Structural control concept for load reduction of offshore wind turbines

This chapter introduces the structural control concept for load reduction of OWTs. Theories for both passive and active structural control are introduced. Particularly, a spar-type FOWT is used as the study case to demonstrate the load mitigation effectiveness of the proposed structural control methods. For the passive case, design optimization process is performed on a TMD installed in the spar platform, and the obtained numerical simulation results have indicated the both their effectiveness and limits regarding different system parameters and installations. Regarding the active case, a gain scheduling H2/H∞ active structural full-state feedback controller is designed for an HMD installed at the tower top of a spar-type FOWT, aiming at both reducing tower bottom load and mitigating the aerodynamic disturbance. The results demonstrate that more load reduction could be achieved at the expense of more energy consumption. At the same time, this will bring the risk of instability. Moreover, the full-state feedback controller is not very practical from a technical point of view due to the lack of sensors and measurement inaccuracy.