Robust hierarchical control strategy for heaving wave energy converters

This paper considers the hierarchical control strategy for enhancing the captured and converted powers in heaving wave energy converters. The hierarchical control strategy consists of a higher hierarchical controller (HHC) and a lower hierarchical controller (LHC). The main role of the HHC is to provide the optimum reference for the LHC. The LHC follows the reference despite the existence of perturbations and disturbance. In this study, the HHC is designed to maximize the conversion between the captured (mechanical) power and the converted (electrical) power. The proposed HHC generates a look-up table that contains the values of the intrinsic resistance for various sea-states. The sliding mode control is deployed as the LHC. The effectiveness of the proposed HCS is tested using the simulation result in monochromatic and polychromatic sea-states, as well as in the nominal and perturbation cases.