Doctor of Philosophy / Department of Electrical and Computer Engineering / Behrooz Mirafzal / In this dissertation, a new topology for Direct-Drive Wind Turbines (DDWTs) with a new power electronics interface and a low-voltage generator design is presented. In the presented power electronics interface, the grid - side converter is replaced by a boost Current Source Inverter (CSI) which eliminates the required dc-bus capacitors resulting in an increase in the lifetime of DDWTs. The inherently required dc-link inductor for this topology is eliminated by utilizing the inductance of the Permanent Magnet Synchronous Generator (PMSG). The proposed three-phase boost CSI is equipped with Reverse-Blocking IGBTs (RB-IGBT) and the Phasor Pulse Width Modulation (PPWM) switching pattern to provide a 98% efficiency and high boost ratios ([superscript V]LL/V[subscript dc]) up to 3.5 in a single stage. In this dissertation, Phasor Pulse Width Modulation (PPWM) pattern for the boost – CSI is also modified and verified through simulation and experimental results. In order to realize potential capabilities of the boost inverter and to assist its penetration into renewable energy systems, the boost inverter dynamic behaviors are studied in this dissertation. Then, the developed models are verified using circuit simulations and experiments on a laboratory-scale boost – CSI equipped with RB-IGBTs. The developed dynamic models are used to study the stability of the boost – CSI through root locus of small signal poles (eigenvalues) as control inputs and load parameters vary within the boost inverter's operating limits. The dynamic models are also used to design the control schemes for the boost – CSI for both stand-alone and grid-tied modes of operation. The developed controllers of the boost – CSI are verified through simulation and experimental results. In this dissertation, the boost – CSI steady-state characterization equations are also developed and verified. The developed boost – CSI is used to replace the grid - side converter in a DDWT. A reliability analysis on the power electronics interface of an existing and developed topology is presented to demonstrate the increase in the mean time between failures. The boost – CSI enables conversion of a low dc voltage to a higher line-to-line voltage enabling the implementation of a low-voltage generator. This further enables a reduction in the number poles required in DDWT generators. The feasibility of the presented low-voltage generator is investigated through finite element computations. In this dissertation, a 1.5MW low-voltage generator designed for the proposed topology is compared with an existing 1.5MW permanent magnet synchronous generator for DDWTs to demonstrate the reduction in the volume, weight, and amount of permanent magnet materials required in the generator. The feasibility of the developed system is supported by a set of MATLAB/Simulink simulations and laboratory experiments on the closed-loop stand-alone and grid-tied systems.

Dans cette recherche, l'auteur met l'accent à la fois sur une optimisation de la conception pour une (MV-MMC: Medium Voltage Modular Multilevel Converter) utiliser comme un DC/AC ou AC/DC et à deuxième fois sur la grille pour les modules IGBT qui sont utilisés dans ce type d'application. Par exemple, les convertisseurs de MMC sont utilisés dans les systèmes d'alimentation des navires électriques avec les buses de moyenne tension de courant continu (en anglais: medium-voltage direct current (MVDC)). Pour une telle application, selon le document IEEE, la tension du bus DC peut être jusqu'à 35kV. Par conséquent, les systèmes de commande rapprochée pour piloter le grille des modules IGBT pour les applications MVDC-MMC sont des principaux problèmes en termes d'architectures et des besoins de haute isolation galvanique. Ainsi, cette thèse fournit des solutions pour répondre à ces problèmes. L'étude inclut également les études d'un matériau diélectrique qui est utilisé comme matériau d'isolation. Les résultats des essais expérimentaux d'un matériau diélectrique proposé pour différentes épaisseurs des couches pour maintenir des niveaux de tension d'isolation sont également fournis pour valider clairement cette étude. En effet, un convertisseur MMC compose d'un certain nombre de cellules de conversion connectés en série. Une cellule (sous-module de convertisseur) est classiquement constitué de deux modules IGBT. Sur la base de la topologie de la cellule, l'architecture d'un pilote de grille contestée pour les modules de puissance à semi-conducteurs est proposée et comparée à celle classique en termes de besoins des niveaux de tension d'isolation galvanique, la taille de la cellule de convertisseur, etc. / In this research, the author focuses on both a design optimization for a Medium Voltage Modular Multilevel Converter (MV-MMC) use as a DC/AC or AC/DC converter and gate drivers systems for IGBT modules which are used in this kind of application. For example, the MMC converters are used in Medium-Voltage Direct Current (MVDC) electrical ship power systems. For such application, according to IEEE document, the DC bus voltage can be up to 35kV. Hence, gate drivers’ systems for IGBT modules for MVDC-MMC applications are major concerns in terms of architectures and insulation voltage capabilities. Thus, this dissertation provides solutions to answer these problems. The study also includes the studies of a dielectric material which is used as insulation material. The results of experimental tests of a proposed dielectric material for different layers thicknesses to sustain different insulation voltage levels are also provided to clearly validate this study. Actually, a MMC converter composes of a number of converter cells connected in series. One cell (converter’s sub-module) is classically composed of two IGBT modules. Based on the cell topology, a challenged gate driver’s architecture for power semiconductor modules is proposed and compared to the classical one in terms of high and low galvanic insulation voltage levels’ requirements, converter’s cell size, etc.

Orientador: Dr. Alfeu J. Sguarezi Filho / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Engenharia Elétrica, 2016. / A energia eólica é uma fonte de energia renovável com diversas vantagens e sua participação na matriz energética mundial está crescendo a cada ano. Nos últimos anos, as plantas eólicas têm passado por grandes mudanças devido às novas tecnologias desenvolvidas para as Smart Grids (SG). Cada vez mais, os sistemas de conversão de energia eólicos estão utilizando arquiteturas de comunicação mais desenvolvidas para possibilitar o compartilhamento de dados e medidas em fazendas eólicas inteligentes. Nesse contexto, a proposta desse estudo é um controle sem fio para um gerador de indução gaiola de esquilo (GIGE) de velocidade variável conectado coma rede elétrica. O sistema de comunicação sem fio é empregado para enviar as potências de referência para o controlador do GIGE com a confiabilidade necessária para garantir a qualidade da energia fornecida pelo aerogerador. Neste trabalho, no controle do gerador é utilizada a técnica de controle do Controle Direto de Torque (CDT) e controle orientado pela tensão (COT) para a conexão com a rede elétrica. Para o sistema de comunicação sem fio, foram utilizadas duas estratégias de baixo custo e ampla cobertura nacional, baseadas nas redes de dados GPRS e EGPRS. O desempenho do sistema é avaliado através de diversas simulações e testes. / Wind energy is a renewable source of energy with several advantages and the participation in the global energy matrix is increasing every year. In recent years, the wind farms were changing with the advance of new technologies developed for the Smart Grid (SG). Increasingly, wind energy conversion systems are using more developed communication architectures to enable data sharing and intelligent measures in wind farms. In this context, the purpose of this study is a wireless controller for a variable speed Squirrel Cage Induction Generator (SCIG) connected to the grid. The wireless system is used to send the reference powers for SCIG controller with the reliability needed to ensure the quality of the power supplied by the wind turbine. In this paper, in the generator's control is used the Control Direct Torque (CDT) technique and Control-Driven Voltage (COT) technique for connection to the power grid. For the wireless communication system, they used two low-cost strategies with national coverage, based on GPRS and EGPRS data networks. The system performance is evaluated through various simulations and tests.

Made available in DSpace on 2014-06-11T19:22:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-08-27Bitstream added on 2014-06-13T19:28:00Z : No. of bitstreams: 1 sampaio_lp_me_ilha.pdf: 1553174 bytes, checksum: 4a7ad1f1c4400135903509fd327b3112 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho propõe uma nova abordagem na metodologia de operação para o inversor Boost monofásico, como estrutura base para o aproveitamento de fontes alternativas e renováveis de energia elétrica. Considerando-se que equipamentos eletro/eletrônicos convencionais em CA (corrente alternada) necessitam, normalmente, de níveis e formato de tensão diferentes daqueles fornecidos por essas fontes de energia, o inversor proposto é uma estrutura integrada que tem a capacidade de operar como conversor elevador de tensão e inversor, apresentando um número reduzido de componentes e rendimento maior, quando comparado às formas tradicionais de se associar em cascata o conversor elevador com o inversor. O projeto convencional do inversor fonte de corrente (CSI) exige uma indutância elevada de entrada, além disso, o modelo a pequeno sinais do CSI é semelhante ao do conversor Boost no modo de condução contínua, apresentando um zero no semi-plano direito na função de transferência para o controle da tensão de saída, sendo que este zero causa o conhecido efeito de fase não-mínima. Desta forma, uma metodologia especial de projeto é apresentada resultando numa indutância Boost reduzida e numa técnica de controle utilizando um sistema multi-malhas, com alimentação direta, devidamente projetada de forma a possibilitar elevadas dinâmicas de transferência de energia. Adicionalmente, o inversor apresenta tensão de saída com reduzidas distorções harmônicas (DHT), número reduzido de componentes de potência e, consequentemente, elevada densidade de potência. Neste trabalho são apresentadas as análises qualitativa e quantitativa do inversor, a modelagem e técnica de controle proposta, metodologia de projeto, os principais resultados de simulação e experimentais com a finalidade de demonstrar a viabilidade de aplicação da proposta. / This work presents a new methodology for the operation and control of a single-phase current-source Boost Inverter, it is used as base structure for alternative and renewable electric energy sources. The electro/electronics devices normally require eletrical source in AC (alternate current) in different voltage levels and shapes those provided by the alternative and renewable electrical sources. The proposed inverter is an integrated structure able to operate as step-up DC-DC converter and inverter, it presents a reduced number of components, high efficiency when compared with the traditional technique of step-up and inverter for cascade association. The conventional design of current source inverter (CSI) require a large boost inductance, therefore, the small-signal model is similar to continuous-current-mode (CCM) Boost converter, which has a right-half-plane (RHP) zero in its control-to-output transfer function, and this RHP zero causes the well-known non-minimum-phase effects. In this context, a special design with small boost inductance and a multi-loop control is proposed in order to assure stability and very fast dynamics. Furthermore, the inverter presents output voltage with very low total harmonic distortion (THD), reduced number of components and high power density. In addition, this work presents the Boost CSI operation, the proposed control technique, the main simulation and experimental results in order to demonstrate the feasibility of the proposal.

Orientador: Carlos Alberto Canesin / Banca: Falcondes Jose Mendes de Seixas / Banca: Denizar Cruz Martins / Resumo: Este trabalho propõe uma nova abordagem na metodologia de operação para o inversor Boost monofásico, como estrutura base para o aproveitamento de fontes alternativas e renováveis de energia elétrica. Considerando-se que equipamentos eletro/eletrônicos convencionais em CA (corrente alternada) necessitam, normalmente, de níveis e formato de tensão diferentes daqueles fornecidos por essas fontes de energia, o inversor proposto é uma estrutura integrada que tem a capacidade de operar como conversor elevador de tensão e inversor, apresentando um número reduzido de componentes e rendimento maior, quando comparado às formas tradicionais de se associar em cascata o conversor elevador com o inversor. O projeto convencional do inversor fonte de corrente (CSI) exige uma indutância elevada de entrada, além disso, o modelo a pequeno sinais do CSI é semelhante ao do conversor Boost no modo de condução contínua, apresentando um zero no semi-plano direito na função de transferência para o controle da tensão de saída, sendo que este zero causa o conhecido efeito de fase não-mínima. Desta forma, uma metodologia especial de projeto é apresentada resultando numa indutância Boost reduzida e numa técnica de controle utilizando um sistema multi-malhas, com alimentação direta, devidamente projetada de forma a possibilitar elevadas dinâmicas de transferência de energia. Adicionalmente, o inversor apresenta tensão de saída com reduzidas distorções harmônicas (DHT), número reduzido de componentes de potência e, consequentemente, elevada densidade de potência. Neste trabalho são apresentadas as análises qualitativa e quantitativa do inversor, a modelagem e técnica de controle proposta, metodologia de projeto, os principais resultados de simulação e experimentais com a finalidade de demonstrar a viabilidade de aplicação da proposta. / Abstract: This work presents a new methodology for the operation and control of a single-phase current-source Boost Inverter, it is used as base structure for alternative and renewable electric energy sources. The electro/electronics devices normally require eletrical source in AC (alternate current) in different voltage levels and shapes those provided by the alternative and renewable electrical sources. The proposed inverter is an integrated structure able to operate as step-up DC-DC converter and inverter, it presents a reduced number of components, high efficiency when compared with the traditional technique of step-up and inverter for cascade association. The conventional design of current source inverter (CSI) require a large boost inductance, therefore, the small-signal model is similar to continuous-current-mode (CCM) Boost converter, which has a right-half-plane (RHP) zero in its control-to-output transfer function, and this RHP zero causes the well-known non-minimum-phase effects. In this context, a special design with small boost inductance and a multi-loop control is proposed in order to assure stability and very fast dynamics. Furthermore, the inverter presents output voltage with very low total harmonic distortion (THD), reduced number of components and high power density. In addition, this work presents the Boost CSI operation, the proposed control technique, the main simulation and experimental results in order to demonstrate the feasibility of the proposal. / Mestre

Distance relays due to their selectivity and operating speed are used in HV/EHV line protection. The dynamic nature of Mho characteristic, which happens to be most primitive technique in line protection implemented with distance relaying, is built by using the measurement of local voltage and current signals. These signals have been influenced substantially by fault resistance and the source impedance feeding the line. In case of different generation sources, the source impedance and fault characteristic also change accordingly. Environmental benefit of wind turbine technology is making it a potential source of energy. These wind turbine-generating units (WTGU) use rugged induction/synchronous machines along with power electronics converters as controlling equipment. This gives a new challenge to distance relays, as the fault current contribution of these sources depends on the converter operational principle. In this thesis a typical wind farm of Indian systems are modeled in an IN-HOUSE tool developed as part of fault analysis on wind farm system. Directly connected and front-end converter based wind turbines with their interconnections are modeled in this simulation tool. Fault voltage and current waveforms are obtained for all types of wind turbine-generating units with both radial and LILO (Loop in Loop out) connection. PSCAD based modeling has been done for DFIG type of wind turbines. The fault waveforms are generated to evaluate relay performance. Five case studies having both Radial and Loop in Loop out (LILO) connection of wind farms are simulated. These case studies generate approximately 20000 cases, which are analyzed for distance relay performance studies. In addition, the analysis is further verified on relay hardware having three characteristics, namely Self Polarized Mho (SPM), Quadrature Polarized Mho (QPM) and Quadrilateral (QUAD) characteristics. The detailed studies are carried out in this thesis to ensure and suggest the system operators with appropriate relay characteristics to be used for transmission line protection in the case of wind farms interconnected to Grid. Based on the studies carried out in the thesis, LILO connection has no impact on distance relay characteristic. In radially connected wind farms, grid side relay will operate reliably for all types of faults. It has been recommended in the thesis that wind farm side distance relay characteristics should be adjusted based on the types of wind turbines (Type-1, Type-2, Type-3 and Type-4). Based on the investigations carried out in the thesis, voltage based phase selector has been recommended for Type-4 WTGU based wind farms.

In the past two decades the core aircraft technology is going through a drastic change. The traditional technologies that is almost half a century old, is going through a complete revamp. In the new “More Electric Aircraft” technology many mechanical, pneumatic and hydraulic systems are being replaced by electrical and power electronic systems. Airbus-A380, Boeing B-787 are the pioneers in the family of these new breed of aircrafts. As the aircraft technology is moving towards “More Electric”, more and more electric motors and motor controllers are being used in new aircrafts. Number of electric motor drive systems has increased by about ten times in more electric aircrafts compared to traditional aircrafts. Weight of any electric component that goes into aircraft needs to be low to reduce the overall weight of aircraft so as to improve the fuel efficiency of the aircraft. Hence there is an increased need to reduce weight of motors and motor controllers in commercial aircraft. High speed ironless axial flux permanent magnet brushless dc motors are becoming popular in the new more-electric aircrafts because of their ability to meet the demand of light weight, high power density, high efficiency and high reliability. However, these motors come with very low inductance, which poses a big challenge to the motor controllers in controlling the ripple current in motor windings. Multilevel inverters can solve this problem. Three-level inverters are proposed in this thesis for driving axial flux BLDC motors in aircraft. Majority of the motors in new more electric aircrafts are in the power range of 2kW to 20kW, while a few motor applications being in the range of 100kW to 150kW. Motor controllers in these applications run from 270Vdc or 540Vdc bus which is the standard in new more electric aircraft architecture. Multilevel Inverter is popular in the industry for high power and high voltage applications, where high-voltage power switching devices like IGBT, GTO are popularly used. However multilevel inverters have not been tried in the low power range which is appropriate for aircraft applications. A detail analysis of practical feasibility of constructing three-level inverter in lower power and voltage level is presented in this thesis. Analysis is presented that verify the advantages of driving low voltage and low power (300Vdc to 600Vdc and less than 100kW) motors with multilevel inverters. Practical considerations for design of MOSFET based three-level inverter are investigated and topological modifications are suggested. The effect of clamping diodes in the diode clamped multilevel inverters play an important role in determining its efficiency. SiC diodes are proposed to be used as clamping diodes. Further, it is realised that power loss introduced by reverse recovery of MOSFET body diode prohibits use of MOSFET in hard switched inverter legs. Hence, a technique of avoiding the reverse recovery losses of MOSFET body diode in three-level NPC inverter is conceived. The use of proposed multilevel inverter topology enables operation at high switching frequency without sacrificing efficiency. High switching frequency of operation reduces the output filter requirement, which in turn helps reducing size of the inverter. In this research work elaborate trade-off analysis is done to quantify the suitability of multilevel inverters in the low power applications. For successful operation of three-level NPC inverter in aircraft electrical system, it is important for the DC bus structure in aircraft electric primary distribution system to be compatible to drive NPC inverters. Hence a detail study of AC to DC power conversion system as applied to commercial aircraft electrical system is done. Multi-pulse rectifiers using autotransformers are used in aircrafts. Investigation is done to improve these rectifiers for future aircrafts, such that they can support new technologies of future generation motor controllers. A new 24-pulse isolated transformer rectifier topology is proposed. From two 15º displaced 6-phase systems feeding two 12-pulse rectifiers that are series connected, a 24-pulse rectifier topology is obtained. Though, windings of each 12-pulse rectifiers are isolated from primary, the 6-phase generation is done without any isolation of the transformer windings. The new 24-pulse transformer topology has lower VA rating compared to standard 12-pulse rectifiers. Though the new 24-pulse transformer-rectifier solution is robust and simple, it adds to the weight of the overall system, as compared to the present architecture as the proposed topology uses isolated transformer. Non-isolated autotransformer cannot provide split voltage at the dc-link that creates a stable mid-point voltage as required by the three-level NPC inverter. Hence, a new front-end AC-DC power conversion system with switched capacitor is conceived that can support motor controllers driven by three-level inverters. Laboratory experimental results are presented to validate the new proposed topology. In this proposed topology, the inverter dc-link voltage is double the input dc-link voltage. An intense research work is performed to understand the operation of Trapezoidal Back EMF BLDC motor driven by three-Level NPC inverter. Operation of BLDC motor from three-Level inverter is primarily advantageous for low inductance motors, like ironless axial flux motors. For low inductance BLDC motor, very high switching frequency is required to limit the magnitude of ripple current in motor winding. Three-level inverters help limiting the magnitude of motor ripple current without increasing the switching frequency to very high value. Further, it is analysed that dc link mid-point current in three-level NPC inverter for driving trapezoidal BLDC motor has a zero average current with fundamental frequency same as switching frequency. Because of this, trapezoidal BLDC motors can easily be operated from three-level NPC inverter without any special attention given to mid-point voltage unbalance. One non-ideal condition arrives in practical implementation of the inverter that leads to non-zero average mid point current. Unequal gate drive dead time delays from one leg to other leg of inverter introduce dc-link mid-point voltage unbalance. For the motoring mode operation of trapezoidal BLDC motor drive, simple gate drive logic is researched that eliminates need of the gate drive dead-time, and hence solves the mid-point voltage unbalance issue. Simple closed loop control scheme for mid-point voltage balancing also is also proposed. This control scheme may be used in applications where very precise control of speed and torque ripple is warranted. All the investigations reported in this thesis are simulated extensively on MATHCAD and MATLAB platform using SIMULINK toolbox. A laboratory experimental set-up of three-Level inverter driving axial flux BLDC motor is built. The three-level inverter, operating from 300Vdc bus is built using 500V MOSFETs and 600V SiC diodes. All the control schemes are implemented digitally on digital signal processor TMS320F2812 DSP platform and GAL22V10B platforms. Experimental results are collected to validate the theoretical propositions made in the present research work. At the end, in chapter 5, some future works are proposed. A new external voltage balance circuit is proposed where the inverter dc-link voltage is same as the input dc-link voltage. This topology is based on the resonant converter principle and uses a lighter resonant inductor than prior arts available in literature. Detail simulation and experimentation of this topology may be carried out to validate the industrial benefits of this circuit. It is also thought that current source inverters may work as an alternative to voltage source inverters for driving BLDC motors. Current source inverters eliminate use of bulky DC-link capacitors. Long term reliability of current source inverters is higher than voltage source inverters due to the absence of possibility of shoot-through. Further, in voltage source inverters, the voltage at the motor terminal is limited by the source voltage (dc-link voltage). This issue is eliminated in current source inverters. An interface circuit is conceived to reduce the size of dc-link inductors in current source inverters, pending detail analysis and experimental verification. The interface circuit bases its fundamentals on the principles of operation of multilevel inverters for BLDC motors that is presented in this thesis.

Indiana University-Purdue University Indianapolis (IUPUI) / This thesis proposes a family of non-isolated bidirectional converter in order to interface dc and ac variables. Such power electronics solutions guarantee: (i) bidirectional power flow between dc and ac converter sides, (ii) independent control in both converter sides, (iii) high level of integration with a reduction of one power switch and its drive circuits, (iv) implementation of two functions by using a unique power conversion stage and (v) reduction of the capacitor losses. Despite proposing new power converter solutions, this thesis presents an analysis of the converters in terms of pulse-width-modulation (PWM) strategy, dc-link capacitor variables, and suitable a control approach. Solutions for single-phase, three-phase and three-phase four-wire systems are proposed by employing a converter leg with three switches. A possible application of this converter is in Vehicle-to-Grid (V2G) systems and interfacing dc microgrid with a utility grid. In addition to the new power electronics converters proposed in this thesis, an experimental setup has been developed for validation of the simulated outcomes. The proof-of-concept experimental setup is constituted by: DSP, Drivers & Integrating Board, Power Supply and, Power Converter & Heat-Sink .