• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 10
  • 8
  • 1
  • 1
  • Tagged with
  • 20
  • 7
  • 7
  • 6
  • 6
  • 6
  • 4
  • 4
  • 4
  • 4
  • 4
  • 4
  • 3
  • 3
  • 3
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Vilken rekryteringsmetod är effektivast? : En teoretisk studie av personalförsörjningen till militären

Hedkvist, Anders January 2005 (has links)
<p>Uppsatsen presenterar de ekonomiska problem som är förenliga med olika rekryteringssystem</p><p>till militärtjänstgöring. Dagens situation i Europa är att länder lämnar det gamla</p><p>värnpliktsystemet för att övergå till frivilliga rekryteringssystem. Det svenska förslaget</p><p>innebär ett ökat inslag av frivillighet och försvarsmakten får en mer kostnadseffektiv</p><p>personalrekrytering. För individen kommer nuvärdet på framtida inkomster stiga eftersom det</p><p>blir mer tid till sysselsättning på den civila arbetsmarknaden, när den obligatoriska tiden</p><p>kortas ner. Den negativa effekten av det nya förslaget är att försvarsmakten håller kvar</p><p>inslaget av värnplikt och individen erhåller en lön som inte stämmer överens med</p><p>reservationslönen.</p>
2

Vilken rekryteringsmetod är effektivast? : En teoretisk studie av personalförsörjningen till militären

Hedkvist, Anders January 2005 (has links)
Uppsatsen presenterar de ekonomiska problem som är förenliga med olika rekryteringssystem till militärtjänstgöring. Dagens situation i Europa är att länder lämnar det gamla värnpliktsystemet för att övergå till frivilliga rekryteringssystem. Det svenska förslaget innebär ett ökat inslag av frivillighet och försvarsmakten får en mer kostnadseffektiv personalrekrytering. För individen kommer nuvärdet på framtida inkomster stiga eftersom det blir mer tid till sysselsättning på den civila arbetsmarknaden, när den obligatoriska tiden kortas ner. Den negativa effekten av det nya förslaget är att försvarsmakten håller kvar inslaget av värnplikt och individen erhåller en lön som inte stämmer överens med reservationslönen.
3

Hybrid Dynamical Systems: Modeling, Stability and Interconnection / Hybride Dynamische Systeme: Modellierung, Stabilität und Zusammenschaltung

Promkam, Ratthaprom January 2019 (has links) (PDF)
This work deals with a class of nonlinear dynamical systems exhibiting both continuous and discrete dynamics, which is called as hybrid dynamical system. We provide a broader framework of generalized hybrid dynamical systems allowing us to handle issues on modeling, stability and interconnections. Various sufficient stability conditions are proposed by extensions of direct Lyapunov method. We also explicitly show Lyapunov formulations of the nonlinear small-gain theorems for interconnected input-to-state stable hybrid dynamical systems. Applications on modeling and stability of hybrid dynamical systems are given by effective strategies of vaccination programs to control a spread of disease in epidemic systems. / Entwicklung eines Frameworks für hybride dynamische Systeme zur Decomkosition oder Komposition solcher Systeme. Untersuchung der Stabilität von gekoppelten hybriden Systemen.
4

Utvärdering av energianvändningen i ett produktionskök på Svartsö i Stockholms skärgård : Undersökning av förutsättningarna för ett PV-vind hybridsystem och energibesparande lösningar

Khoshlahge-Yazdi Jöhnemark, Behroz, Spinelli Scala, Robin January 2015 (has links)
The EU Directive 20-20-20 places high demands on new buildings and activities designed with a focus on sustainability with low climate impact. The use of renewable energy technologies are becoming increasingly important to lower carbon emissions and ensuring a sustainable and environmentally friendly energy supply. This becomes especially important in energy-intensive activities like office buildings or commercial kitchens which are characterized by high internal heat generation from appliances, machinery and people. By providing the business with electricity from renewable energy sources and recovering excess heat both money and the environment can be saved. The starting point of this study was to investigate a planned commercial kitchen on Svartsö in the Stockholm archipelago that is supposed to produce organic fresh baby food. The company behind the business wishes to profile their activities climate and environmentally friendly. The purpose of the study was to investigate the electricity production potential for a PV-wind hybrid systems on Svartsö and examine how much of this electricity can be integrated directly in the business. The building's energy need was calculated by a constructed model in the energy calculation program VIP-Energy. To estimate the production potential of the renewable micro-generation simulations of a PV-wind hybrid system with location-specific weather data from SMHI was designed and performed in Matlab. The study provides analysis and reflections of the results. The conclusion is that the electricity usage profile of the business correlates well with the production profile of solar power while wind power is expensive in relation to solar power.
5

Integrering av Savonius-vindturbiner och solpaneler / Integration of Savonius wind turbines and solar panels

Kihlberg, Kristofer January 2018 (has links)
This thesis considers the integration between Savonius wind turbines and photovoltaics to form a hybrid power system. Different integration techniques were studied to find the most suited technique and the necessary components. The hybrid system was then to be compared with a solar panel system of equal sizing to investigate whether it could compete in terms of production and profitability. A model of the hybrid systems was built in MATLAB Simulink to simulate the production of the systems. Simulations used SMHI measurement data over wind speeds, solar radiation and temperature, with data resolution of one hour for 2017. The Swedish electricity trading market was also studied to determine which guidelines and prices that apply when selling electricity to the grid. The investment costs for the systems were estimated to allow economic conclusions to be drawn. The result was that a hybrid system had a higher power delivery to the load but the total production was higher for the solar system. The hybrid system couldn’t compete with the profitability of the solar system in the studied case. Possible reasons for the result was that the wind resources at the tested location wasn’t enough and that the price for wind turbines was high. Conclusions was that the price of the turbines needs to decrease in order to make the hybrid system more competitive. For hybrid systems that contain wind turbines, it is important that the chosen site has good wind resources to take advantage of the potential of the turbines.
6

Development of characteristics for electric hydrofoils / Utveckling av egenskaper för elektriska bärplansbåtar

Bhalli, Afzaal, Fransson, Carl, Wessman, Max, Ihrfelt, Sophia January 2023 (has links)
Denna rapport belyser två olika perspektiv på hur man skulle kunna lösa problemet med att elektrifiera bärplansbåtar. En tillämpning av bränslecell hybrid som kommer ge upphov till ökad räckvidd samt applikationen av ett snabbladdningssystem för minskad laddningstid vid kortare sträckor.  Olika laddningsmodeller av batterier undersöktes och efter dessa utvecklades en optimal snabbladdningskurva som tar hänsyn till olika degraderingsmekanismer i batteriet. Vidare diskuterades hur denna kunde anpassas till ett 12s, 63 Ah batteri som skulle användas för att åka sträckan Tranholmen till Ropsten.  Undersökning av hybrida batterier och bränslecellsystem visade att PEM-system som drivs av syrgas var betydligt mer effektiva gentemot PEM som använder luft. Dock på grund av den ökade komplexiteten är dessa mer lämpliga för användning hos större bärplansbåtar. Förändringar av systemets tryck ledde till påverkan på effektiviteten hos PEM-cellen. Utöver det bestämdes en lämplig hybridsystemmodell för användning på Float SAM plattformen.
7

Intäktsanalys av vindkraft som reglerresurs : Med och utan batterilager / Revenue Analysis of Wind Power as a Grid Regulation Resource : With and Without Battery Storage

Abran, Eszter, Andersson, Elin January 2023 (has links)
In order to ensure a stable power system, a balance between production and consumption at every given moment is necessary. An indication of this balance is the system frequency, which deviates from its nominal value in case of imbalance. With an increasing share of weather dependent energy in the Nordic synchronous system, such as wind power, the need for stabilizing services are becoming even more crucial. Ancillary services are a way of keeping the frequency stabilized, they are provided by different actors in the power system with flexible production or consumption. This contributes to increasing or decreasing the input and output of energy to the system when needed. Ancillary services are procured in separate markets that are structured and designed by the transmission system operator, Svenska kraftnät. This thesis investigates wind power and its potential of providing ancillary services in the Swedish power system. The report presents two different studies which are performed based on two specific wind farms in Sweden. Firstly, the possibility of providing ancillary services by the wind farms alone are considered with emphasis on the economic profitability. A model is used to present a theoretical maximum of income based on historical production and market data from 2022. The second study has an additional aspect of combining the wind farms with a battery energy storage system (BESS), creating a hybrid system, to examine the potential improvement of income for the company. Due to the production being dependent on weather conditions, the BESS can provide additional contribution when needed. The second study is performed using an optimization model in order to optimize the use of the BESS for the simulated period. The results presented an increase of revenues when participating on the ancillary service markets for both studies. The first study showed that down regulating services were the most profitable, this being FCR-D down and aFRR down. With the hybrid system, the profitability was even more significant. It demonstrated a big potential of participating on the FFR market during the summer and FCR-D during winter. Furthermore, the hybrid system also showed an increase in participation on the up-regulating markets. Without the BESS, the windfarm is forced to curtail production toparticipate in the up-regulating markets, which proved to be less profitable than participating on down-regulating markets. The results also give an understanding of the cycling of the BESS and how this affects the results and the BESS lifetime. With coming market development, the conditions on the ancillary service markets is expected to change, the effect of this is considered in a sensitivity analysis. Finally, the studies collectively show the opportunity for wind power to contribute to stabilizing the power system and ensuring the security of energy supply in the Nordicsynchronous system.
8

Systemdesign för miljövänliga och kostnadseffektiva reservkraftsystem : Undersökning av alternativa reservkraftsystem för en livsmedelsindustri

Clarstedt, Philip January 2024 (has links)
Backup power is essential to supply important functions in society with electricity in case of a blackout. Today in Sweden most backup generators are based on diesel fuel and seldom used, but they are still associated with bad environmental impact while operating. What if a backup system could be designed to increase its value and at the same time lower the environmental impact? This study has investigated alternative solutions for backup power and applied them on a specific case. A food providing industry with great variations in their load profile (40 - 240 kW) is looking for a backup solution able to supply the industry for 12 h in case of a blackout. The study started off by investigating different techniques and their suitability for providing backup power, such as diesel generators (DG), battery energy storage systems (BESS), micro gas turbines (MGT) and fuel cells (FC). Most suitable to be compared with the traditional diesel solutions in terms of cost, climate and technique was found to be two hybrid systems. The first one a combination of a DG and BESS and the second a combination of a MGT and BESS. The two hybrid systems were primarily dimensioned to a size of 100 kW (DG/MGT) with a 350/350 kWh/kW BESS based on terms and after analyzing the industry's load profile. The two hybrid systems were compared with a 350 kW DG in two aspects over a time frame of 15 years, life cycle costs (LCC) and carbon dioxide emissions. Compared with only DG the result showed a 15% LCC increase and a 26% emission reduction for the hybrid solution with DG + BESS. For MGT + BESS the LCC increase was 30% but the emission reduction was 52%. Included into the LCC analysis is utilization of the BESS for grid services such as peak shaving, arbitrage and grid support which had a major positive economic impact. The LCC results were however sensitive to changes in some parameters such as investment costs and rates. Finally, the study tried to optimize the cost and climate performance of the two hybrid systems. By reducing a few terms, sizing of the systems could be adjusted. This resulted in both hybrid systems being more profitable and climate friendly with a larger DG/MGT and a smaller complementing BESS for peak loads, outperforming the only DG solution.
9

Ersätta APU:n med SOFC-GT Hybridsystem inom luftfarten

Sarwari, Javid, Heidari, Abbas January 2018 (has links)
The current Auxiliary Power Unit (APU) contributes a lot to the greenhouse effect in terms of emissions, and in the form of noise and also is very heavy. The need for more electricity has increased in aircrafts and therefore major aircraft suppliers like Boeing and Airbus want to switch to more electric aircraft (MEA) which is lighter and has less environmental impacts. The purpose of this work is to investigate the possibilities of replacing today's traditional APU with fuel cells. In this work presents six different common fuel cell types which used commercially in various areas in the market. We have also analyzed and investigated the most suitable fuel cell types and have chosen to apply the SOFC-GT Hybrid Systems. We have investigated and compared both systems with pros and cons. We have used different methods in this work including the FOI3-method and Safran &amp; Honeywell for calculations of emissions for all systems. Finally, we have analyzed and investigated the emissions, noise and weight for both systems. / Nuvarande Auxiliary Power Unit (APU) bidrar mycket negativt till växthuseffekten i form av emissionsutsläpp och även i form av buller och är dessutom mycket tunga. Behovet av mer elektricitet ökar i flygplan och därför vill stora flygplanstillverkare såsom Boeing och Airbus övergå till more electric aircraft (MEA) vilket är lättare och har mindre miljöpåverkan. Syftet med detta arbete är att undersöka möjligheterna av att ersätta dagens traditionella APU mot bränsleceller. I detta arbete presenteras sex olika bränslecellstyper som finns på marknaden och används kommersiellt inom olika områden. Vi har analyserat och undersökt de lämpligaste bränslecellstyper för applicering och därefter har vi valt att implementera SOFC- GT Hybridsystemen. Vi har undersökt och jämfört båda systemens för- och nackdelar. Metodmässigt används bland annat FOI3-Metoden och Safran &amp; Honeywell för beräkningar av utsläpp av emissioner för samtliga system. Slutligen har vi analyserat och undersökt skillnader i utsläpp av emissioner, buller och vikt för båda systemen.
10

Optimierendes Energiemanagement von Brennstoffzelle-Direktspeicher-Hybridsystemen

Bocklisch, Thilo 21 April 2010 (has links) (PDF)
Die Dissertation beschreibt ein neues optimierendes Energiemanagement-Verfahren für Brennstoffzelle-Direktspeicher-Hybridsysteme. Den Ausgangspunkt bildet die Analyse der Schwankungseigenschaften spezifischer Energiezeitreihen: des Photovoltaik-Energieangebots und des elektrischen Verbrauchs von Haushalten. Konzepte zur zeitgestaffelten Zerlegung, Modellierung und Prognose werden vorgestellt. Der zweite Teil der Dissertation beschäftigt sich mit den Grundlagen von Aufbau und Funktion eines Brennstoffzelle-Direktspeicher-Hybridsystems und präsentiert Ergebnisse experimenteller und theoretischer Untersuchungen einer PEM-Brennstoffzelle, einer Supercap-Einheit, einer Lithium-Ionen Batterie sowie eines speziell entwickelten DC/DC-Wandlers. Praxistaugliche Modelle zur Beschreibung des Klemmenverhaltens, des Ladezustands und der auftretenden Wandlungsverluste werden vorgestellt. Der dritte Teil der Dissertation präsentiert ein neues optimierendes Energiemanagement-Verfahren. Optimierungsziele sind die Minimierung des Wasserstoffverbrauchs bei gleichzeitiger Reduzierung der dynamischen Brennstoffzellen-Beanspruchung. Das Verfahren basiert auf den drei Steuerungsebenen: Primärregelung, Sekundärregelung und Systembetriebsführung. Schwerpunkt bildet die Sekundärregelung auf der Basis einer speziellen Struktur aus Laderegler und Lastfolgeregler sowie zwei Blöcken zur aktiven Begrenzung des Leistungsgradienten und des Arbeitsbereichs der Brennstoffzelle. Die Funktion und Leistungsfähigkeit des Energiemanagement-Verfahrens werden an einem Simulations- und an einem Experimentiersystem nachgewiesen. Anwendungsbeispiele werden gegeben. / The dissertation presents a new optimizing energy management concept for fuel cell-direct storage-hybrid systems. Initially, the characteristics of specific energy time series are investigated on the basis of real measurement data. A new concept for the multi-scale analysis, modelling and prediction of fluctuating photovoltaic supply and electric load demand profiles is developed. The second part of the dissertation starts with a discussion of the benefits of and the basic coupling and control principles for fuel cell-direct storage-hybrid systems. The typical characteristics of a PEM-fuel cell, a metal hydride hydrogen storage, a lithium-ion battery and a supercap unit are presented. A new modular DC/DC-converter is described. Results from experimental and theoretical investigations of the individual components and the overall hybrid system are discussed. New practicable models for the voltage-current-curve, the state of charge behaviour and the conversion losses are presented. The third part of the dissertation explains the new energy management concept. The optimization of power flows is achieved by a control-oriented approach, employing a) the primary control of bus voltage and fuel cell current, b) the secondary control to limit fuel cell current gradient and operating range and to perform direct storage charge control, and c) the system control to optimally adjust secondary control parameters aiming for a reduction of dynamic fuel cell stress and hydrogen consumption. Results from simulations and experimental investigations demonstrate the benefits and high capabilities of the new optimizing energy management concept. Examples of stationary and portable applications conclude the dissertation.

Page generated in 0.0347 seconds