Precision blade deflection measurement system using wireless inertial sensor nodes

Structural health monitoring on wind turbine blades is a great enhancement for operational safety and failure avoidance. Blade deflection is a key parameter, which is a function of blade geometry and material properties. The absolute blade deflection is affected by wind load, gravitational, and centrifugal forces and must exceed neither material stress limits nor tower clearance. In this paper, we introduce a novel method for real time reconstruction of blade movement using inertial measurement units (IMUs) located at defined positions along the blade. An algorithm is introduced that combines IMU measurements and a priori information of the fundamental blade mode shapes to accurately reconstruct the blade movement. A low-power wireless sensor node for blade deflection monitoring is presented. The autonomous sensor node is equipped with an IMU together with a low-power wireless transceiver and powered by a compact translational electromagnetic energy harvester. Sufficient energy is harvested each rotor revolution for continuous measurement data streaming within the wind turbine's operating range. A data stream of six-axis IMU measurements enables real time, three-dimensional reconstruction of the entire blade movement in the back end positioned in the tower. The reconstruction of blade tip deflection is possible even under high wind turbulences with a minimum accuracy of 0.22 m for an onshore 5 MW and 0.58 m for an offshore 15-MW reference turbine. The complete system has been tested thoroughly under conditions similiar to a real wind turbine. Realistic stimulation of the reconstruction algorithm is performed by means of OpenFAST simulations.