M.Ing. / The purpose of this study is to introduce a new three-phase AC-DC-DC converter topology with low electromagnetic interference (EMI) and unity power factor. This converter topology is obtained by merging the three-phase boost-rectifier and the full-bridge resonant-transition converter into a single, unique converter topology. This converter's boost-stage is completely soft-switched, in contrast with conventional topologies. Thus, each switch in the converter is soft-switched, and therefore the converter --is named the three-phase All Soft-Switching Unity Power Factor Converter (ASSUP). Due to the zerovoltage switching of each switch, this converter has lower switching losses as well as EMI-levels than the conventional design. In the conventional design, the boost-stage, used for power factor correction, and the actual power converter, i.e. the full-bridge DC-DC converter, are realized in two seperate stages with two separate controllers. In contrast, the converter proposed here consists of one stage only, with one controller. The first topic discussed is a theoretical background on both low-frequency power quality (power factor and THD), and high-frequency power quality (EMI). This background is necessary for comparing the proposed converter with the conventional converter. Secondly, an in-depth analysis of both the three-phase boost-rectifier and the full-bridge resonanttransition converter is done. This analysis is crucial in the analysis of the three-phase ASSUP, which is discussed thirdly. For each of the converters, a typical switching waveform is divided into unique intervals, for which the appropriate expressions are derived. The design of the practical component values is also discussed, as well as the control method for each of the converters. The three-phase ASSUP, introduced here, is lastly experimentally compared with the cascade-connection of the three-phase boost-rectifier and the full-bridge resonant-transition converter.

M.Ing. / Electromagnetic Compatibility (EMC) of electronic equipment is currently an important design parameter. Layout play a significant role in the EMC of power electronic converters. This thesis describes an investigation undertaken into the electromagnetic effects of converter layout. Typical detrimental effects identified during experimental work are presented. Possible causes for these effects are discussed. The experimental work is based on a systematic approach, which starts with a basic single switch chopper and ends in a split supply half-bridge converter. Interconnection modelling and SPICE simulations of layout affects are investigated next. The focus falls on analytical equations for extraction and simplified simulation circuits to make the process generally accessible. Typical resonant frequencies present in some of the experimental circuits are investigated with the help of analytically extracted parameters. The possibility of minimizing detrimental layout effects through impedance matching of interconnections and their terminations, is investigated next, since the previous section quantified layout parameters. Distributed vs. lumped element modelling of interconnections, and the boudary in between, are discussed. Simulation and experimental results are presented. Since maximum fuctionality and power, and minimum cost, per volume drives product development, all elements of a circuit should be investigated for the possibility of realizing secondary or even tertiary functions contributing to normal circuit operation. This is the focus of the last part of this thesis. Employing interconnections as low-pass or surge filters are investigated. Several waveforms are used to test experimental interconnection structures. Lumped and distributed modelling of these strucutres are discussed. The thesis concludes with a theoretical investigation into the possibility of dissipation of surge-energy instead of reflection utilizing interconnection-structures. One of these structures utilizes the skin- and proximity effect to realize low-pass behaviour.

M.Ing. / This thesis investigates why electromagnetic interference (EMI) and electromagnetic compatibility (EMC) problems exist and how EMI is generated, measured and limited. This investigation is done with reference to power systems and satellite earth stations. To understand the full extend of EMI generation from power systems on satellite earth stations, it was necessary to do a study of EMI, in order to understand EMI in its simplest form. This study consists of the following work: •A background study investigates the components of EMI, how EMI are generated and manifest in electric systems, methods to limit conducted EMI, a theoretical model on how to estimate conducted EMI quantities and EMI measurement techniques. •A conducted EMI model with which the parasitic impedances could be controlled was developed. With this model it could then be determined how conducted EMI would manifest in 3-wire circuit designs and how conducted EMI could be reduced in such circuits. •It was investigated how inductive coupling and capacitive coupling can be reduced. Time and frequency domain measurements were used to investigate the effects of these couplings. It was also of great importance to understand how EMI from measurement set-ups could influence measurements to give inaccurate results. This work investigated how high frequency measurements can be done effectively, how high frequency circuit designs can be improved and how parasitic impedances can be limited in high frequency equipment. •The expected EMI problem at the Klipheuwel wind farm was analysed. Simulations of expected EMI levels, worst case scenarios and measurements taken there showed that no significant EMI are generated from the wind generators and that power systems don’t hold a threat to satellite earth stations, if the necessary precautions are taken.

The diploma thesis deals with the influence of magnetic and electromagnetic fields on signals transmitted by optical fibers. Subsequently, the results of individual measured values are evaluated and analyzed, which were measured using an interferometer and a polarimeter. The first part deals with the theoretical analysis of the principles of interference and polarization of light. It further explains the basic operation of the above-mentioned devices as well as the immunity of the optical fiber to EMI. The second part of the work presents selected devices and technologies that were used as a source of electromagnetic or magnetic radiation. Subsequently, individual phenomena are plotted both in the course of time and with the help of a spectrogram or Poincaré sphere. From the measured results we can conclude that the commonly available technologies, which were selected for the diploma thesis, will not cause greater negative problems to the signal on measured frequencies in optical fibre, that could degrade the transmitted signal.

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Medium Voltage (MV) power conversion systems are essential in high power applications to address the increasing demand of energy and the increasing penetration of renewable energy sources. MV power electronics converters are the key elements for power conversion in MV systems and are the focus of this study. Multilevel converter topologies are promising topologies in MV applications because of their reduced voltage stress on devices, excellent output quality, reduced semiconductor losses, lower common mode voltage among other advantages. However, they may suffer from the large number of switching devices and capacitors, as well as the need to regulate capacitor voltages. SiC MOSFETs can achieve higher switching speeds, higher switching frequencies, higher voltage ratings, higher operation temperatures compared to traditional Si devices. They have shown promise to increase the efficiency and power density of the converters, but may suffer from higher voltage overshoots, increased Electromagnetic Interference (EMI) emission and so on. In SiC-based multilevel converters, the features of multilevel topologies, and the features of SiC MOSFETs are coupled together. The benefits, challenges, and solutions of using SiC MOSFETs in multilevel converters are studied explicitly in this work. With the high switching speeds and high switching frequencies of SiC MOSFETs, and the large number of switches and capacitors in multilevel topologies, SiC-based multilevel converters need to be studied while considering high-frequency voltage and current behaviors and the interactions among them at different locations. Firstly, the use of SiC-based multilevel converter in the high-speed motor drive application is explored. A three-phase inverter is designed and built employing five-level Stacked Multicell Converter topology and SiC MOSFETs. The benefits and challenges of using multilevel converter topology and using SiC MOSFETs for this application are explored. A fitting topology is selected, and a prototype is designed, both with attentions paid to deal with the high switching speeds of SiC MOSFETs. The inverter is verified through experiments to meet all specifications with a high efficiency. Then a unique type of converter, converters with Integrated Capacitor Blocked Transistor (ICBT) cells are studied. Unlike the traditional methods, there are no fast-developing voltage unbalances, or high cell capacitor voltage ripples in ICBT-based converters. The ideal operation principle is analyzed and verified by the simulation results. Then the impacts of non-idealities on the operation are analyzed, and a control method is proposed for this type of converter. The operation and control of ICBT-based converters are verified by experimental results to achieve low cell capacitor voltage ripples and excellent voltage balance in Medium Voltage high power applications. Lastly, the conducted EMI emission in SiC-based multilevel converters are studied. Four SiC-based multilevel converters are studied, with the focus on the power circuit in one converter and the auxiliary circuits in the other three converters. The complexity of noise generation and propagation in multilevel converters is presented. The conducted EMI disturbances are experimentally evaluated, analyzed, and effectively mitigated in all four cases. / Doctor of Philosophy / Medium Voltage (MV) power conversion systems are essential in high power applications to address the increasing demand of energy and the increasing penetration of renewable energy sources. MV power electronics converters are the key elements for power conversion in MV systems and are the focus of this study. Multilevel converter topologies are promising topologies in MV applications because of their reduced voltage stress on devices, excellent output quality, reduced semiconductor losses, lower common mode voltage among other advantages. However, they may suffer from the large number of switching devices and capacitors, as well as the need to regulate capacitor voltages. SiC MOSFETs can achieve higher switching speeds, higher switching frequencies, higher voltage ratings, higher operation temperatures compared to traditional Si devices. They have shown promise to increase the efficiency and power density of the converters, but may suffer from higher voltage overshoots, increased Electromagnetic Interference (EMI) emission and so on. In SiC-based multilevel converters, the features of multilevel topologies, and the features of SiC MOSFETs are coupled together. The benefits, challenges, and solutions of using SiC MOSFETs in multilevel converters are studied explicitly in this work. With the high switching speeds and high switching frequencies of SiC MOSFETs, and the large number of switches and capacitors in multilevel topologies, SiC-based multilevel converters need to be studied while considering high-frequency voltage and current behaviors and the interactions among them at different locations. Firstly, the use of SiC-based multilevel converter in the high-speed motor drive application is explored. A three-phase inverter is designed and built employing five-level Stacked Multicell Converter topology and SiC MOSFETs. The benefits and challenges of using multilevel converter topology and using SiC MOSFETs for this application are explored. A fitting topology is selected, and a prototype is designed, both with attentions paid to deal with the high switching speeds of SiC MOSFETs. The inverter is verified through experiments to meet all specifications with a high efficiency. Then a unique type of converter, converters with Integrated Capacitor Blocked Transistor (ICBT) cells are studied. Unlike the traditional methods, there are no fast-developing voltage unbalances, or high cell capacitor voltage ripples in ICBT-based converters. The ideal operation principle is analyzed and verified by the simulation results. Then the impacts of non-idealities on the operation are analyzed, and a control method is proposed for this type of converter. The operation and control of ICBT-based converters are verified by experimental results to achieve low cell capacitor voltage ripples and excellent voltage balance in Medium Voltage high power applications. Lastly, the conducted EMI emission in SiC-based multilevel converters are studied. Four SiC-based multilevel converters are studied, with the focus on the power circuit in one converter and the auxiliary circuits in the other three converters. The complexity of noise generation and propagation in multilevel converters is presented. The conducted EMI disturbances are experimentally evaluated, analyzed, and effectively mitigated in all four cases.

Electricity is the fastest-growing type of end-use energy consumption in the world, and its generation and usage trends are changing. Hence, the power electronics that control the flow and conversion of electrical energy are an important research area. Advanced power electronics with improved efficiency, power density, reliability, and functionality are critical in data center, transportation, motor drive, renewable energy, and grid applications, among others. Wide-bandgap power semiconductors are enabling power electronics to meet these growing demands, and have thus begun appearing in commercial products, such as traction and solar inverters. Looking ahead, even greater strides can be made in medium-voltage systems due to the development of silicon carbide power devices with voltage ratings exceeding 10 kV. The ability of these devices to switch higher voltages faster and with lower losses than existing semiconductor technologies will drastically reduce the size, weight, and complexity of medium-voltage systems. However, these devices also bring new challenges for designers. This dissertation will present a package for 10 kV silicon carbide power MOSFETs that addresses the enhanced electric fields, greater electromagnetic interference, worsened dynamic imbalance, and higher heat flux issues associated with the packaging of these unique devices. Specifically, due to the low and balanced parasitic inductances, the power module prototype is able to switch at record speeds of tens of nanoseconds with negligible ringing and voltage overshoot. An integrated common-mode current screen contains the current that is generated by these fast voltage transients within the power module, rather than flowing to the system ground. This screen connection simultaneously increases the partial discharge inception voltage by reducing the electric field strength at the triple point of the insulating ceramic substrate. Further, field-grading plates are used in the bus bar to reduce the electric field strength at the module terminations. The heat flux is addressed by employing direct-substrate, jet-impingement cooling. The cooler is integrated into the module housing for increased power density. / Ph. D. / Electricity is the fastest-growing type of end-use energy consumption in the world, and its generation and usage trends are changing. Hence, the power electronics that control the flow and conversion of electrical energy are an important research area. Advanced power electronics with improved efficiency, power density, reliability, and functionality are critical in data center, transportation, motor drive, renewable energy, and grid applications, among others. Wide-bandgap power semiconductors are enabling power electronics to meet these growing demands, and have thus begun appearing in commercial products, such as traction and solar inverters. Looking ahead, even greater strides can be made in medium-voltage systems due to the development of silicon carbide power devices with voltage ratings exceeding 10 kV. The ability of these devices to switch higher voltages faster and with lower losses than existing semiconductor technologies will drastically reduce the size, weight, and complexity of medium-voltage systems. However, these devices also bring new challenges for designers. This dissertation will present a package for 10 kV silicon carbide power MOSFETs that addresses the enhanced electric fields, greater electromagnetic interference, worsened dynamic imbalance, and higher heat flux issues associated with the packaging of these unique devices. Specifically, due to the low and balanced parasitic inductances, the power module prototype is able to switch at record speeds of tens of nanoseconds with negligible ringing and voltage overshoot. An integrated common-mode current screen contains the current that is generated by these fast voltage transients within the power module, rather than flowing to the system ground. This screen connection simultaneously increases the partial discharge inception voltage by reducing the electric field strength at the triple point of the insulating ceramic substrate. Further, field-grading plates are used in the bus bar to reduce the electric field strength at the module terminations. The heat flux is addressed by employing direct-substrate, jet-impingement cooling. The cooler is integrated into the module housing for increased power density.

Interference is a major problem in modern wireless communications systems. No longer are background noise and average power loss the limiting factors in system capacity corruption of the available spectrum by multiple access and nearby interference provides the upper limit to system capacity. If the exponential growth of commercial wireless communications is to continue, systems must effectively deal with the increasingly crowded and corrupted spectrum. Direct Sequence Spread Spectrum modulation (DS-SS) combined with Time Dependent Processing represents a valid approach to meeting the needs of future communications systems. Traditionally, the exploitation of cyclostationarity in digital communications signals has been reserved for the hostile communication environments faced by the military. However, the advent of cost-effective, high-speed DSP chips and associated processing hardware have made Time Dependent Processing a viable commercial technology. This thesis presents several forms of the Time Dependent Adaptive Filter (TDAF) which are able to fully exploit the cyclostationarity and high degree of spectral correlation in certain DS-SS signals. It is shown that these optimal TDAFs are able to combat interference from noise, multipath, signals with dissimilar modulation, and signals with similar modulation (multiple access interference). Performance gains are achieved without a knowledge of the specific type of interference and depend solely on the high degree of spectral correlation in DS-SS signals. It is shown that properly designed DS-SS CDMA systems that utilize the TDAF can achieve spectral efficiencies which are within 10% of FDM/TDM systems. Furthermore, these systems retain the benefits of wideband modulation and universal frequency reuse traditionally associated with CDMA systems. The net result is a tremendous increase in system user capacity and signal reception quality. / Master of Science