Swedish company Ocean Harvesting Technologies is developing the sixth generation of its wave energy converter InfinityWEC, including the implementation and evaluation of a moment-based model predictive control (MPC) in its simulation model.
According to Ocean Harvesting, a ball screw manufactured by NSK works as an actuator that has a linear-to-rotational motion ratio, high efficiency, low weight, and long life.
However, it is sensitive to side forces and bending moments from the power take-off (PTO) due to buoy surge motion and high speeds in large waves. This issue has been addressed with a new linear guide system and increased control force, said Ocean Harvesting.
With increased control force, the MPC can now control and limit the system’s velocity and stroke, simplifying design and improving smoothness. The buoy can be pulled down, and the PTO can be locked in a contracted state to avoid peak loads during storms.
“The combination of ball screw actuators with our hydrostatic pre-tension system is a very efficient solution to provide the control force needed in the PTO,” said Mikael Sidenmark , CEO at Ocean Harvesting.
“The solution benefits from the use of advanced model predictive control algorithms to optimize the force applied to the buoy in every given moment, resulting in both outstanding annual energy production and the ability to constrain the velocity and stroke in the PTO.”
In 2024 and early 2025, the focus is on completing the full-scale design for InfinityWEC generation 6, implementing the moment-based MPC algorithm in the control system, and preparing for the 1:3 scale sea trial project planned for 2025-2026. Ocean Harvesting is raising €450,000 in a financing round for these activities, inviting new investors to participate.
In March 2023, Ocean Harvesting collaborated with researchers to implement a new type of controller called a nonlinear moment-based MPC , developed at the Centre for Ocean Energy Research (COER) at Maynooth University in Ireland.
This controller substantially improves energy output and is fast enough to run on a real-time control system.