On the Integration of Electromagnetic Railguns with Warship Electric Power Systems
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On the integration of electromagnetic railguns with warship electric power systems Ian Whitelegg A thesis submitted for the degree of Doctor of Philosophy Department of Mechanical Engineering University College London 2016 1 Statement of originality Statement of originality I, Ian Whitelegg confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. Ian Whitelegg University College London DATE: Signed: 2 Abstract Abstract Electromagnetic railguns have reached levels of maturity whereby they are now being considered for installation on warships. A critical review of previous research in this field has highlighted the potential adverse impact that electromagnetic railguns may have on the supply quality of electric power systems. Currently, there is limited collective knowledge of this impact particularly when configured in a topology representative of a candidate warship. This research explores the impact of electromagnetic railguns on a candidate warship electric power system. This research employs a validated gas turbine alternator model of the Rolls-Royce MT30 capable of assessing performance when powering an electromagnetic railgun. A novel control circuit to interface the electromagnetic railgun with the gas turbine alternator and control the rate of fire was developed. A mathematical analysis of the system was then undertaken to understand the challenges in greater detail. A system model was then developed to explore the transient and harmonic impact of electromagnetic railgun firing on the warship electric power system using time-domain simulations. The key finding of this research is that the current practice of warship electric power system design is not robust enough to withstand electromagnetic railgun operations and that under-voltage, under-frequency, over-frequency and excessive waveform distortion result due to the high power demand of the electromagnetic railgun. To mitigate these consequences it is recommended that firing constraints be placed on the electromagnetic railgun and the maximum waveform distortion at the high voltage bus be limited to 8% total harmonic distortion. Failure to adhere to the recommended limits may result in the mal-operation, reduced efficiency and reduced life expectancy of the electric power system. 3 Dedications Dedications To my parents, who believed studying electrical engineering was a good bet. 4 Acknowledgements Acknowledgements Sophia, for three years of unwavering support throughout this most selfish act. Thank you. My primary supervisor and mentor Professor Bucknall whose guidance, patience and encouragement made the completion of this thesis a reality. Frequently challenged, too frequently perhaps, yet rarely mistaken. My secondary supervisor Professor Wrobel, for keeping the grease on the wheels, the penny pinchers at bay and for always fighting my corner throughout my time at UCL. Mark Selfridge for instilling in me levels of professionalism and self-discipline that I will continue to develop and carry with me throughout my engineering career. I could not have wished for a better start. Ben Thorp and Paul Hannawi from Rolls-Royce for answering endless questions, emails and phone calls without ever showing a moments frustration. Perhaps most importantly, for taking the risk and having the trust and belief that I would return their faith and support with something useful. Bernard Twomey from Lloyd’s Register and Konrad Yearwood from Transport for London for giving up their own time to discuss ideas, review my research and proof read this thesis. Dr Nick Bradbeer, Lucy Collins, Andrea Grech La Rosa, Dr Rachel Pawling and the guy who comes in and wanders about who isn’t a marine engineer, can’t remember his name. All have provided me a stimulating, supportive and humorous place to work over the past three years. You embody UCL. Colin Wormald, for almost always being there when I have needed him. I guess it’s time to head for the hills. My family and friends. The Big5, a philosophy in itself. 5 Contents Contents On the integration of electromagnetic railguns with warship electric power systems 1 Statement of originality 2 Abstract 3 Dedications 4 Acknowledgements 5 Contents 6 List of figures 12 List of tables 19 Nomenclature 21 Abbreviations 26 Chapter 1 Introduction 28 1.1 Motivation 28 1.2 Research aims 30 1.3 Thesis outline 31 1.4 Research contributions 32 1.5 Contributions to the literature 33 6 Contents Chapter 2 Literature review 34 2.1 Introduction 34 2.2 A review of electric warships 34 2.2.1 A historical review of electric warships 35 2.2.2 The state-of-the-art in warship electric power system technology 35 2.2.3 A review of QPS standards 43 2.3 A review of EM railguns 46 2.3.1 Potential EM railgun ESDs 48 2.3.2 Pulsed loads in parallel industries 50 2.4 A critical review of integrating EM railguns with warship power systems 51 2.5 Summary 62 Chapter 3 Problem formulation 67 3.1 Introduction 67 3.2 EM railgun system concept of operation 68 3.3 The impact of EM railgun operation on QPS 70 3.3.1 Generator AVR 71 3.3.2 Generator governor 74 3.4 Electrically integrating EM railguns with warship electric power systems 75 3.4.1 Thyristor rectifier charging control bridge characteristics 80 3.4.2 ESD capacitor load characteristics 86 3.4.3 Control relationships between warship electric power system and EM railgun 87 3.5 Electric warship QPS considerations in the context of EM railgun operation 88 3.6 Summary 89 Chapter 4 Modelling 90 7 Contents 4.1 Introduction 90 4.2 Software selection 91 4.3 Warship electric power system performance tool 91 4.3.1 Modelling purpose 91 4.3.2 Modelling requirement 92 4.3.3 Modelling assumptions and limitations 93 4.3.4 Performance tool system diagram 94 4.4 Gas turbine alternator model 95 4.4.1 Gas turbine and governor model 95 4.4.2 Synchronous alternator model 97 4.4.3 AVR model 105 4.4.4 GTA model parameter selection 106 4.4.5 GTA model limitations 108 4.5 EM railgun ESD charging circuit model 109 4.5.1 Six-pulse thyristor rectifier and pulse generator model 109 4.5.2 EM railgun ESD charging circuit controller 110 4.5.3 EM railgun ESD charging circuit model limitations 112 4.6 EM railgun ESD model 112 4.6.1 EM railgun ESD model parameter selection 113 4.6.2 EM railgun ESD model limitations 114 4.7 Electric power transmission system model 114 4.7.1 Generator and EM railgun cable model 115 4.7.2 Isolation transformer model 115 4.7.3 Electric power transmission system model limitations 116 4.8 Validation and verification 116 4.8.1 GTA model validation 117 8 Contents 4.8.2 EM railgun ESD charging circuit model verification 120 4.8.3 EM railgun ESD model verification 122 4.8.4 Electric power transmission system model verification 123 4.9 Summary 123 Chapter 5 Results 125 5.1 Introduction 125 5.2 Investigation justification 126 5.3 Single shot firing 128 5.3.1 Investigation description 129 5.3.2 Single shot firing investigation results 130 5.3.3 Single shot case study 133 5.3.4 Single shot firing results summary 137 5.4 Continuous firing 138 5.4.1 Investigation description 139 5.4.2 Continuous firing investigation results 142 5.4.3 Continuous firing case study 144 5.4.4 Exploring the limits of continuous firing 155 5.4.5 Continuous firing results summary 159 5.5 Summary 160 Chapter 6 Discussion 162 6.1 Introduction 162 6.2 Transient impact 163 6.2.1 Results 163 6.2.2 Consequences 167 9 Contents 6.2.3 Mitigations 169 6.3 Harmonic impact 171 6.3.1 Harmonic analysis 172 6.3.2 Harmonic impact on current carrying conductors 174 6.3.3 Harmonic impact on machines comprising iron cores 176 6.3.4 Harmonic impact on power cables 177 6.3.5 Harmonic impact summary 178 6.3.6 Results 178 6.3.7 Consequences 186 6.3.8 Mitigations 194 6.4 Harmonic filter design process 200 6.4.1 Ascertain harmonics to be targeted 200 6.4.2 Determine the reactive power requirement of the harmonic source 202 6.4.3 Define required filter bandwidth 203 6.4.4 Calculate filter component values 204 6.4.5 Harmonic filter design response and summary 205 6.5 Power system performance with the 5th harmonic attenuated 206 6.5.1 Harmonic filter connection to the main bus 207 6.5.2 Harmonic filter response examination 208 6.5.3 Impact of attenuating the 5th harmonic during EM railgun operations on power system performance 210 6.5.4 Attenuating the 5th harmonic in the context of the generator capability diagram 216 6.5.5 Summary 218 6.6 Concluding arguments and system solution recommendation 219 6.6.1 Concluding arguments 220 6.6.2 System solution recommendation 222 10 Contents Chapter 7 Conclusions and further work 223 7.1 Introduction 223 7.2 Summary of the research findings 224 7.3 Recommendations for the naval design authority 226 7.4 Recommendations for further work 227 7.4.1 Modification of GTA load shed logic 227 7.4.2 Mechanical and thermal impact on the GTA during EM railgun firing 227 7.4.3 Further develop ESD charging bridge controller 228 7.4.4 Explore alternative power converters to charge the EM railgun ESD 228 References 230 Appendix A Six-pulse thyristor rectifier waveforms 241 Appendix B Software selection 244 Appendix C Simulink model schematics 245 Appendix D Synchronous alternator model equations 251 Appendix E GT and load model validation confirmation letter from Rolls-Royce 252 Appendix F Synchronous alternator data sheet 254 Appendix G Cable model parameter calculations 259 Appendix H GTA model validation 261 Appendix I Performance tool user guide 266 Appendix