Shunt Diodes Research Articles

Musical chairs algorithm for parameters estimation of PV cells

Solar photovoltaic (PV) energy systems are representing the most attractive source of energy, especially with the continuous reduction of manufacturing costs. The new systems' sizing and cost estimation depend mainly on the accurate modeling of the PV cells. The modeling of the PV cells is based on one-diode modeling with five unknown parameters or the more accurate modeling based on two-diode modeling that have seven unknown parameters, or with a higher number of shunt diodes modeling with a higher number of unknown parameters. An accurate and fast estimation of the PV cell parameters will help designers to build their decision based on accurate results, where any small variation of these parameters can spoil the results obtained from the modeling and can produce an unwise decision. A high number of studies are introduced in the literature to estimate these parameters. These studies are different in the accuracy of results and the time consumed to get these results. Some of these studies used metaheuristic algorithms which are characterized by slow convergence and may cause inaccurate results. For this reason, a recent optimization algorithm called the musical chairs algorithm (MCA) is introduced in this paper to estimate these parameters faster and more accurately than many metaheuristic algorithms. The idea behind the use of MCA is to have a high number of search agents in the beginning to enhance the exploration and continuously reduce this number to enhance exploitation at the end of optimization and reduce the convergence time. The results obtained from using 10 optimization algorithms showed that the error associated with MCA is 20% of the average error of the other optimization algorithms. Moreover, the MCA never misses the global minimum of error which was not the case in other optimization algorithms. The MCA obtained these results in 40% of the time consumed by other optimization algorithms. These results of the MCA showed its superiority compared to other optimization algorithms.

Mono-crystalline silicon photovoltaic cells under different solar irradiation levels

In this research, partial shading influences on the efficiency of photovoltaic modules are explored. First, mathematical modeling of the Mono-crystalline PV module in case of various irradiation levels is presented. A performance assessment of a PV module by considering the electrical influence of the partial shading are then presented. The PVSYST software is used to explain the behavior of a cell or a group of shaded cells in a PV module. The tool allowed a good understanding of the functions of shunt diodes when one or more cells are shaded. Finally, this simulation is applied to the Algerian site of Béchar. In spite of shadowing and an inclination of 30°, the obtained results are good along the year with a maximum power point. The simulation has given the maximum of energy.

Optimal model for additional operation of the storage system for photovoltaic wind power plants

This paper discusses methods for modeling and optimizing photovoltaic and wind power plants for the integrated use of solar and wind energy. The results of modeling the dependence of the characteristics of the solar battery and wind power plants on the input parameters are presented. Changes in the output volt-ampere and power parameters depending on environmental conditions are considered. Various programming methods for mathematical modeling of power plants are presented. Methods for optimizing the output characteristics of solar cells by connecting shunt diodes are presented. The operation of solar panels is analyzed on the basis of mathematical modeling of processes. The influence of weather conditions, temperature, and light on the output parameters of solar installations was studied. The advantages of integrated use of solar and wind installations with an energy storage system are also considered. We consider the prediction of wind speeds based on various distribution functions.

Simulating Large Area, High Intensity AM0 Illumination – Test Results from Bepicolombo and Solar Orbiter Qualification

Two ESA high temperature missions, BepiColombo and Solar Orbiter, are planned to start in 2018. Severe environmental conditions with sun intensities up to 10.6 resp. 12.8 solar constants will be encountered during both missions.Different tests have been performed to qualify the main component for the solar array, the solar cell. The key qualification test for these high temperature, high intensity missions is a combined test which exposes a large number of cells simultaneously to the complete AM0 spectrum at the required irradiance and temperature.During the last European Space Power Conference in 2014, the development and performance of the appropriate test setup in the VTC1.5 chamber located at ESTEC was presented. In the meanwhile, the BepiColombo 4000 hour qualification test is successfully finished. This paper summarizes the results of the qualification test and highlights the main findings.Specifically, the following topics will be treated. Different methods like electrical performance, thermo-optical and external quantum efficiency measurements have been used to characterize the behaviour of the solar cells after illumination under these conditions. A special focus has been put on the electrical performance. A comparison to other solar cell qualification tests under solely UV radiation has been undertaken. The results have also been compared to a theoretical model. However, the paper will not cover only characterization results but will also give some insight in challenges experienced during the test execution itself. Deviating from other solar cell qualification tests, a representatively equipped photovoltaic assembly on carbon fibre reinforced cyanate has also been included. On these coupon segments, solar cell assemblies connected to shunt diodes and placed next to optical surface reflectors have been exposed to AM0 illumination to qualify the solar cells including their surroundings which therefore covers also contamination effects. Last but not least, first results from the Solar Orbiter qualification are presented. This test with additional 1000 hours and increased intensity has been completed recently.

Plasma-charging effects on submicron MOS devices

Plasma-charging damage on gate dielectrics of MOS devices is an important issue because of shrinking dimension, plasma nonuniformity, and effects on high-k gate dielectrics. A comprehensive study of plasma-charging effects on the electrical properties of MOS devices was investigated in this work. Shunt diodes were used to estimate the charging polarity distribution. For high-frequency application, the 1/f noise was found to be a promising index for assessing plasma-charging damage. Gate oxynitride formed by two-step nitridation was demonstrated to have better electrical reliability as compared to the conventional one-step nitridation, especially accompanied by amorphous silicon gate electrode. This improvement could be attributed to the relaxation of interface stress by amorphous silicon gate electrode and the suppression of hydrogen effects by gate oxynitride using two-step nitridation. Plasma-charging damage on Si/sub 3/N/sub 4/ and Ta/sub 2/O/sub 5/ gate dielectrics with high dielectric constant was also investigated. For MOS devices with Si/sub 3/N/sub 4/ film, the leakier characteristic and shorter time to breakdown reveal its inferior reliability. For MOS devices with Ta/sub 2/O/sub 5/ gate dielectric, the trap-assisted current mechanism makes a thicker physical thickness of Ta/sub 2/O/sub 5/ film more susceptible to plasma-charging-induced damage. Smaller physical thickness of Ta/sub 2/O/sub 5/ film in MOS devices is favorable due to the better reliability and comparable plasma-induced electrical degradation.

A SIMPLIFIED METHOD FOR DETERMINING THE AVAILABLE POWER AND ENERGY OF A PHOTOVOLTAIC ARRAY

A practical method of calculating the power and energy capabilities of a PV array source is presented in this paper. The method is based on power flow relationships with average values for constants and actural measurements of key variables, solar irradiance and module temperature on an hourly basis or other discrete time intervals. Included in this paper is an example for a PV plant and a simple procedure for constructing and validating the math model The method is applicable to any PV array configuration which is operating normally, i.e., when no PV modules are bypassed by the shunt diodes. The array can comprise one or more PV modules. The accuracy of this method is dependent upon proper selection of the values of various constants in the math model as well as how well the model has been validated. The calculation and display of maximum power capability in real-time have been implemented in several PV plants. Some of them have found it to be very useful for operation, maintenance, performance analysis, and energy utilization improvement purposes.

Optimized structure of a three-level photovoltaic sub-array to prevent damage due to failed cells

A computer program is used to simulate the behaviour of a photovoltaic field in the presence of shadowed or failed cells. A series-parallel-series structure with shunt diodes, i.e. a module of a field, has been simulated for a wide range of parameter values. A plot of the field power loss against the parameter values allows the optimal set of parameter values to be chosen; they define the optimized structure of the field module in the sense that the minimum power loss is obtained for a given percentage of failed cells.

Electrical output of shadowed solar arrays

The effects of shadows on the current-voltage characteristics of solar cell circuits are studied and used for the development of several mathematical models. These models describe circuits of any geometry with or without shunt or blocking diodes. For efficient analyses of larger arrays the concept of the shadowing factor is developed. All models are useful in analyses performed by hand or digital computer, using theoretical or empirical input data.

Protection of implanted pacemakers from excessive electrical energy of D.C. shock

Studies were performed on implanted pacemakers subjected to electroshock in 55 dogs. With exposure to 400 w.sec., electrical energies of 18 ma. and 29 v. were recorded in the epicardial lead system and energies of 1,000 ma. and 350 v. recorded in the epicardial ground plate lead systems. One of 20 Medtronic pacemakers having the bipolar lead system configuration was damaged in the experiment. Three of five Cordis Corporation pacemakers without protective zener diode circuitry were damaged. The addition of shunt diodes in the Cordis pacemaker input/output terminals provided a significant measure of protection. Implanted pacemakers may be made less vulnerable to electrical shock by incorporating components with adequate transient breakdown ratings and by employing electrodes of small surface area, small interelectrode distance and electrode orientation perpendicular to the defibrillator paddles.