Axial segmentation and magnets losses of SMPM machines using 2D FE method

A prototype generator for application in hybrid electric vehicles has been developed. This generator has a fractional-slot concentrated winding and a surface mounted permanent magnet (SMPM) rotor. The magnets are laminated in the axial direction to reduce the eddy current losses and to prevent excessive heating of the magnets. However, lamination of the magnets increases the production cost of the generator. To reduce production cost the relation between magnet lamination thickness (and consequently the number of magnet laminations) and rotor losses is investigated. To optimize a generator design for cost, the number of laminations should be low, while losses in the magnets should not overheat the magnets. Investigating the effect of axial lamination of the magnets on the eddy current losses requires a 3D FEM simulation, which is time consuming. To overcome this problem, a 2D FEM model is used where a correction factor is implemented. The correction factor is used to include the end effects in the magnets, which are neglected in a 2D model. These end effects can not be neglected because of the low ratio of magnet length to magnet width. With this method, the magnet losses are calculated for a number of magnet laminations, with different lamination widths in the axial direction. The calculation results are validated by using a 3D FEM time harmonics simulation.