Constraining impedance-based controllers: generalised framework and experimental validation

Abstract Wave energy converters (WECs) hold significant potential in the global energy market, though their high energy costs compared to traditional sources remain a challenge. Recent research has focused on power maximisation strategies to make WECs more competitive, with optimisation-based control methods offering one solution. However, these methods are often complex and difficult to implement in real-time scenarios. Simpler, non-optimisation-based approaches, such as impedance based control, have gained interest due to their ease of implementation and ability to provide representative control actions. Despite their advantages, impedance based controllers often suffer from unconstrained control forces, potentially leading to suboptimal performance and exceeding the validity range of the system model. This study introduces a novel constrained impedance based control strategy that maintains the simplicity of traditional methods while addressing the limitations of unconstrained controllers. The proposed approach is experimentally validated using the Wavestar prototype at the Aalborg facility in Denmark, under both monochromatic and panchromatic wave conditions. Results show that the constrained controller effectively confines the device motion within predefined limits, improving power output under nonlinear force saturation. These findings demonstrate that constrained impedance-based control can provide more accurate and practical control actions, enhancing the performance of WECs in real-world applications.