First and High Order Sliding Mode Control of a DFIG-Based Wind Turbine

Abstract

Wind energy has many advantages, because it does not pollute and is an inexhaustible source of energy. In this paper, we study the dynamical behavior of the Horizontal Axis Wind Turbine (HAWT) with MPPT (Maximum Power Point Tracking) algorithm and a pitch control, using a Doubly Fed Induction Generator (DFIG). The DFIG stator is directly linked to the grid; the rotor is connected via a back-to-back converter. To ensure a maximal power extraction, we use the MPPT algorithm combined with a PI controller to generate the maximum power and to force the system to work at the maximum operation point. The pitch control is used to protect the Wind Turbine (WT) against high wind speed. Field Oriented Control (FOC) based on a Sliding Mode (SM) first order and high order (super-twisting) are compared. These schemes control the stator active and reactive powers as well as the stator power factor and improve the power quality injected in the grid. Simulations illustrate the active and reactive power control of the HAWT by adjusting the rotor voltages of the DFIG. We choose the two rotor currents to define the sliding surfaces, in order to avoid the measurement of the electromagnetic torque and stator active and reactive powers. Adequate simulations results with Matlab-Simulink of the whole system including the MPPT algorithm, pitch control and SM controllers are presented and discussed.     

A blind digital audio watermarking scheme based on EMD and UISA techniques

In this paper, a new perceptual spread spectrum audio watermarking scheme is discussed. The watermark embedding process is performed in the Empirical Mode Decomposition (EMD) domain, and the hybrid watermark extraction process is based on the combination of EMD and ISA (Independent Subspace Analysis) techniques, followed by the generic detection system, i.e. inverse perceptual filter, predictor filter and correlation based detector. Since the EMD decomposes the audio signal into several oscillating components–the intrinsic mode functions (IMF)–the watermark information can be inserted in more than one IMF, using spread spectrum modulation, allowing hence the increase of the insertion capacity. The imperceptibility of the inserted data is ensured by the use of a psychoacoustical model. The blind extraction of the watermark signal, from the received watermarked audio, consists in the separation of the watermark from the IMFs of the received audio signal. The separation is achieved by a new proposed under-determined ISA method, here referred to as UISA. The proposed hybrid watermarking system was applied to the SQAM (Sound Quality Assessment Material) audio database (Available at http://sound.media.mit.edu/mpeg4/audio/sqam/) and proved to have efficient detection performances in terms of Bit Error Rate (BER) compared to a generic perceptual spread spectrum watermarking system. The perceptual quality of the watermarked audio was objectively assessed using the PEMO-Q (Tool for objective perceptual assessment of audio quality) algorithm. Also, using our technique, we can extract the different watermarks without using any information of original signal or the inserted watermark. Experimental results exhibit that the transparency and high robustness of the watermarked audio can be achieved simultaneously with a substantial increase of the amount of information transmitted. A reliability of 1.8 10^???4 (against 1.5 10^???2 for the generic system), for a bit rate of 400 bits/s, can be achieved when the channel is not disturbed.     

Scheduling cross docking operations under full,partial and no information on inbound arrivals

Cross docking is a logistic technique which seeks to reduce the inventory holding, order picking, transportation costs and delivery time. Little attention has been given to the transshipment operations inside a cross dock. In this article, we study the transshipment scheduling problem in a single receiving and a single shipping door cross dock under three scheduling policies: In the first policy, we assume to have complete information on the order of arrivals and the contents of all inbound trucks. The second and the third policies assume the availability of partial and no information on the sequence of upcoming trucks. An optimal graph based model is proposed for the full information case, and a polynomial time algorithm is given. Heuristics are developed for the other two cases. The comparison of the costs associated to each policy helps evaluating the value of information in cross dock scheduling problems.     

Different bacteriophage resistance mechanisms in Streptococcus salivarius subsp. thermophilus.

Streptococcus salivarius subsp. thermophilus strain NST5 exhibited a temperature-dependent defence mechanism against the virulent bacteriophages phi B1.2 and phi A1.1. It was active at 42 degrees C but not at 30 degrees C as demonstrated by a significant increase of both plaque size and efficiency of plaquing. This defence mechanism did not affect host-dependent phage replication and did not interfere with phage adsorption to NST5. These results suggest that it interfered with phage development. The phages phi T33, phi T58, phi D1, phi T21 and phi T9, belonging to the same phage type as phi B1.2, were examined for their ability to infect NST3 and NST5. Restriction modification systems of different specificity were detected in NST3 and NST5; host-dependent phage replication was detected at 30 and 42 degrees C; an abortive defence mechanism was detected in NST5 which was active at 42 degrees C, but not 30 degrees C, and was independent of restriction modification action or interference with phage adsorption. Our investigations of phage-host interactions showed that the two Str. salivarius subsp. thermophilus strains studied avoided attack by related bacteriophages by evolving at least three different resistance systems.     

Emphysematous cystitis: apropos of 2 cases

Emphysematous cystitis is a rare infectious disease of the lower urinary tract. Its reputedly serious prognosis is related to treatment failures revealing ignorance concerning its pathophysiological mechanisms. Two cases of this disease were seen in our department, both in diabetic men over the age of 70 years with a history of prostatism. They presented to the emergency department with complete urinary retention and alteration of the general state and fever. Urine culture isolated Klebsiella pneumoniae in both cases. Treatment consisted of bladder drainage associated with adapted antibiotic therapy and control of diabetes. A suprapubic prostatectomy was subsequently performed in one case and transurethral prostatic resection was performed in the other case. The prognosis of this disease depends on early diagnosis and rapid introduction of effective treatment.     

Drug induced rhabdomyolysis: case report

Rhabdomyolysis results from skeletal muscle injury leading to the release of intracellular contents into blood and urine. Its diverse aetiology includes severe exercise, muscle trauma or ischaemia, metabolic disorders, infections and exposure to drugs and toxins. Known risk factors include heredity disorders of glycogen and lipid metabolism as well as a history of substance abuse. A case of rhabdomyolysis associated with exposure to opiates and benzodiazepines is described and the pathogenesis and treatment are reviewed. The rhabdomyolysis was complicated by acute renal failure; the patient fully recovered. It is suggested that rhabdomyolysis should be borne in mind in patients presenting with altered mental status, or fluid and electrolyte abnormalities, in particular, if they also give a history of substance abuse.     

An estimate of the macroscopic yield surfaces of powder compacts using the kinematic approach of the yield design theory

The 3D compaction of a square array of spherical particles of uniform size is studied using the kinematic approach of the yield design theory. The densification is assumed to occur by plastic deformation at the mutual zone contacts between grains where the dissipation is localized. The compaction response of the array of spherical particles is considered in term of representative unit cell of the aggregate submitted to axisymmetrical loading conditions. Approximate macroscopic yield surfaces resulting from hydrostatic and closed die compaction are constructed at various stages of densifications. The size and shape of the yield surfaces depend upon the loading history as well as the relative density of the compact. Finite element simulations have also been performed in order to validate to some extent the results provided by the kinematic approach of the yield design theory and to examine the evolution of macroscopic yield surface with the degree of compaction.     

Performance analysis of a solar chimney power plant in the southwestern region of Algeria

In this paper, we present the performance analysis of a solar chimney power plant expected to provide the remote villages located in Algerian southwestern region with electric power. Solar energy and the psychometric state of the air in the south of Algeria are important to encourage the full development of solar chimney power plant for the thermal and electrical production of energy for various uses. We are interested in Adrar where solar radiation is better than other areas of Algeria. The obtained results show that the solar chimney power plant can produce from 140 to 200 kW of electricity on a site like Adrar during the year, according to an estimate made on the monthly average of sunning. This production is sufficient for the needs of the isolated areas.     

Seasonal variations in chemical composition and fumigant activity of five Eucalyptus essential oils against three moth pests of stored dates in Tunisia

The present work investigates seasonal variation in chemical composition of essential oils isolated from leaves of five Eucalyptus species (Namely: Eucalyptus camaldulensis, Eucalyptus astringens, Eucalyptus leucoxylon, Eucalyptus lehmannii and Eucalyptus rudis) and assesses their fumigant activity against three stored-date moth pests: Ephestia kuehniella, Ephestia cautella and Ectomyelois ceratoniae.GC and GC–MS analyses showed that chemical composition varied with Eucalyptus species and seasons. The five essential oils contained 1,8-cineole, α-pinene, and α-terpineol as major common compounds. Of the other major constituents, β-pinene and p-cymene were only present in E. rudis essential oil. In addition, o-cymene was specific only to E. camaldulensis and E. rudis essential oils. Oil yields were the highest and generally richer in toxic compounds during the summer season.Results demonstrated that fumigant toxicity varied with season, insect species, essential oil concentration and exposure time. E. camaldulensis essential oil was more toxic against E. cautella and E. kuehniella. LC₅₀ values were respectively 11.07 and 26.73 μl/l air while LT₅₀ values were 13.49 and 30.46 h. However, for E. ceratoniae, E. rudis essential oil was more effective, with LC₅₀ and LT₅₀ values of 31.4 μl/l air and 36.1 h respectively. For all pest species, fumigant activity was strongest for the summer season oils. E. cautella was the most sensitive species.     

Mechanical properties and adhesion of TiN monolayer and TiN/TiAlN nanolayer coatings

In this work, TiN monolayer and TiN/TiAlN nanolayer coatings were deposited on 100C6 (AISI 52100) steel substrate by Physical vapor deposited (PVD) magnetron sputtering system. The morphological characterization was evaluated using an atomic force microscopy. The mechanical properties were determined by nanoindentation test. The adhesion was investigated by both microindentation and scratch test. The results show that the TiN/TiAlN nanolayer coating have the more rough surface and the better mechanical properties and adhesion compared to TiN monolayer coating. The effect of microstructural and mechanical proprieties on the adhesion behavior was further discussed. It was found that the improvement in adhesion of nanolayer system is in part due to the increase in plastic deformation resistance and the enhancement of mechanical properties (hardness and elastic modulus) and to the structure with a small grain size and a high number of interfaces.