Analysis and Experimental Verification of Losses in a Concentrated Wound Interior Permanent Magnet Machine

It is well known that additional space harmonics in the air-gap magnetomotive force (MMF) distribution of the concentrated non-overlapping windings (CW) cause additional losses in the machine. This is especially so for machines used for traction applications where the machine requires to operate over its rated speed and frequency. In this paper, the authors investigates losses present in an interior permanent magnet (IPM) machine with CW designed to achieve a very wide field weakening range. Losses were quantified analytically and also using finite element methods. Loss estimations were experimentally verified in a constructed prototype machine. Based on the analysis, key losses were identified. The optimization process to minimize these losses and of improving efficiency were discussed in details. The segregation of the losses in the studied machine indicates that the losses in the magnet are much smaller compared to the rotor and stator core losses caused by the slot harmonics. Therefore, core loss minimization techniques for this type of machine will involve reduction of slot harmonics. Also, copper loss is found to be the most dominating component of the total loss. Hence, copper loss minimization should be part of the design optimization process.