Receding-Horizon Pseudospectral Control for Energy Maximization of Oscillating-Water-Column Wave Energy Systems

Wave energy, harnessed by wave energy converters (WECs), has the potential to significantly contribute to the renewable energy mix. To improve the commercial viability of WECs, the design of control strategies for maximizing the produced energy is vital. This work specifically focuses on energy maximizing control for oscillating-water-column (OWC) WECs, using a receding-horizon pseudospectral (RHPS) optimal control method. With pseudospectral control, the continuous time OWC energy maximizing optimal control problem is directly transcribed, by discretizing both state, and control, variables, into a finite-dimensional nonlinear program. Due to the importance of turbine performance, OWC control typically aims to maximize turbine efficiency, albeit ignoring the impact of rotational speed on hydrodynamic performance. With the RHPS optimal control approach developed in this paper, a better trade-off between turbine and hydrodynamic performance is achieved and, therefore, energy production is improved.

I. Introduction

Wave energy converters (WECs) harness wave energy, which is an almost untapped renewable energy resource that can significantly reduce greenhouse gas emissions [1]. However, in comparison to other renewable resources, the cost of producing energy using waves is relatively high. To improve WECs commercial viability, it is essential to reduce the levelized cost of energy (LCoE), defined as

$$\begin{equation*}\text{LCoE}=\frac{\text{Capital costs}+\text{Operational costs}}{\text{Produced energy over the WEC lifetime}},\tag{1}\end{equation*}$$ associated with wave energy projects. To this end, the development of energy maximising control strategies is vital [2].