Field Testing LIDAR-Based Feed-Forward Controls on the NREL Controls Advanced Research Turbine

Researchers at the National Renewable Energy Laboratory (NREL) and the University of Stuttgart are designing, implementing, and testing advanced feedback and feed-forward controls for multimegawatt wind turbines that will help reduce the cost of wind energy. Past wind turbine controllers have depended on turbine feedback measurements to determine the controller pitch commands. In this setup, wind speed disturbances can only be corrected after their effects have been detected in the turbine's loads and dynamic response, which causes a delayed control response due to turbine and pitch actuator dynamics. LIght Detection And Ranging (LIDAR) systems can provide information regarding the approaching wind field to the controller in advance, thereby increasing the controller's available reaction time and allowing pitch actuation to occur in advance to mitigate wind disturbance effects. Feed-forward control algorithms that use these "look ahead" wind speed measurements can improve load mitigation and controller performance compared to feedback only controllers. This paper describes the development and field testing of a feed-forward collective pitch control algorithm to show its effects on speed regulation in above-rated wind speeds. The controller is implemented and field tested on one of the Controls Advanced Research Turbines (CARTs) at NREL. The wind speed measurements to the feed-forward controller are provided by BlueScout Technologies' Optical Control System (OCS) LIDAR mounted on the nacelle of the CART3. Results show that inclusion of the LIDAR measurement into the control system leads to further rejection of the wind disturbance at low frequencies when compared to feedback alone. This in turn provides confidence that LIDAR technology could be used to obtain load reductions with wind turbine controls.