Sliding Mode Control of a Nonlinear Wave Energy Converter Model

Tania Demonte Gonzalez,Gordon G Parker,Wayne W Weaver,Enrico Anderlini

doi:10.3390/jmse9090951

Abstract

The most accurate wave energy converter models for heaving point absorbers include nonlinearities, which increase as resonance is achieved to maximize the energy capture. Over the power production spectrum and within the physical limits of the devices, the efficiency of wave energy converters can be enhanced by employing a control scheme that accounts for these nonlinearities. This paper proposes a sliding mode control for a heaving point absorber that includes the nonlinear effects of the dynamic and static Froude-Krylov forces. The sliding mode controller tracks a reference velocity that matches the phase of the excitation force to ensure higher energy absorption. This control algorithm is tested in regular linear waves and is compared to a complex-conjugate control and a nonlinear variation of the complex-conjugate control. The results show that the sliding mode control successfully tracks the reference and keeps the device displacement bounded while absorbing more energy than the other control strategies. Furthermore, due to the robustness of the control law, it can also accommodate disturbances and uncertainties in the dynamic model of the wave energy converter.

Highlights

In this study, the nonlinear FK forces are incorporated using a variation of the algebraic solution proposed by Giorgi et al This paper proposes a second-order Sliding Mode Control (SMC) strategy that incorporates the nonlinear Froude-Krylov forces to reduce the discrepancies between the mathematical model and the actual system
This study aims to improve the energy extraction performance of wave energy converters (WECs) where its sliding mode control (SMC) can exploit the WEC’s improvemodel the energy nonlinear terms.extraction performance of WECs where its SMC can exploit the WEC’s nonlinear model terms. of this study consist of first, the derivation of algebraic nonThe main contributions
Three different control strategies have been presented and applied to a spherical heaving point absorber wave energy converter. These control strategies have shown promising results when used in linear models of WECs

Summary

Introduction

Academic Editors: Giuseppe Giorgi and Sergej Antonello Sirigu. The generation of electricity from ocean waves has gained special attention. Studies of the potential global market for wave power showed that the world’s wave power resource is estimated to be two TW [1]. Waves have a very high power density, requiring smaller devices to capture the energy carried by the incoming waves. Wave energy can improve energy security by complementing the output of other renewable energy sources, reducing the storage needs. Phased development has helped reduce risks, the wave energy sector is still in its infancy, with recent prototype wave energy converters (WECs) having a Levelized Cost of Energy (LCoE) in the range of $120–$470/MWh [2]. Technological advances are required to reduce the LCoE

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