فهرست مطالب

  • Volume:8 Issue: 3, 2014
  • تاریخ انتشار: 1393/06/29
  • تعداد عناوین: 8
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  • Maryam Imani Pages 1-6
    In this paper, we propose a new method for channel estimation based on a combination of pilots and pseudopilots in OFDM systems. In the proposed method, we use just only from half of number of minimum necessary pilots that is required to obtain the minimum MSE of LS channel estimation with the same preceded efficiency. Also, our simulation results show that using the same number of used pilots in conventional method for channel estimation, we obtain better efficiency using proposed method in a MIMO-OFDM system.
  • Alireza Siadatan Pages 7-14
    This paper presents a newsensorless rotor position detection for a Three-phase single switch SR motor with regeneration capability at standstill mode. The proposed method is based on the dependency of phase current waveform at turn off time to rotor position angle. It is shown that the combination of a motor with single switch per phase converter and a transient voltage suppressor (TVS) circuit define a resonant circuit. It means, the resonance frequency of the circuit depends on the rotor position. In this method, the rotor position is achieved by inspecting of regeneration current results of applied high frequency and low level diagnostic pulses to the motor phases at the beginning step. To obtain the rotor position of switched reluctance motors (SRMs) by meaning of the overlap of rising voltage measurements. During this interval, rotor position is detected by exchanging energy between the phase and source repeatedly in one cycle of a phase current. The resulting current magnitudes are measured and compared to detect the rotor position. The new configuration enables the motor for self-starting without any other mechanism or starting device. The prototype controller was simulated, fabricated, and tested in laboratory and experimental results of the proposed SRM drive system are presented.
  • Morteza Nojavan, Heresh Seyedi, Arash Mahari, Kazem Zare Pages 15-24
    In this paper, a novel protection coordination optimization algorithm is proposed. The purpose is to maximize the disperse generation penetration and, at the same time, to minimize the operating time of fuses. A novel optimization technique, the Imperialistic Competition Algorithm (ICA), is applied to solve the problem. The results of simulations confirm that the proposed method leads to lower operating times of protective devices and higher possible DG penetration, compared with the traditional coordination techniques.
  • Attitude control of satellite with PWPF modulator using predictive control algorithms
    Ehsan Chegeni, Mehdi Zandieh, Javad Ebrahimi Pages 25-31
    In this paper, we use generalized incremental predictive control to stabilize attitude of satellite. We compare GPC with GIPC algorithm and present that GIPC has better performance. The three-axis attitude control systems are activated in pulse mode. Consequently, a modulation of the torque command is compelling in order to avoid high non-linear control action. This work considers the Pulse-Width Pulse-Frequency modulator is composed of a Schmitt trigger, a first order filter, and a feedback loop. PWPF modulator has several advantages over classical bang-bang controllers such as close to linear operation, high accuracy, and reduced propellant consumption.
  • Fereshteh Poorahangaryan, Sona Morajab, Azadeh Kiani Sarkaleh Pages 33-40
    Automatic classification of electrocardiogram (ECG) arrhythmias is essential to timely and early diagnosis of conditions of the heart. In this paper, a new method for ECG arrhythmias classification using wavelet transform (WT) and neural networks (NN) is proposed. Here, we have used a discrete wavelet transform (DWT) for processing ECG recordings, and extracting some time-frequency features. In addition, we have combined the features extracted by DWT with ECG morphology and heartbeat interval features, to obtain our final set of features to be used for training a Multi-Layer Perceptron (MLP) neural network. The MLP Neural Network performs the classification task. In recent years, many algorithms have been proposed and discussed for arrhythmias detection. the results reported in them, have generally been limited to relatively small set of data patterns. In this paper 26 recordings of the MIT-BIH arrhythmias data base have been used for training and testing our neural network based classifier. The simulation results of best structure show that the classification accuracy of the proposed method is 94.72% over 360 patterns using 26 files including normal and five arrhythmias.
  • Amirhoshang Mazinan Pages 41-47
    The main contribution of the present research arises from developing the traditional methods in the area of segmentation of brain magnetic resonance imaging (MRI). Contemporary research is now developing techniques to solve the whole of considerable problems in this field, such as the fuzzy local information c-mean (FLICM) approach that incorporate the local spatial and the gray level information. It should be noted that the present approach is robust against noise, although the high computational complexity is not truly ignored. A novel approach in segmentation of brain MRI has been investigated and presented through the proposed research. Because of so many noises embedded in the acquiring procedure, like eddy currents, the segmentation of the brain MR is now tangibly taken into account as a difficult task. Fuzzy-based clustering algorithm is one of the solutions in the same way. But, it is so sensitive to change through noise and other imaging artifacts. The idea of combining the genetic algorithm (GA) and particle swarm optimization (PSO) for the purpose of generalizing the FLICM is the ultimate goal in the present investigation, since the computational complexity could actually be reduced. The experiments with a number of simulated images as well as the clinical MRI data illustrate that the proposed approach is applicable and effective.
  • Alireza Ganjovi Pages 49-66
    A kinetic model based on Particle in Cell - Monte Carlo Collision (PIC-MCC) model is used for parametric study of the damage due to partial discharges activity into the surroundings dielectrics of a narrow channel encapsulated within the volume of a dielectric material. The parameters studied are applied electric field, channel dimensions and gas pressure. After application of an electric field across a dielectric material which contains a narrow channel, repeated ionization process starts in the gaseous medium of narrow channel. Charged particles, especially electrons, gain energy from the electric field across narrow channel and cause damage into dielectric surfaces of narrow channel on impact. The dependence of the electron energy distribution function (EEDF) on the applied electric field is studied. These estimations are performed based on the number of C-H bond-scissions produced by the impacting electrons of a single PD pulse. Based on this technique, the consequent damage into the solid dielectric and the time required to increase surface conductivity is computed. The formation of acid molecules due to interaction of PD pulse with polymer surface in presence of air and humidity causes changes in the surface conductivity of the surrounding dielectrics of the narrow channels. It is observed that the extent of damage caused by a PD is primarily determined by the total number of impacting electrons capable of producing bond-scission at the dielectric. Parameters that effectively cause an increase in the number of energetic electrons increase effective damage as well as surface conductivity of surrounding dielectrics.
  • Ayub Soltani, Mahmoud Ghasemi, Khalil Mafinezhad Pages 67-73
    In this paper we have proposed a new switch or structure for reducing actuation voltage. This switch is compared with four conventional structures considering the force range of 1uN to 3uN. We have used the ANSYS software for design and simulation for the switch parameters such as actuation voltage, collapse voltage, spring constant and resonant frequency. Small size (half the size of other proposed materials), which can reduce the manufacturing cost, and also low-valued spring constant, which results in actuation voltage reduction, are among more noticeable features of the proposed switch.