1. Simulation study of different OPM-MEG measurement componentsUrban Marhl, Tilmann Sander, Vojko Jazbinšek, 2022, izvirni znanstveni članek Opis: Magnetoencephalography (MEG) is a neuroimaging technique that measures the magnetic fields of the brain outside of the head. In the past, the most suitable magnetometer for MEG was the superconducting quantum interference device (SQUID), but in recent years, a new type has also been used, the optically pumped magnetometer (OPM). OPMs can be configured to measure multiple directions of magnetic field simultaneously. This work explored whether combining multiple directions of the magnetic field lowers the source localization error of brain sources under various conditions of noise. We simulated dipolar-like sources for multiple configurations of both SQUID- and OPM-MEG systems. To test the performance of a given layout, we calculated the average signal-to-noise ratio and the root mean square of the simulated magnetic field; furthermore, we evaluated the performance of the dipole fit. The results showed that the field direction normal to the scalp yields a higher signal-to-noise ratio and that ambient noise has a much lower impact on its localization error; therefore, this is the optimal choice for source localization when only one direction of magnetic field can be measured. For a low number of OPMs, combining multiple field directions greatly improves the source localization results. Lastly, we showed that MEG sensors that can be placed closer to the brain are more suitable for localizing deeper sources.
Ključne besede: magnetoencephalography, optically pumped magnetometers, superconducting quantum interference device, volume conductor, boundary element method, equivalent current dipole, source localization, ambient noise, spontaneous brain noise
Objavljeno v DKUM: 16.12.2024; Ogledov: 0; Prenosov: 2
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2. Transient circuit simulation of arc-free current breaking by resistance riseDareer Bin Khalid, Michael Rock, Luigi Piegari, 2021, izvirni znanstveni članek Opis: There has been intensive research and development in the field of Circuit breakers, whether DC and AC, or low voltage and high voltage. The result of this has led to the production of highly reliable circuit breakers that accompany a built-in arc extinguishing system. However, the purpose of this study is to give the basics for arc-free current breaking with fast interruption of fault currents, e.g., in surge protective devices (SPD) for AC and DC systems, by means of a time-dependent resistor with fast rising resistance. This investigation shall illustrate how the current can be driven almost to zero with a steadily time increasing resistance, and interrupted completely without an electric arc. The basic aim of the conducted transient circuit simulations is to determine suitable time functions for the current or resistance and necessary initial and final resistances. This paper will discuss the "optimisation conditions", a switching time as short as possible, small switch-off overvoltage, and possibly an energy conversion in the resistor as low as possible is set using ATP-EMTP and analytical calculations.
Ključne besede: current breaking, ATP-EMTP, time-dependent resistance, optimisation, concave functions, convex functions
Objavljeno v DKUM: 13.11.2023; Ogledov: 439; Prenosov: 4
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3. Three-Phase load current reconstruction using singleshunt current measurement and modified vector modulation for three-level DC-AC converter : doctoral dissertationHaris Kovačević, 2022, doktorska disertacija Opis: This doctoral thesis focuses on the development of Space Vector Modulation (SVM) techniques adjusted for single-shunt current measurement and applied to the three-level three-phase voltage source inverter. Based on the single-shunt current measurement, three-phase load currents are then reconstructed.
An overview of existing multilevel topologies and their main operating principles is provided within the thesis. To evaluate proposed SVM techniques adjusted for single-shunt current measurement, a three-level three-phase diode clamped voltage source inverter topology is selected. The main advantages of the selected topology are high efficiency, reduced semiconductor stress, the low capacitance of DC-link capacitors, etc. To reconstruct the three-phase load currents, a single-shunt is positioned inside the middle branch of the DC-link.
An overview of existing modulation techniques for two-level and multilevel inverters is provided within the thesis. To reconstruct three-phase load currents, three SVM methods are proposed within the thesis. Due to the lack of a current measurement window, while the voltage vector is positioned near sector or region boundary areas, additional modifications are required. The first SVM method shifts the SVM signals to ensure the minimum current measurement window needed for measurement with minimum additional vector injection. Such an approach ensures the high modulation index values greater than 0.8 with the smallest current ripple due to the SVM signal symmetry. The second method intentionally injects the colinear voltage vector into the existing vector combination to ensure the minimum time window required for current measurement. As a drawback, a smaller modulation index compared to the first method can be achieved. As an advantage, a very low modulation index of less than 0.2 can be achieved. The third method simplifies the second method by using a single SVM pattern. Such a method can be used only for very low modulation indexes and can be applied for two-level and three-level inverters.
The proposed SVM methods are implemented within the Digital Signal Processor (DSP). Experimental results confirm the proper operation of the proposed methods applied to the three-level diode clamped voltage source inverter.
Ključne besede: single-shunt, three-level inverter, SVM modification, current reconstruction, vector injection
Objavljeno v DKUM: 09.03.2023; Ogledov: 396; Prenosov: 62
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4. MOS-FET as a current sensor in power electronics convertersRok Pajer, Miro Milanovič, Branko Premzel, Miran Rodič, 2015, izvirni znanstveni članek Opis: This paper presents a current sensing principle appropriate for use in power electronics’ converters. This current measurement principle has been developed for metal oxide semiconductor field effect transistor (MOS-FET) and is based on UDS voltage measurement. In practice, shunt resistors and Hall effect sensors are usually used for these purposes, but the presented principle has many advantages. There is no need for additional circuit elements within high current paths, causing parasitic inductances and increased production complexity. The temperature dependence of MOS-FETs conductive resistance RDS−ON is considered in order to achieve the appropriate measurement accuracy. The “MOS-FET sensor” is also accompanied by a signal acquisition electronics circuit with an appropriate frequency bandwidth. The obtained analogue signal is therefore interposed to an A-D converter for further data acquisition. In order to achieve sufficient accuracy, a temperature compensation and appropriate approximation is used (RDS−ON = RDS−ON(Vj)). The MOS-FET sensor is calibrated according to a reference sensor based on the Hall-effect principle. The program algorithm is executed on 32-bit ARM M4 MCU, STM32F407.
Ključne besede: power electronics, converters, MOS-FET, current measurement, thermal model
Objavljeno v DKUM: 22.06.2017; Ogledov: 1467; Prenosov: 365
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5. Operation impact of the ICEM power testing laboratory on the Slovenian power networkMarjan Stegne, Jože Pihler, Jože Voršič, 2007, izvirni znanstveni članek Ključne besede: močnostni laboratoriji, močnostna preskušanja, preskusni tokovi, padci napetosti, simulacije, elektroenergetsko omrežje, high-power laboratory, power testing, test current, voltage drop, simulation, power system
Objavljeno v DKUM: 10.07.2015; Ogledov: 1912; Prenosov: 39
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8. Zeta potential determination of polymeric materials using two differently designed measuring cells of an electrokinetic analyzerHermina Bukšek, Thomas Luxbacher, Irena Petrinić, 2010, izvirni znanstveni članek Opis: The so-called zeta potential can be determined through electrokinetic measurements and indicates the status regarding surface charges along the interface between solids and liquids. Surface charge gives us information about the condition, quality, and characteristics of a macroscopic surface in the polar medium. In our study the zeta potential was determined using a 'SurPASS' electrokinetic analyzer based on the streaming current and streaming potential measurements. The aim of the research was to compare the results of two differently designed measuring cells ('Adjustable Gap Cell' and 'Clamping Cell') but operating on the same principle. In order to investigate this problem, the zeta potential was determined for the three polymeric materials: poly(ethylene terephthalate) foil, thin-film polyamide composite membranes for nanofiltration and reverse osmosis. The results obtained with 'Clamping Cell' versus 'Adjustable Gap Cell' showed differences in zeta potential, where the 'Adjustable Gap Cell' gave more reproducible results. One reason for this behaviour could be the different geometries of the streaming channels. A more likely reason is the design of the 'Clamping Cell', that requires a sample size larger than necessary for zeta potential determination.
Ključne besede: electrical double layer, zeta potential, electrokinetic analyser, streaming current potential, polymeric materials
Objavljeno v DKUM: 31.05.2012; Ogledov: 3316; Prenosov: 129
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10. PROS AND CONS OF THE CURRENCY BOARD-CASE OF BULGARIAZornitsa Daskalova Krasimirova, 2010, delo diplomskega seminarja/zaključno seminarsko delo/naloga Opis: The investigated topic is such that retains its importance throughout time as it tends to be a good lesson on the misconduct of monetary policy of one country during turbulent and drastic economic and political changes, and the following actions meant to bridle back the economy to its stable performance. The focus of this thesis is of Bulgaria and the way it coped with the galloping hyperinflation in the late nineties of the previous century.
My main motivation and reason behind writing this thesis is first the fact that I am Bulgarian, who has the language know-how and the access to vaster sources describing and delving into the investigated topic. Furthermore, I am familiar with the culture that stands behind and affects in many aspects the decisions that happened to be decisive for those tumultuous times, thus I can give a better insight on the topic to the people observing from abroad. Therefore, I have attempted to give an objective and straightforward analysis and explanation behind the history, structure, past and present challenges of the Bulgarian currency board, and its advantages and disadvantages that it has had in the country. I hope the information is clear and useful enough to create awareness in the other EU countries of the main arguments and disputes surrounding this pegged system and in general help toward forming a basis for a proper decision making.
There were some limitations in the course of work; i.e denied access to some of the materials and articles as they are available only when accessed from Bulgaria. Despite the difficulties, I managed to get a broad scope of sources- domestic and international ones, to come up with the final coherent piece of work that I have the honour to present to you. Further down, in the Introduction part, I have elaborated deeper on the way how I have prepared and structured the investigated topic of my bachelor thesis.
Ključne besede: currency board, “orthodox” currency board, pegged currency, anchor currency, monetary policy, Bulgarian monetary policy, economic crisis, financial crisis, inflation, depreciation, current account deficit, ERM 2, Bulgarian politics, Bulgaria, EU, IMF, Bulgarian National Bank, Eurozone
Objavljeno v DKUM: 05.05.2011; Ogledov: 3012; Prenosov: 133
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