Loading...
Search for:
harmonic-analysis
0.018 seconds
Total 144 records
Design and Implementation of a Programmable AC Load Based on 4-Leg Multilevel Converter
, M.Sc. Thesis Sharif University of Technology ; Zolghadri, Mohammad Reza (Supervisor)
Abstract
One of the challenges that always exists in the field of Testing the performance of converters, uninterruptible power supplies (UPSs) , etc. is to provide various types of loads to be applied to these equipments and test the quality of their performance in various load conditions. Leading or Lagging Power Factor loads, harmonic loads and non-linear loads are mainly required in this investigation. The use of inductors, resistors, capacitors and other devices for these tests is an old solution. Their disadvantages include high price, large volume and very high power loss, which was the initial idea of making programmable loads. A current source converter with the ability to Sink and source the...
The Dynamics of a Group of Diffeomorphisms of the Sphere and the Linearization Problem
, M.Sc. Thesis Sharif University of Technology ; Safari, Mohammad (Supervisor) ; Nassiri, Meysan (Supervisor)
Abstract
In chis chcsis we consider a work by Dmitry Dolg:opyat and Raphac) Kriko rian (on Simulcanoous Lincariwtion of Diffcomorphisms of Sphere) and a recent preprint by Jonathan Dc\Vitt (Simulrn.ncous Lincarization of Diffco morphisms of Isotropic Manifolds). Suppasc /1,h,...,J.. arc pcrturbacions of rotations R1, R2 , ...,Rn of the sphere which generate SOd+I (d 2). \\Tc c". plian how it can be shown that all /; can besimn)tancously conjugated to some new rotations when all the Lyapunov cxponcms of the rcndom walk a.,:;.,sociatc to {/;}arc zero. This rcsn1t is applied to obtain stable ergodicity when d is even.The idea is co translate al1 the information co a linear setting and approach chc...
Determination of Current Harmonics Cost in Distribution Transformers
, Ph.D. Dissertation Sharif University of Technology ; Mokhtari, Hossein (Supervisor)
Abstract
Transformers are vital components of power networks, responsible for converting electricity from one voltage level to another. They are designed to operate under sinusoidal conditions, but the increasing use of non-linear loads and power electronic devices has caused a spike in harmonic pollution in power networks. These harmonics result in increased losses in transformers, leading to a reduction in capacity, accelerated aging, and a shortened life. The associated costs incurred by these issues include reduced energy sales for electricity companies and premature replacement costs. In this thesis, it is assumed that the transformer is affected by harmonics and ambient temperature, and other...
Toroidal Transformer Life Estimation Under Non-Sinusoidal Supply
, M.Sc. Thesis Sharif University of Technology ; Oraee Mirzamani, Hashem (Supervisor)
Abstract
Due to increase in nonlinear loads in today’s applications, the percent of harmonic content has been increased. Transformers are one of the electrical system components that are subjected to these harmonics. The failure of such equipment is an important consideration. Such failure is because of the hotspot temperature rises over the normal temperature withstanding of internal insulation. The increments of hotspot temperature can decrease the transformer insulation life. Totally, because of the presence of many parameters, precise investigation of loss of life is very difficult. Hence, the only meaning of loss of life in this project is the loss of insulation life under heat stresses....
Investigation of Causes of Increased 5th Harmonic in Azarbayjan Regional Electricity Grid and Subject to Provide Practical Solutions to Reduce it
,
M.Sc. Thesis
Sharif University of Technology
;
Mokhtari, Hossein
(Supervisor)
Abstract
Iran's electrical grid is connected to the Eastern Turkey grid via Khoy-Basqale 400KV transmission line. Harmonic mesurements indicate high level of the 5th harmonic voltage in Azarbayjan grid which is magnified in Van substation. According to Iran international obligations and economic losses caused by the high level of harmonics in Azerbaijan regional electricity grid, a comprehensive study is required. Early studies showed that this unprecedented increase in the 5th harmonic voltage is due to the small harmonic loads scattered throughout the network. The aim of this thesis is to perform a comprehensive harmonic analysis of Azerbaijan network due to scattered harmonic loads. In this...
Analysis of Oscillations in Linear Fractional Order Systems
, M.Sc. Thesis Sharif University of Technology ; Tavazoei, Mohammad Saleh (Supervisor)
Abstract
This thesis studies undamped oscillations generated by marginally stable fractional order linear time invariant (LTI) systems. In this study, the concept of integral curve is developed for fractional order LTI systems. The proposed concept is obtained based on equivalent integer order linear time varying (LTV) systems. Then, an analytical approach is proposed to be used for harmonic analysis of such oscillations in marginally stable commensurate order LTI systems. Also, it is shown that the Q-semi norm of the limit sets for a trajectory of these systems can be analytically determined based on the Q-semi norm of the initial condition, where Q is a specific matrix. Moreover, this result is...
Wide adjustable range LLC resonant converter's maximum switching frequency for realizing the ZVS operation
, Article Proceedings - 2010 18th Iranian Conference on Electrical Engineering, ICEE 2010, 11 May 2010 through 13 May 2010 ; 2010 , Pages 745-752 ; 9781424467600 (ISBN) ; Rashidian, B ; Zolghadri, M. R ; Alavi, M. H ; Sharif University of Technology
Abstract
In this paper, the FHA and a simple TDA approaches have been used to derive the normalized maximum switching frequency of wide adjustable range LLC resonant converter for realizing the ZVS operation even under the worst-case conditions. By accounting the resonant current higher harmonics, more accurate expressions are derived. These analyses demonstrate that the normalized maximum switching frequency depends on the dead-time and the converter inductance ratio. It also depends on the ratio of the converter resonant capacitor and the effective capacitance appeared in parallel with the power MOSFETs drain-sources. The simulated and experimental results are in good agreement with the derived...
Wettability alteration of calcite rock from gas- repellent to gas-wet using a fluorinated nanofluid: A surface analysis study
, Article Journal of Natural Gas Science and Engineering ; Volume 83 , 2020 ; Shafiei, Y ; Shayesteh, M ; Dehghan Monfared, A ; Ghazanfari, M. H ; Sharif University of Technology
Elsevier B.V
2020
Abstract
Wettability alteration analysis form gas-repellent to gas-wet with the aid of chemical agents has been subjected of numerous studies. However, fundamental understanding of the effect of surface tension of liquid on repellency strength, the change in the intermolecular forces due to the adsorption of nanoparticles onto the rock surfaces, and exposure of treated rock in brine are not well discussed in the available literature. In this study, X-ray diffraction, Atomic Force Microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were applied to characterize the treated and fresh samples. Dynamic and static contact angle measurements were then combined with six methods...
Upper and lower bounds for the maximum number of frequencies that can be generated by a class of fractional oscillators
, Article IEEE Transactions on Circuits and Systems I: Regular Papers ; Volume 66, Issue 4 , 2019 , Pages 1584-1593 ; 15498328 (ISSN) ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
This paper deals with investigating the maximum number of frequencies generated by an oscillator in the case that a half number of integrators in the conventional dynamic structure of this oscillator are replaced by fractional integrators with an identical order. First, an upper bound for the maximum number of frequencies, which can exist in a steady state response of the oscillator, with respect to the number of integrators, is obtained. Then, on the basis of the recent advances in the field of determinant-based representations of bivariate polynomials, a lower bound is found for the maximum number of sinusoidal components in the steady state oscillations generated by the oscillator. A...
Two phase modal analysis of nonlinear sloshing in a rectangular container
, Article Ocean Engineering ; Volume 38, Issue 11-12 , August , 2011 , Pages 1277-1282 ; 00298018 (ISSN) ; Firouz Abadi, R. D ; Ghasemi, M ; Sharif University of Technology
2011
Abstract
Sloshing, or liquid free surface oscillation, in containers has many important applications in a variety of engineering fields. The modal method can be used to solve linear sloshing problems and is the most efficient reduced order method that has been used during the previous decade. In the present article, the modal method is used to solve a nonlinear sloshing problem. The method is based on a potential flow solution that implements a two-phase analysis on sloshing in a rectangular container. According to this method, the solution to the mass conservation equation, with a nonpenetration condition at the tank walls, results in velocity potential expansion; this is similar to the mode shapes...
Time-series analysis of TCP/RED computer networks, an empirical study
, Article Chaos, Solitons and Fractals ; Volume 39, Issue 2 , 2009 , Pages 784-800 ; 09600779 (ISSN) ; Haeri, M ; Sharif University of Technology
2009
Abstract
Packet-level observations show that the TCP/RED congestion control systems exhibit complex non-periodic oscillations which vary with the network/RED parameter variations. In this paper, it is investigated whether such complex behaviors are due to nonlinear deterministic chaotic dynamics or do they originate from nonlinear stochastic dynamics. To do this, various methods of linear and nonlinear time series analyses have been applied to the packet-level data gathered from a typical network simulated in ns-2. The results of the analysis for a wide range of variations in averaging weight of RED (as the most important bifurcation factor in TCP/RED networks) show that such behaviors are not due to...
Time and space harmonics in brushless doubly-fed machine
, Article 2011 19th Iranian Conference on Electrical Engineering, ICEE 2011, 17 May 2011 through 19 May 2011 ; May , 2011 , Page(s): 1 - 6 ; ISSN :21647054 ; 9789644634284 (ISBN) ; Jandaghi, B ; Oraee, H ; Sharif University of Technology
2011
Abstract
Brushless Doubly fed machines have two stator windings and an especial cage rotor. The main advantage of the machine is higher reliability in compare with DFIGs. Cross coupling is the mechanism, which provides indirect coupling of the two stator windings. In this paper, time and space harmonics in a BDFM are studied to find a criterion for evaluating different rotor designs and better cross coupling, based on the space harmonics. Then the equivalent space and time harmonic circuits are established, using basic equivalent circuit. Finally, the effects of these harmonics on the torque-speed characteristic are studied
The effect of higher order harmonics on second order nonlinear phenomena
, Article Optics Communications ; Volume 343 , May , 2015 , Pages 124-130 ; 00304018 (ISSN) ; Borji, A ; Sharif University of Technology
Elsevier
2015
Abstract
A new method which is a combination of the harmonic balance and finite difference techniques (HBFD) is proposed for complete time-harmonic solution of the nonlinear wave equation. All interactions between different harmonics up to an arbitrary order can be incorporated. The effect of higher order harmonics on two important nonlinear optical phenomena, namely, the second harmonic generation (SHG) and frequency mixing is investigated by this method and the results are compared with well-known analytical solutions. The method is quite general and can be used to study wave propagation in all nonlinear media
The control of electron quantum trajectories on the high-order harmonic generation of CO and N2 molecules in the presence of a low frequency field
, Article Journal of Chemical Physics ; Volume 148, Issue 14 , 2018 ; 00219606 (ISSN) ; Sadighi Bonabi, R ; Mohsen Nia, M ; Irani, E ; Sharif University of Technology
American Institute of Physics Inc
2018
Abstract
In the present work, an efficient method is theoretically investigated for extending high-order harmonics and ultrashort attosecond pulse generation in N2 and CO molecules by using the time-dependent density functional theory approach. Our results show that by utilizing chirped laser field in the presence of a low frequency field, not only is the harmonic cutoff extended remarkably but also the single short quantum trajectory is selected to contribute to the harmonic spectra. When a low frequency field is added to the two-color chirped laser field, the long quantum trajectories are suppressed and only the short quantum trajectories contribute to the higher harmonic emission mechanism. As a...
The application of numerical Laplace inversion methods for type curve development in well testing: A comparative study
, Article Petroleum Science and Technology ; Volume 29, Issue 7 , 2011 , Pages 695-707 ; 10916466 (ISSN) ; Dejam, M ; Ghazanfari, M. H ; Sharif University of Technology
2011
Abstract
In this work the Fourier series and Zakian and Schapery methods are considered to numerically solve the Laplace transform of a pressure distribution equation for radial flow and to generate the type curves for three different boundary conditions. The results show that the Schapery method leads to approximate solutions for small values of dimensionless time. For large values, however, this method is almost accurate and hence is recommended because it is fast to apply compared to other algorithms. It has been found that the accuracy of the Schapery method for early time prediction can be improved to almost a perfect match with analytical results through multiplying the Schapery relation by a...
Tensor spherical harmonics theories on the exact nature of the elastic fields of a spherically anisotropic multi-inhomogeneous inclusion
, Article Journal of the Mechanics and Physics of Solids ; Volume 61, Issue 4 , April , 2013 , Pages 1124-1143 ; 00225096 (ISSN) ; Khorshidi, A ; Sharif University of Technology
2013
Abstract
Eshelby's theories on the nature of the disturbance strains due to polynomial eigenstrains inside an isotropic ellipsoidal inclusion, and the form of homogenizing eigenstrains corresponding to remote polynomial loadings in the equivalent inclusion method (EIM) are not valid for spherically anisotropic inclusions and inhomogeneities. Materials with spherically anisotropic behavior are frequently encountered in nature, for example, some graphite particles or polyethylene spherulites. Moreover, multi-inclusions/inhomogeneities/ inhomogeneous inclusions have abundant engineering and scientific applications and their exact theoretical treatment would be of great value. The present work is devoted...
Technique for online tracking of a utility harmonic impedance using by synchronising the measured samples
, Article IET Generation, Transmission and Distribution ; Volume 10, Issue 5 , 2016 , Pages 1240-1247 ; 17518687 (ISSN) ; Mokhtari, H ; Sharif University of Technology
Institution of Engineering and Technology
Abstract
Utility harmonic impedance estimation is an important stage for the study and control of electrical networks power quality such as harmonic sharing determination between a utility and a customer at a point of common coupling (PCC). In this estimation, non-invasive methods, as compared with invasive methods, are more desirable since they do not need to apply intentional disturbances to the power network and can work based on natural load fluctuations. The only concern about such methods is the method accuracy. These methods require simultaneous and synchronous measurements of the voltage and current at the PCC. However, one of the causes of error in the utility harmonic impedance measurement...
Surface waves on a half-space due to a time-harmonic loading on an inertial strip foundation
, Article Journal of Vibration and Acoustics, Transactions of the ASME ; Volume 135, Issue 5 , 2013 ; 10489002 (ISSN) ; Vafai, A ; Choobbasti, A. J ; Malidarreh, N. R ; Szidarovszky, F ; Sharif University of Technology
2013
Abstract
An analytical approach has been applied to obtain the solution of Navier's equation for a homogeneous, isotropic half-space under an inertial foundation subjected to a timeharmonic loading. Displacement potentials were used to change the Navier's equation to a system of wave-type equations. Calculus of variation was employed to demonstrate the contribution of the foundation's inertial effects as boundary conditions. Use of the Fourier transformation method for the system of Poisson-type equations and applying the boundary conditions yielded the transformed surface displacement field. Direct contour integration has been employed to achieve the surface waves. In order to clarify the...
Suppression of harmonic perturbations and bifurcation control in tracking objectives of a boiler-turbine unit in power grid
, Article Nonlinear Dynamics ; Vol. 76, Issue. 3 , 2014 , pp. 1693-1709 ; ISSN: 0924090X ; Vossoughi, G ; Alasty, A ; Sharif University of Technology
Abstract
In the presence of harmonic disturbances, boiler-turbine units may demonstrate quasi-periodic behaviour due to the occurrence of various types of bifurcation. In this article, a nonlinear model of boiler-turbine unit is considered in which drum pressure, electric output and drum water level are controlled via manipulation of valve positions for fuel, steam and feed-water flow rates. For bifurcation control in tracking problem, two controllers are designed based on gain scheduling and feedback linearization (FBL). To investigate the efficiency of control strategies, three cases are considered for desired tracking objectives (a sequence of steps, ramps/steps, and a combination of them)....
Study of the numerical artifacts in differential analysis of highly conducting gratings
, Article Optics Letters ; Volume 33, Issue 2 , 2008 , Pages 159-161 ; 01469592 (ISSN) ; Mehrany, K ; Jazayeri, A. H ; Sharif University of Technology
2008
Abstract
Li's Fourier factorization rule [J. Opt. Soc. Am. A 13, 1870 (1996)] was recently shown to be problematic to apply to highly conducting metallic gratings. We provide further information about the applicability of different differential methods and are concerned with the relation of observed numerical artifacts, the total number of retained space harmonics, the presence of both positive and negative permittivity inside the groove region, and the validity of Li's inverse rule. Two different cases corresponding to lossless and low-loss binary metallic gratings are considered, and it is shown that an increase in the number of retained space harmonics can relieve the presence of numerical...