A Constant-Pressure Hydraulic PTO System for a Wave Energy Converter Based on a Hydraulic Transformer and Multi-Chamber Cylinder

Chenglong Li, Dahai Zhang, Weijie Zhang, Xiaodong Liu, Ming Tan, Yulin Si and Peng Qian
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Chenglong Li: Ocean College, Zhejiang University, Zhoushan 316021, China
Dahai Zhang: Ocean College, Zhejiang University, Zhoushan 316021, China
Weijie Zhang: Ocean College, Zhejiang University, Zhoushan 316021, China
Xiaodong Liu: Ocean College, Zhejiang University, Zhoushan 316021, China
Ming Tan: Ocean College, Zhejiang University, Zhoushan 316021, China
Yulin Si: Ocean College, Zhejiang University, Zhoushan 316021, China
Peng Qian: Ocean College, Zhejiang University, Zhoushan 316021, China

Energies, 2021, vol. 15, issue 1, 1-18

Abstract: This paper presents a constant-pressure hydraulic PTO system that can convert stored pressure energy into electrical energy at a stable speed through hydraulic motors and generators. A multi-chamber cylinder can be connected to the main power generation circuit by check valves, and the motor displacement can be controlled by a fuzzy controller to maintain the main power generation circuit under stable pressure. The hydraulic transformer can control the forces applied to the floater. The hydrodynamic parameters of the floater are calculated by AQWA, and the optimal PTO damping of the hydraulic system is analyzed as the target of transformer control. MATLAB/Simulink and AMESim are used to carry out the co-simulation. Three kinds of wave elevation time-series for the specific state are designed for the simulation. In the co-simulation, three approaches are carried out for the simulation including no control strategy, fuzzy control with a fixed transformer ratio, and fuzzy control with a variable transformer ratio. Under the fuzzy control with a fixed transformer ratio, the floater displacement and captured energy do not increase significantly, but the oil pressure fluctuation is very stable, which indicates that the fuzzy controller maintains the stability of the main power circuit. While under fuzzy control with a variable transformer ratio, the power generation is not larger than those under no control strategy or fuzzy control with a fixed transformer ratio, which proves that this hydraulic transformer concept is less efficient.

Keywords: wave energy; PTO; fuzzy control; hydraulic transformer; multi-chamber cylinder (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
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