Interior PM Machines Using Ferrite to Replace Rare-Earth Surface PM Machines

Since the cost of rare-earth permanent magnets (PMs), such as NdFeB and SmCo, is more and more increasing, there is a great interest in designing PM machines without adopting such rare-earth PMs, i.e., replacing them with cheaper ferrite magnets. Referring to the interior PM (IPM) machines, the expected performance reduction is limited owing to the anisotropic structure: The reluctance (REL) torque component compensates for the use of low-energy PMs. This paper investigates the convenience of adopting ferrite magnets in an IPM machine (sometimes also referred to as PM-assisted synchronous REL machine), instead of a rare-earth surface-mounted PM machine. It is shown that, even though a lengthening of the stack length is required, the anisotropic PM machine that adopts ferrite magnets may represent a valid competitor of a surface PM machine with rare-earth PMs.