Frequency Based Cellular Microgrid Control Demand Side Management and Supply Side Management Using Grid Frequency in a Cellular Microgrid
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Frequency Based Cellular Microgrid Control Demand Side Management and Supply Side Management using Grid Frequency in a Cellular Microgrid Thijs Vral Technische Universiteit Delft F REQUENCY B ASED C ELLULAR M ICROGRID C ONTROL D EMAND S IDE M ANAGEMENTAND S UPPLY S IDE M ANAGEMENTUSING G RID F REQUENCYINA C ELLULAR M ICROGRID by Thijs Vral in partial fulfilment of the requirements for the degree of Master of Science in Sustainable Energy Technology Electrical Sustainable Energy at the Delft University of Technology, to be defended publicly on Monday September 19, 2016 at 14:00. Student number: 4414578 Supervisor: Prof.dr.eng. P.Bauer Thesis committee: Dr.ir. L.M. Ramirez Elizondo Dr.ir. J.L. Rueda Torres Thesis committee guests: Ir. E. Raaijen, Alfen BV Ir. R. van Wesenbeeck, Alfen BV An electronic version of this thesis is available at http://repository.tudelft.nl/. A BSTRACT In the world as we know it, huge transitions are ongoing. By now, everyone has heard the words Global Warming and seen news articles and documentaries about the dangers of climate change. Multiple approaches have been described to tackle these problems, of which one is switching to a fully renewable energy supply. This means switching to a situation where the energy resources will be of a decentralized kind. More importantly, the energy resources of tomorrow will not be as controllable as they are today. Establishing this transaction is not an easy job, turning towards distributed renewable energy sources as main energy supplier brings along a lot of new challenges. The introduction of cellular microgrids can offer tools to facilitate this. On top of that, it can offer benefits in terms of increasing the electrification rate in currently non-electrified regions. These cellular microgrids exist of islanded systems: small cells with respective loads, energy suppliers and buffers, that can be interconnected in order to support each other. One drawback of current solutions is that they rely on dedicated communication equipment, in order to reach the required operations. Introducing the necessity of communication tools has a negative impact on the system costs, complexity and reliability. For this, a proposal for the concept of a microgrid was made, enabling the microgrid to have a modular structure, thus to work satisfactorily both when working independently and when interconnected with other cells. On top of that, the grid is flexible both in terms of types of end-users and energy resources, and it grants a means of demand and supply side management. This ensures that a microgrid powered by uncontrollable renewable resources operates in a stable and satisfactory way on the longer term. This is fulfilled while omitting the need for dedicated communication equipment. In order to allow an exchange of information between actors, local grid parameters are used: the grid voltage and frequency. To achieve this, droop speed control is applied, though its static nature is adapted in order to make it represent the actual state of the microgrid. This way, a modular grid is established, to which different actors contribute according to their capabilities and setpoints. After designing the control strategy, first and foremost its stability is tested and improved. Subsequently, the controller is implemented and tested using advanced simulation software. The results show that the proposed strategy is effectively able to fulfil the requirements: it is possible to interface multiple inverter-based microgrids, without the need of adding dedicated communication equipment, and give the microgrids the decision over power sharing, load shedding and renewable energy curtailment, depending on their state of energy and power. Keywords: Cellular Microgrid, Islanding, Demand Side Management, Supply Side Management, Battery Storage, Distributed Renewable Energy Sources, Droop Control iii A CKNOWLEDGEMENTS After about nine months of work, I can honestly say that I am delighted that I am writing these words. The graduation project is finished, and very soon I should be an engineer from TU Delft. Of course, I was not alone during this process, therefore I would like to use this page to thank some people. I would like to thank my supervisors from TU Delft, Pavol Bauer and Laura Ramirez, for introducing me to the CSGriP project, and subsequently guiding me throughout the thesis and the graduation process. My daily supervisor, Seyedmahdi Izadkhast, has proven to be a very helpful person throughout the thesis. I remind the hours of discussions in his office, trying to find solutions to the ever arising problems. The work would have been less complete if not for Mahdi. Furthermore, I want to thank Jose Rueda Torres for his willingness to complete the thesis committee. Two important people that come to my mind are Evert Raaijen and René van Wesenbeeck, my supervisors from the company Alfen. It was Evert who took the time to have a discussion with me, almost one and a half year ago, and offered me an internship in Alfen. After successfully finishing this, the graduation project was offered as well. I would like to thank Evert and René for the interesting discussions we had during the time I was in Alfen, for their insights and steering whenever needed. Furthermore, I definitely cannot forget Jeyakrishna Sridhar; my dear friend JK. Thank you for making me familiar with the project, answering all my small questions, for guiding me around Alfen, and for the interesting discussions we had in the office and on the bike. Finally, I want to thank the rest of the team from Alfen, for the many nice moments during the days I was there. A special word can be placed for my colleague and friend Nikos Bilidis, with whom I cooperated intensively throughout the thesis process, given the common ground of our projects. Throughout the year, by means of long discussions that sometimes took us really far, I learned a lot from the collaboration. Also other students and friends, to mention Antía, Ivan and Behzad, helped me a lot throughout the process, not only on scientific grounds, but also in offering me a listening ear whenever needed. Building further on this, I would like to finalize this letter with expressing my greatest gratitude to my family, and all my friends from Delft and Belgium, for the nice times and for the never-ceasing support. Thijs Vral Delft, September 2016 v C ONTENTS List of Figures xi List of Tables xv 1 An Introduction to the Project1 1.1 Motivation and Existing Problems................................1 1.2 Research Goals..........................................3 1.2.1 Research Questions....................................4 1.3 Methodology...........................................4 1.4 Contributions of the Thesis....................................5 1.5 Alfen BV..............................................5 1.6 Organization of the Document..................................6 2 Background Review on Cellular Microgrids7 2.1 Scientific Literature: A Review..................................7 2.1.1 Introduction........................................7 2.1.2 Microgrids in the Smart Grid Concept...........................8 2.1.3 Power Electronics..................................... 10 2.1.4 Prospection of the Controller............................... 13 2.1.5P/ f and Q/V Droop Schemes............................... 15 2.1.6 Power Quality....................................... 25 2.1.7 Distributed Energy Resources............................... 25 2.1.8 Demand Side Management................................ 29 2.1.9 Supply Side Management................................. 36 2.1.10 Energy Storage....................................... 38 2.1.11 Gaps in the Literature................................... 40 2.2 A Short History of SOPRA and CSGriP............................... 41 2.2.1 Introductory........................................ 41 2.2.2 Main Requirements.................................... 42 2.2.3 Application Goal...................................... 44 2.2.4 Expected Outcome CSGriP Project............................. 48 2.2.5 Preceding Work Controller................................. 49 2.2.6 Gaps in the Preceding Work................................ 50 2.3 Summary of the Chapter..................................... 50 3 A Stroll Through the Controller 53 3.1 Introduction........................................... 53 3.2 Grid Forming Controller..................................... 54 3.2.1 Modelling......................................... 54 3.2.2 Storage System....................................... 57 3.2.3 Overall Controller..................................... 58 3.2.4 Frequency Controller................................... 59 3.2.5 Voltage Controller..................................... 67 3.3 Energy Consumers........................................ 68 3.3.1 Load Modelling...................................... 68 3.3.2 Load Shedding....................................... 69 vii viii C ONTENTS 3.4 Distributed Renewable Energy Sources.............................. 70 3.4.1 DRES Modelling...................................... 70 3.4.2 DRES Curtailing...................................... 71 3.5 Summary of the Chapter..................................... 71 4 Stability of the System 73 4.1 Small-signal Stability....................................... 73 4.1.1 Small Signal Model..................................... 74 4.1.2 Eigenvalue Analysis.................................... 76 4.1.3 Discussion and Reservations................................ 77 4.2 Steady-state Stability......................................