A Fractional Slot Axial Flux PM Direct Drive

The paper deals with an axial-flux PM synchronous motor (AFPMSM) for a direct wheel drive. Its main feature is the armature winding of the fractional slots type. The choice of a concentrated non-overlapping winding allows a large number of pole pairs to be designed. The paper is aimed at emphasizing the special features of the whole motor drive. Therefore, both machine and control design aspects are targeted. Encoder-less operation of the drive is particularly critical. A vector control scheme is illustrated. A sliding-mode rotor flux estimation scheme is investigated. Its performances are experimentally compared to the encoder operation