High Voltage Direct Current Transmission

DRAGAN JOVCIC, PHD, is director of Aberdeen HVDC Research Centre and a Professor with the University of Aberdeen, Scotland, UK. He has published approximately 130 articles related to HVDC and power electronics applications to transmission systems, is a senior member of IEEE, and a member of CIGRE. Professor Jovcic is the editor of IEEE Transactions on Power Delivery and has been editor-in-chief of two special issues related to HVDC.

• Preface xviiPart I HVDC with Current Source Converters 11 Introduction to Line Commutated HVDC 31.1 HVDC Applications 31.2 Line Commutated HVDC Components 41.3 DC Cables and Overhead Lines 71.3.1 Introduction 71.3.2 Mass-impregnated Cables 71.3.3 Low-pressure Oil-filled Cables 71.3.4 Extruded Cross-linked Polyethylene Cables 81.4 LCC HVDC Topologies 81.5 Losses in LCC HVDC Systems 101.6 Conversion of AC Lines to DC 101.7 Ultra High Voltage HVDC 122 Thyristors 132.1 Operating Characteristics 132.2 Switching Characteristics 142.3 Losses in HVDCThyristors 182.4 Valve Structure andThyristor Snubbers 202.5 Thyristor Rating Selection and Overload Capability 223 Six-pulse Diode and Thyristor Converter 253.1 Three-phase Uncontrolled Bridge 253.2 Three-phase Thyristor Rectifier 273.3 Analysis of Commutation Overlap in a Thyristor Converter 283.4 Active and Reactive Power in a Three-phase Thyristor Converter 323.5 Inverter Operation 334 HVDC Rectifier Station Modelling, Control and Synchronisation with AC System 374.1 HVDC Rectifier Controller 374.2 Phase-locked Loop 384.3 Master-level HVDC Control 405 HVDC Inverter Station Modelling and Control 435.1 Inverter Controller 435.1.1 Control Structure 435.1.2 Extinction Angle Control 435.1.3 DC Voltage Control 445.1.4 DC Current Control at Inverter 455.2 Commutation Failure 456 HVDC System V–I Diagrams and Operating Modes 496.1 HVDC Equivalent Circuit 496.2 HVDC V–I Operating Diagram 496.3 HVDC Power Reversal 517 HVDC Analytical Modelling and Stability 577.1 Introduction to Converter and HVDC Modelling 577.1.1 Detailed Switching Transients Modelling 577.1.2 Modelling with Switchings 577.1.3 Analytical Dynamic Modelling of Converters 587.1.4 Phasor Modelling 587.2 HVDC Analytical Model 587.3 CIGRE HVDC Benchmark Model 607.4 Converter Modelling, Linearisation, and Gain Scheduling 607.5 AC System Modelling for HVDC Stability Studies 647.6 LCC Converter Transformer Model 677.7 DC System Including DC Cable 687.7.1 DC Cable/Line Modelling as a Single 𝜋 Section 687.7.2 Controller Model 697.7.3 Complete DC System Model 697.8 Accurate DC Cable Modelling 707.8.1 Wideband Cable Model 707.8.2 Cable Higher-order Analytical Model in State Space 727.9 HVDC–HVAC System Model 767.10 Analytical Dynamic Model Verification 777.11 Basic HVDC Dynamic Analysis 777.11.1 Eigenvalue Analysis 777.11.2 Eigenvalue Sensitivity Study 777.11.3 Influence of PLL Gains 797.12 HVDC Second Harmonic Instability 807.13 100 Hz Oscillations on the DC Side 828 HVDC Phasor Modelling and Interactions with AC System 838.1 Converter and DC System Phasor Model 838.2 Phasor AC System Model and Interaction with DC System 848.3 Inverter AC Voltage and Power Profile as DC Current is Increasing 868.4 Influence of Converter Extinction Angle 888.5 Influence of Shunt Reactive Power Compensation 888.6 Influence of Load at the Converter Terminals 888.7 Influence of Operating Mode (DC Voltage Control Mode) 888.8 Rectifier Operating Mode 909 HVDC Operation with Weak AC Systems 959.1 Introduction 959.2 Short Circuit Ratio and Equivalent Short Circuit Ratio 959.2.1 Definition of SCR and ESCR 959.2.2 Operating Difficulties with Low SCR Systems 989.3 Background on Power Transfer Between Two AC Systems 999.4 Phasor Study of Converter Interactions with Weak AC Systems 1019.5 System Dynamics (Small Signal Stability) with Low SCR 1019.6 Control and Main Circuit Solutions for Weak AC Grids 1029.7 LCC HVDC with SVC 1039.8 Capacitor Commutated Converters for HVDC 1049.9 AC System with Low Inertia 10610 Fault Management and HVDC System Protection 11110.1 Introduction 11110.2 DC Line Faults 11110.3 AC System Faults 11310.3.1 Rectifier AC Faults 11310.3.2 Inverter AC Faults 11410.4 Internal Faults 11510.5 System Reconfiguration for Permanent Faults 11610.6 Overvoltage Protection 11911 LCC HVDC System Harmonics 12111.1 Harmonic Performance Criteria 12111.2 Harmonic Limits 12211.3 Thyristor Converter Harmonics 12311.4 Harmonic Filters 12411.4.1 Introduction 12411.4.2 Tuned Filters 12611.4.3 Damped Filters 12811.5 Non-characteristic Harmonic Reduction Using HVDC Controls 132Bibliography Part I: Line Commutated Converter HVDC 133Part II HVDC with Voltage Source Converters 13712 VSC HVDC Applications and Topologies, Performance and Cost Comparison with LCC HVDC 13912.1 Application of Voltage Source Converters in HVDC 13912.2 Comparison with LCC HVDC 14112.3 HVDC Technology Landscape 14212.4 Overhead and Subsea/Underground VSC HVDC Transmission 14312.5 DC Cable Types with VSC HVDC 14712.6 Monopolar and Bipolar VSC HVDC Systems 14712.7 VSC HVDC Converter Topologies 14812.7.1 HVDC with Two-level Voltage Source Converter 14812.7.2 HVDC with Neutral Point Clamped Converter 15012.7.3 MMC VSC HVDC Transmission Systems 15112.7.4 MMC HVDC Based on FB Topology 15312.8 VSC HVDC Station Components 15512.8.1 AC CB 15512.8.2 VSC Converter Transformer 15512.8.3 VSC Converter AC Harmonic Filters 15612.8.4 DC Capacitors 15612.8.5 DC Filter 15712.8.6 Two-level VSC HVDC Valves 15812.8.7 MMC Valves and Cells 15912.9 AC Inductors 16012.10 DC Inductors 16113 IGBT Switches and VSC Converter Losses 16513.1 Introduction to IGBT and IGCT 16513.2 General VSC Converter Switch Requirements 16613.3 IGBT Technology 16613.3.1 IGBT Operating Characteristics 16713.3.2 Fast Recovery Anti-parallel Diode 17113.4 High Power IGBT Devices 17113.5 IEGT Technology 17213.6 Losses Calculation 17313.6.1 Conduction Loss Modelling 17313.6.2 Switching Loss Modelling 17413.7 Balancing Challenges in Two-level IGBT Valves 17813.8 Snubbers Circuits 17914 Single-phase and Three-phase Two-level VSC Converters 18114.1 Introduction 18114.2 Single-phase VSC 18114.3 Three-phase VSC 18414.4 Square-wave, Six-pulse Operation 18514.4.1 180∘ Conduction 18514.4.2 120∘ Conduction 18815 Two-level PWM VSC Converters 19315.1 Introduction 19315.2 PWM Modulation 19315.2.1 Multipulse with Constant Pulse Width 19315.2.2 Modulating Signal 19415.3 Sinusoidal Pulse Width Modulation 19515.4 Third Harmonic Injection 19715.5 Selective Harmonic Elimination Modulation 19815.6 Converter Losses for Two-level SPWMVSC 19815.7 Harmonics with PWM 20115.8 Comparison of PWM Modulation Techniques 20316 Multilevel VSC Converters in HVDC Applications 20516.1 Introduction 20516.2 Modulation Techniques for Multilevel Converters 20716.3 Neutral Point Clamped Multilevel Converter 20816.4 Half Bridge MMC 21016.4.1 Operating Principles of Half-bridge MMC 21016.4.2 Capacitor Voltage Balancing 21216.4.3 MMC Cell Capacitance 21416.4.4 MMC Arm Inductance 21516.4.5 MMC with Fundamental Frequency Modulation 21816.4.6 MMC with PWM Modulation 21816.5 Full Bridge MMC 22216.5.1 Operating Principles 22216.6 Comparison of Multilevel Topologies 22417 Two-level VSC HVDC Modelling, Control, and Dynamics 22717.1 PWM Two-level Converter Average Model 22717.1.1 Converter Model in an ABC Frame 22717.1.2 Converter Model in the ABC Frame Including Blocked State 22917.2 Two-level PWM Converter Model in DQ Frame 23017.3 VSC Converter Transformer Model 23117.4 Two-level VSC Converter and AC Grid Model in the ABC Frame 23117.5 Two-level VSC Converter and AC Grid Model in a DQ Rotating Coordinate Frame 23217.6 VSC Converter Control Principles 23317.7 The Inner Current Controller Design 23417.7.1 Control Strategy 23417.7.2 Decoupling Control 23417.7.3 Current Feedback Control 23517.7.4 Controller Gains 23617.8 Outer Controller Design 23717.8.1 AC Voltage Control 23717.8.2 Power Control 23817.8.3 DC Voltage Control 23917.8.4 AC Grid Support 24017.9 Complete Two-level VSC Converter Controller 24017.10 Small Signal Linearised VSC HVDC Model 24217.11 Small Signal Dynamic Studies 24217.11.1 Dynamics of Weak AC Systems 24217.11.2 Impact of PLL Gains on Robustness 24418 Two-level VSC HVDC Phasor-domain Interaction with AC Systems and PQ Operating Diagrams 24718.1 Power Exchange Between Two AC Voltage Sources 24718.2 Converter Phasor Model and Power Exchange with an AC System 24918.3 Phasor Study of VSC Converter Interaction with AC System 25218.3.1 Test System 25218.3.2 Assumptions and Converter Limits 25218.3.3 Case 1: Converter Voltages Are Known 25318.3.4 Case 2: Converter Currents are Known 25418.3.5 Case 3: PCC Voltage is Known 25418.4 Operating Limits 25418.5 Design Point Selection 25518.6 Influence of AC System Strength 25818.7 Influence of AC System Impedance Angle (Xs/Rs) 25818.8 Influence of Transformer Reactance 25818.9 Influence of Converter Control Modes 26218.10 Operation with Very Weak AC Systems 26219 Half Bridge MMC: Dimensioning, Modelling, Control, and Interaction with AC System 26919.1 Basic Equations and Steady-state Control 26919.2 Steady-state Dimensioning 27219.3 Half Bridge MMC Non-linear Average Dynamic Model 27519.4 Non-linear Average Value Model Including Blocked State 27619.5 HB MMC HVDC Start-up and Charging MMC Cells 27819.6 HB MMC Dynamic DQ Frame Model and Phasor Model 27919.6.1 Assumptions 27919.6.2 Zero Sequence Model 28219.6.3 Fundamental Frequency Model in DQ Frame 28219.6.4 Second Harmonic Model in the D2Q2 Coordinate Frame 28419.7 Second Harmonic of Differential Current 28619.8 Complete MMC Converter DQ Model in Matrix Form 28619.9 Second-harmonic Circulating Current Suppression Controller 28719.10 Simplified DQ Frame Model with Circulating Current Controller 29019.11 Phasor Model of MMC with Circulating Current Suppression Controller 29519.12 Simplified Dynamic MMC Model Using Equivalent Series Capacitor CMMC 29619.13 Full Dynamic Analytical HB MMC Model 30019.14 HB MMC Controller and Arm Voltage Control 30119.15 MMC Total Series Reactance and Comparison with Two-level VSC 30419.16 MMC Interaction with AC System and PQ Operating Diagrams 30620 Full Bridge MMC Converter: Dimensioning, Modelling, and Control 30920.1 FB MMC Arm Voltage Range 30920.2 Full Bridge MMC Converter Non-linear Average Model 30920.3 FB MMC Non-linear Average Model Including Blocked State 31020.4 Full Bridge MMC Cell Charging 31220.5 Hybrid MMC Design 31320.5.1 Operation Under Low DC Voltage 31320.5.2 Overmodulation Requirements 31420.5.3 Cell Voltage Balancing Under Low DC Voltage 31520.5.4 Optimal Design of Full Bridge MMC 31520.6 Full Bridge MMC DC Voltage Variation Using a Detailed Model 31820.7 FB MMC Analytical Dynamic DQ Model 32020.7.1 Zero Sequence Model 32020.7.2 Fundamental Frequency Model 32120.8 Simplified FB MMC Model 32120.9 FB MMC Converter Controller 32221 MMC Converter Under Unbalanced Conditions 32521.1 Introduction 32521.2 MMC Balancing Controller Structure 32621.3 Balancing Between Phases (Horizontal Balancing) 32621.4 Balancing Between Arms (Vertical Balancing) 32821.5 Simulation of Balancing Controls 33021.6 Operation with Unbalanced AC Grid 33221.6.1 Detecting Positive and Negative Sequence Components 33221.6.2 Controlling Grid Current Sequence Components with MMC 33622 VSC HVDC Under AC and DC Fault Conditions 33922.1 Introduction 33922.2 Faults on the AC System 33922.3 DC Faults with Two-level VSC 34022.4 Influence of DC Capacitors 34522.5 VSC Converter Modelling Under DC Faults and VSC Diode Bridge 34522.5.1 VSC Diode Bridge Average Model 34522.5.2 Phasor Model of VSC Diode Bridge Under DC Fault 34822.5.3 Simple Expression for VSC Diode Bridge Steady-state Fault Current Magnitude 35122.6 VSC Converter Mode Transitions as DC Voltage Reduces 35222.7 DC Faults with Half Bridge Modular Multilevel Converter 35422.8 Full Bridge MMC Under DC Faults 35623 VSC HVDC Application For AC Grid Support and Operation with Passive AC Systems 35923.1 VSC HVDC High Level Controls and AC Grid Support 35923.2 HVDC Embedded Inside an AC Grid 36023.3 HVDC Connecting Two Separate AC Grids 36123.4 HVDC in Parallel with AC 36123.5 Operation with a Passive AC System and Black Start Capability 36223.6 VSC HVDC Operation with Offshore Wind Farms 36223.7 VSC HVDC Supplying Power Offshore and Driving a MW-Size Variable Speed Motor 365Bibliography Part II: Voltage Source Converter HVDC 366Part III DC Transmission Grids 37124 Introduction to DC Grids 37324.1 DC versus AC Transmission 37324.2 Terminology 37424.3 DC Grid Planning, Topology, and Power Transfer Security 37524.4 Technical Challenges 37624.5 DC Grid Building by Multiple Manufacturers – Interoperability 37624.6 Economic Aspects 37725 DC Grids with Line Commutated Converters 37925.1 Multiterminal LCC HVDC 37925.2 Italy–Corsica–Sardinia Multiterminal HVDC Link 38025.3 Connecting the LCC Converter to a DC Grid 38125.3.1 Power Reversal 38125.3.2 DC Faults 38225.3.3 AC Faults 38325.4 Control of LCC Converters in DC Grids 38325.5 Control of LCC DC Grids Through DC Voltage Droop Feedback 38425.6 Managing LCC DC Grid Faults 38525.7 Reactive Power Issues 38725.8 Employing LCC Converter Stations in Established DC Grids 38726 DC Grids with Voltage Source Converters and Power Flow Model 38926.1 Connecting a VSC Converter to a DC Grid 38926.1.1 Power Reversal and Control 38926.1.2 DC Faults 38926.1.3 AC Faults 38926.2 Multiterminal VSC HVDC Operating in China 39026.3 DC Grid Power Flow Model 39026.4 DC Grid Power Flow Under DC Faults 39527 DC Grid Control 39927.1 Introduction 39927.2 Fast Local VSC Converter Control in DC Grids 39927.3 DC Grid Dispatcher with Remote Communication 40127.4 Primary, Secondary, and Tertiary DC Grid Control 40227.5 DC Voltage Droop Control for VSC Converters in DC Grids 40327.6 Three-level Control for VSC Converters with Dispatcher Droop 40527.6.1 Three-level Control for VSC Converters 40527.6.2 Dispatcher Controller 40627.7 Power Flow Algorithm When DC Powers are Regulated 40627.8 Power Flow and Control Study of CIGRE DC Grid Test System 41127.8.1 CIGRE DC Grid Test System 41127.8.2 Power Flow After Outage of the Largest Terminal 41328 DC Circuit Breakers 41728.1 Introduction 41728.2 Challenges with DC Circuit Opening 41728.2.1 DC Current Commutation 41728.2.2 DC Current Suppression and Dissipation of Energy 41828.3 DC CB Operating Principles and a Simple Model 41828.4 DC CB Performance Requirements 42028.4.1 Opening Speed 42028.4.2 DC CB Ratings and Series Inductors 42028.4.3 Bidirectional Current Interruption 42128.4.4 Multiple Open/close Operations in a Short Time 42128.4.5 Losses, Size, and Weight 42128.4.6 Standardisation 42128.5 Practical HV DC CBs 42228.6 Mechanical DC CB 42228.6.1 Operating Principles and Construction 42228.6.2 Mathematical Model and Design Principles 42428.6.3 Test Circuit for DC CB Simulation 42628.6.4 Simulation of DC Fault Clearing 42728.6.5 Negative Fault Current Interruption 42728.6.6 Multiple Open/close Operations in a Short Time 42828.6.7 Mechanical DC CB for High Voltages 42928.7 Semiconductor-based DC CB 43028.7.1 Topology and Design 43028.7.2 Self-protection of Semiconductor Valves 43228.7.3 Simulation of Fault Current Interruption 43228.8 Hybrid DC CB 43428.8.1 Topology and Design 43428.8.2 Hybrid DC CB for High Voltages 43528.8.3 Simulation of Fault Current Interruption 43628.8.4 Bidirectional Operation 43728.8.5 Fault Current Limiting 43829 DC Grid Fault Management and Protection System 44129.1 Introduction 44129.2 Fault Current Components in DC Grids 44229.3 DC System Protection Coordination with AC System Protection 44429.4 DC Grid Protection System Development 44529.5 DC Grid Protection System Based on Local Measurements 44629.5.1 Protection Based on DC Current and Current Differential 44629.5.2 Rate of Change of Voltage Protection 44729.6 Blocking MMC Converters Under DC Faults 45029.7 Differential DC Grid Protection Strategy 45229.8 Selective Protection for Star-topology DC Grids 45529.9 DC Grids with DC Fault-tolerant VSC Converters 45629.9.1 Grid Topology and Strategy 45629.9.2 VSC Converter with Increased AC Coupling Reactors 45729.9.3 LCL VSC Converter 45929.9.4 VSC Converter with Fault Current Limiter 46129.10 DC Grids with Full Bridge MMC Converters 46130 High Power DC/DC Converters and DC Power Flow Controlling Devices 46530.1 Introduction 46530.2 Power Flow Control Using Series Resistors 46630.3 Low-stepping-ratio DC/DC Converters (DC Choppers) 46930.3.1 Converter Topology 46930.3.2 Converter Controller 47030.3.3 DC/DC Chopper Average Value Model 47130.3.4 H-Bridge DC/DC Chopper 47330.4 Non-isolated MMC-based DC/DC Converter (M2DC) 47330.4.1 Introduction 47330.4.2 Modelling and Design 47430.4.3 Design Example and Comparison with MMC AC/DC 47730.4.4 Controller Design 47930.4.5 Simulation Responses 48030.5 DC/DC Converters with DC Polarity Reversal 48430.6 High-stepping-ratio Isolated DC/DC Converter (Dual Active Bridge DC/DC) 48430.6.1 Introduction 48430.6.2 Modelling and Control 48630.6.3 Simulated Responses 48730.7 High-stepping-ratio LCL DC/DC Converter 49030.8 Building DC Grids with DC/DC Converters 49230.9 DC Hubs 49530.10 Developing DC Grids Using DC Hubs 49630.11 North Sea DC Grid Topologies 496Bibliography Part III: DC Transmission Grids 500Appendix A Variable Notations 503Appendix B Analytical Background to Rotating DQ Frame 505B.1 Transforming AC Variables to a DQ Frame 505B.2 Derivative of an Oscillating Signal in a DQ Frame 507B.3 Transforming an AC System Dynamic Equation to a DQ Frame 507B.4 Transforming an n-Order State Space AC System Model to a DQ Frame 509B.5 Static (Steady-state) Modeling in a Rotating DQ Coordinate Frame 510B.6 Representing the Product of Oscillating Signals in a DQ Frame 511B.7 Representing Power in DQ Frame 512Appendix C System Modeling Using Complex Numbers and Phasors 515Appendix D Simulink Examples 517D.1 Chapter 3 Examples 517D.2 Chapter 5 Examples 517D.3 Chapter 6 Examples 519D.4 Chapter 8 Examples 521D.5 Chapter 14 Examples 523D.6 Chapter 16 Examples 524D.7 Chapter 17 Examples 527Index 535