Balancing Power Absorption and Losses via Optimal Inertial Reaction Mass Operation in Wave Energy Converters

Recent advances in wave energy exploitation high-light the potential of Wave Energy Converters (WECs) to significantly contribute to global clean energy demands. Numerous concepts for ocean wave energy harvesting have been developed, with specific attention to Internal Reaction Mass (IRM) systems, which are able to enclose the mechanical and electrical conversion stage within the floating hull itself, substantially reducing mantainance costs. Recent studies propose optimising the performance of IRM systems by adjusting the behaviour of the internal mass via optimal control procedures, significantly improving mechanical power available at the Power Take-Off (PTO). However, these studies often overlook energy losses associated with altering the internal mass dynamics itself, rendering any performance enhancement conclusions potentially overoptimistic. This paper addresses this gap by proposing a modified control objective that penalises these losses, offering a balanced approach to optimising the overall performance IRM WEC systems. The resulting optimal control problem is transcribed in a direct fashion, using moment-based theory, resulting in a finite-dimensional tractable nonlinear program, with application to a gyropendulum-based WEC. We show that the modified control objective is effectively able to trade-off the energy available at the PTO with the corresponding gyropendulum losses.