Електротехнички факултет [Научни радови] / Faculty of Electrical Engineering [Scientific papers]

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Fast and Reliable Locating of Points with the Maximum Value of Total Electromagnetic Fild Using a Modern Experimental Method for Radio Coverage in Urban Environment
(Hindawi, 2014) Medjedovic, Petar S.; Suka, Darko S.
This research has been performed within the project “prediction, measurement, and analysis of composite electromagnetic field of artificial radiation sources,” funded by theMinistry of Science and Technology of the Republic of Srpska, Bosnia and Herzegovina. The ultimate goal of the project is the installation of a monitoring network for continuous measurement and recording of nonionizing electromagnetic (EM) radiation levels in the wider area of Banja Luka city centre covering about 10 km2. For this reason it was necessary tomake an optimal choice from a dozen ofmeasurement points with themaximumvalue levels of total EM field. It was a difficult task, because in this case, with the resolution of 5m× 5m, approximately 400,000 points should be examined. Therefore, the pedestrian zones, areas, and routes with significantly smaller surfaces but with the largest flow of people have been examined, so the time required for their mapping with values of total EM field has been reduced to a more realistic framework. In this paper, in the volume allowed by the defined criteria, a fast and reliable experimental method has been described, which has been examined at one of the studied areas in the named project, with surface of 0.008 km2.
Development of Integral Environment in Matlab/Simulink for FPGA
(VSB-Technical University of Ostrava, Czech Republic, 2014) JOKIC, Dejan; LABURA, Slobodan; STANKOVSKI, Stevan
In this paper is presented realization of integral environment which consists of software and hardware components for the purpose of programming Altera DE boards. Software component is Toolbox FPGA Real Time which enables simple use of Matlab/Simulink with DSP Builder for the purpose of realization of control structures. Hardware component are Interface cards that make connection of DE board with object of control possible. Simulation and experimental results of DC motor control indicate the usefulness of the proposed concept.
Using ICT to Support Alumni Data Collection in Higher Education
(Faculty of Teacher Education, University of Zagreb, 2014) Mijić, Danijel; Janković, Dragan
Getting feedback from external stakeholders, especially alumni and employers, is a challenging task for higher education institutions. It is important for many reasons, such as providing information to policy makers, assessing quality of academic programmes, adapting academic programmes to labour market needs, and marketing purposes. Alumni and employer surveys are usually used as methods for collecting data from stakeholders. Research suggests that major problems in data collection are related to efficiency and effectiveness of data collection process. This paper presents a different method of data collection supported by ICT. A specially designed web portal equipped with advanced alumni tracking and communication features was developed and used for alumni data collection. The web portal was evaluated after a period of real operation by analyzing collected data and conducting an online survey. The evaluation results showed that the web portal could be used as effective, efficient, and useful tool for alumni data collection and communication between alumni and higher education institutions.
Single-phase phase locked loop with DC offset and noise rejection for photovoltaic inverters
(Wiley, 2014) Lubura, Slobodan; Šoja, Milomir; Lale, Srđan; Ikić. Marko
Proper work of grid-connected converters requires an accurate detection of phase angle, frequency and amplitude of grid voltage. Phase locked loops (PLLs) based on synchronous reference frame theory can be used for estimation of these grid parameters. One of the issues that could appear during estimation of grid parameters is appearance of DC offset in measured grid voltage. This DC component (offset) is usually entered in PLL structure via measurement and A/D conversion process. Undesirable induced DC offset could appear as part of the reference sine current of photovoltaic inverters or other grid-connected converters. A lot of standards define allowed PV inverter’s DC current injection in the grid. In this study, we propose an improved PLL structure with capability to fully reject DC offset and noise which could appear in measured input grid voltage. The key component of the proposed PLL is two-phase generator with a closed control loop for DC offset and noise rejection. Obtained simulation and experimental results show that the proposed PLL structure can solve important issues of presence of noise and DC offset in measured grid voltage. The proposed PLL structure shows excellent dynamical performances in conditions of fast changes of grid parameters.
Some examples of photorefractive oscillators
(2015) Ljuboje, Zoran
The photorefractive effect presents a periodical change of the refractive index of an optical environment under the influence of a coherent light. An interesting phenomenon which occurs at this effect is optical phase conjugation (PC). Photorefractive oscillators, that is photorefractive mirrors present important decides in photorefractive optics and their function is based on photorefractive effect. In these oscillators, a phase-conjugated light beam occurs. The basic characteristics of photorefractive oscillators, such as reflectivity, the existance of the oscillation threshold and the threshold of the coupling strength are explained by the so-called grating-action method. This is analysed on a ring oscillator, semilinear mirror and linear mirror.
Application of internet of things in food packaging and transportation
(Inderscience Enterprises Ltd, 2015) Maksimović, Mirjana; Vujović, Vladimir; Omanović-Mikličanin, Enisa
Food safety is a scientific field which includes a number of routines and inspections at every stage of the food chain that should be adopted to avoid potentially dangerous health risks. Novel and efficient solutions across the supply chain are the consequence of constant upgrades of information and communication technologies. With the help of internet of things (IoT) connected testing equipment, food quality can be monitored at any point from farm to table, connecting at the same time food producers, transportation and hospitality/retail companies. Relying on the fact that food transporting and packaging units are the most critical points in food production, the survey of IoT applications in food packaging and transportation is given in this paper. To demonstrate the significance of IoT appliance and defined concepts, a proposal of low cost solution based on IoT for real-time food traceability and monitoring in food transportation process is presented.
AN INTEGRATED FUZZY AHP AND TOPSIS MODEL FOR SUPPLIER EVALUATION
(University of Belgrade, Serbia, 2016) MAKSIMOVIĆ, Mirjana; MILOŠEVIĆ, Vladimir
Wireless Sensor Networks (WSNs) consist of wireless sensor nodes, where the choice of their deployment scheme depends highly on the type of sensors, their application, and the environment they will operate in. The performance of WSNs can be affected if the network is deployed under different topologies. In this paper various strategies for positioning nodes in WSNs for fire detection (grid, triangular and strip) are discussed. We propose the proper placement of the smoke sensors to satisfy two important network design objectives: to maximize the network lifetime after fire ignition, and to achieve full coverage by using a minimum number of sensors (especially in a deterministic node deployment).
A Comparative Study of Voltage, Peak Current and Dual Current Mode Control Methods for Noninverting Buck-Boost Converter
(Academic Mind, Belgrade, 2016) Bošković, Marko Č.
This paper presents a comparison of voltage mode control (VMC) and two current mode control (CMC) methods of noninverting buck-boost converter. The converter control-to-output transfer function, line-to-output transfer function and the output impedance are obtained for all methods by averaging converter equations over one switching period and applying small-signal linearization. The obtained results are required for the design procedure of feedback compensator to keep a system stable and robust. A comparative study of VMC, peak current mode control (PCMC) and dual-current mode control (DCMC) is performed. Performance evaluation of the closed-loop system with obtained compensator between these methods is performed via numerical simulations.
Preventive Thermographic Diagnostic of a HV Busbar Disconnector
(Faculty of Electrical Engineering Banja Luka, Bosnia and Herzegovina, 2016) Šaraba, Predrag; Ljuboje, Zoran; Popović, Božidar; Krsmanović, Dražan
For the purpose of increasing quality, continuity and, at the same time, of increasing reliability and decreasing the losses in an electric power system (EPS), there is an emerging need for preventive diagnostic testing. From the standpoint of an electric power system availability, it is desirable to perform as many tests as possible without a violation of operating conditions of the system itself. The paper presents the thermographic testing of a HV disconnector, as an online testing with the aim of preventive maintenance and condition diagnosis of particular elements, as well as the suggestions for taking adequate measures with the aim of removing potential malfunctions. For the testing results to be quality and to give a reliable information, the load of a facility must be bigger that 50% of the nominal power. On the basis of obtained thermograms, the analysis of the disconnector and its contacts is performed, as well as of the contacts towards other elements in the facility.
The Role of Green Internet of Things (G-IoT) and Big Data in Making Cities Smarter, Safer and More Sustainable
(University of Bahrain, 2017) Maksimovic, Mirjana
The world population growth and increased demands for limited goods consequently imply the necessity for more efficient use of materials and resources. As the novel advances in Information and Communication Technology (ICT) have totally revolutionized the numerous areas, their utilization at the same time possesses a negative influence on the human health and the environment. For that reason, the society is going toward the greener future where the usage of raw and non-renewable materials and resources will be reduced while energy consumption and pollution will be decreased. As ICT can be considered as a tool for addressing environmental problems, Green Internet of Things (G-IoT) takes one of the most important roles on the way to create a green and sustainable place for living. Big data analysis is essential in achieving valuable insights from voluminous and various G-IoT generated data. The obtained knowledge enables easier decision-making, forecasting and other activities regarding smart city services, and in return contributes to a continuous improvement of G-IoT technologies. Hence, even the vision of smart and sustainable cities has already become a reality, the G-IoT approaches and insights achieved from Big data analysis will make cities significantly smarter, safer and more sustainable. This paper tries to summarize the role of novel technology advancements and Big data’ achievements in the process of creating cities where the quality of life will be enhanced alongside reduced pollution and more efficient utilization of goods. It has been shown that G-IoT and Big data operating symbiotically successfully contribute to the fruition of smart and sustainable city vision.
Stable Takagi-Sugeno Fuzzy Control Designed by Optimization
(2017) Vrkalovic, Sasa; Teban, Teodor-Adrian; Borlea, Ioan-Daniel
This paper presents the design of Takagi-Sugeno fuzzy controllers in state feedback form using swarm intelligence optimization algorithms. Three such algorithms are used: Particle Swarm Optimization, Simulated Annealing and Gravitational Search Algorithms. Sufficient stability conditions are expressed in terms of linear matrix inequalities considered as constraints in the optimization problem solved by swarm intelligence algorithms. Simulation results concerning an inverted pendulum system are given for illustration of the proposed design.
An Algorithm for transformer hot spot temperature determining
(Wydawnictwo SIGMA - N O T Sp. z o.o., Poland, 2017) JOKIC, Srdjan; MIJIC, Danijel; MATIC, Petar
This paper presents an algorithm for the winding temperature change estimation and the hot spot temperature determining of an oil filled power transformer. The proposed algorithm is based on the functional relation between the change of winding resistance and the measured oil temperature. The temperature changes approximation is based on the method of least squares. The proposed method is applied in the software for a field test instrument and verified by the field experiments.
A telehealth system for automated diagnosis of asthma and chronical obstructive pulmonary dise
(2018) Gurbeta, Lejla; Badnjevic, Almir; Maksimovic, Mirjana; Omanovic-Miklicanin, Enisa; Sejdic, Ervin
This paper presents the development and real-time testing of an automated expert diagnostic telehealth system for the diagnosis of 2 respiratory diseases, asthma and Chronic Obstructive Pulmonary Disease (COPD). The system utilizes Android, Java, MATLAB, and PHP technologies and consists of a spirometer, mobile application, and expert diagnostic system. To evaluate the effectiveness of the system, a prospective study was carried out in 3 remote primary healthcare institutions, and one hospital in Bosnia and Herzegovina healthcare system. During 6 months, 780 patients were assessed and diagnosed with an accuracy of 97.32%. The presented approach is simple to use and offers specialized consultations for patients in remote, rural, and isolated communities, as well as old and less physically mobile patients. While improving the quality of care delivered to patients, it was also found to be very beneficial in terms of healthcare
Model-Free Sliding Mode and Fuzzy Controllers for Reverse Osmosis Desalination Plants
(CESER Publications, 2018) Vrkalovic, Sasa; Lunca, Elena-Cristina; Borlea, Ioan-Daniel
This paper presents model-free sliding mode controllers and Takagi-Sugeno fuzzy controllers for the flux and conductivity control of Reverse Osmosis Desalination Plants (RODPs). The RODPs are Multi Input-Multi Output processes and two separate controllers are designed in Single Input-Single Output control systems. The design of the model-free sliding mode controllers is done by Lyapunov’s stability theory. The Takagi-Sugeno fuzzy controllers are designed by considering linear matrix inequalities as constraints in an optimization problem solved by a Grey Wolf Optimizer algorithm. Simulation results are included.
BGP Anomaly Detection with Balanced Datasets
(University of Osijek, 2018) OBRADOVIĆ, Slobodan; ĆOSOVIĆ, Marijana
We use machine learning techniques to build predictive models for anomaly detection in the Border Gateway Protocol (BGP). Imbalanced datasets of network anomalies pose limitations to building predictive models for anomaly detection. In order to achieve better classification performance measures, we use resampling methods to balance classes in the datasets. We use undersampling, oversampling and combination techniques to change class distributions of the datasets. In this paper we build predictive models based on preprocessed network anomaly datasets of known Internet network anomalies and observe improvement in classifier performance measures compared to those reported in our previous work. We propose to use resampling combination techniques on datasets along with Decision Tree and Naïve Bayes classifiers in order to achieve the best trade-off between (1) the F-measure and the length of model training time, and (2) avoiding overfitting and loss of information
Analysis of the Band-Pass and Notch Filter with Dynamic Damping of Fractional Order Including Discrete Models
(ETF – School of Electrical Engineering, University of Belgrade, 2018) Bošković, Marko; Šekara, Tomislav B.; Rapaić, Milan R.; Lutovac, Budimir; Daković, Miloš; Govedarica, Vidan
The paper presents analysis of the second order band-pass and notch filter with a dynamic damping factor βd of fractional order. Factor βd is given in the form of fractional differentiator of order , i.e. βd=β/s, where β and  are adjustable parameters. The aim of the paper is to exploit an extra degree of freedom of presented filters to achieve the desired filter specifications and obtain a desired response in the frequency and time domain. Shaping of the frequency response enables achieving a better phase response compared to the integer-order counterparts which is of great concern in many applications. For the implementation purpose, the paper presents a comparison of four discretization techniques: the Osutaloup’s Recursive Algorithm (ORA+Tustin), Continued Fractional Expansion (CFE+Tustin), Interpolation of Frequency Characteristic (IFC+Tustin) and recently proposed AutoRegressive with eXogenous input (ARX)-based direct discretization method.
BGP Anomaly Prediction Using Ensemble Learning
(2019) Cosovic, Marijana; Junuz, Emina
This paper investigates anomalies such as worms, power outages, and routing table leak (RTL) events occurring in Border Gateway Protocol (BGP) that can cause connectivity and data loss issues. Ensemble learning is a machine learning model employing multiple classifiers in order to reliably identify network anomalies. We use bagging, boosting, and random forests ensemble models trained on network anomaly datasets for classification improvement. Models were compared with respect to the following performance metrics: F-measure, Matthews correlation coefficient (MCC), Receiver operating characteristic (ROC) curve, precision-recall (PR) curves and model execution time. We observed improvement in performance measures when ensemble classifiers realized in Python were used in comparison to our previously reported results on single classifiers. Further improvement in most performance measures was observed by using sampling techniques (oversampling and undersampling) on anomalous datasets. This approach increases model execution time which is not favorable for real-time anomaly detection models.
APPLICATION OF TIME-AVERAGED AND INTEGRAL-BASED MEASURE FOR MEASUREMENT RESULTS VARIABILITY REDUCTION IN GSM/DCS/UMTS SYSTEMS
(Oxford University Press, 2019) Šuka, Darko; Pejović, Predrag; Simić-Pejović, Mirjana
Since EMF levels from wireless telecommunication networks are non-stationary and exhibit large temporal variations, the use of continuous measurements during extended periods (preferably 24 h or longer) with a data-logging system is required. Because of the short-term variations of E field, the 6-min measurements and 6-min averaged results to obtain the mean level strength at a given place appear to be dependent on the time of measurements during the day. This paper presents a new (integral-based) measure to evaluate electromagnetic exposure. The new measure is a pure physical descriptor of the amount of exposed energy density (a parameter accumulated from instantaneous power density values in time). To confirm previous observations, continuous measurements with personal exposure metre were recorded 24 h a day for two weeks at every location in urban area, 14 different locations in total. Additionally, to check temporal variations and repeatability of exposure assessment, a week of prolonged measurements was taken 6 months later, making in total three weeks of measurements at 2 locations. Day-to-day repeatability of RF-EMF exposure was analysed through the time-averaged and integral-based measure. The analysis is based on approximately 5.1 million data samples (1.7 million for each band). The ratio between the maximum and minimum instantaneous (maximum and minimum 6-min averaged) E field values during the day could reach up to 25 dB (20 dB). Therefore, great variability in the results may occur. By applying the 24 h time-averaged and integral-based measure on a 24 h data set of measurements, the variability of daily exposure could stay within ±20% of the week mean level obtained either with the time-averaged or integral-based measure. Both, the time-averaged E field and integral-based power density exposures of the general public in all locations were found to be well below the general public exposure limits of the ICNIRP guidelines.
What’s in the Box: Design of an Open Didactic Robot Environment
(MDPI, 2020) Jokić, Dejan; Lubura, Slobodan; Ristović, Milica; Stankovski, Stevan; Rajs, Vladimir; Šiljak, Harun
We present a realization of a didactic robot environment for robot PUMA 560 for educational and research purposes. Robot PUMA 560 is probably the mathematically best-described robot, and therefore it is frequently used for research and educational purposes. Adeveloped control environment consists of a robot controller and teach pendant. The advantage of using a personally developed solution is its open structure, which allows various tests and measurements to be performed, and that is highly convenient for educational and research purposes. The motivation behind the design of this personal didactic robot control environment arose from a survey for students after the first Summer School on Mechatronic Systems. The student questionnaire revealed severe discrepancies between theory and practice in education. Even though the primary purpose of the new control environment for robot PUMA 560 was research, it was established that it is a viable lab resource that allows for the connection between theoretical and industrial robotics. It was used for the duration of four Summer Schools and university courses. Since then, it has been fully integrated into International Burch University’s Electrical and Electronics Engineering curriculum through several courses on the bachelor and master levels for multidisciplinary problem-based learning (PBL) projects.
Two Open Solutions for Industrial Robot Control: The Case of PUMA 560
(MDPI, 2020) Jokić, Dejan; Lubura, Slobodan; Rajs, Vladimir; Bodić, Milan; Šiljak, Harun
In this paper we present two di erent, software and reconfigurable hardware, open architecture approaches to the PUMA 560 robot controller implementation, fully document them and provide the full design specification, software code and hardware description. Such solutions are necessary in today’s robotics and industry: deprecated old control units render robotic installations useless and allow no upgrades, advancements, or innovation in an inherently innovative ecosystem. For the sake of simplicity, just the first robot axis is considered. The first approach described is a PC solution with data acquisition I/O board (Humusoft MF634). This board is supported with Matlab Real-TimeWindows Toolbox for real-time applications and thus whole controller was designed in Matlab environment. The second approach is a robot controller developed on field programmable gate arrays (FPGA) board. The complexity of FPGA design can be overcome by using a third party software package, such as self-developed Matlab FPGA Real Time Toolbox. In both cases, parameters of motion controller are calculated by using simulation of the PUMA 560 robot first axis motion. Simulations were conducted in Matlab/Simulink using Robotics Toolbox.

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