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

Content: Part I HVDC with Current Source Converters 10 1 Introduction to Line Commutated HVDC 11 1.1 HVDC Applications 11 1.2 Line Commutated HVDC Components 12 1.3 DC Cables and Overhead Lines 13 1.4 LCC HVDC Topologies 14 1.5 Losses in LCC HVDC Systems 15 1.6 Conversion of AC Lines to DC 16 1.7 Ultra High Voltage HVDC 17 2 Thyristors 18 2.1 Operating Characteristics 18 2.2 Switching Characteristic 19 2.3 Losses in an HVDC Thyristors 21 2.4 Valve Structure and Thyristor Snubbers 24 2.5 Thyristor Rating Selection and Overload Capability 26 3 6-Pulse Diode and Thyristor Converter 27 3.1 3-Phase Uncontrolled Bridge 27 3.2 3-Phase Thyristor Rectifier 29 3.3 Analysis of Commutation Overlap in a Thyristor Converter 30 3.4 Active and Reactive Power in a 3-Phase Thyristor Converter 33 3.5 Inverter Operation 34 4 HVDC Rectifier Station Modelling, Control and Synchronisation with AC System 37 4.1 HVDC Rectifier Controller 37 4.2 Phase Locked Loop (PLL) 38 4.3 Master Level HVDC Control 40 5 HVDC Inverter Station Modelling and Control 41 5.1 Inverter Controller 41 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 47 7 HVDC Analytical Modelling and Stability 52 7.1 Introduction to Converter and HVDC Modelling 52 7.2 HVDC Analytical Model 53 7.3 CIGRE HVDC Benchmark Model 53 7.4 Converter Modelling, Linearisation and Gain Scheduling 54 7.5 AC System Modelling For HVDC Stability Studies 55 7.6 LCC Converter Transformer Model 57 7.7 DC System Including DC Cable 58 7.8 Accurate DC Cable Modelling 60 7.9 HVDC-HVAC System Model 66 7.10 Analytical Dynamic Model Verification 66 7.11 Basic HVDC Dynamic Analysis 67 7.12 HVDC Second Harmonic Instability 68 7.13 100Hz Oscillations on DC Side 70 8 HVDC Phasor Modelling and Interactions with AC System 71 8.1 Converter and DC System Phasor Model 71 8.2 Phasor AC System Model and Interaction with DC System 71 8.3 Inverter AC Voltage and Power Profile As DC Current Is Increasing 73 8.4 Influence of Converter Extinction Angle 74 8.5 Influence of Shunt Reactive Power Compensation 74 8.6 Influence of Load At the Converter Terminals 75 8.7 Influence of Operating Mode (DC Voltage Control Mode) 75 8.8 Rectifier Operating Mode 77 9 HVDC Operation with Weak AC Systems 79 9.1 Introduction 79 9.2 Short Circuit Ratio and Equivalent Short Circuit Ratio 79 9.3 Background on Power Transfer Between Two AC Systems 82 9.4 Phasor Study of Converter Interactions with Weak AC Systems 83 9.5 System Dynamics (Small Signal Stability) with Low SCR 84 9.6 Control and Main Circuit Solutions for Weak AC Grids 85 9.7 LCC HVDC with SVC (Static Var Compensator) 85 9.8 Capacitor Commutated Converters for HVDC 88 9.9 AC System with Low Inertia 89 10 Fault Management and HVDC System Protection 91 10.1 Introduction 91 10.2 DC Line Faults 91 10.3 AC System Faults 93 10.4 Internal Faults 95 10.5 System Reconfiguration for Permanent Faults 96 10.6 Overvoltage Protection 97 11 LCC HVDC System Harmonics 99 11.1 Harmonic Performance Criteria 99 11.2 Harmonic Limits 99 11.3 Thyristor Converter Harmonics 100 11.4 Harmonic Filters 101 11.5 Non-Characteristic Harmonic Reduction Using HVDC Controls 108 Bibliography Part I Line Commutated Converter HVDC 109 Part II HVDC with Voltage Source Converters 111 12 VSC HVDC Applications and Topologies, Performance and Cost Comparison with LCC HVDC 112 12.1 Application of Voltage Source Converters (VSC) in HVDC 112 12.2 Comparison with Line Commutated Converter (LCC) HVDC 113 12.3 HVDC Technology Landscape 114 12.4 Overhead and Subsea/Underground VSC HVDC Transmission 116 12.5 DC Cable Types with VSC HVDC 116 12.6 Monopolar and Bipolar VSC HVDC Systems 117 12.7 VSC HVDC Converter Topologies 117 12.8 VSC HVDC Station Components 122 12.9 AC Inductors 127 12.10 DC Inductors 127 13 IGBT Switches and VSC Converter Losses 129 13.1 Introduction to IGBT and IGCT 129 13.2 General VSC Converter Switch Requirements 129 13.3 IGBT Technology 129 13.4 High Power IGBT Devices 134 13.5 IEGT Technology 134 13.6 Losses Calculation 135 13.7 Balancing Challenges in 2-Level IGBT Valves 139 13.8 Snubbers Circuits 139 14 Single Phase and 3-Phase 2-Level VSC Converters 141 14.1 Introduction 141 14.2 Single Phase Voltage Source Converter 141 14.3 Three Phase Voltage Source Converter 143 14.4 Square Wave, Six Pulse Operation 143 15 2-Level PWM VSC Converters 150 15.1 Introduction 150 15.2 PWM Modulation 150 15.3 Sinusoidal Pulse Width Modulation (SPWM) 151 15.4 Third Harmonic Injection (THI) 153 15.5 Selective Harmonic Elimination Modulation (SHE) 154 15.6 Converter Losses for Two-Level SPWM VSC 154 15.7 Harmonics with Pulse Width Modulation (PWM) 156 15.8 Comparison of PWM Modulation Techniques 158 16 Multilevel VSC Converters in HVDC Applications 160 16.1 Introduction 160 16.2 Modulation Techniques for Multilevel Converters 161 16.3 Neutral Point Clamped Multilevel Converter 162 16.4 Half Bridge Modular Multilevel Converter (HB MMC) 163 16.5 Full Bridge Modular Multilevel Converter (FB MMC) 173 16.6 Comparison of Multilevel Topologies 176 17 2-Level VSC HVDC Modelling, Control and Dynamics 177 17.1 PWM 2-Level Converter Average Model 177 17.2 2-Level PWM Converter Model in DQ Frame 179 17.3 VSC Converter Transformer Model 180 17.4 2-Level VSC Converter and AC Grid Model in ABC Frame 180 17.5 2-Level VSC Converter and AC Grid Model in DQ Rotating Coordinate Frame 181 17.6 VSC Converter Control Principles 182 17.7 The Inner Current Controller Design 182 17.8 Outer Controller Design 185 17.9 Complete 2-Level VSC Converter Controller 188 17.10 Small Signal Linearised VSC HVDC Model 188 17.11 Small Signal Dynamic Studies 191 18 2-Level VSC HVDC Phasor-Domain Interaction with AC Systems and PQ Operating Diagrams 193 18.1 Power Exchange Between Two AC Voltage Sources 193 18.2 Converter Phasor Model and Power Exchange with AC System 195 18.3 Phasor Study of VSC Converter Interaction with AC System 197 18.4 Operating Limits 199 18.5 Design Point Selection 200 18.6 Influence of AC System Strength 201 18.7 Influence of AC System Impedance Angle (Xs/Rs) 201 18.8 Influence of Transformer Reactance 202 18.9 Influence of Converter Control Modes 202 18.10 Operation with Very Weak AC Systems 203 19 Half Bridge MMC: Dimensioning, Modelling, Control and Interaction with AC System 210 19.1 Basic Equations and Steady-State Control 210 19.2 Steady-State Dimensioning 214 19.3 Half Bridge MMC Non-Linear Average Dynamic Model 215 19.4 Nonlinear Average Value Model Including Blocked State 217 19.5 HB MMC HVDC Start-Up and Charging MMC Cells 218 19.6 HB MMC Dynamic DQ Frame Model and Phasor Model 219 19.7 Second Harmonic of Differential Current 224 19.8 Complete MMC Converter DQ Model in Matrix Form 225 19.9 Second Harmonic Circulating Current Suppression Controller 226 19.10 Simplified DQ Frame Model with Circulating Current Controller 229 19.11 Phasor Model of MMC with Circulating Current Suppression Controller 232 19.12 Simplified Dynamic MMC Model Using Equivalent Series Capacitor CMMC 233 19.13 Full Dynamic Analytical HB MMC Model 235 19.14 HB MMC Controller and Arm Voltage Control 237 19.15 MMC Total Series Reactance and Comparison with 2-Level VSC 238 19.16 MMC Interaction with AC System and PQ Operating Diagrams 240 20 Full Bridge MMC Converter: Dimensioning, Modelling and Control 242 20.1 FB MMC Arm Voltage Range 242 20.2 Full Bridge MMC Converter Non-Linear Average Model 242 20.3 FB MMC Nonlinear Average Model Including Blocked State 243 20.4 Full Bridge MMC Cell Charging 244 20.5 Hybrid MMC Design 245 20.6 Full-Bridge MMC DC Voltage Variation Using a Detailed Model 250 20.7 FB MMC Analytical Dynamic DQ Model 251 20.8 Simplified FB MMC Model 253 20.9 FB MMC Converter Controller 253 21 MMC Converter Under Unbalanced Conditions 256 21.1 Introduction 256 21.2 MMC Balancing Controller Structure 256 21.3 Balancing Between Phases (Horizontal Balancing) 257 21.4 Balancing Between Arms (Vertical Balancing) 258 21.5 Simulation of Balancing Controls 259 21.6 Operation with Unbalanced AC Grid 263 22 VSC HVDC Under AC and DC Fault Conditions 266 22.1 Introduction 266 22.2 Faults on the AC System 266 22.3 DC Faults with 2-Level VSC 267 22.4 Influence of DC Capacitors 270 22.5 VSC Converter Modelling Under DC Faults and VSC Diode Bridge 271 22.6 VSC Converter Mode Transitions As DC Voltage Reduces 277 22.7 DC Faults with Half-Bridge Modular Multilevel Converter 278 22.8 Full Bridge MMC Under DC Faults 280 23 VSC HVDC Application for AC Grid Support and Operation with Passive AC Systems 284 23.1 VSC HVDC High Level Controls and AC Grid Support 284 23.2 HVDC Embedded Inside an AC Grid 285 23.3 HVDC Connecting Two Separate AC Grid 285 23.4 HVDC in Parallel with AC 286 23.5 Operation with a Passive AC System and Black Start Capability 286 23.6 VSC HVDC Operation with Offshore Wind Farms 287 23.7 VSC HVDC Supplying Power Offshore and Driving a MW Size Variable Speed Motor 288 Bibliography Part II Voltage Source Converter HVDC 290 Part III DC Transmission Grids 292 24 Introduction to DC Grids 293 24.1 DC Versus AC Transmission 293 24.2 Terminology 293 24.3 DC Grid Planning, Topology and Power Transfer Security 294 24.4 Technical Challenges 294 24.5 DC Grid Building By Multiple Manufacturers -Interoperability 295 24.6 Economic Aspects 295 25 DC Grids with Line Commutated Converters 297 25.1 Multiterminal LCC HVDC 297 25.2 Italy-Corsica-Sardinia Multiterminal HVDC Link 298 25.3 Connecting LCC Converter to a DC Grid 298 25.4 Control of LCC Converters in DC Grids 300 25.5 Control of LCC DC Grids Through DC Voltage Droop Feedback 301 25.6 Managing LCC DC Grid Faults 302 25.7 Reactive Power Issues 303 25.8 Employing LCC Converter Stations in Established DC Grids 303 26 DC Grids with Voltage Source Converters and Power Flow Model 304 26.1 Connecting VSC Converter to a DC Grid 304 26.2 Operating Multiterminal VSC HVDC in China 304 26.3 DC Grid Power Flow Model 306 26.4 DC Grid Power Flow Under DC Faults 308 27 DC Grid Control 311 27.1 Introduction 311 27.2 Fast Local VSC Converter Control in DC Grids 311 27.3 DC Grid Dispatcher with Remote Communication 313 27.4 Primary, Secondary and Tertiary DC Grid Control 313 27.5 DC Voltage Droop Control for VSC Converters in DC Grids 314 27.6 3-Level Control for VSC Converters with Dispatcher Droop 315 27.7 Power Flow Algorithm When DC Powers Are Regulated 316 27.8 Power Flow and Control Study of CIGRE DC Grid Test System 320 28 DC Circuit Breakers 325 28.1 Introduction 325 28.2 Challenges with DC Circuit Opening 325 28.3 DC CB Operating Principles and a Simple Model 326 28.4 DC CB Performance Requirements 327 28.5 Practical HV DC CBs 328 28.6 Mechanical DC Circuit Breaker 329 28.7 Semiconductor Based DC Circuit Breaker 337 28.8 Hybrid DC Circuit Breaker 339 29 DC Grid Fault Management and Protection System 345 29.1 Introduction 345 29.2 Fault Current Components in DC Grids 346 29.3 DC System Protection Coordination with AC System Protection 347 29.4 DC Grid Protection System Development 348 29.5 DC Grid Protection System Based On Local Measurements 349 29.6 Blocking MMC Converters Under DC Faults 352 29.7 Differential DC Grid Protection Strategy 355 29.8 Selective Protection for Star-Topology DC Grids 356 29.9 DC Grids with DC Fault-Tolerant VSC Converters 357 29.10 DC Grids with Full Bridge MMC Converters 361 30 High Power DC/DC Converters and DC Power Flow Controlling Devices 364 30.1 Introduction 364 30.2 Power Flow Control Using Series Resistors 365 30.3 Low Stepping Ratio DC/DC Converters (DC Choppers) 367 30.4 Non-Isolated MMC-Based DC/DC Converter (M2DC) 370 30.5 DC/DC Converters with DC Polarity Reversal 378 30.6 High Stepping Ratio Isolated DC/DC Converter (Dual Active Bridge DC/DC) 379 30.7 High Stepping Ratio LCL DC/DC Converter 384 30.8 Building DC Grids with DC/DC Converters 385 30.9 DC Hubs 387 30.10 Developing DC Grids Using DC Hubs 388 30.11 North Sea DC Grid Topologies 389 Bibliography Part III DC Transmission Grids 392 31 Appendix I Variable Notations 394 32 Appendix II - Analytical Background to Rotating DQ Frame 395 32.1 Transforming AC Variables to DQ Frame 395 32.2 Derivative of an Oscillating Signal in DQ Frame 397 32.3 Transforming an AC System Dynamic Equation to DQ Frame 397 32.4 Transforming N-Order State Space AC System Model to DQ Frame 398 32.5 Static (Steady-State) Modelling in Rotating DQ Coordinate Frame 400 32.6 Representing Product of Oscillating Signals in DQ Frame 400 32.7 Representing Power in DQ Frame 401 33 Appendix III - System Modelling Using Complex Numbers and Phasors 405 34 Appendix IV - Simulink Examples 407 Chapter 3 Examples 407 Chapter 5 Examples 408 Chapter 6 Examples 408 Chapter 8 Examples 410 Chapter 14 Examples 411 Chapter 16 Examples 412 Chapter 17 Examples 414