On the Optimal Pole Width for Direct Drive Linear Wave Power Generators Using Ferrite Magnets

Abstract

Abstract:In this work, ferrite magnet linear generators for wave power applications are considered. These machines operate at unusually low speeds, around and even below 1 m/s, at which the optimal geometry differs from standard machines, since the copper loss and the force density become considerably more important. The focus is on translator design, and analytical two-dimensional (2D) expressions for the optimal 2D geometry are derived. Finite Element Analysis (FEA) is also applied to verify the analytical expressions and to determine effects from leakage fluxes and iron saturation. Demagnetization of ferrite magnets is also discussed and calculations are made to show the demagnetization situation for the magnets in different geometries. Finally, an example generator design is made to illustrate the findings. This generator is compared to three other generator concepts. It is concluded that ferrite magnet generators can have at least nearly the same shear stress as surface mounted neodymium magnet generators at low speed if the airgap is 3 mm or less, provided that a proper pole length is chosen, and that they can be economically competitive to neodymium magnet generators for wave power. It is also concluded that the demagnetization situation for the magnets can be severe, and that the choice of magnet grade and pole length is crucial in this respect.

Addressing the Magnet Mounting Problem for Double-Sided TFM Machines With Flux-Concentrating Setup

“…L OW cost and efficient direct driven energy conversion is difficult to accomplish for many low speed renewable energy applications, since the resistive losses then become a larger fraction of the power and since the power density naturally becomes low [1]- [3]. To substantially reduce these losses and increase the power density, transverse flux machines (TFMs) and similar machines such as Vernier hybrids [4] belonging to the variable-reluctance permanent magnet machine (VRPM) family can be employed.…”