05 Fakultät Informatik, Elektrotechnik und Informationstechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6
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Item Open Access Precise voltage measurement for power electronics with high switching frequencies(2018) Nitzsche, Maximilian; Zehelein, Matthias; Tröster, Nathan; Roth-Stielow, JörgIn this paper different approaches in precise measurement of gate voltages as well as drain-source voltages of modern SiC and GaN transistors are compared. An approach to calculate the necessary bandwidth of a voltage probe to reproduce the voltage slope is presented. Furthermore, state-of-the-art voltage probes are compared in means of bandwidth, common mode reduction and response on EMI.Item Open Access Informationsmodelle mit intelligenter Auswertung für den Digitalen Zwilling(2020) Müller, Manuel; Ashtari Talkhestani, Behrang; Jazdi, Nasser; Rosen, Roland; Wehrstedt, Jan Christoph; Weyrich, MichaelDie zunehmende Komplexität hochautomatisierter Systeme bringt neue Herausforderungen bei der Verwaltung ihrer Modelle entlang des gesamten Lebenszyklus des Systems mit sich - von der Kundenakquise über Engineering und Rekonfiguration bis hin zum Systemrecycling. Der Digitale Zwilling ist ein Konzept, welches über den gesamten Lebenszyklus eines Assets hinweg das Management dieser Modelle sicherstellen kann. Es unterstützt jedoch nicht die automatisierte Modellerweiterung. Hier setzt diese Arbeit an. Die Anreicherung des Digitalen Zwillings um Modellverständnis und KI-Algorithmen zur eigenständigen Modellerweiterung bildet die Grundlager des vorgestellten Konzepts. Über die intelligente Auswertung der Informationsmodelle -angereichert mit aktuellen Prozessdaten- erkennt der Digitale Zwilling, wenn Modelle an ihre Grenzen stoßen. Zwei mögliche Ursachen für diesen Sachverhalt werden genauer betrachtet: (1) es fehlt eine Fähigkeit oder Information (2) der Gültigkeitsbereich des Modells wurde verlassen. Für beide Zustände wird ein Verfahren vorgeschlagen, welches auf Basis kooperativer Information aus dem Wertschöpfungsnetzwerk automatisiert eine Lösung findet. Die Evaluierung des Konzepts anhand eines Szenarios aus der Logistik und aus der Produktion liefert vielversprechende Ergebnisse.Item Open Access Einfluss der Abschlussimpedanz von Hochvoltkabeln auf Funkstörgrößen in elektrisch angetriebenen Kraftfahrzeugen(2012) Reuter, Martin; Waible, Manuel; Tenbohlen, Stefan; Köhler, WolfgangIn diesem Beitrag wird die Frage untersucht, welche Auswirkung die Fehlanpassung von Kfz-Hochvoltkabeln auf EMV-Störgrößen in der Komponentenmessung nach CISPR 25 hat.Item Open Access Assessment of overload capabilities of power transformers by thermal modelling(2011) Schmidt, Nicolas; Tenbohlen, Stefan; Skrzypek, Raimund; Dolata, BartekThis contribution presents an approach to determine the overload capabilities of oil-cooled power transformers depending on the ambient temperature. For this purpose the investigated method introduces a simplified, empirical based thermal model that predicts changes in oil temperature with high accuracy. This model considers the entire transformer as a single, homogenous tempered body with a certain thermal capacity. All electrical losses are perceived as an input of equally distributed heat and assumed to be the sum of the load and no-load losses given by the transformer design. In contrary to earlier approaches the heat exchange with the ambience is modelled as a complex function depending first of all on the temperature difference between the transformer and its surroundings. Furthermore, the loading rate, material properties, levels of temperatures and emerging temperature gradients are taken into account as influencing factors determining the heat exchange. To display the behaviour of a specific transformer, the model employs several empirical factors. For determination of these empirical factors an evaluation time of two to four representative weeks of transformer operation is found to be sufficient. To validate the created model and test its operational reliability, measuring data from several ONAN- and ONAF-transformers are consulted. These data sets comprise the top oil and ambient temperature as well as the loading rate and the status of the cooling system. Furthermore, the corresponding name plate data is integrated. Subsequently to the calculation of the top oil temperature, the maximum constant loading rate resulting in a hot-spot temperature below critical level is determined based upon the remarks of IEC 60076 - 7 [1]. Finally, a characteristic linear function for each investigated transformer displaying the maximum loading rate depending solely on the ambient temperature is derived. In case of the investigated ONAN- and ONAF-transformers within a power range of 31.5 - 63 MVA, significant overload potentials could be disclosed.Item Open Access Comprehensive comparison of a SiC MOSFET and Si IGBT based inverter(2019) Nitzsche, Maximilian; Cheshire, Christoph; Fischer, Manuel; Ruthardt, Johannes; Roth-Stielow, JörgThe investment which is necessary to replace Si IGBTs with SiC MOSFETs in medium to high power DC-AC inverters needs to be balanced carefully against the advantages SiC offers. This paper compares a 20 kW Si IGBT inverter with a 20 kW SiC MOSFET inverter. The power semiconductor components are operated identically in a modular half bridge module to ensure comparability. Thereby the measurement of the switching losses is explicitly not the focus but the overall efficiency while taking volume, current ripple, switching frequency and inductance into account. The limits of reasonable operating range shall be evaluated and an overview on the benefits of SiC on system level will be given.Item Open Access Suitability of ultra high frequency partial discharge measurement for quality assurance and testing of power transformers(2013) Tenbohlen, Stefan; Siegel, Martin; Beltle, Michael; Reuter, MartinWell known reasons for local failures in power transformers are caused by partial discharges (PD) in the electric insulation. Continuous deterioration over time increases the defect which finally can lead to a breakdown of the entire insulation. The importance of PD measurement is accommodated by standardized electrical measurement according to IEC 60270 [1] which is required for acceptance certificates at routine testing. Therefore, the apparent charge QIEC has become an important value for transformer quality. Since a couple of years, alternative measurement methods for PD are used. Originally developed for gas insulated systems [2], [3], ultra high frequency (UHF) measurement found its way into transformer diagnosis over the last years [4]. To become an accepted quality factor, UHF has to be proven a reliable testing method, which can bear up against electrical measurements. Therefore, the general physics of UHF PD has to be considered at first. Ultra-high-frequency antennas measure electromagnetic emissions of PD directly in-oil inside a transformer. It becomes apparent, that UHF measurement usually is advantageous concerning external disturbances. Compared to the electric measurement, the UHF method is robust against external signals [5], which makes it suitable for both, offsite measurement at routine testing under laboratory conditions with low ambient noise and onsite, e.g. after transportation and installation of transformers with usually high noise levels. These considerations make the UHF method interesting as supplement for transformer routine tests. Therefore, a sensor calibration or at least a validation of its sensitivity is required [6] comparable to the electrical measurement. To provide profound knowledge of the equipment, the antenna factor (AF) of the UHF sensor needs to be determined under inside-transformer conditions. This contribution shows the determination of the UHF sensor’s AF using a Gigahertz-Transversal-Electro-Magnetic Setup (GTEM cell). To meet inside-transformer conditions, an oil-filled GTEM cell is required for correct permittivity. Correction factors can then be introduced to minimize measurement errors and to establish better comparability of different UHF sensors. Hence, a standard test setup can be defined.Item Open Access Influence of termination impedance on conducted emissions in automotive high voltage networks(2012) Reuter, Martin; Tenbohlen, Stefan; Köhler, WolfgangThis contribution investigates the effect of changed network topologies within HV systems on component level EMC tests. Therefore the recent state of art in component level testing is presented and the differences of LV and HV network topologies are discussed. An adaption of the component level test setup for HV components is introduced and a minimized HV system investigated. Results of a case study on an inverter for a hybrid car are presented and the impact of the measurements in the design of HV systems will be discussed.Item Open Access Water saturation limits and moisture equilibrium curves of alternative insulation systems(2011) Tenbohlen, Stefan; Jovalekic, Mark; Bates, Lisa; Szewczyk, RadoslawA method developed for establishing moisture equilibrium curves for any combination of liquid and solid insulation is presented in this paper. Moisture saturation curves for natural and synthetic esters have been presented in the temperature range up to 140°C together with curve for mineral oil as a reference. Sorption isotherms have been established for cellulose based and aramid fiber based materials. Eventually, the moisture equilibrium diagrams have been created for given combinations of solids and liquids. Moisture equilibrium curves have been created for combinations of mineral oil and ester fluids with aramid fiber based papers and boards, as they are commonly used in alternative insulation systems. The new curves give information on moisture distribution within the alternative insulation systems and may be critical for setting the material choices, design rules and maintenance guidelines for equipment using these combinations. Only then the materials could be used optimally and their specific characteristics could bring full range of benefits to the equipment. Also the condition monitoring and diagnostics for the purpose of asset management will be more reliable when these new characteristics are used. It has been observed that insulation components made of aramid insulation may have lower water content comparing to cellulose based conventional materials at the same water content measured in dielectric liquid. As a result, the performance of aramid insulation components may be less sensitive to moisture in oil (aging processes, dielectric strength, partial discharge performance) comparing to conventional systems based on cellulose.Item Open Access Power electronic systems for electric aircraft(2020) Roth-Stielow, Jörg; Nitzsche, MaximilianElectric aviation poses several unique challenges which influence the development of power electronic systems for electric flight. This presentation focuses on the aspects of redundancy, semiconductor material (especially silicon carbide SiC), electromagnetic compatibility and reliability. These topics are discussed in relation to recent developments regarding electric aviation such as e.g. distributed electric propulsion (DEP) and modularity of power electronic systems.Item Open Access Impedance analysis of automotive high voltage networks for EMC measurements(2011) Reuter, Martin; Tenbohlen, Stefan; Köhler, Wolfgang; Ludwig, A.This paper deals with a method of determining the high-frequency impedances of automotive HV power networks. A Vector Network Analyzer (VNA) is used to measure Scattering parameters of different HV power cables and an automotive Li-Ion accumulator battery. Matrix conversions allow calculating an impedance network, which is able to represent an automotive HV networks.