Structural Dynamic Considerations in Wind Turbine Design - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 591

Figure 10-2. Operating map of the fixed-pitch Gamma 60 HAWT, showing the inter-
action of broad-range variable speed with yaw control of peak power. (a) Power output
and yaw angle vs. wind speed (b) Rotor speed and turbine shaft torque vs. wind speed
In most of the wind turbine control concepts currently applied or under study, the prime
objective is control of torque or power. The accompanying thrust load is usually not selec-
ted as a parameter to be directly controlled. One reason for this is that the limiting of shaft
torque can be accomplished with a much slower control rate than is required for limiting
thrust. This is especially true if the power train is made torsionally soft, which is becoming
a more common design practice. The significance of thrust loads in the design of bearings,
towers, and foundations varies substantially between turbines that are stall-, pitch-, or
yaw-controlled, and also between constant-speed and variable-speed power trains. It is