A maximum power point tracker for PV systems using a high performance boost converter

This work deals with the design and experimental implementation of a MPP-tracker for photovoltaic systems, which is a high efficiency dc/dc boost converter operating in continuous conduction mode (CCM). The converter is able to draw maximum power from the PV panel for a given solar radiation level and environment temperature by adjusting the duty cycle of the converter. Additionally, a passive nondissipative turn-on turn-off snubber is used, so that high efficiency and reduced electromagnetic interference (EMI) levels due to the soft switching operation can be obtained. The snubber improves the converter efficiency since the energy that would be dissipated during turning on and turning off is transferred to the load. The control technique, implemented with a single-chip microcontroller 80C51, is based on the perturbation and observation method, where the maximum power point is tracked with periodical calculation of the panel output power. Simulation and experimental results describe the performance of the proposed MPP-tracker.     

Photovoltaic powered regulated cathodic protection system

The cathodic protection (CP) system objective is to protect metallic structures against corrosion caused by chemical reaction between metallic structures and surrounding mediums, such as soil or water. To overcome such a problem, a sacrificing anode is connected to the protected structure (which acts as a cathode) through a DC power supply. As a result, a current passes from the sacrificing anode to the protected cathode. This leads to anode corrosion rather than causing the cathode (protected structure) corrosion. To stop the corrosion, the protected structure requires a constant current determined by structure metal, area, and the surrounding medium. The major difficulty in achieving this condition is the variation of surrounding medium resistivity due to climatic condition changes. For example, rains as well as humidity decrease soil resistivity, and as a result the DC current increases and a harmful overprotection may take place. Both corrosion and overprotection are harmful for the metallic structure. Conventional CP systems resolve this problem by manual adjustment of DC voltage periodically to obtain a constant current. Such adjustment depends on the personal experience of the technician and the accuracy of the measuring equipment used. Accordingly, the adjustment is subject to personal and measuring equipment errors. Moreover, if the interval between two successive adjustments is relatively long, structure corrosion becomes significant, which may have drastic consequences. To overcome the aforementioned difficulties associated with the conventional CP system, an automatically regulated CP system is discussed in this article. The proposed system senses the variations of the surrounding medium resistivity and adjusts the DC voltage of the system automatically so that the DC current is kept constant at the required level. The design of a solar photovoltaic system to supply the CP system by the required DC power is also discussed.     

Textile composite double dome stamping simulation using a non-orthogonal constitutive model

Stamping is one of the most effective ways to form textile composites in industry for providing high-strength, low-weight and cost-effective products. This paper presents a fully continuum mechanics-based approach for stamping simulation of textile fiber reinforced composites by using finite element (FE) method. A previously developed non-orthogonal constitutive model is used to represent the anisotropic mechanical behavior of textile composites under large deformation during stamping. Simulation are performed on a balanced plain weave composite with 0°/90° and ±45° as initial yarn orientation over a benchmark double dome device. Simulation results show good agreement with experimental output in terms of a number of parameters selected for comparison. The effects of meshing and shear moduli obtained from bias extension test and picture frame test on forming simulation results are also investigated.     

Efficient sign based normalized adaptive filtering techniques for cancelation of artifacts in ECG signals: Application to wireless biotelemetry

In this paper, several simple and efficient sign based normalized adaptive filters, which are computationally superior having multiplier free weight update loops are used for cancelation of noise in electrocardiographic (ECG) signals. The proposed implementation is suitable for applications such as biotelemetry, where large signal to noise ratios with less computational complexity are required. These schemes mostly employ simple addition, shift operations and achieve considerable speed up over the other least mean square (LMS) based realizations. Simulation studies shows that the proposed realization gives better performance compared to existing realizations in terms of signal to noise ratio and computational complexity.     

Optical study of zinc blend SnS and cubic In2S3:Al thin films prepared by chemical bath deposition

Multilayers of zinc blend SnS crystalline thin film have been deposited onto glass substrates by a chemical bath deposition (CBD) method. The envelope method, based on the optical transmission spectrum taken at normal incidence, has been successfully applied to determine the layer thickness and to characterize optical properties of thin films having low surface roughness. Optical constants such as refractive index n, extinction coefficient k, as well as the real (??_r) and imaginary (??_i) parts of the dielectric constant were determined from transmittance spectrum using this method. Obtained low value of the extinction coefficient in the transparency domain is a good indication of film surface smoothness and homogeneity. To perform the heterojunction structure based on SnS absorber material, cubic In₂S₃:Al was deposited on SnO₂:F/glass as window layer using CBD with different aluminum content. Optical properties of these films were evaluated.     

The impact of electrode dielectric coating on the insulationintegrity of GIS/GITL with metallic particle contaminants

Coating the inside surface of gas insulated switchgear (GIS) enclosures with a dielectric film reduces the deleterious effect of electrode surface roughness, impedes the development of metallic particle initiated microdischarges, increases the field required to lift particles, and reduces the charge acquired by particles, all of which help alleviate the adverse effect of contaminating metallic particles on insulation withstand. The performance of particle-contaminated compressed gas systems with dielectric coated electrodes is analyzed. Two mechanisms for the transfer of charge from electrodes to contaminating particles are considered, namely, conduction through the coating layer and microdischarges in the surrounding gas. The paper presents an electrostatic study of the particle lifting fields with dielectric covered electrodes. The overall breakdown strength of the system is evaluated and the results are discussed in the light of experimental findings     

Mechanical alloying and thermoelectric properties of Zn4Sb3

Thermoelectric Zn₄Sb₃ bulk specimens were produced by mechanical alloying of elemental powders and consolidated by hot pressing. Single phase Zn₄Sb₃ was not obtained using a nominal stoichiometric composition, but near single phase Zn₄Sb₃ with remnant elemental Zn having a relatively high density was produced using a nominally 11.7 at.% Zn rich powders. Phase transformations during mechanical alloying were systematically investigated using XRD and SEM. Thermoelectric and transport properties were evaluated for the hot pressed specimens and compared with results of analogous studies.     

One world, one hope: the cost of providing antiretroviral therapy to all nations

OBJECTIVE: To estimate the potential direct cost of making triple combination antiretroviral therapy widely available to HIV-positive adults and children living in countries throughout the world. METHODS: For each country, antiretroviral costs were obtained by multiplying the annual cost of triple antiretroviral therapy by the estimated number of HIV-positive persons accessing therapy. Per capita antiretroviral costs were computed by dividing the antiretroviral costs by the country's total population. The potential economic burden was calculated by dividing per capita antiretroviral costs by the gross national product (GNP) per capita. All values are expressed in 1997 US dollars. RESULTS: The potential cost of making triple combination antiretroviral therapy available to HIV-positive individuals throughout the world was estimated to be over US$ 65.8 billion. By far the greatest financial burden was on sub-Saharan Africa. The highest per capita drug cost in this region would be incurred in the subregions of Southern Africa (US$ 149) followed by East Africa (US$ 116), Middle Africa (US$ 44), and West Africa (US$ 42). In the Americas, subregional data indicated the highest per capita drug cost would be in the Latin Caribbean (US$ 22), followed by the Caribbean (US$ 17), Andean Area (US$ 7), the Southern Cone (US$ 6), North America (US$ 6), and Central American Isthmus (US$ 5). In Asia and Europe the percentage of the GNP necessary to finance drug therapy was less than 1% in most countries examined. CONCLUSION: Our results demonstrate that the cost of making combination antiretroviral therapy available worldwide would be exceedingly high, especially in countries with limited financial resources.     

Analysis of the IAEA research reactor benchmark problem by the RETRAC-PC code

A basic approach to perform safety analysis of a nuclear research reactor consists in using deterministic methods to verify that the established acceptance criteria related to fuel integrity are fulfilled during all the stages of the facility lifetime. These methods should be validated against a large set of experimental and postulated transients. Since measured data are not easily available in the literature, the IAEA defined typical transients in a generic 10-MW MTR nuclear reactor core as a benchmark test for computational tools verification. In this framework, an assessment study of the coupled kinetic–thermal–hydraulic RETRAC-PC code is presented herein. The considered cases include the analysis of core dynamic under ramp positive reactivity insertion, and loss of flow transients. In general, the obtained results are satisfactory and agree with results obtained by other similar codes.