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Active Damping of LLCL Filters Using PR Control for Grid-Connected Three-Level T-Type Converters
Payam Alemi,Seon-Yeong Jeong,Dong-Choon Lee 전력전자학회 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.3
In this paper, an active damping control scheme for LLCL filters based on the PR (proportional-resonant) regulator is proposed for grid-connected three-level T-type PWM converter systems. The PR controller gives an infinite gain at the resonance frequency. As a result, the oscillation can be suppressed at that frequency. In order to improve the stability of the system in the case of grid impedance variations, online grid impedance estimation is applied. Simulation and experimental results have verified the effectiveness of the proposed scheme for three-phase T-type AC/DC PWM converters.
Electric double layers interactions under condition of variable dielectric permittivity
Payam, Amir Farrokh,Fathipour, Morteza Techno-Press 2010 Interaction and multiscale mechanics Vol.3 No.2
In this paper, a theoretical method has been developed for the electric double layer interaction under condition of the variable dielectric permittivity of water. Using Poisson-Boltzmann equation (PBE), for one plate and two plates having similar or dissimilar constant charge or constant potential, we have investigated the electric double layer potential, its gradient and the disjoining pressure as well as the effect of variation of dielectric permittivity on these parameters. It has been assumed that plates are separated by a specific distance and contain a liquid solution in between. It is shown that reduction of the dielectric permittivity near the interfaces results in compression of electric double layers and affects the potential and its gradient which leads to a decreased electrostatic repulsion. In addition, it is shown that variation of dielectric permittivity in the case of higher electrolyte concentration, leads to a greater change in potential distribution between two plates.
Utilizing Fiber Reinforced Concrete as the Concrete Face of Rockfill Dams
Payam Salajegheh,Ghassem Habibagahi,S. Mohammad Sadegh Sahraeian 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.3
Construction of concrete faced rockfill dams (CFRD) includes pouring rock materials as the main body of the dam and compacting the rockfill to an acceptable compaction level. Then, a reinforced concrete slab is constructed on the upstream surface of dam to transfer water pressure to the rockfill materials. Considering the high permeability of rockfill materials, the concrete slab serves as a sealing element on the upstream side. Indeed, the required characteristics of concrete face are adequate flexibility in case of long-term settlement of dam, durability and its sufficiency in waterproofing the dam. In this study, to improve the quality of concrete face, increase its flexibility, optimize the construction cost and enhance the bearing capacity of concrete in tension, developed by bending moment in the face slab, three types of prevalent fibers (polypropylene, MEXO200 and steel) are utilized. The performance of each fiber is compared with the conventional reinforced concrete specimens by conducting some bending tests. Furthermore, carrying out numerical simulation, the efficacy of each fiber on performance of face slab is investigated. Based on the results, the fibers, especially the steel fibers, are suitable to substitute rebars of the conventional reinforced concrete employed as the concrete face of CFRDs. The steel fiber reinforced concrete has adequate capacity and ductility to mitigate the expected deformations from reservoir loading on the upstream face of CFRDs.
( Payam Hosseinzadeh Kasani ),( Seung Min Oh ),( Yo Han Choi ),( Sang Hun Ha ),( Hyungmin Jun ),( Kyu Hyun Park ),( Han Seo Ko ),( Jo Eun Kim ),( Jung Woo Choi ),( Eun Seok Cho ),( Jin Soo Kim ) 한국축산학회(구 한국동물자원과학회) 2021 한국축산학회지 Vol.63 No.2
The objectives of this study were to evaluate convolutional neural network models and computer vision techniques for the classification of swine posture with high accuracy and to use the derived result in the investigation of the effect of dietary fiber level on the behavioral characteristics of the pregnant sow under low and high ambient temperatures during the last stage of gestation. A total of 27 crossbred sows (Yorkshire × Landrace; average body weight, 192.2 ± 4.8 kg) were assigned to three treatments in a randomized complete block design during the last stage of gestation (days 90 to 114). The sows in group 1 were fed a 3% fiber diet under neutral ambient temperature; the sows in group 2 were fed a diet with 3% fiber under high ambient temperature (HT); the sows in group 3 were fed a 6% fiber diet under HT. Eight popular deep learning-based feature extraction frameworks (DenseNet121, DenseNet201, InceptionResNetV2, InceptionV3, MobileNet, VGG16, VGG19, and Xception) used for automatic swine posture classification were selected and compared using the swine posture image dataset that was constructed under real swine farm conditions. The neural network models showed excellent performance on previously unseen data (ability to generalize). The DenseNet121 feature extractor achieved the best performance with 99.83% accuracy, and both DenseNet201 and MobileNet showed an accuracy of 99.77% for the classification of the image dataset. The behavior of sows classified by the DenseNet121 feature extractor showed that the HT in our study reduced (p < 0.05) the standing behavior of sows and also has a tendency to increase (p = 0.082) lying behavior. High dietary fiber treatment tended to increase (p = 0.064) lying and decrease (p < 0.05) the standing behavior of sows, but there was no change in sitting under HT conditions.
Payam Darbandi,Farhang Pourboghrat 한국소성가공학회 2011 기타자료 Vol.2011 No.8
Superconducting radio frequency (SRF) niobium cavities are widely used in high-energy physics to accelerate particle beams in particle accelerators. The performance of SRF cavities is affected by the microstructure and purity of the niobium sheet, surface quality, geometry, etc. Following optimum strain paths in the forming of these cavities can significantly control these parameters. To select these strain paths, however, information about the mechanical behavior, microstructure, and formability of the niobium sheet is required. In this study the Barlat 2000 yield function has been used as a yield function for high purity niobium. Results from this study showed that, due to intrinsic behavior, it is necessary to evolve the anisotropic coefficients of Barlat’s yield function in order to properly model the plastic behavior of the niobium sheet. The accuracy of the newly developed evolutionary yield function was verified by applying it to the modeling of the hydrostatic bulging of the niobium sheet. Also, in a separate attempt crystal plasticity finite element method was use to model the behavior of the polycrystalline niobium sheet with a particular initial texture.
Minimization of DC-Link Capacitance for NPC Three-level PWM Converters
Payam Alemi,Dong-Choon Lee(이동춘) 전력전자학회 2011 전력전자학술대회 논문집 Vol.2011 No.7
This paper presents a control algorithm that minimizes the DC-link capacitance by decreasing the capacitor current. The capacitor current can be nullified by a feedback compensation term which is calculated from the power balance in the AC/DC converter. As a result, voltage variation in the DC-link is reduced further, which makes a large reduction in the size of DC-link capacitors which are expensive and have limitations in life time. Simulations are performed with two 80uF DC-link capacitors, which can be replaced by film capacitors.
Comparative Analysis of Power Losses for Three-Level T-Type and NPC PWM Inverters
Payam Alemi(알레미파얌),Dong-Choon Lee(이동춘) 전력전자학회 2014 전력전자학회 논문지 Vol.19 No.2
In this paper, an analysis of power losses for the three-level T-type and neutral-point clamped (NPC) PWM inverters is presented, in which the conduction and switching losses of semiconductor devices of the inverters are taken into account. In the inverter operation, the conduction loss depends on the modulation index (MI) and power factor (PF), whereas the switching loss depends on the switching frequency. Power losses for the T-type and NPC inverters are analyzed and calculated at the different operating points of MI, PF and the switching frequency, in which the four different models of semiconductor devices are adopted. In the case of lower MI, the NPC-type is more efficient than the T-type, and vice versa. The validity of the power loss analysis has been verified by the simulation results.