Extension and improvement of synchronous linear generator based point absorber operation in high wave excitation scenarios

Aitor Saenz-Aguirre,Alain Ulazia,Gabriel Ibarra-Berastegui,Jon Saenz

doi:10.1016/j.oceaneng.2021.109844

Aitor Saenz-Aguirre, Alain Ulazia + Show 2 more

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https://doi.org/10.1016/j.oceaneng.2021.109844

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Journal: Ocean Engineering	Publication Date: Sep 30, 2021
Citations: 8	License type: cc-by

Affiliation: University of the Basque Country

Abstract

The exploitation of marine wave energy resource has led to the design of numerous Wave Energy Converter (WEC) configurations. The power absorption of a WEC is tightly related to its physical properties and the characteristics of the incoming wave front. Additionally, the operational range of a WEC is limited to certain characteristics of the incoming waves. These restrictions are usually related to limitations in the maximum force of the Power Take-off (PTO) system and the safety of the WEC. As a result, the power production of the WEC must be stopped during sea states of high wave elevation. With the objective of improving the operation of a WEC during these sea states, a Field Weakening (FW) control functionality is proposed to be implemented in the control system of a single-body linear in heave oscillating point absorber with a Permanent Magnet Synchronous Linear Generator (PMSLG) based electrical PTO system. The aim of the aforementioned functionality is to attenuate the magnetic flux in the PMSLG during sea states of high wave elevation. The influence of the size of a WEC on the benefits of the proposed FW functionality is also studied. To that end, two point absorbers with different size are analysed with NEMOH and a wave-to-wire (W2W) model of each WEC is developed. This W2W model enables analysis of the performance and power production of the WECs at different sea states of interest. The obtained results show a remarkable improvement of the operation of a WEC with the implementation of the FW strategy during sea states of high excitation, which leads to an extension of its operation and subsequent additional energy/hydrogen generation.

Highlights

The design, manufacture and installation of Wave Energy Converters (WECs) has remarkably grown since the early 1980s (Babarit, 2015)
With the objective of improving the operation of a WEC during these sea states, a Field Weakening (FW) control functionality is proposed to be implemented in the control system of a single-body linear in heave oscillating point absorber with a Permanent Magnet Synchronous Linear Generator (PMSLG) based electrical Power Take-off (PTO) system
Instantaneous wave elevation data corresponding to a sea state defined by a significant wave height of Hs = 8 m and a wave peak period of Tp = 8 s have been generated for the validation of the proposed FW functionality

Summary

Introduction

The design, manufacture and installation of Wave Energy Converters (WECs) has remarkably grown since the early 1980s (Babarit, 2015). Among WECs, point absorbers have recently gained in interest due to their reduced dimensions and remarkable power absorption capability in relation to their size (Faizal et al, 2014) These point absorbers, designed to absorb the kinetic energy of the waves in offshore sites, oscillate as a result of the hydrodynamic excitation generated by the waves in the device. This mechanical motion is converted into electrical energy. Regarding their classification (Falcao, 2010), point absorbers are principally categorized with respect to their physical location related to the ocean water level. Point absorbers can be classified with respect to the number of bodies forming the wave energy exploitation device (Falnes, 1999; Korde, 2003; Wang et al, 2018)

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