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High Voltage Direct Current Transmission: Converters, Systems and DC Grids, 2nd Edition

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High Voltage Direct Current Transmission: Converters, Systems and DC Grids, 2nd Edition

Dragan Jovcic

ISBN: 978-1-119-56661-8 July 2019 560 Pages

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Description

Presents the latest developments in switchgear and DC/DC converters for DC grids, and includes substantially expanded material on MMC HVDC

This newly updated edition covers all HVDC transmission technologies including Line Commutated Converter (LCC) HVDC; Voltage Source Converter (VSC) HVDC, and the latest VSC HVDC based on Modular Multilevel Converters (MMC), as well as the principles of building DC transmission grids.

Featuring new material throughout, High Voltage Direct Current Transmission: Converters, Systems and DC Grids, 2nd Edition offers several new chapters/sections including one on the newest MMC converters. It also provides extended coverage of switchgear, DC grid protection and DC/DC converters following the latest developments on the market and in research projects. All three HVDC technologies are studied in a wide range of topics, including: the basic converter operating principles; calculation of losses; system modelling, including dynamic modelling; system control; HVDC protection, including AC and DC fault studies; and integration with AC systems and fundamental frequency analysis. The text includes:

  • A chapter dedicated to hybrid and mechanical DC circuit breakers
  • Half bridge and full bridge MMC: modelling, control, start-up and fault management
  • A chapter dedicated to unbalanced operation and control of MMC HVDC
  • The advancement of protection methods for DC grids
  • Wideband and high-order modeling of DC cables
  • Novel treatment of topics not found in similar books, including SimPowerSystems models and examples for all HVDC topologies hosted by the 1st edition companion site.

High Voltage Direct Current Transmission: Converters, Systems and DC Grids, 2nd Edition serves as an ideal textbook for a graduate-level course or a professional development course.

Preface xvii

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 4

1.3 DC Cables and Overhead Lines 7

1.3.1 Introduction 7

1.3.2 Mass-impregnated Cables 7

1.3.3 Low-pressure Oil-filled Cables 7

1.3.4 Extruded Cross-linked Polyethylene Cables 8

1.4 LCC HVDC Topologies 8

1.5 Losses in LCC HVDC Systems 10

1.6 Conversion of AC Lines to DC 10

1.7 Ultra High Voltage HVDC 12

2 Thyristors 13

2.1 Operating Characteristics 13

2.2 Switching Characteristics 14

2.3 Losses in HVDCThyristors 18

2.4 Valve Structure andThyristor Snubbers 20

2.5 Thyristor Rating Selection and Overload Capability 22

3 Six-pulse Diode and Thyristor Converter 25

3.1 Three-phase Uncontrolled Bridge 25

3.2 Three-phase Thyristor Rectifier 27

3.3 Analysis of Commutation Overlap in a Thyristor Converter 28

3.4 Active and Reactive Power in a Three-phase Thyristor Converter 32

3.5 Inverter Operation 33

4 HVDC Rectifier Station Modelling, Control and Synchronisation with AC System 37

4.1 HVDC Rectifier Controller 37

4.2 Phase-locked Loop 38

4.3 Master-level HVDC Control 40

5 HVDC Inverter Station Modelling and Control 43

5.1 Inverter Controller 43

5.1.1 Control Structure 43

5.1.2 Extinction Angle Control 43

5.1.3 DC Voltage Control 44

5.1.4 DC Current Control at Inverter 45

5.2 Commutation Failure 45

6 HVDC System VI Diagrams and Operating Modes 49

6.1 HVDC Equivalent Circuit 49

6.2 HVDC V–I Operating Diagram 49

6.3 HVDC Power Reversal 51

7 HVDC Analytical Modelling and Stability 57

7.1 Introduction to Converter and HVDC Modelling 57

7.1.1 Detailed Switching Transients Modelling 57

7.1.2 Modelling with Switchings 57

7.1.3 Analytical Dynamic Modelling of Converters 58

7.1.4 Phasor Modelling 58

7.2 HVDC Analytical Model 58

7.3 CIGRE HVDC Benchmark Model 60

7.4 Converter Modelling, Linearisation, and Gain Scheduling 60

7.5 AC System Modelling for HVDC Stability Studies 64

7.6 LCC Converter Transformer Model 67

7.7 DC System Including DC Cable 68

7.7.1 DC Cable/Line Modelling as a Single 𝜋 Section 68

7.7.2 Controller Model 69

7.7.3 Complete DC System Model 69

7.8 Accurate DC Cable Modelling 70

7.8.1 Wideband Cable Model 70

7.8.2 Cable Higher-order Analytical Model in State Space 72

7.9 HVDC–HVAC System Model 76

7.10 Analytical Dynamic Model Verification 77

7.11 Basic HVDC Dynamic Analysis 77

7.11.1 Eigenvalue Analysis 77

7.11.2 Eigenvalue Sensitivity Study 77

7.11.3 Influence of PLL Gains 79

7.12 HVDC Second Harmonic Instability 80

7.13 100 Hz Oscillations on the DC Side 82

8 HVDC Phasor Modelling and Interactions with AC System 83

8.1 Converter and DC System Phasor Model 83

8.2 Phasor AC System Model and Interaction with DC System 84

8.3 Inverter AC Voltage and Power Profile as DC Current is Increasing 86

8.4 Influence of Converter Extinction Angle 88

8.5 Influence of Shunt Reactive Power Compensation 88

8.6 Influence of Load at the Converter Terminals 88

8.7 Influence of Operating Mode (DC Voltage Control Mode) 88

8.8 Rectifier Operating Mode 90

9 HVDC Operation with Weak AC Systems 95

9.1 Introduction 95

9.2 Short Circuit Ratio and Equivalent Short Circuit Ratio 95

9.2.1 Definition of SCR and ESCR 95

9.2.2 Operating Difficulties with Low SCR Systems 98

9.3 Background on Power Transfer Between Two AC Systems 99

9.4 Phasor Study of Converter Interactions with Weak AC Systems 101

9.5 System Dynamics (Small Signal Stability) with Low SCR 101

9.6 Control and Main Circuit Solutions for Weak AC Grids 102

9.7 LCC HVDC with SVC 103

9.8 Capacitor Commutated Converters for HVDC 104

9.9 AC System with Low Inertia 106

10 Fault Management and HVDC System Protection 111

10.1 Introduction 111

10.2 DC Line Faults 111

10.3 AC System Faults 113

10.3.1 Rectifier AC Faults 113

10.3.2 Inverter AC Faults 114

10.4 Internal Faults 115

10.5 System Reconfiguration for Permanent Faults 116

10.6 Overvoltage Protection 119

11 LCC HVDC System Harmonics 121

11.1 Harmonic Performance Criteria 121

11.2 Harmonic Limits 122

11.3 Thyristor Converter Harmonics 123

11.4 Harmonic Filters 124

11.4.1 Introduction 124

11.4.2 Tuned Filters 126

11.4.3 Damped Filters 128

11.5 Non-characteristic Harmonic Reduction Using HVDC Controls 132

Bibliography Part I: Line Commutated Converter HVDC 133

Part II HVDC with Voltage Source Converters 137

12 VSC HVDC Applications and Topologies, Performance and Cost Comparison with LCC HVDC 139

12.1 Application of Voltage Source Converters in HVDC 139

12.2 Comparison with LCC HVDC 141

12.3 HVDC Technology Landscape 142

12.4 Overhead and Subsea/Underground VSC HVDC Transmission 143

12.5 DC Cable Types with VSC HVDC 147

12.6 Monopolar and Bipolar VSC HVDC Systems 147

12.7 VSC HVDC Converter Topologies 148

12.7.1 HVDC with Two-level Voltage Source Converter 148

12.7.2 HVDC with Neutral Point Clamped Converter 150

12.7.3 MMC VSC HVDC Transmission Systems 151

12.7.4 MMC HVDC Based on FB Topology 153

12.8 VSC HVDC Station Components 155

12.8.1 AC CB 155

12.8.2 VSC Converter Transformer 155

12.8.3 VSC Converter AC Harmonic Filters 156

12.8.4 DC Capacitors 156

12.8.5 DC Filter 157

12.8.6 Two-level VSC HVDC Valves 158

12.8.7 MMC Valves and Cells 159

12.9 AC Inductors 160

12.10 DC Inductors 161

13 IGBT Switches and VSC Converter Losses 165

13.1 Introduction to IGBT and IGCT 165

13.2 General VSC Converter Switch Requirements 166

13.3 IGBT Technology 166

13.3.1 IGBT Operating Characteristics 167

13.3.2 Fast Recovery Anti-parallel Diode 171

13.4 High Power IGBT Devices 171

13.5 IEGT Technology 172

13.6 Losses Calculation 173

13.6.1 Conduction Loss Modelling 173

13.6.2 Switching Loss Modelling 174

13.7 Balancing Challenges in Two-level IGBT Valves 178

13.8 Snubbers Circuits 179

14 Single-phase and Three-phase Two-level VSC Converters 181

14.1 Introduction 181

14.2 Single-phase VSC 181

14.3 Three-phase VSC 184

14.4 Square-wave, Six-pulse Operation 185

14.4.1 180 Conduction 185

14.4.2 120 Conduction 188

15 Two-level PWM VSC Converters 193

15.1 Introduction 193

15.2 PWM Modulation 193

15.2.1 Multipulse with Constant Pulse Width 193

15.2.2 Modulating Signal 194

15.3 Sinusoidal Pulse Width Modulation 195

15.4 Third Harmonic Injection 197

15.5 Selective Harmonic Elimination Modulation 198

15.6 Converter Losses for Two-level SPWMVSC 198

15.7 Harmonics with PWM 201

15.8 Comparison of PWM Modulation Techniques 203

16 Multilevel VSC Converters in HVDC Applications 205

16.1 Introduction 205

16.2 Modulation Techniques for Multilevel Converters 207

16.3 Neutral Point Clamped Multilevel Converter 208

16.4 Half Bridge MMC 210

16.4.1 Operating Principles of Half-bridge MMC 210

16.4.2 Capacitor Voltage Balancing 212

16.4.3 MMC Cell Capacitance 214

16.4.4 MMC Arm Inductance 215

16.4.5 MMC with Fundamental Frequency Modulation 218

16.4.6 MMC with PWM Modulation 218

16.5 Full Bridge MMC 222

16.5.1 Operating Principles 222

16.6 Comparison of Multilevel Topologies 224

17 Two-level VSC HVDC Modelling, Control, and Dynamics 227

17.1 PWM Two-level Converter Average Model 227

17.1.1 Converter Model in an ABC Frame 227

17.1.2 Converter Model in the ABC Frame Including Blocked State 229

17.2 Two-level PWM Converter Model in DQ Frame 230

17.3 VSC Converter Transformer Model 231

17.4 Two-level VSC Converter and AC Grid Model in the ABC Frame 231

17.5 Two-level VSC Converter and AC Grid Model in a DQ Rotating Coordinate Frame 232

17.6 VSC Converter Control Principles 233

17.7 The Inner Current Controller Design 234

17.7.1 Control Strategy 234

17.7.2 Decoupling Control 234

17.7.3 Current Feedback Control 235

17.7.4 Controller Gains 236

17.8 Outer Controller Design 237

17.8.1 AC Voltage Control 237

17.8.2 Power Control 238

17.8.3 DC Voltage Control 239

17.8.4 AC Grid Support 240

17.9 Complete Two-level VSC Converter Controller 240

17.10 Small Signal Linearised VSC HVDC Model 242

17.11 Small Signal Dynamic Studies 242

17.11.1 Dynamics of Weak AC Systems 242

17.11.2 Impact of PLL Gains on Robustness 244

18 Two-level VSC HVDC Phasor-domain Interaction with AC Systems and PQ Operating Diagrams 247

18.1 Power Exchange Between Two AC Voltage Sources 247

18.2 Converter Phasor Model and Power Exchange with an AC System 249

18.3 Phasor Study of VSC Converter Interaction with AC System 252

18.3.1 Test System 252

18.3.2 Assumptions and Converter Limits 252

18.3.3 Case 1: Converter Voltages Are Known 253

18.3.4 Case 2: Converter Currents are Known 254

18.3.5 Case 3: PCC Voltage is Known 254

18.4 Operating Limits 254

18.5 Design Point Selection 255

18.6 Influence of AC System Strength 258

18.7 Influence of AC System Impedance Angle (Xs/Rs) 258

18.8 Influence of Transformer Reactance 258

18.9 Influence of Converter Control Modes 262

18.10 Operation with Very Weak AC Systems 262

19 Half Bridge MMC: Dimensioning, Modelling, Control, and Interaction with AC System 269

19.1 Basic Equations and Steady-state Control 269

19.2 Steady-state Dimensioning 272

19.3 Half Bridge MMC Non-linear Average Dynamic Model 275

19.4 Non-linear Average Value Model Including Blocked State 276

19.5 HB MMC HVDC Start-up and Charging MMC Cells 278

19.6 HB MMC Dynamic DQ Frame Model and Phasor Model 279

19.6.1 Assumptions 279

19.6.2 Zero Sequence Model 282

19.6.3 Fundamental Frequency Model in DQ Frame 282

19.6.4 Second Harmonic Model in the D2Q2 Coordinate Frame 284

19.7 Second Harmonic of Differential Current 286

19.8 Complete MMC Converter DQ Model in Matrix Form 286

19.9 Second-harmonic Circulating Current Suppression Controller 287

19.10 Simplified DQ Frame Model with Circulating Current Controller 290

19.11 Phasor Model of MMC with Circulating Current Suppression Controller 295

19.12 Simplified Dynamic MMC Model Using Equivalent Series Capacitor CMMC 296

19.13 Full Dynamic Analytical HB MMC Model 300

19.14 HB MMC Controller and Arm Voltage Control 301

19.15 MMC Total Series Reactance and Comparison with Two-level VSC 304

19.16 MMC Interaction with AC System and PQ Operating Diagrams 306

20 Full Bridge MMC Converter: Dimensioning, Modelling, and Control 309

20.1 FB MMC Arm Voltage Range 309

20.2 Full Bridge MMC Converter Non-linear Average Model 309

20.3 FB MMC Non-linear Average Model Including Blocked State 310

20.4 Full Bridge MMC Cell Charging 312

20.5 Hybrid MMC Design 313

20.5.1 Operation Under Low DC Voltage 313

20.5.2 Overmodulation Requirements 314

20.5.3 Cell Voltage Balancing Under Low DC Voltage 315

20.5.4 Optimal Design of Full Bridge MMC 315

20.6 Full Bridge MMC DC Voltage Variation Using a Detailed Model 318

20.7 FB MMC Analytical Dynamic DQ Model 320

20.7.1 Zero Sequence Model 320

20.7.2 Fundamental Frequency Model 321

20.8 Simplified FB MMC Model 321

20.9 FB MMC Converter Controller 322

21 MMC Converter Under Unbalanced Conditions 325

21.1 Introduction 325

21.2 MMC Balancing Controller Structure 326

21.3 Balancing Between Phases (Horizontal Balancing) 326

21.4 Balancing Between Arms (Vertical Balancing) 328

21.5 Simulation of Balancing Controls 330

21.6 Operation with Unbalanced AC Grid 332

21.6.1 Detecting Positive and Negative Sequence Components 332

21.6.2 Controlling Grid Current Sequence Components with MMC 336

22 VSC HVDC Under AC and DC Fault Conditions 339

22.1 Introduction 339

22.2 Faults on the AC System 339

22.3 DC Faults with Two-level VSC 340

22.4 Influence of DC Capacitors 345

22.5 VSC Converter Modelling Under DC Faults and VSC Diode Bridge 345

22.5.1 VSC Diode Bridge Average Model 345

22.5.2 Phasor Model of VSC Diode Bridge Under DC Fault 348

22.5.3 Simple Expression for VSC Diode Bridge Steady-state Fault Current Magnitude 351

22.6 VSC Converter Mode Transitions as DC Voltage Reduces 352

22.7 DC Faults with Half Bridge Modular Multilevel Converter 354

22.8 Full Bridge MMC Under DC Faults 356

23 VSC HVDC Application For AC Grid Support and Operation with Passive AC Systems 359

23.1 VSC HVDC High Level Controls and AC Grid Support 359

23.2 HVDC Embedded Inside an AC Grid 360

23.3 HVDC Connecting Two Separate AC Grids 361

23.4 HVDC in Parallel with AC 361

23.5 Operation with a Passive AC System and Black Start Capability 362

23.6 VSC HVDC Operation with Offshore Wind Farms 362

23.7 VSC HVDC Supplying Power Offshore and Driving a MW-Size Variable Speed Motor 365

Bibliography Part II: Voltage Source Converter HVDC 366

Part III DC Transmission Grids 371

24 Introduction to DC Grids 373

24.1 DC versus AC Transmission 373

24.2 Terminology 374

24.3 DC Grid Planning, Topology, and Power Transfer Security 375

24.4 Technical Challenges 376

24.5 DC Grid Building by Multiple Manufacturers – Interoperability 376

24.6 Economic Aspects 377

25 DC Grids with Line Commutated Converters 379

25.1 Multiterminal LCC HVDC 379

25.2 Italy–Corsica–Sardinia Multiterminal HVDC Link 380

25.3 Connecting the LCC Converter to a DC Grid 381

25.3.1 Power Reversal 381

25.3.2 DC Faults 382

25.3.3 AC Faults 383

25.4 Control of LCC Converters in DC Grids 383

25.5 Control of LCC DC Grids Through DC Voltage Droop Feedback 384

25.6 Managing LCC DC Grid Faults 385

25.7 Reactive Power Issues 387

25.8 Employing LCC Converter Stations in Established DC Grids 387

26 DC Grids with Voltage Source Converters and Power Flow Model 389

26.1 Connecting a VSC Converter to a DC Grid 389

26.1.1 Power Reversal and Control 389

26.1.2 DC Faults 389

26.1.3 AC Faults 389

26.2 Multiterminal VSC HVDC Operating in China 390

26.3 DC Grid Power Flow Model 390

26.4 DC Grid Power Flow Under DC Faults 395

27 DC Grid Control 399

27.1 Introduction 399

27.2 Fast Local VSC Converter Control in DC Grids 399

27.3 DC Grid Dispatcher with Remote Communication 401

27.4 Primary, Secondary, and Tertiary DC Grid Control 402

27.5 DC Voltage Droop Control for VSC Converters in DC Grids 403

27.6 Three-level Control for VSC Converters with Dispatcher Droop 405

27.6.1 Three-level Control for VSC Converters 405

27.6.2 Dispatcher Controller 406

27.7 Power Flow Algorithm When DC Powers are Regulated 406

27.8 Power Flow and Control Study of CIGRE DC Grid Test System 411

27.8.1 CIGRE DC Grid Test System 411

27.8.2 Power Flow After Outage of the Largest Terminal 413

28 DC Circuit Breakers 417

28.1 Introduction 417

28.2 Challenges with DC Circuit Opening 417

28.2.1 DC Current Commutation 417

28.2.2 DC Current Suppression and Dissipation of Energy 418

28.3 DC CB Operating Principles and a Simple Model 418

28.4 DC CB Performance Requirements 420

28.4.1 Opening Speed 420

28.4.2 DC CB Ratings and Series Inductors 420

28.4.3 Bidirectional Current Interruption 421

28.4.4 Multiple Open/close Operations in a Short Time 421

28.4.5 Losses, Size, and Weight 421

28.4.6 Standardisation 421

28.5 Practical HV DC CBs 422

28.6 Mechanical DC CB 422

28.6.1 Operating Principles and Construction 422

28.6.2 Mathematical Model and Design Principles 424

28.6.3 Test Circuit for DC CB Simulation 426

28.6.4 Simulation of DC Fault Clearing 427

28.6.5 Negative Fault Current Interruption 427

28.6.6 Multiple Open/close Operations in a Short Time 428

28.6.7 Mechanical DC CB for High Voltages 429

28.7 Semiconductor-based DC CB 430

28.7.1 Topology and Design 430

28.7.2 Self-protection of Semiconductor Valves 432

28.7.3 Simulation of Fault Current Interruption 432

28.8 Hybrid DC CB 434

28.8.1 Topology and Design 434

28.8.2 Hybrid DC CB for High Voltages 435

28.8.3 Simulation of Fault Current Interruption 436

28.8.4 Bidirectional Operation 437

28.8.5 Fault Current Limiting 438

29 DC Grid Fault Management and Protection System 441

29.1 Introduction 441

29.2 Fault Current Components in DC Grids 442

29.3 DC System Protection Coordination with AC System Protection 444

29.4 DC Grid Protection System Development 445

29.5 DC Grid Protection System Based on Local Measurements 446

29.5.1 Protection Based on DC Current and Current Differential 446

29.5.2 Rate of Change of Voltage Protection 447

29.6 Blocking MMC Converters Under DC Faults 450

29.7 Differential DC Grid Protection Strategy 452

29.8 Selective Protection for Star-topology DC Grids 455

29.9 DC Grids with DC Fault-tolerant VSC Converters 456

29.9.1 Grid Topology and Strategy 456

29.9.2 VSC Converter with Increased AC Coupling Reactors 457

29.9.3 LCL VSC Converter 459

29.9.4 VSC Converter with Fault Current Limiter 461

29.10 DC Grids with Full Bridge MMC Converters 461

30 High Power DC/DC Converters and DC Power Flow Controlling Devices 465

30.1 Introduction 465

30.2 Power Flow Control Using Series Resistors 466

30.3 Low-stepping-ratio DC/DC Converters (DC Choppers) 469

30.3.1 Converter Topology 469

30.3.2 Converter Controller 470

30.3.3 DC/DC Chopper Average Value Model 471

30.3.4 H-Bridge DC/DC Chopper 473

30.4 Non-isolated MMC-based DC/DC Converter (M2DC) 473

30.4.1 Introduction 473

30.4.2 Modelling and Design 474

30.4.3 Design Example and Comparison with MMC AC/DC 477

30.4.4 Controller Design 479

30.4.5 Simulation Responses 480

30.5 DC/DC Converters with DC Polarity Reversal 484

30.6 High-stepping-ratio Isolated DC/DC Converter (Dual Active Bridge DC/DC) 484

30.6.1 Introduction 484

30.6.2 Modelling and Control 486

30.6.3 Simulated Responses 487

30.7 High-stepping-ratio LCL DC/DC Converter 490

30.8 Building DC Grids with DC/DC Converters 492

30.9 DC Hubs 495

30.10 Developing DC Grids Using DC Hubs 496

30.11 North Sea DC Grid Topologies 496

Bibliography Part III: DC Transmission Grids 500

Appendix A Variable Notations 503

Appendix B Analytical Background to Rotating DQ Frame 505

B.1 Transforming AC Variables to a DQ Frame 505

B.2 Derivative of an Oscillating Signal in a DQ Frame 507

B.3 Transforming an AC System Dynamic Equation to a DQ Frame 507

B.4 Transforming an n-Order State Space AC System Model to a DQ Frame 509

B.5 Static (Steady-state) Modeling in a Rotating DQ Coordinate Frame 510

B.6 Representing the Product of Oscillating Signals in a DQ Frame 511

B.7 Representing Power in DQ Frame 512

Appendix C System Modeling Using Complex Numbers and Phasors 515

Appendix D Simulink Examples 517

D.1 Chapter 3 Examples 517

D.2 Chapter 5 Examples 517

D.3 Chapter 6 Examples 519

D.4 Chapter 8 Examples 521

D.5 Chapter 14 Examples 523

D.6 Chapter 16 Examples 524

D.7 Chapter 17 Examples 527

Index 535