Among the multilevel (ML)-voltage source converters (VSCs) for medium voltage (MV) and high power (HP) applications, the most used power topology is the three level (3L)-neutral point clamped (NPC)-VSC, due to its features such as common direct current (DC)-bus capability with medium point, absence of switches in series-connection, low part count, and straightforward control. The use of MV-insulated gate bipolar transistor (IGBT) modules as power switches offers further advantages like inexpensive gate drivers and survival capability after short-circuit. However, the IGBT modules have a reduced life cycle due to thermal stress generated by load cycles. Despite the advantages of the 3L-NPC-VSC, its main drawback is the uneven power loss distribution among its power devices. To address this issue and to improve other characteristics, more advanced ML converters have been developed. The 3L-active neutral point clamped (ANPC)-VSC allows an improved power loss distribution thanks to its additional IGBTs, which increase the number of feasible zero-states, but needs a loss balancing scheme to choose the proper redundant zero-state and a more complex commutation sequence between states. The 3L-neutral point piloted (NPP)-VSC improves the power loss distribution thanks to the use of series-connected switches between the output terminal and the positive and negative DC-link terminals. Other advanced power topologies with higher amount of levels include the 5L-ANPC-VSC, which has a flying capacitor per phase to generate the additional levels; and the 5L-stacked multicell converter (SMC), which needs two flying capacitors per phase. The goal of this work is to is to evaluate the performance of the aforementioned NPC-type ML converters with common DC-link, included the ones with flying capacitors, in terms of the power loss distribution and the junction temperature of the most stressed devices, which define, along with the nominal output voltage, the maximum power the converter can deliver. A second objective of this work is to describe the commutations of a MV 3L-ANPC-VSC phase leg prototype with IGBT modules, including all the intermediate switching states to generate the desired commutations.:Figures and Tables V Glossary XIII 1. Introduction 1 2. State of the art of medium voltage source converters and power semiconductors 5 2.1. Overview of medium voltage source converters 5 2.1.1. Multilevel Voltage Source Converter topologies 6 2.1.2. Application oriented basic characteristic of IGCTs and IGBTs 10 2.1.3. Market overview of ML-VSCs 11 2.2. IGBT modules for MV applications 12 2.2.1. Structure and Function 12 2.2.2. Electrical characteristics of the IGBT modules 15 2.2.3. Power losses and junction temperatures estimation 17 2.2.4. Packaging 19 2.2.5. Reliability and Life cycle of IGBT modules 21 2.2.6. Market Overview 23 2.3. Summary of Chapter 2 23 3. Structure, function and characteristics of NPC-based VSCs 25 3.1. The 3L-NPC-VSC 25 3.1.1. Power Topology 25 3.1.2. Switching states, current paths and blocking voltage distribution 26 3.1.3. Modulation of three-level inverters 28 3.1.4. Power loss distribution 32 3.1.5. “Short” and “long” commutation paths 33 3.2. The 3L-NPP-VSC 34 3.2.1. Power Topology 34 3.2.2. Switching states, current paths and blocking voltage distribution 35 3.2.3. Power Loss distribution 36 3.3. The 3L-ANPC-VSC 37 3.3.1. Power Topology 37 3.3.2. Switching states, current paths and blocking voltage distribution 38 3.3.3. Commutations and power loss distribution 39 3.3.4. Loss balancing schemes 57 3.4. The 5L-ANPC-VSC 60 3.4.1. Power Topology 60 3.4.2. Switching states, current paths and blocking voltage distribution 61 3.4.3. Commutation sequences 62 3.4.4. Power Loss distribution 70 3.4.5. Modulation and balancing strategies of capacitor voltages 70 3.5. The 5L-SMC 74 3.5.1. Power Topology 74 3.5.2. Switching states, current paths and blocking voltage distribution 75 3.5.3. Commutations and power loss distribution 78 3.5.4. Modulation and balancing strategies of capacitor voltages 80 3.6. Summary of Chapter 3 81 4. Comparative evaluation and performance of NPC-based converters 83 4.1. Motivation and goal of the comparisons 83 4.2. Basis of the comparison 83 4.2.1. Simulation scheme 85 4.2.2. Losses and thermal models for (4.5 kV, 1.2 kA) IGBT modules 86 4.2.3. Operating points, modulation, controllers and general parameters 88 4.2.4. Life cycle estimation 94 4.3. Simulation results of the 3.3 kV 3L-VSCs 97 4.3.1. Loss distribution and temperature at equal phase current 97 4.3.2. Maximum phase current 109 4.3.3. Life cycle 111 4.4. Simulation results of the 6.6 kV 5L and 3L-VSCs 115 4.4.1. Loss distribution and temperature at equal phase current 115 4.4.2. Maximum phase current 120 4.4.3. Life cycle 128 4.5. Summary of Chapter 4 132 5. Experimental investigation of the 3L-ANPC-VSC with IGBT modules 135 5.1. Goal of the work 135 5.2. Description of the 3L-ANPC-VSC test bench 136 5.2.1. Medium voltage stage 136 5.2.2. Gate drivers and digital signal handling 138 5.2.3. Measurement equipment 139 5.3. Double-pulse test and commutation sequences 140 5.3.1. Description of the double-pulse test for the 3L-ANPC-VSC 140 5.3.2. Commutation sequences for the double-pulse test 142 5.4. Commutation measurements 142 5.4.1. Switching and transition times 144 5.4.2. Type I commutations 145 5.4.3. Type I-U commutations 150 5.4.4. Type II commutations 150 5.4.5. Type III commutations 157 5.4.6. Comparison of the commutation times 157 5.4.7. Stray inductances of the “short” and “long” commutations 163 5.5. Summary of Chapter 5 167 6. Conclusions 169 Appendices 173 A. Thermal model of IGBT modules 175 A.1. General “Y” model 175 A.2. “Foster” thermal circuit 177 A.3. “Cauer” thermal circuit 178 A.4. From “Foster” to “Cauer” 179 A.5. Temperature comparison using “Foster” and “Cauer” networks 181 B. The “Rainflow” cycle counting algorithm 183 C. Description of the wind generator example 187 C.1. Simulation models 188 C.1.1. Wind turbine 188 C.1.2. Synchronous generator, grid and choke filter 189 C.1.3. Converters 189 C.2. Controllers 190 C.2.1. MPPT scheme 190 C.2.2. Pitch angle controller 191 C.2.3. Generator side VSC 192 C.2.4. Grid side VSC 193 D. 3D-surfaces of the maximum load currents in NPC-based converters 195 Bibliography 201 Bibliography 201 / Unter den Multilevel-Spannungsumrichtern für Mittelspannungs- und Hochleistungsanwendungen ist die am häufigsten verwendete Leistungstopologie der NPC-VSC, wegen seinen Merkmalen wie die Gleichstrom-Bus fähigkeit mit mittlerem Punkt, das Fehlen von Schaltern in Reihenschaltung, eine geringe Anzahl von Bauteilen und eine einfache Steuerung. Die Verwendung von Bipolartransistor Modulen mit isolierter Gate-Elektrode als Leistungsschalter bietet weitere Vorteile wie kostengünstige Gatetreiber und Überlebensfähigkeit nach einem Kurzschluss. Die IGBT-Module haben jedoch aufgrund der durch Lastzyklen erzeugten thermischen Belastung eine verkürzte Lebensdauer. Trotz der Vorteile des 3L-NPC-VSC ist der Hauptnachteil die ungleichmäßige Verteilung der Leistungsverluste zwischen den Leistungsgeräten. Um dieses Problem zu beheben und andere Eigenschaften zu verbessern, wurden fortgeschrittenere ML-Konverter entwickelt. Das 3L-ANPC-VSC ermöglicht dank seiner zusätzlichen IGBTs eine verbesserte Verlustleistungsverteilung, wodurch die Anzahl der möglichen Null-Zustände erhöht wird, es ist jedoch ein Verlustausgleichsschema erforderlich, um den richtigen redundanten Null-Zustand, und benötigt auszuwählende komplexere Kommutierungssequenz zwischen Zuständen. Das 3L-NPP-VSC verbessert die Verlustleistungsverteilung durch die Verwendung von in Reihe geschalteten Schaltern zwischen der Ausgangsklemme und den positiven und negativen Zwischenkreisklemmen. Andere fortgeschrittene Leistungstopologien mit einer höheren Anzahl von Stufen umfassen den 5L-ANPC-VSC, der pro Phase einen fliegenden Kondensator zur Erzeugung der zusätzlichen Stufen aufweist; und den 5L-SMC, der pro Phase zwei fliegende Kondensatoren benötigt. Das Ziel dieser Arbeit ist es, die Leistung der oben genannten NPC-VSC, einschließlich der mit fliegenden Kondensatoren, hinsichtlich der Verlustleistungsverteilung und der Sperrschichttemperatur der am stärksten beanspruchten Geräte zu bewerten. Diese definieren zusammen mit der Nennausgangsspannung die maximale Leistung, die der Umrichter liefern kann. Ein zweites Ziel dieser Arbeit ist die Beschreibung der Kommutierungen eines MV 3L-ANPC-VSC- Prototyps mit IGBT-Modulen einschließlich aller Zwischenschaltzustände, um die gewünschten Kommutierungen zu erzeugen.:Figures and Tables V Glossary XIII 1. Introduction 1 2. State of the art of medium voltage source converters and power semiconductors 5 2.1. Overview of medium voltage source converters 5 2.1.1. Multilevel Voltage Source Converter topologies 6 2.1.2. Application oriented basic characteristic of IGCTs and IGBTs 10 2.1.3. Market overview of ML-VSCs 11 2.2. IGBT modules for MV applications 12 2.2.1. Structure and Function 12 2.2.2. Electrical characteristics of the IGBT modules 15 2.2.3. Power losses and junction temperatures estimation 17 2.2.4. Packaging 19 2.2.5. Reliability and Life cycle of IGBT modules 21 2.2.6. Market Overview 23 2.3. Summary of Chapter 2 23 3. Structure, function and characteristics of NPC-based VSCs 25 3.1. The 3L-NPC-VSC 25 3.1.1. Power Topology 25 3.1.2. Switching states, current paths and blocking voltage distribution 26 3.1.3. Modulation of three-level inverters 28 3.1.4. Power loss distribution 32 3.1.5. “Short” and “long” commutation paths 33 3.2. The 3L-NPP-VSC 34 3.2.1. Power Topology 34 3.2.2. Switching states, current paths and blocking voltage distribution 35 3.2.3. Power Loss distribution 36 3.3. The 3L-ANPC-VSC 37 3.3.1. Power Topology 37 3.3.2. Switching states, current paths and blocking voltage distribution 38 3.3.3. Commutations and power loss distribution 39 3.3.4. Loss balancing schemes 57 3.4. The 5L-ANPC-VSC 60 3.4.1. Power Topology 60 3.4.2. Switching states, current paths and blocking voltage distribution 61 3.4.3. Commutation sequences 62 3.4.4. Power Loss distribution 70 3.4.5. Modulation and balancing strategies of capacitor voltages 70 3.5. The 5L-SMC 74 3.5.1. Power Topology 74 3.5.2. Switching states, current paths and blocking voltage distribution 75 3.5.3. Commutations and power loss distribution 78 3.5.4. Modulation and balancing strategies of capacitor voltages 80 3.6. Summary of Chapter 3 81 4. Comparative evaluation and performance of NPC-based converters 83 4.1. Motivation and goal of the comparisons 83 4.2. Basis of the comparison 83 4.2.1. Simulation scheme 85 4.2.2. Losses and thermal models for (4.5 kV, 1.2 kA) IGBT modules 86 4.2.3. Operating points, modulation, controllers and general parameters 88 4.2.4. Life cycle estimation 94 4.3. Simulation results of the 3.3 kV 3L-VSCs 97 4.3.1. Loss distribution and temperature at equal phase current 97 4.3.2. Maximum phase current 109 4.3.3. Life cycle 111 4.4. Simulation results of the 6.6 kV 5L and 3L-VSCs 115 4.4.1. Loss distribution and temperature at equal phase current 115 4.4.2. Maximum phase current 120 4.4.3. Life cycle 128 4.5. Summary of Chapter 4 132 5. Experimental investigation of the 3L-ANPC-VSC with IGBT modules 135 5.1. Goal of the work 135 5.2. Description of the 3L-ANPC-VSC test bench 136 5.2.1. Medium voltage stage 136 5.2.2. Gate drivers and digital signal handling 138 5.2.3. Measurement equipment 139 5.3. Double-pulse test and commutation sequences 140 5.3.1. Description of the double-pulse test for the 3L-ANPC-VSC 140 5.3.2. Commutation sequences for the double-pulse test 142 5.4. Commutation measurements 142 5.4.1. Switching and transition times 144 5.4.2. Type I commutations 145 5.4.3. Type I-U commutations 150 5.4.4. Type II commutations 150 5.4.5. Type III commutations 157 5.4.6. Comparison of the commutation times 157 5.4.7. Stray inductances of the “short” and “long” commutations 163 5.5. Summary of Chapter 5 167 6. Conclusions 169 Appendices 173 A. Thermal model of IGBT modules 175 A.1. General “Y” model 175 A.2. “Foster” thermal circuit 177 A.3. “Cauer” thermal circuit 178 A.4. From “Foster” to “Cauer” 179 A.5. Temperature comparison using “Foster” and “Cauer” networks 181 B. The “Rainflow” cycle counting algorithm 183 C. Description of the wind generator example 187 C.1. Simulation models 188 C.1.1. Wind turbine 188 C.1.2. Synchronous generator, grid and choke filter 189 C.1.3. Converters 189 C.2. Controllers 190 C.2.1. MPPT scheme 190 C.2.2. Pitch angle controller 191 C.2.3. Generator side VSC 192 C.2.4. Grid side VSC 193 D. 3D-surfaces of the maximum load currents in NPC-based converters 195 Bibliography 201 Bibliography 201

Background. Game developers are continuously searching for new ways of populating their vast game worlds with competent and engaging Non-Player Characters (NPCs), and researchers believe Deep Reinforcement Learning (DRL) might be the solution for emergent behavior. Consequently, fusing NPCs with DRL practices has surged in recent years, however, proposed solutions rarely outperform traditional script-based NPCs. Objectives. This thesis explores a novel method of developing an adversarial DRL NPC by combining Reinforcement Learning (RL) algorithms. Our goal is to produce an agent that surpasses its script-based opponents by first mimicking their actions. Methods. The experiment commences with Imitation Learning (IL) before proceeding with supplementary DRL training where the agent is expected to improve its strategies. Lastly, we make all agents participate in 100-deathmatch tournaments to statistically evaluate and differentiate their deathmatch performances. Results. Statistical tests reveal that the agents reliably differ from one another and that our learning agent performed poorly in comparison to its script-based opponents. Conclusions. Based on our computed statistics, we can conclude that our solution was unsuccessful in developing a talented hostile DRL agent as it was unable to convey any form of proficiency in deathmatches. No further improvements could be applied to our ML agent due to the time constraints. However, we believe our outcome can be used as a stepping-stone for future experiments within this branch of research.

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Ces travaux de thèse consistent en la conception et la réalisation d’une chaîne de tractionintégrée pour véhicule hybride plug-in. L’étude s’oriente vers une solution de convertisseur mutualisé,dans l’objectif de partager la traction et les modes chargeurs de batteries, la structure en NPC à 3niveaux est retenue. Le chargeur monophasé se base une topologie de redresseur à MLI monophaséavec trois bras entrelacés, avec l’utilisation des enroulements du moteur pour le filtrage. En chargeurtriphasé nous adaptons la topologie pour réaliser un montage en double boost triphasé. Pour chaqueconfiguration, les passifs sont dimensionnés pour répondre aux contraintes en courant BF et HF. Lecontrôle adopté se base sur les correcteurs résonants. Enfin, un prototype de 5 kW a été réalisé pourvalider les différents modes de l’application.Dans une seconde partie, nous proposons une solution de chargeur isolé sans étage continu auprimaire à double ponts actifs (DAB). La topologie est modélisée au premier harmonique et unecommande assurant l’absorption sinusoïdale est étudiée. Une configuration isolée triphasée permetl’accès aux puissances plus élevées ainsi que la réduction des ondulations de courant BF en sortie. / This thesis consists on the design and realization of a plug-in hybrid vehicle integrated tractiondrive supply. The work turns to a solution of a mutualized converter, in the objective to imagine asolution which shared drive and battery chargers modes, the three-level NPC topology has beenretained. The single phase charger is based on an interleaved PWM rectifier, and motor windings areused as smoothing inductors. A double-boost PFC configuration is introduced to ensure the threephasecharger. Passives are sized in each configuration in order to take in account the whole currentconstraints (LF and HF). The PFC behavior is based on the resonant controllers. Then, a 5 kWprototype has been realized to validate the different application modes.In a second part, a single-stage isolated charger based on a Dual-Active-Bridge (DAB) isproposed. The topology is modeled to the fundamental and the PFC control law is studied. A threephaseconfiguration is simulated in order to achieve higher charging powers and to reduce batterycurrent low-frequency ripple.

香港在西元1997年7月1日正式脫離英屬殖民地，回歸中國成為中華人民共和國領土的一部分，為了維持香港的穩定繁榮，中共以一國兩制、港人治港做為治港方針，並以中國憲法及在1990年通過並推行香港特別行政區基本法相關條例作為法律依據，給予港人高度自治的權力。 基本法推行至今業已九年，九年當中，中國最高立法機關全國人大常委會對基本法當中的模糊地界先後進行了包括「居港權案」、「雙普選案」以及「特首任期」案等三次釋法；人大釋法雖是寫入中華人民共和國憲法與基本法當中的合理權力，但在這三次釋法的過程中，仍存在有釋法的合法性、與中央是否干涉香港自治的爭議，這些爭議引起香港各界極大的討論，同時也影響了港人對一國兩制在港推行的信心。 香港特區基本法是以中國憲法做為依據的，其法律地位從屬於憲法，換言之，香港特區的自治權乃是由國家主權所派生出之地方自治權利。然而，所謂「一國兩制」，其最高原則就在於所謂「高度自治」之精神，因此，三次主要由北京當局主導的釋法行動難免引發中央過度干涉香港事務的疑慮，本文針對三次人大釋法之源起、內容、過程、及其所引發的爭議為主軸，試圖釐清中共中央是否意圖箝制香港的自治權限、抑或相關爭議只是港人過度恐慌所致？此外，特區政府與特區行政長官在釋法的過程當中又扮演何種角色？他們是否曾如實地反應民意？或者只是積極地配合中央，在相當程度上放棄自我管治的權利？這都是文中所欲釐清的焦點。撰者寄望能由本研究看出中共所大力宣揚的思想成就──「一國兩制」是否真能確實落實，也可為台灣在思考對中國大陸政策時更具體的思考方向。 關鍵詞：香港、基本法、一國兩制、人大釋法、中港關係 / Hong Kong has been a Special Administrative Region (SAR) of People’s Republic of China (PRC) since 1997, it maintains a high degree autonomy except it matters of defense and foreign affairs. It has well-established institutions that support the rule of law and vigorous civil society by the Basic Law. The Basic Law has been published in nine years. During this period, The Standing Committee of PRC’s National People’s Congress (NPC) has been approved to interpret the law for three times. Although the interpretation rights of The Standing Committee of NPC is undeniable, those moves are still causing a great deal of concerns---such as the validity of judicial procedure of interpretations and whether the PRC government interfere with the Hong Kong’s autonomy affairs or not, and so on…. Those controversial issues are not only causing a huge controversy over Hong Kong society, but also lower people's confidence in “one country, two systems”. If the Standing Committee of NPC’s thrice interpretation actions were just reflecting part of NPC membership’s opinions and Bejing’s will but totally disregarded of the view of the Hong Kong people. It will not only cripple the power of legal interpretation of Hong Kong’s judicial body. And even worse, it might cause Hong Kong’s judicial system towards to the mainland one. Meanwhile, by vesting power jointly with Bejing and the HK chief executive, the mainland authorities have succeeded in bring public opinions in HK under their thumb. This essay is aimed at the thrice interpretations, including the source, contents, process and the following issues. The NPC interpretations will have a deep impact on the development of HK’s judicial and political system. I believe, by observing the following situation after the interpretations in the HK, we will have a better understanding of the “one country, two systems”. Keywords：Hong Kong, Basic Law, One country two systems, the NPC interpretations, National People’s congress.

The purpose of the study was to get a better understanding of how players’ engagement is affected by the narrative techniques which are used in the game Dark Souls II. The four most prominent narrative techniques that were analyzed in Dark souls II were cutscenes, item descriptions, NPC’s and environmental storytelling. Qualitative and Quantitative data was collected in a questionnaire that was posted on the forum/ “subreddit” Dark souls II. The answers from 100 questionnaires were analyzed using content analysis methodology. It could be concluded in this thesis that narrative techniques that interfere with the players sense of freedom will reduce their engagement within the game. An example in Dark souls II is when the player is forced to summon NPC’s to boss fights in order to progress in the NPC’s storyline. This also works the other way around: i.e. the player experiences increased engagement if the narrative techniques allow the player to decide over their own actions. An example in Dark Souls II is when the player is given the opportunity to kill friendly NPC’s. / Syftet med denna studie var att få en bättre förståelse för hur spelarens engagemang påverkas av de narrativa tekniker som används i spelet Dark Souls II. De fyra mest framstående narrativa tekniker som identifierades i Dark Souls II var Cutscenes, föremålsbeskrivningar, NPC’s och miljöberättande. Kvalitativ och kvantitativa data samlades genom en enkät som lades upp på Dark Souls II forum/ ”subreddit”. Svaren från 100 deltagare tolkades med koder samt kategorier genom metodologin innehållsanalys. I denna studie kunde det konstateras att narrativa tekniker som negativt påverkar spelarens frihet, kommer reducera deras engagemang i spelet. Detta noterades bland annat när spelare var tvungna att kalla på NPC’s till bossfighter för att kunna fortsätta denna NPC’s uppdrag. Det angavs även att detta fungerade åt andra hållet, när spelarens förmåga att kunna ta egna beslut tilläts så ökade även spelarens engagemang i spelet. Detta noterades i spelmekaniken att spelaren bland annat tilläts döda fredliga NPC’s.

In the past two decades the core aircraft technology is going through a drastic change. The traditional technologies that is almost half a century old, is going through a complete revamp. In the new “More Electric Aircraft” technology many mechanical, pneumatic and hydraulic systems are being replaced by electrical and power electronic systems. Airbus-A380, Boeing B-787 are the pioneers in the family of these new breed of aircrafts. As the aircraft technology is moving towards “More Electric”, more and more electric motors and motor controllers are being used in new aircrafts. Number of electric motor drive systems has increased by about ten times in more electric aircrafts compared to traditional aircrafts. Weight of any electric component that goes into aircraft needs to be low to reduce the overall weight of aircraft so as to improve the fuel efficiency of the aircraft. Hence there is an increased need to reduce weight of motors and motor controllers in commercial aircraft. High speed ironless axial flux permanent magnet brushless dc motors are becoming popular in the new more-electric aircrafts because of their ability to meet the demand of light weight, high power density, high efficiency and high reliability. However, these motors come with very low inductance, which poses a big challenge to the motor controllers in controlling the ripple current in motor windings. Multilevel inverters can solve this problem. Three-level inverters are proposed in this thesis for driving axial flux BLDC motors in aircraft. Majority of the motors in new more electric aircrafts are in the power range of 2kW to 20kW, while a few motor applications being in the range of 100kW to 150kW. Motor controllers in these applications run from 270Vdc or 540Vdc bus which is the standard in new more electric aircraft architecture. Multilevel Inverter is popular in the industry for high power and high voltage applications, where high-voltage power switching devices like IGBT, GTO are popularly used. However multilevel inverters have not been tried in the low power range which is appropriate for aircraft applications. A detail analysis of practical feasibility of constructing three-level inverter in lower power and voltage level is presented in this thesis. Analysis is presented that verify the advantages of driving low voltage and low power (300Vdc to 600Vdc and less than 100kW) motors with multilevel inverters. Practical considerations for design of MOSFET based three-level inverter are investigated and topological modifications are suggested. The effect of clamping diodes in the diode clamped multilevel inverters play an important role in determining its efficiency. SiC diodes are proposed to be used as clamping diodes. Further, it is realised that power loss introduced by reverse recovery of MOSFET body diode prohibits use of MOSFET in hard switched inverter legs. Hence, a technique of avoiding the reverse recovery losses of MOSFET body diode in three-level NPC inverter is conceived. The use of proposed multilevel inverter topology enables operation at high switching frequency without sacrificing efficiency. High switching frequency of operation reduces the output filter requirement, which in turn helps reducing size of the inverter. In this research work elaborate trade-off analysis is done to quantify the suitability of multilevel inverters in the low power applications. For successful operation of three-level NPC inverter in aircraft electrical system, it is important for the DC bus structure in aircraft electric primary distribution system to be compatible to drive NPC inverters. Hence a detail study of AC to DC power conversion system as applied to commercial aircraft electrical system is done. Multi-pulse rectifiers using autotransformers are used in aircrafts. Investigation is done to improve these rectifiers for future aircrafts, such that they can support new technologies of future generation motor controllers. A new 24-pulse isolated transformer rectifier topology is proposed. From two 15º displaced 6-phase systems feeding two 12-pulse rectifiers that are series connected, a 24-pulse rectifier topology is obtained. Though, windings of each 12-pulse rectifiers are isolated from primary, the 6-phase generation is done without any isolation of the transformer windings. The new 24-pulse transformer topology has lower VA rating compared to standard 12-pulse rectifiers. Though the new 24-pulse transformer-rectifier solution is robust and simple, it adds to the weight of the overall system, as compared to the present architecture as the proposed topology uses isolated transformer. Non-isolated autotransformer cannot provide split voltage at the dc-link that creates a stable mid-point voltage as required by the three-level NPC inverter. Hence, a new front-end AC-DC power conversion system with switched capacitor is conceived that can support motor controllers driven by three-level inverters. Laboratory experimental results are presented to validate the new proposed topology. In this proposed topology, the inverter dc-link voltage is double the input dc-link voltage. An intense research work is performed to understand the operation of Trapezoidal Back EMF BLDC motor driven by three-Level NPC inverter. Operation of BLDC motor from three-Level inverter is primarily advantageous for low inductance motors, like ironless axial flux motors. For low inductance BLDC motor, very high switching frequency is required to limit the magnitude of ripple current in motor winding. Three-level inverters help limiting the magnitude of motor ripple current without increasing the switching frequency to very high value. Further, it is analysed that dc link mid-point current in three-level NPC inverter for driving trapezoidal BLDC motor has a zero average current with fundamental frequency same as switching frequency. Because of this, trapezoidal BLDC motors can easily be operated from three-level NPC inverter without any special attention given to mid-point voltage unbalance. One non-ideal condition arrives in practical implementation of the inverter that leads to non-zero average mid point current. Unequal gate drive dead time delays from one leg to other leg of inverter introduce dc-link mid-point voltage unbalance. For the motoring mode operation of trapezoidal BLDC motor drive, simple gate drive logic is researched that eliminates need of the gate drive dead-time, and hence solves the mid-point voltage unbalance issue. Simple closed loop control scheme for mid-point voltage balancing also is also proposed. This control scheme may be used in applications where very precise control of speed and torque ripple is warranted. All the investigations reported in this thesis are simulated extensively on MATHCAD and MATLAB platform using SIMULINK toolbox. A laboratory experimental set-up of three-Level inverter driving axial flux BLDC motor is built. The three-level inverter, operating from 300Vdc bus is built using 500V MOSFETs and 600V SiC diodes. All the control schemes are implemented digitally on digital signal processor TMS320F2812 DSP platform and GAL22V10B platforms. Experimental results are collected to validate the theoretical propositions made in the present research work. At the end, in chapter 5, some future works are proposed. A new external voltage balance circuit is proposed where the inverter dc-link voltage is same as the input dc-link voltage. This topology is based on the resonant converter principle and uses a lighter resonant inductor than prior arts available in literature. Detail simulation and experimentation of this topology may be carried out to validate the industrial benefits of this circuit. It is also thought that current source inverters may work as an alternative to voltage source inverters for driving BLDC motors. Current source inverters eliminate use of bulky DC-link capacitors. Long term reliability of current source inverters is higher than voltage source inverters due to the absence of possibility of shoot-through. Further, in voltage source inverters, the voltage at the motor terminal is limited by the source voltage (dc-link voltage). This issue is eliminated in current source inverters. An interface circuit is conceived to reduce the size of dc-link inductors in current source inverters, pending detail analysis and experimental verification. The interface circuit bases its fundamentals on the principles of operation of multilevel inverters for BLDC motors that is presented in this thesis.

The still increasing demand of electrical energy and the rising popularity of renewable energy sources in today's world are two important developments that necessitate the need for innovative solutions in the field of power electronics. Parallel operation of converters is one possible method in trying to bridge an increased current demand. The classical two-level converters, which are the standard in low voltage applications, are rarely adopted in medium and high voltage applications due to the voltage limits on power semiconductor devices. That is one reason for the growing popularity of multilevel converter topologies in medium and high-voltage applications. Although an increase in the number of voltage levels of a multilevel converter has its advantages, there are also challenges posed due to the increased number of switching devices. This has resulted in three-level converters being the most popular compared to converters of higher voltage levels. In this dissertation, the unified operation of parallel connected three-level converter units as a multilevel converter of higher voltage levels is proposed. The mathematical basis for operating parallel connected converter units as a single multilevel converter and the governing equations for such systems are derived. The analysis and the understanding of these equations are important for assessing practicality of the system and devising appropriate control structures. Parallel operation of converter units operating as multilevel converter have their own set of challenges, the two foremost being that of load-sharing and the possibility of circulating and cross currents. Developing solutions to address these challenges require a thorough understanding of how these manifest in the proposed system. Algorithms are then developed for tackling these issues. The control structures are designed and the developed algorithms are implemented. The operation of the system is verified experimentally. / Die weiterhin steigende Nachfrage nach elektrischer Energie und die zunehmende Verwendung erneuerbarer Energiequellen in der heutigen Welt sind zwei wichtige Entwicklungen, die die Notwendigkeit innovativer Lösungen im Bereich der Leistungselektronik erfordern. Der Parallelbetrieb von Stromrichtern ist eine mögliche Methode, um einen erhöhten Strombedarf zu decken. Der klassische Zweipunkt-Spanungszwischenkreisstromrichter, der bei Niederspannungsanwendungen weit verbreitet ist, wird aufgrund der Spannungsgrenzen für Leistungshalbleiterbauelemente zunehmend weniger in Mittel- und Hochspannungsanwendungen eingesetzt. Die begrenzte Spannungsbelastbarkeit der Leistungshalbleiterbauelemente ist ein Grund für die wachsende Beliebtheit von Mehrpunkt-Stromrichtertopologien in Mittelund Hochspannungsanwendungen. Obwohl eine Erhöhung der Anzahl der Spannungsstufen eines Mehrpunkt-Stromrichters Vorteile hat, gibt es auch Herausforderungen und Nachteile aufgrund der erhöhten Anzahl von Leistungshalbleitern. Dies hat dazu geführt, dass der Dreipunkt-Stromrichter die verbreiteste Topologie im Vergleich zu anderen Stromrichtern mit einer höheren Anzahl von Spannungsstufen ist. In dieser Dissertation wird der Betrieb von parallel geschalteten Dreipunkt-Stromrichtereinheiten als ein Mehrpunkt-Stromrichter mit erhöhter Anzahl an Spannungsstufen vorgeschlagen. Die mathematische Basis für den Betrieb von parallel geschalteten Stromrichtereinheiten als ein Mehrpunkt-Stromrichter und die beschreibenden Gleichungen eines solchen Systems werden abgeleitet. Die Analyse und das Verständnis dieser Gleichungen sind wichtig für die Beurteilung der Praktikabilität des Systems und die Erarbeitung geeigneter Regelstrukturen. Der parallele Betrieb von Stromrichtereinheiten hat seine eigenen Herausforderungen, wobei die beiden wichtigsten die Lastverteilung und die Möglichkeit von Kreis- und Querströmen sind. Die Entwicklung von Lösungen zur Bewältigung dieser Herausforderungen erfordert ein gründliches Verständnis dafür, wie sich diese Phänomene in dem vorgeschlagenen System manifestieren. Algorithmen zur Lösung dieser Probleme werden anschlieend entwickelt. Die Regelstrukturen werden entworfen und die entworfenen Algorithmen implementiert. Die Funktionsweise des Systems wird experimentell überprüft.

Die vorliegende Arbeit befasst sich mit einem detaillierten Vergleich von Mehrpunkt-Schaltungstopologien mit zentralem Gleichspannungszwischenkreis für den Einsatz in Mittelspannungsanwendungen. Im Rahmen dieser Untersuchungen wird die 3-Level Neutral Point Clamped Spannungswechselrichter Schaltungstopologie (3L-NPC VSC) sowohl mit Multilevel Flying Capacitor (FLC) als auch mit Multilevel Stacked Multicell (SMC) Schaltungstopologien verglichen, wobei unter Verwendung von aktuell verfügbaren IGBT-Modulen Stromrichterausgangsspannungen von 2.3 kV, 4.16 kV und 6.6 kV betrachtet werden. Neben der grundlegenden Funktionsweise wird die Auslegung der aktiven Leistungshalbleiter und der passiven Energiespeicher (Zwischenkreiskondensatoren, Flying Capacitors) für die untersuchten Stromrichtertopologien dargestellt. Unter Berücksichtigung verschiedener Modulationsverfahren und Schaltfrequenzen werden Kennwerte für den Oberschwingungsgehalt in der Ausgangsspannung und dem Ausgangsstrom vergleichend evaluiert. Die installierte Schalterleistungen, die Halbleiterausnutzungsfaktoren, die Stromrichterverlustleistungen sowie die Verlustleistungsverteilungen werden für die betrachteten Stromrichtertopologien detailliert gegenübergestellt und bewertet. / The thesis deals with a detailed comparison of voltage source converter topologies with a central dc-link energy storage device for medium voltage applications. The Three-Level Neutral Point Clamped Voltage Source Converter (3L-NPC VSC) is compared with multilevel Flying Capacitor (FLC) and Stacked Multicell (SMC) Voltage Source Converters (VSC) for output voltages of 2.3 kV, 4.16 kV and 6.6 kV by using state-of-the-art 6.5 kV, 3.3 kV, 4.5 kV and 1.7kV IGBTs. The fundamental functionality of the investigated converter topologies as well as the design of the power semiconductors and of the energy storage devices (Flying Capacitors and Dc-Link capacitors) is described. The installed switch power, converter losses, the semiconductor loss distribution, modulation strategies and the harmonic spectra are compared in detail.

Die vorliegende Arbeit befasst sich mit einem detaillierten Vergleich von Mehrpunkt-Schaltungstopologien mit zentralem Gleichspannungszwischenkreis für den Einsatz in Mittelspannungsanwendungen. Im Rahmen dieser Untersuchungen wird die 3-Level Neutral Point Clamped Spannungswechselrichter Schaltungstopologie (3L-NPC VSC) sowohl mit Multilevel Flying Capacitor (FLC) als auch mit Multilevel Stacked Multicell (SMC) Schaltungstopologien verglichen, wobei unter Verwendung von aktuell verfügbaren IGBT-Modulen Stromrichterausgangsspannungen von 2.3 kV, 4.16 kV und 6.6 kV betrachtet werden. Neben der grundlegenden Funktionsweise wird die Auslegung der aktiven Leistungshalbleiter und der passiven Energiespeicher (Zwischenkreiskondensatoren, Flying Capacitors) für die untersuchten Stromrichtertopologien dargestellt. Unter Berücksichtigung verschiedener Modulationsverfahren und Schaltfrequenzen werden Kennwerte für den Oberschwingungsgehalt in der Ausgangsspannung und dem Ausgangsstrom vergleichend evaluiert. Die installierte Schalterleistungen, die Halbleiterausnutzungsfaktoren, die Stromrichterverlustleistungen sowie die Verlustleistungsverteilungen werden für die betrachteten Stromrichtertopologien detailliert gegenübergestellt und bewertet.:Inhaltsverzeichnis Liste der Variablen i Liste der Abkürzungen v 1 Einleitung 1 2 Überblick von Mittelspannungsstromrichtertopologien und Leistungshalbleitern 3 2.1 Mittelspannungsumrichtertopologien 3 2.2 Leistungshalbleiter 8 3 Aufbau und Funktion von Mittelspannungsstromrichtertopologien 10 3.1 Neutral Point Clamped Stromrichter (NPC) 10 3.1.1 3-Level Neutral Point Clamped Stromrichter (3L-NPC) 10 3.1.2 Mehrstufige NPC-Umrichter 21 3.2 Flying Capacitor Stromrichter (FLC) 23 3.2.1 3-Level Flying Capacitor Stromrichter (3L-FLC) 23 3.2.2 4-Level Flying Capacitor-Stromrichter (4L-FLC) 33 3.2.3 Mehrstufige Flying Capacitor-Stromrichter (NL-FLC) 39 3.3 Stacked Multicell Stromrichter (SMC) 43 3.3.1 5L-Stacked Multicell Stromrichter (5L-SMC) 43 3.3.2 N-Level Stacked Multicell Umrichter (NL-SMC) 51 4 Modellierung und Auslegung der Stromrichter 59 4.1 Verlustmodell 59 4.1.1 Sperrschichttemperaturen 64 4.2 Auslegung der Leistungshalbleiter 65 4.2.1 Stromauslegung 67 4.2.2 Worst-Case Arbeitspunkte 69 4.3 Auslegung der Zwischenkreiskondensatoren 75 4.3.1 Spannungszwischenkreis 76 4.3.2 Lastseitige Strombelastung und resultierende Spannungswelligkeit im Spannungszwischenkreis 77 4.3.3 Abhängigkeit der Strombelastung und der Spannungswelligkeit im Spannungszwischenkreis vom Frequenzverhältnis mf 95 4.3.4 Netzseitige Zwischenkreiseinspeisung 97 4.3.4.1 Zwischenkreiseinspeisung mit idealisiertem Transformatormodell 98 4.3.4.2 Zwischenkreiseinspeisung mit erweitertem Transformatormodell 101 4.3.5 Simulation des Gesamtsystems 104 4.4 Auslegung der Flying Capacitors 107 4.4.1 Strombelastung der Flying Capacitors 109 4.4.2 Spannungswelligkeit über den Flying Capacitors 113 4.4.3 Abhängigkeit der Spannungswelligkeit der Flying Capacitors vom Frequenzverhältnis mf 124 4.4.4 Auswirkung der Spannungswelligkeit der Flying Capacitors auf die Ausgangsspannungen 126 5 Vergleich der Stromrichtertopologien 129 5.1 Daten für den Stromrichtervergleich 129 5.2 Basis des Vergleiches 132 5.3 Vergleich für einen 2,3 kV Mittelspannungsstromrichter 134 5.3.1 Vergleich bei verschiedenen Schaltfrequenzen 134 5.3.2 Vergleich bei maximaler Trägerfrequenz 142 5.4 Vergleich für einen 4,16 kV Mittelspannungsstromrichter 146 5.4.1 Vergleich bei verschiedenen Schaltfrequenzen 146 5.4.2 Vergleich bei maximaler Trägerfrequenz 153 5.5 Vergleich für einen 6,6 kV Mittelspannungsstromrichter 156 5.5.1 Vergleich bei verschiedenen Schaltfrequenzen 156 5.5.2 Vergleich bei maximaler Trägerfrequenz 162 5.6 Vergleich von 2,3 kV, 4,16 kV und 6,6 kV Mittelspannungsstromrichtern 165 5.6.1 Vergleich bei identischer installierter Schalterleistung SS 165 5.6.2 Vergleich bei einer identischen Ausgangsleistung 167 6 Zusammenfassung und Bewertung 171 Anhang 175 A. Halbleiterverlustmodell 175 Referenzen 177 / The thesis deals with a detailed comparison of voltage source converter topologies with a central dc-link energy storage device for medium voltage applications. The Three-Level Neutral Point Clamped Voltage Source Converter (3L-NPC VSC) is compared with multilevel Flying Capacitor (FLC) and Stacked Multicell (SMC) Voltage Source Converters (VSC) for output voltages of 2.3 kV, 4.16 kV and 6.6 kV by using state-of-the-art 6.5 kV, 3.3 kV, 4.5 kV and 1.7kV IGBTs. The fundamental functionality of the investigated converter topologies as well as the design of the power semiconductors and of the energy storage devices (Flying Capacitors and Dc-Link capacitors) is described. The installed switch power, converter losses, the semiconductor loss distribution, modulation strategies and the harmonic spectra are compared in detail.:Inhaltsverzeichnis Liste der Variablen i Liste der Abkürzungen v 1 Einleitung 1 2 Überblick von Mittelspannungsstromrichtertopologien und Leistungshalbleitern 3 2.1 Mittelspannungsumrichtertopologien 3 2.2 Leistungshalbleiter 8 3 Aufbau und Funktion von Mittelspannungsstromrichtertopologien 10 3.1 Neutral Point Clamped Stromrichter (NPC) 10 3.1.1 3-Level Neutral Point Clamped Stromrichter (3L-NPC) 10 3.1.2 Mehrstufige NPC-Umrichter 21 3.2 Flying Capacitor Stromrichter (FLC) 23 3.2.1 3-Level Flying Capacitor Stromrichter (3L-FLC) 23 3.2.2 4-Level Flying Capacitor-Stromrichter (4L-FLC) 33 3.2.3 Mehrstufige Flying Capacitor-Stromrichter (NL-FLC) 39 3.3 Stacked Multicell Stromrichter (SMC) 43 3.3.1 5L-Stacked Multicell Stromrichter (5L-SMC) 43 3.3.2 N-Level Stacked Multicell Umrichter (NL-SMC) 51 4 Modellierung und Auslegung der Stromrichter 59 4.1 Verlustmodell 59 4.1.1 Sperrschichttemperaturen 64 4.2 Auslegung der Leistungshalbleiter 65 4.2.1 Stromauslegung 67 4.2.2 Worst-Case Arbeitspunkte 69 4.3 Auslegung der Zwischenkreiskondensatoren 75 4.3.1 Spannungszwischenkreis 76 4.3.2 Lastseitige Strombelastung und resultierende Spannungswelligkeit im Spannungszwischenkreis 77 4.3.3 Abhängigkeit der Strombelastung und der Spannungswelligkeit im Spannungszwischenkreis vom Frequenzverhältnis mf 95 4.3.4 Netzseitige Zwischenkreiseinspeisung 97 4.3.4.1 Zwischenkreiseinspeisung mit idealisiertem Transformatormodell 98 4.3.4.2 Zwischenkreiseinspeisung mit erweitertem Transformatormodell 101 4.3.5 Simulation des Gesamtsystems 104 4.4 Auslegung der Flying Capacitors 107 4.4.1 Strombelastung der Flying Capacitors 109 4.4.2 Spannungswelligkeit über den Flying Capacitors 113 4.4.3 Abhängigkeit der Spannungswelligkeit der Flying Capacitors vom Frequenzverhältnis mf 124 4.4.4 Auswirkung der Spannungswelligkeit der Flying Capacitors auf die Ausgangsspannungen 126 5 Vergleich der Stromrichtertopologien 129 5.1 Daten für den Stromrichtervergleich 129 5.2 Basis des Vergleiches 132 5.3 Vergleich für einen 2,3 kV Mittelspannungsstromrichter 134 5.3.1 Vergleich bei verschiedenen Schaltfrequenzen 134 5.3.2 Vergleich bei maximaler Trägerfrequenz 142 5.4 Vergleich für einen 4,16 kV Mittelspannungsstromrichter 146 5.4.1 Vergleich bei verschiedenen Schaltfrequenzen 146 5.4.2 Vergleich bei maximaler Trägerfrequenz 153 5.5 Vergleich für einen 6,6 kV Mittelspannungsstromrichter 156 5.5.1 Vergleich bei verschiedenen Schaltfrequenzen 156 5.5.2 Vergleich bei maximaler Trägerfrequenz 162 5.6 Vergleich von 2,3 kV, 4,16 kV und 6,6 kV Mittelspannungsstromrichtern 165 5.6.1 Vergleich bei identischer installierter Schalterleistung SS 165 5.6.2 Vergleich bei einer identischen Ausgangsleistung 167 6 Zusammenfassung und Bewertung 171 Anhang 175 A. Halbleiterverlustmodell 175 Referenzen 177