Showing papers on "Stand-alone power system published in 1996"

Electric car drive system provided with hybrid battery and control method

Abstract: In an electric car drive system having a car drive motor powered by a mounted direct current power supply, a control system including a signal generating means is provided to generate signals which control motor speed. The direct current power supply is composed of a power battery having secondary cells connected to the motor and an energy battery formed by fuel cells connected in parallel to said power battery via an energy battery control switch. The electric car drive system is composed of a charge control means which charges the power battery using the energy battery if the charge of the power battery is below the specified value when said key switch is turned off, and suspends charging if the charge is equal to or greater than the specified value. A battery current and voltage control controls a voltage increasing circuit connected between the energy battery and the power battery based on the current or voltage of any one of the power battery, energy battery or motor and keeps the voltage of the direct current power supply within a specified range.

Voltage sags: effects, mitigation and prediction

Abstract: Customers all over the world experience problems due to power system voltage sags. Computers, industrial control systems, and adjustable-speed drives are especially notorious for their sensitivity. Tripping of high-power adjustable-speed drives is probably the main voltage sag problem. The number of trips depends strongly on the equipment sensitivity. Prediction methods are needed to quantify this aspect of the quality of the power supply. From utility and manufacturer's data, a customer can assess the compatibility between a piece of equipment and the electricity supply.

A bifunctional utility connected photovoltaic system with power factor correction and UPS facility

Abstract: In this paper, a novel utility connected photovoltaic power generation system with unity power factor and uninterruptable power system facility and its control strategy are proposed. The proposed photovoltaic (PV) system is connected in parallel between the utility and load. The PV system provides an uninterruptable voltage to the load, a maximum power tracking to solar array, and power factor correction to the utility. The proposed system has the following advantages compared with the conventional utility connected PV system: harmonic elimination function; feeding the photovoltaic energy to the utility; and providing the uninterruptible power source battery to the load. In the case where the photovoltaic array system is in a state of poor power generation, the battery and capacitor of the PV system are charged by a three phase utility source and the inverter in the PV system only provides the reactive current to eliminate the harmonic current exited on the utility. In the normal operation mode, the PV system supplies active power to the load and reactive power to the utility in order to maintain the unity power factor and to regulate AC load voltage.

Highly programmable backup power scheme

Abstract: Heavily relied upon network devices require backup power systems. To efficiently allocate power, a highly programmable backup power system is desired. The present invention discloses a redundant power supply unit that provides backup power to network devices. The redundant power supply unit will supply power to the network devices in the case that their local internal power supplies fail. Furthermore, if there is a power outage from the utility company, the redundant power supply will supply power to the network devices from a internal battery pack. When the internal battery pack is engaged, the redundant power supply uses programmed control logic that controls how the power from internal battery pack will be allocated. Specifically, since the power from the batteries is limited, it can be used to power some network devices for a certain amount of time and other network devices for a longer amount of time. Furthermore, the power from the batteries can be allocated depending on the voltage level of the battery thus, when the battery voltage drops below a certain threshold the power supply may disconnect power to some units and maintain power to others.

Photovoltaic power generation system

Abstract: PROBLEM TO BE SOLVED: To charge a storage battery by a solar battery at the same time even in parallel operation with an external power source and take maximum electric power out of the solar battery as to the photovollaic power generation system. SOLUTION: When a solar battery feed system consisting of the solar battery 1 and an inverter 2 and the external power source 10 are in parallel operation, charging control over the storage battery 3 is performed by a bidirectional DC/DC converter 9 installed in the charging/discharging path of the storage battery 3 to limit a decrease in the impedance of a solar battery load circuit at this charging time to less than a specific value and in this state, a maximum power follow-up control circuit 12 which makes the input voltage of the inverter 2 follows up a set voltage corrected according to circumferential conditions such as sunshine conditions is made to function to perform maximum power follow-up control over the solar battery 1 under solar battery load impedance control by the output control of the inverter 2 having its input voltage corrected by this circuit, thereby taking optimum electric power corresponding to the changing sunshine state out of the solar battery 1 and charging the storage battery 3 at the same time.

Regenerative power system

Abstract: A regenerative-type hybrid power system A regenerative-type hybrid power system (20), according to the present invention, comprises a first car (30) having a load (13) that comprises an electric load for driving; an electric power generation device (40, 4, 5) comprising at least one of electric power supply devices among a first electric power supply device (40) which is provided on the first car to generate electric power, second electric power supply devices (5) which are provided on the ground to generate electric power and transmit and transform the generated power, and third electric power supply devices (4) which are provided on other cars to supply electric power to the outside that is surplus;a regenerative fuel cell (7), for storing the chemical energy by utilizing the electric power that is supplied from the electric power generation device and regenerating the stored chemical energy, which comprises a water electrolysis device (9), a storage device (10) for storing up at least the electrolyzed hydrogen and the oxygen, a fuel cell (11) for generating electricity using the stored hydrogen and oxygen as fuel, and a heat exchanger (8) for the water electrolysis device, the storage device and the fuel cell; a regenerative control device (12) for controlling regeneration of the electric power by the regenerative fuel cell (7) to supplement lack of the electric power that is supplied to the load (13) The hybrid power system of this invention can realize a high speed energy conversion and storage system as well as a high power generation system to maintain high energy weight and volume efficiency, the purpose of this invention, the high speed energy conversion and storage and the high power generation of electricity, can be realized in a form to maintain high energy weight and volume efficiency

Power controller for solar battery

Abstract: PROBLEM TO BE SOLVED: To provide the power controller which complements defects of a conventional power control method for a solar battery and derives maximum output from the solar battery. SOLUTION: Ordinary MPPT control is normally performed, and the operation point of the solar battery is varied in longer cycles and over a winder search range than the MPPT control to take in a voltage signal and a current signal. When voltage-power characteristics have two peaks, an original operation point if the original operation point is at the peak where maximum power is obtained or an other operation point if the operation point where the maximum power is obtained is at the other peak is selected, thereby setting the voltage at the selected operation point as a set value.

Small power systems fed by hydro, photovoltaic, wind turbines and diesel generators

Abstract: This paper presents software simulation and experimental verification of the dynamic behaviour of small autonomous power systems with alternative power sources, such as Wind Turbines, small Hydroelectrics and Photovoltaics. The combination of the Hydroelectric power plants and the Diesel generators is of great interest since they have very different rates of power change. For the effective integration of the Photovoltaic (PV) devices into the utility grid, a method for controlling the Inverter's operation is proposed. According to this method the Power demand from the network is monitored and control signals adjust the angle and the magnitude of the Inverter's voltage. It is shown that this method improves power quality and stability of the interconnected system.

Thermoelectric generators in photovoltaic hybrid systems

Abstract: The supply of distant electric devices that cannot be connected to the public electricity grid for reasons of cost, waiting time or due to the need of local flexibility has been a major problem. To date, the power supply of such stand-alone systems has been based mainly on battery-buffered fossil-fueled motor-generators. Apart from the consumption of limited fossil fuel reserves, the disadvantages of these systems include the creation of noise and exhaust gases, the constant need to obtain fuel and, most important, the high amount of maintenance and repairs. For these reasons, and due to the progress in regenerative energy conversion made in the last decade, battery-buffered PV power systems are used more and more often. Their advantages are high reliability and low cost of repairs. However, far away from the equator, where solar radiation is very low during the winter, large PV generators are needed to guarantee sufficient reliability. Therefore, system costs are high. Another disadvantage is that the battery lifetime in PV power systems is significantly reduced compared to its lifetime in fossil fueled systems. To avoid these disadvantages, the PV generator can be combined with fossil fueled power generators. In the medium power range, from 10 W up to several hundred W, thermoelectric generators appear to be particularly qualified because of their reliability and lifetime. In this paper, a (so called) "photovoltaic hybrid system" is compared to a purely PV power system on the basis of model calculations starting with the solar radiation situation on the Earth's surface.

Power generation installation making use of solar energy

Abstract: PROBLEM TO BE SOLVED: To provide a power generation installation, making use of solar energy, whose economical effect is high by a method wherein a storage battery which shares a solar cell and an inverter is installed and the storage battery can be charged with the generated power of the solar cell. SOLUTION: In a power generation installation making use of solar energy, a solar cell 8 is linked to a power system, and electric power is supplied to low-voltage loads 6, 6. In the power generation system, a storage battery 12 and a received-power detector 5 are installed, the storage battery 12 is discharged when electric power supplied from the power system exceeds definite electric power, the discharge operation of the storage battery 12 is stopped when the electric power is at the definite electric power or lower, and the storage battery 12 is charged at any time. COPYRIGHT: (C)1998,JPO

A learning curve approach to projecting cost and performance in thin film photovoltaics

Abstract: The current cost of electricity generated by PV power is still extremely high with respect to utility power and there remain questions as to whether PV power can ever be competitive with electricity generated by fossil fuels. A previous paper by the authors supplied an objective framework for considering this important question and introduced analytical tools to define and project the technical/economic status of PV power through the year 2010. In this paper, we update this previous work in the context of the announcements by Amoco/Enron Solar of projected sales of PV power in 1997 at rates considerably less than the US average.

A control system for improved battery utilization in a PV-powered peak-shaving system

Abstract: Photovoltaic (PV) power systems offer the prospect of allowing a utility company to meet part of the daily peak system load using a renewable resource. Unfortunately, some utilities have peak system-load periods that do not match the peak production hours of a PV system. Adding a battery energy storage system to a grid-connected PV power system will allow dispatching the stored solar energy to the grid at the desired times. Batteries, however, pose system limitations in terms of energy efficiency, maintenance, and cycle life. A new control system has been developed, based on available PV equipment and a data acquisition system, that seeks to minimize the limitations imposed by the battery system while maximizing the use of PV energy. Maintenance requirements for the flooded batteries are reduced, cycle life is maximized, and the battery is operated over an efficient range of states of charge. This paper presents design details and initial performance results on one of the first installed control systems of this type.

Development of a simple photovoltaic system for interconnection of utility power system

Abstract: A simple photovoltaic power regeneration system for interconnection with a utility power system is described. The developed photovoltaic system of 3 kW has the following characteristics: (1) the power generated by a solar battery can be regenerated to the utility power source with a sinusoidal current waveform of specified power factor; (2) the solar battery is optimally controlled to get the maximum output power with high speed; (3) to maintain safety, the solar battery is isolated from the utility power system by the inverter involving a high frequency transformer; and (4) the maximum efficiency of the regenerative inverter is 93.6%. In the experiments, a solar battery simulator is employed instead of a solar battery to realize low cost and small size of the experimental system.

Solar power generator

Abstract: PROBLEM TO BE SOLVED: To reduce power consumption by providing a switch control means for a solar battery voltage monitoring section and interrupting power supply to a power converter and a control section at night when the voltage of solar battery drops by opening a switch for controlling power supply between a main power supply section and a distribution line, thereby preventing power consumption. SOLUTION: A monitor power supply section 12 converts power being supplied from a distribution line 6 into DC power and supplies driving power constantly to a solar battery voltage monitoring section 11 which is thereby operated constantly. When the voltage of a solar battery 1 drops to a control stop voltage at sunset, a switch 14 is opened to turn off power supply to a main power supply section 13 thus interrupting main power supply to an inverter (power converter) 3, a control section 9, etc. Since power is not supplied uselessly to various circuit parts in the inverter 3, the control section 9, etc., at night, power consumption in these circuit parts is prevented, thus reducing total power consumption significantly. COPYRIGHT: (C)1998,JPO

Photovoltaic power generation for air-conditioning system based on predictive control

Abstract: In this paper, an auxiliary power supply scheme using photovoltaic power generation for an air conditioning system and a novel control strategy are proposed. The proposed auxiliary power supply system employs a boost power converter, a bidirectional power converter and photovoltaic arrays. The boost power converter, controlled by a predictive control strategy, provides maximum power tracking (MPT) state on the photovoltaic (PV) arrays as well as power generation facility function on the AC utility grid. Furthermore the bidirectional power converter controls the power flow balance between the loads and two different power sources according to the condition of the load power and the supplied power from photovoltaic arrays. It is shown that the maximum power tracking of the PV arrays, the unit power factor of AC utility grid and the descent input DC voltage regulation of the air conditioning system are achieved by the proposed predictive control strategy. The controller design procedure for the proposed approach is detailed. Simulation results on a laboratory prototype system are also discussed.

Regenerative system for electric motor car

Abstract: PROBLEM TO BE SOLVED: To effectively use electric power generated during regenerative stage without using high-priced complicated circuit in an electric motor car driven by a motor 1 using a battery 2 as an energy source. SOLUTION: A capacitor 3 is provided for storing electricity generated during regeneration. A motor 1 is connected to a capacitor 3 from regeneration time to the driving thereafter. After the consumption of the effective electricity in capacitor 3, the motor 1 is connected to a battery 2. Electricity generated during regeneration is stored in the capacitor 3, and its electricity is consumed with priority over electricity generated by the battery 2.

Development and application of a computerised design tool for remote area power supply systems

Abstract: Good design of renewable energy electrical systems is essential to the acceptance of this new technology for widespread use. The systems need to be convincing to consumers in terms of performance reliability and cost-effectiveness, when compared to the traditional options of grid extension or a diesel generator. Essential to the selection of a good design is a thorough design approach. The purpose behind this work was to develop a software package that could guide the user in the design process for renewable power systems. The software, known as RESSAD (Renewable Energy System Simulation And Design), had at its core a simulation model, known as RESIM (Renewable Energy SEMulation). The model predicts the performance of renewable standalone and renewable diesel hybrid systems. A system simulation model can be easily misused if there is not a good understanding of the site’s renewable resources and load trends, prior to any simulation, and if the implications of simulation results are not understood. Therefore, to enhance the usefulness of RESIM, a range of design tools were developed for use prior to, and after the simulation. The design tools provide a series of steps that lead to the selection of an initial system design. Industry experience was utilised to establish guiding principles for sound, economical system design. These principles were offered to the user in the form of conclusions on the renewable resource and its relationship to the load, and recommendations for both the system type and the size of components. A broad user group was envisaged for this software, and so the software is user-friendly for the inexperienced designer, while still offering some sophisticated control features. The software also had to be reliable in its predictions and suggestions. This leads to a compromise between model complexity, to ensure sufficient accuracy, and user-friendliness, which entails a minimum number of input data, that are readily available. Validation of RESIM was carried out to establish the level of accuracy that could be achieved with the model. Monitored data from both renewable standalone and hybrid systems were used in the validation process and a comparison was made with another simulation program, PVFORM, in order to further assess the PV model incorporated in RESIM. A need was identified for more reliable monitored data for such validation purposes. Case studies were conducted to test the usefulness of the software, including the design tools. Renewable systems were sized and simulated for three different load ranges at seven Australian locations and the most economical designs were investigated with further simulations. The conclusions from these studies supported this approach in system design, and showed the need for further work to identify design principles, especially for the larger systems meeting loads over 20kWh/day. Economic indicators, such as the net present cost, are the final outcome from the software and viewed as the key determinants of final system design. The validation process indicated the simulation accuracy of RESIM for renewable hybrid systems ranged from 2.5 to 15.5% for diesel operating hours per day and 6.1 to 8.7% for daily fuel consumption. Applying the worst errors to these parameters in the case studies produced errors in the net present cost of 8% for diesel/ inverter systems and under 2.5% for small renewable hybrid systems.

System interconnection operating method for hybrid power supply system involving photovoltaic power generation and wind power generation

Abstract: PROBLEM TO BE SOLVED: To increase the utilization factor and availability factor of a hybrid power supply system involving photovoltaic power generation and wind power generation and lengthen the lives of batteries. SOLUTION: When the voltage of a battery 3 is lower than a given value, a change-over switch 8 is opened to isolate a hybrid power supply system. A photovoltaic power generation device 1 interconnects an inverter 4 to a system power supply 6 by maximum power follow-up control, and a wind power generation device 2 is used only for charging the battery 3. When the voltage of the battery 3 exceeds the specified value, the change-over switch 8 is closed to direct-current-link the photovoltaic power generation device 1 and the wind power generation device 2. Thus power discharged from the battery 3 and power generated from the photovoltaic power generation device 1 and the wind power generation device 2 is interconnected with the system power supply 6 by controlling the inverter 4 through a fixed power command. COPYRIGHT: (C)1998,JPO

A Changing Electric Power Industry

Abstract: Karl Stahlkopf* recently pointed out that the U.S. electric power industry is undergoing its most profound changes in a century. This movement is in response to the growing role of competitive wholesale power transfers, to regulatory pressures, and to the demands of users of power-sensitive equipment, such as microprocessors. Scientists and engineers using computers and computer-aided equipment need reliable electricity, and many industrial customers are employing sensitive electronic devices to control their machines. A one-cycle interruption in ac supply can cause serious losses of production and information. The total cost of interruptions and voltage sags has been estimated to be $3 billion to $5 billion per year. Providing completely reliable electric power is not easy. Generating plants have thousands of parts, and the failure of a component can cause a sudden shutdown. To increase the overall reliability of electric power, many generating plants are connected in regional transmission systems. The 60-cycle frequency of all the generators in a system must be synchronized, even if those generators are a thousand miles apart. Such a network, with its varying power sources and loads, has complex behaviors. Electric current destined for a consumer often does not flow by the shortest path but proceeds in a loop hundreds of miles long. On occasion, lines have been subjected to excessive currents, causing them to overheat, expand, and sag. A power failure in the eastern United States was greatly magnified when overheated sagging lines touched trees. Applications of new technology are leading to greater reliability and lower maintenance costs of electric power systems. Sensors that can detect and warn of imminent failures are being installed at crucial points. One example is an instrument that detects gases produced by overheated transformers. Another device is programmed to monitor the sine wave in a distributing line. When the line is struck by lightning, the sensor detects a deviation in the shape of the voltage cycle, and thyristors can quickly remedy the voltage deviation. Thyristors are large solid-state devices that consist mainly of elemental silicon doped to create positively or negatively charged regions. Because they can respond in a fraction of a cycle, they will increasingly be used to switch large electrical currents. In computer-controlled industrial processes, problems can be avoided when thyristors quickly switch from a failed feeder to another power source. Electric utilities are under competitive and regulatory pressures to reduce the price of power. In earlier times, most were sole providers of electricity in specific regions. They were regulated by state and local authorities that enabled them to earn a profit and recapture the costs of capital investments. They owned their generating stations, the transmission lines, and the distribution system. Some made costly investments in generating stations that now seem ill-advised. Other utilities were urged by regulators to make long-term commitments to purchase expensive power, some of it from then-fashionable renewable energy sources. Costs to U.S. consumers of electric power now range from about 3 to 16 cents per kilowatt-hour. Large-scale consumers have responded to high costs by building their own generating facilities and by purchasing electricity from unregulated power producers. This search for lower costs has been facilitated by the existence of the large-scale power grids and by regulatory pressure to make the transmission line capabilities of utilities available to competitors. An important result has been the creation of an expanding market for wholesale electric power. For example, Consolidated Edison, which distributes electricity in New York, purchases some electricity from Quebec Hydro and some from Georgia Power. Sources often change hourly, depending on the price quoted by each. Already, 40 percent of the power generated in the United States is sold by a producing company on the wholesale market. New, more efficient generating plants—most notably those using gas-fired combustion turbines—have production costs that are considerably lower than those of many existing plants. Federally mandated open access to transmission networks is expected to further accelerate the growth of bulk power sales. Moreover, as Stahlkopf states, “Deregulation is rapidly making electricity as much of a commodity as pork bellies—complete with an evolving futures market and a variety of sophisticated trading options.”

Remote area power supply: Nyafaru micro hydro power plant

Abstract: Many parts of Southern Africa are without decentralised commercial electrical power, and this case study illustrates how simple technology applied to run-of-river hydroelectric power can be harnessed to provide a viable form of energy to off-grid communities. The paper describes a stand-alone micro-hydroelectric power scheme in a typical Zimbabwean rural community. The Nyafaru Power Project was developed primarily as a pilot project, and it is expected to be used as a model for building similar remote area power supplies to reduce the problem of rural electrification.

Embedded generation: the regulatory angle

Abstract: Embedded generators take many forms. They range from tiny hydroelectric power stations up to a hundred megawatts or so. They can be conventional fossil-fired generators, or powered by renewable energy. They may operate solely as generation, or as part of an industrial process, while combined heat and power plants are making an increasing contribution. This paper puts forward some of the potential benefits-and potential pitfalls-of embedded generation. It is the author's intention to demonstrate that these benefits can accrue both to the generating company and to the distribution system operator.

Electricity generation and transmission in South Africa by 2020: an Eskom planning perspective

Abstract: The demand for electricity in South Africa is expected to double by 2020. To supply this load generation and transmission capacity will have to be expanded. The paper examines three possible future generation scenarios. Each scenario requires a distinctly different transmission expansion programme. The paper emphasises the need for an integrated approach towards the expansion planning of generation and transmission infrastructure. Due to the various options at hand, decisions on new plant can only be made once evaluation of the full cost to the economy and of all the important attributes has been completed.

Hybrid type electric power supply facility

Abstract: PROBLEM TO BE SOLVED: To constitute an efficient electric power system without enlarging the whose scale of the system facility by installing both a fuel cell and a secondary battery (a storage battery) and leveling the load demand to the fuel cell. SOLUTION: This hybrid type electric power source facility is so constituted as to supply electricity to a load side such as a Thrustor 18 through a charging and discharging management apparatus 16 from a fuel cell body 2 and a secondary battery 15 built in a submersible research ship, and when overloading, electricity can be supplied from the secondary battery 15. The secondary battery 15 can be charged from an outer electric source through an electricity receiving connector 30 and is normally float-charged by the fuel cell body 2. When the fuel cell body 2 is started, a heater 3a in a circulation water tank 3 is driven through a load circuit 31 and a switch 7 by the secondary battery 15 for preheating of the fuel cell body 2.