Feed-forward control of a nonlinear power take-off simulation for wave energy conversion.

This article focuses on control of the power take-off (PTO) element of a point absorber wave energy converter. The research is based on a nonlinear simulation of a PTO hydraulic circuit, in which the piston velocity and generator torque act as disturbance and control actuator variables respectively, whilst the damping force is the controlled output variable. The piston velocity is generated by a hydrodynamic simulation model that reacts to both the damping force and sea wave profile. The damping force set point will be obtained from a power capture optimisation module and may be time varying. However, it is clear that such an adaptive tuning system also requires high performance `low-level' control of the device actuators, in order to fully realise the benefits of optimisation. In this regard, the present article investigates several forms of Proportional-Integral-Plus (PIP) control, in which the piston velocity is utilised as a feedforward variable. Preliminary simulation experiments suggest that a straightforward, cancellation-based, feedforward structure yields the best disturbance rejection properties