Wells turbine efficiency improvements: experimental application of a speed control strategy

Systems based on the OWC principle allow to convert the sea-wave energy into electrical energy. The potential energy contained in the wave motion is first converted into the pneumatic energy of a bi-directional airflow, generated by the oscillatory displacement of a column of water inside a chamber. Then, an air turbine, such as the Wells turbine, placed at the top of the chamber, converts the pneumatic energy into mechanical energy at its shaft, which can be coupled to an electric motor to produce energy. The turbine’s performance is strongly affected by the non-stationary behavior of the airflow, which continuously changes its intensity. Control solutions based on the variation of the turbine rotational speed can overcome this limitation. This work aims to study a speed-controlled Wells turbine with an experimental approach, making use of a turbine coupled to an Oscillating Water Column (OWC) simulator. A control law for the rotational speed has been defined and applied to the turbine in order to move the turbine’s operating conditions as close as possible to its maximum efficiency point, for the majority of the piston period. The experimental results prove the effectiveness of the proposed control strategy for moving the operating conditions and for obtaining operating conditions close to the best efficiency point for the majority of the wave period.