| 1. |
- Degen, René, 1994-, et al.
(author)
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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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In: International Journal of Automotive Technology. - : Springer Nature. - 1229-9138 .- 1976-3832. ; 24:4, s. 955-968
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Journal article (peer-reviewed)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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| 2. |
- Degen, René, 1994-, et al.
(author)
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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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In: Journal of Transportation Technologies. - : Scientific Research Publishing. - 2160-0473 .- 2160-0481. ; 13:1, s. 87-114
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Journal article (peer-reviewed)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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| 3. |
- Degen, René, 1994-
(author)
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Virtual Test Field for Highly Automated Vehicle Systems in Urban Environments
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Autonomous driving was and is one of the most important research and innovation drivers in the automotive and supplier industry. In addition to the predicted energy savings, a reduction in the number of accidents and their level of damage is also expected. In particular, the functional testing and legislation of highly automated driving functions play a decisive key role here. This results in a justified need for innovation and research and means major challenges for the entire technology sector. Traditional methods such as real-world tests and X-in-the-loop tests for proving functional safety still have their justification, but cannot answer all the questions posed by the diverse requirements in daily use. In particular, urban environments with highly complex traffic scenarios and diverse groups of actors can only be mapped to a limited extent using existing methods.In this work, a novel approach for testing automated vehicle systems in urban environments is presented. The goal is to create a safe and valid environment in which the vehicle under test can interact with real road users under realistic conditions. The basis is a highly realistic virtual model of a German city center. The physical behavior of the vehicle and the pedestrian is measured and transferred to the virtual city model in real time. Sensor models enable the interaction of the vehicle with the virtual environment and the pedestrian. With the help of different studies with different focuses, both individual functionalities as well as the overall functionality are finally evaluated.
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| 4. |
- Fjellstedt, Christoffer
(author)
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Grid connection of offshore renewable energy sources
- 2023
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Licentiate thesis (other academic/artistic)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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| 5. |
- Mörée, Gustav
(author)
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Models of magnetism in electrical machines
- 2023
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Doctoral thesis (other academic/artistic)abstract
- The magnetic field is a fundamental part of an electrical machine, for establishing the torque and inducing voltages and currents. Then acting as the link between mechanical power and electrical power. This thesis will give a comprehensive study of how magnetism could be modeled. Covering how the magnetic field relates to energy transfer, power flow, and the forces of electrical machines.An electromagnetic energy transfer is usually described by Poynting’s vector, which has a different formulation than the power flow of electrical engineering. The main difference is that Poynting’s vector localizes the energy flux in the surrounding electromagnetic fields of a current-carrying conductor, instead of inside the conductor itself.The forces in a machine can be modeled by the field lines of the magnetic flux density. The force density consists of two vector components: the magnetic tension force and the magnetic pressure gradient force. The magnetic tension force acts to straighten curved field lines, based on the curvature of the flux density. The magnetic pressure gradient force acts from areas of high flux to areas of low flux. The force density could describe the forces in a synchronous machine, both for the torque of the load and for the machine’s radial forces between the rotor and the stator.The force density could also be used to improve the understanding of Maxwell stress tensor,as they are easier to illustrate as vectors, compared to the matrix form within the Maxwell stresstensor. It also expresses the location of the force density, which can improve the use of enclosedvolumes when calculating forces based on the divergence theorem with Maxwell stress tensor.
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| 6. |
- Mörée, Gustav, et al.
(author)
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Review of Hysteresis Models for Magnetic Materials
- 2023
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In: Energies. - : MDPI. - 1996-1073. ; 16:9
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Research review (peer-reviewed)abstract
- There are several models for magnetic hysteresis. Their key purposes are to model magnetization curves with a history dependence to achieve hysteresis cycles without a frequency dependence. There are different approaches to handling history dependence. The two main categories are Duhem-type models and Preisach-type models. Duhem models handle it via a simple directional dependence on the flux rate, without a proper memory. While the Preisach type model handles it via memory of the point where the direction of the flux rate is changed. The most common Duhem model is the phenomenological Jiles–Atherton model, with examples of other models including the Coleman–Hodgdon model and the Tellinen model. Examples of Preisach type models are the classical Preisach model and the Prandtl–Ishlinskii model, although there are also many other models with adoptions of a similar history dependence. Hysteresis is by definition rate-independent, and thereby not dependent on the speed of the alternating flux density. An additional rate dependence is still important and often included in many dynamic hysteresis models. The Chua model is common for modeling non-linear dynamic magnetization curves; however, it does not define classical hysteresis. Other similar adoptions also exist that combine hysteresis modeling with eddy current modeling, similar to how frequency dependence is included in core loss modeling. Most models are made for scalar values of alternating fields, but there are also several models with vector generalizations that also consider three-dimensional directions.
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| 7. |
- Mörée, Gustav, et al.
(author)
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Review of Play and Preisach models for hysteresis in magnetic materials
- 2023
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In: Materials. - : MDPI. - 1996-1944. ; 16:6
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Journal article (peer-reviewed)abstract
- This paper studies the properties of the Preisach model and the play model, and compare their similarities. Both are history-dependent hysteresis models that are used to model magnetic hysteresis. They are described as discrete sums of simple hysteresis operators but can easily be reformulated as integral equations of continuous distribution functions using either a Preisach weight distribution function or a play distribution function. The models are mostly seen as phenomenological or mathematical tools but can also be related to friction-like pinning of domain-wall motions, where Rayleigh’s law of magnetic hysteresis can be seen as the simplest case on either the play model or the Preisach model. They are poor at modeling other domain behavior, such as nucleation-driven hysteresis. Yet another hysteresis model is the stop model, which can be seen as the inverted version of the play model. This type of model has advantages for expressions linked to energy and can be related to Steinmetz equation of hysteresis losses. The models share several mathematical properties, such as the congruency property and wiping-out property, and both models have a history of dependence that can be described by the series of past reversal points. More generally, it is shown that the many models can be expressed as Preisach models, showing that they can be treated as subcategories of the Preisach type models. These include the play model, the stop model and also the alternative KP-hysteron model.
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| 8. |
- Mörée, Gustav, et al.
(author)
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The force density in electrical machines modeled as tension and pressure gradients of magnetic field lines
- 2023
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In: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 13:2
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Journal article (peer-reviewed)abstract
- This paper shows how to model the force density in electrical machines based on the field lines of the magnetic flux density. The force density is written as two vector components: the magnetic tension force and the magnetic pressure gradient force. This approach has been applied in physics but never to forces in engineering problems. The magnetic tension force acts to straighten bent field lines, based on the curvature of the flux density. The magnetic pressure gradient force acts from regions of high flux density to regions of low flux density. Both force densities are derived from the Lorentz force using the tnb-frame of Frenet–Serret formulas and shown to be equivalent to the divergence of the Maxwell stress tensor. It is shown how the force density could describe the forces in a synchronous machine, including both the angular torque of the load and the radial forces between the rotor and the stator. It could also be linked to the power flow and thereby to the energy flux of Poynting’s vector. The force densities could be used to improve the understanding of the Maxwell stress tensor, since they are easier to illustrate as vectors compared to the matrix form of the Maxwell stress tensor. It also shows the location of the force density, which could improve the use of enclosing volumes when calculating the force based on the divergence theorem with the Maxwell stress tensor.
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