4. Gain Scheduled H _∞ Control of Wind Turbines for the Entire Operating Range

Two different operating modes can be clearly identified in wind turbine control systems. In low wind speeds, the main control objective is the energy capture maximization, whereas in high wind speeds it is desired to regulate turbine power and speed at their rated values. The fulfillment of these different control objectives implies the transition through low controllability operating conditions that impose severe constraints on the achievable performance. The control task is usually tackled using two separate controllers, one for each operating mode, and a switching logic. Although satisfactory control solutions have been developed for low and high wind speeds, controller design needs refinement in order to improve performance in the transition zone. This chapter overviews a control scheme covering the entire operating range with focus on the transition zone. H _∞ and advanced anti-windup techniques are exploited to design a high performance control solution for both operating modes with optimum performance in the transition zone.