Design and development of a large magnetic gap linear generator for wave energy

Wave energy can be directly converted into electricity if robust linear generators that are suitably shielded from the marine environment can be developed. Encapsulating stator coils is well established in conventional rotating electrical machines to protect the conductors and improve thermal characteristics. In linear machines, lubrication is unusual and one option is to use solid contact bearings located directly in the air-gap. To make space for lubrication and encapsulation, the electrical machines must tolerate a comparatively large magnetic gap. This has consequences on the electric machine design and simply focusing on topologies that have high force density with unachievable small magnetic gaps is not the best approach. This paper compares a flux switching machine to a flux reversal machines for this application, using realistic constraints. The electrical and mechanical design of a prototype, plus progress in its manufacture, is presented.