Optimal control of a broadband vortex-induced vibration energy harvester

Abstract

A vortex-induced vibration energy harvester consists of a relatively long cylinder mounted on a flexible structure. In a flow field, the periodically shedding vortices induce transverse vibrations in the cylinder that is converted to electricity by means of piezoelectric generators. In most vortex-induced vibration harvesters, the output power is considerable only in a narrow band around the wind speed where the vortex shedding frequency matches the natural frequency of the structure. To overcome this limitation, a tuned mass mechanism is employed in the proposed vortex-induced vibration energy harvester that can change the natural frequency of the turbine to match the vortex shedding frequency in a broad band of wind speeds. The tuned mass mechanism should work in close cooperation with the piezoelectric generators to maximize the electric power of the turbine. To this end, a nonlinear piezoaeroelastic model of the system is derived, and a model predictive control technique is formulated to find the optimal control inputs for the tuned mass actuator and the piezoelectric generators. Results of numeric simulations confirmed that the tuned mass mechanism not only increases the velocity band over which the turbine is effective but also increases the peak power output of the turbine by 294%.