A Small-Scale Standalone Wind Energy Conversion System Featuring SCIG, CSI and a Novel Storage Integration Scheme

Small-scale standalone wind turbines provide a very attractive renewable energy source for off-grid remote communities. Taking advantage of variable-speed turbine technology, which requires a partial- or full-scale power converter, and through integrating an energy storage system, smooth and fast power flow control, maximum power point tracking, and a high-quality power is ensured. Due to high reliability and efficiency, permanent magnet synchronous generator seems to be the dominating generator type in gearless wind turbines, employed for off-grid applications. However, wind turbines using geared squirrel-cage induction generator (SCIG) are still widely accepted due to their robustness, simplicity, light weight and low cost. Permanent magnet induction generator, a relatively new induction-based machine, has recently been recognized in the wind energy market as an alternative for permanent magnet synchronous generator. A thorough comparative study, among these three generator types, is conducted in this research in order to enable selection of the most appropriate generator for off-grid wind energy conversion system (WECS), subject to a set of given conditions. The system based on geared SCIG has been shown to be the most appropriate scheme for a small-scale standalone WECS, supplying a remote area. Different topologies of power electronic converters, employed in WECSs, are overviewed. Among the converters considered, current source converter is identified to have a great potential for off-grid wind turbines. Three current-source inverter-based topologies, validated in the literature for on-grid WECS, are compared for off-grid WECS application. Feasibility study and performance evaluation are conducted through analysis and simulation. Among all, the topology composed of three-phase diode bridge rectifier, DC/DC buck converter, and pulse-width-modulated current-source inverter (PWM-CSI) is identified as a simple and low-cost configuration, offering satisfactory performance for a low-power off-grid WECS. A small-scale standalone wind energy conversion system featuring SCIG, CSI and a novel energy storage integration scheme is proposed and a systematic approach for the dc-link inductor design is presented. In developing the overall dynamic model of the proposed wind turbine system, detailed models of the system components are derived. A reduced-order generic load model, that is suitable for both balanced and unbalanced load conditions, is developed and combined with the system components in order to enable steady-state and transient simulations of the overall system. A linear small-signal model of the system is developed around three operating points to investigate stability, controllability, and observability of the system. The eigenvalue analysis of the small-signal model shows that the open-loop system is locally stable around operating points 1 and 3, but not 2. Gramian matrices of the linearized system show that the system is completely controllable at the three operating points and completely observable at operating points 1 and 3, but not 2. The closed-loop control system for the proposed wind turbine system is developed. An effective power management algorithm is employed to maintain the supply-demand power balance through direct control of dc-link current. The generator’s shaft speed is controlled by the buck converter to extract maximum available wind power in normal mode of operation. The excess wind power is dumped when it is not possible to absorb maximum available power by the storage system and the load. The current source inverter is used to control positive- and negative-sequence voltage components separately. The feasibility of the proposed WECS and performance of the control system under variable wind and balanced/unbalanced load conditions are analyzed and demonstrated through simulation. Finally, the proposed WECS is modified by removing the dump load and avoiding the surplus power generation by curtailment of wind power. The operation of the modified system is investigated and verified under variable wind and load conditions

Uncertainty modeling : fundamental concepts and models

This book series represents a commendable effort in compiling the latest developments on three important Engineering subjects: discrete modeling, inverse methods, and uncertainty structural integrity. Although academic publications on these subjects are plenty, this book series may be the first time that these modern topics are compiled together, grouped in volumes, and made available for the community. The application of numerical or analytical techniques to model complex Engineering problems, fed by experimental data, usually translated in the form of stochastic information collected from the problem in hand, is much closer to real-world situations than the conventional solution of PDEs. Moreover, inverse problems are becoming almost as common as direct problems, given the need in the industry to maintain current processes working efficiently, as well as to create new solutions based on the immense amount of information available digitally these days. On top of all this, deterministic analysis is slowly giving space to statistically driven structural analysis, delivering upper and lower bound solutions which help immensely the analyst in the decisionmaking process. All these trends have been topics of investigation for decades, and in recent years the application of these methods in the industry proves that they have achieved the necessary maturity to be definitely incorporated into the roster of modern Engineering tools. The present book series fulfills its role by collecting and organizing these topics, found otherwise scattered in the literature and not always accessible to industry. Moreover, many of the chapters compiled in these books present ongoing research topics conducted by capable fellows from academia and research institutes. They contain novel contributions to several investigation fields and constitute therefore a useful source of bibliographical reference and results repository. The Latin American Journal of Solids and Structures (LAJSS) is honored in supporting the publication of this book series, for it contributes academically and carries technologically significant content in the field of structural mechanics

Enhancing transient performance of microgeneration-dense low voltage distribution networks

In addition to other measures such as energy saving, the adoption of microgeneration driven by renewable and low carbon energy resources is expected to have the potential to reduce losses associated with producing and delivering electricity, combat climate change and fuel poverty, and improve the overall system performance. However, incorporating a substantial volume of microgeneration within a system that is not designed for such a paradigm could lead to conflicts in the operating strategies of the new and existing centralised generation technologies. So it becomes vital for such substantial amount of microgeneration among other decentralised resources to be controlled in the way that local constraints are mitigated and their aggregated response supports the wider system. In addition, the characteristic behaviour of connected microgeneration requires to be understood under different system conditions to ascertain measures of risk and resilience, and to ensure the benefits of microgeneration to be delivered. Therefore, this thesis provides three main valuable contributions of future attainment of sustainable power systems. Firstly, a new conceptual control structure for a system incorporating a high penetration of microgeneration and dynamic load is developed. Secondly, the resilience level of the host distribution network as well as the resilience levels of microgeneration during large transient disturbances is evaluated and quantified. Thirdly, a technical solution that can support enhanced transient stability of a large penetration of LV connected microgeneration is introduced and demonstrated. A control system structure concept based on “a cell concept” is introduced to manage the spread of heavy volumes of distributed energy resources (DERs) including microgeneration such that the useful features of DER units in support of the wider system can be exploited, and the threats to system performance presented by significant connection of passive and unpredictable DERs can be mitigated. The structure also provides simpler and better coordinated communication with DERs by allowing the inputs from DERs and groups of cells to be transferred as collective actions when it moves from a local to a wider system level. The anticipated transient performance problems surrounding the integration of microgeneration on a large basis within a typical urban distribution network are addressed. Three areas of studies are tackled; the increased fault level due to the present of microgeneration, the collective impact of LV connected microgeneration on traditional LV protection performance, and the system fault ride through capabilities of LV connected microgeneration interfaced by different technologies. The possible local impacts of unnecessary disconnection of large amount of microgeneration on the performance of the host distribution network are also quantified. The thesis proposes a network solution based on using resistive-type superconducting fault current limiters (RSFCLs) to prevent the impact of local transient disturbances from expanding and enhance the fault ride through capabilities of a high penetration of microgeneration connected to low voltage distribution networks. A new mathematical approach is developed within the thesis to identify at which condition RSFCL can be used as a significant device to maintain the transient stability of large numbers of LV connected microgeneration. The approach is based on equation solution to determine the minimum required value of the resistive element of RSFCL to maintain microgeneration transient stability, and at the same time additional headroom against switchgear short-circuit ratings is provided. Remote disturbances or a failure to clear remote faults quickly are shown to no longer result in complete unnecessary disconnection of substantial amount of microgeneration

ICT access and use in the remote rural town of Hatherleigh (Devon, UK): towards citizen engagement?

Information communication technologies (ICTs) have reached into everyday life. This emphasises the increasing importance of understanding the relationship between ICTs and society (Giddens 1994; Castells 1996; Walsham 2001). Over the last few decades, ICTs have shaped many aspects of society, and the specific role that ICTs have played in influencing government and governance structures has received particular attention. Today, the term 'governance' is widely used and accepted amongst a variety of academics and practitioners. However, in recent years the processes by which rural areas are governed have changed remarkably. Many scholars accept the conceptual and theoretical debate concerning the actual and potential impact of ICTs as a powerful force shaping governance (Goodwin 1998; MacKinnon 2002), but few have attempted to support their argument by conducting detailed empirical analyses of the role and influence of ICTs for egovernance processes in rural communities. This thesis addresses this gap by analysing the linkages between ICT access and use in a remote rural area of the UK. The thesis presents an in-depth case study analysis of a rural market town (Hatherleigh) located in west Devon. It examines ICT access and use in Hatherleigh considering that individual levels of ICT adoption are uneven, depending on factors such as age, gender, employment and family composition (Ofcom 2006; Selg and Svensoon 2008). It follows a wider call in the area of rural and ICT studies that many remote rural areas face serious challenges in their efforts to benefit from the opportunities offered by ICTs (Woods 2005; Moseley and Owen 2008). The thesis particularly builds on Okot-Uma's (2001), Millard's (2003) and Odendaal's (2003) work on the impact of ICT on governance and potential changes in service delivery to rural areas. To understand the impact of ICTs on e-governance in rural areas more fully, specific emphasis is placed on how Hatherieigh residents use the internet for accessing on-line information and services and how they use the internet to engage with policy stakeholders within and beyond Hatherleigh. A specific focus is placed on analysing barriers affecting e-governance processes ranging from the local to the national scale. Ill The methodology used to collect empirical data is based on a multi-method approach, including questionnaires, interviews and participant observation to explore interactions between Hatherteigh residents and ICTs. The results suggest that ICT has changed the social landscape of rural communities such as Hatherleigh in terms of communication and job opportunities, and that it plays a key role in reducing feelings of distance and isolation. A key result is that the internet plays an important role for e-governance interactions at the regional/national level, but that it only plays a minor role at the local level. A key explanation for these different 'geographies of ICT use' is that remote mral locations such as Hatherleigh are (still) characterized by relatively close-knit communities where physical face-to-face interaction still plays an important role, thereby reducing the need for internet use to access local information. The study also suggests a typology of non-users in Hatherleigh, suggesting that non-users are a highly differentiated group in which some segments are relatively keen to use ICT in the future, while others continue to staunchly resist using ICTs. The latter are a particularly problematic group as they may be 'doubly' excluded by both living in a remote mral area that has lost some of its services (to some extent because of ICT availability) and by not being interested in using ICTs to overcome such disadvantages

Board of Directors Meeting Minutes (October 13, 1997)

This file contains the minutes from the Des Moines Area Community College Board meeting held on October 13, 1997

The Social and Economic Impacts of Gambling

There has been considerable debate about the best methodological and theoretical approach to analyzing the social and economic impacts of gambling, with one of the central issues being how to aggregate the social impacts with the financial impacts to arrive at an overall summative measure. However, there is no reliable way of doing this. Judging the overall positive or negative nature of gambling will always be a subjective determination about the relative importance of the observed social impacts compared to the observed economic impacts. This does not mean that high quality socioeconomic analyses of gambling cannot be conducted. Rather, there are many basic principles for conducting socioeconomic impact studies that can ensure that the obtained results are comprehensive, provide a meaningful accounting of the social impacts of gambling, and are scientifically rigorous. These principles are outlined in the first section of this report. In light of these methodological principles, the second section of this report provided an exhaustive review of what is known about the social and economic impacts of gambling, including a compilation of 492 studies on this topic, and a summary of the findings of these studies in a series of tables organized by impact area and type of gambling. These Summary Tables provide a useful documentation of which types of gambling have been most and least studied, the types of impacts that have been most and least studied, and the general pattern of results in terms of whether a particular form of gambling has found increases, decreases, no impact, or just changes in that impact area. Additionally, these tables provide a reference source for other researchers who may wish to conduct even more in-depth analyses of specific domains or types of gambling.Canadian Consortium for Gambling Research; Alberta Gaming Research Institute; Canadian Centre on Substance Abuse; Gaming Policy and Enforcement Branch of British Columbia; Manitoba Gaming Control Commission; Ministère de la Sante et des Services Sociaux du Québec; Gambling Awareness Foundation of Nova Scotia; Ontario Problem Gambling Research Centre

Impact of Information Society Research in the Global South

Communication Studies; Information Systems Applications (incl. Internet); R & D/Technology Polic

Hedonic analysis of property markets: theory and applications to UK cities

This thesis concerns the hedonic analysis of property markets. In particular, it investigates the extent to which such analysis can reveal household preferences for the avoidance of exposure to transport-related noise pollution. The thesis is divided into three Parts. Part 1 provides a thorough exposition of the economic theory of property markets. It contains two chapters. The first details the establishment of a market-clearing hedonic price equilibrium. The second outlines how the property market model can be used to identify measures of welfare change resulting from exogenous changes in environmental quality. As well as providing possibly the most complete and coherent exposition of this expansive and occasionally confused literature, Part 1 also contributes new insights into welfare measurement when landlords are constrained in their responses to environmental change. The following two Parts of the thesis concern empirical applications of hedonic analysis to property markets. Part 2 is concerned with the estimation of hedonic price functions for the City of Birmingham property market. The unique innovations presented here include the application of techniques for partitioning data in order to improve specification of the hedonic price function and the application of semiparametric estimators in order to redress spatial autocorrelation amongst regression residuals. Finally Part 3 of the thesis concerns itself with welfare analysis. Specifically, it provides a thorough discussion of the implications of the theory in Part 1 for empirical estimation of preference parameters. Following these empirical guidelines and drawing on results from Part 2, welfare estimates for changes in exposure to traffic-related noise pollution are provided. As far as the author is aware, these are the first welfare estimates for noise pollution to be derived from a hedonic analysis in a theoretically consistent manner

Boundaries of research : civilian leadership, military funding, and the international network surrounding the development of numerical weather prediction in the United States

American meteorology was synonymous with subjective weather forecasting in the early twentieth century. Controlled by the Weather Bureau and with no academic programs of its own, the few hundred extant meteorologists had no standing in the scientific community. Until the American Meteorological Society was founded in 1919, meteorologists had no professional society. The post-World War I rise of aeronautics spurred demands for increased meteorological education and training. The Navy arranged the first graduate program in meteorology in 1928 at MIT. It was followed by four additional programs in the interwar years. When the U.S. military found itself short of meteorological support for World War II, a massive training program created thousands of new mathematics- and physics-savvy meteorologists. Those remaining in the field after the war had three goals: to create a mathematics-based theory for meteorology, to create a method for objectively forecasting the weather, and to professionalize the field. Contemporaneously, mathematician John von Neumann was preparing to create a new electronic digital computer which could solve, via numerical analysis, the equations that defined the atmosphere. Weather Bureau Chief Francis W. Reichelderfer encouraged von Neumann, with Office of Naval Research funding, to attack the weather forecasting problem. Assisting with the proposal was eminent Swedish-born meteorologist Carl-Gustav Rossby. Although Rossby returned to Stockholm to establish his own research school, he was the de facto head of the Meteorology Project providing personnel, ideas, and a publication venue. On-site leader Jule Charney provided the equations and theoretical underpinnings. Scandinavian meteorologists supplied by Rossby provided atmospheric reality. Six years after the Project began, meteorologists were ready to move their models from a research to an operational venue. Attempts by Air Force meteorologist Philip D. Thompson to co-opt numerical weather prediction (NWP) prompted the academics, Navy, and Weather Bureau members involved to join forces and guarantee that operational NWP would remain a joint activity not under the control of any weather service. This is the story of the professionalization of a scientific community, of significant differences in national styles in meteorology, and of the fascination (especially by non-meteorologists) in exploiting NWP for the control of weather

Bowdoin Orient v.101, no.1-26 (1971-1972)

https://digitalcommons.bowdoin.edu/bowdoinorient-1970s/1002/thumbnail.jp