Development of an Electromagnetic Energy Harvester for Monitoring Wind Turbine Blades

Wind turbine blades experience tremendous stresses while in operation. Failure of a blade can damage other components or other wind turbines. This research focuses on developing an electromagnetic energy harvester for powering structural health monitoring (SHM) equipment inside a turbine blade. The harvester consists of a magnet inside a tube with coils outside the tube. The changing orientation of the blade causes the magnet to slide along the tube, inducing a voltage in the coils which in turn powers the SHM system. This thesis begins with a brief history of electromagnetic energy harvesting and energy harvesters in rotating environments. Next a model of the harvester is developed encompassing the motion of the magnet, the current in the electrical circuit, and the coupling between the mechanical and electrical domains. The nonlinear coupling factor is derived from Faraday's law of induction and from modeling the magnet as a magnetic dipole moment. Three experiments are performed to validate the model: a free fall test to verify the coupling factor expression, a rotating test to study the model with a load resistor circuit, and a capacitor charging test to examine the model with an energy storage circuit. The validated model is then examined under varying tube lengths and positions, varying coil sizes and positions, and variations in other parameters. Finally a sample harvester is presented that can power an SHM system inside a large scale wind turbine blade spinning up to 20 RPM and can produce up to 14.1 mW at 19 RPM.