Optimal Design of an Inset PM Motor With Assisted Barriers and Magnet Shifting for Improvement of Torque Characteristics

This paper presents an optimal design of an inset permanent magnet (PM) motor for improved torque characteristics. The key of the design is to introduce a bidirectional way of magnet shifting, along with assisted air barriers, into an inset PM motor, where magnets are shifted clockwise or anti-clockwise as needed. The introduced bidirectional shifting way lowers the requirement for shifting space between poles and also can reduce undesirable radial force to decrease vibration and noise. Moreover, the proposed inset PM motor can guarantee the torque density with great reduction of on-load torque ripple because the assisted air barriers can not only enhance the utilization of reluctance torque but also will not introduce any other torque harmonic and even can reduce torque ripple further. Also, the analytical expressions of torques are established and the appropriate angles of magnets shifting and assisted air barriers are, respectively, chosen to obtain low torque ripple and optimal torque density. Finally, these theoretical analyses are verified by the finite-element method.