Thesis (M.S.C.I.T.)--Regis University, Denver, Colo., 2005. / Title from PDF title page (viewed on Dec. 5, 2005). Includes bibliographical references.

In conventional centralized power systems, power is generated mostly by large synchronous generators (SGs), where the frequency of the grid depends on the rotational frequency of the prime mover. If there are any sudden changes in the load, the rotor inertia property restrains the changes in frequency and keeps the system stable. During transient periods, rotor kinetic energy of the rotor is injected into the grid to balance power supply between generation and load. With the recent high penetration of renewable energy sources (RES), the power grid is undergoing structural changes with an increased inverter-based distributed generation. Since inverter based power sources do not have inertia as conventional synchronous machines (SM), high penetration of inverters may cause instability and sharp voltage fluctuations in the grid. If inverter based power sources could be configured as regular SM by introducing virtual inertia and damping property, many of the problems, such as frequency regulation, islanded operation, and parallel operation of inverter-based DGs will be resolved. This thesis investigates mathematical modeling and control of VSG’s to emulate the inertia and damping property of SMs. Simulation results are presented on the modeling and closed-loop performance of VSGs for an island microgrid. / Electrical and Computer Engineering

Because renewable energy sources are environment-friendly and inexhaustible, more and more renewable energy power plants have been integrated into power grids worldwide. To compensate for their inherent variability, STATCOMs are typically installed at the point of common coupling (PCC) to help their operation by regulating the PCC voltage. However under different contingencies, PCC voltage fluctuations in magnitude and frequency may impede the STATCOM from tracking the grid frequency correctly, hence worsening its overall compensation performance, and putting at risk the operation of the power plant. Further, the virtual synchronous machine (VSM) concept has recently been introduced to control grid-connected inverters emulating the behavior of rotating synchronous machines, in an effort to eliminate the shortcomings of conventional d-q frame phase-locked loops (PLL). In this dissertation, the VSM concept is extended by developing a STATCOM controller with it, which then behaves like a fully-adjustable synchronous condenser, including the adjustment of its "virtual" inertia and impedance. An average model in two D-Q frames is proposed to analyze the inherent dynamics of the VSM-based STATCOM controller with insight into impacts from the virtual parameters and a design guideline is then formulated. The proposed controller is compared against existent d-q frame STATCOM control strategies, evincing how the VSM-based approach guarantees an improved voltage regulation performance at the PCC by adjusting the phase of its compensating current during frequency fluctuations, in both simulation and experiment. Secondly, the dynamics of the VSM-based STATCOM controller in large signal sense is studied, especially its capability to ride through faults. Analysis is carried out with phasors to obtain a fundamental understanding at first and followed by state space equations to predict the transients analytically, which is validated by matching both simulation and experiment. The effects of two outer loops are also reviewed and some possible solutions are suggested and evaluated. Moreover, the relationship between the virtual inertia and the actual inertia is established and the dc capacitor sizing is discussed in a possibly more economical way. The start-up process of a VSM-based STATCOM is presented to implement a practical prototype as well. / Master of Science

published_or_final_version / Electrical Engineering / Master / Master of Science in Engineering

Synchronous interaction between adolescent mothers with preterm infants in the Neonatal Intensive Care Unit was examined in this study. Understanding the characteristics of synchrony in adolescent mother and premature infant interactions during this early period in the development of the relationship provides direction for the development of nursing strategies to foster synchronous interaction in the neonatal intensive care unit (NICU) setting and, subsequently, positive developmental outcomes for preterm infants. The research design was a one-group, pretest-posttest, exploratory intervention assessing synchronous interaction using the Nursing Child Assessment Feeding Scale (NCAFS) among 27 adolescent mothers and their premature infants in the NICU. The study examined the differences in adolescent mother-premature infant interaction in the NICU environment prior to an intervention and within 48 hours after receiving the Preterm Infant Cues Intervention (PICI). Additional variables including stress, social support, age of the adolescent mother and preterm infant, ethnicity, length of stay in the NICU, and preterm infant weight were considered. Results showed a statistically significant difference between Time 1 and Time 2 synchronous interaction measurements indicating that the PICI may have resulted in the adolescent mother better understanding the preterm infant’s behavior. The Caregiver Total Scale score (t = -3.93, p < .001) and the Total Scale score (t = -3.96, p < .001) were the two main scales that the PICI could have affected. There were no correlations among the other independent variables and the dependant variable. Future research should focus on a large scale longitudinal study to measure synchronous interaction over multiple time points beginning in the NICU carrying through the first year of child development. Adding a qualitative component to future studies would provide further insight into experience of adolescent mothers with preterm infants. / text

No description available.

Synchronous distributed groupware is a class of software applications allowing a geographically distributed group of people to collaborate in real time. There are different types of groupware, e.g., collaborative editing software, distributed meeting support tools, and multiplayer games. However, collaborators in groupware can become disconnected from the session. Disconnections can range in duration from a few seconds (e.g., due to a network outage) to hours or days (e.g., stowing a laptop while flying). Disconnection causes information loss and makes it difficult for users to understand both the state of the workspace and the current activities of other people upon reconnection. Thus, it is important to handle disconnection in groupware. However, handling disconnection is difficult for groupware developers. They need to determine varieties of strategies in order to address different disconnection scenarios. These strategies determine how stored information can be manipulated as the system waits for a disconnected user to rejoin, and how information should be replayed upon reconnection. If disconnection lasts for a long time, developers need to select and combine strategies in order to manage a trade-off between performance requirements (e.g., delivering stored information as quickly as possible upon reconnection) and understandability requirements (e.g., allowing users to watch missed information in an understandable manner). Developers might not know how to implement such strategies in a reusable manner. Because of this lack of knowledge in handling disconnection, developers might build disconnection-aware groupware applications that will not address the range of wide variety of user-level requirements that arise from different disconnection scenarios. Moreover, as there are a few disconnection-aware groupware applications, developers might not know the overhead (e.g., additional message transmission time, memory usage and programming complexity) of handling disconnection in synchronous groupware in practice. In order to mitigate developers’ problems to handle disconnection in synchronous groupware, this thesis provides codified solutions that capture and organize a wide range of strategies for handling disconnection, that manage the performance and understandability trade-off through selecting and combining suitable strategies and that show how to implement the strategies in a reusable manner. In order to determine the overhead of handling disconnection, a toolkit is developed following the designed solutions, and different applications are constructed using the toolkit. User studies and performance analyses are conducted that evaluate the toolkit and demonstrate its quality goals, such as offering simple application programming interface (API), high performance, and supporting different disconnection scenarios and timeframes. / Thesis (Ph.D, Computing) -- Queen's University, 2013-04-29 17:52:00.165

This thesis focuses upon a series of empirical studies which examine communication and learning in online glocal communities within higher education in Sweden. A recurring theme in the theoretical framework deals with issues of languaging in virtual multimodal environments as well as the making of identity and negotiation of meaning in these settings; analyzing the activity, what people do, in contraposition to the study of how people talk about their activity. The studies arise from netnographic work during two online Italian for Beginners courses offered by a Swedish university. Microanalyses of the interactions occurring through multimodal video-conferencing software are amplified by the study of the courses’ organisation of space and time and have allowed for the identification of communicative strategies and interactional patterns in virtual learning sites when participants communicate in a language variety with which they have a limited experience. The findings from the four studies included in the thesis indicate that students who are part of institutional virtual higher educational settings make use of several resources in order to perform their identity positions inside the group as a way to enrich and nurture the process of communication and learning in this online glocal community. The sociocultural dialogical analyses also shed light on the ways in which participants gathering in discursive technological spaces benefit from the opportunity to go to class without commuting to the physical building of the institution providing the course. This identity position is, thus, both experienced by participants in interaction, and also afforded by the ‘spaceless’ nature of the online environment.

No description available.

This thesis investigates the development of a machine which is termed as singly salient reluctance (SSR) motor and its drive system. The stator of SSR motor is identical to that of a conventional induction motor or any other ac machine. Its rotor has salient poles with internal flux barriers or flux guides. This research covers the detailed designs of the SSR motors and their magnetic circuit analysis using finite element method (FEM). The parameters which are important for designing the SSR motor are investigated. This investigation resulted in designs which have low manufacturing cost as well as high torque per ampere, efficiency and power factors. This thesis also researches the different drive system for the SSR motor. The SSR motor is tested as a variable speed drive with closed loop control and supplied with dc source. Therefore for this purpose a controller system is designed and built. In addition, the SSR motor supplied by ac source using open loop control is also tested for synchronous operation. Some of the proposed designs are built and their performance compared with their predicted analysis. The SSR motors showed a competitive performance compared with equivalent induction motor in both efficiency and power factor. However the validity of the theoretical designs is assessed by comparing them with experimental results. Quite good agreement between experimental and theoretical evaluations has been achieved. In addition, suggested further improvements for SSR motors and drive systems are discussed. / Doctor of Philosophy (PhD)