A steady state solution (x˙=0) for this ONX-0914 model can be calculated as a function of wind speed vw; such solutions will be used in section 4.1 to linearize the model. Fig. 4 shows the optimal trajectory (i.e. the one that maximizes the generated power) for power output, rotor speed, tower displacement and pitch angle under steady state conditions. Tower displacement velocity and pitch rate are zero under steady state operation.
Fig. 4. Optimal trajectory under steady state conditions with vw [m/s] on x-axis.Figure optionsDownload full-size imageDownload as PowerPoint slide
Region 3 is characterized by high wind speeds, in proton case greater than 11 m/s. In these conditions the operation can no longer continue at constant pitch angle, since the mechanical power needs to be limited in order not to exceed the generator's rated power. Thus, as the wind speed increases, the pitch angle must be increased so that the angle of attack, and hence the lift on the blades, decreases. The aim in this region is thus power limitation.