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razani--ramin
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Modification in Topology and Control Method for Improving Performance of Modular Multilevel Converter in 2N+1 and N+1 Modulation
, M.Sc. Thesis Sharif University of Technology ; Parniani, Mostafa (Supervisor)
Abstract
In Modular Multilevel converter, it is necessary to attain different objectives simultaneously. One of the most effective control methods which can cope with this kind of systems is the Model Predictive Control (MPC). This method predicts the values of control objectives based on different feasible states and determines the optimal one using cost functions. The number of feasible states can increase when the number of switches increases in the converter. This makes the MPC unable to be applied in the MMCs with hundereds of submodules (SMs) in each arm because of its heavy computational burden. In this thesis, a modified model predictive control is proposed to reduce the computational burden....
Application of double-cell arrangement in planar laser-induced fluorescence experiments
, Article Review of Scientific Instruments ; Volume 76, Issue 8 , 2005 , Pages 1-5 ; 00346748 (ISSN) ; Ahmadi, H ; Razani, M ; Sharif University of Technology
2005
Abstract
This paper describes a double-cell method, which offers some advantages in image capturing and analysis of the planar laser-induced fluorescence (PLIF) experiments. Double static-cell and circulating-static designs are tested and the fluorescence results are reported. The static-static design offers some advantages when comparing the fluorescence signals for two different dyes, the effect of additives, and of oxidation, whereas the circulating-static design provides an effective method to study the thermal contributions of the measured signal, the photostability of a particular dye, the effect of adding agents, and the quenching effects on a dye under study. In this experiment Rhodamine-WT...
Effect of Surface Treatment on Bioactivity of Ti-6Al-4V Alloy
, M.Sc. Thesis Sharif University of Technology ; Asgari, Sirous (Supervisor)
Abstract
In this research Ti-6Al-4V samples were surface treated with acid, alkali and sandblasting treatment. Alkali treatment parameter was the NaOH concentration. The results of roughness measurement demonstrate that increase in NaOH Concentration results in rougher surface. Sandblasting produces rough surfaces in the scale of 1 to 10 micrometers. Acid treatment reduces initial roughness and the resultant roughness is in the under micrometer scale. After surface treatment, samples were soaked in simulated body fluid for invitro assessment. Results of this analysis indicate that sample with sandblasting+chemical treatment has the best invitro bioactivity. Chemical+sandblasting treated sample shows...
An enhanced hybrid modular multilevel converter for improved performance
, Article IEEE Transactions on Power Electronics ; 2018 ; 08858993 (ISSN) ; Ravanji, M. H ; Parniani, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
This paper proposes an enhanced hybrid modular multilevel converter (MMC), which utilizes a combination of halfbridge submodules (HBSM) and at least one full-bridge submodule (FBSM). In the proposed structure, FBSMs work with half of the HBSMs nominal voltage in each arm. Due to the presence of FBSMs, HBSMs switching frequency drops significantly, which reduces the converter power loss compared to half-bridge based MMCs. Furthermore, because of redundant FBSMs, (2N+1)-modulation can be employed to generate the output voltage without increasing the circulating current, thus the converter performance is improved notably. Besides, with the redundant FBSMs the converter can continue its...
A modified indirect model predictive control for modular multilevel converters
, Article 2017 25th Iranian Conference on Electrical Engineering, ICEE 2017, 2 May 2017 through 4 May 2017 ; 2017 , Pages 1366-1371 ; 9781509059638 (ISBN) ; Ravanji, M. H ; Parniani, M ; Sharif University of Technology
2017
Abstract
Modular multilevel converter (MMC) is among the promising topologies used in high-voltage/power purposes, especially for high-voltage direct-current (HVDC) transmission systems. In this paper, a modified model predictive control (MPC) strategy for an MMC-HVDC system is presented. In the proposed MPC strategy, output current, circulating current and capacitors voltage are controlled separately. In order to reduce the computational burden of the controller, the output current is controlled directly without any optimization. For suppression of the circulating current, capacitors voltage variations are employed to settle the converter arms voltages to their reference values. In addition, the...
Enhanced hybrid modular multilevel converter with improved reliability and performance characteristics
, Article IEEE Transactions on Power Electronics ; Volume 34, Issue 4 , 2019 , Pages 3139-3149 ; 08858993 (ISSN) ; Ravanji, M. H ; Parniani, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
This paper proposes an enhanced hybrid modular multilevel converter (MMC), which utilizes a combination of half-bridge submodules (HBSM) and at least one full-bridge submodule (FBSM). In the proposed structure, FBSMs work with half of the HBSMs nominal voltage in each arm. Due to the presence of FBSMs, HBSMs switching frequency drops significantly, which reduces the converter power loss compared to half-bridge based MMCs. Furthermore, because of redundant FBSMs, (2N + 1)-modulation can be employed to generate the output voltage without increasing the circulating current, thus, the converter performance is improved notably. Besides, with the redundant FBSMs, the converter can continue its...
An existence-uniqueness theorem for a class of boundary value problems
, Article Fixed Point Theory ; Volume 13, Issue 2 , 2012 , Pages 589-592 ; 15835022 (ISSN) ; Pournaki, M. R ; Razani, A ; Sharif University of Technology
2012
Abstract
In this paper the solutions of a two-endpoint boundary value problem is studied and under suitable assumptions the existence and uniqueness of a solution is proved. As a consequence, a condition to guarantee the existence of at least one periodic solution for a class of Liénard equations is presented
A note on periodic solutions of Riccati equations
, Article Nonlinear Dynamics ; Volume 62, Issue 1-2 , 2010 , Pages 119-125 ; 0924090X (ISSN) ; Pournaki, M. R ; Razani, A ; Sharif University of Technology
2010
Abstract
In this note, we show that under certain assumptions the scalar Riccati differential equation x′=a(t)x+b(t)x 2+c(t) with periodic coefficients admits at least one periodic solution. Also, we give two illustrative examples in order to indicate the validity of the assumptions
Extending protection selectivity in low voltage DC microgrids using compensation gain and artificial line inductance
, Article Electric Power Systems Research ; Volume 188 , 2020 ; Vahidi, B ; Razani, R ; Nafisi, H ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Vulnerability of power electronic converters in DC microgrids in case of fault occurrence in DC cables necessitates using a fast fault detection and isolation scheme. In this paper, a modified, fast and selective protection scheme has been presented, which provides the required tripping of low voltage DC (LVDC) microgrids. This protection scheme has been developed based on the natural characteristics of the fault current, in which the first and second derivatives of the fault current have been employed to define thresholds for discriminating between faulted and non-faulted situations. To enhance fault detection capability of the protection scheme, definition of thresholds have been improved...
On the complexity of isoperimetric problems on trees [electronic resource]
, Article Discrete Applied Mathematics ; Volume 160 Issue 1-2, January, 2012 Pages 116-131 ; Javadi, Ramin ; Sharif Univercity of Technology
Abstract
This paper is aimed at investigating some computational aspects of different isoperimetric problems on weighted trees. In this regard, we consider different connectivity parameters called minimum normalized cuts/isoperimetric numbers defined through taking the minimum of the maximum or the mean of the normalized outgoing flows from a set of subdomains of vertices, where these subdomains constitute a partition/subpartition. We show that the decision problem for the case of taking k-partitions and the maximum (called the max normalized cut problem NCP^M), and the other two decision problems for the mean version (referred to as IPP^m and NCP^m) are NP-complete problems for weighted trees. On...
Design and operation of an evanescent optical fiber sensor
, Article Optics and Lasers in Engineering ; Volume 45, Issue 1 , 2007 , Pages 12-18 ; 01438166 (ISSN) ; Bahar, M ; Razani, M ; Abrishami, M ; Asadpour, A ; Sharif University of Technology
2007
Abstract
Design and operation of an optical fiber sensor based on the intensity modulation is reported in this article. Two distinct mechanisms are considered for the optical power loss and the sensor operation is explained in terms of these effects. The dominant loss mechanism is found to be the evanescent loss and based on this phenomenon the optical fiber sensor is designed. Performance of this sensor is tested as a liquid level sensor for water and the experimental results are reported. The dry and wet signals for this probe are measured for a series of measurements and important factors concerning the design and operation of sensor are described. The precision of measured values, reproducibility...
A note on periodic solutions of matrix riccati differential equations
, Article Applied Mathematics E - Notes ; Volume 21 , 2021 , Pages 179-186 ; 16072510 (ISSN) ; Mokhtarzadeh, M. R ; Pournaki, M. R ; Razani, A ; Sharif University of Technology
Tsing Hua University
2021
Abstract
In this note, we show that under certain assumptions the matrix Riccati differential equation X′ = A(t)X + XB(t)X + C(t) with periodic coeffi cients admits at least one periodic solution. Also, we give an illustrative example in order to indicate the validity of the assumptions and the novelty of our result. © 2021, Tsing Hua University. All rights reserved
Effect of material properties on the mechanical performance of nitinol esophageal stent: finite element analysis [electronic resource]
, Article Materials Science Forum ; Volumes 773 - 774, 2014, 9-17 ; Sadrnezhaad, K ; Kokabi, H. A ; Razani, M ; Mohagheghi, A. H ; Sharif University of Technology
Abstract
Stent placement has been a main approach to treat gastrointestinal diseases during past decade. Nitinol superelastic stents have been considered as a solution to such difficulties as restenosis after implantation, low twisting ability, inadequate radial mechanical strength and inappropriate dynamic behaviors associated with the ducts. In this paper, effects of Af temperatures on mechanical performance of z-shaped Nitinol wire stent under crimping test for clinical applications are investigated by finite element simulation. Having 60% crimping and high radial resistive strength, favorable superelastic behaviors are attained at Af temperature of 22°C. The performance of the stent is seen to be...
Friction stir welding parameters optimization of heterogeneous tailored welded blank sheets of aluminium alloys 6061 and 5083 using response surface methodology
, Article Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture ; Volume 226, Issue 12 , 2012 , Pages 2013-2022 ; 09544054 (ISSN) ; Dariani, B. M ; Hossein Kokabi, A ; Razani, N. A ; Sharif University of Technology
2012
Abstract
Today, tailored welded blank sheets have found various applications in automotive, aeronautic and many other industrial fields. One of the most efficient methods for production of tailored welded blank sheets is application of the friction stir welding process. In the present article, the effect of friction stir welding parameters on the microstructure and mechanical properties of heterogeneous tailored welded blank sheets made from aluminium alloys of types 5083-H12 and 6061-T6 with the similar thickness of 1.5 mm is studied. The considered parameters are rotational speed of the tool, linear speed of the tool, pin diameter and shoulder diameter. In order to come by a tailored welded blank...
On the isoperimetric spectrum of graphs and its approximations [electronic resource]
, Article Journal of Combinatorial Theory, Series B ; Volume 100, Issue 4, July 2010, Pages 390–412 ; Hajiabolhassan, Hossein ; Javadi, Ramin ; Sharif University of Technology
Abstract
In this paper1 we consider higher isoperimetric numbers of a (finite directed) graph. In this regard we focus on the nth mean isoperimetric constant of a directed graph as the minimum of the mean outgoing normalized flows from a given set of n disjoint subsets of the vertex set of the graph. We show that the second mean isoperimetric constant in this general setting, coincides with (the mean version of) the classical Cheeger constant of the graph, while for the rest of the spectrum we show that there is a fundamental difference between the nth isoperimetric constant and the number obtained by taking the minimum over all n-partitions. In this direction, we show that our definition is the...
On nodal domains and higher-order Cheeger inequalities of finite reversible Markov processes [electronic resource]
, Article Stochastic Processes and their Applications ; Volume 122, Issue 4, April 2012, Pages 1748–1776 ; Javadi, Ramin ; Miclo, Laurent ; Sharif Univercity of Technology
Abstract
Let LL be a reversible Markovian generator on a finite set View the MathML sourceV. Relations between the spectral decomposition of LL and subpartitions of the state space View the MathML sourceV into a given number of components which are optimal with respect to min–max or max–min Dirichlet connectivity criteria are investigated. Links are made with higher-order Cheeger inequalities and with a generic characterization of subpartitions given by the nodal domains of an eigenfunction. These considerations are applied to generators whose positive rates are supported by the edges of a discrete cycle ZNZN, to obtain a full description of their spectra and of the shapes of their eigenfunctions, as...
Exact Dynamic Simulation and Control for Hydrotreating Unit of Tehran Refinery
, M.Sc. Thesis Sharif University of Technology ; Bozorgmehri, Ramin (Supervisor)
Abstract
Since steady state behavior of a plant is affected by the change of various inputs to the plant, the transient behavior of the chemical plants are also very important in their general performance. On the other hand, catalytic hydrotreating is one of the most important processes in crude oil refining process in many aspects such as economical, technical and environmental. Thus, the goal of this project was dynamic simulation and control of catalytic hydrotreating unit (UNIFINER Unit) of Tehran Refinery with using the HYSYS software. To fulfill this target, data that were necessary for simulation were gathered from Unifiner unit of Tehran refinery at first. Then, steady state simulation of the...
Object Oriented Plantwide System Identification with Black Box Model
, M.Sc. Thesis Sharif University of Technology ; Bozorgmehry, Ramin (Supervisor)
Abstract
In control engineering we want to set dynamic behavior of the system to a desired one and having a model that simulate systems behavior is necessary . System identification is a branch of chemical engineering that provide us this model , which divided into different branches itself . In this project we use object oriented programming to design and implement a software that support black box models such as Neural networks in addition to Mechanistic models (Which was implemented in previous project ) for identification . We use UML and C++ language in C++ Borland Builder in this project
Study of Interaction Between Environmental and Design in Optimization of Chemical Processes
, M.Sc. Thesis Sharif University of Technology ; Bozorgmehri, Ramin (Supervisor)
Abstract
Traditionally, chemical Process design is focused on the selection of technologies and optimization based on economic consideration .In the 1970’s because of the global energy crisis, other consideration consider with economic goals .in this study we are eager to provide design procedures and guidance for optimizing chemical processes simultaneously based on economic and environmental aspects .this optimization is applied to production maleic anhydride(MA) from n-butane feedstock .an optimization algorithm based on the genetic algorithm with four decision variables(recycle flow ratio ,air to feed ratio ,solvent flow and reactor temperature ).for including dynamic objective in optimization...
Modeling Solar Hydrogen Fuel Cell System for Residential Application
, M.Sc. Thesis Sharif University of Technology ; Roshandel, Ramin (Supervisor)
Abstract
The gradual exhaustion of oil and gas resources and the various problems involved in their pollution makes it necessary to promote a renewable energy system. One of the most interesting developments of standalone systems based on the utilization of hydrogen is solar hydrogen system. Central and southern Iran exhibit an excellent solar climate which makes them ideal places for solar hydrogen systems. The economy of Iran is based on oil and it has one of the largest reserves of oil and gas in the world but the reserves would not be enough to meet the domestic and export markets starting in three to four decades. Moreover, elimination of energy subsidies in Iran, will led to more tendencies to...