*3.4. Actuator Models*

Once the set-point values of the blade pitch angles and generator torque are calculated by the respective controllers, they are passed to the actuator models of the controller (see Figure 2). The actuator models are used to model the additional inertial effects of the physical actuators. These models can be very accurate depending on the individual needs of the calculation.

For the TUB Controller, a simple second-order linear model was chosen to model both the pitch actuators and the generator model. The second-order model has the same mathematical description as a second-order low-pass filter, namely Equation (A2). This model is also used for the yaw actuator in the yaw runaway event. The individual cut-off frequencies and damping ratios for the actuators and the generator model are supplied as parameters by the user. For the brake actuator, a simple first-order linear model as described by Equation (A1) is used. The time constant is supplied by the user.
