Thesis (MTech (Electrical Engineering)))--Cape Peninsula University of Technology, 2011. / This thesis presents an investigation into the generic tools, hardware and firmware, involved in power electronic converter control and feedback. The aim was to determine the optimal controller architecture through research of existing controllers. As soon as the architecture was established, design of the controller commenced. Explanations for the various components selected were provided. The design considerations when designing a printed circuit board (PCB) with mixed signals was also presented. The theory behind the control of a multicell converter as well the practical implementation of the control scheme in firmware was presented.

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / Este trabalho apresenta o estudo e desenvolvimento de um conversor com capacitor comutado para o acionamento de diodos emissores de luz (LED) de potÃncia, alimentado a partir da rede elÃtrica de baixa tensÃo. Diferente dos conversores tradicionais de corrente contÃnua, a corrente direcionada aos LEDs à fornecida por meio de capacitores comutados. O conversor proposto ainda difere dos conversores convencionais baseados no capacitor comutado, pois utiliza uma indutÃncia para evitar o carregamento e o descarregamento forÃado dos capacitores comutados, reduzindo os picos de corrente e a emissÃo eletromagnÃtica do circuito. O conversor proposto apresenta correÃÃo do fator de potÃncia inerente e pode proporcionar isolaÃÃo atravÃs de capacitores. TambÃm se propÃe a utilizaÃÃo de duas topologias de filtro LC sintonizado (filtro LC paralelo e LC sÃrie) para reduzir a ondulaÃÃo da corrente de saÃda do conversor, evitando a utilizaÃÃo de capacitores eletrolÃticos. Um estudo teÃrico do conversor proposto à realizado atravÃs das anÃlises qualitativa e quantitativa, nas quais sÃo determinados os esforÃos de tensÃo e corrente nos principais componentes e tambÃm as perdas nos componentes do conversor. Um protÃtipo de laboratÃrio de 51 W com tensÃo de entrada eficaz de 220 V à projetado e testado experimentalmente. Os resultados de simulaÃÃo e experimentais sÃo apresentados e discutidos, demostrando a viabilidade tÃcnica do conversor proposto. Para a condiÃÃo de carga nominal o conversor apresenta rendimento de 75,3% e fator de potÃncia de entrada de 0,996, respeitando os limites de emissÃo de harmÃnicos determinados pela norma IEC 61000-3-2. Com a aplicaÃÃo do filtro LC paralelo, conectado em sÃrie com os LEDs, obtÃm-se ondulaÃÃo de corrente de saÃda de aproximadamente 68%, sendo essa topologia a que apresenta melhor desempenho, entre os filtros testados, estando apta a substituir o capacitor eletrolÃtico de saÃda. / This work presents a study and development of a switched capacitor-based converter to drive high power light emitting diodes (LEDs) fed from the main grid. Unlike to conventional constant current dc drivers, the current through LEDs is provided by a switched capacitor. The proposed converter approach differs from the traditional switched-capacitor-based one, because it uses an inductance to avoid the forced charging and discharging operation, reducing current spikes and EMI in the circuit. The proposed converter provides inherent power factor correction and it can provide isolation by capacitors. It is also proposed the use of two tuned LC filter topologies (parallel LC filter and series LC filter) to reduce the output current ripple, avoiding the use of large electrolytic capacitors. A theoretical analysis of the proposed converter is performed via quantitative and qualitative analysis, which determines the voltage and current efforts in main components and also losses in the converter. A 51 W, 220 V RMS laboratory prototype is designed and tested experimentally. Simulation and experimental results are presented and discussed demonstrating the technical feasibility of the proposed converter. At rated load, the converter features an efficiency of 75.3% and an input power factor of 0.996, while respecting emission limits of harmonics determined by IEC 61000-3-2. For the application of the parallel LC filter, connected in series with LED array, it is obtained output current ripple of approximately 68%. This topology presented better performance, between tested topologies, being able to replace the output electrolytic capacitor.

M.Ing. / This study covers the problem of a periodic distortion and it's electronic compensation. The description and definition of power transfer in a single-phase electrical network is investigated. The various techniques for achieving optimal power transfer are then derived. From this the principle of the compensation of reactive power in an electrical power network is derived using the definition of power transfer. In order to evaluate and illustrate this principle a system configuration, consisting of a controlled source of reactive power is used. Due to the complexity of the system it was initially decided that a computer simulation would serve as an analytical aid. This provides the opportunity to conduct a thorough investigation into the functioning of the proposed compensator. Using the knowledge thus gained. an experimental system was developed. The simulated system is compared to practically obtained results in an experimentally developed compensator in order to evaluate the accuracy and reliability of the simulation. The study then concentrates on the characterization of the two systems as applied in the compensation of reactive power. This analysis also contributes to the identification of deficiencies in the system. The study then concludes with a critical evaluation of the work and suggestions for improvement. This includes the optimization of the total system and the application in industrial power networks.

D. Ing. / Power electronics refers to electronic processing of electrical power. In this process the electrical power is controlled by switching of power semiconductor devices as well as electromagnetically stored in electrical and magnetic fields while the energy flow is directed through selective conduction paths. The losses/power-efficiency of all these actions is of paramount importance in the processing. The lack for standardisation and the absence of a modular approach is a barrier to the development of more compact systems. Recently more research resources have been invested in development of integrated power electronic modules as an attempt to solve this problem. By integrating power electronic components, an increase in the power density is achieved, which unfortunately also leads to higher internal heat-generation and higher operating temperatures. This has an unfavourable effect on electronic behaviour and the reliability of the structures. In order to maintain the advances made in volume reduction of integrated power electronics, efficient and cost effective methods for removing heat is of essence. In this investigation the performance of rectangular cross-section embedded solid-state heatextraction inserts to increase thermal heat spreading and the reduction of steady-state peak temperatures was evaluated theoretically and experimentally. Theoretically, the cross sectional aspect ratio of such inserts was thermally optimised for a wide range of dimensional, thermal, and material property conditions. Possible materials investigated for use as heat extractors in power electronics include aluminium nitride, beryllium oxide, and synthetic diamond. The presence of interfacial thermal resistance was theoretically found to have a significant detrimental influence on the thermal performance of an integrated heat-extraction system and should be minimised as far as possible. For conditions commonly found in integrated power passives, continuous embedded heatextraction layers are proposed. Theoretically it is shown that such inserts can aid in the increase of power density by reducing the temperature increase per unit volume of heat-generation. Experimental test results corresponded closely with the theoretically expected allowed increase in heat-generation that could be accommodated due to the heat-extraction action of the inserts. As an experimental system, insertion of aluminium nitride into ferrite in an integrated electromagnetic power passive module was investigated. An increase of 187% in the effective power density could be achieved due to the presence of aluminium nitride heat-extraction layers embedded into ferrite. Preliminary magnetic flux density optimisation, in terms of the volume fraction occupied by a parallel-layered heat-extraction system, was performed for a wide range of heat-extraction materials, and interfacial resistance values.

D.Ing. (Electrical and Electronic Engineering) / This thesis presents a series of analyses developed for several voltage source inverter topologies, which are indispensable in aiding the understanding and the design of these circuits. It describes the groundwork that is required for the development of custom design software for voltage source inverters. The different circuits that can be designed by using this program, are analyzed using conventional circuit analysis techniques. The equations are used to simulate the switching behaviour and to specify the required or recommended ratings of the main devices. The custom design program can be used to design three different topologies of voltage source inverters: a) hard switching (snubberless) six pulse bridge; b) hard switching (snubberless) six pulse bridge, equipped with a simple voltage clamp; and c) soft switching (snubbed) six pulse bridge, equipped with a conventional dissipative snubber circuit. The snubberless behaviour of a voltage source inverter leg is both experimentally and analytically investigated. Approximate equations are formulated which can be used to. determine the peak ratings of the main devices in the inverter, taking the reverse recovery of the freewheel diodes into account. The snubberless behaviour of an inverter leg, equipped with a simple voltage clamp across the dc link, is experimentally and theoretically investigated. Equations for design and determining the required peak ratings of the main devices are developed. It is shown that the simple voltage clamp can operate in two different modes, either as a fast discharging or as a slow discharging voltage clamp and that the ranges of applicability of thetwo modes of operation are different. Design rules for both modes of operation are presented. In order to develop the design equations for a snubbed inverter leg a suitable topology had to be identified first. A method for objectively comparing different inverter toplogies is proposed in this thesis, according to which the minimum on- and off-states of the main devices in the different topologies are compared for identical applications. This method is used to compare four different snubbed voltage source inverter topologies both theoretically and experimentally. As both methods indicate that the conventional snubber circuit allows the highest PWM switching frequency of the uncontrolled snubber circuits, this circuit is further investigated in its dissipative topology to develop the equations required for simulation and for inclusion in the program. The influence of snubber circuits on inductive inverter loads is also investigated. It is shown that for normal snubber sizes the effect of dead time forms the larger part of the output voltage distortion and that the effects of the snubber elements are normally of secondary importance. The effect of asymmetry of a specific snubber circuit on inverter loads is investigated and it is found that it introduces a de component in the output voltage. Finally the application of linear snubbers to switches that exhibit tail-forming characteristics is analyzed and optimized. The results allow the designer to minimize the total losses of the converter by identifying the optimal snubber size. The theoretical results are experimentally verified

D.Ing. (Electrical and Electronic Engineering) / Solid state converters are showing considerable progress in all applications for power electronics, mainly because of the advances made in the field of power semiconductor devices. Higher frequencies and power ratings of converters are therefore possible, leading to more and more applications for these solid state converters in induction heating. The available knowledge in this fast evolving field is however limited, leading to numerous research possibilities. It is none the less important to learn to crawl before attempting to run and a systematic line is therefore followed in this research. The combination of the heating-coil and work-piece is a challenging electromagnetic problem, resembling a transformer with a short circuited secondary. The heating of the work-piece to above the Curie temperature causes considerable variations in the parameters of the load. A study of the influence of temperature on the physical properties of the heated material is therefore made to obtain an understanding of these variations and is aided by Finite Element Simulations. Numerous circuit topologies and switching strategies are possible candidates for induction heating, and a collection of more than thirty converters is presented. Each of these has its own advantages and disadvantages, of which a good understanding is necessary to obtain the most suitable converter for a certain application in this field. The behaviour of some of the most popular converters under typical load variations is investigated to facilitate the final decision. This knowledge is then applied to some every day applications. A converter is chosen both for an induction cooker and a surface heater, after the specific requirements for each have been identified. A detailed design procedure and experimental results are presented...

M.Ing. (Electrical And Electronic Engineering) / DC to AC converters are used daily in industry, shipping and aviation as power .. supplies, standby power supplies or uninterrupted power supplies. Power levels vary from a few watts to several megawatts. This thesis investigates a composite converter with a high frequency link as such a DC to AC converter. There are two basic building blocks, the primary inverter as a push-pull inverter and the secondary converter as a cyclo-converter. A existing 2.5kVA system with bipolar transistors in the primary inverter and asymmetrical thyristors in the secondary converter is investigated. In the primary inverter, regenerative snubbers are used to minimise switching losses. A second 2.5kVA system with mosfets in the primary inverter and IGBT's in the secondary is developed. Switching losses in the primary inverter are minimised by including a resonant circuit concisting of a non-linear inductor and linear capacitor. This resonant circuit in the primary inverter, was originally simmulated by a PSPICE simmulation program, after which it was build up experimentally. The simmulated results and experimental results coincided, and development of the secondary converter started. The switches in the secondary had to comply to two conditions viz, low conducting lossses and the ability to switch at switching frequencies higher than 20kHz. IGBT's were consequently chosen and were implemented with the necessary gate drive circuits. With the higher switching frequency of 25kHz to the 5kHz of the first system, the ripple on the load current was significantly reduced. Furthermore, the construction of the composite converter with the gate drive switches was easy and compact, and the total cost of developing such a converter were reduced.

The increase in demand for renewable energy sources has been exponential in recent years and is mainly driven by factors that include the growth of greenhouse emissions and the decline in fossil fuel reservoirs. Photovoltaic (PV) energy, one of the more prominent renewable energy sources, produces electricity directly from sunlight, noiselessly and harmlessly to the environment. Additionally, PV energy systems are easy to install and financially supported by many governments, which has helped disseminate PV technology worldwide. The total generated power from PV installations (and the number of installations) has increased more than two-fold during the past 3 years, so that now more than 177 GW of PV-generated power is delivered per year. Researchers have been led to work on the obstacles facing PV systems from different perspectives, including: installation cost, inconsistency, and conversion and interface efficiency. The aim of this thesis is to design a high-efficiency PV inverter system configuration. The contribution to the knowledge in this thesis can be divided into two parts. The first part contains a critical analysis of different maximum power point tracking (MPPT) techniques. The second part provides a detailed design of the inverter system, which consists of a boost converter and a low-frequency H-bridge. Together, the three parts in this contribution present a complete high efficiency PV inverter system. The proposed system maintains high-efficiency energy delivery by reducing the number of high-frequency switches, which waste a significant amount of energy and reduce system efficiency. In order to show the superiority of the proposed configuration, a power loss analysis comparison with the other existing configurations is presented. In addition, different scenarios have been simulated with Matlab/Simulink. The results of these simulations confirm the distinction of the proposed configuration as well as its low-loss, high-efficiency characteristics which is rated at 98.8%.

M.Ing. (Electrical and Electronics) / The increased use of power electronic equipment in power networks prompted the development of various topologies to compensate for the distortion in the power networks. The various compensator topologies employ a vast range of converters for the compensation of the different non-active power components. The compensators are either designed to eliminate a specific non-active power component, or a combination of converters is used to simultaneously compensate for several non-active components. The choice of compensator depends largely on the type of load, the distortion levels in the power network, the effectiveness of the compensator and very importantly, the cost implications for the user. Under constant load conditions a particular compensator would suffice. It is however not the case when the load and the accompanied distortion varies with time, which is the case with present non-linear, dynamic high power loads on the network. In these cases,. a need for another compensator or compensation strategy, that is more effective in compensating the changing load condition, exists. It would therefore be advantageous to construct a single compensator from various converters -the hybrid compensator -, so as to enable the user to compensate effectively at all times the distortion caused by his load. In order to be able to operate such a hybrid compensator cost-effectively an intelligent control system capable of constantly monitoring the load and updating the compensation strategy, is needed. Keeping in mind that, with the technology available today, compensators can effectively operate for periods in excess of twenty years, it makes sound economical sense to operate the compensator as cost-optimally as possible. This dissertation investigates the development of an artificial neural network based controller for the cost-optimal control of a hybrid compensator. The hybrid compensator considered consists of the following: A 21 kVAR three phase FF-TCR compensator with LC-fiIters tuned at the 5th, 7th,11th and 13th harmonic frequencies and a 6 kVA three-phase dynamic power filter. The hybrid compensator is to be applied for the compensation of a 25 KVA non-linear load (Inductively loaded controlled rectifier). The above mentioned compensators have been modelled to agree with experimental pilot plants. The complete system with low-level controllers was simulated with EMTP (The Electromagnetic Transients Program). This simulation was used to verify the intelligent controller operation. The neural network based controller that is investigated, consists of a Backpropagation-trained neural network, that continuously analyses the load conditions, considers the operational characteristics and losses of the hybrid compensator and proposes a cost-optimal compensation strategy for the hybrid compensator. The modelling of the hybrid compensator's operational losses and characteristics to enable the cost-effective operation thereof is discussed. Special attention is given to the modelling of the cost-effective control strategy, in the training data used for the training of the neural network controller. The training of the neural network controller, and an evaluation of its behaviour when applied to two different hybrid compensator structures, is also given.

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.