Dissertations / Theses on the topic 'Microinverter'

Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2012.
Title as it appears in MIT degrees awarded program, September 19, 2012: A new topology for high-efficiency solar microinverters Cataloged from PDF version of thesis.
Includes bibliographical references (pages 95-96).
Previous work has been done to develop a microinverter for solar photovoltaic applications consisting of a high-frequency series resonant inverter and transformer section connected to a a cycloconverter that modulates the resonant current into a single-phase 240 VRMS utility line. This thesis presents a new stacked full-bridge topology that improves upon the previous high-frequency inverter section. By utilizing new operating modes to reduce the reliance on frequency control and allowing for the use of lower blocking voltage transistors, the operating frequency range of the HF inverter is reduced and efficiency is increased, especially at low output powers and lower portions of the line cycle. The design of an experimental prototype to test the stacked full-bridge HF inverter topology is presented along with test results that demonstrate the success of the topology. Future improvements to increase performance are also suggested.
by Kesavan Yogeswaran.
M. Eng.

Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 101-102).
The flyback micro-inverter with a pseudo-dc link has traditionally been used for injecting only active power in to the power distribution network. In this thesis, a new approach will be proposed to control the micro-inverter to supply reactive power to the grid which is important for grid voltage support. Circuit models and mathematical analyses are developed to explain underlying issues such as harmonic distortion, and power losses, which can limit the reactive power support capability. A novel current decoupling circuit is proposed to effectively mitigate zero crossing distortion. Simulations and experimental results are provided to support the theoretical propositions.
by Edwin Fonkwe Fongang.
S.M.

With the decrease in availability of non-renewable energy sources coupled with the increase in the amount of energy required for the operation of personal electronic devices there has been an increased focus on developing systems that take advantage of renewable energy sources. Renewal energy sources such as photovoltaic (PV) panels have become more popular due to recent developments in PV panel manufacturing that decreases material costs and improves energy harvesting efficiency. Since PV sources are DC sources power conversion stages have to be used in order to interface this power to the existing electrical utility system. The structure of large scale PV systems usually consists of several PV panels connected in series to achieve a high input source voltage that can be fed into a high power centralized DC-AC inverter. The drawback to this approach is that when the PV panels are subjected to less than ideal conditions. If a single PV panel is subjected to drastically less solar irradiation during cloud conditions, then its output power will drop dramatically. Since this panel is series connected with the other PV panels, their current output is also dragged low decreasing the power output of the system. Algorithms that have the power converter operate at different input conditions allow the system to operate at a maximum power point (MPP), however this only allows the system to operate at a higher power point and not the true MPP. To get around this limitation a new PV system implementation was created by giving each panel its own DC-AC power conversion system. This configuration gives each panel the ability to operate at its own MPP increasing the total system energy harvest. Another advantage of the single panel DC-AC microinverter power conversion stage is that the outputs are parallel connected to the utility grid easily allowing the ability to expand the system without having to shut down the entire system. The most prevalent implementation of the microinverter consists of a single power converter that uses the PV low voltage DC and outputs high voltage AC. In order to ensure that the double line AC ripple does not propagate to the PV panel a large bank of electrolytic capacitors are used to buffer the ripple. There is concern that the electrolytic capacitor will degrade over time and affect the system efficiency. To get around having to use electrolytic capacitors a two stage microinverter has been proposed. The two stage microinverter consists of a DC-DC converter that steps up the low DC voltage of the PV panel to high voltage DC and the second stage is a DC-AC inverter that takes the high voltage DC and converts it to high voltage AC. There is a capacitor that connects the two power converter stages called the DC link capacitor which can buffer the double line energy ripple without using electrolytic capacitors. This thesis focuses on the review of several DC-AC inverter topologies suitable for use in PV microinverter systems. Operation capabilities such as common mode noise and efficiency are compared. The main focus of the review is to determine the optimal DC-AC inverter using the performance metrics of cost, efficiency and common mode performance. A 250 W prototype is built for each inverter topology to verify its performance and operation.
Master of Science

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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Os sistemas fotovoltaicos conectados à rede tem como finalidade a conversão da energia solar em energia elétrica. No Brasil, recentemente foi dado o primeiro passo efetivo com a publicação pela ANEEL da Resolução Normativa n° 482. Esta resolução, publicada em 17 de abril de 2012, possibilita à um consumidor doméstico e comercial possuir um sistema de microgeração de energia (hidráulica, solar, eólica, biomassa ou cogeração qualificada) conectado à rede elétrica e fazer compensação de energia. Neste trabalho foi instalado em caráter experimental, no Laboratório de Energias Renováveis da Unisinos, um sistema fotovoltaico conectado à rede com uso de um modelo de microinversor, e buscou-se por meio desta instalação e do monitoramento, analisar o comportamento elétrico e energético do sistema. O sistema é composto por um módulo monocristalino LG255S1C de 255 Wp conectado a um microinversor ENPHASE M215 de 215 W. O período de monitoramento foi de 1° de agosto até 20 de dezembro de 2014. Uma central de aquisição de dados Agilent HP 34970A foi empregada para coletar dados de irradiância no plano do gerador fotovoltaico, corrente e tensão na entrada e saída do microinversor, temperatura de uma célula FV no centro do módulo fotovoltaico e temperatura no dissipador do microinversor. Também foi utilizado como medidor o analisador de energia Fluke 43B, que coleta os dados de potência ativa, potência reativa e potência aparente injetada na rede elétrica pelo sistema. Índices de qualidade de energia como a distorção harmônica total de corrente e fator de deslocamento também foram medidos. A eficiência média diária máxima, considerando a incerteza, medida no microinversor empregado foi de 95,18 % e é semelhante aos valores de eficiência média diária dos microinversores de primeira e segunda geração. O sistema fotovoltaico monitorado com o uso do microinversor atingiu o valor máximo de desempenho global de 0,93. A produção de energia máxima diária em corrente alternada foi de 1,49 kWh. Estima-se, levando em consideração este valor, que a produção mensal pode ser de até 44,7 kWh. Isto significa uma redução de 58 % no consumo de energia em uma residência, levando em consideração o custo de disponibilidade e o sistema instalado em uma residência com consumo médio mensal da região nordeste que é de 120 kWh.
Photovoltaic grid-connected systems aims the conversion of solar energy into electrical energy. In Brazil, was recently given the first effective step with the publication by ANEEL Normative Resolution No. 482. This resolution published on 17 th April, 2012, enables domestic and commercial consumers have an energy microgeneration system (hydro, solar, wind, biomass or qualified cogeneration) connected to mains power and make compensation. In this work was mounted on an experimental character, in the Renewable Energy Laboratory of Unisinos, a photovoltaic grid-connected system that uses a microinverter model, and through this installation and monitoring, analyse the electrical and energetical behavior of the system. The system consists of a 255 Wp LG255S1C monocrystalline module, connected to a 215 W ENPHASE M215 microinverter. The monitoring period was 1 st August to 20 th December, 2014. A central acquisition of Agilent HP 34970A data was used to collect data irradiance in the plane of the PV array, current and voltage at the input and output of microinverter, temperature of a PV cell in the center of the PV module and the microinverter sink. It was also used as a measuring the energy analyzer Fluke 43B, which collects the data of active power, reactive power and apparent power injected into the grid by the system. Power quality indices as the total harmonic current distortion and displacement factor were also measured. The maximum daily average efficiency, considering the uncertainty, measured on the employed microinverter was 95.18 % and is similar than the daily average efficiency values of microinverters of first and second generation. The photovoltaic system monitored using the microinverter peaked overall performance of 0.93. The production maximum daily energy into alternating current was 1.49 kWh. It is estimated taking into account the value that the monthly production can achieved 44.7 kWh. This means a reduction of 58 % in the consumption of a residence considering the availability cost and that the system is installed in a residence with the northest comsumption whose the average monthly consumption is 120.00 kWh.

Energy Harvesting from Exercise Machines (EHFEM) is an ongoing project pursuing alternate forms of sustainable energy for Cal Poly State University. The EHFEM project seeks to acquire user-generated DC power from exercise machines and sell that energy back to the local grid as AC power. The end goal of the EHFEM project aims to integrate a final design with existing elliptical fitness trainers for student and faculty use in Cal Poly’s Recreational Center. This report examines whether including the DC-DC converter in the EHFEM setup produces AC power to the electric grid more efficiently and consistently than an EHFEM system that excludes a DC-DC converter. The project integrates an overvoltage protection circuit, a DC-DC converter, and a DC-AC microinverter with an available elliptical trainer modified to include an energy converting circuit. The initial expectation was that a DC-DC converter would increase, when averaged over time, the overall energy conversion efficiency of the EHFEM system, and provide a stable voltage and current level for the microinverter to convert DC power into AC power. In actuality, while including a DC-DC converter in a test setup allows the EHFEM system to function with less frequent interruptions, this occurs at the cost of lower efficiency. Testing demonstrates the EHFEM project can convert user-generated DC mechanical power into usable AC electrical power. Retrofitting existing equipment with the EHFEM project can reduce Cal Poly’s energy cost.

Multilevel inverters offer many well-known advantages for use in high-voltage and high-power applications, but they are also well suited for low-power applications. A single phase inverter is developed in this paper to deliver power from a residential-scale system of Photovoltaic panels to the utility grid. The single-stage inverter implements a novel control technique for the reversing voltage topology to produce a stepped output waveform. This approach increases the granularity of control over the PV systems, modularizing key components of the inverter and allowing the inverter to extract the maximum power from the systems. The adaptive controller minimizes harmonic distortion in its output and controls the level of reactive power injected to the grid. A computer model of the controller is designed and tested in the MATLAB program Simulink to assess the performance of the controller. To validate the results, the performance of the proposed inverter is compared to that of a comparable voltage-sourced inverter.

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Elétrica, 2017.
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Esta dissertação de mestrado apresenta o procedimento utilizado no projeto e construção de um protótipo de microinversor fotovoltaico, capaz de processar energia de um módulo fotovoltaico de silício cristalino de até 250 W de potência e injetá-la na rede elétrica com 220 V de valor eficaz de tensão e 60 Hz de frequência. O trabalho compreende revisão bibliográfica em microinversores comerciais, normas para conexão à rede elétrica, caracterização de geradores fotovoltaicos, topologias aplicadas a microinversores e influência das correntes de modo comum na operação desses equipamentos. Optou-se por processar a energia em dois estágios de conversão. O primeiro, cc-cc, é composto por um conversor Boost com célula de ganho. O segundo, cc-ca, principal foco desta dissertação, é o conversor em ponte completa com modulação dois níveis. A estratégia de controle é baseada em compensação da corrente injetada na rede elétrica, com imposição, por PLL, de uma forma de onda senoidal em fase com a tensão; regulação do barramento cc principal; técnica de MPPT; método de anti-ilhamento; partida suave de todo o sistema; algoritmos de proteção; e desacoplamento dos estágios cc-cc e cc-ca por filtragem ativa. A experimentação do sistema projetado e construído contou com resultados satisfatórios e de acordo com teoria e simulação.

Abstract : This Master's Thesis presents the design and construction procedure of a photovoltaic (PV) micro-inverter prototype capable of absorbing energy from a 250 W crystalline silicon PV module and injecting into a 220 V / 60 Hz utility grid. The work includes a literature review on commercial micro-inverters, standards for connectins to grid, characterization of photovoltaic generators, topologies applied to microinverters and influence of common mode currents in the operation of these equipments. Two stages of conversion were choosen to process the energy. The first, dc-dc, is composed by a Boost converter with gain cell. The second, dc-ac, main focus of this work, is the Full-Bridge converter with two level sinusoidal modulation. The control strategy is based on current compensation; dc link voltage controlling; PLL; MPPT; anti-islanding method; soft start of the entire system; protection algorithms; and decoupling of the dc-dc and dc-ac stages by active filtering. The experimentation of the designed and constructed system reached satisfactory results, according to theory and simulation.

Microinverter has become a new trend for photovoltaic (PV) grid-tie systems due to its advantages which include greater energy harvest, simplified system installation, enhanced safety, and flexible expansion. Since an individual microinverter system is typically attached to the back of a PV module, it is desirable that it has a long lifespan that can match PV modules, which routinely warrant 25 years of operation. In order to increase the life expectancy and improve the long-term reliability, electrolytic capacitors must be avoided in microinverters because they have been identified as an unreliable component. One solution to avoid electrolytic capacitors in microinverters is using a two-stage architecture, where the high voltage direct current (DC) bus can work as a double line ripple buffer. For two-stage electrolyte-free microinverters, a high boost ratio dc-dc converter is required to increase the low PV module voltage to a high DC bus voltage required to run the inverter at the second stage. New high boost ratio dc-dc converter topologies using the hybrid transformer concept are presented in this dissertation. The proposed converters have improved magnetic and device utilization. Combine these features with the converter's reduced switching losses which results in a low cost, simple structure system with high efficiency. Using the California Energy Commission (CEC) efficiency standards a 250 W prototype was tested achieving an overall system efficiency of 97.3%. The power inversion stage of electrolyte-free microinverters requires a high efficiency grid-tie inverter. A transformerless inverter topology with low electro-magnetic interference (EMI) and leakage current is presented. It has the ability to use modern superjunction MOSFETs in conjunction with zero-reverse-recovery silicon carbide (SiC) diodes to achieve ultrahigh efficiency. The performance of the topology was experimentally verified with a tested CEC efficiency of 98.6%. Due to the relatively low energy density of film capacitors compared to electrolytic counterparts, less capacitance is used on the DC bus in order to lower the cost and reduce the volume of electrolyte-free microinverters. The reduced capacitance leads to high double line ripple voltage oscillation on DC bus. If the double line oscillation propagates back into the PV module, the maximum power point tracking (MPPT) performance would be compromised. A control method which prevents the double line oscillation from going to the PV modules, thus improving the MPPT performance was proposed. Finally, a control technique using a single microcontroller with low sampling frequency was presented to effectively eliminate electrolyte capacitors in two-stage microinverters without any added penalties. The effectiveness of this control technique was validated both by simulation and experimental results.
Ph. D.

Orientadores: Ernesto Ruppert Filho, Marcelo Gradella Villalva
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
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Resumo: Este trabalho apresenta uma contribuição à pesquisa e ao desenvolvimento de microinversores monofásicos para sistemas fotovoltaicos de energia solar conectados à rede elétrica de baixa tensão. O objetivo principal da pesquisa é apresentar o projeto, a construção e os resultados experimentais de um microinversor eletrônico que processa a energia proveniente de um painel fotovoltaico e faz a conexão deste dispositivo com a rede El. São apresentados estudos teóricos e simulações sobre painéis fotovoltaicos, sobre a modelagem e o controle de conversores eletrônicos e sobre o algoritmo de rastreamento do ponto de máxima potência. São apresentados resultados experimentais obtidos com um microinversor experimental desenvolvido em laboratório, constituído de dois estágios de conversão (CC-CC e CC-CA)
Abstract: This thesis presents a contribution to research and development of single-phase micro-inverters for low voltage grid-connected photovoltaic systems. The main goal of this research is to present the project, the development and experimental results of an electronic micro-inverter that processes the energy from a photovoltaic panel and connects this device to the main grid. Theoretical studies and simulations on photovoltaic panels are shown, as the modeling and control of the electronic converters and the maximum power point tracking algorithm. Results with an experimental microinverter consisting of two stages (DC-DC and DC-AC) are also shown
Mestrado
Energia Eletrica
Mestre em Engenharia Elétrica

Dissertação para obtenção do Grau de Mestre em Energias Renováveis – Conversão Eléctrica e Utilização Sustentáveis
Nowadays, the photovoltaic (PV) energy is presented as one of the most promising source of clean energy, and so a good way for greenhouse gas emissions mitigation and reduce the fossil fuel dependence. Within it, the photovoltaic energy has caused a huge interest in the electronic converters, and the need to improve their efficiency and reducing their cost. With this work I present a solution for a module scale grid-connected single-phase inverter. The solution consists in a two-stage inverter insolated with a grid line transformer. The two-stage inverter is composed by a DC-DC converter and a DC-AC converter connected through a DC-link capacitor. The DC-DC converter in case is a boost converter used to elevate the voltage from the PV module to a higher level. For the DC-AC converter it is used a full-bridge inverter, and both the DC-DC and the DC-AC converters use the IGBTs form an integrated module with its respective drivers. To the boost control it is implemented a Maximum Power Point Tracking algorithm that can optimize the power extraction from the PV source and for the inverter it is used a sliding mode hysteretic control. Once this inverter is conceived to work connected to the grid, a single-phase PLL system is used to synchronize the injected current to grid voltage. All the control part is made digitally using an Arduino Uno board, which uses an Atmel microcontroller.

FREIRE, F. J. L. Microinversor monofásico baseado na derivação da topologia flyback para sistema de geração fotovoltaica. 2015. 132 f. Dissertação (Mestrado em Engenharia Elétrica) - Centro de Tecnologia, Universidade Federal do Ceará, Fortaleza, 2015.
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The study proposes the design and implementation of a single phase inverter of single stage obtained the derivation of four flybacks converters CC - CC operating in discontinuous mode and associated in parallel modules. This arrangement reduces the amount of magnetic and decreases current efforts in primary transformers and minimizes fluctuations i n photovoltaic module. Among the main properties of micro inverter flyback (MIF) this research, the primary keys work with SPWM switching at high frequency and lagged in one hundred and eighty degrees, while the secondary keys are controlled by PWM's compl ementary. To validate the research, we will develop a prototype that will effect the processing power connecting a photovoltaic panel with 200W power in resistive loads with senoidais characteristics. The proposed system is based on the configuration of th e integrated module drive (MIC), which, in turn, has lower losses in the semi - conductors and magnetic elements of the topology, when compared to complex centralized photovoltaic systems. Among the applications of micro inverter flyback are: supply of remote systems, power electronics devices, small water pumping stations, connections to the grid, among others. Despite the low power, micro inverter has electrical characteristics essential for the insertion in the energy matrix, such as: insulation betwe en the source and the load, types of voltages and currents waves in output with little distortion and frequency of the network. The results obtained in the laboratory show that the micro inverter flyback operating in open loop gets yields close to 90% bein g delivered to the load about 180W. Thus, the ease of construction, the use of fewer components and results collected experimentally enable the micro inverter flyback to perform the CC - CA conversion of photovoltaic systems of small powers connected in sing le - phase linear loads with senoidais characteristics or interconnected to the electric grid
A pesquisa desenvolve o projeto e a implementação de um microinversor monofásico de estágio único obtido da derivação de quatro conversores flybacks CC-CC operando no modo descontínuo e associado em módulos paralelos. Este arranjo reduz o volume dos magnéticos, diminui os esforços de correntes nos primários dos transformadores, bem como minimiza as oscilações no módulo fotovoltaico. Em meio as principais propriedades do microinversor flyback (MIF) desta pesquisa, as chaves dos primários atuam com comutação SPWM em alta frequência e defasadas em cento e oitenta graus, enquanto as chaves dos secundários são comandadas por PWM’s complementares. Para validar a pesquisa será desenvolvido um protótipo que efetuará o processamento de energia interligando um painel fotovoltaico com 200 W de potência, em cargas resistivas com características senoidais. O sistema proposto está fundamentado na configuração módulo inversor integrado (MIC), que por sua vez, possui menores perdas nos semicondutores e elementos magnéticos da topologia, quando comparado aos complexos sistemas fotovoltaicos centralizados. Dentre as aplicações do microinversor flyback encontram-se: abastecimento de sistemas remotos, alimentação de aparelhos eletroeletrônicos, pequenas estações de bombeamentos de água, conexões a rede elétrica, entre outros. Apesar da baixa potência, o microinversor apresenta características elétricas essenciais a inserção na matriz energética, tais como: isolação entre a fonte e a carga, formas de ondas de tensões e correntes na saída com pequenas distorções e na frequência da rede. Os resultados obtidos em laboratório revelam que o microinversor flyback operando em malha aberta obtém rendimentos próximos a 90%, sendo entregue à carga cerca de 180 W. Sendo assim, a facilidade na construção, a utilização de poucos componentes e os resultados coletados experimentalmente habilitam o microinversor flyback a realizar a conversão CC-CA de sistemas fotovoltaicos de pequenas potências conectados em cargas lineares monofásicas com características senoidais ou interligados à rede elétrica

A pesquisa desenvolve o projeto e a implementaÃÃo de um microinversor monofÃsico de estÃgio Ãnico obtido da derivaÃÃo de quatro conversores flybacks CC-CC operando no modo descontÃnuo e associado em mÃdulos paralelos. Este arranjo reduz o volume dos magnÃticos, diminui os esforÃos de correntes nos primÃrios dos transformadores, bem como minimiza as oscilaÃÃes no mÃdulo fotovoltaico. Em meio as principais propriedades do microinversor flyback (MIF) desta pesquisa, as chaves dos primÃrios atuam com comutaÃÃo SPWM em alta frequÃncia e defasadas em cento e oitenta graus, enquanto as chaves dos secundÃrios sÃo comandadas por PWMâs complementares. Para validar a pesquisa serà desenvolvido um protÃtipo que efetuarà o processamento de energia interligando um painel fotovoltaico com 200 W de potÃncia, em cargas resistivas com caracterÃsticas senoidais. O sistema proposto està fundamentado na configuraÃÃo mÃdulo inversor integrado (MIC), que por sua vez, possui menores perdas nos semicondutores e elementos magnÃticos da topologia, quando comparado aos complexos sistemas fotovoltaicos centralizados. Dentre as aplicaÃÃes do microinversor flyback encontram-se: abastecimento de sistemas remotos, alimentaÃÃo de aparelhos eletroeletrÃnicos, pequenas estaÃÃes de bombeamentos de Ãgua, conexÃes a rede elÃtrica, entre outros. Apesar da baixa potÃncia, o microinversor apresenta caracterÃsticas elÃtricas essenciais a inserÃÃo na matriz energÃtica, tais como: isolaÃÃo entre a fonte e a carga, formas de ondas de tensÃes e correntes na saÃda com pequenas distorÃÃes e na frequÃncia da rede. Os resultados obtidos em laboratÃrio revelam que o microinversor flyback operando em malha aberta obtÃm rendimentos prÃximos a 90%, sendo entregue à carga cerca de 180 W. Sendo assim, a facilidade na construÃÃo, a utilizaÃÃo de poucos componentes e os resultados coletados experimentalmente habilitam o microinversor flyback a realizar a conversÃo CC-CA de sistemas fotovoltaicos de pequenas potÃncias conectados em cargas lineares monofÃsicas com caracterÃsticas senoidais ou interligados à rede elÃtrica.
The study proposes the design and implementation of a single phase inverter of single stage obtained the derivation of four flybacks converters CC - CC operating in discontinuous mode and associated in parallel modules. This arrangement reduces the amount of magnetic and decreases current efforts in primary transformers and minimizes fluctuations i n photovoltaic module. Among the main properties of micro inverter flyback (MIF) this research, the primary keys work with SPWM switching at high frequency and lagged in one hundred and eighty degrees, while the secondary keys are controlled by PWM's compl ementary. To validate the research, we will develop a prototype that will effect the processing power connecting a photovoltaic panel with 200W power in resistive loads with senoidais characteristics. The proposed system is based on the configuration of th e integrated module drive (MIC), which, in turn, has lower losses in the semi - conductors and magnetic elements of the topology, when compared to complex centralized photovoltaic systems. Among the applications of micro inverter flyback are: supply of remote systems, power electronics devices, small water pumping stations, connections to the grid, among others. Despite the low power, micro inverter has electrical characteristics essential for the insertion in the energy matrix, such as: insulation betwe en the source and the load, types of voltages and currents waves in output with little distortion and frequency of the network. The results obtained in the laboratory show that the micro inverter flyback operating in open loop gets yields close to 90% bein g delivered to the load about 180W. Thus, the ease of construction, the use of fewer components and results collected experimentally enable the micro inverter flyback to perform the CC - CA conversion of photovoltaic systems of small powers connected in sing le - phase linear loads with senoidais characteristics or interconnected to the electric grid

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This work presents a study and a development of a current source microinverter, based on the ?uk converter operating in discontinuous conduction mode, for microgeneration purposes based on photovoltaic systems. In this sense, we carried out a steady-state analysis of the ?uk converter, in order to establish the design criteria for the ?uk microinverter. All peripheral systems required for the microinverter operation have also been developed, and are included in this study, namely: the MPPT, PLL, and islanding detection algorithms. All control systems, i.e., the MPPT, PLL, and anti-islanding detection algorithms, were implemented in the DS1104 R&D controller board, from dSPACE?, using MATLAB/Simulink? to program it.
Este trabalho apresenta o estudo e o desenvolvimento de um microinversor de corrente, baseado no conversor ?uk, operando no modo de condu??o descont?nua, para a aplica??o em microgera??o fotovoltaica. Inicialmente, s?o desenvolvidos estudos de car?ter qualitativo e quantitativo do comportamento do microinversor de corrente baseado no conversor ?uk, os quais culminaram no desenvolvimento de crit?rios para o dimensionamento do conversor ?uk, que desempenha um papel central na estrutura do microinversor proposto. Sistemas perif?ricos necess?rios para a opera??o do microinversor, assim como aqueles exigidos pelas concession?rias de energia el?trica para a aplica??o em sistemas de microgera??o s?o estudados e desenvolvidos nessa disserta??o. Para tanto, a implementa??o de todos os sistemas de controle, ou seja, os algoritmos de MPPT, de sincronismo, e de detec??o da opera??o ilhada, foram realizados em ambiente MATLAB/Simulink? associada ? uma placa de desenvolvimento do fabricante alem?o dSPACE?, modelo DS1104, a qual permite o controle em tempo real dos transistores do microinversor.

Orientadores: Ernesto Ruppert Filho, Marcelo Gradella Villalva
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
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Resumo: O objetivo deste trabalho é a construção de um conversor eletrônico de potência monofá-sico completo para conexão à rede elétrica de distribuição de baixa tensão alimentado por painel fotovoltaico Painéis fotovoltaicos comerciais geram uma tensão contínua que varia entre 20 e 50V, dependendo do tipo de painel e da ocorrência ou não de conexão entre os mesmos; sendo necessário, portanto, a adequação dos níveis de tensão gerados pelo painel com o nível de tensão da rede elétrica de distribuição, na qual ele será conectado. O conversor eletrônico de potência utilizado neste trabalho é constituído de dois estágios sendo o primeiro CC ¿ CC e o segundo, um inversor, CC ¿ CA. Ele será controlado de duas maneiras: a primeira será responsável pelo con-trole da tensão de entrada do conversor CC - CC e pela injeção de potência no conversor CC - CA o qual, além de ser o responsável pela transformação da tensão contínua em alternada também é responsável pelo sincronismo do conversor CC - CA com a rede elétrica. São apresentados resultados de simulação do funcionamento do conversor para geração fotovoltaica de energia elétrica, sua malha de controle e o funcionamento do sistema elétrico completo. O projeto com-pleto dos conversores e dos circuitos auxiliares bem como os resultados experimentais obtidos em laboratório são apresentados
Abstract: The objective of this work is the construction of a complete single-phase power electronic converter for grid connection of low voltage distribution powered by photovoltaic panels. Photo-voltaic panels generates a DC voltage that varies between 20 and 50V, depending on the type of panel and presence or absence of connection between them, it is necessary, therefore, the ade-quacy of voltage levels generated by the panel with the voltage level of the electrical distribution network, in which it is connected. The power electronic converter used in this study consists of two stages with the first is a dc ¿ dc converter and the second is a dc-ac converter, frequency inverter. It will be controlled in two ways: the first is responsible for controlling the input voltage of the dc-dc converter and the power injection in the ac-dc converter which, besides being res-ponsible for the transformation into alternating voltage is also responsible by the synchronism of the converter dc-ac with the utility grid. Simulation results of the converter operation connected to the utility grid are presented, its network control and operation of the complete electrical sys-tem. The complete design of converters and auxiliary circuits and the experimental results obtai-ned in the laboratory are presented
Mestrado
Energia Eletrica
Mestre em Engenharia Elétrica

Neste trabalho é proposto o desenvolvimento de um novo microinversor de estágio único para aplicação em sistemas fotovoltaicos. A topologia apresentada é baseada na combinação do conversor Cuk com uma estrutura de indutores chaveados para obtenção de um maior ganho estático e um circuito inversor em ponte completa conectado à rede. A estrutura de indutores chaveados apresentada nesse trabalho reduz esforços de tensão e corrente nas chaves semicondutoras. Com o objetivo de facilitar o controle, a etapa CC do microinversor opera em modo de condução descontínua (DCM). Para injetar corrente senoidal com baixa distorção harmônica à rede, é aplicado às chaves semicondutoras da etapa CC uma modulação por largura de pulso senoidal (SPWM). As chaves semicondutoras do circuito inversor em ponte completa são comandadas na frequência da rede, reduzindo perdas por chaveamento. Por se tratar de uma topologia inédita, são apresentados os modos de operação e a análise matemática do conversor CC-CC Cuk com alto ganho estático. Posteriormente, são realizadas a análise teórica e a estratégia de controle do microinversor proposto. Os resultados experimentais são expostos para discutir o funcionamento da topologia proposta, através de simulações e da implementação de um protótipo de 180 W.
The development of a novel single stage microinverter is proposed. The presented topology is based on the combination of the Cuk converter with a switched inductor structure to obtain a higher static gain, and a full-bridge inverter circuit. The presented switched inductor structure reduces voltage and current stresses on the power switches. In order of simplify the control, the stage CC of the microinverter operate in discontinuous conduction mode (DCM). To inject sinusoidal current with low harmonic distortion to the grid, a sinusoidal pulse width modulation (SPWM) is applied in the power switches. The switches of the full-bridge invertes are commanded in low frequency, in order to reduce switching losses. Operation modes and math analysis of the novel CC-CC converter are presented. Moreover, the math analysis and control strategy of proposed microinverter topology are exposed. Furthermore, experimental results are performed to analyze the proposed topology operation, by software simulations and implementation of a 180 W prototype.

En la actualidad, los conceptos de generación distribuida y microrredes (microgrids) están despertando un gran interés en la comunicad científica, al presentar ventajas claras sobre los esquemas centralizados como son: su inherente redundancia, la mejora de la eficiencia en el transporte de energía eléctrica al aproximar los puntos de generación y de consumo, así como la posibilidad de integración de fuentes de energía renovable. En este contexto, la tesis plantea como aspectos novedosos la propuesta de un esquema de control reconfigurable para la operación de un microinversor fotovoltaico (convertidor electrónico concebido para procesar la energía procedente de un panel fotovoltaico individual) tanto en modo aislado como interconectado con una red eléctrica. Normalmente, tales unidades operan en conexión a la red eléctrica, funcionando como una fuente de corriente. El objetivo de la tesis es la concepción de técnicas que permitan dotar a los microinversores con la funcionalidad adicional de poder trabajar como fuente de tensión para operar en modo aislado, sin necesidad de utilizar sistemas adicionales de almacenamiento de energía (en la actualidad, baterías). Por otra parte, en la tesis se ha propuesto un nuevo algoritmo de detección de funcionamiento en isla (o modo aislado), basado en la inyección de un segundo armónico de corriente en la corriente de salida del microinversor y posterior evaluación de cómo éste interactúa con la red eléctrica. La técnica propuesta se basa en el procesado de la señal devuelta por la red mediante el algoritmo Goertzel de identificación de componentes armónicas. En la tesis se demuestra que las propuestas realizadas permiten la reconfiguración de los controladores del modo fuente de corriente a fuente de tensión, y viceversa, sin transitorios peligrosos para el microinversor ni para las cargas locales cercanas al mismo. Los resultados analíticos se han validado mediante simulaciones detalladas y ensayos experimentales llevados a cabo en un microinversor fotovoltaico 180 W.
Trujillo Rodríguez, CL. (2011). Concepción de controladores reconfigurables para microinversores fotovoltaicos operando como unidades autónomas de generación de energía en microrredes [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/14275
Palancia

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This work presents a study and a development of a microinverter, based on Zeta converter, as well as, the development of an islanding detection algorithm, based on the reduction of the maximum duty cycle of the converter. The objective is to achieve a reduction on the output voltage of the microinverter, so that it is possible to detect the islanding operation when the power grid is offline. In order to validate the proposed study the project of Zeta converter is presented, as well as, the implementation of the islanding algorithm in Matlab/Simulink? platform. The algorithm developed, in this project, presents outstanding results, since the variation of the microinverter output voltage amplitude resulted in an effective technique to detect islanding, as observed by simulations, which were performed in accordance with the standard IEEE 929.
Este trabalho apresenta o estudo e o desenvolvimento de um microinversor baseado no conversor Zeta e de um algoritmo de detec??o da opera??o ilhada, baseado na redu??o do ciclo de trabalho m?ximo do conversor. O objetivo ? conseguir uma redu??o na tens?o de sa?da do microinversor, para que seja poss?vel detectar a opera??o ilhada, caso a rede el?trica de distribui??o n?o esteja mais presente. A fim de validar o estudo proposto, foi apresentado o projeto do conversor Zeta e tamb?m a implementa??o do algoritmo de detec??o da opera??o ilhada em ambiente Matlab/Simulink?. O algoritmo desenvolvido apresentou ?timo desempenho, uma vez que a varia??o na amplitude da tens?o de sa?da do microinversor resultou em uma t?cnica efetiva para a detec??o da opera??o ilhada, considerando ensaios de laborat?rio realizados segundo a norma IEEE 929, e n?o resultou em degrada??o adicional da forma de onda da corrente entregue ? rede el?trica pelo microinversor.

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This work presents the study and development of a modification proposal of the classical MPPT - P&O approach, based on the utilization of the power and voltage derivatives in PV panel terminals. The contribution of this study consists in the employment of the time derivative of voltage that is used to determine converter duty cycle step size instantly. The proposed MPPT approach when compared to the classical P&O, presents some advantages like as: better dynamic response, steady state error reduction and robustness (considering different irradiation and temperature profiles). In order to validate this study, a microinverter prototype based on flyback converter, using this new approach, was implemented aiming to connect PV panels to the mains. Microinverter control strategy was held on Matlab/Simulink® environment in association to a data processing board (DS1104 from dSPACE®).
Este trabalho apresenta o estudo e o desenvolvimento de uma proposta de modificação do método de MPPT P&O clássico com base na utilização da derivada da potência e da derivada da tensão nos terminais dos painéis PV. A contribuição deste trabalho consiste no emprego da derivada da tensão dos painéis, a qual é utilizada para determinar a variação instantânea do ciclo de trabalho do conversor. O método de MPPT proposto em comparação com o método P&O convencional apresentou melhor desempenho considerando-se a resposta dinâmica, o erro de estado estacionário e a robustez (contra diferentes perfis de irradiância e de temperatura). A fim de validar este estudo, um protótipo de um microinversor com base no conversor flyback, usando a abordagem proposta, foi implementado com o objetivo de conectar painéis fotovoltaicos à rede elétrica. A estratégia de controle do microinversor foi realizada em ambiente Matlab/Simulink® em associação a uma placa de processamento de dados (DS1104 da dSPACE®).

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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES
Funda??o de Amparo ? Pesquisa do Estado do Rio Grande do Sul - FAPERGS
This work presents the study and development of a modification proposal of the classical MPPT - P&O approach, based on the utilization of the power and voltage derivatives in PV panel terminals. The contribution of this study consists in the employment of the time derivative of voltage that is used to determine converter duty cycle step size instantly. The proposed MPPT approach when compared to the classical P&O, presents some advantages like as: better dynamic response, steady state error reduction and robustness (considering different irradiation and temperature profiles). In order to validate this study, a microinverter prototype based on flyback converter, using this new approach, was implemented aiming to connect PV panels to the mains. Microinverter control strategy was held on Matlab/Simulink? environment in association to a data processing board (DS1104 from dSPACE?).
Este trabalho apresenta o estudo e o desenvolvimento de uma proposta de modifica??o do m?todo de MPPT P&O cl?ssico com base na utiliza??o da derivada da pot?ncia e da derivada da tens?o nos terminais dos pain?is PV. A contribui??o deste trabalho consiste no emprego da derivada da tens?o dos pain?is, a qual ? utilizada para determinar a varia??o instant?nea do ciclo de trabalho do conversor. O m?todo de MPPT proposto em compara??o com o m?todo P&O convencional apresentou melhor desempenho considerando-se a resposta din?mica, o erro de estado estacion?rio e a robustez (contra diferentes perfis de irradi?ncia e de temperatura). A fim de validar este estudo, um prot?tipo de um microinversor com base no conversor flyback, usando a abordagem proposta, foi implementado com o objetivo de conectar pain?is fotovoltaicos ? rede el?trica. A estrat?gia de controle do microinversor foi realizada em ambiente Matlab/Simulink? em associa??o a uma placa de processamento de dados (DS1104 da dSPACE?).

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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Este trabalho avalia experimentalmente as tecnologias string, microinversor e conversor c.c.-c.c., de modo a contribuir para a construção do conhecimento científico da aplicação das diferentes arquiteturas de interligação de geradores fotovoltaicos à rede elétrica convencional. Para isso são utilizados diferentes sistemas instalados no laboratório do GEDAE/UFPA, Região Norte do país. Comparou-se os desempenhos de acordo com as informações nos diferentes mecanismos de aquisição de dados disponíveis no laboratório. Tendo em vista que alguns desses mecanismos de aquisição de dados fornecem somente o valor da energia acumulada ao longo do dia, foi dado um enfoque na operação global dos diferentes sistemas analisados. Contudo, naqueles sistemas onde maiores detalhes da operação foram monitorados, seja por sistemas de aquisição do próprio equipamento ou por equipamentos existentes no laboratório (osciloscópio digital Fluke, wattímetro, etc), análises pontuais importantes, mais detalhadas da operação do sistema, foram desenvolvidas. Os resultados obtidos mostram que o conversor c.c.-c.c. apresentou desempenhos superiores aos demais sistemas monitorados. Contudo constatou-se a ocorrência de problemas devido ao processo de pareamento dos conversores c.c.-c.c. na operação do sistema que permanecem até os dias de hoje.
This work aims to experimentally evaluate the string, microinverter and d.c.-d.c. converter technologies, in order to contribute to scientific knowledge construction in applications of the different interconnection architectures of photovoltaic generators to the conventional electric grid. For this, were used different systems installed at GEDAE’s laboratory (UFPA), located in northern region of the country. It was compared the performances according to the information from different data acquisition mechanisms available in the laboratory. In face of some of these data acquisition mechanisms provide only the value of energy accumulated throughout the day, a focus was given on the overall operation of the different systems analyzed. However, in those systems which greater operational details were monitored, either by the equipment's own acquisition system or already existing equipment in the laboratory (Fluke Digital Storage Oscilloscope, Digital Power Meter, etc.), important point analyzes with more detailed operation of the system were performed. The obtained results show that the d.c.-d.c. converters system presented superior performance to the other monitored systems. However, it has been found the occurrence of problems due to the pairing process of the d.c.-d.c. power converters in the operation of such systems that remain until now.

abstract: The demand for cleaner energy technology is increasing very rapidly. Hence it is important to increase the eciency and reliability of this emerging clean energy technologies. This thesis focuses on modeling and reliability of solar micro inverters. In order to make photovoltaics (PV) cost competitive with traditional energy sources, the economies of scale have been guiding inverter design in two directions: large, centralized, utility-scale (500 kW) inverters vs. small, modular, module level (300 W) power electronics (MLPE). MLPE, such as microinverters and DC power optimizers, oer advantages in safety, system operations and maintenance, energy yield, and component lifetime due to their smaller size, lower power handling requirements, and module-level power point tracking and monitoring capability [1]. However, they suer from two main disadvantages: rst, depending on array topology (especially the proximity to the PV module), they can be subjected to more extreme environments (i.e. temperature cycling) during the day, resulting in a negative impact to reliability; second, since solar installations can have tens of thousands to millions of modules (and as many MLPE units), it may be dicult or impossible to track and repair units as they go out of service. Therefore identifying the weak links in this system is of critical importance to develop more reliable micro inverters. While an overwhelming majority of time and research has focused on PV module eciency and reliability, these issues have been largely ignored for the balance of system components. As a relatively nascent industry, the PV power electronics industry does not have the extensive, standardized reliability design and testing procedures that exist in the module industry or other more mature power electronics industries (e.g. automotive). To do so, the critical components which are at risk and their impact on the system performance has to be studied. This thesis identies and addresses some of the issues related to reliability of solar micro inverters. This thesis presents detailed discussions on various components of solar micro inverter and their design. A micro inverter with very similar electrical specications in comparison with commercial micro inverter is modeled in detail and veried. Components in various stages of micro inverter are listed and their typical failure mechanisms are reviewed. A detailed FMEA is conducted for a typical micro inverter to identify the weak links of the system. Based on the S, O and D metrics, risk priority number (RPN) is calculated to list the critical at-risk components. Degradation of DC bus capacitor is identied as one the failure mechanism and the degradation model is built to study its eect on the system performance. The system is tested for surge immunity using standard ring and combinational surge waveforms as per IEEE 62.41 and IEC 61000-4-5 standards. All the simulation presented in this thesis is performed using PLECS simulation software.
Dissertation/Thesis
Masters Thesis Electrical Engineering 2015

碩士
明志科技大學
電機工程系碩士班
107
This thesis presents the design and implementation of the gallium-nitride (GaN) power transistor based microinverter. In this system, a high step-up gain active clamp flyback converter with dual-buck inverter is implemented to convert dc power generated by solar cells with varying-voltage to single-phase electrical power with constant-voltage and constant-frequency. The GaN power transistors are used in the inverter due to their breakthrough of material limits, and the characteristics such as high breakdown voltage, high electron velocity, and thus the GaN power transistors are discussed. The dual-buck inverter operated under grid-connected mode using phase-locked loop algorithm can provide a single-phase source with fast response, stable and low harmonic distortion power. Then, a high-performance and low-cost microcontroller (TMS320F28035) is used to control the system for reducing the circuit complexity. A prototype of 300 W microinverter is developed under grid-connected operations, while the rated output voltage is 110V and the frequency is 60 Hz. Besides, the experimental data show that the voltage and current harmonic distortions of single-phase electrical power is below 5%, which justify the performance of the proposed microinverter.

碩士
明志科技大學
電機工程系碩士班
103
This study is concerned with the simulstion of microinverter for solar power conversion systems. The DC voltage generated by solar cells with varying-voltage is converted to single-phase AC power with constant-voltage and constant-frequency. The coupled inductors and double-boost topology is proposed to maintain voltage stability at output side and decrease the size and cost of the system. The maximum power point tracking control and voltage zero-crossing detection method are implemented to operate in grid-connected fashions. In this thesis, the coupled inductors, double-boost microinverter and solar cells with maximum power point tracking control are built and simulated by Matlab/Simulink. The prototype of 230W power conversion system can feed proper power in stand-alone and in parallel with the utility power system, while the rated effective output voltage is 220V and the frequency is 60 Hz.

碩士
國立高雄第一科技大學
電子工程系碩士班
106
In this paper, a solar-powered wireless charging micro-inverter integrated circuit (IC) and system is proposed. This design will combine micro-inverter, energy harvesting and wireless charging technologies to operate the proposed IC and system at the high efficient condition. In this design, the solar-powered is input energy, the transmitter transfers the energy to the receiver with magnetic induction technology. And the microinverter output AC voltage to the load. Owing to the output power of solar panels and battery is affected by environmental factors, the diagnosis is very important for the proposed IC and system. The sensing conditions including voltage and current were used to build an analysis system in the proposed tool. Then, the proposed tool can be used to diagnose the operation conditions of the synthesized ICs for the monitor and maintenance processes. This IC had been taped out through the design flow of the National Chip Implementation Center (CIC). Then, the IC is fabricated with TSMC 0.35μm 2P4M 3.3V/5V mixed-signal process and the total area is 1.070*1.070 mm2.

The grid connected PV plants comprising of the PV cells and the power electronic inverters are a widely used technology in distributed power generation systems based on renewable energy sources. Microinverters form an extensive part of the ongoing research in this field. This thesis focuses on the inverter section of the microinverter. The cost and efficiency of the grid connected inverter is a chief contributing factor in the overall system price. The MOSFETs used in the DC/AC inverter are usually hard switched causing a lot of EMI noise and losses in the inverter. This is true for both, single and three phase inverters. A low switching frequency is desirable to increase the efficiency, which in turn imposes a large compromise in designing the output filter. In this thesis, switching losses have been minimized by incorporating zero voltage switching at switch turn on and variable dead-time control at switch turn off. The soft switching technique is based on control algorithms and involves no use of any auxiliary circuit. Also, the size of the output filter is reduced without increasing the switching frequency, by employing multiple paralleled inverters. The interleaving technique that is usually used in dc/dc converters is extended for dc/ac inverters and is well employed to maintain the quality of the current fed into the utility grid. In this way, at low switching frequency, high efficiency and reduced cost and sizes are achieved. The study is validated through simulation and lab experiments. The novel control circuit was first implemented using analog circuitry. After assessing the performance of the analog version of the proposed controller, it was then digitally implemented through the Field Programmable Gate Array (FPGA) technique.
Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2012-04-30 15:06:26.071

Dissertação de mestrado integrado em Engenharia Eletrónica Industrial e Computadores
Nos últimos séculos, tem-se assistido a uma crescente procura e exploração de combustíveis fósseis com o intuito de saciar as necessidades energéticas da sociedade. O aumento populacional aliado à revolução industrial, iniciada no princípio do século XIX, levou a uma frenética exploração das fontes de energia causando danos ambientais irreparáveis. Esta tendência necessita de ser controlada de modo a permitir um desenvolvimento sustentável. Como tal, é urgente encontrar um modo de contornar as desvantagens inerentes ao uso dos combustíveis fósseis, surgindo assim as energias renováveis, como é o caso da energia solar fotovoltaica. Contudo, de forma a possibilitar a integração de fontes de energia renovável na rede elétrica, existe uma necessidade de mudar o paradigma energético, tornando-se evidente o papel crucial que as tecnologias de armazenamento de energia irão desempenhar. Desta forma, no presente documento de dissertação é descrito o Desenvolvimento de um Microinversor com Armazenamento Local de Energia para Aplicações Solares Fotovoltaicas, bem como todas as etapas inerentes à conceção deste projeto. Um microinversor é um dispositivo de eletrónica de potência que permite a interface de uma fonte de energia renovável, e.g., módulo solar fotovoltaico, com a rede elétrica, tendo como principal característica a possibilidade de extrair, de uma forma independente, a máxima potência disponível em cada módulo. Para a conceção do microinversor, é apresentada uma topologia inovadora para o conversor CC-CC que permite a interface de um módulo fotovoltaico com um banco de baterias e com o barramento CC, com apenas dois MOSFETs. No sistema de controlo do conversor CC-CC, encontra-se incluído um algoritmo de MPPT, que fará com que a sua operação se dê sempre no ponto de máxima potência do módulo, e um algoritmo responsável pelo carregamento adequado das baterias. Por sua vez, este é seguido de um conversor CC-CA, que tem como finalidade a sintetização de uma corrente sinusoidal para injetar a energia produzida na rede elétrica. Para a realização deste projeto de dissertação foi necessário o estudo, dimensionamento e implementação de todo o hardware que constitui o microinversor apresentado, desde os circuitos de condicionamento de sinal dos diversos sensores utilizados, passando pelos circuitos lógicos do sistema digital de controlo, até aos circuitos de potência, incluindo os elementos magnéticos alta-frequência. De igual modo, foi realizado um estudo e consequente desenvolvimento de todos os algoritmos de controlo necessários para a implementação deste projeto.
In the past few centuries, it has been seen a huge fossil fuels exploration aiming to satisfy society’s energetic needs. The population growth combined with industrial revolution, started in the beginning of the XIX century, led to a frenetic exploitation of energy sources causing irreparable environmental damage. This trend needs to be controlled in order to generate sustainable development. Therefore, it’s urgent to find a way to avoid the inherent disadvantages of fossil fuels. For that, renewable energy sources, like solar photovoltaic energy, appear as valid solution. However, in order to enable the integration of renewable energy sources into the grid, it is required to change the energy paradigm, which will evidence the crucial role that energy storage technologies will play. Thus, in the present master dissertation document is described the development of a micro-inverter with local energy storage for solar photovoltaic applications, as well as all the intrinsic stages to this project’s conception. A micro-inverter is a power electronics device which allows a renewable energy source interface, e.g., photovoltaic panel, with the power grid. The main feature of this device is the capability to extract, in an independent way, the maximum power available of each solar photovoltaic module. For the micro-inverter’s assembly, an innovative topology for the DC-DC converter is presented. This provides an interface of a photovoltaic module with a battery bank and the DC bus, with only two MOSFETs. A MPPT algorithm is included in the DC-DC converter, which will make it operate in the module’s maximum power point the entire time, and a battery charging algorithm. This converter is followed by a DC-AC converter, whose purpose is to synthesize a sinusoidal current and inject the produced energy in the power grid. In order to carry out this dissertation project, it was necessary to study, design and implement all the presented topology’s hardware, passing through the logic circuits of signal conditioning, to the power hardware, that include the magnetic circuits of high frequency. Likewise, a study of the control algorithms necessary for the integration of this project was carried out.

Dissertação de mestrado integrado em Engenharia Eletrónica Industrial e Computadores
Nos últimos tempos têm aumentado os problemas do aquecimento global e da crise energética mundial, o que faz com que se dê uma maior importância ao desenvolvimento de novas técnicas de produção de energia elétrica através de fontes renováveis, uma vez que estas possibilitam uma redução do consumo de combustíveis fósseis, e da poluição. Uma das formas de produção de energia que tem revelado uma grande margem de crescimento é a geração através de painéis solares fotovoltaicos, o que é justificado por várias razões, nomeadamente por existir uma grande disponibilidade da fonte de energia, o Sol, por existir uma grande diversidade de painéis solares fotovoltaicos e pelo seu custo de operação reduzido. Os painéis solares geram uma tensão DC na saída, como a grande maioria das cargas são alimentados com tensão AC sinusoidal (230 V, 50 Hz) é imprescindível usar inversores para converter a tensão de DC para AC. Este trabalho de dissertação de mestrado tem como objetivo principal reduzir o efeito de sombra (de uma nuvem, ou objeto próximo) sobre um módulo fotovoltaico e, para tal, foi desenvolvido um microinversor para um módulo fotovoltaico de baixa potência, de modo a injetar energia na rede elétrica. O microinversor implementa uma metodologia de controlo que segue o ponto de máxima potência (MPPT), de modo a otimizar a extração de energia elétrica do painel a que este está ligado. Inicialmente foi feito um levantamento do estado da arte relativamente às tecnologias dos atuais microinversores de baixa/média potência, com intuito de selecionar a melhor relação de custo. Seguidamente foi escolhida a topologia do microinversor. Relativamente à topologia foi efetuado o seu dimensionamento, uma simulação computacional para validar o seu correto funcionamento, e por fim implementou-se um protótipo e são apresentados resultados experimentais.
In recent times has increased the problems of global warming and the global energy crisis, which gives greater importance to the development of novel techniques for electricity generation through renewable sources, since they enable a reduction in the consumption of fossil fuels, and pollution’ costs. One source of energy generation that have a large margin of growth is photovoltaic solar panels, because of several reasons, especially for having a great availability of the energy source, the Sun, its simplicity, and a great diversity of solar panels technologies, and also the reduced cost of operation. The solar panels generate a DC output voltage, since the great majority of loads are usually fed by sinusoidal AC voltage (230 V, 50 Hz) it is essential to use inverters to convert the DC voltage into AC voltage. This dissertation work has as its main objective to reduce the shadow effect on a photovoltaic module and for that, it was developed a micro-inverter for a PV module to inject energy into the power grid. The micro-inverter implements a control methodology that follows the maximum power point tracking (MPPT) to optimize the extraction of electrical power from the panel. Initially it was made a survey of the state of the art of the technologies related to the micro-inverter, in order to select the best cost relationship. Then it was selected a topology to implement the micro-inverter. Regarding the topology it was performed its sizing, some computer simulation to validate its operation, and finally it was implemented a prototype and presented some experimental results obtained with it.

Η παρούσα διδακτορική διατριβή αναφέρεται σε οικιακά Φ/Β συστήματα συνδεδεμένα στο δίκτυο χαμηλής τάσης, τα οποία αξιοποιούν την τεχνολογία των Φ/Β Πλαισίων Εναλλασσομένου Ρεύματος (Φ/Β Πλαίσια Ε.Ρ. – AC-PV Modules). Πρόκειται για Φ/Β διατάξεις μικρής ισχύος (έως 300W), οι οποίες δημιουργούνται από την ενσωμάτωση ενός μόνο Φ/Β πλαισίου και ενός μετατροπέα (ενός η πολλών σταδίων) συνεχούς τάσης σε μονοφασική εναλλασσόμενη τάση, σε μια αυτοτελή ηλεκτρονική διάταξη. Για το λόγο αυτό ονομάζονται και Φ/Β πλαίσια με ενσωματωμένο μετατροπέα (Module Integrated Converters, MIC). Στα συστήματα αυτά οι απαιτήσεις για επίτευξη υψηλού βαθμού απόδοσης, για την καλύτερη εκμετάλλευση της παρεχόμενης ηλιακής ενέργειας, καθώς και ρεύματος ημιτονοειδούς μορφής στην έξοδο είναι αδιαμφισβήτητες. Βασικός σκοπός της παρούσας διατριβής είναι η συμβολή της στον τομέα των Φ/Β μονάδων διεσπαρμένης παραγωγής και επικεντρώνεται στην ενδελεχή ανάλυση, στη βελτιστοποίηση της λειτουργικής συμπεριφοράς, στον υπολογισμό των απωλειών στα στοιχεία του μετατροπέα, στην παραμετροποίηση και τελικά στο βέλτιστο σχεδιασμό ενός αντιστροφέα ρεύματος τύπου Flybcak (Flyback Current Source Inverter – Flyback CSI). Οι κύριοι στόχοι που έπρεπε να εκπληρωθούν για την ολοκλήρωση της παρούσας διατριβής ήταν:  Η ενδελεχής ανάλυση της λειτουργίας του αντιστροφέα για δύο διαφορετικές στρατηγικές ελέγχου που εφαρμόζονται σε αυτόν.  Ο κατά το δυνατόν ακριβέστερος υπολογισμός των απωλειών στα στοιχεία του Flyback CSI, καθώς και η παραμετροποίηση των σχέσεων αυτών.  Ο βέλτιστος σχεδιασμός του Flyback CSI, ο οποίος βασίζεται στη διατύπωση της μεγιστοποίησης του σταθμισμένου βαθμού απόδοσης ως πρόβλημα βελτιστοποίησης.  Η υλοποίηση του ελέγχου της λειτουργίας του μετατροπέα μέσω ψηφιακού μικροελεγκτή, καταργώντας τον ήδη υφιστάμενο αναλογικό έλεγχο. Αρχικά η μελέτη επικεντρώνεται σε μία πρώτη τεχνική ελέγχου, η οποία ωθεί τον μετατροπέα να λειτουργεί στην περιοχή της ασυνεχούς αγωγής (Discontinuous Conduction Mode, DCM). Στη συνέχεια προτείνεται μία δεύτερη τεχνική ελέγχου η οποία, αφ' ενός μεν αναγκάζει το μετατροπέα να λειτουργεί στο όριο συνεχούς και ασυνεχούς αγωγής (Boundary between Continuous and Discontinuous Conduction Mode, BCM), αφ' ετέρου δε παρέχει καθαρά ημιτονοειδές ρεύμα στην έξοδο. Με την προτεινόμενη νέα τεχνική ελέγχου, που ονομάσθηκε i-BCM (improved BCM) και αποτελεί βελτίωση της υπάρχουσας στη βιβλιογραφία τεχνικής ελέγχου BCM, βελτιώνεται σημαντικά ο συντελεστής ισχύος στην έξοδο του αντιστροφέα, παρέχοντας στο δίκτυο καθαρά ημιτονοειδές ρεύμα. Οι δύο διαφορετικές στρατηγικές ελέγχου διαμορφώνουν διαφορετικές κυκλωματικές συνθήκες. Για τις δύο περιπτώσεις αναπτύσσονται αναλυτικές εκφράσεις τόσο για τη μέση, όσο και για την ενεργό τιμή των ρευμάτων που διαρρέουν όλα τα στοιχεία του μετατροπέα (ημιαγωγικά στοιχεία, Μ/Σ κλπ). Επιπρόσθετα, εξάγονται κριτήρια για τα ασφαλή όρια λειτουργίας του μετατροπέα με γνώμονα την καταπόνηση των ημιαγωγικών στοιχείων ισχύος από υψηλές τιμές τάσης και ρεύματος. Ιδιαίτερο βάρος δίνεται στον υπολογισμό της διακύμανσης της τάσης του πυκνωτή του φίλτρου εξόδου, η οποία αναπτύσσεται και πάνω στα ημιαγωγικά στοιχεία του μετατροπέα, επηρεάζοντας την επιλογή τους. Στην συνέχεια, προσδιορίζονται μέσω αναλυτικών μαθηματικών σχέσεων οι απώλειες αγωγής και οι διακοπτικές απώλειες των ημιαγωγικών στοιχείων και προσεγγίζονται, με ιδιαίτερη λεπτομέρεια, οι απώλειες του μετασχηματιστή (τυλιγμάτων και πυρήνα) και για τις δύο προαναφερθείσες στρατηγικές ελέγχου, δεδομένου ότι η διακοπτική συχνότητα λειτουργίας του μετατροπέα είναι υψηλή. Για το λόγο αυτό απαιτείται εις βάθος μελέτη της υπάρχουσας βιβλιογραφίας, επιλογή ή επινόηση των κατάλληλων μοντέλων απωλειών σε ένα Μ/Σ (πυρήνα και χαλκού) και προσήκουσα προσαρμογή αυτών στις κυκλωματικές συνθήκες του αντιστροφέα Flyback. Παράλληλα με την ανάλυση των απωλειών πραγματοποιείται και η παραμετροποίηση του συστήματος. Η διαδικασία αυτή στηρίζεται στη διαχείριση των εξισώσεων κατά τέτοιο τρόπο ώστε να προσδιορίζονται όλες οι μεταβλητές και οι σταθερές του μετατροπέα, καθώς και οι παράμετροι από τις οποίες εξαρτώνται οι απώλειες, με τον απλούστερο δυνατό τρόπο. Συνεπώς, έχει δοθεί ιδιαίτερη έμφαση στην διαχείριση των αναλυτικών σχέσεων ώστε οι απώλειες, χωρίς έκπτωση στην ακρίβεια, να εξαρτώνται από τον ελάχιστο δυνατό αριθμό παραμέτρων. Με αυτό τον τρόπο η μελέτη είναι πλήρης αλλά περιορίζεται η πολυπλοκότητα, με αποτέλεσμα να προκύπτουν μόνο τέσσερις ανεξάρτητες σχεδιαστικές μεταβλητές. Στο επόμενο στάδιο, πραγματοποιείται ο βέλτιστος σχεδιασμός του Flyback CSI, ο οποίος βασίζεται στη διατύπωση της μεγιστοποίησης του σταθμισμένου βαθμού απόδοσης ως πρόβλημα βελτιστοποίησης. Αυτό, πρακτικά, σημαίνει τον προσδιορισμό της αντικειμενικής συνάρτησης (objective ή cost function), των σχεδιαστικών μεταβλητών και σταθερών, των περιοριστικών συνθηκών και τον ορισμό του πεδίου τιμών αυτών. Ο σταθμισμένος βαθμός απόδοσης αποτελεί την αντικειμενική συνάρτηση, ενώ οι προδιαγραφές εισόδου και εξόδου του μετατροπέα αποτελούν τις σχεδιαστικές σταθερές.. Με τη χρήση μίας στοχαστικής μεθόδου βελτιστοποίησης, η οποία αναδείχτηκε ως η πιο κατάλληλη έπειτα από εκτεταμένη βιβλιογραφική αναζήτηση, προσδιορίζονται οι τιμές των τεσσάρων σχεδιαστικών μεταβλητών και επιτυγχάνεται ο μέγιστος δυνατός σταθμισμένος βαθμός απόδοσης. Η επίτευξη του στόχου ολοκληρώνεται με την ανάπτυξη ενός νέου επαναληπτικού αλγορίθμου, με τον οποίο, βάσει των εξισώσεων των απωλειών, επιτυγχάνεται ο βέλτιστος σχεδιασμός του Flyback CSI και για τις δύο διαφορετικές τεχνικές ελέγχου. Επιπροσθέτως, υλοποιείται ο έλεγχος της λειτουργίας του μετατροπέα μέσω ψηφιακού μικροελεγκτή, καταργώντας τον ήδη υφιστάμενο αναλογικό έλεγχο. Η αλλαγή της φιλοσοφίας υλοποίησης του ελέγχου προσφέρει μεγαλύτερη ευελιξία και ανεξάντλητες δυνατότητες στην κατάστρωση και υιοθέτηση διαφορετικών στρατηγικών ελέγχου. Ιδιαίτερα, κατά τη λειτουργία στο όριο μεταξύ συνεχούς και ασυνεχούς αγωγής (i-BCM), με κατάλληλο προγραμματισμό του μικροελεγκτή εξαλείφεται η ανάγκη για μέτρηση των ρευμάτων στα τυλίγματα του μετασχηματιστή. Ο μικροελεγκτής που χρησιμοποιείται είναι ο dspic30F4011 της εταιρείας Microchip ο οποίος διαθέτει μεγάλη υπολογιστική ικανότητα και μία πληθώρα περιφερειακών που επιτρέπουν αυτοματοποίηση κάποιων λειτουργιών, όπως η διαδικασία σύνδεσης και αποσύνδεσης με το δίκτυο και η δυνατότητα ενσωμάτωσης της μονάδας ανίχνευσης του μέγιστου σημείου ισχύος (M.P.P.T) της Φ/Β γεννήτριας στην ίδια ψηφιακή μονάδα. Τέλος, υλοποιήθηκαν εργαστηριακά πρωτότυπα με βάση τις βέλτιστες παραμέτρους που υπολογίσθηκαν σε κάθε περίπτωση σύμφωνα την προτεινόμενη μέθοδο βελτιστοποίησης και ακολούθησε πειραματική επιβεβαίωση με χρήση ενός αναλυτή ισχύος υψηλής ακρίβειας, για την επιβεβαίωση των θεωρητικών προσεγγίσεων. Επιπλέον, μελετήθηκε η ευεργετική επίδραση της συνδυαστικής χρήσης των δύο τεχνικών ελέγχου στην πυκνότητα ισχύος
This thesis pertains to domestic on-grid PV systems that utilize the AC-PV Modules technology. These low power PV topologies (up to 300W) are implemented by integrating one PV Module and a single phase inverter (one or multi stage), in one independent electronic apparatus. For this reason they are called Module Integrated Converters (MIC). The most important requirements for these systems are the higher possible efficiency - in order to take advantage of the supplied solar energy – and the pure sinusoidal output current. The main purpose of this thesis is to contribute to the field of the dispersed PV power generation. Thus, it focuses on the thorough analysis, the behaviour optimization, the components losses estimation, the parameterization and finally the optimal design of Flyback current source inverter (Flyback CSI). The main objectives fulfilled in this thesis are: • The detailed analysis of the inverter behaviour for two different semiconductor control strategies. • The precise losses calculation of all the components of the Flyback CSI. • The optimal design of the Flyback CSI, which is based on maximizing the weighted efficiency. • The implementation of the semiconductor control via a digital microcontroller, eliminating the existing analogue control. Initially, the study focuses on a first control technique that forces the inverter to function in Discontinuous Conduction Mode (DCM). On the other hand, a second control technique that forces the inverter to function on the Boundary between Continuous and Discontinuous Mode (BCM) is proposed. This new control technique is named i-BCM (improved BCM) and it is an improved version of the BCM control technique found in the literature. This new control scheme significantly improves the power factor of the inverter output. The inverter injects pure sinusoidal current to the grid. The two different control strategies form different circuit conditions. Analytical expressions for the average and the rms value of the current, flowing through the components (semiconductors, transformers e.t.c), for both cases are developed. In addition, new operating boundaries of the semiconductors for the safe operation of the inverter based on the analysis of the voltage and current that stresses the semiconductors, are proposed. Special attention is given on the calculation of the voltage deviation on the output filter capacitor. This voltage deviation is caused by the switching operation of the inverter and affects the selection of the semiconductors and the voltage level that can handle. Furthermore, the conduction losses and the switching losses of the semiconductors are determined through analytical, mathematical equations. Because of the inverter high switching frequency, the transformer losses (copper and core), are calculated with special attention to detail. For this reason, an in depth examination of the existing literature takes place that leads to the selection of the appropriate core and copper loss models. The models are adequately adjusted to the circuit conditions of the Flyback inverter topology. The system is parameterized along with the losses analysis. All the equations are manipulated in such a way that simplifies the determination of all the variables and all the constants of the inverter and the loss dependent parameters. Consequently, special emphasis is given to the manipulation of the analytical equations, without affecting the accuracy, in order to express the losses using the minimum number of independent variables. Therefore, the study is complete but the complexity is eliminated and the independent design variables are only four. The optimization problem is the maximization of the weighted efficiency. The optimal design of the Flyback CSI is implemented based on this formulation. As a next step, the objective (or cost) function, the design variables and constants, the constraints and their range need to be defined. The weighted efficiency is the objective function whereas the input and the output specifications of the inverter are the design constants. After an extensive literature research, a stochastic optimization method is chosen as the most appropriate to determine the values of the four design variables in order to achieve the highest weighted efficiency. A new iterative algorithm, which uses the losses equations, is developed to achieve the optimal design of the Flyback CSI for both control strategies. Moreover, the control of the inverter is implemented via a digital microcontroller, eliminating the existing analogue control. This changes the way of controlling the inverter and offers flexibility and limitless possibilities in implementing and adopting various control strategies. Specifically, under the i-BCM control scheme, the need for measuring the current of the transformer windings is eliminated by using an appropriate algorithm. The microcontroller used in this research is dspic30F4011 developed by Microchip. Its good computational capacity and the variety of peripherals enable the automation of some functions such as connection and disconnection from the grid and the integration of the maximum power point tracking (M.P.P.T.) on the same digital unit. Finally, laboratory prototypes are implemented, based on the optimal parameters calculated for every case, using the proposed optimization method. The experimental procedure confirmed the theoretical approximations. A high precision power analyser was used. Furthermore, the beneficial effect of the combined use of the two control power techniques on the power density is also studied.