SERBIAN JOURNAL OF ELECTRICAL ENGINEERING
Vol. 19, No. 1, February 2022
CONTENTS
High Voltage Gain Resonant DC-DC Converter with VM Cells for Renewable Sources Applications
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DOI: https://doi.org/10.2298/SJEE2201001H
Abstract: Due to the widespread impact of renewable energy resources on high power density grids,
transmission at the DC regime has been considered more useful than AC transmission systems.
The findings of this study suggest the application of a ripple-free input current resonant DC-DC converter
possessing high voltage gain and high efficiency as being more suitable for renewable energy systems.
Applying variable switching frequency control systems, the proposed converter discussed here is
generally operated at the critical conduction mode for soft switching of the semiconductor switches.
Using the resonance mechanism, the proposed converter causes a decrease in the turn-on loss of the power switch
without needing additional semiconductor gadgets. It leads to a reduction in the reverse-recovery losses of the rectifying diodes.
Also, analysis and design consideration of the proposed converter are presented with excellent performance.
Keywords: Resonant DC-DC Converter, Renewable Energy, Voltage Multiplier.
Multi-conductor Transmission Line with Non-linear Impedances: Application to 50Hz Studies
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DOI: https://doi.org/10.2298/SJEE2201015L
Abstract: This paper presents an algorithm for the evaluation of currents
and voltages along a multi-conductor transmission line having non-linear impedances due to the presence of ferromagnetic conductors;
we assume that these impedances are function of the current carried by the relevant conductor so that the equivalent circuit
modelling the line is non-linear and has to be solved by means of an iterative procedure.
The present paper can be considered as a generalization of our previous works successfully applied to single-conductor lines
with earth return. Some examples of application to typical 50-60Hz interference studies between power/railway lines on
telecommunication cables and pipelines are shown.
Keywords: Multi-conductor transmission lines, Ferromagnetic conductors, Electromagnetic interference,
Electromagnetic compatibility, Non-linearity.
Temperatures of Different Face Regions of Healthy People Measured by a Thermal Camera
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DOI: https://doi.org/10.2298/SJEE2201033C
Abstract: Body temperature is an important indicator that may indicate
the possibility of the existence of various pathological conditions and diseases. In the head and neck area,
an infrared camera allows accurate temperature measurements of all regions of interest.
The analysis of temperature characteristics of the region of interest of the head and neck in healthy subjects in terms
of comparison of values in relation to the side of the face in the same person, and the comparison of values
relative to the sex of the subjects is the topic of this research. These analyses are performed to create
temperature maps of the face and determine physiological values. The research was conducted with the participation
of 30 healthy people, 16 women and 14 men of different ages. Thermal imaging was performed in controlled conditions
with infrared thermographic camera Varioscan 3021ST, while the software package IRBIS Professional 2.2 was used
for thermogram analysis. Results show that the temperatures in female subjects at the submandibular region are
significantly lower than in male subjects with an average temperature difference of 0.46°C, and the temperatures
in female subjects at the supraorbital region are on average 0.5°C higher than in male subjects.
Keywords: Face thermal Map, Infrared radiation, Thermal imaging.
Distortion of Electric Field Homogeneity Between Two Thin Toroidal Electrodes by a Dielectric Sphere
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DOI: https://doi.org/10.2298/SJEE2201045M
Abstract: We assess the influence of a radius and a relative permittivity of
an isotropic dielectric sphere on electric field homogeneity.
The homogenous electric field is generated using two thin toroidal electrodes, charged by equal charges of opposite signs.
The Poisson equation is solved by a method of separation of variables.
Increase in a relative permittivity of the sphere and in its radius, produces more distortions of the electric field homogeneity.
Keywords: Dielectric sphere, Electrostatic, Homogeneous electrostatic field, Toroidal electrodes.
Proximity Effect in a Thin Two-layer Tubular Conductor Caused by a Parallel Filament
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DOI: https://doi.org/10.2298/SJEE2201057F
Abstract: In this paper, we determine in a closed form the current distribution
in a thin two-layer tubular conductor with a sinusoidal current in the presence of a filament with an equal but opposite current.
The method of treating the problem consists in solving an integral equation for the current density in one layer
which enables to find the current density in the other layer by imposing equality of the tangen-tial components of
the electric fields at the layer interface.
An important factor, the AC to DC resistance ratio for the conductor is also found in a closed form.
Some numerical examples, for current distribution and resistance ratio, versus frequency or geometry parameters, are presented.
Keywords: Skin effect, Proximity effect, Current distribution, Integral equation, AC to DC resistance ratio.
Snort IDS System Visualization Interface for Alert Analysis
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DOI: https://doi.org/10.2298/SJEE2201067G
Abstract: Over the past decades, the rapid Internet development
and the growth in the number of its users have raised various security issues.
Therefore, it is of great importance to ensure the security of the network in order to enable
the safe exchange of confidential data, as well as their integrity.
One of the most important components of network attack detection is an Intrusion Detection System (IDS).
Snort IDS is a widely used intrusion detection system, which logs alerts after detecting potentially dangerous network packets.
A major challenge in network monitoring is the high volume of generated IDS alerts.
A necessary step in successful network protection is the analysis of the great amount of logged alerts
in search of deviations from normal traffic that may indicate an intrusion.
The goal of this paper is to design and implement a visualization interface for IDS alert analysis,
which graphically presents alerts generated by Snort IDS. Also, the proposed system classifies
the alerts according to the most important attack parameters, and allows the users to understand
evolving network situations and easily detect possible traffic irregularities.
An environment in which the system has been tested in real-time is described, and the results of attack detection
and classification are given. One of the detected attacks is analyzed in detail,
as well as the method of its detection and its possible consequences.
Keywords: Intrusion Detection, Alert Analysis, Snort, Visualization.
Lung Sound Classification Using Wavelet Transform and Entropy to Detect Lung Abnormality
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DOI: https://doi.org/10.2298/SJEE2201079R
Abstract: Lung sounds provide essential information about the health of the lungs
and respiratory tract. They have unique and distinguishable patterns associated with the abnormalities in these organs.
Many studies attempted to develop various methods to classify lung sounds automatically.
Wavelet transform is one of the approaches widely utilized for physiological signal analysis.
Commonly, wavelet in feature extraction is used to break down the lung sounds into several sub-bands
before calculating some parameters. This study used five lung sound classes obtained from various sources.
Furthermore, the wavelet analysis process was carried out using Discrete Wavelet Transform (DWT) and
Wavelet Package Decomposition (WPD) analysis and entropy calculation as feature extraction.
In the DWT process, the highest accuracy obtained was 97.98% using Permutation Entropy (PE),
Renyi Entropy (RE), and Spectral Entropy (SEN). In WPD, the best accuracy achieved is 98.99 %
when 8 sub-bands and RE are used. These results are relatively competitive compared with previous studies
using the wavelet method with the same datasets.
Keywords: Wavelet transform, Sub-bands, Entropy, Feature reduction, Classifier.
Robust DOA Estimation of Complex Correlated Signals in Non-Gaussian CES Distributed Models
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DOI: https://doi.org/10.2298/SJEE2201099A
Abstract: The sample covariance matrix (SCM) is commonly used in
direction-of-arrival (DOA) estimation methods when the noise or observations are circular complex Gaussian (C CG) distributed.
However, with a very heavy-tailed non-Gaussian noise model, the SCM-based DOA estimation methods fail to provide
an accurate estimate of DOA.
This paper presents a numerical analysis of the resolving capability of subspace-based circular (C) and non-circular (NC)
multiple signal classification (MUSIC) DOA estimation methods of arbitrarily narrowband correlated signal sources
corrupted by circular complex elliptical symmetric (C CES) distributed noise.
It evaluates the robustness of these methods for correlated C and NC sources by employing the robust complex
M-estimators instead of SCM.
It study also the effects of correlation on robust MUSIC-based DOA estimation algorithms accuracy
as a function of the magnitude and phase of the correlation coefficients.
Simulations results show that the NC MUSIC algorithm which requires fewer sensor elements yields robust
estimates of DOA for correlated sources than the C MUSIC algorithm using the M-estimators.
Keywords: DOA estimation, Correlated signal sources, Heavy-tailed non-Gaussian noise and observations,
Complex elliptical symmetric distributions, Robust M-estimators.