Showing papers on "Grid-connected photovoltaic power system published in 2005"

A review of single-phase grid-connected inverters for photovoltaic modules

Abstract: This review focuses on inverter technologies for connecting photovoltaic (PV) modules to a single-phase grid. The inverters are categorized into four classifications: 1) the number of power processing stages in cascade; 2) the type of power decoupling between the PV module(s) and the single-phase grid; 3) whether they utilizes a transformer (either line or high frequency) or not; and 4) the type of grid-connected power stage. Various inverter topologies are presented, compared, and evaluated against demands, lifetime, component ratings, and cost. Finally, some of the topologies are pointed out as the best candidates for either single PV module or multiple PV module applications.

Flyback inverter controlled by sensorless current MPPT for photovoltaic power system

Abstract: This paper presents a flyback inverter controlled by sensorless current maximum power point tracking (MPPT) for a small photovoltaic (PV) power system. Although the proposed system has small output power such as 300 W, a few sets of small PV power systems can be easily connected in parallel to yield higher output power. When a PV power system is constructed with a number of small power systems, the total system cost will increase and will be a matter of concern. To overcome this difficulty, this paper proposes a PV system that uses no expensive dc current sensor but utilizes the method of estimating the PV current from the PV voltage. The paper shows that the application of this novel sensorless current flyback inverter to an MPPT-operated PV system exhibits satisfactory MPPT performance similar to the one exhibited by the system with a dc current sensor as well. This paper also deals with the design method and the operation of the unique flyback inverter with center-tapped secondary winding.

Solar array inverter with maximum power tracking

Abstract: An inverter for use in connecting a DC power source to the utility grid includes a single DC-DC conversion stage, maximum (source) power tracking, and current control based on feed-forward compensation as a function of an input power commanding voltage, rectified utility line voltage, and either a scaled and squared inverse or a scaled inverse of RMS utility line voltage. Various embodiments also include over-voltage, over-current, under-voltage, and over-temperature protection, and a stand-by battery with its battery management control, while others adapt a multiple-channel front-end distributed power system with distributed maximum power tracking to serve as a single DC power source input to the inverter system downstream with controllers, emergency or auxiliary loads, and alternative current feedback control systems for providing an in-phase output current with respect to the utility grid voltage while absorbing maximum power available from the DC power source and minimally utilizing the stand-by battery for maximal system reliability.

Photovoltaic solar energy generation

Abstract: What Is Photovoltaics?.- Physics of Solar Cells.- Silicon Solar Cell Material and Technology.- Crystalline Thin-Film Silicon.- Other Materials, New Concepts, and Future Developments.- Solar Cells and Solar Modules.- PV Systems.- PV Systems: Installation Possibilities.- Environmental Impacts by PV Systems.- Efficiency and Performance of PV Systems.- PV Markets Support Measures and Costs.- The Future of PV.- Other (Perhaps Competing) CO2-Free Energy Sources.- Popular Killing Arguments Against PV and Why They Are Not Valid.

Short-term scheduling of battery in a grid-connected PV/battery system

Abstract: We present in this paper a short-term scheduling of battery in security-constrained unit commitment (SCUC). For economical operation and control purposes, electric power users with photovoltaic (PV)/battery systems are interested in the availability and the dispatch of PV/battery power on an hourly basis, which is a cumbersome task due to the complicated operating patterns of PV/battery. The details of battery model in the PV/battery system are presented in this paper. The paper applies a Lagrangian relaxation-based optimization algorithm to determine the hourly charge/discharge commitment of battery in a utility grid. The paper also applies a network flow programming algorithm for the dispatch of committed battery units. The paper analyzes the impact of grid-connected PV/battery system on locational pricing, peak load shaving, and transmission congestion management. An eight-bus test system is used to study the operational pattern of aggregated PV/battery and demonstrate the advantages of utilizing PV/battery systems in the electric utility operation.

Implementation and test of an online embedded grid impedance estimation technique for PV inverters

Abstract: New and stronger power quality requirements are issued due to the increased amount of photovoltaic (PV) installations. In this paper different methods are used for continuous grid monitoring in PV inverters. By injecting a noncharacteristic harmonic current and measuring the grid voltage response it is possible to evaluate the grid impedance directly by the PV inverter, providing a fast and low-cost implementation. This principle theoretically provides an accurate result of the grid impedance but when using it in the context of PV integration, different implementation issues strongly affect the quality of the results. This paper also presents a new impedance estimation method including typical implementation problems encountered, and it also presents adopted solutions for online grid impedance measurement. Practical tests on an existing PV inverter validate the chosen solution.

Energy, cost and LCA results of PV and hybrid PV/T solar systems

Abstract: Hybrid photovoltaic/thermal (PV/T) solar systems provide a simultaneous conversion of solar radiation into electricity and heat. In these devices, the PV modules are mounted together with heat recovery units, by which a circulating fluid allows one to cool them down during their operation. An extensive study on water-cooled PV/T solar systems has been conducted at the University of Patras, where hybrid prototypes have been experimentally studied. In this paper the electrical and thermal efficiencies are given and the annual energy output under the weather conditions of Patras is calculated for horizontal and tilted building roof installation. In addition, the costs of all system parts are included and the cost payback time is estimated. Finally, the methodology of life cycle assessment (LCA) has been applied to perform an energy and environmental assessment of the analysed system. The goal of this study, carried out at the University of Rome ‘La Sapienza’ by means of SimaPro 5·1 software, was to verify the benefits of heat recovery. The concepts and results of this work on energy performance, economic aspects and LCA results of modified PV and water-cooled PV/T solar systems, give a clear idea of their application advantages. From the results, the most important conclusion is that PV/T systems are cost effective and of better environmental impact compared with standard PV modules. Copyright © 2005 John Wiley & Sons, Ltd.

Power extractor circuit

Abstract: The present invention discloses power extractor circuit used to capture the power of a solar cell array during its less-than-optimum conditions. Under reduced incident solar radiation, the low power level supplied by the solar cell array normally would not be adequate to operating a load, but with the presence of the power extractor circuit, the low power generated by the solar panel would be accumulated to a high enough level to overcome the energy barrier of the battery or the load. The power extractor circuit preferably comprises a voltage and current booster circuit, and is designed to operated at all power levels of the solar cell array: low power level to provide the booster function during the low power period of the solar cell array, and high power level to prevent component failure during the normal operation of the solar cell array. Many power extractor circuits can also be installed in series to cover a wide range of power level of the solar cell array. The present invention power extractor circuit can also be used in other power sources to utilize the portion of power which normally would have been lost.

Nanosatellite solar cell regulator

Abstract: A solar cell regulator in a nanosatellite includes a pulse width modulated DC-DC boost converter and a peak power tracking controller for converting solar cell power to bus power for charging of system batteries and powering loads while the controller controls the pulse width modulation operation of the converter for sensing solar cell currents and voltages along a power characteristic curve of the solar cell for peak power tracking, for determining any power data point, including a peak power point, an open circuit voltage point, and a short circuit current point along the power characteristic curve of the solar cell, and for communicating the power data to a satellite processor for monitoring the performance of the solar cell during operational use of the satellite.

Boost-buck inverter variable structure control for grid-connected photovoltaic systems

Abstract: The present work describes the analysis, modeling and design of a power conditioning system for grid-connected photovoltaic (PV) systems. The designed power stage consists of a transformerless boost-buck converter. The power conditioning system's control scheme includes a variable structure controller to assure output unity power factor. To maximize the steady-state input-output energy transfer ratio a linear controller is designed out of a large-signal sampled data model of the system. The achievement of the DC-AC conversion and the efficient PV's energy extraction are validated with simulation results.

Power quality : interactions between distributed energy resources,the grid, and other customers

Abstract: This paper presents the three aspects of power quality concerning distributed energy resources (DER). The voltage quality experienced by a DER unit impacts the performance of the unit: bad voltage ...

Multi-tier benefit optimization for operating the power systems including renewable and traditional generation, energy storage, and controllable loads

Abstract: A plurality of power generating assets are connected to a power grid. The grid may, if desired, be a local grid or a utility grid. The power grid is connected to a plurality of loads. The loads may, if desired, be controllable and non-controllable. Distribution of the power to the loads is via a controller that has a program stored therein that optimizes the controllable loads and the power generating assets. The optimization process is via multi-tier benefit construct.

Method and system for ac power grid monitoring

Abstract: A method and system allows for substantially real-time monitoring of the operational dynamics of power plants (16, 18, 20) and other components comprising an AC power grid, by using information collected from a network of power grid frequency detection and reporting devices (22, 24, 26). The invention allows for the substantially real-time detection and reporting of certain power grid events such as power plant trips.

Development of an Analog Maximum Power Point Tracker for Photovoltaic Panel

Abstract: Maximum power point trackers (MPPT) are used to operate a solar photovoltaic (PV) panel at its maximum power point (MPP) A number of tracking algorithms have been used in the past A simple and cheap analog MPPT has been simulated and constructed The MPP tracking algorithm is based on the fact that the MPP voltage is approximately a fixed percentage of the open circuit voltage of the PV panel The PV panel is usually disconnected from the load after regular intervals, to record the open circuit voltage In the present work, an unloaded pilot PV panel, with characteristics similar to those of the main PV panel and installed under similar conditions, is used to measure the open circuit voltage The main PV panel is never disconnected from the load, resulting in increased energy output The simulation and experimental results show that the panel tracks the MPP under changing atmospheric and load conditions

Power quality aspects of a future micro grid

Abstract: Due to the increase of distributed generators (DG) in the public grid some parts, with high penetration of DGs, could be transformed into an autonomously operating micro grid. This paper will show how the grid of an existing Holyday park can be changed into an autonomous micro grid. An additional control system as well as additional storage systems and power electronics have to be implemented in order to maintain the balance between load and generated power, and to guarantee the quality of supply on an acceptable level. Therefore a measurement program is running concerning the generated power and the load behavior and some aspects of the quality of supply. This paper is especially focused on the existing harmonic problem coming from the interaction between grid components and installed solar inverters. At the end a new power quality test laboratory is presented

Method for compensating for partial shade in photovoltaic power system

Abstract: There is provided a method for compensating for partial shade using a photovoltaic power system, in which a plurality of serial-connected arrays of solar cell modules are connected in parallel, the arrays are connected to a converter, and a final power is outputted from the converter. The method includes the steps of: connecting an auxiliary power source to each solar cell module; if a low solar radiation is detected by an MPPT controller, supplying a necessary power through the auxiliary power source at a time, thereby maintaining constant voltage and preventing a temporarily shutdown; connecting in parallel the solar cell modules of the serial- connected arrays in multi-stages; and varying an operating voltage ratio of the solar cell module by controlling an off duty cycle of each chopper at the MPPT controller, thereby generating maximum output from the serial-connected array of each solar cell module.

Solar powered water pumping systems

Abstract: Agricultural technology is changing rapidly. Farm machinery, farm building and production facilities are constantly being improved. Agricultural applications suitable for photovoltaic (PV) solutions are numerous. These applications are a mix of individual installations and systems installed by utility companies when they have found that a PV solution is the best solution for remote agricultural need such as water pumping for crops or livestock. A solar powered water pumping system is made up of two basic components. These are PV panels and pumps. The smallest element of a PV panel is the solar cell. Each solar cell has two or more specially prepared layers of semiconductor material that produce direct current (DC) electricity when exposed to light. This DC current is collected by the wiring in the panel. It is then supplied either to a DC pump, which in turn pumps water whenever the sun shines ,or stored in batteries for later use by the pump. The aim of this article is to explain how solar powered water pumping system works and what the differences with the other energy sources are.

Smoothing of PV system output by tuning MPPT control

Abstract: A PV system's power output is not stable and fluctuates depending on weather conditions. Using a battery is one feasible measure to stabilize a PV system's power output, but it requires additional costs and results in additional waste of used batteries. In this paper, we propose a new measure for smoothing the short-term change in a PV system's power output, which is performed by tuning the characteristics of Maximum Power Point Tracking (MPPT) control without additional equipment. In our proposed measure, when the insolation increases rapidly, the operation point of MPPT control changes to a new point where the maximum power is not generated with the current insolation, so that the rate of increase in the PV system's power output is limited to a certain value. In order to evaluate the effect of the proposed measure on the operation of electric power systems, we evaluated the required capacity of generators for load-frequency control (LFC). It was revealed that the additional LFC capacity is not required even in the case where penetration of PV systems reaches 5% of the utility system's total capacity if the proposed measure is applied to all PV systems. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(2): 10–17, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20106

A "real world" examination of PV system design and performance

Abstract: There is no substitute for experience when it comes to designing a PV power system. Almost all system requirements are unique in some way and the ability to anticipate the on-site challenges and design the system accordingly can help ensure an optimum system performance. It's the system performance that is measured and noted by the system user, not the solar panel performance. Although the solar panel usually gets blamed when performance is less than expected, it is usually a system problem such as a poor choice of components, inefficient system architecture, poor installation techniques, or possibly, the wrong PV technology for the application. Especially for the larger PV systems, the key challenge is to design a system that matches the requirements, the environment, location and application, resulting in a high level of performance.

Irradiance equalization method for output power optimization in plant oriented grid-connected PV generators

Abstract: A dynamic interconnection of PV modules based on an irradiance equalization algorithm in grid-connected systems based on a plant oriented configuration is presented The maximum output power at the PV generator level obtained with approach is similar to that obtained in the module integrated configuration

A study on the tracking photovoltaic system by program type

Abstract: In order to increase the efficiency of PV system, it is generally used three method the first is the increasing the efficiency of solar cell, the second is the energy conversion system included MPPT control algorithm and the third is the using solar tracking system. In solar tracking system, it is used DC motors, special motors like step motors, servo motors, real time actuators, to operate moving parts. DC motors are normally used to operate solar tracking system but it is highly expensive to maintain and repair. In this paper, it is proposed 150 W solar tracking system. Proposed system designed as the normal line of the solar cell always runs parallel the ray of the sun. In this paper proposed system can minimize the solar cosign loss of the photovoltaic system

Anti-islanding method and system for distributed power generation systems

Abstract: An electrical power supply system connected to an electrical grid, includes at least one source of electrical power, an inverter which receives power from the electrical source and delivers power to a local load, and a connection to the electrical grid. The system also includes a control unit for controlling the inverter, which interrupts the delivery of power by the inverter when at least one electrical parameter of the system exceeds a threshold value. The system also includes anti-islanding logic which detects at least one symptom of an islanding condition of the system and, when the symptom is detected, to cause a variation in the power level delivered by the inverter.

Boost-buck inverter variable structure control for grid-connected photovoltaic systems with sensorless MPPT

Abstract: The present work describes the analysis, modeling and control of a transformerless boost-buck power inverter used as a DC-AC power conditioning stage for grid-connected photovoltaic (PV) systems. The power conditioning system's control scheme includes a variable structure controller to assure output unity power factor and a sensorless maximum power point tracking (MPPT) algorithm to optimize the PV energy extraction. To maximize the steady-state input-output energy transfer ratio a discrete linear controller is designed from a large-signal sampled data model of the system. The achievement of the DC-AC conversion at unity power factor and the efficient PVs energy extraction are validated with simulation results.

Removal of DC offset current from transformerless PV inverters connected to utility

Abstract: Some electricity supply authorities in Australia allow PV inverters of up to 10 kW output to be directly connected to their grid network. The benefits of avoiding the use of power transformers in such PV applications are higher conversion efficiency of the PV system and lower costs. These benefits however, can only be realised if the level of DC offset current injected from such transformerless inverter systems is maintained within the stringent limits governed by Australian Standard AS4777.2. Currently, there is a lack of evidence that the level DC offset current can be economically and efficiently maintained within these legal limits. In this paper, it is shown that irrespective of its source, the DC offset current can be maintained within these limits without sacrificing the overall conversion efficiency of the inverter system. Simulation and experimental results are presented to confirm that this simple, cost effective technique can be used to measure and separate small magnitudes of DC offset currents from large values of AC currents without compromising the dynamic response of the current feedback loop. This new technique can also be used to improve the quality of the power supplied by PV inverters that use power transformers.

Valuing the Time-Varying Electricity Production of Solar Photovoltaic Cells

Abstract: Solar PV panels generate electricity only during daylight hours and generate more electricity when the sun is shining more intensely. As a result, in summer-peaking electricity systems, such as California and most of the U.S., power from PVs is produced disproportionately at times when the value of electricity is high. Thus, a valuation of solar PV electricity production that uses only the average wholesale cost of electricity will tend to undervalue the power. Yet, that is what happens by default in many installations because solar PVs are generally located at the end-user's premises and those end-users are often billed on a flat per kilowatt-hour rate that does not reflect time-varying valuation. As a result, the benefits to many owners of solar PV in reduced electricity bills do not reflect the true time-varying valuation of the power the panels produce. I use solar PV production information in conjunction with wholesale price data and simulations to estimate the actual wholesale value of power from solar PVs and the degree of bias that occurs from using a constant price to value electricity generated by solar PVs. I find that in the California locations I analyze, the most credible long-run valuation of solar PV power is 29%-48% greater than results from valuation at a flat-rate tariff, depending on the location of the PV panels. If the end user is billed on a time-of-use tariff (a simple peak/off-peak price system), however, I find that the misvaluation of wholesale power from solar PVs is approximately zero.