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| 2. |
- Hedlund, Magnus, 1986-, et al.
(author)
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Eddy Currents in a Passive Magnetic Axial Thrust Bearing for a Flywheel Energy Storage System
- 2017
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In: International journal of applied electromagnetics and mechanics. - 1383-5416 .- 1875-8800. ; 54:3, s. 389-404
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Journal article (peer-reviewed)abstract
- Two types of passive magnetic lift bearings were evaluated in terms of thrust force and eddy current losses. The first type of bearings were based on two sets of segmented Halbach arrays mounted in repulsive mode, and the second type was based on ring-magnets. The eddy-currents studied arose in the bearing due to manufacturing variations of magnetic remanence, and due to non-radial magnetization. Both a 3D time-dependent and a quasi-stationary Finite-Element Method (FEM) formulation were used, and the simulated results were compared with lift-force measurements from experiment. The losses were found (by FEM) to be in the order of 25 W at a rotational speed of 30000 rpm while lifting a 45 kg rotor with a stiffness of 359 N/mm.
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| 4. |
- Abrahamsson, Johan, 1977-, et al.
(author)
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A Fully Levitated Cone-Shaped Lorentz-Type Self-Bearing Machine With Skewed Windings
- 2014
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In: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 50:9
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Journal article (peer-reviewed)abstract
- Brushless dc coreless electric machines with double-rotor and single-stator configuration have very low losses, since the return path of the magnetic flux rotates with the permanent magnets. The eddy-current loss in the stator is additionally very small due to the lack of iron, making it ideal for kinetic energy storage. This paper presents a design for self-bearing rotor suspension, achieved by placing the stator windings skewed on a conical surface. A mathematical analysis of the force from a skewed winding confined to the surface of a cone was found. The parametric analytical expressions of the magnitude and direction of force and torque were verified by finite-element method simulations for one specific geometry. A dynamic model using proportional-integral-differential control was implemented in MATLAB/Simulink, and the currents needed for the self-bearing effect were found by solving an underdetermined system of linear equations. External forces, calculated from acceleration measurements from a bus in urban traffic, were added to simulate the dynamic environment of an electrical vehicle.
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| 5. |
- Abrahamsson, Johan, 1977-, et al.
(author)
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High-Speed Kinetic Energy Buffer : Optimization of Composite Shell and Magnetic Bearings
- 2014
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In: IEEE Transactions on Industrial Electronics. - 0278-0046 .- 1557-9948. ; 61:6, s. 3012-3021
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Journal article (peer-reviewed)abstract
- This paper presents the design and optimization of a high-speed (30 000 r/min) kinetic energy storage system. The purpose of the device is to function as an energy buffer storing up to 867 Wh, primarily for utility vehicles in urban traffic. The rotor comprises a solid composite shell of carbon and glass fibers in an epoxy matrix, constructed in one curing. The shell is optimized using a combined analytical and numerical approach. The radial stress in the shell is kept compressive by integrating the electric machine, thereby avoiding delamination. Radial centering is achieved through eight active electromagnetic actuators. The actuator geometry is optimized using a direct coupling between SolidWorks, Comsol, and Matlab for maximum force over resistive loss for a given current density. The optimization results in a system with 300% higher current stiffness than the reference geometry with constant flux area, at the expense of 33% higher power loss. The actuators are driven by semipassive H bridges and controlled by an FPGA. Current control at 20 kHz with a noise of less than 5 mA (95% CI) is achieved, allowing position control at 4 kHz to be implemented.
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| 6. |
- Abrahamsson, Johan, 1977-
(author)
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Kinetic Energy Storage and Magnetic Bearings : for Vehicular Applications
- 2014
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Doctoral thesis (other academic/artistic)abstract
- One of the main challenges in order to make electric cars competitive with gas-powered cars is in the improvement of the electric power system. Although many of the energy sources currently used in electric vehicles have sufficientlyhigh specific energy, their applicability is limited due to low specific power. It would therefore be advantageous to create a driveline with the main energy storage separated from a smaller energy buffer, designed to have high power capabilities and to withstand frequent and deep discharge cycles. It has been found that rotating kinetic energy storage in flywheels is very well suited for this type of application.A composite shell, comprising an inner part made of glassfiber and an outer part made of carbonfiber, was analyzed analytically and numerically, designed, and constructed. The shell was fitted onto a metallic rotor using shrinkfitting. The cost of the shell, and the complexity of assembly, was reduced by winding the glass- and carbonfiber consecutively on a mandrel, and curing the complete assembly simultaneously. Thereby, the shell obtained an internal segmentation, without the need for fitting several concentric parts onto each other. The radial stress inside the composite shell was kept compressive thanks to a novel approach of using the permanent magnets of the integrated electric machine to provide radial mechanical load during rotation.Two thrust bearing units (one upper and one lower) comprising one segmented unit with the permanent magnets in a cylindrical Halbach configuration and one non-segmented unit in a up/down configuration were optimized, constructed and tested. Each thrust bearing unit generated 1040 N of repelling force, and a positive axial stiffness of 169 N/mm at the nominal airgap of 5 mm. Two radial active magnetic bearings (one upper and one lower) were optimized, constructed and tested. By parameterizing the shape of the actuators, a numerical optimization of force over resistive loss from the bias currentcould be performed. The optimized shape of the electromagnets was produced by watercutting sheets of laminated steel. A maximum current stiffness of120 N/A at a bias current of 1.5 A was achieved.
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| 7. |
- Ayob, Mohd Nasir, et al.
(author)
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A remotely controlled sea level compensation system for wave energy converters
- 2019
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In: Energies. - : MDPI. - 1996-1073. ; 12:10
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Journal article (peer-reviewed)abstract
- The working principle of the wave energy converter (WEC) developed at Uppsala University (UU) is based on a heaving point absorber with a linear generator. The generator is placed on the seafloor and is connected via a steel wire to a buoy floating on the surface of the sea. The generator produces optimal power when the translator's oscillations are centered with respect to the stator. However, due to the tides or other changes in sea level, the translator's oscillations may shift towards the upper or lower limit of the generator's stroke length, resulting in a limited stroke and a consequent reduction in power production. A compensator has been designed and developed in order to keep the generator's translator centered, thus compensating for sea level variations. This paper presents experimental tests of the compensator in a lab environment. The wire adjustments are based on online sea level data obtained from the Swedish Meteorological and Hydrological Institute (SMHI). The objective of the study was to evaluate and optimize the control and communication system of the device. As the device will be self-powered with solar and wave energy, the paper also includes estimations of the power consumption and a control strategy to minimize the energy requirements of the whole system. The application of the device in a location with high tides, such as Wave Hub, was analyzed based on offline tidal data. The results show that the compensator can minimize the negative effects of sea level variations on the power production at the WEC. Although the wave energy concept of UU is used in this study, the developed system is also applicable to other WECs for which the line length between seabed and surface needs to be adjusted.
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| 9. |
- Ayob, Mohd Nasir, et al.
(author)
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Small-Scale Renewable Energy Converters for Battery Charging
- 2018
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In: Journal of Marine Science and Engineering. - : MDPI. - 2077-1312. ; 6:1
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Journal article (peer-reviewed)abstract
- This paper presents two wave energy concepts for small-scale electricity generation. In the presented case, these concepts are installed on the buoy of a heaving, point-absorbing wave energy converter (WEC) for large scale electricity production. In the studied WEC, developed by Uppsala University, small-scale electricity generation in the buoy is needed to power a tidal compensating system designed to increase the performance of the WEC in areas with high tides. The two considered and modeled concepts are an oscillating water column (OWC) and a heaving point absorber. The results indicate that the OWC is too small for the task and does not produce enough energy. On the other hand, the results show that a hybrid system composed of a small heaving point absorber combined with a solar energy system would be able to provide a requested minimum power of around 37.7W on average year around. The WEC and solar panel complement each other, as the WEC produces enough energy by itself during wintertime (but not in the summer), while the solar panel produces enough energy in the summer (but not in the winter).
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