<p>The ongoing and rapidly accelerating integration of inverter-based resources (IBRs), such as solar panels, into power distribution systems has heightened the importance of computational tools that can be used to study the dynamics of such systems. IBRs use power electronics to interface the energy sources to the grid, thereby introducing faster dynamics than their electromechanical counterparts, which could lead to instabilities in distribution systems and microgrids. Hence, there is a need for conducting simulations of distribution systems containing large numbers of single- and three-phase inverters, which could be operating under either grid-following or grid-forming modes.</p> <p>A key objective of this thesis is to derive detailed, high-fidelity models of inverters and their controls in the context of unbalanced distribution networks. In addition, a diesel synchronous generator model is derived, for the sake of completeness. The main contribution of this work is that these models are developed for use in a novel simulation toolbox called Dynamic Simulation Tool using a Sparse Tableau Approach in Python, DynaSTPy (pronounced dynasty). This thesis outlines how the components can be modeled in the sparse tableau framework as electrical networks with topology described using a node-branch incidence matrix. In addition, the thesis explains how controller dynamics and constraints can be handled within this framework. These models are tailored to seamlessly integrate into the DynaSTPy toolbox. The proposed approach can be readily extended to model other such components in the future.</p>

Approved for public release; distribution is unlimited / The naval vessels of the future will require lighter, more compact, and more versatile power electronics systems. With the advent of the DC Zonal Electrical Distribution System, more innovative approaches to the conversion of the dc bus power to ac power for motor drives will enhance the efficiency and warfighting capability of tomorrow's ships. This thesis explores the concept of a hybrid dc-ac power converter that combines a hysteresis controlled inverter with a six-step bulk inverter. A six-step bulk inverter is built from discrete components and tested in simulation and hardware. The two inverters are connected in parallel to provide a high-fidelity current source for a three-phase load. The addition of the hysteresis inverter to the bulk inverter adds a closed current loop for more robust control and improves the quality of the output load current. / Major, United States Marine Corps

Master of Science / Department of Electrical and Computer Engineering / Ruth Douglas Miller / This thesis presents the design of two models for permanent-magnet direct-drive wind turbines. The models are of a 10 kW and a 5 MW wind turbine, which are representative of residential scale and commercial scale turbines respectively. The models include aerodynamic and mechanical simulations through the FAST software, as well as concurrent electrical simulations through the SimPowerSystems toolbox for MATLAB/Simulink. The aim is to provide wind turbine designers and researchers with a comprehensive simulation tool that they can use to design and test many different aspects of a wind turbine. The particular novelty of these models is their high level of detail in electromechanical simulations. For each model, a generator speed controller was designed in a reference frame attached to the generator’s rotor, and was executed with a 3-phase active rectifier using space-vector pulse-width modulation. Also for each model, active and reactive power controllers were designed in a reference frame synchronous with the grid, and were executed with a 3-phase inverter using space-vector pulse-width modulation. Additionally, a blade pitch controller was designed for the 5 MW model. Validation of the models was carried out in the MATLAB/Simulink environment with satisfactory results.

Thesis Submitted in Partial Fulfilment of the Requirements for the Degree of Master of Technology: Electrical Engineering (Energy) in the Department of Electrical, Electronic and Computer Engineering at the Cape Peninsula University of Technology, South Africa. / In photovoltaic power systems, the DC/AC conversion efficiency depends on weather conditions causing PV inverters to operate under fluctuating input power from PV modules. The peak efficiency stated by the inverter manufacturers are often used by project designers to estimate how much power PV plants can produce. However, the varying nature of the DC input power to the inverters, occasioned by varying irradiation and temperature, leads to deviations of the actual efficiency from the peak efficiency. Literature surveys prove that inverter efficiencies must be evaluated against local irradiation profiles to get more precise annual energy yield estimations, since meteorological conditions and solar irradiation profiles vary from one site to another around the planet.

Submitted by Cátia Araújo (catia.araujo@unipampa.edu.br) on 2017-01-24T14:12:57Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Controle Adaptativo Aplicado a Conversores com Filtro LCL co.pdf: 2879378 bytes, checksum: a4bb30418fb9767ce153f5d1d4203eff (MD5) / Approved for entry into archive by Cátia Araújo (catia.araujo@unipampa.edu.br) on 2017-01-24T14:16:10Z (GMT) No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Controle Adaptativo Aplicado a Conversores com Filtro LCL co.pdf: 2879378 bytes, checksum: a4bb30418fb9767ce153f5d1d4203eff (MD5) / Made available in DSpace on 2017-01-24T14:16:10Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Controle Adaptativo Aplicado a Conversores com Filtro LCL co.pdf: 2879378 bytes, checksum: a4bb30418fb9767ce153f5d1d4203eff (MD5) Previous issue date: 2016-07-01 / A disseminação de conversores estáticos para os mais diversos fins de aplicação teve grande crescimento a partir da década de 80. Pode-se destacar sua utilização em aplicações tais como em filtragem ativa e geração distribuída. Esta ultima associada a implementação de microrredes de energia e associadas intrinsecamente as chamadas redes elétricas inteligentes. Tradicionalmente quando estes conversores são utilizados para fins de conexão com a rede utiliza-se um filtro em série com o conversor a fim de suprimir harmônicos oriundos do processo de comutação das suas chaves semicondutoras. Estes filtros são, em geral, do tipo L ou LCL, sendo que, devido a sua maior capacidade de atenuação de componentes harmônicas associada a comutação do conversor o filtro LCL é preferencialmente empregado para esta finalidade. Porem, a utilização do filtro LCL, por se tratar de um filtro de terceira ordem, requer uma estratégia de controle mais complexa não só para a rejeição de distúrbios provindos da rede como também para manter a estabilidade do sistema. Para tratar tais problemas diversos trabalhos na literatura ponderam entre diferentes escolhas da variável de controle, como a corrente de saída do conversor ou a de saída do filtro e diversas técnicas de controle como deadbeat, controle por histerese, entre outras. Este trabalho aborda a utilização da corrente média ponderada do filtro LCL de saída como variável de controle a fim de simplificar o problema de controle resultante da utilização deste tipo de filtro. Utilizou-se uma técnica de Controle por Modelo de Referência em conjunto com um Controlador Adaptativo com ação Feedforward como estratégia para garantir a estabilidade e rejeição de distúrbios no sistema. Também foi realizada uma abordagem com objetivo de garantir a estabilidade do sistema frente a situações de saturação da ação de controle a ser sintetizada pelo conversor, utilizando uma t_ecnica de Controle por Modelo de Referência Adaptativo e novamente um Controlador Adaptativo com ação Feedforward. São realizadas análises e provas matemáticas da estabilidade dos controladores em conjunto com resultados de simulação e experimentais demonstrando a aplicabilidade da proposta. / The widespred use of static converters for different application purposes experienced a grown mainly since 80's, with a great increase of interest in recent years. It is possible to highlight their use in grid connected systems such as in power filters and distributed generation sources. The last contributed for the dissemination of microgrids and the advent of smartgrids. For grid connected applications, a filter is used to interface the converter with the grid in order to suppress the harmonic content due to the switching process of the converter. These filters may be purely inductive or of L type, or inductive-capacitive inductive or of LCL type. Due to its higher harmonic attenuation capacity, the LCL filter is preferably employed. However the LCL filter has some disadvantages quite evident. For example, it is a third-order filter, wich requires more complex control strategy not only to reject disturbances arisen from the grid, but also for stability and control purposes. To address such problems, several works in the literature consider different choices regarding the controlled quantity namely, the converter current or the grid current, and several control techniques such as deadbeat, hysteresis control, PI in synchronous reference frame, among others. This work discusses the use of the weighted average current of the LCL-filter as a control variable in order to alleviate the problem of control resulting from the use of this type of filter. It was used Model Reference Control in conjunction with an Adaptive Feedforward Cancellation scheme as a strategy to ensure stability and disturbance rejection for the system. It was also applied an approach to ensure the stability of the system facing situations of saturation of the control action using a Model Reference Adaptive Controller with an Adaptive Feedforward Cancellation scheme, designed to cope with the effect of saturation. Mathematical analysis and proofs of stability are presented with simulation and experimental results, that demonstrate the applicability of the proposal.

Doctor of Philosophy / Department of Electrical and Computer Engineering / Behrooz Mirafzal / Voltage source inverters (VSIs) are an essential interface for grid integration of renewable energy resources. Grid-tied VSIs are employed in power grids to integrate distributed generation units, e.g. photovoltaic arrays, wind turbines and energy storage units, to the utility and extract the maximum energy from the DG units in an efficient manner. However, the stability of VSIs and by extension the entire DG system can be degraded under abnormal grid conditions. In this dissertation, new control and switching techniques for stability and power quality improvement of grid-tied VSIs under abnormal grid conditions are presented. For grids with a low inertia and a low short-circuit ratio, commonly referred to as weak grids, grid connection may make VSIs susceptible to voltage distortion and instability. In this dissertation, through root locus analysis of a detailed state-space model, the design of several circuit and control parameters of the grid-tied VSI are evaluated for improving stability in weak grids. It is shown that grid-side filter inductances can be increased for stable operation of VSIs in weak grids. Accordingly, a virtual inductance emulating the effect of an increased inductance in the grid-side filter is developed in this dissertation, which enables stable operation of VSIs in weak grids without the tradeoffs, i.e. additional voltage drop, increased cost and larger size, associated with a larger inductor. The virtual inductance scheme is realized through the injection of a feedforward current element in the VSI controller through a gain component. The measured grid currents, which are sensed for regular VSI controller operation, are employed as the feedforward component eliminating the need for any additional sensors for the utilization of this control scheme. Furthermore, a direct model reference adaptive control (MRAC) scheme is employed in this dissertation to tune the virtual inductance gain block according to a stable reference model for varying grid conditions. The use of direct MRAC scheme allows tuning of the virtual inductance block without the need for a plant parameter estimation stage. The virtual inductance scheme enables stable operation of VSIs in weak grids without system parameter redesign, thereby maintaining the steady-state performance of the system. The efficacy of the virtual inductance feedforward scheme is verified through hardware tests carried out on a three-phase grid-tied experimental setup. Along with extracting energy from the DG sources, grid-tied VSIs are capable of providing various ancillary services to the utility under abnormal conditions. However, providing ancillary services could drive the inverter voltages beyond the linear modulation region resulting in grid current distortions, which could violate the requirements for grid integration of DGs. An atypical pulse width modulation (PWM) technique is proposed in this dissertation, which maximizes the dc-bus utilization of VSIs, which in turn enables the VSIs to supply the maximum extracted power from the DG units to the grid when providing ancillary services while operating in the linear modulation region. The switching scheme is realized by injecting common mode components in the PWM references, computed based on instantaneous reference magnitudes. The proposed scheme is suitable when providing both symmetrical and asymmetrical ancillary services. In this dissertation, negative-sequence compensation and harmonic compensation are employed as instances of symmetrical and asymmetrical ancillary services. The proposed scheme can be integrated with any control scheme and carrier-based PWM combinations. The efficacy of the proposed atypical PWM scheme is verified through both simulation and hardware tests.

Submitted by Silvana Teresinha Dornelles Studzinski (sstudzinski) on 2016-12-22T15:57:00Z No. of bitstreams: 1 Gerson Luis Garcia de Pinho_.pdf: 2989815 bytes, checksum: 548880c60cc2c4757d2e0df6e97150cb (MD5) / Made available in DSpace on 2016-12-22T15:57:00Z (GMT). No. of bitstreams: 1 Gerson Luis Garcia de Pinho_.pdf: 2989815 bytes, checksum: 548880c60cc2c4757d2e0df6e97150cb (MD5) Previous issue date: 2016-11-17 / UNISINOS - Universidade do Vale do Rio dos Sinos / Este trabalho objetiva dissertar sobre os diversos fatores que produzem a queima dos motores elétricos de indução alimentados por inversores de frequência. Com o avanço da eletrônica de potência e o aumento da necessidade de variação de velocidade dos motores elétricos de indução em aplicações na indústria, a utilização de inversores de frequência tornou-se cada vez mais difundida. Em razão desse fato, surgiu uma nova preocupação entre os fabricantes e usuários de motores elétricos com relação à qualidade do sistema isolante, pois tornou-se objeto de estudo o fato de as altas frequências de chaveamento dos inversores de frequência provocarem picos de tensão sobre os terminais dos motores elétricos, podendo levar à ruptura do dielétrico do material isolante, requerendo sistemas de isolação mais resistentes. Apresenta-se nesta pesquisa o aquecimento do motor em sua estrutura geral, provocando a deterioração do isolamento dos condutores, bem como fenômenos físicos diretamente envolvidos. As características construtivas dos motores de indução e o grau de comprometimento destas em relação ao aumento da temperatura do motor elétrico desencadeiam um processo de “envelhecimento precoce” do motor. Portanto, o estudo do comportamento térmico tornou-se imprescindível no projeto de um motor elétrico de indução. Além de dissertar sobre os diversos fatores que produzem a queima dos motores elétricos de indução alimentados por inversores de frequência, o presente trabalho propõe a criação de índices de qualidade da energia para esses casos, para que sirvam de subsídios em estudos sobre a vida útil do motor elétrico. A metodologia utilizada para construção desses índices contempla uma média harmônica entre os índices de qualidade do inversor, cabo e motor, propostos neste trabalho. Ademais, visa fornecer dados para serem utilizados em projetos de novos equipamentos que possam medir esses índices. / This work aims to discuss the various factors that produce the burning of induction motors fed by frequency inverters. With the advancement of power electronics and the increased need for speed variation of induction motors in industrial applications, the use of frequency inverters has become increasingly widespread. Because of this fact, a new concern arose among the manufacturers and users of electric motors with regard to the quality of the insulation system, since it became the object of study that the high switching frequencies of the frequency inverters cause peaks of voltage over the Terminals of electric motors, which may lead to the rupture of the dielectric of the insulation material, requiring more resistant insulation systems. This study presents the heating of the motor in its general structure, causing the deterioration of the insulation of the conductors, as well as physical phenomena directly involved. The constructive characteristics of the induction motors and the degree of their engagement in relation to the increase in the temperature of the electric motor trigger an "early aging" of the engine. Therefore, the study of thermal behavior has become essential in the design of an electric induction motor. In addition to discussing the different factors that produce the combustion of induction motors fed by frequency inverters, the present work proposes the creation of energy quality indices for these cases, in order to be useful in studies on the useful life of the Electric motor The methodology used to construct these indices contemplates a harmonic average between the quality indices of the inverter, cable and motor proposed in this work. In addition, it aims to provide data to be used in new equipment projects that can measure these indices.

All power electronics consist of solid state devices that generate heat. Managing the temperature of these devices is critical to their performance and reliability. Traditional methods involving liquid-cooling systems are expensive and require additional equipment for operation. Air-cooling systems are less expensive but are typically less effective at cooling the electronic devices. The cooling system that is used depends on the specific application. Until recently, silicon based devices have been used for the solid-state devices in power electronics. Newly developed silicon-carbide based wide band gap devices operate at maximum temperatures higher than traditional silicon devices. Due to the permissible increase in operating temperatures, it has been proposed to develop an air-cooling system for an inverter consisting of silicon carbide devices. This thesis presents recent research efforts to develop the proposed air-cooling system. The thermal performance of the each design iteration was determined by numerical simulations via the finite element method in both steady state and transient mode using COMSOL Multi-physics software version 3.5a. For all simulations presented in this thesis, the heat dissipated in the MOSFETS and diodes are specified as functions of current, voltage, switching frequency, and junction temperature. For both the steady state and transient simulations, the junction temperature was determined iteratively. Additionally in the transient simulations, the current distribution is a function of time and was deduced from the EPA US06 drive cycle. After several design iterations, a thermally feasible design has been reached. This design is presented in detail in this thesis. Under transient simulations of the final design, the maximum junction temperatures were determined to be below 146 ºC for air flow rates of 30 and 60 CFM, which is substantially lower than the 250 ºC maximum allowable junction temperature of Si-C devices. However for steady state simulations, junction temperatures were found to be much higher than the transient simulations. It was determined that a minimum flow rate of 50 CFM is required to meet the temperature requirements of the Si-C devices under steady state operating conditions. The power density of this air-cooled final design is 11.75 kW/L, and it is competitive with liquid-cooled systems.

No description available.

Thin-film transistors (TFTs) capable of low-voltage and high-frequency operation will be required to reduce the power consumption of next generation electronic devices driven by microelectronic components such as inverters, ring oscillators, and backplane circuits for mobile displays. To produce high performance TFTs, transparent oxide-semiconductors are becoming an attractive alternative to hydrogenated amorphous silicon (a-Si:H)- and organic-based materials because of their high electron mobility vlaues and low processing temperatures, making them compatible with flexible substrates and opening the potential for low production costs. Practical electronic devices are expected to use p- and n-channel TFT-based complementary inverters to operate with low power consumption, high gain values, and high and balanced noise margins. The p- and n-channel TFTs should yield comparable output characteristics despite differences in the materials used to achieve such performance. However, most oxide semiconductors are n-type, and the only high performance, oxide-based TFTs demonstrated so far are all n-channel, which prevents the realization of complementary metal-oxide-semiconductor (CMOS) technologies. On the other hand, ambipolar TFTs are very attractive microelectronic devices because, unlike unipolar transistors, they operate independently of the polarity of the gate voltage. This intrinsic property of ambipolar TFTs has the potential to lead to new paradigms in the design of analog and digital circuits. To date, ambipolar TFTs and their circuits, such as inverters, have shown very limited performance when compared with that obtained in unipolar TFTs. For instance, the electron and hole mobilities typically found in ambipolar TFTs (ATFTs) are, typically, at least an order of magnitude smaller than those found in unipolar TFTs. Furthermore, for a variety of circuits, ATFTs should provide balanced currents during p- and n-channel operations. Regardless of the selection of materials, achieving these basic transistor properties is a very challenging task with the use of current device geometries. This dissertation presents research work performed on oxide TFTs, oxide TFT-based electronic circuits, organic-inorganic hybrid complementary inverters, organic-inorganic hybrid ambipolar TFTs, and ambipolar TFT-based complementary-like inverters in an attempt to overcome some of the current issues. The research performed first was to develop low-voltage and high-performance oxide TFTs, with an emphasis on n-channel oxide TFTs, using high-k and/or thin dielectrics as gate insulators. A high mobility electron transporting semiconductor, amorphous indium gallium zinc oxide (a-IGZO), was used as the n-channel active material. Such oxide TFTs were employed to demonstrate active matrix organic light emitting diode (AMOLED) display backplane circuits operating at low voltage. Then, high-performance hybrid complementary inverters were developed using unipolar TFTs employing organic and inorganic semiconductors as p- and n-channel layers, respectively. An inorganic a-IGZO and pentacene, a widely used organic semiconductor, were used as the n- and p-channel semiconductors, respectively. By the integration of the p-channel organic and n-channel inorganic TFTs, high-gain complementary inverters with high and balanced noise margins were developed. A new approach to find the switching threshold voltage and the optimum value of the supply voltage to operate a complementary inverter was also proposed. Furthermore, we proposed a co-planar channel geometry for the realization of high-performance ambipolar TFTs. Using non-overlapping horizontal channels of pentacene and a-IGZO, we demonstrate hybrid organic-inorganic ambipolar TFTs with channels that show electrical properties comparable to those found in unipolar TFTs with the same channel aspect ratios. A key characteristic of this co-planar channel ambipolar TFT geometry is that the onset of ambipolar operation is mediated by a new operating regime where one of the channels can reach saturation while the other channel remains off. This allows these ambipolar TFTs to reach high on-off current ratios approaching 104. With the new design flexibility we demonstrated organic-inorganic hybrid ambipolar TFT-based complementary-like inverters, on rigid and flexible substrates, that show a significant improvement over the performance found in previously reported complementary-like inverters. From a materials perspective, this work shows that future breakthroughs in the performance of unipolar n-channel and p-channel semiconductors could be directly transposed into ambipolar transistors and circuits. Hence, we expect that this geometry will provide new strategies for the realization of high-performance ambipolar TFTs and novel ambipolar microelectronic circuits.