# Parametric Analysis of Control Techniques for 15 MW Semi-Submersible Floating Wind Turbine
## 4 Controller Evaluation  
### Parametric Study  
To improve the control performance of the proposed control algorithm and analyze its trend with respect to the control parameters, parametric simulations were conducted for the feedforward control, IPC, peak shaving, and the nacelle feedback control techniques. For each control algorithm added to reduce the fatigue loads and the platform motion, the control performance was compared with the baseline control algorithm. Each simulation was conducted for 600 s under the normal turbulence model (NTM) and normal sea state (NSS) conditions, which are recommended as normal operating conditions in the international guidelines for the floating offshore wind turbine development by the International Electrotechnical Commission (IEC) [30; 31]. The NTM and NSS conditions define turbulence  
Figure 12: Flowchart for the controller implementation in OpenFAST. intensity, wave height, and wave period for a given wind speed based on their respective spectrum models. These conditions have been employed in numerous studies as standard environmental conditions for verifying control performance [12; 13; 18; 20]. Figure 13 shows the simulation results of the feedforward control and the IPC compared with the baseline control for the wind speed, wave elevation, rotor speed, blade pitch angle, generator torque, generator power, platform pitch motion, tower-base fore-aft bending moment, and the blade-root flap-wise bending moment, respectively. Since both feedforward control and IPC were designed for operation in the above-rated wind speed region, the NTM and NSS conditions corresponding to the mean wind speed of 20 m/s were applied. These conditions include the turbulence intensity of 14.4%, the significant wave height of 3.62 m, and the peak spectral wave period of 8.52 s. In the case of Figure 13a, it was observed that the feedforward control mitigated the rotor speed and the power fluctuations compared with the baseline control, primarily in situations where the wave fluctuations increased, around 20, 100, 300, and 550 s. This indicates that the pitch control sensitivity, which varies with the wave fluctuations, is adequately managed by the feedforward controller and that it has also been shown to slightly reduce the platform pitch motion. In Figure 13b, the IPC resulted in a reduction in the blade-root flap-wise loads compared with the baseline control. The reduced loads were observed at the 1-revolution frequency component of the individual blade loads, and the blade fatigue loads were significantly reduced throughout the entire time span. Figure 14 shows the simulation results of the peak shaving and the nacelle feedback control compared with the baseline control. Since peak shaving was designed for the rated wind speed region, the NTM and NSS conditions corresponding to the mean wind speed  
Figure 13: The simulation results of the target FOWT (**a**) for the baseline controller (red solid lines) and the feedforward controller (blue solid lines); (**b**) for the baseline controller (red solid lines) and the IPC controller (blue solid lines). The black line represents the wind speed and wave elevation inputs used in the simulation. of 12 m/s were applied. These conditions include the turbulence intensity of 20.0%, the significant wave height of 1.84 m, and the peak spectral wave period of 7.44 s. In the case of the nacelle feedback control, which is designed for the control in the above-rated wind speed region, the same conditions as the simulation in Figure 13 were applied. In Figure 14a, the peak shaving was able to reduce the maximum platform pitch motion and the tower load compared with the baseline control. This was mainly observed around 20 and 500 s when the minimum blade pitch angle near the rated wind speed was limited by peak shaving. It was found that as the thrust peak was shaved, the maximum platform pitch motion and tower load were also reduced. In Figure 14b, nacelle feedback control showed a reduction in the platform pitch motion compared with the baseline control.