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

Abstract

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.

Validating a Wave-to-Wire Model for a Wave Energy Converter—Part II: The Electrical System

“…Although specific W2W models can be designed for different PTO systems, all WECs with the purpose of generating electricity require electric generators, either linear [20,21] or rotational [22,23]. Hence, the model for the electric generator is an essential part of any W2W model for electricity-generating WECs, regardless of the type of PTO system.…”

Kinerja Model Fisik Konverter Energi Ombak Rangkaian Gear Searah pada Periode Ombak yang Bervariasi

“…Penelitian pada bidang pemanfaatan ombak telah menarik perhatian beberapa peneliti antara lain (Hansen, et al, 2014) memanfaatkan ombak sebagai sumber energi terbarukan dengan memanfaatkan pergerakan naik turun ombak untuk menggerakkan sebuah pompa hidrolik yang dihubungkan dengan turbin untuk memutar generator listrik. Kelly dkk (Kelly, et al, 2013) mengusulkan kombinasi antara pembangkit listrik tenaga ombak terapung dengan pembangkit listrik tenaga angin untuk mengatasi variasi energi listrik yang dihasilkan.…”

Modeling Innovative Power Take-Off Based on Double-Acting Hydraulic Cylinders Array for Wave Energy Conversion

“…This functionality improves the capability of adjusting the restraining force indicated by Hansen [31], who uses three different high pressure accumulators and a multi-chambered hydraulic cylinder to obtain up to thirteen available areas. The availability of these areas together with the possibility of changing the geometrical position of each hydraulic cylinder, as indicated in Table 1, along with the change on the operation pressure allows the application of a greater quantity of restraining torques.…”

“…Generally in current systems, the adjustment of the force applied by the PTO is carried out by modifying the pressure [6,17,28,29] or by modifying the available areas of the hydraulic cylinders to apply a discrete force [30,31]. The PTOs based on the modified area technique use a Discrete Displacement Cylinder (DDC) in order to employ different forces.…”