• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 30
  • 10
  • Tagged with
  • 40
  • 40
  • 40
  • 40
  • 40
  • 40
  • 5
  • 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

Conducted and Radiated Electromagnetic Interference in Modern Electrified Railways with Emphasis on Pantograph Arcing

Midya, Surajit January 2009 (has links)
Arcing from the pantograph, a commonly observed phenomenon, is knownto be a major source of wideband electromagnetic emission which is more pronounced during the winter. Experience within the railway industry has shown that this source of EMI and its characteristics need to be understood thoroughly for solving the associated EMI issues in the desired fashion. This thesis investigates EMI generation from pantograph arcing. The First phase of the work is based on experimental investigations and analyses conducted on a test setup which closely resembles pantographcontact wire interaction. Different possible mechanisms of the pantograph arcing and inuencing parameters like speed of the train, loadcurrent, voltage level, power factor etc. are identified. It was found that pantograph arcing is a polarity dependent phenomenon. It generates transients and asymmetrically distorted voltage and current waveforms. This in turn generates a net DC component and odd and even harmonics(up to order 10 was measured). In the second phase, different characteristics of these high frequency emission and inuencing parameters have been analyzed and presented. Presence of wideband high frequency components in the range from afew ten kHz to a few hundred MHz at measured current, electric and magnetic elds were confirmed. 10-90 % risetimes for current was measured from 5 ns to typically around 25 ns, whereas for electric field this is ranged from fraction of onens to 25 ns. Although there are variations, the rise times of the measuredtime domain waveform of current, electric and magnetic seems to have correlation with the higher frequency components. It was understood that major high frequency components measured could be from: (a) thearcing itself, (b) radiation from connected cables/wires, (c) resonance inthe associated circuits and (d) associated digital circuitry.This wideband electromagnetic emission causes interference in traction power, signalling and train control systems. Their possible propagation paths and consequences on different equipments are also elaborated. / QC 20100803
2

Analysis of a novel Transversal Flux Machine with a tubular cross-section for Free Piston Energy Converter application

Cosic, Alija January 2010 (has links)
Constantly growing need for oil, all over the world, has caused oil price to rise rapidly during the last decade. High oil prices have made fuel economy as one of the most important factors when consumers are buying their cars today. Realizing this, many car manufacturers have developed or are looking for some alternative solutions in order to decrease fuel consumption. Combining two different technologies in a vehicle, the so called hybrid vehicle, can be seen as the first step toward a better and more sustainable development. There are several different solutions for hybrid vehicles today, among the best known are the Serie Electric Hybrid Vehicle (SEHV), the Parallel Electric Hybrid Vehicle (PEHV) and the Serie-Parallel Hybrid Electric Vehicle (SPEHV). By integrating a combustion engine with a linear electric machine into one unit, a system that is called Free Piston Energy Converter (FPEC) is achieved. The FPEC is suitable for use in a SEHV. Other application areas like stand alone generator are also possible. In this report a novel Transverse Flux Machine (TFM) with a tubular cross section of the translator has been investigated. Application of the machine in a FPEC has put tough requirement on the translator weight, specific power and force density. Different configurations of the winding arrangements as well as the magne tarrangement have been investigated. It has been concluded that the buried magnet design suffers from high leakage flux and is thus not asuitable TFM concept. Instead the surface mounted magnet design has been chosen for further investigation. An analytical model has been developed and a prototype machine has been built based on the analytical results. In order to have a better understanding of the machine characteristic a 3D-FEM analysis has been performed. The results from the analytical model, FEM model and measurements are analyzed and compared. The comparison between the measured and FEM-simulated results shows very good agreement. Furthermore, the results from the analytical model indicates that it can be successfully developed for further analysis and optimization of the design to give a cost-effective solution of the novel generato for mass production. / Det ständigt växande behovet av oljan runt om i världen, har fått oljepriset att stiga snabbt under det senaste decenniet. Detta har gjort bränsleekonomin till en av de viktigaste faktorer när konsumenterna väljer sina bilar i dag. Många biltillverkare har därför utvecklat eller söker efter alternativa lösningar till dagens förbränningsmotorer i hopp om att minska bränsleförbrukningen. Ett hybridfordon, ett fordon som är försedd med fler än en energiomvandlare, kan ses som ett första steg mot en bättre och mer hållbar utveckling. Det finns flera olika lösningar för hybridfordon i dag, bland de mest kända är Seriehybrid, Parallellhybrid och Serie-Parallelhybridfordon. Genom att integrera en förbränningsmotor med en linjär elektriskmaskin, erhålls ett system som kallas Frikolvsenergiomvandlare. Dennna typ av energiomvandlare lämpar sig bäst för användning i en seriehybridfordon, men andra användningsområden som fristående generator är också möjliga. I denna avhandling har en ny typ av Transversalflödesmaskin (TFM) med en cirkulärt tvärsnitt undersökts. Tillämpningen av maskinen i en Frikolvsenergiomvandlare har medfört tuffa krav på translatorvikten, specifikeffekten och kraftdensiteten. Olika lindnings- och magnetkonfiguratationer har undersökts. Forskningen har visat att designen med begravdamagneter lider av stort läckflöde och är därför inte lämplig för det nya TFM koncept. Istället har designen med ytmonterade magneter valts för vidare undersökning. En analytisk modell har utvecklats och en prototyp maskin har byggts med utgångspunkt i analysresultaten. För att få en bättre förståelse avmaskinkarakteristiken har en 3D-FEM modell tagits fram och analyserats. Resultaten från den analytiska modellen, FEM modellen och mätningar har analyserats och jämförts. Överensstämmelsen mellan de simulerade och de uppmätta resultaten är mycket bra. Dessutom, resultaten från den analytiska modellen visar på att modellen kan framgångsrikt användas för fortsatt analys och optimering av maskinen för att ge en kostnadseffektivlösning för masstillverkning. / QC 20101102
3

Voltage sag ride-through of AC drives : control and analysis

Pietiläinen, Kai January 2005 (has links)
<p>This thesis focuses on controller design and analysis for induction motor (IM) drives, flux control for electrically excited synchronous motors with damper windings (EESMs), and to enhance voltage sag ride-through ability and analysis for a wind turbine application with a full-power grid-connected active rectifier. The goal is to be able to use the existing equipment, without altering the hardware. Further, design and analysis of the stabilization of DC-link voltage oscillations for DC systems and inverter drives is studied, for example traction drives with voltage sags in focus.</p><p>The proposed IM controller is based on the field-weakening controller of Kim and Sul [31], which is further developed. Applying the proposed controller to voltage sag ride-through gives a cheap and simple ride-through system.</p><p>The EESM controller is based on setpoint adjustment for the field current controller. The analysis also concerns stability for the proposed flux controller.</p><p>The DC-link stabilization algorithm is designed following Mosskull [38], where a component is added to the current controller. The algorithm is further developed.</p><p>Analysis is the main focus, and concerns the impact of the different parameters involved. Proper parameter selection for the controller, switching frequency, and DC-link capacitor is given.</p><p>The impact of voltage sags is investigated for a power-grid-connected rectifier. Here, we analyze the impact of different types of voltage sags and phase-angle jumps. The analysis gives design rules for the DC-link capacitor and the switching frequency.</p><p>Experimental results and simulations verify the theoretical results.</p>
4

A review of lifetime assessment of tranformers and the use of Dissolved Gas Analysis

Karlsson, Sabina January 2008 (has links)
<p>The Reliability-Centred Asset Maintenance (RCAM) is a structured approach to determine maintenance strategies for electric power system which is developed at KTH School of Electrical Engineering. RCAM focus on reliability aspects of the system and one of the main steps in RCAM in to modeling the relationship between reliability and the elect of maintenance for critical components within the system. The transformer has been identified as a critical component within a power system and in spring 2006 the Ph.D project “<i>Life time modeling and management of</i> <i>transformers</i>” was started within the RCAM group. The overall goal for the project is to develop a quantitative model for the lifetime distribution of a transformer with the final goal to implement the developed model into a maintenance planning.</p><p>Dissolved Gas Analysis (DGA) is a widely used technique to estimate the condition of oil-immersed transformers. Incipient faults within the transformer may be detected by analyzing the gases which are dissolved in the transformer-oil. The objective of this thesis is mainly to analyze available data from DGA, and investigate if this kind of data may be useful in quantitative modeling of the transformers reliability.</p><p>One conclusion from this work is that the difficulty in modeling the transformers reliability lies mainly in the limited availability of adequate data. Transformer is a reliable device and since the number of failures in critical in mathematical modeling of a component´s reliability it becomes very difficult to determine such models. Another aspect is the difficulty to draw conclusions about a transformer´s condition only from the DGA results. Although there are standards available for this purpose the DGA interpretation should also be based on other information about the particular transformed such as size, construction and operation circumstance. During this work no sources have been found from which the correlation between DGA data and probability for transformer failures could be estimated. For this reasons the proposed failure rate function in this work is based on several subjective assumptions and has not been possible to verify.</p>
5

Voltage sag ride-through of AC drives : control and analysis

Pietiläinen, Kai January 2005 (has links)
This thesis focuses on controller design and analysis for induction motor (IM) drives, flux control for electrically excited synchronous motors with damper windings (EESMs), and to enhance voltage sag ride-through ability and analysis for a wind turbine application with a full-power grid-connected active rectifier. The goal is to be able to use the existing equipment, without altering the hardware. Further, design and analysis of the stabilization of DC-link voltage oscillations for DC systems and inverter drives is studied, for example traction drives with voltage sags in focus. The proposed IM controller is based on the field-weakening controller of Kim and Sul [31], which is further developed. Applying the proposed controller to voltage sag ride-through gives a cheap and simple ride-through system. The EESM controller is based on setpoint adjustment for the field current controller. The analysis also concerns stability for the proposed flux controller. The DC-link stabilization algorithm is designed following Mosskull [38], where a component is added to the current controller. The algorithm is further developed. Analysis is the main focus, and concerns the impact of the different parameters involved. Proper parameter selection for the controller, switching frequency, and DC-link capacitor is given. The impact of voltage sags is investigated for a power-grid-connected rectifier. Here, we analyze the impact of different types of voltage sags and phase-angle jumps. The analysis gives design rules for the DC-link capacitor and the switching frequency. Experimental results and simulations verify the theoretical results. / QC 20101012
6

The Plausibility of implementing Receive Antenna Diversity in the Downlink of CDMA450 system

Sayago Montilla, David January 2010 (has links)
No description available.
7

Network Analyzer Functionality Simulator

Rodriguez, Ramón January 2007 (has links)
<p>The objective of this thesis work was to implement all the hardware and software necessary to simulate the functionality of a Vector Network Analyzer (VNA). With equipment that is already available, and is common in a measurement station, the most common functions of a VNA were implemented, using an Vector Signal Generator, that provide the signal for testing, and a Vector Signal Analyzer, to make all the amplitude and phase measurements. With these instruments and the appropriate software that control them, the basic functionality of a Vector Network Analyzer can be achieved with a reasonable accuracy. With this system, we can reduce costs, avoiding the need of a real VNA and take advantage off instruments that are already available in a laboratory. A Complete measurement system of all four scattering parameters is proposed at the end of the report for future implementation. With this implementation all the different S-parameter measurements were made with an acceptable accuracy that can be comparable to a commercial VNA.</p>
8

DEVELOPMENT OF AN EMI MEASUREMENT SYSTEM : Performance Analysis of Bluetooth communication under noise environment

Perez, Felix, Ferrer, Javier January 2008 (has links)
<p>This thesis is a project carried out at the “Centre for RF Measurements Technology of Gävle”. The first aim of this work was basically to develop an EMI measurement system, to that purpose, it has been used an EMI Tester receiver, Spectrum Analyzer and a broadband antenna. Tables and graphics are shown to provide the values of the different detectors utilized.</p><p>Using this measurement system, an interference file was recorded and then inserted in a Bluetooth communication model. The interference file was simulated with Matlab Simulink, to check how the interference affected the communication; the effects of the signal degradation are presented in a graphic.</p><p>Finally a real Bluetooth communication was established using two Bluetooth modules from Free2Move Company, to prove that the effect of microwave oven interferences produces the increase of transmission time and therefore decrease the Throughput.</p>
9

Tjockleksmätning med ultraljud : <em>Icke konventionell metod med signalbehandling</em>

Östlin, Anders January 2010 (has links)
<p>Tjockleksmätning av rör med ultraljud görs typiskt genom att mäta tiden mellan två efterföljande ekon av en utsänd puls. Detta är ofta en svår process som är känslig för störningar och påverkan utifrån. Denna rapport beskriver hur detta i stället kan göras i frekvensdomänen för att minska effekterna av dessa problem.</p><p>För att göra detta härleds en signalmodell som beskriver de effekter som är nödvändiga för att utföra mätningarna. Utifrån signalmodellen togs metoder fram för att analysera och fastställa tjockleken på den uppmätta signalen.</p><p>En av metoderna fungerar så bra att den skulle kunna användas.</p> / <p>Ultrasonic thickness gauging of steel tubes is typically performed by observing the time difference between two following echoes. This process is often connected to various problems regarding interference. This thesis describes how to avoid these problems by using signal processing and analyzing the signals in the frequency domain.</p><p>To achieve these results a signal model that describes the necessary effects is derived. From this model different measurement methods to analyze and determine the thickness are developed.</p><p>One of the methods proved to be useful.</p>
10

Network Analyzer Functionality Simulator

Rodriguez, Ramón January 2007 (has links)
The objective of this thesis work was to implement all the hardware and software necessary to simulate the functionality of a Vector Network Analyzer (VNA). With equipment that is already available, and is common in a measurement station, the most common functions of a VNA were implemented, using an Vector Signal Generator, that provide the signal for testing, and a Vector Signal Analyzer, to make all the amplitude and phase measurements. With these instruments and the appropriate software that control them, the basic functionality of a Vector Network Analyzer can be achieved with a reasonable accuracy. With this system, we can reduce costs, avoiding the need of a real VNA and take advantage off instruments that are already available in a laboratory. A Complete measurement system of all four scattering parameters is proposed at the end of the report for future implementation. With this implementation all the different S-parameter measurements were made with an acceptable accuracy that can be comparable to a commercial VNA.

Page generated in 0.0763 seconds