Simple and Accurate Computation of Rotor Eddy-Current Losses in Surface-Mounted Permanent Magnet Machines Accounting for Magnet Circumferential Segmentation

Abstract

Extensive literature has been produced on the investigation of eddy current losses in Surface-mounted Permanent Magnet (SPM) electric machines in presence of circumferential segmentation by analytical solution of two-dimensional (2D) models. What is missing in the present literature and constitutes the aim of this paper is a simple but accurate procedure enabling the designer to quickly and easily estimate the impact of circumferential segmentation on permanent-magnet loss reduction. The problem is hereinafter addressed in two stages: first the Helmholtz equation is solved in the permanent magnet region neglecting segmentation; then suitable gauge fixing terms are added to the vector potential and eddy current field solutions to account for segmentation. Unlike existing approaches, the method leads to manageable formulas whose accuracy is extensively assessed against finite element simulations on an example SPM machine equipped with a fractional-slot concentrated winding. Furthermore, simple practical rules are derived and validated regarding the impact of magnet segmentation on permanent-magnet losses caused by air-gap magnetic field space harmonics of different orders.

Keywords

• Eddy currents
• electric machines
• losses
• permanent magnets
• SPM machines