Distributed Low Power OnBlade Control for Wind Turbine Load Mitigation

The economic viability of wind energy is critically dependent upon robust, long duration operation, while minimizing outages and costs for repair and ongoing maintenance. Active load mitigation offers a way to control both peak and fatigue inducing loads so as to forestall major failures, preclude costly repairs and service interruptions, and extend the life of wind turbine blades, generator components and the entire turbine system. Mitigation of loads requires some form of adaptation of the turbine to variable conditions (e.g., atmospheric turbulence, wind speed variation, turbine to turbine interaction, tower shadow), and these needs can be addressed through an application of “smart” materials based devices to provide on blade aerodynamic control. A novel actuation system, previously developed for onblade helicopter rotor control applications, is proposed for use on wind turbines as a means of actively mitigating excessive wind turbine loads. The device uses shape memory alloy (SMA) materials as its prime mover, is compact, low power, and robust, and can be designed as an integral member of a rotor blade or as a separate retrofit device to enhance existing wind turbine installations. Thanks to the SMA material’s high resistivity, direct electric actuation is possible, and the unit is self-locking, requiring no additional power to maintain its new orientation once actuated. Applications include active load control of extended length wind turbine blades, low speed performance improvement on existing and new blade systems, and improved blade endurance and fatigue life through reduction of vibratory loads from atmospheric and upwind wind turbine turbulence. The Phase I/II research program is to understand and address the scaling issues associated with transitioning this technology from helicopter aerospace applications to wind turbine blade design and operational use (under Phase I), and then, under Phase II, execute a design/build/test program to validate the actuation concept’s effectiveness at load reduction, and suggest improvements and modifications necessary to implement these actuators on both future turbine rotors and as a retrofit improvement onto existing rotors on installed turbines. Commercial Applications and Other Benefits: The principal immediate application of this work is to provide additional control mechanisms to improve the efficiency and reliability of wind turbine rotors and wind turbine systems. The actuator and adaptive load control system technology to be developed as part of this effort could be used for new turbine designs and also be applied to retrofit existing wind energy systems for improved performance and structural life. The net effect of their use would support reducing the operating costs of wind turbines, thereby improving their power conversion capability and enhancing their power quality. Key Words: Wind energy, wind turbine blade, load alleviation, fatigue, vibration, wind turbine control, shape memory alloys, active control, smart materials