A Comparison of Smart Rotor Control Approaches Using Trailing Edge Flaps and Individual Pitch Control

Modern wind turbines have been steadily increasing in size, and have now become very large, with recent models boasting rotor diameters greater than 120 m. Reducing the loads experienced by the wind turbine rotor blades is one means of lowering the cost of energy of wind turbines. Wind turbines are subjected to significant and rapid fluctuating loads, which arise from a variety of sources including: turbulence in the wind, tower shadow, wind shear, and yawed flow conditions. “Smart rotor control” concepts have emerged as a major topic of research in the attempt to reduce fatigue loads on wind turbines. In this approach, aerodynamic load control devices are distributed along the span of the wind turbine blade, and through a combination of sensing, control, and actuation, these devices dynamically control the loads on the blades. This research investigates the load reduction potential of smart rotor control devices, namely trailing edge flaps (TEFs), in the operation of a 5 MW wind turbine in the aeroelastic design code “GH Bladed.” Specifically in this paper, the fatigue load reductions achieved using trailing edge flaps are evaluated, and the performance is compared to another promising load reduction technique, individual pitch control. A feedback control approach is implemented for load reduction, which utilizes a multiblade coordinate transformation, so that variables in the rotating frame of reference can be mapped into a fixed frame of reference. Single input single output (SISO) control techniques for linear time invariant (LTI) systems are then employed to determine the appropriate response of the TEFs based on the loads on the blades. The use of TEFs and this control approach is shown to effectively reduce the fatigue loads on the blades, relative to a baseline controller. The load reduction potential is also compared to an alternative individual pitch control approach, in the time and frequency domain. The effects on the pitch and power systems are briefly evaluated, and the limitations of the analysis are assessed.