Discrete Displacement Hydraulic Power Take-Off System for the Wavestar Wave Energy Converter

Rico Hjerm Hansen, Morten Kramer, Enrique Vidal

Research output: Contribution to journalJournal articleResearchpeer-review

75 Citations (Scopus)

Abstract

The Wavestar Wave Energy Converter (WEC) is a multiple absorber concept, consisting of 20 hemisphere shaped floats attached to a single platform. The heart of the Wavestar WEC is the Power Take-Off (PTO) system, converting the wave induced motion of the floats into a steady power output to the grid. In the present work, a PTO based on a novel discrete displacement fluid power technology is explored for the Wavestar WEC. Absorption of power from the floats is performed by hydraulic cylinders, supplying power to a common fixed pressure system with accumulators for energy smoothing. The stored pressure energy is converted into electricity at a steady pace by hydraulic motors and generators. The storage, thereby, decouples the complicated process of wave power absorption from power generation. The core for enabling this PTO technology is implementing a near loss-free force control of the energy absorbing cylinders. This is achieved by using special multi-chambered cylinders, where the different chambers may be connected to the available system pressures using fast on/off valves. Resultantly, a Discrete Displacement Cylinder (DDC) is created, allowing near loss free discrete force control. This paper presents a complete PTO system for a 20 float Wavestar based on the DDC. The WEC and PTO is rigorously modeled from incident waves to the electric output to the grid. The resulting model of +600 states is simulated in different irregular seas, showing that power conversion efficiencies above 70% from input power to electrical power is achievable for all relevant sea conditions.
Original languageEnglish
JournalEnergies
Volume6
Issue number8
Pages (from-to)4001-4044
Number of pages44
ISSN1996-1073
DOIs
Publication statusPublished - 2013

Fingerprint

Takeoff
Converter
Hydraulics
Energy
Force control
Force Control
Absorption
Hydraulic motors
Wave power
Grid
Hemisphere
Output
Absorber
Conversion efficiency
Power generation
Electricity
Absorbing
Smoothing
Irregular
Generator

Keywords

  • Wave energy
  • PTO
  • Wavestar
  • Hydraulics
  • WEC

Cite this

Hansen, Rico Hjerm ; Kramer, Morten ; Vidal, Enrique. / Discrete Displacement Hydraulic Power Take-Off System for the Wavestar Wave Energy Converter. In: Energies. 2013 ; Vol. 6, No. 8. pp. 4001-4044.
@article{f10641c703a34d4e9e4f6354c0a0c4bb,
title = "Discrete Displacement Hydraulic Power Take-Off System for the Wavestar Wave Energy Converter",
abstract = "The Wavestar Wave Energy Converter (WEC) is a multiple absorber concept, consisting of 20 hemisphere shaped floats attached to a single platform. The heart of the Wavestar WEC is the Power Take-Off (PTO) system, converting the wave induced motion of the floats into a steady power output to the grid. In the present work, a PTO based on a novel discrete displacement fluid power technology is explored for the Wavestar WEC. Absorption of power from the floats is performed by hydraulic cylinders, supplying power to a common fixed pressure system with accumulators for energy smoothing. The stored pressure energy is converted into electricity at a steady pace by hydraulic motors and generators. The storage, thereby, decouples the complicated process of wave power absorption from power generation. The core for enabling this PTO technology is implementing a near loss-free force control of the energy absorbing cylinders. This is achieved by using special multi-chambered cylinders, where the different chambers may be connected to the available system pressures using fast on/off valves. Resultantly, a Discrete Displacement Cylinder (DDC) is created, allowing near loss free discrete force control. This paper presents a complete PTO system for a 20 float Wavestar based on the DDC. The WEC and PTO is rigorously modeled from incident waves to the electric output to the grid. The resulting model of +600 states is simulated in different irregular seas, showing that power conversion efficiencies above 70{\%} from input power to electrical power is achievable for all relevant sea conditions.",
keywords = "Wave energy, PTO, Wavestar, Hydraulics, WEC",
author = "Hansen, {Rico Hjerm} and Morten Kramer and Enrique Vidal",
year = "2013",
doi = "10.3390/en6084001",
language = "English",
volume = "6",
pages = "4001--4044",
journal = "Energies",
issn = "1996-1073",
publisher = "M D P I AG",
number = "8",

}

Discrete Displacement Hydraulic Power Take-Off System for the Wavestar Wave Energy Converter. / Hansen, Rico Hjerm; Kramer, Morten; Vidal, Enrique.

In: Energies, Vol. 6, No. 8, 2013, p. 4001-4044.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Discrete Displacement Hydraulic Power Take-Off System for the Wavestar Wave Energy Converter

AU - Hansen, Rico Hjerm

AU - Kramer, Morten

AU - Vidal, Enrique

PY - 2013

Y1 - 2013

N2 - The Wavestar Wave Energy Converter (WEC) is a multiple absorber concept, consisting of 20 hemisphere shaped floats attached to a single platform. The heart of the Wavestar WEC is the Power Take-Off (PTO) system, converting the wave induced motion of the floats into a steady power output to the grid. In the present work, a PTO based on a novel discrete displacement fluid power technology is explored for the Wavestar WEC. Absorption of power from the floats is performed by hydraulic cylinders, supplying power to a common fixed pressure system with accumulators for energy smoothing. The stored pressure energy is converted into electricity at a steady pace by hydraulic motors and generators. The storage, thereby, decouples the complicated process of wave power absorption from power generation. The core for enabling this PTO technology is implementing a near loss-free force control of the energy absorbing cylinders. This is achieved by using special multi-chambered cylinders, where the different chambers may be connected to the available system pressures using fast on/off valves. Resultantly, a Discrete Displacement Cylinder (DDC) is created, allowing near loss free discrete force control. This paper presents a complete PTO system for a 20 float Wavestar based on the DDC. The WEC and PTO is rigorously modeled from incident waves to the electric output to the grid. The resulting model of +600 states is simulated in different irregular seas, showing that power conversion efficiencies above 70% from input power to electrical power is achievable for all relevant sea conditions.

AB - The Wavestar Wave Energy Converter (WEC) is a multiple absorber concept, consisting of 20 hemisphere shaped floats attached to a single platform. The heart of the Wavestar WEC is the Power Take-Off (PTO) system, converting the wave induced motion of the floats into a steady power output to the grid. In the present work, a PTO based on a novel discrete displacement fluid power technology is explored for the Wavestar WEC. Absorption of power from the floats is performed by hydraulic cylinders, supplying power to a common fixed pressure system with accumulators for energy smoothing. The stored pressure energy is converted into electricity at a steady pace by hydraulic motors and generators. The storage, thereby, decouples the complicated process of wave power absorption from power generation. The core for enabling this PTO technology is implementing a near loss-free force control of the energy absorbing cylinders. This is achieved by using special multi-chambered cylinders, where the different chambers may be connected to the available system pressures using fast on/off valves. Resultantly, a Discrete Displacement Cylinder (DDC) is created, allowing near loss free discrete force control. This paper presents a complete PTO system for a 20 float Wavestar based on the DDC. The WEC and PTO is rigorously modeled from incident waves to the electric output to the grid. The resulting model of +600 states is simulated in different irregular seas, showing that power conversion efficiencies above 70% from input power to electrical power is achievable for all relevant sea conditions.

KW - Wave energy

KW - PTO

KW - Wavestar

KW - Hydraulics

KW - WEC

U2 - 10.3390/en6084001

DO - 10.3390/en6084001

M3 - Journal article

VL - 6

SP - 4001

EP - 4044

JO - Energies

JF - Energies

SN - 1996-1073

IS - 8

ER -