Abstract
The latching control represents an attractive alternative to increase the power absorption of wave energy converters (WECs) by tuning the phase of oscillator velocity to the wave excitation phase. However, increasing the amplitude of motion of the floating body is not the only challenge to obtain a good performance of the WEC. It also depends on the efficiency of the power take-off system (PTO). This study aims to address the actual power performance and operation of a heaving point absorber with a direct mechanical drive PTO system controlled by latching. The PTO characteristics, such as the gear ratio, the flywheel inertia, and the electric generator, are analyzed in the WEC performance. Three cylindrical point absorbers are also considered in the present study. A wave-to-wire model is developed to simulate the coupled hydro-electro-mechanical system in regular waves. The wave energy converter (WEC) performance is analyzed using the potential linear theory but considering the viscous damping effect according to the Morison equation to avoid the overestimated responses of the linear theory near resonance when the latching control system is applied. The latching control system increases the mean power. However, the increase is not significant if the parameters that characterize the WEC provide a considerable mean power. The performance of the proposed mechanical power take-off depends on the gear ratio and flywheel. However, the gear ratio shows a more significant influence than the flywheel inertia. The operating range of the generator and the diameter/draft ratio of the buoy also influence the PTO performance.
Highlights
The technology of harnessing wave energy is in the pre-commercial stage
More than thousand wave energy converter (WEC) patents have been registered since 1980 (Amir et al 2016) and more than hundred wave power pilot projects have been installed over the past few years (ITTC 2014)
The oscillating body of WEC is a heaving point absorber with cylinder geometry (Figure 1)
Summary
The technology of harnessing wave energy is in the pre-commercial stage. More efficient power performance must be achieved introducing a lower cost of energy competitive to the more mature renewable sources, such as wind and solar. A PTO system is the WEC’s component responsible for converting kinetic energy from the oscillator into electricity It has a direct influence on the efficiency of the WEC. Air turbines represent one of the first modern technologies to drive the research on wave energy converters It is used in oscillating water column types (Heath et al 2000; Clément et al 2002). Overtopping devices use the hydro turbine PTO system to generate electricity using the seawater’s potential energy accumulated in a basin (Christensen et al 2005; Liu et al 2017) This system offers a high efficiency and low maintenance. This research aims to address the actual power performance and operation of a wave energy converter with a direct-drive mechanical PTO system controlled by latching. The viscous damping effect contribution is considered through the Morison-like quadratic damping term (Morison et al 1950)
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