Simple bottom-up hierarchical control strategy for heaving wave energy converters

Abstract

The objective of this study was to improve the power captured in heaving wave energy converters using a simple robust hierarchical control strategy (HCS). A HCS comprises a higher level controller (HLC) and a lower level controller (LLC). The HLC provides a reference velocity for the buoy, which is in-phase with the wave’s excitation force. The LLC follows the reference despite the uncertainties in the model. We propose a new HCS called bottom-up HCS (BU-HCS), where the LLC is designed before the HLC. The LLC is implemented using a feedback controlled system with a simple lead-lag compensator as its controller. The lead-lag compensator is designed using H∞ theory with the objectives of maximizing the robustness and tracking properties of the LLC while minimizing the control force of the power take-off (PTO) device.