This term project’s aim is to theoreticaly analyze thermal phenomena and losses in electrical power devices, describe the design and application of UniGear ZS1 type switchgear, put together a computer simulation model for thermal calculations of current and optimized solution and finally to discuss obtained results and compare them with experimentally acquired values. The main objective of this project is to determine, whether simulation is a viable and reliable enough method, that it could replace the costly real life physical testing. Modelling of the progress of thermal processes in different parts of the examined busbar will be done in computer aided design program Solidworks and its simulation plugin Flow Simulation.

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

Energy security, global warming, and climate change have been a major source of global discussions and development. Likewise, the rising cost of electricity for consumers and exponential demand for energy are major factors driving the incremental growth and integration of sustainable forms of energy generation into power the system cycle. Distributed generation resources are majorly integrated into the electricity distribution system at the medium voltage (MV) and low voltage (LV) level of the utility grid system. Unexpected power outages on an electricity distribution network can lead to an islanding situation, in which a distributed generation system continues to supply power to the electricity grid. It is highly recommended by operational standards that, under such conditions, a distributed generation system is disconnected from the grid within a short period to prevent damage to power equipment and ensure personnel safety. The decoupling process requires an islanding detection method (IDM). Such detection methods are implemented in grid-tied power electronic converters (PEC) to detect and prevent islanding conditions.  The thesis investigates and describes an active islanding detection method, the active frequency drift with positive feedback. It also covers the parameter design and the analysis of the non–detection zone. The effectiveness of the method was verified through MATLAB/SIMULINK simulation

No description available.

This work investigates the voltage scaling feasibility of several low voltage SiC MOSFET modules operated as a single series-connected switch using active gate control. Both multilevel and two-level topologies are capable of achieving higher blocking voltages in high-power converter applications. Compared to multilevel topologies, two-level switching topologies are of interest due to less complex circuitry, higher density, and simpler control techniques. In this work, to balance the voltage between series-connected MOSFETs, device turn-off speeds are dynamically controlled on active gate-drivers using active gate control. The implementation of the active gate control technique (specifically, turn-off dv/dt control) is described in this thesis. Experimental results of the voltage balancing behavior across eight 1.7 kV rated SiC MOSFET devices in series (6 kV total dc bus voltage) with the selected active dv/dt control scheme are demonstrated. Finally, the voltage balancing performance and switching behavior of series-connected SiC MOSFET devices are discussed. / Master of Science / According to ABB, 40% of the world's power demand is supplied by electrical energy. Specifically, in 2018, the world's electrical demand has grown by 4% since 2010. The growing need for electric energy makes it increasingly essential for systems that can efficiently and reliably convert and control energy levels for various end applications, such as electric motors, electric vehicles, data centers, and renewable energy systems. Power electronics are systems by which electrical energy is converted to different levels of power (voltage and current) depending on the end application. The use of power electronics systems is critical for controlling the flow of electrical energy in all applications of electric energy generation, transmission, and distribution. Advances in power electronics technologies, such as new control techniques and manufacturability of power semiconductor devices, are enabling improvements to the overall performance of electrical energy conversion systems. Power semiconductor devices, which are used as switches or rectifiers in various power electronic converters, are a critical building block of power electronic systems. In order to enable higher output power capability for converter systems, power semiconductor switches are required to sustain higher levels of voltage and current. Wide bandgap semiconductor devices are a particular new category of power semiconductors that have superior material properties compared to traditional devices such as Silicon (Si) Insulated-Gate Bipolar Junction Transistors (IGBTs). In particular, wide bandgap devices such as Silicon Carbide (SiC) Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) have better ruggedness and thermal capabilities. These properties provide wide bandgap semiconductor devices to operate at higher temperatures and switching frequencies, which is beneficial for maximizing the overall efficiency and volume of power electronic converters. This work investigates a method of scaling up voltage in particular for medium-voltage power conversion, which can be applied for a variety of application areas. SiC MOSFET devices are becoming more attractive for utilization in medium-voltage high-power converter systems due to the need to further improve the efficiency and density of these systems. Rather than using individual high voltage rated semiconductor devices, this thesis demonstrates the effectiveness of using several low voltage rated semiconductor devices connected in series in order to operate them as a single switch. Using low voltage devices as a single series-connected switch rather than a using single high voltage switch can lead to achieving a lower total on-state resistance, expectedly maximizing the overall efficiency of converter systems for which the series-connected semiconductor switches would be applied. In particular, this thesis focuses on the implementation of a newer approach of compensating for the natural unbalance in voltage between series-connected devices. An active gate control method is used for monitoring and regulating the switching speed of several devices operated in series in this work. The objective of this thesis is to investigate the feasibility of this method in order to achieve up to 6 kV total dc bus voltage using eight series-connected SiC MOSFET devices.

For decades, the Silicon-based semiconductors have been the solution for power electronics applications. However, these semiconductors have approached their limits of operation in blocking voltage, working temperature and switching frequency. Due to material superiority, the relatively-new wide-bandgap semiconductors such as Silicon-Carbide (SiC) MOSFETs enable higher voltages, switching frequencies and operating temperatures when compared to Silicon technology, resulting in improved converter specifications. The current study tries to investigate the impact of emerging medium-voltage SiC MOSFETs on industrial motor drive application, where over a quarter of the total electricity in the world is being consumed. Firstly, non-commercial SiC MOSFETs at 3.3 kV and 400 A rating are characterized to enable converter design and simulation based on them. In order to feature the best performance out of the devices under test, an intelligent high-performance gate driver is designed embedding required functionalities and protections. Secondly, total of three converters are targeted for industrial motor drive application at medium-voltage and high-power range. For this purpose the cascaded H-bridge, the modular multilevel converter and the 5-L active neutral point clamped converters are designed at 4.16-, 6.9- and 13.8 kV voltage ratings and 3- and 5 MVA power ratings. Selection of different voltage and power levels is done to elucidate variation of different parameters within the converters versus operating point. Later, comparisons are done between the surveyed topologies designed at different operating points based on Si IGBTs and SiC MOSFETs. The comparison includes different aspects such as efficiency, power density, semiconductor utilization, energy stored in converter structure, fault containment, low-speed operation capability and parts count (for a measure of reliability). Having the comparisons done based on simulation data, an H-bridge cell is implemented using 3.3 kV 400 A SiC MOSFETs to evaluate validity of the conducted simulations. Finally, a novel method is proposed for series-connecting individual SiC MOSFETs to reach higher voltage devices. Considering the fact that currently the SiC MOSFETs are not commercially available at voltages higher above 1.7 kV, this will enable implementation of converters using medium-voltage SiC MOSFETs that are achieved by stacking commercially-available 1.7 kV MOSFETs. The proposed method is specifically developed for SiC MOSFETs with high dv/dt rates, while majority of the existing solutions could only work merely with slow Si-based semiconductors. / Ph. D. / Despite their mature technology and low manufacturing cost, the traditional Si-based power semiconductors had reached their limitations in operation from different points of view. The SiC MOSFETs which are the new generation of power semiconductors however seem to be able to shift the existing boundaries of operation for the Si-based semiconductors, resulting in significant improvement in design and operation of power electronics converters. This dissertation focuses on investigating the impact of emerging medium-voltage SiC MOSFETs on industrial motor drives, which consume over 28% of the total electricity used in the world. Firstly, the state-of-the-art non-commercial 3.3 kV SiC MOSFETs are characterized. Characterization of the devices is done to extract their key features such as switching and conduction losses, to enable loss calculation and performance evaluation in any target application. Since the mentioned devices are not commercial yet, the gate driving circuitry that can feature the best performance out of them are not commercially available either. Thus, the characterization process starts with design of an intelligent high-performance gate driver for the devices under test. Secondly, total of three topologies that are targeted for the study are discussed and their basics of operation is investigated. For this purpose the cascaded H-bridge, the modular multilevel converter and the 5-L active neutral point clamped converters are designed at three different voltage levels (4.16-, 6.9- and 13.8 kV) and two power levels (3- and 5 MVA). Selection of different voltage and power levels is done to enable comparison from different aspects as the operating point changes. Later, comparisons are done between the surveyed topologies designed at different operating points using different semiconductor technologies. The performed comparisons provide an unbiased input for the manufacturers and customers of these converters for selection of the target topology in motor drive application. Also to verify validity of the conducted simulations and calculations, a full-bridge converter cell is experimentally implemented using 3.3 kV 400 A SiC MOSFETs. Finally, a novel method is proposed for series-connecting lower-voltage SiC MOSFETs to reach higher-voltage devices. As of late 2017, the medium-voltage SiC MOSFETs are not commercially available. Also it is expected that upon commercialization, their price will be multiple times of that of low-voltage SiC MOSFETs. Thus, connecting lower-voltage SiC MOSFETs in series is an effective way of achieving higher-voltage devices and take advantage of superior properties if the SiC MOSFETs, while the availability and high cost problems are taken care of.

In this dissertation, a design approach for medium voltage (MV) PCB-based components, such as the dc bus, is detailed. Key considerations, including electric field (E-field) grading near power terminals and PCB edges, cable feedthroughs, and the integration of components, are explored from the perspective of E-field management. A design example of a 3-level dc bus for a 6 kV-1 MW Power Electronics Building Block (PEBB) is presented. This PEBB was assembled using an array of low-voltage (LV) capacitors to create 3 kV PCB-based capacitor daughtercards, applying the same design principles as the dc bus. The scalability of this design approach is demonstrated with a 9-level dc bus rated for 24 kV. The insulation quality and MV performance of all PCBs have been assessed through partial discharge (PD) analysis using an Omicron MPD 600. The high-voltage (HV) design approach takes into account the mitigation of peak electric field intensity to minimize insulation degradation caused by electrical stress. In addition to electrical stress, the current carrying capacity (CCC) of these printed circuit boards (PCBs) was assessed concerning steady-state thermal performance and short-circuit (SC) robustness. Multiple configurations were examined to determine the current density, with the aim of reducing temperature. The insulation performance following repetitive fault events was monitored. Although the Partial Discharge Inception Voltage (PDIV) reduced by 50% after 140 SC faults, it remained higher than the operational voltage. This demonstrates the feasibility of utilizing HV PCBs in practical applications. Finally, the insulation performance of a complete 6 kV PEBB assembly was assessed. The PEBB was assembled component by component, with a focus on tracking the PDIV at each stage. This approach allowed for the qualification of the PEBB for use in a 24 kV PEBB-based converter with a common mode (CM) PDIV of 33.2 kV. Subsequently, multiple PEBBs underwent testing to simulate their operation within a 24 kV converter configuration, ensuring dependable performance when assembled. Custom support structures were also designed and tested to accommodate the 24 kV PCB bus and dc-link capacitors, serving as interconnections between multiple phase legs and the external voltage source. / Doctor of Philosophy / Power electronic converters are used in many applications ranging from low power to high. Some applications include cellphone chargers, electric vehicle chargers, and even power distribution systems on land and sea. The electronics devices that are at the heart of these converters are rapidly advancing. Newer devices are being fabricated using so-called wide bandgap (WBG) materials such as silicon carbide as opposed to their older silicon counterparts. These WBG devices allow power converters to shrink in size due to their enhanced performance. As these device technologies evolve, the need to completely redesign systems to fully leverage their benefit arise. In this dissertation, the work centers around computer based simulations, coupled with hardware experiments, to design custom components that will allow engineers to significantly reduce the size and weight of medium voltage (MV) power electronic converters while also increasing their power. The printed circuit board (PCB) is a standard component used in every day electronics. They are used to host electronic components while creating precise electrical connections between them. Although these are very useful in circuits operating at lower voltages, their use has not been widely explored for applications requiring higher voltage such those as where these advancing WBG devices would provide the most benefit. A design method is introduced which allows these boards to be used at relatively high voltage (HV). The robustness of these HV PCBs were evaluated to ensure the feasibility of their continued use after multiple fault events. The size of power converter can be largely affected by the cooling system. Although the WBG devices can withstand higher temperature operation, the temperature of the device can still be a limiting factor. It is preferred to extract heat from the devices, allowing them to process more power. A standard component of cooling systems using forced air is the heatsink. The standard heatsink has corners that create sharp corners which are not ideal in high voltage systems; spacing between components must be increases to mitigate the effects caused by these sharp corners. Computer simulations were used to aid in the design of a heatsink profile which eliminates these sharp corners and was shown to reduce the clearance between cooling system components by up to 50%. Each component was individually designed and tested to ensure its reliable operation. However, it's crucial to verify their performance when assembled with other components. In addition to designing components for high voltage operation, the insulation system for a complete converter assembly was evaluated. Once a full converter was successfully qualified, a similar approach was taken to evaluate multiple converters when assembled together, much like building blocks, to construct even larger converters. This rigorous testing and assembly process ensures the reliable operation of the entire system.

The trend in power electronics converters is to be highly efficient, compact, reliable, and cost-effective. Conventionally, power converters supply or consume power from the low-voltage utility, which impacts the size and efficiency of the system. For example, the recent proliferation of electric vehicles has demanded the rapid installation of dc fast chargers (DCFC) across the country. However, most of the commercial DCFCs operate at 480 V transferring hundreds of kilowatts, resulting in large line currents which could hinder the size, cost, and efficiency of conventional DCFCs. Conversely, modular multilevel power topologies can be directly tied to the medium-voltage (MV) grid, eliminating the line-frequency transformer and the bulky line cable requirements. Among these topologies, the cascaded H-bridge (CHB) has been extensively used in the industry for MV-high-power applications because of its cost and efficiency in this operation range. Thus, it is one of the prevalent topologies for MV solid-state transformers (SSTs) The asymmetrical hybrid binary CHB (HBCHB) allows increased output voltage levels at the expense of modularity. Based on the HBCHB, a converter new modular topology regarded as the pseudo-binary CHB (PBCHB) is proposed for the ac-dc front-end stage SSTs. To operate the PBCHB, a new hybrid modulator is developed to operate the three modular structures of the PBCHB with step-like sinusoidal waveforms at near-line-frequency commutations while an asymmetrical floating capacitor (FC) module operates at high-frequency PWM commutation. The FC module does not transfer active power but serves only as a power quality enhancer of the PBCHB. However, the modular structures symmetrically transfer all the power from the MV grid to the load. With the SST structure of the PBCHB, the dc-link voltages of the H-bridges are naturally balanced; yet the proposed hybrid modulator enables equal power transfer in the three modular structures. In addition, a controller for the FC voltage is designed, analyzed, and implemented in the proposed hybrid modulator The effectiveness of the proposed front-end SST with the proposed modulation and control technique is verified in a 1.2 kV/3 kW single-phase prototype, where each module was able to transfer 1kW each. Electromagnetic interference (EMI) also impacts the cost, size, and reliability of three-phase systems because they may require bulky EMI filters to avoid self-pollution and polluting the grid. The common-mode voltage (CMV) is one important factor of EMI emissions. Thus, reducing or eliminating it could improve the cost and size of the system. Space vector pulsewidth modulation (SVWPM) can directly design the CMV output and the switching sequence of three-phase converters. However, its implementation can become complex in converters with many levels such as MV grid-tied SST converters. This dissertation uses the digital gh coordinate and proposes a set of computations to easily retrieve the converter states with a reduced CMV and generate a symmetrical switching sequence with reduced number of commutations. To do this, a single vector among the nearest three vectors (NTVs) is sufficient to implement the switching sequence for the reduced commutation and reduced CMV SVPWM. Additionally, the dc bus can be fully utilized. Unlike conventional approaches, the developed technique is easily scalable because its computational complexity does not depend on the number of levels of the converter. The proposed reduced CMV technique was verified in a three-phase 15-level 311 V/600 W unit. Moving forward in the objective of CMV reduction, a new jk-coordinate system for multilevel converters is proposed for SVPWM with eliminated CMV. With the jk coordinates, the converter states that yield zero CMV (ZCMV) can be directly computed. In addition, a single jk vector is sufficient to generate the switching sequences of NTVs. Moreover, the switching sequences feature reduced losses for high-power-factor applications in the phase that naturally commutes twice during a sampling period. Similarly, the computation burden of the ZCMV SVPWM technique presented in this dissertation is not affected by the number of levels of the converter, thus, it is scalable. The three-phase 15-level 311 V/600 W prototype was utilized to verify this technique. / Doctor of Philosophy / The recent demands for fast chargers for electric vehicles (EV), photovoltaic (PV) energy integration, and data centers for artificial intelligence (AI) have driven the research and development of efficient, compact, and cost-effective power electronic solutions. Under these motivations, the solid-state transformer (SST) is a power electronics configuration that can benefit the EV, PV, AI, and several other applications. By eliminating the requirement of a line-frequency transformer, SSTs can be directly connected to the medium-voltage (MV) grid, reducing the weight and volume, and improving efficiency. The main reason for these advantageous attributes is the utilization of multilevel ac/dc or dc/ac converters. Among these, the cascaded H-bridge (CHB) converter has been extensively used in the industry for MV-high-power applications because of its cost, fault tolerance, and efficiency, making it a favorable converter for MV SSTs. Symmetrical modules in the CHB must commutate at the same pulsewidth modulation (PWM) when operating in an SST. An asymmetrical configuration such as the hybrid binary CHB (HBCHB) allows increased output voltage levels and low-frequency commutation at the expense of modularity. This dissertation proposes a pseudo-binary CHB (PBCHB) inspired by the HBCHB to obtain low-frequency commutations, thus, negligible switching losses in the SST. The PBCHB has symmetrical modules that transfer balanced active power with negligible switching losses while an asymmetrically smaller module enhances the power quality with PWM operation. To do this, a new hybrid modulator and controller were designed, analyzed, and verified in this dissertation. The effectiveness of the proposed front-end PBCHB-based SST with the developed modulation and control techniques is verified in an MV 1.2 kV/3 kW single-phase prototype. Electromagnetic interference (EMI) filters can impact the cost, size, and reliability of SSTs. The common-mode voltage (CMV) that power converters generate is one type of EMI emissions that could impact the cost and size of the system. The modulation technique called space vector pulsewidth modulation (SVWPM) has the freedom to design a switching sequence able to reduce or eliminate the CMV. However, implementing the SVPWM can become complex in MV grid-tied SST converters (PBCHB, CHB, HBCHB) with many voltage levels. This dissertation uses the digital gh coordinate system and a new jk coordinate system to reduce and eliminate the CMV, respectively. These coordinates systems have the advantage of reduced computational complexity in multilevel converters with large number of output voltage levels increases. The proposed techniques can retrieve back the abc signals for the PWM drivers without repetitive iterations. Moreover, the proposed techniques can generate symmetrical switching sequences with reduced number of commutations and switching losses in the converter. To do this, the computation of a single vector among the nearest three vectors is sufficient to implement the switching sequences of SVPWM. As a result, the computational complexity of the SVPWM techniques in this dissertation is constant and does not vary with the number of output voltage levels, making them easily scalable solutions compared to previous solutions in the literature. The proposed reduced and eliminated CMV SVPWM techniques were verified in a three-phase 15-level 311 V/600 W HBCHB unit in inverting mode.

Satisfaire les besoins en énergie de manière responsable est possible grâce aux énergies renouvelables, notamment éoliennes et solaires. Cependant ces centres de captation d’énergie sont éloignés dans zones de consommation. Le transport de l’énergie via des réseaux HVDC (haute tension courant continu) permet un rendement et une flexibilité avantageuse face au transport HVAC (haute tension courant alternatif). Ceci est rendu possible grâce aux convertisseurs utilisant l’électronique de puissance. Les récents développements sur les semi-conducteurs à large bande interdite, plus particulièrement le carbure de silicium (SiC) offrent la possibilité de concevoir ces convertisseurs plus simples, utilisant des briques technologiques de plus fort calibre (≤ 10 kV). Cependant le packaging, essentiel à leur bon fonctionnement, ne suit pas ces évolutions. Dans cette thèse, nous explorons les technologies actuelles ainsi que les limites physique et normatives liées au packaging haute tension. Des solutions innovantes sont proposées pour concevoir un module de puissance haute tension, impactant que faiblement les paramètres connexes (résistance thermique, isolation électrique et paramètres environnementaux). Les éléments identifiés comme problématiques sont traités individuellement. La problématique des décharges partielles sur les substrats céramiques métallisés est développée et une solution se basant sur les paramètres géométriques a été testée. Le boitier standard type XHP-3 a été étudié et une solution permettant de le faire fonctionner à 10 kV à fort degré de pollution a été développée. / The supply of carbon-free energy is possible with renewable energy. However, windfarms and solar power plants are geographically away from the distribution points. Transporting the energy using the HVDC (High Voltage Direct Current) technology allow for a better yield along the distance and result in a cost effective approach compared to HVAC (High Voltage Alternative Current) lines. Thus, there is a need of high voltage power converters using power electronics. Recent development on wide bandgap semiconductors, especially silicon carbide (SiC) allow a higher blocking voltage (around 10 kV) that would simplify the design of such power electronic converters. On the other hand, the development on packaging technologies needs to follow this trend. In this thesis, an exploration of technological and normative limitation has been done for a high voltage power module design. The main hot spot are clearly identified and innovative solutions are studied to provide a proper response with a low impact on parasitic parameters. Partial Discharges (PD) on ceramic substrates is analyzed and a solution of a high Partial Discharge Inception Voltage (PDIV) is given based on geometrical parameters. The XHP-3 like power modules are studied and a solution allowing a use under 10 kV at a high pollution degree (PD3) is given.

Bei der Zustandsbewertung von Kabeln steht derzeit das Mittelspannungsnetz im Fokus der Betrachtungen. Das Mittelspannungsnetz verbindet das Hochspannungsnetz mit dem Niederspannungsnetz und nimmt damit eine besondere Bedeutung ein. Störungen in diesem Netz wirken sich direkt als Versorgungsunterbrechung auf den Letztverbraucher aus. Rund 80 bis 85 % der Versorgungsunterbrechungen resultieren aus Problemen im Mittelspannungsnetz, sodass dortige Aktivitäten den größten Hebel bei der Steigerung der Versorgungsqualität entwickeln. Mittels Zustandsbewertung von Kabeln können verdeckte Fehler aufgedeckt oder deren Alterungszustand bestimmt werden. Nicht jeder diagnostizierte Fehler führt unmittelbar zum Ausfall. Er beschleunigt jedoch die Alterung, die letztendlich zum Ausfall führt. Die Arbeit beschäftigt sich mit der Identifizierung von Fehlern in Mittelspannungskabelmuffen im Zusammenhang mit der Alterung, um die Restlebensdauer auszunutzen und dem Ausfall zuvorzukommen. / By evaluating the status of cables, hidden errors can be detected or their aging condition can be determined. Not every diagnosed fault leads directly to failure. However, it accelerates aging, which ultimately leads to failure. The work deals with the identification of faults in medium-voltage cable joints in connection with aging in order to exploit the remaining life and to prevent the failure.