Wind turbines are large, complex dynamically flexible structures that operate in turbulent and unpredictable environmental conditions where efficiency and reliability are highly dependent upon a well-designed control strategy. The possibility to quickly influence aerodynamic loads acting on the individual blades allows for a hybrid pitch control objective that includes a high frequency dynamic attenuation component with respect to fatigue load reduction. Active aerodynamic devices are potential candidates for this component. With the increasing size of wind turbine blades, the need for more sophisticated load control techniques has induced interest in locally distributed aerodynamic control systems (eg trailing edge flaps) with built-in intelligence on the blades (such as smart structures). Several researchers have started to investigate the benefits of using advanced control for wind turbine rotor aerodynamics and geometry. In McCoy and Griffin, 1 two major categories of rotor aerodynamic modifications were investigated; active aerodynamic devices and actively controlled retractable blade rotors. Both studies indicated cost savings through reduced system loads and increased energy capture. There are various options for utilizing active distributed flaps along the blade span for load reduction. Van Dam et. al., 2–4 have investigated, both computationally with CFD investigations and through experimental wind tunnel testing, the feasibility of using microtabs for active load control. Andersen, et. al. 5 have developed deformable trailing edge geometry and control algorithms which also showed fatigue load reduction for both the flapwise blade root moments and the tower root moments. By enabling the trailing edge at the outboard portion of the blade to move quickly and independently, local fluctuations in the aerodynamic forces can be compensated. In Barlas and van Kuik6 an overview of smart rotor control technology for wind turbines is given.

Most recently, Barlas and van Kuik7 have employed a new aeroservoelastic tool to evaluate varying single and multi-flap per each blade control strategies that primarily concentrate on Singe-Input Single-Output (SISO) Proportional-Integral-Derivative (PID) style distributed flap control systems as a proof-of-concept. This paper presents a modern Multi-Input Multi-Output (MIMO) control system design procedure based on distributed flap actuation and appropriate sensor feedback along the outboard of each blade that seamlessly integrates with a blade independent pitch control strategy. This modern controller design is modeled and analyzed with the new state-of-the-art comprehensive aeroservoelastic simulator, called DU SWAMP, 7 which is implemented in the Matlab/Simulink environment. 8 In addition, this paper builds upon recent developments in Active Aerodynamic Load Control (AALC) strategies currently being investigated at Sandia National Laboratories Wind and Water Power Technologies department. 9–14