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.
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    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.
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    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.
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    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.
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    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.