Magnetic plucked meso-scale piezoelectric energy harvester for low-frequency rotational motion

Wind energy is one of the most attractive renewable energy sources; however, wind turbine blades suffer from erosion caused by sand particles carried by strong winds. The surface condition monitoring system installed on a wind turbine blade requires power, but directly connecting a cable from a stationary generator to rotating blade is difficult. In this paper, a well-packaged piezoelectric energy harvester (PEH) is proposed for installation on the blade to convert the low-frequency rotational motion into electric energy. The package, 52 mm in diameter and 14 mm thick, consists of a small clamp with a bearing and a meso-scale PEH, repelling magnets, and an outer cover with a pendulum. The PEH, redesigned in a tapered shape, has improved output performance and long-term reliability owing to the greater flexibility and low stress concentration. Because the typical rotational speed of a wind turbine varies from 5 rpm (0.08 Hz) to 30 rpm (0.5 Hz), a frequency up-conversion method is introduced to accommodate the PEH working under its off-resonant-frequency rotation. The output performance of the PEH was thoroughly tested on a lab-scale wind turbine blade. Additionally, an equivalent circuit model was established to described the nonlinear electromechanical behavior of the PEH during the magnetic plucking. Finally, the PEH was tested under practical rotation of a wind turbine for 24 h. The resulting daily energy of 1.2 J indicates the proposed rotational PEH is a promising solution for the autonomous monitoring of wind turbines.