Coordination of impedance controllers and flexible power for curative congestion management in real-time applications

As the share of feed-in from renewable energy sources rises in German electricity grids, established preventive congestion management processes are called into question. Curative congestion management may increase the utilization of already existing grid capacity without the large investments necessary for conventional grid expansion. The curative paradigm shift requires fast reacting remedial measures, such as innovative power flow controlling devices, as well as reliable algorithms to determine and activate them in due time. This work shows how an automated system can coordinate distributed FACTS devices, that influence a power line's series reactance, and active power from flexible units to solve line overloads in high voltage grids. First, linear sensitivities for gradual reactance changes are derived. Based on this, an optimization and a heuristic approach for automated curative coordination of both types of remedial measures is conceptualized as well as implemented and tested in simulations. Then, the heuristic approach is implemented within a distributed agent-based control algorithm, along with fallback strategies to be executed if agent communication fails. This system is then tested in a laboratory setup to evaluate its real-time applicability. The laboratory setup consists of multiple (Power) Hardware-in-the-Loop modules to create an experimental environment considering many real-world factors that are usually neglected in software simulations. This way, not just the agent algorithm itself, but also the influence of communication delays, reaction times of real power flow controlling devices as well as the integration into a control center environment are evaluated

Zur tierärztlichen Ausbildung in Großbritannien und in der Bundesrepublik Deutschland

The objective of this dissertation was to depict the structural parallels and differences of veterinary education in Germany and Great Britain from the point of view of the general framework as outlined by the European Commission. One of the main differences was the definition of the occupational area of veterinary surgeons and therefore the objectives of veterinary training. While the veterinary occupational image in Great Britain targeted to animal health care, the occupational image of veterinarians in Germany was aimed towards an "polyvalent" veterinary scientist. This difference was to be reflected strongly in the undergraduate education. Already the assessment of the number to the veterinary course presented significant differences. While in Great Britain the number of admitted candidates to the veterinary course was determined by the British veterinary schools and the professional association for veterinary surgeons, the number of applicants in Germany was calculated by a formula which was defined in the "Kapazitätsverordnung". Therefore the profession in Germany was not as protected as its counterpart in Great Britain. Major discrepancies between the University of Cambridge and the Ludwig-Maximilians Universität, Munich could be found in the admission procedures. The University of Cambridge had a specific and very complex admission procedure. Various parameters shall provide to select only the most skilled applicants to sign on the course. As the number of applicants in Germany exceeded the number of places as well, the places were distributed by a central agency, the ZVS, in accordance with the entry criteria: partly taking in consideration the marks of the Abitur and partly the date of application. Simplification of the course curriculum was the main characteristic of the Cambridge course. In order to prevent repetitions of the course content, modules were formed covering a variety of subjects. In addition the practical application of the modules was emphasised. Therefore the Cambridge course showed a reduction in overall hours and para-clinical subjects as well as an orientation towards clinical practice. The target objective to introduce the students into research work was achieved by imbedding small research projects into the course. The obligation to provide adequate training in food safety was poorly achieved by the Cambridge curriculum, when compared to the Munich one. With respect to the advanced academic training, the Munich degree of a Doktor der Veterinärmedizin could correspond to three different research degrees in Great Britain: the Certificate of Postgraduate Study, the Master of Science or the Master of Philosophy. The degree of a Doctor of Philosophy was comparable to the Tiermedizinischen Habilitation on a scientific point of view but an examination of the pedagogical skills was only performed for the Tiermedizinischen Habilitation. The differences in the continuous professional development (CPD) systems in Great Britain and Germany are mainly noticable by their organisation. While the German CPD - system was one-staged and controlled through the regional professional association, the British established a three-stage CPD system, which was controlled centrally. As this dissertation aimed to discuss the strengths and weaknesses of the veterinary education in Germany and Great Britain it had to point out on the one hand the practical and efficient clinical training in Cambridge and on the other hand the widespread training on food safety in Munich.Das Ziel dieser Dissertation ist die Darstellung der strukturellen Parallelen und Unterschiede der tierärztlichen Aus- und Weiterbildung in Deutschland und Großbritannien im Rahmen der durch die Europäische Kommission gesetzten Bedingungen. Einer der wichtigsten Unterschiede ist die Definition des tiermedizinischen Berufsfeldes und somit des Ausbildungsziels. Während in Großbritannien ein auf die tierärztliche Praxis abgestimmtes Berufsbild vorherrscht, wird in Deutschland ein "polyvalenter" tiermedizinischer Wissenschaftler bevorzugt. Dieser Unterschied schlägt sich markant in der universitären Ausbildung nieder. Schon die Bemessung der Zulassungszahlen zum Studium weisen deutliche Unterschiede auf. Während in Großbritannien die Zulassungszahlen durch die Ausbildungsstätten und die tierärztliche Standesvertretung festgelegt werden, wird die Zulassungszahl in Deutschland über die Berechnungsformel der Kapazitätsverordnung definiert. Die in Großbritannien praktizierte Standessicherung kann so in Deutschland nicht stattfinden. Große Unterschiede finden sich bei den Zulassungsverfahren beider Ausbildungsstätten. Das für die University of Cambridge spezifische Zulassungsverfahren ist sehr komplex. Anhand zahlreicher Parameter sollen nur die für das Studium geeignetesten Studenten selektiert werden. Da auch in Deutschland die Zahl der Bewerber das Studienplatzangebot übersteigt, werden die Studienplätze durch eine zentrale Einrichtung, die ZVS, in verschiedenen Quoten nach den Kriterien Abiturnote und Wartezeit vergeben. Charakteristisch für das Cambridger Curriculums ist die Vereinfachung des Studienaufbaus. Um Wiederholungen des Lehrstoffes zu vermeiden, wurden die Lerninhalte fächerübergreifend zu Modulen zusammengefasst. Zudem wurde großen Wert auf die praktische Anwendung des erlernten Wissens gelegt. Daher zeichnet sich das Cambridger Studium sowohl durch eine Reduktion von Gesamtstundenzahl und paraklinischen Fächern als auch durch eine deutlich Praxisorientierung aus. Die Zielsetzung, die Studenten auch an wissenschaftliches Arbeiten heranzuführen, zeichnet sich durch die ins Studium integrierten Forschungsarbeiten ab. Das Thema "Lebensmittelsicherheit" spielt in der Cambridger Ausbildung im Vergleich zur Münchner allerdings nur eine untergeordnete Rolle. Bezüglich der akademischen Weiterbildung fällt auf, dass dem Münchner Grad des Doktors der Veterinärmedizin drei Forschungsgrade unterschiedlichen Nivaus gegenüberstehen: das "Certificate of Postgraduate Study", der "Master of Science" und der "Master of Philosophy" . Der tiermedizinischen Habilitation entspricht der Grad des "Doctor of Philosophy", wobei diesem eine Überprüfung seiner pädagogischen Fähigkeiten fehlt. Die Unterschiede, die die praktischen Weiterbildungssysteme in Großbritannien und in Deutschland kennzeichnen, ergeben sich im wesentlichen aus ihrer Organisation. Während in Deutschland ein einstufiges Weiterbildungssystem existiert, das durch eine regionale Standesvertretung kontrolliert wird, wurde in Großbritannien ein zentrales dreistufiges Weiterbildungssystem mit verschiedenen Niveaus etabliert. Da die vorliegende Untersuchung versucht, Stärken und Mängel der tiermedizinischen Aus- und Weiterbildung darzustellen, muss in diesem Zusammenhang auf die praxisbezogenere effizientere Ausbildung in Cambridge, aber auch auf die umfassendere lebensmittelkundliche Ausbildung in München verwiesen werden

Social interactions dominate speed control in driving natural flocks toward criticality

Flocks of birds exhibit a remarkable degree of coordination and collective response. It is not just that thousands of individuals fly, on average, in the same direction and at the same speed, but that even the fluctuations around the mean velocity are correlated over long distances. Quantitative measurements on flocks of starlings, in particular, show that these fluctuations are scale-free, with effective correlation lengths proportional to the linear size of the flock. Here we construct models for the joint distribution of velocities in the flock that reproduce the observed local correlations between individuals and their neighbors, as well as the variance of flight speeds across individuals, but otherwise have as little structure as possible. These minimally structured, or maximum entropy models provide quantitative, parameter-free predictions for the spread of correlations throughout the flock, and these are in excellent agreement with the data. These models are mathematically equivalent to statistical physics models for ordering in magnets, and the correct prediction of scale-free correlations arises because the parameters - completely determined by the data - are in the critical regime. In biological terms, criticality allows the flock to achieve maximal correlation across long distances with limited speed fluctuations

Emergence of collective changes in travel direction of starling flocks from individual birds fluctuations

One of the most impressive features of moving animal groups is their ability to perform sudden coherent changes in travel direction. While this collective decision can be a response to an external perturbation, such as the presence of a predator, recent studies show that such directional switching can also emerge from the intrinsic fluctuations in the individual behaviour. However, the cause and the mechanism by which such collective changes of direction occur are not fully understood yet. Here, we present an experimental study of spontaneous collective turns in natural flocks of starlings. We employ a recently developed tracking algorithm to reconstruct three-dimensional trajectories of each individual bird in the flock for the whole duration of a turning event. Our approach enables us to analyze changes in the individual behavior of every group member and reveal the emergent dynamics of turning. We show that spontaneous turns start from individuals located at the elongated edges of the flocks, and then propagate through the group. We find that birds on the edges deviate from the mean direction of motion much more frequently than other individuals, indicating that persistent localized fluctuations are the crucial ingredient for triggering a collective directional change. Finally, we quantitatively show that birds follow equal radius paths during turning allowing the flock to change orientation and redistribute risky locations among group members. The whole process of turning is a remarkable example of how a self-organized system can sustain collective changes and reorganize, while retaining coherence.Comment: 18 pages, 2 Videos adde

Inselstreit zwischen Japan und China gefährdet die regionale Stabilität in Ostasien

Im September 2012 kaufte die japanische Regierung Teile der zwischen China und Japan umstrittenen Diaoyu/Senkaku-Inselgruppe von seinen privaten Besitzern. Dies löste eine heftige Krise in den Beziehungen der beiden Staaten aus und droht die ganze Region zu destabilisieren. Die Inselgruppe ist aus wirtschaftlichen und strategischen Erwägungen interessant. In ihrem Umfeld liegen große Öl- und Gasreserven sowie reiche Fischgründe, ihre Lage ermöglicht die Kontrolle wichtiger Schifffahrtswege. Seine Explosivität zieht der Konflikt jedoch aus dem historisch belasteten Verhältnis zwischen China und Japan, an dem sich insbesondere der auf chinesischer Seite anwachsende Nationalismus immer wieder entzündet. Dieser nationalistische Druck auf beiden Seiten erklärt, warum sowohl die chinesische als auch die japanische Führung im Streit um die Diaoyu/ Senkaku-Inselgruppe nicht nachgeben können. Weiter erschwert wird die Schlichtung des Konflikts durch den Führungswechsel in China und die Unterhauswahlen in Japan. Statt die Proteste zu beruhigen, müssen die Führungen beider Staaten innenpolitisch Stärke demonstrieren. Die USA ermutigen mit ihrer Entscheidung, verstärkt militärisch im Pazifikraum aufzutreten, indirekt ihren Verbündeten Japan und provozieren gleichzeitig China. Die chinesische Führung fühlt sich durch die US-amerikanische Politik des "Pivot to the Pacific" ("zum Pazifik umschwenken") in ihrem Handlungsspielraum in Ostasien zunehmend eingeschränkt. Neben dem Konflikt um die Diaoyu/Senkaku-Inselgruppe bestehen zahlreiche weitere maritime Territorialdispute in Ost- und Südostasien. Die Region ist also nicht nur als Zentrum der Weltwirtschaft von äußerster Wichtigkeit, sondern wird immer mehr auch zur sicherheitspolitischen Hauptbühne des 21. Jahrhunderts. Sie darf daher von der EU nicht vernachlässigt werden, die vielmehr eine vermittelnde Rolle spielen kann

Operation strategies of battery energy storage systems for preventive and curative congestion management in transmission grids

Anticipating and relieving congestions is an ongoing challenge for transmission system operators. Distributed grid-scale battery energy storage systems enable operators to shift power flows and remedy congestion through virtual power lines and grid boosters. This paper includes battery energy storage systems in a combined preventive and curative congestion management optimization. First, it analyzes the impact of the two operational strategies in a case study of the German transmission grid. Furthermore, it outlines curative ad-hoc measures to overcome uncertainties during operational planning and real-time operation. The simulation results indicate that battery energy storage systems further increase the use of curative measures and reduce congestion management costs

Effect of a prebiotic mixture on intestinal comfort and general wellbeing in health

Specific carbohydrates, i.e. prebiotics such as fructo-oligosaccharide (FOS), are not digested in the small intestine but fermented in the colon. Besides beneficial health effects of an enhanced bifidobacteria population, intestinal gas production resulting from fermentation can induce abdominal symptoms. Partial replacement with slowly fermented acacia gum may attenuate side effects. The aim was to compare the effects of FOS with those of a prebiotic mixture (50% FOS and 50% acacia gum; BLEND) and a rapidly absorbed carbohydrate (maltodextrin) on general intestinal wellbeing, abdominal comfort and anorectal sensory function. Twenty volunteers (eight male and twelve female; age 20-37 years) completed this double-blind, randomised study with two cycles of a 2-week run-in phase (10g maltodextrin) followed by 5 weeks of 10g FOS or BLEND once daily, separated by a 4-week wash-out interval. Abdominal symptoms and general wellbeing were documented by telephone interview or Internet twice weekly. Rectal sensations were assessed by a visual analogue scale during a rectal barostat test after FOS and BLEND treatment. Both FOS and BLEND induced more side effects than maltodextrin. Belching was more pronounced under FOS compared with BLEND (P=0·09 for females; P=0·01 for males), and for self-reported general wellbeing strong sex differences were reported (P=0·002). Urgency scores during rectal barostat were higher with FOS than BLEND (P=0·01). Faced with a growing range of supplemented food products, consumers may benefit from prebiotic mixtures which cause fewer abdominal side effects. Sex differences must be taken in consideration when food supplements are use