Power Constrained Optimal Control of Wave Energy Converters

Abstract

The general goal of control methods developed for Wave Energy Converter (WEC) technologies is to improve the amount of energy captured by the WEC from the wave. However, most WEC control methods require some power to be supplied from the grid (reactive power) to drive the floater towards resonance at intervals to improve the device's overall performance. Such controls’ reactive power and motion requirements sometimes become large and unrealistic. Additionally, a power take-off (PTO) unit capable of fulfilling a sizeable reactive power requirement will be expensive and complex, if not impossible. In this work, an optimal control formulation that aims to maximize the harvested energy while constraining the reactive power not to exceed a realistic threshold is derived using Pontryagin Minimum Principle. The optimal control formulation is derived for a single WEC device with irregular excitation. Low fidelity numerical simulations are presented comparing the proposed power-constrained Bang Singular Bang (PCBSB) control to an Optimal Resistive Loading (ORL) control.