Towards realistic non-linear receding-horizon spectral control of wave energy converters. (December 2018)

• Record Type: Journal Article
• Authors: Mérigaud, Alexis; Ringwood, John V.
• Is Part Of: Control engineering practice. Volume 81(2018)
• Page Start: 145
• Page End: 161
• Publication Date: 2018-12
• Subjects: Wave energy converters -- Power maximisation -- Optimal control -- Receding-horizon control -- Fourier spectral control -- Constraints -- Non-linear systems -- Trajectory tracking -- Extended Kalman filter -- Measurement noise -- Gaussian process; Automatic control -- Periodicals; 629.89
• DOI: 10.1016/j.conengprac.2018.08.024
• Languages: English
• ISSNs: 0967-0661

Abstract

Abstract: Non-linear, power-maximising control of wave energy converters (WECs) can be achieved within a receding-horizon control framework, whereby an upper loop calculates a reference trajectory in real-time, ensuring maximal power absorption under operational constraints, while a tracking loop drives the device along the generated trajectory. This paper articulates the four fundamental components of such a control strategy: reference generation calculations, tracking loop, and wave excitation estimation and forecasting . The upper-loop optimisation problem is efficiently solved through a Fourier spectral method, taking into account non-linear dynamics and constraints. Tracking is achieved through a linear state feedback, combined with a non-linear feed-forward term. An extended Kalman filter is used for excitation force estimation, based on noisy WEC position and acceleration measurements. Finally, wave excitation forecasts are based on a linear predictor, whose coefficients are derived from the wave spectrum (on a sea-state-by-sea-state basis). The practical issues and trade-offs, which arise when the four components listed above are combined within a practical implementation, are investigated by means of realistic numerical simulations, using a WEC model comprising a combination of static and velocity-dependent non-linear forces. Highlights: Receding-horizon optimal control of wave energy converters (WECs) is studied. The reference trajectory is updated in real time using Fourier spectral control. Trajectory tracking is ensured using combined feed-forward and feedback terms. The only measurements are the WEC position and acceleration, with noisy sensors. Wave estimation and forecasting are solely based on available measurements.