# Height Control System for Wind Turbines Based on Critical Wind Speed Calculation
## 3 Proposed Materials and Methods  
For the development of a linear actuator control system designed to lower the wind turbine during strong winds proposed in our research, various components were analyzed and investigated. This section provides a detailed description of the PID controller in use, the rationale for selecting the target values for the controller, a description of the chosen linear actuator, its mathematical model, and the details of the system integration, including sensors and the frequency converter. A PID controller is used to control a system with feedback, allowing the desired output value to be achieved by minimizing the error between the setpoint (SP) and the current process variable [23; 24]. The block diagram of the wind turbines with a PI controller is shown in Figure 1.  
Figure 1 illustrates the automatic control system used to lower the rotor of the Onipko wind turbine under strong wind conditions. The system includes the following components:  
* Anemometer: Measures wind speed \(V_{w}(t)\) and outputs a corresponding voltage signal \(V_{a}(t)\). * PI Controller: Takes the anemometer's output as input and calculates the control signal \(U(t)\) based on the error between the setpoint and the measured position. The PI controller uses proportional (K\({}_{\text{p}}\)) and integral (K\({}_{\text{i}}\)) gains to optimize the control signal. * Frequency Converter: Converts the control signal \(U(t)\) into an output frequency \(F(t)\) to control the speed of the linear actuator. * Linear Actuator: Lowers the turbine's rotor based on the output frequency from the frequency converter, adjusting its position \(y(t)\). * Potentiometer: Measures the current position of the rotor and feeds this value back to the controller to ensure accurate adjustment. Figure 1: Schematic of the wind turbine height control system. The closed-loop feedback mechanism ensures safe and precise operation, protecting the turbine from mechanical damage during high wind speeds by lowering the rotor to a safer position. The diagram shown in Figure 2 represents an automatic control system using a PID controller to lower the wind turbine rotor during strong winds. The wind speed sensor (anemometer) measures the current wind speed and activates the control system if the wind speed exceeds a set threshold value. The setpoint is chosen as 40% of the full actuator stroke, determined based on the safety and efficiency requirements of the system. The difference between this set value and the current actuator position (\(e=r-y\)) is fed into the PI controller, which consists of proportional (KP) and integral (KI) components. These components adjust the control signal (u) proportionally to the current error, the accumulated error, and the rate of change in the error, respectively. The sum of these outputs forms the control signal that acts on the linear actuator, lowering the wind turbine rotor. A linear potentiometer installed on the actuator measures the current position of the actuator and feeds this information back into the system as feedback (linear displacement). In strong winds, the controller generates a control signal that activates the linear actuator to lower the rotor, reducing its rotational speed to a safe level, and ensuring the stable and safe operation of the wind turbine. The setpoint value of 40% is chosen to balance safety and efficiency: it sufficiently reduces the wind impact on the wind turbine when wind speed exceeds the threshold without requiring a complete lowering of the structure. The Onipko rotor wind turbine was selected as the focus of this study due to its unique design, which, while highly efficient at low wind speeds, presents particular vulnerabilities to strong winds and uneven load distribution. These characteristics make it an ideal candidate for testing the rotor-lowering system, which aims to protect the rotor from damage during high wind events by reducing mechanical stress on the system [25].