Model Following Robust Control of a Wavestar-prototype Wave Energy Converter: Part 1 Control

Abstract

Focused on the numerical model of a Wavestar-like wave energy converter (WEC) developed in WEC-Sim, this paper describes a model-following concept to design a robust controller based on a hierarchical structure of tracking control. This low-level controller has the purpose of forcing the WEC system to follow the reference position and velocity trajectories for maximum power absorption from irregular waves. The simultaneous tracking of position and velocity can deal with physical limits of the device by setting proper reference signals. The high-level part of the control aims to calculate the optimal reference signals for the controller. It is assumed that the reference information is derived in Part 2. The low-level part of the hierarchical structure is to design a robust controller to enhance the WEC system robustness against system uncertainties and modelling errors. Two robust control approaches are proposed: (i) a mixed robust controller based on a combination of linear quadratic regulator (LQR) and H∞ performance, and (ii) a sliding mode controller which has simple structure and strong robustness.