Correlation between Rotating LIDAR Measurements and Blade Effective Wind Speed

Preview wind speed measurements from a forward looking Light Detection and Ranging (LIDAR) system located in the hub of a wind turbine can be used by a feedforward blade pitch control system to mitigate structural loads. For individual blade pitch control, a separate preview estimate of the e ective wind speed encountered by each blade must be available. One way of providing an estimate of the blade e ective wind speed is to implement a hub mounted spinning lidar that scans the wind eld at the rotational rate of the rotor such that the measured wind will reach the blade after some delay. In this way, both the lidar measurement and the wind turbine blade rotationally sample the wind eld. The bene t gained by using preview wind speed measurements strongly depends on the correlation between the measured wind and the wind that interacts with the blades. In this research, the coherence between rotating lidar measurements and blade e ective wind speed is calculated and analyzed using a spectral model of the wind eld. The simulated wind eld uses an isotropic von Karman spectrum and contains a model of wind evolution described by a longitudinal spatial coherence function. The coherence between stationary measurements and stationary blade e ective wind speeds decreases to zero near the 1P rotational frequency of the turbine. However, measurement coherence between rotating lidar measurements and blade e ective wind speed remains much higher and does not decay until higher frequencies.