# Load Prediction Control Study of a Pitch Control System for Large Offshore Wind Turbines
## 4 Experimental and Simulation Results  
### Simulation  
The joint simulation models of AMEsim (2020.1) and MATLAB (R2021a) for hydraulic cylinder position PID control and load disturbance compensation control are constructed, respectively, as shown in Figure 7.  
According to the pitch system design requirements for electrical and hydraulic component selection, selection is completed according to the sample information to set the simulation parameters of each component, as shown in Table 1 below, for some of the parameters of the simulation model used in this paper. Figure 6: Hydraulic cylinder load disturbance compensation position control transfer function control flow chart. Figure 7: Joint simulation model of AMEsim and MATLAB. The simulation curve of the pitch angle 8 versus the position of the hydraulic cylinder when the servomotor is running at a fixed speed of 2700 r/min with the system open loop is shown in Figure 8. From the figure, the pitch system designed in this paper can realize the variation of pitch angle from \(-3.5\) to 90\({}^{\circ}\), and there is an obvious nonlinear correlation between the hydraulic cylinder displacement and the pitch angle. A sinusoidal signal of 0.05 Hz was applied to the hydraulic cylinder. The simulation results for both PID and LDC control are presented in Figure 9. The curves indicate that the designed LDC control method demonstrated rapid tracking of the sinusoidal signal, without amplitude decay. Compared to that for PID control, the LDC achieved a 50.6% reduction in maximum tracking error. The displacement variance between the PID control and the target signal was 41.15, whereas the LDC control exhibited a variance of only 2.02. This represents a 95.1% improvement in positional accuracy (evaluated via displacement variance) for LDC over PID. These results confirm that the LDC control outperforms PID in tracking sinusoidal signals. Setting the displacement step signal of the hydraulic cylinder from 100-700 mm, its simulation results for PID control and LDC control are shown in Figure 10. The time required to reach the steady state under PID control is 14.4 s, and the time required to reach the warm pond under LDC control is 13.8 s. A simulation performance comparison of LDC and PID control strategies is shown in Table 2. \begin{table}
\begin{tabular}{c c c} \hline
**Serial Number** & **Parameter Name** & **Value** \\ \hline
1 & Max system pressure & 35 MPa \\
2 & Rated system pressure & 26 MPa \\
3 & Cylinder structure parameters & 200-140-800 mm \\
4 & Hydraulic pump displacement & 80 mL/r \\
5 & Rated motor speed & 1800 r/min \\
6 & Max motor speed & 2700 r/min \\
7 & Servo motor moment of inertia & 6.073\(\cdot 10^{-2}\) kg\(\cdot\)m\({}^{2}\) \\
8 & Hydraulic pump moment of inertia & 6.05\(\cdot 10^{-2}\) kg\(\cdot\)m\({}^{2}\) \\ \hline \end{tabular}
\end{table} 
Table 1: Partial parameters of the main components of the simulation model. Figure 8: Hydraulic cylinder displacement vs. pitch angle curve. The pitch change process can be divided into a power adjustment portion between 0 and 35\({}^{\circ}\) and a wind turbine protection adjustment portion between 35 and 90\({}^{\circ}\). The \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Instruction Signal** & **Parameter** & **PID Control** & **LDC Control** \\ \hline Step signal & & & \\ (100-700 mm) & Settling time & 14.4 s & 13.8 s \\ Sinusoidal signal & Maximum tracking error & 12.66 mm & 2.42 mm \\ (50 mm, 0.05 HZ) & Displacement variance & 41.5 & 2.02 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation performance comparison of LDC and PID control strategies. Figure 10: Simulation results of the step signal. Figure 9: Simulation results of sinusoidal signal.