Localized Aggregation of Diverse Energy Sources for Rural Electrification Using Microgrids

Extension of electrical service to large rural populations in developing nations is a key requirement to realize human development goals set forth by international agencies. This paper presents the case for distributed generation in the form of microgrids, which should be the preferred path towards rural electrification in developing communities and a vital complement to expensive centralized grid expansion. The technical features of frequency and voltage control for distributed generation devices in a microgrid are discussed along with a presentation of their stability attributes. Computer simulation results and experimental results from a laboratory scale microgrid are also presented.     

Microgrids and Distributed Generation

Application of individual distributed generators can cause as many problems as it may solve. A better way to realize the emerging potential of distributed generation is to take a system approach which views generation and associated loads as a subsystem or a “microgrid.” The sources can operate in parallel to the grid or can operate in island, providing utility power station services. The system will disconnect from the utility during large events (e.g., faults and voltage collapses), but may also intentionally disconnect when the quality of power from the grid falls below certain standards. Utilization of waste heat from the sources will increase total efficiency, making the project more financially attractive. University of Wisconsin laboratory verification of microgrid control concepts are included.     

A Different Race: The Philosophy

The infrastructure of a nation is the foundation of the nation's ability to compete in world markets, maintain a credible deterrence, influence other nations, and create surpluses for use in social programs. Part of the infrastructure that a nation will depend on economically and militarily in the 21st century will be located in space. Space, besides being an economic, technical, and strategic opportunity for various companies and countries, can also be a way to use engineering and technology to improve the condition of the human race. This paper explains a strategy for reprogramming money from the development and deployment of strategic offensive weapons and their delivery systems to developing the facilities and capabilities needed for nations to be active participants in the exploration and industrialization of space. The creation of the infrastructure needed to pioneer the space frontier will require all engineering professions, especially civil engineering, to stretch and reach for the stars.     

Turbine Plant Efficiency: Taking Inertia and Friction Forces into account

A feasible variant of the equation is proposed to relate the efficiency of a turbine plant to the kinetic energy of the gas/steam flow: ηi = 1/[(1/ηmin)?(ΔPuse+ΔPfr)i/ΔPinert], where ηi=turbine plant efficiency in an i state (Ti,Pi); ΔPuse, ΔPfr=kinetic energy of the moving flow used on carrying out effective work and used on overcoming friction between the jets of gas and between the friction parts of the turbine, respectively; ηmin=minimum efficiency attained at a given temperature of the gas flow; ΔPinert=kinetic energy of the moving flow used on overcoming the inertia forces of the turbine. Employment of abovementioned equation in processing experimental data makes it possible to estimate ηmin, as well as ΔPinert. The equation facilitates functional monitoring of an operating turbine cycle and can be useful in upgrading and optimizing individual units or in designing new turbines.     

Customer-Focused Assessment of Electric Power Microgrids

The cost-effectiveness of interconnected microgrid systems with combined heat and power is examined for 36 cases involving six microgrid applications in six different U.S. locations. In the baseline analysis, microgrids are found to be good investments in areas with relatively high “spark spreads” (electricity/natural gas price differentials). Customers with a higher value for electric reliability realize greater benefits. Results become more favorable over time if the rate of increase of electricity prices is at least 60% of the rate of increase of natural gas prices—a plausible scenario in states with substantial natural-gas fired capacity. Sensitivity analyses reveal that the choice of microgrid customer mix has a much greater impact on system economics than climate. Economies of scale are shown to be fairly modest for the systems considered here, but microgrids do show clear benefits over traditional single customer distributed generation. If performance goals of current U.S. Department of Energy research programs for IC engines and microturbines are met, rates of return for microgrid investments increase 10–20%.     

Slack Bus Modeling and Cost Analysis of Distributed Generator Installations

The installation and operation of distributed generators (DGs) has great potential for local utilities to improve distribution system reliability and lower their operating and expansion planning costs. To evaluate this potential, distribution system analyses must reflect its new operating environment with significant DG. Resulting tools can be utilized by both utilities and DG owners to improve their decision making algorithms. As such, this work investigates two different slack bus models for unbalanced distribution power flow and their impacts on subsequent cost analysis. The models include the traditional single slack bus model which assigns the substation as the slack bus and a distributed slack bus model which assigns slack to the substation and DGs according to network-based participation factors. Detailed expressions for cost analysis which directly depend on the distributed slack bus model are presented and discussed. Simulations illustrate that the different slack bus models have significant impacts on cost analysis. The difference in estimated annual profit for local utilities reached up to 265% using the different slack models.     

Active Control of Flexural Vibrations in Beams

The feasibility of using piezoelectric actuators to control the flexural oscillations of large structures in space is investigated. Piezoelectric actuators have the advantage of exerting localized bending moments. In this way, vibration is controlled without exciting rigid body modes in the structure. The actuators are used in collocated sensor∕driver pairs to form a feedback control system. The sensor produces a voltage that is proportional to the dynamic stress at the sensor location, and the driver produces a force that is proportional to the voltage applied to it. The analog control system amplifies and phase shifts the sensor signal to produce the voltage signal that drives the driver piezoelectric. The feedback control system is demonstrated to increase the first mode damping in a cantilever beam by up to 85%, depending on the amplifier gain. An analytical model of the control system is developed. The estimated and measured vibration control compare favorably. A simulated free‐free beam is fabricated and instrumented with a distribution of piezoelectric sensor∕driver pairs. The purpose is to evaluate the damping efficiency of the control system when the piezoelectrics are not optimally positioned at points of high stress in the beam. The control system is found to reduce the overall vibration response to impact by a factor of two.     

Reactive Power Adequacy in Distribution Networks with Embedded Distributed Energy Resources

This paper addresses reactive power adequacy problems in distribution networks that include a significant number of distributed energy resources. The voltage profile of the distribution network is analyzed under increasing amounts of generation provided by the distributed energy resources. Both static and dynamic voltage disruption phenomena resulting from increasing distributed generation are described and the need for remedial actions identified. Different reactive power control schemes are then proposed to keep both an appropriate voltage profile and an appropriate voltage stability margin. Finally, an economic appraisal of remedial actions is carried out and the responsible parties identified. Results from a realistic case study are presented and discussed. Conclusions are duly drawn.     

Combined Heat and Power as a Feature of Energypark

The use of combined heat and power (CHP) in manufacturing plants that have relatively large thermal and power loads has long been recognized as an efficient alternative that also translates to less fuel consumption, i.e., less polluting of the environment. Making use of the full potentials of this mature concept still faces several technical and regulatory challenges. The concept of an ecopark is one that creates a cluster of industrial plants in close proximity, so that relevant inputs and outputs of the park can be optimized and shared by the park affiliates in order to maximize economic and environmental benefits. The design objectives of such an ecopark are large and include travel time, raw material bulk pricing, energy use, toxic substances, local resources, infrastructure, and regulations and operation guidelines, etc. Solving a problem with so many design objectives may be complex, requiring an extensive organizational network, intricate planning, and flexibility even once the design is completed. The ecopark, with its primary optimizing tool, a CHP system, is introduced in this paper to show how to achieve optimum energy use by a cluster of appropriately selected plants. The manufacturing park optimized for maximum energy efficiency, called an energypark, can then work hierarchically toward adopting more useful performance and waste-related parameters as secondary objectives for further optimization whenever possible.     

Strategies for Developing Countries to Expand Their Shares in the Global Construction Market: Phase-Based SWOT and AAA Analyses of Korea

Korea’s level of competitiveness in the global construction market has significantly improved over the years; from being an underdeveloped country in the 1960s, Korea is currently one of the top ten countries in terms of revenue in the global construction market. In general, an international construction business entails various risks and requires advanced financing and managerial and technical ability to become competitive. Therefore, it is challenging for developing countries to expand their share in the global construction market. In this regard, the case of the Korean international construction business (KICB) may serve as a benchmark for other countries aspiring to enter or reinforce their status in the global construction market. To this end, the strategies to achieve and maintain competitiveness need to be analyzed chronologically rather than focusing only on a particular period, especially the current status. This paper details the history of KICB, showing its evolution over the past 40?years, divided into four major phases that correspond with significant events. Moreover, the important aspects for securing competitive advantage in the market are clarified using four sets of strength, weakness, opportunity, and threat (SWOT) analyses. In addition, the strategic evolution over the four major phases is explored by introducing the adaptation, aggregation, and arbitrage (AAA) framework. The research findings indicate that the strategies adopted by KICB for achieving competitiveness included presenting a memorable performance in a primary country of a particular region (adaptation) during the initial phase, achieving economies of scale in a few regions during the development phase (aggregation), developing international specialization during the depression phase (arbitrage), and adapting to receive orders in a severely competitive market while coping with the local industry protection policy during the resurrection phase (adaptation).     

Integrated Water Management for the 21st Century: Problems and Solutions

Most of the projected global population increases will take place in third world countries that already suffer from water, food, and health problems. Increasingly, the various water uses (municipal, industrial, and agricultural) must be coordinated with, and integrated into, the overall water management of the region. Sustainability, public health, environmental protection, and economics are key factors. More storage of water behind dams and especially in aquifers via artificial recharge is necessary to save water in times of water surplus for use in times of water shortage. Municipal wastewater can be an important water resource but its use must be carefully planned and regulated to prevent adverse health effects and, in the case of irrigation, undue contamination of groundwater. While almost all liquid fresh water of the planet occurs underground as groundwater, its long-term suitability as a source of water is threatened by nonpoint source pollution from agriculture and other sources and by aquifer depletion due to groundwater withdrawals in excess of groundwater recharge. In irrigated areas, groundwater levels may have to be controlled with drainage or pumped well systems to prevent waterlogging and salinization of soil. Salty drainage waters must then be handled in an ecologically responsible way. Water short countries can save water by importing most of their food and electric power from other countries with more water, so that in essence they also get the water that was necessary to produce these commodities and, hence, is virtually embedded in the commodities. This “virtual” water tends to be a lot cheaper for the receiving country than developing its own water resources. Local water can then be used for purposes with higher social, ecological, or economic returns or saved for the future. Climate changes in response to global warming caused by carbon dioxide emission are difficult to predict in space and time. Resulting uncertainties require flexible and integrated water management to handle water surpluses, water shortages, and weather extremes. Long-term storage behind dams and in aquifers may be required. Rising sea levels will present problems in coastal areas.