Analytical Analysis of Electromagnetic Torque and Magnet Utilization Factor for Two Different PM Machines With SPM and HUPM Rotor Topologies

Permanent magnet (PM) machines with a harmonic utilization PM (HUPM) rotor show advantages in terms of magnet utilization and magnet weight reduction compared to common PM rotors. In this article, an analytic approach to estimate the electromagnetic torque, torque density, and magnet utilization of PM machines is presented. Two different rotor types, i.e., the surface-mounted PM (SPM) rotor and the HUPM rotor, have been chosen for analysis. The impact of geometry scaling on electromagnetic performances with a focus on torque characteristics and magnet utilization is studied. The 2-D finite element analysis (FEA) has been used to validate the analytical model. The analysis shows that the toque characteristics and the magnet weight of both machines are strongly affected by the outer machine dimensions and current loading. However, due to the higher utilization factor for the HUPM rotor, the magnet weight of this machine type can be reduced.