| 1. |
- Marin, Gustav, et al.
(författare)
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Stiffness and strength properties of five paperboards and their moisture dependency
- 2019
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Ingår i: Paper Conference and Trade Show, PaperCon 2019. - : TAPPI Press. - 9781510893948 ; , s. 1193-1208
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Konferensbidrag (refereegranskat)abstract
- Five folding box boards made on the same paperboard machine have been analyzed. The paperboards were from the same product series but had different grammage (235, 255, 270, 315, 340 g/m2) and different bending stiffness. The paperboards are normally used to make packages, and since the bending stiffness and grammage varies the packages performance will be different. Finite element simulations can be used to predict these differences. However, the stiffness and strength properties then need to be known. For efficient determination of the three-dimensional properties in MD, CD and ZD, it is proposed that the whole paperboard should be characterized with the following tests: in-plane tension, ZD tension, shear strength profiles and two-point bending. The stiffness and strength properties have with the proposed setups been determined at different relative humidity (20, 50, 70 and 90 % RH), and the mechanical properties have been evaluated as function of moisture ratio. The results showed a linear relation between mechanical properties and moisture ratio for each paperboard. The data was then normalized with data for the standard climate (50 % RH) and investigated as a function of moisture ratio. The results indicated that the normalized mechanical properties for all paperboards coincided along one single line and could therefore be expressed as a linear function of moisture ratio and two constants. Consequently, the study indicates that it is possible to obtain the mechanical properties of a paperboard, by knowing the structural properties for the preferred level of RH and the mechanical property for the standard climate (50 % RH and 23 °C).
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| 2. |
- Alahakoon, Sanath, et al.
(författare)
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Emerging Energy Storage Solutions for Transportation Electrification - A view
- 2019
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Ingår i: International Journal of Engineering and Technology Innovation. - : Taiwan Assoc Engineering & Technology Innovation. - 2223-5329 .- 2226-809X. ; 9:2, s. 75-90
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Forskningsöversikt (refereegranskat)abstract
- Energy storages have caught the attention of transportation community r the past several years. Rsecent developments in hybrid and plug-in ectric vehicles together with novel concepts in transportation such as ectric highways are the reasons for raising the role of energy orages in transportation to such a significant level. Performance mands for energy storage solutions vary significantly from one ansportation application to the other, making it difficult for the ientific community to converge to a single energy storage solution at caters all. This paper reviews the key performance demands of the jor transportation applications. It also investigates the aracteristics of emerging energy storage solutions and assess their itability for those reviewed transportation applications.
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| 5. |
- Bessegato, Luca, 1989-, et al.
(författare)
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Control and Admittance Modeling of an AC/AC Modular Multilevel Converter for Railway Supplies
- 2020
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Ingår i: IEEE transactions on power electronics. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0885-8993 .- 1941-0107. ; 35:3, s. 2411-2423
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Tidskriftsartikel (refereegranskat)abstract
- Modular multilevel converters (MMCs) can be configured to perform ac/ac conversion, which makes them suitable as railway power supplies. In this paper, a hierarchical control scheme for ac/ac MMCs for railway power supplies is devised and evaluated, considering the requirements and the operating conditions specific to this application. Furthermore, admittance models of the ac/ac MMC are developed, showing how the suggested hierarchical control scheme affects the three-phase and the single-phase side admittances of the converter. These models allow for analyzing the stability of the interconnected system using the impedance-based stability criterion and the passivity-based stability assessment. Finally, the findings presented in this paper are validated experimentally, using a down-scaled MMC.
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| 6. |
- Bessegato, Luca, et al.
(författare)
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Control and Admittance Modeling of an AC/AC Modular Multilevel Converter for Railway Supplies
- 2019
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Ingår i: IEEE transactions on power electronics. - 0885-8993 .- 1941-0107.
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Tidskriftsartikel (refereegranskat)abstract
- Modular multilevel converters (MMCs) can be configured to perform ac/ac conversion, which makes them suitable as railway power supplies. In this paper, a hierarchical control scheme for ac/ac MMCs for railway power supplies is devised and evaluated, considering the requirements and the operating conditions specific to this application. Furthermore, admittance models of the ac/ac MMC are developed, showing how the suggested hierarchical control scheme affects the three-phase and the single-phase side admittances of the converter. These models allow for analyzing the stability of the interconnected system using the impedance-based stability criterion and the passivity-based stability assessment. Finally, the findings presented in this paper are validated experimentally, using a down-scaled MMC.
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| 7. |
- Bessegato, Luca, et al.
(författare)
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Control of Direct AC/AC Modular Multilevel Converters Using Capacitor Voltage Estimation
- 2016
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Ingår i: 2016 18TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'16 ECCE EUROPE). - : IEEE.
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Konferensbidrag (refereegranskat)abstract
- This paper applies a control method based on current control and sum-capacitor-voltage estimation to the direct ac/ac modular multilevel converter. As capacitor voltages are estimated, their measurements are not needed in the high-level control, which simplifies the communication between the main controller and the submodules of the converter. The stability of the internal dynamics of the converter, using the aforementioned control method, is studied using Lyapunov stability theory, proving that the system is globally asymptotically stable. The behavior of the converter is simulated focusing on three-phase 50 Hz to single-phase 16 (2)/(3) Hz conversion, which is typical for railway power supply systems of some European countries. Simulation results are in agreement with the expected behavior of the converter, both in steady-state and dynamic situations.
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| 8. |
- Bessegato, Luca, 1989-
(författare)
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Modeling of Modular Multilevel Converters for Stability Analysis
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modular multilevel converters (MMCs) have recently become the state-of-the-art solution for various grid-connected applications, such as high-voltage direct current (HVDC) systems and flexible alternating current transmission systems (FACTS). Modularity, scalability, low power losses, and low harmonic distortion are the outstanding properties that make MMCs a key technology for a sustainable future. The main objective of this thesis is the modeling of grid-connected MMCs for stability analysis. The stability of the interconnected system, formed by the converter and the ac grid, can be assessed by analyzing the converter ac-side admittance in relation to the grid impedance. Therefore, a method for the calculation of the ac-side admittance of MMCs is developed. This method overcomes the nonlinearities of the converter dynamics and it can be easily adapted to different applications. Moreover, the effects of different control schemes on the MMC ac-side admittance are studied, showing how the converter admittance can be reshaped. This is a useful tool for system design, because it shows how control parameters can be selected to avoid undesired grid-converter interactions. This thesis also studies ac/ac MMCs for railway power supplies, which are used in countries with a low-frequency railway grid, such as Germany (16.7 Hz) and Sweden (16 2/3 Hz). A hierarchical control scheme for these converters is devised and evaluated, considering the requirements and the operating conditions specific to this application. Furthermore, admittance models of the ac/ac MMC are developed, showing how the suggested hierarchical control scheme affects the three-phase and the single-phase side admittances of the converter. For computing the insertion indices, an open-loop scheme with sum capacitor voltage estimation is applied to the ac/ac MMC. Lyapunov stability theory is used to prove the asymptotic stability of the converter operated with the proposed control method. This specific open-loop scheme is also adapted to a modular multilevel matrix converter, which performs three-to-three phase direct conversion. Finally, this thesis presents the design of a down-scaled MMC prototype for experimental verification, rated at 10 kW with 30 full-bridge submodules. The hardware and the software are designed to be easily reconfigurable, which makes the converter suitable for different research projects focused on MMCs. Experiments on this down-scaled MMC are used to support and validate the key results presented throughout the thesis.
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| 9. |
- Bitsi, Konstantina
(författare)
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On Electrical Machine Topologies for Electric Vehicle Applications
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The deployment of electric vehicles is considered a viable solution towardsreducing the global greenhouse-gas emissions and fossil-fuel consumption. Inorder to produce highly efficient and economically feasible electrical drivesystems, the selection of suitable electric motor designs is a key step.The target of this work is to identify, analyze and compare suitable elec-trical machine topologies for automotive applications based on highly coupledand conflicting criteria. For this purpose, an evolutionary multi-objective op-timization is developed that can yield a set of Pareto-optimal solutions and,thus, offer different compromises among the considered design-objectives. Theefficacy of the algorithm is demonstrated, rendering it an important tool forthe subsequent analysis.In the first part of this thesis, the investigation of pole-phase changinginduction machines is presented. A special induction machine topology withwound, independently-controlled stator coils (WICSC) is introduced. Thestator-winding configuration in this machine permits the individual energiza-tion and current control of the toroidal coil in each stator slot, thus facilitatingthe real-time change of both phase and pole number. The 2D magnetic and3D thermal finite-element method (FEM) models of this machine are devel-oped, as well as an analytical transient model of the current dynamics. Adetailed investigation of the behavior of pole-phase changing induction ma-chines and the impact of their design on the selection of optimum pole-phaseoperations throughout the entire operating region is performed. Specifically,three WICSC machines that were originally designed with 2, 4 and 6 fixedmagnetic poles are evaluated as pole-phase changing machines with the aim ofdetermining the overall improvement in terms of torque per ampere capabilityand efficiency.The second part of this work is focused on the design and performance ofaxial-flux induction machines (AFIMs). An electromagnetic sizing algorithmfor the design of AFIMs is developed, which adopts a geometrical approachto the design problem, while minimizing the use of empirical factors. Theeffectiveness of this algorithm is experimentally validated, using a commercialdouble-stator AFIM utilized as an integrated starter generator in a hybridelectric vehicle application. Moreover, in order to assess the benefits of pole-changing in axial-flux structures, the optimization of an interior-permanentmagnet synchronous machine, a radial-flux WICSC machine and a double-rotor axial-flux WICSC machine is carried out for a heavy vehicle applicationand the comparison of their Pareto-optimal solutions is presented.
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| 19. |
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| 20. |
- Sadarangani, Chandur, 1946-, et al.
(författare)
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Arrangement Related to Seatbelts
- 2001
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Patent (populärvet., debatt m.m.)abstract
- The invention includes an arrangement related to seatbelts (1) adapted to a vehicle, having at all events two securing points (2a, 2b), intended for the belt, which points are related to a chassis (3a) belonging to the vehicle, at all events one of the securing points (2b) belonging to the belt consisting of a reel (40), drivable by an electric motor (4), in order to be able to reel belt sections or parts near the securing points (2d) thereon with an intention of being able to hold belt stretchings (2e, 2f) stretched against a person's chest and/or trunk portion or vice versa. One or more sensors are adapted to, at a value occurring above a selected limit value, let said electric motor (4) be activated to drive the reel (40) in a direction in order to increase the stretching force in said belt, and said electric motor consists of a polyphase motor. Said polyphase motor (4) is designed to present a low electric inductance and/or a high torque density, in order to thereby be able to provide a relatively high starting torque, high torque and endure high overload during intermittent operation conditions.
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| 21. |
- Sadarangani, Chandur, 1946-, et al.
(författare)
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Hybriddrivsystem : [Hybrid drive system)
- 1995
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Patent (populärvet., debatt m.m.)abstract
- A hybrid drive system includes an internal combustion engine with an output shaft. An energy converter is connected to the output shaft via a coupling. The energy converter has first and second rotors which are rotatable at different speeds in relation to each other. At least one of the rotors is provided with one or more windings which are supplied with current from a current converter. The current converter is supplied with direct current from a direct current source. A transmission with variable gear ratio is coupled to one of the rotors. The transmission and the current converter cooperate via a control arrangement. The control arrangement comprises a control unit for controlling rotational speed and torque of the internal combustion engine and the energy converter.
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| 22. |
- Skoglund, Mattias, et al.
(författare)
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Dual mode locomotives - System studies of new freight locomotives for Sweden
- 2008
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Ingår i: Proceedings of IEEE/ASME Joint Railroad Conference. - 9780791848128 ; , s. 263-268
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Konferensbidrag (refereegranskat)abstract
- A conceptual study for a Swedish dual-mode locomotive is presented. The primary energy sources are AC electricity from an overhead catenary system or a diesel-electric generator system. The study focuses on analysing how freight operations and locomotive utilisation can be improved and how it can affect environmental aspects of freight operations. Based on project experiences and operative demands, a system proposal has been presented. The rated power output is considerably higher in electric mode compared to diesel mode. The reason for this being higher power demand on electrified main lines compared to branch lines and yards lacking overhead catenary where the power need is lower. The starting tractive effort will however be the same regardless of electric mode or diesel mode, making it possible to haul the same train weight in both propulsion modes. The study has shown that dual-mode locomotives for Swedish freight operations are most interesting in order to improve operations, degree of utilisation and environmental performance.
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| 23. |
- Skoglund, Mattias, et al.
(författare)
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The Swedish T43H Hybrid Locomotive
- 2009
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Ingår i: 16th ITS World Congress.
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Konferensbidrag (refereegranskat)abstract
- Experiences from the Swedish hybrid locomotive (T43H) are presented. The locomotive has a series hybrid propulsion system with a comparatively small diesel engine and a large battery pack. Original layout was a traditional diesel-electric power train. Indications from switch operations show fuel savings of 37 to 50 % with the hybrid locomotive. The Swedish experiences are thus in parity with North American experiences showing savings between 30 and 80 %. The evaluation showed that hybrid locomotives in switch duty have significant advantages compared to conventional diesel locomotives in terms of reducing fuel consumption and improving environmental performance.
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| 24. |
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| 25. |
- Zhang, Hongyang, et al.
(författare)
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Loop-at-a-Time Stability Analysis for Grid-Connected Voltage-Source Converters
- 2021
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Ingår i: IEEE Journal of Emerging and Selected Topics in Power Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 2168-6777 .- 2168-6785. ; 9:5, s. 5807-5821
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Tidskriftsartikel (refereegranskat)abstract
- The instability phenomena caused by converter–grid interactions can be prevented by designing controllers with adequate stability margins. Yet, the multiple-input–multiple-output (MIMO) dynamics of grid-connected voltage-source converters (VSCs) complicate the stability analysis for the controller design. To tackle this challenge, this article presents a loop-at-a-time stability analysis for grid-connected VSCs, which not only shows close correlations with the generalized Nyquist criterion for MIMO systems but also enables to quantify the stability margins of individual closed loops. Moreover, the interactions between the closed loops can be analyzed. Test cases with numerical sensitivity analysis, simulations, and field measurements of a converter validate the theory.
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| 26. |
- Zhang, Hongyang
(författare)
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On Modeling and Stability Analysis of Grid-Connected Voltage Source Converters
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With increasing deployment of voltage source converters (VSCs) in the grid, instability phenomena due to converter--grid interactions have been observed. Modeling and stability analysis of grid-connected VSCs have become popular research topics. Moreover, the power system is losing its inertia with increased penetration of renewable energy resources. Large and fast frequency deviations tend to vary more frequently compared to the conventional grid. The control and modeling of VSCs in the low-inertia grid is thus a crucial topic. The main objective of this thesis is the small-signal modeling and stability analysis of grid-connected VSCs. As a result of the asymmetrical synchronous reference ($ dq $) frame dynamics, the structure of the dynamical system is multi-input multi-output (MIMO). Conventionally, the small-signal stability analysis for such a system is conducted either by the modal-analysis approach or the impedance based method, which is based on MIMO. In this thesis, methods for modeling and analyzing a MIMO system using a single-input single-output (SISO) approach are developed. Compared to conventional methods, the SISO methods overcome the difficulties of defining the stability margins for individual closed loops. Moreover, the methods provide intuitive solutions to the design of controllers for individual closed loops. The thesis also investigates the control and modeling of grid-connected VSCs connected to low-inertia grids. It is illustrated that, for improvement of network frequency dynamics, a VSC with proper energy storage is capable to emulate inertial response from a synchronous machine. Moreover, other frequency control strategies are shown to be beneficial, compared to the inertial emulation. In addition, the inaccuracies for the $ dq $-frame small-signal model, in the presence of phase jumps and frequency deviations, are investigated. It is concluded that the inaccuracy of the small-signal model always exists under phase jumps. In the presence of frequency deviation, the stability analysis shall be evaluated at the steady-state operating point of the frequency.
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| 27. |
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| 28. |
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| 29. |
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| 30. |
- Östlund, Stefan, 1961-, et al.
(författare)
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An Integrated Adaptive Maintenance Concept
- 2010
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Ingår i: International Conference on Condition Monitoring and Diagnosis 2010. - Tokyo, Japan.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this paper, we present a novel maintenance concept based on condition monitoring and dynamic maintenance packaging, by showing how to connect the information flow from low-level sensors to high-level operations and planning under uncertainty. Today, condition-based maintenance systems are focused on data collection and custom-made rule based systems for data analysis. In many cases, the focus is on measuring "everything" without considering how to use the measurements. In addition, the measurements are often noisy and the future is unpredictable which adds a lot of uncertainty. As a consequence, maintenance is often planned in advance and not replanned when new condition data is available. This often reduces the benefits of condition monitoring. The concept is based on the combination of robust, dynamically adapted maintenance optimization and statistical data analysis where the uncertainty is considered. This approach ties together low-level data acquisition and high-level planning and optimization. The concept has been illustrated in a context of rail vehicle maintenance, where measurements of brake pad and pantograph contact strip wear is used to predict the near future condition, and plan the maintenance activities.
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| 31. |
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| 32. |
- Östlund, Stefan, 1961-, et al.
(författare)
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Condition Monitoring of Pantograph Contact Strip
- 2008
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Ingår i: IET Seminar Digest. - : IEE. - 9780863419270
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Konferensbidrag (refereegranskat)abstract
- A common issue in electric railway operation is the wearofthepantographcontact strip. This is especially pronounced with ice or rime frost on the overhead line that causes arcing between the contact strip and the contact wire. To monitor the contact strip it is possible to utilise the fact that arcing between the contact strip and the overhead line generates a DC component in the AC locomotive current. The paper presents a method forconditionbased maintenanceofthe contact strip. The wearofthe contact strip is predicted bymonitoringthe running distanceofthepantographas well as the DC componentofthe locomotive current. To evaluate the method, measurements have been carried out on a Swedish Re locomotive during winterconditions.
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| 33. |
- Östlund, Stefan, 1961-, et al.
(författare)
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Designing, implementing and maintaining a first year project course in Electrical engineering
- 2008
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Ingår i: European Journal of Engineering Education. - : Taylor & Francis. - 0304-3797 .- 1469-5898. ; 33:2, s. 231-242
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Tidskriftsartikel (refereegranskat)abstract
- Being a modern electrical engineer does not only require state of the art skills in areas such as transfer and processing of information, electronics, systems engineering, and biomedical electrical engineering; it also requires generic engineering skills such as oral and written communication, team building, interpersonal skills, and the ability to take the responsibility of solving assigned tasks. In the development of a new electrical engineering curriculum, it was considered a challenge to introduce these generic engineering skills in a more applicable way. The approach described in this paper has been very successful in implementing and maintaining a challenging first year project based engineering course with a high level of training of generic engineering skills.
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| 44. |
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| 45. |
- Östlund, Stefan, 1961-, et al.
(författare)
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Responsible internationalisation : Guidelines for reflection on international academic collaboration
- 2020
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Rapport (populärvet., debatt m.m.)abstract
- Premise– Internationalisation has a number of positive effects on research and higher education.– Today, researchers at higher education institutions (HEIs) in Sweden collaborate to a greater extent with a larger number of countries than earlier.– Collaborations with researchers from countries whose scientific and political systems, culture and laws differ significantly from ours entail other and sometimes greater challenges.– There is an increased need for informed assessments of the contents and consequences of international collaborations before, during and after a project.– This document has been drawn up in collaboration between STINT, Karolinska Institutet, KTH Royal Institute of Technology and Lund University. The background to this work is the growing debate on values and ethical considerations in international collaborations in connection to HEIs in several countries.– The document is intended to serve as support for reflection and as the basis for discussion of strategic decisions on internationalisation. The purpose is to aid researchers, research directors, department heads, and university administration in assessing collaborations and structuring discussions on how the HEI, department or research group should approach international collaboration.
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| 46. |
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| 47. |
- Östlund, Stefan, 1961-
(författare)
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Vehicle performance and Technology
- 1997
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Ingår i: Efficient Train Systems for Future Passenger Services. - : KTH Royal Institute of Technology. ; , s. 79-99
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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