Approaching maximum power conversion with exergy-based adaptive wave-by-wave control of a wave energy converter

This paper investigates wave-by-wave control of a single-mode wave energy converter driven to operate such that the oscillation velocity closely matches the hydrodynamically optimum velocity for best power absorption. Such control requires prediction of the wave profile using up-wave measurements. The goal of this research is to implement adaptive trajectory-tracking control using on-line estimation of mechanical and hydrodynamic parameters, where the hydrodynamically optimum velocity variation provides the reference trajectory. In a step-wise approach to this goal, this paper assumes that perfect predictions of the wave profile are available, and further that the impulse response functions representing the radiation and exciting forces are also fully known. The rest mass, infinite-frequency added mass, hydrostatic stiffness, and linearized viscous damping are estimated on line. The present method relies on feedback and feedforward forces derived based on a Lyapunov function comprised of a system Hamiltonian that combines the mechanical and information exergy functions.