Offshore Wind Energy Technology

OLIMPO ANAYA-LARA is a Reader in the Wind Energy and Control Centre at the University of Strathclyde, Glasgow, UK. JOHN O. TANDE is a Chief Scientist with SINTEF Energy Research and Director of NOWITECH, Norway. KJETIL UHLEN is a Professor in Electrical Power Systems at the Norwegian University of Science and Technology (NTNU), Norway. KARL MERZ is a Research Scientist at SINTEF Energy Research, Norway.

• Notes on Contributors xiiiForeword xviiPreface xixAcronyms xxiSymbols (Individual Chapters) xxvAbout the Companion Website xxxi1 Introduction 1John O. Tande1.1 Development of Offshore Wind Energy 11.2 Offshore Wind Technology 51.3 Levelized Cost of Energy 61.4 Future Offshore Wind Development 91.5 References 102 Energy Conversion Systems for Offshore Wind Turbines 13Olimpo Anaya‐Lara2.1 Background 132.2 Offshore Wind Turbine Technology Status 142.3 Offshore Wind Turbine Generator Technology 142.4 Wind Turbine Generator Architectures 172.4.1 Fixed‐speed Wind Turbines 172.4.2 Variable‐speed Wind Turbines 182.4.2.1 Type II Wind Turbine Generator 182.4.2.2 Type III DFIG Wind Turbine Generator 192.4.2.3 Type IV FRC Wind Turbine Generator 202.5 Generators for Offshore Wind Turbines 212.5.1 New Generator Technologies and Concepts 222.5.1.1 Direct‐driven DFIG 222.5.1.2 Conventional Direct‐driven RFPMSG 222.5.1.3 Direct‐driven iPMSG 232.5.1.4 Superconducting Generator 232.5.1.5 High-Voltage Variable-Capacitance Direct Current Generator 232.6 Power Electronic Converters for MW Wind Turbine Generators 242.6.1 Technical and Operational Requirements 242.6.2 Back‐to‐back Connected Power Converters 252.6.2.1 LV Converters 252.6.2.2 MV Converters 272.6.3 Passive Generator‐side Converters 282.6.4 Converters for Six‐phase Generators 282.6.5 Power Converters Without DC‐link – Matrix Converters 302.7 Wind Generators Compared to Conventional Power Plant 302.7.1 Local Impacts 312.7.1.1 Circuit Power Flows and Busbar Voltages 312.7.1.2 Protection Schemes, Fault Currents and Switchgear Rating 312.7.1.3 Power Quality 322.7.2 System‐wide Impacts 322.7.2.1 Power System Dynamics and Stability 322.7.2.2 Reactive Power and Voltage Support 332.7.2.3 Frequency Support 332.8 Acknowledgements 332.9 References 343 Modelling and Analysis of Drivetrains in Offshore Wind Turbines 37Amir Rasekhi Nejad3.1 Introduction 373.2 Drivetrain Concepts 393.2.1 Gearbox Configurations, Cost and Efficiency 393.3 Gearbox Failures 423.4 State‐of‐the-art Wind Turbine Gearbox Design Codes 443.5 Drivetrain Modelling and Analysis 443.5.1 Decoupled Approach 463.5.2 Multibody System (MBS) Modelling 483.5.2.1 General 483.5.2.2 Gear Model in MBS 503.5.2.3 Bearing Model in MBS 513.5.3 Gear Stress Analysis 533.5.4 Bearings Fatigue Analysis 543.5.5 Effect of Geometrical Errors 553.5.6 Effect of Misalignments 553.5.7 Flexibility in the Planetary Stage 553.6 Limit State Design 563.6.1 FLS, ULS and ALS Design Check 573.6.2 Ultimate Limit State (ULS) Design Check 583.6.3 Fatigue Limit State (FLS) Design Check 603.6.3.1 Gears 603.6.4 Structural Reliability Analysis Method 633.6.4.1 Uncertainties 633.6.4.2 Model Uncertainties 643.6.4.3 Failure Function 663.6.4.4 ULS and FLS Structural Reliability Analysis 673.7 Drivetrains in Floating Wind Turbines 693.7.1 Gearbox on TLP, spar and semi‐submersible turbines versus land‐based wind turbines 693.8 Condition Monitoring and Inspection 773.8.1 Model‐based Fault Detection 783.8.2 Gearbox Vulnerability Map 793.9 Drivetrains in Fault Conditions 823.10 5‐MW Reference Offshore Drivetrain 883.11 References 944 Fixed and Floating Offshore Wind Turbine Support Structures 103Erin E. Bachynski4.1 Introduction 1034.2 Bottom‐fixed Support Structures 1044.3 Floating Support Structures 1074.4 Design Considerations 1094.5 Conceptual Design 1114.5.1 Initial Design Criteria 1114.5.2 Design by Upscaling 1144.5.3 Preliminary Analysis 1154.6 Loads in the Marine Environment 1194.6.1 Aerodynamic Loads 1194.6.2 Hydrodynamic Loads 1224.6.3 Additional Marine Loads 1254.7 Global Dynamic Analysis of Offshore Wind Turbines 1264.7.1 Short‐term Numerical Global Analysis 1274.7.2 Long‐term Numerical Global Analysis 1314.7.3 Experimental Analysis of OWTs 1324.8 Conclusions 1354.9 References 1365 Offshore Wind Turbine Controls 143Karl Merz and Morten D. Pedersen5.1 Control Objectives, Sensors and Actuators 1455.1.1 Control Objectives 1455.1.1.1 Power Production and Rotor Speed Control 1455.1.1.2 Load Reduction, Load Rejection and Active Damping 1475.1.1.3 Power Command Tracking 1495.1.1.4 Supervisory Control Functions and Fault Handling 1495.1.2 Available Control Actions and Sensors 1505.2 Control Algorithms 1515.2.1 Overview of Algorithms 1525.2.1.1 Single‐input, Single‐output Controls 1525.2.1.2 Advanced Controls 1525.2.2 Realization of a Controller for a 10‐MW Wind Turbine 1555.3 A Linear Aeroelastic Loads Model for Closed‐loop System Dynamics 1595.3.1 Aerodynamic Model 1595.3.2 Structural Model 1615.3.3 Electrical Systems 1645.3.3.1 Generator 1655.3.3.2 Converter 1655.3.3.3 DC‐Link 1675.3.3.4 Transformer 1675.3.4 Pitch Actuators 1675.3.5 A Unified, Linear, Time‐invariant State‐Space Model 1685.3.6 Comments on Linearity 1695.4 Basic Rotor Speed Control in Operating Regions I and II 1755.4.1 Region I 1755.4.1.1 Stability and Performance of the MPPT Algorithm 1755.4.1.2 Structural Flexibility 1795.4.1.3 Region I Control of the ORT, with Reduced‐order Dynamics 1805.4.2 Region II 1865.4.2.1 Region II Control of the ORT 1875.5 Active Damping and Load Reduction 1975.5.1 A Virtual Induction Generator for Edgewise Stability 1985.5.2 Tower Side‐to‐side Damping Using the Generator 2015.5.3 Tower Fore–aft Damping Using Blade Pitch 2115.5.4 Individual Blade Pitch Control 2165.6 Power Command Tracking 2225.6.1 Operating Strategy 2235.6.2 Tuning the Converter Control of Generator Power 2265.6.3 Power Tracking Performance 2305.7 Conclusions 2325.8 References 2336 Offshore Wind Farm Technology and Electrical Design 239David Campos-Gaona, Olimpo Anaya‐Lara and John O. Tande6.1 AC Collectors for Offshore Wind Turbines 2406.1.1 Radial Cluster Topology 2416.1.2 Single‐sided Ring Clustered Topology 2416.1.3 Double‐sided Ring Topology 2426.1.4 Star Topology 2436.1.5 Multiring Topology 2436.1.6 Summary of the Characteristics of Different AC Topologies 2446.1.7 Example of an AC Collector Topology for a Low‐power Offshore Wind Farm: Horns Rev 1 2446.1.8 Example of an AC Collector Topology for a High Power Offshore Wind Farm: the Greater  Gabbard 2456.2 DC Collectors for Offshore Wind Turbines 2476.2.1 Parallel DC Collector System 2476.2.2 DC Collectors for Series Connections 2476.2.3 Hybrid Topology 2496.3 Connection Layout Options for a Cluster of Offshore Wind Farms 2496.3.1 The Offshore AC Hub 2506.3.2 Multiterminal HVDC Option: The DC General Ring Topology 2516.3.3 Multiterminal HVDC Option: The DC Star Topology 2526.3.4 Multiterminal HVDC Option: The DC Star with a General Ring Topology 2526.3.5 Multiterminal HVDC Option: The Wind Farm Ring Topology 2536.4 Protection of Offshore Wind Farms 2556.4.1 Switchgear at Substation Level 2556.4.2 Switchgear at Array Level 2566.4.3 Grounding of Offshore Wind Farms 2576.4.4 Protection Zones in Offshore Wind Farms 2596.4.4.1 Wind Generator Protection Zone 2606.4.4.2 Feeder Protection Zone 2636.4.4.3 Busbar Protection Zone 2646.4.4.4 High Voltage Transformer Protection Zone 2666.5 Acknowledgements 2666.6 References 2667 Operation and Maintenance Modelling 269Thomas Michael Welte, Iver Bakken Sperstad, Elin Espeland Halvorsen‐Weare, Øyvind Netland, Lars Magne Nonås, and Magnus Stålhane7.1 Introduction 2707.2 O&M Modelling for Offshore Wind Farms 2727.2.1 Classification of Models 2727.2.2 State‐of‐the‐art in Modelling 2757.2.3 Decision Problems and Model Application 2787.3 Decision Support Tools Developed by NOWITECH 2787.3.1 NOWIcob 2807.3.2 Vessel Fleet Optimization Models 2837.3.3 Routing and Scheduling 2847.3.4 Use of Different Models and Synergetic Interactions 2887.3.5 Model Validation and Verification 2897.4 Application of Models – Examples and Case Studies 2917.4.1 Cost‐Benefit Evaluation of Remote Inspection 2917.4.1.1 Simulation Cases in NOWIcob 2937.4.1.2 Results of the Cost‐Benefit Analysis 2937.4.1.3 Laboratory Evaluation 2947.4.1.4 Remote Inspection after NOWITECH 2957.4.2 O&M Vessel Fleet Optimization 2967.5 Outlook 2977.6 References 3008 Supervisory Wind Farm Control 305Karl Merz, Olimpo Anaya‐Lara, William E. Leithead and Sung‐ho Hur8.1 Background 3058.2 Control Objectives 3068.3 Sensory Systems 3078.4 Wind Farm System Model 3088.4.1 Wind and Wakes 3088.4.1.1 Stochastic Wind Field Models 3098.4.1.2 Wake Propagation Models 3098.4.1.3 CFD Models 3108.4.1.4 Comments on Wind Field Models 3108.4.2 Ocean Waves 3118.4.3 Structures 3118.4.4 Electrical System 3128.5 Control Strategies 3138.5.1 Control at the PCC 3138.5.1.1 HVAC Transmission 3148.5.1.2 HVDC Transmission 3168.5.1.3 Comments on Controlling Output at the PCC 3178.5.2 Dispatch of Power Set‐Points in Response to TSO Requirements 3178.5.2.1 Proportional Dispatch 3188.5.2.2 Optimum Dispatch 3198.5.3 Power Dispatch in Response to Wakes and Gusts 3208.5.3.1 Heat and Flux (ECN) 3218.5.3.2 Load Reduction 3228.5.4 Operation as a Function of Electricity Price 3258.5.5 Including Operation and Maintenance Aspects in the Cost Function 3268.6 Wind Farm Controller for Improved Asset Management 3278.6.1 Power Adjusting Controller (PAC) 3298.6.2 Rules and Operation for Power Output Curtailment 3318.6.3 Case Study 3348.7 Acknowledgements 3388.8 References 3389 Offshore Transmission Technology 345Olimpo Anaya‐Lara and John O. Tande9.1 Introduction 3459.2 HVAC Transmission 3469.3 VSC‐HVDC Transmission 3499.3.1 Components of a Typical VSC‐HVDC 3509.3.1.1 VSC Converter 3509.3.1.2 Coupling Transformers 3519.3.1.3 Smoothing Reactors 3519.3.1.4 AC Harmonic Filters 3519.3.1.5 DC Capacitors 3519.3.1.6 DC Cables 3519.3.2 VSC‐HVDC Steady‐state Model 3529.3.3 VSC‐HVDC Dynamic Model 3549.3.4 VSC‐HVDC Control System 3569.3.4.1 Inner Controller Design 3579.3.4.2 Outer Controller Design 3599.4 Offshore Grid Systems 3609.4.1 Multiterminal VSC‐HVDC Networks 3609.4.2 Configurations of Multiterminal DC Transmission Systems 3629.5 Low-Frequency Alternating Current (LFAC) 3629.6 Offshore Substations 3679.7 Reactive Power Compensation Equipment 3699.7.1 Static VAR Compensator (SVC) 3699.7.2 Static Compensator (STATCOM) 3729.8 Subsea Cables 3739.8.1 AC Subsea Cables 3759.8.2 DC Subsea Cables 3759.8.3 Modelling of Underground and Subsea Cables 3759.9 Acknowledgement 3769.10 References 37610 Grid Integration and Control for Power System Operation Support 381Kjetil Uhlen10.1 Power System Interconnection 38110.2 Operation and Control 38310.2.1 Power Balancing Control (Frequency and Voltage Control) 38310.2.2 Power System Security (and Congestion Management) 38510.3 Performance Requirements and System Services (Including Grid Codes) 38610.4 Provision of System Services from Offshore Wind Farms 38910.4.1 Power Quality 39010.4.2 Fault Ride Through 39110.4.3 Frequency Control 39110.4.3.1 Inertia 39210.4.3.2 Power System Stabilizer 39310.4.4 Voltage Control 39410.4.5 Energy Storage, Secondary Control and System Protection 39510.5 References 39511 Market Integration and System Operation 397Kjetil Uhlen11.1 Purpose and Overview of Electricity Markets 39711.1.1 Forward/Future Market 39811.1.2 Day‐ahead Market 39811.1.3 Intra‐day Market 39911.1.4 Real‐time Balancing Markets 39911.1.5 Other Market Arrangements 40011.1.5.1 Capacity Markets 40011.1.5.2 Secondary Control and AGC 40011.2 Market Coupling and Transmission Allocation 40011.3 Offshore Wind as a Market Participant 40211.4 Support Schemes in an Integrated Market 40211.5 Challenges for Future Market Design 40411.6 References 405Appendix 407Index 415