Interior PM machines using Ferrite to substitute rare-earth surface PM machines

Since the cost of rare-earth permanent magnet (PM), such as NdFeB and SmCo, is more and more increasing, there is a great interest in designing PM machines without adopting such a rare-earth PMs, that is, replacing them with cheaper Ferrite magnet. Referring to the interior PM machines, the expected performance reduction is limited thanks to the anisotropic structure, compensating the use of low energy PMs by means of the reluctance torque component. This paper investigates the convenience of adopting Ferrite magnet in an interior PM machine (sometimes also referred to as PM assisted synchronous reluctance machine), instead of rare-earth surface PM machine. It is shown that, even though a slight lengthening of the stack length, the anisotropic PM machines, using Ferrite magnets, may represents a valid competitor of a surface PM machine.