An aerodynamic moment-controlled surface for gust load alleviation on wind turbine rotors

A method is described for limiting transient gust loading on horizontal-axis wind turbine rotors. The technique, known as aerodynamic moment control, is implemented by enclosing a pitchable section of the blade in an active control loop, using the external aerodynamic load as feedback variable. The actuator operates within an outer control loop, typically based on electrical power output. The properties of the actuator have been investigated by linear analysis, based on a constant-speed 330-kW wind turbine with active power control, and pitchable blade tips. Two cases were compared, in which the tip actuator was first implemented using position feedback (position control), then subsequently using aerodynamic moment feedback (moment control). The disturbance rejection properties of the overall power controller were found to improve in the latter case. A prototype aerodynamic moment controller has been demonstrated in wind tunnel tests. The controller was configured for an inherently unstable wing section, representing the pitchable tip of a wind turbine blade, at approximately 1/3 full scale. The response to external disturbances was investigated by introducing harmonic perturbations into the upstream airflow. The system successfully demonstrated the principle of aerodynamic moment feedback, although the actuator exhibited somewhat modest gust response characteristics due to the use of velocity feedback to enhance damping. The results of the tests, and the design implications for a full-scale wind turbine, are discussed