Liste des publications
Annealing duration in?uence on dip-coated CZTS thin ?lms properties obtained by sol-gel method
The e?ect of annealing duration on structural and optical properties of dip-coated crystallineCZTS thin ?lms was studied. The obtained samples were investigated by several techniques suchas XRD, Raman spectroscopy, SEM, UV–vis spectroscopy and Photoluminescence. Being con-?rmed by Raman spectroscopy, XRD analysis reveals the formation of kesterite tetragonal phasewith preferential orientation along (112) direction. The grain size tends to increase as the an- nealing duration increases, a result con?rmed by SEM. The last shows smooth, uniform, homo-geneous and densely packed grains. Optical measurement analysis reveals that layers have re- latively high absorption coe?cient in the visible spectrum with a band gap reduction of1.62−1.50 eV which is quite close to the optimum value for a solar cell. The photoluminescence distinguishes broad bands that have maximums of intensity limited between 1.50 and 1.62 eV, corresponding to the optical band gap of the CZTS. Voir les détails
Mots clés : Kesterite, sol-gel, Thin films, Dip-coating CZTS, Photoluminescence
A Robust Adaptive Fuzzy Fast Terminal Synergetic Voltage Control Scheme for DC/DC Buck Converter
In this paper, an adaptive fuzzy fast terminal synergetic voltage control scheme for DC/DC buck converter is proposed based on recently developed synergetic theory and a terminal attractor method. The advantages of presented synergetic control include the characteristics of finite time convergence, insensitive to parameters variation and chattering free phenomena. Rendering the design more robust, fuzzy logic systems are used to approximate the unknown parameters in the proposed controller without calling upon usual model linearization and simplifications. Taking the DC/DC buck converter in continuous conduction mode as an example, the algorithm of proposed synergetic control is analyzed in detail. All the simulation results demonstrate the effectiveness and the high dynamic capability of the proposed AF-FTSC control technique over the FTSC strategy. Voir les détails
Mots clés : synergetic control, fuzzy logic system; terminal technique; finite time convergence; DC/DC buck converter.
Annealing duration influence on dip-coated CZTS thin films properties obtained by sol-gel method
The effect of annealing duration on structural and optical properties of dip-coated crystallineCZTS thin films was studied. The obtained samples were investigated by several techniques suchas XRD, Raman spectroscopy, SEM, UV–vis spectroscopy and Photoluminescence. Being con-firmed by Raman spectroscopy, XRD analysis reveals the formation of kesterite tetragonal phasewith preferential orientation along (112) direction. The grain size tends to increase as the an- nealing duration increases, a result confirmed by SEM. The last shows smooth, uniform, homo-geneous and densely packed grains. Optical measurement analysis reveals that layers have re- latively high absorption coefficient in the visible spectrum with a band gap reduction of1.62−1.50 eV which is quite close to the optimum value for a solar cell. The photoluminescence distinguishes broad bands that have maximums of intensity limited between 1.50 and 1.62 eV,corresponding to the optical band gap of the CZTS.Kesterite,Sol-gel,Thin-film,Dip-coating,CZTS,Photoluminescence Voir les détails
Mots clés : Kesterite, sol-gel, Thin-film, Dip-Coating, CZTS, Photoluminescence
A Comparison Study: Direct and Indirect ModeControl of Perturb and Observe-MPPT Algorithmsfor Photovoltaic System
The Perturb and Observe P&O algorithm hasbeen widely used in most real-world applications due to itssimplicity of implementation in the control loops. Its main idea isto adjust the operating point of photovoltaic PV panels to ensurea good tracking behavior of a desired Maximum Power PointMPP. The P&O algorithm is one of the most used MPPTalgorithms to extract the electrical energy of PV panels underdifferent weather conditions. This can be done via the directcontrol mode of the DC-DC boost converter which commonlylinked by an external resistive load. However, the given electricalpower of the P&O-MPPT algorithm becomes fluctuating in thesmall time range, especially when the current MPP is graduallyapproaching the desired one. It provides unfortunately a steadystatepower oscillation problem and a loss of electrical energy at asudden change of climatic conditions. The indirect control modeof the DC-DC boost converter via P&O-MPPT algorithm isadopted as an alternative key to avoid the above mentioneddrawbacks where electrical performances are well enhanced interm of transient and steady-states of the given output powerresponse, the MPP tracking accuracy, the given electrical energyratio and so on. This goal can be reached through the followingsteps. The desired reference voltage perturbation is firstlycomputed by the standard P&O algorithm using the MPPmeasurements recorded through the actual PV panel at thestandard test condition STC (i.e., nominal absolute temperatureand nominal solar irradiance). It then compared by the actualvoltage perturbation generated by the closed loop P&O-MPPTscheme, providing thus the discrepancy voltage perturbation.Finally, a Proportional-Integral-Derivative PID controller givenin the P&O-MPPT inner loop scheme is used to mitigate as muchas possible the previous voltage error perturbation. This yields adesired duty cycle perturbation of the DC-DC boost converterwhich allowing reaching a good trade-off between both transientstatespeed and steady-state stationary of the output powerresponse. Simulation results confirm the effectiveness of theindirect control mode of the P&O –MPPT algorithm over thedirect control mode of same algorithm for several suddenchanges in weather conditions and wide variations of the resistiveload. Voir les détails
Mots clés : PV system, Boost converter, P&O algorithm, Direct and indirect control modes
Predictive Control of a Grid Connected PV System Incorporating Active power Filter functionalities
This article proposes a multifunction of a double stage grid connected photovoltaic (PV) system, with insertion the active power filter (APF) functionalities. This system is used to compensate the harmonics currents, compensate reactive power, supply the nonlinear loads and inject the PV system's active power into grid. This study is based on grid side, a perturb and observe algorithm is used to extract the maximum power point tracking (MPPT) from the PV array regardless of solar irradiance. On the grid side, a modified instantaneous active and reactive power theory (P-Q) based on a multi-variable filter (MVF) is applied to correctly identify the harmonics currents reference under distorted source voltage condition, also a modified predictive current control (PCC) algorithm is used to generate the switching signals for the source voltage inverter in order to ensure compensate reactive power and harmonic currents, feed the non linear load and inject the surplus of active powerinto the grid. In Matlab/Simulink™ software environment, the performance of the proposed control scheme is investigated under load change and irradiance change conditions. Simulations results demonstrate that the proposed PCC of the APF ensure a manage of active power exchanges with the grid with power factor correction. Furthermore, the grid current recovers its sinusoidal waveform with a total harmonic distortion (THD) meet to IEEE-519 standard. Voir les détails
Mots clés : Photovoltaic system (PV), activ power filter (APF), Predictive current control (PCC), active and reactive power theory (P-Q), multivariable filter (MVF), total harmonic distortion (THD)
Optimization of TIG Welding Process Parameters for X70-304LDissimilar Joint Using Taguchi Method
The optimization of mechanical properties of the welded joints requires a statisticalapproach such as Taguchi experimental designs associated with experimental techniques andlaboratory characterizations. The aim of this work is to propose a method of optimization of themechanical performances of a TIG dissimilar welding of two grades of steels: a high strength lowalloy steel X70 and an austenitic stainless steel 304L. The experimental designs were chosenaccording to the Taguchi method L9. The metallurgical characterization includes opticalmicroscopy, SEM microscopy, EDX analyses and mechanical tests to establish a relationshipbetween welding parameters, microstructures and mechanical behavior in different dissimilar weldregions. The results showed that the hardness is more strongly related to microstructural evolutionthan tensile strength of dissimilar joint. It was found that gas flow is the main significant TIGwelding parameter affecting dissimilar weld characteristics. Voir les détails
Mots clés : hardness, tensile test, ANOVA, Dissimilar welds, Taguchi method
Surface peformances of PVD ZrN coatings in biological environments
Zirconium nitride (ZrN) thin films were deposited by reactive RF magnetron sputtering on Ti-6Al-4V and Si (100) substrates for potential use in biomedical applications. The tribological behaviour was evaluated against bovine bone in dry condition using a pin-on-disc apparatus. Abrasion is the primary wear mechanism observed in ZrN/bone contact. The corrosion properties were determined through two electrochemical techniques: potentiodynamic polarization and electrochemical impedance spectroscopy. The coatings with reduced oxygen content provided: (i) good resistance against corrosion when exposed to physiological solution and (ii) better anti-bioadhesion against Staphylococcus aureus bacteria. Voir les détails
Mots clés : PVD coating, ZrN, wear, corrosion, bioadhesion
Arc Voltage Signals-Based Flicker Effect Analysis Using SampEn Multi-scale Entropy Algorithm
Real-time monitoring in the steel and metallurgical production sector is of great importance. To ensurecompetitiveness, the industrial process will have to innovate and evolve towards better quality. Therefore, the monitoring of the voltage signal in Electric Arc Furnace (EAF) has a vital role in keeping a nominal operation of electrical components in order to achieve high performance. A new monitoring method based on multi-scale Sample Entropy (SampEn) (MSE) algorithm for EAF voltage flicker is proposed. In the proposed method, different percentages of flicker effect analysis are presented. The current voltage characteristic of the EAF in conjunction with MSE and comparison of observed values with those predicted from a Cassie and Mayr model built using nominally healthy data are analysed. In order to achieve the classification procedure, five extracted features are used to adapt the subtractive clustering network for each state of the flicker effect and the performance of the classifier during the training is given with success. Voir les détails
Mots clés : Electric Arc Furnace (EAF), Power quality, Voltage flicker, Voltage unbalance, SampEn Multi-scale entropy algorithm, subtractive clustering
Numerical study of parameters affecting pressure drop of power-law fluid in horizontal annulus for laminar and turbulent flows
Efficient hydraulics program of oil and gas wells has a crucial role for the optimization of drilling process. In the present paper, a numerical study of power-law fluid flow through concentric (E = 0.0) and eccentric annulus (E = 0.3, E = 0.6 and E = 0.9) was performed for both laminar and turbulent flow regimes utilizing a finite volume method. The effects of inner pipe rotation, flow behavior index and diameter ratio on the pressure drop were studied; furthermore, the appearance and development of secondary flow as well as its impact on the pressure drop gradient were evaluated. Results indicated that the increment of the inner pipe rotation from 0 to 400 rpm is found to decrease pressure drop gradient for laminar flow in concentric annulus while a negligible effect is observed for turbulent flow. The beginning of secondary flow formation in the wide region part of the eccentric annulus (E = 0.6) induces an increase of 9% and a slight increase in pressure drop gradient for laminar and turbulent flow, respectively. On the other hand, the variation of the flow behavior index and diameter ratio from low to high values caused a dramatic increase in the pressure drop. Streamlines in the annulus showed that the secondary flow is mainly induced by eccentricity of the inner pipe where both high values of diameter ratio and low values of flow behavior index tend to prevent the secondary flow to appear. Voir les détails
Mots clés : Computational fluid dynamics (CFD) Power-law fluid Pressure drop Secondary flow
CHARACTERIZATION OF IRON ORE AND SCALE FOR SYNTHESIZING VINYL PAINT
As part of the development of iron ore deposits in Algeria and a concern for the preservation of the environment, we are planning to characterize two materials for a possible synthesis of vinyl paint in this study. Iron ore is a red iron oxide pigment with an oolitic structure containing phosphorus. The second material is a steel by-product (scale) that should be recycled. This study covers the characterization of these two components through Chemical analysis, Particle size analysis, Thermal analysis (TGA, DSC), the Observation by SEM, X-Ray Diffraction analysis and Spectrophotometric analysis. Chemical analysis showed that the pigment contains 53.18% of total iron and mostly the gangue is dominated by silica and alumina. Scale in turn contains 73.83% of iron in the form of iron oxides (FeO, Fe3O4 and Fe2O3). Grinding tests illustrated that the scale is much more suitable for grinding than pigment. The granulometric analysis gave a volume distribution of the particles with a size between 0.7 and 32 µm for scale and 0.6 to 40 µm for the pigment and their specific areas are 1.6 and 1.5 m2/g. TGA and DSC showed that the iron pigment loses weight with phase dissolution by consuming energy when the temperature increases. Scale gains weight by the formation of a new phase with heat. Scanning electron microscope of red iron pigment showed a grain aggregate formed rounded over at least iron oxide and gangue. The EDS analysis illustrated a predominance of iron with four predominant oxides in the case of iron ore deposits. Chemical elements forming these four oxides are silicon, calcium, aluminum and magnesium. The SEM of scale showed a homogeneous structure composed of sizes of iron oxide grains and shapes ranging from 1 µm to 10 µm. X-ray diffraction analysis showed that the iron in the pigment is in the form of hematite (Fe2O3) and goethite (FeO(OH)). A tiny portion is combined with silica as fayalite (Fe2SiO4). The iron in the calamine is in the form of the three oxides (FeO, Fe2O3 and Fe3O4). Spectrophotometric tests showed that both materials have virtually no absorption and maximum reflection (100%) in the visible range Voir les détails
Mots clés : Pigment iron, scale (calamine), Simultaneous thermal analysis, X-ray diffraction, Spectrophotometry