Iskanje po katalogu digitalne knjižnice

Opis: Gallium nitride (GaN) technology has emerged as a transformative solution in the semiconductor industry due to its exceptional performance in highpower and high-frequency applications. With its inherent radiation resilience, GaN is particularly suited for environments such as space electronics and nuclear instrumentation. While static parameter testing under radiation has been extensively studied, dynamic parameter degradation—including propagation delays, rise/fall times, and efficiency losses—remains underexplored. These dynamic characteristics are useful for applications requiring precise timing, signal integrity, and rapid response, such as satellite communication and nuclear systems. This study evaluates the radiation resilience of three commercially available GaN transistors during a 100-krad (Si) Co-60 gamma irradiation campaign, with a focus on both static and dynamic parameters. Static parameters, such as threshold voltage and ON-state resistance, exhibited minimal degradation, while a larger change was observed in gate current. In contrast, dynamic parameters revealed smaller changes, including faster propagation delays and reduced efficiency, with variability observed across device types. The findings support a device-specific co-design of transistors and driver electronics for radiation-tolerant power stages
Ključne besede: Co-60 gamma, drain current, gallium nitride, GaN, gamma irradiation, gate current, in situ measurements, propagation delay, rise and fall times, voltage threshold
Objavljeno v DKUM: 17.10.2025; Ogledov: 0; Prenosov: 6
Celotno besedilo (1,97 MB)

Opis: This paper analyzes the influence of inverter-interfaced distributed generations’ (IIDGs) response during transmission network faults. The simplest and safest solution is to switch IIDGs off during network faults without impacting the network voltages. A more elaborate and efficient concept, required by national grid codes, is based on controlling the IIDGs’ currents, involving positive- and negative-sequence voltage measured at the connection point. In this way the magnitude and phase of the injected currents can be adjusted, although the generated power will depend on the actual line voltages at the connection point. Therefore, an improved concept is proposed to adjust IIDGs’ fault current injection through the required active and reactive power, employing the same voltage characteristics. The proposed, i.e., power-based concept, is more definite than the currentbased one, since the required power will always be generated. The discussed concepts for the fault current injection by IIDGs were tested in different 110-kV networks with loop and radial topologies, and for different short-circuit capabilities of the aggregated network supply. Based on extensive numerical calculations, the power-based concept during transmission networks faults generates more reactive power compared to the current-based concept. However, the voltage support by IIDGs during transmission networks faults, regardless of the concept being used, is influenced mainly by the short-circuit capability of the aggregated network supply. As regards distance protection operation, it is influenced additionally by the network topology, i.e., in radial network topology, the remote relay’s operation can be delayed due to a largely seen impedance.
Ključne besede: distributed generation, fault current injection, voltage support, distance protection, transmission network faults
Objavljeno v DKUM: 16.06.2025; Ogledov: 0; Prenosov: 8
Celotno besedilo (1,39 MB)
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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: 10
Celotno besedilo (5,06 MB)
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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: 85
Celotno besedilo (12,21 MB)

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: 41
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