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Zünd- und Brennverhalten von Pflanzenölkraftstoff und Übertragung auf einen Motor der Abgasstufe V
(2020)
Durch den Ersatz von Dieselkraftstoff durch Rapsölkraftstoff (R100) können Treibhausgasemissionen reduziert werden. Für einen störungsfreien Betrieb eines Motors mit Rapsölkraftstoff sind jedoch Modifikationen an Motorkomponenten und Motorsteuergerät notwendig, um eine effiziente Verbrennung im Motor zu erreichen.
Ziel des Vorhabens ist die Erarbeitung von Grundlagen zur Auslegung der Motorsteuerung pflanzenöltauglicher Offroad-Motoren mit moderner Abgasnachbehandlung mit anschließender entsprechender Abstimmung der Motorapplikation am Prüfstand. Grundlegende Untersuchungen der physikalischen Prozessabläufe von R100 bei der Einspritzung werden an einem hydraulischen Druckanstiegsanalysator (HDA) und einer Hochdruck-Hochtemperatur-Kammer (HDHT-Kammer) durchgeführt. Unterschiede im Zünd- und Brennverhalten werden in einer Konstantvolumenbrennkammer untersucht. Abschließend werden die Erkenntnisse am Motorenprüfstand auf einen DEUTZ-Motor übertragen, dessen Einspritzsystem auch bei den grundlegenden Untersuchungen verwendet wurde.
Die Ergebnisse zeigen, dass das Einspritzverhalten von R100 eine höhere Sensitivität gegenüber Kraftstofftemperaturvariationen aufweist als Dieselkraftstoff. Bei niedrigen raftstofftemperaturen sind mit R100 ein längerer Öffnungsverzug und eine geringere Einspritzmenge festzustellen. Um diesen Einfluss bei der Einspritzstrategie zu kompensieren, ist die Kenntnis der Kraftstofftemperatur im Injektor notwendig. Eine weitere Herausforderung stellt die Gemischaufbereitung dar, hier führen unter anderem die höhere Viskosität und höhere Siedetemperaturen von R100 zu einem schmäleren Spritzwinkel und verzögerter Verdampfung im Vergleich zum Dieselkraftstoff. Eine Erhöhung des Einspritzdrucks und höhere Temperaturen und Drücke in der Brennkammer verbessern die Gemischaufbereitung.
Bei Bedingungen von mittlerer und hoher Last ist der Zündverzug von R100 kürzer und das Verbrennungsverhalten ähnlich zum Dieselkraftstoff. Eine geringere Wärmefreisetzung von R100 wird durch den geringeren Heizwert verursacht. Unter Bedingungen von niedriger Last und Motorstart ist ein längerer Zündverzug von R100 im Vergleich zum Dieselkraftstoff festzustellen. Eine Steigerung des Einspritzdrucks und höhere Brennkammerdrücke und -temperaturen führen bei beiden Kraftstoffen zu kürzeren Zündverzügen, der Einfluss dieser Parameter ist jedoch für R100 stärker als für Dieselkraftstoff. Voreinspritzungen führen bei beiden Kraftstoffen zu einer Verkürzung des Zündverzugs der Haupteinspritzung und zu einer geringeren Wärmefreisetzungsrate.
Am Motorprüfstand ist bei gleicher Motorapplikation mit R100 eine geringere Leistung als mit Dieselkraftstoff festzustellen. Nach Angleichung der Motorleistung durch Anhebung der Einspritzmenge von R100 sind im Rohabgas Stickstoffoxid (NOX)- und Kohlenstoffmonoxidemissionen auf gleichem Niveau zu Dieselkraftstoff zu beobachten sowie geringere Partikelemissionen. Unter Verwendung eines DoE Vorgehens kann der Partikel-NOX - trade-off von R100 optimiert und Einstellparameter gefunden werden, in denen sowohl niedrigere NOX als auch niedrigere Partikelemissionen im Vergleich zum Dieselkraftstoff resultieren.
Das installierte Abgasnachbehandlungssystem, bestehend aus einem Dieseloxidationskatalysator (DOC), Dieselpartikelfilter (DPF) und selektivem katalytischem Reduktionssystem (SCR), arbeitet für beide Kraftstoffe ähnlich und es scheint keine Anpassung der Dosierungsstrategie der wässrigen Harnstofflösung notwendig zu sein. Eine Regeneration des Partikelfilters mit R100 war nach Optimierung der Einstellparameter der Drosselklappe möglich.
Motorkaltstart und Leerlauf sind herausfordernde Betriebsphasen, die für R100 einer weiteren Optimierung bedürfen. Eine Temperierung von R100 im Injektor auf 50–60 °C sowie eine Kompensation der Einspritzmenge in Abhängigkeit von der Kraftstofftemperatur sind mögliche Verbesserungsmaßnahmen. Zudem kann durch einen früheren Einspritzbeginn von R100 das Verbrennungsverhalten angepasst werden. Die Motorprüfstandsuntersuchungen bestätigen qualitativ die Erkenntnisse die mit dem hydraulischen Druckanstiegsanalysator (HDA), der Hochdruck-Hochtemperatur-Kammer (HDHT-Kammer) und der Konstantvolumenbrennkammer gewonnen wurden.
Weitere Untersuchungen sind notwendig, um die Ergebnisse auf einen baugleichen, in einer mobilen Arbeitsmaschine eingebauten Motor zu transferieren, damit Informationen zur Dauerhaltbarkeit unter realen Bedingungen erhalten werden können. Weiterführende Forschungsarbeiten sind im Bereich der Betriebsphasen des Motorkaltstarts und Leerlaufs mit Rapsölkraftstoff nötig, um einen dauerhaft störungsfreien Betrieb in diesen Betriebsphasen zu erreichen. Die erzielten Erkenntnisse deuten darauf hin, dass hier noch viel Verbesserungspotenzial vorhanden ist.
Tonal components can be regarded as one of the most relevant components for interior sound quality of electric vehicles, especially at low speeds. Sources for these tones are for example the vehicles' drivetrains but also other technical components. Depending on the driving conditions, due to the interaction of various dominant sources, audible tone complexes can occur. Similar to musical intervals, the different frequency ratios within these complexes can result in consonant or dissonant sensations. The strength of this sensation does not only depend on the frequency relation of the tones but also on their relative levels. In this study, different musical intervals were subjectively rated in terms of their specific consonant or dissonant character. Using an adaptive procedure, sound pairs, each consisting of a two-tone signal, where adjusted to equal dissonance by varying the level of the second tone of one of the two-tone signals. Using the same paradigm, also pairs of equal vehicle sound quality were obtained. With these results, it is possible to quantify dissonance, and theinfluence of dissonance on sound quality expressed in terms of level differences of two-tone signals. These results can help to make the concept of dissonance more useful for sound-engineering applications.
In Folge der Verschärfung der gesetzlichen Abgasnormen wurden für direkt-einspritzende Benzinmotoren Partikelfilter notwendig. Zur Beladungsüberwachung können aufgrund stark unterschiedlicher Rahmenbedingungen die aus Dieselmotoren bekannten Systeme, wie dem Differenzdrucksensor, nur eingeschränkt übernommen werden. Ein hochfrequenzbasiertes Verfahren koppelt mittels Antennen elektromagnetische Wellen in das Filtergehäuse ein, deren Ausbreitungsverhalten durch die dielektrischen Eigenschaften des eingelagerten Rußes beeinflusst wird. Hierdurch kann bei Auswertung von Transmissionsdämpfung oder Resonanzfrequenzen die Rußbeladung direkt detektiert werden.
In order to comply with future emission regulations, the use of particulate filters in vehicles with direct injection gasoline engines is essential. The current amount of soot and ash in the filter is calculated by a soot load model in the electronic control unit in combination with a differential pressure sensor determining the pressure drop over the particulate filter. Active regeneration is initiated if the calculated amount of soot or the measured differential pressure is too high. This is associated with additional fuel consumption. An on-board diagnosis for the particulate filter is currently not part of the Euro 6d emission standard. For future exhaust emission standards, on-board diagnosis or active monitoring of the particulate filter is conceivable. One of the benefits of monitoring is the fact that unnecessary active regenerations can be avoided. As a result, there is no additional fuel consumption due to misinterpretations of the amount of soot in the filter. For active monitoring of the particulate filter, a radiofrequency (RF-) sensor, that detects the soot loading of the filter with electromagnetic waves directly, can be used. Such a system has the advantage that by utilizing the filter as a sensor more precise information about the current state of the filter, e.g. a possible damage, can be provided. Worst-case considerations of filter damages, tested at an engine test bench show the advantages which are entailed by a system like that. By means of partial regeneration of the particulate filter it is demonstrated how the remaining amount of soot in the filter can be detected in a better way in comparison to the differential pressure sensor by using the RF-sensor.
Die Richtlinie VDI 2500 „Faserseile“ hat 1990 erstmals zusammenfassend den Stand der Technik auf dem Gebiet der Faserseile dargestellt und wertvolle Infor-mationen über Aufbau, Auswahl, Konfek-tionierung und Überwachung von Faser-seilen gegeben. Die jetzt erscheinende zweite Auflage enthält eine Vielzahl wichtiger technischer Neuerungen für die Praxis. Zu nennen sind hier die hochfesten Fasern und deren Beschichtung sowie die erstmals systematisch aufgeführten Sei-lendverbindungen und ein Ausblick auf die zukünftig bedeutsamen sogenannten Hybridseile. Eine Checkliste hilft bei der richtigen Auswahl und Bemessung von Faserseilen. Bei den Normen wurde – soweit möglich – auf europäische Normen verwiesen.
We present a theoretical approach for calculating the state of stress induced by a uniform magnetic field in confined magnetoactive elastomers of arbitrary shape. The theory explicitly includes the magnetic field generated by magnetizable spherical inclusions in the sample interior assuming a non-linear magnetization behavior. The initial spatial distribution of particles and its change in an external magnetic field are considered. This is achieved by the introduction of an effective demagnetizing factor where both the sample shape and the material microstructure are taken into account. Theoretical predictions are fitted to the stress data measured using a specifically designed experimental setup. It is shown that the theory enables the quantification of the effect of material microstructure upon introducing a specific microstructural factor and its derivative with respect to the extensional strain in the undeformed state. The experimentally observed differences between isotropic and anisotropic samples, compliant and stiff elastomer matrices are explained.
tabilizing the effects of greenhouse gas emissions on the atmosphere is a key step towards solving the global climate change problems. Storage technologies play an essential role in compensating the discrepancy between surplus energy and peak times. Sorption processes, in particular, offer an environment friendly way for almost loss-free heat (of adsorption or absorption) and cold storage. This work is dedicated first to analytically investigate the potential of applying NaY-Water/Zeolite as a working pair for heat and cold storage upon utilizing high temperature heat. It turned out that, the mass of the adsorber heat exchanger increases the useful specific heat stored from 229 kWh/tzeolite for the ideal storage to 538 kWh/tzeolite or even higher depending on the thermal capacity of the adsorber heat exchanger (AdsHX). Contrary to that trend, COP will decrease with increasing the thermal capacity of the AdsHX. Sensible heat losses between charging and discharging phases do have a negative effect on both stored heating capacity and COP.
In addition, an innovative hybrid steam power cum adsorption storage process is introduced and analytically investigated at different ambient conditions and time scenarios for on-peak and off-peak durations over the day. The introduced hybrid process seems quite promising in achieving electrical power production and efficiency enhancements during peak load durations. The extent of enhancing both performance indicators increases with increasing the ambient temperature difference between peak and off-peak times.
It is discussed that the classical effective medium theory for the elastic properties of random heterogeneous materials is not congruous with the effective medium theory for the electrical conductivity. In particular, when describing the elastic and electro-conductive properties of a strongly inhomogeneous two-phase composite material, the steep rise of effective parameters occurs at different concentrations. To achieve the logical concordance between the cross-property relations, a modification of the effective medium theory of the elastic properties is introduced. It is shown that the qualitative conclusions of the theory do not change, while a possibility of describing a broader class of composite materials with various percolation thresholds arises. It is determined under what conditions there is an elasticity theory analogue of the Dykhne formula for the effective conductivity. The theoretical results are supported by known experiments and show improvement over the existing approach. The introduction of the theory with the variable percolation threshold paves the way for describing the magnetorheological properties of magnetoactive elastomers. A similar approach has been recently used for the description of magneto-dielectric and magnetic properties.
In composite materials, with field-dependent restructuring of the filler material (changes in the mutual arrangement of inclusions), the presence of an external magnetic field induces anisotropy of the dielectric properties, even if the composite is isotropic in the absence of an external field. A modified effective medium approximation is proposed for the calculation of the components of effective permittivity within a class of composites with reconfigurable microstructure, where both phases (the filler and the matrix) are isotropic and the inclusions have spherical shape. The effective physical properties are calculated in the parallel and perpendicular directions to an applied field. The appearance of the anisotropy of the permittivity is simulated by the introduction of two not-equal, possibly variable (field-dependent) percolation thresholds. The implications, of the proposed theoretical approach, are demonstrated for the case of the dielectric properties of magnetoactive elastomers (MAEs). In MAEs with soft polymer matrices, the mutual arrangement of micrometer-sized magnetic inclusions can significantly change in an applied magnetic field. A reasonable agreement between theory and experiment at a measurement frequency of 1 kHz is found, and is improved in comparison to the previous models. The components of the effective permittivity tensor, characterizing the dielectric properties along the direction of the applied magnetic field and in the orthogonal direction, grow with an increasing field. This growth is more pronounced for the permittivity component in the field direction. The possible extensions of the theoretical model and future directions of research are discussed. The presented theoretical approach can be useful for the application-driven development of a number of smart materials, in particular electro- and magnetorheological gels, elastomers and fluids.
Elongations of magnetoactive elastomers (MAEs) under ascending–descending uniform magnetic fields were studied experimentally using a laboratory apparatus specifically designed to measure large extensional strains (up to 20%) in compliant MAEs. In the literature, such a phenomenon is usually denoted as giant magnetostriction. The synthesized cylindrical MAE samples were based on polydimethylsiloxane matrices filled with micrometer-sized particles of carbonyl iron. The impact of both the macroscopic shape factor of the samples and their magneto-mechanical characteristics were evaluated. For this purpose, the aspect ratio of the MAE cylindrical samples, the concentration of magnetic particles in MAEs and the effective shear modulus were systematically varied. It was shown that the magnetically induced elongation of MAE cylinders in the maximum magnetic field of about 400 kA/m, applied along the cylinder axis, grew with the increasing aspect ratio. The effect of the sample composition is discussed in terms of magnetic filler rearrangements in magnetic fields and the observed experimental tendencies are rationalized by simple theoretical estimates. The obtained results can be used for the design of new smart materials with magnetic-field-controlled deformation properties, e.g., for soft robotics.
Large twists of a soft tube (hollow cylinder) in helical magnetic fields are presented for the first time. Such a phenomenon is usually denoted as the Wiedemann effect. The tube is fabricated from a soft magnetoactive elastomer material with the shear modulus of about 56 kPa. The composite material comprises 80 mass% of micrometer-sized iron particles embedded into a polydimethylsiloxane matrix. The circular magnetic field is generated by an electric current in a straight wire passing through the inner hole of the tube. The maximum value of approximately 350″/cm is observed in a longitudinal magnetic field of a few kA/m overlapped with a circumferential magnetic field of about 1.4 kA/m on the surface of the inner hole. A pronounced hysteresis in the dependence of the Wiedemann effect on the circular magnetic field is found. The ways to enhance the Wiedemann twist in magnetoactive elastomers are discussed. The observed large effect is promising for application in magnetic-field controlled torsional actuators, in particular for soft robotics.
A new biofuel concept is developed, enabling the usage of vegetable oils and glycerol derivatives in mixtures with biodiesel. This concept significantly enhances the biodiesel production's profitability and thus strongly contributes to the sustainability of future biofuels. After simple addition reactions with building block chemicals, less hydrophilic glycerol derivatives are obtained, which are compatible with biofuels. Even more, the products of the reactions of glycerol with acetone or butyric acid, referred to as solketal and tributyrin, respectively, lead to promising biofuels in mixtures with rapeseed oil and its biodiesel. Due to their low freezing points, they act as cloud and freezing point depressants, when added to vegetable oil/biodiesel blends. Further, since their viscosity is close to common biodiesel, biofuels containing high amounts of vegetable oil and even more glycerol derivatives than they arise during the biodiesel production can be obtained. Thus, this new class of biofuels enables adaptable compositions depending on the application and also the usage as drop-in fuel without any or just few percent of further additives. After optimising the formulations, ignition delay, exhaust gas recirculation, fuel consumption and combustion process measurements were performed in an unmodified upto-date diesel engine. The experiments showed that the properties of the formulated biofuels are either similar to or even better than diesel. The hydrotropy of the glycerol derivatives in these mixtures enables the potential to implement water into biofuels, so-called hydrofuels, reducing nitrogen oxide emissions and leading to further optimised dropin fuels.
Unified Methodology to Identify the Potential Application of Seasonal Sorption Storage Technology
(2020)
In this study, the definition of a new methodology for a preliminary evaluation of the working boundary conditions under which a seasonal thermal energy storage (STES) system operates is described. The approach starts by considering the building features as well as the reference heating system in terms of solar thermal collectors’ technology, ambient heat sinks/source, and space heating distribution systems employed. Furthermore, it is based on a deep climatic analysis of the place where the STES needs to be installed, to identify both winter and summer operating conditions. In particular, the STES energy density is evaluated considering different space heating demands covered by the STES (ranging from 10% up to 60%). The obtained results demonstrate that this approach allows for the careful estimation of the achievable STES density, which is varies significantly both with the space heating coverage guaranteed by the STES as well as with the ambient heat source/sink that is employed in the system. This confirms the need for careful preliminary analysis to avoid the overestimation of the STES material volume. The proposed approach was then applied for different climatic conditions (e.g., Germany and Sweden) and the volume of one of the most attractive composite sorbent materials reported in the literature, i.e., multi-wall carbon nanotubes (MWCNT)-LiCl, using water as the working fluid, needed for covering the variable space heating demand in a Nearly Zero Energy Building (NZEB) was calculated. In the case of Swedish buildings, it ranges from about 3.5 m3 when 10% of the space heating demand is provided by the STES, up to 11.1 m3 when 30% of the space heating demand is provided by the STES.
This paper proposes the possible switching synchronization strategies of an automotive dual-inverter against the background of minimizing the RMS DC-link capacitor current. The publication mainly focuses on the straight-ahead motion of a rear axle with one electric drive per wheel. In addition to it, a dual-inverter consisting of two subinverters with a common DC-link capacitor is taken into consideration. These sub-inverters each have three phases and are based on a 2-level voltage-source-topology. To control the electrical machines, the continuous Space-Vector-Modulation strategy is used. For this application, different control signal synchronization strategies of the two sub-inverters of the dualinverter are presented. Apart from the existing strategies, this paper proposes a new method, which inherits a compromise between low complexity and high effectiveness. In contrast to previous publications, the resulting capacitor currents are quantified and subsequentlyevaluated. This novel quantification, which is dependent on the dual-inverter’s operating point, provides a base for targeted dimensioning of the capacitor. Moreover, this forms the foundation for further investigations of vehicle’s cornering, as well as for the possible synchronization of stand-alone inverters. In the context of this publication, the presented results are verified by experimentally determined data of a motor-inverter system.
The vapor pressures of two binary mixtures containing 2-trifluoroethanol (TFE) + 1,3-dimethyl-2-imidazolidinone (DMI) and TFE + 2-pyrrolidone (PYR), were investigated at temperatures T = (274.15 to 423.15) K using two different static method installations. Both combinations were modelled using an extended Clausius-Clapeyron equation with concentration dependent parameters and the NRTL equation with temperature dependent parameters. The best fit was obtained using the NRTL equation.
Power-to-Gas technologies in the energy sector and their role in the fight against climate change
(2020)
Megathema Wasserstoff: Power-to-X im Kontext der Energiewende und des Klimaschutzes in Deutschland
(2020)
The flow of superfluid helium-4 at very low temperatures around an oscillating microsphere has been studied in detail. At small oscillation amplitudes the drag force is linear in velocity amplitude. Above a critical velocity amplitude vc a transition from potential flow to turbulent flow is signaled by a large and nonlinear drag force that scales as (v2 - v2 c ), where vc is found to be independent of temperature (below 1 K) and of driving force. Interestingly, the critical velocity is found to scale as vc ~ √κω, where κ = h/m ≈ 10−7 m2/s (h is Planck's constant and m is the mass of a helium-4 atom) is the circulation quantum of the superfluid vortices and ω/2π is the oscillation frequency ranging from about 120 Hz to 700 Hz. We also observe slightly above vc that the flow pattern is unstable and switches intermittently between potential flow and turbulence. From time series recorded at constant drive and temperature we have investigated the statistical properties of this switching phenomenon. In this talk the universal law vc ~ √κω will be discussed in detail. It can be derived theoretically in various ways: firstly, from a qualitative but very general argument based on the "superfluid Reynolds number" Rs = vl/κ where v is the flow velocity and l is a characteristic length scale, secondly, and in more detail, from Kopnin's equation of the time dependence of the vortex line density, and, finally, we have obtained this law rigorously by dynamical scaling of the equations of motion of vortex dynamics.
To identify the sound quality of fuel injection systems as a frontloading measure, a system test bench has been developed that simulates the structure and airborne noise emission. The setup of the system test bench includes an assembly of the acoustical relevant engine parts and an encapsulated drive for the high-pressure pump. A specific control unit enables a high variability for the operation strategy of the injection system.
The focus of this study is on the development of a methodology to analyze and optimize the sound quality of gasoline direct injectors in critical operation points by suitable active means. For this, the injection parameters in engine idle have been identified and subsequently transferred to the system test bench. Additionally, the injection parameters have been optimized acoustically and the impacts on the key functions regarding injection rating and shot-to-shot scattering of the injected fuel mass are discussed.
Due to the transition to renewable energy sources and the increasing share of electric vehicles and smart grids, batteries are gaining in importance. Battery management systems (BMSs) are required for optimal, reliable operation. In this paper, existing BMS topologies are presented and evaluated in terms of reliability, scalability and flexibility. The decentralisation of BMSs and associated advantages are shown. A scalable, reconfigurable BMS based on a distributed architecture of self-organized, locally controlled nodes is proposed. For distributed system control, producers, batteries and consumers each are equipped with a local microcontroller based control unit, which monitors and controls the local parameters with its own computing and communication resources. Features, advantages and challenges to overcome of the proposed approach are described.
Reliability of structures and infrastructures is a major issue in structural engineering. Structural standards have traditionally been mainly concerned with public safety preventing loss of life or injury; this view has been shifting in recent years towards minimisation of economic loss. This contribution discusses the reliability differentiation principle in modern standards. Its aim is to achieve uniform risk levels for the various classes of structures. Codified criteria for reliability differentiation and risk informed decisions inherent in standards and especially in the Eurocodes are critically reviewed. It is shown that the classification of structures based on consequences of failure is an approach that has not been widely implemented in everyday design. Practical rules for the classification and implementation in design are needed and related proposals are presented.
This paper decribes the concept of a course on control theory as a minor subject in the department of electrical engineering at the OTH Regensburg. The basis for a new concept is the idea of contructive alignment. The whole teaching module is devided in two blocks. The first block contains the teaching of the knowledge about control theory with an integrated approach for lectures, exercises and practical sessions. In the second block the students attent a practical work package to have the possibility to applicate and deepen their knowledge. To foster active participation the students are asked to document and reflect their work with the course context in an electronic portfolio. The exam of this module consists of three parts with respect to the different competencies obtained during the module. This concept develops not only the knowledge on control theory but personal and social competencies which are of growing interest. The aim of the paper is to present the idea of the concept. Following papers will illustrate the development process and the results obtained later on.
The reduction of the energy demand of existing buildings is the main objective of building refurbishment. Managing the heat radiation properties of the wall construction is a possible way to develop highly effective and resource efficient insulation materials and concepts. The application of infrared reflective wall paints and coatings has been studied since the latter half of the 20th century. A brief review of the literature gives an account of the current research status. One has to realise that the conclusions are not uniformly consistent but depend strongly on the specific boundary conditions and investigated parameters. The study presented here discusses the usage of infrared reflective wall paint in conjunction with heat insulation for historic brick masonry. The possible energy savings are linked to the resulting thermal comfort. We identify critical parameters that must be taken into account when using infrared reflective wall paint and derive recommended design rules for the refurbishment of such building types. The findings prove that infrared reflective wall paint can decrease heat losses by 18% and up to 22% if comfort conditions are considered. Increasing energy savings can also cause the negative effect of high radiative asymmetry. Thus, each configuration must be observed in detail.
Wind turbines play a crucial role in the revolution towards renewable resources. They need to be economically competitive to be sustainable. This still requires to lower the cost of energy (COE). To this end, nonlinear model predictive control (NMPC) is used within this paper. As known from literature, NMPC significantly improves the energy extracting performance as well as the mitigation of tower loads of wind turbines. As it is shown in this paper, the drivetrain fatigue strength drops disproportionally in parallel, which either increases the demands on the turbine design or decreases the lifetime of drivetrain components. Without additional boundary conditions to the underlying optimal control problems (OCPs), the application of energy-maximizing NMPC might so even raise the COE. Only penalizing axial torque oscillations by quadratic terms decreases energy-extracting performance below the level of classical wind turbine controllers. This makes more sophisticated conditions necessary. In this paper, the increase of the drivetrain damage by NMPC is analyzed, and appropriate boundary conditions are derived, to balance the two contradicting objectives of energy maximization and drivetrain load mitigation. An NMPC approach based on indirect methods is used, to obtain a solution of the OCPs very efficiently. It applies the Hamilton equations and Pontryagin's maximum principle. Its accuracy and efficiency to solve OCPs was presented over the last decades.
Im Rahmen des Projektes C/sells wurden mehrere Mittelspannungsnetze modelliert, um die aktuellen Spannungsverhältnisse und Leitungsauslastungen nachbilden zu können. Zudem wurden, angelehnt an den Netzentwicklungsplan, Szenarien für den zukünftigen PV-Zubau und die potenzielle Entwicklung der Elektromobilität entworfen. Auf Basis der Ergebnisse lässt sich eine Netzanalyse hinsichtlich Spannungs- und Stromgrenzwertüberschreitungen sowie zu deren potenziellen Auftrittszeitpunkten und Auftrittsdauern durchführen. Parallel wurde anhand von Sensitivitätsanalysen untersucht, welche Wirksamkeit Flexibilitätseinsätze an den verschiedenen Netzknoten auf den Engpass haben. Dadurch kann bestimmt werden, wie effektiv die verfügbaren, in der Regel örtlich gebundenen Flexibilitätsanbieter eingesetzt werden können. Da die Sensitivitäten arbeitspunktabhängig sind, wurden verschiedene Zeitpunkte im Jahresverlauf berechnet und die jeweilige Änderungen der Wirksamkeit ausgewertet. Neben der Höhe der Leistungsabweichung wurde die Flexibilitätsanforderung auch anhand der Einsatzzeitpunkte und Einsatzdauer sowie anhand der Häufigkeit der nötigen Flexibilitätseinsätze charakterisiert. Aus den gewonnenen Erkenntnissen soll abgeleitet werden, inwiefern sich der flexible Einsatz der Verbrauchsanlagen in der Netzplanung verankern lässt. Besonders relevant ist deshalb, mit welcher Verlässlichkeit die Flexibilität abgerufen werden kann. Eine sehr hohe Verlässlichkeit lässt sich je nach Flexibilitätsanbieter möglicherweise nicht oder nur zu sehr hohen Preisen gewährleisten. Die Eignung der Flexibilitätseinsätze wird somit sowohl aus technischer als auch aus wirtschaftlicher Sicht bewertet. Da eine vollständige Verlässlichkeit ohnehin nicht sichergestellt werden kann (technische Störungen einer Anlage, Wettereinflüsse, etc.), werden auch Fallback-Strategien, z. B. Einspeisespitzenkappung, in die Analyse einbezogen.
In Zusammenarbeit mit den Kreiswerken Cham wurde an der OTH Regensburg das Trinkwasserversorgungsgebiet mit allen relevanten Pumpen und Hochbehältern nachgebildet. Mithilfe des Modells kann die aktuelle, füllstandgesteuerte Betriebsweise unter Einhaltung der Randbedingungen (Grenzwerte der Behälterfüllstände, elektrische Verschaltung der Pumpen) simuliert werden. Daraus lässt sich auch das gesicherte, für die Netzplanung geeignete Flexibilitätspotenzial anhand der Leistungsabweichung gegenüber dem regulären Fahrplan, der Einsatzdauer, dem Einsatzzeitpunkt und der Pause zwischen den Flexibilitätsabrufen charakterisieren. In einem Feldversuch wurde vordergründig untersucht, inwiefern der Einsatz von Flexibilität in der Trinkwasserversorgung technisch umsetzbar ist.
In this paper it is presented how the network calculation program PowerFactory is used to implement automated network planning algorithms. PowerFactory’s internal functions and data sets are discussed and it is shown how the functions and data sets have been extended by specially developed scripts to enable the automation of network planning steps. Finally, the methodology applied to calculate grid use cases is briefly discussed.
Investigation of Shifted PWM Methods for a Dual Three-Phase System to Reduce Capacitor RMS Current
(2020)
Mild hybrid automotive topologies containing a 48V high power (>15 kW) electric drive system demand a high integration of power electronics and electrical machine. A multi-phase motor winding topology helps to keep the per-phase operating currents to a reasonable level. Close integration and multi-phase system have led to a drive system with dual 3-phase systems supplied by a common 48V DC-link, which allows to shift PWM patterns for reduction of DC-link capacitor ripple current and size. This paper derives some basic rules for combinations of common PWM methods for dual 3-phase systems without magnetic cross-coupling. Experimental measurements verify simulated results.
This paper presents a convolutional neural network (CNN) which can be used for forecasting electricity load profiles 36 hours into the future. In contrast to well established CNN architectures, the input data is one-dimensional. A parameter scanning of network parameters is conducted in order to gain information about the influence of the kernel size, number of filters and number of nodes. Furthermore, different dropout methods are applied to the CNN and are evaluated. The results show that a good forecast quality can already be achieved with basic CNN architectures, the dropout improves the forecast. The method works not only for smooth sum loads of many hundred consumers, but also for the load of single apartment buildings.
Many modern composites consist of dielectric polymer matrices containing embedded spherical particles. These particles can be electrically conducting and often have magnetic properties. In order to accurately model and simulate such materials, precise calculation of the electrical capacitance between identically sized spheres is required. This is of particular relevance at microscopic dimensions where many smart material-based micro devices are concerned. This may appear trivial for a small number of particles. However, many methods or their analysis appear to be questionable or not applicable at reduced dimensions. In this work, the various methods of analysis are scrutinized before being compared with both simulation and direct measurements. It is surprising to note that of the many works investigated only 3 are in close agreement with both simulation and measurement.
Graphical abstract
This paper deals with the precise calculation of the electrical capacitance between two conducting spheres of equal, or near equal size.The calculations have been verified by both experimental measurements and simulation. Algorithms in MatLab (Octave) format have been included in the supporting information.
This paper concerns a comprehensive investigation of time-dependent electroadhesion (EA) force degradation. EA shear force tests on different object materials (a PET, glass, ABS, and wood plate) have shown that force degradation was dominated by residual polarization charges trapped in the EA pad dielectric rather than in the substrate dielectric from which the object to be prehended is made. In order to explain this dynamic physical phenomenon, a model of dielectric polarization and depolarization has been proposed. According to the derived relationship between EA force and discharge time, three different methods intended to mitigate this problem has been compared: (1) the natural discharge method, (2) the high voltage resistor discharge method, and (3) the discharge prior to field polarity reversal method. These methods are useful for generating repeatable and stable EA forces, which are required for the characterization of EA pads and their subsequent employment in material handling, mobile robot crawling and climbing tasks.
Die Akzeptanz unter Bewohnern und Bewohnerinnen gewinnt bei hoch komplexen, technisch anspruchsvollen energetischen Sanierungen als „Innovationsmotor“ zunehmend an Relevanz. Der Beitrag basiert auf zwei Fallstudien zur partizipativen Nutzereinbindung bei energetischen Sanierungen im genossenschaftlichen Wohnbau historischer Stadtquartiere in Regensburg. Neben einer sozialverträglichen Sanierung wurde jeweils ein hohes Maß an Energieeffizienz bei den technischen Lösungen ange-strebt. Haushaltsbefragungen und qualitative Interviews zeigen die hohe Akzeptanz von Sanierungsmaßnahmen, sofern die Senkung der Energiekosten die erhöhte Miete kompensiert. Abschließend werden Akzeptanzfaktoren wie Partizipation, Vertrauen, Sozialverträglichkeit und Autarkie erörtert.
We derive a new 3D model for magnetic particle imaging (MPI) that is able to incorporate realistic magnetic fields in the reconstruction process. In real MPI scanners, the generated magnetic fields have distortions that lead to deformed magnetic low-field volumes with the shapes of ellipsoids or bananas instead of ideal field-free points (FFP) or lines (FFL), respectively. Most of the common model-based reconstruction schemes in MPI use however the idealized assumption of an ideal FFP or FFL topology and, thus, generate artifacts in the reconstruction. Our model-based approach is able to deal with these distortions and can generally be applied to dynamic magnetic fields that are approximately parallel to their velocity field. We show how this new 3D model can be discretized and inverted algebraically in order to recover the magnetic particle concentration. To model and describe the magnetic fields, we use decompositions of the fields in spherical harmonics. We complement the description of the new model with several simulations and experiments, exploring the effects of magnetic fields distortion and reconstruction parameters on the reconstruction.
Die Energiewende führt zu neuen Herausforderungen für Verteilungsnetzbetreiber hinsichtlich der Er-bringung von Systemdienstleistungen, der Integration weiterer Erzeugungsanlagen und Lasten sowie der Gewährleistung einer hohen Versorgungssicherheit und normgerechten Spannungsqualität. Die De-ckung der auftretenden Blindleistungsbedarfe seitens der Netzbetriebsmittel, Verbraucher und Erzeu-gungsanlagen gewinnt durch den Wegfall der Großkraftwerke für Netzbetreiber zunehmend an Bedeu-tung. Das Projekt SyNErgie beschäftigt sich diesbezüglich mit der Entwicklung neuartiger Blindleis-tungsmanagementsysteme für Mittelspannungsnetze. Ziel ist es, das bisher ungenutzte, freie Blindleis-tungspotential betrieblicher Kompensationsanlagen und dezentraler Erzeugungsanlagen (allgemein: Blindleistungsquellen) zu nutzen, um die Blindleistungsänderungsfähigkeit eines Verteilungsnetzes zu erhöhen. Diese Arbeit beschäftigt sich mit der Entwicklung eines zentralen Blindleistungsregelsystems, bei dem Blindleistungsquellen auf Basis von „Optimal Power Flow“-Berechnungen über eine zentrale Recheninstanz angesteuert werden. Zum Einsatz kommt dabei ein Optimierungsalgorithmus, der auf Basis des aktuellen Netzzustandes (Spannungs- und Auslastungsreserven) und des aktuellen Blindleis-tungspotentials der Blindleistungsquellen einen bedarfsoptimalen Abruf koordiniert. Das zentrale Re-gelverfahren wird in Netzmodellen verschiedenartiger Mittelspannungsnetzgruppen und unterschiedli-cher Art und Anzahl von Blindleistungsquellen angewendet sowie im Hinblick auf variierende Zielvor-gaben und Randbedingungen evaluiert und diskutiert.
The fracture propagation and arrest control for pipelines transporting rich natural gases and high vapor pressure liquids is based on the Battelle Two-Curve Model (BTCM). Distinct limitations of this model were demonstrated for past and modern steels and gas mixtures. These can be related to the insufficient description of individual physical processes and interactions between the pipe material and transported mixture during the running ductile fracture. In the past, fluid-structure interaction (FSI) models enabled a more sophisticated, coupled analysis of the failure scenario. To quantify their capability of describing the multi-physical processes, the FSI models need to be verified by experimental data from full-scale burst tests (FSBT). Therefore, this paper deals with the simulation of five FSBTs from the literature on API grade X65 pipes with different pipe geometries, mixtures and initial conditions. The FSI is modeled by the coupled Euler-Lagrange (CEL) method. The modified Mohr-Coulomb (MMC) model is implemented in the CEL framework to describe the deformation and ductile fracture in the X65/L450 pipes. 3D Euler equations are used to calculate the mixture decompression with the GERG-2008 equation of state defining the volumetric behavior of a CO2-rich mixture, CH4 and H2. The extended model considers the effect of soil backfill on the pipe deformation and inertia. The numerical predictions agree well with the experimental findings in terms of the crack propagation speed and arrest length underlining the capability of the developed numerical tool.