Loading...
Search for:
loading
0.012 seconds
Total 1751 records
Performance evaluation of thyristor-based static transfer switch with respect to cross current
, Article IEEE/PES Transmission and Distribution Conference and Exhibition 2002 : Asia Pacific, Yokahama, 6 October 2002 through 10 October 2002 ; Volume 2, Issue ASIA PACIFIC , 2002 , Pages 1326-1331 ; Sharif University of Technology
2002
Abstract
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...
Loading and unloading behaviour of a thermoplastic disc
, Article International Journal of Pressure Vessels and Piping ; Volume 78, Issue 9 , 2001 , Pages 637-645 ; 03080161 (ISSN) ; Shirazi, R ; Sharif University of Technology
2001
Abstract
The calculation of loading and residual stresses, and associated strains and displacements, are reported for shrink fitted rotating discs at elevated temperatures. A range of material behaviour is considered including unloading described by an actual material curve, or modelled by isotropic of kinematic hardening with a variable Bauschinger effect. Various collapse loads are obtained and discussed for design boundaries. The influence of reloading on the residual stresses is also studied. It is shown that after the first few loadings of a disc, the residual stress field becomes constant. © 2001 Elsevier Science Ltd. All rights reserved
Load profile flattening considering EV’s initial and final SoC and arrival and departure times
, Article Iranian Journal of Electrical and Electronic Engineering ; Volume 18, Issue 4 , 2022 ; 17352827 (ISSN) ; Ehyaei, A. F ; Haeri, M ; Sharif University of Technology
Iran University of Science and Technology
2022
Abstract
In distribution networks, failure to smooth the load curve leads to voltage drop and power quality loss. In this regard, electric vehicle batteries can be used to smooth the load curve. However, to persuade vehicle owners to share their vehicle batteries, we must also consider the owners' profits. A challenging problem is that existing methods do not take into account the vehicle owner demands including initial and final states of charge and arrival and departure times of vehicles. Another problem is that battery capacity of each vehicle varies depending on the type of vehicle; which leads to uncertainties in the charging and discharging dynamics of batteries. In this paper, we propose a...
Analysis of High Voltage Switching Power Supply With Minimum Switching Frequency Considerations for Constant and Pulsed Load
,
M.Sc. Thesis
Sharif University of Technology
;
Kaboli, Shahriyar
(Supervisor)
Abstract
The growth of high voltage dc-dc switching power supplies in various applications such as medical, industrial and laboratory research is undeniable. Design of these power supplies, respect to their expectation have some restrictions. Among the main characteristics, appropriate output voltage regulation, high efficiency, fast dynamic response and low EMI problems, are expected. Transformers constraints as one of the key components of high voltage dc-dc switching power supplies, plays essential role in the selection of converter topology and its control algorithm. In this thesis, first, with regard to issues of high frequency and high voltage transformers, provides a good approximation model...
Development of Optimum Model Transient Energy Flow in the Residential Building Unit
, M.Sc. Thesis Sharif University of Technology ; Sattari, Sorena (Supervisor)
Abstract
Analysis of energy flow which effectively leads to reducing energy consumption in buildings is of major importance. The following research is the development of methodology and simulation of energy in the residential buildings and realization of the methods by means of FORTRAN software. In the process of modeling energy flow, in order to evaluate thermal comfort and calculate building’s thermal load, the dynamic and integrated interaction of these parameters must be appraised. The continuous and integrated study required that Mass and energy flow, for various component of building, and their interaction be examined. These factors could not be assessed using simple and reliable methods. In...
Derating of transformers under non-linear load current and non-sinusoidal voltage - An overview
, Article IET Electric Power Applications ; Volume 9, Issue 7 , August , 2015 , Pages 486-495 ; 17518660 (ISSN) ; Ghazizadeh, M ; Oraee, H ; Sharif University of Technology
Institution of Engineering and Technology
2015
Abstract
The increasing application of non-linear loads in power system causes additional losses in transformers resulting in premature damage. Manufactures and users of transformers realise the importance of this phenomenon and it is vital to adopt a procedure to prevent it thereby enhancing the reliability of power system. To achieve this, the most common method is derating of transformers. This paper intends to review derating of transformers under nonsinusoidal operation, for which all available approaches are classified into four major methods including IEEE recommended, analytical, experimental and finite elements based method. For each method, the fundamental theory, significant factors...
Evaluation of variable permeability model in simulation of seismic behavior of uniform level and gently sloping sand layers
, Article Earth Sciences Research Journal ; Volume 24, Issue 3 , 2020 , Pages 328-336 ; Seyfi, S ; Shahir, H ; Sharif University of Technology
Universidad Nacional de Colombia
2020
Abstract
In this study, a fully coupled dynamic finite element model was employed for numerical simulation of the response of level to gently sloping saturated sand layers subjected to cyclic loading. This model utilized a critical state two-surface-plasticity constitutive model to simulate the cyclic behavior of sandy soil. Moreover, a recently proposed variable permeability function was implemented in the numerical model to reflect the effects of soil permeability variations during the liquefaction phenomenon. The numerical model was validated by simulating a number of well-documented geotechnical centrifuge tests with different relative density of sand, base acceleration time history, and surface...
Nonlinear seismic behavior of RC frames with RC braces
, Article Asian Journal of Civil Engineering ; Volume 9, Issue 6 , 2008 , Pages 577-592 ; 15630854 (ISSN) ; Mohseni, M. M ; Sharif University of Technology
2008
Abstract
Braced frames, besides other structural systems, such as moment resisting frames or shear walls, have been an effective and valuable method to enhance structures against lateral loads. In wind or seismic excitations, inclined elements react as truss web elements which would bear compression or tension stresses. This axial reaction results in less moments and therefore smaller sizes in beam and column sections with respect to members in similar moment resisting frame. However, low tensile strength of concrete material, made it a challenge to use in inclined members. In practice, there have been various methods to consider this defect such as disengagement of brace elements in tension or...
Temperature integrated load sharing of paralleled modules
, Article 2006 1st IEEE Conference on Industrial Electronics and Applications, ICIEA 2006, Singapore, 24 May 2006 through 26 May 2006 ; 2006 ; 078039514X (ISBN); 9780780395145 (ISBN) ; Zolghadri, M. R ; Walters, M ; Homaifar, A ; Sharif University of Technology
2006
Abstract
Paralleling power modules is designed to share system loads (stresses) equally to improve system reliability. Due to variations in the parameters in the power converter system, temperature mismatches may occur. These mismatches may lead to unequal life expectancy of individual converters in the total system. It is believed that equalizing the operating temperature of the semiconductor devices may improve total system reliability. In this paper a new thermal-based load-sharing scheme for parallel converters is proposed. In this scheme, the load current is redistributed among parallel converters based on the temperature of the converters. The main goal is to minimize the relative temperature...
Enhanced frequency droop method for decentralized power sharing control in DC microgrids
, Article IEEE Journal of Emerging and Selected Topics in Power Electronics ; Volume 9, Issue 2 , 2021 , Pages 1290-1301 ; 21686777 (ISSN) ; Peyghami, S ; Mokhtari, H ; Blaabjerg, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2021
Abstract
This article proposes two novel approaches to improve the superimposed frequency droop scheme for the control of dc microgrids (MGs). Conventional voltage-based control strategies suffer from issues such as undesirable voltage regulations, poor power sharing among the sources, and negative effects of line resistances on the equivalent droop characteristics. To overcome these challenges, a superimposed frequency droop scheme has been introduced. However, this method suffers from three major issues: 1) instability in terms of load variation, which is due to the location of system dominant poles; 2) limitation in system loading due to the limitation in the transferred reactive power; and 3)...
An improved model for optimal under voltage load shedding: Particle swarm approach
, Article 2006 IEEE Power India Conference, New Delhi, 10 April 2006 through 12 April 2006 ; Volume 2005 , 2005 , Pages 723-728 ; 0780395255 (ISBN); 9780780395251 (ISBN) ; Mozafari, B ; Ranjbar, A. M ; Sharif University of Technology
2005
Abstract
Under voltage load shedding is one of the most important tools to avoid voltage instability. In this paper an optimal load shedding algorithm is developed. This approach is based on the concept of the static voltage stability margin and its sensitivity value at the maximum loading point or the collapse point. The traditional load shedding objective is extended to incorporate both technical and economical effects of load shedding. The voltage stability criterion is modeled as a soft constraint into load shedding scheme. The proposed methodology is implemented over the IEEE14 bus system and solved using a mathematical (GAMS/CONOPT) and two heuristic (P.S.O & GA) methods. © 2006 IEEE
Harmonic filter design consideration for a Tire-Rubber factory
, Article 5th IASTED International Conference on Power and Energy Systems, EuroPES 2005, Benalmadena, 15 June 2005 through 17 June 2005 ; 2005 , Pages 380-383 ; 14827891 (ISSN) ; Mokhtari, H ; Hamza M. H ; IASTED ; Sharif University of Technology
2005
Abstract
Increase in the number of non-linear loads has increased harmonic pollution in industries, resulting in lower power factor and more losses. Harmonics may also lead to adverse conditions in cases they match a resonance frequency existing in the system. To alleviate the problems of harmonics, tuned harmonic filters are used. However, design and installation of passive elements in power systems or industries requires special attentions due to the possible resonances that may occur. In this paper, a Tire-Rubber company is analyzed for a filter installation. Harmonic analysis is performed, and site measurements are examined. Cautions to be taken for design consideration are then discussed
Experimental study on cyclic behavior of trapezoidally corrugated steel shear walls
, Article Engineering Structures ; Volume 48 , March , 2013 , Pages 750-762 ; 01410296 (ISSN) ; Mofid, M ; Vafai, A ; Sharif University of Technology
2013
Abstract
This paper presents the research works on the cyclic behavior of trapezoidally corrugated as well as unstiffened steel shear walls. A series of experimental studies were carried out on the half-scale, one-story, single-bay steel shear walls with unstiffened and trapezoidally corrugated panels. This experimental study was conducted to compare the stiffness, strength, ductility ratio and energy dissipation capacity of three different steel shear walls: unstiffened, trapezoidally vertical corrugated and trapezoidally horizontal corrugated. Gravity loads were not applied at the top of the walls and horizontal load was applied at the top of each specimen. Loading sequence was applied as...
WQLB: WiMAX QoS aware load balancing protocol
, Article Proceedings - 2012 IEEE 12th International Conference on Computer and Information Technology, CIT 2012 ; 2012 , Pages 615-622 ; 9780769548586 (ISBN) ; Aghdam, S. M ; Sharif University of Technology
2012
Abstract
Mobile Worldwide Interoperability for Microwave Access (Mobile WiMAX) is a wireless access technology based on IEEE 802.16e. The two most important concepts are introduced in the MAC layer of Mobile WiMAX networks, handover and load balancing. In this paper, we have focused on balancing the load of the system, using handover mechanisms suggested by mobile WiMAX. The proposed algorithm, WQLB, concentrates on controlling the system load and keeping it in a balanced state by using a handover process. Also, the algorithm is designed to utilize resources efficiently, supporting QoS. As load definition is an essential criterion in load balancing algorithms, we have suggested a new load model for...
Molecular dynamics investigation of β-SiC behavior under three-axial tensile loading
, Article Journal of Computational and Theoretical Nanoscience ; Volume 8, Issue 11 , 2011 , Pages 2187-2192 ; 15461955 (ISSN) ; Simchi, A ; Besharati Givi, M. K ; Rajabpour, A ; Sharif University of Technology
2011
Abstract
Molecular dynamics (MD) simulations were used to study the mechanical behaviour of β-SiC at nano-scale under tensile loading. Effects of loading rate and tensile temperature on the mechanical properties and failure were studied. Modified embedded-atom method (MEAM) potential and Berendsen thermostat were utilized for modelling. Periodic boundary conditions were employed and the behaviour of material was analyzed under three-axial loading condition at which the stress- strain relation was acceptably size independent. It is shown that with increasing the loading rate from 5 m/s to 70 m/s, the failure strain increases without a remarkable change in the stress-strain relationship. The MD...
Robust analysis and design of power system load frequency control using the Kharitonov's theorem
, Article International Journal of Electrical Power and Energy Systems ; Vol. 55, issue , 2014 , p. 51-58 ; Shiroei, M ; Ranjbar, A. M ; Sharif University of Technology
Abstract
This paper presents a robust decentralized proportional-integral (PI) control design as a solution of the load frequency control (LFC) in a multi-area power system. In the proposed methodology, the system robustness margin and transient performance are optimized simultaneously to achieve the optimum PI controller parameters. The Kharitonov's theorem is used to determine the robustness margin, i.e., the maximal uncertainty bounds under which the stable performance of the power system is guaranteed. The integral time square error (ITSE) is applied to quantify the transient performance of the LFC system. In order to tune the PI gains, the control objective function is optimized using the...
Supervisory predictive control of power system load frequency control
, Article International Journal of Electrical Power and Energy Systems ; Vol. 61, issue , October , 2014 , p. 70-80 ; Ranjbar, A. M ; Sharif University of Technology
Abstract
Objective: The objective of this paper is to develop a hierarchical two-level power system load frequency control. Design: At the button level, standard PI controllers are utilized to control area's frequency and tie-line power interchanges. At the higher layer, model predictive control (MPC) is employed as a supervisory controller to determine the optimal set-point for the PI controllers in the lower layer. The proposed supervisory predictive controller computes the optimal set-points such that to coordinate decentralized local controllers. Blocking and coincidence point technology is employed to alleviate the computational effort of the MPC. In order to achieve the best closed loop...
Strategic charging method for plugged in hybrid electric vehicles in smart grids; A game theoretic approach
, Article International Journal of Electrical Power and Energy Systems ; Volume 53, Issue 1 , December , 2013 , Pages 499-506 ; 01420615 (ISSN) ; Bahrami, S ; Ranjbar, A. M ; Oraee, H ; Sharif University of Technology
2013
Abstract
Implementation of various incentive-based and time-based load management strategies has great potential to decrease peak load growth and customer electricity bill cost. In recent years, developments in Plug in Hybrid Electric Vehicles (PHEVs) have provided various environmental and economic advantages. However, high penetration of electric vehicles in to the grid may cause high peak loads at different times of the days. Using advanced metering and automatic chargers makes it possible to optimize the charging cost, and release generation capacities to provide sustainable electricity supply. Using an appropriate encouraging program is a simple way for vehicle owners to manage their energy...
Nitrogen removal from high organic loading wastewater in modified Ludzack-Ettinger configuration MBBR system
, Article Water Science and Technology ; Volume 72, Issue 8 , October , 2015 , Pages 1274-1282 ; 02731223 (ISSN) ; Borghei, S. M ; Tahmasebian, S ; Andalibi, M. R ; Sharif University of Technology
IWA Publishing
2015
Abstract
A moving bed biofilm reactor with pre-denitrification configuration was fed with a synthetic wastewater containing high chemical oxygen demand (COD) and ammonia. By changing different variables including ammonium and COD loading, nitrification rate in the aerobic reactor and denitrification rate in the anoxic reactor were monitored. Changing the influent loading was achieved via adjusting the inlet COD (956-2,096 mg/L), inlet ammonium (183-438 mg/L), and hydraulic retention time of the aerobic reactor (8, 12, and 18 hours). The overall organic loading rate was in the range of 3.60-17.37 gCOD/m2·day, of which 18.5-91% was removed in the anoxic reactor depending on the operational conditions....
Comparison of artificial intelligence based techniques for short term load forecasting
, Article Proceedings - 3rd International Conference on Business Intelligence and Financial Engineering, BIFE 2010, 13 August 2010 through 15 August 2010 ; 2010 , Pages 6-10 ; 9780769541167 (ISBN) ; Hadavandi, E ; Abbasian Naghneh, S ; Sharif University of Technology
2010
Abstract
The past few years have witnessed a growing rate of attraction in adoption of Artificial Intelligence (AI) techniques to solve different engineering problems. Besides, Short Term Electrical Load Forecasting (STLF) is one of the important concerns of power systems and accurate load forecasting is vital for managing supply and demand of electricity. This study estimates short term electricity loads of Iran by means of Adaptive Neuro-Fuzzy Inference System (ANFIS), Artificial Neural Networks (ANN) and Genetic Algorithm (GA) which are the most successful AI techniques in this field. In order to improve forecasting accuracy, all AI techniques are equipped with preprocessing concept, and effects...