Showing papers on "Stand-alone power system published in 2000"

Past, present and future of grid connected photovoltaic- and hybrid-power-systems

Abstract: As a short introduction on the general development and forecast of world market in photovoltaics (PV) are presented. The general classification introduces grid connected, stand alone, large scale and roof-top PV-systems. The core of presentation concentrates on the development and trends of converters for grid connected PV-systems. The novel multi-string converter is introduced representing one of the major trends in PV system technology towards modular PV-system design based on string converter technology with low specific costs and optimal energy yield. A brief excursion into the area of hybrid power systems deals with the development of hybrid power system technology using some representative examples installed by SMA around the world. As one of the future trends in that area a new bi-directional battery-converter for a modularly-structured hybrid power system technology is introduced.

Using power line carrier communications to prevent islanding [of PV power systems]

Abstract: Islanding of grid-connected photovoltaic (PV) power systems jeopardizes personnel and equipment and must therefore be prevented. Existing islanding prevention schemes are undesirable because they fail for certain relatively common customer loads and when more than one PV power system is present, degrade PV power quality, reduce system efficiency, and increase system complexity. These problems can be overcome using power line carrier communications. (PLCC) and an inexpensive, purpose-designed receiver. The use of PLCC for islanding prevention is discussed. In this paper, including considerations for maximum anti-islanding effectiveness. Also, a low-cost receiver for a commercial PLCC system is described and demonstrated. This receiver demonstrates the feasibility of PLCC-based islanding prevention.

A grid-interactive photovoltaic uninterruptible power supply system using battery storage and a back up diesel generator

Abstract: This paper presents a practical implementation of a grid interactive photovoltaic uninterruptible power supply (UPS) system using battery storage and a back up diesel generator. The system incorporates 2.5 kWp of photovoltaic arrays, a 10 kVA power conditioning unit capable of operating in both inverting and charging modes, and a 300-Ah battery bank. Two such systems were installed in two Indian cities. The project was implemented using soft loans available in India through a World Bank Loan for photovoltaic market development. The system has been working satisfactorily since May 1997 and has demonstrated the capability of the system to provide uninterrupted power, demand side management function and load voltage stabilization in a grid which experiences frequent blackouts and under/over voltage problems. Some results from the field installation are also included in this paper.

An off-board station and an electricity exchanging system suitable for use with a mobile vehicle power system

Abstract: A mobile vehicle power supply system and an electricity exchanging system enhance the economic viability of different modes of transportation that incorporate generators, such as electric motors and fuel cells, to generate electricity. The power supply system provides for the off-board use of the electric power generated by the generator of a mobile vehicle, such as an electric car. Off-board use, or use remote from the vehicle, of the electrical power includes the delivery of power to a remote site. Off-board stations are provided for delivery of fuel to the vehicle and/or for receiving the electrical power generated by the fuel cell. The off-board station and the vehicle are appropriately equipped for quick and easy interconnection such that electrical power can be exchanged between the vehicle and off-board station and the electricity exchanging system. The electricity exchanging system is configured for installation at numerous locations for allowing a mobile vehicle operator to purchase or sell electricity. The operator employs a user authorization element to assist the recording or tracking of electricity exchanged between the vehicle and the electricity exchanging system.

Power supply system for distributed source

Abstract: PROBLEM TO BE SOLVED: To provide a power supply system for a distributed source, installing a distributed power source system in a plot of a power user by a power supply provider to perform power supply to the user, diagnosis of system operation, etc. SOLUTION: This system includes a distributed power source system 16, supplying power of commercial frequency to a load 8 of a specific user, additionally performing system linkage and a system managing means 15 connected to each distributed power source system via a communication network 12; the distributed power source system 16 includes a solar battery 1, a fuel cell 2, a storage battery 3, a power converter means 4 for system-linking power output from these power-generating means, a power condition monitor means 6, and a system control means 7; and the system control means 7 communicates operating information of the distributed power source system 16 to the system managing means 15 and controls the operating condition of the power converter means 4, according to the indication received from the system-managing means 15.

Re-dispatching generation to increase power system security margin and support low voltage bus

Abstract: This article proposes a new method to increase a power system's security margin and/or support its low voltage bus by re-dispatching generator outputs, using a normal vector found at a voltage collapse boundary or a low voltage boundary (LVB). This method uses the normal vector as an indicator to change the generation direction so that more power can be transferred before reaching a boundary of a critical limit such as the voltage collapse boundary or LVB, etc. The method has been tested in the simulation on several systems and shows predicted results. It can be applied to many practical power systems to enhance the system's security, or to increase the system's transfer capability. It also provides technical guidance for an open access transmission in a deregulated environment, when bidding results are shown as generation patterns.

Fuel cell power systems, direct current voltage converters, fuel cell power generation methods, power conditioning methods and direct current power conditioning methods

Abstract: Fuel cell power systems, direct current voltage converters, fuel cell power generation methods, power conditioning methods and direct current power conditioning methods are provided. According to one aspect of the invention, a fuel cell power system includes a plurality of terminals adapted to couple with a load; a fuel cell configured to convert chemical energy into direct current electrical energy having a variable voltage potential; and a converter coupled intermediate the fuel cell and the terminals, the converter being configured to convert the direct current electrical energy having the variable voltage potential into direct current electrical energy having a substantially constant voltage potential.

Photovoltaic power generation apparatus and control method thereof

Abstract: A photovoltaic power generation apparatus having a plurality of power converters, respectively connected to a plurality of solar battery arrays, for converting direct-current power generated by the solar battery arrays to alternating-current power so as to provide the alternating-current power to a commercial power system. The photovoltaic power generation apparatus is so constructed that the plurality of power converters do not simultaneously suspend operation when an abnormal state is detected, in order to prevent generation of an electrical stress or reduction of the power generation amount caused by simultaneous operation suspension of the power converters or repeated operation suspension and operation resume. When the power generation amount of each solar battery array is different, a power converter connected to the solar battery array of the smallest power generation amount is set in the first-to-suspend condition.

Costs of voltage security in electricity markets

Abstract: As open access market principles are applied to power systems, an increased emphasis is being placed on determining ways to price different auxiliary services. The present paper studies the incorporation of voltage security into an optimal power flow formulation to analyze the aggregated costs associated with guaranteeing adequate voltage security levels in the system. Thus, several hybrid optimal power flow formulations that both minimize generation costs and maximize distance to collapse are proposed and used to compare operational costs of power systems at different loading and voltage security levels. Basic principles of electricity markets are then used to propose a method to determine appropriate adjustments of control parameters accounting for the voltage stability of a power network.

Control and interfacing of bi-directional inverters for off-grid and weak grid photovoltaic power systems

Abstract: Photovoltaics (PV) is one of the most cost-effective, reliable and durable energy sources to provide electricity in remote areas not connected to a grid. In some parts of the world grid-connected PV systems also help utilities to alleviate the need to install or operate costly power plants by supplementing and meeting high peak hours of electricity demand. The key to the widespread application of PV power plants is the availability of efficient and low cost power electronic equipment. A photovoltaic generator is a current source depending on solar radiation intensity and temperature. Simple charge controllers and DC-DC converters with maximum power point tracking are used to interface solar panels with batteries. There are different types of inverters for converting the DC power from batteries and/or solar panels to AC power. This paper describes the application of bi-directional inverters for remote area power systems using PV, diesel generators and battery storage. Use of bidirectional inverters to improve power quality and reliability in weak grids is also presented.

Battery-driven dynamic power management of portable systems

Abstract: Battery life-time extension is a primary design objective for portable systems. Traditionally, battery life-time has been prolonged mainly by reducing average power consumption of system components. A careful analysis of discharge characteristics and the adoption of accurate high-level battery models in system-level design open new opportunities for life-time extension. In this paper, we introduce dynamic power management (DPM) policies specifically tailored to battery-powered systems. Battery-driven DPM strives to enhance life-time by automatically adapting discharge rate and current profiles to battery state-of-charge. The distinctive feature of these policies is the control of system operation based on the observation of battery output voltage. The effectiveness of the proposed policies and, more in general, of the idea of accounting for battery behavior during system design, is proved by the experiments carried out on a realistic case study, namely, an MP3 audio player.

Advanced voltage regulation method at the power distribution systems interconnected with dispersed storage and generation systems

Abstract: Summary form only given as follows. DSGs (dispersed storage and generation systems) in power distribution systems impact on the conventional voltage regulation method. Therefore, there is the possibility that the customers' voltage violates the permissible limits. In this paper, we propose the MLDC (multiple line drop compensation) voltage regulation method which considers the unbalanced load diversity among feeders, the operations of DSGs, and the hysteretic tap changing mechanism of ULTC (under load tap changer). The result from a case study shows that the proposed MLDC method can be practically applied to the voltage regulation method at the power distribution system interconnected with DSGs and severely unbalanced load diversity among feeders.

A novel high performance utility interactive photovoltaic inverter system

Abstract: This paper presents a novel photovoltaic inverter system that can achieve not only a sinusoidal AC output current synchronized with the utility line voltage but also a generation power control on each of the photovoltaic modules connected in series. The proposed inverter system is composed of a half bridge inverter and novel generation control circuit that can compensate for the reduction in output power caused by the shadow covering the photovoltaic modules. The proposed generation control circuit can make the operation point on each of the photovoltaic modules correspond to the maximum power point individually, and the generation power control on each of the photovoltaic modules is executed only by detecting the total output power of the photovoltaic system. Furthermore, the low frequency ripple voltages on the series-connected DC bus capacitors caused by the utility interactive inverter operation are reduced owing to the effect of the generation control circuit. Hence, the average value of photovoltaic generation power is much increased. The effectiveness of the proposed system is confirmed experimentally and through simulation results.

Power storage device and control method of distributed power supply system equipped therewith

Abstract: PROBLEM TO BE SOLVED: To surely restrain fluctuations in output to a power system due to a distributed power supply, such as wind power generation and solar power generation by preventing a power storage part from having storage shortage or being kept in a fully charged condition. SOLUTION: This distributed power supply system 10 is provided with a power storage device 1 consisting of the distributed power supply 9, the power storage part 2, a power-regulating part 3, and a control part 4 and is connected to the power system 12. The control part 4 consists of an output detecting part 5, a storage detecting part 6, a target value setting part 7, and a regulating output control part 8. It detects an output P of the distributed power supply 9 and the storage amount of the power storage part 2, presets an output target value P0 for restraining fluctuations in the output to the power system 12 by the distributed power supply 9 according to the storage amount, and controls the power regulating part 3 so that the output to the power system 12 reaches the output target value P0.

Towards dynamic security-constrained congestion management in open power market

Abstract: Security and reliability are major concerns in the deregulated and unbundled electricity supply industry due to the increased number of market participants and the changing demand patterns. This letter presents an approach and investigates the impact of incorporating dynamic security considerations in an open market environment. It is possible to reschedule the real power generation along with curtailment of real power loads/transactions to make the system dynamically secure after a fault. A conceptually plausible and computationally feasible approach for the solution of this problem has been developed for a system with a mix of pool and contract dispatches.

An improved approach to reduce harmonics in the utility interface of wind, photovoltaic and fuel cell power systems

Abstract: In this paper, an improved approach to reduce harmonics in the utility interface of wind, photovoltaic and fuel cells power systems is presented. The approach is based on circulating third harmonic current injection to reduce utility line current harmonics in SCR converters. In this paper, a new injected current shape is computed from analysis to achieve sinusoidal utility line currents. A controllable single switch boost converter connected in shunt is employed to circulate the new injected current shape. A method to implement the proposed approach under varying load conditions is shown. Analysis, design, limitations, simulation and experimental result are presented.

An improved method for controlling an EDLC-battery hybrid stand-alone photovoltaic power system

Abstract: Stand-alone photovoltaic power systems are potential power sources for wireless and optical telecommunications equipment and solar home systems. For these systems to be practical, the batteries used to store the power must have a long lifetime. We have proposed a stand-alone photovoltaic power system that uses an electric double-layer capacitor (EDLC) with lead-acid batteries. This system reduces the number of battery charge-and-discharge cycles and maintains the optimal charging voltage by using EDLC discharge power. In this paper, we describe the system's circuit configuration, operation, and conversion efficiency analysis. An improved method is described for controlling the system. It increases the system's power-conversion efficiency by keeping the capacitor voltage high. Simulation of a 250 W photovoltaic system showed that it reduces the power conversion losses in the system by about 35%.

Voltage security considerations in an open power market

Abstract: The deregulation of the electric power industry in Europe is the major issue nowadays. The new environment raises questions concerning all sectors of the electric power industry. Nevertheless, the transmission system is the key point in market development since it puts constraints to the market operation due to technical requirements. Especially, in systems having weak connections among areas, congestion problems arise due to line overloading or to voltage security requirements. This paper focuses on topics concerning voltage security in a deregulated power market and related market issues. Results by the application of the proposed methodology in the Greek Electric Power System (EPS) are presented.

Role of the electric vehicle as a distributed resource

Abstract: The growing concern about environmental degradation, and increasing amounts of greenhouse gas emissions from automobiles have generated significant interests among citizens, auto manufacturers and governments around the world to develop affordable and workable electric vehicles. Both fuel cell and electric battery operated vehicles are being considered for commercial deployment within the next five years. The availability of such technologies will offer new opportunities for distributed energy sources for partially meeting household electricity demand. The unique concept presented in this paper deals with using the electric vehicle (EV) as a home-based power plant supplying electricity during hours of high price, and under emergency situations. Such dual-use opportunity for the EV will allow the EV owner to get financial benefits that can be used for servicing the car/battery lease expenses. This paper deals with modeling the available capacity for stationary electricity output (while the vehicle is not on the road), the proper charging sequence, forecasting the load servicing capability of the EV battery or the fuel cell, and the system level load impact when the batteries are charged. The load servicing capability of the dual-purpose EV (DPEV) will determine the type of loads and duration of supply that can be provided by the on-board power plant.

Energy system providing continual electric power using wind generated electricity coupled with fuel driven electrical generators

Abstract: The process provides constant electric power from a combination of a wind energy generator and a firm secondary generator. The wind energy generator and the secondary generator supply electricity directly to a utility transmission system. The secondary generator must be able to provide power on demand that will meet a utility's needs. The secondary generator is preferably a natural gas turbine, but may be a hydrogen fuel cell, a diesel internal combustion engine, or any other similar technology.

Impact of distribution efficiency on generation and voltage stability

Abstract: On-going changes in the electric utility industry are imposing ever stricter constraints upon the operators of transmission networks. The increase in peak load and reduced power margins in the network may under certain circumstances conspire to produce brownouts, or even blackouts, especially when compounded with low probability contingencies. The challenge is also imposed on generation capacity to meet such requirements. An efficient and inexpensive way of coping with those effects is by maintaining sufficient reactive support along the feeders to provide a flat voltage profile, thus allowing deeper levels of voltage reduction when needed. The paper describes how the beneficial effects of voltage reduction allow avoiding adding new capacity to meet peak demand, but also increasing voltage stability margins.

Method for optimally operating co-generation of electricity and heat and optimally operating district heating power plant

Abstract: A method for optimally operating co-generation of electricity and heat in which the district heating power range is divided to a lower range and a higher range is characterized in that: base load electricity and regulation electricity are produced with a steam turbine operating like a condensing turbine; the lower heating power range (B) is produced mainly by heat pumps using the energy of the exhaust steam of the turbine as an energy source; peak-load power and wintertime regulation electricity are produced with a peak-load engine; and the higher heating power range (A3, A4) is produced partially by heat pumps using said energy as the energy source and partially by the exhaust gas heat of said peak-load engine. Both the elctricity and the heat are produced with a remarkably higher fuel utilization rate and significantly more electricity in relation to heat is produced than with conventional district heating power plants. The invention concerns also an optimally operating district heating power plant realizing the above method. At the initial stage of the operation of the district heating power plant, the district heating load being partial, a bigger amount of electricity may be produced of a fuel unit than at the final stage of the operation with a full district heating load. Extra peak power at short notice may be produced with the peak-load engine with a better fuel utilization rate than with the previously known solutions.

FRIENDS: forwarding to future power delivery system

Abstract: In this paper, many issues on a new type of power delivery system named FRIENDS (flexible, reliable and intelligent electrical energy delivery system) are discussed. FRIENDS is one of most promising future power delivery systems under deregulated circumstances. The purpose of FRIENDS is to develop a desirable structure for future power delivery systems where distributed generators and distributed energy storage systems are allocated near the demand side, and to develop reliable and energy conservation oriented operating strategies of the power systems. The future power delivery system will be more and more consumer friendly and will be a more and more essential part of the total energy delivery system.

An effective DP solution for optimal generation expansion planning under new environment

Abstract: Under the existing electricity market in Japan, partial retail wheeling in a power generation system has been implemented accompanying the independent power producers' (IPPs) tender for the part of electric power generation of a utility. At same time, the environmental problem (CO/sub 2/ emission etc) is becoming a more and more important task to solve. For utility companies, the IPPs' participation and environmental impact should be considered simultaneously when making an optimal generation expansion plan under new environment. This paper discusses the probability of IPPs' participant for a utility company and proposes an approach for determining the optimal generation mix including IPPs under limited CO/sub 2/ emission. Based on the successive approximations DP (SADP) algorithm, an optimal generation expansion plan including IPPs, which coordinates the economy and supply reliability is obtained. The feasibility of the proposed approach is demonstrated by using a test power system.

An economic analysis of the self commitment of thermal units

Abstract: Given the load profile of an electricity market and the capabilities of the set of generators supplying power to that market, it is likely that at any given point in time, available supply will exceed demand. If only a subset of generators is required, some method is required to commit and de-commit generators. In the past, system operators have employed a centralized method of unit commitment. Deregulation of the electricity industry throws doubt on the continued suitability of this method due to fairness issues and availability of accurate cost data. This paper examines the performance of decentralized unit commitment, where dispatch of generators is determined by offer curves submitted into a spot market by power producers.

Power supply device of ac elevator

Abstract: PROBLEM TO BE SOLVED: To provide a power supply device of an AC elevator having high energy utilization, which can be easily realized. SOLUTION: This power supply device is provided with a chargeable battery, a power supply circuit for causing charging and discharging for the battery, and a control circuit for controlling the input voltage to an inverter. In the power supply device, the battery is charged by regenerative power of a motor, and the generated power of the battery is fed to the inverter.