Liste des publications
Fault-tolerant power extraction strategy for photovoltaic energy systems
Photovoltaic (PV) arrays are subject to various types of environmental disturbances and component-related faults that affect their normal operation and result in a considerable energy loss. The nonlinear current-voltage (I-V) characteristic curve of the PV array prevents the detection and isolation of the faults and also makes the tracking of the maximum power operating point (MPP) more difficult. Fault detection and identification (FDI) techniques have been proposed to detect the presence of faults and isolate them. Many maximum power point tracking (MPPT) methods have been proposed to find the best operating point in the presence of disturbed environmental conditions. However, existing FDI methods do not consider the tracking of the MPP in faulted operating conditions, and available MPP tracking methods do not consider the occurrence of faults in the PV system. The objective of this study is to propose a fault-tolerant control (FTC) strategy to detect the presence of abnormal operating conditions and reconfigure the MPPT procedure to search for the new suboptimal operating point. The FDI method is based on monitoring the PV panel generated power for the presence of abrupt changes; the MPPT reconfiguration is based on a combination between Incremental Conductance (IncCond) Algorithm and an Improved Current-based Particle Swarm Optimization (ICPSO) tracking technique. Simulation and experimental results show an excellent performance of the proposed FTC method in the presence of various types of faults. Voir les détails
Mots clés : Fault-tolerant control (FTC), Particle swarm optimisation (PSO), Photovoltaic (PV) arrays, Line-Ground fault, Line-line fault, Partial shading, Maximum Power Point Tracking (MPPT)
Robust fuzzy c-means clustering algorithmusing non-parametric Bayesian estimation in wavelet transform domain for noisy MR brain image segmentation
The major drawback of the fuzzy c-means (FCM) algorithm is its sensitivity to noise. The authors propose a new extended FCM algorithm based a non-parametric Bayesian estimation in the wavelet transform domain for segmenting noisy MR brain images. They use the Bayesian estimator to process the noisy wavelet coefficients. Before segmentation based on FCM algorithm, they use an a priori statistical model adapted to the modelisation of the wavelet coefficients of a noisy image.The main objective of this wavelet-based Bayesian statistical estimation is to recover a good quality image, from a noisy imageof poor quality. Experimental results on simulated and real magnetic resonance imaging brain images show that their proposed method solves the problem of sensitivity to noise and offers a very good performance that out performs some FCM-based algorithms. Voir les détails
Mots clés : fuzzy C-means algorithm, Non-Parametric Bayesian Estimation, Wavelet transform, image segmentation, MR Brain Images
Investigation of microstructure and mechanical properties of phosphocalcic bonesubstitute using the chemical wet method
Selection of calcium phosphate base materials in reconstructive bone surgery is justified by the surprising similarities in chemical compositions with human bones. The closest to natural apatite material is the hydroxyapatite (HAp) which has a chemical composition based on calcium and pho sphate (Ca 10 (PO 4 )6 (OH)2 ). In this study, HAp is synthesized using the wet precipitation method from hydrated calcium chloride (CaCl 2 ,12H 2 O) and di-sodium hydrogen phosphate di-hydrate (HNa 2 PO4,2H 2 O). The powder is calcinated at 900°C and 1200°C in order to compare with sintered condition at 1150°C. Vickers microhardness tests and X-ray diffraction analyzes are used for the characterization of the crystalline material. Mechanical properties ( HV , σe, σ r , and K C ) and the degree of crystallinity (X c) are discussed according to heat treatment temperatures. Results indicate that heat trea ting the powder at 1200°C increased crystallinity up to 72%. At the same time, microhardness increased with temperature and even outmatched the sintered case at 1150°C. Fracture toughness is ameliorated with increasing heat treatment tempera ture by more than two folds. Voir les détails
Mots clés : Biomaterials, hydroxyapatite, chemical wet method, mechanical properties, heat treatment
Study of reliability index for high-density polyethylene based on pipestandard dimension ratio and fracture toughness limits
The reliability of high-density polyethylene (HDPE) pipes remains a central issue for gas transportation and distribution net-works. The objective of this study is to investigate the estimation of reliability index ( β) for a plastic pipe using the critical stressintensity factor ( KIC) as the maximum limit for safe operating conditions. Simulations are performed as a function of operatingpressure, crack length, and standard dimension ratio (SDR) for three fracture toughness levels (low, moderate, and high). Inaddition, the study compares results from three hoop stress calculations methods (thin, thick, and ISO plastic pipe equation).Based on design recommendation for reliability index, it is found that both operating pressure and crack length show comparablebehaviors. However, the thick wall pipe results overestimate (β) for every KIClevel. In all cases, it is found that the higher thecritical stress intensity factor, the better the reliability index. Results obtained with the standard ISO pipe formula are morerealistic, as they are usually around the design recommendation, i.e., SDR basis indicates that it is a true conservative designapproach incorporating both upper and lower thickness limits. The importance of all variables (thickness, diameter, crack length,pressure, and fracture toughness) is also discussed Voir les détails
Mots clés : HDPE pipe . Critical stress intensity factor . Standard dimension ratio (SDR) . Crack length . Reliability index . Importance of variables
Study of a double fed induction generator usingmatrix converter: Case of wind energy conversionsystem
Due to the growing of the power electronics, especial attention has been given to the use ofnew generation of power converters, AC/AC matrix converter to which provide a directpower converter AC/AC, bi-directional power flow, almost sinusoidal input and outputwaveform. In this paper, we present the performance study of a variable-speed windturbine based on doubly fed induction generator fed by matrix converter using themaximum power point tracking method to extract the maximum power available. Thewhole system is presented in d-q-synchronous reference frame. The control scheme istested and the performances are evaluated by simulation results. The simulation resultsobtained under MatLab/Simulink show the effectiveness and validity of the consideredcontrol. Voir les détails
Mots clés : Wind turbine, Control, Maximum power tracking, matrix converter, doubly fed induction generator
Application of Direct Power Control in Wind EnergyConversion System
This paper describes the performance evaluation of thedirect power control for a three-phase pulse with modulationinverter fed by a variable speed wind energy conversion system.This, to ensure a maximum power point tracking of a wind.Proposed direct power control strategy is implemented in the d-qreference frame. The system modeling and control scheme areimplemented on Matlab/Simulink. The simulation results show thatthe use of the direct Power Control provide nearly sinusoidal inputwave form current, constant switching frequency operation,regulation of unity power factor in the connection of the grid sideconverter with the grid and the maintain of the DC-link voltageconstant. Finely, the results verify the validity and effectiveness ofthe proposed control. Voir les détails
Mots clés : Renewable energies, wind energy conversion system, Direct power control, simulation
Microstructure, Corrosion and Magnetic Behavior of an Aged Dual-Phase Stainless Steel
In the present work, the effect of the precipitation phenomena on corrosion and magnetic behavior of an aged dual-phase stainless steel was investigated. Aging treatment caused the precipitation of the σ phase, chromium carbides and secondary austenite, which was accompanied by the shifting of the δ/γ interfaces inside the δ ferrite grains. Aging between 700 and 850 °C strongly deteriorated the pitting corrosion resistance of the studied material. Magnetic investigation of the aged material using the vibration sample magnetic technique revealed the sensitivity of the intrinsic magnetic properties to the smallest microstructural change. This was confirmed by the Eddy current technique that led also to the evaluation of the aging-induced localized corrosion. Voir les détails
Mots clés : σ phase, aging treatment, DSS, Magnetic Properties, microstructure, Pitting corrosion
A method for mechanical property assessment across butt fusion weldedpolyethylene pipes
The use of high-density polyethylene pipes in gas and water distribution networks is steadily growing worldwide. If the resistanceof plain pipes is at present time well established using appropriately designed standards, welding issues continue to be globallyapproached equally in terms of structure and mechanical properties. Consequently, further practical investigations should beaimed at studying mechanical properties in the weld region which includes the melt zone and its heat-affected zones. This workpresents a method based on removing layers in order to assess localized variances in mechanical properties throughout the weldseam in both radial and circumferential directions. An experimental plan based on specific machining operations allowed testing39 standard specimens representing the weld volume matter in three concentric layers for given pipe dimensions and theircounterpart standard unwelded ones. The typical stress–strain behavior of semi-crystalline materials is preserved in weldedand unwelded specimens but with different characteristic limits. At the weld inner layers, properties such as elastic modulus,yield, and failure stresses displayed lower values, whereas in welded outer layers, the tendency is inversed. The cold drawingextend remained approximately steady for unwelded and welded cases across the pipe wall. This property is less affected by thepresence of the weld as it described a constant material flow which is mostly a function of available material quantity for yielding.The approach developed in this study gives consistent indications on welding quality around the pipe weld and across thethickness. Accordingly, outermost and innermost welded layers may exhibit lower or even bad-quality welds as imperfectionscan concentrate stresses at the joint interface because of cold weld problems. Such method enabled detecting 23% of failures atthe weld seam from outer and inner layers while the middle layer did not reveal any failure at the weld. The causes of thisbehavior are approached using crystallinity evolution in welded and unwelded pipes. Voir les détails
Mots clés : HDPE pipe . Butt fusion welding . Mechanical properties . Radial direction . Circumferential direction . St ru ct ur al variances
EFFECT OF ELECTRICAL CURRENT ON FRICTION AND WEAR BEHAVIOR OF COPPER AGAINST GRAPHITE FOR LOW SLIDING SPEEDS
Copper-graphite is an important tribological material used in the applications of electrical sliding contact like generators and electrical brushes. A series of experimental tests were conducted on a pin-disc tribometer in air and dry sliding condition. The pair of material was subjected to electric current ranging from 0 to 10A, normal loads of 5 to 30N and sliding speed of 0.5m/s. The duration of each test was 30 minutes. Experimental results indicated that the friction coefficient decreases and wear rate increases with increasing load with and without applied electric current. The changes in surface chemistry and topography of the tribo-surfaces were characterized using Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). This later technique was used to analyze the transfer of pin materials to the counterface, and also to understand how copper and graphite influence the tribological properties. Results indicated that, electric current and normal load have more or less significant influence on the tribological behavior of the pair of materials and the effect of oxide layer created at interface of the pairs in contact. Voir les détails
Mots clés : friction, wear, Contact temperature, load, Electric current.
Structure, magnetic and microwave studies of mechanically alloyed powders Fe45Ni35Co20
Nanocrystalline Fe-35 wt%Ni-20 wt%Co has been prepared by using a high-energy planetary ball mill with increasing milling time from 4 to 36 h. Microstructural characterisations showed the development of an face-centred cubic nanostructured Fe-35 wt%Ni-20 wt%Co alloy with an average crystallite size of 8 nm. The magnetic investigation revealed that the nanostructures obtained from a milling time of 36 h have the highest magnetic saturation and the lowest coercive field. In addition, the hardness and the electromagnetic absorption of the Fe-35 wt%Ni-20 wt%Co alloy were found to increase with the milling time. These evolutions could be attributed to the crystallite size and the strain variations in the samples during milling. Voir les détails
Mots clés : nanostructure, magnetic, nanocristalline, Mechanical Alloying, Fe, Co