| 1. |
- Anttila, Sara, et al.
(författare)
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Grid Forming inverters : A review of the state of the art of key elements for microgrid operation
- 2022
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 15:15
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Forskningsöversikt (refereegranskat)abstract
- In the past decade, inverter-integrated energy sources have experienced rapid growth, which leads to operating challenges associated with reduced system inertia and intermittent power generation, which can cause instability and performance issues of the power system. Improved control schemes for inverters are necessary to ensure the stability and resilience of the power system. Grid-forming inverters dampen frequency fluctuations in the power system, while grid-following inverters can aggravate frequency problems with increased penetration. This paper aims at reviewing the role of grid-forming inverters in the power system, including their topology, control strategies, challenges, sizing, and location. In order to facilitate continued research in this field, a comprehensive literature review and classification of the studies are conducted, followed by research gaps and suggestions for future studies.
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| 2. |
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| 3. |
- Anttila, Sara
(författare)
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Power control strategies for renewable energy systems : The inverter's role in future power systems
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Connecting more non-dispatchable renewable energy sources (RESs) will result in a higher power variability and a lower system inertia when the synchronous generators are replaced by inverter-connected RES. Inverter control can be divided in three categories: grid-following, grid-forming (GFM) and grid-supporting. A literature review of inverter control strategies identifies the GFM control as having an important role in maintaining system stability assuming near 100 % inverter-connected RES. Critical aspects of the inverter control are also identified; the control need to function autonomously, be able to remain connected during transient events and be insensitive to grid topology.Combining various RES is also shown to improve system stability. The combination of RES that has been investigated in most studies is wind, solar and wave power. Wave power is still a young technology compared to solar and wind power. It generates higher power fluctuations over short time periods with a significant difference between average and maximum power. Additionally, wave power parks (WPPs) are often connected via long cables which contribute reactive power to the grid. These challenges has to be considered to maintain system stability and power quality when connecting a WPP to the grid.In a Power Hardware-In-the-Loop study of how a WPP affects the power quality at the point of common coupling (PCC), it is found that the impact is highest for WPPs with fewer generators as the variability is reduced when several generators are excited at different times. Energy storage is also shown to have a significant impact on the power quality at the PCC with reduced flicker, total harmonic distortion and power and voltage variability. A simulation study also shows the positive impact of energy storage on power variability and the role of inverter control in reactive power compensation.
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| 4. |
- Axell, Cecilia, et al.
(författare)
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Facts for youngsters : Contextualised technology or fragmented artefacts? A study on portrayals of technology in picture books from a gender perspective
- 2015
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Ingår i: PATT 29 Plurality and Complementarity of Approaches in Design and Technology Education, Marseille, France, April 2015. - Marseille : Presses Universitaires de Provence. - 9782853999946 ; , s. 42-48
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Technology is a field with strong connections to the female/male dichotomy and children's gender stereotyping starts as early as the age of two (Berner, 2004; Nisbet, Pendergast & Reynolds, 1998; Turja, Endepohls-Ulpe & Chatoney, 2009). According to the Swedish Curriculum for the Preschool, the preschool should strive to ensure that children ”develop their ability to identify technology in everyday life, and explore how simple technology works” (Lpfö98/2010, p. 10). The preschool also has a goal to actively counteract traditional gender roles and patterns (Lpfö98/2010, p. 4). An important part of children's activities in preschool relates to picture books. A government investigation states that the preschool, through its activities (among them ”reading aloud”) is an arena where societal norms can either be preserved or challenged (SOU 2006:75). Books about cars, airplanes, boats etc. often serve as an introduction to human applications of technology. Based on these, children start to identify and categorize the technologies they encounter in everyday life.The aim of this study is consequently to investigate the technological content from a gender perspective in a selection of picture books, more specifically; how do the books content preserve or challenge preschool children's view of technology and gender? Preschools use books from libraries in their daily activities, therefore the empirical material in this study is derived from the library section ”facts for youngsters”. A thematic analysis was employed to discover the dominant themes within the books. The result of the study shows that there is a focus on how separate artefacts function but no detailed explanation on how these artefacts are connected or what kind of implications they have in a societal context. There also seems to be an emphasis on traditionally masculine coded technology. This study will serve as a basis for a comparative study between two preschools, one where gender and technology is a prioritised goal and one where it is not.
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| 5. |
- Axell, Cecilia, 1965-, et al.
(författare)
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Preschoolers’ Conceptions of Technological Artefacts and Gender in Picture Books
- 2016
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Ingår i: PATT-32 Proceedings Technology Education for 21st Century Skills. - : ITEEA. ; , s. 57-64
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Konferensbidrag (refereegranskat)abstract
- Picture books are a frequent element of daily preschool activities (Damber, Nilsson & Ohlsson, 2013; Simonsson, 2004; SOU 2006:75). They are important pedagogical tools that can help children acquire an understanding of the everyday technology they come in contact with, as well as the human application of technology (Axell, 2015; Axell & Boström, 2015). These are skills that are emphasised in the Swedish preschool curriculum. In the curriculum it is also stated that the preschool should counteract traditional gender patterns and gender roles (Skolverket, 2010). However, an investigation of a selection of picture books aimed at preschool children shows that the books content is somewhat problematic. Many of the picture books provide a focus on the function of separate artefacts without any sort of context or explanation of their implications in a societal context. There also tends to be an emphasis on traditional masculine-coded technology in the books. Building and making and working with machines is depicted as a male activity. The male stereotype is essentially connected with different kinds of vehicles like cars, airplanes, motorbikes, tractors etc. (Axell & Boström, 2015; See also Holbrok, 2008). Based on these previous findings, the aim of this pilot study was to obtain an initial concept about how children’s literature may influence preschool children’s view on technological artefacts. The study was conducted through semi-structured interviews with four five-year-olds, two girls and two boys. Through a thematic analysis (Braun & Clarke, 2006) three overarching themes were identified: The relationship between design and function, anthropomorphic animals as users of artefacts, and gender and artefacts. Some of the key findings were that the 5-year-olds did not know what “technology” is, but had good knowledge about tools. Additionally, they did not genderise any of the artefacts included in the study.
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| 6. |
- Axell, Cecilia, 1965-, et al.
(författare)
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Technology in children's picture books as an agent for reinforcing or challenging traditional gender stereotypes
- 2021
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Ingår i: International journal of technology and design education. - Switzerland : Springer. - 0957-7572 .- 1573-1804. ; 31, s. 27-39
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Tidskriftsartikel (refereegranskat)abstract
- Technology is a field with strong connections to the female/male dichotomy. Children start to stereotype everyday life regarding this dichotomy as early as the age of two. The preschool, through its activities—among them reading aloud from picture books—is an arena where societal norms can be either preserved or challenged. Books about different artefacts, e.g. cars, airplanes and boats, often serve as an introduction for children about the human application of technology and may influence how they identify and categorise the technology they encounter in everyday life. The aim of this study was to investigate the technological content in a selection of picture books from a gender perspective. Since preschools in Sweden often use books from libraries in their daily activities, the empirical material was derived from the library sections Facts for youngsters and Technology for youngsters, aimed at children aged 1–3 and 3–6. A thematic analysis was used to discover the dominant themes within the books. The results show that there is a focus on how separate artefacts function but no detailed explanation of how these artefacts are connected or what kind of implications they have in a societal context. There also seems to be an emphasis on traditionally masculine coded technology.
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| 7. |
- Axell, Cecilia, 1965-, et al.
(författare)
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Unveiling Biases: An Exploration of ChatGPT-3.5-generated ‘Technology Stories’
- 2023
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Ingår i: The 40th International Pupils’ Attitudes Towards Technology Conference Proceedings 2023. - : Liverpool John Moores University. ; , s. 1-10
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Konferensbidrag (refereegranskat)abstract
- A technology that is increasingly affecting our daily lives is artificial intelligence (AI). An example of such a technology is ChatGPT-3.5, which has received a lot of attention recently. ChatGPT-3.5 is a text generator that is developed on a large number of existing texts. Currently, there is a debate about negative consequences in education, for example, if students let the chatbot write texts for them. In this study, however, our point of departure is on how ChatGPT-3.5 and storytelling can be used as a tool in teacher education to develop students’ critical thinking in relation to technology.A main objective of technology as a school subject is to prepare pupils to act in a technology-intensive world, which includes critical thinking about technology and its impact on individuals, society, and nature. However, a critical aspect of technology education is that it easily becomes an unreflective doing without a meaningful context. A way to circumventing this problem is to use storytelling in technology teaching.This is a pre-study for a coming project aiming to let teacher students create stories using ChatGPT-3.5 and then critically analyse the technological content in the stories. In this pre-study, we gave ChatGPT-3.5 the instruction to generate ten shorter stories for children with a focus on technology. A qualitative content analysis shows that there are several dominant themes within the stories, and that the chatbot presents a view of technology that is mainly positive and without any critical reflection on its effects on individuals, nature and society. Furthermore, in the stories, high-tech male coded technology is a dominating theme. The pre-study highlights the importance of critical thinking and reflections when using AI tools in technology teacher education. It also indicates that stories generated by a chatbot can be a steppingstone to visualise technology bias and contribute to developing teacher students’ critical gaze.
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| 8. |
- Baudoin, Antoine, et al.
(författare)
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Assessment of Thermal Cycling in a Rectifier For WavePower Generation
- 2016
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Konferensbidrag (refereegranskat)abstract
- Natural convection allows for passive cooling which isused in many engineering applications. Placing dissipatingcomponents on a common vertical heatsink can be opti-mized to give the best possible cooling capacity. In thisstudy, a numerical model for three-dimensional conjugatedconvective and conductive heat transfer was used to evalu-ate the distribution of up to 36 ush-mounted rectangularheaters. The temperature proles and the heat uxes werecompared with experimental data for validation. The dis-sipated power was set as an input parameter and the op-timal distribution was selected as the one with the lowesttemperature elevation. Two dierent heuristicsa geo-metric parameter and an articial neural networkwereproposed and evaluated as alternatives to heavy CFD cal-culations.
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| 9. |
- Baudoin, Antoine
(författare)
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Cooling Strategies for Wave Power Conversion Systems
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Division for Electricity of Uppsala University is developing a wave power concept. The energy of the ocean waves is harvested with wave energy converters, consisting of one buoy and one linear generator. The units are connected in a submerged substation. The mechanical design is kept as simple as possible to ensure reliability.The submerged substation includes power electronics and different types of electrical power components. Due to the high cost of maintenance operations at sea, the reliability of electrical systems for offshore renewable energy is a major issue in the pursuit of making the electricity production economically viable. Therefore, proper thermal management is essential to avoid the components being damaged by excessive temperature increases.The chosen cooling strategy is fully passive, and includes no fans. It has been applied in the second substation prototype with curved heatsinks mounted on the inner wall of the pressurized vessel. This strategy has been evaluated with a thermal model for the completed substation. First of all, 3D-CFD models were implemented for selected components of the electrical conversion system. The results from these submodels were used to build a lumped parameter model at the system level.The comprehensive thermal study of the substation indicates that the rated power in the present configuration is around 170 kW. The critical components were identified. The transformers and the inverters are the limiting components for high DC-voltage and low DC-voltage respectively. The DC-voltage—an important parameter in the control strategy for the WEC—was shown to have the most significant effect on the temperature limitation.As power diodes are the first step of conversion, they are subject to large power fluctuations. Therefore, we studied thermal cycling for these components. The results indicated that the junction undergoes repeated temperature cycles, where the amplitude increased with the square root of the absorbed power.Finally, an array of generic heat sources was optimized. We designed an experimental setup to investigate conjugate natural convection on a vertical plate with flush-mounted heat sources. The influence of the heaters distribution was evaluated for different dissipated powers. Measurements were used for validation of a CFD model. We proposed optimal distributions for up to 36 heat sources. The cooling capacity was maximized while the used area was minimized.
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| 10. |
- Baudoin, Antoine, et al.
(författare)
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Experimental Optimization of Passive Cooling of a Heat Source Array Flush-Mounted on a Vertical Plate
- 2016
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 9:11
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Tidskriftsartikel (refereegranskat)abstract
- Heat sources, such as power electronics for offshore power, could be cooled passively—mainly by conduction and natural convection. The obvious advantage of this strategy is its high reliability. However, it must be implemented in an efficient manner (i.e., the area needs to be kept low to limit the construction costs). In this study, the placement of multiple heat sources mounted on a vertical plate was studied experimentally for optimization purposes. We chose a regular distribution, as this is likely to be the preferred choice in the construction process. We found that optimal spacing can be determined for a targeted source density by tuning the vertical and horizontal spacing between the heat sources. The optimal aspect ratio was estimated to be around two.
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