Switching control for constrained wave energy converters

This paper addresses the problem of designing a control that maximizes the harvested energy of a wave energy converter, in the presence of displacement constraints. The feasible displacement range is split into two segments. In the first segment (the inner segment), an unconstrained optimal control is used. In the outer segment, a constraint control is used. For the unconstraint control in the inner segment, a singular arc control is implemented which is proved to maximize the harvested energy when there are no constraints. In the outer segment, two methods for constrained control are investigated and compared. The first method is a linear quadratic control that penalizes the displacement along with maximizing the harvested energy. The second method implements a nonlinear damping control that forces higher damping for higher displacement. Both concepts are compared to a linear quadratic control that penalizes the displacement over the whole displacement range. Numerical simulations are conducted and results demonstrate the superiority of the switching control concept when irregular waves are simulated.