Liste des documents
A Copper Oxide (CuO) Thin Films Deposited by Spray Pyrolysis Method
A simple and low-cost procedure (spray pyrolysis) was used to elaborate a copper oxide thin films on ordinary glass substrates. A copper nitrate was used and dissolved in two different solutions (Water, Methanol) S1 and S2 respectively in order to obtain an equal concentration; CS1,S2=0.5M. The spray pyrolysis deposition made at fixed temperature T=500°C and different volumes of S1 or S2 on the glass substrates. The X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-vis spectrophotometry were used to determinate the structural, morphological and optical properties of CuO thin films. The X-ray diffraction patterns confirm the presence of the polycrystalline phase of CuO as monoclinic crystal structure with preferential orientation along (110), (002), (111), (200) and (020). Their optical band gaps ranged from 3.95 to 4.02eV for thin films made with S1, and from 1.6 to 1.95eV for thin films made with S2 with a high absorbency in the visible region, which is in agreement with the values of the literature. Voir les détails
Mots clés : Copper oxide, Thin films, Spray pyrolysis, Band Gaps, XRD, SEM.
Improved Cu2O/AZO Heterojunction by Inserting a Thin ZnO Interlayer Grown by Pulsed Laser Deposition
Cu2O/ZnO:Al (AZO) and Cu2O/ZnO/AZO heterojunctions have been deposited on glass substrates by a unique three-step pulsed laser deposition process. The structural, optical, and electrical properties of the oxide films were investigated before their implementation in the final device. X-ray diffraction analysis indicated that the materials were highly crystallized along the c-axis. All films were highly transparent in the visible region with enhanced electrical properties. Atomic force and scanning electron microscopies showed that the insertion of a ZnO layer between the Cu2O and AZO films in the heterojunction enhanced the average grain size and surface roughness. The heterojunctions exhibited remarkable diode behavior and good rectifying character with low leakage current under reverse bias. The presence of the ZnO interlayer film significantly reduced the parasitic and leakage currents across the barrier, improved the quality of the heterostructure, made the energy band between AZO and Cu2O layers smoother, and eliminated the possibility of interface recombination, leading to much longer electron lifetime. Voir les détails
Mots clés : Heterojunctions, ZnO, Cu2O, AZO, pulsed laser deposition, solar cells
Optimal pump excitation frequency for improvement of damage detection by nonlinear vibro acoustic modulation method in a multiple scattering sample
We present a method to systematically optimize nonlinear damage detection in multiple scattering media by the nonlinear Vibro-Acoustic Modulation (VAM) technique. The latter consists here of exciting a medium simultaneously with a high frequency ultrasonic sinusoidal burst and with a low frequency continuous sinusoidal wave. Modulation of the high frequency (probe) by the low frequency (pump) is made possible by the presence of nonlinear scatterers, i.e. cracks, defects. A signal processing technique consisting of a closed loop system drives the automatic adaptation of the pumping frequency, yielding to the optimization of the nonlinear modulation (NM) of the output probing coda signal without a priori information on the medium and the scatterers. The correlation coefficient between a reference output probe signal without the pumping wave and an output modulated probe signal with a pumping wave was considered as our cost function. A multiple scattering solid beam where nonlinear scatterers can be controllably added or removed is designed and tested. The first step of this study is an empirical search of the correlation coefficient dependency on the pumping frequency to verify the performances of the proposed method. Then the implemented optimization algorithm based on genetic algorithm (GA) is used to find automatically the optimal pumping frequency. The obtained optimization results show a good agreement with the empirical study. Moreover, the genetic algorithm allowed to find the optimal pump frequency adapted to each configuration of nonlinear scatterers. This relatively fast search of the optimal nonlinear response could be extended to nonlinear scatterer imaging applications using the information on the resonant modes spatial shapes together with the associated optimal response. Voir les détails
Mots clés : Optimal command, Genetic algorithm, Nonlinear- Vibro Acoustic Modulation, Crack detection
Optimal pump excitation frequency for improvement of damage detection by nonlinear vibro acoustic modulation method in a multiple scattering sample.
We present a method to systematically optimize nonlinear damage detection in multiple scattering media by the nonlinear Vibro-Acoustic Modulation (VAM) technique. The latter consists here of exciting a medium simultaneously with a high frequency ultrasonic sinusoidal burst and with a low frequency continuous sinusoidal wave. Modulation of the high frequency (probe) by the low frequency (pump) is made possible by the presence of nonlinear scatterers, i.e. cracks, defects. A signal processing technique consisting of a closed loop system drives the automatic adaptation of the pumping frequency, yielding to the optimization of the nonlinear modulation (NM) of the output probing coda signal without a priori information on the medium and the scatterers. The correlation coefficient between a reference output probe signal without the pumping wave and an output modulated probe signal with a pumping wave was considered as our cost function. A multiple scattering solid beam where nonlinear scatterers can be controllably added or removed is designed and tested. The first step of this study is an empirical search of the correlation coefficient dependency on the pumping frequency to verify the performances of the proposed method. Then the implemented optimization algorithm based on genetic algorithm (GA) is used to find automatically the optimal pumping frequency. The obtained optimization results show a good agreement with the empirical study. Moreover, the genetic algorithm allowed to find the optimal pump frequency adapted to each configuration of nonlinear scatterers. This relatively fast search of the optimal nonlinear response could be extended to nonlinear scatterer imaging applications using the information on the resonant modes spatial shapes together with the associated optimal response. Voir les détails
Mots clés : Optimal command, Genetic algorithm, Nonlinear Vibro Acoustic Modulation, Crack detection
Early stages of copper microparticles electrodeposition on polypyrrole film
In this work, we studied the electrodeposition of copper (Cu) microparticles on polypyrrole (PPy) ?lms using cyclic voltammetry and chronoamperometry techniques. The initial stages of Cu deposition were investigated by performing current transients. Models based on Scharifker and Hills calculations were established to determine the nucleation and growth type. The results suggest that the deposition of Cu proceeds via an instantaneous nucleation followed by three-dimensional (3D) di?usion-limited growth. The values of the number density of active sites N∞ and di?usion coe?cient D were also determined. Voir les détails
Mots clés : composites, copper, electrodeposition, polymer, thin film
Diagnosis Method for GTO Open Switch FaultApplied to Reconfigurable Three-Level 48-PulseSTATCOM
In the recent years, several research worksare focusing on the use of STATCOM in electrical net-works because it is used to regulate the voltage, to im-prove the dynamic stability of the power system be-sides allowing better management of the power ?ow.All these positive tasks have guaranteed an importantposition of STATCOM within a family of Flexible Al-ternating Current Transmission System (FACTS). Inthis paper study, the control and operation of a threelevels 48-pulse GTO based STATCOM is implementedwith series connected transformers. The system may,unfortunately, be prone to GTO switch faults and there-fore may a?ect reactive power transiting. In this pa-per, a new diagnostic approach is proposed based onthe Single-Sided Amplitude Spectrum (SSAS) methodof the three-leg converter currents for detection and lo-calization of open-circuit faults. The integration of theSTATCOM recon?gurable fault tolerant to the systemis also considered to ensure service continuity. Sev-eral results are presented and discussed in this paperto illustrate the performance of the STATCOM fault-tolerant diagnostic. Voir les détails
Mots clés : Detection, diagnosis, FACTS, GTO, open switch fault, recon?guration, SSAS, STATCOM
CONTRIBUTION À LA RÉCONFIGURATION D’ONDULEUR ÀTOLÉRANCE DE PANNE APPLIQUÉE AU PARC ÉOLIEN CONNECTÉAU RÉSEAU ÉLECTRIQUE
Cet article propose une nouvelle technique de diagnostic basée sur les vecteurs de Park associés aux coordonnées polaires pour ladétection et la localisation des défauts de circuit- ouvert (CO), ainsi que l’intégration de l’onduleur reconfigurable à tolérance depanne afin de permettre la continuité de service du système du parc éolien. Le modèle utilisé est celui d'une éolienne à vitessevariable couplée à une génératrice asynchrone à double alimentation (GADA) connecté au réseau électrique via unconvertisseur à tolérance de panne pour améliorer les performances après l’apparition du défaut. Ce convertisseur est utilisé àbase d’IGBT pour l’obtention d’une précision acceptable avec des fréquences de commutation élevées. Ce modèle est bienadapté pour l'observation des harmoniques et la performance dynamique du système de contrôle sur des périodes de tempsrelativement courtes (généralement des centaines de millisecondes à une seconde). Cette méthode permet d'extraire l'énergiemaximale du vent lors d’une faible vitesse du vent en optimisant la vitesse de la turbine tout en minimisant les contraintesmécaniques sur la turbine pendant les rafales de vent. Pour illustrer l’amélioration de diagnostic des défauts en circuit ouvert duconvertisseur à tolérance de panne, plusieurs résultats sont présentés et discutés dans cet article. Voir les détails
Mots clés : Génératrice asynchrone à double alimentation (GADA) Turbine, Onduleur, diagnostic, détection, localisation, Reconfiguration, défaut, Circuit- ouvert, Insulated gate bipolar transistor (IGBT).
CONTRIBUTION TO RECONFIGURATION OF FAULT-TOLERANT INVERTER APPLIED TO THE WIND PARK CONNECTED TO THE ELECTRICAL NETWORK
This paper proposes a new diagnostic technique based on Park vectors associated with polar coordinates for the detection and location of open circuit (OC) faults, as well as the integration of fault-tolerant reconfigurable inverter in order to enable continuity of service of the wind farm system. The model used is that of a variable speed wind turbine coupled to a double-fed induction generator (DFIG) connected to the power grid via a fault-tolerant converter to improve performance after the appearance of the fault. This converter is used based on IGBT to obtain an acceptable accuracy with high switching frequencies. This model is well suited for the observation of harmonics and the dynamic performance of the control system over relatively short periods of time (typically hundreds of milliseconds to one second). This method allows extracting the maximum wind energy during a low wind speed by optimizing the turbine speed while minimizing the mechanical stress on the turbine during gusts of wind. To illustrate the diagnostic improvement of fault-tolerant inverter open circuit faults, several results are presented and discussed in this article. Voir les détails
Mots clés : DFIG Turbine, Inverter, diagnosis, Detection, Location, Reconfiguration, fault, Open-Circuit, IGBT
Effect of heat treatment on surface hardness and tribologicalbehavior of XC38 steel—approach by the experiments plans
This work aims at predicting the micro-hardness of XC38steel using the experiments plans as well asstudy of tribological behavior of thissteel. The heat treatments were considered by adopting thefactorial plans 22 methodology at two factors (temperature ‘T’ and holding time ‘t’), each at two levels(-1, +1). The results obtained allowed lead to a mathematical model predicting the micro-hardness‘Hv’ in every point of the study field. Moreover, the curves of the responses surfaces clearly show theinfluence of two factors studied (T, t) on ‘Hv’. Mechanical characterization of treated samples showedasignificant increase in the micro-hardness, which achieve to 76% for the treated sample at 850 °Cduring 2 h compared to untreated state. An investigation of wear tracks morphology shows thatfriction under a load of 10 N results in predominant adhesive wear, while a load of 2 N favorabrasive wear. Voir les détails
Mots clés : heat treatment, factorial plans, prediction, superficial hardness, tribological behavior
Characterization of the Polylactic acid stretched uniaxial and annealed by Raman spectrometry and Differential scanning calorimetry
In this work, we have been interested in the characterization of the effect of heat treatment and mechanical treatment on the crystallinity of polylactic acid (PLA) film by two techniques, DSC and Raman spectroscopy. The results obtained by the DSC for the stretched film shows the appearance of a broad peak of crystallization around 120 °C, a rise in melting peak in a significant way, which shows that the uniaxial stretching has increased the crystallinity of the PLA, whereas for the annealed film appearance of a double melting peak. The result obtained by Raman spectroscopy shows new peaks appears at 922 cm−1 and 540 cm-1 after stretching and annealed process, indicating the crystallization process. Voir les détails
Mots clés : PLA, glass transition, Raman spectroscopy, DSC