The stalling behavior is a feature of the Wells turbine that limits the generated output power of power plants using this turbine. The NEREIDA wave power plant installed in the harbor of Mutriku in the northern Spanish shoreline constitutes an excellent example of this phenomenon. This article deals with the modeling, simulation and control of an oscillating water column unit within the NEREIDA wave power plant. The stalling behavior is investigated and two control strategies are proposed to avoid it. The first control approach is the airflow control which aims to adjust the airflow in the turbine duct using a proportional–integral–derivative controller tuned with the water cycle algorithm. The second control approach is the rotational speed control adjusting the rotor speed using the rotor-side converter of the back-to-back converter which is wired to the doubly fed induction generator. Results of comparative studies show a power generation improvement even relative to the real measured data.

Control engineering in renewable energy systems is a delicate and tedious task, especially due to the unpredictable nature of the renewable resources, which requires precision and robustness. These requirements can be ensured using intelligent control, which provides better performance than many conventional techniques and methods. This paper focuses on the modeling and the intelligent control of the NEREIDA wave power plant of Mutriku in Spain. In this context, the design of two novel intelligent airflow controls for a stalling-free operation of the Wells turbine-based power take-off system is presented and compared. The airflow control will ensure the avoidance of the stalling behavior using an intelligent PID controller. The first control design methodology is based on the metaheuristic algorithms to ensure the optimization of the controller gains. The second methodology is based on the fuzzy gain scheduling of the gains. Two study cases were performed to compare the optimized-PID and FGS-PID to a conventional PID in two wave conditions. The results show the superior performance of both proposed controls over the conventional PID, providing power generation improvement in regular and irregular waves.