| 1. |
- Abrahamsson, Johan, 1977-, et al.
(författare)
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High-Speed Kinetic Energy Buffer : Optimization of Composite Shell and Magnetic Bearings
- 2014
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Ingår i: IEEE Transactions on Industrial Electronics. - 0278-0046 .- 1557-9948. ; 61:6, s. 3012-3021
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Abrahamsson, Johan, 1977-
(författare)
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Kinetic Energy Storage and Magnetic Bearings : for Vehicular Applications
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 3. |
- Abrahamsson, Johan, et al.
(författare)
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Magnetic bearings in kinetic energy storage systems for vehicular applications
- 2011
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Ingår i: Journal of Electrical Systems. - 1112-5209. ; 7:2, s. 225-236
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Tidskriftsartikel (refereegranskat)abstract
- The rotating Kinetic Energy Storage System (KESS) is suitable as temporary energy storage in electric vehicles due to its insensitivity to the number of charge-discharge cycles and its relatively high specific energy. The size and weight of the KESS for a given amount of stored energy are minimized by decreasing the moment of inertia of the rotor and increasing its speed. A small and fast rotor has the additional benefit of reducing the induced gyroscopic moments as the vehicle turns. The very high resulting rotational speed makes the magnetic bearing an essential component of the system, with the Active Magnetic Bearing (AMB) being the most common implementation. The complexity and cost of an AMB can be reduced by integration with the electric machine, resulting in a bearingless and sensorless electric machine. This review article describes the usage of magnetic bearings for FESS in vehicular applications.
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| 4. |
- Abrahamsson, Johan, et al.
(författare)
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On the Efficiency of a Two-Power-Level Flywheel-Based All-Electric Driveline
- 2012
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 5:8, s. 2794-2817
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents experimental results on an innovative electric driveline employing a kinetic energy storage device as energy buffer. A conceptual division of losses in the system was created, separating the complete system into three parts according to their function. This conceptualization of the system yielded a meaningful definition of the concept of efficiency. Additionally, a thorough theoretical framework for the prediction of losses associated with energy storage and transfer in the system was developed. A large number of spin-down tests at varying pressure levels were performed. A separation of the measured data into the different physical processes responsible for power loss was achieved from the corresponding dependence on rotational velocity. This comparison yielded an estimate of the perpendicular resistivity of the stranded copper conductor of 2.5 x 10(-8) +/- 3.5 x 10(-9). Further, power and energy were measured system-wide during operation, and an analysis of the losses was performed. The analytical solution was able to reproduce the measured distribution of losses in the system to an accuracy of 4.7% (95% CI). It was found that the losses attributed to the function of kinetic energy storage in the system amounted to between 45% and 65%, depending on usage.
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| 5. |
- Abrahamsson, Johan, et al.
(författare)
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Prototype of electric driveline with magnetically levitated double wound motor
- 2010
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Ingår i: Electrical Machines (ICEM), 2010 XIX International Conference on.
-
Konferensbidrag (refereegranskat)abstract
- This paper presents the ongoing work of constructing a complete driveline for an electric road vehicle, using a flywheel as auxiliary energy storage. The flywheel energy storage system (FESS) is connected in series between the main energy storage (batteries) and the wheel motor of the vehicle, allowing the batteries to deliver power to the system in an optimized way, while at the same time making efficient use of regenerative braking. A double wound permanent magnet electric machine is used to electrically separate the two sides. In order to minimize losses, the machine has a double rotor configuration and is suspended with magnetic bearings. A bench test set-up is being constructed to investigate the properties of this system in detail. This set-up will achieve a level of power and energy close to that of a full scale system. This will allow measurements of complete drive cycles to be performed, improving the understanding of the constituting components and optimization of the complete system.
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| 6. |
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| 7. |
- Aguilar, J. A., et al.
(författare)
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Design and sensitivity of the Radio Neutrino Observatory in Greenland (RNO-G)
- 2021
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Ingår i: Journal of Instrumentation. - : Institute of Physics Publishing (IOPP). - 1748-0221. ; 16:3
-
Tidskriftsartikel (refereegranskat)abstract
- This article presents the design of the Radio Neutrino Observatory Greenland (RNO-G) and discusses its scientific prospects. Using an array of radio sensors, RNO-G seeks to measure neutrinos above 10 PeV by exploiting the Askaryan effect in neutrino-induced cascades in ice. We discuss the experimental considerations that drive the design of RNO-G, present first measurements of the hardware that is to be deployed and discuss the projected sensitivity of the instrument. RNO-G will be the first production-scale radio detector for in-ice neutrino signals.
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| 8. |
- Aguilar, J. A., et al.
(författare)
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Hardware Development for the Radio Neutrino Observatory in Greenland (RNO-G)
- 2022
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Ingår i: 37th International Cosmic Ray Conference, ICRC2021. - Trieste, Italy : Proceedings of Science.
-
Konferensbidrag (refereegranskat)abstract
- The Radio Neutrino Observatory in Greenland (RNO-G) is designed to make the first observations of ultra-high energy neutrinos at energies above 10 PeV, playing a unique role in multi-messenger astrophysics as the world's largest in-ice Askaryan radio detection array. The experiment will be composed of 35 autonomous stations deployed over a 5 x 6 km grid near NSF Summit Station in Greenland. The electronics chain of each station is optimized for sensitivity and low power, incorporating 150 - 600 MHz RF antennas at both the surface and in ice boreholes, low-noise amplifiers, custom RF-over-fiber systems, and an FPGA-based phased array trigger. Each station will consume 25 W of power, allowing for a live time of 70% from a solar power system. The communications system is composed of a high-bandwidth LTE network and an ultra-low power LoRaWAN network. I will also present on the calibration and DAQ systems, as well as status of the first deployment of 10 stations in Summer 2021.
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| 9. |
- Aguilar, J. A., et al.
(författare)
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Reconstructing the neutrino energy for in-ice radio detectors
- 2022
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Ingår i: European Physical Journal C. - : Springer Nature. - 1434-6044 .- 1434-6052. ; 82:2
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Tidskriftsartikel (refereegranskat)abstract
- Since summer 2021, the Radio Neutrino Observatory in Greenland (RNO-G) is searching for astrophysical neutrinos at energies > 10 PeV by detecting the radio emission from particle showers in the ice around Summit Station, Greenland. We present an extensive simulation study that shows how RNO-G will be able to measure the energy of such particle cascades, which will in turn be used to estimate the energy of the incoming neutrino that caused them. The location of the neutrino interaction is determined using the differences in arrival times between channels and the electric field of the radio signal is reconstructed using a novel approach based on Information Field Theory. Based on these properties, the shower energy can be estimated. We show that this method can achieve an uncertainty of 13% on the logarithm of the shower energy after modest quality cuts and estimate how this can constrain the energy of the neutrino. The method presented in this paper is applicable to all similar radio neutrino detectors, such as the proposed radio array of IceCube-Gen2.
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| 10. |
- Aihara, Aya, 1989-, et al.
(författare)
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A numerical study of strut and tower influence on the performance of vertical axis wind turbines using computational fluid dynamics simulation
- 2022
-
Ingår i: Wind Energy. - : John Wiley & Sons. - 1095-4244 .- 1099-1824. ; 25:5, s. 897-913
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the influence of the strut and the tower on the aerodynamic force of the blade for the vertical axis wind turbine (VAWT). It has been known that struts degrade the performance of VAWTs due to the inherent drag losses. In this study, three-dimensional Reynolds-averaged Navier-Stokes simulations have been conducted to investigate the effect of the strut and the tower on the flow pattern around the rotor region, the blade force distribution, and the rotor performance. A comparison has been made for three different cases where only the blade; both the blade and the strut; and all of the blade, the strut, and the tower are considered. A 12-kW three-bladed H-rotor VAWT has been studied for tip speed ratio of 4.16. This ratio is relatively high for this turbine, so the influence of the strut is expected to be crucial. The numerical model has been validated first for a single pitching blade and full VAWTs. The simulations show distinguished differences in the force distribution along the blade between two cases with and without struts. Since the wake from the struts interacts with the blades, the tangential force is reduced especially in the downwind side when the struts are considered. The calculated power coefficient is decreased by 43 %, which shows the importance of modeling the strut effect properly for accurate prediction of the turbine performance. The simulations also indicate that including the tower does not yield significant difference in the force distribution and the rotor power.
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| 11. |
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| 12. |
- Aihara, Aya, 1989-, et al.
(författare)
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Aeroacoustic noise prediction of a vertical axis wind turbine using large eddy simulation
- 2021
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Ingår i: International Journal of Aeroacoustics. - : SAGE Publications. - 1475-472X .- 2048-4003. ; 20:8, s. 959-978
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the numerical prediction for the aerodynamic noise of the vertical axis wind turbine using large eddy simulation and the acoustic analogy. Low noise designs are required especially in residential areas, and sound level generated by the wind turbine is therefore important to estimate. In this paper, the incompressible flow field around the 12 kW straight-bladed vertical axis wind turbine with the rotor diameter of 6.5 m is solved, and the sound propagation is calculated based on the Ffowcs Williams and Hawkings acoustic analogy. The sound pressure for the turbine operating at high tip speed ratio is predicted, and it is validated by comparing with measurement. The measured spectra of the sound pressure observed at several azimuth angles show the broadband characteristics, and the prediction is able to reproduce the shape of these spectra. While previous works studying small-scaled vertical axis wind turbines found that the thickness noise is the dominant sound source, the loading noise can be considered to be a main contribution to the total sound for this turbine. The simulation also indicates that the received noise level is higher when the blade moves in the downwind than in the upwind side.
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| 13. |
- Aihara, Aya, 1989-
(författare)
-
Aeroacoustic Prediction for Vertical Axis Wind Turbines
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates the aerodynamic and aeroacoustic prediction of vertical axis wind turbines, using computational fluid dynamics simulations. Noise pollution from wind turbines is one of the disadvantages of wind energy, calling for strategies to reduce noise levels. Yet for vertical axis wind turbines in particular, there is insufficient knowledge of how to identify sound sources and mitigate the sound level. The aim of this study is to predict aerodynamic noise, using large eddy simulation and acoustic analogy, so as to better understand the mechanism of sound generation for vertical axis wind turbines. First, the prediction method is validated for a static single blade in stall. This model is able to capture the dominant frequency, but it does not well reproduce the broadband characteristics. Next, the aerodynamic behavior of the 12 kW H-rotor vertical axis wind turbine is studied, whereby the focus is on the importance of properly modeling the strut influence for an accurate prediction of the blade forces. To achieve this, the flow field is solved for three different tip speed ratios. The results show that the struts significantly affect on the force distribution along the blade. The reduction of the blade force is observed to occur not only at the attachment points of the struts, but also over a large area of the blade section in the downwind side where the blade interacts with the wake created in the upwind. Finally, the noise radiated from the vertical axis wind turbine operating at high tip speed ratio is predicted. Measurements are conducted to validate the prediction, with the experimental data representing the broadband noise characteristics dominant at around 800 Hz. The prediction reproduces the sound pressure level observed at a radial distance of 1.4 rotor diameter, with a few decibels difference. However, these discrepancies become more pronounced at double distance, which can be considered to arise due to the effect of the ground reflection being ignored. The simulation furthermore indicates, that the main sound sources are emitted when the blade rotates in the downwind. It is suggested that future work should properly consider the atmospheric turbulence for more accurate predictions.
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| 14. |
- Aihara, Aya, 1989-, et al.
(författare)
-
Comparison of Three-Dimensional Numerical Methods for Modeling of Strut Effect on the Performance of a Vertical Axis Wind Turbine
- 2022
-
Ingår i: Energies. - : MDPI. - 1996-1073. ; 15:7
-
Tidskriftsartikel (refereegranskat)abstract
- This paper compares three different numerical models to evaluate their accuracy for predicting the performance of an H-rotor vertical-axis wind turbine (VAWT) considering the influence of struts. The strut of VAWTs is one factor that makes the flow feature around the turbine more complex and thus influences the rotor performance. The focus of this study is placed on analyzing how accurately three different numerical approaches are able to reproduce the force distribution and the resulting power, taking the strut effect into account. For the 12 kW straight-bladed VAWT, the blade force is simulated at three tip speed ratios by the full computational fluid dynamics (CFD) model based on the Reynolds-averaged Navier-Stokes (RANS) equations, the actuator line model (ALM), and the vortex model. The results show that all the models do not indicate a significant influence of the struts in the total force over one revolution at low tip speed ratio. However, at middle and high tip speed ratio, the RANS model reproduces the significant decrease of the total tangential force that is caused due to the strut. Additionally, the RANS and vortex models present a clear influence of the struts in the force distribution along the blade at all three tip speed ratios investigated. The prediction by the ALM does not show such distinctive features of the strut impact. The RANS model is superior to the other two models for predicting the power coefficient considering the strut effect, especially at high tip speed ratio.
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| 15. |
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| 16. |
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| 17. |
- Aihara, Aya, 1989-, et al.
(författare)
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Numerical prediction of noise generated from airfoil in stall using LES and acoustic analogy
- 2021
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Ingår i: Noise & Vibration Worldwide. - : Sage Publications. - 0957-4565 .- 2048-4062. ; 52:10, s. 295-305
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- This article presents the aerodynamic noise prediction of a NACA 0012 airfoil in stall region using Large Eddy Simulation and the acoustic analogy. While most numerical studies focus on noise for an airfoil at a low angle of attack, prediction of stalled noise has been made less sufficiently. In this study, the noise of a stalled airfoil is calculated using the spanwise correction where the total noise is estimated from the sound source of the simulated span section based on the coherence of turbulent flow structure. It is studied for the airfoil at the chord-based Reynolds number of 4.8 × 105 and the Mach number of 0.2 with the angle of attack of 15.6° where the airfoil is expected to be under stall condition. An incompressible flow is resolved to simulate the sound source region, and Curle’s acoustic analogy is used to solve the sound propagation. The predicted spectrum of the sound pressure level observed at 1.2 m from the trailing edge of the airfoil is validated by comparing measurement data, and the results show that the simulation is able to capture the dominant frequency of the tonal peak. However, while the measured spectrum is more broadband, the predicted spectrum has the tonal character around the primary frequency. This difference can be considered to arise due to insufficient mesh resolution.
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| 18. |
- Andersson, Emil, et al.
(författare)
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Vortex filament method 3D analysis of design parameters for counter-rotating axis floating tilted turbine
- 2023
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Ingår i: EERA DeepWind conference 2023. - : Institute of Physics Publishing (IOPP).
-
Konferensbidrag (refereegranskat)abstract
- The Counter-Rotating Axis Floating Tilted turbine (CRAFT) is a new design for floating off-shore wind power, which utilizes a low center of gravity and allows the tower to tilt to mitigate costs for platforming.In this study, 3D simulations of the CRAFT have been performed to investigate the effect from the tower's tilt angle on the aerodynamics of the turbine using a vortex filament method. Due to lack of empirical data of the CRAFT, the method has been benchmark tested against a previous project on a vertical axis wind turbine.Using this method, the blades' twist angle has been set to achieve good lift-to-drag ratio along the entire blade. Furthermore, the blades' chord length has been determined for optimal Tip Speed Ratio (TSR) 6 when the tower is tilted 30 degrees from vertical position.The CRAFT has been simulated vertically and tilted 15°, 30° and 45°, for TSRs ranging between 4 and 9. The power coefficients (CP) and normal forces have been determined, and velocity plots are presented to show how the near-wake develops.The results from this study serves as a basis for further development and design of the CRAFT.
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| 19. |
- Anker, A., et al.
(författare)
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A search for cosmogenic neutrinos with the ARIANNA test bed using 4.5 years of data
- 2020
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP PUBLISHING LTD. - 1475-7516. ; :3
-
Tidskriftsartikel (refereegranskat)abstract
- The primary mission of the ARIANNA ultra-high energy neutrino telescope is to uncover astrophysical sources of neutrinos with energies greater than 10(16) eV. A pilot array, consisting of seven ARIANNA stations located on the surface of the Ross Ice Shelf in Antarctica, was commissioned in November 2014. We report on the search for astrophysical neutrinos using data collected between November 2014 and February 2019. A straight-forward template matching analysis yielded no neutrino candidates, with a signal efficiency of 79%. We find a 90% confidence upper limit on the diffuse neutrino flux of E-2 Phi = 1.7 x 10(-6) GeV cm(-2) s(-1) sr(-1) for a decade wide logarithmic bin centered at a neutrino energy of 10(18),eV, which is an order of magnitude improvement compared to the previous limit reported by the ARIANNA collaboration. The ARIANNA stations, including purpose built cosmic-ray stations at the Moore's Bay site and demonstrator stations at the South Pole, have operated reliably. Sustained operation at two distinct sites confirms that the flexible and adaptable architecture can be deployed in any deep ice, radio quiet environment. We show that the scientific capabilities, technical innovations, and logistical requirements of ARIANNA are sufficiently well understood to serve as the basis for large area radio-based neutrino telescope with a wide field-of-view.
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| 20. |
- Anker, A., et al.
(författare)
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Neutrino vertex reconstruction with in-ice radio detectors using surface reflections and implications for the neutrino energy resolution
- 2019
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP PUBLISHING LTD. - 1475-7516. ; :11
-
Tidskriftsartikel (refereegranskat)abstract
- Ultra high energy neutrinos (E-nu >10(16.5) eV) are efficiently measured via radio signals following a neutrino interaction in ice. An antenna placed O(15 m) below the ice surface will measure two signals for the vast majority of events (90% at E-nu = 10(18) eV): a direct pulse and a second delayed pulse from a reflection off the ice surface. This allows for a unique identification of neutrinos against backgrounds arriving from above. Furthermore, the time delay between the direct and reflected signal (D'n'R) correlates with the distance to the neutrino interaction vertex, a crucial quantity to determine the neutrino energy. In a simulation study, we derive the relation between time delay and distance and study the corresponding experimental uncertainties in estimating neutrino energies. We find that the resulting contribution to the energy resolution is well below the natural limit set by the unknown inelasticity in the initial neutrino interaction. We present an in-situ measurement that proves the experimental feasibility of this technique. Continuous monitoring of the local snow accumulation in the vicinity of the transmit and receive antennas using this technique provide a precision of O(1mm) in surface elevation, which is much better than that needed to apply the D'n'R technique to neutrinos.
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| 21. |
- Anker, A., et al.
(författare)
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Probing the angular and polarization reconstruction of the ARIANNA detector at the South Pole
- 2020
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Ingår i: Journal of Instrumentation. - : IOP PUBLISHING LTD. - 1748-0221. ; 15:9
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Tidskriftsartikel (refereegranskat)abstract
- The sources of ultra-high energy (UHE) cosmic rays, which can have energies up to 10(20) eV, remain a mystery. UHE neutrinos may provide important clues to understanding the nature of cosmic-ray sources. ARIANNA aims to detect UHE neutrinos via radio (Askaryan) emission from particle showers when a neutrino interacts with ice, which is an efficient method for neutrinos with energies between 10(16) eV and 10(20) eV. The ARIANNA radio detectors are located in Antarctic ice just beneath the surface. Neutrino observation requires that radio pulses propagate to the antennas at the surface with minimum distortion by the ice and firn medium. Using the residual hole from the South Pole Ice Core Project, radio pulses were emitted from a transmitter located up to 1.7 km below the snow surface. By measuring these signals with an ARIANNA surface station, the angular and polarization reconstruction abilities are quantified, which are required to measure the direction of the neutrino. After deconvolving the raw signals for the detector response and attenuation from propagation through the ice, the signal pulses show no significant distortion and agree with a reference measurement of the emitter made in an anechoic chamber. Furthermore, the signal pulses reveal no significant birefringence for our tested geometry of mostly vertical ice propagation. The origin of the transmitted radio pulse was measured with an angular resolution of 0.37 degrees indicating that the neutrino direction can be determined with good precision if the polarization of the radio-pulse can be well determined. In the present study we obtained a resolution of the polarization vector of 2.7 degrees. Neither measurement show a significant offset relative to expectation.
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| 22. |
- Anker, A., et al.
(författare)
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Targeting ultra-high energy neutrinos with the ARIANNA experiment
- 2019
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Ingår i: Advances in Space Research. - : Elsevier BV. - 0273-1177 .- 1879-1948. ; 64:12, s. 2595-2609
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Tidskriftsartikel (refereegranskat)abstract
- The measurement of ultra-high energy (UHE) neutrinos (E > 10(16) eV) opens a new field of astronomy with the potential to reveal the sources of ultra-high energy cosmic rays especially if combined with observations in the electromagnetic spectrum and gravitational waves. The ARIANNA pilot detector explores the detection of UHE neutrinos with a surface array of independent radio detector stations in Antarctica which allows for a cost-effective instrumentation of large volumes. Twelve stations are currently operating successfully at the Moore's Bay site (Ross Ice Shelf) in Antarctica and at the South Pole. We will review the current state of ARIANNA and its main results. We report on a newly developed wind generator that successfully operates in the harsh Antarctic conditions and powers the station for a substantial time during the dark winter months. The robust ARIANNA surface architecture, combined with environmentally friendly solar and wind power generators, can be installed at any deep ice location on the planet and operated autonomously. We report on the detector capabilities to determine the neutrino direction by reconstructing the signal arrival direction of a 800 m deep calibration pulser, and the reconstruction of the signal polarization using the more abundant cosmic-ray air showers. Finally, we describe a large-scale design - ARIA - that capitalizes on the successful experience of the ARIANNA operation and is designed sensitive enough to discover the first UHF neutrino.
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| 23. |
- Apelfröjd, Senad, et al.
(författare)
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A Review of Research on Large Scale Modern Vertical Axis Wind Turbines at Uppsala University
- 2016
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 9:7
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Forskningsöversikt (refereegranskat)abstract
- This paper presents a review of over a decade of research on Vertical Axis Wind Turbines (VAWTs) conducted at Uppsala University. The paper presents, among others, an overview of the 200 kW VAWT located in Falkenberg, Sweden, as well as a description of the work done on the 12 kW prototype VAWT in Marsta, Sweden. Several key aspects have been tested and successfully demonstrated at our two experimental research sites. The effort of the VAWT research has been aimed at developing a robust large scale VAWT technology based on an electrical control system with a direct driven energy converter. This approach allows for a simplification where most or all of the control of the turbines can be managed by the electrical converter system, reducing investment cost and need for maintenance. The concept features an H-rotor that is omnidirectional in regards to wind direction, meaning that it can extract energy from all wind directions without the need for a yaw system. The turbine is connected to a direct driven permanent magnet synchronous generator (PMSG), located at ground level, that is specifically developed to control and extract power from the turbine. The research is ongoing and aims for a multi-megawatt VAWT in the near future.
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| 24. |
- Bengtsson, Rhodel, et al.
(författare)
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Feasiblity of wooden towers for offshore wind turbines: Creep and fatigue predictions
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Long-term experiences with vertical axis wind turbines constructed with wood are positive, and show that wood towers are a viable alternative to conventional steel towers on land. Wood is a renewable material in contrast to steel and concrete and could steer a more sustainable use of raw material for future wind farms. The obvious drawback of moisture-induced softening and degradation in off-shore settings can be mitigated by efficiently sealing the tower using a barrier coating. In that case, fatigue sensitivity and creep deformations are the main design concerns. In this paper through finite element simulations of a floating tilted vertical-axis wind turbine, it was shown that fatigue issues can be resolved with proper design of the mast and the blade joints keeping the stress concentrations at bay. The numerical results also indicated that creep displacements are negligible. The review and calculations reinforce the assumption that the fast developments seen in timber high-rise building can also be expected for off-shore wind turbine towers.
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| 25. |
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| 26. |
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| 27. |
- Bernhoff, Hans, et al.
(författare)
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Wave energy resources in sheltered sea areas : A case study of the Baltic Sea
- 2006
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 31:13, s. 2164-2170
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Tidskriftsartikel (refereegranskat)abstract
- Wave energy is a renewable source, which has not yet been exploited to a large extent. So far the main focus of wave energy conversion has been on the large wave energy resources of the great oceans on northern latitudes. However, large portions of the world potential wave energy resources are found in sheltered waters and calmer seas, which often exhibit a milder, but still steady wave climate. Examples are the Baltic Sea, the Mediterranean and the North Sea in Europe, and ocean areas closer to the equator. Many of the various schemes in the past consist of large mechanical structures, often located near the sea surface. In the present work we instead focus on wave power plants consisting of a number of small wave energy converters, forming large arrays. In this context, we look at advantageous arrangements of point absorbers, and discuss the potential of the Baltic Sea as a case study.
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| 28. |
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| 29. |
- Bolund, Björn, 1978-
(författare)
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Electric Power Generation and Storage Using a High Voltage Approach
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Production and consumption of electricity have grown enormously during the last century. No mater what the primary source of energy is, almost all generation of electricity comes from conversion of a rotational movement in a generator. The aim of this thesis is to see how high voltage technology influence production and storage of electricity. Power flow in the generators used to convert mechanical movement to electric energy is analyzed using Poynting‘s vector. The impact of new generator technology for efficient extraction of hydroelectric power is shown. Simulation of a large permanent magnet turbo generator is presented. A flywheel storage system for electric vehicles utilizing high voltage technology is also presented. In pulsed power applications, a cheap method for intermediate storage of energy during milliseconds, which enables an inductive primary storage is presented and experimentally tested.
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| 30. |
- Bolund, Björn, et al.
(författare)
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Flywheel energy and power storage systems
- 2007
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Ingår i: Renewable & sustainable energy reviews. - : Elsevier BV. - 1364-0321 .- 1879-0690. ; 11:2, s. 235-258
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Tidskriftsartikel (refereegranskat)abstract
- For ages flywheels have been used to achieve smooth operation of machines. The early models where purely mechanical consisting of only a stone wheel attached to an axle. Nowadays flywheels are complex constructions where energy is stored mechanically and transferred to and from the flywheel by an integrated motor/generator. The stone wheel has been replaced by a steel or composite rotor and magnetic bearings have been introduced. Today flywheels are used as supplementary UPS storage at several industries world over. Future applications span a wide range including electric vehicles, intermediate storage for renewable energy generation and direct grid applications from power quality issues to offering an alternative to strengthening transmission. One of the key issues for viable flywheel construction is a high overall efficiency, hence a reduction of the total losses. By increasing the voltage, current losses are decreased and otherwise necessary transformer steps become redundant. So far flywheels over 10 kV have not been constructed, mainly due to isolation problems associated with high voltage, but also because of limitations in the power electronics. Recent progress in semi-conductor technology enables faster switching and lower costs. The predominant part of prior studies have been directed towards optimising mechanical issues whereas the electro technical part now seem to show great potential for improvement. An overview of flywheel technology and previous projects are presented and moreover a 200 kW flywheel using high voltage technology is simulated.
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| 31. |
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| 32. |
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| 33. |
- Bülow, Fredrik, 1980-
(författare)
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A Generator Perspective on Vertical Axis Wind Turbines
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The wind energy conversion system considered in this thesis is based on a vertical axis wind turbine with a cable wound direct drive PM generator. Diode rectifiers are used to connect several such units to a single DC-bus and a single inverter controls the power flow from the DC-bus to a utility grid. This work considers the described system from a generator perspective i.e. the turbine is primarily seen as a torque and the inverter is seen as a controlled load.A 12 kW VAWT prototype with a single turbine has been constructed within the project. The power coefficient of this turbine has been measured when the turbine is operated at various tip speed ratios. This measurement determines both how much energy the turbine can convert in a given wind and at what speed the turbine should be operated in order to maximise the energy capture. The turbine torque variation during the revolution of the turbine has also been studied.A PM generator prototype has been constructed in order to study power loss in the stator core at low electrical frequencies. Heat exchange between the stator and the air-gap between the stator and the rotor has been studied. Heat exchange between the stator and the air-gap is increased by turbulence caused by the rotor. The generator was also used in a demonstration of a DC-grid where two diode rectified PM generators supplied power to a single DC load. An initial study of an inverter suitable for grid connection of the 12 kW PM generator has been performed.Several turbine control strategies are evaluated in simulations. The control strategies only require the parameter "turbine speed" to determine the optimal system load.
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| 34. |
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| 35. |
- Bülow, Fredrik, et al.
(författare)
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No-load core loss prediction of PM generator at low electrical frequency
- 2012
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 43, s. 389-392
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Tidskriftsartikel (refereegranskat)abstract
- A method for measurement of frequency dependent electromagnetic core loss of a permanent magnet generator is presented. Core loss of a PM generator is measured at electrical frequencies ranging from 4 to 14 Hz. Core loss in the same interval is simulated using the finite element method and frequency domain loss separation. The specific loss is both extrapolated from specific loss at 50 Hz and measured directly at 4, 8, 12 and 16 Hz. Core loss simulations based on extrapolated specific loss are 38–53% smaller than measured loss. Core loss simulations based on specific loss measured at 4, 8, 12 and 16 Hz are 19–23% smaller than measured loss.
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| 36. |
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| 37. |
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| 38. |
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| 39. |
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| 40. |
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| 41. |
- de Santiago, Juan, 1979-, et al.
(författare)
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Calculation of Tooth Ripple Losses in Solid Poles
- 2015
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Ingår i: Electric power components and systems. - : Taylor & Francis. - 1532-5008 .- 1532-5016. ; 43:3, s. 245-251
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Tidskriftsartikel (refereegranskat)abstract
- Tooth ripple losses in solid salient poles are calculated with analytical and semi-empirical methods. A numerical method based on the finite element method is presented in this article. The distribution of the eddy currents induced by the tooth ripple is obtained with this new method. The traditional analytic approach is based on some assumptions on the eddy current losses distribution that are finally verified with the Finite Element Method simulations presented. Analytic solutions of tooth ripple losses are only applicable to distributed windings with a homogeneous slot pitch while the method presented is applicable both to distributed and concentrated windings.
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| 42. |
- de Santiago, Juan, et al.
(författare)
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Comparison between axial and radial flux PM coreless machines for flywheel energy storage
- 2010
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Ingår i: Journal of Electrical Systems. - 1112-5209. ; 6:2
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Tidskriftsartikel (refereegranskat)abstract
- The need of a deeper understanding of coreless machines arises with new magnetic materials with higher remanent magnetization and the spread of high speed motors and generators. High energy density magnets allow complete ironless stator motor/generators configurations which are suitable for high speed machines and specifically in flywheel energy storage. Axial-flux and radial-flux machines are investigated and compared. The limits and merits of ironless machines are presented. An analytic solution of Maxwell’s equations is used to calculate the properties of axial-flux and radial-flux ironless generators. This method is used to investigate the influence of several parameters such as diameter and airgap width. Two machines have been calculated with FEM techniques and results are compared to validate the analytic method. Simulations conclude that end winding effects are more significant for axial-flux than for radialflux topologies. Radial-flux machines are more suitable for high speed ironless stators. The optimum values of some machine parameters are significantly different for ironless machines in comparison to slotted and slotless machines, such as outer radius to inner radius for axial-flux topologies. High speed coreless machines for energy storage and other applications required 3D FEM analysis for accurate results.
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| 43. |
- de Santiago, Juan, et al.
(författare)
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Dual voltage driveline for vehicle applications
- 2010
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Ingår i: International Journal of Emerging Electric Power Systems. - USA : Berkeley Electronic Press. - 2194-5756 .- 1553-779X. ; 11:3, s. 20 pp.-
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a novel driveline where the load and the energy source are operated at different voltage levels and they are galvanically insulated. The element that couples both part of the driveline is a Two Voltage Level Machine (TVLM). The machine is formed of a self-excited rotor and a stator with two sets of electrically isolated windings for adjustable speed drive applications. Both sets of these three phase windings are independently operated at different voltages. The equivalent circuit of the TVLM is deduced and phasor diagrams are presented. A complete driveline is simulated and the performance of the complete system is discussed. The driveline is applicable in flywheel energy storage systems for vehicles and power conditioning in renewable energy production.
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| 44. |
- de Santiago, Juan, et al.
(författare)
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Electrical Motor Drivelines in Commercial All Electric Vehicles : a Review
- 2012
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Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 61:2, s. 475-484
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a critical review of the drivelines in all Electric Vehicles (EVs). The motor topologies that are the best candidates to be used in EVs are presented. The advantages and disadvantages of each electric motor type are discussed from a system perspective. A survey of the electric motors used in commercial EVs is presented. The survey shows that car manufacturers are very conservative when it comes to introducing new technologies. Most of the EV’s in the market mount a single induction or permanent magnet motor with a traditional mechanic driveline with a differential. The study illustrates that comparisons between the different motors are made difficult by the large number of parameters and the lack of a recommended test scheme. The authors propose that a standardized drive cycle is used to test and compare motors.
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| 45. |
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| 46. |
- de Santiago, Juan, et al.
(författare)
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Filter Influence on Rotor Losses in Coreless Axial Flux Permanent Magnet Machines
- 2013
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Ingår i: Advances in Electrical and Computer Engineering. - 1582-7445 .- 1844-7600. ; 13:1, s. 81-86
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the eddy current losses induced in the rotor of coreless Axial-Flux machines. The calculation of eddy currents in the magnets requires the simulation of the inverter and the filter to obtain the harmonic content of the stator currents and FEM analysis of the magnets in the rotor. Due to the low inductance in coreless machines, the induced eddy current losses in the rotor remain lower than in traditional slotted machines. If only machine losses are considered, filters in DC/AC converters are not required in machines with wide airgaps as time harmonic losses in the rotor are very low. The harmonic content both from simulations and experimental results of a DC/AC converter are used to calculate the eddy currents in the rotor magnets. The properties of coreless machine topologies are investigated and some simplifications are proposed for time efficient 3D-FEM analysis. The time varying magnetic field can be considered constant over the magnets when the pole is divided in several magnets. The simplified FEM method to calculate eddy current losses is applicable to coreless machines with poles split into several magnets, although the conclusions are applicable to all coreless and slotless motors and generators.
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| 47. |
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| 48. |
- de Santiago Ochoa, Juan, et al.
(författare)
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Design Parameters Calculation of a Novel Driveline for Electric Vehicles
- 2009
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Ingår i: World Electric Vehicle Journal. - 2032-6653. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- A driveline for electric vehicles is presented. The propulsion system is operated at a higher voltage than the primary energy source. The batteries selected as the primary energy source deliver power to the vehicle through a motor-generator wounded with two electrically isolated sets of windings, named Two Voltage Level Machine (TVLM). The dynamic behaviour of a vehicle operating according to a standard drive cycle is studied. Parameters of the driveline such as power rates and size of the flywheel are obtained by optimization. A description of the performance of a TVLM is also presented through its equivalent circuit and the control of the machine. Special attention to the system losses is presented. A scale prototype has been constructed and tested under a drive cycle, demonstrating the system performance of the system.
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| 49. |
- de Santiago Ochoa, Juan
(författare)
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FEM Analysis Applied to Electric Machines for Electric Vehicles
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electric vehicle technology is an interdisciplinary field in continuous development. It appears to be a margin for improvements. The Division for Electricity at Uppsala University is doing significant research in the field. The present thesis investigates electric machines for vehicular applications, both in the driveline and in the traction motor. Section 1 presents a driveline with two galvanically isolated voltage levels. A low power side is operated at the optimum voltage of the batteries, while a high power side is operated at a higher voltage leading to higher efficiencies in the traction motor. Both sides are coupled through a flywheel that stabilizes the power transients inherent to a drive cycle. A review of electric machine topologies for electric vehicles is presented in Section 2. The permanent magnet excited machine is the most suitable technology for an electric driveline. Section 3 is devoted to numerical models applied to electric machines. The equivalent circuit of a motor/generator with two sets of windings is first presented. This machine couples both sides of the driveline and drives the rotor of the flywheel. The electric parameters are calculated with custom FEM models. A discussion on slotless machines concludes with a simple model to analyze the magnetic field from one static 3D simulation. The tooth ripple losses in solid salient poles are also analyzed with a novel FEM approach. A complete description of the losses in electric machines gives a proper background for further discussion on efficiency. Section 4 presents the experimental work constructed to validate the theoretical models. The experiments include an axial flux, single wounded prototype, an axial flux, double wound prototype and a planed radial flux coreless prototype. Section 5 focuses on traction motors for electric vehicles. A simulated prototype illustrates a design and calculation process. The loss theory and the numerical methods presented in Section 3 are applied.
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| 50. |
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