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Tesi sul tema "Frequency stability"

Autore: Grafiati
Pubblicato: 4 giugno 2021
Ultima modifica: 14 marzo 2023

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1

Nocera, Aurelio <1994&gt. "High Frequency Trading and Financial Stability". Master's Degree Thesis, Università Ca' Foscari Venezia, 2020. http://hdl.handle.net/10579/16789.

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Over the last three decades, financial markets have undergone through an epochal revolution. The main driver of this profound change has been, as always, technology. Trading floors are not anymore full of yelling traders who shout orders from one side of the exchange to the other. People now need to adapt their mental picture of financial markets to a new representation: no more humans, only a collection of silent servers which collect and storage terabytes of data. In the first chapter, I will explore how financial markets have reached this new macro and micro organization. I will present the difference between algorithmic (AT) and high frequency trading (HFT). Then I will explain the reason why speed has become a crucial factor for financial markets. For this purpose, I will introduce the concepts of co-location, latency and nanosecond. Then I will discuss some trending market dynamics, such as exchanges’ fragmentation, competition between “light” and “dark” platforms and predatory behaviors. In the second chapter I will discuss the role of high frequency traders and their relative weight with respect to other players. A discussion of their main trading strategies, which kind of stocks they prefer and how they capture information from the market will follow. With regards to the latest point, I will also explore the relationship between HFT, big data and artificial intelligence. I will conclude my thesis exploring how and why HFT have had a huge and profound impact on financial markets stability. Therefore, I will deal with huge events as the Flash Crash and Flash Dash. Moreover, I will address which role regulators have played and could play in the future with respect to this topic. In this chapter, I will also present some results of my empirical research.
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Ismael, Alexander. "Comparison of fast frequency reserve strategies for Nordic grid frequency stability". Thesis, Uppsala universitet, Institutionen för elektroteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-411503.

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How long would modern society cope with a power outage, what would happen to vital systems that we today take for granted in modern society. The Nordic electricity grid is facing a major shift where electricity production from non-renewable sources are to be replaced increasingly by renewable sources. By increasing the penetration of wind and solar power the electric power system might be exposed to disturbances due to decreasing inertia as a result of the electricity transition. Currently the electric power system has different reserves to use to maintain frequency stability but there are other reserves that could help further in the fight for the balance between electricity production and consumption. This project examines whether the new reserve service, fast frequency reserve (FFR), can help the existing frequency containment reserve for disturbed (FCR-D) operation. Therefore, two experiments were conducted using the simulation tool ARISTO, addressing relevant issues involving frequency stability. Motivation for the hypothesis was to investigate if FFR could reduce the frequency transients and improve frequency variations by developing various setups and cases when inertia was retained and when the system inertia was reduced at different stages. The results of the experiments showed that the global minimum frequency, nadir, had increased for all test cases compared to the reference case when using FFR, this proved that the FFR in fact help reducing frequency transients. The results showed furthermore that when the FFR had a duration time of 30 seconds compared to only 5 seconds, the frequency variations could be improved for certain setups for experiment 2.
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Saarinen, Linn. "The Frequency of the Frequency : On Hydropower and Grid Frequency Control". Doctoral thesis, Uppsala universitet, Elektricitetslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-308441.

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Variations in the electricity consumption and production connected to the power system have to be balanced by active control. Hydropower is the most important balancing resource in the Nordic system, and will become even more important as the share of variable renewable energy sources increases. This thesis concerns balancing of active power, especially the real-time balancing called frequency control. The thesis starts in a description of the situation today, setting up models for the behaviour of hydropower units and the power system relevant to frequency control, and comparing the models with experiments on several hydropower units and on the response of the Nordic grid. It is found that backlash in the regulating mechanisms in hydropower units have a strong impact on the quality of the delivered frequency control. Then, an analysis of what can be done right now to improve frequency control and decrease its costs is made, discussing governor tuning, filters and strategies for allocation of frequency control reserves. The results show that grid frequency quality could be improved considerably by retuning of hydropower governors. However, clear technical requirements and incentives for good frequency control performance are needed. The last part of the thesis concerns the impact from increased electricity production from variable renewable energy sources. The induced balancing need in terms of energy storage volume and balancing power is quantified, and it is found that with large shares of wind power in the system, the energy storage need over the intra-week time horizon is drastically increased. Reduced system inertia due to higher shares of inverter connected production is identified as a problem for the frequency control of the system. A new, linear synthetic inertia concept is suggested to replace the lost inertia and damping. It is shown that continuously active, linear synthetic inertia can improve the frequency quality in normal operation and decrease wear and tear of hydropower units delivering frequency control.
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Dahlborg, Elin. "Grid frequency stability from a hydropower perspective". Licentiate thesis, Uppsala universitet, Elektricitetslära, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-444453.

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Many AC grids suffer from decreased frequency stability due to less system inertia. This has increased the risk of large-scale blackouts. This thesis and its papers address the frequency stability problem from a hydropower perspective. Grid frequency stability assessments often require accurate system inertia estimates. One approach is to estimate the inertia of all individual power plants and sum up the results. We implemented three inertia estimation methods on a Kaplan unit and compared their results. The generator contributed with 92-96% of the unit inertia, which verified the results from previous studies. However, the three methods estimated slightly different values for the unit inertia, which raises the question of when to use which method. Hydropower often deliver frequency control, yet we found no studies which validate Kaplan turbine models for large grid frequency disturbances on strong grids. Therefore, we performed frequency control tests on a Kaplan unit, implemented three hydropower models, and compared the simulation results to the measurement data. The models overestimated the change in output power and energy delivered within the first few seconds after a large change in frequency. Thus, it is important to have sufficient stability margin when using these types of hydropower models to assess the grid frequency stability. The Nordic transmission system operators are updating their frequency control requirements. We used measurement data and simulation models to assess whether improved runner blade angle control could help a Kaplan unit fulfill the coming requirements. The results showed that improved runner control does not improve the performance sufficiently for requirements fulfillment. The requirements are based on an assumption on minimum system inertia and became easier to fulfill if they were implemented with more system inertia. Thus, more inertia could allow more participants to deliver frequency control in the Nordic grid.
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5

MARTINEZ, DIANA MARGARITA GARCIA. "VOLTAGE STABILITY ASSESSMENT CONSIDERING PRIMARY FREQUENCY CONTROL AND FREQUENCY-DEPENDENT LINE PARAMETERS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2015. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=25603@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
A crescente demanda de energia elétrica faz com que a complexidade dos sistemas elétricos de potência seja cada vez maior, associado às limitações na expansão do sistema de transmissão, resulta na operação dos sistemas elétricos mais próximos de seus limites, tornando-os vulneráveis a problemas de estabilidade de tensão. Nesse contexto, faz-se necessário o desenvolvimento de ferramentas computacionais capazes de representar os sistemas elétricos mais adequadamente, melhorando assim as condições de análise. Neste trabalho são apresentadas três modelagens do fluxo de carga mais completas que a modelagem clássica, a saber: a modelagem de múltiplas barras swing, a modelagem com regulação primária e a modelagem com parâmetros da rede de transmissão variáveis com a frequência. Uma vez utilizadas na solução do problema do fluxo de carga estas modelagens são estendidas para a realização do cálculo dos índices de estabilidade de tensão das barras de carga, barras de tensão controlada e barras swing. Testes numéricos com um sistema-teste de 6 barras são apresentados para a verificação da aplicabilidade e adequação dos modelos analisados.
The growing demand for electricity increases the complexity of electric power systems which, when combined with limitations in the expansion of transmission systems, results in the operation of electrical systems closer to their limits, making them vulnerable to voltage stability problems. In this context, there is a gap in the market for the development of computational tools that can represent the electrical systems more appropriately, thereby improving the conditions of analysis. The present study formulates three non-classical load flow representations: multiple swing buses, primary frequency control, and frequency dependent transmission network parameters. Once used in the load flow problem solving, these models are also extended to allow the calculation of voltage stability indices of load buses, controlled voltage buses and swing buses. Numerical tests with a 6-bus test system are presented to verify the applicability and adequacy of the proposed models.
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6

Tan, Hui Boon. "Disentangling low-frequency versus high-frequency economic relationships via regression parameter stability tests". Diss., Virginia Tech, 1995. http://hdl.handle.net/10919/38575.

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7

Hewes, Dominic [Verfasser]. "Frequency Stability in Sustainable Power Systems: Effects of Reduced Rotational Inertia on Frequency Stability in the European Transmission System / Dominic Hewes". München : Verlag Dr. Hut, 2020. http://d-nb.info/1219469866/34.

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8

Zhang, Xiao Meny. "The mutation frequency and genome stability of measles virus". Thesis, Queen's University Belfast, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.546455.

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9

Wan, Kin Wa. "Advanced numerical and digital techniques in frequency stability analysis". Thesis, University of Portsmouth, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.237843.

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10

Virgilio, Gianluca. "Is high-frequency trading a threat to financial stability?" Thesis, University of Hertfordshire, 2017. http://hdl.handle.net/2299/18841.

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The purpose of this thesis is: (i) to produce an in-depth data analysis and computer-based simulations of the market environment to investigate whether financial stability is affected by the presence of High-Frequency investors; (ii) to verify how High-Frequency Trading and financial stability interact with each other under non-linear conditions; (iii) whether non-illicit behaviours can still lead to potentially destabilising effects; (iv) to provide quantitative support to the theses, either from the audit trail data or resulting from simulations. Simulations are provided to test whether High-Frequency Trading: (a) has an impact on market volatility, (b) leads to market splitting into two tiers; (c) takes the lion's share of arbitrage opportunities. Audit trail data is analysed to verify some hypotheses on the dynamics of the Flash Crash. The simulation on the impact of High-Frequency Trading on market volatility confirms that when markets are under stress, High-Frequency Trading may cause volatility to significantly increase. However, as the number of ultra-fast participants increases, this phenomenon tends to disappear and volatility realigns to its standard values. The market tiering simulation suggests that High-Frequency traders have some tendency to deal with each other, and that causes Low-Frequency traders also to deal with other slow traders, albeit at a lesser extent. This is also a kind of market instability. High-Frequency Trading potentially allows a few fast traders to grab all the arbitrage-led profits, so falsifying the Efficient Market Hypothesis. This phenomenon may disappear as more High-Frequency traders enter the competition, leading to declining profits. Yet, the whole matter seems a dispute for abnormal gains only between few sub-second traders. All simulations have been carefully designed to provide robust results: the behaviours simulated have been drawn from existing literature and the simplifying assumptions have been kept to a minimum. This maximises the reliability of the results and minimizes the potential of bias. Finally, from the data analysis, the impact of High-Frequency Trading on the Flash Crash seems significant; other sudden crashes occurred since, and more can be expected over the next future. Overall, it can be concluded that High-Frequency Trading shows some controversial aspects impacting on financial stability. The results are at a certain extent confirmed by the audit trail data analysis, although only indirectly, since the details allowing the match between High-Frequency traders and their behaviour are confidential and not publicly available Nevertheless, the findings about HFT-induced volatility, market segmentation and sub-optimal market efficiency, albeit not definitive, suggest that careful monitoring by regulators and policy-makers might be required.
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11

Chen, Jian. "Accurate frequency estimation with phasor angles". Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-12042009-020203/.

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12

Popelář, Vojtěch. "Vliv kompenzace kabelových sítí na stabilitu blízkých zdrojů". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2014. http://www.nusl.cz/ntk/nusl-220691.

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This thesis deals with the infulence of compensation cabel network on the stability of nearby power source. This issue is topical with the increase in the ratio of cable networks 110 kV in large cities. The work examines the theoretical concept of stability and factors that affect it. Mainly discusses the stability angle rotor of a synchronous machina. The practical part is performed in MODES software, that performs dynamic simulation of the behavior of the model. In this case, it will be behavior of synchronous machine during short-circuit in network at different values of compensation of this network.
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13

Davies, Guy R. "Investigating the low-frequency stability of BiSON's resonant scattering spectrometers". Thesis, University of Birmingham, 2011. http://etheses.bham.ac.uk//id/eprint/1609/.

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The main focus of the thesis is the study of low-degree low-frequency solar p modes from the analysis of high-resolution power spectra generated from 20 years of high-quality data collected by the Birmingham Solar Oscillations Network (BiSON) Resonant Scattering Spectrometers (RSS). To that end we present a novel model of the RSS and its observations that allows for the determination of a significant improvement in calibration for ground-based Sun-as-a-star Doppler velocity observations. We show that the previously neglected multiple scattering in the RSS vapour cell is significant and demonstrate its impact on the spatial weighting to the solar disk, combining the new instrumental weighting with a detailed treatment of terrestrial atmospheric effects and a model of the solar surface velocity field. The resulting simulation allows for the development of a new and successful correction for differential atmospheric extinction generating up to a 25% increase in the signal-to-noise ratio at low frequencies (0.8 to 1.3 mHz). The improvement in signal to noise allows for the detection of low-frequency p modes with small associated errors in frequency and together with the fitting of mode structure, produces estimates of mode linewidth and power. Over the frequency range 972 to 1850 microHz we find the exponent of the frequency-linewidth dependence to be 7.5(0.4).
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14

Xizhou, Zhang, e Yao Jun. "Analysis of Frequency Stabilization and Modulation of Airborne Telemetry Transmitter". International Foundation for Telemetering, 1993. http://hdl.handle.net/10150/608850.

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International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada
This paper analyzes the feature of frequency stability and modulation of airborne telemetry transmitters. According to the characteristic of telemetry information transmission, several methods for frequency stabilization and modulation are briefly compared. Emphasis is given to discuss frequency dividing phase- locked frequency modulation and on-off keying modulation and FM/on- off keying double modulation. With the view of raising frequency stability and modulation sensibility, extending the linear range of modulation, the contradiction between frequency stabilization and modulation should be coordinated properly. In addition, a compatible method between conventional telemetry channel and super fast signal telemetry channel is introduced. A satisfactory result has been acquired with those views and methods used in engineering application.
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15

Qureshi, Fassahat Ullah. "Fast frequency response services for low inertia power systems". Thesis, The University of Sydney, 2019. http://hdl.handle.net/2123/20764.

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Power systems in the world are undergoing a major transformation due to the displacement of conventional synchronous generators (SGs) and increasing penetration of non-synchronous renewable energy sources (NS-RES) in the electricity grids. A computationally efficient analytical tool incorporating FFR services to determine the frequency performance of a low synchronous inertia power system is a major contribution of this thesis. First, we study the impact of high penetration of NS-RES on the frequency stability of the electricity grids. Second, we study the impact of reduced synchronous inertia on the power system stability of the electricity grid. Third, we study the frequency stability of a low inertia power system by means of the time domain simulations. We considered the impact of different grid topologies on the frequency performance of the system because frequency dynamics are also affected by grid topology in a power system. Furthermore, we developed a wind-based FFR service and used that service to improve the frequency stability of a low inertia power system. Finally, we developed a computationally efficient analytical tool incorporating FFR services to improve the frequency stability of a low inertia power system by avoiding computationally expensive simulations. The tool identifies the locations in a low inertia power system that are highly sensitive to the disturbance by computing rate of change of frequency (RoCoF) sensitivities with respect to synchronous inertia for the placement of FFR services in those locations. Hence in this thesis, we have presented both simulation-based and system-theoretic approaches to improve the frequency stability of the FGs by using FFR services that will help policymakers to determine and improve the frequency performance of a low inertia power system.
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16

Diederichs, Benedikt [Verfasser], e Armin [Akademischer Betreuer] Iske. "Sparse Frequency Estimation : Stability and Algorithms / Benedikt Diederichs ; Betreuer: Armin Iske". Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://d-nb.info/1175584649/34.

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Diederichs, Benedikt Verfasser], e Armin [Akademischer Betreuer] [Iske. "Sparse Frequency Estimation : Stability and Algorithms / Benedikt Diederichs ; Betreuer: Armin Iske". Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://nbn-resolving.de/urn:nbn:de:gbv:18-95079.

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18

Schwarzbach, Christoph. "Stability of finite element solutions to Maxwell's equations in frequency domain". Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2009. http://nbn-resolving.de/urn:nbn:de:bsz:105-24780.

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Eine Standardformulierung der Randwertaufgabe für die Beschreibung zeitharmonischer elektromagnetischer Phänomene hat die Vektor-Helmholtzgleichung für das elektrische Feld zur Grundlage. Bei niedrigen Frequenzen führt der große Nullraum des Rotationsoperators zu einem instabilen Lösungsverhalten. Wird die Randwertaufgabe zum Beispiel mit Hilfe der Methode der Finiten Elemente in ein lineares Gleichungssystem überführt, äußert sich die Instabilität in einer schlechten Konditionszahl ihrer Koeffizientenmatrix. Eine stabilere Formulierung wird durch die explizite Berücksichtigung der Kontinuitätsgleichung erreicht. Zur numerischen Lösung der Randwertaufgaben wurde eine Finite-Elemente-Software erstellt. Sie berücksichtigt unter anderem unstrukturierte Gitter, räumlich variable, anisotrope Materialparameter sowie die Erweiterung der Maxwell-Gleichungen durch Perfectly Matched Layers. Die Software wurde anhand von Anwendungen in der marinen Geophysik erfolgreich getestet. Insbesondere demonstriert die Einbeziehung von Seebodentopographie in Form einer stetigen Oberflächentriangulierung die geometrische Flexibilität der Software
The physics of time-harmonic electromagnetic phenomena can be mathematically described by boundary value problems. A standard approach is based on the vector Helmholtz equation in terms of the electric field. The curl operator involved has a large, non-trivial kernel which leads to an instable solution behaviour at low frequencies. If the boundary value problem is solved approximately using, e. g., the finite element method, the instability expresses itself by a badly conditioned coefficient matrix of the ensuing system of linear equations. A stable formulation is obtained by taking the continuity equation explicitly into account. In order to solve the boundary value problem numerically a finite element software package has been implemented. Its features comprise, amongst others, the treatment of unstructured meshes and piecewise polynomial, anisotropic constitutive parameters as well as the extension of Maxwell’s equations to the Perfectly Matched Layer. Successful application of the software is demonstrated with examples from marine geophysics. In particular, the incorporation of seafloor topography by a continuous surface triangulation illustrates the geometric flexibility of the software
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Osborn, Christopher Eric. "Protection, Automation, and Frequency Stability Analysis of a Laboratory Microgrid System". DigitalCommons@CalPoly, 2018. https://digitalcommons.calpoly.edu/theses/1828.

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Due to increasing changes in the power industry, Cal Poly San Luis Obispo's electrical engineering department introduced a set of initiatives to adequately equip students with the skills and knowledge to interact with new technologies. Specifically, the department proposed a microgrid and power systems protection and automation laboratory to strengthen students' knowledge of microprocessor-based relays. This paper outlines a microgrid laboratory system that fulfills the initiative's goal and proposes a collection of laboratory experiments for inclusion in a new laboratory course at Cal Poly. The experiments provide students with practical experience using Schweitzer Engineering Laboratory (SEL) relays and teach fundamental concepts in semi-automated generator synchronization and power system data acquisition. The microgrid laboratory system utilizes SEL relays and a centralized SEL controller to automate frequency regulation through load shedding, power factor correction, generator and utility synchronization, and relay protection group switching.
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20

Hamza, Haval Rawf. "The impacts of high-frequency trading on the financial markets’ stability". Kent State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=kent1428416050.

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Garmroodi, Doiran Mehdi. "Sensitivity Analysis for Future Grid Stability Studies". Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/15978.

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The increasing penetration of converter-interfaced generators (CIGs) has raised concerns about the stability and security of future grids (FGs). These resources affect power systems dynamics in many ways including reducing system inertia, interacting with existing generators, changing power flow paths, etc. In this thesis, we carry out a sensitivity study to explore the structural impacts from CIGs on the damping and frequency stability of power systems. Initially, we study the impact of the intermittent power from wind turbine generators (WTGs) on the damping of the electromechanical oscillations in power systems. It will be shown that the inability of WTGs to provide synchronizing and damping torque to the system jeopardize the small signal stability of power systems. Stable operation regions, in terms of wind penetration and tie-line power, are derived and the impact of load flexibility on these regions are discussed. Next, we have studied the impact of the inertia distribution on the damping of the inter-area modes in power systems. It is shown that tie-line power has a significant role on the damping of the inter-area modes. Moreover, we show that dynamic voltage control and inertia emulation can be utilized to improve the damping of the system. By developing an oscillatory recovery model for power system loads, we have also studied the impact of load oscillations on the damping of the inter-area modes. It is shown that the load dynamics can have a significant influence on the electromechanical oscillations of power systems. Finally, the frequency support capability of WTGs is investigated and the performance of different techniques in utilizing the kinetic energy of the WTGs to assist the frequency stability of power systems is evaluated. A novel time-variable droop characteristic is proposed to enhance the contribution of WTGs in supporting system frequency.
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Andersson, Oskar. "Inclusion of Wind Turbines into Frequency Support Services : Exploring frequency stability issues and comparing regulation power market products". Thesis, Uppsala universitet, Institutionen för elektroteknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-435076.

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There is a trend in Sweden towards increasing the electricity production from renewable energy sources in the electric grid. The increased share of renewables could be seen as essential for Sweden to be able to meet the obligated climate goals. Integration of renewables will enable Sweden to be a progressive part in reducing greenhouse gases and decreasing the global warming. However, one issue with renewable energy sources is the inverter governed production. This, together with the decommission of larger synchronous generators, results in decreasing the inertia and increasing the instability inthe grid.  This thesis is dedicated to elaborating on frequency stability issues and investigating how Variable Speed Wind Turbines (VSWT) could contribute towards stabilized operation when included in frequency support services.  The study is generated through an extensive research process where focus areas are identified. Questions are purposed and then discussed through interviews with experienced people in the field. Estimated power production series from a wind turbine park (WTP) are applied in a constructed model to study the possibilities appearing when  including VSWTs in frequency support services. The income generated from including VSWTs in different regulation power market services is with the model compared against solely procuring the production capacity on the day ahead market. The studied frequency support services are then compared altogether to generate favorable solutions. The study examines both economic as well as technical features of the inclusion of VSWTs in frequency support services.  Results found in the study were that inclusion of wind turbines for power regulation purposes could be seen as increasingly manageable and needed in the electric grid. The maturity of technical solutions alongwith a transition in the regulation power market could be observed as leading factors. The diversification of regulation abilities and the increasing economic incentives in the regulation power market was also found to be important reasons for including wind turbines in the regulation power market. In the study, it was also found thataggregating the power production from several VSWT could increase the ability to deliver the studied services.  It was concluded that inclusion of VSWT in the frequency containment reserve during disturbed operation for down-regulation purposes as well as the fast frequency reserve was the most promising frequency support products for the inclusion of wind turbines. When including battery energy storages and to a larger part managing the durability demands for the services then the frequency contain reserve for normal operation and the frequency containment reserve for disturbed operation for upregulation purposes could be observed as preferable alternatives. Regulation abilities were concluded as achievable with the use of pitch and torque regulation techniques available in the variable speed wind turbine.
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23

Herman, Gregory S. "Terahertz Local Oscillator Via Difference Frequency Generation in III-V Semiconductors Using Frequency Stabilized Lasers". Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/306995.

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Terahertz (THz) heterodyne receiver systems are required by NASA to monitor gas concentrations related to the Earth's ozone depletion. To this end, NASA needs compact, solid state, tunable THz local oscillators. THz LOs have been developed using three means: 1) All-electronic LOs using mixers in combination with Gunn oscillators, 2) Hybrid Photo-electronic LOs using a cw analog of the Auston switch, and 3) All-photonic THz LOs using coherent sources, such as vapor lasers or solid-state Quantum Cascade Lasers, and down converting lasers using nonlinear crystals. In this dissertation, we began with two frequency stabilized Nd:YAG lasers, locked to a common reference cavity, as a starting point to having a stable input into a nonlinear optical frequency conversion system. Following this, we explored the nonlinear crystals useful for THz generation, and the phasematching schemes that could be employed by each. We concluded by settling on highly insulating III-V semiconductor crystals as the proper choice of nonlinear element, and put together a new phasematching method that is most useful for them.
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Háněl, Petr. "Měření frekvenční stability oscilátorů v časové oblasti". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2014. http://www.nusl.cz/ntk/nusl-220360.

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The thesis focuses on measurements of oscillators’ frequency stability. The theoretical part describes the basic concepts of measurement of frequency, measuring systems and measurement errors. The second part of thesis describes the design of measurement system. The design contains all data for build prototype and software, including all source codes.
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Liljeblad, Jonathan F. D. "Biomimetic Membranes: : Molecular Structure and Stability Studies by Vibrational Sum Frequency Spectroscopy". Licentiate thesis, KTH, Surface and Corrosion Science, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-24465.

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In the research presented in this licentiate thesis the surface specific technique Vibrational Sum Frequency Spectroscopy, VSFS, combined with the Langmuir trough has been utilized to investigate Langmuir monolayers and Langmuir-Blodgett (LB) deposited mono- and bilayers of phospholipids. Their molecular structure, stability, and hydration were probed to gain additional understanding of important properties aiming at facilitating the use of such layers as model systems for biological membranes.

VSFS was applied to in situ studies of the degradation of Langmuir monolayers of 1,2-diacyl-phosphocholines with identical C-18 chains having various degrees of unsaturation. The time-dependent change of the monolayer area at constant surface pressure as well as the sum frequency intensity of the vinyl-CH stretch at the C=C double bonds were measured to monitor the degradation. It was shown that a rapid degradation of the monolayers of unsaturated phospholipids occurred when exposed to the laboratory air compared to the fully saturated lipid, and that the degradation could be inhibited by purging the ambient air with nitrogen. The degradation was attributed to oxidation mediated by reactive species in the air.

The molecular structure and order of Langmuir monolayers of 1,2-distearoyl-phosphocholine (18:0 PC) and their hydrating water were investigated at different surface pressures using VSFS. The spectroscopic data indicated a well ordered monolayer at all surface pressures with a more intense signal at higher pressures attributed to the subsequent increase of the number density and more ordered lipid molecules due to the tighter packing. Water molecules hydrating the headgroups or being in contact with the hydrophobic parts were observed and distinguished by their vibrational frequencies, and found to have different average orientations.

Additionally, monolayers of 18:0 PC, its fully deuterated analogue, and 1,2-distearoyl-phosphoserine (18:0 PS) were Langmuir-Blodgett (LB) deposited on CaF2 substrates and VSFS was used to investigate the structure and order of the films as well as the hydrating water. The CH-region, water region, and lower wavenumber region containing phosphate, ester, carboxylic acid, and amine signals were probed to obtain a complete picture of the molecule. The data indicates that all deposited monolayers formed a well ordered and stable film and the average orientation of the aliphatic chains was determined using the antisymmetric methyl stretch.


I forskningen som presenteras i denna licentiatavhandling har den ytspecifika vibrationssumfrekvensspektroskopin, VSFS, använts tillsammans med Langmuirtråget för att studera Langmuir-monolager och Langmuir-Blod-gett (LB) deponerade monolager och bilager av fosfolipider. För att utvidga förståelsen av egenskaper som är viktiga för att underlätta användandet av dem som modellsystem för biologiska membran undersöktes såväl deras molekylära struktur som stabilitet och hydratisering.

VSFS användes för att genomföra in situ-studier av nedbrytningen av Langmuir-monolager av 1,2-diacyl-fosfokoliner med identiska 18 kolatomer långa sidokedjor med varierande antal omättade kol-kol-bindningar. För att övervaka nedbrytningen mättes såväl den tidsberoende förändringen av monolagernas area vid konstant yttryck som sumfrekevensintensiteten från dubbelbindningarnas CH-vibration. När monolagerna bestående av omättade fosfolipider utsattes för laboratorieluften bröts de ner hastigt jämfört med det helt mättade monolagret. Denna nedbrytning som sannolikt orsakades av reaktiva ämnen i luften kunde inhiberas fullständigt genom att ersätta den omgivande luften med kvävgas.

Den molekylära strukturen och ordningen hos Langmuir-monolager av 1,2-distearoyl-fosfokolin (18:0 PC) och deras hydratiseringsvatten undersöktes vid olika yttryck med VSFS. Den spektroskopiska datan visar att monolagerna är välordnade vid alla yttryck samt att sumfrekvenssignalens styrka ökar med ökande yttryck på grund av såväl det större antalet molekyler per ytenhet som den högre ordningen då molekylerna packas tätare. Vattenmolekyler som hydratiserar huvudgrupperna eller är i kontakt med hydrofoba delar och har olika medelorientering observerades och kunde identifieras genom sina vibrationsfrekvenser.

Vidare deponerades monolager av 18:0 PC, dess fullt deuterade analog och 1,2-distearoyl-fofsfoserin (18:0 PS) på substrat av CaF2 och VSFS användes för att undersöka filmernas struktur och ordning såväl som hydratiseringsvattnet. CH- och vattenregionerna samt lågvågtalsområdet som innehåller fosfat-, ester-, karboxylsyra- och aminsignaler undersöktes för att få en fullständig bild av den molekylära strukturen. Data visar att alla deponerade monolager bildade en välordnad och stabil film och kolvätekedjornas medelorientering bestämdes med hjälp av signalen från den antisymmetriska metylvibrationen.


QC 20100924
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26

Laury, John. "Transient Stability in Low Frequency Railways with Mixed Electronic and Rotational Generation". Licentiate thesis, Luleå tekniska universitet, Energivetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26485.

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Abstract (sommario):
Transient stability concerns the ability of a power system to maintain synchronism after a large disturbance. Transient stability plays an important role in guaranteeing operational security and reliability and has been extensively studies for large 50 Hz and 60 Hz transmission systems. However, transient stability of low frequency railway grids has not been properly investigated.As low frequency railway grids operate at another frequency than the public grid, conversion of frequency is needed. This conversion is performed by Rotary Frequency Converters or by Static Frequency Converters. These two types of converters have a different impact on stability. In this thesis, the overall aim is to obtain knowledge on transient stability in low frequency railway grids, with focus on the Swedish synchronous-synchronous railway grid with a mix of Rotary and Static Frequency Converters.The transient stability problem is approached by developing a simplified model of a Static Frequency Converter that can be used for the stability studies in low frequency railways. The Static Frequency Converter is modelled as single phase generator with an equivalent inertia and damping. However as Static Frequency converters cannot handle currents much above their ratings, current limitation is implemented. The current limitation is needed to avoid unnecessary tripping of the converter during fault or other high current situations. With the model developed for a Static Frequency Converter and with a simplified model of a Rotary Frequency Converter, transient stability studies have been performed for several test systems representing the Swedish railway grid.The simulations performed shows the appearance of power oscillations after a large disturbance, between a Static Frequency Converter and a Rotary Frequency Converter when these are operating in parallel. The simulations also showed that the systems studied were stable for realistic values of the fault-clearing time.
Godkänd; 2016; 20160510 (johlau); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: John Laury Ämne: Elkraftteknik/Electric Power Engineering Uppsats: Transient Stability in Low Frequency Railways with Mixed Electronic and Rotational Generation Examinator: Professor Math Bollen, Institutionen för teknikvetenskap och matematik, Avdelning: Energiteknik, Luleå tekniska universitet. Diskutant: Docent Thorsten Schütte, STRI AB, Västerås Tid: Fredag 17 juni, 2016 kl 10.00 Plats: Skellefteå, Luleå tekniska universitet
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27

Warren, Lauren Half Hartmann Marilyn Dina. "Comparing the frequency, overlap, stability, and predictive utility of preclinical dementia constructs". Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2007. http://dc.lib.unc.edu/u?/etd,739.

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Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2007.
Title from electronic title page (viewed Dec. 18, 2007). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Psychology." Discipline: Psychology; Department/School: Psychology.
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28

Brighty, Christopher Charles. "An investigation into the frequency stability of non-oven controlled crystal oscillators". Thesis, Open University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303036.

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29

Jiangnan, Xi. "Frequency Stability Analysis of the Nordic Power Systemwith New Hydropower Governor Settings". Thesis, KTH, Elektriska energisystem, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-179143.

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Abstract (sommario):
The Nordic power system is under continuous development. New productionsources and loads are installed at a high rate and old ones are taken out of operation.This development gradually alters the power system dynamics. The NordicTransmission System Operators (TSOs) have observed that the frequency qualityis gradually decreasing and recognized a number of reasons for this. Theautomatic frequency containment reserve (FCR-N) is in place to keep the electricfrequency within the interval 50 +/- 0.1 Hz during normal operation. Thisfunction is mainly provided by a number of hydropower plants where the turbinegovernor is set to control the discharge in proportion to the measured frequencydeviation. In later years it has been shown that the disturbance damping is verylow in an interval around 1/60 Hz and it is believed that proper tuning of theturbine governors that provide FCR-N can help mitigating this problem. Newregulator settings have been suggested in a recent study performed at Vattenfalland Uppsala University to improve the performance of the FCR-N, yet keepingthe system robust and the wear on participating units at a minimum. It is nowdesired to investigate the possible eects of new governor settings on the overallpower system stability. This thesis work consists of three main parts. First of all, a reduced Nordicpower system model is constructed in Simpow and validated with PMU datafrom the TSO. Secondly, the frequency responses with the newly suggestedgovernor settings have been investigated when introducing a disturbance into thesystem. Thirdly, the eects of the new governor settings on electro-mechanicaloscillations are investigated. In a word, the overall performance for new governorsettings are tested in a large scale power system model in this thesis work.
Det nordiska kraftsystemet ar under standig forandring. Nya produktionskalloroch laster ansluts och gamla tas ur bruk. Detta paverkar gradvis kraftsystemetsdynamik. De nordiska systemoperatorerna (TSOerna) har erfarit att frekvenskvalitetengradvis forsamras, och att det kan nnas era orsaker till detta.Den automatiska primarregleringsreserven (FCR-N) ska halla frekvensen inomintervallet 50 +/-0,1 Hz under normaldrift. Reserven levereras av ett stort antalvattenkraftverk, dar turbinregulatorn reglerar vattenodet genom turbinen proportionelltmot den uppmatta frekvensavvikelsen. Pasenarear har man kunnatvisa att dampningen av storningar med periodtider runt 60 sekunder ar dalig,och man tror att problemet skulle kunna avhjalpas med battre intrimning avturbinregulatorparametrarna. En studie utford pa Vattenfall och Uppsala Universitethar tagit fram ett forslag panya turbinregulatorinstallningar som skaforbattra prestandan i regleringen utan att forsamra systemets robusthet elleroka slitaget pavattenkraftaggregaten. Nu vill man undersoka om de foreslagnainstallningarna kan ha nagon negativ inverkan pakraftsystemets stabilitet. Det har examensarbetet bestar av tre delar. I den forsta delen satts en reduceradmodell av det nordiska elnatet upp i programmet Simpow, och en validering avmodellen gors med hjalp av PMU-data. I den andra delen undersoks frekvenssvaretfran den nya modellen med de foreslagna turbinregulatorinstallningarna. I den tredje delen undersoks de nya turbinregulatorinstallningarnas inverkanpasystemets elektromekaniska oscillationer. Med andra ord satestas i dettaexamensarbete nya turbinregulatorinstallningar i en detaljerad och storskaligkraftsystemmodell.
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30

Rosado, Sebastian Pedro. "Voltage Stability and Control in Autonomous Electric Power Systems with Variable Frequency". Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/29616.

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This work focuses on the safe and stable operation of an autonomous power system interconnecting an AC source with various types of power electronic loads. The stability of these systems is a challenge due to the inherent nonlinearity of the circuits involved. Traditionally, the stability analysis in this type of power systems has been approached by means of small-signal methodology derived from the Nyquist stability criterion. The small-signal analysis combined with physical insight and the adoption of safety margins is sufficient, in many cases, to achieve a stable operation with an acceptable system performance. Nonetheless, in many cases, the margins adopted result in conservative measures and consequent system over designs. This work studies the system stability under large-perturbations by means of three different tools, namely parameter space mapping, energy functions, and time domain simulations. The developed parameters space mapping determines the region of the state and parameter space where the system operation is locally stable. In this way stability margins in terms of physical parameters can be established. Moreover, the boundaries of the identified stability region represent bifurcations of the system where typical nonlinear behavior appears. The second approach, based on the Lyapunov direct method, attempts to determine the region of attraction of an equilibrium point, defined by an operation condition. For this a Lyapunov function based on linear matrix inequalities was constructed and tested on a simplified autonomous system model. In Addition, the third approach simulates the system behavior on a computer using a detailed system model. The higher level of model detail allows identifying unstable behavior difficult to observe when simpler models are used. Because the stability of the autonomous power system is strongly associated with the characteristics of the energy source, an improved voltage controller for the generator is also presented. The generator of an autonomous power system must provide a good performance under a wide variety of regimes. Under these conditions a model based controller is a good solution because it naturally adapts to the changing requirements. To this extent a controller based on the model of a variable frequency synchronous generator has been developed and tested. The results obtained show a considerable improvement performance when compared to previous practices.
Ph. D.
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31

Aramane, Pranav. "Stability Analysis and Design of a Tracking Filter for Variable Frequency Applications". UKnowledge, 2018. https://uknowledge.uky.edu/ece_etds/117.

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The work presented in this thesis is a frequency adaptive tracking filter that can be used in exact tracking of power frequencies and rejection of unwanted harmonics introduced during power disturbances. The power synchronization process includes power converters and other equipment that have many non-linear components that introduce unwanted harmonics. This new design is motivated by the requirement of a filter that can filter all the harmonics and exactly track a rapidly varying fundamental frequency with little time delay and phase error. This thesis analyzes the proposed filter mathematically based on Lyapunov theory and simulations are presented to show the performance of the design in rapid frequency variations.
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32

Obradovic, Danilo. "Coordinated Frequency Control Between Interconnected AC/DC Systems". Licentiate thesis, KTH, Elkraftteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-280156.

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With ambitions of reducing the environmental pollution, power systems integrate larger shares of Renewable Energy Sources (RES) to phase out conventional thermal and nuclear generators. Since RES (such as wind and solar power) are connected to the grid through power electronics devices, they do not inherently contribute to system inertia. With decreasing inertia, the Instantaneous Frequency Deviation (IFD), which follows a power unbalance, is significantly impacted. Frequency Containment Reserves (FCR) are designed to provide a fast dynamic response, counteract power imbalances and stabilize the frequency within a short time interval. Besides inertia, the significant factors affecting frequency behavior are the available amount of FCR and the capability of their fast and stable response. System operators define the list of requirements that a generating unit has to satisfy to participate in FCR. Generators, which are the major part of FCR, have different governors and turbines properties. This study assesses the dynamical performance of typical generators in both open-loop testing and closed-loop varying inertia systems. The goal is to evaluate if specific FCR requirements present a sufficient condition for the desired response, and which governor properties are capable of satisfying them. As an additional, and sometimes necessary, support to FCR, HVDC interconnections are utilized in the form of Emergency Power Control (EPC). This thesis investigates which of the EPC methods performs appropriately in terms of IFD improvement, closed-loop stability, and power and energy provided. The analysis is a continuation from the previous investigation on FCR, and mainly compare two EPC methods related to Nordic Power System (NPS) test case: ramp/step method which is currently implemented in the NPS, and droop frequency-based EPC, proposed by this study for the future operation in the NPS. Apart from ensuring a proper system frequency response, the influence of implemented HVDC supplementary active power control is analyzed to rotor angle stability. In further, this thesis presents a comprehensive analysis of the impact that proposed HVDC supplementary power control has on the linearized dynamics of power systems. By building a generic system, this analytical study is the first of its kind that includes both higher order generator dynamics, and local angle/frequency input of the controller. The methodological approach here analytically formulates the impact the HVDC supplementary control has mainly on the generator synchronizing and damping torque components. The positive impact of the droop frequency-based HVDC power support is highlighted using both single and multi-machine systems. In that way, the implementation of desired droop frequency-based HVDC control to mainly improve system frequency is motivated furthermore. It shows that a proper HVDC supplementary control may impose the various positive impacts for future variable and low inertia scenarios, and ensure a proper power system sustainability.

QC 20200907


multiDC - Advanced Control and Optimization Methods for AC and HVDC Grids
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33

Sharma, Abhinav. "ESTIMATING THE EFFECTS OF BLASTING VIBRATIONS ON THE HIGH-WALL STABILITY". UKnowledge, 2017. https://uknowledge.uky.edu/mng_etds/38.

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The stability of the high-walls is one of the major concerns for open pit mines. Among the various factors affecting the stability of high-walls, blast vibrations can be an important one. In general, worldwide the established respective government regulations and industry standards are used as guidance to determine the maximum recommended levels of the peak particle velocity and frequency from the blast to avoid any effects on the structures around the mining project. However, most of the regulations are meant for buildings or houses and do not concern high-walls. This thesis investigates the response of high-walls under the effects of vibrations from mine blasting. In this research, the relationship between the high-wall response, the geometry of the slope, the frequency and the amplitude, of the ground vibration produced by blasting, is explored using numerical models in 3DEC. The numerical models were calibrated initially with data collected using seismographs installed in a surface mine operation and recording vibrations produced by an underground mine drill and blast operation. Once the calibration was accomplished, a parametric study was developed to explore the relationships between various parameters under study and its impact on the stability of high-walls.
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34

Omer, Khaled A. E. "An in-vitro evaluation of resonant frequency analysis to measure fixed bridge stability". Thesis, University of Liverpool, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.570458.

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Conventional fixed bridge prostheses may fail due to one or more loose retainers, which may be difficult to diagnose. An objective and reproducible investigation to identify, at an early stage, loosening of a retainer could be of significant benefit. The aims of the current series of investigations were to record retrospectively the clinical performance of different types of conventional fixed prostheses used to replace missing teeth and to determine whether Resonance Frequency Analysis (RFA) was capable of measuring bridge stability, in-vitro. One hundred and twenty two patients with 168 bridges were referred to two consultants at the Department of Restorative Dentistry at Liverpool Dental Hospital between Jan 2004 - Dec 2008 with fixed prosthesis problems. Fixed-fixed designs were the most common (77.9%), with cantilever bridges constituting 19.0% of the total. The most frequent cause of failure (39.0%) was associated with a post and core abutment. Apical pathology was found in 20.2%, dental caries in 14.8% and loss of retention in 11.9%. Fixed-fixed bridges were therefore chosen for further study. In-vitro pilot studies were subsequently undertaken to determine the feasibility of using resonance frequency analysis (RFA) on all-metal fixed-fixed bridges affixed to different models (wholly dental stone, or incorporating a simulated periodontal ligament) and to determine a reliable method to record this using an Osstell Mentor apparatus. The use of a buccal approach to record RF A values was validated. Based on the results from the pilot studies and a subsequent power analysis to set sample size, 100 models with standardised acrylic tooth abutment analogues and simulated periodontal ligaments were fabricated. All-metal fixed-fixed bridges were constructed from the first molar to the first premolar using standardised methods on models based with dental stone to mimic 100% (n=SO) or SO% (n=SO) bone support. In each case, two equal groups of 2S specimens had either both retainers cemented, (control group) or the premolar left uncemented (test group) to mimic clinical failure, cemented by a second operator to allow blind analysis. A magnetic component (Smartpeg) was subsequently cemented to the bridge using low-shrink composite resin and the Osstell Mentor used to measure bridge stability expressed as Bridge Stability Quotients (BSQ). The BSQ recorded at the premolar site in both 100% and SO% bone support models demonstrated a highly statistical significant difference (p<0.003) between the control and test groups. ROC analysis determined that a cut-off point was BSQ >60 suggesting that the fixed bridge was stable (cemented to both abutments) whereas a BSQ >59 indicated a risk of the bridge being uncemented to the premolar. All 100% bone support models were subsequently tested to failure in tension using a Universal Testing Machine with a SOO (N) load cell and cross-head speed of 10mm/min. 37% of specimens from the control group debonded at loads between 82 to 120N with the other 63% failing through extraction of the analogue/fracture of the model. 89.2% of the test group specimens failed by extraction of the tooth analogue from one or both ends at loads below SON. Statistical analysis using Kruskal Wallis tests demonstrated that the destructive testing could detect a highly statistically significant difference between the test and control group (P<0.0001) These investigations identified mechanical and biological factors associated with failure of conventional fixed bridges and demonstrated that resonance frequency analysis measurements was able to identify, reliably and non-destructively, stable bridges and those with one retainer uncemented, in-vitro. With further developments of the technique it may be possible to identify fixed-fixed bridge failure clinically and provide appropriate early clinical intervention.
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35

Martínez, Sanz Inmaculada. "Control of AC/DC systems for improved transient stability and frequency support provision". Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/25956.

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Abstract (sommario):
In this thesis, control of future AC/DC systems for improved system dynamic performance is studied. The objective is to determine mechanisms for providing AC network services (e.g. frequency support, damping, etc.) through coordinated control of HVDC power converters and FACTS devices while considering increased levels of wind generation. In particular, this work addresses some of the concerns associated with the stability of the future Great Britain (GB) transmission network as it evolves to support low carbon generation scenarios and the use of DC grids to integrate offshore renewable resources and form a sub-sea interconnection across Europe. The contributions of this thesis are in two main areas: emergency control for power system stabilization and exchange of frequency support across a DC grid. Fast control of FACTS devices and HVDC links can be exercised as a post-fault corrective action to maintain system stability without the need of constraining pre-fault transfer levels. This work employs a model predictive control (MPC) scheme that relies on system wide-area measurements to preserve the system stability after critical contingencies. MPC can explicitly account for system constraints and changing operating conditions and is therefore suited for on-line applications and power electronic actuators with limited short-term overload capability. The effectiveness of the proposed approach is demonstrated using time domain simulations on representative equivalent models of the future GB transmission network. A detailed analysis of the dynamic behaviour and stability issues associated with the GB transmission grid have also been presented. In the DC grid context, this thesis investigates the provision of frequency services considering frequency droop loops in the control of the converters. The interaction between onshore AC systems and a DC grid is analyzed through an extended steady-state formulation. A methodology for providing frequency response from offshore wind farms connected through a DC grid is also proposed. The performance of this scheme is illustrated both analytically and also through simulation results.
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36

FERRARI, MASSIMO. "FINANCIAL STABILITY AND UNCONVENTIONAL POLICIES". Doctoral thesis, Università Cattolica del Sacro Cuore, 2017. http://hdl.handle.net/10280/35715.

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Abstract (sommario):
This thesis explores the relation between fiancial stability and macroeconomic policy. The first chapter tackles the topic of financial stability from the point of wiev of a the single bank. In that model banks take explicitly into account the probability of default of their counterparties on the interbank market. In this way, an endogenous constraint to the credit supply is defined. That constraint evolves along the business cycle. I show that monetary policy alone is not able to ease credit conditions during a crisis. The second chapter nests a complex network model inside a state-of-the-art DSGE model. Using the tools of network analysis it is possible to trace how contagion spreads between banks (i.e. what is the likelihood that the default of one bank spreds to other banks, how many institution are affected) and how its probability avolves following exogenous shocks. With this tool I test partial equilibrium macropolicy tools (i.e. direct lendings to banks) and the effectiveness of monetary policy during crisis. Finally, in the last chapter I analyze, with high frequency data, the impact of conventional and unconventional monetary policy surprises, finding that the response of markets to menetary policy increased over time.
Questa tesi studia la relazione tra stabilità finanziaria e politica economica. Il primo capitolo della tesi affronta l'argomento della stabilità finanziaria dal punto di vista della singola banca. In quel modello ciascuna banca tiene esplicitamente in considerazine la probabilità di insulvenza delle sue controparti sul mercato interbancario. In questo modo si genera un vincolo endogeno all'offerta di credito. Tale vincolo evolve con il ciclo economico. Il modello mostra come la politica monetaria da sola non sia sufficiente a migliorare le condizioni del credito sui mercati finanziari dureante le crisi. Il secondo capitolo inserisce un modello di network all'interno di un mdoello DSGE standard. Analizzando il modello di network è possibile seguire come il contagio si diffonda tra le banche (qual è la probabilità che l'insolvenza di una banca si diffonda ad altre, qaule il numero di istituzioni coinvolte) e come tale probabilità evolva a seguito di shock esogeni. Con questi strumenti è possibile valutare politiche microeconomiche (per esempio prestiti diretti alle banche) e l'efficacia della politica moentaria durante le crisi. Infine, nell'ultimo capitolo, utilizzando dati ad alta frequenza, stimo l'impatto di shock di politica monetaria (convenzionali e non) trovando che la sensibilità dei mercati è aumentanta nel tempo.
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37

FERRARI, MASSIMO. "FINANCIAL STABILITY AND UNCONVENTIONAL POLICIES". Doctoral thesis, Università Cattolica del Sacro Cuore, 2017. http://hdl.handle.net/10280/35715.

Testo completo
Abstract (sommario):
This thesis explores the relation between fiancial stability and macroeconomic policy. The first chapter tackles the topic of financial stability from the point of wiev of a the single bank. In that model banks take explicitly into account the probability of default of their counterparties on the interbank market. In this way, an endogenous constraint to the credit supply is defined. That constraint evolves along the business cycle. I show that monetary policy alone is not able to ease credit conditions during a crisis. The second chapter nests a complex network model inside a state-of-the-art DSGE model. Using the tools of network analysis it is possible to trace how contagion spreads between banks (i.e. what is the likelihood that the default of one bank spreds to other banks, how many institution are affected) and how its probability avolves following exogenous shocks. With this tool I test partial equilibrium macropolicy tools (i.e. direct lendings to banks) and the effectiveness of monetary policy during crisis. Finally, in the last chapter I analyze, with high frequency data, the impact of conventional and unconventional monetary policy surprises, finding that the response of markets to menetary policy increased over time.
Questa tesi studia la relazione tra stabilità finanziaria e politica economica. Il primo capitolo della tesi affronta l'argomento della stabilità finanziaria dal punto di vista della singola banca. In quel modello ciascuna banca tiene esplicitamente in considerazine la probabilità di insulvenza delle sue controparti sul mercato interbancario. In questo modo si genera un vincolo endogeno all'offerta di credito. Tale vincolo evolve con il ciclo economico. Il modello mostra come la politica monetaria da sola non sia sufficiente a migliorare le condizioni del credito sui mercati finanziari dureante le crisi. Il secondo capitolo inserisce un modello di network all'interno di un mdoello DSGE standard. Analizzando il modello di network è possibile seguire come il contagio si diffonda tra le banche (qual è la probabilità che l'insolvenza di una banca si diffonda ad altre, qaule il numero di istituzioni coinvolte) e come tale probabilità evolva a seguito di shock esogeni. Con questi strumenti è possibile valutare politiche microeconomiche (per esempio prestiti diretti alle banche) e l'efficacia della politica moentaria durante le crisi. Infine, nell'ultimo capitolo, utilizzando dati ad alta frequenza, stimo l'impatto di shock di politica monetaria (convenzionali e non) trovando che la sensibilità dei mercati è aumentanta nel tempo.
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38

Hou, Aili. "Analysis of the deflections, vibrations, and stability of leaning arches". Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/45088.

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In recent years, leaning arches have been used in frameworks for some tent structures. Various people have studied the behavior of a single vertical arch; however, only a few researchers have considered the three-dimensional behavior of arches and leaning arches. The objective of this thesis is to analyze the three-dimensional nonlinear behavior of leaning arches, particularly the load-deflection and load-frequency relationships, and to provide a basis for future design guidelines. In this study, vertical arches of different shapes and load combinations are analyzed in order to compare with previous results given by other researchers. Then, the behavior of single tilted arches with different tilt angles is considered. Finally, a leaning arch structure, with two arches inclined to each other and joined at the top, is considered. The load displacement and load-frequency relationships, as well as some buckling modes, are discussed and presented in both tabular and graphical formats.
Master of Science

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39

Showers, Obu Samson. "Enhanced frequency regulation functionality of grid-connected PV system". Thesis, Cape Peninsula University of Technology, 2019. http://hdl.handle.net/20.500.11838/3070.

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Abstract (sommario):
Thesis (MEng (Electrical Engineering))--Cape Peninsula University of Technology, 2019
Electric utilities are confronted with challenges like rising fuel costs, aging equipment, increasing energy demand, frequency regulation and the difficulty to integrate renewable energy resources into the grid. The presence of photovoltaic (PV) penetration on the utility grid is also increasing significantly in recent years. With the recent rise in PV penetration and the advancement of the global PV industry, there is an urgent and a necessary need to introduce features in PV systems that will make them respond smartly. However, much of these can be addressed without negatively affecting the total performance and power quality of the grid. Hence, engaging smart Grid technologies, and leveraging the benefits of the distributed nature of PV, new prospects to unearth value can be created. Through the implementation of progressive energy storage techniques, efficient two-way communications, a grid-tied PV system can create significant value, mostly through improved PV contribution in grid support functions like frequency regulation. An enhanced frequency regulation functioning scheme for a grid-connected photovoltaic (PV) system is modelled in MATLAB/Simulink software environment. The system is designed to operate in grid ancillary services precisely, frequency regulation function. The model consists of a Photovoltaic (PV) plant with a battery connected to the grid through a three-phase inverter. A bi-directional DC-DC converter between the grid and the battery system is included. The model has a battery storage system that provide steady and regular active/reactive powers available while the grid transmit specific amounts of power needed for a specific duration. According to the design, either the grid or the PV system depending on the dominant energy situation charges the battery. The battery is designed to discharge only when the grid demands energy from the PV and if the PV system fails to meet the demanded active power or reactive power. The PV system and the battery storage is integrated with the grid with the aid of dc-ac inverter in such a manner that bi-directional flow of active and reactive power is achieved. A 1 MW PV system is connected to the utility grid through a three-phase voltage source inverter system. The grid nominal frequency is set at 50 Hz under normal operation. However, the frequency decreased when the PV was not producing required power hence, the battery responded almost instantaneously and returned the frequency to the nominal frequency. The effectiveness of battery storage system for utility grid frequency regulation was substantiated from the simulation results attained.
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40

Askari, Behrooz. "An advanced frequency-domain code for boiling water reactor (BWR) stability analysis and design /". Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17720.

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41

Grgic, Biljana. "Influence of the impeller and tank geometry on low-frequency phenomena and flow stability". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0001/MQ34369.pdf.

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42

Eklund, Anders. "Microwave Frequency Stability and Spin Wave Mode Structure in Nano-Contact Spin Torque Oscillators". Doctoral thesis, KTH, Integrerade komponenter och kretsar, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-188546.

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The nano-contact spin torque oscillator (NC-STO) is an emerging device for highly tunable microwave frequency generation in the range from 0.1 GHz to above 65 GHz with an on-chip footprint on the scale of a few μm. The frequency is inherent to the magnetic material of the NC-STO and is excited by an electrical DC current by means of the spin torque transfer effect. Although the general operation is well understood, more detailed aspects such as a generally nonlinear frequency versus current relationship, mode-jumping and high device-to-device variability represent open questions. Further application-oriented questions are related to increasing the electrical output power through synchronization of multiple NC-STOs and integration with CMOS integrated circuits. This thesis consists of an experimental part and a simulation part. Experimentally, for the frequency stability it is found that the slow but strong 1/f-type frequency fluctuations are related to the degree of nonlinearity and the presence of perturbing, unexcited modes. It is also found that the NC-STO can exhibit up to three propagating spin wave oscillation modes with different frequencies and can randomly jump between them. These findings were made possible through the development of a specialized microwave time-domain measurement circuit. Another instrumental achievement was made with synchrotron X-rays, where we image dynamically the magnetic internals of an operating NC-STO device and reveal a spin wave mode structure with a complexity significantly higher than the one predicted by the present theory. In the simulations, we are able to reproduce the nonlinear current dependence by including spin wave-reflecting barriers in the nm-thick metallic, magnetic free layer. A physical model for the barriers is introduced in the form of metal grain boundaries with reduced magnetic exchange coupling. Using the experimentally measured average grain size of 30 nm, the spin wave mode structure resulting from the grain model is able to reproduce the experimentally found device nonlinearity and high device-to-device variability. In conclusion, the results point out microscopic material grains in the metallic free layer as the reason behind the nonlinear frequency versus current behavior and multiple propagating spin wave modes and thereby as a source of device-to-device variability and frequency instability.
Dagens snabba utveckling inom informationsteknik drivs på av ständigt växande informationsmängder och deras samhällsanvändning inom allt från resursoptimering till underhållning. Utvecklingen möjliggörs till stor del hårdvarumässigt av miniatyrisering och integrering av elektroniska komponenter samt trådlös kommunikation med allt större bandbredd och högre överföringshastighet. Det senare uppnås främst genom utnyttjande av högre radiofrekvenser i teknologiskt tidigare oåtkomliga delar av spektrumet. Frekvensutnyttjandet har det senaste årtiondet ökat markant i mikrovågsområdet med typiska frekvenser runt 2.4 GHz och 5.2-5.8 GHz. I den spinntroniska oscillatorn (STO:n) möjliggörs frekvensgenerering i det breda området från 0.1 GHz upp till över 65 GHz av en komponent med mikrometerstorlek som kan integreras direkt i CMOS-mikrochip. Till skillnad från i konventionella radiokretsar med oscillatorer konstruerade av integrerade transistorer och spolar, genereras mikrovågsfrekvensen direkt i STO:ns magnetiska material och omvandlas därefter till en elektrisk signal genom komponentens magnetoresistans. Dessa materialegenskaper möjliggör ett tillgängligt frekvensband med extrem bredd i en och samma STO, som därtill kan frekvensmoduleras direkt genom sin styrström och på så sätt förenklar konstruktionen av sändarsystem. STO:ns icke-linjära egenskaper kan potentiellt också användas för att i en och samma komponent blanda ned mottagna mikrovågssignaler och på så sätt förenkla konstruktionen även av mikrovågsmottagare. STO:ns signalegenskaper bestäms av det magnetiska materialets fysik i form av magnetiseringsdynamik driven av elektriskt genererade spinnströmmar. I denna avhandling studeras denna dynamik experimentellt med särskilt fokus på frekvensstabiliteten i den hittills mest stabila STO-typen; nanokontakts-STO:n. Genom mätningar i tidsdomän av STO:ns elektriska signaler runt 25 GHz har frekvensstabiliteten funnits hänga samman med den typ av icke-linjärt beteende som också funnits vara utmärkande för tillverkningsvariationen i komponenterna. Mikroskopiska undersökningar av materialet visar att en trolig källa till denna variation är den magnetiska metallens uppbyggnad i form av korn i storleksordningen 30 nm, och datorsimuleringar av en sådan materialstruktur har visats kunna reproducera de experimentella resultaten. Därtill har en metod utvecklats för att med röntgenstrålning direkt mäta de små, magnetiska mikrovågsrörelserna i materialet. Denna röntgenteknik möjliggör detaljerade experimentella studier av magnetiseringsdynamiken och kan användas för att verifiera och vidareutveckla den existerande teorin för mikrovågsspinntronik. Sammantaget förs STO-teknologin genom denna studie ett steg närmare sina tänkbara samhällsbreda tillämpningar inom snabb, trådlös kommunikation för massproducerade produkter med integrerad sensor- och datorfunktionalitet.

QC 20160620

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43

Ung, Niklas. "The effects of backlash on the frequency stability in a hydro based power system". Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-235268.

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The generated and consumed power should always be in balance in a power system. Any energy from a power imbalance will be stored as kinetic energy in the system's rotating mass leading to a changed frequency. To keep the frequency within acceptable limits hydropower plants are used to counteract power imbalances. The hydropower plants are however introduc­ing a nonlinearity, namely backlash. This complicates the behavior of the system, e.g. a limit cycle behavior can arise. A limit cycle is a standing oscillation and will force the system to move away from what is desired. Oscillations will cause extra wear and tear in the machinery and prevents the system from keeping the frequency fixed. This thesis investigates when this phenomenon occurs and how different system parameters affect the outcome. The Nordic power system is considered in this report. The system is modeled as a single generator, scaled to the total regulating capacity, and then connected to a simplified model that focuses on the dynamics of the rotating masses. Two different approaches are used. Describing function analysis is used to predict limit cycles in the frequency domain and a time domain approach is used to determine an invariant set for the system that includes possible limit cycles. The latter approach is easily extendible and does not simplify the nonlinearity in contrast with the describing function method. The analysis concludes that limit cycles can occur in the Nordic power system and in a similar low inertia case. It illustrates the difference between two types of feedback and the relation between and a stability margin and the existence of limit cycles. Furthermore, a numerical robustness analysis is performed to study of the robustness of one limit cycle and limit cycle-free solution of the system.
Genererad och konsumerad effekt ska alltid vara lika i ett elektriskt kraftsystem. Energinunder en obalans lagras som kinetisk energi i systemets roterande massor vilket leder till att frekvensen iindras. Fi:ir att bibehalla en stabil frekvens anviinds vattenkraftverk fcir att kom­ pensera fcir skillnaden mellan produktion och konsumtion. Vattenkraftverken har dock i <less mekaniska system ett glapp. Detta komplicerar systemets beteendet och kan gi:ira att syste­ met sjiilvsviinger. Dessa sjiilvsviingningar kallas fcir limit cycles och tvingar systemet att bi:irja sviinga. Konsekvensen blir att mekanisk utrustning slits oni:idigt mycket och att systemet inte bibehaller en stabil frekvens. Denna uppsats undersi:iker niir limit cycles uppstar och hur olika systemparametrar fciriindrar <less beteende. Det nordiska kraftsystemet anviinds i rapporten. Systemet iir modellerat som en ensam generator, skalad till hela systemets reglerstyrka, och sedan kopplat till en simplifierad modell som modellerar dynamiken hos de roterande massor­ na. Tva olika tillviigagangssiitt anviinds. Analys med en beskrivande funktion anviinds fi:ir att fcirutspa limit cycles och en alternativ metod anviinds fcir att hitta ett invariant set som inne­ sluter potentiella limit cycles. Den sistniimnda metoden kan liitt expanderas och simplifierar inte glappet vilket gi:irs i den fi:irstniimnda.Analysen konstaterar att limit cycles kan fi:irekomma i det nordiska kraftsystemet och i ett liknande fall med lag sviingmassa. Den illustrerar iiven skillnaden mellan tva olika aterkopp­ lingar och relationen mellan en stabilitetsmarginal och fi:irekomsten av limit cycles. Vidare analyseras robustheten av en limit cycle och limit cycle fritt beteende genom en numeriskrobusthetsanalys.
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44

Emami, Tooran. "A bridge from stability to robust performance design of PID controllers in the frequency domain". Diss., Wichita State University, 2009. http://hdl.handle.net/10057/2560.

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A graphical technique for finding proportional integral derivative (PID) controllers that stabilize a given single-input-single-output (SISO) linear time-invariant (LTI) system of any order system with time-delay has been solved. In this research, a method is introduced for finding all achievable PID controllers that also satisfy an H sensitivity, complementary sensitivity, weighted sensitivity, robust stability, or robust performance constraint. These problems can be solved by finding all PID controllers that simultaneously stabilize the closedloop characteristic polynomial and satisfy constraints defined by a set of related complex polynomials. There are several key advantages of this procedure. It does not require the plant transfer function model, but depends only on the frequency response. The ability to include the timedelay in the nominal model of the system will often allow for designs with reduced conservativeness in plant uncertainty and an increase in size of the set of all PID controllers that robustly stabilize the system and meet the performance requirements.
Thesis (Ph.D.)--Wichita State University, College of Engineering, Dept. of Electrical Engineering and Computer Science
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45

Perera, Sam Prasanna Kurukulasuriya, e Sumith Ruwan Dharmasiri Kachchakaduge. "SMART VAR Generator to Manage Grid Voltage Stability issue of Low Frequency Switching Photovoltaic Inverters". Thesis, Högskolan i Gävle, Avdelningen för bygg- energi- och miljöteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-20595.

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Solar power, clean and abundant, is considered as a vital contributor in the effort of transforming world energy-mix to pollution-free and natural-regenerative sources.   The solar micro inverters have gained greater visibility during the past several years due to their higher efficiency, greater performances, longer life expectancy and many other benefits. But, integrating small scale [<15kW] renewable energy sources, especially the low frequency switching solar inverters to the low voltage distribution grid has its own challenges due to their inability to generate reactive power to maintain the static voltage stability of the grid. Higher level of solar penetration has identified as a potential cause of low voltage grid instability due to lack of reactive power feeding and their tendency to keep on increasing the voltage higher than grid at the point of common connection [PCC] in order to inject the current to the grid. The studies and experience in voltage stability issues has resulted in introducing many new grid regulations to manage the grid voltage stability throughout the world. The new regulation, VDE-AR-N-4105-2011 is a German grid regulation standard specifically focuses on the low voltage grid connected power generators. This regulation has addressed the reactive power requirements in terms of power factor and supply management to maintain the grid static voltage variation less than 3% at the PCC, when connecting any type of distributed power generators to the low voltage network. This report discuss about the voltage stability issues related to low frequency switching inverters and present a solution to comply with low voltage grid regulation - VDE-AR-N-4105-2011; a SmartVar Generator concept, theory, design and functionality.
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46

Thompson, Fiona Hilary. "Changing flood frequency in Scotland : implications for channel geomorphology, ecology and management". Thesis, University of Plymouth, 2017. http://hdl.handle.net/10026.1/9667.

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The effect of climate on the fluvial system has long been investigated due the significant impact it can have on a river’s hydrological regime and fluvial processes. In recent years this interest has increased as global changes in climate are expected to bring more frequent high magnitude flood events globally and to North West Europe in particular. Despite the knowledge that the frequency and magnitude of floods is to increase, less is known about the geomorphological implications of this for river channels and where channel instability is likely to occur at both the river network and national scale. This is certainly the case in Scotland where increased flooding is expected and large floods have been abundant over the last two decades. To manage Scottish river catchments effectively in the future, in terms of hazard mitigation and nature conservation, river managers need to be able to predict not only how climate will impact flood magnitude and frequency in Scotland but the effect these changes will have on the internal dynamics of river channels in terms of erosion, sediment transport and deposition, and morphological dynamics. Such knowledge will ensure adequate measures are implemented to reduce fluvial risks to humans and to maintain and preserve valuable river habitats and linked species. In this thesis, several novel methods incorporating field, laboratory and GIS-based analysis, have been investigated as a means of predicting how climate change will affect channel stability in Scottish rivers and the implications of this for river management and river ecology. This includes (i) analysing the potential change in the frequency of geomorphologically-active flood flows with climate change; (ii) the use of stream power thresholds to predict changes in channel stability on a national scale with climate change; and (iii) using a Digital River Network developed using geospatial data to predict changes in the rate of bedload transfer and channel stability with climate change. Studies were undertaken on 13 different rivers across Scotland from north to south and east to west. vii As a case study of ecological implications, the thesis also examines how changes in habitat and stability of freshwater pearl mussels (Margaritifera margaritifera) may be altered by increased flooding. Predictions of the frequency of geomorphic activity, channel stability, rate of bedload transfer, and the stability of freshwater pearl mussel habitat with climate change are discussed along with the methods used to obtain these outcomes. The results all suggest an increase in the frequency and rate at which bedload is transferred through the river system and an increased frequency of flood flows resulting in greater channel instability. Morphological responses vary spatially with some river reaches experiencing greater increased erosion and transport potential than others. Climate change effects on the freshwater pearl mussel are: increased occasions of disturbance and transport downstream and the importance of specific populations in more stable environments for ensuring population recovery post flooding is highlighted. It is hoped that the methodologies developed for predicting changes in channel stability with climate change will provide useful screening tools to regulatory agencies which can be developed further to assist management decisions in the future which aim to reduce fluvial hazards and maintain good quality river environments for the species that inhabit it. The approaches used in this study allow for the identification of areas at high risk of morphological and ecological change, and the pro-active planning and management of sediment-related river management issues and nature conservation.
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Sjölund, Maria. "Development and Stability of Antibiotic Resistance". Doctoral thesis, Uppsala University, Clinical Bacteriology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4523.

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Antibiotic resistance is of current concern. Bacteria have become increasingly resistant to commonly used antibiotics and we are facing a growing resistance problem. The present thesis was aimed at studying the impact of antibiotic treatment on pathogenic bacteria as well as on the normal human microbiota, with focus on resistance development.

Among the factors that affect the appearance of acquired antibiotic resistance, the mutation frequency and biological cost of resistance are of special importance. Our work shows that the mutation frequency in clinical isolates of Helicobacter pylori was generally higher than for other studied bacteria such as Enterobacteriaceae; ¼ of the isolates displayed a mutation frequency higher than Enterobacteriaceae defective mismatch repair mutants and could be regarded as mutator strains.

In H. pylori, clarithromycin resistance confers a biological cost, as measured by decreased competitive ability of the resistant mutants in mice. In clinical isolates, this cost could be reduced, consistent with compensatory evolution stabilizing the presence of the resistant phenotype in the population. Thus, compensation is a clinically relevant phenomenon that can occur in vivo.

Furthermore, our results show that clinical use of antibiotics selects for stable resistance in the human microbiota. This is important for several reasons. First, many commensals occasionally can cause severe disease, even though they are part of the normal microbiota. Therefore, stably resistant populations increase the risk of unsuccessful treatment of such infections. Second, resistance in the normal microbiota might contribute to increased resistance development among pathogens by interspecies transfer of resistant determinants.

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48

Zhang, Yang. "Design of wide-area damping control systems for power system low-frequency inter-area oscillations". Online access for everyone, 2007. http://www.dissertations.wsu.edu/Dissertations/Fall2007/y_zhang_112007.pdf.

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49

Fioravanti, André. "H∞ analysis and control of time-delay systems by methods in frequency domain". Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00627352.

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This thesis addresses the H∞ analysis and control of continuous commensurate time-delay systems by frequential methods. First, the asymptotic behavior of the chains of poles are studied, and the conditions of stability for neutral systems with poles approaching the imaginary axis are given. The same analysis is done for fractional systems. In the sequel, a numerical method able to locate all the stability windows as well as the unstable root-locus for classical and fractional system is given. We conclude the analysis part by providing the stability crossing curves of a class of distributed delay system. Starting the synthesis part, we design PID controllers for unstable fractional systems using a small-gain theorem approach. Finally, using the Rekasius substitution, we construct a linear time invariant comparison system that allows us to get information about stability and H∞-norm for classical time-delay systems. Using this approach it is possible to design state and output feedback controllers, as well as linear filters for this class of systems.
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50

Goldhacker, Markus [Verfasser], e Elmar [Akademischer Betreuer] Lang. "Frequency-resolved dynamic functional connectivity and scale stability of connectivity-states / Markus Goldhacker ; Betreuer: Elmar Lang". Regensburg : Universitätsbibliothek Regensburg, 2017. http://d-nb.info/1124679944/34.

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