Numerical Study of Control Effects on Negative Damping Mitigation and Global Performance Enhancement in FOWTs

Under combined wind and wave conditions, the coupled interaction between the floating offshore wind turbine (FOWT) platform and the controller can induce negative damping, leading to amplified pitch motion. This study investigates two control strategies to mitigate this issue. The first is peak shaving control, which limits rotor thrust using blade pitch control. The second is floating feedback control, which modifies the blade pitch based on the fore–aft tower-top velocity. Time-domain simulations were carried out using OpenFAST and validated against KRISO experimental data. Negative damping was first examined under regular waves and steady wind, confirming that both control strategies reduced its effects. Subsequently, irregular waves and turbulent wind at a mean wind speed of 13 m/s were applied to evaluate performance under DLC 1.3 and DLC 1.6 conditions. Results showed that improvements were most significant in the low-frequency range, and the combined controller―implementing both strategies simultaneously―provided the greatest overall benefits. Under DLC 1.6, the combined controller reduced maximum pitch motion, nacelle acceleration, and blade/tower loads by 33%, 13%, and 29%, respectively, while increasing mean power output by 1.5% compared with the Base controller. These improvements were even more pronounced under extreme turbulence, highlighting the potential of combined control strategies to enhance FOWT performance.