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In der vorliegenden Masterarbeit wurden verschiedene Ansteuerungsstrategien für den Betrieb von dreiphasigen Active-Neutral-Point-Clamped- (ANPC) Mittelspannungs-Netzumrichtern mit Siliziumkarbid (SiC) Halbleiterschaltelementen untersucht. Durch die Vielzahl an aktiven Schaltelementen können bei der ANPC-Topologie zur Modellierung des gewünschten Ausgangssignals zahlreiche unterschiedliche Ansteuerungsstrategien eingesetzt werden. Je nach gewählter Ansteuerungsstrategie können so unter anderem die Faktoren Schalt- und Durchlassverluste, Wirkungsgrad, Verlustverteilung, Schalter- und Ausgangsschaltfrequenz, der Oberschwingungsanteil des Ausgangssignals, sowie die maximale Spannungsbelastung der Halbleiter beeinflusst werden.
Neben der elektrotechnischen Beschreibung der aktuell eingesetzten Umrichter-Technologien wurden in dieser Arbeit primär aus aktuellen Veröffentlichungen und Dissertationen verschiedene Möglichkeiten für die Ansteuerung von ANPC-Umrichter zusammengetragen und insgesamt sieben Sinus-Pulsweiten-Modulationsstrategien (S-PWM) im Detail untersucht. Hierbei wurde für jede vorgestellte Modulationsstrategie das Grundfunktionsprinzip aufgezeigt und analysiert, sowie die sich daraus ergebenden Vor- und Nachteile herausgearbeitet.
Anschließend wurden alle vorgestellten S-PWM-Strategien in der Schaltungssimulationssoftware PLECS implementiert und diese in verschiedenen Betriebszuständen simuliert. Die Simulation ergab, dass sich bei der ANPC-ALD-Strategie eine bestmögliche Verlustverteilung zwischen den Halbleiterelementen einstellt, bei der ANPC-OOZS-Strategie die geringsten Durchlassverluste entstehen und bei den Strategien ANPC-DF, -12, -R2:1 und -SSLD im Bereich der Nulldurchgänge des Ausgangssignals an den inneren Halbleitern kurzzeitige kritische Überspannungen auftreten. Bei den Strategien ANPC-11-Sync, -ALD und -OOZS treten dagegen keine Überspannungen an den Halbleitern auf.
Ausgehend von diesen Simulationsergebnissen wurden die Strategien ANPC-DF, -ALD und -OOZS für den potentiellen Einsatz in Mittelspannungsumrichtern ausgewählt, auf einem FPGA-Board implementiert und damit eine geeignete Niederspannungstestplattform in Betrieb genommen. Durch praktische Messungen auf dieser Testplattform konnten die Simulationsergebnisse in einem ersten Schritt verifiziert werden. Sowohl das erstellte Simulationsmodell als auch die in Betrieb genommene Testplattform können somit zukünftig für weitere Untersuchungen im Bereich der ANPC-Umrichter-Ansteuerungsstrategien eingesetzt werden.
This thesis has the purpose to investigate the oil price as the global economic factor but also to examine its implications on the worldwide economy. Thereby the determinants of the oil price are investigated by tackling the oil price itself from three different perspectives – the supply and demand framework, the prevailing world oil market structure as well as from the perspective of already statistically proven oil price determinants. In addition, the arising macroeconomic implications of oil price fluctuations on oil-importing and oil-exporting countries are examined. The investigation based on a thought experiment demonstrates the supply and demand framework to be unable to fully explain all past price changes. The examination on the prevailing market structure identifies the world oil market to be best described as a supply, pure, closed, partial and collusive form of an oligopoly. Analyzing the competitive behavior of the world oil market on three levels identifies non-OPEC producers’ competition to behave in a Cournot manner whereas among OPEC producers Saudi Arabia is identified to be a Stackelberg-follower with certain conditions while at the same time permanently bearing the ambition to become the Stackelberg-leader. The identification on the best describing oligopoly model for the overall industry is inconclusive. Investigating OPEC’s cartel hypothesis does not fully exclude its collusive behavior but denies the OPEC to be described as a prime example of a cartel. The examination of already existing econometric analyses identified a total of 13 determinants to play a key role in the oil price definition process. Investigating the arising macroeconomic implications of oil price fluctuations show oil price changes to be of great importance for the overall economic performance and is best described as a form of a positive of negative vicious circle in which the interconnected second or even third round effects intensify the implications on the macroeconomic activity.
The pivotal role of the service industry in the economy is increasing over the last decades, as shown by the significant contribution to the GDP made by travel and tourism. Among the varied range of travel companies, this paper focuses on travel agencies. The objective of the thesis is to find out the key drivers, which lead to the success of European travel agencies and to point out the factors that make them unable to compete and develop sustainably. This paper uses the PESTEL model, Porter’s Five Forces model analysis, flywheel concept and spontaneously conducted interviews with travel and tourism industry experts. A case study approach is adopted. There is also the analysis of the financial statements, business model and strategies of the top 15 world-leading travel agencies to find out the market structures and competitors’ behaviors. From the collected data and examination, three primary factors that lead to the sustainable development of travel agencies and four main factors that decreed the failure were identified. Besides, the research also finds out the answer for the three research questions: technology is the disruptive forces in the travel agency industry, there will be no monopoly in this industry at least in the next medium-term, and the adaptation of a new business model is possible. Finally, the study proposed a sustainable development model for a European travel agency as well as directions for future relevant research.
Nowadays, big sport events such as Olympic Games are not only an exciting carnival for sports enthusiasts, but also a good opportunity for the host country/city to accelerate its economic development. After more than 40 years of development, Computable General Equilibrium has been proved to be a very powerful tool to analyze the impact of big sports events on host country/city. In this paper, 2008 Beijing Olympic Games will be used as the target case to study the impact on the economy. A Supply model and a demand model will be established according to CGE theory to describe the case. This paper is not focused on the detail but the whole picture of Beijing’s economy by analyzing the industrial structure changes under the influences of hosting the Olympic. Beijing’s industrial structure development will also be analyzed in this paper.
This thesis aims to provide a comprehensive and systematic analysis about the growing popularity of Korean pop music (K-pop) worldwide in recent years. On one hand, the international expansion of K-pop can be understood as a result of the strategic planning and business execution that are created and carried out by the entertainment agencies. On the other hand, external circumstances such as the rise of social media also create a wide array of opportunities for K-pop to broaden its global appeal. The research explores the ways how the interplay between external circumstances and organizational strategies has jointly contributed to the global circulation of K-pop. The research starts with providing a general descriptive overview of K-pop. Following that, quantitative methods are applied to measure and assess the international recognition and global spread of K-pop. Next, a systematic approach is used to identify and analyze factors and forces that have important influences and implications on K-pop’s globalization. The analysis is carried out based on three levels of business environment which are macro, operating, and internal level. PEST analysis is applied to identify critical macro-environmental factors including political, economic, socio-cultural, and technological. On the industrial level, major forces that shape the music industry in which K-pop’s business operates are evaluated based on the framework of Porter’s Five Forces. External environmental analysis is followed by the review of the global strategies of major Korean entertainment companies in achieving their organizational objective of turning K-pop into a successful global business. We identify all the key value-creating activities ranging from talent acquisition to customer relationship management in the value chain of K-pop’s industry, and analyze how each of these activities have contributed to K-pop’s success in the global market. In conclusion, the recent success of K-pop on the global stage can be understood as the rewards for the capability of its internal strategy to anticipate and capitalize new opportunities in external environment.
This thesis investigates the effect choice options in e-commerce applications have on consumers’ decision making. Previous research showed that a large number of options
can affect consumers negatively. However, the conditions for such choice overload are unclear. After reviewing the existing research, the amount of information (entropy)
contained in a choice set and individual differences were determined as possible influencing factors in an online environment. In a choice experiment, choice sets with
varying information loads and an assessment of the Big Five personality traits were used to test the impact of the two identified factors on choice avoidance behavior. Results from chi-square-tests and a logistic regression model suggest choice overload but without entropy having an effect. A logistic regression model revealed that extraverted consumers are easier overloaded. A low Neuroticism score was found to be related to less occurrence of a too-much-choice-effect. Consumers with a high Openness score on the other hand choose one of the presented options more often and were therefore less often
overwhelmed by the assortment. An interaction effect between personality and the amount of entropy was not found. These findings extend the research on choice overload and offer valuable input for marketers targeting consumers online.
The Syrian Refugee Crisis in Germany has been lately a constant research topic in many fields; politics, economics, cultural, social and safety aspects etc. popping up in all the news worldwide. Everybody is concerned about it and tackling it from a different point of view. Some believe that it a mutual benefit to both the country (Germany) and the refugees. As Germany benefits a lot form the cheap labor of migrant workers in the different industries. Specially the fast growing industries like the rural ones. Others fear that they will weaken the German culture and economy. And that they are burdens on the national people and will cause many problems.
In this paper two aspects of the challenges facing the Syrian refugees in Germany are discussed: the first is their integration and acculturation with the German society and the second is the challenges facing the refugees in entering the German labor market and case studies of Syrian entrepreneurs who developed their own family businesses in Germany are presented. The interviews were held with Syrian refugees in the state of Baden-Württemberg in 2015/2016 in Arabic language. The groups that were interviewed were in Villingen-Schwenningen and Stuttgart. An analysis of the cases presented along with the findings of the surveys and interviews are presented and finally some recommendations are suggested.
Subject of the thesis at hand is the analysis of symmetric block ciphers with a block length of 32 bit. It is meant to give a comprising overview over the topic of 32 bit block ciphers. The topic is divided in the examination of three questions. It contains a list of state of the art block ciphers with a block length of 32 bit. The block ciphers are being described, focussing on the encryption function. An SPN-based cipher with 32 bit block length is being proposed by rescaling the AES cipher.
The 32 bit block length results in certain security issues. These so called risk factors are analysed and mitigating measures are proposed. The result of the thesis is, that 32 bit block ciphers can be implemented in a secure manner. The use of 32 bit ciphers should be limited to specific use-cases and with a profound risk analysis, to determine the protection class of the data to be encrypted.