Showing papers on "Grid-connected photovoltaic power system published in 2004"

Spacecraft Power Systems

Abstract: POWER SYSTEM FUNDAMENTALS Satellite Overview Near-Earth Space Environment Power System Options Photovoltaic-Battery System Environmental Effects Power System Requirements Design Process and Trades PV-BATTERY SYSTEM Solar Array Battery Power Electronics and Magnetics Distribution Harness and Protection Ancillary Components POWER SYSTEM PERFORMANCE Energy Balance and Power Management Dynamic Performance and Stability Electromagnetic Interference and Compatibility Electrostatic Discharge Reliability and Derating Integration and Testing SPECIAL POWER SYSTEMS Interplanetary and Deep-Space Missions Radioisotope Thermoelectric Generator Dynamic Systems with Alternator High-Power High-Voltage Systems Electric Propulsion Fuel Cell Power Flywheel Energy Storage Superconductors in Space Microwave Beam Power Satellite

Power quality from multiple grid-connected single-phase inverters

Abstract: This paper reports on a study into the aggregate power quality from multiple grid connected inverters. Measurements are presented for individual single-phase inverters generating into the low voltage network under a range of operational conditions, and for groups of similar converters connected at the same point on the network. Some results from the modeling of multiple inverter interaction are also presented. Particular attention is given to power factor, the harmonic content of the generated currents, and dc injection.

A novel hybrid isolated generating system based on PV fed inverter-assisted wind-driven induction Generators

Abstract: Isolated renewable energy systems based on hybrid wind-solar sources are considered as feasible and reliable options instead of wind-diesel systems. An isolated hybrid scheme employing a simple three-phase square-wave inverter to integrate a photovoltaic array with a wind-driven induction generator has been proposed for the first time. A dynamic mathematical model of the hybrid scheme with variables expressed in d-q synchronous reference frame has been developed. The model is implemented in the power system blockset platform and a comparison has been made between transients simulated and transients obtained in an experimental prototype. Close agreement between experimental and the simulated waveforms has been observed, which validates the model.

PV Thermal systems: PV panels supplying renewable electricity and heat

Abstract: With PV Thermal panels sunlight is converted into electricity and heat simultaneously. Per unit area the total efficiency of a PVT panel is higher than the sum of the efficiencies of separate PV panels and solar thermal collectors. During the last 20 years research into PVT techniques and concepts has been widespread, but rather scattered. This reflects the number of possible PVT concepts and the accompanying research and development problems, for which it is the general goal to optimise both electrical and thermal efficiency of a device simultaneously. The aspects that can be optimised are, amongst others, the spectral characteristics of the PV cell, its solar absorption and the internal heat transfer between cells and heat-collecting system. Another important level of optimisation is for the PVT device geometry and the integration into a system. The electricity and heat demand and the temperature level of the heat determine the choice for a certain system set-up. With an optimal design, PVT systems can supply buildings with 100% renewable electricity and heat in a more cost-effective manner than separate PV and solar thermal systems and thus contribute to the long-term international targets on implementation of renewable energy in the built environment.

Operation of a prototype microgrid system based on micro-sources quipped with fast-acting power electronics interfaces

Abstract: The paper presents experimental results from the operation of a prototype microgrid system, installed in the National Technical University of Athens, which comprises a PV generator, battery energy storage, local load and a controlled interconnection to the LV grid. Both the battery unit and the PV generator are connected to the AC grid via fast-acting DC/AC power converters. The converters are suitably controlled to permit the operation of the system either interconnected to the LV network, or in stand-alone (island) mode, with a seamless transfer from the one mode to the other. The paper provides a technical description of the system components and the control concept implemented, along with extensive measurement results which demonstrate its capability to operate in the aforementioned way.

A novel real-time simulation technique of photovoltaic generation systems using RTDS

Abstract: For the performance test of photovoltaic (PV) generation systems, actual system apparatuses: a solar panel, converter system, and load facilities should be installed. It is also hardly possible to compare a maximum power point tracking (MPPT) control scheme with others under the same weather and load conditions in an actual PV generation system. One of the possible alternatives is to realize a transient simulation scheme for PV generation systems under real weather conditions of insolation and surface temperature of solar cell. The authors propose a novel real-time simulation method for PV generation systems under real weather conditions using a real-time digital simulator (RTDS). V--I curves of a real PV panel are tested using electric load device, and a hypothetical network of the tested PV panel is created on the RTDS by arranging electrical components from the customized component model libraries. The real weather conditions, insolation, and temperature of the PV panel, are interfaced through the analog input ports of the RTDS for real-time simulation. The outcomes of the simulation demonstrate the effectiveness of the proposed simulation technique, and also show that cost-effective verification of availability and stability of PV generation systems is possible using the built-in simulator.

Microprocessor-controlled new class of optimal battery chargers for photovoltaic applications

Abstract: A simple, fast and reliable technique for charging batteries by solar arrays is proposed. The operating point of a battery is carefully forced near the maximum power point of solar cells under all environmental (e.g., insolation, temperature, degradation) conditions. Optimal operation of solar arrays is achieved using the Voltage-Based Maximum Power Point Tracking (VMPPT) technique and the charger operating point is continuously adjusted by changing the charging current. An optimal solar battery charger is designed, simulated and constructed. Experimental and theoretical results are presented and analyzed. The main advantages of the proposed solar battery charger as compared with conventional ones are shorter charge time and lower cost.

Power converter for a solar panel

Abstract: A solar array power generation system includes a solar array electrically connected to a control system. The solar array has a plurality of solar modules, each module having at least one DC/DC converter for converting the raw panel output to an optimized high voltage, low current output. In a further embodiment, each DC/DC converter requires a signal to enable power output of the solar modules.

Solar power generation apparatus, solar power generation system, and method of manufacturing solar power generation apparatus

Abstract: A solar cell assembly including a plurality of solar cells is formed on a common substrate, and a DC/DC converter which converts the output from the solar cell is connected to each solar cell to constitute a solar power generation apparatus. The output from the solar power generation apparatus is converted into an AC power by an inverter and supplied to a load or commercial AC power system. Since the arrangement is simplified, the manufacturing cost can be reduced, and the influence of partial shade or a variation in characteristic decreases.

A novel optimum operating point tracker of the solar cell power supply system

Abstract: When the solar array is used as an input power source, the optimum operating point tracker is often employed to exploit more effectively the solar array as an electric power source and to obtain the maximum electric power at all times even when the light intensity and environmental temperature of the solar array are varied. Usually, the optimum operating point is determined by computing the electric power from the solar array power supply with a microcomputer, DSP and so forth. However, such a method has the problems of the complex control circuit configuration, high cost and low control speed. From this viewpoint, this paper proposes a new optimum operating point tracker of the solar cell power supply system, in which inexpensive pn-junction diodes are used to generate the reference voltage of the operating point of the solar array. Using the proposed method, the high degree of the solar array optimum point tracking performance can be obtained, even when the light intensity and environmental temperature of the solar array are varied. Furthermore, the proceeding paper provides the operation principle, design-oriented analysis and so forth, of the proposed solar cell power supply system.

Stability of grid-connected PV inverters with large grid impedance variation

Abstract: Photovoltaic (PV) inverters used in dispersed power generation of houses in the range of 1-5 kW are currently available from several manufacturers. However large grid impedance variation is challenging the control and the grid filter design in terms of stability. In fact the PV systems are well suited for loads connected in a great distance to the transformer (long wires) and the situation becomes even more difficult in low-developed remote areas characterized by low power transformers and long distribution wires with high grid impedance. Hence a theoretical analysis is needed because the grid impedance variation leads to dynamic and stability problems both in the low frequency range (around the current controller bandwidth frequency) as well as in the high frequency range (around the LCL-filter resonance frequency). In the low frequency range the possible variation of the impedance challenges the design of resonant controllers adopted to mitigate the effect of the grid harmonic distortion on the grid current. In the high frequency range the grid impedance influence the frequency characteristic of the filter and the design of passive or active damping (to ensure stability) becomes more difficult. In this paper both topics are addressed and discussed with simulation and experimental results.

Online grid measurement and ENS detection for PV inverter running on highly inductive grid

Abstract: Photovoltaic (PV) and other sources of renewable energy are being used increasingly in grid-connected systems, for which stronger power quality requirements are being issued. Continuous grid monitoring should be considered so as to provide safe connections and disconnections from the grid. This letter gives an overview of the methods used for online grid measurement with PV inverters. Emphasis is placed on a method based on the injection of a noncharacteristic harmonic in the grid. Since this injection is regarded as a disturbance for the grid, different issues, i.e., the influence on total harmonic distortion (THD), the accuracy of line impedance measurement and the ENS (German abbreviation of Main Monitoring units with allocated Switching Devices) detection are studied. Laboratory results conducted on an existing PV inverter are presented to demonstrate the behavior of the PV inverter under different grid conditions. Some of the injection parameters are tuned in order to get an accurate measurement of line impedance.

A study on the optimal voltage for MPPT obtained by surface temperature of solar cell

Abstract: Photovoltaic(PV) system has been studied and watched with keen interest due to a clean and renewable power source. But, the output power of PV system is not only unstable but uncontrollable, because the maximum power point tracking (MPPT) of PV system is still hard with the tracking failure under the sudden fluctuation of irradiance. Authors suggest that the optimal voltage for MPPT be obtained by only solar cell temperature. Having an eye on that the optimal voltage point of solar cell is in proportion to its panel temperature, with operating the power converter whose operating point keeps its input voltage to the optimal voltage imagined by the surface's temperature of PV panel, the maximum power point becomes tenderly possible to be tracked. In order to confirm the availability of the proposed control scheme both control methods are simulated not only on the various angle of sampling time of switching control, but also with the real field weather condition. As the results of that, the conversion efficiency between PV panel and converter of the proposed control scheme was much better than that of the power comparison MPPT control, and what is better, the output voltage of PV panel was extremely in stable when the optimal voltage for MPPT is obtained by only solar cell temperature.

Concerns generated by islanding [electric power generation]

Abstract: The purpose of this article is to discuss islanding operation and to provide end-users with items to consider when determining distributed generation plant and equipment design requirements. Islanding is operating an electric generating plant without an external voltage and frequency reference. Operating in parallel is the opposite of islanding. This article attempts to describe the valid concerns that grid operators have regarding distributed generators. Grid computing could offer an inexpensive and efficient means for participant to compete in providing reliable, cheap and sustainable electrical energy supply. With a keen awareness of the issues involved and open communication among the grid operators, generator control system manufacturers, clients and design firms, distributed generators can be operated in islanded mode without negatively impacting the grid and can continue to support facility operations.

A new method of on-line grid impedance estimation for PV inverter

Abstract: The recent increase in photovoltaic (PV) installations calls for new and better power quality requirements with respect to connection to the grid supply. Therefore, different methods are typically used for continuous grid monitoring, usually by using external devices. In this paper a new method for on-line measuring the grid impedance is presented. The presented method requires no extra hardware being accommodated by typical PV inverters, sensors and CPU, to provide a fast and low cost approach of on-line impedance measurement. By injecting a noncharacteristic harmonic current and measuring the voltage grid response it is possible to evaluate the grid impedance. Practical test on an existing PV inverter validate the new method.

Method of controlling a wind turbine connected to an electric utility grid

Abstract: The invention relates to a method of controlling a wind turbine connected to an electric utility grid during malfunction in said electric utility grid (9). The method comprises the steps of detecting a malfunction in said electric utility grid and operating at least two control units of said power converter (12) in relation to at least one power converter limit value. The invention also relates to a control system for a wind turbine connected to a utility grid and a wind turbine.

Don't let the sun go down on PV [photovoltaic systems]

Abstract: In response to global issues for the generation and delivery of electrical power, photovoltaic (PV) and other renewable energy technologies are gaining acceptance as a way of maintaining and improving living standards without harming the environment PV could help mitigate energy crises by reducing peak demand and securing the delivery of power in congested locations by decentralizing the power generation This article shows the challenges of photovoltaic in restructured power systems PV technologies could provide more secure mode of operation for power system during peak load hours when the systems are constrained and locational marginal prices are high

Power utility maximization for multiple-supply systems by a load-matching switch

Abstract: For embedded systems that rely on multiple power sources (MPS), power management must distribute the power by matching the supply and demand in conjunction with the traditional power management tasks. Proper load matching is especially critical for renewable power sources such as solar panels and wind generators, because it directly affects the utility of the available power. This paper proposes a power distribution switch and a source-consumption matching algorithm that maximizes the total utility of the available power from these ambient power sources. Our method yields over 30% more usable power than conventional MPS designs.

Plug in to grid computing

Abstract: This article discusses the potential benefits of grid computing for future power networks. It is also intended to alert the power system community to the concept of grid computing and to initiate a discussion of its potential applications in future power systems. Much like the Web, the grid can operate over the Internet or any other suitable computer networking technology. Grid computing offers an inexpensive and efficient means for participants to compete (but also cooperate) in providing reliable, cheap, and sustainable electrical energy supply. It also provides a relatively inexpensive new technology allowing the output of embedded generators to be monitored and, when necessary, controlled. Basically, the ability of grid-enabled systems to interact autonomously is vital for small generators where manned operation is likely to be viable.

Artificial neural network based models for forecasting electricity generation of grid connected solar PV power plant

Abstract: This paper presents an artificial neural network (ANN) approach for forecasting the performance of electric energy generated output from a working 25-kWp grid connected solar PV system and a 100-kWp grid connected PV system installed at Minicoy Island of Union Territory of Lakshadweep Islands. The ANN interpolates among the solar PV generation output and relevant parameters such as solar radiation, module temperature and clearness index. In this study, three ANN models are implemented and validated with reasonable accuracy on real electric energy generation output data. The first model is univariate based on solar radiation and the output values. The second model is a multivariate model based on module temperature along with solar radiation. The third model is also a multivariate model based on module temperature, solar radiation and clearness index. A forecasting performance measure such as percentage root mean square error has been presented for each model. The second model, which gives the most accurate results, has been used in forecasting the generation output for another PV system with similar accuracy.

Power conversion apparatus for solar power generation

Abstract: PROBLEM TO BE SOLVED: To attain improvement of system power generation efficiency by independently performing maximum power follow-up relating to each solar battery array, in a system interconnection inverter connecting in parallel a plurality of the solar battery arrays input. SOLUTION: In the power conversion apparatus for solar power generations with a plurality of solar battery modules 8a, 8b, 8c serving as the power source, boost chopper parts 26a, 26b, 26c for performing maximum power follow-up of each solar battery module 8a, 8b, 8c for every thereof and a DC/DC converter of waveform forming parts 34a, 34b, 34c, 34d, etc. are provided, maximum power is led through from each solar battery module 8a, 8b, 8c thereafter to be collectively converted into an AC output by an inverter 23, a DC/AC converter 36, etc. COPYRIGHT: (C)2004,JPO&NCIPI

The application of slide technology in PV maximum power point tracking system

Abstract: In this paper, a new MPPT system has been developed, consisting of a buck-type dc/dc converter, which is controlled by a micro-controller-based unit. Based on the nonlinear characteristics of photovoltaic (PV), these paper designs a VSS controller to realize the maximum power output of PV arrays and introduces the system fundamental. Comparing with other techniques used in the past, the use of the proposed MPPT control improves the PV system performance. And the results of simulation and experiment are present.

A Study on Simulations of the Power Output and Practical Models for Building Integrated Photovoltaic Systems

Abstract: With the rapid increase in Building Integrated Photovoltaic (BIPV) systems and the popularity of photovoltaic (PV) applications, a simple but accurate model to calculate the power output of PV modules is crucial for evaluating systems. In addition, in the analysis of energy payback, two factors, the power output (maximum power output) model of PV modules and the representative local weather data, affect calculations of tire energy savings and the payback time of BIPV systems. Most studies take the efficiency of PV modules as constant when calculating the energy payback time of PV systems, and ignore the influence of solar radiation and temperature on the results of the calculation. This study tries to develop one simple, practical, yet more accurate model for describing the characteristics of the power output of PV modules. It develops a model for describing the I-V characteristics of PV modules according to the equivalent circuits of solar cells, by which an accurate but complicated model of the maximum power output (MPO) can be achieved. Taking this MPO model as a benchmark, two other application models from other studies are evaluated and examined. One simplified application model for describing the maximum power output of PV modules is then derived from the results of the simulation. Once the solar radiation on PV panels and the ambient temperature are known, the power output of BIPV systems or PV systems can be calculated accurately and easily.