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Discrete Displacement Hydraulic Power Take-Off System for the Wavestar Wave Energy Converter
Department of Energy Technology, Aalborg University, Pontoppidanstrade 101, Aalborg DK-9220, Denmark
Wavestar, Park Alle 350A, Broendby DK-2605, Denmark
* Author to whom correspondence should be addressed.
Received: 14 May 2013; in revised form: 28 June 2013 / Accepted: 15 July 2013 / Published: 7 August 2013
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
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MDPI and ACS Style
Hansen, R.H.; Kramer, M.M.; Vidal, E. Discrete Displacement Hydraulic Power Take-Off System for the Wavestar Wave Energy Converter. Energies 2013, 6, 4001-4044.
Hansen RH, Kramer MM, Vidal E. Discrete Displacement Hydraulic Power Take-Off System for the Wavestar Wave Energy Converter. Energies. 2013; 6(8):4001-4044.
Hansen, Rico H.; Kramer, Morten M.; Vidal, Enrique. 2013. "Discrete Displacement Hydraulic Power Take-Off System for the Wavestar Wave Energy Converter." Energies 6, no. 8: 4001-4044.