Dissertations / Theses on the topic 'Dynamic behavior of power grids'

This thesis presents research results on the effects of tap changing dynamic modeling on power system mid-to-long term voltage behavior. The modeling of tap changing dynamics in voltage stability studies is first addressed. The dynamic operation of an on-load-tap—changing transformer is represented by a highly nonlinear, discrete and time—delay embedded model, which is suitable to mid-to—long term voltage stability studies. Different discrete tap models and their continuous approximations with respect to time and tap position are introduced. The initial emphasis is on studying the influences of different discrete and continuous tap models on voltage stability properties. Combining the tap changer dynamics with the detailed load dynamics, the impacts of different tap models on system voltage behavior are illustrated via theoretical analysis and simulation. It is shown that different stability regions are associated with different continuous tap models and significantly influence the system/voltage behavior, especially under heavily loaded system conditions. The Lyapunov stability method is used to predict the stability region. Limit cycle phenomena are observed in systems with discrete tap models due to the inherent nonlinearities present in these models, the tap dynamics and its interaction with the load dynamics. Conditions for existence of limit cycles are derived via the describing function method. Cases when discrete tap models and their corresponding continuous approximations result in different and / or similar system behavior are also illustrated. Further, a detailed study is given on. the voltage oscillation phenomenon in power systems with on-load—tap—changers. Two kinds of oscillations are considered, namely the well-known voltage oscillations due to tap hunting and oscillations due to tap— load interactions. The focus is on the limit cycle caused by the tap-load interaction. The effects of tap deadband and other parameters such as tap delay time and load recovery time on the existence of system cyclic behavior are carefully investigated. It. is shown that whether or not the limit cycle can be avoided by adjusting the tap deadband depends mainly on the load characteristics. Trajectory sensitivity analysis offers useful information on the influence of parameters on system cyclic behavior. Next, consideration is given to the coordination of a tap changer, as a voltage control device, with other controls, such as a switching capacitor. Using the results of voltage stability analysis as a framework, a new approach for the coordination of dissimilar control actions is derived for arresting voltage collapse. The benefits of coordination of tap locking and capacitor switching are demonstrated foi two possible situations. Firstly, prior capacitor switching at some buses is shown to expand the stability regioh and provide sufficient time for successful tap locking. Secondly, locking taps at some buses can slow the system deterioration and provides time for capacitor switching. The results obtained not only highlight the importance of tap dynamics modeling in voltage behavior studies, but also give an insight into system voltage stability evaluatiofi and control involving on—load-tap—changer dynamics.

Current power systems have remained qualitatively similar to how the were in the last century, especially with respect to the interaction with the end-users. Though present global challenges are putting pressure and questioning their architecture. The increasing demand for electricity - that has become an essential commodity, fundamental for all activities of today's lifestyle - coupled with the concerns about climate change and the need to improve the quality and reliability of the provision urge a modernization of the network. A modernization that needs: to be low carbon, to be reliability and security improving, and to develop new models of customer relationship. Indeed, the thesis deals with important issues that are today in the limelight, such as: i) the importance of the electricity sector in the implementation of climate change mitigation strategies, ii) the innovation of the electricity network as a strategy for reducing emissions, iii) the design of new policies of management of renewable energies and of the new services available, iv) the need to actively involve the users of the network into new styles of consumption / production of energy. All of this is evaluated in a context of evolving energy policies, where the relative long-term importance of the different power generating technologies is changing, especially after the recent events in Japan. The thesis aims at demonstrating the need to promote a qualitative transformation in the system architecture of the “grid” to make it suitable for managing the complexity of the economic scenarios and advanced services that characterize the emerging “knowledge society”, in compliance with the objectives of environmental sustainability and in response to concerns about global climate change. Indeed, because of these concerns and of social and political acceptability issues of nuclear power, as we know it today, the energy scenarios for the next few decades see the emergence of an increasingly important role for renewable energy sources. The general assumption of the thesis is that such a change in the sources of production is likely to cause a major qualitative leap in the power grid. This transformation may induce the evolution of the electricity grid from a classical architecture, top-down and hierarchical, to a more innovative architecture, that will configure the grid (more and more) as a “social ecosystem”, able to include the empowerment of all its stakeholders and to enhance, in particular, the more active role of all users of the new network services. To demonstrate and operationalize the complex nature of this change and the emerging trends, the thesis is organized into three integrated papers that develop and disentangle the system effects of the two technologies that today seem to be at the basis of the possible evolution: Super-Grids and Smart-Grids. The analysis will be conducted using a qualitative-quantitative methodological approach through simulations for both technologies and their integration. The first paper - New electricity generation networks and climate change: the economic potential of national and trans-national super-grids powered by Concentrated Solar Power - develops the analysis of Super-Grids. More in detail, it analyses the system effects and the technological and economic opportunities of transmitting large amounts of electricity over long distances, for the stabilization of anthropogenic emissions of greenhouse gases, with particular attention to the resulting geopolitical dynamics. The analysis is conducted using the simulation platform WITCH, an Integrated Assessment Model (IAM), able to compare this option with other mitigation opportunities, in a framework of intertemporal optimization of resources. In particular, the focus is on the production of electricity from concentrated solar power (CSP) in areas of high solar intensity in places located far from demand centres and, until now, not economically advantageous. The quantitative analysis focuses on the electricity supply made available by the Super-Grid - both domestically and for export/import - evaluating their economic, technological and CO2 mitigation potentials. We have analyzed, in particular, the EU-MENA trade case, though, the results can be expanded qualitatively to consider also the North-South European energy axis, extending the analysis of the geopolitical implications. The second paper - Smart-Grids and Climate Change. Consumer adoption of smart energy behaviour: a system dynamics approach to evaluate the mitigation potential - develops the analysis of Smart-Grids. More in detail, it analyses the system effects of engaging with consumers. More specifically, it looks at the impacts of allowing consumers to: (i) manage more actively and consciously their consumption patterns; (ii) participate to innovative contracting; (iii) generate electricity for own consumption and /or to inject into the grid. Particular interest is directed to the increase in variety of user behaviour (shift, demand response, home automation, generation), caused by the implementation of Smart-Grids, which allows: (i) to form new relationships among actors of the network, (ii) to trigger new processes of “micro production” for energy self-sufficiency to be integrated into the network; and to (iii) improve the management and optimization of the power network. In short, to transform the network into a “sensitive network” capable of opening new organizational spaces/times of action. The analysis is conducted by means of simulations of the adoption dynamics of “smart energy behaviours” by citizens, using the methodology of System Dynamics (J. Forrester) to address the complexity of the dynamics involved. The quantitative analysis focuses on the power supply made available by the change in consumption patterns and by domestic generation, in a “energy self-sufficiency” perspective and on the impacts in terms of demand, system costs and opportunities for mitigation. The qualitative analysis studies the organizational transformations, and the social and cultural evolutions induced by the new interactivity with the end-user The concept of Smart Grid connects the power system to the emerging qualitative transformations and scenarios of the “Knowledge Society” and its newly empowered “Smart Prosumer”. In the third paper - Super & Smart Grid integrated investment scenarios: Green Sustainable Energy Management Strategies & Scenarios - the complex effects of Super and Smart Grid are analysed together. The paper is divided in two parts: the first one where Super and Smart Grids are integrated in one simulation environment to conduct an in-depth economic analysis, and the second part where they are jointly evaluated and compared considering the effects of the innovation of the electricity grid on different levels: environmental, technological, economic, organizational, social and geopolitical, by means of the GEMS (Green Energy Management Strategies foe sustainable scenarios) multi-level evaluation function: GEMS = (Env, Tech, Ec, Org, Soc, GeoP). The proposal is to identify an approach for the analysis and management of the various strategies of green energy generation, that is able to grasp the complexities and interactions of the multiple effects induced by the different options. The quantitative analysis focuses on the integration of the power supply made available jointly by Super and Smart Grids. The qualitative analysis has investigated the new dynamics of empowerment among all the stakeholders involved and the possible impacts on various levels. The synergies of system integration, related to the potential mix of Super and Smart Grids, to manage the evolution of green electricity are also analysed. Concluding, the thesis started with a substantial economic and computational approach, and then was expanded to take into account qualitative aspects that govern the dynamics of the complex “social ecosystem” in play. In synthesis, we analyze the quali-quantitative system effects induced by the impact of the innovation processes in the power network, in an energy market that is not able, alone and in a classical economic perspective, to jointly optimize aspects concerning the environment, technology, organizational structures, economics, society and geopolitics, that are put into play by the introduction of these technological options. These tools are also needed to manage the inevitable conflicts of interest that will arise with the change. We propose an approach “beyond grid parity”, in the sense that we aim at analyzing a broader concept of “costs”, to: (i) identify the paths of evolution of the electrical system in the scenarios of the knowledge society, (ii) the nature and extent of the processes involved, and (iii) to assess the feasibility of accepting the challenge of a low-carbon economy based on renewable energy.

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California<br>Data collected during July 1999 at Edwards EAFB by the Advanced Range Telemetry (ARTM) program is examined to characterize the dynamic behavior of multipath interference in an aeronautical telemetry channel. Multipath fade events are analyzed in the frequency domain to show how these fades appear, evolve, and disappear from the channel. A channel model and examples from the channel sounding data are used to show the dynamic nature of these fade events. The Doppler power spectrum is used to quantify the exact time-varying nature of the multipath fade events. The coherence time, or the amount of time the channel can be viewed as unchanging, is obtained from the Doppler power spectrum and is calculated to be 100 ms in the data sets examined in this paper. This implies that adaptive multipath mitigation techniques must have an adaptation bandwidth of 10 Hz.

Ce travail de recherche a été principalement motivé par les avantages importants apportés par la technologie UTBB FDSOI aux applications analogiques et RF de faible puissance. L'objectif principal est d'étudier le comportement dynamique du transistor MOSFET du type UTBB FDSOI et de proposer des modèles prédictifs et des recommandations pour la conception de circuits intégrés RF, en mettant un accent particulier sur le régime d'inversion modérée. Après une brève analyse des progrès réalisés au niveau des architectures du transistor MOSFET, un état de l’art de la modélisation du transistor MOSFET UTBB FDSOI est établi. Les principaux effets physiques impliqués dans le transistor à double grille avec une épaisseur du film de 7 nm sont passés en revue, en particulier l’impact de la grille arrière, à l’aide de mesures et de simulations TCAD. La caractéristique gm/ID en basse fréquence et la caractéristique ym/ID proposée pour la haute fréquence sont étudiées et utilisées dans une conception analogique efficace. Enfin, le modèle NQS haute fréquence proposé reproduit les mesures dans toutes les conditions de polarisation y compris l’inversion modérée jusqu’à 110 GHz<br>This research work has been motivated primarily by the significant advantages brought about by the UTBB FDSOI technology to the Low power Analog and RF applications. The main goal is to study the dynamic behavior of the UTBB FDSOI MOSFET in light of the recent technology advances and to propose predictive models and useful recommendations for RF IC design with particular emphasis on Moderate Inversion regime. After a brief review of progress in MOSFET architectures introduced in the semiconductor industry, a state-of-the-art UTBB FDSOI MOSFET modeling status is compiled. The main physical effects involved in the double gate transistor with a 7 nm thick film are reviewed, particularly the back gate impact, using measurements and TCAD. For better insight into the Weak Inversion and Moderate Inversion operations, both the low frequency gm/ID FoM and the proposed high frequency ym/ID FoM are studied and also used in an efficient first-cut analog design. Finally, a high frequency NQS model is developed and compared to DC and S-parameters measurements. The results show excellent agreement across all modes of operation including very low bias conditions and up to 110 GHz