Showing papers on "Stand-alone power system published in 2006"

Wind turbines emulating inertia and supporting primary frequency control

Abstract: The increasing penetration of variable-speed wind turbines in the electricity grid will result in a reduction of the number of connected conventional power plants. This will require changes in the way the grid frequency is controlled. In this letter, a method is proposed to let variable-speed wind turbines emulate inertia and support primary frequency control. The required power is obtained from the kinetic energy stored in the rotating mass of the turbine blades.

Can microgrids make a major contribution to UK energy supply

Abstract: Almost all the electricity is generated in the UK as part of a centralised power system designed around large fossil fuel or nuclear power stations. This power system is robust and reliable but the efficiency of power generation is low, resulting in large quantities of waste heat. The principal aim of this paper is to investigate an alternative concept: the energy production by small scale generators in close proximity to the energy users, integrated into microgrids. Microgrids - de-centralised electricity generation combined with on-site production of heat - bear the promise of substantial environmental benefits , brought about by a higher efficiency and by facilitating the integration of renewable energy sources such as photovoltaic arrays or wind turbines. By virtue of good match between generation and load, microgrids have a low impact on the electricity network, despite a potentially significant level of generationby interemittent energy sources. The paper discusses the technical and economic issues associated with this novel concept, giving an overview of the generator technologies, the current regulatory framework in the UK, and the barriers that have to be overcome if microgrids are to make a major contribution to the UK energy supply. The focus of this study is a microgrid of domestic users powered by small Combined Heat and Power generators and photovoltaics. Focusing on the energy balance between the generation and load, it is found that the optimum combination of the generators in the microgrid - consisting of around 1.4 kWp PV array per household and 45% household ownership of micro-CHP generators - will maintain energy balance on a yearly basis if suplemented by energy storage of 2.7 kWh per household. We find that there is no fundamental technological reason why microgrids cannot contribute an appreciable part of UK energy demand. Indeed, an estimate of cost indicates that the microgrids considered in this study would supply electricity at a cost comparable with the present electricity supply if the current support mechanisms for photovoltaics were maintained. Combining photovoltaics and micro-CHP and a smallbattery requirement gives a microgrid that is independent of the national electricity network. In the short term, this has particular benefits for remote communities but more wide-ranging possibilities open up in the medium to long term. Microgrids could meet the need to replace current generation nuclear and coal fired power stations, greatly reducing the demand on the transmission and distribution network.

Value Analysis of Battery Energy Storage Applications in Power Systems

Abstract: Stressed and less secure power system operating conditions have encouraged both power utilities and large power consumers to look for bulk energy storage systems. Battery energy storage systems (BESS) have excellent records and are used for decades in power systems. This paper describes a methodology for a monetary value analysis of the BESS for load leveling, control power and peak shaving applications. The purpose of this value analysis is to highlight the application with the highest financial benefit for the owner of the BESS. To determine the overall economic viability, revenue of each application has been compared with capital and operating costs over the BESS lifetime. The results of the value analysis show that primary control power is the application that most likely will be asked for by utilities during next 3-5 years

Method and apparatus for power electronics and control of plug-in hybrid propulsion with fast energy storage

Abstract: A plug-in hybrid propulsion system includes a fast energy storage device that preserves battery life, where the energy storage elements of the hybrid drive train may be charged with externally supplied electricity as well as energy from the engine or regenerative braking. Electronic switches, passive electronics, an enclosure, controller circuitry, and/or control algorithms are used to manage the flow of power between a fuel powered engine, a battery, a fast energy storage system, traction motors, a charger, ancillary systems, an electrical distribution system, and/or a drive train.

Equivalencing the collector system of a large wind power plant

Abstract: As the size and number of wind power plants (also called wind farms) increases, power system planners will need to study their impact on the power system in more detail. As the level of wind power penetration into the grid increases, the transmission system integration requirements becomes more critical. A very large wind power plant may contain hundreds of megawatt-size wind turbines. These turbines are interconnected by an intricate collector system. While the impact of individual turbines on the larger power system network is minimal, collectively, wind turbines can have a significant impact on the power systems during a severe disturbance such as a nearby fault. Since it is not practical to represent all individual wind turbines to conduct simulations, a simplified equivalent representation is required. This paper focuses on our effort to develop an equivalent representation of a wind power plant collector system for power system planning studies. The layout of the wind power plant, the size and type of conductors used, and the method of delivery (overhead or buried cables) all influence the performance of the collector system inside the wind power plant. Our effort to develop an equivalent representation of the collector system for wind power plants is an attempt to simplify power system modeling for future developments or planned expansions of wind power plants. Although we use a specific large wind power plant as a case study, the concept is applicable for any type of wind power plant.

A Compact Digitally Controlled Fuel Cell/Battery Hybrid Power Source

Abstract: A compact digitally controlled fuel cell/battery hybrid power source is presented in this paper. The hybrid power source composed of fuel cells and batteries provides a much higher peak power than each component alone while preserving high energy density, which is important and desirable for many modern electronic devices, through an appropriately controlled dc/dc power converter that handles the power flow shared by the fuel cell and the battery. Rather than being controlled to serve only as a voltage or current regulator, the power converter is regulated to balance the power flow to satisfy the load requirements while ensuring the various limitations of electrochemical components such as battery overcharge, fuel cell current limit (FCCL), etc. Digital technology is applied in the control of power electronics due to many advantages over analog technology such as programmability, less susceptibility to environmental variations, and low parts count. The user can set the FCCL, battery current limit, and battery voltage limit in the digital controller. A control algorithm that is suitable for regulating the multiple variables in the hybrid system is described by using a state-machine-based model; the issues about embedded control implementation are addressed; and the large-signal behavior of the hybrid system is analyzed on a voltage-current plane. The hybrid power source is then tested through simulation and validated on real hardware. This paper also discusses some important issues of the hybrid power source, such as operation under complex load profiles, power enhancement, and optimization of the hybrid system. The design presented here can not only be scaled to larger or smaller power capacities for a variety of applications but also be used for many other hybrid power sources

Plug-in hybrid vehicle with fast energy storage

Abstract: This invention relates to plug-in hybrid propulsion systems where the energy storage element of the hybrid drive train may be charged with externally supplied electricity as well as energy from the engine or regenerative braking. The invention is a plug-in hybrid system with a fast energy storage and delivery system. In a preferred embodiment the invention comprises a fuel powered engine, a battery, a fast energy storage system, power converters, controllers, drive motors, an electrical distribution system, and a drive train. Additionally, the invention relates to plug-in hybrids that provide services to the electrical utility when the vehicle is connected to the utility grid.

Wind Power Impact on System Frequency Deviation and an ESS based Power Filtering Algorithm Solution

Abstract: Wind power is the fastest growing renewable energy. However due to its stochastic nature, fluctuating wind power results in adverse impacts on power systems, including system frequency deviations. Study on system frequency response in this paper shows power systems are more sensitive to the medium frequency power fluctuations (between 0.01 and 1 Hz), while the majority of wind power fluctuations are located in that regions and below. For small standalone power systems, even a modest wind penetration will lead to considerable system frequency deviation by the wind. To diminish the wind power impact on system frequency, an energy storage system (ESS) based wind power filtering algorithm is proposed in this paper, aimed at attenuation of those medium frequency fluctuations. Electromagnetic transient simulation results quantitatively demonstrate the effectiveness of this algorithm; the wind power is smoothed out and the system frequency deviations are limited to an acceptable level

Control Strategies for Distributed Power Generation Systems Operating on Faulty Grid

Abstract: The distributed power generation based on renewable energy sources such as wind and sun experiences a high penetration in the power systems around the world, having in some countries a large contribution to the total energy production. In order to protect the distribution and transmission systems, the grid operators are more and more talking about the ability of the distribution systems (mainly wind turbines WT systems) to behave as a conventional power plant. This paper discusses the possibilities of the distributed power generation systems (DPGS) to deliver power when grid disturbances are present in the utility network. The focus is set more on the control strategies for active power generation, and mainly on the creation of the reference currents which fulfill the demanded output power. Considerations about reactive power are also stated. Experimental results are presented in order to validate the theory behind the proposed control strategies on faulty grid.

Power management of hybrid photovoltaic - fuel cell power systems

Abstract: Photovoltaic (PV) solar energy systems are widely used as an important alternative energy source. To overcome the problem of intermittent power generation, PV power systems may be integrated with other power sources. Fuel cells are an attractive option because of high efficiency, modularity and fuel flexibility; however, one main week point is their slow dynamics. On the other hand, current technology batteries by themselves are usually insufficient to provide the long-term energy that the increasing loads require. Hybrid systems composed of fuel cells and batteries can be integrated with PV power systems to provide uninterrupted high-quality power. The goal of this study is to design an effective power management system for a PV/fuel cell/battery hybrid power system so that the combination can be used as a reliable power source. In this paper, the structure of the hybrid power system is described, and control strategies for power management of the hybrid power system are discussed. The proposed hybrid power system is then verified by numerical simulation.

Survey of the Power Conditioning System for PV Power Generation

Abstract: This paper is a survey on photovoltaic (PV) power conditioning systems (PCS) and their control strategies. Different inverter structures used in the PCSs are summarized. A novel Z-Source inverter based PCS is presented. The requirements and standards of PV PCS are also introduced.

Electricity meter with power supply load management

Abstract: An electricity meter for monitoring electric power consumed from a service line is disclosed. The electricity meter includes a power consumption metering system for measuring the amount of power consumed from the service line, a peripheral device providing a non-critical function, a power converter, and a load management system. The metering system includes a controller and data storage for storing power consumption data. The power converter provides an unregulated voltage output at the terminals of a capacitor for powering the metering system. The load management system selectively couples and decouples the peripheral device from the power converter. The load management system senses the unregulated voltage to determine whether to couple or decouple the peripheral device. A load management system for an electricity meter and a method of managing the loads on the power system of an electricity meter are also disclosed.

Grid-connected hybrid PV/wind power generation system with improved DC bus voltage regulation strategy

Abstract: The objective of this paper is to propose an improved dc bus voltage regulation strategy for the grid-connected PV/Wind power generation system. The proposed dc bus voltage regulation strategy can reduce the variation of the dc bus voltage and the size of the dc bus capacitor bank, significantly. Also, the change of the injected ac current amplitude will be moderate and the power quality of the utility can be improved. A 1.2 kW prototype system is built and tested to verify the feasibility of the proposed dc bus voltage regulation strategy. Hardware experimental results are shown to confirm the performance of the proposed dc bus voltage regulation strategy.

Effects of PV Grid-Connected System Location on a Distribution System

Abstract: The grid-connected photovoltaic (PV) power generation system is expected to be more widespread in distribution systems due to increasing fossil-fuel cost. Recent advances in PV technology and great demand has led to cost reductions. This paper presents the effects of PV system installation location on the power quality of the distribution system. A measurement setup is prepared for a PV grid-contected system. The system consists of a PV array and a grid-connected inverter. The measured data are used to investigate the effects of a PV system. A feeder line with PV system is simulated in Matlab. This study focuses on both radial and loop operated distribution system. The distribution system's power quality, in terms of voltage, active power, total losses, and power factor of the network are presented. The simulation results show that implementation of the PV grid-connected system could improve the power quality of a distribution feeder.

Lift truck with hybrid power source

Abstract: A lift truck power source includes a hybrid power supply including a storage battery, a capacitor bank, and optionally a fuel cell. The capacitor bank stores power produced during regeneration by either the truck traction system or the lift system and delivers current when current demand exceeds that delivered by the fuel cell. The storage battery or fuel cell acts as a main power supply to deliver current at a rate sufficient to power the lift truck. When the fuel cell is the main power supply, the storage battery stores power during times when current demand is less than that delivered by the fuel cell and delivers current at times when current demand is greater than that delivered by the fuel cell. When the storage battery is the main power supply, the fuel cell supplements the power delivered by the storage battery, and can also recharge the storage battery.

Consumer-sited power management system and method

Abstract: A system and method provide emergency back-up power for communications, security and other systems of an electric power consumer, and for peak-shifting of the electrical load so that electricity is generated and stored when demand is low, and the stored power is used when demand is high Embodiments include providing an electric power management device having a battery and a communication system at the premises of a consumer of electricity, and connecting the power management device to an electric power provider The battery is charged at an off-peak time when a demand for electricity is low, as determined by the electric power provider; and discharged to provide electricity to the consumer at a time when the demand for electricity is high, as determined by the electric power provider The charging and discharging is controlled by the electric power provider

Modeling and Control of a Grid-connected Wind/PV Hybrid Generation System

Abstract: This paper deals with power control of a wind and solar hybrid generation system for interconnection operation with electric distribution system. The proposed system consists of a variable-speed direct-drive wind generator, wind-side converter, solar array, dc-dc converter and grid interface inverter. Power control strategy is to extract the maximum energy available from varying condition of wind speed and solar irradiance while maintaining power quality at a satisfactory level. In order to capture the maximum power, variable speed control is employed for wind turbine and maximum power point tracking is applied for photovoltaic system. The grid interface inverter transfers the energy drawn from the wind turbine and PV array into the grid by keeping common dc voltage constant. Modeling and simulation study on the entire control scheme is carried out using a power system transient analysis tool, PSCAD/EMTDC. The simulation results show the control performance and dynamic behavior of the wind/PV system

Study on Field Demonstration of Multiple Power Quality Levels System in Sendai

Abstract: Presented are reports on the development of a multiple power quality level supply system that provides five kinds of high quality electric power at the same time. The system utilizes both renewable energy and utility and supplies consumers with various kinds of electric power of high quality. It gives consumers the advantages of low cost and reduces the amount of space needed for existing such power converters as UPSs. It also contributes to promoting the introduction of renewable energy. We conducted a field experiment of this system. Over the course of one year, we measured the demand pattern of an experimental field. We then developed a system that was suitable for it. Furthermore, the effects will be studied for about one year and half demonstration by the field.

Very Large-Scale Deployment of Grid-Connected Solar Photovoltaics in the United States: Challenges and Opportunities

Abstract: This paper analyzes the potential for solar photovoltaics (PV) to be deployed on a very large scale and provide a large fraction of a system's electricity. It explicitly examines how the hourly availability of PV interacts with the limited flexibility of traditional electricity generation plants. The authors found that, under high penetration levels and existing grid-operation procedures and rules, the system will have excess PV generation during certain periods of the year. This excess PV generation results in increased costs, which can increase dramatically when PV provides on the order of 10%-15% of total electricity demand in systems that are heavily dependent on inflexible baseload steam plants. Measures to increase penetration of PV are also discussed, including increased system flexibility, increased dispatchable load, and energy storage.

Effects of FACTS Devices on a Power System Which Includes a Large Wind Farm

Abstract: Nowadays, power systems are facing new challenges, such as increasing penetration of renewable energy sources, in particular wind generation, growing demands, limited resources, and competitive electricity markets. Under these conditions, the power systems has had to confront some major operating problems in voltage regulation, power flow control, transient stability, and damping of power oscillations, etc. Flexible AC transmission system (FACTS) devices can be a solution to these problems. This paper investigates the application of FACTS devices on a 12-bus multimachine benchmark power system including a large wind farm. A STATCOM and an SSSC are added to this power network to provide dynamic voltage control for the wind farm, dynamic power flow control for the transmission lines, relieve transmission congestion and improve power oscillation damping and transient stability