Offshore wind energy generation : control, protection, and integration to electrical systems

The offshore wind sector's trend towards larger turbines, bigger wind farm projects and greater distance to shore has a critical impact on grid connection requirements for offshore wind power plants. This important reference sets out the fundamentals and latest innovations in electrical systems and control strategies deployed in offshore electricity grids for wind power integration.

Includes:

All current and emerging technologies for offshore wind integration and trends in energy storage systems, fault limiters, superconducting cables and gas-insulated transformers Protection of offshore wind farms illustrating numerous system integration and protection challenges through case studies Modelling of doubly-fed induction generators (DFIG) and full-converter wind turbines structures together with an explanation of the smart grid concept in the context of wind farms Comprehensive material on power electronic equipment employed in wind turbines with emphasis on enabling technologies (HVDC, STATCOM) to facilitate the connection and compensation of large-scale onshore and offshore wind farms Worked examples and case studies to help understand the dynamic interaction between HVDC links and offshore wind generation Concise description of the voltage source converter topologies, control and operation for offshore wind farm applications Companion website containing simulation models of the cases discussed throughout

Equipping electrical engineers for the engineering challenges in utility-scale offshore wind farms, this is an essential resource for power system and connection code designers and pratitioners dealing with integation of wind generation and the modelling and control of wind turbines. It will also provide high-level support to academic researchers and advanced students in power and renewable energy as well as technical and research staff in transmission and distribution system operators and in wind turbine and electrical equipment manufacturers.

Author Notes

Edgar Lenymirko Moreno-Goytia, Reader, Instituto Tecnológico de Morelia, México Dr Moreno-Goytia has researched power electronic-based equipment and measurement systems development. He designed and built a Thyristor Controlled Series Compensator and its control to operate in a voltage fluctuations environment, and has been involved in evaluating the impact of wind generation on the electrical grid. Dr Moreno-Goytia has published over thirty papers in international conferences and journals and is a member of IEEE and IET.

Olimpo Anaya-Lara, Senior Lecturer, Institute for Energy and Environment , University of Strathclyde, Glasgow, UK Dr Anaya-Lara has researched power electronic equipment, control systems development, and stability and control of power systems with increased wind energy penetration. He has developed control strategies for Flexible Alternating Current Transmission System devices (FACTS), and designed control schemes for marine applications using advanced control techniques. He is a member of the CIGRE Working Group B4-39, two International Energy Agency Annexes, also the IEEE and IET. He has published over thirty-five journals, ninety papers and co-authored three books.

David Campos-Gaona, Research Assistant, Instituto Tecnológico de Morelia, México Mr Campos-Gaona has investigated electronics-based solutions to electrical networks such as digital power meters, DSP based protection algorithms, and protection systems for wind turbines. He developed electronic equipment such as residential digital power meter with a wireless communication port. He was a research assistant with the SUPERGEN FlexNet, and is member of the IEEE. He has published several papers and conference proceedings.

Grain Philip Adam, Research Fellow, University of Strathclyde, Glasgow, UK Grain received a Ph.D. degree in power electronics from Strathclyde University in 2007. He is currently with the Department of Electronic and Electrical Engineering, Strathclyde University, and his research interests are multilevel inverters, electrical machines and power systems control and stability.

Preface	p. xi
About the Authors	p. xiii
Acronyms and Symbols	p. xv
1 Offshore Wind Energy Systems	p. 1
1.1 Background	p. 1
1.2 Typical Subsystems	p. 1
1.3 Wind Turbine Technology	p. 4
1.3.1 Basics	p. 4
1.3.2 Architectures	p. 6
1.3.3 Offshore Wind Turbine Technology Status	p. 7
1.4 Offshore Transmission Networks	p. 8
1.5 Impact on Power System Operation	p. 9
1.5.1 Power System Dynamics and Stability	p. 10
1.5.2 Reactive Power and. Voltage Support	p. 10
1.5.3 Frequency Support	p. 11
1.5.4 Wind Turbine Inertial Response	p. 11
1.6 Grid Code Regulations for the Connection of Wind Generation	p. 12
Acknowledgements	p. 13
References	p. 14
2 DFIG Wind Turbine	p. 15
2.1 Introduction	p. 15
2.1.1 Induction Generator (JG)	p. 15
2.1.2 Back-to-Back Converter	p. 16
2.1.3 Gearbox	p. 16
2.1.4 Crowbar Protection	p. 16
2.1.5 Turbine Transformer	p. 17
2.2 DFIG Architecture and Mathematical Modelling	p. 17
2.2.1 IG in the abc Reference Frame	p. 17
2.2.2 IG in the dqO Reference Frame	p. 23
2.2.3 Mechanical System	p. 27
2.2.4 Crowbar Protection	p. 29
2.2.5 Modelling of the DFIG B2B Power Converter	p. 30
2.2.6 Average Modelling of Power Electronic Converters	p. 33
2.2.7 The dc Circuit	p. 35
2.3 Control of the DFIG WT	p. 36
2.3.1 PI Control of Rotor Speed	p. 36
2.3.2 PI Control of DFIG Reactive Power	p. 39
2.3.3 PI Control of Rotor Currents'	p. 41
2.3.4 PI Control of dc Voltage	p. 42
2.3.5 PI Control of Grid-side Converter Currents	p. 45
2.4 DFIG Dynamic Performance Assessment	p. 47
2.4.1 Three-phase Fault	p. 41
2.4.2 Symmetrical Voltage Dips	p. 51
2.4.3 Asymmetrical Faults	p. 53
2.4.4 Single-Phase-to-Ground Fault	p. 54
2.4.5 Phase-to-Phase Fault	p. 55
2.4.6 Torque Behaviour under Symmetrical Faults	p. 56
2.4.7 Torque Behaviour under Asymmetrical Faults	p. 58
2.4.8 Effects of Faults in the Reactive Power Consumption of the IG	p. 59
2.5 Fault Ride-Through Capabilities and Grid Code Compliance	p. 60
2.5.1 Advantages and Disadvantages of the Crowbar Protection	p. 60
2.5.2 Effects of DFIG Variables over Its Fault Ride-Through Capabilities	p. 61
2.6 Enhanced Control Strategies to Improve DFIG Fault Ride-Through Capabilities	p. 62
2.6.1 The Two Degrees of Freedom Internal Model Control (IMC)	p. 62
2.6.2 IMC Controller of the Rotor Speed	p. 65
2.6.3 IMC Controller of the Rotor Currents	p. 66
2.6.4 IMC Controller of the dc Voltage	p. 67
2.6.5 IMC Controller of the Grid-Side Converter Currents	p. 69
2.6.6 DFIG IMC Controllers Tuning for Attaining Robust Control	p. 70
2.6.7 The Robust Stability Theorem 70 References	p. 72
3 Fully-Rated Converter Wind Turbine (FRC-WT)	p. 73
3.1 Synchronous Machine Fundamentals	p. 73
3.1.1 Synchronous Generator Construction	p. 73
3.1.2 The Air-Gap Magnetic Field of the Synchronous Generator	p. 74
3.2 Synchronous Generator Modelling m the dq Frame	p. 79
3.2.1 Steady-State Operation	p. 81
3.2.2 Synchronous Generator with Damper Windings	p. 82
3.3 Control of Large Synchronous Generators	p. 85
3.3.1 Excitation Control	p. 86
3.3.2 Prime Mover Control	p. 87
3.4 Fully-Rated Converter Wind Turbines	p. 88
3.5 FRC-WT with Synchronous Generator	p. 89
3.5.1 Permanent Magnets Synchronous Generator	p. 90
3.5.2 FRC-WT Based on Permanent Magnet Synchronous Generator	p. 92
3.5.3 Generator-Side Converter Control	p. 93
3.5.4 Modelling of the dc Link	p. 96
3.5.5 Network-Side Converter Control	p. 98
3.6 FRC-WT with Squirrel-Cage Induction Generator	p. 100
3.6.1 Control of the FRC-IG Wind Turbine	p. 100
3.7 FRC-WT Power System Damper	p. 105
3.7.1 Power System Oscillations Damping Controller	p. 105
3.7.2 Influence of Wind Generation on Network Damping	p. 107
3.7.3 Influence of FRC-WT Damping Controller on Network Damping	p. 108
Acknowledgements	p. 110
References	p. 112
4 Offshore Wind Farm Electrical Systems	p. 113
4.1 Typical Components	p. 113
4.2 Wind Turbines for Offshore - General Aspects	p. 113
4.3 Electrical Collectors	p. 115
4.3.1 Wind Farm Clusters	p. 118
4.4 Offshore Transmission	p. 118
4.4.1 HVAC Transmission	p. 118
4.4.2 HVDC Transmission	p. 120
4.4.3 CSC-HVDC Transmission	p. 122
4.4.4 VSC-HVDC Transmission	p. 128
4.4.5 Multi-Terminal VSC-HVDC Networks	p. 140
4.5 Offshore Substations	p. 141
4.6 Reactive Power Compensation Equipment	p. 144
4.6.1 Static Var Compensator (SVC)	p. 144
4.6.2 Static Compensator (STATCOM)	p. 147
4.7 Subsea Cables	p. 150
4.7.1 Ac Subsea Cables	p. 150
4.7.2 Dc Subsea Cables	p. 150
4.7.3 Modelling of Underground and Subsea Cables	p. 150
Acknowledgements	p. 151
References	p. 151
5 Grid Integration of Offshore Wind Farms - Case Studies	p. 155
5.1 Background	p. 155
5.2 Offshore Wind Farm Connection Using Point-to-Point VSC-HVDC Transmission	p. 156
5.3 Offshore Wind Farm Connection Using HVAC Transmission	p. 159
5.4 Offshore Wind Farm Connected Using Parallel HVAC/VSC-HVDC Transmission	p. 161
5.5 Offshore Wind Farms Connected Using a Multi-Terminal VSC-H VDC Network	p. 164
5.6 Multi-Terminal VSC-HVDC for Connection of In lei-Regional Power Systems	p. 168
Acknowledgements	p. 171
References	p. 171
6 Offshore Wind Farm Protection	p. 173
6.1 Protection within the Wind Farm ac Network	p. 173
6.1.1 Wind Generator Protection Zone	p. 174
6.1.2 Feeder Protection Zone	p. 178
6.1.3 Busbar Protection Zone	p. 179
6.1.4 High - Voltage Transformer Protection Zone	p. 180
6.2 Study of Faults in the ac Transmission Line of an Offshore DFIG Wind Farm	p. 180
6.2.1 Case Study 1	p. 181
6.2.2 Case Study 2	p. 181
6.3 Protections for dc Connected Offshore Wind Farms	p. 184
6.3.1 VSC-HVDC Converter Protection Scheme	p. 184
6.3.2 Analysis of dc Transmission Line Fault	p. 185
6.3.3 Pole-to-Pole Faults	p. 186
6.3.4 Pole-to-Earth Fault	p. 187
6.3.5 HVDC dc Protections: Challenges and Trends	p. 188
6.3.6 Simulation Studies of Faults in die dc Transmission Line of an Offshore DF1G Wind Farm	p. 188
Acknowledgements	p. 192
References	p. 192
7 Emerging Technologies for Offshore Wind Integration	p. 193
7.1 Wind Turbine Advanced Control for Load Mitigation	p. 193
7.1.1 Blade Pitch Control	p. 193
7.1.2 Blade Twist Control	p. 194
7.1.3 Variable Diameter Rotor	p. 194
7.1.4 Active Flaw Control	p. 195
7.2 Converter Interface Arrangements and Collector Design	p. 195
7.2.1 Conveners on Turbine	p. 195
7.2.2 Converters on Platform	p. 198
7.2.3 Ac Collection Options: Fixed or Variable Frequency	p. 200
7.2.4 Evaluation of> Higher (	p. 202
7.3 Dc Transmission Protection	p. 203
7.4 Energy Storage Systems (EESs)	p. 204
7.4.1 Batteries	p. 205
7.4.2 Super Capacitors	p. 205
7.4.3 Flywheel Storage System	p. 205
7.4.4 Pumped-Hydro Storage	p. 206
7.4.5 Compressed Air Storage Systems	p. 206
7.4.6 Superconducting Magnetic Energy Storage (SMES)	p. 206
7.5 Fault Current Limiters (FCLs)	p. 207
7.6 Sub-Sea Substations	p. 207
7.7 HTSCs, GITs and GILs	p. 208
7.7.1 HTSCs, (High-Temperature Superconducting Cables)	p. 208
7.7.2 GITs (Gas-Insulated Transformers)	p. 208
7.7.3 GILs (Gas-Insulated Lines)	p. 209
7.8 Developments in Condition Monitoring	p. 209
7.8.7 Partial Discharge Monitoring in HV Cables	p. 209
7.8.2 Transformer Condition Monitoring	p. 210
7.8.3 Gas-Insulated Switchgear Condition Monitoring	p. 211
7.8.4 Power Electronics Condition Monitoring	p. 211
7.9 Smart Grids for Large-Scale Offshore Wind Integration	p. 213
7.9.7 VPP Control Approach	p. 216
7.9.2 Phasor Measurement Units	p. 217
Acknowledgements	p. 217
References	p. 18
Appendix A Voltage Source Converter Topologies	p. 223
A.1 Two-Level Converter	p. 223
A.1.1 Operation	p. 223
A.1.2 Voltage Source Converter Square-Mode Operation	p. 224
A.1.3 Pulse Width Modulation	p. 225
A.2 Neutral-Point Clamped Converter	p. 240
A.2.1 Selective Harmonic Elimination	p. 242
A.2.2 Sinusoidal Pulse Width Modulation	p. 244
A.3 Flying Capacitor (FC) Multilevel Converter	p. 247
A.4 Cascaded Multilevel Converter	p. 248
A 5 Modular Multilevel Converter	p. 249
References	p. 258
Appendix B Worked-out Examples	p. 271
Index	p. 279

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