Showing papers on "Grid-connected photovoltaic power system published in 1987"

The Effects of Moving Clouds on Electric Utilities with Dispersed Photovoltaic Generation

Abstract: As the incident solar radiation on a utility service area changes, the power generated by utility-interactive solar photovoltaic (PV) generators dispersed throughout that area also changes. The utility must follow these changes with its own generation, just as it now follows normal fluctuations in customer load. This paper presents the results of a simulation designed to assess the maximum possible changes in PV generation that a utility can expect over certain time intervals for different service area sizes. The simulation can be used with a power flow program to study the actual effects of dispersed residential PV generation on a utility.

The Quality of Load Matching in a Direct-Coupling Photovoltaic System

Abstract: The quality of load matching in a photovoltaic system determines the quality of system performance and the degree of the solar cells utilization. In a matched system, the operation of the load-line is close to the maximum power-line of the solar cell (SC) generator. Some load-lines inherently exhibit a relatively good matching when they are directly connected to the SC generator; for others, the matching is rather poor, and therefore, requires the inclusion of a maximum-power-point-tracker (MPPT) in the system. This present study deals with the performance analysis of six common types of loads that are directly connected to the SC generator, and defines a factor that describes the quality of matching of the load to the solar cells. The results of the study indicate the compatibility of the different loads when powered by solar cells, and will assist the designer of the photovoltaic system in considering whether to include an MPPT. The quality of load matching is defined here as the ratio of the load input power to the SC generator maximum power as a function of the solar insolation, or as a function of the solar time. The six loads are: an ohmic load, a storage battery, an ohmic load and storage battery, a water electrolyzer, a power conditioner--constant power load, and a dc motor driving volumetric and centrifugal pumps.

Microprocessor-Controlled SIT Inverter for Solar Energy System

Abstract: A microprocessor-controlled static induction transistor (SIT) inverter is proposed to link a solar battery with a utility ac power line. The main control objectives are to optimize the power flow from the solar battery to the utility power line and to compensate the reactive power, including harmonic distortion. The performance is well realized by the experimental setup.

On the Control and Stability of Grid Connected Photovoltaic Sources

Abstract: A methodology is proposed for the effective integration of photovoltaic (PV) devices into the electric utility distribution network operations. The dispersed PV generator is viewed as an active device used to improve system stability by appropriately modulating the power conditioning unit's output power. Disturbances on the utility system can be damped out by injecting this power into the grid in such a way so that the net effect is a cancellation of undesirable oscillations. The approach is implemented by monitoring the oscillating power and generating control signals which shape accordingly the interface unit's output power. Successful implementation of the scheme relies heavily on the speed and flexibility with which the electronic inverter moves power from the primary source/storage facility to the utility lines. Simulation studies, using the proposed control approach, indicate that application of these policies may result in reduced load following requirements for conventional power generating units, increase the value and acceptability of new energy technologies, and improve power quality and stability of the interconnected system.

The UoSAT-2 spacecraft power system

Abstract: Four panels of Si solar cells provide power to charge packs of NiCd battery cells via a battery charge regulator. Regulated + 10 V, − 10 V and + 5 V supplies from a centralized power regulating system, as well as + 14 V unregulated battery voltage, are supplied to a power distribution module which uses bipolar transistors to switch power as required to different loads. As UoSAT is in eclipse for over one-third of its orbit, batteries with good cyclic performance must be provided. UoSAT-2 operates on a negative power budget where the power required to keep all systems fully operational is greater than the solar power available. Consequently, significant groundstation effort is required to monitor and manage the power system. Future satellites may incorporate a microprocessor-driven control element in a further step towards system autonomy.

An integrated approach to space station power system autonomous control

Abstract: Space Station electrical power management must be accomplished autonomously in order to decrease both airborne and ground support costs. Attention is presently given to the augmentation of terrestrial utility algorithmic decision aids for power dispatching for space station use, using expert systems to direct power demand analyses and the integration of results into operational decisions. Functions to be thus managed encompass power scheduling, energy allocation, failure cause diagnoses, goal proposal and plan preparation, consequence evaluation, and execution plan selection. The operating states of the system are normal, preventive, emergency, and restorative.

Utility compatibility of nonisolated residential power conditioners

Abstract: Nonisolated power conditioner (PCS) designs can improve the efficiency of grid-connected photovoltaic (PV) systems. They can replace material-intensive hardware with process-intensive hardware, promising cost reductions in future PCSs when they are produced in large quantities. Several technical issues have been studied to ensure that the nonisolated, or transformerless, utility-interactive designs can be used. The technical issues include possible dc injection into the utility or local loads, unbalanced output, and limited options for array protection and grounding. Two nonisolated prototypes have been developed as part of the DOE PV program and are being evaluated at Sandia National Laboratories. This paper describes the results of the development and evaluation efforts.

Interface circuit between solar cell and commercial AC bus

Abstract: Since the power generated by a solar cell depends strongly on the weather condition, particularly the intensity of the solar light, these cells are usually employed in combination with secondary batteries. However, the latter has problems in maintainability and safety. Therefore it is desirable to use ac power in place of a secondary battery if the solar cells are used in general households. For such a purpose, it is necessary to insert between the solar cell and the ac power source an inexpensive interface circuit that is simple and reliable. In this paper, an interface circuit made of a voltage-controlled variable-frequency oscillator, an inverter and a coupling inductor is reported. With this circuit, it became possible to extract an almost maximum power from the solar cell at the varying solar intensity. The output is converted to ac and connected automatically with the commercial ac source. The operating principle and the experimental results will be reported.

Performance characteristics of a combination solar photovoltaic heat engine energy converter

Abstract: A combination solar photovoltaic heat engine converter is proposed Such a system is suitable for either terrestrial or space power applications The combination system has a higher efficiency than either the photovoltaic array or the heat engine alone can attain Advantages in concentrator and radiator area and receiver mass of the photovoltaic heat engine system over a heat-engine-only system are estimated A mass and area comparison between the proposed space station organic Rankine power system and a combination PV-heat engine system is made The critical problem for the proposed converter is the necessity for high temperature photovoltaic array operation Estimates of the required photovoltaic temperature are presented

Computer modeling of the American Power Conversion Corporation photovoltaic power conditioning system

Abstract: This report summarizes the development of a computer model of the American Power Conversion Corporation's Sunsine 2000 photovoltaic power conditioning unit. This work was performed as part of the National Photovoltaics Program within the United States Department of Energy and was supervised by Sandia National Laboratories. The overall objective of the national program is to promote the development of low cost, reliable terrestrial photovoltaic systems for widespread use in residential, commercial, and utility applications. The purpose of the effort reported herein is to provide an adequately detailed mode of the Sunsine 2000 unit interactive power conditioning unit to allow simulation of the photovoltaic system/utility dynamic interaction. This report contains adequate details of the computer model, in block diagram form, which may be readily incorporated into a computer simulation program. Also included are representative computer studies that illustrate the dynamic characteristics of the photovoltaic system during the following startup, step changes in reference voltage, changes in solar insolation, short circuits, and islanding (isolation).

Reliability models for Space Station power system

Abstract: This paper presents a methodology for the reliability evaluation of Space Station power system. The two options considered are the photovoltaic system and the solar dynamic system. Reliability models for both of these options are described along with the methodology for calculating the reliability indices.

Control and Power Conditioning for Photovoltaic Power Supply Systems

Abstract: The characteristic features of components installed in photovoltaic supply plants are pointed out, and the proposals for power conditioning design resulting from these are explained.

Space station electrical power distribution analysis using a load flow approach

Abstract: The space station's electrical power system will evolve and grow in a manner much similar to the present terrestrial electrical power system utilities. The initial baseline reference configuration will contain more than 50 nodes or busses, inverters, transformers, overcurrent protection devices, distribution lines, solar arrays, and/or solar dynamic power generating sources. The system is designed to manage and distribute 75 KW of power single phase or three phase at 20 KHz, and grow to a level of 300 KW steady state, and must be capable of operating at a peak of 450 KW for 5 to 10 min. In order to plan far into the future and keep pace with load growth, a load flow power system analysis approach must be developed and utilized. This method is a well known energy assessment and management tool that is widely used throughout the Electrical Power Utility Industry. The results of a comprehensive evaluation and assessment of an Electrical Distribution System Analysis Program (EDSA) is discussed. Its potential use as an analysis and design tool for the 20 KHz space station electrical power system is addressed.