Real-time load-side control of electric power systems

Two trends are emerging from modern electric power systems: the growth of renewable (e.g., solar and wind) generation, and the integration of information technologies and advanced power electronics. The former introduces large, rapid, and random fluctuations in power supply, demand, frequency, and voltage, which become a major challenge for real-time operation of power systems. The latter creates a tremendous number of controllable intelligent endpoints such as smart buildings and appliances, electric vehicles, energy storage devices, and power electronic devices that can sense, compute, communicate, and actuate. Most of these endpoints are distributed on the load side of power systems, in contrast to traditional control resources such as centralized bulk generators. This thesis focuses on controlling power systems in real time, using these load side resources. Specifically, it studies two problems.

(1) Distributed load-side frequency control: We establish a mathematical framework to design distributed frequency control algorithms for flexible electric loads. In this framework, we formulate a category of optimization problems, called optimal load control (OLC), to incorporate the goals of frequency control, such as balancing power supply and demand, restoring frequency to its nominal value, restoring inter-area power flows, etc., in a way that minimizes total disutility for the loads to participate in frequency control by deviating from their nominal power usage. By exploiting distributed algorithms to solve OLC and analyzing convergence of these algorithms, we design distributed load-side controllers and prove stability of closed-loop power systems governed by these controllers. This general framework is adapted and applied to different types of power systems described by different models, or to achieve different levels of control goals under different operation scenarios. We first consider a dynamically coherent power system which can be equivalently modeled with a single synchronous machine. We then extend our framework to a multi-machine power network, where we consider primary and secondary frequency controls, linear and nonlinear power flow models, and the interactions between generator dynamics and load control.

(2) Two-timescale voltage control: The voltage of a power distribution system must be maintained closely around its nominal value in real time, even in the presence of highly volatile power supply or demand. For this purpose, we jointly control two types of reactive power sources: a capacitor operating at a slow timescale, and a power electronic device, such as a smart inverter or a D-STATCOM, operating at a fast timescale. Their control actions are solved from optimal power flow problems at two timescales. Specifically, the slow-timescale problem is a chance-constrained optimization, which minimizes power loss and regulates the voltage at the current time instant while limiting the probability of future voltage violations due to stochastic changes in power supply or demand. This control framework forms the basis of an optimal sizing problem, which determines the installation capacities of the control devices by minimizing the sum of power loss and capital cost. We develop computationally efficient heuristics to solve the optimal sizing problem and implement real-time control. Numerical experiments show that the proposed sizing and control schemes significantly improve the reliability of voltage control with a moderate increase in cost.

Switching Patterns and Steady-State Analysis of Grid-Connected and Stand-Alone Single-Stage Boost-Inverters for PV Applications

Renewable or sustainable energy (SE) sources have attracted the attention of many countries because the power generated is environmentally friendly, and the sources are not subject to the instability of price and availability. This dissertation presents new trends in the DC-AC converters (inverters) used in renewable energy sources, particularly for photovoltaic (PV) energy systems. A review of the existing technologies is performed for both single-phase and three-phase systems, and the pros and cons of the best candidates are investigated. In many modern energy conversion systems, a DC voltage, which is provided from a SE source or energy storage device, must be boosted and converted to an AC voltage with a fixed amplitude and frequency. A novel switching pattern based on the concept of the conventional space-vector pulse-width-modulated (SVPWM) technique is developed for single-stage, boost-inverters using the topology of current source inverters (CSI). The six main switching states, and two zeros, with three switches conducting at any given instant in conventional SVPWM techniques are modified herein into three charging states and six discharging states with only two switches conducting at any given instant. The charging states are necessary in order to boost the DC input voltage. It is demonstrated that the CSI topology in conjunction with the developed switching pattern is capable of providing the required residential AC voltage from a low DC voltage of one PV panel at its rated power for both linear and nonlinear loads. In a micro-grid, the active and reactive power control and consequently voltage regulation is one of the main requirements. Therefore, the capability of the single-stage boost-inverter in controlling the active power and providing the reactive power is investigated. It is demonstrated that the injected active and reactive power can be independently controlled through two modulation indices introduced in the proposed switching algorithm. The system is capable of injecting a desirable level of reactive power, while the maximum power point tracking (MPPT) dictates the desirable active power. The developed switching pattern is experimentally verified through a laboratory scaled three-phase 200W boost-inverter for both grid-connected and stand-alone cases and the results are presented.

Acceptance of smartphone-based mobile shopping:mobile benefits, customer characteristics, perceived risk and the impact of application context

Despite their generally increasing use, the adoption of mobile shopping applications often differs across purchase contexts. In order to advance our understanding of smartphone-based mobile shopping acceptance, this study integrates and extends existing approaches from technology acceptance literature by examining two previously underexplored aspects. Firstly, the study examines the impact of different mobile and personal benefits (instant connectivity, contextual value and hedonic motivation), customer characteristics (habit) and risk facets (financial, performance, and security risk) as antecedents of mobile shopping acceptance. Secondly, it is assumed that several acceptance drivers differ in relevance subject to the perception of three mobile shopping characteristics (location sensitivity, time criticality, and extent of control), while other drivers are assumed to matter independent of the context. Based on a dataset of 410 smartphone shoppers, empirical results demonstrate that several acceptance predictors are associated with ease of use and usefulness, which in turn affect intentional and behavioral outcomes. Furthermore, the extent to which risks and benefits impact ease of use and usefulness is influenced by the three contextual characteristics. From a managerial perspective, results show which factors to consider in the development of mobile shopping applications and in which different application contexts they matter.

How much are translation studies in debt to Soren Kierkegaard?

The significance of Jacques Derrida's philosophical contribution to translation studies is becoming more widely acknowledged, thanks to authors such as Lawrence Venuti, Kaisa Koskinen, Rosemary Arrojo, Lieven Tack and africa Vidal Claramonte. However, what remains unknown is the debt which Derrida owes to the thinking of SOren Kierkegaard. This article sets out this legacy for the purposes of presenting some basic principles of deconstruction and in order to further promote its dissemination in the area of translation studies. At the same time, this article aims to be both a tribute to the Danish philosopher and a recognition of his contribution to modern-day thinking. Ultimately, the objective of this piece of research is to demonstrate how the ramifications of Kierkegaard's ideas are still relevant and, to a certain extent, are present in the area of translation studies. Among other things, this article shows how notions which are so fundamental to Kierkegaardian thinking, such as subjectivity', decision', instant' or impossible' echo in several recent texts regarding translation studies.

Efectos de una intervención educativa en la promoción de la actividad física, los conocimientos y comportamientos saludables para la prevención del cáncer colorrectal en jóvenes de una institución educativa secundaria en Bogotá Colombia

El cáncer colorrectal es un serio problema de salud pública a nivel mundial. Evidencias epidemiológicas han sugerido que al menos el 50% de la enfermedad puede ser prevenida mediante un estilo de vida saludable. Las intervenciones educativas surgen como una herramienta clave de movilización social para la prevención y han sido sugeridas desde las autoridades nacionales para el control del cáncer en el país.

Repensar=Reutilizar. o abandono como oportunidade. Fábrica Robinson: o instante na construção de um tempo provisório

Esta investigação procura mostrar/problematizar programas que questionem a reutilização de lugares, através de uma proposta de projeto provisório de arquitetura, no panorama do Património Industrial, num processo de revitalização. O intuito é procurar modelos/ações que possam responder às transformações, partindo do problema do abandono, dos espaços pós-industriais. O objetivo principal consiste em criar um processo de aproximação à problemática da reutilização cujo processo de elaboração de projeto encontra nas suas formas de produção e operação um discurso que faz a síntese entre prática artística, posição curatorial e arquitetura, na elaboração de um programa para um lugar revitalizando-o. O objeto deste estudo faz parte de uma investigação de pesquisa por projeto e encontra lugar no conjunto arquitetónico da Fábrica Robinson, em Portalegre, cuja apropriação inicial de parte do Convento de S. Francisco dá hoje lugar ao Espaço Robinson. O reconhecimento deste conjunto, como lugar de encontro entre um passado recente e um futuro pendente, marcou a proposta projetual. Proposta de projeto temporário cujo conceito estabelece a viabilidade de apropriação como forma de atuação provisória, subjacente ao ato de reutilizar, criando novos programas de ocupação, promovendo novas ideias e definições de património e assim devolvendo o significado às estruturas industriais vazias. O que preservar e como conservar pode demarcar a importância de salvaguarda deste património e a previsão da sua transmissão para o futuro, fixada pela ideia de preservação. A Fábrica Robinson e a revitalização urbana deste espaço configura, hoje, uma nova oportunidade para estes conjuntos arquitetónicos, e a importância da sua salvaguarda, na valorização do Património Industrial. O trabalho pretende demonstrar a ordem de relação entre programa e lugar no debate interdisciplinar e a hipótese de concretização projetual que preencha um vazio temporalmente suspenso; ABSTRACT: Rethinking = Reuse: The abandonment as opportunity Robinson Factory: The instant in the construction of a provisory time This research aims to show architectural programs that question the reuse of places in the context of industrial heritage, through an architectural design, in a revitalization process. The aim is to look to models / actions that, starting with the abandonment problem, may answer to the post-industrial spaces transformations. The main goal is to create an approximation process to the problem of reuse, whose project design process finds in its production and operations forms a symbiosis between artistic practice, curatioral approach and architecture, in the development of a program to revitalize a place. The object of this study is part of a research project / research by design concerning the architectural complex Fábrica Robinson located in Portalegre, whose original appropriation of part of Convento de S. Francisco is today occupied by Espaço Robinson. The acknowledgment of this complex as a space placed in-between a recent past and a pending future marked the design proposed. A temporary design proposal whose concept establishes the validity of the temporary action, underlying to the act of reuse, creating new occupation programs, promoting new ideas and heritage definitions and thus given back meaning to the empry industrial structures. What to preserve and how to save may mark the importance of safeguarding this heritage and the prediction of its transmission to the future, set by the idea of preservation. The Fábrica Robinson and the urban regeneration of this area sets itself as a new opportunity to safeguard these architectural ensembles and enhance the value of the industrial heritage. This study intend to show the relationship between the program and a vacant place, through a temporary proposal, supported by the interdisciplinary debate and the hypothesis of design implementation that completes a void temporarily suspended.