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), therefore enabling to consider both curvature and radial end-effects on the air-gap magnetic field, as well as the back-iron magnetic saturation. For a more comprehensive assessment of the electromagnetic performance, a 3D analytical technique to calculate the coil self-inductance is also developed, which can be applied whatever the coil shape. These procedures provides a very fast calculation of the main electromagnetic quantities by acting 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. A check by means of corresponding 3D FEAs proves the effectiveness of the proposed design method.