High Voltage Direct Current Transmission: Converters, Systems and DC Grids

This comprehensive reference guides the reader through all HVDC technologies, including LCC (Line Commutated Converter), 2-level VSC and VSC HVDC based on modular multilevel converters (MMC) for an in-depth understanding of converters, system level design, operating principles and modeling. Written in a tutorial style, the book also describes the key principles of design, control, protection and operation of DC transmission grids, which will be substantially different from the practice with AC transmission grids. The first dedicated reference to the latest HVDC technologies and DC grid developments; this is an essential resource for graduate students and researchers as well as engineers and professionals working on the design, modeling and operation of DC grids and HVDC. Key features: * Provides comprehensive coverage of LCC, VSC and (half and full bridge) MMC-based VSC technologies and DC transmission grids. * Presents phasor and dynamic analytical models for each HVDC technology and DC grids. * Includes HVDC protection, studies of DC and AC faults, as well as system-level studies of AC-DC interactions and impact on AC grids for each HVDC technology. * Companion website hosts SIMULINK SimPowerSystems models with examples for all HVDC topologies. Professor Dragan Jovcic, University of Aberdeen, Scotland, UK Professor Jovcic has been with the University of Aberdeen since 2004. Between 2000 and 2004 he worked as a Lecturer with the University of Ulster. He was a Design Engineer in the New Zealand power industry between 1999 and 2000, and a visiting professor on a 6-months appointment at McGill University, Canada in 2008. His research career has focused on HVDC, FACTS and DC grids. Professor Jovcic has published around 80 articles related to HVDC and power electronics applications, to transmission systems. He has supervised numerous externally funded research projects with the total budget of over 2.5million. He has thirteen years of university teaching experience in the subjects of electrical engineering and control in UK. Professor Jovcic is Senior member of IEEE and a CIGRE member; he is also a member of three CIGRE working groups. Dr Khaled Ahmed, University of Aberdeen, Scotland, UK Dr Ahmed has been working in the renewable energy field for more than eight years. He has been a researcher on two main projects sponsored by the EPSRC research council. He is a senior member of the IEEE industrial electronics society and has published over 53 technical papers in refereed journals and conferences related to renewable energy applications, modular multilevel converter based applications, and HVDC systems. Dr Ahmed has eleven years of university teaching experience in the subjects of electrical engineering, power electronics and control in Egypt and the UK. Recently, he was part of a 2-lecturer team who designed and delivered a continuing professional development (CPD) course on HVDC for the SSE HVDC technology engineering team (SSE is a leading electricity and gas company, operating mainly in the UK and Ireland). Contents Preface xi Part I HVDC with Current Source Converters 1 1 Introduction to Line-Commutated HVDC 3 1.1 HVDC Applications 3 1.2 Line-Commutated HVDC Components 5 1.3 DC Cables and Overhead Lines 6 1.4 LCC HVDC Topologies 7 1.5 Losses in LCC HVDC Systems 9 1.6 Conversion of AC Lines to DC 10 1.7 Ultra-High Voltage HVDC 10 2 Thyristors 12 2.1 Operating Characteristics 12 2.2 Switching Characteristic 13 2.3 Losses in HVDC Thyristors 17 2.4 Valve Structure and Thyristor Snubbers 20 2.5 Thyristor Rating Selection and Overload Capability 22 3 Six-Pulse Diode and Thyristor Converter 23 3.1 Three-Phase Uncontrolled Bridge 23 3.2 Three-Phase Thyristor Rectifier 25 3.3 Analysis of Commutation Overlap in a Thyristor Converter 26 3.4 Active and Reactive Power in a Three-Phase Thyristor Converter 30 3.5 Inverter Operation 31 4 HVDC Rectifier Station Modelling, Control and Synchronization with AC Systems 35 4.1 HVDC Rectifier Controller 35 4.2 Phase-Locked Loop (PLL) 36 5 HVDC Inverter Station Modelling and Control 40 5.1 Inverter Controller 40 5.2 Commutation Failure 42 6 HVDC System V-I Diagrams and Operating Modes 45 6.1 HVDC-Equivalent Circuit 45 6.2 HVDC V-I Operating Diagram 45 6.3 HVDC Power Reversal 48 7 HVDC Analytical Modelling and Stability 53 7.1 Introduction to Converters and HVDC Modelling 53 7.2 HVDC Analytical Model 54 7.3 CIGRE HVDC Benchmark Model 56 7.4 Converter Modelling, Linearization and Gain Scheduling 56 7.5 AC System Modelling for HVDC Stability Studies 58 7.6 LCC Converter Transformer Model 62 7.7 DC System Model 63 7.8 HVDC-HVAC System Model 65 7.9 Analytical Dynamic Model Verification 65 7.10 Basic HVDC Dynamic Analysis 66 7.11 HVDC Second Harmonic Instability 70 7.12 Oscillations of 100 Hz on the DC Side 71 8 HVDC Phasor Modelling and Interactions with AC System 72 8.1 Converter and DC System Phasor Model 72 8.2 Phasor AC System Model and Interaction with the DC System 73 8.3 Inverter AC Voltage and Power Profile as DC Current is Increasing 75 8.4 Influence of Converter Extinction Angle 76 8.5 Influence of Shunt Reactive Power Compensation 78 8.6 Influence of Load at the Converter Terminals 78 8.7 Influence of Operating Mode (DC Voltage Control Mode) 78 8.8 Rectifier Operating Mode 80 9 HVDC Operation with Weak AC Systems 82 9.1 Introduction 82 9.2 Short-Circuit Ratio and Equivalent Short-Circuit Ratio 82 9.3 Power Transfer between Two AC Systems 85 9.4 Phasor Study of Converter Interactions with Weak AC Systems 89 9.5 System Dynamics (Small Signal Stability) with Low SCR 90 9.6 Control and Main Circuit Solutions for Weak AC Grids 90 9.7 LCC HVDC with SVC (Static VAR Compensator) 91 9.8 Capacitor-Commutated Converters for HVDC 93 9.9 AC System with Low Inertia 93 10 Fault Management and HVDC System Protection 98 10.1 Introduction 98 10.2 DC Line Faults 98 10.3 AC System Faults 101 10.4 System Reconfiguration for Permanent DC Faults 103 10.5 Overvoltage Protection 106 11 LCC HVDC System Harmonics 107 11.1 Harmonic Performance Criteria 107 11.2 Harmonic Limits 108 11.3 Thyristor Converter Harmonics 109 11.4 Harmonic Filters 110 11.5 Noncharacteristic Harmonic Reduction Using HVDC Controls 118 Bibliography Part I Line Commutated Converter HVDC 119 Part II HVDC with Voltage Source Converters 121 12 VSC HVDC Applications and Topologies, Performance and Cost Comparison with LCC HVDC 123 12.1 Voltage Source Converters (VSC) 123 12.2 Comparison with Line-Commutated Converter (LCC) HVDC 125 12.3 Overhead and Subsea/Underground VSC HVDC Transmission 126 12.4 DC Cable Types with VSC HVDC 129 12.5 Monopolar and Bipolar VSC HVDC Systems 129 12.6 VSC HVDC Converter Topologies 130 12.7 VSC HVDC Station Components 135 12.8 AC Reactors 139 12.9 DC Reactors 139 13 IGBT Switches and VSC Converter Losses 141 13.1 Introduction to IGBT and IGCT 141 13.2 General VSC Converter Switch Requirements 142 13.3 IGBT Technology 142 13.4 Development of High Power IGBT Devices 147 13.5 IEGT Technology 148 13.6 Losses Calculation 148 13.7 Balancing Challenges in Series IGBT Chains 154 13.8 Snubbers Circuits 155 14 Single-Phase and Three-Phase Two-Level VSC Converters 156 14.1 Introduction 156 14.2 Single-Phase Voltage Source Converter 156 14.3 Three-Phase Voltage Source Converter 159 14.4 Square-Wave, Six-Pulse Operation 159 15 Two-Level PWM VSC Converters 167 15.1 Introduction 167 15.2 PWM Modulation 167 15.3 Sinusoidal Pulse-Width Modulation (SPWM) 168 15.4 Third Harmonic Injection (THI) 171 15.5 Selective Harmonic Elimination Modulation (SHE) 172 15.6 Converter Losses for Two-Level SPWM VSC 173 15.7 Harmonics with Pulse-Width Modulation (PWM) 175 15.8 Comparison of PWM Modulation Techniques 178 16 Multilevel VSC Converters 180 16.1 Introduction 180 16.2 Modulation Techniques for Multilevel Converters 182 16.3 Neutral Point Clamped Multilevel Converter 183 16.4 Flying Capacitor Multilevel Converter 185 16.5 H-Bridge Cascaded Converter 186 16.6 Half Bridge Modular Multilevel Converter (MMC) 187 16.7 MMC Based on Full Bridge Topology 200 16.8 Comparison of Multilevel Topologies 208 17 Two-Level PWM VSC HVDC Modelling, Control and Dynamics 209 17.1 PWM Two-Level Converter Average Model 209 17.2 Two-Level PWM Converter Model in DQ Frame 210 17.3 VSC Converter Transformer Model 212 17.4 Two-Level VSC Converter and AC Grid Model in ABC Frame 213 17.5 Two-Level VSC Converter and AC Grid Model in DQ Rotating Coordinate Frame 213 17.6 VSC Converter Control Principles 214 17.7 The Inner Current Controller Design 215 17.8 Outer Controller Design 218 17.9 Complete VSC Converter Controller 221 17.10 Small-Signal Linearized VSC HVDC Model 224 17.11 Small-Signal Dynamic Studies 224 18 Two-Level VSC HVDC Phasor-Domain Interaction with AC Systems and PQ Operating Diagrams 226 18.1 Power Exchange between Two AC Voltage Sources 226 18.2 Converter Phasor Model and Power Exchange with an AC System 230 18.3 Phasor Study of VSC Converter Interaction with AC System 232 18.4 Operating Limits 234 18.5 Design Point Selection 236 18.6 Influence of AC System Strength 239 18.7 Influence of Transformer Reactance 243 18.8 Operation with Very Weak AC Systems 247 19 Half Bridge MMC Converter: Modelling, Control and Operating PQ Diagrams 254 19.1 Half Bridge MMC Converter Average Model in ABC Frame 254 19.2 Half-Bridge MMC Converter-Static DQ Frame and Phasor Model 257 19.3 Differential Current at Second Harmonic 262 19.4 Complete MMC Converter DQ Model in Matrix Form 263 19.5 Second Harmonic Circulating Current Suppression Controller 264 19.6 DQ Frame Model of MMC with Circulating Current Controller 267 19.7 Phasor Model of MMC with Circulating Current Suppression Controller 269 19.8 Dynamic MMC Model Using Equivalent Series Capacitor CMMC 270 19.9 Full Dynamic Analytical MMC Model 273 19.10 MMC Converter Controller 275 19.11 MMC Total Series Reactance in the Phasor Model 275 19.12 MMC VSC Interaction with AC System and PQ Operating Diagrams 277 20 VSC HVDC under AC and DC Fault Conditions 280 20.1 Introduction 280 20.2 Faults on the AC System 280 20.3 DC Faults with Two-Level VSC 281 20.4 Influence of DC Capacitors 286 20.5 VSC Converter Modelling under DC Faults and VSC Diode Bridge 287 20.6 Converter-Mode Transitions as DC Voltage Reduces 294 20.7 DC Faults with Half-Bridge Modular Multilevel Converter 294 20.8 DC Faults with Full-Bridge Modular Multilevel Converter 298 21 VSC HVDC Application for AC Grid Support and Operation with Passive AC Systems 302 21.1 VSC HVDC High-Level Controls and AC Grid Support 302 21.2 HVDC Embedded inside an AC Grid 303 21.3 HVDC Connecting Two Separate AC Grids 304 21.4 HVDC in Parallel with AC 304 21.5 Operation with a Passive AC System and Black Start Capability 305 21.6 VSC HVDC Operation with Offshore Wind Farms 305 21.7 VSC HVDC Supplying Power Offshore and Driving a MW-Size Variable-Speed Motor 307 Bibliography Part II Voltage Source Converter HVDC 309 Part III DC Transmission Grids 311 22 Introduction to DC Grids 313 22.1 DC versus AC Transmission 313 22.2 Terminology 314 22.3 DC Grid Planning, Topology and Power-Transfer Security 314 22.4 Technical Challenges 315 22.5 DC Grid Building by Multiple Manufacturers 316 22.6 Economic Aspects 316 23 DC Grids with Line-Commutated Converters 317 23.1 Multiterminal HVDC 317 23.2 Italy-Corsica-Sardinia Multiterminal HVDC Link 318 23.3 Connecting LCC Converter to a DC Grid 319 23.4 Control of LCC Converters in DC Grids 321 23.5 Control of LCC DC Grids through DC Voltage Droop Feedback 321 23.6 Managing LCC DC Grid Faults 323 23.7 Reactive Power Issues 325 23.8 Large LCC Rectifier Stations in DC Grids 325 24 DC Grids with Voltage Source Converters and Power-Flow Model 326 24.1 Connecting a VSC Converter to a DC Grid 326 24.2 DC Grid Power Flow Model 327 24.3 DC Grid Power Flow under DC Faults 331 25 DC Grid Control 334 25.1 Introduction 334 25.2 Fast Local VSC Converter Control in DC Grids 334 25.3 DC Grid Dispatcher with Remote Communication 336 25.4 Primary, Secondary and Tertiary DC Grid Control 337 25.5 DC Voltage Droop Control for VSC Converters in DC Grids 338 25.6 Three-Level Control for VSC Converters with Dispatcher Droop 339 25.7 Power Flow Algorithm When DC Powers are Regulated 340 25.8 Power Flow and Control Study of CIGRE DC Grid-Test System 344 26 DC Grid Fault Management and DC Circuit Breakers 349 26.1 Introduction 349 26.2 Fault Current Components in DC Grids 350 26.3 DC System Protection Coordination with AC System Protection 352 26.4 Mechanical DC Circuit Breaker 352 26.5 Semiconductor Based DC Circuit Breaker 355 26.6 Hybrid DC Circuit Breaker 359 26.7 DC Grid-Protection System Development 361 26.8 DC Grid Selective Protection System Based on Current Derivative or Travelling Wave Identification 362 26.9 Differential DC Grid Protection Strategy 363 26.10 DC Grid Selective Protection System Based on Local Signals 364 26.11 DC Grids with DC Fault-Tolerant VSC Converters 365 27 High Power DC/DC Converters and DC Power-Flow Controlling Devices 372 27.1 Introduction 372 27.2 Power Flow Control Using Series Resistors 373 27.3 Low Stepping-Ratio DC/DC Converters 376 27.4 High Stepping Ratio Isolated DC/DC Converter 383 27.5 High Stepping Ratio LCL DC/DC Converter 383 27.6 Building DC Grids with DC/DC Converters 385 27.7 DC Hubs 387 27.8 Developing DC Grids Using DC Hubs 390 27.9 North Sea DC Grid Topologies 390 Bibliography Part III DC Transmission Grids 394 Appendix A Variable Notations 396 Appendix B Analytical Background for Rotating DQ Frame 398 Appendix C System Modelling Using Complex Numbers and Phasors 409 Appendix D Simulink Examples 411 Index 000