# 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 |

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**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