| 1. |
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| 2. |
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| 3. |
- Kontos, Sofia, et al.
(författare)
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An Overview of MnAl Permanent Magnets with a Study on Their Potential in Electrical Machines
- 2020
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 13:21
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, hard magnetic materials for future use in electrical machines are discussed. Commercialized permanent magnets used today are presented and new magnets are reviewed shortly. Specifically, the magnetic MnAl compound is investigated as a potential material for future generator designs. Experimental results of synthesized MnAl, carbon-doped MnAl and calculated values for MnAl are compared regarding their energy products. The results show that the experimental energy products are far from the theoretically calculated values with ideal conditions due to microstructure-related reasons. The performance of MnAl in a future permanent magnet (PM) generator is investigated with COMSOL, assuming ideal conditions. Simplifications, such as using an ideal hysteresis loop based on measured and calculated saturation magnetization values were done for the COMSOL simulation. The results are compared to those for a ferrite magnet and an NdFeB magnet. For an ideal MnAl hysteresis loop, it would be possible to replace ferrite with MnAl, with a reduced weight compared to ferrite. In conclusion, future work for simulations with assumptions and results closer to reality is suggested.
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| 4. |
- Leijon, Jennifer, et al.
(författare)
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Freshwater and Lithium from Desalination Powered by Marine Energy Sources
- 2020
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Ingår i: International Journal of Offshore and Polar Engineering. - : International Society of Offshore and Polar Engineers. - 1053-5381. ; 30:3, s. 283-285
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Tidskriftsartikel (refereegranskat)abstract
- To our knowledge, this paper represents an initial study of a novel concept in freshwater and lithium extraction from desalination powered off-grid by marine renewable energy sources. The project's background is interest in the local supply of lithium for the growing numbers of electric vehicles. The desalination technologies investigated are reverse osmosis and electrodialysis. The collocation of the marine resources, possibly available and future technical solutions, and demands for freshwater and lithium suggest that the proposed system could be interesting to study further.
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| 5. |
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| 6. |
- Leijon, Jennifer, et al.
(författare)
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Marine renewable energy sources for desalination, generating freshwater and lithium
- 2019
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Ingår i: Proceedings of the International Offshore and Polar Engineering Conference. - 1098-6189 .- 1555-1792. ; 1, s. 562-568
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Konferensbidrag (refereegranskat)abstract
- A novel concept is presented on lithium extraction of desalination from marine renewable energy sources. The wave-and marine current energy converters designed at Uppsala University in Sweden are evaluated as potential drivers of desalination processes, off-grid, for both local lithium extraction and freshwater production. Also, aqueous mining for other minerals is briefly discussed. Calculations, estimating the freshwater and lithium production from desalination plants powered by marine renewable energy sources, are presented. It is estimated that a medium-sized desalination plant, producing 7500 m3/day, could also generate 1.28 kg lithium daily, utilizing reverse osmosis desalination and electrodialysis, powered by marine energy converter parks. To the best of our knowledge, this concept has never previously been suggested in literature.
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| 7. |
- Leijon, Jennifer, et al.
(författare)
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Study of an Altered Magnetic Circuit of a Permanent Magnet Linear Generator for Wave Power
- 2018
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- The wave energy converter (WEC) studied and developed at Uppsala University in Sweden is a point absorbing buoy connected to a linear generator (LG) on the seabed. Previous studies have improved the sustainability of the generator, changing its magnets from Nd2Fe14B-magnets to ferrites. In this paper, the magnetic circuit of the linear generator is further studied. Ferrite magnets of two different types (Y30 and Y40) are studied along with different shapes of pole shoes for the system. The finite element method (FEM) simulations in a program called Ace are performed. The results show that a linear generator including both Y30 and Y40 magnets and shortened T-shaped pole shoes can generate a similar magnetic energy in the airgap as a linear generator only containing Y40 magnets and rectangular pole shoes. This shows that the magnetic circuit can be altered, opening up sizes and strengths of magnets for different retailers, and thereby possibly lowering magnet cost and transportation. This work was previously presented as a conference at the European Wave and Tidal Energy Conference (EWTEC) 2017 in Cork, Ireland; this manuscript has been carefully revised and some discussions, on magnet costs for example, have been added to this paper.
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| 8. |
- Leijon, Jennifer, 1990-, et al.
(författare)
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Variable renewable energy sources for powering reverse osmosis desalination, with a case study of wave powered desalination for Kilifi, Kenya
- 2020
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Ingår i: Desalination. - : Elsevier BV. - 0011-9164 .- 1873-4464. ; 494:114669
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Tidskriftsartikel (refereegranskat)abstract
- An analysis of reverse osmosis powered by ocean wave power is provided. A commercially available desalination system is connected via a DC/AC converter to a variable DC source and the input voltage is altered to emulate the response of a renewable energy system. Specifically, wave data from Kilifi in Kenya during 2015 is used. The wave resource variations provide variations in estimated power output from a wave energy converter, as well as in estimated freshwater production from a wave powered desalination system. Up to three wave energy converters for desalination are investigated for Kilifi. Also, a hybrid system including solar and wave power is proposed. The experiments show that reverse osmosis desalination systems can function at power levels below the rated values, but with lower freshwater flowrates. It is concluded that wave power, or wave power combined with PV systems, may be considered as power sources for desalination, with or without battery storage.
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| 9. |
- Parwal, Arvind, et al.
(författare)
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Experimental Test of Grid Connected VSC to Improve the Power Quality in a Wave Power System
- 2018
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Ingår i: 2018 5th International Conference on Electric Power and Energy Conversion Systems, EPECS 2018. - 9781538664575
-
Konferensbidrag (refereegranskat)abstract
- This paper provides an overview of electric power conversion system installed at the Lysekil research site, located at the west coast of Sweden. The electric power conversion system consists of rectifiers, rectifying the power from the wave energy converters, a DC-link and a grid-tied inverter. The paper focuses on the performance of the inverter and the filter and presents experimental results obtained during the grid integration.
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| 10. |
- Parwal, Arvind, et al.
(författare)
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Grid impact and power quality assessment of wave energy parks: Different layouts and power penetrations using energy storage
- 2021
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Ingår i: JOURNAL OF ENGINEERING-JOE. - : Institution of Engineering and Technology (IET). - 2051-3305. ; 2021:8, s. 415-428
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Tidskriftsartikel (refereegranskat)abstract
- Power fluctuations induced by wave energy converters (WECs) may reflect negative impact on the power quality of the power grid. Assessing their impact is an important step to ensure the grid compliance level of the energy park. The IEC 61000-4-15 standard classifies the allowable disturbances in the grid. This study analysed and assessed the grid impact in terms of flicker, harmonic distortion and voltage variations. The assessments were performed without energy storage and compared when using the energy storage. A single WEC is emulated as an irregular power output of a real WEC using a combined model of power take-off in the Simulink model. Time series based on data obtained in earlier offshore experiments, conducted at the Lysekil research site in Sweden, is used to emulate a wave energy park (WEP) power in a land-based test rig in real-time power hardware-in-the-loop simulations. A total of three and ten WECs are emulated by introducing a time delay in the time series to investigate the grid impact in each layout. Flicker emissions, voltage variations, individual and total harmonics of the voltage at the connection point in each layout are studied and compared with the limits to be grid compliant for layouts of the WEP. In addition, voltage and current harmonics for the single WEC and individual harmonics in each phase of the voltage are measured and analysed to assess the compliance level of the WEP.
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| 11. |
- Parwal, Arvind, et al.
(författare)
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Grid integration and a power quality assessment of a wave-energy park
- 2019
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Ingår i: IET Smart Grid. - UK : Institution of Engineering and Technology (IET). - 2515-2947. ; 2:4, s. 625-634
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Tidskriftsartikel (refereegranskat)abstract
- This study presents a step toward the grid connection of a wave-energy park through an electric power conversion system (EPCS) developed and installed for the wave-energy harvesting in Lysekil, Sweden. The EPCS comprises a rectifier, a DC bus, and an inverter followed by a harmonic filter (HF). The higher- and lower-order harmonics injected by the inverter in a power quality context are investigated. The lower-order voltage harmonics partially distort the voltage-source inverter output grid current. A phase-locked loop-based (PLL) grid-phase tracking is used to attenuate the lower-order harmonics by reflecting the grid harmonics in the inverter output. An expression for the grid-current harmonics as a function of the grid-voltage harmonics has been derived and implemented. A mathematical model is derived to obtain a transfer function for the PLL, and finally, proportional–integral gains are tuned for stable system operation. An HF for mitigating the higher-order harmonics has been implemented. The total harmonic distortion is evaluated experimentally, and the results fulfil the grid-code requirements at various frequencies and harmonic orders.
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| 12. |
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| 13. |
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| 14. |
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| 15. |
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| 16. |
- Blennow, Jörgen, 1966, et al.
(författare)
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Active High Voltage Insulation
- 2002
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Ingår i: Journal of Electrostatics. ; 55:2, s. 159-172
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Tidskriftsartikel (refereegranskat)
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| 17. |
- Chatzigiannakou, Maria Angeliki
(författare)
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Offshore deployments of marine energy converters
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The depletion warning of non-renewable resources, such as gas, coal and oil, and the imminent effects of climate change turned the attention to clean and fossil fuel-free generated electricity. University research groups worldwide are studying solar, wind, geothermal, biomass and ocean energy harvesting. The focus of this thesis is the wave and marine current energy researched at the division of Electricity at Uppsala University (UU). The main drawbacks that hinder the commercialization of marine energy converter devices is a high installation, operation, maintenance and decommissioning cost. Furthermore, these processes are highly weather dependent and thus, can be time consuming beyond planning. In this thesis, an evaluation of the cost, time and safety efficiency of the devices’ offshore deployment (both wave and marine current), and a comparative evaluation regarding the safety in the use of divers and remotely operated vehicles (ROVs) are conducted. Moreover, a risk analysis study for a common deployment barge while installing an UU wave energy converter (WEC) is presented with the aim to investigate the failure of the crane hoisting system.The UU wave energy project have been initiated in 2001, and since then 14 WECs of various designs have been developed and deployed offshore, at the Lysekil research site (LRS), on the Swedish west coast and in Åland, Finland. The UU device is a point absorber with a linear generator power take off. It is secured on the seabed by a concrete gravity foundation. The absorbed wave energy is transmitted to shore through the marine substation (MS) where all the generators are interconnected. In 2008 an UU spin-off company, Seabased AB (SAB), was established and so far has developed and installed several WECs and two MSs, after the UU devices main principle. SAB deployments were conducted in Sotenäs, Sweden, at the Maren test site (MTS) in Norway; and in Ada Foah, Ghana. The active participation and the thorough study of the above deployments led to a cost, time and safety evaluation of the methods followed. Four main methods were identified and the most suitable one can be chosen depending on the deployment type, for example, for single or mass device deployment.The first UU full scale marine current energy converter (MCEC) was constructed in 2007 at the Ångström Laboratory and deployed at Söderfors, in the river Dalälven in March 2013. The UU turbine is of a vertical axis type and is connected to a directly driven permanent magnet synchronous generator of a low-speed. With this deployment as an example, four MCEC installation methods were proposed and evaluated in terms of cost and time efficiency.A comparative study on the use of divers and ROVs for the deployment and maintenance of WECs at the LRS has been carried out, showing the potential time and costs saved when using ROVs instead of divers in underwater operations. The main restrictions when using divers and ROVs were presented. Most importantly, the modelling introduced is generalized for most types of wave energy technologies, since it does not depend on the structure size or type.Finally, a table of safe launch operation of a WEC is presented. In this table the safe, restrictive and prohibitive sea states are found for a single WEC deployment, using a barge and a crane placed on it. The table can be utilized as a guidance for offshore operations safety and can be extended for a variety of device types and vessels.
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| 18. |
- Chatzigiannakou, Maria Angeliki, et al.
(författare)
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Offshore deployments of wave energy converters by Uppsala University, Sweden
- 2019
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Ingår i: Marine Systems and Ocean Technology. - : Springer Science and Business Media LLC. - 1679-396X .- 2199-4749. ; 14:2-3, s. 67-74
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Tidskriftsartikel (refereegranskat)abstract
- Ocean can provide an inexhaustible amount of energy. Many marine energy converters have been developed but most of them have not surpassed the experimental phase due to the high costs in installation, operation, and maintenance. Since 2002 Uppsala University has developed and deployed several units of wave energy converters of various designs. The Uppsala University wave energy converter concept consists of a linear generator directly connected to a point absorber buoy that is mounted on a concrete gravity foundation. Uppsala University deployments have been carried out using different deployment vessels and methods. Three main methods were utilized for these deployments that are discussed in terms of cost, manpower, and time efficiency. Depending on the desired outcome—multiple- or single-device deployment, low budget, etc.—one of the proposed methods can be used for the optimal outcome.
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| 19. |
- Chen, WenChuang, et al.
(författare)
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Numerical modelling of a point-absorbing wave energy converter in irregular and extreme waves
- 2017
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Ingår i: Applied Ocean Research. - : Elsevier BV. - 0141-1187 .- 1879-1549. ; 63, s. 90-105
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Tidskriftsartikel (refereegranskat)abstract
- Based on the Navier-Stokes (RANS) equations, a three-dimensional (3-D) mathematical model for the hydrodynamics and structural dynamics of a floating point-absorbing wave energy converter (WEC) with a stroke control system in irregular and extreme waves is presented. The model is validated by a comparison of the numerical results with the wave tank experiment results of other researchers. The validated model is then utilized to examine the effect of wave height on structure displacements and connection rope tension. In the examined cases, the differences in WEC’s performance exhibited by an inviscid fluid and a viscous fluid can be neglected. Our results also reveal that the differences in behavior predicted by boundary element method (BEM) and the RANS-based method can be significant and vary considerably, depending on wave height.
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| 20. |
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| 21. |
- Degen, René, 1994-, et al.
(författare)
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Development of a Lidar Model for the Analysis of Borderline Cases Including Vehicle Dynamics in a Virtual City Environment in Real Time
- 2023
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Ingår i: International Journal of Automotive Technology. - : Springer Nature. - 1229-9138 .- 1976-3832. ; 24:4, s. 955-968
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Tidskriftsartikel (refereegranskat)abstract
- Advanced driver assistance systems are an important step on the way towards the autonomous driving. However, there are new challenges in the release of increasingly complex systems. For the testing of those systems many test kilometers are necessary to represent sufficient diversity. Hence, the virtual testing of driver assistance systems brings new opportunities. In virtual environments, it is possible to run a much higher distance in a short time. Simultaneously, the complexity of the environment and the test scenarios are individually adjustable. It is possible to test scenarios that are not feasible in a real environment due to a risk of injury. A big challenge is the physical correct implementation of real vehicles and their components into the Virtual Reality. To enable a realistic virtual testing the vehicles surrounding sensors need to be modeled adequately. Thus, this paper presents an approach for the implementation of a Lidar model into a Virtual Reality. A physical Lidar model is combined with a real-time capable vehicle dynamics model to investigate the influence of vehicle movements to the sensor measurements. The models are implemented into a highly realistic virtual city environment. Finally, a test campaign shows the influence of the Lidars physics and the vehicle dynamics on the detection results.
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| 22. |
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| 23. |
- Degen, René, 1994-, et al.
(författare)
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Methodical Approach to Integrate Human Movement Diversity in Real-Time into a Virtual Test Field for Highly Automated Vehicle Systems
- 2022
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Ingår i: Journal of Transportation Technologies. - : Scientific Research Publishing. - 2160-0473 .- 2160-0481. ; 12:3, s. 296-309
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Tidskriftsartikel (refereegranskat)abstract
- Recently, virtual realities and simulations play important roles in the development of automated driving functionalities. By an appropriate abstraction, they help to design, investigate and communicate real traffic scenario complexity. Especially, for edge cases investigations of interactions between vulnerable road users (VRU) and highly automated driving functions, valid virtual models are essential for the quality of results. The aim of this study is to measure, process and integrate real human movement behaviour into a virtual test environment for highly automated vehicle functionalities. The overall system consists of a georeferenced virtual city model and a vehicle dynamics model, including probabilistic sensor descriptions. By motion capture hardware, real humanoid behaviour is applied to a virtual human avatar in the test environment. Through retargeting methods, which enable the independency of avatar and person under test (PuT) dimensions, the virtual avatar diversity is increased. To verify the biomechanical behaviour of the virtual avatars, a qualitative study is performed, which funds on a representative movement sequence. The results confirm the functionality of the used methodology and enable PuT independence control of the virtual avatars in real-time.
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| 24. |
- Degen, René, et al.
(författare)
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Methodical Approach to the Development of a Radar Sensor Model for the Detection of Urban Traffic Participants Using a Virtual Reality Engine
- 2021
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Ingår i: Journal of Transportation Technologies. - : Scientific Research Publishing. - 2160-0473 .- 2160-0481. ; 11:2, s. 179-195
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Tidskriftsartikel (refereegranskat)abstract
- New approaches for testing of autonomous driving functions are using VirtualReality (VR) to analyze the behavior of automated vehicles in variousscenarios. The real time simulation of the environment sensors is still a challenge.In this paper, the conception, development and validation of an automotiveradar raw data sensor model is shown. For the implementation, theUnreal VR engine developed by Epic Games is used. The model consists of asending antenna, a propagation and a receiving antenna model. The microwavefield propagation is simulated by a raytracing approach. It uses the methodof shooting and bouncing rays to cover the field. A diffused scatteringmodel is implemented to simulate the influence of rough structures on thereflection of rays. To parameterize the model, simple reflectors are used. Thevalidation is done by a comparison of the measured radar patterns of pedestriansand cyclists with simulated values. The outcome is that the developedmodel shows valid results, even if it still has deficits in the context of performance.It shows that the bouncing of diffuse scattered field can only be doneonce. This produces inadequacies in some scenarios. In summary, the papershows a high potential for real time simulation of radar sensors by using raytracing in a virtual reality.
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| 25. |
- Degen, René, 1994-, et al.
(författare)
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Stereoscopic Camera-Sensor Model for the Development of Highly Automated Driving Functions within a Virtual Test Environment
- 2023
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Ingår i: Journal of Transportation Technologies. - : Scientific Research Publishing. - 2160-0473 .- 2160-0481. ; 13:1, s. 87-114
-
Tidskriftsartikel (refereegranskat)abstract
- The need for efficient and reproducible development processes for sensor and perception systems is growing with their increased use in modern vehicles. Such processes can be achieved by using virtual test environments and virtual sensor models. In the context of this, the present paper documents the development of a sensor model for depth estimation of virtual three-dimensional scenarios. For this purpose, the geometric and algorithmic principles of stereoscopic camera systems are recreated in a virtual form. The model is implemented as a subroutine in the Epic Games Unreal Engine, which is one of the most common Game Engines. Its architecture consists of several independent procedures that enable a local depth estimation, but also a reconstruction of a whole three-dimensional scenery. In addition, a separate programme for calibrating the model is presented. In addition to the basic principles, the architecture and the implementation, this work also documents the evaluation of the model created. It is shown that the model meets specifically defined requirements for real-time capability and the accuracy of the evaluation. Thus, it is suitable for the virtual testing of common algorithms and highly automated driving functions.
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| 26. |
- Ekergård, Boel, 1985-, et al.
(författare)
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Longitudinal end effects in a linear wave power generator
- 2020
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:2
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Tidskriftsartikel (refereegranskat)abstract
- Even though the magnetic circuit of a linear electric machine is very similar to a rotating electric machine, they diverge in one fundamental property. The linear generator is open in both ends, i.e., the magnetic circuit is non-symmetric. This paper investigates and discusses the drawbacks of this non-symmetric design in a linear permanent magnet generator, installed in a wave energy conversion system. A two-dimensional geometry has been utilized for the numerical calculations in a finite element method simulation tool. The results present an increased cogging force and significant core losses in the translator as consequences of the longitudinal ends in the machine.
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| 27. |
- 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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| 28. |
- Eklund, Petter, 1989-, et al.
(författare)
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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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| 29. |
- Elamalayil Soman, Deepak, et al.
(författare)
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Cross-Regulation Assessment of DIDO Buck-Boost Converter for Renewable Energy Application
- 2017
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 10:7
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Tidskriftsartikel (refereegranskat)abstract
- When medium- or high-voltage power conversion is preferred for renewable energy sources, multilevel power converters have received much of the interest in this area as methods for enhancing the conversion efficiency and cost effectiveness. In such cases, multilevel, multi-input multi-output (MIMO) configurations of DC-DC converters come to the scenario for integrating several sources together, especially considering the stringent regulatory needs and the requirement of multistage power conversion systems. Considering the above facts, a three-level dual input dual output (DIDO) buck-boost converter, as the simplest form of MIMO converter, is proposed in this paper for DC-link voltage regulation. The capability of this converter for cross regulating the DC-link voltage is analyzed in detail to support a three-level neutral point clamped inverter-based grid connection in the future. The cross-regulation capability is examined under a new type of pulse delay control (PDC) strategy and later compared with a three-level boost converter (TLBC). Compared to conventional boost converters, the high-voltage three-level buck boost converter (TLBBC) with PDC exhibits a wide controllability range and cross regulation capability. These enhanced features are extremely important for better regulating variable output renewable energy sources such as solar, wind, wave, marine current, etc. The simulation and experimental results are provided to validate the claim.
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| 30. |
- Fjellstedt, Christoffer
(författare)
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Grid connection of offshore renewable energy sources
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In order to achieve net zero emissions from the electricity sector, the proportion of renewable energy sources connected to the electrical grid needs to be increased significantly in the coming years. Established renewable energy sources, such as wind power and solar power, will certainly be crucial in achieving this. However, marine energy sources, like marine current power and wave power, have the potential to significantly contribute to the increase of electricity from renewable energy. An important area of study to enable the use of marine energy sources is how to construct electrical systems for offshore renewable energy. Therefore, this thesis addresses some challenges regarding the grid connection of offshore renewable energy.Two important questions for offshore renewable energy are how the offshore electrical grid is constructed and how the power is transmitted to the shore. In the thesis, a review of AC and DC collection grid topologies is presented. Furthermore, HVAC and HVDC transmission for offshore applications are compared in a literature review. It is concluded that for transmission distances longer than 50 km to 100 km, the preferred technology appears to be HVDC.Regardless of how the offshore collection grid is constructed, the energy converters need to be connected to the collection grid and the distribution grid. Uppsala University has deployed a marine current energy converter in the river Dalälven in Söderfors, Sweden. The electrical grid connection system at the test site is based on a B2B converter technology. In the thesis, a simulation model of the grid connection system of the energy converter is presented.The grid connection system at the Söderfors test site includes an LC-filter connected to a power transformer. A novel transfer function is derived for this system and the transfer function is verified with simulations and experimental investigations. It is shown that the derived transfer function is able to capture the frequency response of the experimental system.
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| 31. |
- Fjellstedt, Christoffer
(författare)
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Studies of the Grid Connection of Offshore Renewable Energy Sources : Technologies and Simulations
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A substantial increase in renewable energy sources connected to the electrical grid is imperative to achieve net-zero emissions from the electricity sector. Marine energy sources, like marine current power and wave power, have the potential to significantly contribute to the increase of electricity from renewable energy sources. A crucial aspect of enabling marine energy utilization is the development of electrical systems for offshore renewable energy. Hence, this thesis addresses challenges regarding the grid connection of offshore renewable energy.Two important questions for offshore renewable energy are how to construct the offshore electrical grid and how to transmit the power to the shore. This thesis provides a review of AC and DC collection grid topologies and compares HVAC and HVDC transmission for offshore applications. It is concluded that HVDC is the preferred technology for transmission distances exceeding 50 to 100 km.Regardless of the configuration of the offshore collection grid, the energy converters must be connected to the collection and distribution grid. Uppsala University has deployed a marine current energy converter in the river Dalälven in Söderfors, Sweden. The grid connection system at the test site is based on a back-to-back converter technology. In the thesis, a simulation model of the grid connection system of the energy converter is presented. The simulation model is used to evaluate MPPT methods for marine current power. An advanced hydrodynamic model based on a two-dimensional free vortex method is utilized for this purpose. Additionally, a low-complexity hydrodynamic model is incorporated into the simulation model to assess electrical grids for marine current energy. One AC and one DC collection grid, each comprising five marine current energy converters, are compared. Furthermore, three DC collection grids, each with ten marine current energy converters, are assessed and compared.The grid connection system at the Söderfors test site includes an LC filter connected to a power transformer. A novel transfer function is derived for this system, and the transfer function is verified with simulations and experimental investigations. It is shown that the derived transfer function accurately captures the frequency response of the experimental system.
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| 32. |
- Forslund, Johan, 1985-, et al.
(författare)
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Power And Energy Needed For Starting A Vertical Axis Marine Current Turbine
- 2017
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Konferensbidrag (refereegranskat)abstract
- A marine current power station has been deployed in Söderfors, Sweden. It comprises a five bladed fixed pitch vertical axis H-rotor turbine directly connected to a permanent magnet synchronous generator. The turbine is rated for 1.3 m/s, but at lower water speeds the turbine is generally not self starting. This paper investigates the energy and power needed to at low speeds start the turbine electrically with a BrushLess DC (BLDC) motor until he turbines gives a net positive torque to the generator. A range of startup BLDC powers have been investigated. It is shown that for three water speeds (0.98 m/s, 1.04 m/s and 1.16 m/s) the energy needed for start up is equivalent to less than 1.2 s of power production at maximum power capture of the turbine. The startup time is mostly dependent on BLDC power setting, not on water speed. A BLDC power of 1/7th of rated power of the machine is enough to start the machine within 2 seconds. The results suggest that a higher BLDC power than that will not significantly reduce the startup time nor reduce the energy needed (increase the efficiency of the startup process). The water speed has the highest impact on the time it takes to recover the energy needed for startup once the BLDC power is well above the losses in the system.
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| 33. |
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| 34. |
- 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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| 35. |
- 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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| 36. |
- Frost, Anna E., 1988-, et al.
(författare)
-
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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| 37. |
- Frost, Anna E., 1988-, et al.
(författare)
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Power flow in the air gap of linear electrical machines by utilization of the Poynting vector : Part 2 - Simulations
- 2022
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Ingår i: The Journal of Engineering. - : Institution of Engineering and Technology. - 2051-3305. ; 2022:9, s. 883-891
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Tidskriftsartikel (refereegranskat)abstract
- Different types of linear generators are simulated and their power flow in the air gap is investigated. The results are compared to the analytical expressions derived in Part 1. The simulations and the analytical expressions in Part 1 show the same general behavior, but the magnitudes are lower for the analytical expressions. One explanation for the difference in magnitude can be that the harmonics of the electric and magnetic fields contribute to the power flow, which is not accounted for in the analytical expressions. Due to results from Part 1, it is investigated if changing the number of poles can decrease the tangential power flow while the normal power flow stays the same. As was suspected, changing the number of poles affected several other factors, which lead to an increase in the normal power flow when increasing the number of poles, even though the electrical power was the same. The tangential power flow also decreased for three out of four generators. Thereby, increasing the number of poles with the same length of the machine, at the cost of reduced pole-pitch, should be done with precaution.
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| 38. |
- Frost, Anna E., 1988-, et al.
(författare)
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What influences the Generator Damping atPartial Stator Overlap in a Linear Generator for Wave Power?
- 2021
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Ingår i: Proceedings of the 14th European Wave and Tidal Energy Conference. ; , s. 2245-1-2245-11
-
Konferensbidrag (refereegranskat)abstract
- Experimental data is fitted against partial overlap between the stator and the translator to different powers from one to four to see which relations can be found between electric power, copper losses, other losses, and the dampening force. The other losses consist of iron losses and frictional losses together. The results differ depending on whether the translator is moving up or down, especially for the electric power. Why that is would need further studies to explain. The electric power shows mainly a quadratic dependence on partial overlap, but a cubic dependence as well cannot be excluded, especially when the translator is moving down. The copper losses shows aquadratic dependence on partial stator overlap. The other losses show mostly a linear dependence on the partial stator overlap. The dampening force shows mainly a linear dependence on partial overlap, but a quadratic dependence as well cannot be excluded, but this is probably since the electric power and the copper losses affect the dampening force except when there is no load.
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| 39. |
- Hettiarachchi, Pasan, 1977-
(författare)
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Measurements of X-Ray Emission from Laboratory Sparks and Upward Initiated Lightning
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In 1925 Nobel laureate R. C. Wilson predicted that high electric fields of thunderstorms could accelerate electrons to relativistic energies which are capable of generating high energetic radiation. The first detection of X-rays from lightning was made in 2001 and from long sparks in 2005. Still there are gaps in our knowledge concerning the production of X-rays from lightning and long sparks, and the motivation of this thesis was to rectify this situation by performing new experiments to gather data in this subject.The first problem that we addressed in this thesis was to understand how the electrode geometry influences the generation of X-rays. The results showed that the electrode geometry affects the X-ray generation and this dependency could be explained using a model developed previously by scientists at Uppsala University. The other missing information was the distribution of energy. Using a series of attenuators, we observed how the X-ray photons were attenuated as a function of barrier thickness and using a simple model we obtained the average and the maximum energy of X-rays. All the studies conducted previously was based on the lightning impulses, but in switching impulses, the voltage waveform rises very slowly compared to lightning impulses, and according to some scientists the rate of rise is an important parameter in X-ray development. Our study showed that the switching impulses were as efficient as lightning impulses in generating X-rays even though the rate of rise of voltage in switching impulses was hundreds of times slower.All the observations on X-ray generation from lightning by other scientists were based on either natural downward lightning flashes or triggered lightning in Florida. The first experiments to study the X-ray generation from upward lightning flashes systematically was conducted within this thesis work at Gaisberg Tower in Austria. The results showed that the X-ray emissions from these flashes were much weaker than the ones produced by either natural downward or triggered lightning. An attempt was made to explain this observation by invoking the possible differences in the charge distribution of leaders associated with the triggered lightning flashes in Florida and upward initiated lightning flashes at Gaisberg tower.
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| 40. |
- Hettiarachchi, Pasan, et al.
(författare)
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Time Domain Analysis of the Lightning Interaction with Wave Energy Converters
- 2018
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Ingår i: 2018 34th international conference on lightning protection (ICLP 2018). - New York : IEEE. - 9781538666357
-
Konferensbidrag (refereegranskat)abstract
- In this work, we present a simulated study of lightning interactions with wave power generators submerged in seawater in Lysekil, in the southwest coast of Sweden. A time domain 3D electromagnetic simulation involving a Wave Energy Converter (WEC) and the surrounding seawater, air, and the current injection to the WEC from a typical return stroke of a lightning is conducted. The results show that the injected current to the wave power generator is considerably low even under a direct lightning strike. The study also shows that the wave-shape of the injected current to the WEC is significantly altered from a typical return stroke current impulse. It is concluded that likelihood of damages to the WEC or injection of electrical surges to the electrical grid is low. However, in order fully understand the implications of lightning strikes to a WEC further studies should be conducted.
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| 41. |
- Hultman, Erik, et al.
(författare)
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An updated cable feeder tool design for robotized stator cable winding
- 2018
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Ingår i: Mechatronics. - : Elsevier BV. - 0957-4158 .- 1873-4006. ; 49, s. 197-210
-
Tidskriftsartikel (refereegranskat)abstract
- We have previously suggested a method for robotized stator winding of cable wound electric machines and demonstrated the method successfully in full-scale experiments. The cable feeder tool used to handle the cable during the complete winding process is an essential component of this robot cell. To take the robot winding method to the next level, into an industrial product, require further developments regarding durability, independency, flexibility and implementability. In this paper, we present an updated cable feeder tool design. This tool is designed to be used in a robot cell for cable winding of the third-generation design of the Uppsala University Wave Energy Converter generator stator. In this work, three cable feeder tool prototypes have been constructed, experimentally evaluated and validated for the intended application. Key performance parameters are presented and discussed, including suggestions for further developments. We completed a durable, compact, high performance tool design, with fully integrated control into industrial robot controllers. The experimental results presented in this article are very promising and hence, the updated cable feeder tool design represents another important step towards an industrial solution for robotized stator cable winding.
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| 42. |
- Hultman, Erik, et al.
(författare)
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Automated Cable Preparation for Robotized Stator Cable Winding
- 2017
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Ingår i: Machines. - : MDPI AG. - 2075-1702. ; 5:2
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Tidskriftsartikel (refereegranskat)abstract
- A method for robotized cable winding of the Uppsala UniversityWave Energy Converter generator stator has previously been presented and validated. The purpose of this study is to present and validate further developments to the method: automated stand-alone equipment for the preparation of the winding cables. The cable preparation consists of three parts: feeding the cable from a drum, forming the cable end and cutting the cable. Forming and cutting the cable was previously done manually and only small cable drums could be handled. Therefore the robot cell needed to be stopped frequently. The new equipment was tested in an experimental robot stator cable winding setup. Through the experiments, the equipment was validated to be able to perform fully automated and robust cable preparation. Suggestions are also given on how to further develop the equipment with regards to performance, robustness and quality. Hence, this work represents another important step towards demonstrating completely automated robotized stator cable winding.
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| 43. |
- Hultman, Erik, et al.
(författare)
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Integration of real-world project tasks in a course on automation and robot engineering
- 2019
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Ingår i: IEEE Global Engineering Education Conference, EDUCON. - : Institute of Electrical and Electronics Engineers (IEEE). - 2165-9567 .- 2165-9559. ; April-2019, s. 107-114, s. 107-114
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Konferensbidrag (refereegranskat)abstract
- © 2019 IEEE. The modern engineering profession requires classical technical skills combined with creativity and a high proficiency in cooperation and sustainable development. Research indicates that the engineering education should adapt better to this. This paper introduces a teaching approach where open-ended project tasks are fully integrated into a complete course, in a context relating to the students' future working life. The teaching approach was implemented in a course on automation and robot engineering. Extensive written student course evaluations, the students' examination results and the teachers' experience were used for evaluation and compared with the previous classical course. Both the students and the teachers greatly appreciated the course. It was strongly indicated that the students' theoretical knowledge and understanding of the subject had benefited, both with regards to the technical depth and to the non-technical engineering skills. It is likely that the presented teaching approach can be used also in other engineering courses.
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| 44. |
- Hultman, Erik, et al.
(författare)
-
Robotized stator cable winding
- 2018
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Ingår i: Robotics and Computer-Integrated Manufacturing. - : Elsevier BV. - 0736-5845 .- 1879-2537. ; 53, s. 197-214
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Tidskriftsartikel (refereegranskat)abstract
- Automated stator winding assembly has been available for small and medium sized conventional electric machines for a long time. Cable winding is an alternative technology developed for medium and large sized machines in particular. In this paper we present, evaluate and validate the first fully automated stator cable winding assembly equipment in detail. A full-scale prototype stator cable winding robot cell has been constructed, based on extensive previous work and experience, and used in the experiments. While the prototype robot cell is adapted for the third design generation of the Uppsala University Wave Energy Converter generator stator, the winding method can be adapted for other stator designs. The presented robot cell is highly flexible and well prepared for future integration in a smart production line. Potential cost savings are indicated compared to manual winding, which is a backbreaking task. However, further work is needed to improve the reliability of the robot cell, especially when it comes to preventing the kinking of the winding cable during the assembly.
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| 45. |
- Kamf, Tobias, 1987-
(författare)
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A Method for Calibrating Work-Piece Orientation : Using a Dual-Axis MEMS Inclinometer
-
Ingår i: Robotics and Computer-Integrated Manufacturing. - 0736-5845 .- 1879-2537.
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Tidskriftsartikel (refereegranskat)abstract
- An accelerometer based alignment system designed to align robotic tools and work-pieces in a Cartesian coordinate system is presented, with potential applications within the automated production industry. An overview of the underlying theory, used hardware, micro-controller implementation and performed experiments is presented. The developed theoretical model and prototype hardware is veried against both simulations and experiments, evaluating their performance and practical limitations. For a set of 2000 random initial misalignments with an amplitude in the range of 0° to 10°, the system achieved an alignment accuracy with a 3-sigma bound of 0.023° in the XY plane and 0.14° along the Z-axis. On average the used robot needed 20.86 s to align the used tool to stated accuracy.
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| 46. |
- Kamf, Tobias, et al.
(författare)
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Automated Mounting of Pole-Shoe Wedges in Linear Wave Power Generators-Using Industrial Robotics and Proximity Sensors
- 2017
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Ingår i: Machines. - : MDPI AG. - 2075-1702. ; 5:1
-
Tidskriftsartikel (refereegranskat)abstract
- A system for automatic mounting of high tolerance wedges inside a wave power linear generator is proposed. As for any renewable energy concept utilising numerous smaller generation units, minimising the production cost per unit is vital for commercialization. The linear generator in question uses self-locking wedges, which are challenging to mount using industrial robots due to the high tolerances used, and because of the fact that any angular error remaining after calibration risks damaging the equipment. Using two types of probes, mechanical touch probes and inductive proximity sensors, combined with a flexible robot tool and iterative calibration routines, an automatic mounting system that overcomes the challenges of high tolerance wedge mounting is presented. The system is experimentally verified to work at mounting speeds of up to 50mms(-1), and calibration accuracies of 0.25mm and 0.1 degrees are achieved. The use of a flexible robot tool, able to move freely in one Cartesian plane, was found to be essential for making the system work.
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| 47. |
- Leijon, Mats, 1958-, et al.
(författare)
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A wave power unit, a buoy, use of a wave power unit and a method for producing electric energy
- 2008
-
Patent (populärvet., debatt m.m.)abstract
- The invention relates to a wave power unit with a buoy, adapted to float on a water surface. An electric generator is connected to the buoy through connection means. According to the invention the buoy when floating on a water surface and when seen in a direction perpendicular to the water surface has the shape of a closed loop enclosing an inner opening. The invention also relates to a buoy for a wave power unit, which buoy has the corresponding features as above. Further, the invention relates to the use of the invented wave power unit and to a method for producing electric energy with the invented wave power unit.
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| 48. |
- Lindblad, Liselotte, et al.
(författare)
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Portable Data Acquisition System for Offshore Applications
- 2019
-
Ingår i: IEEE Journal of Oceanic Engineering. - 0364-9059 .- 1558-1691. ; 44:3, s. 719-727
-
Tidskriftsartikel (refereegranskat)abstract
- In the development of ocean energy technologies, full-scale sea trials have proven technically challenging and expensive. As a contribution to the development of flexible, reliable, and affordable measurement systems for such sea trials, this paper presents and evaluates a portable data acquisition system. The system offers a cheap and flexible option for when and where signal infrastructure at site is not available. It is battery powered and consists of a sensor system and a logger unit. The sensor system is placed inside the object of study, which for this application is a wave power generator standing on the seafloor. The logger unit, which contains a logger with integrated data storage and a battery, is placed outside the object of study in a submersible and retrievable vessel. Sensor output is carried with 4-20-mA current signals between the sensor system and the logger, which makes the system directly compatible with a wide range of industrial sensors. For the specific setup implemented in this paper, the sensor system was used to measure voltage and current inside the generator. Beyond this, the system is designed to be adaptable for a wider range of sensors, with 16 individual signals and a sampling frequency up to 1 kHz. The custom logger is programmable and offers many options to apply different logging schedules and to limit the sensor system power supply accordingly. Evaluations show that the implemented system offers 5-22 weeks of 1-kHz and 16-bmonitoring of 16 signals, depending on a chosen logging schedule. Suggestions are also given for how to raise the operation time up to 50 weeks. The system has been tested offshore for the collection of power production data from two wave energy converters, with good results.
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| 49. |
- Loncarski, Jelena, 1983-, et al.
(författare)
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Comparison of Output Current Ripple in Single and Dual Three-Phase Inverters for Electric Vehicle Motor Drives
- 2015
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 8:5, s. 3832-3848
-
Tidskriftsartikel (refereegranskat)abstract
- The standard solution for the traction system in battery powered electric vehicles (EVs) is a two-level (2L) inverter feeding a three-phase motor. A simple and effective way to achieve a three-level (3L) inverter in battery-supplied electric vehicles consists of using two standard three-phase 2L inverters with the open-end winding connection of standard three-phase ac motors. The 3L inverter solution can be usefully adopted in EVs since it combines several benefits such as current ripple reduction, increment of phase motor voltage with limited voltage ratings of the two battery banks, improvement in system reliability, etc. The reduction in current ripple amplitude is particularly relevant since it is a source of electromagnetic interference and audio noise from the inverter-motor power connection cables and from the motor itself. By increasing the inverter switching frequency the ripple amplitude is reduced, but the drive efficiency decreases due to the proportionally increased switching losses. In this paper the peak-to-peak ripple amplitude of the dual-2L inverter is evaluated and compared with the corresponding ripple of the single-2L inverter, considering the same voltage and power motor ratings. The ripple analysis is carried out as a function of the modulation index to cover the whole modulation range of the inverter, and the theoretical results are verified with experimental tests carried out by an inverter-motor drive prototype.
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| 50. |
- Manyahi, M. J., et al.
(författare)
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Transient response of transformer with XLPE insulation cable winding design
- 2005
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Ingår i: International Journal of Electrical Power & Energy Systems. - : Elsevier BV. - 0142-0615 .- 1879-3517. ; 27:1, s. 69-80
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Tidskriftsartikel (refereegranskat)abstract
- Significant advances in XLPE insulation cables that have higher electric field strength withstand capability have made it possible to apply these high voltage (HV) cables as windings in generators and transformers. Therefore, the recent advent of HV generator (Powerformer) that can be connected directly to the power transmission line has motivated the design of HV transformer (Dryformer) that performs one step transformation from transmission to distribution voltage levels. Since the dryformer will be connected directly to transmission lines, they will be subjected to transients resulting from direct and indirect lightning strikes as well as fast switching surges from Gas insulated circuit breakers. This paper presents the results of experimental studies on the cable winding power transformer (Dryformer) to study its response to various transients. Experimental investigations have been carried to obtain the transformer model parameters based on terminal measurement of admittance functions using Network Analyser, and hence for comparing the model predictions with experimentally obtained responses. The model has been successfully used in estimating the dryformer transient responses at its terminals due to surge application of various front times and peak amplitudes that are representative of lightning and switching caused transients. Experiment and simulation results show that there are considerable differences in the transient response characteristics of dryformer windings as compared to that of transformers with traditional winding design. These differences on transient responses are discussed in perspective of their basic difference in winding design features.
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