As power electronic based controllers and loads become more prevalent in power systems, there is a growing concern about how the harmonics generated by these controllers and loads affect the power quality of the system. One widely used power electronic based load is the Variable Frequency Drive (VFDs) used to vary the speed of an induction motor; whereas a common example of a power electronic based controller used in power systems is the Static VAR Compensator (SVC) for improving a system’s power factor. In this thesis, the harmonic content and overall performance of a system including both a VFD and a SVC will be studied and analyzed. Specifically, the cases of no compensation, static capacitor compensation, and power electronic based static VAR compensation are examined. A small-scale model of a system for study was constructed in lab. Several cases were then performed and tested to simulate a system which contained both fixed and power electronic based harmonic generating loads. The performance of each case was determined by total harmonic current and voltage distortions, true power factor, and RMS current levels at different points in the system.

This thesis investigates a relatively new method for harvesting wind energy by using flexible piezoelectric polymers with additional sails to increase their ability to harvest wind energy. This paper also introduces a new topology deemed the “stacked buck” that allows for multiple inputs to a system with a single output. Derivations and analysis detail the workings of the “stacked buck” with a laboratory test to show a working model. This paper also reports another experiment done in a wind tunnel to analyze the capability of the piezoelectric polymers as sources to the “stacked buck” topology with measurements of the power output. The results of this thesis demonstrate that because the design is very modular, it is possible to scale the proposed wind energy harvesting system for small power applications.

Lorsqu’un concepteur de systèmes d’électronique de puissance est engagé dans un processus de pré-design, c’est-à-dire la définition du cahier des charges du système, il doit surmonter plusieurs difficultés. La première étant de trouver grâce à son expérience et à la littérature, toutes les architectures, topologies de conversion et technologies de composants susceptibles de répondre aux besoins du système.A partir de cette éventail, le concepteur doit en éliminer un certain nombre via des arguments qualitatifs ou quantitatifs jusqu’à ce qu’il n’en reste plus qu’un nombre très restreint. Il est primordial pour le concepteur que parmi les choix restant, celui-ci en connaisse les limites de design pour définir avec certitude le plan de développement du produit et les problématiques futures à résoudre. En d’autres termes, il lui faut définir la juste formulation du problème qui lui est posée.Posséder une méthode lui permettant d’atteindre cet objectif en toute confiance et dans les délais impartis est fortement désirable. Ceci est l’objet de cette thèse.Nous proposons donc une nouvelle approche basée sur le pré-dimensionnement par optimisation dans le monde continu (imaginaire) de systèmes d’électronique de puissance. La méthode proposée utilise en effet un algorithme d’optimisation basé sur le calcul du gradient du modèle du système. Cet algorithme permet de gérer un très grand nombre de paramètres de design, autrement dit permet d’explorer un large éventail de solutions dans le monde imaginaire. Il nécessite donc des modèles de systèmes d’électronique de puissance continus et dérivables avec des variables d’optimisation continues (imaginaires) malgré le caractère discret des composants utilisés en électronique.Les présents travaux de thèse ont donc consistés à proposer des modèles d’optimisation continus et dérivables d’un convertisseur Buck entrelacé utilisé dans un aéronef appelé « Stratobus » et à valider ces modèles d’optimisation par une démarche expérimentale sur un prototype complet. Ces modèles ont ensuite été utilisés pour le pré-dimensionnement de ce convertisseur dans le cadre du projet Stratobus permettant dans un premier temps une étude sur le mode de conduction et les matériaux magnétique minimisant la masse du convertisseur, puis une analyse de l’impact de variation de cahier des charges sur la masse du convertisseur. Enfin, les convertisseurs étant construits à partir de composants électroniques choisis sur étagère, une procédure de discrétisation a été mise en place pour revenir au monde réel. / When a designer of power electronics systems is involved in a pre-design process, i.e. the definition of the system specifications, he/she has to overcome several difficulties. The first is to find, based on its experience and literature, all the architectures, conversion topologies and component technologies that can meet the needs of the system.From this list of possibilities, the designer must eliminate a certain number of them via qualitative or quantitative arguments until only a small number remains. It is essential for the designer that he/she knows the design limits of each remaining choices to define with certainty the product development plan and the future design issues to be solved. In other words, it must define the correct problem formulation.Having a method to achieve this objective with confidence and on schedule is highly desirable. This is the purpose of this thesis.We therefore propose a new approach based on preliminary design by optimization in the continuous (imaginary) world of power electronics systems. The proposed method uses an optimization algorithm based on the calculation of the gradient of the system model. This algorithm allows to manage a very large number of design parameters, in other words to explore a wide range of solutions in the imaginary world. It therefore requires continuous and differentiable models of power electronics systems with continuous (imaginary) optimization variables despite the discrete nature of the components used in electronics.The present thesis work has thus consisted in proposing continuous and derivable optimization models of an interleaved Buck converter used in an aircraft called "Stratobus" and validating these optimization models by an experimental approach on a complete prototype. These models have then been used for the pre-dimensioning of this converter as part of the Stratobus project. Firstly a study on the conduction mode and magnetic materials minimizing the mass of the converter has been performed. And then the impact of variation of the specifications on the mass of the converter has been analyzed. Finally, since the converters are built from electronic components chosen off the shelf, a discretization procedure has been set up to return to the real world.

Abstract not available

<p>The purpose of this degree project was to build laboratory equipment for a new course in power electronics that starts this autumn 2010 at Uppsala University. The equipment is intended for student labs and it covers the most important areas of the course including rectifying, buck-/boost-converters and PWM-modulation. It is built as one sealed unit where all the electronics are built-in but visible and it has a connection board where students safely can connect the different circuits. The project has advanced from theoretical studies of circuit design, choosing of components and simulations to drawing the printed circuit board (PCB), soldering, case building, final testing and troubleshooting - basically most steps from an early idea to a final product. Measurements on the final product gave about the same results as the earlier simulations of the circuits and the result is overall satisfying.</p> / <p>Syftet med det här examensarbetet var att bygga laborationsutrustning till en ny kurs i kraftelektronik som börjar hösten 2010 på Uppsala Universitet. Utrustningen är avsedd för studentlaborationer och den täcker de viktigaste delarna av kursen inklusive likriktning, buck-/boost-omvandlare och pulsbreddsmodulering (PWM). Laborationsutrustningen är byggd som en sluten enhet där all elektronik är inbyggd men synlig och den har en kopplingsplatta där studenterna säkert kan koppla ihop olika kretsar. Projektet har sträckt sig från teoretiska studier inklusive kretsdesign, komponentval och simuleringar till ritande av kretskortet (PCB-kortet), lödning, byggande av höljet, sluttestning och felsökning - i huvudsak de flesta stegen från en tidig idé till en färdig produkt. Mätningar på den färdiga produkten är ganska lika de tidigare simuleringarna av kretsarna och resultatet är totalt sett tillfredställande.</p>

This thesis presents the concept of a "distributed HVDC converter" for offshore wind farms. The proposed converter topology allows series interconnection of wind turbines obviating the necessity of transformers and an offshore platform. Each wind turbine is equipped with a 5MW permanent-magnet synchronous generator and an ac-dc-dc converter. The converter topology is a diode rectifier (ac-dc) cascaded with a single-switch step-down converter (dc-dc). The dc-dc stage allows the current to flow at all times in the dc link while regulating generator torque. The receiving end is equipped with a conventional thyristor-based HVDC converter. The inverter station is located onshore and it regulates the dc link current to be constant. Stability of the configuration and independent operation of the wind turbines are validated through simulations using the PSCAD/EMTDC software package. Protection for some key dc fault scenarios are discussed and a possible protection strategy is proposed.

University of Macau / Faculty of Science and Technology / Department of Electrical and Computer Engineering

University of Macau / Faculty of Science and Technology / Department of Electrical and Computer Engineering

This thesis presents the concept of a "distributed HVDC converter" for offshore wind farms. The proposed converter topology allows series interconnection of wind turbines obviating the necessity of transformers and an offshore platform. Each wind turbine is equipped with a 5MW permanent-magnet synchronous generator and an ac-dc-dc converter. The converter topology is a diode rectifier (ac-dc) cascaded with a single-switch step-down converter (dc-dc). The dc-dc stage allows the current to flow at all times in the dc link while regulating generator torque. The receiving end is equipped with a conventional thyristor-based HVDC converter. The inverter station is located onshore and it regulates the dc link current to be constant. Stability of the configuration and independent operation of the wind turbines are validated through simulations using the PSCAD/EMTDC software package. Protection for some key dc fault scenarios are discussed and a possible protection strategy is proposed.

This thesis evaluates a series hybrid electric drivetrain design for use in parking patrol vehicles. Due to the particular attributes of this application, it is proposed that the design would improve the energy efficiency of such a vehicle. The scheme is evaluated in depth through the use of electromagnetic transient simulation tools, which are used to create a highly accurate model of the vehicle. A prototype vehicle of the same design is built, and used to verify and improve the accuracy of the simulation model. The simulation model is then used to predict the energy efficiency of the series hybrid design for parking patrol. This simulation based design strategy is proposed as a method for more rapid and cost effective design of hybrid electric vehicles. / October 2007