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—Ocean wave energy is a renewable energy which remains costly for large-scale electricity generation. Although the oscillating water column (OWC) wave energy converter (WEC) is a promising device type with a rectifying air turbine and generator which convert alternating airflow induced by the water motion into kinetic energy then to electric energy, there are still several challenges to overcome to achieve commercial energy production. A first step is deploying multiple devices close to each other in WEC parks, to save cost associated with mooring lines and power transmission cables and a second step is applying control at each stage of energy conversion to increase the electric energy output of the devices and ensure a safe operation. Herein, we first present a state-space model of a park of seven hydrodynamically interacting floating OWC WECs in all degrees of freedom with nonlinear PTO dynamics and a shared, quasi-static mooring model. The electric power flow is modeled by considering the conversion losses from the AC generators over a DC link, including a storage unit to the grid connection. Secondly, the OWC WEC park is expressed from a higher hierarchical level as an automaton driven by discrete events. Finally, we use a standard supervisory control approach to enable different local control schemes to ensure a save operation of the individual WEC and the park. The supervisor has good adaptability potential for different WECs and the incorporation of safety mechanisms. 

This article presents the state-of-the-art application of a Unified Power Flow Controller (UPFC) to directly interface ocean wave energy converters (WEC) with the utility grid. It is shown that the transformer flux saturation problem at variable low-frequency operation poses no technical issue for the ocean power applications because a direct-proportionality relationship exists between frequency and amplitude of the WEC output voltages. We have proposed a direct interface of WEC with the utility grid using a series compensation transformer of the UPFC controller. The shunt input rectification segment of the UPFC acts not only as the DC bus for the UFPC operation but also as an embedded energy storage stage for the WEC. The mathematical formulation and simulation results are presented as a proof-of- concept for FACTS-based WEC-grid integration with the integrated energy storage capability. 

This paper presents a complete mathematical model of an array of three oscillating water column (OWC) wave energy converters (WECs) and the design of a direct generator torque control strategy using a sliding mode control (SMC) to maximize the output power of doubly-fed induction generators (DFIGs) attached to bi-radial turbines that are driven by the oscillating motion of the air inside the OWC tubes. The performance of the proposed control strategy is evaluated in irregular waves scenarios and different angles of arrival of the wave front.