Direct-drive permanent magnet (PM) synchronous machines for wind turbines are large, heavy and thus expensive to build, transport and install. The structure that is required to maintain the airgap clearance is often heavier than the electromagnetically active material. It is shown that the structural material can be estimated early on in the design process for axial-flux and radial-flux machines. By moving to a design without iron in the stator, the forces that the machine structure must deal with can be significantly reduced. The mass of iron-cored and air-cored axial-flux PM synchronous machines for a range of multi-MW wind turbines is compared. Scaling laws for PM generators in direct-drive wind turbines are also developed.

The archimedes wave swing (AWS) is a system that converts ocean wave energy into electric energy. The goal of the research described in this paper is to identify the most suitable generator type for this application. Of the conventional generator types, the three-phase permanent-magnet synchronous generator with iron in both stator and translator is most suitable, because it is cheaper and more efficient than the induction generator, the switched reluctance generator, and the permanent-magnet (PM) generator with an air-gap winding. The paper also proposes a new transverse-flux PM (TFPM) generator topology that could be suitable for this application. This new double-sided moving-iron TFPM generator has flux concentrators, magnets, and conductors on the stator, while the translator only consists of iron.