Stalling-Free Control Strategies for Oscillating-Water-Column-Based Wave Power Generation Plants

The rising use of renewable power generation plants is highlighting the need for an integrated research combining multiple disciplines in order to achieve a commercially competitive technology stage. The demonstrative NEREIDA wave power plant installed in the northern coast of Spain constitutes a good example of this effort. This paper deals with the design, modeling, and control of the oscillating-water-column-based wave energy converter in order to maximize the power output of the NEREIDA power plant. The power optimization relies on two control strategies proposed to avoid the stalling behavior, a characteristic drawback of the Wells turbine, which limits the system's power. The first control strategy is an airflow control using a PID controller tuned by the particle swarm optimization algorithm and its recent memetic variant called fractional particle swarm optimization memetic algorithm. This controller will control a throttle valve to regulate the airflow in the turbine duct. The second one consist of adequately controlling the rotational speed of the generator by means of the rotor-side converter of the back-to-back converter connected to the doubly fed induction generator to provide a swift way to respond to the rapid variations in the turbine speed. The results show that both controls provide a higher power generation compared to the uncontrolled case.