Made available in DSpace on 2016-12-12T20:27:39Z (GMT). No. of bitstreams: 1 Luiz Ricardo Lima.pdf: 7933900 bytes, checksum: 225fa96a5d447127d12b2a23f0483893 (MD5) Previous issue date: 2011-08-12 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work presents a study about the NPC (Neutral Point Clamped) three-level inverter with a modified Undeland snubber and using a Buck-Boost converter to regenerate the energy processed by the snubber. Initially, qualitative and quantitative analysis of this inverter with the presence of the snubber are presented and a project methodology is proposed. The same analysis and project are presented for the Buck-Boost converter and it is shown that this converter can operate under ZVS (Zero Voltage Switching). Next, mathematical models of all circuitry necessary for the realization of the digital control of the inverter are presented and a controller is projected. Using data of the projected NPC inverter, Buck-Boost converter and digital controller, simulation results are presented. These simulations were done using software s Orcad Pspice and Simulink. Finally, implementation details and experimental results of a 1.5 kW, 800 V input voltage, 127 V output voltage and 200 kHz switching frequency prototype are presented. / Este trabalho apresenta um estudo do inversor NPC (Neutral Point Clamped) a três níveis com snubber de Undeland modificado, utilizando um conversor Buck-Boost para regeneração da energia processada pelo snubber. Inicialmente são feitas analises qualitativa e quantitativa desse inversor com a presença do snubber e é apresentada uma metodologia de projeto. As mesmas analises e projeto são feitos para o conversor Buck-Boost e é mostrado como ele pode operar com comutação ZVS (Zero Voltage Switching). A seguir são mostrados os modelos matemáticos de todos os circuitos necessários para se realizar o controle digital do inversor e é apresentado um projeto de controlador digital. Utilizando os dados de projeto do inversor NPC, do conversor Buck-Boost e do controle são apresentados os resultados de simulações feitas nos programas Orcad Pspice e Simulink. Por ultimo, são apresentados detalhes de implementação e resultados experimentais de um protótipo de 1,5 kW, 800 V de tensão de barramento, 127 V de tensão de saída e 200 kHz de freqüência de comutação.

This thesis presents an analytical approach using Root-Loci method for designing optimum passive series RC snubbers for continuous-current synchronous buck switch mode power supply (SMPS). Synchronous buck SMPS is the most popular power converter topology found in modern consumer electronics. It offers relatively good efficiency to target the high-current and low-voltage requirements while it is also relatively inexpensive to implement. Passive series RC snubbers are simple, efficient and cost-effective open-loop equalizer circuit for synchronous buck SMPS. Its purpose is to control and to balance between the rate of rise and the overshoots of transient switching waveform in order to optimize efficiency and reliability Existing methods of RC snubber design are solely based on second-order approximation. It is investigated in this research that this approximation is highly inaccurate in SMPS applications because higher order equivalent models are required for the load path of the SMPS. The results using the RC snubbers obtained from existing method are shown to be unsatisfactory without correlation to the calculations and simulations based on second-order approximation. Optimum RC values obtained using Root-Loci approach presented in this thesis are shown to correlate to both Spice simulation and lab measurements.

This thesis presents an analytical approach using Root-Loci method for designing optimum passive series RC snubbers for continuous-current synchronous buck switch mode power supply (SMPS). Synchronous buck SMPS is the most popular power converter topology found in modern consumer electronics. It offers relatively good efficiency to target the high-current and low-voltage requirements while it is also relatively inexpensive to implement. Passive series RC snubbers are simple, efficient and cost-effective open-loop equalizer circuit for synchronous buck SMPS. Its purpose is to control and to balance between the rate of rise and the overshoots of transient switching waveform in order to optimize efficiency and reliability Existing methods of RC snubber design are solely based on second-order approximation. It is investigated in this research that this approximation is highly inaccurate in SMPS applications because higher order equivalent models are required for the load path of the SMPS. The results using the RC snubbers obtained from existing method are shown to be unsatisfactory without correlation to the calculations and simulations based on second-order approximation. Optimum RC values obtained using Root-Loci approach presented in this thesis are shown to correlate to both Spice simulation and lab measurements.

<p>This master thesis aim to design and evaluate a high power 3-phase DC/AC and AC/AC converter. The purpose is to use it for an electric motor in an aircraft possibly driving electric actuators, a propeller in an UAV or a small vehicle. Factors such as power loss and weight are of importance and will be estimated using known models supplied by various manufacturers of components. Different topologies of semiconductors suitable for this purpose are examined and presented. Extensive resources have been put to properly select the most suitable switching device according to their power loss and weight.</p><p>The need for filters and protective circuits will be estimated according to regulations of common military avionic standards and will be included in the resulting estimation along with simulations to evaluate their need and importance. Snubber circuits will be presented and their specific ability to reduce voltage transients and switching losses will be examined along with some simulations to illustrate their performance. In the final part an estimation of efficiency and weight of higher and lower power models of the same inverter has been made using the same procedure as presented in this paper. Engineering rules have been formed from these estimations to simply be able to calculate the proportions of a future converter of arbitrary rated power.</p>

This master thesis aim to design and evaluate a high power 3-phase DC/AC and AC/AC converter. The purpose is to use it for an electric motor in an aircraft possibly driving electric actuators, a propeller in an UAV or a small vehicle. Factors such as power loss and weight are of importance and will be estimated using known models supplied by various manufacturers of components. Different topologies of semiconductors suitable for this purpose are examined and presented. Extensive resources have been put to properly select the most suitable switching device according to their power loss and weight. The need for filters and protective circuits will be estimated according to regulations of common military avionic standards and will be included in the resulting estimation along with simulations to evaluate their need and importance. Snubber circuits will be presented and their specific ability to reduce voltage transients and switching losses will be examined along with some simulations to illustrate their performance. In the final part an estimation of efficiency and weight of higher and lower power models of the same inverter has been made using the same procedure as presented in this paper. Engineering rules have been formed from these estimations to simply be able to calculate the proportions of a future converter of arbitrary rated power.

With the rise in demand for renewable energy sources, photovoltaics have become increasingly popular as a means of reducing household dependence on the utility grid for power. But solar panels generate dc electricity, a dc to ac inverter is required to allow the energy to be used by the existing ac electrical distribution. Traditional full bridge inverters are able to accomplish this, but they suffer from many problems such as low efficiency, large size, high cost, and generation of electrical noise, especially common mode noise. Efforts to solve these issues have resulted in improved solutions, but they do not eliminate all of the problems and even exaggerate some of them. Soft switching inverters are able to achieve high efficiency by eliminating the switching losses of the power stage switches. Since this action requires additional components that are large and have additional losses associated with them, these topologies have traditionally been limited to higher power levels. The resonant snubber inverter is a soft switching topology that eliminates many of these problems by taking advantage of the bipolar switching action of the power stage switches. This allows for a significant size reduction in the additional parts and elimination of common mode noise, making it an ideal candidate for lower power levels. Previous attempts to implement the resonant snubber inverter have been hampered by low efficiency due to parasitics of the silicon devices used, but, with recent developments in new semiconductor technologies such as silicon carbide and gallium nitride, these problems can be minimized and possibly eliminated. The goal of this thesis is to design and experimentally verify a design of a resonant snubber inverter that takes advantage of new semiconductor materials to improve efficiency while maintaining minimal additional, parts, simple control, and elimination of common mode noise. A 600 W prototype is built. The performance improvements over previous designs are verified and compared to alternative high efficiency solutions along with a novel control technique for the auxiliary resonant snubber. A standalone and grid tie controller are developed to verify that the auxiliary resonant snubber and new auxiliary control technique does not complicate the closed loop control. / Master of Science

Photovoltaic (PV) system is one of the most prominent energy sources, producing electricity directly from sunlight. In additionally, it is easy to install and is supported financially by many governments as part of their strategy to reduce CO2 gas emissions, and to achieve their agreed set of reduction targets by 2020. In the meantime, researchers have been working on the PV system to make it more efficient, easy to maintain, reliable to use and cost effective. In the stand-alone PV system, a battery is required. This is due to the fluctuating nature of the output energy delivered by the PV arrays owing to the weather conditions and the unpredictable behaviour of uses with regard to the consumption of energy. During the hours of sunshine, the PV system is directly feeding the load and any surplus electrical energy is stored in the battery at a constant current. During the night, or during a period of low solar irradiation, the energy is supplied to the load from the battery. However, the stand-alone PV system is designed to provide an acceptable balance between reliability and cost, which is a major challenge to the designer owing to the approaches used to size the PV arrays and the battery bank. As a result, the unpredictable, quick daily changes on the PV output is not dependable. Moreover, battery performance, length of life and energy efficiency depends on the rate at which it is discharged. Therefore, it is essential to use other methods to deal with any quick variation in energy. In this thesis, a super capacitor is used to solve this problem, as it can deal with the fast-changing weather, or a rapid variation in the energy requirements of the customer. A critical evaluation with in-depth analysis of the placement and the implementation for the super-capacitor in the PV standalone system has been carried out. The results show, super-capacitor capacitance and the converter efficiency affect the delivered load energy. However, the bi-directional topology performs better than uni-directional under the same conditions. Finally, a further improvement of the system at component level, has been developed through an energy recovery snubber for the switching transition and achieved a recovery of energy for the resistive load, 94.44% for the turn on transition and 92.86% for the turn off transition. Moreover, for the inductive load, 78.33% and 97.33% of energy has been recovered for the turn on and for the turn off transition respectively.

Switched Reluctance Machine (SRMs) are receiving significant attention for industries and homes in the last decade. Due to their rugged brushless design, high reliable and an outstanding performance over a wide speed range. The stator and rotor of an SRM have a double salient pole and the rotor has no windings and magnets, its torque generating is quite nonlinear and has high torque ripple. Therefore, sophisticated switching and control technologies are needed to improve its driving performance. The cost and performance of SRM drives are highly dependent on the converter topologies and motor structure, so that developments in the convert topologies have been made in parallel with motor design. The objective of this thesis is proposed three phase Switched Reluctance Machine using a fly back resistor C Dump Converter to replace the tradition Bridge Converter. It can reduce switching losses, to reduce converter production cost with a simpler circuit. At the end, a digital signal processor based control system is used to test the laboratory make drives .

Práce se zabývá popisem jednotlivých typů zdrojů s důrazem na izolované topologie. Poté je rozebírána nejvhodnější volba pro zdroj na anodické bondování, kde jsou kladeny požadavky na vysoké výstupní napětí s malým proudem. Další část rozebírá problematická místa návrhu a na co je třeba dávat pozor. Poté je proveden vlastní návrh zdroje s popisem optimalizačních kroků. Tento zdroj je odsimulován. Dva rozdílné přístupy k realizaci takového zdroje jsou poté porovnány a nejlepší je vybrán. Je ukázána možnost, jak realizovat bipolární výstup. V poslední části je tento zroj sestaven a proměřeny jeho parametry.

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