Preliminary Design of an Axial Flux Machine with Careless Stator for Flywheel Applications

The paper presents a procedure for the preliminary design of a permanent magnet axial flux machine (PMAFM) with coreless stator for the power management of a small-scale flywheel energy storage system (FESS). The PMAFM is sized according to the main FESS ratings by means of a 2D analytical formulation elaborated from a simplified 3D finite element analysis (FEA), taking into account both curvature and radial end-effects on the air-gap magnetic field, as well as the PM back-iron magnetic saturation. To complete the electromagnetic performance assessment, the coil self-inductance is calculated by a 3D analytical technique, applicable to any coil shape. These procedures enable a very fast calculation of the main electromagnetic quantities as functions of on the PM and coil sizes. In particular, a parametric analysis is carried out to optimize the PMAFM electromagnetic design, mainly focusing on the reduction of the ohmic losses and of the torque ripple. The comparison with the results of corresponding 3D FEAs proves the effectiveness of the proposed design method.