Linear Optimal Noncausal Control of Wave Energy Converters

Abstract

This paper addresses the fundamental theoretical development of a linear optimal noncausal control for wave energy converters (WECs) in a closed analytic form. It is well known that wave energy converter control is a noncausal control problem, i.e. the future wave information contributes to the present control action. This paper provides a reliable, efficient and simple linear optimal controller with guaranteed stability for WEC control problem. The proposed WEC linear optimal control (LOC) consists of a causal linear state feedback part and an anticausal linear feedforward part to incorporate the influence of future incoming waves. The stability of the closed-loop WEC control system with the proposed linear optimal controller is proven. The contribution of the noncausal term using wave prediction information to the optimal control and the energy output is analyzed quantitatively. The proposed linear controller can be more preferred when constraint satisfaction becomes a less important issue for mild sea states and some well-designed WECs with an ample operation range. The proposed optimal control strategy can be extended for a generic class of energy maximization problems. Numerical simulations are presented to justify the efficacy of the proposed WEC optimal control.

Robust Excitation Force Estimation and Prediction for Wave Energy Converter M4 Based on Adaptive Sliding-Mode Observer

“…where h r is the impulse response function of the radiation force which is a 4 × 4 matrix. For a state-space realization, the convolution term F r = − ∞ −∞ h r (τ )q(t − τ )dτ can be considered as a linear system and be approximated by the following state-space model [4]…”

“…1. Tank experiment of M4 in Manchester [9] the wave excitation force prediction is also needed by noncausal WEC controllers [4] which incorporate the future wave information into the current control decision and the accuracy of wave force prediction relies on the estimation at the current time [5]. A direct measurement of wave excitation force by pressure sensors placed on the WEC wet-surface is reported in [6], while it is neither economically viable nor accurate in many cases.…”

Robust Adaptive Control of an Offshore Ocean Thermal Energy Conversion System

“…wind, solar, wave, tide, thermal energy, etc.) and has attracted increasing attention [1]. Ocean thermal energy provides a vast, persistent and available renewable energy resource and the ocean thermal energy conversion uses the temperature difference between deep cold seawater (4 • C∼7 • C) in 500m∼1000m and shallow warm seawater (25 • C∼28 • C) to derive a heat engine and generate the electric energy further [2], [3], [4].…”

Adaptive Model Predictive Control of Wave Energy Converters

“…latching control [5], phase control [6], declutching control [7], have been investigated based on the impedance matching principle, which suggests that a WEC controller should be designed to adaptively change the dynamics of a WEC so that its resonance frequency can match the predominant frequencies of the incoming waves [8]. Recent studies [9]- [11] show that the WEC control is essentially a constrained optimal control problem and can be tackled by model predictive control (MPC) [12], [13] or MPC-like control algorithms such as pseudospectral control [14]- [16]. Some causal optimal control strategies have also been developed where wave prediction is not used, so that sub-optimality can be achieved, e.g.…”