Multi-objective design optimization of a surface-mounted modular permanent-magnet pole machine

Surface-mounted permanent magnet (SMPM) machines have been proposed in which multiple magnet grades are used to shape the airgap flux density distribution to reduce torque ripple and vibration. A simple application of this concept is to mix permanent magnets of different grade but equal depth in a modular permanent-magnet pole arrangement (MPMP). In this work, the idea of combining multiple magnet grades is used not to reduce cogging torque, but rather to increase torque density. A design model has been developed to describe the operation of the machine and calculate the losses at a given operating point This design model is used in conjunction with a multi-objective optimization method to determine the trade-off between loss and mass for the machine. It is shown that in terms of the loss-mass trade-off the MPMP is superior to the SMPM for the cited specifications.