A novel nonlinear state space model for the hydraulic power take-off of a wave energy converter

Abstract

Since the hydraulic power take-off (PTO) is a widely-utilized transmission device for oscillating-body wave energy converters, its parameter configurations need to be optimized with an accurate dynamic model. To accurately describe the cylinder friction force, the motor loss and the accumulator working patterns, this paper establishes a novel nonlinear state space model for a hydraulic PTO. The model contains a stiction-involved Stribeck curve for the hydraulic cylinder, an improved Jeong's theory for the hydraulic motor and a pressure-bound-related formula for the high-pressure accumulator. The proposed model is simulated in irregular waves and verified via the comparison with the WEC models based on Yang's theory [1]. Furthermore, the research focuses on obtaining optimal PTO parameter configurations with the suitable piston area and resistance, according to the generating ability, energy conversion efficiency and pressure stability. The results show that the piston area has a more significant impact on the generating ability and pressure stability than the resistance but the same influence on the energy conversion efficiency. In general, a small piston area and a minor resistance are the superior configurations at the fixed capacity.