Showing papers on "Stand-alone power system published in 2005"

A new approach to quantify reserve demand in systems with significant installed wind capacity

Abstract: With wind power capacities increasing in many electricity systems across the world, operators are faced with new problems related to the uncertain nature of wind power. Foremost of these is the quantification and provision of system reserve. In this paper a new methodology is presented which quantifies the reserve needed on a system taking into account the uncertain nature of the wind power. Generator outage rates and load and wind power forecasts are taken into consideration when quantifying the amount of reserve needed. The reliability of the system is used as an objective measure to determine the effect of increasing wind power penetration. The methodology is applied to a model of the all Ireland electricity system, and results show that as wind power capacity increases, the system must increase the amount of reserve carried or face a measurable decrease in reliability.

Analytical approaches for optimal placement of distributed generation sources in power systems

Abstract: Summary form only given. Power system deregulation and the shortage of transmission capacities have led to increased interest in distributed generation (DG) sources. Proper location of DGs in power systems is important for obtaining their maximum potential benefits. This paper presents analytical methods to determine the optimal location to place a DG in radial as well as networked systems to minimize the power loss of the system. Simulation results are given to verify the proposed analytical approaches.

Optimal allocation of embedded generation on distribution networks

Abstract: As a result of the restructuring of electricity markets and the targets laid down for renewable energy, increasing amounts of embedded generation (EG) are being connected to distribution networks. To accommodate this new type of generation, the existing distribution network should be utilized and developed in an optimal manner. This paper explains the background to the technical constraints faced by EG projects, and a new methodology is developed using linear programming to determine the optimal allocation of EG with respect to these constraints. The methodology is implemented and tested on a section of the Irish distribution network. Results are presented, demonstrating that the proper placement and sizing of EG is crucial to the accommodation of increasing levels of EG on distribution networks.

PowerMatcher: multiagent control in the electricity infrastructure

Abstract: Different driving forces push the electricity production towards decentralization. As a result, the current electricity infrastructure is expected to evolve into a network of networks, in which all system parts communicate with each other and influence each other. Multi-agent systems and electronic markets form an appropriate technology needed for control and coordination tasks in the future electricity network. We present the PowerMatcher, a market-based control concept for supply and demand matching (SDM) in electricity networks. In a presented simulation study is shown that the simultaneousness of electricity production and consumption can be raised substantially using this concept. Further, we present a field test with medium-sized electricity producing and consuming installations controlled via this concept, currently in preparation.

Flyback inverter controlled by sensorless current MPPT for photovoltaic power system

Abstract: This paper presents a flyback inverter controlled by sensorless current maximum power point tracking (MPPT) for a small photovoltaic (PV) power system. Although the proposed system has small output power such as 300 W, a few sets of small PV power systems can be easily connected in parallel to yield higher output power. When a PV power system is constructed with a number of small power systems, the total system cost will increase and will be a matter of concern. To overcome this difficulty, this paper proposes a PV system that uses no expensive dc current sensor but utilizes the method of estimating the PV current from the PV voltage. The paper shows that the application of this novel sensorless current flyback inverter to an MPPT-operated PV system exhibits satisfactory MPPT performance similar to the one exhibited by the system with a dc current sensor as well. This paper also deals with the design method and the operation of the unique flyback inverter with center-tapped secondary winding.

Solar array inverter with maximum power tracking

Abstract: An inverter for use in connecting a DC power source to the utility grid includes a single DC-DC conversion stage, maximum (source) power tracking, and current control based on feed-forward compensation as a function of an input power commanding voltage, rectified utility line voltage, and either a scaled and squared inverse or a scaled inverse of RMS utility line voltage. Various embodiments also include over-voltage, over-current, under-voltage, and over-temperature protection, and a stand-by battery with its battery management control, while others adapt a multiple-channel front-end distributed power system with distributed maximum power tracking to serve as a single DC power source input to the inverter system downstream with controllers, emergency or auxiliary loads, and alternative current feedback control systems for providing an in-phase output current with respect to the utility grid voltage while absorbing maximum power available from the DC power source and minimally utilizing the stand-by battery for maximal system reliability.

An optimal design of a grid connected hybrid wind/photovoltaic/fuel cell system for distributed energy production

Abstract: This paper proposes a hybrid energy system consisting of wind, photovoltaic and fuel cell designed to supply continuous power to the load. A simple and economic control with DC-DC converter is used for maximum power point tracking and hence maximum power extraction from the wind turbine and photovoltaic array. Due to the intermittent nature of both the wind and photovoltaic energy sources, a fuel cell is added to the system for the purpose of ensuring continuous power flow. The fuel cell is thus controlled to provide the deficit power when the combined wind and photovoltaic sources cannot meet the net power demand. In worst environmental conditions, when there is no output power from the wind or photovoltaic sources, the fuel cell will operate at its rated power of 10 kW. Hence this system under any operating condition will ensure a minimum power flow of 10 kW to the load. This hybrid system allows maximum utilization of freely available renewable energy sources like wind and photovoltaic and demand-based utilization of hydrogen-based fuel cell. The proposed system is attractive owing to its simplicity, ease of control and low cost. Also it can be easily adjusted to accommodate different and any number of energy sources. A complete description of this system is presented along with its simulation results which ascertain its feasibility.

High-efficiency power conversion for low power fuel cell generation system

Abstract: This study presents a newly designed topology for a fuel cell energy source conversion in order to supply a highly reliable utility power. Because the fuel cell has the power quality of low voltage as well as high current due to the electrochemical reaction, a high step-up dc-dc converter is utilized for boosting the fuel cell voltage up to a constant dc-bus voltage for the utilization of later inverter. Moreover, a current-source sine-wave voltage inverter is designed in the sense of voltage-clamping and soft-switching techniques to enable the use of a smaller inductor in the current source circuit and the compression of the voltage stress across switches about two times of the dc-bus voltage. In this power conversion scheme, the output voltage has the salient features of lower distortion, fast dynamic regulating speed and insensitivity to load variation, even under nonlinear loads. In addition, experimental results via an example of a proton exchange membrane fuel cell generation system with 250-W nominal power rating are given to demonstrate the effectiveness of the proposed power conversion strategy. According to the experimental measure, the maximum power inverter efficiency is over 95% and the total harmonic distortions for various load conditions are all within 1.1%.

Frequency control in competitive electricity market dispatch

Abstract: The dynamic and inertial characteristics of electricity systems are evolving with consequences for system frequency control. This issue is particularly important for smaller, more isolated electricity systems, where simple heuristic reserve targets may no longer be sufficient to ensure the security of the system. In a market environment, this issue needs to be dealt with in a systematic way that is compatible with the method of market dispatch to ensure least-cost operation of the system. This paper describes how frequency control constraints can be derived and included into a market dispatch algorithm. Comparisons are made with a conventional reserve target dispatch approach for a real isolated power system. The impact on market prices, cost, and the number and size of problem contingencies is assessed. The effect of increasing amounts of wind capacity is also examined.

Wind energy delivery issues [transmission planning and competitive electricity market operation]

Abstract: Improving economics, environmental benefits, supportive state policies, and the rising costs of competing fuels are all contributing factors towards greater market regulatory interest in wind energy. However, wind energy poses several operational and planning challenges, some of which are beginning to be addressed. While the challenges are significant, they are not insurmountable.

New CHP partnerships offering balancing of fluctuating renewable electricity productions

Abstract: Combined heat and power (CHP) as well as intermittent renewable energy sources (RES) are key elements in future cleaner electricity production systems. This article presents solutions which will integrate fluctuating renewable electricity supplies, such as wind power, into electricity systems using small and medium-sized combined heat and power plants (CHP). Such solutions call for a new organisational setup of partnerships and software tools. The software tools will allow the new partnerships to offer services which are currently only offered by big power plants to electricity markets. The article presents recent results of the development and implementation of such partnerships and focuses on the methodologies and computer tools necessary in order to allow the partnerships to optimise their behaviour on the market. The use of such tools and methodologies makes groups of small CHP plants able to replace large power stations and, at the same time, allows for the integration of a higher share of RES in the electricity supply, resulting in a decrease in both fossil fuels and CO2 emissions.

Making connections [wind generation facilities]

Abstract: Large-scale wind generation facilities have become a very visible component of the interconnected power grid in many options of the United States. Only a decade ago, wind generation facilities were viewed by most power engineers as a novelty, and by simple engineering judgement, it could be safely concluded that the effects of these unique but smaller facilities on system reliability would be negligible. Now, with individual wind generation facilities approaching the output rating of conventional power plants, a deeper understanding of their potential impacts on the interaction with the bulk electric power system is needed.

The future of wind forecasting and utility operations

Abstract: To run the power system most efficiently and effectively, we must focus our attention on the system as a whole rather than on individual components - and this is true regardless of whether or not the system includes wind generation. As larger amounts of wind energy are added to our power systems, we must certainly be aware of the impacts of its variability on the system, but we must also keep in mind that our power systems are already designed to deal with substantial amounts of uncertainty and variability. By making proper use of wind forecasting and integrating it into our control rooms and our systems, we can facilitate the cost-effective use of wind energy as a mainstream component of the energy system.

Flexible multiobjective control of power converter in active hybrid fuel cell/battery power sources

Abstract: Hybrid power sources composed of fuel cells and secondary batteries can combine the high energy density of fuel cells with the high power density of batteries. A dc/dc power converter can be placed between the fuel cell and the battery to balance the power flow and greatly augment the peak output power. This work presents a novel, flexible strategy for multiobjective control of the power converter in the hybrid power source. The control strategy is able to regulate the output current of the fuel cell and the charging current or voltage of the battery while limiting the discharging current of the battery. It can be used in two different configurations without any change. The control strategy is implemented in MATLAB/Simulink and tested by simulation and experiments. Simulation and experimental results show that the multiobjective control strategy is able to select the regulation mode correctly and the fuel cell current, battery current and battery voltage are regulated appropriately. Experiment results demonstrate the great flexibility and generality of the control strategy and validate that the peak power capacity of the active hybrid power source is increased significantly. Simulation and experiment results also show that power converter can be appropriately regulated to meet the multiple objectives required by hybrid power sources.

Unit sizing of stand-alone hybrid wind/PV/fuel cell power generation systems

Abstract: An economic evaluation of a hybrid wind/photovoltaic/fuel cell generation system for a typical home in the Pacific Northwest is performed. In this configuration the combination of a fuel cell stack, an electrolyzer, and a hydrogen storage tank is used for the energy storage system. This system is compared to a traditional hybrid energy system with battery storage. A computer program has been developed to size system components in order to match the load of the site in the most cost effective way. A cost of electricity and an overall system cost are also calculated for each configuration. The study was performed using a graphical user interface programmed in MATLAB.

Battery Energy Storage System for Power Conditioning of Renewable Energy Sources

Abstract: Renewable energy sources such as wind, hydro, etc. are intermittent in nature. Generators connected to the local grid may lead to severe power quality problems. These issues are voltage dip while connection/ disconnection of the generator, uncertainty of supply, unbalanced and distorted power supply. In this paper, the power conditioning of micro hydro driven induction generator connected to the local grid using battery energy storage system (BESS) is simulated for voltage regulation, load leveling, harmonics elimination and power factor improvement

Commercial successes in power storage

Abstract: Large capacity electricity storage systems are in daily use around the world, helping to stabilize the electricity delivery infrastructure and minimize the cost of meeting peak-load requirements. These systems typically operate on a diurnal basis: charging with inexpensive utility energy at night and discharging during periods of peak load demand. Notable successes in electric power storage include medium voltage power quality-UPS (uninterruptible power supply) systems, delivering up to 16 MW, used to safeguard entire industrial facilities and recently commissioned Golden Valley Electric Association battery energy storage system (GVEA BESS), the most power battery system, discharging up to 46 MW and with a specified run time of 15 min. The common factor in these successes is that the storage devices work with, rather than compete against conventional generation. This article describes the functions of these systems and examines other emerging applications in power storage, such as the stabilization of wind farm output. It also addresses other power storage technologies that are achieving commercial successes, such as flywheels and supercapacitors.

Power quality : interactions between distributed energy resources,the grid, and other customers

Abstract: This paper presents the three aspects of power quality concerning distributed energy resources (DER). The voltage quality experienced by a DER unit impacts the performance of the unit: bad voltage ...

On-site power generation system with redundant uninterruptible power supply

Abstract: Disclosed is a method and system for providing constant critical AC electrical load with primary, secondary, and in some cases a tertiary source of power with higher reliability and lower operating and capital costs and lower emissions than the traditional utility supply, uninterruptible power supply (UPS), and battery primary power source, and diesel generator back-up systems that are predominately used today. Specifically, the disclosed system utilizes on-site power generation to provide primary power and includes full utility and UPS/DC storage back-up systems.

The United States of storage [electric energy storage]

Abstract: The collaboration between the states and the DOE's Energy Storage Research Program is proving to be an outstanding success. The selected projects show a good portfolio of advanced energy storage media: a ZnBr flow battery, the NaS battery, supercapacitors, and flywheels. The applications are equally varied: mitigation of substation congestion, grid frequency control, load management, and stabilization of a microgrid. The goal of these partnerships with the states is to demonstrate electric energy storage as a technically viable, cost-effective, and broadly applicable option for increasing the reliability of the electricity system and for electric energy management.

Voltage profile improvement with distributed generation

Abstract: Recent changes in the energy industry initiated by deregulation have accelerated the introduction of distributed generation at the subtransmission and distribution levels. In light of the well-known benefits as well as the various issues involved in DG incorporation, this paper proposes two new quadratic voltage profile improvement indices (VPII/sub 1/ and VPII/sub 2/). The primal-dual interior-point (PDIP) method has been employed to identify the optimal location and real and reactive power generation on the basis of the newly proposed indices. A simplified model of a 33-bus radial distribution system has been simulated in MATLAB to illustrate the use of the new indices.

Power generation system incorporating a vanadium redox battery and a direct current wind turbine generator

Abstract: A power generation system includes a wind turbine generator and a vanadium redox battery to compensate for fluctuations in wind power. The wind turbine generator provides DC power that may be used to charge the vanadium redox battery. Generated DC power may also be used for power distribution and, if required, supplemented by DC power from the vanadium redox battery. The power generation system interfaces with a control system to optimize performance and efficiency.

Electric grid stability and the design of sustainable energy systems

Abstract: Today, in most countries, electricity is produced either on hydropower or on large steam turbines on the basis of fossil fuels or nuclear power. Electricity from distributed generation constitutes only small amounts. Until now, the task of balancing supply and demand and the task of securing frequency and voltage on the grid has been left solely to large production units. Meanwhile, the implementation of cleaner technologies, such as renewable energy, combined heat and power production and energy conservation, is necessary for future sustainable energy systems. Consequently, such distributed production units sooner or later need to contribute to the task of securing a balance between electricity production and consumer demands. This paper presents technical designs of potential future flexible energy systems, which will be able both to balance production and demand and to secure voltage and frequency requirements on the grid.

Vehicle-mounted power supply system

Abstract: A vehicle-mounted power supply system comprises a first storage battery, an automotive generator for generating electrical energy and charging the first storage battery with the generated electrical energy. A second storage battery is connected to an electrical load and a power converter supplies electric energy from the first storage battery to the second storage battery. A controller, or battery-monitoring unit, sets the power converter in a sleep mode when the vehicle engine is stopped, periodically detects the voltage of the second storage battery as a pseudo-open circuit voltage during the sleep mode of the power converter if current of the second storage battery is within a predetermined range, estimates a state of charge of the second storage battery from the detected pseudo-open circuit voltage and sets the power converter in a run mode when the estimated state of charge is lower than a predetermined value.

Vanadium redox battery energy storage and power generation system incorporating and optimizing diesel engine generators

Abstract: A power generation system includes a vanadium redox battery that interfaces with a control system to optimize performance and efficiency The power generation system may include one or more wind turbine generators and one or more diesel fuel generators The control system manages the vanadium redox battery's absorption and power generation to control system stability and system frequency The control system further manages the operation of the wind turbine generators and diesel fuel generators to control system stability and voltage