Performance comparison of partitioned stator machines with NdFeB and ferrite magnets

Partitioned stator (PS) machines employ two separate stators to accommodate armature windings and permanent magnets (PMs) respectively, alleviating the stator space conflict in stator-PM machines and hence significantly boosting the torque density. However, the PM usage volume of PS machines is relatively large and the cost is high, which is undesirable for cost sensitive applications. In this paper, a PS machine employing ferrite PMs is presented, which can take the advantage of large space for PMs in PS machines as well as balance the performance and cost. The electromagnetic characteristics of an optimized ferrite PS machine and an optimized NdFeB PS machine are compared, together with a classic Prius2010 interior-PM (IPM) machine as a baseline for comparison. In addition, the economic issues are considered as well. The predicted results reveal that the NdFeB PS machine can produce much higher torque density but is more expensive than the Prius2010 IPM machine, whilst the ferrite PS machine can significantly reduce the cost and still exhibit comparable performance as the Prius2010 IPM machine and the highest torque per cost. The demagnetization behavior of ferrite PS machine is evaluated and a method to improve the demagnetization withstand capability is proposed. A pair of scaled prototypes are manufactured to validate the finite element predictions.