Optimal selection of PM flux linkage in a PM assisted synchronous reluctance machine

In recent years, there is an increasing interest in adopting synchronous reluctance machines for several applications. This is due to two main factors. The first is the increasing and highly variable cost of rare-earth permanent magnet (PM), such as NdFeB and SmCo. The second is the requirement for more efficient machines with respect to induction machines in general applications. However, a drawback of the synchronous reluctance machine is the low power factor. Such a drawback is compensated by assisting the machine by means of a proper volume of PM material, generally Ferrite, which is introduced in the rotor flux-barriers. The PM flux saturates the rotor iron bridges, increases the power factor of the machine (which corresponds to a decrease of the Volt-Amps ratings of the inverter) and adds a PM flux torque component. This paper investigates how to select the optimal amount of Ferrite magnet in a PM assisted reluctance machine.