Derivation of State-Space Equation of Floating Point-Absorber Wave Energy Converter Under Motion Constraints and Its Numerical Simulation With Nonlinear Model Predictive Control

Abstract

　In this paper, we derive a nonlinear state space equation of a floating point-absorber wave energy converter (FPAWEC) and apply a nonlinear model predictive control (NMPC) to the FPAWEC. To consider motion constraints in float velocities and a configuration constraint in the pitch angle between the float and spar, we used Kane’s equation to obtain the motion equation of the FPAWEC. The generalized coordinates and generalized speeds were selected to ease the formulation of the optimization problem. The accuracy of the state space equation was validated with measured results of the motion of the FPAWEC. To reduce the order of the state space equation used in the NMPC controller, radiation forces and moments that have marginal effects on the FPAWEC motion were neglected. The motion, control force, and power production characteristics of the NMPC were numerically investigated and compared with those of conventional control strategies.