Sharif Digital Repository

Providing clean, continuous and reliable power to many industrial customers has become a necessity. Where possible, sensitive customers are supplied by two medium-voltage utility feeders one of which is used as back up. Thyristor-based Static Transfer Switches (STSs) are able to provide the loads with a fast transfer to the back up feeder when the main one fails. In addition to being fast, the transfer must be performed with no source paralleling which creates a cross current flowing between the main feeder and the back up one. Due to practical limitations, however, in some cases, cross current cannot be avoided. This paper investigates the performance of thyristor-based STSs with respect to... 

We have developed an analytic approach to investigate the effect of group delay ripple on the performance of phase-modulated microwave photonic filter. Two cases with and without ripple are analyzed to clarify the ripple's effects on the performance of microwave-photonic filter. Comparison of our proposed analytical approach with simulated OptiSystem® results shows a good agreement  

We have developed an analytic approach to investigate the effect of group delay ripple of the dispersive devices on the performance of two major building blocks of microwave- photonic filters. Firstly, performance of PM-based block in the presence of an arbitrary group delay ripple (GDR) is analyzed and compared with the ripple-free case to reveal the destructive effects of added group delay ripple. In the next step, we repeat the proposed approach for the AM-based one; again, the performance is compared with the ripple-free case. Two distortion metrics are also introduced to quantify this distortion. Comparison of the performance of two building blocks in the presence of group delay ripple... 

We develop an analytic approach to investigate the effect of reflection amplitude and group delay ripples of the dispersive device on the performance of phase-modulated microwave-photonic filters. Experimental results conform to our proposed analytical approach  

We analyze the VIPA demultiplexer for different reflection profiles, i.e., uniform, graded, and Gaussian. It is shown that VIPA demultiplexer characteristics can be improved dramatically by innovative reflection profile engineering. These improvements enhance the performance of demultiplexers in UWB-Over-Fiber systems  

We have developed an analytic approach to investigate the effect of a sinusoid group delay ripple on the performance of phase-modulated microwave photonic filter. Frequency of fabricated sinusoid ripple determines the pole's frequency of the resulted transfer function. Comparison of our proposed analytical approach with simulated OptiSystem results shows a good agreement  

Despite many efforts into the study of fluids interaction in low salinity water flooding, they are not probing the basics of transport phenomena between the involved phases. This work is aimed to bring new understanding of fluid–fluid interaction during low salinity water flooding through a series of organized experiments in which a crude oil sample with known properties was kept in contact with different brine solutions of various ionic strengths. Measuring brine pH, conductivity and crude oil viscosity and density for a period of 45 days illustrates the strong effect of the contact time and ionic strength on the dissociation of polar components and physical properties of the crude oil and... 

Despite many efforts into the study of fluids interaction in low salinity water flooding, they are not probing the basics of transport phenomena between the involved phases. This work is aimed to bring new understanding of fluid–fluid interaction during low salinity water flooding through a series of organized experiments in which a crude oil sample with known properties was kept in contact with different brine solutions of various ionic strengths. Measuring brine pH, conductivity and crude oil viscosity and density for a period of 45 days illustrates the strong effect of the contact time and ionic strength on the dissociation of polar components and physical properties of the crude oil and... 

In the present study, numerical simulation is used to evaluate the influence of the non-uniform magnetic field on the heat transfer of magnetic nanofluids inside a pinned channel. This article focused on the flow pattern and heat transfer of water-based nanofluids in the presence of a wire in a three-dimensional geometry. In this work, the fluid flow is laminar and constant heat flux is applied on the wall of the channel. A wire in various orientations, in comparison with the axis of the channel, generates the magnetic field. The base fluid is water and Nano-particles (Fe3O4 and Fe) add to base fluid with different volume concentrations (0, 0.5, 1%). The computational fluids dynamic is used... 

TmBa2_xPrxCu3O7+δ and LuBa2_xPrxCu3O7+δ samples with 0.0 < x ≤ 1.0 have been prepared by a solid-state reaction technique. The occurrence of the orthorhombic to tetragonal phase transition, increasing of oxygen content with the increase of Pr doping, and the existence of solubility limit in both systems confirm the correct substitution of Pr at Ba sites. The solubility limit for Pr in the Lu-based samples is less than 0.7, which is less than x = 0.90 for the Tm-based samples. The Tc depression versus doping content in both systems shows that depression of superconductivity by Pr at Ba sites is mostly due to the hole-filling/localization effects. Also, in the Tm-based system, the... 

Due date assignment for customer orders has been studied in various production environments using different modeling approaches. In this paper the researchers consider a production system in which the orders of several customers are produced in a single batch because of the economy of scale. If a batch is completed before receiving customer orders, inventory carrying cost is incurred but if it is completed after receiving customer orders, shortage cost is incurred and finally if the order is delivered after its due date, tardiness cost is charged. The problem is to decide on batch size, due date of batch (imposed on supply process) and lead time (to be quoted to the next coming customers) so... 

Switched Reluctance Motors (SRMs), which are simple and reliable motors, have attracted interest for electric vehicle propulsion systems. It is shown that an SRM offers a good performance at high acceleration and low speed driving conditions. Efficiency map of an electric motor is a very important characteristic specially when the motor is to be used in a wide range of speed and load variations, which is the case in electric propulsion systems. In this research, the efficiency map of an SRM is derived using a combination of the Finite Element Method (FEM) and a mathematical model. This efficiency map has been used for different driving cycles to test the SRM performance as a vehicle... 

Single-phase Tm(Ba2-xPrx)Cu3O 7+δ and Lu(Ba2-xPrx)Cu3O 7+δ compounds with Pr content 0.0 ≤ x ≤ 1.0 have been prepared by solid-state reaction technique. The oxygen content of our samples is more than 7. X-ray diffraction (XRD) patterns demonstrate an orthorhombic to tetragonal transition with an increase in Pr content in both systems. For each system, a solubility limit exists for substitution of Pr at the Ba site. The intergrain region investigated by the thermally activated flux creep (TAFC) and Ambegaokar-Halperin (AH) models, show that the pinning energy decreases with increasing Pr content; it also decreases in each sample with increasing magnetic field as a power-law relation. The... 

This paper presents a new time domain model for electric arc furnaces using MATLAB, The model can simulate both nonlinear and time varying nature of such loads, which create flicker, harmonics, and voltage/current unbalance. In this model, Cassie and Mayr equations are used in three-phase mode and the effects of arc furnace transformer tap changer and flexible cables mutual inductances are considered. The proposed model takes into account the system inter-relation of parameters and arcing conditions as well  

In this paper, a new scheme for position control of a mechanical load driven by a permanent magnet DC motor and a gearbox is presented. The gearbox is assumed to have some amount of backlash. The paper derives a model for the backlash nonlinear behavior. It then proposes a new control structure composed of feedback and feed forward control systems. The feedback control system is designed based on zero backlash. The feed forward part is employed to minimize the backlash effects. The new method is evaluated via simulations in MATLAB/SEVIULINK environment. Simulations results are provided to show the response of the proposed technique to various input references. © 2006 IEEE  

In this paper, by extending Space Vector Modulation (SVM) technique to three-phase four-wire systems, a new strategy is developed for the control of Active Power Filters (APFs). It is shown that the conventional SVM method cannot compensate for the current in the neutral wire in a three-phase four wire system. Simulations have been performed using PSCAD/EMTDC software. Simulation results are provided to prove the ability of the proposed technique in compensating the zero-sequence current. ©2006 IEEE  

Detecting high impedance faults is one of the challenging issues for electrical engineers. Over-current relays can only detect some of the high impedance faults. Distance relays are unable to detect faults with impedance over 100Ω. In this paper, by using an accurate model for high impedance faults, a new wavelet-based method is presented. The proposed method, which employs a 3 level neural network system, can successfully differentiate high impedance faults from other transients. The paper also thoroughly analyzes the effect of choice of mother wavelet on the detection performance. Simulation results which are carried out using PSCAD/EMTDC software are summarized