Σκοπός της παρούσας εργασίας είναι η μελέτη και κατασκευή ενός μετατροπέα ισχύος για την οδήγηση αναρτήσεως αποτελούμενης από μαγνητορεολογικό υγρό. Στην αρχή, γίνεται μία ιστορική αναδρομή στις εξελίξεις στο χώρο των αναρτήσεων. Κατόπιν, αναφέρονται τα χαρακτηριστικά των μαγνητορεολογικών υγρών και των αντίστοιχων αναρτήσεων, με παραδείγματα εφαρμογής τους στην αυτοκινητοβιομηχανία. Στη συνέχεια, παρουσιάζονται τα βασικά χαρακτηριστικά των τροφοδοτικών ισχύος, καθώς και τα συγκριτικά πλεονεκτήματα και μειονεκτήματά τους. Έπειτα παρουσιάζονται οι βασικότερες διατάξεις μετατροπέων ισχύος και τα χαρακτηριστικά τους, τα οποία θα χρησιμεύσουν στην επιλογή της κατάλληλης διάταξης για την παρούσα εφαρμογή. Ακολουθεί η παρουσίαση της θεωρητικής μελέτης της διάταξης forward, η οποία και επιλέχθηκε, ως καταλληλότερη και οι προσομοιώσεις στο πρόγραμμα Matlab, με τις αντίστοιχες εικόνες και πειραματικές τιμές. Τέλος, περιγράφεται η διαδικασία σχεδιασμού και κατασκευής της πλακέτας ισχύος. / The purpose of this diploma thesis is the design and construction of a power converter to drive a magnetorheological suspension. At the beginning, historical developments in the field of suspension are presented. Then, the characteristics of magnetorheological fluids and related suspension systems are described, with examples of their application in the automotive indusrty. Afterwards, it follows an analysis of the key features of the power supplies, along with their comparative advantages and disadvantages. Subsequently, the main power converters and their characteristics are discussed, which will be used in selecting the appropriate device for this application. In the followin paragraphs, the theoretical study of the device forward, which was selected as appropriate, is analyzed and simulated with Matlab application. The corresponding images and experimental values are presented also. Finally, the design and construction of the power converter board circuit is prsented.

This thesis presents an electrical system analysis of a wave energy converter (WEC) for the objective of grid connection. To transfer the enormous amount of power from waves to the load centers, efficient power electronic systems are essential. This thesis includes the modeling of a buoy–translator dynamics and the modeling of a linear permanent magnet generator along with simulation and experimental validation. Diode bridge rectifiers are considered for rectification to avoid the complex linear generator control at the input side. To reduce the size and the cost of energy storage elements, DC voltage regulation is done using a DC/DC converter. To achieve smooth and high power, many WECs need to be connected to a common DC link. A neutral point clamped inverter is considered for the DC/AC conversion due to its advantages over conventional topologies. Various pulse width modulation schemes are tested for the inverter to choose the optimum PWM method. The harmonics in the inverter output voltage is derived numerically and compared with simulation and experiment to understand the effect of dead-time in the inverter operation. Depending on the load current drawn from the inverter, the voltages in the two input capacitors of a three-level neutral point clamped inverter deviates from equilibrium unless the neutral point is grounded. To avoid this voltage imbalance as well as to regulate the DC link voltage a dual output boost converter with pulse delay control is proposed. The modeling, simulation and experiments show an improvement in the compensation voltage using pulse delay control compared to the previously proposed methods in the literature. The synchronous current control and the grid connection of the three-level converter have been accomplished in the laboratory.  Finally, the three-level power converter system has been tested with a linear permanent magnet generator at Lysekil to analyze the controller requirements.

Multilevel inverters have attracted wide interest in both the academic community and the industry for the past decades. Therefore, the investigation and development of modulation strategies in multilevel inverters emerges as a necessity for the industry and researchers. In this doctoral thesis, alternative modulation methods suitable for three-level conventional single-phase inverters and especially for cascade H-bridge multilevel inverters are discussed and proposed. The theory of Equal Areas is reformed and presented and its modifications are proposed. These modifications are compared with other well-known modulation schemes, such as carrier-based modulation schemes and programmed pulse width modulation techniques. The advantage of the modified Equal Areas Pulse Width Modulation (EAPWM) is its algorithmic simplicity due to simple algebraic relationships, which results in less computational effort. A fully mathematical formulation for the Equal Areas modulation is proposed for both conventional and multilevel inverters. The EAPWM is shown to produce well-formed switched output voltages that have low total harmonic distortion at even low switching frequencies. The importance of this thesis is complimented by the results, produced after the implementation of EAPWM in multilevel inverters, which can be used as a more accurate reference when compared with other modulation strategies. Moreover, this direct modulation strategy has been extended to work on higher amplitude modulation ratios, in a linear manner, while entering the over modulation region. In this context, modified algorithms have been developed using different criteria for the calculation of the pulses’ width and their placement inside the time interval. The equal areas method, implemented in conventional single-phase inverters, uses odd pulse numbers per half cycle, holding integer frequency ratios in contrast to its implementation in multilevel inverters, where non-integer frequency ratios occur due to the level-by-level application. The application of the method is verified by simulations together with experimental work using a full-scale prototype inverter.

This thesis presents the work performed by the author on the application of resonantmode techniques to commercially-orientated off-line converters. An extensive review of resonant-mode topologies leads to the development of a method of categorisation of these topologies which allows a greater comprehension of their properties. The categories of converter thus obtained are the conventional resonant converter, the quasi-resonant converter, and the gap-resonant converter. The gap-resonant converter is selected for further investigation. An analysis reveals the limited load and input voltage capabilities of this converter, and hence leads to the introduction of a pre-regulating converter to improve reliability and commercial viability. High-frequency techniques are explored and reported, and new techniques are developed in several areas in order to extend the concept of the gap-resonant converter to a realworld practical design. Subjects explored include the high speed driving of power MOSFETs, MOSFET and diode switching losses, high frequency magnetic materials and core losses, and skin and proximity effects. The techniques developed are used in the design of a 30OW, off-line converter with an input voltage range of 165V to 380V after rectification, and a ten-to-one output load range.

In his thesis, CONDUCTED EMC MODELLING IN MODERN DC-DC POWER CONVERTERS, the conducted electromagnetic effects of high-density high-switching frequency modern power converters are studied. The noise source and noise path were modelled and the results calibrated to accredited noise levels. A VHF frequency model was developed and verified using different analysis packages and compared for accuracy, affordability and ease of use. Noise modes were separated and verified for accuracy. The mechanisms of the noise modes were studied and noise mitigation techniques presented. / Thesis (PhD)--University of Pretoria, 2017. / Electrical, Electronic and Computer Engineering / PhD / Unrestricted

This thesis discusses two different photovoltaic systems, organic solar cells, and photonic power converters. The open-source software package Solcore was used to simulate and analyze optoelectronic properties of both systems. It is widely accepted that the transition from a fossil-fuel driven economy is necessary in the coming future. Organic solar cells are an alternative energy generation method with potential for fast energetic and economic payback periods. Bulk heterojunction organic solar cells are a common design, as they have particularly low manufacturing costs due to a simple device architecture. In this work, two bulk heterojunction blends are experimentally assessed using the acceptor molecule silicon phthalocyanine (bis(tri-n-butyl silyl oxide) silicon phthalocyanine ((3BS)2-SiPc) as a potential low-cost non-fullerene alternative to the typical acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PC₆₁BM). These acceptors are compared within blends with the typical donor compound poly(3-hexylthiophene) (P3HT), and also poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo [1,2-b:4,5-b’]dithiophene))-alt-(5,5-(1′,3′-di-2- thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c’]dithiophene-4,8-dione)] (PBDB-T). Device performance was assessed under standard conditions, increased angles of incidence, and reduced light intensities. Devices with the P3HT:(3BS)2-SiPc blend achieved a power conversion efficiency (PCE) of 3.6%, which outperformed P3HT:PC₆₁BM devices with a PCE of 3.0% due to a higher open-circuit voltage (VOC) of 0.76 V as opposed to 0.53 V. The PBDB-T:(3BS)2-SiPc achieved a high VOC of 1.09 V, but had a lower PCE of 3.4% in relation to the PBDB-T:PC₆₁BM device with a PCE of 6.4% and a VOC of 0.78 V. Photonic power converters are devices in optical networks that allow for optical power transmission rather than the conventional method of electrical power transmission. This provides benefits such as electrical isolation and resistance to electromagnetic interference, along with the ability to propagate along the same cable as data. These power converters are used to convert optical power to electrical power, and operate similarly to a solar cell with a narrow bandwidth. Multijunction designs are often used for increased operating voltage and efficiency. In such designs employing a vertical architecture, the bottom-most junction has the largest thickness along with the lowest efficiency due to increased recombination losses. To improve this lower efficiency, light trapping techniques can be employed to decrease the junction thickness while retaining the optical thickness. In this work, a current-matched 5- junction GaAs photonic power converter was simulated with both metallic and distributed Bragg reflectors at the rear of the device. These reflectors allowed for the thinning of the bottommost junction, which resulted in an increase in efficiency and overall power output of the power converter.

No description available.

Switched electronic systems are used in a huge number of everyday domestic and industrial utilities: liquid crystal displays, home appliances, lighting, personal computers, power plants, transportation vehicles and so on. Efficient operations of all such applications depend on the essential "hidden work" done by switched electronic systems, whose behavior is determined by a suitable interconnection and control of analog and digital devices. As a motivation of this work, we consider the DC-DC power converters. This thesis contributes to provide hybrid and nonlinear control problem solutions to several types of power converters. In the first part we are interested in the problem of voltage regulation of power converters operating in discontinuous conducting mode. Two power converters are considered: the boost converter and the buck-boost converter. The system does not admit a (continuous--time) average model approximation, hence is a hybrid system where the control objective is the generation of a periodic orbit and the actuator commands are switching times. Our main contribution is a simple robust algorithm that gives explicit formulas for the switching times without approximations. Simulation and experimental results that illustrate the robustness of the scheme to parameter uncertainty, as well as performance comparisons with current practice, are presented. In the second part a class of power converters that can be globally stabilized with an output-feedback PI controller has been identified. Moreover, we will prove that the I&I observer can be combined with the PI controller preserving the GAS properties of the closed-loop. The class is characterized by a simple linear matrix inequality. The new controller is illustrated with the widely-popular, and difficult to control, single-ended primary inductor converter, for which simulation and experimental results are presented.

Les systèmes électroniques commutés sont de plus en plus utilisés dans plusieurs domaines domestiques ou industriels: les écrans à cristaux liquides, les appareils électroménagers, l'éclairage, les ordinateurs personnels, les centrales électriques, les véhicules de transport et ainsi de suite. L'efficacité des opérations de toutes les applications dépend du travail essentiel réalisé par des systèmes électroniques à commutation, dont le comportement est déterminé par une interconnexion et un contrôle appropriés des dispositifs analogiques et numériques. Comme motivation de ce travail, nous considérons les convertisseurs DC-DC de puissance. Cette thèse contribue à fournir des solutions aux problèmes de contrôle hybrides et non linéaires des plusieurs types de convertisseurs de puissance. Dans la première partie nous intéressons au problème de la régulation de la tension des convertisseurs de puissance fonctionnant dans le mode de conduction discontinue. Deux convertisseurs de puissance sont considérés: le convertisseur boost et le convertisseur buck-boost. L'objectif de commande est la génération d'une orbite périodique. Notre principale contribution est un algorithme simple et robuste qui donne des formules explicites pour les temps de commutation sans approximations. Les résultats de simulation et expérimentaux sont présentés. Dans la deuxième partie une classe de convertisseurs de puissance qui peut être globalement stabilisé avec un contrôleur PI a été identifiée. Par ailleurs, nous allons prouver que l'observateur I&I peut être combiné avec le contrôleur PI tout en préservant les propriétés de stabilité asymptotique globale de la boucle fermé. La classe se caractérise par une inégalité matricielle linéaire simple. Le nouveau contrôleur est illustré avec le convertisseur très - populaire, et difficile à contrôler, le SEPIC, pour lequel les résultats de simulation et expérimentaux sont présentés. / Switched electronic systems are used in a huge number of everyday domestic and industrial utilities: liquid crystal displays, home appliances, lighting, personal computers, power plants, transportation vehicles and so on. Efficient operations of all such applications depend on the essential “hidden work" done by switched electronic systems, whose behavior is determined by a suitable interconnection and control of analog and digital devices. As a motivation of this work, we consider the DC-DC power converters. This thesis contributes to provide hybrid and nonlinear control problem solutions to several types of power converters. In the first part we are interested in the problem of voltage regulation of power converters operating in discontinuous conducting mode. Two power converters are considered: the boost converter and the buck-boost converter. The system does not admit a (continuous--time) average model approximation, hence is a hybrid system where the control objective is the generation of a periodic orbit and the actuator commands are switching times. Our main contribution is a simple robust algorithm that gives explicit formulas for the switching times without approximations. Simulation and experimental results that illustrate the robustness of the scheme to parameter uncertainty, as well as performance comparisons with current practice, are presented. In the second part a class of power converters that can be globally stabilized with an output-feedback PI controller has been identified. Moreover, we will prove that the I&I observer can be combined with the PI controller preserving the GAS properties of the closed-loop. The class is characterized by a simple linear matrix inequality. The new controller is illustrated with the widely-popular, and difficult to control, single-ended primary inductor converter, for which simulation and experimental results are presented.

Les travaux de cette thèse portent sur l’analyse de stabilité et la synthèse de commandes robustes pour les systèmes affines à commutation en temps continu en présence d’incertitudes paramétriques constantes. On propose deux méthodes de commande permettant de garantir la stabilité asymptotique globale des systèmes affines à commutation avec paramètres inconnus. La première approche est basée sur l’estimation des paramètres inconnus et la reconstruction de l’état d’équilibre associée pour permettre d’appliquer une commande robuste adaptative. La seconde méthode est basée sur une augmentation d’état par l’ajout d’une action intégrale dans la boucle de commande qui garantit une erreur statique nulle. Pour chaque approche, deux lois de commande sont proposées. Une méthode du type « min switching » qui sélectionne la commutation la plus apte à stabiliser le système et une méthode de type « Embedded » permettant de générer une commande polytopique des différents modes possibles. Les résultats sont appliqués aux convertisseurs de puissance de topologie Flyback avec preuve de stabilité dans les deux modes de conduction (continue et discontinue) / This PhD thesis is focused on stability analysis and robust control synthesis for continuous time switching affine systems in presence of constant parametric uncertainties. Two control methods are proposed to guarantee global asymptotic stability of switching affine systems with unknown parameters. The first approach is based on the estimation of the unknown parameters and the reconstruction of the related equilibrium state to allow the application of a robust adaptive control. The second method is based on a state augmentation by adding an integral action in the control loop that guarantees a null steady state error. For each approach, two control laws are proposed. A "min switching" method that selects the most suitable mode to stabilize the system and an "Embedded" method that generates a polytopic control of the different possible modes. The results are applied to Flyback topology power converters with proof of stability in both conduction modes (continuous and discontinuous)