Intuitive LTI energy-maximising control for multi-degree of freedom wave energy converters: The PeWEC case

• Published in: Ocean engineering Vol. 256; p. 111444
• Main Authors: Carapellese, Fabio, Pasta, Edoardo, Paduano, Bruno, Faedo, Nicolás, Mattiazzo, Giuliana
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.07.2022
• Subjects: Energy-maximising control; Impedance-matching; Optimal control; Wave energy; Wave energy converter; Impedance-matching; Wave energy converter; Wave energy; Energy-maximising control; Optimal control
• ISSN: 0029-8018; 1873-5258
• DOI: 10.1016/j.oceaneng.2022.111444

Energy-maximising wave energy conversion control strategies are commonly based upon direct optimal control theory, where the control problem is discretised and transcribed into a nonlinear programme, and a solution is found via numerical routines. Though appealing from an optimality viewpoint, the real-time application of such strategies to realistic (complex) wave energy systems, such as the PeWEC device, can become potentially challenging, due to its intrinsic multiple degree-of-freedom (DoF) nature. Furthermore, this pendulum-based system is not only multi-DoF in its nature, but also underactuated, i.e. only one mode, associated to the pendulum mechanism installed inside the wave-excited floating body, can be effectively actuated. We propose, in this paper, a set of four simple and intuitive energy-maximising controllers for the PeWEC system based, upon linear time-invariant (LTI) systems. We achieve this by deriving the so-called impedance-matching conditions for the PeWEC, and extending well-established LTI controllers, originally designed for fully actuated single-DoF systems, to this multi-DoF underactuated case. In particular, we explore, design, and synthesise both feedback, and feedforward configurations, making explicit emphasis in their main characteristics. Furthermore, we provide a performance assessment for each of the proposed controllers, showing their energy-maximising capabilities for the wave resource characterising the Mediterranean Sea. •Impedance matching condition for a multi-DoF device, naturally underactuated.•Control oriented modelling applied to PeWEC, actuated by the pendulum mode of motion.•Development of four intuitive energy-maximising controllers for the PeWEC based upon LTI systems.•Synthesis of feedback, and feedforward configurations.