Control Design for Floating Offshore Wind Turbines
Mustafa Abdelrahman School of Engineering and Computer Science, the University of Hull
The floating offshore wind turbine (FOWT) technology is emerging and attracting increased attentionThe floating offshore wind turbine (FOWT) technology is emerging and attracting increased attentiondue to possibility of installing turbines far away from shore in deep water to get access to strongerand more consistent wind with less shear. In addition, in offshore environment there is a potential toinstall giant turbines to harness more energy, without worrying about limited-site and visual/ acousticpollution, typically existing in onshore and near-shore locations. However, the FOWT technology hasseveral challenges; among them is the requirement to have stable platform to carry the wind turbinesystems components (tower, nacelle, blades … etc.). Stabilizing the platform with the lowest possiblesize and cost is a topic that researchers address using advanced control systems. The stable platformis directly linked with reduced fatigue on the turbine tower and other components.In land based wind turbines, a control systems for 1) blade pitch angles and 2) generator torque isessential element that is used increase both efficiency and safety of the turbine during operation.However, the available literature shows that these fixed-based wind turbine control approachescannot be directly used with FOWT; an instability can result. Hence, several modified/improvedcontrol techniques are tailored to cope with this problem. There are 3 categories that has beenidentified for FOWT control: 1) Basic PI/PID controllers with gain scheduling carefully modified toaccount for the platform instability problem, 2) Advanced control methods such as 𝐻∞ , ModelPredictive Control (MPC) and Disturbance Accommodation Control (DAC) that can address all FOWTcontrol objectives in a simultaneous multi-objective way, and 3) Structural control which includeaddition of extra actuator in the FOWT, e.g. in the nacelle or platform, to help in reducing platformmotion in such a way to avoid instability and reduce fatigues. Each of the three categories has its ownpros and cons with a lack of comparative studies between them in terms of cost, reliability andperformance.
In our current research, two main point are to be investigated:
• Potential of using advanced control techniques combined with technique for rejecting thewave disturbance through the use of Unknown Input Estimation (UIE) methods. It is expectedthat UIE can improve the performance of FOWT, in terms of power and rooter speedregulation, structural fatigue reduction and platform stabilization.
• Rationale of multi-objective control with extra actuator(s) installed in FOWT platform.