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Gaafar, Mahmoud A.,Dousoky, Gamal M.,Ahmed, Emad M.,Shoyama, Masahito,Orabi, Mohamed The Korean Institute of Power Electronics 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.4
This paper investigates the active damping of grid-connected LCL filter resonance using high-pass filter (HPF) of the grid current. An expression for such HPF is derived in terms of the filter components. This expression facilitates a general study of the actively damped filter behavior in the discrete time domain. Limits for the HPF parameters are derived to avoid the excitation of unstable open loop poles since such excitation can reduce both the damping performance and the system robustness. Based on this study, straightforward co-design steps for the active damping loop along with the fundamental current regulator are proposed. A numerical example along with simulation and experimental results are presented to verify the theoretical analyses.
Gaafar, Mahmoud A.,Ahmed, Emad M.,Shoyama, Masahito The Korean Institute of Power Electronics 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.4
A novel active damping strategy for the LCL filter resonance is proposed using the grid current and the capacitor voltage. The proposed technique is deduced in the continuous time domain and a discussion for its discrete implementation is presented. According to the proposed technique, instability of the open loop system, which results in non-minimum phase behavior, can be avoided over wide range of resonant frequencies. Moreover, straightforward co-design steps for both the fundamental current regulator and the active damping loops can be used. A numerical example along with experimental results are introduced to validate the proposed strategy performance over wide range of resonant frequencies.
Mahmoud A. Gaafar,Emad M. Ahmed,Masahito Shoyama 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.4
A novel active damping strategy for the LCL filter resonance is proposed using the grid current and the capacitor voltage. The proposed technique is deduced in the continuous time domain and a discussion for its discrete implementation is presented. According to the proposed technique, instability of the open loop system, which results in non-minimum phase behavior, can be avoided over wide range of resonant frequencies. Moreover, straightforward co-design steps for both the fundamental current regulator and the active damping loops can be used. A numerical example along with experimental results are introduced to validate the proposed strategy performance over wide range of resonant frequencies.
M.S. Gaafar,S.Y. Marzouk,H.A. Zayed,L.I. Soliman,A.H. Serag El-Deen 한국물리학회 2013 Current Applied Physics Vol.13 No.1
Mixed alkali borate glasses doped with CoO, have been prepared by the melt quenching technique. Elastic properties and FT-IR spectroscopic studies have been employed to study the role of CoO and the mixed alkali effect on the structure of the investigated glass system. Elastic properties and Debye temperature have been investigated using sound wave velocity measurements at 4 MHz at room temperature. The density, molar volume and glass transition temperatures were employed to investigate the structure of these glasses. Infrared spectra of these glasses revealed that the borate network is affected by the increase in the concentration of CoO content and the mixed alkali oxides. These results are interpreted in terms of the change in the topology of these glass structures. The elastic moduli are observed to increase with the increase of CoO content due to the increased average bond connectivity.
Mahmoud A. Gaafar,Gamal M. Dousoky,Emad M. Ahmed,Masahito Shoyama,Mohamed Orabi 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.4
This paper investigates the active damping of grid-connected LCL filter resonance using high-pass filter (HPF) of the grid current. An expression for such HPF is derived in terms of the filter components. This expression facilitates a general study of the actively damped filter behavior in the discrete time domain. Limits for the HPF parameters are derived to avoid the excitation of unstable open loop poles since such excitation can reduce both the damping performance and the system robustness. Based on this study, straightforward co-design steps for the active damping loop along with the fundamental current regulator are proposed. A numerical example along with simulation and experimental results are presented to verify the theoretical analyses.
Ibrahim A. Salem,Gaafar A. El Bahariya,Bothina T. El Dosuky,Eman F. Refaey,Ahmed H. Ibrahim,Amr B. ElDeeb 한국분석과학회 2024 분석과학 Vol.37 No.1
Abu Gurdi area is located in the South-eastern Desert of Egypt which considered as volcanic massivesulfide deposits (VMS). The present work aims at investigating the ore mineralogy of Abu Gurdi region inaddition to the effectiveness of the hydrometallurgical route for processing these ores using alkaline leachingfor the extraction of Zn, Cu, and Pb in the presence of hydrogen peroxide, has been investigated. The factorsaffecting the efficiency of the alkaline leaching of the used ore including the reagent composition, reagentconcentration, leaching temperature, leaching time, and Solid /Liquid ratio, have been investigated. It was notedthat the sulfide mineralization consists mainly of chalcopyrite, sphalerite, pyrite, galena and bornite. Gold isdetected as rare, disseminated crystals within the gangue minerals. Under supergene conditions, secondary copperminerals (covellite, malachite, chrysocolla and atacamite) were formed. The maximum dissolution efficienciesof Cu, Zn, and Pb at the optimum leaching conditions i.e., 250 g/L NaCO3 - NaHCO3 alkali concentration,for 3 hr., at 250℃, and 1/5 Solid/liquid (S/L) ratio, were 99.48 %, 96.70 % and 99.11 %, respectively. Anapparent activation energy for Zn, Cu and Pb dissolution were 21.599, 21.779 and 23.761 kJ.mol−1, respectively,which were between those of a typical diffusion-controlled process and a chemical reaction-controlled process. Hence, the diffusion of the solid product layer contributed more than the chemical reaction to control the rateof the leaching process. High pure Cu(OH)2, Pb(OH)2, and ZnCl2 were obtained from the finally obtained leachliquor at the optimum leaching conditions by precipitation at different pH. Finally, highly pure Au metal wasseparated from the mineralized massive sulfide via using adsorption method.
F.H. Abd El-kader,S.A. Gaafar,K.H. Mahmoud,S.I. Bannan,M.F.H. Abd El-kader 한국물리학회 2008 Current Applied Physics Vol.8 No.1
Differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), UV/visible spectra and colour detection of pristine and cirradiated undoped and eosin-doped 70/30 (wt/wt%) PVA/glycogen has been measured. The kinetic parameters such as the activation energy, entropy, enthalpy and free energy for all investigated samples were determined using Coats–Redfern relation. The shift of Tg position towards lower temperatures with increasing c-doses reflect that the degradation process is the predominant one. The values of absorbance and optical parameters in UV/visible range for c-irradiated blend sample doped with eosin showed no significant variation with increasing c-doses. This reflects that the addition of eosin to 70/30 (wt/wt%) PVA/glycogen makes it more resistant to c-radiolysis. The calculated colour parameters such as L*, U*, V*, C*, hue and Ye were found to be dependent on addition of eosin and c-irradiation. Differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), UV/visible spectra and colour detection of pristine and cirradiated undoped and eosin-doped 70/30 (wt/wt%) PVA/glycogen has been measured. The kinetic parameters such as the activation energy, entropy, enthalpy and free energy for all investigated samples were determined using Coats–Redfern relation. The shift of Tg position towards lower temperatures with increasing c-doses reflect that the degradation process is the predominant one. The values of absorbance and optical parameters in UV/visible range for c-irradiated blend sample doped with eosin showed no significant variation with increasing c-doses. This reflects that the addition of eosin to 70/30 (wt/wt%) PVA/glycogen makes it more resistant to c-radiolysis. The calculated colour parameters such as L*, U*, V*, C*, hue and Ye were found to be dependent on addition of eosin and c-irradiation.
Ultrasonic relaxation in Zinc–Borate glasses
G.E. El-Falaky,M.S. Gaafar,N.S. Abd El-Aal 한국물리학회 2012 Current Applied Physics Vol.12 No.2
Borate glasses in the system (1 - x) [29Na2O - 4Al2O3 - 67B2O3] - x ZnO with (x ¼ 0, 5, 10, 15, 20, 25, 30,and 35 mol%), have been prepared by the melt quenching technique. The longitudinal ultrasonic attenuation of the prepared sample has been measured using the pulse echo technique at ultrasonic frequencies 2, 4, 6 and 8 MHz in the temperature range between 160 and 300 K. The results showed welldefined peak whose position shifts toward higher temperature with increasing frequency. The mean activation energy is strongly composition sensitive. The position and overall shape of the loss peaks in dependence on composition were analyzed in terms of an assumed loss of standard linear solid type with low dispersion, and a broad distribution of Arrhenius-type relaxation with temperature independent relaxation strength. The dependence of ultrasonic attenuation on temperature has been interpreted in terms of a thermally activated relaxation process which arises when ultrasonic waves disturb the equilibrium of an atom moving in a double-well potential in the glass network. The dependence of activation energy on composition suggests that the structure of these glasses changes at 15 mol% ZnO concentration.