Edinson Franco

Model-Based Degradation Analysis of Photovoltaic Modules Through Series Resistance Estimation

The long power production warranties guaranteed by the manufacturers of photovoltaic (PV) modules (25 years) are a vital factor for the economical viability of PV systems. Nevertheless, recent studies have demonstrated that the modules may experience an early degradation, which turns into the reduction of the power production or even the damage of the entire PV module. In this paper, a method aimed at detecting the module degradation is introduced. It detects and quantifies the degradation by means of two indicators, which are aimed at estimating the increment of the modules series resistance, this parameter being one of the most affected by some degradation mechanisms. The increase of the series resistance value is estimated through the evaluation of the error in predicting the position of the maximum power point, which is obtained by comparing the experimental measurements with the single-diode model. The proposed method is experimentally validated, and it is compared with other methods reported in the literature. The results show that the proposed indicators are able to accurately estimate the increments of the series resistance with a low sensitivity to the irradiance and temperature values. This feature improves the accuracy and the reliability of the diagnosis processes and monitoring systems.

Quantification of photovoltaic module degradation using model based indicators

One of the most important characteristics of the photovoltaic (PV) modules is their long lifetime (around 25 years). However, recent investigations have shown that PV modules may suffer significant degradation before that time; that is why the development of diagnostic techniques is important for the customers of PV systems. In this paper two indicators to quantify the degradation of a PV module are presented. Such indicators use the single-diode model to represent a PV module without degradation and combine such information with the experimental measurements to estimate the increase in the series resistance and/or the decrease in the parallel resistance with respect to reference values. The estimation of those variations allows the quantification of the module degradation. Simulation results comparing the proposed indicators with the fill factor (a traditional indicator to quantify the electrical quality of a PV module), and other indicators to estimate the series resistance are presented to illustrate the advantages of the proposed indicators.

METODOLOGÍA DE DISEÑO E IMPLEMENTACIÓN DE UN SISTEMA PARA GENERACIÓN DE CAMPOS MAGNÉTICOS UNIFORMES CON BOBINAS HELMHOLTZ CUADRADA TRI-AXIAL

The design and implementation methodology of a system to generate low-magnitude and low-frequency uniform magnetic fields on a specific volume using a tri-axial square Helmholtz coil is presented. The designing procedure is based on theoretical concepts and simulations from simple mathematical expressions that relate the area, with uniform magnetic field, with the length of the coils. Also, the computational model is constructed and simulated using finite element software. It is observed that theoretical results are consistent with simulation model results and the magnetic field measurement tests. It is concluded that the design methodology allows establishing a simplified and repeatable procedure to obtain a uniform magnetic field in the volume of interest suitable for in-vitro or in-vivo studies.

Design Study for a Cellular Culture Bioreactor Coupled with a Magnetic Stimulation System

This article presents a design study performed to integrate a cellular culture bioreactor along with an external magnetic stimulation system, aimed at creating ideal environmental conditions that allow for cellular culture and cellular tissue growth to take place in three dimensions, under a sterile environment favorable for the development of bioorganic grafts which have been exposed to controlled electromagnetic fields. The different systems that have been designed and constructed are described along with their particular characteristics and all general considerations that were taken into account during the design process are presented, as well as the main variables that must be considered during implementation in order to guarantee constant and adequate function of the integrated systems, as well as reproducible results.

Modeling of photovoltaic fields in mismatching conditions by means of inflection voltages

This paper presents a suitable algorithm for modeling photovoltaic fields operating under mismatching conditions. It is based on the detailed non-linear model (including series and parallel resistors) of all PV modules composing the PV field. The main advantage is in the possibility to express each PV module voltage as an explicit function of the current by using the Lambert-W function, thus the PV field is analyzed string-by-string and one equation is constructed by equalizing the string voltage with the voltages of all active modules and the blocking diode. Then the field current is calculated by adding the currents of all strings for a same string voltage. The computational burden and accuracy of the proposed algorithm was tested experimentally and compared with previous approach proposed in literature. A string of 4 PV panels has been used as test bench and the maximum power has been evaluated by considering and by neglecting the series and parallel resistors in the PV models. The power and current relative mean errors between the experimental and estimated values were 1.80 % (0.57 W) and 4.23 % (1.02 W), respectively, demonstrating that the relative error in the estimation of the maximum power can be improved by almost 50% adopting the complete PV model.

Resultados preliminares del crecimiento de tejido celular usando un bioreactor con sistema de estimulación magnética

This article presents the preliminary results obtained from an earlier publication of a design study performed to integrate a cellular culture bioreactor along with an external magnetic stimulation system, which was aimed at creating ideal environmental conditions that allowed for cellular culture and cellular tissue growth to take place in three dimensions, under a sterile environment favorable for the development of bioorganic grafts which were exposed to controlled electromagnetic fields. Cellular tissue was used from cellular lines of Normal Human Skin Fibroblast (NHSF) and was seeded on bio-synthetic scaffolds synthesized from polylactic acid (PLA) and Chitosan mixtures. The cellular tissue covered scaffold was then introduced into the cellular culture bioreactor, subsequently it was filled with cellular culture medium and put under dynamic flow conditions in while at the same time using the external magnetic stimulation system to irradiate the cellular tissue with controlled magnetic fields. The results present static tests of cell growth where the maximum change in growth was after 48 hours when the cells were exposed to a 1 mT, 60 Hz magnetic field; they proliferated at a rate of 52% without Chitosan, 75% with Chitosan and 53% under dynamic flow versus the non-exposed cellular tissue. These results have allowed us to continue our experimentation techniques to evaluate changes in 3-dimensional growth of magnetically stimulated tissues under dynamic flow.