Wireless structural health monitoring of wind turbine blades using an energy harvester as a sensor

Structural Health Monitoring (SHM) of wind turbine blades is critical to improve the reliability of wind turbines. A health monitoring algorithm was developed that utilizes energy harvesters as sensors. An accumulated energy sensor is described in which an energy harvester mounted on the surface of the wind turbine blade converts low frequency vibrational strain energy from the blade to electrical charge, that is subsequently stored to power an RF transmitter. The premise of this sensing approach is that the timing of data output from the RF transmitter, which is tied to the charging time, is indicative of the structural health. The time between data transmission pulses will be reduced if the blade stiffness decreases. The SHM algorithm compares data transmission time for the three blades to identify the onset of blade damage. To demonstrate the effectiveness of the algorithm, an expected energy harvester signal transmission rate is established from blade strain data from a 2.5 MW wind turbine. The transmission rates for the three blades are compared to establish a threshold for "healthy" blades. Simulated damage corresponding to approximately 20% increase in harvested energy can be detected by the SHM algorithm.