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 Radiation mitigation techniques for EIVE satellite mission payload computer(2022) Bischof, TobiasDie Satellitenmission ’Exploratory In-orbit Verification of an E/W-band link’ (EIVE) demonstriert die breitbandige Datenübertragung von der niedrigen Erdumlaufbahn zur Erde mit Datenraten von bis zu 15 Gbits−1.Umden korrekten Betrieb des EIVE-Satelliten sicherzustellen und die Strahlungseinwirkungen auf die Schaltung von EIVE zu reduzieren, sind Strahlungsminderungstechniken für den Nutzlastcomputer erforderlich. Daher untersucht diese Arbeit die Strahlungsminderungstechniken, Mechanismen für den Schutz des FPGA-Konfigurationsspeichers und implementiert robuste Kodierungsmechanismen der E/W-Band-Validierungsdateien. Die Untersuchungen und die implementierten Ansätze stehen dabei im Einklang mit den Leistungsbeschränkungen der Mission.Item Open Access Power quality mitigation via smart demand-side management based on a genetic algorithm(2022) Eisenmann, Adrian; Streubel, Tim; Rudion, KrzysztofIn modern electrical grids, the number of nonlinear grid elements and actively controlled loads is rising. Maintaining the power quality will therefore become a challenging task. This paper presents a power quality mitigation method via smart demand-side management. The mitigation method is based on a genetic algorithm guided optimization for smart operational planning of the grid elements. The algorithm inherits the possibility to solve multiple, even competing, objectives. The objective function uses and translates the fitness functions of the genetic algorithm into a minimization or maximization problem, thus narrowing down the complexity of the addressed high cardinality optimization problem. The NSGA-II algorithm is used to obtain feasible solutions for the auto optimization of the demand-side management. A simplified industrial grid with five different machines is used as a case study to showcase the minimization of the harmonic distortion to normative limits for all time steps during a day at a specific grid node, while maintaining the productivity of the underlying industrial process.Item Open Access Digital pre- and post-equalizers for in-car data transmission over plastic optical fibers(2014) Voigt, Yixuan; Speidel, Joachim (Prof. Dr.-Ing. )Lately, a hot topic in the automobile industry is the development of the in-vehicle infotainment communication network based on the media oriented system transport (MOST) standard, where a cost-effective optical physical layer composed of light emitting diodes (LED), plastic optical fibers (POF) and positive-intrinsic-negative photodiodes (PIN PD) is used by the in-car network. The latest MOST150 standard has specified a transmission speed of 150 Mbit/s, while the next MOST generation is targeted at multi-Gbit/s. Obviously, the very limited bandwidth of the current physical layer will weigh on the future MOST generations. However, it is important to evaluate the potential of the current physical layer, for the reason that the car-manufacturers may continue using the low-cost and easily operable POFs and LEDs. The objective of this dissertation is to increase the data-rate for the next MOST generation from 150 Mbit/s to 2 ∼ 3 Gbit/s, based upon the current MOST150 optical physical layer. The main emphasis lies in investigating electronic signal processing techniques to detect the multi-level pulse-amplitude modulated (MPAM) signal transmitted through the noisy dispersive POF-based optical channel. To be specific, four different transmission schemes are studied respectively: the post-equalization scheme using either linear or decision-feedback equalizer, the joint pre- and post-equalization scheme, the non-linear Tomlinson-Harashima precoding (THP) scheme, and the bidirectional decision feedback equalization (BiDFE) scheme. In the BiDFE scheme, a novel trellis-based BiDFE (TB-BiDFE) equalizer is proposed. Their performances are investigated by means of theoretical analysis and computer simulations. As will be shown, with the help of electronic equalizers and error-correcting code, the final bitrate is able to reach 3 Gbit/s over a 10 m standard step-index POF, despite the use of a low-cost LED transmitter.Item Open Access Novel characterization techniques for the study of the dynamic behavior of silicon carbide power MOSFETs(2022) Salcines, Cristino; Kallfass, Ingmar (Prof. Dr.-Ing.)This dissertation provides insight into the dynamic behavior of SiC power MOSFETs from their inherent static IV and CV characteristics. While conventional dynamic measurements extracted from a DPT or a similar dynamic test-bench yield accurate quantitative data, the static IV and CV characteristics of a power semiconductor device offer more qualitative information to delve into the root mechanisms responsible for its dynamic behavior. Conventional characterization techniques are limited to power levels way below those which the power device withstands in the application. As a result, the static IV and CV characteristics attained by available measurement solutions are reduced to a limited scope of bias conditions insufficient to infer information about the dynamic behavior of the power device. This work tackles this gap and proposes novel measurement techniques that enable the characterization of the static IV and CV characteristics of SiC power MOSFETs at the full range of bias conditions the power device goes through in the application. Iso-thermal IV characteristics of a commercially available SiC power MOSFET are measured up to 40 kW power (instantaneous 50 A and 800 V) at junction temperatures ranging from 25°C to 175 °C. The CV characteristics are mapped at drain-source and gate-source bias combinations of VDS = 0 - 40 V and VGS = 0 - 20 V, respectively, at junction temperatures ranging from 25°C to 150 °C. The results of these measurements reveal unique insights into the electrical characteristics of SiC power MOSFETs which impact their performance in the application and explain unclear phenomena observed in their dynamic behavior. On the one hand, the intrinsic capacitances of the SiC power MOSFET extend their non-linearity, function of both VGS and VDS, to the saturation region of the power device. Moreover, they are also affected by the junction temperature of the power device. The impact of these in the voltage commutation speed of the device under different switching conditions is thoroughly analyzed in the thesis. On the other hand, the IV characteristics of the SiC power MOSFET reveal the existence of short channel effects that drastically affect the transconductance of the power device in its high voltage saturation region. Furthermore, the measurements show a positive temperature coefficient of the drain current in the high voltage saturation region of the SiC power device, attributed to the density of trap energy states in the SiC/SiO2 interface. These effects effectively lower the plateau voltage of the device and lead to faster current commutation speeds in the application than those expected from the datasheet values. The insights revealed by the proposed characterization techniques are intended to help fine-tune semiconductor technology processes and improve the accuracy of simulation models to achieve a higher grade of optimization in the design of future SiC-based energy conversion circuits.Item Open Access Digital self-interference cancellation using FPGA for in-band full-duplex radios(2023) Roge, Swapnil SunilConventionally, the transmission and the reception of signals in a particular wireless communication system is performed using the half-duplex method, wherein the transmitter and the receiver signals are either time-multiplexed or frequency-multiplexed. However, in case of an in-band full-duplex system, the bidirectional communication of signals is performed simultaneously in the same frequency band, which improves the spectral efficiency of these systems by a factor of two as compared to the traditional half-duplex systems. Therefore, the in-band full-duplex communication systems can double the data rate provided by the half-duplex communication systems, thereby making the former a matter of interest across the wireless research community. However, the in-band full-duplex systems have theirownset of disadvantages. The major challenge is the self-interference imposed by the high-power transmitter signal on the incoming low-power receiver signal, which further degrades the latter and negatively impacts its estimation. Out of the various methodologies to mitigate the self-interference from the receiver signal, this work focuses on the digital self-interference cancellation techniques. In this thesis, the effects of the self-interference signal on the receiver signal are examined. Furthermore, the different digital self-interference cancellation methods employed for suppressing the self-interference are comparatively analysed. Finally, the field-programmable gate array based implementation of the various digital self-interference cancellation algorithms and their respective performance results are presented as well.Item Open Access FPGA implementation of an energy-efficient real-time image compression algorithm for the EIVE satellite mission(2021) Wiewel, FlorianIn this thesis three commonly used image compression algorithms are analyzed in terms of computational complexity, rate-distortion performance and execution time in order to find the most suitable basis for the implementation of an energy-efficient and real time image compression algorithm for the EIVE satellite mission. The selected algorithm is than modified to reduce its complexity while keeping its performance at a comparable level to the base algorithm. Afterwards the algorithm is implemented in the programmable logic part of a Xilinx Zynq UltraScale+ MPSoC device. Finally, the performance of the algorithm implemented on hardware is determined and compared to the performance of an implementation using a high-level scripting language and the performance of its base algorithm.Item Open Access Frequency-agile bandpass delta-sigma modulator for microwave transmitters(2019) Schmidt, Martin; Berroth, Manfred (Prof. Dr.-Ing.)A large part of the power consumption for mobile communications can be allotted to power amplifiers. Class-S power amplifiers promise a very high power efficiency, especially for modern communication standards. An important part of the Class-S power amplifier is the modulator that converts the input signal into a binary pulse sequence. A switching-mode power amplifier can amplify this sequence efficiently. This work covers the implementation of such a modulator as a bandpass delta-sigma modulator. The goal is an output signal which fulfills the requirements of the mobile communication standard UMTS (Universal Mobile Telecommunications System) in a frequency range which is as large as possible. The thesis starts with the basics of mobile communications, with power amplifiers and with the requirements for the transmit signals for UMTS. Based on a discrete-time lowpass delta-sigma modulator, a continuous-time bandpass delta-sigma modulator is derived. Due to project constraints a bipolar technology is selected for the implementation. Current-mode logic is used for amplifiers and latches in the digital part. Different circuits for a transconductance amplifier are derived and evaluated. A novel, switchable capacitance is presented. With the switchable capacitance a large frequency range of the modulator becomes possible. Two modulators are designed. The first modulator is not tunable and fulfills the UMTS requirements for the downlink channel from the base station to the user equipment at a signal frequency of 2.2 GHz. The second modulator uses the switchable capacitance and covers a frequency range between 1.55 GHz and 2.45 GHz. It fulfills the UMTS requirements within the frequency range between 1.8 GHz and 2.45 GHz.Item Open Access Channel estimation and precoding in closed-loop distributed multi-antenna systems(2015) Wild, Thorsten; Speidel, Joachim (Prof. Dr.-Ing.)Today’s wireless cellular systems are limited by inter-cell interference. Coordinated multi-point transmission and reception (CoMP) is a promising approach to cope with this problem. Here, multiple base stations act as a distributed antenna system, exchanging coordination information and potentially user data via backhaul in order to reduce this interference, increasing spectral efficiency and generating a more homogeneous user experience throughout the entire cell, especially at the currently weak cell edges. This dissertation aims at enabling coordinated multi-point systems by dealing with its current realization challenges. Accurate channel knowledge is required both at transmitter and receiver side in order to realize the CoMP gains. Hence, practical channel estimation algorithms are investigated and developed in order to get as accurate channel knowledge as possible with manageable computational complexity under realistic system operation points. Especially the often neglected obtainment of statistical parameter knowledge is included here, which is challenging under dynamic user scheduling conditions. A multi-user multi-cell channel estimator is provided which, even for larger number of coordinated cells, can get receiver performance fairly close to performance with perfect channel knowledge. Furthermore, different downlink precoding and receive combining strategies are compared against each other under imperfect channel knowledge. As the number of coordinated cells - the cluster size - is limited in practice, mobiles at cluster edges suffer from inter-cluster interference. A novel patented precoding and control signaling scheme is introduced in order to deal with the inter-cluster interference.Item Open Access Optimized planning of distribution grids considering grid expansion, battery systems and dynamic curtailment(2021) Laribi, Ouafa; Rudion, KrzysztofThe increasing integration of renewable energies into the grid is calling for the expansion of the power transport capacities in the distribution system. Yet, the expansion of the grid could require long authorization procedures and cannot be always asserted. Therefore, a higher utilization of the existing grid is becoming increasingly necessary today. This paper proposes a new time series-based planning method for distribution systems using classical grid expansion instruments as well as innovative planning instruments such as battery storage systems (BSS) and dynamic power curtailment (DPC). These planning instruments could be applied individually or combined. The aim of the BSS and DPC application is to enable a higher utilization of the grid at minimal costs. The proposed method, which has been implemented as an automated planning algorithm, determines the cost optimal grid reinforcement measures that ensure the prevention of prognosticated congestions in the considered grid. Furthermore, the application of the proposed planningmethod on the considered power system has proven that a combination of BSS and grid expansion could be more economical than an individual application of BSS and grid expansion.Item Open Access Pressure characteristics and chemical potentials of constrained LiFePO4/C6 cells(2018) Singer, Jan Patrick; Kropp, Timo; Kuehnemund, Martin; Birke, Kai PeterConstraining lithium-ion cells increases the cyclic lifetime. However, depending on an expected volume expansion during charge and discharge cycling, defining the optimal constraining pressure range is not straightforward. In this study, we investigate a lithium iron phosphate/graphite pouch cell at four initial constraining pressure levels. As a function of C-Rate, the thermodynamic principle of the non-monotonic pressure curve during full charge and discharge cycles is evaluated. Using the rubber balloon model to calculate the chemical potential of lithium iron phosphate and discussing the relationship between the chemical potential and pressure, we illustrate the pressure curve qualitatively. By applying differential pressure analysis, we evaluate the resulting pressure curves of a single graphite stage. Approaching a fundamental understanding of reduced cycling lifetime of full cells with unknown material composition, we allocate the stages and stage transitions of graphite as well as the phase transition of lithium iron phosphate. Local extreme values in the differential pressure analysis indicate phase and stage transitions. These values can identify critical operating conditions that should be considered for defining the optimum initial constraining pressure range.