# Parametric Analysis of Control Techniques for 15 MW Semi-Submersible Floating Wind Turbine
## 4 Controller Evaluation
### Parametric Study
The reduction in the pitch motion was primarily observed around 50 and 400 s, where the platform pitch fluctuations were relatively larger, and as a result, the tower loads were also reduced. Table 2 quantitatively compares the control performance resulting from changes in control parameters for the feedforward, IPC, peak shaving, and nacelle feedback controls, compared with the baseline control. The control parameters include the feedforward gain, IPC gain, maximum allowable thrust percentage, and the nacelle feedback gain, each normalized into four levels with similar intervals. Since the objective of this parametric study is to identify performance trends based on the control parameters, the control parameters were selected through a trial-and-error process aimed at achieving reasonable control performance. However, to ensure justification, the control parameters were, where possible, selected based on previously established values that had been used for the IEA 15 MW  
Figure 14: The simulation results of the target FOWT (**a**) for the baseline controller (red solid lines) and the peak shaving controller (blue solid lines); (**b**) for the baseline controller (red solid lines) and the nacelle feedback controller (blue solid lines). The black line represents the wind speed and wave elevation inputs used in the simulation. wind turbine [18]. For example, in the case of peak shaving, studies have applied 75% as the maximum allowable thrust percentage; thus, the range of control parameters was chosen around this value, covering four cases. To compare the performance of each control technique, primary performance indicators such as the mean power, standard deviation of the rotor speed, and the platform pitch motion, as well as the damage equivalent load (DEL) for the tower base fore-aft load and the blade-root flap-wise load, are presented. As the control parameters increase, the feedforward controller reduces the variations in the rotor speed and platform pitch motion, but the tower and blade loads are slightly increased. When the feedforward control parameters are at their highest level among the four levels, all loads become unstable. For the IPC, as the control parameters increase, blade loads are gradually reduced, but the variations in the rotor speed, platform pitch motion, and tower-base loads are slightly increased. When the control parameters for the individual pitch control are at their highest level, the platform pitch motion and the tower loads worsen. The peak shaving results in a gradual reduction in the platform pitch motion and the tower loads as the control parameters increase, but there is a slight decrease in the mean power. The nacelle feedback control significantly reduces the platform pitch motion as the control parameters increase. However, if the control parameters reach the highest level, the rotor speed deviation and blade loads worsen. Therefore, the control parameters of level 2 were selected for each part of the overall control algorithm with a focus on preventing the deterioration of other performance indicators.