Torque Enhancement of Surface-mounted Permanent Magnet Synchronous Machines via Axial Assisted Magnets

A torque enhancement scheme using axial assisted magnets (AAMs) for surface-mounted permanent magnet synchronous machines (SPMSMs) is proposed in this paper. It divides the total permanent magnets into two parts viz. main magnets mounted on the rotor surface, and axial assisted magnets at the end of the rotor, with the restriction of the same volume of magnets. According to the theoretical derivation and the finite element (FE) analyses, the proposed design can effectively enhance the output torque and air gap flux density after the optimization of size parameters of main and axial assisted magnets, while the machine outer size, armature current, and volume of total magnets are designed to be the same as the conventional structures of SPMSMs. Besides, the output torque of the proposed SPMSM with AAMs is optimized by way of sequential optimization and a prototype machine is fabricated afterward. Compared with the conventional SPMSM, the proposed design can increase the rated torque by 6.9% in experiments while the value of peak-to-peak torque ripple is kept almost the same.