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  • 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.
331

Harmonisk strömsimulering i inverterbaserade värmepumpar / Harmonic current simulation in inverter-based heat pumps

Magnusson, Alexander January 2023 (has links)
An electrical distribution network supplies power to many households at a time. Each house has various types of electrical appliances which consume different levels of power depending on its function and the load it supplies. An ideal case would be when no appliances cause power disturbances, however, in reality, many electrical appliances (e.g. refrigerators, computers, heat pumps, etc.), due to their inherent characteristics. The distribution network is now fed back with non-sinusoidal power, called harmonics, causing inefficiencies and potential failure in other appliances connected to the same network. Harmonics are the additional frequency components to the fundamental sinusoidal voltage or current (e.g. 50Hz fundamental frequency in Europe). To avoid the malfunction of the network, each electrical appliance in any household has to comply with the standard IEC 61000-3-2 (current rating $<$16A) defined by the International Electrotechnical Commission (IEC). According to these standards, current harmonics have been observed up to 40th harmonics. If the fundamental frequency is 50 Hz, then harmonic currents up to 2000 Hz have to be considered. Usually, the harmonics are quantified by the measurement when the appliance has been constructed at which point changes are costly and time-consuming.  This thesis investigates the possibility to model these appliances at an early stage of development enabling cost-effective and quick improvements. The model is achieved by reducing a heat pump into a set of chokes, an EMI filter, a rectifier, and a load represented by a variable current source to simulate the compressor which draws the majority of power the system uses. The state-of-the-art, referred to as white box modeling, uses schematics to model these components while this thesis presents a methodology to model without schematics, referred to as black box modeling.  For the black box model, impedance of the components is measured and equivalent circuits are modeled accordingly in Simulink to simulate the harmonics. The validity of a black box simulation model from the equivalent circuit extracted by the impedance measurements is investigated in this thesis. The black box modeling is compared with the white box modeling and measurements for the purpose of verification.   The result is good but more work is needed. The black box model is verified using two different systems which are similarly accurate. Simulating harmonics at a higher power level yields better results. The black box model is more accurate than the white box model, mainly due to the inclusion of parasitics in the EMI filter. Possible additional harmonics generation in unmodeled components is investigated and found to be insignificant.
332

Mätning av övertoner i belysningsnät

Ramstedt, Andreas January 2022 (has links)
No description available.
333

Prediction of Non-Equilibrium Heat Conduction in Crystalline Materials Using the Boltzmann Transport Equation for Phonons

Mittal, Arpit 21 October 2011 (has links)
No description available.
334

Conductive interferences from multiple EC-motor installation : To measure and mitigate harmonics

Aitman, Victor January 2022 (has links)
Products produced by a Swedish company are requested to be investigated regarding their harmonic and inter-harmonic currents injected into the public supply system to comply with the Swedish standard SS-EN IEC 61000-3-2, Electromagnetic compatibility (EMC).    On behalf of Systemair Sweden AB, this bachelor thesis aims firstly to investigate if their product, PAFEC 4225 WH (Air Curtain), complies with standard SS-EN IEC 61000-3-2, and if not, what measures should be taken; and secondly to develop a low-cost instrument for the measurement of harmonics and inter-harmonics according to standard IEC 61000-4-7 related to the requirements on equipment used in standard SS-EN IEC 61000-3-2. To this purpose, the standards have been looked into thoroughly, the preconditions for measurements have been studied in detail, and external meetings with a consultant at Delta Development Technology AB have been performed. Measurements of the harmonic spectrum generated by PAFEC 4225 WH have been performed first at Systemair Sweden AB’s Technical center in Skinnskatteberg, and later at Delta Development in Västerås. After this, a low-cost instrument was developed, including hardware and software design and implementation. The hardware implementation consists of a circuit board designed using EasyEDA (an online PCB Design Tool), a NI myDAQ (a data acquisition device made by National Instruments), and an enclosure designed with Solidworks and made with a 3D-printer. The software implementation was conducted using LabVIEW – a graphical programming language.  A few measurements were performed using instruments complying IEC 61000-4-7 at Delta Development, and later with the low-cost instrument. Different line chokes were measured. The results showed that a 15 mH line choke connected in series with each motor would make the PAFEC 4225 WH comply with SS-EN IEC 61000-3-2. The results from the low-cost instrument did not match Delta Developments results regarding harmonic and inter-harmonic content. The difference could be caused by unfinished algorithm, different measurements conditions, and missing anti-aliasing-filter.          For the future work it is recommended that Systemair Sweden AB can either develop the low-cost instrument or buy an existing instrument that complies with IEC 61000-4-7, to enable to do measurements that comply with SS-EN IEC 61000-3-2. One does also need to investigate the grid during low activity or consider buying a signal generator for the purpose of fulfilling the preconditions to enable measurements. It is also recommended that further measurements are performed with the proposed line choke installed to check for any change in performance of the product.
335

The Influence of Temperature on the Dielectric Losses of Epoxy Resin Under Harmonic Distorted Voltages

Linde, Thomas, Backhaus, Karsten, Schlegel, Stephan, Loh, Jun Ting, Kornhuber, Stefan 14 September 2022 (has links)
The insulation of the electrical equipment in medium and high-voltage grids is subjected to significant electrical and thermal stresses. The switching characteristic of the increasing number of power electronic devices in electric grids leads to the distortion of the voltage waveform which causes additional dielectric losses in insulation materials. The consequent dielectric heating and elevated temperatures present a risk of thermal breakdown and generally accelerated ageing. This manuscript presents how temperatures up to the glass transition and severely distorted sinusoidal voltages influence the dielectric losses in epoxy resin samples. The impact of additional dielectric losses is depicted and the risk of thermal runaway is assessed by comparing the distorted voltage stress to a pure sinusoidal oscillation. The ratio between the losses at distorted voltage and sinusoidal voltage declines with increasing temperature, reducing the risk of thermal runaway even at high temperatures and significant voltage distortion. A generalization of the risk assessment is given based on the discussion of the results and simple standardized measurement techniques.
336

Analysis of Electric Disturbances from the Static Frequency Converter of a Pumped Storage Station

Rosado, Sebastian Pedro 12 August 2001 (has links)
The present work studies the disturbances created in the electric system of a pumped storage power plant, which is an hydraulic generation facility where the machines can work as turbines or pumps, by the operation of a static frequency converter (SFC). The SFC is used for starting the synchronous machines at the station when in the pump mode. During the starting process several equipment is connected to the SFC being possible to get affected by the disturbances generated. These disturbances mainly include the creation of transient overvoltages during the commutation of the semiconductor devices of the SFC and the introduction of harmonics in the network currents and voltages. This work analyzes the possible effects of the SFC operation over the station equipment based on computer simulations. For this purpose, the complete system was modeled and the starting process simulated in a computer transient simulator program. The work begins with a general review of the effects of electric disturbances over high voltage equipment and in particular of the disturbances generated by power electronics conversion equipment. Then the models for the different kind of equipment present in the system are discussed and formulated. The control system that governs the operation of the SFC during the starting process is analyzed later as well as the operation conditions. Once the model of the system is set up, the harmonic analysis of the electric network is done by frequency domain and time domain methods. Time domain methods are also employed for the analysis of the commutation transient produced by the SFC operation. Finally, the simulation results are used to evaluate the impact of the SFC operation on the station equipment, especially on the generator step up transformer. / Master of Science
337

APPLICATIONS OF ACOUSTIC RADIATION MODES IN ACOUSTIC HOLOGRAPHY AND STRUCTURAL OPTIMIZATION FOR NOISE REDUCTION

Jiawei Liu (18419274) 22 April 2024 (has links)
<p dir="ltr">Acoustic holography is a powerful tool in the visualization of sound fields and sound sources. It provides engineers and researchers clear insights into sound fields as well as their sound sources. Some widely-used methods include Nearfield Acoustical Holography (NAH), Statistically Optimized Nearfield Acoustic Holography (SONAH) and the Equivalent Source Method (ESM). SONAH and ESM were developed specifically to tackle the intrinsic deficiency of the Fourier-based NAH which requires that the sound field fall to negligible levels at the edges of the measurement aperture, a requirement rarely met in practice. Besides the aforementioned methods, the Inverse Boundary Element Method (IBEM) can be used, given sufficient measurements and computational resources. As useful as they are in visualizing the sound field, none of these methods can provide direct guidance on potential design modifications of the observed structure in order to unequivocally reduce sound power radiation. Acoustic radiation mode analysis has previously been primarily associated with active noise control applications. Since the radiation modes radiate sound power independently, it is only necessary to modify the surface vibration patterns so that they do not couple well with the radiation modes in order to guarantee a reduction of the radiated sound power. Since the radiation modes are orthogonal and complete, they can be used as the basis functions through which the source surface vibration can be described. Therefore, an acoustic holography method based on the acoustic radiation modes will enable the sound power ranking of the modal components of the surface vibration pattern, and in turn, point out the component(s) which should be targeted in order to reduce the overall sound power. However, use of the acoustic radiation modes in the inverse procedure comes with a price: the detailed geometry of the object to be measured must be obtained, thus enabling the calculation of acoustic radiation modes and the modal pressures. But this is not an issue for original equipment manufacturers given that almost all prototypes are now designed with CAD, as is the case with the engine example to be described next.</p><p dir="ltr">In modern engine design, downsizing and reducing weight while still providing an increased amount of power has been a general trend in recent decades. Traditionally, an engine design with superior NVH performance usually comes with a heavier, thus sturdier structure. Therefore, modern engine design requires that NVH be considered in the very early design stage to avoid modifications of engine structures at the last minute, when very few changes can be made. NVH design optimization of engine components has become more practical due to the development of computer software and hardware. However, there is still a need for smarter algorithms to draw a direct relationship between the design and the radiated sound power. At the moment, techniques based on modal acoustic transfer vectors (MATVs) have gained popularity in design optimization for their good performance in sound pressure prediction. Since MATVs are derived based on structural modes, they are not independent with respect to radiated sound power. In contrast, as noted, acoustic radiation modes are an orthogonal set of velocity distributions on the structure’s surface that contribute to the radiated sound power independently. As a result, it is beneficial to describe structural vibration in terms of acoustic radiation modes in order to identify the velocity distributions that contribute the majority of the radiated sound power. Measures can then be taken to modify the identified vibration patterns to reduce their magnitudes, which will in turn result in an unequivocal reduction of the radiated sound power. A workflow of the structural optimization procedure is proposed in this dissertation.</p><p dir="ltr">While acoustic radiation modes have great efficiencies in describing radiated acoustic power, the computation of acoustic radiation modes can be time consuming. In the last chapter of this thesis, a novel way of calculating acoustic radiation modes is proposed, which differs from the traditional singular value decomposition of the power radiation resistance matrix, and which is more efficient than previously proposed procedures. </p><p><br></p>
338

Evaluating Power Quality in the Microgrid on Arholma Island

Nilsson, Anna January 2024 (has links)
The purpose of this thesis is to evaluate a selection of power quality parameters (harmonic distortion and voltage variations) in the microgrid on Arholma Island in the Stockholm archipelago, Sweden. Measurements of harmonic distortion, total harmonic distortion, and voltage magnitudes is evaluated and compared prior to and after the installation of the microgrid. Furthermore, a comparison is made between grid-connected mode and island operation mode where also the frequency is analysed. The measured values are compared against regulatory limits.  The microgrid is owned and managed by the company Vattenfall, who provides the data used for the evaluation. The microgrid consists of two battery energy storage systems and a small photovoltaic system. The central energy management system has different use cases, for example peak shaving and voltage regulation. At the time when this thesis is conducted, the microgrid has been up and running continuously for approximately 8 months, from September, 2023 to April, 2024. A power quality meter has been collecting data at the point of common coupling (connection to the mainland) for a period of two years, i.e., from April, 2022, which is one year prior to the installation of the microgrid in mid-April, 2023. The microgrid is also operated in island operation mode for three short periods on April 18, 2024.  The data analysis is executed in Excel and Matlab. The results show that all measured harmonics (2nd to 25th), and total harmonic distortion stays well within regulatory limits throughout the whole measuring period. The microgrid does not seem to make the harmonic magnitude increase in general, although there is a slight increase during island operation mode for certain harmonics. Only on one occasion (with the exception of a planned maintenance outage) does the voltage drop below the levels of what is considered as good voltage quality during the two-year measurement period. Also, during island operation mode, the frequency show less variations than during grid-connected mode. / Syftet med detta examensarbete är att utvärdera ett urval av elkvalitetsparametrar (spänningsdistorsion/övertoner och spänningsvariationer) i mikronätet på ön Arholma i Stockholms skärgård, Sverige. Mätdata för övertoner, total övertonsdistorsion och spänningsamplitud utvärderas och jämförs före och efter installationen av mikronätet. Dessutom görs en jämförelse mellan nätanslutet läge och ö-driftläge, där även frekvensen analyseras. De uppmätta värdena jämförs med föreskrivna gränsvärden. Mikronätet ägs och förvaltas av företaget Vattenfall, och tillhandahåller den data som används för utvärderingen. Mikronätet består av två batterilagringssystem och ett litet solcellssystem. Det centrala kontrollsystemet har olika funktioner, till exempel ”peak shaving” och spänningsreglering. Vid t idpunkten då detta examensarbete genomförs har mikronätet varit i drift kontinuerligt i cirka 8 månader, från september 2023 till april 2024. En elkvalitetsmätare har samlat in data vid sammankopplingspunkten mot fastlandet under en period av två år, dvs. från april 2022, vilket är ett år före installationen av mikronätet i mitten av april 2023. Mikronätet körs i ö-drift under tre korta perioder den 18 april 2024. Dataanalysen utförs i Excel och Matlab. Resultaten visar att alla uppmätta övertoner (2:a till och med 25:e) och total övertonsdistorsion håller sig väl inom regulatoriska gränser genom hela mätperioden. Mikronätet verkar inte bidra till att övertonernas magnitud ökar i allmänhet, men en liten ökning för vissa övertoner kan ses i samband med att mikronätet körs i ö-drift. Endast vid ett tillfälle (med undantag för ett planerat underhållsavbrott) under den tvååriga mätperioden sjunker spänningen under nivåerna för vad som anses vara god spänningskvalitet. Resultaten visar även att frekvensen varierar mindre vid ö-drift än när mikronätet är sammankopplat med fastlandsnätet.
339

Comparison of Dielectric Loss Measuring Methods on Epoxy Samples under Harmonic Distorted Voltages

Linde, Thomas, Backhaus, Karsten 21 November 2024 (has links)
The increasing number of power electronic devices in medium voltage networks lead to a harmonic distortion of the voltage waveforms in electrical systems. Medium frequency components up to several kHz are superimposed on the fundamental grid voltage. The distorted voltage waveforms stresses the insulation systems due to the additional current and hence additional dielectric losses. The heat generated from dielectric losses is suspected to be an accelerator to insulation ageing below partial discharge inception. Therefore, the systematic assessment of the losses and their correct quantification is crucial to designing reliable insulation systems with a high lifetime. The investigation of losses under nonsinusoidal and distorted voltage waveforms is not trivial and has been subject to little research to date, compared to investigations at 50 or 60 Hz. In this paper, several approaches of quantifying dielectric losses under multifrequent voltage waveforms are presented and compared. The losses of cast resin specimens are quantified with a test setup using a reference measurement method. The loss computation algorithms range from previously utilised Extrapolation and Superposition approaches to a direct power measurement technique. The results presented in this contribution show that the different measurement procedures provide considerably different outcomes for which possible explanations are given. The presented data indicates that realistic field strength conditions should be ensured in order to quantify the losses under distorted voltage waveformes correctly.
340

Hypernuclear bound states with two /\-Particles

Grobler, Jonathan 11 1900 (has links)
The double hypernuclear systems are studied within the context of the hyperspherical approach. Possible bound states of these systems are sought as zeros of the corresponding three-body Jost function in the complex energy plane. Hypercentral potentials for the system are constructed from known potentials in order to determine bound states of the system. Calculated binding energies for double- hypernuclei having A = 4 − 20, are presented. / Physics / M.Sc. (Physics)

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