A Control Framework for Ocean Wave Energy Conversion Systems: The Potential of Moments

The control of wave energy converters (WECs) to maximize power capture is a challenging problem. In particular, the nature of the wave excitation, which is in general panchromatic (or multi-sinusoidal), presents a reciprocating energy source that needs to be rectified through some means. In addition, the development of suitable control-oriented models is also challenging, requiring correct representation of system hydrodynamics and power take-off (PTO) components, while also lending themselves to control synthesis and real-time computational performance, along with a challenging optimal control problem. This article presents a moment-based mathematical framework for the formulation and solution of WEC control. It shows that moments are ideally suited to WEC control in terms of their ability to accurately characterize the nature of the wave excitation force (and the consequent evolutions in the system variables) while also gracefully including hydrodynamic and PTO nonlinearities as well as a natural extension to WEC arrays. Model reduction, to mold the system model into a control-friendly form, is also a feature of this framework.