Effect of the numbers of slots and barriers on the optimal design of synchronous reluctance machines

This paper analyzes the impact of the numbers of stator slots and rotor layers on the optimal design of synchronous reluctance (SyR) machines. Eighteen SyR machine examples have been designed by means of a multi-objective optimization algorithm and finite element analysis so to maximize torque and minimize torque ripple. Twelve, twenty-four and forty-eight slot stators are considered, associated to rotors with fourpoles and one to six flux barriers per pole. The results of the comparative analysis show that high numbers of slots and layers are beneficial for maximizing the torque and the power factor, and that torque ripple and iron loss minimization require precise matches between the slots and the layers, which are not necessarily the same for the two purposes. Finally, for some slot/layer combinations the optimization algorithm produces nonconventional barrier distributions, very promising is some cases. A fast finite element evaluation is used for the evaluation of thousands of candidate machines during the optimization, whereas an accurate transient with motion finite element analysis stage is used for the off-line characterization of the final designs.