Application of the Latching Control System on the Power Performance of a Wave Energy Converter Characterized by Gearbox, Flywheel, and Electrical Generator

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.

A Review of Offshore Renewable Energy in South America: Current Status and Future Perspectives

“…In the totality of 107 scientific publications on ORE in Brazil, a total of 46 include offshore wind subjects, including theoretical, technical and economic potential assessment [22,28,[44][45][46], resource complementarity including hydropower, offshore wind and offshore solar [47,48], offshore wind environmental [34] and social [49] impacts and regulatory aspects [36]. Research about wave energy in Brazil started in 2000, focusing mainly on wave resource potential [50,51], wave-to-wire modeling [52], geometry optimization [53] and control systems and strategies [30,[54][55][56], experimental tests including dry tests [57] and reduced scale models in wave tank [58], economic feasibility [27] and environmental aspects [59] of WECs. Some works, including [31,60] and [23], are examples of studies that addressed tidal, ocean current and OTEC, respectively.…”

“…The system is a point absorber WEC type with a capacity of 50 kW that consists of an oscillating buoy, a bottom-mounted support structure and a direct mechanical-drive PTO system. More details about the system can be found in [30,53,54]. Another project is a new model of a tidal power plant proposed by Neto et al [60] for the Bacanga Estuary located in São Luis, the estate of Maranhão.…”

Study of a New Wave Energy Converter with Perturb and Observe Maximum Power Point Tracking Method

“…The stored energy is used when the point absorber and the electric generator are uncoupled. The point absorber considered in the present work has been studied by [20] and is described in Table 1. The complexity of the WEC operation is simplified in Figure 3.…”

“…z is the body velocity, u is the undisturbed velocity of the fluid and A is the cross-sectional area of the floating body. The value of the drag coefficient C d assumed in this study is 1.85; the drag coefficient of the point absorber considered has been calculated by [20]. The viscous damping force 𝐹 is calculated based on the drag force described in [41], but rewritten according to [42], see Equation (14).…”

“…As reported in [9], PTO systems based on direct mechanical drive are very well-known and used by 31 developers from all over the world. This system can be composed of a rack and pinion, unidirectional bearings, a belt drive system, a pulley system or a screw mechanism [20][21][22][23][24][25]. The maintenance cost of these components is the challenge of this system because they are exposed to high load cycles; the size of the gearbox represents another problem in some cases [9].…”