Showing papers on "Electricity generation published in 2002"

General model for representing variable speed wind turbines in power system dynamics simulations

Abstract: A tendency to erect ever more wind turbines can be observed in order to reduce the environmental consequences of electric power generation. As a result of this, in the near future, wind turbines may start to influence the behavior of electric power systems by interacting with conventional generation and loads. Therefore, wind turbine models that can be integrated into power system simulation software are needed. In this contribution, a model that can be used to represent all types of variable speed wind turbines in power system dynamics simulations is presented. First, the modeling approach is commented upon and models of the subsystems of which a variable speed wind turbine consists are discussed. Then, some results obtained after incorporation of the model in PSS/E, a widely used power system dynamics simulation software package, are presented and compared with measurements.

Micropower generation using combustion: Issues and approaches

Abstract: The push toward the miniaturization of electro-mechanical devices and the resulting need for micro-power generation (milli-watts to watts) with low-weight, long-life devices has led to the recent development of the field of micro-scale combustion. The concept behind this new field is that since batteries have low specific energy, and liquid hydrocarbon fuels have a very high specific energy, a miniaturized power generating device, even with a relatively inefficient conversion of hydrocarbon fuels to power would result in increased lifetime and/or reduced weight of an electronic or mechanical system that currently requires batteries for power. In addition to the interest in miniaturization, the field is also driven by the potential fabrication of the devices using Micro Electro Mechanical Systems (MEMS) or rapid prototyping techniques, with their favorable characteristics for mass production and low cost. The micro-power generation field is very young, and still is in most cases in the feasibility stage. However, considering that it is a new frontier of technological development, and that only a few projects have been funded, it can be said that significant progress has been made to date. Currently there is consensus, at least among those working in the field, that combustion in the micro-scale is possible with proper thermal and chemical management. Several meso-scale and micro-scale combustors have been developed that appear to operate with good combustion efficiency. Some of these combustors have been applied to energize thermoelectric systems to produce electrical power, although with low overall efficiency. Several turbines/engines have also been, or are being, developed, some of them currently producing positive power, also with low efficiency to date. Micro-rockets using solid or liquid fuels have been built and shown to produce thrust. Hydrogen-based micro size fuel cells have been successfully developed, and there is a need to develop reliable reformers (or direct-conversion fuel cells) for liquid hydrocarbons so that the fuel cells become competitive with batteries. In this work, some of the technological issues related to meso and micro-scale combustion and the operation of thermochemical devices for power generation will be discussed. Some of the systems currently being developed will be presented and described.

Integration of distributed energy resources. The CERTS Microgrid Concept

Abstract: Evolutionary changes in the regulatory and operational climate of traditional electric utilities and the emergence of smaller generating systems such as microturbines have opened new opportunities for on-site power generation by electricity users. In this context, distributed energy resources (DER)--small power generators typically located at users' sites where the energy (both electric and thermal) they generate is used--have emerged as a promising option to meet growing customer needs for electric power with an emphasis on reliability and power quality. The portfolio of DER includes generators, energy storage, load control, and, for certain classes of systems, advanced power electronic interfaces between the generators and the bulk power provider. This white paper proposes that the significant potential of smaller DER to meet customers' and utilities' needs can be best captured by organizing these resources into MicroGrids.

A techno-economic comparison of power production by biomass fast pyrolysis with gasification and combustion

Abstract: This paper presents an assessment of the technical and economic performance of thermal processes to generate electricity from a wood chip feedstock by combustion, gasification and fast pyrolysis. The scope of the work begins with the delivery of a wood chip feedstock at a conversion plant and ends with the supply of electricity to the grid, incorporating wood chip preparation, thermal conversion, and electricity generation in dual fuel diesel engines. Net generating capacities of 1–20 MWe are evaluated. The techno-economic assessment is achieved through the development of a suite of models that are combined to give cost and performance data for the integrated system. The models include feed pretreatment, combustion, atmospheric and pressure gasification, fast pyrolysis with pyrolysis liquid storage and transport (an optional step in de-coupled systems) and diesel engine or turbine power generation. The models calculate system efficiencies, capital costs and production costs. An identical methodology is applied in the development of all the models so that all of the results are directly comparable. The electricity production costs have been calculated for 10th plant systems, indicating the costs that are achievable in the medium term after the high initial costs associated with novel technologies have reduced. The costs converge at the larger scale with the mean electricity price paid in the EU by a large consumer, and there is therefore potential for fast pyrolysis and diesel engine systems to sell electricity directly to large consumers or for on-site generation. However, competition will be fierce at all capacities since electricity production costs vary only slightly between the four biomass to electricity systems that are evaluated. Systems de-coupling is one way that the fast pyrolysis and diesel engine system can distinguish itself from the other conversion technologies. Evaluations in this work show that situations requiring several remote generators are much better served by a large fast pyrolysis plant that supplies fuel to de-coupled diesel engines than by constructing an entire close-coupled system at each generating site. Another advantage of de-coupling is that the fast pyrolysis conversion step and the diesel engine generation step can operate independently, with intermediate storage of the fast pyrolysis liquid fuel, increasing overall reliability. Peak load or seasonal power requirements would also benefit from de-coupling since a small fast pyrolysis plant could operate continuously to produce fuel that is stored for use in the engine on demand. Current electricity production costs for a fast pyrolysis and diesel engine system are 0.091/kWh at 1 MWe when learning effects are included. These systems are handicapped by the typical characteristics of a novel technology: high capital cost, high labour, and low reliability. As such the more established combustion and steam cycle produces lower cost electricity under current conditions. The fast pyrolysis and diesel engine system is a low capital cost option but it also suffers from relatively low system efficiency particularly at high capacities. This low efficiency is the result of a low conversion efficiency of feed energy into the pyrolysis liquid, because of the energy in the char by-product. A sensitivity analysis has highlighted the high impact on electricity production costs of the fast pyrolysis liquids yield. The liquids yield should be set realistically during design, and it should be maintained in practice by careful attention to plant operation and feed quality. Another problem is the high power consumption during feedstock grinding. Efficiencies may be enhanced in ablative fast pyrolysis which can tolerate a chipped feedstock. This has yet to be demonstrated at commercial scale. In summary, the fast pyrolysis and diesel engine system has great potential to generate electricity at a profit in the long term, and at a lower cost than any other biomass to electricity system at small scale. This future viability can only be achieved through the construction of early plant that could, in the short term, be more expensive than the combustion alternative. Profitability in the short term can best be achieved by exploiting niches in the market place and specific features of fast pyrolysis. These include: •countries or regions with fiscal incentives for renewable energy such as premium electricity prices or capital grants; •locations with high electricity prices so that electricity can be sold direct to large consumers or generated on-site by companies who wish to reduce their consumption from the grid; •waste disposal opportunities where feedstocks can attract a gate fee rather than incur a cost; •the ability to store fast pyrolysis liquids as a buffer against shutdowns or as a fuel for peak-load generating plant; •de-coupling opportunities where a large, single pyrolysis plant supplies fuel to several small and remote generators; •small-scale combined heat and power opportunities; •sales of the excess char, although a market has yet to be established for this by-product; and •potential co-production of speciality chemicals and fuel for power generation in fast pyrolysis systems.

Charge balance control schemes for cascade multilevel converter in hybrid electric vehicles

Abstract: This paper presents transformerless multilevel converters as an application for high-power hybrid electric vehicle (HEV) motor drives. Multilevel converters: (1) can generate near-sinusoidal voltages with only fundamental frequency switching; (2) have almost no electromagnetic interference or common-mode voltage; and (3) make an HEV more accessible/safer and open wiring possible for most of an HEV's power system. The cascade inverter is a natural fit for large automotive hybrid electric drives because it uses several levels of DC voltage sources, which would be available from batteries, ultracapacitors, or fuel cells. Simulation and experimental results show how to operate this converter in order to maintain equal charge/discharge rates from the DC sources (batteries, capacitors, or fuel cells) in an HEV.

Optimal acquisition and aggregation of offshore wind power by multiterminal voltage-source HVDC

Abstract: This paper addresses the exploitation of the offshore wind energy. A good example is in the shallow coastal waters around the Baltic Sea where there is high potential for wind turbines, located 10-30 km from the shore. The underwater transmission of power to shore has to be by cables. Therefore, DC transmission is required to avoid the large capacitive reactance currents of AC cables. This paper describes the optimal acquisition and aggregation of wind power by multiterminal high-voltage direct current based on sinusoidal pulse-width-modulated, three-phase voltage-source converters connected at their AC terminals to the wind turbine generators.

Self-scheduling of a hydro producer in a pool-based electricity market

Abstract: This paper addresses the self-scheduling of a hydro generating company in a pool-based electricity market. This company comprises several cascaded plants along a river basin. The objective is to maximize the profit of the company from selling energy in the day-ahead market. This paper proposes a 0/1 mixed-integer linear programming model to account, in every plant, for the nonlinear and nonconcave three-dimensional (3-D) relationship between the power produced, the water discharged, and the head of the associated reservoir. Additionally, start-up costs due mainly to the wear and tear are considered. Finally, different realistic case studies are analyzed in detail.

Control techniques of Dispersed Generators to improve the continuity of electricity supply

Abstract: It is expected that dispersed generation (DG) will play an increasing role in electric power systems in the near future. Among the benefits that DG can give to the power system operators and to the electricity customers, one of the most attractive is the possibility of improving the continuity of power supply. DG plants can be designed to supply portions of the distribution grid in the event of an upstream supply outage. Techniques for controlling DG plants that use feedback of only locally measurable variables are presented. This solution allows correct system operation and switching between parallel and isolated modes without needing online communication of control signals between the generators. The control technique is described with particular reference to inverter-interfaced systems (micro-turbines, fuel cells). Simulations of sample cases including different size and type of generators are presented.

Final Test and Evaluation Results from the Solar Two Project

Abstract: Solar Two was a collaborative, cost-shared project between 11 U. S. industry and utility partners and the U. S. Department of Energy to validate molten-salt power tower technology. The Solar Two plant, located east of Barstow, CA, comprised 1926 heliostats, a receiver, a thermal storage system, a steam generation system, and steam-turbine power block. Molten nitrate salt was used as the heat transfer fluid and storage media. The steam generator powered a 10-MWe (megawatt electric), conventional Rankine cycle turbine. Solar Two operated from June 1996 to April 1999. The major objective of the test and evaluation phase of the project was to validate the technical characteristics of a molten salt power tower. This report describes the significant results from the test and evaluation activities, the operating experience of each major system, and overall plant performance. Tests were conducted to measure the power output (MW) of the each major system, the efficiencies of the heliostat, receiver, thermal storage, and electric power generation systems and the daily energy collected, daily thermal-to-electric conversion, and daily parasitic energy consumption. Also included are detailed test and evaluation reports.

Impacts of distributed generation on power system transient stability

Abstract: It is expected that increasing amounts of new generation technologies will be connected to electrical power systems in the near future. Most of these technologies are of considerably smaller scale than conventional synchronous generators and are therefore connected to distribution grids. Further, many are based on technologies different from the synchronous generator, such as the squirrel cage induction generator and high or low speed generators that are grid coupled through a power electronic converter. When connected in small amounts, the impact of distributed generation on power system transient stability will be negligible. However, if its penetration level becomes higher, distributed generation may start to influence the dynamic behavior of the power system as a whole. In this paper, the impact of distributed generation technology and penetration level on the dynamics of a test system is investigated. It is found that the effects of distributed generation on the dynamics of a power system strongly depend on the technology of the distributed generators.

Towards a Competitive Market for Reactive Power

Abstract: This paper presents the design of a competitive market for reactive power ancillary services. Generator reactive power capability characteristics are used to analyze the reactive power costs and subsequently to construct a bidding framework. The reactive power market is settled on uniform price auction, using a compromise programming approach based on a modified optimal power flow model. The paper examines market power issues in these markets and identifies locations where strategic market power advantages are present that need to be removed through investments in reactive power devices.

Adaptive power flow method for distribution systems with dispersed generation

Abstract: Recently, there has been great interest in the integration of dispersed generation units at the distribution level. This requires new analysis tools for understanding system performance. This paper presents an adaptive distributed power flow solution method based on the compensation-based method. The comprehensive distributed system model includes three-phase nonlinear loads, lines, capacitors, transformers, and dispersed generation units. The numerical properties of the compensation-based power flow method are compared and analyzed under different situations, such as load unbalance, sudden increase of one-phase loads, degree of meshed loops, number of generator nodes and so on. Based on these analyses, an adaptive compensation-based power flow method is proposed that is fast and reliable while maintaining necessary accuracy. It is illustrated that this adaptive method is especially appropriate for simulation of slow dynamics.

Windmill modeling consideration and factors influencing the stability of a grid-connected wind power-based embedded generator

Abstract: Generation of electricity using wind power has received considerable attention worldwide in recent years. In order to investigate the impacts of the integration of wind farm into utilities' network, various windmill models have been developed. One such impact is related to the critical clearing time (CCT) of the wind power based embedded generators (WPBEGs). The work in this paper has shown that oversimplification of the modeling of windmill mechanical drive train could introduce significant error in the value of the CCT that defines the stability limit of an integrated wind farm. This paper also reports investigation into the factors that influence the dynamic behavior of the WPBEGs following network fault conditions. It is shown that wind farm CCT can be affected by various factors contributed by the host network. Results obtained from several case studies are presented and discussed. This investigation is conducted on a simulated grid-connected wind farm using EMTP.

Power from marine currents

Abstract: This paper describes the rationale and the engineering approach adopted for the development of technology for converting the kinetic energy in marine currents for large-scale electricity generation. Although the basic principles involved are relatively straightforward and well understood, being similar to those of a wind turbine, a practical and cost-effective large-scale system designed to extract the kinetic energy of flowing water has yet to be developed. This paper describes the research and development being undertaken through an industrial consortium with the aim of achieving this goal for the first time, i.e. to achieve the world's first commercially viable systems for delivering power from marine currents.

Human Powered Piezoelectric Batteries to Supply Power to Wearable Electronic Devices

Abstract: Consumer electronic equipments are becoming small, portable devices that provide users with a wide range of functionality, from communication to music playing. The battery technology and the power consumption of the device limit the size, weight and autonomous lifetime. One promising alternative to batteries (and fuel cells, that must be refueled as well) is to use the parasitic energy dissipated in the movement of the wearer of the device to power it. We analyze in this work the current state-of-the-art and the future prospect of energy conversion from mechanical movement in the human environment to electrical energy based upon the piezoelectric effect. This is an interdisciplinary field where material technology and electrical circuits have to advance together to improve the conversion efficiency in order to reach the energy demands of the typical portable consumer electronic devices that will become in this way autonomous wearable devices.

A maximum power control of wind generator system using a permanent magnet synchronous generator and a boost chopper circuit

Abstract: The wind generator system using a boost chopper for generation control of permanent magnet synchronous generator is proposed. And, the theoretical analysis of characteristics of power generation is discussed. By replacing the main circuit composition of generator and boost chopper with the equivalent circuit, characteristics for generating power and DC output voltage were expressed by the function of duty ratio of the boost chopper and generator rotational frequency. Electric power supplied from the generator is characterized by the condition of the load with the peak point. Therefore, the optimum duty ratio for obtaining the maximum power was theoretically determined by differentiating the characteristic equation of generating power with respect to duty ratio of the boost chopper. It was verified experimentally by the construction of the simulator of the wind generator system, and the validity of derivation technique for the maximum power point was confirmed.

Multiple input DC-DC power converter for fuel-cell powered hybrid vehicles

Abstract: Customer demands for greater acceleration, performance, and vehicle range in pure EVs plus mandated requirements to further reduce emissions in HEVs increase the appeal for combined on-board energy storage systems and generators. This paper deals with a multiple input DC-DC power converter devoted to combine the power flow of multi-source on-board energy systems. The proposed energy storage arrangement includes fuel cell generator, ultracapacitor tank, and battery system. Possibility of optimization of the output capacitors bank in relation to the RMS value of the current ripple is investigated.

Use of load control to regulate voltage on distribution networks with embedded generation

Abstract: Since 1994 Econnect has, in conjunction with Northern Electric PLC, investigated the use of consumer load control as a new and innovative method to actively regulate distribution system voltage when affected by the operation of embedded generators [1],[2]. There are a number of issues that can limit the installed capacity of embedded generators; these are often voltage related, and the most common is steady state voltage rise. A number of techniques can be applied to limit steady state voltage rise, some of which are static in time (e.g., network reinforcement) and some dynamic (e.g., power factor control). This paper discusses the issue of excess steady state voltage rise and the methods of limitation that can be applied with specific reference to wind generation. The new and innovative approach using consumer load control is discussed and compared with the existing methods using a simulation case study.

Photovoltaic power generation system with storage batteries

Abstract: An object of the present invention is to provide a system capable of reducing optimally peak demand for power by using small capacity storage batteries. The present invention was made to provide a photovoltaic power generation system which links with a utility power system, feeds electric power generated by a solar cell device to an inverter in order to convert the electric power into alternating current, and supplies the alternating current to a power consumption section. The photovoltaic power generation system comprises storage batteries for storing electric power and a switch control device for switching to output electric power from the solar cell device to the storage batteries or the inverter. Also the photovoltaic power generation system controls discharge of the electric power stored in the storage batteries with reference to a specific period of high power demand represented by a fluctuation curve of power demand, and supplies the electric power from the storage batteries along with generation power from the solar cell device to the inverter.

Combined fuel cell and fuel combustion power generation systems

Abstract: A power generation system is provided which converts chemical energy in one or more fuels into electrical and/or mechanical power. The system includes both fuel cells to directly convert electrical energy in a fuel into electrical power and at lest one combustor and expander to generate mechanical power, optionally than converted to electrical power in a generator. Fuel cell products disclosed from the fuel cell are entered into the combustor to be heated along with products of combustion created in the combustor and expanded in the expander along with the products of combustion.