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Ghana suffers from frequent power outages, which can be compensated by off-grid energy solutions. Photovoltaic-hybrid systems become more and more important for rural electrification due to their potential to offer a clean and cost-effective energy supply. However, uncertainties related to the prediction of electrical loads and solar irradiance result in inefficient system control and can lead to an unstable electricity supply, which is vital for the high reliability required for applications within the health sector. Model predictive control (MPC) algorithms present a viable option to tackle those uncertainties compared to rule-based methods, but strongly rely on the quality of the forecasts. This study tests and evaluates (a) a seasonal autoregressive integrated moving average (SARIMA) algorithm, (b) an incremental linear regression (ILR) algorithm, (c) a long short-term memory (LSTM) model, and (d) a customized statistical approach for electrical load forecasting on real load data of a Ghanaian health facility, considering initially limited knowledge of load and pattern changes through the implementation of incremental learning. The correlation of the electrical load with exogenous variables was determined to map out possible enhancements within the algorithms. Results show that all algorithms show high accuracies with a median normalized root mean square error (nRMSE) <0.1 and differing robustness towards load-shifting events, gradients, and noise. While the SARIMA algorithm and the linear regression model show extreme error outliers of nRMSE >1, methods via the LSTM model and the customized statistical approaches perform better with a median nRMSE of 0.061 and stable error distribution with a maximum nRMSE of <0.255. The conclusion of this study is a favoring towards the LSTM model and the statistical approach, with regard to MPC applications within photovoltaic-hybrid system solutions in the Ghanaian health sector.
Fundamental hydrogen storage properties of TiFe-alloy with partial substitution of Fe by Ti and Mn
(2020)
TiFe intermetallic compound has been extensively studied, owing to its low cost, good volumetric hydrogen density, and easy tailoring of hydrogenation thermodynamics by elemental substitution. All these positive aspects make this material promising for large-scale applications of solid-state hydrogen storage. On the other hand, activation and kinetic issues should be amended and the role of elemental substitution should be further understood. This work investigates the thermodynamic changes induced by the variation of Ti content along the homogeneity range of the TiFe phase (Ti:Fe ratio from 1:1 to 1:0.9) and of the substitution of Mn for Fe between 0 and 5 at.%. In all considered alloys, the major phase is TiFe-type together with minor amounts of TiFe2 or \b{eta}-Ti-type and Ti4Fe2O-type at the Ti-poor and rich side of the TiFe phase domain, respectively. Thermodynamic data agree with the available literature but offer here a comprehensive picture of hydrogenation properties over an extended Ti and Mn compositional range. Moreover, it is demonstrated that Ti-rich alloys display enhanced storage capacities, as long as a limited amount of \b{eta}-Ti is formed. Both Mn and Ti substitutions increase the cell parameter by possibly substituting Fe, lowering the plateau pressures and decreasing the hysteresis of the isotherms. A full picture of the dependence of hydrogen storage properties as a function of the composition will be discussed, together with some observed correlations.
Im Rahmen dieser Arbeit wurden Resorcinol-Formaldehyd-Aerogele zur Anwendung in Kreislaufwärmerohren (LHP) als Dochtmaterial entwickelt. Aerogele als Dochtmaterial bilden aufgrund der hohen Porosität und der effektiven Kapillarwirkung eine gute Grundvoraussetzung für Stoff- und Wärmetransport. Diese Eigenschaften können zu einer Verbesserung der Kühlleistung einer Wärmepumpe beitragen. Dazu wurden Aerogele in Dochtform synthetisiert und anschließend erfolgte die Bestimmung der skelettalen Dichte, umhüllenden Dichte, Porosität und Gaspermeabilität. Zusätzlich wurde ein Test zum Schwellverhalten entwickelt. Außerdem wurden die Proben zur Fa. Allatherm gesendet, um die Anforderungen an die entwickelten RFAerogele in Dochtform zu prüfen. Die mechanische Bearbeitbarkeit der Aerogele konnte verbessert werden. Die Porosität und die Gaspermeabilität der untersuchten Aerogele lagen in einem optimalen Bereich. Nur die Durchgangsporengröße der Aerogele, die mittels Gasblasendruck-Analyse bestimmt wurde, benötigt weitere Rezeptentwicklungen und Messungen, um die größte Durchgangspore in Richtung 1 µm einzugrenzen.
The simultaneous operation of multiple different semiconducting metal oxide (MOX) gas sensors is demanding for the readout circuitry. The challenge results from the strongly varying signal intensities of the various sensor types to the target gas. While some sensors change their resistance only slightly, other types can react with a resistive change over a range of several decades. Therefore, a suitable readout circuit has to be able to capture all these resistive variations, requiring it to have a very large dynamic range. This work presents a compact embedded system that provides a full, high range input interface (readout and heater management) for MOX sensor operation. The system is modular and consists of a central mainboard that holds up to eight sensor-modules, each capable of supporting up to two MOX sensors, therefore supporting a total maximum of 16 different sensors. Its wide input range is archived using the resistance-to-time measurement method. The system is solely built with commercial off-the-shelf components and tested over a range spanning from 100Ω to 5 GΩ (9.7 decades) with an average measurement error of 0.27% and a maximum error of 2.11%. The heater management uses a well-tested power-circuit and supports multiple modes of operation, hence enabling the system to be used in highly automated measurement applications. The experimental part of this work presents the results of an exemplary screening of 16 sensors, which was performed to evaluate the system’s performance.
Die Matrix ist eine der entscheidenden Hauptkomponenten oxidkeramischer Faserverbundwerkstoffe (Ox-CMCs). Im Herstellungsprozess stellen typischerweise keramische Schlicker die Ausgangsbasis für die spätere Ausbildung der Matrix im CMC dar. Die Aufbereitungsart und -dauer keramischer Schlicker haben dabei wesentlichen Einfluss auf die Verarbeitungseigenschaften des Schlicker und die Eigenschaften der späteren Matrix. In dieser Arbeit wird der Einfluss verschiedener Aufbereitungsparameter auf die Schlickereigenschaften und das Sinterverhalten untersucht. Dazu werden zwei Aufbereitungsverfahren, Planeten- und Ringspaltkugelmühle, eingesetzt sowie Mahlkörpermaterialien (Al2O3 und ZrO2), Additive (Glycerin) und Aufbereitungsdauer gezielt verändert. Es wurden Partikelgrößenverteilung, Rheologie und Feststoffgehalt ermittelt, sowie die Mikrostruktur und Schwindung analysiert. Im Vergleich zur Ringspaltkugelmühle konnte eine definierte Partikelgrößenverteilung mit der Planetenkugelmühle bereits nach einem Drittel der Zeit erreicht werden. Zusätzlich wird mit zunehmender Mahldauer auch die Neigung zur Thixotropie beobachtet. Bei zu langer Aufbereitungsdauer, aber fast identischer Partikelgrößenverteilung führt dieser Effekt zu Problemen bei der Herstellung von Ox-CMCs über das Wickelverfahren. Insgesamt ist dieses Verhalten stärker ausgeprägt bei Schlickern mit wenig Glyceringehalt. Gleichzeitig werden bei Schlickern mit gleichen Feststoffanteilen, aber höherem Glycerinanteil niedrigere Viskositäten gemessen. Mit zunehmendem Glyceringehalt steigt der Gewichtsverlust, jedoch nimmt die Sinterschwindung der Proben ab. Die in dieser Arbeit dargestellten Ergebnisse können für die Optimierung des Wicklungsprozesses zur CMC-Herstellung genutzt werden.
The aim of this thesis is to investigate and optimize the camera system which is used for Filtered Rayleigh Scattering (FRS) measurement systems. Theoretical considerations about the integration of interference filters explain state-of-the-art accuracy limitations. Based on that promising modifications of the established FRS system are presented: test results indicate that frequency fringes - artifacts distorting FRS scans - are minimized by positioning the spectral bandpass filter between camera and first lens. As a tradeoff, the signal level decreases by 70 % to 75% depending on the beam path through the molecular filter. Furthermore, reference measurements without a bandpass filter account for a non-negligible iodine fluorescence background of about 1% of typical signal levels. All things considered following these results FRS systems can now be systematically optimized towards specific measurement tasks.
The need for innovation around the control functions of inverters is great. PV inverters were initially expected to be passive followers of the grid and to disconnect as soon as abnormal conditions happened. Since future power systems will be dominated by generation and storage resources interfaced through inverters these converters must move from following to forming and sustaining the grid. As “digital natives” PV inverters can also play an important role in the digitalisation of distribution networks. In this short review we identified a large potential to make the PV inverter the smart local hub in a distributed energy system. At the micro level, costs and coordination can be improved with bidirectional inverters between the AC grid and PV production, stationary storage, car chargers and DC loads. At the macro level the distributed nature of PV generation means that the same devices will support both to the local distribution network and to the global stability of the grid. Much success has been obtained in the former. The later remains a challenge, in particular in terms of scaling. Yet there is some urgency in researching and demonstrating such solutions. And while digitalisation offers promise in all control aspects it also raises significant cybersecurity concerns.
Further development on globally convergent algorithms for solution of stationary network problems is presented. The algorithms make use of global non-degeneracy of Jacobi matrix of the system, composed of Kirchhoff's flow conservation conditions and transport element equations. This property is achieved under certain monotonicity conditions on element equations and guarantees an existence of a unique solution of the problem as well as convergence to this solution from an arbitrary starting point. In application to gas transport networks, these algorithms are supported by a proper modeling of gas compressors, based on individually calibrated physical characteristics. This paper extends the modeling of compressors by hierarchical methods of topological reduction, combining the working diagrams for parallel and sequential connections of compressors. Estimations are also made for application of topological reduction methods beyond the compressor stations in generic network problems. Efficiency of the methods is tested by numerical experiments on realistic networks.
The formulation of transport network problems is represented as a translation between two domain specific languages: from a network description language, used by network simulation community, to a problem description language, understood by generic non-linear solvers. A universal algorithm for this translation is developed, an estimation of its computational complexity given, and an efficient application of the algorithm demonstrated on a number of realistic examples. Typically, for a large gas transport network with about 10K elements the translation and solution of non-linear system together require less than 1 sec on the common hardware. The translation procedure incorporates several preprocessing filters, in particular, topological cleaning filters, which accelerate the solution procedure by factor 8.
Abschlussbericht zum BMBF-Fördervorhaben Enabling Infrastructure for HPC-Applications (EI-HPC)
(2020)
Failure prognostic builds up on constant data acquisition and processing and fault diagnosis and is an essential part of predictive maintenance of smart manufacturing systems enabling condition based maintenance, optimised use of plant equipment, improved uptime and yield and to prevent safety problems. Given known control inputs into a plant and real sensor outputs or simulated measurements, the model-based part of the proposed hybrid method provides numerical values of unknown parameter degradation functions at sampling time points by the evaluation of equations that have been derived offline from a bicausal diagnostic bond graph. These numerical values are computed concurrently to the constant monitoring of a system and are stored in a buffer of fixed length. The data-driven part of the method provides a sequence of remaining useful life estimates by repeated projection of the parameter degradation into the future based on the use of values in a sliding time window. Existing software can be used to determine the best fitting function and can account for its random parameters. The continuous parameter estimation and their projection into the future can be performed in parallel for multiple isolated simultaneous parametric faults on a multicore, multiprocessor computer.
The proposed hybrid bond graph model-based, data-driven method is verified by an offline simulation case study of a typical power electronic circuit. It can be used to implement embedded systems that enable cooperating machines in smart manufacturing to perform prognostic themselves.
AErOmAt Abschlussbericht
(2020)
Das Projekt AErOmAt hatte zum Ziel, neue Methoden zu entwickeln, um einen erheblichen Teil aerodynamischer Simulationen bei rechenaufwändigen Optimierungsdomänen einzusparen. Die Hochschule Bonn-Rhein-Sieg (H-BRS) hat auf diesem Weg einen gesellschaftlich relevanten und gleichzeitig wirtschaftlich verwertbaren Beitrag zur Energieeffizienzforschung geleistet. Das Projekt führte außerdem zu einer schnelleren Integration der neuberufenen Antragsteller in die vorhandenen Forschungsstrukturen.
3D Time-of-Flight (ToF)
(2015)
3D Time-of-Flight (ToF)
(2012)
3D-Imaging
(2009)
