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.

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.

In low power, battery-operated, portable applications, like cell phones, PDAs, digital cameras, etc., miniaturization at a low cost is a prominent driving factor behind product development and marketing efforts. As such, power supplies in portable applications must not only conform and adapt to their highly integrated on-chip and in-package environments but also, more intrinsically, respond quickly to fast load dumps to achieve and maintain high accuracy. The frequency-compensation network, however, limits speed and regulation performance because, in catering to all combinations of the output capacitor, its equivalent series resistance Resr, and the power inductor resulting from tolerance and modal design targets, it must compensate the worst-case condition and therefore restrain the performance of all other possible scenarios. Sigma-delta control, which addresses this issue in buck converters by easing its compensation requirements and offering one-cycle transient response, has not been able to simultaneously achieve high bandwidth, high accuracy, and wide LC-Resr compliance in boost (step-up) converters. This thesis investigates and presents techniques to achieve sigma-delta control in boost converters by essentially using explicit current and voltage control loops. The proposed techniques are developed conceptually and analytical expressions for stability range and transient response are derived. The proposed concepts are validated and quantified through PCB and IC prototypes to yield 1.41 to 6 times faster transient response than the state of the art in current-mode boost supplies, and this without any compromise in LC-Resr compliance range.

M. Tech. Electrical Engineering / Investigates the reasons behind the poor performance of distance relays on series compensated lines. In order to achieve this objective, a case study will be established in a power system software (DigSilent Power Factory). Furthermore, a practical incident that occurred on Eskom's compensated network will be examined. However, prior to investigating the performance of the distance relay on transmission lines, there are some other critical aspects that have to be thoroughly understood. These aspects include amongst others: transmission line modelling ; numeric relay algorithms ; distance protection philosophies ; series compensation phenomena ; analysis of distance relays performance on both compensated and uncompensated lines and the action and influence of the MOV. The study will provide a better understanding regarding the dynamic behaviour of the impedance protection relay under fault conditions on series compensated lines and the behaviour of the MOV during a fault.

Conventionally, system simulations of induction motor drives use lumped parameters model of the motor. This approach assumes motor parameters to be constant during the entire operation of the drive. Unfortunately, these are known to vary significantly over the operating range of the motor due to factors such as magnetic saturation, skin effects, and operating temperature. The variations in motor parameters affect motor output and control parameters resulting in degraded drive performance. One way of overcoming this problem is by coupling the field model of the induction motor with the drive simulation. By replacing the lumped parameters model with the field model, the influence of different operating conditions on motor parameters can be taken into account dynamically. In this thesis such an approach is investigated by coupling the finite element analysis of an induction motor with the system simulation of the field oriented controlled drive. The results obtained for the coupled simulation are promising and possible future works to make this method of simulation more accurate and reliable are recommended.

Solar photovoltaic (PV) systems are distributed energy sources that are an environmentally friendly and renewable source of energy. However, solar PV power fluctuates due to variations in radiation and temperature levels. Furthermore, when the solar panel is directly connected to the load, the power that is delivered is not optimal. A maximum peak power point tracker is therefore necessary for maximum efficiency. A complete PV system equipped maximum power point tracking (MPPT) system includes a solar panel, MPPT algorithm, and a DC-DC converter topology. Each subsystem is modeled and simulated in a Matlab/Simulink environment; then the whole PV system is combined with the battery load to assess the overall performance when subjected to varying weather conditions. A PV panel model of moderate complexity based on the Shockley diode equation is used to predict the electrical characteristics of the cell with regard to changes in the atmospheric parameter of irradiance and temperature. In this dissertation, five MPPT algorithms are written in Matlab m-files and investigated via simulations. The standard Perturb and Observe (PO) algorithm along with its two improved versions and the conventional Incremental Conductance (IC) algorithm, also with its two-stage improved version, are assessed under different atmospheric operating conditions. An efficient two-mode MPPT algorithm combining the incremental conductance and the modified constant voltage methods is selected from the five ones as the best model, because it provides the highest tracking efficiencies in both sunny and cloudy weather conditions when compared to other MPPT algorithms. A DC-DC converter topology and interface study between the panel and the battery load is performed. This includes the steady state and dynamic analysis of buck and boost converters and allows the researcher to choose the appropriate chopper for the current PV system. Frequency responses using the state space averaged model are obtained for both converters. They are displayed with the help of Bode and root locus methods based on their respective transfer functions. Following the simulated results displayed in Matlab environment for both choppers, an appropriate converter is selected and implemented in the present PV system. The chosen chopper is then modeled using the Simulink Power Systems toolbox and validates the design specifications. The simulated results of the complete PV system show that the performances of the PV panel using the improved two-stage MPPT algorithm provides better steady state and fast transient characteristics when compared with the conventional incremental conductance method. It yields not only a reduction in convergence time to track the maximum power point MPP, but also a significant reduction in power fluctuations around the MPP when subjected to slow and rapid solar irradiance changes. / Thesis (M.Sc.Eng)-University of KwaZulu-Natal, Durban, 2011.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Includes bibliographical references (p. 170-177).

Thesis (MEng)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: This thesis presents the design of a DSP based controller system for an auxiliary converter for generic energy storage connection to a line-interactive power compensator. The aim is to utilize a wide range of energy storage systems and incorporate them into the existing power compensator. This was done by adding a second converter to the system. The new controller was developed to control this converter and thereby the energy storage. A study was done on lead acid batteries, flow batteries and flywheels in order to gain a basic understanding of these systems and identify the requirements for their control. Based on these findings, a new DSP based controller and measuring system was developed. To test the new system a dc to dc converter was implemented for the control of lead acid and flow batteries. A dc to ac converter was also tested for the control of flywheel energy storage. / AFRIKAANSE OPSOMMING: Die tesis handeloor die ontwerp van'n DSP gebaseerde beheerstelsel vir 'n Iyninteraktiewe on-onderbreekbare kragbron met drywings-kompensasie met 'n hulp omsetter vir algemene enegiestoor koppeling. The doel is om 'n wye verskeindheid energie store in die huidige drywings elektroniese stelsel te inkorporeer. 'n Tweede omstetter is by die stelsel gevoeg om die energie stelsel te beheer. 'n Nuwe beheerder is ontwikkel om die omsetter te beheer en daardeur die energie stoor. Loodsuur batterye, vloei batterye en vliegwiele is ondersoek om 'n basiese begrip te vorm en te identifiseer wat nodig is vir die beheer van sulke energie store. Die nuwe DSP beheerder en meetstelsel is ontwikkel gebaseer op hierde ondervindings. Om die nuwe beheerstelsel te toets is 'n gs na gs omsetter geïmplementeer vir die beheer van loodsuur en floei batterye. Die omsetter is geherkonfigureer na 'n gs na ws opstelling en getoets. Die konfigurasie word gebruik vir die beheer van vliegwiele.