Hesam Sadeghi | AmirKabir University Of Technology (original) (raw)

Papers by Hesam Sadeghi

ABSTRACT The Optimized Harmonic Stepped Waveform (OHSW) technique is an effective method for redu... more ABSTRACT The Optimized Harmonic Stepped Waveform (OHSW) technique is an effective method for reduction of multi-level inverter's harmonics. This technique is very efficient for improving the quality of multi-level inverter output voltage. It is usually assumed that cascaded multi-level inverters have equal DC sources. In practice, however, this will not be happened even if the DC sources are nominally equal. In addition, in some applications the DC sources can be regulated. Employing adjustable DC sources can increase degree of freedom to eliminate more harmonics in OHSW technique and therefore can result in substantial improvement in the total harmonic distortion (THD). In this paper first, the 7-level cascaded inverter structure is briefly described. Then, the basic idea and concept of three-phase and single-phase OHSW technique is described. Ultimately, the results obtained by simulation for the OHSW technique are analyzed and the using OHSW in multi-level inverter with constant DC sources is compared with adjustable DC sources. Genetic Algorithm (GA) is used as a powerful tool to calculate optimal switching angles. Computer simulations show that more harmonics can be eliminated in OHSW technique by employing adjustable DC sources which can be controlled.

IEEE Transactions on Microwave Theory and Techniques, 2006

ABSTRACT This paper presents a modeling technique to predict the output signal of an open-ended r... more ABSTRACT This paper presents a modeling technique to predict the output signal of an open-ended rectangular waveguide probe when scanning an arbitrary-shape crack in a lossy conductor with finite conductivity. The loss of the specimen is taken into account by using surface impedance at the surface. The technique discretizes the crack shape and applies the generalized scattering matrix technique to obtain the output signal. To validate the model proposed in this paper, the results of the proposed method are compared with the measurement results and those obtained using a finite-element code. The model is used to obtain appropriate inversion curves for determining crack depth measurement from the probe output signal

2007 International Conference on Electrical Machines and Systems (ICEMS), 2007

Simulation tools for hybrid electric vehicles are divided into steady state and dynamic models. T... more Simulation tools for hybrid electric vehicles are divided into steady state and dynamic models. Tools with steady- state models are useful for system-level analysis whereas tools that utilize dynamic models give in-depth information about the behavior of sublevel components. For accurate prediction of hybrid electric vehicle performance, dynamic modeling of motor and other component is necessary. This paper presents the

IEEE Transactions on Industry Applications, 2021

A decentralized adaptive scheme is proposed in this article for protection coordination for micro... more A decentralized adaptive scheme is proposed in this article for protection coordination for microgrids with topological and operational uncertainties. This protection coordination scheme is performed in two stages. In the first stage, a traditional fault protection is deployed to clear the fault. If the fault is isolated successfully, the protection system returns to the regular fault-free state. If the fault is not cleared due to operational uncertainties in the protection system, the second stage of protection coordination is initiated. In this stage, based on a federation structure, a set of agents around the fault location negotiate to reach the best protection coordination strategy upon the occurrence of a single or multiple fault(s). Considering the operational uncertainties of the respective circuit breakers and communication links, the best fault clearance strategy is determined by analyzing the probability of correct operation of all proposed strategies and considering the least number of probable load outages. Two major factors impacting the probability of correct operation are fault currents flowing through the respective circuit breakers and the latency of the communication links. The efficiency of the proposed scheme is demonstrated by comparing the simulation results with their experimental counterparts and those obtained using the conventional centralized and decentralized adaptive methods.

2009 13th International Symposium on Antenna Technology and Applied Electromagnetics and the Canadian Radio Science Meeting

... Antennas Propagat., vol. 38, no. 10, pp. 16771683, Oct. 1990. [6] AA Lestari, AG Yarovoy, an... more ... Antennas Propagat., vol. 38, no. 10, pp. 16771683, Oct. 1990. [6] AA Lestari, AG Yarovoy, and LP Ligthart, RC-loaded bow-tie antenna for impulse radiation, IEEE Trans. Antennas Propagat., vol. 52, no. 10, pp. 25552563, Oct. 2004. ...

In this paper we report on an experiment in which we show that the focusing property of time reve... more In this paper we report on an experiment in which we show that the focusing property of time reversal holds when the scattering medium in the time-reversed phase deviates moderately from the medium in the directtime phase. Keywords-time reversal; focusing electromagnetic fields; mismatched media;

Fatigue and stress crack detection in metallic structures is of utmost importance to the in-servi... more Fatigue and stress crack detection in metallic structures is of utmost importance to the in-service inspections of metallic components. Beside the crack detection, the prediction of the crack size leads to a better estimation of the useful life of the metal in service. Currently, there are several prominent nondestructive testing (NDT) techniques for detecting and sizing surface cracks in metals each of which possesses certain limitations and disadvantages, including the potential drop technique, the eddy current technique, and the surface magnetic field measurement technique.

2011 XXXth URSI General Assembly and Scientific Symposium, 2011

In this paper, a parallel finite difference time domain (FDTD) code is developed for the calculat... more In this paper, a parallel finite difference time domain (FDTD) code is developed for the calculation of the horizontal electric field above ground for three distances of 2 Km, 5 Km and 10 Km from the return stroke channel. An electromagnetic model of lightning is adopted for the purpose of simulation. The obtained results are compared with those simulated by Cooray-Rubinstein formula (CR). The effect of ground's conductivity on the electric field value is also investigated. The results show that the accuracy of CR formula decreases as the ground's conductivity decreases or distance of observation point from the lightning channel becomes larger.

2009 IEEE International Symposium on Electromagnetic Compatibility, 2009

We discuss the reasons why some return stroke models do not reproduce one of the characteristic f... more We discuss the reasons why some return stroke models do not reproduce one of the characteristic features of the electromagnetic fields radiated by lightning, namely the far-field inversion of polarity with a zero crossing occurring in the tens of microseconds range. A property of time-domain radiation requires that far fields predicted by lightning return stroke channel models exhibit a zero

2003 IEEE Bologna Power Tech Conference Proceedings,, 2003

ABSTRACT A new antenna theory approach is utilized to compute current distributions along the cha... more ABSTRACT A new antenna theory approach is utilized to compute current distributions along the channel and electromagnetic fields due to a lightning return stroke. This model uses the method of moments (MoM) in the frequency domain for solving the governing electric field integral equation (EFIE). For the excitation of the wire antenna a new current source model is presented. In order to include effects of lossy ground, a simple modified image theory is applied. The method is adapted to the transient nature of lightning using an appropriate FFT algorithm.

2007 18th International Zurich Symposium on Electromagnetic Compatibility, 2007

A model-based parameter estimation (MBPE) technique is proposed to reduce the number of frequency... more A model-based parameter estimation (MBPE) technique is proposed to reduce the number of frequency-domain calculation points required for the evaluation of space-time current distribution along a lightning return stroke channel. In applying this technique to a rational function model for the channel current distribution, a uniform-like and a two-stage adaptive sampling strategies are investigated. To obtain height dependent current distribution

We present a modeling technique for the interaction of an elliptical-shape crack in a metal with ... more We present a modeling technique for the interaction of an elliptical-shape crack in a metal with an open-ended waveguide. The crack is first modeled by an appropriate number of short rectangular waveguides. The mode-matching technique is then used to calculate the scattering matrix of the new segmented waveguide structure. The probe reflection coefficient of the dominant mode is finally calculated for various positions of the crack in order to predict the probe output signal. To demonstrate the accuracy of the model, we consider cracks of various aspect ratios. The comparison of our results with those obtained using a commercial finite element code validates the model introduced in this paper.

2005 IEEE/ACES International Conference on Wireless Communications and Applied Computational Electromagnetics, 2005

... Thin-Wire Electric Field Integral Equations Amir Geranmayeh, Rouzbeh Moini, and SH Hesam Sade... more ... Thin-Wire Electric Field Integral Equations Amir Geranmayeh, Rouzbeh Moini, and SH Hesam Sadeghi Electrical Engineering Department of Amirkabir University of Technology Tehran, 15914, Iran moini@aut.ac.ir ... [5] RD Nevels, JC Goswami, and H. Tehrani, Semi-orthogonal ...

2007 IEEE Lausanne Power Tech, 2007

In this paper a new method based on discrete wavelet transform is proposed. The method can determ... more In this paper a new method based on discrete wavelet transform is proposed. The method can determine the line voltage notch indices for the power quality monitoring purpose. One cycle of the line voltage is decomposed with discrete wavelet transform and then obtained details are used for calculation of the notch indices. Various wavelet functions are tested and the suitable

Progress In Electromagnetics Research, 2010

In this paper, a new technique is developed to evaluate efficiently the Sommerfeld integrals aris... more In this paper, a new technique is developed to evaluate efficiently the Sommerfeld integrals arising from the problem of a current element radiating over a lossy half-space. The annihilation of the asymptote and the branch-point singular behavior of the spectral Green's function is used in this technique. The contributions of the subtracted asymptotic and singularity terms are calculated analytically. The annihilation results in a remaining integral that is very smooth and can be calculated adaptively by using Gaussian quadratures and extrapolation methods to accelerate the convergence of the oscillating integrand. The accuracy and efficiency of the new technique has been confirmed by comparison with literature, and the commercial software NEC. The application of the proposed technique provides a robust and rapid procedure to calculate spatial Green's functions which can be used in ground-wave propagation, and lightning return stroke channel modeling.

Power Tech Conference, 2007

Journal of Geophysical Research, 2009

In this paper, we investigate the reasons why some return stroke models do not reproduce one of t... more In this paper, we investigate the reasons why some return stroke models do not reproduce one of the characteristic features of the electromagnetic fields radiated by lightning, namely the far-field inversion of polarity with a zero crossing occurring in the tens of microseconds range. This study leads to physical insights into the behavior of the return stroke attenuation and speed as a function of height. Making reference to the properties of time domain far fields, we show that any one of the existing lightning return stroke channel models, including the electromagnetic models, sometimes known as Antenna Theory models, and the engineering models, should be able to predict a zero crossing in the far field as long as the duration of the return stroke current and the height of the channel are finite. However, the present versions of most of the available engineering and electromagnetic models predict the zero crossing to occur at times that fall well beyond those observed experimentally. We identify three mechanisms responsible for the time of occurrence of the reversal of polarity in the far fields: the current attenuation along the channel, the duration of the return stroke current, and the return stroke speed. The analysis of the MTLE and MTLL engineering models shows that the higher the attenuation of the current along the channel, the earlier the polarity reversal of the vertical electric field. Also, for a given value of the attenuation factor, higher propagation speeds correspond to earlier polarity reversal times. For the TCS model, in which the only adjustable parameter is the return-stroke speed, we show that the far-field zero crossing occurs considerably later than the values predicted by both the MTLE and the MTLL models. This is shown to be essentially due to the fact that the decrease of the current wave along the channel according to the TCS model is less pronounced than the current attenuation predicted by the MTLE and MTLL models. Furthermore, it is shown that, in the electromagnetic models, a uniformly distributed resistance along the channel does not lead to a zero crossing in the tens of microseconds range even for large resistance values. This is due to the significant increase of the current pulse duration, as it propagates along the channel as a result of the dispersion effect. The correct zero crossing time, however, can indeed be successfully reproduced if a nonlinear channel resistance is used, which prevents the significant increase of the current pulse duration as it propagates up the channel. Finally, based on the predictions of the MTLE, MTLL, and TCS models, it is shown that the zero crossing time decreases as the observation point moves farther away from the lightning channel, with the amount of variation of less than 10%.

NDT & E International, 2008

... [1] DJ Daniels, Ground penetrating radar: 2nd edition, IEE Radar Sonar Navig Ser 15 (2004). [... more ... [1] DJ Daniels, Ground penetrating radar: 2nd edition, IEE Radar Sonar Navig Ser 15 (2004). [2] MAH Lopez, SG Garcia, AR Bretones, MF Pantoja and RG Martin, A resistively loaded thin wire antenna for mine detection, Subsurface Sensing Technol Appl 2 (2001), pp. ...