A double-sided tubular linear synchronous generator for wave-energy conversion

Abstract

In the field of renewable energy, ocean wave energy is one of the least commercialised resources. This is mainly attributable to the harsh environment and the technical requirements of the environment. In recent years, a vast array of new technologies have been developed for this application. Of these, some have considered the oscillatory action of the ocean waves conducive to the use of linear generators in direct-drive actuators. Linear generators may be classi ed into either tubular machines, which encapsulate the magnetic ux very well, or single- and double-sided at machines. Double-sided at layouts exhibit very high force capabilities because of the presence of a second air-gap. A Double-Sided Tubular machine is proposed which exhibits the force density of a doublesided

at machine combined with the superior ux e ciency of a tubular machine. The hypothesis of the present research is that this new layout will accentuate these bene ts beyond the potential of the double-sided at linear machine layout. The machine's performance was quanti ed on the basis of its force capability, the mathematics of which are dealt with in detailed magnetic vector potential calculations. Simulations of two full-scale machine designs and a prototype machine were performed using Finite-Element Analysis. Fourier analysis was employed extensively to quantify the performance of the designs. The mathematical model developed through this work is fairly accurate. The calculated machine performance deviates from the simulated and measured force capabilities by at most 1.54% for all cases which are presented. A simulated comparison between the double-sided at layout and the double-sided tubular layout indicates that the latter may have up to a 47% smaller volume than the former and use as little as a 83% of the permanent-magnet material as the former. The results are compelling in terms of the possible advantages of the layout. The machine deserves further investigation, mainly into the mechanical design and integration into a complete wave-energy converter system. Notably, the bearing system requires investigation with due cognisance given to the nature of the application. Consideration may also be given to the use of soft-magnetic composites to eliminate the obstacles that tapered laminations pose in the commercialisation of tubular machines.