# Hydraulic Power Take-Off Concepts for Wave Energy Conversion System: A Review

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## Abstract

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## 1. Introduction

## 2. Multi-Concepts of Hydraulic Power Take-Off System

#### 2.1. Variable-Pressure Concept

#### 2.2. Constant-Pressure Concept

#### 2.2.1. Constant-Pressure Hydraulic PTO Based on Two-Check Valves Concepts

#### 2.2.2. Constant-Pressure Hydraulic PTO Based on Four-Check Valves Concepts

#### 2.2.3. Constant-Pressure Hydraulic PTO Based on Directional Control Valves Concepts

#### 2.2.4. Constant-Pressure Hydraulic PTO Based on Hydraulic Transformer Concepts

## 3. Review of Control Strategies Used in Hydraulic PTO System

#### 3.1. Hydraulic Accumulator with an Active Control Valve Mechanism

#### 3.2. Hydraulic Cylinder with an Active Control Valve Mechanism

#### 3.3. Hydraulic Transformer or Hydraulic Motor with a Digital Control Mechanism

#### 3.4. Control Mechanism in Conditioning Module

## 4. Benefits and Challenges of the Hydraulic PTO System

## 5. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## Nomenclature

DoE | Department of Energy |

EMEC | European Marine Energy Centre |

FSA | Force switching algorithm |

HP | High-pressure |

IEA | International Energy Agency |

LP | Low-pressure |

MEC | Maximum efficiency converting |

MPC | Model predictive control |

MPPT | Maximum power point tracking |

OES | Ocean Energy System |

OWC | Oscillating water column |

PDDFC | Pressure drop database as the feedback control |

PI | Proportional-integral |

PS | Pseudo-spectral |

PTO | Power take-off |

PWM | Pulse width modulation |

SB | Shape-based |

WAB | Wave-activated-bodies |

WEC | Wave energy converter |

WPEA | Wave power extraction algorithm |

## References

- Melikoglu, M. Current status and future of ocean energy sources: A global review. Ocean Eng.
**2018**, 148, 563–573. [Google Scholar] [CrossRef] - Tedeschi, E.; Carraro, M.; Molinas, M.; Mattavelli, P. Effect of control strategies and power take-off efficiency on the power capture from sea waves. IEEE Trans. Energy Convers.
**2011**, 26, 1088–1098. [Google Scholar] [CrossRef] - Zhang, X.; Tian, X.; Xiao, L.; Li, X.; Chen, L. Application of an adaptive bistable power capture mechanism to a point absorber wave energy converter. Appl. Energy
**2018**, 228, 450–467. [Google Scholar] [CrossRef] - Ocean Energy Systems. Annual Report, An Overview of Ocean Energy Activities in 2017; The Executive Committee of Ocean Energy Systems: Lisbon, Portugal, 2017. [Google Scholar]
- BCS. Incorporated U.S. Department of Energy Wind and Water Power Program Funding in the United States: Conventional Hydropower Projects, FY 2008—FY 2010; U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy: Washington, DC, USA, 2008.
- Press Release: EMEC Guides Marine Energy Centre in China: EMEC: European Marine Energy Centre. Available online: http://www.emec.org.uk/press-release-emec-guides-marine-energy-centre-in-china-2/ (accessed on 29 July 2019).
- Rusu, E.; Onea, F. A review of the technologies for wave energy extraction. Clean Energy
**2018**, 2, 10–19. [Google Scholar] [CrossRef] - Drew, B.; Plummer, A.R.; Sahinkaya, M.N. A review of wave energy converter technology. Proc. Inst. Mech. Eng. Part A J. Power Energy
**2009**, 223, 887–902. [Google Scholar] [CrossRef] - Titah-Benbouzid, H.; Benbouzid, M. An up-to-date technologies review and evaluation of wave energy converters. Int. Rev. Electr. Eng.
**2015**, 10, 52–61. [Google Scholar] [CrossRef] - de O. Falcão, A.F. Wave energy utilization: A review of the technologies. Renew. Sustain. Energy Rev.
**2010**, 14, 899–918. [Google Scholar] - Lasa, J.; Antolin, J.C.; Angulo, C.; Estensoro, P.; Santos, M.; Ricci, P. Design, Construction and Testing of a Hydraulic Power Take-Off for Wave Energy Converters. Energies
**2012**, 5, 2030–2052. [Google Scholar] [CrossRef] - Pecher, A.; Kofoed, J.P. (Eds.) Handbook of Ocean Wave Energy; Ocean Engineering & Oceanography; Springer International Publishing: Cham, Switzerland, 2017; Volume 7, ISBN 978-3-319-39888-4. [Google Scholar]
- Hong, Y.; Waters, R.; Boström, C.; Eriksson, M.; Engström, J.; Leijon, M. Review on electrical control strategies for wave energy converting systems. Renew. Sustain. Energy Rev.
**2014**, 31, 329–342. [Google Scholar] [CrossRef] - Wang, L.; Isberg, J.; Tedeschi, E. Review of control strategies for wave energy conversion systems and their validation: The wave-to-wire approach. Renew. Sustain. Energy Rev.
**2018**, 81, 366–379. [Google Scholar] [CrossRef] - Falcão, A.F.O.; Henriques, J.C.C. Oscillating-water-column wave energy converters and air turbines: A review. Renew. Energy
**2016**, 85, 1391–1424. [Google Scholar] [CrossRef] - Shalby, M.; Walker, P.; Dorrell, D.G. Modelling of the multi-chamber oscillating water column in regular waves at model scale. Energy Procedia
**2017**, 136, 316–322. [Google Scholar] [CrossRef] - Doyle, S.; Aggidis, G.A. Development of multi-oscillating water columns as wave energy converters. Renew. Sustain. Energy Rev.
**2019**, 107, 75–86. [Google Scholar] [CrossRef] - Contestabile, P.; Crispino, G.; Di Lauro, E.; Ferrante, V.; Gisonni, C.; Vicinanza, D. Overtopping breakwater for wave Energy Conversion: Review of state of art, recent advancements and what lies ahead. Renew. Energy
**2020**, 147, 705–718. [Google Scholar] [CrossRef] - Takao, M.; Setoguchi, T. Air Turbines for Wave Energy Conversion. Int. J. Rotating Mach.
**2012**, 2012, 1–10. [Google Scholar] [CrossRef] - Henriques, J.C.C.; Gomes, R.P.F.; Gato, L.M.C.; Falcão, A.F.O.; Robles, E.; Ceballos, S. Testing and control of a power take-off system for an oscillating-water-column wave energy converter. Renew. Energy
**2016**, 85, 714–724. [Google Scholar] [CrossRef] - Pico OWC. Available online: http://www.pico-owc.net/cms.php?page=542&wnsid=dbb177dd9668f08318 207830330904df (accessed on 29 July 2019).
- Boake, C.B.; Whittaker, T.J.T.; Folley, M.; Ellen, H. Overview and Initial Operational Experience of the LIMPET Wave Energy Plant. In Proceedings of the Twelfth International Offshore and Polar Engineering Conference, Kitakyushu, Japan, 26–31 May 2002; Volume 12. [Google Scholar]
- Kofoed, J.P.; Frigaard, P. Hydraulic Evaluation of the LEANCON Wave Energy Converter; Department of Civil Engineering, Aalborg University: Aalborg, Denmark, 2008. [Google Scholar]
- Babarit, A. Working Principles and Technologies of Wave Energy Conversion. In Wave Energy Conversion; Elsevier: Amsterdam, The Netherlands, 2018; pp. 99–151. ISBN 9781785482649. [Google Scholar]
- Liu, Z.; Shi, H.; Cui, Y.; Kim, K. Experimental study on overtopping performance of a circular ramp wave energy converter. Renew. Energy
**2017**, 104, 163–176. [Google Scholar] [CrossRef] - Igic, P.; Zhou, Z.; Knapp, W.; MacEnri, J.; Sørensen, H.C.; Friis-Madsen, E. Multi-megawatt offshore wave energy converters—Electrical system configuration and generator control strategy. IET Renew. Power Gener.
**2010**, 5, 10. [Google Scholar] [CrossRef] - Vicinanza, D.; Di Lauro, E.; Contestabile, P.; Gisonni, C.; Lara, J.L.; Losada, I.J. Review of Innovative Harbor Breakwaters for Wave-Energy Conversion. J. Waterw. Port, Coast. Ocean Eng.
**2018**, 145. [Google Scholar] [CrossRef] - Anderlini, E.; Forehand, D.I.M.; Bannon, E.; Abusara, M. Reactive control of a wave energy converter using artificial neural networks. Int. J. Mar. Energy
**2017**, 19, 207–220. [Google Scholar] [CrossRef] - Rhinefrank, K.; Schacher, A.; Prudell, J.; Brekken, T.K.A.; Stillinger, C.; Yen, J.Z.; Ernst, S.G.; Von Jouanne, A.; Amon, E.; Paasch, R.; et al. Comparison of direct-drive power takeoff systems for ocean wave energy applications. IEEE J. Ocean. Eng.
**2012**, 37, 35–44. [Google Scholar] [CrossRef] - Liang, C.; Ai, J.; Zuo, L. Design, fabrication, simulation and testing of an ocean wave energy converter with mechanical motion rectifier. Ocean Eng.
**2017**, 136, 190–200. [Google Scholar] [CrossRef] - Osse, T.J.; Meinig, C.; Stalin, S.; Milburn, H. The PRAWLER, a vertical profiler powered by wave energy. In Proceedings of the OCEANS 2015-MTS/IEEE Washington, Washington, DC, USA, 19–22 October 2015; pp. 1–8. [Google Scholar]
- Velez, C.; Qu, Z.; Lin, K.-C.; Jin, S. Design, Modeling and Optimization of an Ocean Wave Power Generation Buoy. Mar. Technol. Soc. J.
**2014**, 48, 51–60. [Google Scholar] [CrossRef] - Dang, T.D.; Nguyen, M.T.; Phan, C.B.; Ahn, K.K. Development of a Wave Energy Converter with Mechanical Power Take-Off via Supplementary Inertia Control. Int. J. Precis. Eng. Manuf. Technol.
**2019**, 6, 497–509. [Google Scholar] [CrossRef] - Dang, T.D.; Phan, C.B.; Ahn, K.K. Design and Investigation of a Novel Point Absorber on Performance Optimization Mechanism for Wave Energy Converter in Heave Mode. Int. J. Precis. Eng. Manuf. Technol.
**2019**, 6, 477–488. [Google Scholar] [CrossRef] - Sang, Y.; Karayaka, H.B.; Yan, Y.; Zhang, J.Z.; Muljadi, E.; Yu, Y.H. Energy extraction from a slider-crank wave energy converter under irregular wave conditions. In Proceedings of the OCEANS 2015-MTS/IEEE Washington, Washington, DC, USA, 19–22 October 2015; pp. 1–7. [Google Scholar]
- Ozkop, E.; Altas, I.H. Control, power and electrical components in wave energy conversion systems: A review of the technologies. Renew. Sustain. Energy Rev.
**2017**, 67, 106–115. [Google Scholar] [CrossRef] - Xiao, X.; Xiao, L.; Peng, T. Comparative study on power capture performance of oscillating-body wave energy converters with three novel power take-off systems. Renew. Energy
**2017**, 103, 94–105. [Google Scholar] [CrossRef] - Sang, Y.; Karayaka, H.B.; Yan, Y.; Yilmaz, N.; Souders, D. Ocean (Marine) Energy. In Comprehensive Energy Systems; Elsevier: Amsterdam, The Netherlands, 2018; Volume 1–5, pp. 733–769. ISBN 9780128095973. [Google Scholar]
- Piscopo, V.; Benassai, G.; Cozzolino, L.; Della Morte, R.; Scamardella, A. A new optimization procedure of heaving point absorber hydrodynamic performances. Ocean Eng.
**2016**, 116, 242–259. [Google Scholar] [CrossRef] - Weber, J.; Mouwen, F.; Parish, A.; Robertson, D. Wavebob—Research & Development Network and Tools in the Context of Systems Engineering. In Proceedings of the Eighth European Wave and Tidal Energy Conference, Uppsala, Sweden, 7–10 September 2009; pp. 416–420. [Google Scholar]
- Brekken, T.K.A.; von Jouanne, A.; Han, H.Y. Ocean wave energy overview and research at Oregon State University. In Proceedings of the 2009 IEEE Power Electronics and Machines in Wind Applications, Lincoln, NE, USA, 24–26 June 2009; pp. 1–7. [Google Scholar]
- SINN Power|Wave Energy Converter (WEC) Modules. Available online: https://www.sinnpower.com /wave-energy-converter-modules (accessed on 29 July 2019).
- Lejerskog, E.; Boström, C.; Hai, L.; Waters, R.; Leijon, M. Experimental results on power absorption from a wave energy converter at the Lysekil wave energy research site. Renew. Energy
**2015**, 77, 9–14. [Google Scholar] [CrossRef] - Baker, N.J.; Mueller, M.A.; Raihan, M.A.H. All electric drive train for wave energy power take off. In Proceedings of the 5th IET International Conference on Renewable Power Generation (RPG) 2016, London, UK, 21–23 September 2016; Institution of Engineering and Technology: London, UK, 2016; pp. 1–6. [Google Scholar]
- Gaspar, J.F.; Calvário, M.; Kamarlouei, M.; Guedes Soares, C. Power take-off concept for wave energy converters based on oil-hydraulic transformer units. Renew. Energy
**2016**, 86, 1232–1246. [Google Scholar] [CrossRef] - Hansen, R.H.; Kramer, M.M.; Vidal, E.; 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. [Google Scholar] [CrossRef] - de O. Falcão, A.F.; António, A.F. Modelling and control of oscillating-body wave energy converters with hydraulic power take-off and gas accumulator. Ocean Eng.
**2007**, 34, 2021–2032. [Google Scholar] - Zou, S.; Abdelkhalik, O. Control of Wave Energy Converters with Discrete Displacement Hydraulic Power Take-Off Units. J. Mar. Sci. Eng.
**2018**, 6, 31. [Google Scholar] [CrossRef][Green Version] - Yemm, R.; Pizer, D.; Retzler, C.; Henderson, R. Pelamis: Experience from concept to connection. Philos. Trans. R. Soc. A Math. Phys. Eng. Sci.
**2012**, 370, 365–380. [Google Scholar] [CrossRef][Green Version] - Wave Star. Wavestar prototype at Roshage: Performance Data for ForskVE Project No 2009-1-10305 Phase 1 & 2; Wave Star A/S: Brondby, Denmark, 2012. [Google Scholar]
- How It Works—Eco Wave Power. Available online: https://www.ecowavepower.com/our-technology/how-it-works/ (accessed on 29 July 2019).
- WaveRoller—AW Energy Oy. Available online: http://aw-energy.com/waveroller/#technology (accessed on 29 July 2019).
- Penalba, M.; Giorgi, G.; Ringwood, J.V. Mathematical modelling of wave energy converters: A review of nonlinear approaches. Renew. Sustain. Energy Rev.
**2017**, 78, 1188–1207. [Google Scholar] [CrossRef][Green Version] - Li, Y.; Yu, Y.-H. A synthesis of numerical methods for modeling wave energy converter-point absorbers. Renew. Sustain. Energy Rev.
**2012**, 16, 4352–4364. [Google Scholar] [CrossRef] - Penalba, M.; Ringwood, J.V.; Penalba, M.; Ringwood, J.V. A Review of Wave-to-Wire Models for Wave Energy Converters. Energies
**2016**, 9, 506. [Google Scholar] [CrossRef][Green Version] - Windt, C.; Davidson, J.; Ringwood, J.V. High-fidelity numerical modelling of ocean wave energy systems: A review of computational fluid dynamics-based numerical wave tanks. Renew. Sustain. Energy Rev.
**2018**, 93, 610–630. [Google Scholar] [CrossRef][Green Version] - Lin, Y.; Bao, J.; Liu, H.; Li, W.; Tu, L.; Zhang, D. Review of hydraulic transmission technologies for wave power generation. Renew. Sustain. Energy Rev.
**2015**, 50, 194–203. [Google Scholar] [CrossRef] - Gaspar, J.F.; Calvário, M.; Kamarlouei, M.; Soares, C.G. Design tradeoffs of an oil-hydraulic power take-off for wave energy converters. Renew. Energy
**2018**, 129, 245–259. [Google Scholar] [CrossRef] - Penalba, M.; Sell, N.P.; Hillis, A.J.; Ringwood, J.V.; Penalba, M.; Sell, N.P.; Hillis, A.J.; Ringwood, J.V. Validating a Wave-to-Wire Model for a Wave Energy Converter—Part I: The Hydraulic Transmission System. Energies
**2017**, 10, 977. [Google Scholar] [CrossRef][Green Version] - Hansen, R.H.; Andersen, T.O.; Pedersen, H.C. Model Based Design of Efficient Power Take-Off Systems for Wave Energy Converters. In Proceedings of the 12th Scandinavian International Conference on Fluid Power, SICFP, Tampere, Finland, 18–20 May 2011; pp. 1–15. [Google Scholar]
- Costello, R.; Ringwood, J.V.; Weber, J. Comparison of Two Alternative Hydraulic PTO Concepts for Wave Energy Conversion. In Proceedings of the 9th European Wave and Tidal Energy Conference (EWTEC), Southampton, UK, 5–9 September 2011. [Google Scholar]
- Gaspar, J.F.; Kamarlouei, M.; Sinha, A.; Xu, H.; Calvário, M.; Faÿ, F.X.; Robles, E.; Soares, C.G. Speed control of oil-hydraulic power take-off system for oscillating body type wave energy converters. Renew. Energy
**2016**, 97, 769–783. [Google Scholar] [CrossRef] - Kurniawan, A.; Pedersen, E.; Moan, T. Bond graph modelling of a wave energy conversion system with hydraulic power take-off. Renew. Energy
**2012**, 38, 234–244. [Google Scholar] [CrossRef] - Tri, N.M.; Truong, D.Q.; Thinh, D.H.; Binh, P.C.; Dung, D.T.; Lee, S.; Park, H.G.; Ahn, K.K. A novel control method to maximize the energy-harvesting capability of an adjustable slope angle wave energy converter. Renew. Energy
**2016**, 97, 518–531. [Google Scholar] [CrossRef] - Ding, B.; Cazzolato, B.S.; Arjomandi, M.; Hardy, P.; Mills, B. Sea-state based maximum power point tracking damping control of a fully submerged oscillating buoy. Ocean Eng.
**2016**, 126, 299–312. [Google Scholar] [CrossRef] - Yang, L.; Moan, T. Dynamic analysis of wave energy converter by incorporating the effect of hydraulic transmission lines. Ocean Eng.
**2011**, 38, 1849–1860. [Google Scholar] [CrossRef] - de O. Falcão, A.F. Phase control through load control of oscillating-body wave energy converters with hydraulic PTO system. Ocean Eng.
**2008**, 35, 358–366. [Google Scholar] - Yang, L.; Moan, T. Numerical Modeling of Wear Damage in Seals of a Wave Energy Converter with Hydraulic Power Take-Off under Random Loads. Tribol. Trans.
**2010**, 54, 44–56. [Google Scholar] [CrossRef] - Engin, C.D.; Yeşildirek, A. Designing and modeling of a point absorber wave energy converter with hydraulic power take-off unit. In Proceedings of the 4th International Conference on Electric Power and Energy Conversion Systems (EPECS), Sharjah, UAE, 24–26 November 2015. [Google Scholar]
- So, R.; Casey, S.; Kanner, S.; Simmons, A.; Brekken, T.K.A. PTO-Sim: Development of a Power Take Off Modeling Tool for Ocean Wave Energy Conversion. In Proceedings of the 2015 IEEE Power & Energy Society General Meeting, Denver, CO, USA, 26–30 July 2015. [Google Scholar]
- Beirão, P.; Malça, C.; Beirão, P.; Malça, C. Hydraulic Power Take-off and Buoy Geometries Charac-terisation for a Wave Energy Converter. Energy Power Eng.
**2013**, 5, 72–77. [Google Scholar] [CrossRef] - Song, R.; Ming, Y.; Xiaohua, D. Intermittent wave energy generation system with hydraulic energy storage and pressure control for stable power output. J. Mar. Sci. Technol.
**2018**, 23, 802–813. [Google Scholar] [CrossRef][Green Version] - Wang, D.; Lu, K. Design optimization of hydraulic energy storage and conversion system for wave energy converters. Prot. Control Mod. Power Syst.
**2018**, 3, 7. [Google Scholar] [CrossRef] - Chehaze, W.; Chamoun, D.; Bou-Mosleh, C.; Rahme, P. Wave Roller Device for Power Generation. Procedia Eng.
**2016**, 145, 144–150. [Google Scholar] [CrossRef][Green Version] - Liu, Z.; Qu, N.; Han, Z.; Zhang, J.; Zhang, S.; Li, M.; Shi, H. Study on energy conversion and storage system for a prototype buoys-array wave energy converter. Energy Sustain. Dev.
**2016**, 34, 100–110. [Google Scholar] [CrossRef] - Costa, P.R.; Garcia-Rosa, P.B.; Estefen, S.F. Phase control strategy for a wave energy hyperbaric converter. Ocean Eng.
**2010**, 37, 1483–1490. [Google Scholar] [CrossRef] - Zhang, W.; Liu, Y.; Luo, H.; Xue, G.; Zhang, J. Experimental and Simulative Study on Accumulator Function in The Process of Wave Energy Conversion. Polish Marit. Res.
**2016**, 23, 79–85. [Google Scholar] [CrossRef][Green Version] - Cargo, C.J.; Hillis, A.J.; Plummer, A.R. Optimisation and control of a hydraulic power take-off unit for a wave energy converter in irregular waves. Proc. Inst. Mech. Eng. Part A J. Power Energy
**2014**, 228, 462–479. [Google Scholar] [CrossRef][Green Version] - Cargo, C.J.; Plummer, A.R.; Hillis, A.J.; Schlotter, M. Determination of optimal parameters for a hydraulic power take-off unit of a wave energy converter in regular waves. Proc. Inst. Mech. Eng. Part A J. Power Energy
**2012**, 226, 98–111. [Google Scholar] [CrossRef] - Yue, X.; Chen, Q.; Wang, Z.; Geng, D.; Yan, D.; Jiang, W.; Wang, W. A novel nonlinear state space model for the hydraulic power take-off of a wave energy converter. Energy
**2019**, 180, 465–479. [Google Scholar] - Shi, H.; Cao, F.; Liu, Z.; Qu, N. Theoretical study on the power take-off estimation of heaving buoy wave energy converter. Renew. Energy
**2016**, 86, 441–448. [Google Scholar] [CrossRef] - Do, H.T.; Dang, T.D.; Ahn, K.K. A multi-point-absorber wave-energy converter for the stabilization of output power. Ocean Eng.
**2018**, 161, 337–349. [Google Scholar] [CrossRef] - Cargo, C.J.; Hillis, A.J.; Plummer, A.R. Strategies for active tuning of Wave Energy Converter hydraulic power take-off mechanisms. Renew. Energy
**2016**, 94, 32–47. [Google Scholar] [CrossRef][Green Version] - Ricci, P.; Lopez, J.; Santos, M.; Ruiz-Minguela, P.; Villate, J.L.L.; Salcedo, F.; de O. Falcão, A.F. Control strategies for a wave energy converter connected to a hydraulic power take-off. IET Renew. Power Gener.
**2011**, 5, 234. [Google Scholar] [CrossRef] - Dießel, D.; Bryans, G.; Verdegem, L.; Murrenhoff, H. Wavepod a transmission for wave energy converters—Set-up and testing. Int. J. Fluid Power
**2015**, 16, 75–82. [Google Scholar] [CrossRef] - Zhang, D.H.; Li, W.; Zhao, H.T.; Bao, J.W.; Lin, Y.G. Design of a hydraulic power take-off system for the wave energy device with an inverse pendulum. China Ocean Eng.
**2014**, 28, 283–292. [Google Scholar] [CrossRef] - Lin, Y.G.; Tu, L.; Zhang, D.H.; Liu, H.W.; Li, W. A study on dual-stroke pendulum wave energy conversion technology based on a water/oil integrated transmission system. Ocean Eng.
**2013**, 67, 27–34. [Google Scholar] [CrossRef] - Henderson, R. Design, simulation, and testing of a novel hydraulic power take-off system for the Pelamis wave energy converter. Renew. Energy
**2006**, 31, 271–283. [Google Scholar] [CrossRef] - Liu, C.; Yang, Q.; Bao, G. Performance investigation of a two-raft-type wave energy converter with hydraulic power take-off unit. Appl. Ocean Res.
**2017**, 62, 139–155. [Google Scholar] [CrossRef] - Liu, C.; Yang, Q.; Bao, G. Influence of hydraulic power take-off unit parameters on power capture ability of a two-raft-type wave energy converter. Ocean Eng.
**2018**, 150, 69–80. [Google Scholar] [CrossRef] - Hansen, R.H.; Andersen, T.O.; Perdersen, H.C. Analysis of discrete pressure level systems for Wave Energy Converters. In Proceedings of the 2011 International Conference on Fluid Power and Mechatronics, Beijing, China, 17–20 August 2011; pp. 552–558. [Google Scholar]
- Pedersen, H.C.C.; Hansen, R.H.H.; Hansen, A.H.H.; Andersen, T.O.O.; Bech, M.M.M. Design of full scale wave simulator for testing Power Take Off systems for wave energy converters. Int. J. Mar. Energy
**2016**, 13, 130–156. [Google Scholar] [CrossRef] - Hansen, R.H.; Kramer, M.M. Modelling and Control of the Wavestar Prototype. In Proceedings of the 9th European Wave and Tidal Energy Conference: EWTEC, Southampton, UK, 5–9 September 2011; pp. 1–10. [Google Scholar]
- Hansen, R.H. Design and Control of the PowerTake-Off System for a Wave Energy Converter with Multiple Absorbers; Aalborg University, Department of Energy Technology: Aalborg, Denmark, 2013. [Google Scholar]
- Gaspar, J.F.; Kamarlouei, M.; Sinha, A.; Xu, H.; Calvário, M.; Faÿ, F.-X.; Robles, E.; Guedes Soares, C. Analysis of electrical drive speed control limitations of a power take-off system for wave energy converters. Renew. Energy
**2017**, 113, 335–346. [Google Scholar] [CrossRef] - Jama, M.; Wahyudie, A.; Noura, H. Robust predictive control for heaving wave energy converters. Control Eng. Pract.
**2018**, 77, 138–149. [Google Scholar] [CrossRef] - Wilson, D.; Bacelli, G.; Coe, R.G.; Bull, D.L.; Abdelkhalik, O.; Korde, U.A.; Robinett, R.D. A Comparison of WEC Control Strategies; Sandia National Labs: Albuquerque, NM, USA, 2016. [Google Scholar]
- Babarit, A.; Clément, A.H. Optimal latching control of a wave energy device in regular and irregular waves. Appl. Ocean Res.
**2006**, 28, 77–91. [Google Scholar] [CrossRef] - Babarit, A.; Guglielmi, M.; Clément, A.H. Declutching control of a wave energy converter. Ocean Eng.
**2009**, 36, 1015–1024. [Google Scholar] [CrossRef][Green Version] - Anderlini, E.; Forehand, D.I.M.; Bannon, E.; Abusara, M. Control of a Realistic Wave Energy Converter Model Using Least-Squares Policy Iteration. IEEE Trans. Sustain. Energy
**2017**, 8, 1618–1628. [Google Scholar] [CrossRef][Green Version] - Anderlini, E.; Forehand, D.I.M.; Bannon, E.; Xiao, Q.; Abusara, M. Reactive control of a two-body point absorber using reinforcement learning. Ocean Eng.
**2018**, 148, 650–658. [Google Scholar] [CrossRef] - Ringwood, J.V. Control Optimisation and Parametric Design. In Numerical Modelling of Wave Energy Converters; Academic Press: Cambridge, MA, USA, 2016; pp. 229–251. ISBN 9780128032107. [Google Scholar]
- Choi, K.-S.; Yang, D.-S.; Park, S.-Y.; Cho, B.-H. Design and performance test of hydraulic PTO for wave energy converter. Int. J. Precis. Eng. Manuf.
**2012**, 13, 795–801. [Google Scholar] [CrossRef] - Hansen, A.H.; Asmussen, M.F.; Bech, M.M. Model predictive control of a wave energy converter with discrete fluid power power take-off system. Energies
**2018**, 11, 635. [Google Scholar] [CrossRef][Green Version] - Wang, K.; Sheng, S.; Zhang, Y.; Ye, Y.; Jiang, J.; Lin, H.; Huang, Z.; Wang, Z.; You, Y. Principle and control strategy of pulse width modulation rectifier for hydraulic power generation system. Renew. Energy
**2019**, 135, 1200–1206. [Google Scholar] [CrossRef]

**Figure 1.**Illustration of hydraulic power take-off (PTO) in wave energy conversion system (adapted from [55]).

**Figure 8.**Classification of control strategies in a wave conversion system according to different criteria.

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**MDPI and ACS Style**

Jusoh, M.A.; Ibrahim, M.Z.; Daud, M.Z.; Albani, A.; Mohd Yusop, Z.
Hydraulic Power Take-Off Concepts for Wave Energy Conversion System: A Review. *Energies* **2019**, *12*, 4510.
https://doi.org/10.3390/en12234510

**AMA Style**

Jusoh MA, Ibrahim MZ, Daud MZ, Albani A, Mohd Yusop Z.
Hydraulic Power Take-Off Concepts for Wave Energy Conversion System: A Review. *Energies*. 2019; 12(23):4510.
https://doi.org/10.3390/en12234510

**Chicago/Turabian Style**

Jusoh, Mohd Afifi, Mohd Zamri Ibrahim, Muhamad Zalani Daud, Aliashim Albani, and Zulkifli Mohd Yusop.
2019. "Hydraulic Power Take-Off Concepts for Wave Energy Conversion System: A Review" *Energies* 12, no. 23: 4510.
https://doi.org/10.3390/en12234510