# Load Prediction Control Study of a Pitch Control System for Large Offshore Wind Turbines
## 3 Load Disturbance Compensation Model  
Offshore wind turbines operate in environments characterized by highly dynamic wind speed and directional variations. Environmental factors such as waves, tides, and currents impose dynamic stresses on the turbine's tower and foundation structures. These disturbances propagate through the system, ultimately generating significant load fluctuations within the pitch control mechanism.  
Moreover, these load perturbations directly degrade the positional control accuracy of the pump-controlled pitch system. To address this, the real-time state monitoring of the disturbances is proposed to dynamically counteract hydraulic cylinder displacement fluctuations induced by such perturbations.  
Using Equation (5), hydraulic cylinder load force balance equation can be obtained as follows:  
\[F_{L}=A_{p1}P_{1}-A_{p2}P_{2}-M_{t}\ddot{x}_{p}-B_{p}\dot{x}_{p}-Kx_{p}, \tag{13}\]  
From Equation (13), the load force of the hydraulic cylinder can be observed in real time through the hydraulic cylinder displacement and system pressure, and its model is shown in Figure 4.  
From the aforementioned load disturbance observation, relatively accurate observed load values can be obtained. Based on the control mechanism of the pump-controlled cylinder system, compensatory control is implemented for system variations caused by load disturbances. This approach effectively suppresses or even eliminates the impact of load disturbances on the rotational speed control of the system. Compensation control for load disturbance, based on the mathematical model of the pump control system, yields the load disturbance compensation control principle shown in Figure 5.  
By the principle of structural invariance, \(F_{1}\) is taken as the observation and is set as a feed-forward compensator for \(G\)(\(s\)); then, the effect of \(F_{1}\) on the displacement of the hydraulic cylinder will be canceled out, compensating for the control of load disturbances as follows:  
\[G(\mathbf{s})\cdot K(\mathbf{s})=F(\mathbf{s}), \tag{14}\]  
where \(F(s)\) is the transfer function from the load disturbance \(F_{1}\) to the disturbance injection point (\(P_{\mathrm{h}}\)), which can be expressed as follows:  
\[F(\mathbf{s})=\frac{K_{e}}{A^{2}{}_{P1}}(\frac{V_{t}}{2\beta_{e}K_{c}}s+1), \tag{15}\]  
\(K\)(s) is the transfer function from the perturbation compensation point (\(\partial\)) to the perturbation injection point (\(P_{\mathrm{h}}\)), which can be expressed as follows:  
\[K(\mathbf{s})=\frac{D_{p}}{A_{P1}}, \tag{16}\]  
The coupled Equations (14)-(16) give the mathematical model of the pump-controlled motor load disturbance compensation as follows:  
\[G(\mathbf{s})=\frac{K_{e}}{D_{P}A_{P1}}(\frac{V_{t}}{2\beta_{e}K_{c}}s+1) \tag{17}\]  
Figure 4: Load prediction model diagram.  
Figure 5: Schematic diagram of load disturbance compensation transfer function.  
Based on the load observation of the pump control cylinder system, combined with the load disturbance compensation mathematical model obtained from the above structural non-deformation principle, the hydraulic cylinder load disturbance compensation position control transfer function block diagram is shown in Figure 6. The introduction of fuzzy control techniques into the design of compensator _G(s)_ utilizes the strong robustness of fuzzy controllers to overcome the shortcomings of linear controllers with poor immunity to interference to improve the control performance.