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.
Highlights
In the context of a resource crisis and environmental pollution, the development of clean resources is the only way out of the current predicament
The transformer ratio and motor displacement are not controlled, and they are all set to constants
This paper reviews the main components of the existing PTOs hydraulic system, and proposes a constant-pressure hydraulic PTO system for the wave energy converter based on a hydraulic transformer and multi-chamber cylinder, which can convert the stored pressure energy into electrical energy at a stable speed through hydraulic motors and generators
Summary
In the context of a resource crisis and environmental pollution, the development of clean resources is the only way out of the current predicament. Wave energy is expected to replace fossil fuels to contribute to the future electricity supply [2]. Extracting this energy is technically and economically challenging, and equipment development is still at an early stage [3,4,5]. According to their working principle, existing WECs can be divided into three categories: oscillating water column, oscillating bodies, and overtopping devices [6]. This paper focuses on the oscillating body WEC characterized by a heaving response in the water
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