abstract: Two major challenges in the transformer-less, single-phase PV string inverters are common mode leakage currents and double-line-frequency power decoupling. In the proposed doubly-grounded inverter topology with innovative active-power-decoupling approach, both of these issues are simultaneously addressed. The topology allows the PV negative terminal to be directly connected to the neutral, thereby eliminating the common-mode ground-currents. The decoupling capacitance requirement is minimized by a dynamically-variable dc-link with large voltage swing, allowing an all-film-capacitor implementation. Furthermore, the use of wide-bandgap devices enables the converter operation at higher switching frequency, resulting in smaller magnetic components. The operating principles, design and optimization, and control methods are explained in detail, and compared with other transformer-less, active-decoupling topologies. A 3 kVA, 100 kHz single-phase hardware prototype at 400 V dc nominal input and 240 V ac output has been developed using SiC MOSFETs with only 45 μF/1100 V dc-link capacitance. The proposed doubly-grounded topology is then extended for split-phase PV inverter application which results in significant reduction in both the peak and RMS values of the boost stage inductor current and allows for easy design of zero voltage transition. A topological enhancement involving T-type dc-ac stage is also developed which takes advantage of the three-level switching states with reduced voltage stress on the main switches, lower switching loss and almost halved inductor current ripple. In addition, this thesis also proposed two new schemes to improve the efficiency of conventional H-bridge inverter topology. The first scheme is to add an auxiliary zero-voltage-transition (ZVT) circuit to realize zero-voltage-switching (ZVS) for all the main switches and inherent zero-current-switching (ZCS) for the auxiliary switches. The advantages include the provision to implement zero state modulation schemes to decrease the inductor current THD, naturally adaptive auxiliary inductor current and elimination of need for large balancing capacitors. The second proposed scheme improves the system efficiency while still meeting a given THD requirement by implementing variable instantaneous switching frequency within a line frequency cycle. This scheme aims at minimizing the combined switching loss and inductor core loss by including different characteristics of the losses relative to the instantaneous switching frequency in the optimization process. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2017

abstract: Traditional approaches to modeling microgrids include the behavior of each inverter operating in a particular network configuration and at a particular operating point. Such models quickly become computationally intensive for large systems. Similarly, traditional approaches to control do not use advanced methodologies and suffer from poor performance and limited operating range. In this document a linear model is derived for an inverter connected to the Thevenin equivalent of a microgrid. This model is then compared to a nonlinear simulation model and analyzed using the open and closed loop systems in both the time and frequency domains. The modeling error is quantified with emphasis on its use for controller design purposes. Control design examples are given using a Glover McFarlane controller, gain sched- uled Glover McFarlane controller, and bumpless transfer controller which are compared to the standard droop control approach. These examples serve as a guide to illustrate the use of multi-variable modeling techniques in the context of robust controller design and show that gain scheduled MIMO control techniques can extend the operating range of a microgrid. A hardware implementation is used to compare constant gain droop controllers with Glover McFarlane controllers and shows a clear advantage of the Glover McFarlane approach. / Dissertation/Thesis / Ph.D. Electrical Engineering 2013

Este trabalho tem como principal objetivo apresentar um estudo, uma modelagem e uma simulação de um inversor de comutação suave para aplicação em um filtro ativo para instalações de baixa e média potência. Inicialmente apresenta uma revisão bibliográfica sobre inversores de comutação suave, onde os mesmos são classificados em função do local onde o circuito auxiliar de comutação suave está inserido, gerando três classificações básicas: comutação de linha, comutação de carga e comutação de chave. Três processos de comutação suave são apresentados: comutação em zero de tensão, comutação em zero de corrente e comutação em zero de corrente e zero de tensão. Dentro deste contexto apresentam-se as diversas topologias de inversores de comutação suave. Uma análise de comutação de um inversor em um filtro ativo monofásico é apresentada e o inversor ZCT com duas chaves auxiliares é selecionado para ser aplicado no referido filtro. Uma modelagem completa do inversor ZCT com duas chaves auxiliares é apresentada e corroborada pela comparação dos resultados de simulação obtidos a partir do modelo teórico com os resultados obtidos por meio de simulações realizadas no SPICE. A Modelagem do inversor ZCT com duas chaves auxiliares culmina em uma nova metodologia de projeto, onde é possível determinar com grande exatidão a máxima corrente de carga para a qual o inversor ainda opera no modo ZCT. Diversas simulações realizadas no Simulink/Matlab e no SPICE comprovam as comutações suaves em zero de corrente nas chaves do inversor e também o desempenho dinâmico do mesmo quando operando em um filtro ativo paralelo. / This work shows the study, the selection and the analysis of a soft-switched inverter for an ac single-phase active power filter. For this, various topologies of the soft-switched inverters are classified based upon the location of the auxiliary circuit and the topology that achieves the goals for application in the active power filter is selected. Three commutation processes are presented: zero voltage switching (ZVS), zero current switching (ZCS) and zero current and zero voltage switching (ZCZVS). The ZCT inverter with 2 auxiliaries switches is selected for the application in an ac single-phase active power filter: this topology reduces the turn-on losses and practically eliminates the turn-off losses of all IGBTs of the inverter. Some new guidelines to project the ZCT inverter with 2 auxiliaries switches are presented, achieving an accurate calculation of the maximum load current for operation in ZCT. The results of the simulation from Simulink/Matlab and SPICE prove some goals of the ZCT inverter: the ZCT inverter with 2 auxiliaries switches reduces the total losses when compared with the hard-commutation inverter and the dynamic performance of the ZCT inverter applied in an ac single-phase active power filter is showed.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Este trabalho apresenta uma topologia de inversor multinÃvel hÃbrido simÃtrico trifÃsico de cinco nÃveis, concebido a partir das estruturas meia ponte e inversor com grampeamento ativo do neutro, adequado para aplicaÃÃes com alta tensÃo e alta potÃncia. SÃo apresentados os possÃveis estados de comutaÃÃo, lÃgica de acionamento, cÃlculo dos esforÃos nos semicondutores, assim como um estudo de perdas. Duas estratÃgias de modulaÃÃo sÃo selecionadas possibilitando a operaÃÃo concomitante de metade dos interruptores em baixa frequÃncia (60 Hz) e a outra em alta frequÃncia (1020 Hz), reduzindo o nÃmero de comutaÃÃes, consequentemente as perdas nos semicondutores e o conteÃdo harmÃnico da tensÃo de saÃda. Para validar a proposta, foi desenvolvido um protÃtipo com potÃncia de 7,5 kVA e tensÃo de saÃda eficaz de linha 380 V. AlÃm disso, à apresentada a implementaÃÃo de ambas as modulaÃÃes no dispositivo lÃgico programÃvel escolhido, FPGA. Os resultados experimentais da estrutura trifÃsica validam a topologia proposta. A estrutura, operando com a modulaÃÃo baseada na PD-PWM, apresentou DHT de 29,71% e WTHD de 1,93%, enquanto que a baseada na CSV-PWM apresentou DHT de 38,45% e WTHD de 7,21%. AlÃm disso, o rendimento da estrutura proposta à superior se comparado ao da topologia Half-Bridge/NPC, conforme esperado em funÃÃo das perdas na estrutura Half-Bridge/NPC serem maiores e mal distribuÃdas. / This work presents a new topology of a hybrid five-level inverter, conceived from the halfbridge and active neutral point clamped structures, suitable for high-voltage, high-power applications. The possible commutation stages, the switching drive logic, the semiconductors stresses mathematical analysis, and the losses study are presented. Two modulation techniques were selected in order to allow low-frequency (60 Hz) switches operate together with high-frequency switches (1020 Hz), reducing the number of commutations and, consequently, the overall losses and the output voltage total harmonic distortion. In order to validate the proposal, it was developed a 7.5 kVA prototype and AC line output voltage of 380 V. The digital implementation from both modulation techniques on the chosen programmable logic device FPGA is also presented. The experimental results relative to the three-phase structure validate the proposed topology. The topology, operating with the modulation based on Sinusoidal In-Phase Disposition - PWM, presented a THD of 29.71%, and WTHD of 1.93%, while the one based on the Centered Space Vector - PWM presented a THD of 38.45%, and a WTHD of 7.21%. Besides, the overall efficiency is superior when compared to the Half-Bridge/NPC topology, as expected, due to the fact that losses on this structure are higher and misdistributed.

Submitted by Rosangela Silva (rosangela.silva3@unioeste.br) on 2018-06-25T23:49:50Z No. of bitstreams: 2 Joao_Luiz_ Fontana_Figueiredo.pdf: 3144216 bytes, checksum: 115906953fe12769294f97e9078a752d (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2018-06-25T23:49:50Z (GMT). No. of bitstreams: 2 Joao_Luiz_ Fontana_Figueiredo.pdf: 3144216 bytes, checksum: 115906953fe12769294f97e9078a752d (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2018-03-08 / The population advances quickly in the regard to the increase in consumption energy in many forms. Brazil, considered the "breadbasket of the world", has innumerable grain storage units in his territory, and these, consume a lot of energy in their reception, drying and storage processes. Particularly in the process of receiving grains, there is a large energy consumption in the discharged platforms responsible for receiving the products in bulk. These discharged platforms are operated by hydraulic pumps driven by an electric motor, which operates uninterruptedly throughout the basculation pro-cess. The present work aims to perform a study of energy efficiency in the basculation system of the discharged platform, from the use of electric devices to control the oper-ation of the engine. For this purpose, two scenarios were established. The first sce-nario considers the platform in its current state, with engine starting made by a star-triangle key. In the second scenario, star-delta start is switched off, and a frequency inverter and a programmable logic controller (PLC) are coupled to control the electric motor. For the two scenarios, the active and reactive energy consumptions were meas-ured in the discharged platform using an energy analyzer, and the costs of the energy consumed in the period of one year were calculated. Finally, the discounted Payback was calculated to evaluate the economic feasibility of installing the proposed equip-ment. The results obtained were as follows: For the current scenario, the energy used to raise a ton was 35.44.10-3 kWh/ton, for the proposed scenario, with a frequency inverter, this index was 32.78.10-3 kWh/ton. With an annual projection, the current sce-nario would consume the equivalent of 10,921.35 kWh and the proposed scenario 10,100.81 kW, generating an annual savings with equipment installation of R$721.49, and the discounted Payback found of approximately 31 years. It can be concluded, therefore, that there is a reduction of electric energy consumption from the use of the frequency inverter, but the time of return of the invested capital is very long, making the proposal economically unfeasible. / A população avança a cada dia no tocante ao aumento do consumo de energia, nas suas mais variadas formas. O Brasil, considerado o “celeiro do mundo”, possui inúme-ras unidades de armazenamento de grãos em seu território, as quais, por sua vez, consomem energia significativa em seus processos de recepção, secagem e armaze-nagem. Particularmente, no processo de recepção de grãos, existe um grande con-sumo de energia nas plataformas de descarga responsáveis por receber os produtos a granel. Essas plataformas de descarga são operadas por bombas hidráulicas, aci-onadas por um motor elétrico, que opera de forma ininterrupta durante todo o processo de basculamento. O presente trabalho visa realizar um estudo de eficiência energé-tica, no sistema de basculamento da plataforma de descarga, a partir da utilização de dispositivos elétricos para controle do funcionamento do motor. Para tal finalidade, foram estabelecidos dois cenários. O primeiro cenário considera a plataforma em seu estado atual, com partida do motor feita por uma chave estrela-triângulo. No segundo cenário, a partida com chave estrela-triângulo é desligada e são acoplados um inver-sor de frequência e um controlador lógico programável (CLP), para fazer o controle do motor elétrico. Para os dois cenários, foram medidos os consumos de energia ativa e reativa na plataforma de descarga, utilizando um analisador de energia; além disso, foram calculados os custos da energia consumida, no período de um ano. Por fim, foi calculado o Payback, descontado para avaliar a viabilidade econômica da instalação dos equipamentos propostos. Os resultados obtidos foram os seguintes: Para o cená-rio atual, a energia gasta para bascular uma tonelada foi de 35,44.10-3 kWh/ton; para o cenário proposto, com inversor de frequência, o índice foi de 32,78.10-3 kWh/ton. Realizando uma projeção anual, o cenário atual consumiria o equivalente a 10.921,35 kWh; diante do cenário proposto, o índice foi de 10.100,81 kW, gerando uma econo-mia anual, com a instalação dos equipamentos, de R$721,49; o Payback descontado encontrado foi de 31 anos aproximadamente. Pode-se concluir, portanto, que existe uma redução de consumo de energia elétrica a partir da utilização do inversor de fre-quência, porém, o tempo de retorno do capital investido é muito longo, tornando a proposta inviável economicamente.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / This work analyzes a voltage regulator applied to low-voltage single-phase distribution networks, especially long distribution rural distribution lines with problems to comply with voltage level standards. This voltage regulator is classified as D-STATCOM (Distribution Static Synchronous Compensator), since it is composed of a single-phase PWM inverter connected in parallel with the point common coupling through a second-order LC filter, composing a third order circuit (LCL circuit) with the line inductance. A digital control system is proposed for the D-STATCOM in this dissertation, composed of three voltage loops: the damping, the control loop of the AC voltage, which controls the voltage supplied by the regulator control loop and the DC voltage control loop, responsible for regulating the DC bus voltage. Moreover, a full-state feedback controller is used to achieve active damping of the LCL filter resonance. Finally, experimental results are presented to demonstrate the efficiency of the proposed control system / Neste trabalho é realizado um estudo acerca de um regulador de tensão aplicado a redes de distribuição monofásicas de baixa tensão, especialmente para longas linhas de distribuição rurais que apresentam problemas de adequação dos níveis de tensão. A topologia do regulador de tensão classifica-se como D-STATCOM (Distribution Static Synchronous Compensator), uma vez que é composto por um inversor PWM (Pulse Width Modulation) monofásico conectado em paralelo com o ponto de acoplamento comum através de um filtro LC, compondo um sistema de terceira ordem (LCL) com a indutância da rede. Um sistema de controle digital para o D-STATCOM é proposto nesta Dissertação, sendo composto por três malhas de tensão: a de amortecimento, a malha de controle da tensão CA, responsável pelo controle da tensão fornecida pelo regulador e a malha de controle da tensão CC, responsável pela regulação da tensão do barramento CC. Além disso, emprega-se uma retroação de estados a fim de realizar o amortecimento ativo do filtro LCL. Por fim, resultados experimentais são apresentados para demonstrar a eficiência do sistema de controle proposto.

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Cette thèse concerne le couplage des systèmes photovoltaïques (PV) au réseau de distribution du point de vue contrôle/commande et rejet de perturbation. Le raccordement au réseau induit des couplages aux effets parfois indésirables. Le problème majeur est dû aux creux de tension provoqué par des court-circuits, à la foudre ou encore à certaines manœuvres. Dans ce contexte, des déconnexions apparaissent et parfois sont non-jutifiées, tout particulièrement en cas de défaut sur un départ adjacent BT/HTA; en cas d'un fort taux de pénétration de systèmes PV, une telle déconnexion qui serait généralisée peut avoir des conséquences néfastes. Les travaux de cette thèse se sont focalisés sur ce problème de couplage : effet des systèmes PV sur le réseau et réaction des systèmes PV face aux perturbations du réseau. A cet effet, des adaptations aux protections découplage sont proposées pour une intégration harmonieuse du système PV. Des stratégies de gestion de l'énergie ont été également mises au point participation à l'amélioration de la qualité de l'énergie localement et pour la tenue des systèmes PV aux perturbations. / This thesis concerns the coupling of photovoltaic (PV) to the distribution network in terms of control/command and disturbance decoupling. The connection of PV system to the grid induces the coupling some unwanted effects. The major problem is due to voltage sags caused by short circuits, lightning or some operations. In this context, disconnections occur and sometimes are unjustifies, especially in case of fault on LV/MV adjacent feeder and in case of a high penetration of PV systems, a such disconnection can provoke adverse consequences. The work of this thesis focused on the problem of coupling: effect of PV systems on the network and reaction of PV system facing network disturbance. For this purpose, adaptations to the decoupling protections are proposed for harmonious integration of PV. Strategies for energy management were also developed participation in improving the quality of local energy and for the holding of PV systems to disturbances.

Inverters play key roles in connecting sustainable energy (SE) sources to the local loads and the ac grid. Although there has been a rapid expansion in the use of renewable sources in recent years, fundamental research, on the design of inverters that are specialized for use in these systems, is still needed. Recent advances in power electronics have led to proposing new topologies and switching patterns for single-stage power conversion, which are appropriate for SE sources and energy storage devices. The current source inverter (CSI) topology, along with a newly proposed switching pattern, is capable of converting the low dc voltage to the line ac in only one stage. Simple implementation and high reliability, together with the potential advantages of higher efficiency and lower cost, turns the so-called, single-stage boost inverter (SSBI), into a viable competitor to the existing SE-based power conversion technologies. The dynamic model is one of the most essential requirements for performance analysis and control design of any engineering system. Thus, in order to have satisfactory operation, it is necessary to derive a dynamic model for the SSBI system. However, because of the switching behavior and nonlinear elements involved, analysis of the SSBI is a complicated task. This research applies the state-space averaging technique to the SSBI to develop the state-space-averaged model of the SSBI under stand-alone and grid-connected modes of operation. Then, a small-signal model is derived by means of the perturbation and linearization method. An experimental hardware set-up, including a laboratory-scaled prototype SSBI, is built and the validity of the obtained models is verified through simulation and experiments. Finally, an eigenvalue sensitivity analysis is performed to investigate the stability and dynamic behavior of the SSBI system over a typical range of operation.