing Limited. - 0306-8293 .- 1758-6712. ; 48:3, s. 456-476
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The purpose of this paper is to examine the effects of immigration on the labour market outcomes of low-educated natives (i.e. residents without a university diploma). Using the labour market competition theory, which argues that the labour market effects of natives depend on the skill set of immigrants, the paper addresses whether immigrants are complementary to or substitutes for native workers.Design/methodology/approach: Longitudinal matched employer–employee data on Sweden are used to estimate how low-educated natives, in regions experiencing the greatest influx of refugees from the Balkan wars, responded to this supply shock with regard to real wages, employment and job mobility between 1990 and 2003.Findings: First, the analysis shows that low-educated native workers respond to the arrival of immigrants with an increase in real wages. Second, although employment prospects in general worsened for low-skilled workers in most regions, this is not attributable to the regions experiencing the largest supply shock. Third, there are indications that low-skilled natives in immigration-rich regions are more likely to change workplace, particularly in combination with moving upwards in the wage distribution.Originality/value: Rather than seeing an emergence of the commonly perceived displacement mechanism when an economy is subject to a supply shock, the regional findings suggest that high inflows of immigrants tend to induce a mechanism that pulls native workers upwards in the wage distribution. This is important, as the proportion of immigrants is seldom evenly distributed within a nation.
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| 3. |
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| 4. |
- Bayati, Zahra, 1958, et al.
(författare)
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Nytt centrum mot rasism får fel vetenskaplig inriktning
- 2015
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Ingår i: Göteborgs Posten. - 1103-9345. ; :2015-06-14
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- När rasism ska förstås som något som kan lösas genom att lära ut tolerans undergrävs förtroendet för regeringens satsning. Dessutom saknas det etnisk/rasifierad mångfald bland forskargruppen.
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| 5. |
- Broadaway, K Alaine, et al.
(författare)
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Loci for insulin processing and secretion provide insight into type 2 diabetes risk.
- 2023
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Ingår i: American Journal of Human Genetics. - : Elsevier. - 0002-9297 .- 1537-6605. ; 110:2, s. 284-299
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Tidskriftsartikel (refereegranskat)abstract
- Insulin secretion is critical for glucose homeostasis, and increased levels of the precursor proinsulin relative to insulin indicate pancreatic islet beta-cell stress and insufficient insulin secretory capacity in the setting of insulin resistance. We conducted meta-analyses of genome-wide association results for fasting proinsulin from 16 European-ancestry studies in 45,861 individuals. We found 36 independent signals at 30 loci (p value < 5 × 10-8), which validated 12 previously reported loci for proinsulin and ten additional loci previously identified for another glycemic trait. Half of the alleles associated with higher proinsulin showed higher rather than lower effects on glucose levels, corresponding to different mechanisms. Proinsulin loci included genes that affect prohormone convertases, beta-cell dysfunction, vesicle trafficking, beta-cell transcriptional regulation, and lysosomes/autophagy processes. We colocalized 11 proinsulin signals with islet expression quantitative trait locus (eQTL) data, suggesting candidate genes, including ARSG, WIPI1, SLC7A14, and SIX3. The NKX6-3/ANK1 proinsulin signal colocalized with a T2D signal and an adipose ANK1 eQTL signal but not the islet NKX6-3 eQTL. Signals were enriched for islet enhancers, and we showed a plausible islet regulatory mechanism for the lead signal in the MADD locus. These results show how detailed genetic studies of an intermediate phenotype can elucidate mechanisms that may predispose one to disease.
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| 6. |
- D. Silva, Marcelo, 1995-, et al.
(författare)
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On the Mitigation of Leakage Flux in Spoke Type Permanent Magnet Synchronous Machines
- 2022
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Ingår i: 2022 International Conference on Electrical Machines (ICEM). - : IEEE. - 9781665414333 - 9781665414326 ; , s. 302-308
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Konferensbidrag (refereegranskat)abstract
- The use of rare-earth elements in permanent magnets rises economic, environmental and supply-chain related concerns. Instead, ferrite magnets have been researched as an alternative. The magnetic flux concentration capacity of the Spoke Type Permanent Magnet Synchronous Motor (PMSM) and the low magnetic remanence of the ferrite magnet make them complementary strategies towards the desirable performance. However, if restricted to conventional manufacturing processes and materials, the mechanical design is a challenging step of the development of these machines. This paper explores how mechanical constraints impact electromagnetic performance. To access the interdependency of the performance and the mechanical constraints, finite element analyses are done both in the mechanical and electromagnetic domain. The results show that the mechanical constraints have an impact on the performance, although it is possible to reduce it by adapting the design to the electromagnetic and mechanical properties of the electrical steel.
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| 7. |
- Eklund, Petter, 1989-, et al.
(författare)
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A Complete Design of a Rare Earth Metal-Free Permanent Magnet Generator
- 2014
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Ingår i: Machines. - Basel, Switzerland : Multidisciplinary Digital Publishing Institute. - 2075-1702.
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Tidskriftsartikel (refereegranskat)abstract
- The price of rare-earth metals used in neodymium-iron-boron (NdFeB) permanent magnets (PMs) has fluctuated greatly recently. Replacing the NdFeB PMs with more abundant ferrite PMs will avoid the cost insecurity and insecurity of supply. Ferrite PMs have lower performance than NdFeB PMs and for similar performance more PM material has to be used, requiring more support structure. Flux concentration is also necessary, for example, by a spoke-type rotor. In this paper the rotor of a 12 kW NdFeB PM generator was redesigned to use ferrite PMs, reusing the existing stator and experimental setup. Finite element simulations were used to calculate both electromagnetic and mechanical properties of the design. Focus was on mechanical design and feasibility of construction. The result was a design of a ferrite PM rotor to be used with the old stator with some small changes to the generator support structure. The new generator has the same output power at a slightly lower voltage level. It was concluded that it is possible to use the same stator with either a NdFeB PM rotor or a ferrite PM rotor. A ferrite PM generator might require a larger diameter than a NdFeB generator to generate the same voltage.
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| 8. |
- Eklund, Petter, 1989-, et al.
(författare)
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Air Gap Magnetic Flux Density Variations due to Manufacturing Tolerances in a Permanent Magnet Synchronous Generator
- 2016
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Ingår i: 2016 XXII INTERNATIONAL CONFERENCE ON ELECTRICAL MACHINES (ICEM). - : IEEE. - 9781509025381 ; , s. 93-99
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Konferensbidrag (refereegranskat)abstract
- The impact of manufacturing tolerances on the performance of a permanent magnet synchronous generator is investigated. A generator with a flux concentrating spoke-type rotor, with ferrite permanent magnets, is used in the investigation. Measurements of the air gap magnetic flux density, the air gap length, as well as the magnetization and size of the permanent magnets have been performed. Correlations are calculated and causalities are discussed. It is found that the permanent magnets used are below tolerance in remanent magnetic flux density, that the air gap length is smaller than specified, and that the resulting air gap magnetic flux density is lower than specified. From the results it can be concluded that the design should be made with tolerances in mind and that quality control of parts, especially of PM magnetization, is important for machine performance.
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| 9. |
- Eklund, Petter, 1989-
(författare)
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Design of Rare Earth Free Permanent Magnet Generators
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Low speed permanent magnet (PM) synchronous generators (SGs) are commonly used in renewable energy. Rare earth (RE) PMs such as neodymium-iron-boron are a popular choice due to their high performance. In 2011 supply and cost issues were added to the previously existing environmental concerns regarding REPM raw materials as the world's major producer China imposed export restrictions. This thesis aims to investigate and propose design solutions for PMSGs that do not use REPMs. Two approaches are used: to design generators using the cheaper and more abundant ferrite PM materials, and to investigate how properties of new PM materials influence SG design.A ferrite PM rotor is designed to replace a REPM rotor in an experimental 12 kW wind power generator. The new design employs a flux concentrating spoke type rotor to achieve performance similar to the old REPM rotor while using ferrite PMs. The ferrite PM rotor design is built. The air gap length, magnetic flux density in the air gap, PM remanence, and voltage at both load and no load are measured. The generator has lower no load voltage than expected, which is mainly explained by lower than specified remanence of the ferrite PMs in the prototype. With the measured remanence inserted into the calculations some discrepancy remains. It is found that the discrepancy can be explained by the magnetic leakage flux in the end regions of the spoke type rotor, which is not modeled in the two dimensional simulations used for the design calculations.To investigate the influence of PM material properties three different PM rotor topologies are optimized for torque production using PM materials described by their remanence, recoil permeability, and demagnetization resistance. Demagnetization is considered using currents determined by a novel, winding design independent short circuit model. It is found that the spoke type rotor gives the highest torque of the three rotor topologies for low remanence materials as long as the PMs have sufficient demagnetization resistance. For high remanence materials the surface mounted PM rotor can give higher torque if the demagnetization resistance is high, but otherwise a capped PM rotor gives higher torque.
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| 10. |
- Eklund, Petter, 1989-, et al.
(författare)
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Experimental Evaluation of a Rare Earth-Free Permanent Magnet Generator
- 2021
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Ingår i: IEEE Transactions on Energy Conversion. - Piscataway : Institute of Electrical and Electronics Engineers (IEEE). - 1558-0059 .- 0885-8969. ; 36:1, s. 3-10
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Tidskriftsartikel (refereegranskat)abstract
- Low speed, high torque machines are used in wind turbines where the turbine rotor is directly connected to the generator. A permanent magnet synchronous generator using high-energy rare-earth permanent magnets (PMs) is one common choice for this application, but rare-earth PMs have supply insecurities and cost risks. A rare-earth free 32-pole PM generator, using ferrite PMs in a spoke-type rotor, for use in a 12 kW experimental wind turbine is built and tested. Voltages and currents at load and no load are measured, as well as the magnetic field in the end regions of the machine. The generator can deliver the required power at nominal speed and has low harmonic content in the output. The electrical measurements are compared to two-dimensional finite element design calculations and the experimental results are lower than expected from simulations. The measured voltage is lower than expected, requiring a higher current than calculated for the rated power. Three-dimensional magnetic field simulations show that there are leakage flux paths in the end-regions that the two-dimensional design calculations overlook, explaining the discrepancy between simulations and measurements.
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| 11. |
- Eklund, Petter, 1989-, et al.
(författare)
-
Magnetic End LeakageFlux in a Spoke Type Rotor Permanent Magnet SynchronousGenerator
- 2017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The spoke type rotor can be used to obtain magnetic flux concentration in permanent magnet machines. This allows the air gap magnetic flux density to exceed the remanent flux density of the permanent magnets but gives problems with leakage fluxes in the magnetic circuit. The end leakage flux of one spoke type permanent magnet rotor design is studied through measurements and finite element simulations. The measurements are performed in the end regions of a 12 kW prototype generator for a vertical axis wind turbine. The simulations are made using three dimensional finite elements to calculate the magnetic field distribution in the end regions of the machine. Also two dimensional finite element simulations are performed and the impact of the two dimensional approximation is studied. It is found that the magnetic leakage flux in the end regions of the machine is equal to about 20 % of the flux in the permanent magnets. The overestimation of the performance by the two dimensional approximation is quantified and a curve-fitted expression for its behavior is suggested.
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| 12. |
- Eklund, Petter, 1989-, et al.
(författare)
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The influence of permanent magnet material properties on generator rotor design
- 2019
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 12:7
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Tidskriftsartikel (refereegranskat)abstract
- Due to the price and supply insecurities for rare earth metal-based permanent magnet (PM) materials, a search for new PM materials is ongoing. The properties of a new PM material are not known yet, but a span of likely parameters can be studied. This paper presents an investigation on how the remanence and recoil permeability of a PM material affect its usefulness in a low speed, multi-pole, and PM synchronous generator. Demagnetisation is also considered. The investigation is carried out by constrained optimisation of three different rotor topologies for maximum torque production for different PM material parameters and a fixed PM maximum energy. The rotor topologies used are surface mounted PM rotor, spoke type PM rotor and an interior PM rotor with radially magnetised PMs. The three different rotor topologies have their best performance for different kinds of materials. The spoke type PM rotor is the best at utilising low remanence materials as long as they are sufficiently resistant to demagnetisation. The surface mounted PM rotor works best with very demagnetisation resistant PM materials with a high remanence, while the radial interior PM rotor is preferable for high remanence materials with low demagnetisation resistance.
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| 13. |
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| 14. |
- Eklund, Petter, 1989-, et al.
(författare)
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Winding Design Independent Calculation Method for Short Circuit Currents in Permanent Magnet Synchronous Machines
- 2018
-
Ingår i: 2018 XIII International Conference on Electrical Machines (ICEM). ; , s. 1021-1027
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Konferensbidrag (refereegranskat)abstract
- When designing permanent magnet (PM) synchronous machines the demagnetizing effect of short circuit currents on the PMs needs to be considered. In some cases there can be a need to estimate the demagnetizing field from the winding without knowing the winding scheme. To do this a lumped parameter model of the dynamics of the magnetic field and armature current density distribution is proposed. Validation of the model using two different machines shows acceptable agreement. The proposed model is found to be useful for its particular purpose of determining the approximate short circuit current distribution in the armature without knowing the winding design.
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| 15. |
- Eriksson Barman, Sandra, 1985, et al.
(författare)
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Modeling and solving vehicle routing problems with many available vehicle types
- 2015
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Ingår i: Springer Proceedings in Mathematics & Statistics. - Cham : Springer International Publishing. - 2194-1009 .- 2194-1017. - 9783319185668
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Konferensbidrag (refereegranskat)abstract
- Vehicle routing problems (VRP) involving the selection of vehicles from a large set of vehicle types are hitherto not well-studied in the literature. Such problems arise at Volvo Group Trucks Technology, who faces an immense set of possible vehicle configurations, of which an optimal set needs to be chosen for each specific combination of transport missions. Another property of real-world VRP’s that is often neglected in the literature is that the fuel resources required to drive a vehicle along a route is highly dependent on the actual load of the vehicle. We define the fleet size and mix VRP with many available vehicle types, called many-FSMVRP, and suggest an extended set-partitioning model of this computationally demanding combinatorial optimization problem. To solve the extended model, we have developed a method based on Benders’ decomposition, the subproblems of which are solved using column generation, and the column generation subproblems being solved using dynamic programming; the method is implemented with a so-called projection-of-routes procedure. The resulting method is compared with a column generation approach for the standard set-partitioning model. Our method for the extended model performs on par with column generation applied to the standard model for instances such that the two models are equivalent. In addition, the utility of the extended model for instances with very many available vehicle types is demonstrated. Our method is also shown to efficiently handle cases in which the costs are dependent on the load of the vehicle. Computational tests on a set of extended standard test instances show that our method, based on Benders’ algorithm, is able to determine combinations of vehicles and routes that are optimal to a relaxation (w.r.t. the route decision variables) of the extended model. Our exact implementation of Benders’ algorithm appears, however, too slow when the number of customers grows. To improve its performance, we suggest that relaxed versions of the column generation subproblems are solved, and that the set-partitioning model is replaced by a set-covering model.
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| 16. |
- Eriksson, Elina, 1979-, et al.
(författare)
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Addressing Students’ Eco-anxiety when Teaching Sustainability in Higher Education
- 2022
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Ingår i: Proceedings - 2022 International Conference on ICT for Sustainability, ICT4S 2022. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 88-98
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Konferensbidrag (refereegranskat)abstract
- The widespread awareness and the sense of urgency and helplessness regarding the ongoing sustainability crisis (climate change, biodiversity loss etc.) can evoke feelings of grief, sorrow, despair and anxiety. Those emotions are seldom discussed in computing or in computing education. They can have detrimental effects on the well-being of students and others, and also lead to inaction. But concern can on the other hand also be a catalyst for learning. In this paper, we present results and reflections from a research and development project in our introductory course to sustainability and ICT focusing on emotions in sustainability education. We focus on “eco-anxiety” and ask: 1) How is eco-anxiety communicated by students and teachers?, 2) In what ways do students receive support to deal with eco-anxiety? and 3) What could be done to better address eco-anxiety in computing education? We here present an analysis of how we have responded to the phenomenon of eco-anxiety, what activities have been added to the course and an evaluation of these interventions. The results are based on joint reflections that have been guided by literature, a small-scale ethnographic study as well as a course evaluation. The paper will end with recommendations for other ICT4S educators on how they can start addressing eco-anxiety in their education.
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| 17. |
- Eriksson, Sandra, 1979-, et al.
(författare)
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Comparison of Simulation Methods for Angular Dependency when Modeling Demagnetization
- 2023
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Ingår i: 2023 IEEE International Magnetic Conference, INTERMAG. - : Institute of Electrical and Electronics Engineers (IEEE). - 9798350332469
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Konferensbidrag (refereegranskat)abstract
- Rare earth element free magnets, such as ferrites, are weaker than their more common alternatives and therefore more prone to demagnetization. Additionally, in permanent magnet electrical machines they are commonly tangentially magnetized and placed in a spoke-type geometry to enhance the magnetic field. In this geometry, the magnets are subject to inclined fields, which are normally not accounted for when evaluating demagnetization risk. In this paper, different methods for demagnetization of permanent magnets are applied to two motors under two distinct loading conditions and the results are compared. It is concluded that it is more important to consider inclined fields when studying ferrite magnets than rare earth element magnets. The common, simplified method of omitting inclined fields is shown to be the most conservative method for evaluating demagnetization. However, more precise results can be reached with methods taking inclined fields into account, especially if the models are adapted for the specific magnet type. Two motors with similar performance have been designed, one with rare earth element magnets and one with ferrites. The motor with ferrites is more sensitive to demagnetization and the bulk of the magnet reaches the demagnetization limit at a lower current than for the motor with rare earth element-based magnets. Finally, demagnetization of magnets is compared for two different rotor positions, emphasizing the importance of considering rotor position when evaluating demagnetization risk.
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| 18. |
- Eriksson, Sandra, 1979-
(författare)
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Design of Permanent-Magnet Linear Generators with Constant-Torque-Angle Control for Wave Power
- 2019
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 12:7
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a simulation method for direct-drive permanent-magnet linear generators designed for wave power. Analytical derivations of power and maximum damping force are performed based on Faraday's law of induction and circuit equations for constant-torque-angle control. Knowledge of the machine reactance or the load angle is not needed. An aim of the simulation method is to simplify comparison of the maximum damping force, losses, and cost between different generator designs at an early design stage. A parameter study in MATLAB based on the derived equations is performed and the effect of changing different generator parameters is studied. The analytical calculations are verified with finite element method (FEM) simulations and experiments. An important conclusion is that the copper losses and the maximum damping force are mainly dependent on the rated current density and end winding length. The copper losses are inherently large in a slow-moving machine so special consideration should be taken to decrease the end winding length. It is concluded that the design of the generator becomes a trade-off between material cost versus high efficiency and high maximum damping force.
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| 19. |
- Eriksson, Sandra, 1979-
(författare)
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Direct Driven Generators for Vertical Axis Wind Turbines
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wind power is a renewable energy source that is increasingly used all over the world. Most wind turbines have a horizontal axis of rotation but a few have a vertical axis of rotation. The concept presented in this thesis is a straight-bladed vertical axis wind turbine with a direct driven cable-wound permanent magnet synchronous generator. A comparison of the two different types of wind turbines, vertical axis wind turbines and horizontal axis wind turbines, have been performed considering several different aspects. However, the main focus in this thesis is on the generator. Several generators have been modelled with a combined field and circuit model, which has been solved by using the finite element method. A 12 kW generator has been designed, which has a high overall efficiency and a high overload capability. The generator has been constructed at the department and was tested in the laboratory before being mounted in a vertical axis wind turbine. Results from experiments correspond well with results from simulations. The generator has been tested for different loading conditions and the harmonic content of the voltage has been analysed. A 12 kW vertical axis wind turbine was completed and tests have been performed. The results are encouraging and further studies on the prototype will be performed in the future. The simulation method has been used to study electromagnetic losses in several generators. The comparison showed that the average losses should be considered when a variable speed generator for wind power is designed and it concluded that the design optimization process becomes a compromise between lowering the electromagnetic losses and having high overload capability. When constructing a wind turbine, it is important to consider vibrations in the structure. Torsional vibrations in the drive shaft connecting the turbine to the rotor of the generator have been studied. It is shown that a direct driven generator is to prefer over an induction generator with a gearbox when torsional vibrations are concerned. This thesis is based on eight papers all concerning vertical axis wind turbines with three of them focusing on the generator.
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| 20. |
- Eriksson, Sandra, 1979-, et al.
(författare)
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Effect of magnetic properties on performance of electrical machines with ferrite magnets
- 2021
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Ingår i: Journal of Physics D. - Bristol : Institute of Physics Publishing (IOPP). - 0022-3727 .- 1361-6463. ; 54:5
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Tidskriftsartikel (refereegranskat)abstract
- The increased focus on ferrite magnets makes it interesting to investigate their suitability in electrical machines such as generators for wind power and motors for electric cars. Efforts are currently being made to improve the magnetic properties of ferrites. A simulation method is used to investigate how different magnetic properties such as remanence, coercivity and intrinsic coercivity affect the performance of electrical machines, here quantified as output torque. It is also ensured that the magnet is not partly demagnetized during a short-circuit event. Simulations are performed through a two-dimensional finite-element-based simulation method. Not all combinations of magnetic properties will render a usable design and it is therefore investigated how high the required values are for different magnetic properties as well as how high an output torque can be achieved. It is concluded that increasing the remanence or the coercivity can be quantified as an improved energy product, whereas improvement of the intrinsic coercivity enables the magnet to have a more optimal shape and thereby have a working point where the energy product is maximized. In addition it is found that for a fixed available magnetic energy, the performance does not change significantly with increasing remanence.
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| 21. |
- Eriksson, Sandra, 1979-
(författare)
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Permanent Magnet Synchronous Machines
- 2019
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 12:14
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Interest in permanent magnet synchronous machines (PMSMs) is continuously increasing worldwide, especially with the increased use of renewable energy and electrification of transports. This special issue contains the successful invited submissions of fifteen papers to a Special Issue of Energies on the subject area of Permanent Magnet Synchronous Machines. The focus is on permanent magnet synchronous machines and the electrical systems they are connected to. The presented work represents a wide range of areas. Studies of control systems, both for permanent magnet synchronous machines and for brushless DC motors, are presented and experimentally verified. Design studies of generators for wind power, wave power and hydro power are presented. Finite element method simulations and analytical design methods are used. The presented studies represent several of the different research fields on permanent magnet machines and electric drives.
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| 22. |
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| 23. |
- Frost, Anna E., 1988-
(författare)
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In the Air Gap of Linear Generators for Wave Power
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wave power conversion is one type of renewable electricity generation. Within wave power, there are many different concepts, whereof some utilizes linear generators for converting the energy in the ocean waves into electricity. A linear generator consists of a translator, which is moving and have magnets of alternating polarity, and a stator, which have conductors sur-rounded by laminated steel. Between the translator and stator is an air gap, which is only a few millimeters wide. All linear generators for wave power, to the author’s knowledge, are permanent-magnet synchronous generators. This thesis looks into the forces and power flow in the air gap of linear generators for wave power, with the purpose of improving their future performance. The studies have focused on permanent magnet synchronous generators for wave power, but several of the results should also be applicable for other applications of linear elec-trical machines.Depending on the design of the linear generators, the translator can move so long that it only partially overlap the stator. This is common among several different wave power concepts with linear generators. When the stator is only partially overlapped by the stator it is denoted as partial stator overlap. It is studied how partial stator overlap affects the generated electric-ity, the absorbed energy, and the tangential and normal force in the air gap. The generated electricity and absorbed energy of a linear generator are quadratically dependent on the partial stator-translator overlap is shown through Faraday’s law and simulations. Experimental data showed that the absorbed energy is both linearly and quadratic depending on partial stator over-lap, where the linear dependence is at least partially due to frictional losses. Simulated results confirm that voltage is linearly dependent on partial stator overlap, which means quadratic de-pendence between generated electric and partial stator overlap. The simulated forces showed a linear dependence.Decades ago, the Poynting vector was used to derive an expression for the power flow in the air gap of rotating electrical machines. In this thesis the equivalent expressions for both flat and tubular linear electrical machines were derived. The analytical results were also compared with results from simulations. Both the analytical expressions and simulations showed that tubular and flat linear electrical machines have slightly different behavior.
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| 24. |
- Frost, Anna E., et al.
(författare)
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Partial Stator Overlap in a Linear Generator for Wave Power : An Experimental Study
- 2017
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Ingår i: Journal of Marine Science and Engineering. - : MDPI AG. - 2077-1312. ; 5:4
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a study on how the power absorption and damping in a linear generator for wave energy conversion are affected by partial overlap between stator and translator. The theoretical study shows that the electrical power as well as the damping coefficient change quadratically with partial stator overlap, if inductance, friction and iron losses are assumed independent of partial stator overlap or can be neglected. Results from onshore experiments on a linear generator for wave energy conversion cannot reject the quadratic relationship. Measurements were done on the inductance of the linear generator and no dependence on partial stator overlap could be found. Simulations of the wave energy converter's operation in high waves show that entirely neglecting partial stator overlap will overestimate the energy yield and underestimate the peak forces in the line between the buoy and the generator. The difference between assuming a linear relationship instead of a quadratic relationship is visible but small in the energy yield in the simulation. Since the theoretical deduction suggests a quadratic relationship, this is advisable to use during modeling. However, a linear assumption could be seen as an acceptable simplification when modeling since other relationships can be computationally costly.
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| 25. |
- 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 1 - Analytical expressions
- 2022
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Ingår i: The Journal of Engineering. - : Institution of Engineering and Technology (IET). - 2051-3305. ; 2022:4, s. 377-388
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Tidskriftsartikel (refereegranskat)abstract
- Analytical solutions and estimations for the power flow in the air gap of linear electrical machines of different geometries are derived from Poynting's theorem. The different geometries considered are flat one-sided, multi-sided, and tubular linear electrical machines. The radial power flow for all considered geometries is dependent on the area of the air gap, the electric field, the magnetic field, and the load angle. The tangential power flow for both flat one-sided and tubular linear electrical machines is dependent of the area of the air gap, number of poles, the electric field, the magnetic field, and the load angle. The number of poles could be increased to decrease the tangential power flow in flat linear electrical machines. The expression for the tangential flow in tubular linear electrical machines is so complicated that it is difficult to draw conclusions from it.
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| 26. |
- 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
-
Ingår i: The Journal of Engineering. - : Institution of Engineering and Technology. - 2051-3305. ; 2022:9, s. 883-891
-
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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| 27. |
- Ibrayeva, Anar, et al.
(författare)
-
Dynamic Modeling of a Generator With Anisotropic Nonlinear Permanent Magnets in Finite Element Method Software
- 2023
-
Ingår i: IEEE Transactions on Magnetics. - : IEEE. - 0018-9464 .- 1941-0069. ; 59:9
-
Tidskriftsartikel (refereegranskat)abstract
- In this article, a method of dynamic modeling of nonlinear permanent magnets (PMs) with recoil lines in 2-D finite element analysis (FEA) software was presented. COMSOL Multiphysics 6.0 FEA software was used in this study. The method is implemented through the variable utilities. The simulation results of a spoke-type synchronous generator for a wind turbine with anisotropic aluminum-nickel-cobalt (Alnico) 5, 8B, and 9 grades were used to exemplify the model and compared. The proposed methodology can be used for the simulation of nonlinear PMs with recoil lines and includes reversible and irreversible losses of magnetization of nonlinear PMs. The effect of the magnetic field from the stator winding on nonlinear PMs during normal operation and short circuits was studied. The modeling results were compared to the model without any demagnetization and a previous study with recoil lines and averaged minimum magnetic flux points. The no-load (NL) voltages were compared before and after a demagnetization. The dynamic model showed considerable demagnetization of Alnico magnets during normal operational and three-phase short circuits. Alnico 5 and 9 showed higher sensitivity to short-circuit currents and the short-circuit currents caused remagnetization of the upper part of the magnet in the opposite direction. The anisotropy of the PM implemented in the model improved the magnetic field simulation inside the magnet and partially protected the magnet from demagnetization by inclined fields. At last, the method was experimentally verified by tests on an iron core.
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| 28. |
- Ibrayeva, Anar, 1988-, et al.
(författare)
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Measurement and Modelling of Hysteresis Curves for Nonlinear Permanent Magnets at Different Inclination Angles
- 2023
-
Ingår i: 2023 IEEE International Magnetic Conference (INTERMAG). - : Institute of Electrical and Electronics Engineers (IEEE). - 9798350332469 - 9798350332476
-
Konferensbidrag (refereegranskat)abstract
- This paper presents the measurement results of the BH/MH curves of the Alnico 8 (LNGT40) with recoil loops and a mathematical model for the calculation of the average magnetic flux density in a cubic permanent magnet. The measurements were performed with a Vibrating Sample Magnetometer (VSM). The magnet samples have a cubic shape with 3 mm sides. BH curves in preferred (easy) and transverse directions and recoil loops were measured and compared to Alnico 9 (LNGT72) as well as to the data from the supplier. The load line of the cubic magnet in 0 A/m applied magnetic field was found. A mathematical model was developed which can approximate the MH a curve for an applied field with an arbitrarily chosen angle between the field and easy axis, given MH a curves for 0o and 90o. Also, a simplified general model of a cubic permanent magnet in the air and calculation results of stored energy and hysteresis losses were presented.
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| 29. |
- Ibrayeva, Anar, et al.
(författare)
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Modelling of Permanent Magnet Synchronous Generator with Non-linear Magnets
- 2021
-
Ingår i: 2021 22nd IEEE International Conference on Industrial Technology (ICIT). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781728157306 ; , s. 209-214
-
Konferensbidrag (refereegranskat)abstract
- In this paper simulation results of a spoke-type synchronous generator for a wind turbine with three different grades of Alnico magnets were presented. COMSOL Multiphysics 5.4 finite element analysis (FEA) based software was used. The proposed model was used for simulation of a synchronous generator with non-linear Alnico magnets with recoil-lines with some approximations and can be used for modelling electrical machines with other non-linear permanent magnets. The geometry of the machines was kept fixed for all scenarios. The model takes into account the irreversible loss of magnetization of non-linear permanent magnets due to the magnetic field from the stator winding during normal operation and short circuit. Modelling results show that Alnico 5 (ArKomax800) magnets have the lowest output power, but they are the least sensitive to change of the load. The generator with Alnico 8 permanent magnets have the highest output power, is good at handling the nominal load but the most sensitive to short circuits. Alnico 9 magnets could be an option if the risk for short circuits is accounted for.
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| 30. |
- 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
-
Ingår i: Energies. - : MDPI. - 1996-1073. ; 13:21
-
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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| 31. |
- Leijon, Jennifer, et al.
(författare)
-
Study of an Altered Magnetic Circuit of a Permanent Magnet Linear Generator for Wave Power
- 2018
-
Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 11:1
-
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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| 32. |
- Lind, Emil, et al.
(författare)
-
Effect of Drive Cycle Quantification on Electric Motor Efficiency
- 2023
-
Ingår i: 12th International Conference on Power Electronics, Machines and Drives (PEMD 2023). - : Institution of Engineering and Technology. - 9781839539503 ; , s. 96-104
-
Konferensbidrag (refereegranskat)abstract
- One way to evaluate real life electric vehicle performance is through drive cycle analysis. However, performing Finite Element Method (FEM) analysis is computationally heavy and optimisation of motor efficiency across all operating points using FEM is time demanding. One way to solve this is by changing the resolution of the drive cycle. The objective of this study is to investigate how different resolutions affect the results, specifically in terms of energy, losses and overall drive cycle efficiency. This study shows, through both analytical calculations and FEM simulations, that it is possible to greatly decrease the number of operating points with only a minimal impact on the overall drive cycle efficiency. There does not seem to exist a universal rule to this which span different drive cycles. However, the quantifications of all drive cycles exhibit a similar pattern, with increased efficiency instability for lower resolutions. For the Worldwide Harmonised Light Vehicles Test Procedure drive cycle, a decrease of 6.4 times in operating points only affects the maximum efficiency deviation by 0.036 percentage points. At this resolution, over half of the energy is distributed along only 25 points, making these a good starting point for electric motor design and optimisation.
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| 33. |
- Lu, Haojiang, et al.
(författare)
-
Dissecting the Impact of Maternal Androgen Exposure on Developmental Programming through Targeting the Androgen Receptor
- 2024
-
Ingår i: Advanced Science. - : John Wiley & Sons. - 2198-3844.
-
Tidskriftsartikel (refereegranskat)abstract
- Women with polycystic ovary syndrome (PCOS) exhibit sustained elevation incirculating androgens during pregnancy, an independent risk factor linked topregnancy complications and adverse outcomes in offspring. Yet, furtherstudies are required to understand the effects of elevated androgens on celltype-specific placental dysfunction and fetal development. Therefore, aPCOS-like mouse model induced by continuous androgen exposure isexamined. The PCOS-mice exhibited impaired placental and embryonicdevelopment, resulting in mid-gestation lethality. Co-treatment with theandrogen receptor blocker, flutamide, prevents these phenotypes includinggerm cell specification . Comprehensive profiling of the placenta bywhole-genome bisulfite and RNA sequencing shows a reduced proportion oftrophoblast precursors, possibly due to the downregulation of Cdx2expression. Reduced expression of Gcm1, Synb, and Prl3b1 is associated withreduced syncytiotrophoblasts and sinusoidal trophoblast giant cells, impairsplacental labyrinth formation. Importantly, human trophoblast organoidsexposed to androgens exhibit analogous changes, showing impairedtrophoblast differentiation as a key feature in PCOS-related pregnancycomplications. These findings provide new insights into the potential cellulartargets for future treatments.
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| 34. |
- Möllerström, Erik, 1984-, et al.
(författare)
-
Turbulence influence on optimum tip speed ratio for a 200 kW vertical axis wind turbine
- 2016
-
Ingår i: Science Of Making Torque From Wind (Torque 2016). - Bristol : IOP Publishing. ; 753
-
Konferensbidrag (refereegranskat)abstract
- The influence of turbulence intensity (TI) on the tip speed ratio for maximum power coefficient, here called λCp-max, is studied for a 200 kW VAWT H-rotor using logged data from a 14 month period with the H-rotor operating in wind speeds up to 9 m/s. The TI - λCp-max relation is examined by dividing 10 min mean values in different turbulence intensity ranges and producing multiple CP(λ) curves. A clear positive relation between TI and λCp-max is shown and is further strengthened as possible secondary effects are examined and deemed non-essential. The established relation makes it possible to tune the control strategy to enhance the total efficiency of the turbine.
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| 35. |
- Potapenko, Tatiana
(författare)
-
Modelling of Ocean Wave Energy Conversion for Increased Power Absorption
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Earth is also called the blue planet, because more than 70 % of its surface is covered by water, mainly in oceans and seas. Wind blowing over the oceans is creating water waves, which can travel thousands of kilometers with just a small energy loss. Despite the abundant potential for the green energy market, wave energy is not yet exploited to the extent of wind and solar energies.There have been numerous attempts to convert wave energy into electricity. The wave energy converter, developed at Uppsala University, Sweden is of a point absorber type. The principal idea lies in utilizing a novel linear generator. The translator is a moving part inside the sub-merged linear generator and it is connected to a buoy, floating on the water surface. The buoy moves with the waves and the translator is dragged up and down relative to the stator. This reciprocal motion induces a voltage in the stator windings.The up-to-date stage of development for wave energy converters poses various issues. Still open challenges hold the technology away from commercial energy production. One of the main goals in wave energy research is to enhance the absorbed power for a single device, as well as for a wave power park of multiple wave energy converters. The power harvest can be increased in different ways, for example by optimizing the buoy, the generator or by implementing control on the operation of the device.This thesis focuses on studying wave energy converters in different wave climates by their power absorption. The main criteria influencing absorbed power are buoy size, weight on the system, damping force and available wave energy potential at the location of interest. The damping force can be computed by different approaches: constant optimal damping, resistive load (replicating passive control of currents in the stator windings) and RC-load (modeling a grid connected linear generator with an active rectification, such as phase angle compensation).Waves have a random nature. Therefore, the grid connection of the linear generator requires special solution. Power fluctuations of converted wave energy by the direct drive linear genera-tor may affect the integration into existing electrical grids. To study the connection of a single wave energy converter, as well as the wave park of three and ten devices, power hardware in the loop experiments have been carried out. The power quality analysis has been performed.Wave power has high potential and it can be integrated into the existing wind and solar energy production towards fully renewable microgrids. Yet, there is a chance of at least one quiet night during the year, when there are no wind and no waves. Estimation of frequency occurrence of absorbed power gives an insight into the regularity of such events. A case study in Hvide Sande, Denmark is presented. A mix of renewable energies (wind, solar and wave) is beneficial, as it gives a more stable energy supply with less variation in power production than when taken individually. Based on 30 years of historical data it is concluded, that the required battery size is sufficiently reduced for the renewable energy mix. The mix of wind, solar and wave has been shown to secure the lowest frequency of zero occurrences in power production and therefore is the most favorable choice for the future.
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| 36. |
- Potapenko, Tatiana, et al.
(författare)
-
Wave energy converter’s slack and stiff connection : study of absorbed power in irregular waves
- 2021
-
Ingår i: Energies. - : MDPI. - 1996-1073. ; 14:23
-
Tidskriftsartikel (refereegranskat)abstract
- Two different concepts of wave energy converter coupled to the novel C-GEN linear generator have been studied numerically, including the evaluation of different buoy sizes. The first concept has a slack connection between the buoy and the generator on the seabed. Another concept is based on a stiff connection between the buoy and the generator placed on an offshore platform. Three different approaches to calculate the damping force have been utilized within this study: the optimal damping coefficient, R-load, and RC-load. R-load is a model for the load applied to a grid-connected generator with passive rectification. RC-load is a model for a phase angle compensation applied to a system with active rectification. The radiation forces originating from the oscillatory motion of the buoy have been approximated using the transfer function in the frequency domain and the vector fitting algorithm. A comparison of the approximation methods is presented, and their accuracy has been evaluated. The advantage of the vector fitting method has been shown, especially for higher approximation orders which fit the transfer function with high accuracy. The study’s final results are shown in terms of the absorbed power for the sea states of March 2018 at Wave Hub, UK.
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| 37. |
- Rossander, Morgan, 1981-, et al.
(författare)
-
Critical Speed Control for a Fixed Blade Variable Speed Wind Turbine
- 2017
-
Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 10:11
-
Tidskriftsartikel (refereegranskat)abstract
- A critical speed controller for avoiding a certain rotational speed is presented. The controller is useful for variable speed wind turbines with a natural frequency in the operating range. The controller has been simulated, implemented and tested on an open site 12 kW vertical axis wind turbine prototype. The controller is based on an adaptation of the optimum torque control. Two lookup tables and a simple state machine provide the control logic of the controller. The controller requires low computational resources, and no wind speed measurement is needed. The results suggest that the controller is a feasible method for critical speed control. The skipping behavior can be adjusted using only two parameters. While tested on a vertical axis wind turbine, it may be used on any variable speed turbine with the control of generator power.
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| 38. |
- Rossander, Morgan, 1981-, et al.
(författare)
-
Frequency analysis of tangential force measurements on a vertical axis wind turbine
- 2016
-
Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596.
-
Konferensbidrag (refereegranskat)abstract
- This paper presents experimental results of the torque ripple obtained from a three bladed 12 kW experimental H-rotor prototype. The measurements are performed by means of load cells installed on the base of the struts and by electrical measurements on the generator. The resulting torques are analysed in terms of frequency spectrum and order spectrum (synchronized with rotation). The measurements are compared to aerodynamic simulations of the turbine. The expected large torque ripple at three times the rotational speed (3 p) is only weakly represented at the hub and in the generator. This suggests that the system is filtering the ripple and/or that the simulations are overestimating the 3 p component. The torque ripple loads on the drive train are therefore lower than anticipated. Even if highly attenuated, most of the low frequencies correlating to aerodynamics are still represented in the generator electrical torque. Given a certain baseline, this opens for possible online monitoring of unbalances in the turbine by electrical measurements.
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| 39. |
- Seznec, Yann, et al.
(författare)
-
The Sound of the Future Home Workshop : Ideating Sonic Prototypes for Sustainable Energy Consumption
- 2023
-
Konferensbidrag (refereegranskat)abstract
- This paper describes an ideation workshop aiming to explore the intersection of sonic interactions and energy use. As part of a larger research project exploring the role that sound can play in efficient energy behaviours, the workshop encouraged users to look for overlaps between their home resource use, potential sonic feedback and the feelings and emotions elicited by both. The workshop design was successful in providing non-experts with space and tools to reflect on the complex relationship between household, sound, energy and our feelings towards them. On a more practical level, 15 “hotspots” were identified where sound and energy concerns could be potentially addressed with sonic interventions, and four speculative prototypes were developed during the workshop each one revealing original considerations and relationships between sound and energy to be developed further in future work.
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| 40. |
- Silva, Marcelo D., 1995-, et al.
(författare)
-
Meta-Models for Torque Optimization of Spoke Type Permanent Magnet Synchronous Machines
- 2023
-
Ingår i: 2023 24th International Conference on the Computation of Electromagnetic Fields (COMPUMAG). - : Institute of Electrical and Electronics Engineers (IEEE). - 9798350301052 - 9798350301069
-
Konferensbidrag (refereegranskat)abstract
- The design of internal permanent magnet synchronous machines (IPMSM) is a complex task that often includes multiple objectives and constraints. Lately, a lot of research has been focused on the reduction or elimination of rare-earth elements (REE). To achieve that, the use of ferrite permanent magnets (PM) and the enhancement of reluctance torque are the most common solutions. In this paper, three different meta-models are developed and used in the optimization process to maximize the torque of a Spoke Type PMSM (Spoke) with ferrite PM taking into consideration both reluctance and magnetic torque. These meta-models are based on 1-dimensional convolutional neural networks (1DCNN), gaussian process regression (GPR) and polynomial chaos expansion (PCE). This study shows that the GPR-based meta-models generally present the lowest absolute error. Although, regardless of the different performance, all three meta-models achieve similar optimized solutions.
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| 41. |
- Silva, Marcelo D., 1995-, et al.
(författare)
-
Model for Angular Dependency of the Intrinsic Coercivity of Ferrite Permanent Magnets
- 2023
-
Ingår i: 2023 IEEE International Magnetic Conference, INTERMAG. - : Institute of Electrical and Electronics Engineers (IEEE). - 9798350332469
-
Konferensbidrag (refereegranskat)abstract
- In internal permanent magnet synchronous machines (IPMSM), the use of ferrite permanent magnets is being studied as an alternative to rare-earth elements-based permanent magnets, such as NdFeB. However, demagnetization measurements of ferrite magnets are rarely published and such information is crucial for an efficient electrical machine design with ferrite magnets. In this paper, we present measurements of partial demagnetization on ferrite permanent magnets subject to inclined external magnetic fields. From the measurements done, mathematical models are developed for Y30 and Y40 samples that defines a relationship between the intrinsic coercivity and the inclination of the external demagnetizing field. Furthermore, from the primary results, the angular dependency of hysteresis losses and relative permeability are also explored, as well as their impact on the design of IPMSM.
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| 42. |
- Silva, Marcelo D., 1995-, et al.
(författare)
-
On the relation between performance and permanent demagnetisation in spoke type machines with ferrite magnets
- 2024
-
Ingår i: IET Electric Power Applications. - : John Wiley & Sons. - 1751-8660 .- 1751-8679. ; 18:8, s. 912-923
-
Tidskriftsartikel (refereegranskat)abstract
- The use of rare earth elements (REE) in permanent magnets (PMs) raises problems in several domains. The supply chain of these is fragile, the prices have shown volatility and its manufacturing has a bigger impact on climate change when compared to the manufacturing of other PMs. Instead, ferrite PMs have been researched as an alternative. This alternative shows a relatively higher demagnetisation risk when compared to REEPMs. Thus, a detailed study on permanent demagnetisation during winding faults is crucial. The authors use the finite element method to evaluate different machine designs, developed under mechanical constraints, and explore several strategies to mitigate permanent demagnetisation. Also, the importance of avoiding permanent demagnetisation is changed gradually in the optimisation process. The results show that the protection of the and performance optimisation are irreconcilable goals. It also highlights the impact of the stator design in decreasing demagnetisation. Additionally, it is shown that the classic notion of avoiding demagnetisation is an ineffective strategy for designing high‐performance machines with ferrite magnets, and instead, it should be integrated into the optimisation process and weighted according to the application demands.
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| 43. |
- Sjökvist, Stefan, 1985-, et al.
(författare)
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Investigation of Permanent Magnet Demagnetization in Synchronous Machines During Multiple Short-Circuit Fault Conditions
- 2017
-
Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 10:10
-
Tidskriftsartikel (refereegranskat)abstract
- Faults in electrical machines can vary in severity and affect different parts of the machine. This study focuses on various kinds of short-circuits on the terminal side of a generic 20 kW surface mounted permanent magnet synchronous generator and how successive faults affect the performance of the machine. The study was conducted with the commercially available finite element method software COMSOL Multiphysics ®" role="presentation">® , and two time-dependent models for demagnetization of permanent magnets were compared, one using only internal models and the other using a proprietary external function. The study is simulation based and the two models were compared to a previously experimentally verified stationary model. Results showed that the power output decreased by more than 30% after five successive faults. In addition, the no-load voltage had become unsymmetrical, which was explained by the uneven demagnetization of the permanent magnets. The permanent magnet with the lowest reduction in average remanence was decreased by 0.8%, while the highest average reduction was 23.8% in another permanent magnet. The internal simulation model was about four times faster than the external model, but slightly overestimated the demagnetization.
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| 44. |
- Sjökvist, Stefan, 1985-, et al.
(författare)
-
Permanent Magnet Working Point Ripple in Synchronous Generators
- 2017
-
Ingår i: The Journal of Engineering. - : Institution of Engineering and Technology (IET). - 2051-3305. ; 2017:5, s. 158-161
-
Tidskriftsartikel (refereegranskat)abstract
- Permanent magnets (PMs) are today widely used in electrical machines of all sorts. With their increase in popularity, the amount of research has increased as well. In this study, the magnetic flux density ripple of the working point of the PMs in a 100 kW PM synchronous generator has been investigated for three different load cases: no load, AC load, and DC load. The PMs will be subjected to a shift in working point as a consequence of the characteristics of the electrical loading. This study is based on finite element method simulations where the ripple of the magnetic flux density in the PMs was recorded at three positions within a PM. The slot harmonic of 7.5 times the electrical frequency (fel)" role="presentation">(fel) was present in the results for all load cases, but mainly at the surface of the PM, as expected. Results showed an unexpected harmonic of 1.5fel" role="presentation">1.5fel , assumed to be an undertone of the slot harmonics. The 6fel" role="presentation">6fel harmonic for the DC load case was significantly higher than for the AC load case and is caused by the current fluctuation during passive rectification. For the studied machine, the added harmonics in the magnetic field due to passive rectification are less than the slot-related harmonics.
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| 45. |
- Sjölund, Jonathan, et al.
(författare)
-
Effect of Pole Shoe Design on Inclination Angle of Different Magnetic fields in Permanent Magnet Machines
- 2021
-
Ingår i: Energies. - : MDPI. - 1996-1073. ; 14:9
-
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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| 46. |
- Sjölund, Jonathan, et al.
(författare)
-
End Effects and Geometric Compensation in a Linear Permanent Magnet Synchronous Generator with Buried Topology
- 2020
-
Ingår i: 2020 International Conference on Electrical Machines (ICEM). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781728199450 ; , s. 455-461
-
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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| 47. |
- Sjölund, Jonathan, et al.
(författare)
-
End Effects and Geometric Compensation in Linear Permanent Magnet Synchronous Generators with Different Topologies
- 2021
-
Ingår i: Designs. - : MDPI AG. - 2411-9660. ; 5:4
-
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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| 48. |
- Sjölund, Jonathan, et al.
(författare)
-
Method for optimizing the magnetic circuit of a linear generator using FEM simulations
- 2020
-
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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- 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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