SERBIAN JOURNAL OF ELECTRICAL ENGINEERING
Vol. 16, No. 2, June 2019
CONTENTS
Application of Huber-Similarity Measure on PD Detection
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DOI: https://doi.org/10.2298/SJEE1902137P
Abstract: Extraction of Partial Discharges (PD) is a key step in diagnosis and evaluation of the power system equipment condition. In field testing, besides high frequency noise and disturbance, Power Frequency (P.F.) harmonics also couple with PD measurement sensors. In order to deal with both types of noises and disturbances, in this paper, a new PD signal extraction algorithm is presented, which is based on a combination of Huber Function, Discrete Cosine Transform (DCT), and norms. This new method, which is introduced as Huber Similarity Measure for Partial Discharge (HSMPD), was evaluated through experimental laboratory constructed PD models. Results show this proposed algorithm successfully extracted PD signals in the presence of baseline and high frequency noises and disturbances. HSMPD can be employed as a backbone in intelligent diagnosis systems for improving the accuracy of PD condition monitoring equipment.
Keywords: Condition Monitoring, Huber Function, Partial Discharge, Signal Detection.
Direct and Indirect Self-Tuning Generalized Minimum Variance Control
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DOI: https://doi.org/10.2298/SJEE1902149K
Abstract: Theoretically, several self-tuning control (STC) algorithms have been developed and many simulation results have proved their feasibility in the past years, but applications of STC are hardly seen. This paper proposes direct and indirect STC plans that can be applied to a chemical process system with a time delay auto-regressive and exogenous model of a varied time constant. The plan controller is a combination of a generalized minimum variance control (GMVC) strategy and an identification algorithm (simplified parameter) called recursive least squares to estimate controller parameters for the direct method and plan parameters for the indirect method. The experimental results show that GMVC is able to track the desired input or set point.
Keywords: Self-Tuning, Time delay, Set point.
Nonlinear Optimization of Proportional-Integral Controller in Doubly-Fed Induction Generator Using the Gradient Extremum Seeking Algorithm
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DOI: https://doi.org/10.2298/SJEE1902161S
Abstract: This paper deals with the problem of nonlinear optimization of proportional-integral (PI) controller in doubly-fed induction generator (DFIG), modeled by the detailed differential-algebraic equations (DAEs), and connected to a power system, where rest of the power system is represented only by measurements in connection point. The basic functions of PI controllers are secondary regulation of speed–active power and reactive power–voltage of multiple DFIGs connected in the same point (typical situation in wind farms). In the presence of PI controllers, stability of the transient responses depends largely on its parameters (proportional and integral part). To calculate optimal parameters of the PI controllers, an ‘Extremum Seeking’ (ES) algorithm was used, more precisely, its version that assumes that gradient can be calculated [hence the name ‘Gradient Extremum Seeking’ (GES)]. Optimization of the PI controller parameters is performed for a list of major disturbance trajectories recorded in historical database. The results obtained using the IEEE 14-bus test system show that PI controller parameters must be carefully chosen. Their effect on transient responses and stability of the power system with major disturbance (short circuit, outage etc.) conditions was additionally studied.
Keywords: Power system, Doubly-fed induction generator (DFIG), Proportional-integral (PI) regulator, Nonlinear parameter optimization, Gradient Extremum Seeking (GES).
Electric Arc Furnace Transformer Secondary Circuit Calculations
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DOI: https://doi.org/10.2298/SJEE1902181C
Abstract: This paper demonstrates a procedure for calculating stress and temperature in the secondary high current circuit of a modern electric arc furnace. At the beginning, the separate parameters that form the electric circuit from the furnace to the bushings of the electrodes are determined. The analysis of these parameters allows the selection of the optimum operational point of the furnace. Thermal and stress analysis of the transformer secondary delta closure is further performed. The procedure is given in detail with all the required equations and is illustrated on a real 110-ton furnace with a 110 MVA transformer.
Keywords: Electric arc furnace, Furnace transformer, Secondary circuit, Stress calculations, Temperature calculations.
A Novel Planar Antenna Array for a Ground-Based Synthetic Aperture Radar
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DOI: https://doi.org/10.2298/SJEE1902195V
Abstract: A MIMO GB-SAR system called MELISSA was put in place to monitor landslides in Italy and the sinking of the Costa Concordia cruise liner in France. It comprises 12 pyramidal horn antennas placed in a linear geometry for transmission, and these are used in the detection of the motion of a target (for example a landslide or other terrestrial deformation). The low half power beam width (19.76° at θ = 90°) of the transmitting radiation pattern of MELISSA results in low coverage area of the target. This paper proposes two alternative types of horn antenna for the current transmitter module of MELISSA, namely the cantenna and coaxial cavity horn antenna, for installation in a 2×6 planar antenna array. A higher value of the 3 dB beamwidth is observed using these arrays (38.320 at θ = 90° and 104.80 at φ = 0° for the cantenna array and 410 at θ = 90° and 140.40 at φ = 0° for the coaxial cavity horn antenna array). The overall gain of the proposed systems is around 10 dBi, and the efficiencies are between 85% and 90%. Using the Dolph Chebyshev beamforming technique on the proposed antenna arrays yields a zero sidelobe level, which improves the overall peak sidelobe ratio of the system and in turn the quality of the images obtained. Our proposed design for the transmitting section of the MELISSA system has applications terrestrial deformation monitoring with higher area coverage.
Keywords: Cantenna, Coaxial cavity horn, Dolph Chebyshev beamforming, GB-SAR, Isolation, MELISSA, Mutual coupling.
The Spatial Separation of Signals by the Curvature of the Wave Front
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DOI: https://doi.org/10.2298/SJEE1902211O
Abstract: In this paper, a new method of spatial separation of several signals with different curvatures of the wave front is proposed. The method is based on the formation of a particular interference field structure of each signal in the location of the receiving antennas by means of a transmitting phased sparse linear array antenna. The peculiarity of the interference electromagnetic field consists in periodically repeating areas in which the amplitude of the useful signal is many times greater than the amplitudes of the other transmitted signals, which are electromagnetic interference. In addition, the electromagnetic interference signal in this area consists of practically two antiphase components. If in this area a reflective passive phased antenna array is placed, which will focus the useful signal while reflecting, it will be increased, and the interference signal will be significantly weakened. This method of signal separation allows simultaneous transmission of several signals in the same frequency band, in one direction and on one polarization, which increases the information transmission speed in communication systems.
Keywords: Spatial signal separation, Wavefront curvature, Reflective passive phased antenna array, Signal-to-noise ratio, Phased sparse antennas array.
A Review to Economic Dispatch of Hybrid Microgrids
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DOI: https://doi.org/10.2298/SJEE1902233V
Abstract: Hybrid Microgrids are being widespread for power generation in remote locations. The improvement in non-conventional energy sources and rise in the price of existing electrical energy production sources led to the advancement of hybrid renewable sources. Economic characteristics of these technologies are adequately capable to include in emerging power generation. Advances and research in solar, wind and other non-conventional energy sources are required to continue for improving their performance, creating techniques for exactly forecasting their outputs and reliably integrating with other conventional sources used for generation. Economic dispatch is being taken into consideration as the optimal output of the electricity generation facilities. These are to be met as per the load at the lowest possible cost. The problem on Economic Dispatch (ED) and different technical constraints considering power balance in the network satisfying the objective are to be formulated. This paper presents a brief review on economic dispatch of hybrid microgrids.
Keywords: Distributed Generation (DG), Hybrid Microgrid, Hybrid Energy Systems, Renewable Energy Sources, Economic Dispatch (ED).
A Chaotic Image Encryption Scheme with Complex Diffusion Matrix for Plain Image Sensitivity
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DOI: https://doi.org/10.2298/SJEE1902247T
Abstract: A chaotic cipher is presented in this paper using 1-Dimensional and 2-Dimensional chaotic maps like logistic, Chebyshev and Arnold cat map. Permutation phase utilizes logistic map followed by Arnold cat map whereas in diffusion phase, Chebyshev’s map is used. Subsequently, another complex diffusion matrix is generated from the original image. This matrix is employed to enhance the diffusion effect further. Eventually, strong input image sensitivity is explored due to this diffusion. Simulation results exhibit that the recommended cipher ensures not only high key and entropy value but also less correspondence between nearby pixels along all directions. The key point of this cipher is the high Number of Pixels Change Rate (NPCR) and Unified Average Changing Intensity (UACI) values. Due to this impact, the proposed cipher produces completely random encrypted images.
Keywords: Logistic Map, Chebyshev’s map, Confusion, Diffusion, NPCR, Chaos, UACI, Image encryption.
An Effective Approach to TV Applications Development – Application Framework
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DOI: https://doi.org/10.2298/SJEE1902267K
Abstract: Android as an operating system is becoming more and more widespread across digital devices. One of the fields in which Android has gained popularity is TV application development. During our years-long work on this platform, we noticed certain issues with current approaches. The most important issues include a lot of boilerplate code and difficult customization which together increase the overall time necessary for the development and contribute to poor code readability thus making the maintenance more difficult. With that in mind, we decided to take our own approach which includes a framework and a library and which enables us to build high-quality and cost-effective TV applications in terms of fast development and easy maintenance. The approach which will be presented in this paper is more effective than other approaches we took for the development of previous TV applications.
Keywords: Java, Android, MVP, Framework, Library, SDK, Handler, TV application, Backend, Information Bus.