Barbosa 2011

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PV Inverters

Text of Barbosa 2011

Jos Nilton Tavares Barbosa Lic. em Engenharia Mecatrnica

PV Inverters for Module Level Applications

Dissertao para obteno do Grau de Mestre em Energias Renovveis Converso Elctrica e Utilizao Sustentveis

Orientador: Doutor Joo Martins, Professor Auxiliar, FCT-UNL

Co-orientador: Doutor Luis Pina, Coordenador de I&D, WS Energia

Setembro 2011 ii iii Dedicated To My Dear FamilyYou Are My Inspiration iv v Acknowledgements First,andforemost,I mustthank myfamilyfortheunconditionalsupportinevery aspect of my life,andinparticularfortheenormousefforttoprovidemeagoodeducation,despiteallthe difficulties. I would like to thank also, every one that for one way or another gave his contribution formypersonal,socialoracademictrainingresponsibleforeachsuccessIhave.Ithankmy tutor and co-tutor, Dr. Joo Martins and Dr. Luis Pina respectively, for all the support during the developmentofthisproject.IthanktheWSEnergiaS.Afortheopportunitytocooperateand learn with them. Finally and not less important I thank my friends and colleagues for all the help andsupport,especiallythosethatalwaysbelievedinme,andhavebeenIrealfellowsinthis journey. Without friends no one would choose to live, despite having all other goods. - Aristotle vi vii Abstract Nowadays,thephotovoltaic(PV)energyispresentedasoneofthemostpromisingsourceof 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,andtheneedtoimprovetheirefficiencyandreducingtheircost.WiththisworkI 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 itis used a full-bridgeinverter, and both the DC-DC and theDC-ACconvertersusetheIGBTsform anintegrated modulewithitsrespectivedrivers.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.Oncethisinverterisconceivedtoworkconnectedtothegrid,asingle-phasePLL systemisusedtosynchronizetheinjectedcurrenttogridvoltage.Allthecontrolpartismade digitally using an Arduino Uno board, which uses an Atmel microcontroller. Keywords: Inverters, Microinverters, Photovoltaic, Power Electronics, Renewable Energies. viii ix Resumo Atualmente, a energia fotovoltaica apresentada como sendo uma das mais promissoras fontes deenergialimpa, eassim umaboa maneirade mitigao dasemissesdos gases com efeito deestufaereduziradependnciadoscombustveisfsseis.Comele,aenergiafotovoltica temdespertadoumenormeinteressenosconversoreselectrnicos,enanecessidadede melhorarasuaeficinciaereduzirosseuscustos.Nopresentetrabalhoapresenta-seuma soluoparainversoresmonofsicosligadosredeescalademodulos.Asoluoconsiste em um inversor de dois estgios com transformador de isolamento. O inversor de dois estgios compostoporumconversorDC-DC e outroDC-AC conectados atravezdeum condensador debarramentoDC.O conversorDC-DC nocasoumconversor boostutilizadoparaelevar a tensodo modulofotovolticoparaum nvelsuperior.Parao conversorDC-ACutilizadoum inversorde pontecompletae para ambososconversores soutilizadosIGBTsdeum mdulo integrado com seus respectivos drivers. Para o controlo do boost implementado um algoritmo de rastreamento do ponto de mxima potncia que optimiza a extrao de energia da fonte PV e para o inversor usado o controlo de modo de deslizamento das correntes. Uma vez que este inversor concebido para funcionar conectado rede, usado um sistema de PLL monofsico para sincronizar a corrente injectada com a tenso da rede. Todo o controlo feito digitalmente usando uma placa Arduino Uno que usa um microprocessador da Atmel. Palavras-chves: Inversores, Microinversores, Electrnica de Potncia, Fotovoltico, Energias Renovveis. x xi Table of Contents Acknowledgementsv Abstract..vii Resumo..............................................................................................................ix Table of Contents.xi List of Figures...xv List of Tablesxix List of Abbreviationsxxi Chapter 1.......................................................................................................................................... 1 Introduction ..................................................................................................................................... 1 1.1Scope - PV Inverters ......................................................................................................... 1 1.2Motivation ......................................................................................................................... 1 1.3Objective ........................................................................................................................... 2 1.4Contributions..................................................................................................................... 2 1.5Thesis organization ........................................................................................................... 3 Chapter 2.......................................................................................................................................... 5 Photovoltaic Inverter Technology State of the Art ....................................................................... 5 2.1General issues on photovoltaic energy ............................................................................. 5 2.1.1 Environmental and Economical Motivations ................................................................. 6 2.1.2 The Need for Efficient Electronic Converters ................................................................ 7 2.2PV Inverters ...................................................................................................................... 8 2.2.1Central Inverters ........................................................................................................ 8 2.2.2 String Inverters ............................................................................................................... 9 2.2.3 Module Inverters........................................................................................................... 10 2.3PV Inverters Topologies ................................................................................................. 10 2.3.1 PV inverter with DC/DC converter and galvanic isolation .......................................... 11 2.3.2 PV inverter with DC/DC converter .............................................................................. 12 2.3.3 PV inverter without DC/DC converter with galvanic isolation .................................... 13 2.3.4 PV inverter without DC/DC converter and isolation.................................................... 13 2.4Pulse Modulation Schemes ............................................................................................. 14 2.4.1 Two levels modulation ................................................................................................. 16 xii 2.4.2 Multi-level modulation ................................................................................................. 16 2.5Harmonic Distortion ....................................................................................................... 17 2.6Energy Storage in Grid-connected PV Plants ................................................................. 18 2.6.1 Batteries in Grid-connected PV Systems...................................................................... 19 2.6.2 Losses caused by the mismatching between the PV plant and the grid ....................... 19 2.6.3 Losses caused by mismatching conditions among PV modules of the PV plant ......... 20 2.6.4Losses caused by the reversed power flow on grids ................................................ 21 2.6MPPT techniques ............................................................................................................ 21 2.7.1 Active MPPTs............................................................................................................... 21 2.7.2 Batteries as passive MPPTs .......................................................................................... 21 2.7Switching devices Technology ....................................................................................... 22 2.8.1 MOSFET ...................................................................................................................... 22 2.8.2 IGBT ............................................................................................................................. 22 2.7.3Parallel Switched MOSFET with IGBT .................................................................. 25 2.9Commercial Inverters...................................................................................................... 27 Chapter 3........................................................................................................................................ 29 Simulation of different topologies in MatLab-Simulink ............................................................... 29 3.1PWM pulse generator ..................................................................................................... 29 3.2PWM inverter with LF transformer ..................................