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Proposed Improvements to the Neutral Beam Injector Power Supply System

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Proposed Improvements to the Neutral Beam Injector Power Supply System ABSTRACT PROPOSED IMPROVEMENTS TO THE NEUTRAL BEAM INJECTOR POWER SUPPLY SYSTEM by Zhen Jiang The tokamak fusion reactor is one of the most promising and well-developed designs for fusion energy production. Scientists around the world use tokamaks to research methods of generating electrical energy from the fusion reaction. Furthermore, efforts are now underway to design a new large sized tokamak, Chinese Fusion Engineering Test Reactor (CFETR), with the aim of demonstrating fusion energy as a viable source of power. As this project is just beginning, it is necessary to evaluate new and emerging technologies that can be used in this endeavor. Power electronics play a crucial role in fusion energy research and are the focus of the thesis. The High Power, Power Supplies (HPPS) transforms electrical energy from the grid into AC and DC signals with extremely high voltage and current magnitudes. For example, the Neutral Beam Injectors (NBI) require a power source that is capable of generating 110 kVDC at nearly 10 MW. This thesis evaluates two new types of technology for use in the NBI power supply; the utilization of new semiconductor switching devices and the application of new circuit topologies. The switching devices used in the existing HPPS all utilize silicon based semiconductors. Within the last ten years, new devices created from Wide Bandgap (WBG) semiconductors have become commercially available. This thesis demonstrates that gains in efficiency are possible by utilizing WBG based power devices in the NBI power supply. It also explores the application of a Modular Multilevel Converters (MMC) as a replacement to the existing topology used in the NBI power supply. It shows that the MMC can be used as both a rectifier for the NBI and an active filter for the electrical grid. The case study for this work is the NBI power supply of Experimental Advanced Superconducting Tokamak in Hefei, China. However, the findings are applicable to CFETR as well as other future designs of tokamak reactors. PROPOSED IMPROVEMENTS FOR THE NEUTRAL BEAM INJECTOR POWER SUPPLY SYSTEM Thesis Submitted to the Faculty of Miami University in partial fulfillment of the requirements for the degree of Master of science by Zhen Jiang Miami University Oxford, Ohio 2017 Adviser: Dr. Mark J. Scott Committee member: Dr. Dmitriy Garmatyuk Committee member: Dr. Donald R.Ucci © 2017 ZHEN JIANG This thesis titled THE PROPOSED IMPROVEMENT FOR NEUTRAL BEAM INJECTOR POWER SUPPLY SYSTEM by Zhen Jiang has been approved for publication by College of Engineering and Computer and Department of Electrical and Computer engineering ____________________________________________________ Dr. Mark J. Scott ____________________________________________________ Dr. Dmitriy Garmatyuk ____________________________________________________ Dr. Donald R.Ucci Table of Contents Acknowledgements ..................................................................................................................................... 1 Chapter 1: Introduction ............................................................................................................................. 1 1.1 Motivation ...................................................................................................................................... 1 1.2 Overview of Power Electronics .................................................................................................... 3 1.3 Thesis Statement .......................................................................................................................... 5 1.4 Chapter Outlines ........................................................................................................................... 6 Chapter 2 Current and Emerging Power Electronic Devices ................................................................ 8 2.1 Power Loss Analysis of Different Switching Devices ................................................................. 8 2.1.1 Diode Power Loss ............................................................................................................... 8 2.1.2 IGBT Power Loss ............................................................................................................... 9 2.1.3 MOSFET Power Loss ...................................................................................................... 11 2.2 Wide Bandgap Semiconductor .................................................................................................. 12 2.2.1 Comparison of GaN, Si, SiC ............................................................................................ 13 2.2.2 SiC Power Devices ............................................................................................................ 14 2.3 Summary of the Chapter ............................................................................................................ 15 Chapter 3: Overview of Tokamak Reactors ........................................................................................... 16 3.1 Nuclear Fusion Reactions ........................................................................................................... 16 3.2 The Tokamaks ............................................................................................................................. 17 3.2.1 The EAST Tokamak ........................................................................................................ 19 3.2.2 The CFETR Tokamak ..................................................................................................... 21 Chapter 4: NBI Power Supply ................................................................................................................. 23 4.1 Background ................................................................................................................................. 23 4.2 Power Supply System.................................................................................................................. 24 4.3 Summary of the Chapter ............................................................................................................ 26 Chapter 5: NBI Power Loss Analysis ...................................................................................................... 27 5.1 Active Rectification ..................................................................................................................... 27 5.2 PSM Physical Calculation .......................................................................................................... 29 iii 5.2.1 Rectifier Power Loss ........................................................................................................ 31 5.2.2 Power Module Power Loss .............................................................................................. 39 5.3 PSIM Simulation Results............................................................................................................ 42 5.3.1 Existing NBI PSM ............................................................................................................ 42 5.3.2 Si IGBT PSM .................................................................................................................... 44 5.3.3 SiC MOSFET PSM .......................................................................................................... 46 5.4 Summary of the Chapter ............................................................................................................ 47 Chapter 6: Improved NBI Topology based on MMC ............................................................................ 49 6.1 Voltage Source Converter Technology...................................................................................... 49 6.2 Modular Multilevel Converter ................................................................................................... 50 6.3 MMC Benefits to NBI Power Supply System ........................................................................... 53 6.3.1 Simplified Distribution System ....................................................................................... 54 6.3.2 Simplified PSM Structure ............................................................................................... 54 6.3.3 RPC and HF ..................................................................................................................... 55 6.3.4 WBG Power Devices ........................................................................................................ 60 Chapter 7 ................................................................................................................................................... 68 7.1 Conclusion ................................................................................................................................... 68 7.2 Future Work ................................................................................................................................ 69 Reference ................................................................................................................................................... 72 iv List of Tables TABLE 1.1 PARAMETER OF CHEMICAL, FISSION AND FUSION ENERGY [7] TABLE 2.1 COMPARISON OF SI , SIC, AND GAN SEMICONDUCTOR PROPERTIES [16], [18] TABLE 3.1 PARAMETERS OF DIFFERENT COILS IN EAST [5], [52] TABLE 3.2 PARAMETERS OF ITER AND CFETR POWER SUPPLY SYSTEM [4], [55] TABLE 4.1 THE PARAMETERS OF THE NBI POWER SUPPLY [5] TABLE 5.1 RATED PARAMETERS FOR
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