Analysis and Comparative Study of Flux Weakening Capability in Fractional-Slot Concentrated Windings

This paper presents a detailed investigation of the winding inductance and the flux weakening capability in fractional-slot motors equipped with concentrated windings. An analytical model has been developed for evaluating the winding inductance by merging existent theories. Subsequently, a simple factor called weakening factor, which is proportional to the d-axis inductance and the pole pair, has been introduced to indicate the level of the flux weakening capability for different pole/slot combinations in the case where the air gap or slot leakage inductance is the dominant component. From the comparative study, it is shown that the multiple 4-pole/3-slot, i.e., S-pp = 1/4, can have the highest flux weakening capability resulting from the highest air gap inductance. The experimental results from several prototype motors, together with finite element analysis, are employed to confirm the validity of key analyses discussed in the paper.