Recent Advances in Direct-Drive Power Take-Off (DDPTO) Systems for Wave Energy Converters Based on Switched Reluctance Machines (SRM)

Abstract

This chapter is focused on Power Take-Off (PTO) systems for wave energy converters (WEC), being one of the most important elements since PTOs are responsible to transform the mechanical power captured from the waves into electricity. It presents Direct-Drive PTO (DDPTO) as one of the most reliable solutions to be adapted to some particular types of WEC, such as point absorbers. A discussion about modularity and adaptability, together with intrinsic characteristics of direct-drive PTOs, is also included. Among the different technologies of electric machines that can be used in direct-drive linear PTOs, switched reluctance machines (SRM) are described in further detail. In particular, the Azimuthal Multi-translator SRM is presented as a suitable solution in order to increase power density and reduce costs. Not only the electric machine, but also the associated power electronics are described in detail. The description includes the different configurations and topologies of power converters and the most appropriate control strategies. Finally, a superconducting linear generator solution is described, presenting it as a reliable alternative for the application of direct-drive PTOs. An example of concept and preliminary design is included in order to highlight the main challenges to be faced during this process.

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

“…thus reducing the average generated power until it reaches zero. This is noticeable in Figures [11][12][13][14], which present the mean power vs. the GR for generators G1 and G2 under different conditions of wave period and height. It is also noticeable that a higher incident power (i.e., higher 𝐻 and lower 𝑇 ) leads to a lower critical value of GR.…”

“…where ρ is the density of the water, A is the cross section of the point absorber and c 33 is the stiffness coefficient. F r is defined according to [39], see Equation (11), whereby the radiation convolution integral is solved by a direct method.…”

“…The technological development of wave energy converters (WECs) is increasing worldwide [9]. Due to its small size, low complexity and low cost, the point absorber is the most studied WEC type [10][11][12][13]. The accessibility of these devices is important for maintenance and repair, as environmental conditions can make this task difficult [14].…”

“…A very important component of the WEC is the power take-off (PTO) system, which represents the mechanism that transforms the kinetic energy of the component that interacts with the wave to generate electricity. The efficiency of the WEC depends mainly on this system; it can be considered as the brain [11] because it can influence the dynamics of the component that interacts with the wave to maximize energy capture. The PTO system is based on a hydraulic [16], pneumatic [17,18] or mechanical system [9,19]; hydraulic and pneumatic components decrease the efficiency of WECs [9].…”

“…The PTO system is based on a hydraulic [16], pneumatic [17,18] or mechanical system [9,19]; hydraulic and pneumatic components decrease the efficiency of WECs [9]. For this reason, in recent years, the application of the direct drive mechanical system and the direct electrical drive system has increased [11]. 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.…”