Assessment of the impact of active tower dampers on tower oscillations in offshore wind turbines

One of the key challenges in enhancing wind turbine reliability and longevity is mitigating tower oscillations, which arise from dynamic wind loads on the rotor and wave-induced excitations at the tower base. This can be achieved using active tower damping techniques. In this study, a model-based approach is used to quantify the impact of active tower dampers on tower oscillations. By focusing on generator torque and pitch angle control, the research explores the coupled dynamics of fore-aft and side-to-side oscillations. A linearized representation of the non-linear system is developed to assess tower oscillations in the full-load operating region. The proposed method quantitatively evaluates the effects of damping controllers directly from the linearised model. The results indicate that implementing fore-aft active tower damping leads to a reduction in tower oscillations in both directions up to 4.7 dB near the tower’s natural frequency. The findings are validated through simulations conducted in OpenFAST, using the 5 MW NREL monopile offshore wind turbine as a case study.