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Two novel clamped-mode resonant converters are analyzed. These clamped-mode converters operate at a constant frequency while retaining many desired features of conventional resonant converters such as fast responses, zero-voltage turn-on or zero-current turn-off, and low EMI levels, etc. The converters are able to regulate the output from no load to full load and are particularly suitable for off-line, high-power applications. To provide insights to the operations and derive design guidelines for the clamped-mode resonant converters, a complete dc characterization of both the clamped-mode series-resonant converter and the clamped-mode parallel-resonant converter, operating above and below resonant frequency, is performed. State-plane analysis techniques are employed. By portraying the converters' operation on a state-plane diagram, various circuit operating modes are identified. The boundaries between different operating modes are determined. The regions for natural and force commutation of the active switches are defined. Important dc characteristics, such as control-to-output transfer ratio, rms inductor current, peak capacitor voltage, rms switch currents, average diode currents, switch turn-on currents, and switch turn-off currents are derived to facilitate the converter designs. To illustrate the converter designs in different operating regions, several design examples are given. Finally, three prototype circuits are built to verify the analytical results. / Ph. D.

A modularized three-dimensional power electronics environment will become increasingly necessary as power converters are more intertwined with the dynamic desires of modern society. This is driven by ever-changing requirements, combined with the desire for quick design cycles, and then further compounded by the increased penetration of electrified technologies. The high demand for various power converters presents a design, manufacturing, and validation burden which can be lessened with a three-dimensional power electronics environment, where power converters of any arbitrary set of voltage, current, or quantity of independent input/outpt requirements can be assembled from a grouping of pre-existing converter modules. This, however, has drawbacks when compared with bespoke power converter designs. Modularization can be complex, lossy, and large, and the resulting converter's overall efficiency and power density will then suffer. To compensate for these costs of modularization, the individual modules must be first be power dense and efficient, and then the framework for grouping modules together must be simple. This dissertation first proposes a high performance Power Conversion Unit (PCU) which is achieved through a unique combination of techniques. The first of these techniques is modification to the ubiqutioius buck converter topology in a form of an adjustment to its output filter. This topological modification results in decreased current ripple handling requirements of the filter, which can be used to reduce its volume. The second topological technique is an additional capacitance placed across the drain-source terminals of each FET, which is used to reduce their turn-off switching energy at the expense of their turn-on switching energy. A variable frequency soft-switching scheme is utitlized to prevent the converter from incurring turn-on losses, and a duty cycle compensation scheme is developed to mitigate the distortions caused by this increased drain-source capacitance. Finally, a process for balancing the PCU design parameters that results in a Pareto frontier of efficiency-power density optimal points is defined, one selected, and a protoype PCU constructed and tested in a three-phase inverter configuration. A framework for the vertical stacking of PCUs is then shown. This framework, named the Manhattan Topology, is a multilevel power converter topology which is defined by a set of series stacked capacitances where there exists a method to transfer power between capacitances. This framework has linear complexity and switching device stress scaling with the number of levels, which yields a simple methodology for grouping modules together in the vertical dimension. Furthermore, it exhibits Partial Power Processing (PPP) characteristics as the power processed internally to the overall converter is less than its output power. This framework is validated for both DC/DC and AC/DC applications and control and conversion of voltages greater than the rating of any individual component within the converter is experimentally demonstrated. Lastly, another three-phase inverter is built using this topological framework and the performance of this vertically-modularized inverter is compared with the non-modularized inverter. It is shown that the three-dimensional modular power electronics environment with optimized PCUs, despite the costs of modularization, is still performance-competitive with the non-modular power electronics environment.

Thesis (MScEng (Electrical and Electronic Engineering))-- University of Stellenbosch, 2006. / This thesis presents the design and implementation of a high voltage DC-DC converter using a series stacked topology. The converter’s specifications were set by Spoornet and the converter forms part of a DC-AC inverter to be installed in Spoornet substations. Different converter topologies will be considered. A high frequency, high power coaxially wound transformer will be analysed, designed and manufactured for this specific converter application. A thermal analysis of the transformer will be carried out. The merits of different control schemes, leading to the choice of an average current mode controller, will be discussed. This controller will be designed and implemented to control the converter. The converter is then simulated to test and verify the controller functionality. A two-level series stacked converter is built and tested to verify the converter design and to test the functionality of the coaxially wound transformer. Finally, the results obtained will be discussed.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / A switching state substitution must be developed that will make use of both single-phase redundancies and three-phase redundancies in the flying-capacitor topology. Losses should be taken into consideration and the algorithm must be designed for implementation on the existing PEC33 system, with on-board DSP (TMS320VC33) and FPGA (EP1K50QC208). The specific power-electronics application is a medium-voltage active filter. Existing capacitor voltage stabilisation schemes are investigated and a capacitor-voltage based algorithm is developed that is investigated in parallel with the Donzel and Bornard algorithm. Detailed simulation models are built for the evaluation of both existing and the proposed algorithm. Three-phase control is also evaluated. Timing analysis of the proposed algorithm shows that a DSP-only implementation of the proposed capacitor-based solution is not feasible. Detail design of the digital controller hereof is implemented in VHDL. Finally, a four-cell controller is fitted into the FPGA. A scalable hardware sorting architecture is utilised.

Electrospinning is a method of using high voltage electric fields to transform polymer solutions into nano-scale fibres. The field has seen significant work on processing different polymers and their resulting fibres but less work has focused the electrospinning process itself. The aim of this thesis is to present experimental observations of charge behaviour in the electrospinning process in the context of the underlying physics typically used to describe electrospinning. This thesis presents a review of existing methods of measuring aspects of the electrospinning process, and reviews published mathematical models of the process as representative examples of the current understanding of the underlying physics that drive the electrospinning phenomena. A novel measurement technique is introduced - high frequency data capture of the electric current flow simultaneously at the high voltage and collector electrode. This is used in three ways: to examine bulk charge density, to measure fibre flight time, and to quantify charge lost from the fibre in flight. Charge density is studied by comparing current and mass flow at the Taylor cone under a wide range of conditions. For 8% PVOH in water a constant bulk charge density was found of 7.7 C/kg. Flight time is studied by determining the time from the application of high voltage to the charged fibre first arriving at the collector electrode. It was found that for 8% PVOH the flight time depended strongly on applied voltage while electrode distance had a negligible effect. Charge loss was studied by comparing the magnitude of the simultaneous current flows in the quasi-steady state to determine if the charge flowing into the Taylor cone arrives with the fibre at the collector. For 8% PVOH, 8% PVOH with ionic salt, 9% PVOH in water and 18% PVB in ethanol, it was found that charge is always lost.

Dans les domaines industriels et en particulier celui du transport, le nombre et la puissance des équipements électriques et électroniques embarqués est en constante augmentation. L’alimentation des équipements électriques et la commande de ces actionneurs nécessitent l’utilisation de convertisseurs d’électronique de puissance à découpage dont la nature perturbatrice n’est plus à démontrer. Afin de prendre en compte la CEM dès la phase de conception d’un produit, les constructeurs doivent disposer d’outils dédiés à la CEM ou à défaut de règles ou techniques de conception spécifiques. C’est dans l’optique de répondre à ces besoins que se sont orientés ces travaux de thèse.La première partie des travaux traite de la modélisation des perturbations conduites des organes de puissance d’une chaîne de traction : un ensemble convertisseur / machine synchrone à rotor bobiné. Cette étude a conduit à un modèle CEM générique d’une structure non isolée quelconque d’électronique de puissance. La deuxième partie a permis de développer une nouvelle méthode de calcul qui ouvre de réelles perspectives quant à la réduction des temps de calcul. Par l’observation et l’étude de signaux sur différents horizons temporels, une technique de reconstitution des perturbations de mode commun par convolution a été proposée. Une troisième partie, consiste à synthétiser les sources de perturbations grâce à l’élaboration de fonctions de transfert décrivant le comportement haute fréquence d’une cellule de commutation. Cette approche immédiatement exploitable en simulation numérique se distingue dans la mesure où elle permet de s’affranchir des non linéarités intrinsèques des composants semi-conducteurs. / In the transport field, whether road, rail, marine or aeronautic, the number and power of embedded electric or electronic devices are constantly increasing. New features, often developed for passengers comfort, are responsible for this increase. Moreover, many actuators which were previously mechanical, thermal or hydraulic are replaced by electrical ones. Those new actuators need an electrical power supply which most of the time rely on power electronics. It is well known that this kind of device generate high levels of disturbances. In order to take into account the electromagnetic compatibility (EMC) at the design stage of a product, builders need tools adapted to EMC or specific conception rules. The work performed during this thesis is geared in order to meet these needs.The first part deals with the modeling of conducted electromagnetic interferences (EMI) of an electrical power train mainly composed by power electronics converter and a wound rotor synchronous machine. Thanks to this study, a generic model of any non-insulated structure of power electronics was developed. The second part consists in developing a new computing method which allows to reduce the time of computing. Based on the observation of signals on different time intervals, a reconstruction technique by convolution product is proposed and applied for a common mode current. The third part deals with the elaboration of sources of disturbances by transfer functions which describe the high frequency behavior of a switching cell. This modeling is directly implementable in a circuit simulation software as it allows to linearize the intrinsic non linear behavior of the semiconductor components.

A method to obtain the exact control-to-output and input-to-output transfer functions for switched DC-to-DC pulse-width modulated power converters is applied to different combinations of operating conditions such as continuous conduction mode (CCM), discontinuous conduction mode (DCM), and discontinuous voltage mode (DVM) and methods of control such as normal voltage mode (NVM), current programming mode (CPM), and V-squared control. The majority of these combinations have not previously had their transfer functions of interest derived to the accuracy provided by the method. The derivation of the method is covered, and the results from its application are verified by simulation. The simulation method is also justied and proposed as an improvement to the methods used by simulation engines for switched mode power supply design such as SIMPLIS.