Stabilisation and energy absorption control for wind-wave hybrid platforms: a generalised LQR approach

Hybrid wind-wave energy conversion platforms, essential in the path towards global decarbonisation, face a challenge in balancing the control objectives of stabilising the platform itself, avoiding any unwanted and potentially dangerous loads on the corresponding turbine, and maximising energy from the incoming wave field via the wave energy conversion mechanism. In particular, the latter objective can generate large motions for the wave energy device, directly conflicting with the former. This study addressesthis issue using a generalised LQR (Linear Quadratic Regulator) control structure. The cost function associated with the LQR controller is tuned to balance absorbed energy from waves and overall platform stabilisation, providing a systematic procedureto effectively incorporate these two criteria. Different controller parametrisations are considered, to provide the most convenient control configuration according to the scenarios the device may encounter in operating conditions. The analysis focuses on a generic semi-submersible platform with a flap-type wave energy converter, providing comprehensive insights in the design and impact of the proposed controller, via extensive numerical assessment.