Rotor loss estimation in permanent magnet machines with concentrated windings

Concentrated windings permanent magnet (PM) machines are widely adopted in the range of sub-fractional power, in fault-tolerant systems, and in low-speed applications with high number-of poles. The non-overlapping windings make the construction simpler and cheaper, with end-connections significantly´ shorter than as usual for distributed windings. Copper losses are reduced accordingly. In addition, for certain numbers of poles, cogging and torque ripple are practically null also without skewing. On the opposite, strong harmonics content affects the magnetic field, resulting in significant losses on the rotor, both in the magnets (eddy currents) and in the iron (minor loops). The accurate calculation of rotor losses is then mandatory for the optimal design. In this paper, a finite element model (FEM) able to handling rotor motion is used for loss prediction. The analysis is developed on a set of 3-phase test machines, all with the same stator but differing in pole number (4 or 8) and rotor iron (laminated or solid).