Wells turbine control in wave power generation plants

In this paper a Wells turbine control is presented. For this purpose, a control scheme for the flow coefficient is derived based on the addition of external resistances in series with the rotor winding of the induction generator connected to the turbine. Due to the stalling behaviour, the generator increases its velocity as the flow coefficient of the turbine approaches the critical point at which the turbine losses power. The proposed control system does appropriately adapt the rotor resistance according to the entry pressure drop. To do so, the control implements a continuous resistance switching depending on the pressure drop and it will be demonstrated that the average power of the turbine and generator are significantly higher in the controlled case than in the uncontrolled one. It is stated that there exist an optimal value of external resistances for each specific range of pressure drop and it is verified that greater input pressure drop does not imply higher power output unless the stalling behaviour is avoided.