On the testing,characterization, and evaluation of PV inverters and dynamic MPPT performance under real varying operating conditions

The increasing number of photovoltaic inverters that are coming on to the PV market stresses the need to carry out a dynamic characterization of these elements and their maximum power point tracking (MPPT) algorithms under real operating conditions. In order to make these conditions repeatable at the laboratory, PV array simulators are used. However, actual simulators, including the commercial simulators, recreate only a single or small set of PV array characteristic curves in which quite commonly theoretical calculations are included in order to simulate irradiance and temperature artificial variations. This is far from being a recreation of the real and long dynamic behavior of a PV array or generator. The testing and evaluation of the performance of PV inverters and MPPT algorithms has to be carried out when the PV system moves dynamically according to real operating conditions, including processes such as rapidly changing atmospheric conditions, partial shadows, dawn, and nightfall. This paper tries to contribute to the analysis of this problem by means of an electronic system that both measures the real evolution of the characteristic curves of PV arrays at outdoor operation and then recreates them at the laboratory to test PV inverters. This way the equipment can highlight the different performances of PV inverters and MPPT techniques when they operate under real operating conditions. As an example, two commercial inverters are tested and analyzed under the recreated behavior of a PV generator during 2 singular days that include processes of partial shading and fast irradiance variations. Copyright © 2007 John Wiley & Sons, Ltd.     

Ester-functionalized poly(3-alkylthiophene) copolymers: Synthesis,physicochemical characterization and performance in bulk heterojunction organic solar cells

The introduction of functional moieties in the donor polymer (side chains) offers a potential pathway toward selective modification of the nanomorphology of conjugated polymer:fullerene active layer blends applied in bulk heterojunction organic photovoltaics, pursuing morphology control and solar cell stability. For this purpose, two types of poly(3-alkylthiophene) random copolymers, incorporating different amounts (10/30/50%) of ester-functionalized side chains, were efficiently synthesized using the Rieke method. The solar cell performance of the functionalized copolymers was evaluated and compared to the pristine P3HT:PCBM system. It was observed that the physicochemical and opto-electronic characteristics of the polythiophene donor material can be modified to a certain extent via copolymerization without (too much) jeopardizing the OPV efficiency, as far as the functionalized side chains are introduced in a moderate ratio (<30%) and that preference is given to side chains with a small molar volume. A range of complementary techniques – UV–Vis spectroscopy, (modulated temperature) differential scanning calorimetry, transmission electron microscopy and X-ray diffraction analysis – indicated that variations in polymer crystallinity, while maintaining a high level of regioregularity, are probably the main factor responsible for the observed differences.     

Experimental validation of the linear drive train for a total artificial heart system

In industrialized countries cardiovascular diseases are the major cause of death. Beside heart transplants, which are a limited option due to the limited number of available human donor hearts, Total Artificial Hearts (TAHs) are the only therapy available for some patients with terminal heart diseases. For various reasons a total implantable artificial heart is desirable, but also sets restrictions in terms of weight and dimensions due to the limited space in the human thorax. Therefore a precise requirement profile is needed for the drive design to provide sufficient force for the blood pump and to avoid oversizing of the drive and to prevent blood damage by overheating.     

Light Emission in the Unipolar Regime of Ambipolar Organic Field‐Effect Transistors

Light emission from ambipolar organic field‐effect transistors (OFETs) is often observed when they are operated in the unipolar regime. This is unexpected, the light emission should be completely suppressed, because in the unipolar regime only one type of charge carrier is accumulated. Here, an electroluminescent diketopyrrolopyrrole copolymer is investigated. Local potential measurements by scanning Kelvin probe microscopy reveal a recombination position that is unstable in time due to the presence of injection barriers. The electroluminescence and electrical transport have been numerically analyzed. It is shown that the counterintuitive unipolar light emission is quantitatively explained by injection of minority carriers into deep tail states of the semiconductor. The density of the injected minority carriers is small. Hence they are relatively immobile and they recombine close the contact with accumulated majority carriers. The unipolar light output is characterized by a constant efficiency independent of gate bias. It is argued that light emission from OFETs predominantly originates from the unipolar regime when the charge transport is injection limited.     

Comparison between two statistical models for prediction of turkey breast meat colour

The aims of the present study were: (1) to determine the relevant objective measurements which could express visual assessment of turkey meat colour; and (2) to use these variables for the early prediction of the colour development of turkey breast meat.

The colour of the meat was assessed subjectively by an expert at a processing plant at 24 hr post mortem, using a four-category scale (score a: light-pale meat, score b: light pink meat or normal meat, score c: dark meat, score d: very dark meat).

Objective measurements included meat pH, temperature, dielectric loss factor, pigment concentration, L^* (lightness), a^* (redness) and b^* (yellowness) colour coordinates determined at different times post mortem.

Colour coordinates and pH were chosen as relevant variables when measured at 1 and 4 hr post mortem and were used in prediction models. Linear analysis (canonical discriminant analysis) showed that the efficiency of prediction was 15%. A non-linear analysis (neural network) gave better prediction; the colour of the meat being correctly predicted for 70% of the muscles.     

An autocorrelation-based time domain analysis technique for monitoring perfusion and oxygenation in transplanted organs

In designing an implantable sensor for perfusion monitoring of transplant organs the ability of the sensor to gather perfusion information with limited power consumption and in near real time is paramount. The following work was performed to provide a processing method that is able to predict perfusion and oxygenation change within the blood flowing through a transplanted organ. For this application, an autocorrelation-based algorithm was used to reduce the acquisition time required for fast Fourier transform (FFT) analysis while retaining the accuracy inherent to FFT analysis. In order to provide data proving that the developed method is able to predict perfusion as accurately as FFT two experiments were developed isolating both periodic and quasi-periodic cardiac frequencies. It was shown that the autocorrelation-based method was able to perform comparably with FFT (limited to a sampling frequency of 300 Hz) and maintain accuracy down to acquisition times as low as 4 s in length.     

Lethal effect of electric fields on isolated ventricular myocytes

Defibrillator-type shocks may cause electric and contractile dysfunction. In this study, we determined the relationship between probability of lethal injury and electric field intensity ($E$ ) in isolated rat ventricular myocytes, with emphasis on field orientation and stimulus waveform. This relationship was sigmoidal with irreversible injury for $E ≫ hbox{50 V/cm}$ . During both threshold and lethal stimulation, cells were twofold more sensitive to the field when it was applied longitudinally (versus transversally) to the cell major axis. For a given $E$, the estimated maximum variation of transmembrane potential ( $Delta V_{max }$) was greater for longitudinal stimuli, which might account for the greater sensitivity to the field. Cell death, however, occurred at lower maximum $Delta V_{max }$ values for transversal shocks. This might be explained by a less steep spatial decay of transmembrane potential predicted for transversal stimulation, which would possibly result in occurrence of electroporation in a larger membrane area. For the same stimulus duration, cells were less sensitive to field-induced injury when shocks were biphasic (versus monophasic). Ours results indicate that, although significant myocyte death may occur in the $E$ range expected during clinical defibrillation, biphasic shocks are less likely to produce irreversible cell injury.      

Solar irradiation and PV module temperature dispersion at a large‐scale PV plant

When evaluating the performance of a photovoltaic (PV) system, it is extremely important to correctly measure the plant operating conditions: incident irradiation and cell temperature. At large‐size PV plants, the possible dispersion of the plant operating conditions may affect the representativeness of the values measured at one single point. The available literature contains many observations on irradiance dispersion (typically associated to high temporal resolution experiments) and its effects on the PV power output (unexpected power transients, power fluctuations, etc.). However no studies have been made on the long‐term energy‐related effects of geographic dispersion of solar irradiation, which could affect, for example, to the uncertainty in determining energy performance indexes like PR. This paper analyses the geographical dispersion in the PV operating conditions observed at low temporal resolutions (day, month and year) at two PV plants located, respectively, in the south of Portugal and the north of Spain. It shows that daily irradiation deviations are significantly higher than is commonly supposed. Furthermore, once the measurement points are a certain distance apart (a few hundred metres), the deviations in irradiation appear to be independent of distance. This could help to determine how many irradiance sensors to install in order to reduce uncertainty. Daily mean temperature differences between different points at a large‐scale PV plant range from 1 to 7 K and are not related to the distance between measurement points. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of autoclaving on dietary fibre content of beetroot (Beta vulgaris). Evaluation by different methods

Modifications of dietary fibre in beetroot during autoclaving have been evaluated by different methods: acid detergent (raw=1.45%; processed=1.17%) and neutral detergent (raw=2.30%; processed=2.00%), the enzymatic-gravimetric method of Asp (raw=3.35%; processed=3.34%), HPLC (raw=1.42%; processed=1.60%) and 3,5-dimethylphenol (raw=0.36; processed=0.28%). The correlation between different methodologies was studied. Autoclaving was carried out at 121°C under pressure for 15 min. Variance analysis indicated that quantitative variations originating in the thermic treatment were not statistically significant (P>0.05).