# Parametric Analysis of Control Techniques for 15 MW Semi-Submersible Floating Wind Turbine
###### Abstract  
In this study, a composite control algorithm based on classical control methods is developed to achieve all control objectives, such as power production, load reduction, and motion reduction, for the floating wind turbine. In previous studies, peak shaving and nacelle feedback were used together to reduce both platform motion and the tower-base loads of floating wind turbines. The new approach presented in this study not only addresses the platform motion and tower loads but also aims to mitigate the rotor speed fluctuations and the blade loads by additionally introducing feedforward control and individual pitch control. This expansion enhances the applicability and control performance of classical control algorithms. To achieve this, parametric simulations were conducted using OpenFAST to assess the effects of control parameter variations for each control technique. The simulation results showed that the proposed control algorithm significantly reduced the rotor speed fluctuations, tower loads, blade loads, and platform motion compared with the baseline controller. floating wind turbine; peak shaving; nacelle feedback; feedforward; individual pitch control; OpenFAST 202515 15 [PERSON]  
et al. showed that IPC was able to reduce oscillations on the blade root by 40% [5]. The fatigue load caused by the rotor thrust can be reduced using peak shaving, which adjusts the blade pitch angle proactively in regions with wind speeds lower than the rated wind speed. [PERSON] et al. found that peak shaving reduced the fore-aft fatigue load on the tower base and the flap-wise fatigue load on the blade root by up to 9% and 14%, respectively [6]. The rotor speed fluctuations can be mitigated by adding a feedforward term to the blade pitch control loop, utilizing wind speed estimated by a wind speed estimator. [PERSON] et al. demonstrated that the feedforward control reduced the standard deviations of the rotor speed by 20% [7]. However, in the case of floating wind turbines, which are continuously exposed not only to wind but also to waves, damping techniques are required not only to mitigate fatigue loads and power fluctuations but also to reduce the platform motion. Structural damping techniques include reducing platform motion by integrating a tuned mass damper (TMD) into the tower. [PERSON] et al. demonstrated through experiments that using the TMD can reduce the peak amplitude of the acceleration and the tower bending moment by 7.8% and 8.8%, respectively [8]. [PERSON] et al. showed that a bounding TMD (PTMD) could achieve approximately 10% greater reduction in peak acceleration amplitude compared with the conventional TMD [9]. [PERSON] et al. improved the performance of the conventional TMD by employing multiple TMDs (MTMD) [10]. Regarding damping techniques through active control, the platform resonance can be avoided by adjusting the control gain so that the blade pitch control frequency is lower than the resonant frequency of the platform. In the study by [PERSON] et al., the detuning technique could increase the damping of platform motion by up to 13% [11]. The fluctuation of the platform pitch motion can be reduced using tower damper structures that were originally developed for fixed wind turbines. According to [PERSON] et al., the feedback control of the tower-top velocity, known as nacelle feedback, could significantly reduce the platform pitch motion [12]. [PERSON] et al. showed that the feedback control of the nacelle angular acceleration was able to reduce the standard deviation of the platform pitch motion and the fore-aft fatigue load at the tower base by approximately 80% and 30%, respectively [13]. The feedforward control, originally developed for fixed wind turbines, could also be used to reduce the power fluctuations in the floating wind turbines. In the study by [PERSON] et al., the feedforward control reduced both the rotor speed and the generator power fluctuations of the floating wind turbines by 81% under gust conditions [14].