AN AERODYNAMIC MOMENT-CONTROLLED SURFACE FOR GUST LOAD ALLEVIATION ONWIND TURBINE ROTORS

A method is described for limiting transient gust loading on horizonta l-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 fee dback variable, The actuator operates within an outer control loop, ty pically based on electrical power output. The properties of the actuat or have been investigated by linear analysis, based on a constant-spee d 330-kW wind turbine with active power control, and pitchable blade t ips, Two cases were compared, in which the tip actuator was first impl emented using position feedback (position control), then subsequently using aerodynamic moment feedback (moment control). The disturbance re jection properties of the overall power controller were found to impro ve in the latter case. A prototype aerodynamic moment controller has b een demonstrated in wind tunnel tests. The controller was configured f or an inherently unstable wing section, representing the pitchable tip of a wind turbine blade, at approximately 1/3 full scale. The respons e to external disturbances was investigated by introducing harmonic pe rturbations into the upstream airflow. The system successfully demonst rated the principle of aerodynamic moment feedback, although the actua tor 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 discu ssed.