Sharif Digital Repository

Z-source family has been widespread in photovoltaic (PV) applications. In trasformerless grid-connected PV systems, the common mode voltage (CMV) time variations, cause the leakage current flow. This current flows through the stray capacitance of the PV panels. For a Z-Source Inverter (ZSI), the CMV would have higher high-frequency harmonics, due to the shoot through states within the switching cycles. In this paper, the CMV of a ZSI is analyzed and a simple method is proposed for the harmonic reduction of the CMV in the ZSI. The CMV reduction method is based on changing the switching states. The CMV in reduced method is compared to the CMV in the traditional ZSI in frequency domain by using... 

Contamination of ictal Electroencephalogram (EEG) signals by muscle artifacts is one of the critical issues related to clinically diagnosing seizure. Over the past decade, several methods have been proposed in time, frequency and time-frequency domain to accurately isolate ictal EEG activities from artifacts. Among denoising approaches Canonical Correlation Analysis (CCA) and Independent Component Analysis (ICA) are widely used. Denoising based on Generalized EigenValue Decomposition (GEVD) is one of the Semi-Blind Source Separation (SBSS) methods which has been recently proposed. In the GEVD-based method, a couple of time-frequency covariance matrices are used. These time-frequency (TF)... 

Generalized frequency division multiplexing (GFDM) is one of the multicarrier modulation candidates proposed for the 5th generation of wireless networks. Among GFDM linear receivers, GFDM MMSE receiver achieves the best error performance for multipath fading channels at the cost of high numerical complexity. Hence, the combination of GFDM match filter (MF) receiver and double-side successive interference cancellation (DSIC) method is used instead. However, there is a significant gap between the error performance of GFDM MMSE and DSIC/MF receivers for the case of employing modern channel coding. Recently, we have proposed a new multicarrier scheme based on GFDM architecture called generalized... 

Extensive experimental studies have been performed to investigate the unsteady boundary layer behavior over a plunging wind turbine blade section. The studies have been undertaken at various combinations of reduced frequencies, Reynolds numbers, and locations. A boundary layer rake has been carefully manufactured and utilized for velocity measurements inside the unsteady boundary layer. The measurement has been conducted in pre-static stall conditions. The reduced frequency and free stream velocity have varied from 0.005 to 0.1, and 30 to 60 m/s, respectively. To cover all possible scenarios, the streamwise positions of measurements have been chosen to be in favorable (x/c = 0.37), almost... 

Partial discharge (PD) measurement is one of the best methods for condition monitoring of transformers. In this paper, we use 5 different types of defects as follows: scratch on winding insulation, bubble in oil, moisture in insulation paper, a very small free metal particle in the transformer tank, and a fixed sharp metal point on the transformer tank, for our PD-related studies. Each type of defect is implemented into 1 of the 5 identical transformer models, which had been developed in the authors' recent work. The continuous wavelet transform is applied to each related measured time-domain PD signals. This process results in an image, for each PD pulse in the time-frequency domain. Using... 

Traditionally, the effects of seismic forces on structures have been mitigated by installing supplemental energy dissipation systems. In this paper, a new approach is explored for the mitigation of earthquake-induced vibrations by obstructing the entrance of seismic energy to the structure through the insertion of some concrete wave barriers within the soil domain. To do so, genetic algorithm (GA) based adaptive optimization methodology is utilized that is capable of finding the efficient layout of the concrete barriers in a manipulated soil zone around the structure. The optimization methodology is coupled with finite element (FE) method for analyzing the complex wave propagation phenomenon... 

The use of acoustic emission (AE) technique for damage diagnostic is typically challenging due to difficulties associated with discrimination of events that occur during different stages of damage that take place in a material or a structure. In this study, an unsupervised kernel fuzzy c-means pattern recognition analysis and the principal component method were utilized to categorize various damage stages in plain and steel fiber reinforced concrete specimens monitored by AE technique. Enhancement of the discrimination and characterization of damage mechanisms were achieved by processing time and frequency domain data. Both domains (time and frequency) were taken into account to propose new... 

In the case that phased array systems are not capable of attenuating interferences, Radio Frequency (RF) front-ends and Analog Digital Converters (ADCs) with a large dynamic range are required to avoid saturation of the receiver. This leads to a higher power consumption. In this paper, employing N-path circuits in Mixer-First receivers, a novel method is introduced in which spatial and frequency blockers are eliminated right before entering the system on the antennas input. In fact using this technique, adjustable spatial notch filter and band-pass frequency filter are implemented to suppress spatial and frequency interferences. The proposed method enhances the robustness and effectiveness... 

Operational modal analysis based on power spectral density transmissibility (PSDT) functions is a useful tool to identify the modal parameters with low sensitivity to excitations. For pole extraction from the PSDT function, a proper parametric identification method such as the polyreference least squares complex frequency-domain method or poly-Max method can be used. Then, the poles are selected from a stabilization diagram (SD) with overestimating the system model order. Therefore, spurious modes can be identified that must be distinguished and removed from the system poles. To reach this aim, many techniques have been proposed and applied. In this paper, a new algorithm is proposed to... 

Energy methods such as Energy Flow and Statistical Energy Analyses have been popularly used to predict the medium to high frequency vibro-acoustic response of several structures. In these energy methods, usually the common simple structural theories are used for simplicity. Since, the effects of shear deformation and rotary inertia at high frequency regions are unavoidable, it is necessary to determine the validity of these theories in each frequency domain. This paper aims to propose a method for defining a criteria to select a proper structural theory based on the order of shear deformation and rotary inertia to be used in vibration analyses. Several common as well as higher-order beam... 

The use of acoustic emission (AE) technique for damage diagnostic is typically challenging due to difficulties associated with discrimination of events that occur during different stages of damage that take place in a material or a structure. In this study, an unsupervised kernel fuzzy c-means pattern recognition analysis and the principal component method were utilized to categorize various damage stages in plain and steel fiber reinforced concrete specimens monitored by AE technique. Enhancement of the discrimination and characterization of damage mechanisms were achieved by processing time and frequency domain data. Both domains (time and frequency) were taken into account to propose new... 

In this paper, we propose an accurate visible light indoor localization system for a smartphone using the commercial light-emitting diode (LED) panels which are used primarily for lighting. Each of designed lighting panel contains a space-colorcoded identifier, a matrix with a unique pattern of spatially separated colored LEDs, for labeling different positioning cells while the lighting color is kept white by balancing the number of different sets of colored LEDs. The advantage of this idea is that we do not use the time-frequency domain of visible light communication (VLC) networks resources for positioning signaling. Our positioning technique called geometrical optics positioning algorithm... 

Vertical vibration of structures due to strong near-field earthquakes could culminate in catastrophic consequences. In this article, the optimum patterns of two types of wave barriers with different geometry configurations, buried in the soil domain, are obtained in order to reduce the vertical acceleration of the top of a circular foundation placed on the soil surface. In order to look into the influence of various soil deposits, six soil deposits with diverse material properties and bedrock depths are examined. The topology optimization procedure for finding the optimum position of the wave barriers has been conducted using coupled finite element-genetic algorithm methodology. First, the... 

For studying the behavior of structure in an earthquake, it is advisable to model the structure as a multi-degrees of freedom system, consisting of numerous single-degree of freedom substructures and pay attention to soil-structure interaction. System identification is divided into two categories: namely time domain method and frequency domain approach. In this paper, a localized substructure identification of shear building considering the soil-structure interaction is presented using a frequency domain approach. In order to deal with noise-corrupted data, a spectral smoothing technique with Parzen's window reduction method is adapted. It is shown that better convergence and accuracy can be... 

A fast algorithm based on the nonlinear dynamical model for the electrocardiogram (ECG) is presented for the precise extraction of the characteristic points of these signals with baseline drift. Using the adaptive bionic wavelet transform, the baseline wander is removed efficiently. In fact by the means of the bionic wavelet transform, the resolution in the time-frequency domain can be adaptively adjusted not only by the signal frequency but also by the signal instantaneous amplitude and its first-order differential, which results in a better baseline wander cancellation. At the next step the parameters of the model are chosen to have the least square error with the original ECG. Determining... 

In this paper, our main purpose is to embed data in the frequency domain of audio signals. Data was embedded by means of Quantization Index Modulation (QIM) in the frequency domain. With this aim, the spectrum of the audio signal was divided into two parts. The first part consisted of the first 19 Barks and the second included the remaining 6 Barks. Each of these parts had a different quantization step size. In order to have large quantization step sizes which yield more robustness, Human Auditory System (HAS) has been used. Decoder detects the watermark signal, without using the original audio signal. Simulation results have shown that this watermarking scheme has better robustness against... 

Dealing with numerical analysis of problems, especially ones with semi-infinite boundaries, scaled boundary finite element method has emerged as one of the efficient tools for the task. Combining the exactness of strong forms with the flexibility of weak formulations makes the method an improvement to its predecessors. Problem with the method arises when the analytical solution of the semi-discretized system is not available, which is the case for numerous problems. In the most recent attempt to solve the issue, a shooting method was proposed for elastostatic problems. Generality of the method removes any concerns regarding the type of governing equations since it no longer needs any... 

Rational function-based models have proved to be very efficient for accurate frequency-dependent modeling of power system components. These models are able to characterize the components terminal behaviours (analysing the admittance matrix) for nodal analysis. This provides a fast convergence and inherent stability to the solution routine of the model. This work presents a general framework for interfacing the dynamic phasor method to the rational models. That would be promising for the electromagnetic transient analysis (under harmonic distortion), in the frequency domain. Therefore, Y-element rational pole-residue models (employing the vector fitting method) are developed. Moreover, the... 

In this paper, the control problem of a wind turbine in region 3 (where the wind velocity is between the rated wind velocity and cut out wind velocity) has been investigated by considering the aerodynamic nonlinear behavior of the wind-structure interaction. The model has been developed by using the blade element momentum (BEM) theory to obtain the aerodynamic torque and aerodynamic loads in edgewise and flapwise directions. For validation, the aerodynamic behavior of the onshore NREL 5 MW turbine has been compared with the Fatigue, Aerodynamics, Structures, and Turbulence (FAST) aeroelastic code in terms of the power coefficient. Wind speed is modelled as a three-dimensional profile with... 

In this paper, different models of gain enhanced amplifier are compared and the most accurate one is chosen. Based on this model, complete symbolic small signal analysis is performed and a design procedure leading to high speed gain boosted amplifier is presented