Control of Floating Wind Turbines

Transcription

1 ENERGY Control of Floating Wind Turbines The challenge and the stakes Patrick Rainey May DNV GL May SAFER, SMARTER, GREENER

2 Contents What is the control system Challenge of controller design for floating turbines The role of the controller in integrated design DNV GL May

3 QUALITY Allen-Bradley MicroLogix POWER RUN FAULT FORCE BAT.LO CONN DCOMM LSP BXB DC POWER V V SINK / SOURCE DC / RELAY OUT V SOURCE AC INPUT VAC VDC SINK / SOURCE DC OUTPUT VDC SOURCE AC/DC OUT RELAY QUALITY Allen-Bradley MicroLogix LSP BXB DC POWER V V SINK / SOURCE DC / RELAY OUT V SOURCE AC INPUT V A C V D C S I N K / S O U R C E QUALITY Allen-Bradley MicroLogix QUALITY POWER RUN FAULT FORCE BAT.LO CONN DCOMM LSP BXB DCPOWER V DCINPUTS VSINK/ SOURCE DC/ RELAYOUT Allen-Bradley VSOURCE AC INPUT VAC MicroLogix POWER RUN FAULT FORCE BAT.LO CONN DCOMM LSP BXB DCPOWER V DCINPUTS VSINK/ SOURCE DC/ RELAYOUT VSOURCE AC INPUT VAC V D C S IN K / S O U R C E V D C S IN K / S O U R C E Turbine Controller Introduction Wind turbines include a large number of complex subsystems Blade pitch, Power converter, Yaw, Vibration monitor POWER RUN FAULT FORCE BAT.LO CONN DCOMM The turbine controller coordinates all these systems Primary control loops Control rotor speed using generator torque Control rotor speed using blade pitch angle Design objectives for primary loops Maintain rotor speed within allowable limits Maximize energy capture Minimize loads DNV GL May

4 Challenge : Low frequency dynamics Platform motion interacts with speed control Non-minimum phase system Bottom line: Difficult to control -> more speed variation DNV GL May

5 Challenge : Low frequency dynamics Platform natural periods chosen to avoid wave excitation However they clash with the wind excitation Wave spectrum Wind spectrum Floating turbine surge mode Floating turbine surge mode Wave spectra of a fully developed sea for different wind speeds according to Moskowitz Wind Spectrum based on work by van der Hoven () DNV GL May

6 The cost of speed variation Cope with the speed variation High voltages in generator -> expensive generator and PCS High relative wind speed at blade tip -> expensive blades High power variation -> expensive PCS, transformer, grid connection Prevent the speed variation Torque control -> high power variation Hydrodynamic damping -> floating platform design constraint Bottom line: speed control does not come cheap DNV GL May

7 Derivative of Moorings x velocity Challenge : Non-linear dynamics Control design and assessment relies on linear systems theory Aerodynamics are non-linear but can reasonably be considered as locally linear around a mean wind speed Hydrodynamic drag is quadratic Morison s equation: F = ρc m Vu + ρc dau u A(,) = -. Plus - tide dependent dynamics Moorings x velocity Bottom line: difficult to predict Conservative design add costs DNV GL May

8 Integrated design the role of the controller Minimization of system cost not subsystem cost Foundation cost vs. turbine cost? Electrical system cost vs. speed control? Power variation vs. load variation? Other % Electrical system % CapEx breakdown Turbine supply cost % The dynamics of the floating system have profound interaction with rotor control Mitigation of non-minimum phase behavior can be made through electrical system or hydrodynamic design Foundatio n supply % T&I % Understanding of whole system required DNV GL May

9 Example: FORCE project Project aim: Reducing Lifetime Cost of Energy for a round offshore turbine Footprint=.m.Hz Footprint=.m.Hz Integrated Design Advanced control Jacket mass Piles mass Transition Tower TOTAL tonnes tonnes tonnes tonnes tonnes Jacket mass Piles mass Transition Tower TOTAL tonnes tonnes tonnes tonnes tonnes Capex reduced through: Stiffer jacket Advanced individual pitch control LiDAR for control Slender flexible blade DNV GL May

10 Conclusion Low frequency dynamics makes floating turbines are more difficult to control than fixed foundation turbines Non-linear dynamics makes floating turbine dynamics more difficult to assess than fixed foundation turbines Control optimization has significant impact on turbine cost DNV GL May

11 Control of Floating Wind Turbines Patrick Rainey + () SAFER, SMARTER, GREENER DNV GL May