Showing papers on "Stand-alone power system published in 2007"

Virtual power plant and system integration of distributed energy resources

Abstract: A concept is presented along with the overarching structure of the virtual power plant (VPP), the primary vehicle for delivering cost efficient integration of distributed energy resources (DER) into the existing power systems. The growing pressure, primarily driven by environmental concerns, for generating more electricity from renewables and improving energy efficiency have promoted the application of DER into electricity systems. So far, DER have been used to displace energy from conventional generating plants but not to displace their capacity as they are not visible to system operators. If this continues, this will lead to problematic over-capacity issues and under-utilisation of the assets, reduce overall system efficiency and eventually increase the electricity cost that needs to be paid by society. The concept of VPP was developed to enhance the visibility and control of DER to system operators and other market actors by providing an appropriate interface between these system components. The technical and commercial functionality facilitated through the VPP are described and concludes with case studies demonstrating the benefit of aggregation (VPP concept) and the use of the optimal power flow algorithm to characterise VPP

Virtual synchronous machine

Abstract: Demands in the area of electrical energy generation and distribution, as a result of energy policies, are leading to far reaching changes in the structure of the energy supply, which is characterised, on the one hand, by the substitution of conventional power stations by renewable energy generation, a decision which has already been made, and, on the other hand, by the changeover from centralised to decentralised energy generation. From an electrical engineering point of view, a new situation will arise for consumers concerning security of supply and power quality, which calls for further technical measures by the grid operators to ensure that the increasingly stringent supply criteria can be met. This article describes a new power electronics based approach which allows a grid compatible integration of predominantly renewable electricity generators even in weak grids making them appear to be electromechanical synchronous machines. As a consequence, all the proven properties of this type of machine which have so far defined the grid continue to do so, even when integrating photovoltaic or wind energy. These properties include, for instance, interaction between grid and generator as in a remote power dispatch, reaction to transients as well as the full electrical effects of a rotating mass. In addition, this new development can be operated in such a way that it provides primary reserve allowing, from a grid point of view, electricity generators such as wind and PV to be regarded as conventional power stations.

Compressed Air Energy Storage in an Electricity System With Significant Wind Power Generation

Abstract: In this paper, a stochastic electricity market model is applied to estimate the effects of significant wind power generation on system operation and on economic value of investments in compressed air energy storage (CAES). The model's principle is cost minimization by determining the system costs mainly as a function of available generation and transmission capacities, primary energy prices, plant characteristics, and electricity demand. To obtain appropriate estimates, notably reduced efficiencies at part load, start-up costs, and reserve power requirements are taken into account. The latter are endogenously modeled by applying a probabilistic method. The intermittency of wind is covered by a stochastic recombining tree and the system is considered to adapt on increasing wind integration over time by endogenous modeling of investments in selected thermal power plants and CAES. Results for a German case study indicate that CAES can be economic in the case of large-scale wind power deployment

Energy Policy Act of 2005

Abstract: This article provides a comprehensive review and describes the impact of the bill on distributed generation, the electricity market, the national electrical grid, and the future of how electricity will be delivered in the United States. The energy policy act of 2005 removes the requirement that utilities purchase power under the condition that the qualifying facility has access to alternative markets. A single IEEE 1547 standard could be applied to any distributed resource interconnection

A Circuit-based Photovoltaic Array Model for Power System Studies

Abstract: Recent interest in distributed generation (DG) due to the opening of the electricity market and the need for alternatives to conventional fossil fuel-based electricity generation has revived interest in grid-connected photovoltaic (PV) systems. Studies need to be performed at the power system level to examine the impacts of grid-connected PV systems and several models for PV arrays have been proposed in the literature for this purpose. However, the complexities of these models and the difficulties of implementing them in software programs can be deterrents to their use. This paper proposes a simple, robust and flexible piecewise linear PV device model for dynamic and transient power system studies. The circuit-based nature of the model is beneficial because it facilitates understanding of the PV device and its behavior in the connected circuit. Software implementation is straightforward and it can even be constructed using standard software library components, as demonstrated using PSCAD/EMTDC.

A Large Wind Power System in Almost Island Operation—A Danish Case Study

Abstract: In Denmark, incorporation of wind power into the power system is increasing whereas power generation from the large conventional power plants is reducing. The common concern has become maintenance of reliable and stable operation of the Danish power system with a large amount of wind power - the large wind power system. At present, maintaining the voltage stability of such a large wind power system relies on strong ac connections to neighboring power systems with sufficient reactive power and voltage control and on control of central power plants in Denmark. This paper presents the results of a stability investigation carried out by the Danish transmission system operator (TSO), Energinet.dk, for the case of almost island operation of the Western Danish wind power system. The main ac lines connecting Western Denmark to the synchronous area of the Union for the Co-ordination of Transmission of Electricity (UCTE) were out of service and the wind power generation was high. The investigation has shown that the reactive power and voltage control of the domestic power plants is essential for maintaining short-term voltage stability of the Western Danish wind power system and becomes even more relevant when ac connections to the strong transmission system of the UCTE are out of service. The results presented in this paper may also be relevant for the operators of the power systems that are in island ac operation and with plans for significant commissioning of wind power - Great Britain, Ireland, Tasmania, etc.

Compressed-air-storing electricity generating system and electricity generating method using the same

Abstract: Disclosed are a compressed air energy-storing electricity generating system and an electricity generating method using the same, in which air of a high pressure is injected into a tank laid under the ground using midnight electricity and surplus produced electricity, and the air of the high pressure in the tank is uniformly discharged so as to drive a generator during a time period when the consumption of electric power is high, thus efficiently managing energy.

Digital Control of an Isolated Active Hybrid Fuel Cell/Li-Ion Battery Power Supply

Abstract: One of the important issues in modern electronic equipment is providing higher peak power while preserving high energy density. Hybrid power sources composed of fuel cells and batteries combine the high-energy capabilities of fuel cells with the high-power capabilities of batteries. DC/DC power converters can appropriately control the power flow shared between the fuel cell and battery system. In this paper, we propose a new implementation of hybrid fuel cell/battery systems. A 50-W isolated power electronic interface system for a hybrid solid-oxide fuel cell (SOFC)/Li-ion battery portable power supply is designed and implemented. The control strategy presented in this paper is able to regulate the output current of the fuel cell, the charging current of the battery, and the output voltage of the power supply. The control strategy is implemented in a DSP and tested by simulation and experiments. Experimental results present the flexibility and generality of the control strategy.

Modeling and Analysis of a Wind/PV/Fuel Cell Hybrid Power System in HOMER

Abstract: In this paper, a hybrid power generation system suitable for remote area application is proposed. This system consists of three renewable energy sources, namely photovoltaic panels, a wind turbine, and a fuel cell. For the production and uniform supply of hydrogen for fuel cell, an electrolyzer and a reformer are also considered in the proposed system. A fuzzy logic power flow controller has been proposed to provide continuous power based on the economic power generation for preliminary analysis. The analysis of such a hybrid system feeding a load center is carried out with the application of HOMER software. Based on simulation results, it has been found that these renewable energy sources would be a feasible solution for distributed generation of electric power for standalone applications at remote locations.

Analysis of the combined use of wind and pumped storage systems in autonomous Greek islands

Abstract: In autonomous islands, the wind penetration is restricted due to technical reasons related with the safe operation of the electrical systems. The combined use of wind power with pumped storage (WPS) systems is considered as a means to exploit the abundant wind potential, increase the wind installed capacity and substitute conventional peak supply. An approach for the simulation of the autonomous electrical systems is proposed and applied in three islands. The simulation is based on the non-dynamic analysis of the electrical system, in order to calculate the energy contribution of the different power units. The aim is to analyse the prospects of WPS systems to decrease the electrical system's cost. The results show that the integration of WPS in autonomous islands may decrease the system's electricity production cost

Power supply system, vehicle with the same, control method of power supply system, and computer readable recording medium which records program for making computer execute the control method

Abstract: Provided is a power supply system capable of maximizing system performance even when charge / discharge characteristics of a plurality of power storage devices are different. A discharge distribution ratio calculation unit calculates, for each power storage device, a remaining power amount up to an SOC where allowable discharge power is limited, and calculates a discharge power distribution ratio of the power storage device according to a ratio of the remaining power amount. To do. The charge distribution rate calculation unit 54 calculates the charge allowable amount up to the SOC where the allowable charge power is limited for each power storage device, and calculates the charge power distribution rate of the power storage device according to the ratio of the charge allowable amount. When power is supplied from the power supply system to the driving force generation unit, each converter is controlled according to the discharge power distribution ratio. When power is supplied from the driving force generation unit to the power supply system, each converter is controlled according to the discharge power distribution ratio. . [Selection] Figure 5

Plug-in Hybrid Vehicles - A Vision for the Future

Abstract: One of the unique advantages of plug-in hybrid vehicles is their capability to integrate the transportation and electric power generation sectors in order to improve the efficiency, fuel economy, and reliability of both systems. This goal is performed via integration of the onboard energy storage units of plug-in vehicles with the power grid by power electronic converters and communication systems. Employing energy storage systems improves the efficiency and reliability of the electric power generation, transmission, and distribution. Similarly, combining an energy storage system with the power train of a conventional vehicle results in a hybrid vehicle with higher fuel efficiency. In both cases, the energy storage system is used to provide load leveling. In this paper, viability of utilizing the same energy storage unit for both transportation and power system applications is discussed. Furthermore, future trends in analysis, design, and evaluation of distributed energy storage system for the power grid using power-electronic-intensive interface are identified.

Control of combined storage and generation in distributed energy resources

Abstract: A microsource is provided, which includes an energy storage device, a power generation device, and a controller. The energy storage device is operably coupled for power transfer to a load through a first power bus. The power generation device is operably coupled for power transfer to the load through a second power bus. The controller determines a mode of operation for the energy storage device and the power generation device based on an energy level of the energy storage device and on the load; determines minimum power set points and maximum power set points for the energy storage device and the power generation device based on the determined mode of operation, on a storage output power measured at the first power bus, and on a generation output power measured at the second power bus; and controls an output power of the energy storage device and an output power of the power generation device based on the determined minimum and maximum power set points.

Technical aspects of status and expected future trends for wind power in Denmark

Abstract: The power system of Denmark is characterized by significant incorporation of wind power. Presently, more than 20% of the annual electricity consumption is covered by electricity-producing wind turbines. The largest increase in grid-incorporated wind power is expected to come from large (offshore) wind farms operating as large wind power plants with ride-through solutions, connected to the high-voltage transmission system and providing ancillary services to the system. In Denmark there are presently two offshore wind farms connected to the transmission system: Horns Rev A (160MW rated power in the western part of the country) and Nysted (165MW rated power at Rodsand in Eastern Denmark). The construction of two more offshore wind farms, totalling 400MW by the years 2008–2010, has been announced. This article presents the status, perspectives and technical challenges for wind power in the power system from the point of view of Energinet.dk, Transmission System Operator of Denmark. Copyright © 2006 John Wiley &Sons, Ltd

A micro power management system and maximum output power control for solar energy harvesting applications

Abstract: A micro power management system is presented for solar energy harvesting applications. An inductor-less solution is proposed which facilitates on-chip integration of the system. We target at applications working in different lighting environments ranging from strong sunlight to dim indoor lighting where the output voltage from the photovoltaic (PV) cells is low. A charge pump is used to step the PV voltage up to charge a battery or directly operate the circuit. The power management system behavior is theoretically analyzed and the control strategy is derived to transfer maximum power from the PV cells to the battery or the circuit. Circuit design and low power techniques for the maximum output power control are proposed for the system. The system was implemented using 0.35μm CMOS process. With the measured PV cells output characteristics, HSPICE simulations for the power management system were carried out to verify the control strategy and to demonstrate the system operation.

Comparison and Analysis of Different Energy Storage Techniques Based on their Performance Index

Abstract: The continuous increase in the level of greenhouse gas emissions and the climb in fuel prices are the main driving forces behind efforts to more effectively utilise various sources of renewable energy (wind and solar energy). However, the large-scale utilisation of this form of energy is possible only if the effective technology for its storage can be developed with acceptable capital and running costs. In the pre-1980 energy context, conversion methods for the "storage of alternate current" were extremely costly, unreliable, or simply were not being used. This, along with the fact that electricity is mass produced, transmitted, and used in AC, has led to the belief that electricity cannot be stored. However, high-performance, inexpensive power electronics able to handle very high power levels have changed all that. It can now be asserted that electricity can be stored, even if it is indirect storage. But this requires that investment and operating costs be kept to an acceptable level, and that the environmental issues be considered. There are various types of storage methods, some of which are already in use, while others are still in development. In this paper, we have taken a look at the main characteristics of the different electricity storage techniques and their field of application (permanent or portable, long-or short-term storage, maximum power required, etc.). These characteristics will serve to make comparisons in order to determine the most appropriate technique for each type of application.

Charge Depleting Energy Management Strategy for Plug-In Hybrid Electric Vehicles

Abstract: A method for managing power distribution from an engine and a battery in a plug-in hybrid electric vehicle whereby battery power is used to meet a driver demand for power and engine power complements battery power when either battery state-of-charge limit or battery discharge power limit would be exceeded, an external power grid being used to restore battery power following battery charge depletion.

Optimal sizing of solar-wind hybrid system

Abstract: Autonomous systems on the basis of solar and wind generators in combination with a battery storage and diesel generator as back up are an option for the supply of electric power to the loads at remote locations. These systems may be configured with solar generator or wind generator alone, or with the combination of both. To decide on system configuration that is best suited to a specific case, it is necessary to identify all possible configurations, that can satisfy the load demand at certain desired reliability level. From these configurations, an optimal one is extracted on the basis of economical analysis. This paper presents the development of a computational model for optimal sizing of solar-wind hybrid energy system (SWHES). The performance of solar and wind system is evaluated through more accurate and practical mathematical models, combining with hourly measured meteorological input data and load data. The reliability measures in terms of loss of power supply probability (LPSP) and the total life cycle cost have been used as the indices for evaluation of different configurations. Load following strategy with a fixed discharge threshold one hour dispatch is used to discharge the stored renewable energy in the battery storage. Methodology used in this model, allows quick identification of optimal configuration based on user's desired reliability level and economical (life cycle cost) performance of system. Program has been developed in MATLAB 6.5 environment using energy balance calculation method.

Power storage apparatus and system

Abstract: PROBLEM TO BE SOLVED: To provide a power storage apparatus equalizing power to be supplied from a commercial power supply, which can be used for various purposes by making it movable. SOLUTION: The power storage apparatus 1 is connectable to a power consuming facility 2 consuming the power supplied from the commercial power supply 51. The apparatus 1 is provided with: a storage battery communication means 36 for receiving a result of detection of power consumption quantity in the power consuming facility 2; an inverter 15 having a function of converting AC power to DC power and a function of converting DC power to AC power; a storage battery 10 to be charged by the power supplied from the power consuming facility 2 via the inverter 15 and supplying the discharged power to the power consuming facility 2 via the inverter 15; and a storage battery control means 30 for controlling the discharging and charging of the storage battery 10 by the inverter 15. The storage battery control means 30 controls the discharging and charging of the storage battery 10 on the basis of a result of detection received by the storage battery communication means 36. COPYRIGHT: (C)2008,JPO&INPIT

Multiple power supply apparatus with improved installability

Abstract: In a multiple power supply apparatus installed in a vehicle, a first power supply system includes a generator and a first battery. The generator is driven by an operation of the engine. The first battery is chargeable by an electrical output of the generator. A second power supply system includes a second battery. The second battery works to supply electrical power to an electrical load installed in the vehicle. A power transfer module is operative to transfer electrical power supplied from the first power supply system based on at least one of the electrical output of the generator and a charged level of the first battery to the second power supply system. The power transfer module is integrally joined to the first battery to constitute a battery module.