DISS. ETH NO. 21882 Operational Flexibility in Electric Power Systems A thesis submitted to attain the degree of DOCTOR OF SCIENCES of ETH ZURICH (Dr. sc. ETH Zurich) presented by ANDREAS ULBIG Dipl.-Ing. (Technische Kybernetik), Universit¨at Stuttgart Dipl^ome de Master recherche, Sup´elec born on 16 September 1981 in Halle (Saale), Germany citizen of Germany accepted on the recommendation of Prof. Dr. G¨oran Andersson, examiner Prof. Dr. David J. Hill, co-examiner Prof. Dr. Martin Greiner, co-examiner 2014 © Andreas Ulbig, Zurich, Switzerland, 2014 ETH Zurich¨ EEH { Power Systems Laboratory Physikstrasse 3 8092 Zurich Switzerland www.eeh.ee.ethz.ch/psl DOI: 10.3929/ethz-a-010337152 Fur¨ meine Familie. Pour ma famille. For my family. Preface This doctoral thesis was written during my time as a PhD student at the Power Systems Laboratory of ETH Zurich¨ from October 2008 to March 2014. First, I would like to express my sincere gratitude to Professor G¨oran Andersson for giving me the opportunity to pursue my PhD studies at the Power Systems Laboratory. Through his support, guidance and, certainly, the granted freedom, he enabled me to follow my own ideas and interests in my research work. I appreciate his generally positive spirit and open-minded attitude towards new research ideas, collabora- tion efforts, and projects throughout the duration of my PhD studies. I would like to sincerely thank Professor David J. Hill from Hong Kong University and Professor Martin Greiner from Aarhus University, Den- mark for their kind willingness to co-examine this doctoral thesis and for the inspiring discussions that we had at various occasions before, certainly during, and finally after my PhD defense. Their long lasting passion for the power & control field, respectively the power & energy field of research is an inspiration. I would like to thank Professor Ning Lu and Dr. Yuri Makarov for hosting my at the Advanced Power & Energy Systems Group at Pacific Northwest National Laboratory (PNNL) in the spring of 2012 and for giving me the opportunity to share my experience of the European TSOs and how they cope with variable Renewable Energy Sources with a North-American TSO community. I would like to thank Professor Duncan Callaway for the opportunity to visit him and his group at University of California, Berkeley in the summer of 2012. I really appreciated the inspiring coffee discussions with him and his attitude to always aspire to push out existing research boundaries. My gratitude also goes to all the people I met in Berkeley and the fun time we spent on-campus as well as outside the campus. v vi Preface Several master students completed their semester thesis or master thesis under my supervision. I would like to acknowledge their motivation, hard work, and often enough also novel research results and insights, part of which contributed to the research presented in this thesis. There are numerous, almost countless, colleagues and friends that I worked with during my time at ETH Zurich¨ at large and at the Power Systems Laboratory in particular. Together we worked, sometimes we struggled but most often we succeeded in our endeavors { we certainly spend together an important and defining time period for all of us. I would like to thank the entire group for the nice, friendly atmosphere and the great fun we had inside and outside the ETL building. Last but not least I am deeply grateful to my family for their tremen- dous amount of support and compassion throughout these years. Andreas Ulbig Zurich, March 2014 Abstract This doctoral thesis deals with operational flexibility in power system operation and analyzes its role for mitigating operation disturbances and improving the grid integration of Renewable Energy Sources (RES). The topic of this thesis is motivated by the increasing challenges for power system operation, mainly due to rising energy shares from vari- able RES but also caused by impacts of power market liberalization, notably higher grid utilization. Operational flexibility is an important property of electric power sys- tems, especially for the transition of existing power systems, many of them based on fossil fuels, to power systems effectively accommodating high shares of variable RES. Availability of sufficient operational flexi- bility is a necessary precondition for the grid integration of large energy shares from variable RES, notably wind turbines and Photovoltaic (PV) units. The provision of operational flexibility can be enabled and im- proved by introducing more sensing, i.e. sensor elements, computation, e.g. in the form of operation optimization schemes, as well as control, i.e. actuators, into power system operation. Improving controllability & observability of power system processes will help to improve power system operation and management, i.e. allowing a more secure, efficient and stable operation. The role of operational flexibility for power sys- tem operation is discussed and analyzed from different angles, ranging from power system modeling approaches to analytic approaches inspired by well-known control theory concepts to qualitative and quantitative simulation-based assessments. A supplementary idea that is discussed is the concept of control-based grid adaptation as an alternative to conventional hardware-based grid adaptation for the operational challenges related to large-scale RES de- ployment. This allows a cost-saving trade-off between costs for compu- tation and communication versus conventional grid investment. vii viii Abstract The doctoral thesis is structured in three parts, each part addressing separate topic streams. Part I { New Challenges & Opportunities in Power Systems An overview of paradigm change in power system operation is given. Some of the important new challenges to power system operation and control, mainly related to the large-scale deployment of variable RES units but also to increasing power market activity and rising electricity demand in conjunction with only limited grid reinforcement at the same time, are illustrated. A discussion of opportunities for mitigating these operational challenges concludes this part. Part II { Modeling Frameworks for Power & Energy Systems An overview of established modeling frameworks for power & energy systems is given. Notably, the Network-Preserving Model Framework and the Energy Hub Concept are presented and the motivation for complementary modeling frameworks is discussed. The Power Nodes Modeling Framework is presented. New contributions and insights to this modeling approach conclude this part. Part III { Modeling & Analysis of Operational Flexibility A discussion of operational flexibility in power systems, necessary flexi- bility metrics and modeling approaches, both for individual units as well as for aggregations (pools) of diverse power system units introduces the topic. Then an analysis of operational flexibility in power systems is presented. First, a purely qualitative analysis of the flexibility of in- dividual power system units and small pools is conducted. Second, a more quantitative analysis of the operational flexibility of the German, Swiss and interconnected European power system is conducted. Kurzfassung Diese Dissertation befasst sich mit der Thematik der operativen Fle- xibilit¨at im Betrieb elektrischer Energiesysteme und analysiert deren Rolle fur¨ die D¨ampfung von Betriebsst¨orungen und die Verbesserung der Netzintegration von fluktuierend-einspeisenden Erneuerbaren Ener- gien (EE). Das Doktoratsthema wird mit der Zunahme an Herausfor- derungen im Stromnetzbetrieb begrundet.¨ Diese werden haupts¨achlich durch den steigenden EE-Anteil im Strommix aber auch durch die Aus- wirkungen der Liberalisierung des Stromsektors, vor allem der h¨oheren Netzauslastung, verursacht. Operative Flexibilit¨at ist eine wichtige Eigenschaft elektrischer Ener- giesysteme, insbesondere fur¨ die Transition der existierenden Energie- systeme, meist basierend auf fossilen Brennstoffen, zu Energiesystemen die hohe Anteile fluktuierender EE effektiv aufnehmen k¨onnen. Die Verfugbarkeit¨ ausreichender operativer Flexibilit¨at ist eine notwendi- ge Voraussetzung fur¨ die Netzintegration grosser Leistungsanteile von fluktuierenden EE, insbesondere von Windturbinen und Photovoltaik- Anlagen. Die Bereitstellung operativer Flexibilit¨at kann durch die Ein- fuhrung¨ von mehr Sensorik, sprich Sensorelementen, Rechenleistung, z.B. in Form betrieblicher Optimierungsmethoden, sowie Regelungs- eingriffen, durch entsprechende Aktuatoren, im Netzbetrieb erm¨oglicht und/oder verbessert werden. Eine gr¨ossere Steuerbarkeit und Beobacht- barkeit von Stromnetzprozessen wird dazu beitragen, Netzbetrieb und -management zu verbessern, damit dieses immer sicher, effizient und stabil betrieben werden kann. Die Rolle operativer Flexibilit¨at fur¨ den Netzbetrieb wird von verschiedenen Blickwinkeln aus diskutiert und analysiert. Diese reichen von Modellierungsans¨atzen fur¨ Energiesysteme zu regelungstheorie-inspirierten analytischen Ans¨atzen hin zu simulati- onsbasierten qualitativen und quantitativen Analysen. ix x Kurzfassung Eine in der Arbeit diskutierte Idee ist das Konzept einer kybernetischen, sprich regelungstechnik-basierten, Stromnetzanpassung als Alternative zur herk¨ommlichen physikalisch-basierten Stromnetzanpassung fur¨ die operativen Herausforderungen des EE-Ausbaus. Dies erlaubt einen kos- tensparenden Kompromiss zwischen den Kosten fur¨ ben¨otigte Rechen- leistung & Kommunikation und denen fur¨ konventionellen Netzausbau. Die Dissertation ist in drei Teile strukturiert,