System Identification of a Multi-Degree-of-Freedom Wave Energy System: Experimental Tests on the SWINGO Device

Achieving economic feasibility in wave energy conversion relies on the development of efficient and reliable control strategies, which require accurate control-oriented models of wave energy systems. However, deriving such models from first-principles-based hydrodynamic approaches can be challenging, as linearisation and small-motion assumptions often lead to discrepancies between theoretical predictions and real-world behaviour. Recognising these limitations, this paper presents a frequency-domain system identification approach applied to a multiple-degree-of-freedom wave energy converter, SWINGO. Experimental tests on a scaled prototype were conducted in a wave basin to obtain system response data under different operating conditions. The identification approach captures the coupled dynamics between the floater and gyropendulum, improving upon boundary-element-method-based models. The identified best linear approximation models are validated across multiple sea states, demonstrating their effectiveness in characterising the system response. Validation results are analysed in terms of normalised mean average percentage error, confirming the approach suitability for control design.