英文硕士论文光伏系统建模 DIGSILENT.pdf

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Comparison of existing PV models and possible integration under EU grid specifications Ioannis-Thomas K. Theologitis Degree project in Electric Power Systems Second Level Stockholm, Sweden 2011 XR-EE-ES 2011:011

Comparison of existing PV models and possible integration under EU grid specifications Ioannis-Thomas K. Theologitis Master of Science Thesis KTH School of Electrical Engineering Division of Electrical Power Systems EPS-2011 SE-100 44 STOCKHOLM

COMPARISON OF EXISTING PV MODELS AND POSSIBLE INTEGRATION UNDER EU GRID SPECIFICATIONS Ioannis-Thomas Theologitis Royal Institute of Technology (KTH), Sweden ©2011 School of Electrical Engineering Kungliga Tekniska Högskolan SE-100 44 Stockholm Sweden The author is officially enrolled to the Sustainable Energy Engineering Master Program (SEE) and belongs to the School of Industrial Engineering and Management and the Department of Energy Technology. The picture of the front cover is taken from the second edition of the book “Planning & Installing Photovoltaic Systems – A guide for installers, architects and engineers”, published by Earthscan and copyrighted by The German Energy Society (Deutsche Gesellshaft für Sonnenenergie (DGS LV Berlin BRB) in 2008. ISBN-13: 978-1-84407-442-6

“Αποσκότισόν με” -Διογένης- “Take me out of the dark” -Diogenes- It was the answer to Great Alexander, when he stood in front of Diogenes and asked him what favour he needs. Diogenes, as a cynic philosopher, answered this phrase to Alexander implying that he was blocking the sun with his body. Cynics believed that the happiness is hidden in simple things as the energy and warmth of the sun and not in material goods.

MSc Thesis Project Abstract KTH, June 2011 Abstract This master thesis investigates the capabilities of a generic grid-connected photovoltaic (PV) model that was developed by DIgSILENT and is part of the library of the new version of PowerFactory v.14.1. The model has a nominal rated peak power of 0.5 MVA and a designed power factor cosφ=0.95. A static generator component, which includes the PV array, the DC bus with the capacitor, the inverter and the control frame, is used to model the PV system. The PV array is considered to operate at the MPP and the generator with cosφ=1. The thesis begins with a short review of the current status of the PV sector, focusing mostly on the types of PV systems and the necessary components that are used in grid-connected systems. Since the PV inverter is the key component, special reference is made to the different technologies applied and to the multifaceted role that inverters should play nowadays supporting the grid’s stability. Technical restrictions and requirements are presented highlighting primarily the German Grid Code for the MV network, which is the benchmark for the analysis of the role and behaviour of the PV model in question. Germany is regarded a very good example to base the study on due to its leading position and experience in the renewable area and its thorough grid specifications. The main part of the report includes a detailed description of the structure of the generic model, presenting the operating procedure of its components as well as model assumptions and simplifications. Various simulations in variable solar irradiation, frequency and voltage conditions are performed in order to conclude in its capabilities. The static voltage support is investigated under cloud effect situation where the changes in active power output of the PV array can influence the voltage stability of the grid at the PCC. The active power control is examined by forcing the grid frequency to deviate beyond specified limits and observing the active power output results. At last, the dynamic voltage support capability (LVRT) is examined by simulating four different short circuit events creating four different voltage dips. The ability of the PV inverter to stay connected and to provide reactive current when necessary is seen. The external grid component is designed to represent a strong grid. The results showed that the model is capable for active power reduction and LVRT behaviour. However, the absence of reactive power control makes it inapplicable for static voltage support. Thus, a PI controller is implemented in order to supply constant reactive power in steady state operation and support the grid stability. At last two different interconnections were built using a slightly modified version of the same generic model with a rated power 1 MVA. The control scheme remained the same. Both configurations were examined statically and dynamically and their results were compared. Small differences were found in terms of reactive power consumption/injection at the PCC. Keywords: Grid-connected Photovoltaic, PV inverter, Grid codes for PV, PV model, DIgSILENT iv

MSc Thesis Project Sammanfatning KTH, June 2011 Sammanfatning Det här examensarbetet undersöker förmågan av en generisk nätanslutna solcell (PV) modell som utvecklades av DIgSILENT och det är en del av biblioteket av den nya versionen av PowerFactory v.14.1. Modellen har en nominell beräknat maximal effekt på 0.5 MVA och en utformad effektfaktor på cosφ=0.95. En stillastående generator beståndsdel, som innehåller PV uppställningen, DC bussen med kondensatorn, strömväxlaren och kontroll ramen, som användes för att utforma PV systemet. PV uppställningen förväntas att användas vid MPP-en och generatorn med cosφ=1. Examensarbetet inleder med en kort genomgång av det nuvarande läget av PV sektorn, som fokus för det mesta på PV system sorter och de viktiga beståndsdelarna som användas i nätanslutna system. Eftersom PV strömväxlaren är den viktigaste beståndsdelen, är särskild hänvisning görs till de olika tillämpade tekniker och den mångfacetterade roll som växelriktare bör spela nuförtiden stödja nätets stabilitet. Tekniska begränsningar och krav presenteras för att belysa främst på den tyska GC för MV nätet, vilket är utgångspunkten för analysen av den roll och beteende av PV modellen i fråga. Tyskland anses ett mycket bra exempel att basera studien på grund av sin ledande ställning och erfarenhet inom förnybar området och dess grundliga specifikationer nätet. Den huvuddelen av rapporten innehåller en detaljerad beskrivning av strukturen för den generiska modellen, som presenterar fungerande förfarandet av dess komponenter samt modellantaganden och förenklingar. Olika simuleringar i varierande solstrålning, frekvens och spänning villkor utförs i syfte att ingå i sin förmåga. Den statiska spänningen understödet undersökas under moln effekt situation där förändringar i aktiv uteffekt PV uppställningen kan påverka spänningsstabilitet i rutnätet på den PCC. Den aktiva effekten kontroll undersöks genom att tvinga nätfrekvens att avvika utöver angivna gränsvärden och observera det aktiva resultatet uteffekt. Äntligen är den dynamiska spänning stöd kapacitet (LVRT) undersöks med hjälp av simulerad fyra olika kortslutning händelser skapa fyra olika spänningsfall. Förmågan hos PV strömväxlaren att hålla kontakten och ge reaktiva strömmen vid behov ses. Det externa komponent i nätet utformats för att representera en stark rutnät. Resultaten visas att modellen har kapacitet för aktiv effekt minskning och LVRT beteende. Men gör det saknas styrning av reaktiv effekt inte tillämpas under statisk spänning stöd. Därför är en PI-regulator som genomförs för att leverera konstant reaktiv effekt i konstant drift och support för stabila nät. Äntligen två olika sammankopplingar byggdes med en något modifierad version av samma generiska modell med en nominell effekt 1 MVA. Kontrollschemat förblevs densamma. Båda konfigurationerna undersöktes statiskt och dynamiskt och resultaten jämfördes. Små skillnader fanns i form av reaktiv effekt förbrukning / insprutning i PCC. Nyckelord: Nätanslutna solcell, PV strömväxlare , Nät koder för PV, PV modell, DIgSILENT v

last friendly and highly professional environment. MSc Thesis Project Acknowledgements KTH, June 2011 five months, ensuring a Acknowledgements At first I wish to thank all the people, who, in whichever way, assisted me to complete this interesting project for my master thesis and made this period an important benchmark for my future professional expectations. From Energynautics GmbH1, Dr Thomas Ackermann, who gave me the opportunity to complete the thesis in his company, Dr Eckehard Tröster, for his patience with all my questions, his valuable advices and insight that gave direction to my work, Rena Kuwahata, who was the initial contact with the company and the person that facilitated my work and life in the new environment, Dr Nis Martensen and Stanislav Cherevatskiy, who shared their experiences in the field whenever those were asked for and in general I wish to thank all the rest of the personnel, who were part of my everyday life the Furthermore, I would like to thank Prof. Lennart Söder for the fruitful pre-presentation and his valid comments and of course Giannis Tolikas for undertaking the translation of the abstract to Swedish. Since it is likely that I forget some people that offered their helped for the completion of this project, I feel obliged to thank them as well. Special thanks should be paid to Panagiotis Giagkalos and Kyriakos Liotsios, who were my classmates, colleagues, but most of all my friends during the last two years of this master. It is important to realize that anytime you can find people that you can count on. May this friendship lasts and don’t leave time and distance to wear it, rather strengthen it through personal or professional common experiences. To Angela Maria Castaño Garcia, for this beautiful journey that still goes on. Her support during this time was more that I could ask for. As far as the thesis concerned, her contribution and effort to the final format of the report was significant. At last, to my beloved family, my parents Konstantinos and Efterpi, and my brother Charalampos, who deserve my eternal gratitude for all that have offered me. Their constant support in every aspect is scarcely reflected on these few sentences here. However, any success in my life so far is mostly charged to them and consequently any success in the future will have their signature as well. Such moments, I feel the need to give space and mention all the people that left something valuable to me. Old friends from Greece that never forget, new friends from different parts of the world, people I met for short period, all of them are the people that with one way or another made this time worth living it again. You are my personal ark. Thank you all and wish you the best. 1 http://www.energynautics.com/ vi

MSc Thesis Project Table of Contents KTH, June 2011 Table of Contents ABSTRACT........................................................................................................................ . IV SAMMANFATNING ........................................................................................................... V ACKNOWLEDGEMENTS .................................................................................................... VI TABLE OF CONTENTS ...................................................................................................... VII LIST OF FIGURES .............................................................................................................. IX LIST OF TABLES ............................................................................................................... XII NOMENCLATURE ........................................................................................................... XIII 1 INTRODUCTION ......................................................................................................... 1 1.1 THE DRIVING FORCE ....................................................................................................... 2 1.2 OVERVIEW OF THE THESIS REPORT ................................................................................ 4 1.3 OBJECTIVES .................................................................................................................... 5 1.4 LIMITATIONS .................................................................................................................. 6 2 BACKGROUND .......................................................................................................... 8 2.1.1 2.1 PV SYSTEMS – OVERVIEW .............................................................................................. 8 I-V CHARACTERISTICS ............................................................................................. 9 2.2 GRID-CONNECTED PV SYSTEMS ................................................................................... 11 2.3 PV INVERTER ................................................................................................................ 12 2.3.1 WHAT IS AVAILABLE – CURRENT STATUS ............................................................ 13 2.3.2 ISSUES WHEN CHOOSING INVERTER ................................................................... 16 2.3.3 ADDITIONAL REQUIREMENTS – ANCILLARY FUNCTIONS .................................... 18 2.4 LOW VOLTAGE RIDE THROUGH (LVRT) REQUIREMENT ............................................... 18 2.4.1 REACTIVE POWER AND ITS IMPORTANCE ........................................................... 19 2.5 GRID REQUIREMENTS FOR PV SYSTEMS ...................................................................... 19 2.5.1 THE NEW GERMAN GRID CODE ........................................................................... 20 2.5.2 THE SITUATION IN THE REST OF EUROPE ............................................................ 25 2.5.3 FURTHER INTERNATIONAL AND EUROPEAN REQUIREMENTS FOR PV ............... 25 3 METHODOLOGY ...................................................................................................... 27 3.1 DESCRIPTION OF THE TOOLS ........................................................................................ 27 3.2 WAYS FOR SIMULATING PV WITH POWERFACTORY .................................................... 27 4 MODEL DESCRIPTION .............................................................................................. 31 4.1 THE BASE MODEL ......................................................................................................... 31 4.2 THE PV GENERATOR ..................................................................................................... 33 4.2.1 THE CONTROL FRAME OF THE PV GENERATOR ................................................... 36 INVESTIGATION UNDER GERMAN GCS ......................................................................... 48 4.3.1 STEADY STATE CONDITION .................................................................................. 48 4.3 vii

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