A novel variable flux memory machine with series hybrid magnets

Abstract

This paper proposes a novel variable flux memory (VFM) machine, in which the “constant” permanent magnet (PM) (CPM) with high coercive force and the “variable” PM (VPM) with low coercive force are alternatively located in the interior-PM (IPM) rotor. Thus, the VPMs and CPMs are magnetically connected in series, with which the CPMs can assist the VPMs to withstand the unintentional demagnetization caused by armature reaction. Therefore, a high armature current can be applied to the machine. Meanwhile, the reluctance torque is retrieved. Thus, a high torque density can be obtained. Based on two-dimensional (2-D) finite element (FE) analysis, the electromagnetic performance of the proposed VFM machine in two extreme magnetization states is firstly evaluated in detail. Then, the demagnetization and re-magnetization characteristics are investigated, in which the working points of VPMs are illustrated. Furthermore, the advantages of improved efficiency of the proposed VFM machine are demonstrated. A prototype machine is manufactured and tested to validate the predictions.