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The electrification of remote islands has long been a subject of research interest, primarily because of their historical reliance on fossil fuels, leading to a significant carbon footprint. Recent advancements in wave energy converters offer a promising avenue to make these islands more self-sustainable while considerably reducing carbon emissions. However, the persistent issue of voltage dips due to weaker grids continues to pose a challenge. This study introduces a multi-mode converter control strategy with the goal of electrifying remote islands, employing a linear generator-based wave energy converter in a unified electrical model. Various scenarios, including voltage dips and mainland grid disconnection, are simulated using MATLAB/Simulink. The study demonstrates the converter's ability to transition swiftly and smoothly in response to these scenarios, ensuring an uninterrupted power supply. Furthermore, the analysis indicates that the power quality at the point of common coupling remains well within acceptable standards.

The power delivered by a voltage source inverter needs to be filtered to fulfill grid code requirements. A commonly used filter technology is the LCL-filter. An issue with the LCL-filter is the occurrence of a resonance peak, which can be mitigated with active or passive damping methods. The transfer function of the filter is often used to investigate the frequency response of the system and propose damping methods. The use of an LC-filter combined with a power transformer to form an LCL-filter has not been extensively investigated. Therefore, the study in this article introduces a model for an LC-filter and power transformer for the grid connection and a derived transfer function for the model. The transfer function for the system is validated with simulations and experimental investigations. The results from simulations and the results from a direct solution of the derived analytical function overlap almost perfectly. The magnitudes of the experimental results are approximately 1 dB lower than the simulation and analytical results before the resonance frequency. At the resonance frequency, the experimental results are approximately 13.4 dB lower. The resonance frequency, however, occurs at approximately the same frequency. It is also concluded that the system is significantly damped.

Både i historien och nutid går det att ta del av skandaler där revisionskvaliteten har varit alldeles för låg, vilket har medfört stora konsekvenser för både samhället och enskilda individer. Att revisionskvaliteten tenderar att fortsätta brista indikerar att det finns ett behov för många intressenter att ta reda på vilka faktorer som kan påverka revisionskvaliteten negativt när revisorerna har som mest att göra. I tidigare forskning har forskarna främst fokuserat på Big-4 eller mindre revisionsföretag, medan denna studie kommer att inkludera dessa grupper tillsammans för att även kunna utläsa skillnader respektive likheter för hur de arbetar för att motverka risker mot revisionskvaliteten. Utifrån vår kvalitativa studie har syftet varit att fånga djupare förståelse samt beskrivningar från kvalificerade revisorer respektive revisorsassistenter från revisionsföretag i Västerbotten. Detta för att ta reda på vilka faktorer som kan påverka revisionskvaliteten negativt under branschens högsäsong. Som författare av denna studie har även målet varit att revisionsföretagen kan lära sig av varandras styrkor och svagheter för att motverka risken att revisionskvaliteten blir lidande. Enligt tidigare forskning finns det många aspekter som har en påverkan på den presterande revisionskvaliteten och att dessa i större grad förekommer med högre arbetsbelastning. Studien visar även på att revisionsprocessen, stress, tid och kompetens är de faktorer som kan ha en negativ påverkan på revisionskvaliteten i Västerbotten. Vidare visar studien även på att det finns en koppling mellan dessa faktorer då de både påverkar och påverkas av varandra. Vår studie har också kunnat utläsa skillnader respektive likheter gällande hur Big-4 och mindre revisionsföretag arbetar för att minska risken för att dessa faktorer ska påverka revisionskvaliteten. Det har bland annat kommit fram att en av de mindre revisionsföretagen anlitat en

Wave energy has been an immense area of interest in research and industry in our move towards a sustainable energy production society due to its high energy density and surface area. However, the grid connection of wave energy converters is still one of the major challenges due to the complexity of varying wave resources (amplitude and frequency). Wave energy converter grid integration can lead to several potential challenges, such as voltage fluctuations, harmonics and flicker. Using an energy storage system can help mitigate a few challenges by balancing the grid demand with the wave energy converter power supply. Hence improving the power quality. This study assesses the power quality of wave energy converters equipped with energy storage against the scenario without any energy storage at different power levels. The power quality in this paper is investigated using total harmonic distortion (THD)of the grid current, dc-link voltage ripple and battery current ripple. The study shows that the addition of a hybrid energy storage system lowers the grid current THDat the point of common coupling (PCC), stabilizes the dc-link voltage ripple and reduces the stress of the battery.

Important questions to enable the use of marine current energy are how the electrical system is designed, how multiple energy converters are interconnected offshore and how the power is transmitted to the shore. The Division of Electricity at Uppsala University have constructed and deployed a marine current energy converter in the river Daläven in Söderfors, Sweden. In the study presented in this article, a model of a near-shore low-voltage AC collection grid and a near-shore low-voltage DC collection grid is presented for the technology at the Söderfors test site. The models are implemented in MATLAB/Simulink. For collection grids of five turbines, it is shown that the proposed control schemes are able to deliver power to the distribution grid. The controllers are able to achieve this even when one turbine is suddenly disconnected from the grid. Furthermore, it is shown that the conduction losses of the DC system are higher than the losses of the AC system for nominal and high water speeds. However, in a qualitative comparison between the systems it is concluded that despite the higher losses, the DC system can be an interesting option. This is because fewer components need to be placed in the turbine, which is beneficial in offshore systems where space is a limiting factor. Furthermore, a DC system can be less expensive since fewer cables are needed.

Anthropogenic activities and their influences on aquatic systems is an important topic, especially considering the growing interest in using the earth's resources in a sustainable way. One of those anthropogenic activities is the introduction of renewable technologies into the aquatic environment such as instream turbines. Environmental studies around those technologies are often still ongoing due to their novelty. During the spring of 2018, juvenile individuals of two salmonid species, Atlantic salmon and brown trout were released upstream a vertical axis instream turbine in the river Dal (Dalälven) in eastern Sweden. The aim of this study was to investigate the swimming behavior of the salmonids around a small-scale prototype vertical axis instream turbine. The swimming pattern and the possible response of avoiding the vertical axis instream turbine were documented with a multi beam sonar. A control area, next to the turbine, was used as reference. No consistent results were shown for trout as they were passing the control area with a statistically high variation, and specimens were rarely observed in proximity of the turbine, neither if the turbine was operating nor at stand still. Salmon clearly avoided the operating turbine, but did not avoid the turbine when it was at stand still, and was often observed swimming straight through the turbine area. These findings indicate that operating this type of instream turbine in a river affects the swimming behavior of Atlantic salmon but is unlikely to affect its migration paths. For brown trout, the statistical results are inconclusive, although data indicate a response of avoiding the turbine. The species are in little risk to suffer physical harm as no fish entered the rotating turbine, despite very turbid water conditions.

Marine energy resources could be crucial in meeting the increased demand for clean electricity. To enable the use of marine energy resources, developing efficient and durable offshore electrical systems is vital. Currently, there are no large-scale commercial projects with marine energy resources, and the question of how to design such electrical systems is still not settled. A natural starting point in investigating this is to draw on experiences and research from offshore wind power. This article reviews different collection grid topologies and key components for AC and DC grid structures. The review covers aspects such as the type of components, operation and estimated costs of commercially available components. A DC collection grid can be especially suitable for offshore marine energy resources, since the transmission losses are expected to be lower, and the electrical components could possibly be made smaller. Therefore, five DC collection grid topologies are proposed and qualitatively evaluated for marine energy resources using submerged and non-submerged marine energy converters. The properties, advantages and disadvantages of the proposed topologies are discussed, and it is concluded that a suitable electrical system for a marine energy farm will most surely be based on a site-specific techno-economic analysis.

This paper presents a simulation model of the grid connection system for a marine current energy converter deployed in the river Dal (Dalälven) at Söderfors, Sweden. The implementation of the model is done in Matlab/Simulink. The experimental station consists of a five-bladed turbine connected to a permanent magnet synchronous generator (PMSG) and a bidirectional back-to-back (B2B) converter for the grid connection. The generator side of the electrical system consists of a 2-level voltage source converter (2L-VSC). The generator side converter is controlled using field-oriented control (FOC) with zero d-axis current. The grid side converter is a 3-level cascaded H-bridge voltage source converter (3L-CHBVSC) and is controlled using voltage oriented control (VOC) with phase-locked loop (PLL). Simulations are run for constant water speeds as well as for stepwise increases of the speed and for real water speeds from the test site. The controllers are confirmed to be able to correctly control the system for the simulated cases. The power losses are evaluated using steady state simulations and the relative power losses are shown to be the smallest for a water speed of around 1.30 m/s. The largest contribution to the total losses is shown to be from the generator.

Syftet med denna studie var att utforma ett koncept som visualiserar grafiska riktlinjer för secondhand-butiker i avsikt att tilltala en bredare målgrupp. Studien baserades på en metod innehållande både kvalitativ och kvantitativ datainsamling. Det teoretiska ramverket innefattade teorier relaterade till varumärkesbyggande, designprinciper vid formgivning samt de grundläggande komponenterna inom grafisk identitet för att säkerställa att välgrundade designbeslut tagits. Det grafiska konceptet skapades genom ett iterativt designarbete baserat på resultat från förstudie, fokusgrupper, digitala enkätundersökningar och tematiska analyser. I den avslutande undersökningen av den slutgiltiga designen samlades kvantitativa data in för att ta reda på om arbetets syfte uppnåtts eller ej. Resultatet visade att det är viktigt att orden second hand inkluderas i logotypen. Tydlighet och enkelhet bör ligga i fokus vid framtagandet av grafiska formspråk för secondhand-butiker för att tilltala en bredare målgrupp. Många respondenter efterfrågade att kopplingen till hållbarhet framhävs. Den mest efterfrågade färgen var grön. Övriga färger ska helst upplevas som miljövänliga, positiva, lugna och inbjudande. Studien resulterade i konceptuella visualiserade riktlinjer. Dessa bestod av en logotyp, fyra färger samt typsnitt. Logotypen är i formen av ett runt emblem, innehållande en symbol som kombinerar ett löv och ett löv och ett hjärta för att symbolisera hållbarhet och välgörenhet., Examensarbetet är utfört vid Institutionen för teknik och naturvetenskap (ITN) vid Tekniska fakulteten, Linköpings universitet

Skanska har identifierat ett problem med att Örebro kommun har hårda restriktioner kring deponier och mängden massor som får lossas där. Då byggtakten under lång tid varit hög i Örebro ser Skanska att många deponier kring Örebro börjar bli fulla. I de fall då närmsta deponi inte har möjlighet att ta emot schaktmassor, orsakar det längre transportsträckor av schaktmassorna till andra deponier. Syftet med denna studie är därför att skapa en beräkningsmodell som jämför olika transportalternativs inverkan på miljön och ekonomin.Beräkningsmodellen i denna rapport har framställts genom litteraturstudier samt intervjuer. En tillämpning av beräkningsmodellen appliceras på två exempel för att illustrera utsläpp och kostnader.Beräkningsmodellen avgränsas till att beräkna utsläpp och kostnader som genereras från transporter av schaktmassor mellan projekt, deponi och täkt.Med hjälp av den framtagna beräkningsmodellen har kostnader och utsläpp illustreras för projektet Marieberg Törsjö 3:14. Två exempel beräknas vilka båda utgår från Marieberg Törsjö 3:14. Antagna föroreningar i marken medför att klassningen av massorna skiljer sig i de två exemplen. Detta medför att regler kring omhändertagning av massorna, arbetssätt och de olika geografiska platserna för deponier och täkter skiljer sig mellan de olika exemplen.I rapporten har en fungerande beräkningsmodell utvecklats, den illustrerar utsläpp och kostnader kopplade till transporten av massorna. Beräkningsmodellen kan användas av företag för att illustrera miljöpåverkan som transporter mellan två olika deponier eller täkter ger upphov till, samt prisskillnaden som de olika alternativen genererar., Skanska has identified a problem that Örebro municipality having severe restrictions on landfills and what masses may be unloaded there. Since the construction rate has been high in Örebro for a long time, Skanska sees that many landfills around Örebro are getting full. In some cases when the nearest landfill is no longer able to receive excavation masses, the company is forced to transport the excavation masses unnecessary distances to other landfills. The purpose of this study is therefore to create a calculation model that compares the impact of different transport alternatives on both the environment and the economy.The calculation model is developed through literature studies and interviews. The calculation tool will be applied to two examples to illustrate emissions and costs.The calculation model is limited to calculating emissions and costs generated from transport of excavation masses between projects, landfills and quarries.Using the theoretical model developed, costs and emissions have been illustrated for the project Marieberg Törsjö 3:14. The two examples based on Marieberg Törsjö 3:14 differ in the classification of the masses. This means that rules regarding the handling of the masses, working methods and the different geographical locations for landfills and quarries differ between the different examples.A conclusion from this study is a working calculation model has been developed that illustrates emissions and costs associated with the transport of the masses. The calculation model can be used by companies to illustrate the environmental impact that transport between two different landfills or quarries generates, as well as the price difference generated by the different alternatives.

Some countries are facing issues on freshwater and electricity production, which can be addressed with the use of renewable energy powered desalination systems. In the following study, a reverse osmosis desalination plant powered by marine current energy converters is suggested. The marine current energy converters are designed at Uppsala University in Sweden, specifically for utilizing low water speeds (1–2 m/s). Estimations on freshwater production for such a system, in South Africa, facing the Indian Ocean was presented and discussed. It is concluded that the desalination plant cannot by itself supply freshwater for a population all the time, due to periods of too low water speeds (<1 m/s), but for 75% of the time. By using ten marine current energy converters, each with a nominal power rating of 7.5 kW, combined with a reverse osmosis desalination plant and water storage capacity of 2800 m3, it is possible to cover the basic freshwater demand of 5000 people. More studies on the hydrokinetic resource of the Western Indian Ocean, system cost, technology development, environmental and social aspects are necessary for more accurate results.

An experimental station for marine current power has been installed in a river. The station comprises a vertical axis turbine with a direct-driven permanent magnet synchronous generator. In measurements of steady-state operation in varying flow conditions, performance comparable to that of turbines designed for significantly higher flow speeds is achieved, demonstrating the viability of electricity generation in low speed (below 1.5 m/s) marine currents., Övriga finansiärer: J. Gust. Richert Memorial Fund och Bixia Environmental Fund., Marin strömkraft

Pedagoger från svenska fritidshem arbetar olika med att leda aktiviteter som syftar till någon form av lärande. Inför denna studie tänkte jag att det nog finns skilda tankar från pedagoger om varför de gör som de gör gällande dessa aktiviteter. I denna studie har syftet varit att lyfta pedagogernas olika tankar och jämföra dem mot varandra och mot tidigare forskning. Källorna bidrar med information om ämnen som fritidshemmets historia och förändringar, informellt lärande och element som kan bidra till välfungerande fritidshem. I studien appliceras ett sociokulturellt perspektiv med fokus på lärande-teorier. Datainsamlingsmetoden bestod av intervjuer med fem pedagoger från tre olika fritidshem. Intervjuerna har transkriberats, kodats, kategoriserats, analyserats och tolkats för att nå resultatet av denna studie. I den avslutande diskussionen påvisas variationerna och likheterna i pedagogernas tankar kring lärarlett lärande på fritidshem. Där tas även potentiella faktorer som kan vara orsak till deras åsikter upp beträffande deras användning av lärarlett lärande. En av slutsatserna som dragits är att pedagoger bör använda sig av både planerade och oplanerade lärandesituationer på fritidshem och se till att locka eleverna till nyfikenhet på lärande.

This paper investigates three load control methods for a marine current energy converter using a vertical axis current turbine (VACT) mounted on a permanent magnet synchronous generator (PMSG). The three cases are; a fixed AC load, a fixed pulse width modulated (PWM) DC load and DC bus voltage control of a DC load. Experimental results show that the DC bus voltage control reduces the variations of rotational speed by a factor of 3.5 at the cost of slightly increased losses in the generator and transmission lines. For all three cases, the tip speed ratio can be kept close to the expected . The power coefficient is estimated to be 0.36 at ; however, for all three cases, the average extracted power was about

The purpose of this study is, based on theories of gender and hegemonic masculinity, to studyhow masculinity and femininity is constructed and reproduced in one of the most popularSwedish podcast: Filip & Fredriks podcast. The main theory in this study is that gender issocially created and sustained by humans through language and interaction with others.The study's research questions is: How are gender roles/gender portrayed in Filip & Fredrik'spodcast? What characteristics are attributed to men and women in Filip & Fredrik's podcast?How does Filip & Fredrik's podcast represents conditions and power relations between menand women?Through an linguistic textual analysis, which is an application of discourse analysis, I seek toget beneath the surface meanings of texts and examine more implicit social meanings andideologies regarding gender. It includes an analysis of metaphors, word choices and syntax.The analysis shows underlying values and ideologies that indicates gender structures in abroader societal context. Choice of words and metaphores in Filip & Fredriks's podcastexpresses symbolism where men and male-typical attributes are highly valued, whilst womanand female-typical attributes is being devalued and representative of the opposite.Masculinities and femininities are also constructed and represented in various ways throughsentence constructions that guides the listeners in certain directions. Men are e.g. more oftenthan women in active roles when Filip and Fredrik describe different processes.Consciously or unconsciously, the presenters language establish and maintain a genderorder, gender roles and gender discourse. Dominant gender ideologies are reinforced in theeveryday conversations in Filip & Fredrik's podcast through linguistic structures and genderideologies inherent in the communication.

As the demand for clean energy continues to grow, there is an increased focus on alternative sources of renewable energy, including marine current power. Similar to wind power, marine current power often requires a maximum power point tracking (MPPT) method to optimize power extraction from the free-flowing water. Despite the growing interest in marine current power, research into MPPT methods for marine current power remains limited. This paper presents a comprehensive investigation of MPPT methods specifically tailored for marine current power, building upon similar research in wind power. Three methods, namely the optimal tip speed ratio (OTSR), optimal torque (OT), and two variants of the perturb and observe (P&O) method, are explored. Using a simulation model developed for a specific marine current energy converter, where hydrodynamic calculations are coupled with electrical simulations, the study demonstrates that the OTSR method achieves MPPT with a comparably fast convergence time. Additionally, the P&O method is shown to achieve MPPT, albeit with a longer convergence time. The proposed implementation of the OT method underperforms but still positions the system close to the optimal operational point.

Marine current energy represents a globally abundant yet largely untapped renewable energy source, offering greater predictability than other sources such as wind. Consequently, it has the potential to play a vital role in the green transition. A critical consideration for harnessing marine current energy is the design of the electrical grid to accommodate multiple turbines. Therefore, this paper presents a study that explores three types of DC collection grids (series, parallel, and star) for a specific marine current energy converter. A simulation model developed for the marine current energy converter is introduced and utilized to assess these topologies for grids comprising ten identical turbines subjected to varying water speeds. The designed topologies are intended for low-voltage and nearshore applications. The simulation results demonstrate that the series collection grid requires a significantly higher DC grid voltage compared to the other topologies for the turbines to operate correctly. Additionally, the study reveals that all three grid topologies can effectively transmit power to the distribution grid with similar power losses.