In some topologies of yokeless and segmented armature (YASA) axial flux permanent-magnet (AFPM) machines, the particular frame structure required to fasten floating teeth can originate stray paths where parasitic currents may circulate. This paper investigates how the amplitude of these currents and the related additional Joule losses depend on the machine size. Reference is made to wind energy generators, rated from some tens of kilowatts up to a few megawatts. The developed model is mainly based on wind turbine basic data of vendor data sheets, and on the quantities evaluated and tested in two YASA AFPM prototypes, rated 50 and 200 kW.

An analytical approach is proposed in developing a lumped parameter thermal model for the stator coils of naturally-cooled Axial-Flux Tooth-Coil Permanent-Magnet Machines. The model comprises one tooth, the coil around it, the air channels between coils and the teeth supporting structure; each component is subdivided into cuboidal or arc sub-elements. An expression of the convective exchange coefficient is proposed to take into account the radial position of each tooth. Experimental results validate the proposed model, which can also be used in the design stage of a machine.

This paper evaluates the parasitic currents that can occur in the structural part of some types of yokeless and segmented armature axial flux permanent magnet machines, where the frame-supporting stator floating teeth can originate stray paths. In this paper, these paths are defined and modeled, and the consequent effects (induced electro motive forces and currents) are estimated. The amount of these effects depends on the machine geometry, the magnetic circuit structure, and the winding layout. In this paper, the analysis is performed on two different rating machines, comparing their results. The model is validated by measurements on the corresponding prototypes.

Electromagnetic torque harmonics commonly exist in electrical drives due to inverter modulation, current harmonic propagation, etc. They excite torsional vibrations on the shaft which are reflected in the electrical quantities, such as stator line currents. In this paper, the existence of current harmonics originating from both voltage harmonics due to inverter modulation and mechanical oscillations in a surface-mounted permanent magnet synchronous machine (SPMSM) drive is analysed in depth. An analytical model which can accurately predict current harmonic amplitudes is presented. The theoretical development is also useful for detecting incipient torsional resonance or for identifying the natural frequencies of the electrical drive, both analytically and experimentally. An experimental setup consisting of a 6.9 kW SPMSM coupled to a dc generator is used to validate the theoretical studies.

Some converter configurations for wind energy systems are proposed. The conversion structures include capacitor loaded diode bridges directly feeding a grid side inverter. Because of the great variation of the PM generator voltage, due to the wide speed range, a winding commutation is adopted between parallel and series connection, at low speeds. Various features are analyzed, concerning converter sizing and operation aspects. Comparative remarks are made among the different conversion solutions.